ASSET v8 - LTE Application Notes - 2.0

ASSETV8.0- LTE Application Notes

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Contents 1

Document Control ......................................................................................... ................................... 3 1.1 Revision History ..................................................................................................................... 3 2 Introduction ........................................................................................ .............................................. 4 2.1 LTE Objective Obj ective and P erformance Requirements .................................................................... .. 4 2.2 High Level System Architecture ............................................................................................. 4 3 LTE Technology Overview ................................................................ .............................................. 6 3.1 Frequency Band and EARFCN ............................................................ ................................... 6 3.1.1 General ............................................................................................................................... 6 3.1.2 LTE Frequency Bands .......................................................... .............................................. 7 3.1.3 Channel Arrangement ............................................................................................ ............. 7 3.2 Frame Structure Str ucture .............................................................. ......................................................... 8 3.2.1 Type 1- FDD .............................................................. ......................................................... 9 3.2.2 Type 2- TDD ...................................................................................................................... 9 3.2.3 Basic Time Unit ......................................................... ....................................................... 10 3.2.4 Subcarrier Spacing ............................................................................................................ 11 3.3 Transport Channels ......................................................................................... ...................... 11 3.3.1 Downlink Transport Channels ......................................................... ................................. 11 3.3.2 Uplink Transport Channels .............................................................. ................................. 12 3.4 Physical Channels ................................................................................ ................................. 12 3.4.1 Downlink Physical Channels ........................................................... ................................. 12 3.4.2 Uplink Physical Channels ................................................................ ................................. 12 3.4.3 Mapping between transport channels and physical channels (Downlink) ........................ 13 3.4.4 Mapping between transport channels and physical channels (Uplink) ............................. 13 3.5 Physical Signals ........................................................................ ............................................ 13 3.5.1 Downlink Physical Signals-Channels ......................................................... ...................... 13 3.5.2 Uplink Physical Signals ........................................................ ............................................ 14 3.6 Multi-Antenna Transmission ................................................................................................ 15 3.6.1 General on MIMO ..................................................... ....................................................... 15 3.6.2 Downlink ............................................................................................................... ........... 15 3.6.3 Uplink .............................................................. ................................................................. 16 3.6.4 MBSFN Transmission ..................................................................... ................................. 16 3.7 Physical Layer Procedure.......................................................... ............................................ 16 3.7.1 Link adaptation ........................................................................................... ...................... 16 3.7.2 Cell search ............................................................................ ............................................ 17 3.8 Physical Layer Meas urements and Indicators ....................................................................... 17 3.8.1 Reference Signal Received Power (RSRP) ............................................................ ........... 17 3.8.2 E-UTRA Carrier RSSI .......................................................... ............................................ 17 3.8.3 Reference Signal Received Quality (RSRQ) .................................................................... 17 3.8.4 DLRS TX Power ............................................. ................................................................. 17 3.8.5 Received Interference Power ................................................................................. ........... 17 3.8.6 Thermal noise power ................................................. ....................................................... 17 3.8.7 Quality, Precoding & Rank Indicators ................................................................... ........... 18 3.9 Radio Resource Ma nagement and Scheduling ........................................................... ........... 18 3.9.1 Radio Bearer Priority and Rate Control ................................................................. ........... 19 3.10 Interference Co-ordination Schemes ............................................................... ...................... 19 3.11 LTE Devices – UE Categories ............................................................. ................................. 20 4 LTE Technology in ASSET ........................................................................................................... 21 4.1 Introduction .......................................................... ................................................................. 21 4.2 Frequency bands ................................................................................................................... 22 4.3 LTE Frame Structure ........................................... ................................................................. 24 4.4 Carriers ................................................................. ................................................................. 26 4.5 Bearers ................................................................................................. ................................. 28

AIRCOM International


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4.6 Services ................................................................ ................................................................. 29 4.7 eNodeB and Cell parameters ................................................................ ................................. 32 4.8 LTE Planners ........................................................................................................................ 32 4.8.1 Physical Cell ID Planner .................................................................. ................................. 32 4.8.2 LTE Frequency Planner ........................................................ ............................................ 33 4.9 Terminal Types ............................................................................................... ...................... 33 4.9.1 Creating a Traffic Raster .................................................................................................. 34 5 LTE Network Performance- Coverage and Capacity Predictions .................................................. 35 5.1 Basic Coverage (RSRP, RSSI, RSRQ) ..................................... ............................................ 37 5.2 MIMO Schemes .............................................................................................. ...................... 39 5.2.1 SU-MIMO – Diversity .......................................................... ............................................ 40 5.2.2 SU-MIMO – Spatial Multiplexing .............................................................. ...................... 41 5.2.3 SU-MIMO – Adaptive Switching ............................................................... ...................... 43 5.2.4 MU-MIMO ............................................................................................................ ........... 47 5.2.5 SU-MIMO and MU-MIMO ............................................................. ................................. 49 5.3 ICIC ...................................................................................................................................... 52 5.3.1 Reuse 1 (Prioritisation) (P rioritisation) ......................................................... ............................................ 53 5.3.2 Soft Frequency Reuse and Reuse Partitioning P artitioning .................................................................. 56 5.4 Schedulers ............................................................ ................................................................. 62

1 1.1

Document Control Revision History Revision Number 1.0 2.0

Date

Name

Revision

05/07/2010 12/03/2012

AIRCOM Product Engineering AIRCOM Product Engineering

Initial version – ASSETv7 ASSET v8



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2

Introduction

This document describes a brief overview of how to model, plan and simulate LTE radio networks with the use of AIRCOM’s radio network planning tools, specifically with ASSET. This version of the LTE application notes has been written to be used alongside V8.0 of the ENTERPRISE suite.

2.1

LTE Objective and Performance Performance Requirements

The main objective behind LTE is the Evolution of the 3GPP radio-access technologies towards highdata-rate, low-latency and packet-optimised radio-access networks. The performance requirements for the first phase of LTE deployment include:

2.2

•

Peak Data Rates (for 20MHz Spectrum), DL: 300 Mbps, UL: 75 Mbps

•

Mobility Support, Up to 500km/h and also opti mised for low speeds (0-15km/h)

•

Reduced Latency with quick response time, <100 ms Control plane , <5ms User plane

•

Coverage (Cell sizes), 5-100km with slight degradation after 30km

•

Spectrum Flexibility (1.4-20 MHz)

•

Cost Effective Rollout by reusing 2G/3G spectrum

High Level System Architecture

The Evolved – Universal Terrestrial Radio Access Network (E-UTRAN) consists of eNodeBs providing the E-UTRA User Plane and Control Plane protocol terminations towards the User Equipment (UE). The eNodeBs are interconnected with each other by means of the X2 interface. The eNodeBs are also connected by means of the S1 interface to the Evolved Packet Core (EPC), more specifically to the Mobility Management Entity (MME) by means of the S1-MME and to the Serving Gateway (S-GW) by means of the S1-U. The S1 interface supports a many-to-many relation between MMEs / S-GWs and eNodeBs. The E-UTRAN architecture is illustrated in Figure 2-1 and 2-1 and can be summarised as follows:

Figure 2-1 LTE Architecture



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•

Evolved-UTRAN: Consists of eNodeBs, X2 interface which connects eNodeBs that need to communicate with each other e.g. for support of handover of UEs, etc. S1 interface, which connects eNodeBs to the EPC

•

MME: responsible for idle mode UE tracking and paging procedure including retransmissions

•

S-GW: Routes and forwards user data packets, acts as Mobility Anchor during inter-eNodeB handovers and between LTE and 3GPP technologies

LTE architecture enables Network Sharing solutions by allowing the service providers to have a separate CN (MME, S-GW, Packet Data Network Gateway (PDN-GW)) while the E-UTRAN (eNodeBs) is jointly shared. This is achieved by the S1-flex Mechanism that has the following characteristics: S1-flex Mechanism: Allows separate CN (MME, S-GW, PDN-GW) and creates pools of MMEs and S-GWs • Allows each eNodeB to be connected to multiple MMEs and SGWs in a pool • Provides support for network redundancy • Facilitates load sharing of traffic across network in the CN, the MME and the S-GW •



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3

LTE Technology Overview

This Chapter provides a brief overview on LTE Technology and it will be used as reference in Chapter 4 where the information presented here is used to model an LTE network in ASSET.

3.1 3.1.1

Frequency Band and EARFCN General

E-UTRA (or LTE as it is commercially marketed) will support operation in a wide range of spectrum allocations, achieved by the flexible transmission bandwidths that are part of the LTE specifications. The main reason for this is that the amount of spectrum available for LTE may significantly vary between different frequency bands and operators. Furthermore, the possibility to operate in different spectrum allocations gives the opportunity for gradual migration of the spectrum from other radio access technologies to LTE. Operation mode can be either Frequency Division Duplex (FDD) or Time Division Duplex (TDD). The LTE physical-layer specifications are bandwidth-agnostic and do not make any particular assumption on the supported transmission bandwidths beyond a minimum value. The basic radioaccess specification, including the physical-layer and protocol specifications, allows for any transmission bandwidth ranging from around 1MHz up to beyond 20MHz in steps of 180 kHz. At the same time, radio-frequency requirements are only specified for a limited subset of transmission bandwidths, corresponding to what is predicted to be relevant spectrum-allocation sizes and relevant migration scenarios. Thus, in practice, LTE radio access supports a limited set of transmission bandwidths, but additional trans mission bandwidths ba ndwidths could be easily supported by simply updating the RF specifications. The following frequency spectrum related terminologies and definitions have been used in 3GPP and will be used throughout this document. Channel bandwidth: The RF bandwidth supporting a single E-UTRA RF carrier with the transmission bandwidth configured in the t he uplink or/and downlink of a cell. The channel bandwidth is measured in MHz and is used as a reference for the transmitter and receiver RF requirements. Transmission bandwidth: Bandwidth of an instantaneous transmission from a UE or eNodeB, measured in Resource Block units. Transmission bandwidth configuration: The highest transmission bandwidth allowed for uplink or downlink in a given Channel Bandwidth, measured in Resource Block (RB) units.

NDL NOffs-DL NOffs-UL NRB NUL BWChannel BWConfig

Downlink E-UTRA Absolute Radio Frequency Channel Number(E-ARFCN) Offset used for calculating downlink E-ARFCN Offset used for calculating uplink E-ARFCN Transmission Bandwidth configuration, expressed in units of resource blocks Uplink E-ARFCN Channel Bandwidth Transmission Bandwidth configuration, expressed in MHz, BW Config = NRB x 180 kHz in the uplink and BW Config = 15 kHz + N RB x 180 kHz in the downlink.

Figure 3-1 shows the relation between the Channel Bandwidth (BW Channel) and the Transmission Bandwidth Configuration (N RB). The channel edges are defined as the lowest and highest frequencies of the carrier separated by the channel bandwidth, i.e. at F C +/- BWChannel /2, where F C is the centre frequency. Also, Table 3-1 summarises the currently supported transmission bandwidth configurations for the defined Channel Bandwidths.



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Channel bandwidth BWChannel [MHz] Transmission Bandwidth Configuration N Configuration N RB RB

1.4

3

5

10

15

20

6

15

25

50

75

100

Table 3-1 Channel Bandwidth and Transmission Bandwidth Configurations Channel Bandwidth [MHz] Transmission Bandwidth Configuration [RB]

C h a n n e l e d g e

Transmission Bandwidth [RB]

C h a n n e l e d g e

R e s o u r c e b l o c k

Active Resource Blocks

DC carrier (downlink only)

Figure 3-1 Definition of Channel Bandwidth and Transmission Transmission Bandwidth Configuration 3.1.2

LTE Frequency Bands

LTE is designed to operate in the frequency bands defined in Table 3-2. E-UTRA Band 1 2 3 4 5 6 7 8 9 10 11 12 13 14 ... 33 34 35

37 38 39 40

Uplink FUL_low – FUL_high 1920 MHz – 1980 MHz 1850 MHz – 1910 MHz 1710 MHz – 1785 MHz 1710 MHz – 1755 MHz 824 MHz – 849 MHz 830 MHz – 840 MHz 2500 MHz – 2570 MHz – 880 MHz 915 MHz 1749.9 MHz – 1784.9 MHz 1710 MHz – 1770 MHz 1427.9 MHz – 1452.9 MHz 698 MHz – 716 MHz 777 MHz – 787 MHz 788 MHz – 798 MHz

1900 MHz 2010 MHz 1850 MHz 1930 MHz 1910 MHz 2570 MHz 1880 MHz 2300 MHz

– – – – – – – –


Downlink FDL_low – FDL_high 2110 MHz – 2170 MHz 1930 MHz – 1990 MHz 1805 MHz – 1880 MHz 2110 MHz – 2155 MHz 869 MHz – 894MHz 875 MHz – 885 MHz 2620 MHz – 2690 MHz – 925 MHz 960 MHz 1844.9 MHz – 1879.9 MHz 2110 MHz – 2170 MHz 1475.9 MHz – 1500.9 MHz 728 MHz – 746 MHz 746 MHz – 756 MHz 758 MHz – 768 MHz


– – – – – – – –


Duplex Mode FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD FDD TDD TDD TDD TDD TDD TDD TDD TDD

Table 3-2 Worldwide standardised LTE Frequency Bands 3.1.3

Channel Arrangement

The channel arrangement depends on the following: Channel Spacing: The spacing between carriers will depend on the deployment scenario, the size of the frequency block available and the Channel Bandwidth. The nominal Channel Spacing between two adjacent LTE carriers is defined as follo wing:



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Nominal Channel Spacing = (BWChannel(1) + BWChannel(2))/2 where, BW Channel(1) and BW Channel(2) are the Channel Bandwidths of the two re spective LTE carriers. The Channel Spacing can be adjusted to optimise performance in a particular deployment scenario. Channel Raster: The Channel Raster is 100 kHz for all bands, which means that the carrier centre frequency must be an integer multiple of 100 kHz. Carrier frequency and E-ARFCN: The carrier frequency in the uplink and downlink is designated by the E-UTRAN E-ARFCN. The relation between E-ARFCN and the carrier frequency in MHz for the downlink and uplink is given by the following equations, where F DL_low, NOffs-DL, FUL_low and NOffs-UL are given in Table 3-3 and N UL \NDL are the uplink\downlink EARFCNs.

FDL = FDL_low + 0.1(NDL – NOffs-DL) FUL = FUL_low + 0.1(NUL – NOffs-UL)

E-UTRA Band 1 2 3 4 5 6 7 8 9 10 11 12 13 14 … 33 34 35 36 37 38 39 40

FDL_low [MHz] 2110 1930 1805 2110 869 875 2620 925 1844.9 2110 1475.9 728 746 758 … 1900 2010 1850 1930 1910 2570 1880 2300

Downlink NOffs-DL 0 600 1200 1950 2400 2650 2750 3450 3800 4150 4750 5000 5180 5280 … 26000 26200 26350 26950 27550 27750 28250 28650

Range of NDL 0 – 599 600 – 1199 1200 – 1949 1950 – 2399 2400 – 2649 2650 – 2749 2750 – 3449 3450 – 3799 3800 – 4149 4150 – 4749 4750 – 4999 5000 – 5179 5180 – 5279 5280 – 5379 … 26000 – 26199 26200 – 26349 26350 – 26949 26950 – 27549 27550 – 27749 27750 – 28249 28250 – 28649 28650 – 29649

FUL_low [MHz] 1920 1850 1710 1710 824 830 2500 880 1749.9 1710 1427.9 698 777 788 … 1900 2010 1850 1930 1910 2570 1880 2300

Uplink NOffs-UL 13000 13600 14200 14950 15400 15650 15750 16450 16800 17150 17750 18000 18180 18280 … 26000 26200 26350 26950 27550 27750 28250 28650

Range of NUL 13000 – 13599 13600 – 14199 14200 – 14949 14950 – 15399 15400 – 15649 15650 – 15749 15750 – 16449 16450 – 16799 16800 – 17149 17150 – 17749 17750 – 17999 18000 – 18179 18180 – 18279 18280 – 18379 … 26000 – 26199 26200 – 26349 26350 – 26949 26950 – 27549 27550 – 27749 27750 – 28249 28250 – 28649 28650 – 29649

Table 3-3 E-UTRA Absolute Radio F requency Channel Number (EARFCN)

3.2

Frame Structure

Downlink and uplink transmissions are organised into radio frames with frame duration of T f = 307200 × T s = 10 ms , where T f is the frame duration and the size of various fields in the time domain is expressed as a number of time units T s

=1

(15000× 2048) seconds. This Base time-unit is

explained later in this section. There are two main radio frame structures: •

Type 1, applicable to FDD

•

Type 2, applicable to TDD

In addition, there is a slightly different frame structure for Multi-Media Broadcast over a Single Frequency Network (MBSFN) support.



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3.2.1

Type 1- FDD

Frame structure Type 1 is applicable to both full duplex and half duplex FDD. Each radio T slot

frame is

= 15360 ⋅ Ts =

T f

=

307200 ⋅ T s

= 10 ms

long and consists of 20 slots of length

0.5 ms , numbered from 0 to 19. A subframe is defined as two consecutive slots

where subframe i consists of slots 2i and 2i + 1 . For FDD, 10 subframes are available for downlink transmission and 10 subframes are available for uplink transmissions in each 10 ms interval. Uplink and downlink transmissions are separated in the frequency domain. In half-duplex FDD operation, the UE cannot transmit and receive at the same time while there are no such restrictions in full-duplex FDD.

Figure 3-2 Type-1 Frame Structure 3.2.2

Type 2- TDD

Frame structure Type 2 is applicable to TDD. Each radio frame of length T f 153600 ⋅ T s

= 5 ms each.

=

307200 ⋅ T s

= 10 ms

consists of two half-frames of length T f =

Each half-frame consists of eight slots of length T slot

= 15360 ⋅ T s =

0.5 ms and

three special fields, Downlink Pilot Time Slot (DwPTS), Guard Period (GP), and Uplink Pilot Time Slot (UpPTS).

Figure 3-3 Type-2 Frame Structure for 5ms switch-point periodicity The length of DwPTS and UpPTS is given by Table 3-4 subject to the total length of DwPTS, GP and UpPTS being equal to 30720 ⋅ T s = 1 ms . The supported uplink-downlink allocations are listed in Table 3-5 where, for each subframe in a radio frame, “D” denotes the subframe is reserved for downlink transmissions, “U” denotes the subframe is reserved for uplink transmissions and “S” denotes a special subframe with the three fields DwPTS, GP and UpPTS. Subframe 1 in all configurations and subframe 6 in configurations 0, 1, 2 and 6 in Table 2 consists of DwPTS, GP and UpPTS. All other subframes are defined as two slots where where subframe i consists of slots 2i and 2i + 1 . Subframes 0 and 5 and DwPTS are always reserved for downlink transmission. In case of 5 ms switch-point periodicity, UpPTS and subframes 2 and 7 are reserved for uplink transmission. In case of 10 ms switch-point periodicity, DwPTS exist in both half-frames while GP and UpPTS only exist in the first half-frame and DwPTS in the second half-frame has a length equal to 30720T s = 1 ms . UpPTS and subframe 2 are reserved for uplink transmission and subframes 7 to 9 are reserved for downlink transmission.



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Special-subframe Configuration

Normal cyclic prefix DwPTS

GP

0

6592 ⋅ T s

1

Extended cyclic prefix UpPTS

DwPTS

GP

21936 ⋅ T s

7680 ⋅ T s

20480 ⋅ T s

19760⋅ T s

8768 ⋅ T s

20480 ⋅ T s

7680 ⋅ T s

2

21952 ⋅ T s

6576 ⋅ T s

23040 ⋅ T s

5120 ⋅ T s

3

24144 ⋅ T s

4384 ⋅ T s

25600 ⋅ T s

2560 ⋅ T s

4

26336 ⋅ T s

2192 ⋅ T s

7680 ⋅ T s

17920⋅ T s

5

6592 ⋅ T s

19744⋅ T s

20480 ⋅ T s

5120 ⋅ T s

6

19760⋅ T s

6576 ⋅ T s

23040 ⋅ T s

2560 ⋅ T s

7

21952 ⋅ T s

4384 ⋅ T s

-

-

-

8

24144 ⋅ T s

2192 ⋅ T s

-

-

-

2192 ⋅ T s

4384 ⋅ T s

UpPTS

2560 ⋅ T s

5120 ⋅ T s

Table 3-4 Configuration of Special Subframe (duration of DwPTS, GP and UpPTS) Uplink-downlink Configuration

Downlink-to-Uplink Switch-point periodicity

Subframe number

0

1

2

3

4

5

6

7

8

9

0

5 ms

D

S

U

U

U

D

S

U

U

U

1

5 ms

D

S

U

U

D

D

S

U

U

D

2

5 ms

D

S

U

D

D

D

S

U

D

D

3

10 ms

D

S

U

U

U

D

D

D

D

D

4

10 ms

D

S

U

U

D

D

D

D

D

D

5

10 ms

D

S

U

D

D

D

D

D

D

D

6

10 ms

D

S

U

U

U

D

S

U

U

D

Table 3-5 Uplink – Downlink Configurations for Type-2 Frames The Basic Time Unit as defined below provides a one to one relation with all frame related parameters 3.2.3

Basic Time Unit

To provide consistent and exact timing definitions, different time intervals within the LTE radio access specification can be expressed as multiple of a basic time unit

T s = 1/ 30720000.

Hence, it

influences every parameter in LTE frames, e.g. Slot Duration: LTE frames consist of 20 slots of 0.5ms each calculated as

T slot =

30720 2

.T s

Subframe Duration: Two slots make one subframe of duration 1 ms calculated as

T subframe

=

30720 .T s

Frame Duration: LTE frames are 10ms o f time length which can be calculated as

T frame


=

307200 .T s


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3.2.4

Subcarrier Spacing

Currently, LTE employs a fixed subcarrier spacing of 15 kHz. However, there is also a reduced subcarrier spacing of 7.5 kHz. This reduced subcarrier spacing specifically targets MBSFN- based multicast/broadcast transmissions. Table 3-6 summarises the frame related parameters. Transmission BW (MHz)

1.4

3.0

5

10

15

20

Slot duration (ms)

0.5

0.5

0.5

0.5

0.5

0.5

Sub-carrier spacing (kHz)

15

15

15

15

15

15

Sampling frequency (MHz)

30.72 /1.92

30.72 /3.84

30.72/7.68

30.72 /15.36

30.72 /23.04

30.72 /30.72

OFDM symbol length (in time units* and excluding 2048/128 cyclic prefix,1 time unit = 1/30.72 MHz)

2048/256

2048/512

2048/1024

2048/1536

2048/2048

OFDM symbol length (micro 66.67 sec)

66.67

66.67

66.67

66.67

66.67

Number of occupied resource 6 blocks

15

25

50

75

100

Occupied sub-carriers

73

181

301

601

901

1201

7

7

7

7

7

7

6

6

6

6

6

6

OFDM per

Normal symbols CP slot Extended CP

Cyclic Prefix 160, A = 0 160, A= 0 160,A = 0 160,A = 0 160,A= 0 Normal CP (CP) length 144, A=1-6 144, A=1-6 144, A=1-6 144, A=1-6 144,A=1-6 where A is the symbol position Extended 512,A= 0-5 512,A= 0-5 512,A= 0-5 512,A= 0-5 512,A=0-5 CP in a slot Cyclic Prefix Normal CP (CP) length (time)micro where A is the sec symbol position Extended in a slot CP

160,A= 0 144,A=1-6 512,A=0-5

5.21, A = 0 5.21, A = 0 5.21, A = 0 5.21, A = 0 5.21, A = 0 5.21, A = 0 4.69, A=14.69, A=1-6 4.69, A=1-6 4.69, A=1-6 4.69, A=1-6 4.69, A=1-6 6 16.67,A= 0-5

16.67,A= 016.67,A= 0-5 5

16.67,A= 0- 16.67,A= 0- 16.67,A= 05 5 5

Table 3-6 LTE frame structure related parameters

3.3 3.3.1

Transport Channels Downlink Transport Channels

BCH (Broadcast Channel): It has a fixed transport format, provided by the specifications. It is used for transmission of the information on the BCCH logical channel. It can be characterised by fixed, predefined transport format and the requirement to be broadcast in the entire coverage area of the cell DLSCH(Downlink Shared Channel): DL-SCH is the transport channel used for transmission of downlink data in LTE. It supports LTE features such as dynamic rate adaptation and channeldependent scheduling in the time and frequency domain, hybrid ARQ, and spatial multiplexing. It also supports discontinuous reception (DRX) to reduce mobile-terminal power consumption while still providing an always on experience, similar to the Continuous Packet Connectivity Connectivity (CPC) mechanism in HSPA.



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PCH(Paging Channel): It is used for transmission of paging information on the PCCH logical channel. The PCH supports DRX to allow the mobile terminal to save battery power by sleeping and waking up to receive the PCH only at predefined time instants. MCH (Multicast Channel): It is used to support MBMS. It is characterised by a semi-static transport format and semi-static scheduling. In case of multi-cell transmission using MBSFN, the scheduling and transport format configuration is coordinated among the cells involved in the MBSFN transmission

3.3.2

Uplink Transport Channels

UL-SCH (Uplink Shared Channel): It is characterised by the possibility to use beamforming; support for HARQ, dynamic link adaptation by varying the transmit power and potentially modulation and coding and also for both dynamic and semi-static resource a llocation. RACH (Random Access Channel(s)): It is characterised by limited control information and collision risk. The possibility of using open loop power control depends on the physical layer solutio n.

3.4

Physical Channels

Physical Channels carry information from higher layers including user data and control information. 3.4.1

Downlink Physical Channels

PBCH (Physical Broadcast Channel): The coded BCH transport block is mapped to four subframes within a 40 ms interval. This 40 ms timing is blindly detected, i.e. there is no explicit signalling indicating 40 ms timing. Each subframe is assumed to be self-decodable, i.e. the BCH can be decoded from a single reception, assuming sufficiently good channel conditions. PCFICH (Physical Control Format Indicator Channel): Informs the UE about the number of OFDM symbols used for the P DCCHs. It is transmitted in every subframe PDCCH (Physical Downlink Control Channel): Informs the UE about the resource allocation of PCH and DL-SCH, and Hybrid ARQ information related to DL-SCH. It also carries the uplink scheduling grant. The downlink control signalling (PDCCH) is located in the first n OFDM symbols where n ≤ 3 and consists of: • • •

Transport format, resource allocation, and hybrid-ARQ information related to DL-SCH, and PCH; Transport format, resource allocation, and hybrid-ARQ information related to UL-SCH; QPSK modulation is used for all control channels

PHICH (Physical Hybrid ARQ Indicator Channel): Carries Hybrid ARQ ACK/NAKs in response to uplink transmissions PDSCH (Physical Downlink Shared Channel): Carries the DL-SCH and PCH PMCH (Physical Multicast Channel): Carries the MCH

3.4.2

Uplink Physical Channels

PUCCH (Physical Uplink Control Channel): Carries Hybrid ARQ ACK/NAKs in response to downlink transmission. It also carr iers Scheduling Request (SR) and CQI reports. PUSCH (Physical Uplink Shared Channel): Carries the UL-SCH PRACH (Physical Random Access Channel): Carries the random access preamble. Used for Call setup



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3.4.3

Mapping between transport channels and physical channels (Downlink)

Figure 3-4 below depicts the mapping between the downlink transport and ph ysical channels

Figure 3-4 Mapping between downlink transport transport and physical channels 3.4.4

Mapping between transport channels and physical channels (Uplink)

Figure 3-5 below depicts the mapping between the uplink transport and physical channels

Figure 3-5 Mapping between uplink transport and physical physical channels

3.5

Physical Signals

Physical Signals handle synchronisation, cell identification and channel estimation. 3.5.1

Downlink Physical Signals-Channels

P-SCH (Downlink Primary Synchronisation Channel): Used for cell search and identification by the UE. Carries part of the cell ID (one of 3 orthogonal sequences). S-SCH (Downlink Secondary Synchronisation Channel): Used for cell search and identification by the UE. It carries the remainder of the cell ID (one of 168 binary sequences). DL RS (Downlink Reference Signal): To carry out downlink coherent demodulation, the mobile terminal needs estimates of the downlink channel. A straightforward way to enable channel estimation in case of OFDM transmission is to insert known reference symbols into the OFDM time-frequency grid. In LTE, these cell specific reference symbols are jointly referred to as the LTE Downlink Reference Signals (DL RSs). These downlink reference symbols are inserted within the first and the third last OFDM symbols of each slot and with a frequency-domain spacing of six subcarriers. Furthermore, there is a frequency-domain staggering of three subcarriers between the first and second reference symbols. Thus within each resource block, consisting of 12 subcarriers, there are four reference symbols. This is true for all subframes except subframes used for MBSFN-based transmission.



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In case of multi antenna transmission, there is one reference signal transmitted per downlink antenna port. The number of downlink antenna ports is equal to 1, 2 or 4. The two-dimensional reference signal sequence is generated as the symbol-by-symbol product of a two-dimensional orthogonal sequence and a two-dimensional pseudo-random sequence. There are 3 different two-dimensional orthogonal sequences and 168 different two-dimensional pseudo-random sequences. Each cell identity (ID) corresponds to a unique combination of one orthogonal sequence and one pseudo-random sequence, thus allowing for 504 unique cell identities. In the reference-signal structure, the frequency-domain positions of the reference symbols are the same between consecutive subframes. However, the frequency-domain positions of the reference symbols may also vary between consecutive subframes, also referred to as reference-symbol frequency hopping . hopping . Thus, the frequency hopping can be described as adding a sequence of frequency offsets , to the basic reference-symbol pattern, with the offset being the same for all reference symbols within a subframe, but varying between consecutive subframes. The reference-symbol positions p positions p in subframe k can thus be expressed as First reference symbols: p(k) = (p0 + 6 Second reference symbols: p(k) = (p0 + 6

i + offset(k)) mod 6 i + 3 + offset(k)) mod 6

・

・

where, i is an integer. The sequence of frequency offsets or the frequency-hopping pattern has a period of length 10, i.e. the frequency-hopping pattern is repeated between consecutive frames. There are 168 different frequency-hopping patterns defined, where each pattern corresponds to one cell-identity group. By applying different frequency-hopping patterns to neighbour cells, the risk that reference symbols of neighbour cells are continuously colliding can be avoided. This is especially of interest if/when reference symbols are transmitted with higher energy compared to the remaining resource elements, also referred to as reference signal energy boosting . 3.5.2

Uplink Physical Signals

DM-RS (Uplink Demodulation Reference Signal): It is used for synchronisation to the UE and UL channel estimation and is associated with transmission of P USCH or PUCCH S-RS (Uplink Sounding Reference Signal): It is used to monitor propagation conditions with UE, however it is not associated with transmission of PUSCH or PUCCH

In Table 3-7 all uplink and downlink Channels and Signals are presented along with their allowable Modulation options. Channels

Link

Modulation

Signals

Link

Modulation

PBCH

DL

QPSK

P-SCH

DL

One of 3 Zadoff-Chu sequences

PDCCH

DL

QPSK S-SCH

DL

Two 31-bit M-sequences (binary) - one of 168 Cell IDs plus other info

RS

DL

OS*PRS defined by Cell ID (P-SCH &S-SCH)

PDSCH

DL

QPSK, 16QAM, 64QAM

PMCH

DL

QPSK, 16QAM, 64QAM

PCFICH

DL

QPSK

PHICH

DL

BPSK

DM-RS

UL

Uth root root Zadoff-Chu

PRACH

UL

QPSK

S-RS

UL

Zadoff-Chu

PUCCH

UL

BPSK, QPSK

PUSCH

UL

QPSK, 16QAM, 64QAM

Table 3-7 Supported modulations for all Physical Channels and Signals



Page 14 of 64

3.6

Multi-Antenna Multi-Antenna Transmission

3.6.1

General on MIMO

LTE supports downlink transmission on 1, 2 or 4 cell specific antenna ports corresponding either to 1, 2 or 4 cell-specific reference signals. On their turn each one of the RS corresponds to one antenna port. The following DL transmission modes are defined for PDSCH • • • • • • • •

3.6.2

Single antenna port; port 0 Single User – MIMO Transmit diversity Open loop spatial multiplexing Closed loop spatial multiplexing Multi User – MIMO Closed-loop Rank=1 pre-coding Single antenna port; port 5 Downlink

For the LTE downlink, the follo wing multiple antenna schemes are supported: Tx diversity: The first and simplest downlink LTE multiple antenna scheme is open-loop Tx diversity. It is identical in concept to the scheme introduced in UMTS Release 99. The more complex, closedloop Tx diversity techniques from UMTS have not been adopted in LTE, which instead uses the more advanced MIMO, which was not part of Release 99. LTE supports either two or four antennas for Tx diversity. Space-Frequency Block Coding (SFBC) is used for two antennas while while a combination of SFBC and Frequency Switching Transmit Diversity (FSTD) is employed for four transmit antennas. Rx diversity: The second downlink scheme, Rx diversity, is mandatory for the UE. It is the baseline receiver capability for which performance requirements will be defined. A typical use of Rx d iversity is maximum ratio combining of the received streams to improve the SNR in poor conditions. Rx diversity provides little gain in good conditions Spatial Multiplexing and SU-MIMO: SU-MIMO (Figure 3-6) includes conventional techniques such as Delay (cyclic for OFDM) Diversity, Transmit \ Receive (spatial) diversity and Spatial Multiplexing and Precoded Spatial Multiplexing. It can be implemented as Open (without feedback) and Closed Loop (with feedback). Diversity techniques improve the signal to interference ratio by transmitting the same stream of single user data from multiple antennas. On the other hand, Spatial Multiplexing increases the per-user data rate or throughput by transmitting multiple streams of data dedicated to for a single user.

Spatial multiplexing and MIMO are supported for two and four antenna configurations. Assuming a two-channel UE receiver, this scheme allows for 2x2 or 4x2 MIMO. A four-channel UE receiver, which is required for a 4x4 configuration, has been defined but is not likely to be implemented in the near future. The most common configuration will will be 2x2 SU-MIMO. In this case the payload data will be divided into the two code-word streams CW0 and CW1 and processed accordingly. Depending on the pre-coding used, each code word is represented at different powers and phases on both antennas. In addition, each antenna is uniquely identified by the position of the reference signals within the frame structure. Cyclic Delay Diversity: In addition to MIMO pre-coding there is an additional option called delay diversity (CDD). This technique adds antenna-specific cyclic time shifts to artificially multi-path on the received signal and prevents signal cancellation caused by the close spacing transmit antennas. The CDD system works by adding the delay only to the data subcarriers leaving the RS subcarriers alone.



cyclic create of the while

Page 15 of 64

3.6.3

Uplink

The baseline configuration of the UE has one transmitter. This configuration was chosen to save cost and battery power, and with this configuration the system can support MU-MIMO (Figure 3-6), i.e., two different UE transmitting in the same frequency and time to the eNodeB. This configuration has the potential to double uplink capacity (in ideal conditions) without i ncurring extra cost to the UE. MUMIMO scheme consists of multiple users separated in spatial domain in both UL and DL sharing the same time-frequency resources. It uses multiple narrow beams to separate users in the spatial domain and can be considered as a hybrid of beamforming and spatial multiplexing. It can ultimately serve more terminals by scheduling multiple terminals using the same resources. This increases the overall cell capacity and the number of simultaneously served terminals. It is suitable for highly loaded cells and for scenarios where the number of served ter minals is more important than the peak user data rates. An optional configuration of the UE is a second transmit antenna, which allows the possibility of uplink Tx diversity and SU-MIMO. The latter offers the possibility of increased data rates depending on the channel conditions. For the eNodeB, receive diversity is a baseline capability and the system will support either two or four receive antennas.

Figure 3-6 SU-MIMO and MU-MIMO

3.6.4

MBSFN Transmission

MBSFN is supported for the MCH transport channel. Multiplexing of transport channels using MBSFN and non-MBSFN transmission is done on a per-sub-frame basis. Additional reference symbols, transmitted using MBSFN are transmitted within MBSFN s ubframes.

3.7 3.7.1

Physical Layer Procedure Link adaptation

Link adaptation (AMC: Adaptive Modulation and Coding) with various modulation schemes and channel coding rates is applied to the shared data channel. The same coding and modulation is applied to all groups of resource blocks belonging to the same Layer 2 Protocol Data Unit (PDU) scheduled to one user within one TTI and within a si ngle stream.



Page 16 of 64

3.7.2

Cell search

Cell search is the procedure by which a UE acquires time and frequency synchronisation with a cell and detects the Cell ID of that cell. LTE cell search supports a scalable overall transmission bandwidth corresponding to 72 sub-carriers and upwards. LTE cell search is based on the primary and secondary synchronisation signals (see chapter 3.5.1 Downlink Physical Signals), the downlink reference signals transmitted in the downlink. The primary and secondary synchronisation signals are transmitted over the central 72 sub-carriers in the first and sixth subframe of each frame. Neighbour-cell search is based on the same downlink signals as the i nitial cell search.

3.8 3.8.1

Physical Layer Measurements and Indicators Reference Signal Received Power (RSRP)

Reference Signal Received Power (RSRP), is determined for a considered cell as the linear average over the power contributions (in [W]) of the resource elements that carry cell-specific reference signals within the considered measurement frequency bandwidth. For RSRP determination the cell-specific reference signals R 0 and if available R 1 can be used. If receiver diversity is in use by the UE, the reported value shall not be lower than the corresponding RSRP of any of the individual diversity branches. 3.8.2

E-UTRA Carrier RSSI

E-UTRA Carrier Received Signal Strength Indicator, comprises the total received wideband power observed by the UE from all sources, including co-channel serving and non-serving cells, adjacent channel interference, thermal noise etc. 3.8.3

Reference Signal Received Quality (RSRQ)

RSRQ is defined as the ratio N ratio N ×RSRP ×RSRP / (E-UTRA carrier RSSI), where N is is the number of RB’s of the E-UTRA carrier RSSI measurement bandwidth. The measurements in the numerator and denominator shall be made over the same set of resource blocks. 3.8.4

DLRS TX Power

Downlink Reference Signal transmit power is determined for a considered cell as the linear average over the power contributions (in [W]) of the resource elements that carry cell-specific reference signals which are transmitted by the eNodeB within its operating system bandwidth. For DL RS TX power determination the cell-specific reference signals R 0 and if available R 1 can be used. The reference point for the DL RS TX p ower measurement shall be the TX antenna connector. 3.8.5

Received Interference Power

Received Interference Power is the uplink received interference power, including thermal noise, within RB

one physical resource block’s bandwidth of N sc resource elements. The reported value shall contain a set of Received Interference Powers of physical resource blocks. The reference point for the measurement shall be the RX antenna connector. In case of receiver diversity, the reported value shall be the linear average of the power in the diversity branches. branches. 3.8.6

Thermal noise power UL

The uplink thermal noise power within the UL system bandwidth consisting of N RB resource blocks is defined as ( N o x W ), ), where N o denotes the white noise power spectral density on the uplink carrier UL

RB

frequency and W = N RB ⋅ N sc

⋅ ∆ f

denotes the UL system bandwidth. The measurement is optionally

reported together with the Received Interference Power measurement, it shall be determined over the



Page 17 of 64

same time period as the Received Interference Power measurement. The reference point for the measurement shall be the RX antenna connector. In case of receiver diversity, the reported value shall be the linear average of the power in the diversity branches. branches. 3.8.7

Quality, Precoding & Rank Indicators

The following indicators are reported by the UE back to the eNodeB CQI (Channel Quality Indicator): It is a 4 bit index pointing into a table of 16 different modulation and coding schemes. It indicates or suggests a combination of modulation and coding scheme that the eNodeB should use to ensure that the BLER (Block Error Ratio) experienced by the UE remains less than 10%. CQI

Modulation Efficiency Actual coding rate

Required SINR

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

QPSK QPSK QPSK QPSK QPSK QPSK 16QAM 16QAM 16QAM 64QAM 64QAM 64QAM 64QAM 64QAM 64QAM

-4.46 -3.75 -2.55 -1.15 1.75 3.65 5.2 6.1 7.55 10.85 11.55 12.75 14.55 18.15 19.25

0.1523 0.07618 0.2344 0.11719 0.3770 0.18848 0.6016 308/1024 0.8770 449/1024 1.1758 602/1024 1.4766 378/1024 1.9141 490/1024 2.4063 616/1024 2.7305 466/1024 3.3223 567/1024 3.9023 666/1024 4.5234 772/1024 5.1152 873/1024 5.5547 948/1024 Table 3-8 CQI Table

PMI (Precoding Matrix Indicator): PMI ensures that the correct spatial domain precoding matrix is applied by the eNodeB so that the transmitted signal matches with the spatial channel experienced by the UE. It is denoted by the Transmit Precoding Matrix Indicator (TPMI) that consists of 3 bit or 6 bit information field for 2 or 4 transmit antennas, respectively. It is compulsory for closed loop spatial multiplexing. RI (Rank Indicator): RI indicates the number of spatial layers that can be supported by the UE based on the channel conditions. The transmission rank selected to be used is dependent on RI as well as other factors (depending on the vendor) such as traffic pattern, available transmission bandwidth etc. RI is compulsory for both open and closed loop spatial multiplexing.

3.9

Radio Resource Management and Scheduling

There are two schedulers in the eNodeB allocating physical resources, one for uplink and one for downlink. The schedulers grant the right to transmit on a per UE basis. The resource assignment consists of Physical Resource Blocks (PRBs) and a Modulation and Coding Scheme (MCS). The resources are allocated for one or multiple TTIs. A PRB consists of certain subcarriers in the frequency domain and one TTI in the time domain as explained in LTE Frame Structure section. The baseline for both uplink and downlink is dynamic scheduling where the PRBs and MCSs can be scheduled for each TTI via a Cell Radio Network Temporary Identifier (C-RNTI) on the L1/L2 control channels. The UE always monitor the control channels in order to find any allocation of uplink or downlink resources when downlink reception is enabled. Predefined resources can also be allocated which the UE can use if no C-RNTI is found on the control channels. In downlink this means the UE does blind decoding of the predefined resources unless a C-



Page 18 of 64

RNTI is found in which case it overrides the predefined allocations for the TTI. In the downlink case the network decodes the resources predefined to the UEs unless the C-RNTI is present. The scheduler should consider a number of factors when taking scheduling decisions. These factors include transport volume, QoS and measurements of the UE radio environment. In both uplink and downlink, measurement reports need to be reported to the eNodeB. 3.9.1

Radio Bearer Priority and Rate Control

In downlink, the eNodeB enforces the Maximum Bit Rate (MBR) of radio bearers with a Guaranteed Bit Rate (GBR) and the Aggregate Maximum Bit Rate (AMBR) of groups of Non-GBR bearers. In the uplink, the Radio Resource Control (RRC) entity controls the uplink rate by giving each bearer a priority and a Prioritised Bit Rate (PBR). For radio bearers with GBR, a MBR is also provided. The radio bearers are served in decreasing priority order up to their PBR. For any remaining resources the bearers are served again in decreasing priority order ensuring that the MBR is not exceeded. If all bearers have a PBR of 0, the first step is skipped and the be arers are served in strict priority order. The eNodeB ensures that the AMBR in uplink is not exceeded, by limiting the total amount of granted resources.

3.10 Interference Co-ordination Schemes To minimise Inter-Cell Interference the following frequency reuse schemes are considered. Frequency Reuse-1 with Prioritisation: Each sector divides the available bandwidth into prioritised (one third) and non-prioritised (two third) sections. The prioritised section is used more often than the non-prioritised one by each sector in order to concentrate the interference that it causes to other sectors. Soft Frequency Reuse: The introduction of power difference between the prioritised and non prioritised spectrum divides the sector into an inner and outer region. Cell Centre Users (CCU) who are users in the inner region can be reached with reduced power compared to Cell Edge Users (CEU) who lie in the outer region. Overall CCUs are assigned with frequency Re-use 1 while CEUs employ frequency Re-use 3. Reuse Partitioning: Reuse is similar to the Soft Frequency Reuse scheme. The total channel bandwidth is divided into two parts and one of the parts uses us es higher power than the other. The lowerlo wer power-part is the same in all sectors. T he higher-power-part is divided between sectors so that each one of them gets one third of the high power spectrum. Overall the lower-power-part employs frequency Re-use 1 while the higher-power-part is configured with a fr equency Re-use 3.

Figure 3-7 Reuse Partitioning



Page 19 of 64

3.11 LTE Devices – UE Categories Five different device capability classes have been standardised. The supported data rates range from 5 to 75Mbps in the UL and 10 to 300Mbps in the DL. Category 5 devices support 64QAM in the uplink while others use QPSK and 16QAM. MIMO transmit and receive diversity are supported by categories 2 to 5. The actual device capabilities also depend on other signalling requirements and not just on these categories. Table 3-9 presents the nominal characteristic for each one of the 5 UE categories.

Parameters

Category 1

Category 2

Category 3

Category 4

Peak Data Rate (DL) Peak Data Rate (UL) Block Size (DL) Block Size (UL) Max. Modulation (DL) Max. Modulation (UL) RF Bandwidth Transmit Diversity Receive Diversity Spatial Multiplexing (DL) Spatial Multiplexing (UL) MU-MIMO (DL) MU-MIMO (UL)

10 Mbps 5 Mbps 10296 5160 64QAM 16QAM 20 MHz 1-4 Tx Yes Optional No Optional Optional

50 Mbps 25 Mbps 51024 25456 64QAM 16QAM 20 MHz 1-4 Tx Yes 2X2 No Optional Optional



Category 5


Table 3-9 UE Categories



Page 20 of 64

4

LTE Technology in ASSET

4.1

Introduction

This chapter presents how LTE technology is modelled in ASSET. The relevant Graphical User Interfaces (GUIs) are explained and suggestions are made on the values to be entered in the various fields to properly design an LTE network network depending on planner’s objectives. The logical order in which the LTE elements are presented is as follows: • • • • • • • • •

Frequency bands – No – No dependencies Frame Structure – No – No dependencies Carriers – Frequency Band and Frame Structure should be decided upon first Bearers – No dependencies Services – Carriers and Bearers should be decided upon first Terminal Types – Services should be decided upon first E-Node B and Cell parameters – Carriers should be d ecided upon first Coverage Predictions (RSRP, RSRQ) – All – All of the above are required Capacity Predictions / Simulation – All – All of the above are required

Frequency Bands

Frame Structure

Carriers

Setup dependencies

Bearers

Services

eNodeB and Cell parameters\Load Levels

Terminal Types

Traffic Raster

Results Capacity Predictions

Coverage RSRQ)

Predictions

(RSRP,

Figure 4-1 LTE modelling in ASSET



Page 21 of 64

4.2

Frequency bands

An LTE network can consist of eNodeBs with cells configured with same or different carrier bandwidths (with overlapping start and end frequencies). In addition, FDD and TDD might co-exist. This overlapping of carriers between different cells can result in co-channel and adjacent-channel interference. The ASSET GUI for defining and selecting the LTE frequency bands is presented below. The 3GPP standard E-UTRA bands are already set up for you; these are not modifiable, but you can rename them. If necessary, you can add customised bands.

Figure 4-2 Definition of LTE frequency bands in ASSET LTE will operate in a wide range of spectrum with simultaneous deployment in different E-UTRA bands. The supported modes of operation are Frequency Division Duplex (FDD), Half Duplex FDD (H-FDD) and Time Division Duplex (TDD). A typical UE would support a certain subset of E-UTRA bands defining the capability to switch bands, roam between national operators and roam internationally. Table 4-1 presents the worldwide standardised LTE bands. The default bands for FDD are 1 to 14 and for TDD 33 to 40. For FDD, the E-ARFCNs are different for uplink and downlink, but for T DD they are the same. The channel bandwidth is measured in MHz and is used as a reference for transmitter and receiver RF requirements. Some E-UTRA bands do not allow operation in the narrow bandwidth modes, i.e. less than 5 MHz while others restrict operations in the wider channel bandwidths, i.e. more than 15 MHz. This is summarised in Table 4-2.



Page 22 of 64

E-UTRA Band 1 2 3 4 5 6 7

Bandwidth UL (MHz) 1920-1980 1850-1910 1710-1785 1710-1755 824-849 830-840 2500-2570

E-ARFCN UL 13000 – 13599 13600 – 14199 14200 – 14949 14950 – 15399 15400 – 15649 15650 – 15749 15750 – 16449

Bandwidth DL (MHz) 2110-2170 1930-1990 1805-1880 2110-2155 869-894 875-885 2620-2690

E-ARFCN DL 0 – 599 600 - 1199 1200 – 1949 1950 – 2399 2400 – 2649 2650 – 2749 2750 – 3449

Duplex Mode FDD FDD FDD FDD FDD FDD FDD

8

880-915

16450 – 16799

925-960

3450 – 3799

FDD

9 10 11 12 13 14 ... 33 34 35 36 37 38 39 40

1749.9-17 84.9 1710-1770 1427.9-14 52.9 698-716 777-787 788-798 … 1900-1920 2010-2025 1850-1910 1930-1990 1910-1930 2570-2620 1880-1920 2300-2400

16800 – 17149 17150 – 17749 17750 – 17999 18000 – 18179 18180 – 18279 18280 – 18379 … 26000 – 26199 26200 – 26349 26350 – 26949 26950 – 27549 27550 – 27749 27750 – 28249 28250 – 28649 28650 – 29649

1844.9-1879 .9 2110-2170 1475.9-1500 .9 728-746 746-756 758-768 … 1900-1920 2010-2025 1850-1910 1930-1990 1910-1930 2570-2620 1880-1920 2300-2400

3800 – 4149 4150 – 4749 4750 – 4999 5000 – 5179 5180 – 5279 5280 – 5379 … 26000 – 26199 26200 – 26349 26350 – 26949 26950 – 27549 27550 – 27749 27750 – 28249 28250 – 28649 28650 – 29649

FDD FDD FDD FDD FDD FDD … TDD TDD TDD TDD TDD TDD TDD TDD

Table 4-1 E-UTRA Bands

Supported Channels (non-overlapping) (non-overlapping) Channel Bandwidth (MHZ)

E-UTRA Band

Downlink Bandwidth

1.4

3

5

10

15

20

1 2 3 4 5 6 7

60 60 75 45 25 10 70

42 53 32 17 -

20 23 15 8 -

12 12 15 9 5 2 14

6 6 7 4 2* 1* 7

4 4* 5* 3 X 4

3 3* 3* 2 X 3*

8

35

25

11

7

3*

-

-

9 10 11 12 13 14 ... 33 34 35 36 37 38 39 40 * X -

35 60 25 18 10 10

12 7 7

6 3 3

7 12 5 3* 2* 2*

3 6 2* 1* 1* 1*

2* 4 1* X X

1* 3 1* X X X

20 4 15 3 60 42 20 12 60 42 20 12 20 4 50 10 40 8 100 UE receiver sensitivity can be relaxed Channel bandwidth too wide for the band Not supported

2 1 6 6 2 5 4 10

1 1 4 4 1 3 6

1 X 3 3 1 2 5

Table 4-2 Supported channel configurations for the LTE bands



Page 23 of 64

Transmission Bandwidth is defined as the bandwidth of an instantaneous transmission from a UE or eNodeB, measured in Resource Blocks (RBs). Six different Channel Bandwidths and their corresponding Transmission Bandwidths have been standardised and are presented in the following table. Channel Bandwidth (MHz) Transmission Bandwidth (MHz) Transmission Bandwidth configuration (N RB) Bandwidth Efficiency (%)

1.4

3

5

10

15

20

1.08

2.7

4.5

9

13.5

18

6

15

25

50

75

100

77

90

90

90

90

90

Table 4-3 Channel Bandwidth and Transmission Bandwidth The Transmission Bandwidth is contained inside the Channel Bandwidth as indicated in t his figure:

Figure 4-3 Channel Bandwidth and Transmission Transmission Bandwidth

4.3

LTE Frame Structure

The following figure shows the LTE Frame Structures dialog box:

Figure 4-4 LTE frame structure definition in ASSET The transmitted signal in one ‘slot’ is described by a Resource Grid consisting of subcarriers and symbols in frequency and time domain, respectively. The smallest part of the resource grid is called Resource Element (RE) and it has dimensions of 1 subcarrier x 1 modulated symbol. A Resource Block



Page 24 of 64

(RB) consists of N consecutive OFDMA symbols x M consecutive subcarriers. This concept is demonstrated in Figure 4-5.

Figure 4-5 Definition of the Resource Element and the Resource Resource Block The standardized RB configurations are given in Table 4-4. Firstly they are separated in three main types, namely Type-1 which is Frequency Division Duplex (FDD), Type-2 which is Time Division Duplex (TDD) and Type-3 that is Multi-Media Broadcast over a Single Frequency Network (MBSFN). Types 1 and 2 can be implemented either with Normal Cyclic Prefix or Extended Cyclic Prefix with a subcarrier spacing of 15\7.5 kHz while Type 3 is implemented only with Extended Cyclic Prefix with a reduced subcarrier spacing of 7.5 kHz. In an OFDM symbol the cyclic prefix is a repeat of the end of the symbol at the beginning. The purpose is to allow multipath to settle before the main data arrives at the receiver. The receiver is arranged to decode the signal after it has settled because this is when the frequencies become orthogonal to one another thus CP acts as a guard interval.

Frame Type

Cyclic Prefix

Subcarrier Spacing (kHz)

Link Direction

# of Subcarriers

# of Symbols

Normal

15

DL

12

7

Extended

15

DL

12 12

6

Normal

15

UL

12

7

Extended

7.5

DL

24

3

Extended

15

UL

12

6

Type 1 – FDD

Type 2 – TDD

Type 3 – MBSFN

Table 4-4 Standardized Resource Block configurations



Page 25 of 64

Default values for LTE Standards Frame Structures Type-1FDDType-1FDDType-2TDDType-2TDDNormal CP Extended CP Normal CP Extended CP

Type3-MBSFN

Duplex mode

FDD

FDD

TDD

TDD

FDD

Configuration

LTE Standards

LTE Standards

LTE Standards

LTE Standards

LTE Standards

Frame duration

10

10

10

10

10

Slots/ subframe

2

2

2

2

2

Subframes

10

10

10

10

10

Cyclic Prefix

Normal

Extended

Normal

Extended

Extended

Subcarrier spacing

15

15

15

15

7.5

TDD frame Config

Greyed-Out

Greyed-Out

1

1

Greyed-Out

RB Symbols DL

7

6

7

6

3

RB Symbols UL

7

6

7

6

6

Subcarriers DL

12

12

12

12

24

Subcarriers UL

12

12

12

12

12

RS Subcarriers

2

2

2

2

12

Table 4-5 Parameter settings for the Default Frame structures in ASSET

4.4

Carriers

Since the appropriate LTE Frequency Band and LTE Frame Structure have been selected or defined (in case the default ones are not the appropriate) then the Carriers can be defined. Figure 4-6 and Figure 4-7 show the ASSET GUI for defining LTE Carriers.

Figure 4-6 Definition of the LTE Carriers in ASSET



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Figure 4-7 Definition of the LTE Carriers in ASSET, Overhead Each LTE Carrier is representing the Channel bandwidth with a certain Transmission Bandwidth Configuration. The relation between Channel Bandwidth and Transmission Bandwidth is shown in Table 4-3. One of the pre-defined Frequency Bands and Frame Structures has to be selected for each one of the carriers. Based on the Frequency Band selection (FDD or TDD according to Table 4-1), only the respective default and user-defined Frame Structures are available in “Frame Structure” drop down list. For example for FDD frequency bands only the FDD frame structures appear in the drop down list. Then, the available Bandwidth within the specific Frequency Band must be specified keeping in mind the restrictions implied by Table 4-2 as some Frequency Bands don’t support all Bandwidth options. The next step is to specify the placement of the Bandwidth chunk within the Frequency Band. This is done by defining the point where the Bandwidth chunk starts (Low point) and then the High Point as well as the E-ARFCNs are automatically calculated. It is important to place the Bandwidth at the right place in the Frequency Band as this will affect co-channel and adjacent-channel interference calculations of overlapping and neighbouring carriers. The number of Resource Blocks, Fast Fourier Transform (FFT) Size and Sampling Factor are auto-completed based on Table 4-6. The Subcarrier Spacing used to calculate Sampling Factor is given in T able 4-5. Channel Bandwidth (MHz)

# of Resource Blocks

FFT Size

1.4

6

128

3

15

256

5

25

512

10

50

1024

15

75

1536

20

100

2048

  

           

Table 4-6 LTE Carrier Parameters



Page 27 of 64

4.5

Bearers

Bearers represent the air interface connections, performing the task of transporting voice and data information between cells and terminal types. After bearers have been defined, you can then decide which ones will be supported by your different services. The following figure presents the ASSET GUI for the definition of LTE Bearers.

Figure 4-8 Definition of LTE Bearers in ASSET The Default Uplink and Downlink LTE bearers are defined per CQI providing 15 DL bearers and 4 UL bearers. CQI is a report sent from the UE to the eNodeB suggesting the appropriate Modulation and Coding to be used by the eNodeB when transmitting in order to maintain a Block Error Ratio (BLER) less than 10% at the RLC level. The eNodeB is finally deciding upon MCS depending on CQI and other (vendor dependent) related measurements. Downlink MCSs are 32. Each default Bearers has Control & Traffic SINR requirements according to Table 3 -8.

Figure 4-9 Bearer SINR requirements requirements



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The following table is a vendor specific mapping of CQIs to MCSs. MCS Index Modulation Coding rate x 1024 Efficiency Comments 0 2 120 0.2344 from CQI table 1 2 157 0.3057 Average Efficiency 2 2 193 0.377 from CQI table 3 2 251 0.4893 Average Efficiency 4 2 308 0.6016 from CQI table 5 2 379 0.7393 Average Efficiency 6 2 449 0.877 from CQI table 7 2 526 1.0264 Average Efficiency 8 2 602 1.1758 from CQI table 9 2 679 1.3262 Average Efficiency 10 4 340 1.3262 overlap 11 4 378 1.4766 from CQI table 12 4 434 1.69535 Average Efficiency 13 4 490 1.9141 from CQI table 14 4 553 2.1602 Average Efficiency 15 4 616 2.4063 from CQI table 16 4 658 2.5684 Average Efficiency 17 6 438 2.5684 overlap 18 6 466 2.7305 from CQI table 19 6 517 3.0264 Average Efficiency 20 6 567 3.3223 from CQI table 21 6 616 3.6123 Average Efficiency 22 6 666 3.9023 from CQI table 23 6 719 4.21285 Average Efficiency 24 6 772 4.5234 from CQI table 25 6 822 4.8193 Average Efficiency 26 6 873 5.1152 from CQI table 27 6 910 5.33495 Average Efficiency 28 6 948 5.5547 from CQI table 29 Implicit TBS signalling with QPSK 30 Implicit TBS signalling with 16QAM 31

Code Rate 0.1171875 0.15332031 0.18847656 0.24511719 0.30078125 0.37011719 0.43847656 0.51367188 0.58789063 0.66308594 0.33203125 0.36914063 0.42382813 0.47851563 0.54003906 0.6015625 0.64257813 0.42773438 0.45507813 0.50488281 0.55371094 0.6015625 0.65039063 0.70214844 0.75390625 0.80273438 0.85253906 0.88867188 0.92578125

Implicit TBS signalling with 64QAM Table 4-7 CQIs to MCS mapping

4.6

Services

To account for the different services offered to the subscriber, you can set up your own services and then allocate the services to terminal types. For example, services might have different costs, data rates, and other requirements such as quality of service (QoS). Some of these factors are determined by the bearers that you assign to a service. T he parameters that yo u specify will influence how the simulation (Chapter 5) behaves and will enable you to examine coverage and service quality for individual types of services. The standard LTE services correspond to QoS Class Identifier (QCI) values of 1 to 9 and are available in ASSET by default. The following figure presents the ASSET GUI for the definition of LTE Services.



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Figure 4-10 Definition of LTE Services in ASSET QoS differentiation, i.e. prioritisation of different services according to their requirements becomes extremely important when the system load gets higher. The most relevant parameters of QoS classes are •

Transfer Delay: This represents how delay sensitive the traffic is. For example, the VoIP class is meant for very delay sensitive traffic while the P2P File Sharing class is delay insensitive.

•

Guaranteed Bit rate: Delay sensitive QoS Classes have guaranteed bit rate requirements. This defines the minimum bearer bit rate that the E-UTRAN must provide and it can be used in admission control and in resource allocation. Each guaranteed bit rate service also has a maximum bit rate demand, i.e. it can't exceed this limit.

•

Allocation and Retention Priority (ARP): Within each QoS class there are different allocation and retention priorities. The primary purpose of ARP is to decide whether a bearer establishment / modification request can be accepted or needs to be rejected in case of resource limitations (typically available radio capacity in case of GBR bearers). In addition, the ARP can be used (e.g. by the eNodeB) to decide which bearer(s) to drop during exceptional resource limitations (e.g. at handover).

It is important to remember that pure prioritisation in packet scheduling alone is not enough to provide full QoS differentiation gains. Users within the same QoS class and ARP class will share the available capacity. If the number of users is simply too high, then they will suffer from bad quality. In that case it is better to block a few users to guarantee the quality of existing connections, like streaming videos. The radio network can estimate the available radio capacity and block an incoming user if there is no room to provide the required bandwidth without sacrificing the quality of existing connections. Table 4-8 presents the standard LTE Services per QCI. Gaming, VoIP, Signalling and Web Browsing are treated as the most delay sensitive Classes while Streaming, E-mail, P2P File Sharing and Chat are not that delay sensitive. Highest Priority in terms of ARP is given to Signalling followed by VoIP and lowest to Chat. Packet Error Loss Rate (PELR) requirements vary with values starting from 10 -2 down to 10-6. The loosest PELR requirements hold for VoIP at 10 -2.



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Name

VoIP QCI-1 Video Call QCI-2 Gaming QCI-3 Streaming QCI-4 Signalling QCI-5

Priority

Packet Delay Budget

Packet Error Loss Rate

Example Services

2

100 ms

10 -2

Conversational Voice

4

150 ms

10 -3

Conversational Video (Live Streaming)

3

3

50 ms

10-3

Real Time Gaming

4

5

300 ms

10 -6

Non-Conversational Non-Conversational Video (Buffered Streaming)

5

1

100 ms

10 -6

IMS Signalling

Resource Type

QCI

1 2

E-mail QCI-6

6

Web browsing QCI-7

7

P2P File Sharing QCI-8

8

Chat QCI-9

9

GBR

Non-GBR

6

300 ms

10 -6

7

100 ms

10 -3

300 ms

-6

8

10

9

Video (Buffered Streaming) TCP-based (e.g., www, www, e-mail, chat, ftp, p2p file sharing, progressive video, video, etc.) Voice, Video (Live Streaming) Interactive Gaming Video (Buffered Streaming) TCP-based (e.g., www, e-mail, chat, ftp, p2p file sharing, progressive video, etc.)

Table 4-8 Definition of Default LTE Services After defining the General Service Parameters one or more Carriers can be related to the Service. Since a supporting Carrier has been assigned to the Service, all UL and DL Bearers will be available for selection as the Supporting Bearers. For example in Figure 4-11 all DL Bearers have been assigned to VoIP Service. A Minimum Bit Rate (Min-GBR) and a Maximum Bit Rate (Max-MBR) have been specified for the service. If a terminal achieves connection to one or more of the available bearers then the eNodeB will firstly allocate enough resources to it in order to achieve the Min-GBR. It will keep allocating more resources to it until the terminal either reaches the Max-MBR ceiling or until there not more resources available due to cell loading. When many services are competing to get assigned to resources from the same eNodeB then the services’ priorities and the eNodeB’s scheduling algorithm (Round Robin, Proportional Fair, Proportional Demand or Max SINR) will determine the proportion of resources to be allocated to each one of them. The most preferable bearer is DL-CQI-15 and the least preferable bearer is DL-CQI-1. ASSET sorts the bearers automatically in descending Throughput or Data Rate.

Figure 4-11 LTE Service, Example of Supporting Bearers Bearers



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4.7

eNodeB and Cell parameters parameters

The LTE Radio Access Network consists of eNodeBs. In ASSET eNodeBs can be defined on the GIS or imported from a spreadsheet using the xml editor. Cell and eNodeB templates may be used to speed up this procedure. The configuration values for the eNodeBs should normally be taken from vendor specifications. As a sort check list the follo wing should be set accordingly: • • • •

Antennas with propagation models Carriers, ICIC schemes, schedulers defined and applied on per cell basis Advanced Antenna Systems (AAS) Settings Transmit Power and Power Channel Offsets

Figure 4-12 Site Database

4.8 4.8.1

LTE Planners Physical Cell ID Planner

In LTE, the Primary and Secondary Synchronisation (P-SCH and S-SCH) signals are employed for initial cell search and detection of Physical Cell Identities (Physical Cell IDs). The LTE Physical Cell ID Planner in ASSET is designed to assign these Physical Cell IDs automatically to each sector with a sophisticated (fixed\automatic) reuse distance algorithm, using multiple filters and schemas and Neighbour relations.

Figure 4-13 PCI Planner



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4.8.2

LTE Frequency Planner

ASSET incorporates an Automatic Frequency Planner (AFP) for the optimum assignment of carriers (Channel Bandwidths) to LTE sectors. In addition to a simple distance based algorithm, AFP uses the Interference matrix for minimizing inter-cell interference. Carrier assignments and conflicts can be visualised and further analysed in an enhanced reporting engine to determine the quality of produced frequency plans.

Figure 4-14 Frequency Planner For a detailed description of the LTE planners’ functionality please refer to ASSET User Reference Guide.

4.9

Terminal Types

The following figure presents the ASSET GUI for the definition of LTE Ter minal Types.

Figure 4-15 Definition of LTE Terminal Types in ASSET In ASSET, terminal types represent the different types of mobile devices in your network, and their distribution. In a modern cellular network, subscribers can have different types of terminals with different characteristics. In ASSET, you can define a variety of terminal types to represent current or projected distribution profiles of the subscribers in your network. You can associate these terminal types with specific or multiple services. Importantly, you can then determine how the traffic will be spread for each service, according to specified distributions in relation to the mapping data. In summary, a terminal type defines the following key characteristics that will in their turn determine the accuracy of the Simulations:



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• • • • •

How much traffic will the terminal type generate in total? How will the traffic be spread geographically? What is the expected mobile speed distribution for this terminal type? With which service will the terminal type be associated? What are the mobile equipment characteristics?

The purpose of master and slave terminal types is so that you can specify geographical distribution settings on a 'master' terminal type, and then experiment with various scaling factors when you spread traffic. If you want to do this, you can define separate 'slave' terminal types with appropriate scaling percentages. Each slave must always be associated with with a 'master' terminal type. 4.9.1

Creating a Traffic Raster

This is usually done per clutter type by assigning a terminal density or a relative weight to each one of the clutters. It is also possible to spread traffic on user defined points, polygons and inside polygons. The percentage of in-building traffic per clutter type can also be specified. For in-building terminals a different fading standard deviation, indoor loss and angular spread will be applied as defined in LTE Clutter Parameters. It is also possible to define the terminals’ Mean Speed, Speed’s Standard deviation, Minimum and Maximum Speed per clutter type. To complete the traffic modelling the Traffic Wizard is run to spread the actual terminals in the area under examination. The Resolution Option for the outcome array should be in alignment with the lowest resolution of the propagation models in use. There is an option to Restrict Traffic to Coverage that ensures that traffic will be spread only in areas where there is coverage. This option should not be used if only initial estimates of the site locations, equipment and configuration needed for a new or expanding network are required. The option to Restrict Traffic to Coverage should be used when the 3G available coverage is required to match that of the LTE network under planning. Having already a set of 2G and 3G sites/cells and assuming that they have been finely optimised over years to cover and serve all wanted areas and traffic it may be required that LTE coverage matches the coverage provided by the old technologies. In this case the coverage predictions for the 2G and 3G cells should be created and the LTE traffic should be restricted to the contour created by them. The actual number of terminals to be served should come from the operator’s OSS statistics and traffic forecasts also taking into account the churn rates and the 2G/3G to LTE customer conversion predicted rates.

Figure 4-16 Example of Traffic Raster or Geographical Geographical Traffic Distribution



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5

LTE Network Performance- Coverage and Capacity Predictions

LTE network performance using the Monte-Carlo simulator can be performed in two different manners with regards to how the cell load levels are specified. In the first case they are specified in the Site Database and specifically under the LTE Parameters tab in the fields of Downlink Load (as a percentage) and Mean UL Interference Level (in dB). The second option is to create a traffic raster spreading the defined LTE Terminal Type(s) and then the cell load levels get calculated by running Simulator Snapshots. In both cases a reference terminal type has to be specified for the calculation process.

Figure 5-1 LTE Simulator Wizard

Figure 5-2 Selection of Filters and Cells

The decision on what resolution should be used for the simulations is based on what propagation models are assigned to the cell antennas. • •

Firstly, it is suggested to use a propagation model at the resolution it has been tuned for . Secondly, it is suggested to use two propagation models. The first one (Primary) should be calculated at high resolution (2-20 meters) and for o a relatively small radius (1-3 km). The second one (Secondary) should be calculated at relatively lower resolution (20o 100 meters) and for a larger radius (3-30km).

This setup will provide high accuracy at the expected serving area of the cell which usually doesn’t span farther than 3km (for urban type of environment). It will also provide good enough accuracy for the calculation of interference caused by the bespoken cell far away from it but and at the same time it will be computationally effective (relatively (relatively fast to calculate as the resolution is low). The number of covering cells mainly affects the accuracy of the interference based calculations. The more cells taken into account, the more accurate the interference values are. A typical value would be 6 to 10. The typical values for Fading Correlation Coefficients are 0.8 for Intra-Site antennas and 0.5 for Inter-Site antennas.

Figure 5-3 Selection of Terminal Type(s)


Figure 5-4 Line of Sight Settings


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It is also important to consider cells with prediction area within the specified region (2D View) as those cells will possibly pick up some of the traffic in the specified area and also increase interference. The Line of Sight Settings allow deactivating certain MIMO schemes based on LOS information. MIMO schemes rely on a low correlation between the signal paths to the transmit elements of an antenna; locations that have LOS to an antenna are more likely to have a high correlation, therefore MIMO gains should not be considered for such locations. Following, a comprehensive presentation and discussion of the ASSET LTE module is presented. It will focus on four main areas, namely basic coverage (RSRP, RSSI and RSRQ), MIMO schemes, InterCell Interference Coordination (ICIC) schemes and Schedulers. An urban area was chosen expanding 6.4 by 4.8 km and covered by 78 eNodeBs bearing 224 cells.



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5.1

Basic Coverage (RSRP, RSSI, RSRQ)

RSRP, RSSI and RSRQ are defined in detail chapter 3.8. An informal definition of these quantities is given hereby: •

Received Signal Reference Power (RSRP) is the indicator of the signal strength coming from the serving cell experienced by a UE at a certain point and time.

•

Received Signal Strength Indicator (RSSI) is the indicator of how much power is received by the UE over its operating bandwidth. The sources of this power include co-channel serving and non-serving cells, adjacent channel interference, thermal noise and so on.

•

Reference Signal Received Quality (RSRQ) is the indicator of the quality of the signal. In this context, quality is expressing how stronger the signal is compared to noise and interference. It is thereafter proportional to RSRP and diversely proportional to RSSI, however it is not a ratio of RSRP over RSSI.

From a terminal point of view a pixel is covered if the required RSRP, RSRQ and BCH/SCH SINR are met.

Figure 5-5 Trial Area

Figure 5-6 LTE Terminal Type

We’ll examine how cell load levels affect the satisfaction of these requirements. Cell Load Setting live on the Cell Params. To start with, SU-MIMO as well as MU-MIMO was disabled on both uplink and downlink at the Cell Params as well as at t he Terminal Type.

Figure 5-7 Site DB Settings - Cell Load Levels



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RSRP (Figure 5-8) is not affected by cell loads. This is the reason why a network is usually firstly dimensioned to provide adequate signal strength at the desired areas.

Figure 5-8 RSRP RSRQ (Figure 5-9) on the other hand is affected by cell loads. Cell loads in essence express how many users are connected to the network. The more active users there exist, the more resources are consumed in the DL and UL interference level rises. This explains why cells’ service areas shrink as the number of users increase. The following figure illustrates an unloaded network and the one after this a heavily loaded network.

Unloaded Network

Loaded Network

Figure 5-9 RSRQ changes depending on Cell Loads



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Finally, the third requirement for BCH/SCH SINR (Figure 5-10) is not affected by the cell load. Although BCH/SCH SINR includes the term I for for interference it is not affected by load as the BCH and SCH channels are positioned in the 6 central RBs of the BandWidth and don’t get interference from RBs carrying traffic.

Figure 5-10 DL BCH/SCH SINR The change in RSRQ (Figure 5-9) coming from the change of the cell load levels is causing changes in the allocated bearers (Figure 5-11), white areas not covered at all. Grey, red and yellow areas covered by the higher CQI bearers. Performance deteriorates as the number of users increase. It is obvious that the area covered by high CQI bearers (or high MCS bearers) that provide high throughput decreases as cell load rises. The mitigation of this effect is one of main objectives of MIMO schemes, ICIC schemes and Schedulers. Unloaded Network

Loaded Network

Figure 5-11 Achievable DL Bearer

5.2

MIMO Schemes

The SU-MIMO and MU-MIMO modes need to be enabled on the Cell, Bearer and Terminal Type. To demonstrate the use of MIMO we will assess the network without MIMO, then with Diversity Only, Spatial Multiplexing (SM) Only, Adaptive Switching (Diversity-SM) and finally MU-MIMO.



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Roughly speaking Diversity is used to improve coverage, SM is used to increase single users’ throughput and MU-MIMO is used to improve the network throughput or to serve more simultaneous users. We will elaborate on each of schemes in more detail.

5.2.1

SU-MIMO – Diversity

As shown in the LTE AAS Parameters look-up table (Figure 5-12) the effect of having 1 TX antenna at the eNodeB and 2 RX antennae at the UE is equivalent to having 2 TX antennae on the eNodeB and one RX antenna on the UE. We will take the simple example of 2 RX elements and 1 TX. Note that we are now examining downlink and the number of RX elements is defined on the Terminal Type.

Figure 5-12 LTE AAS Parameters - Diversity When applying diversity the RSRP plot and the SCH/BSC SINR plot stay the same. RSRQ stays the same as well. What changes, are the SINR requirements for the bearers that are divided by the corresponding table value. The SINR Adjustment can be refined per clutter type using the LTE Cletter Parameters.

Figure 5-13 LTE Clutter Parameters – Diversity As previously mentioned Diversity’s main purpose is to increase coverage and this is done by decreasing the bearers’ SINR requirements. The bearers with the decreased SINR requirements are easier to achieve. By increasing the coverage for each bearer respectively the result will be larger areas with higher CQI bearers. So from a system perspective Diversity perspective Diversity not only increases coverage but network throughput as well. Figure 5-14 and Figure 5-15 depict the change of coverage that results in higher system throughput.



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50% Loaded Network without MIMO

50% Loaded Network with Diversity

Figure 5-14 Achievable DL Bearer without and with Diversity Diversity – Coverage Improvement 50% Loaded Network without MIMO

50% Loaded Network with Diversity

Figure 5-15 DL Data Rate Improvement with Diversity Diversity (2TX by 1 RX) 5.2.2

SU-MIMO – Spatial Multiplexing

Spatial Multiplexing (SM) targets increasing users’ throughput. Depending on the number of TX and RX antennae the user experiences a Rate Gain as shown below:

Figure 5-16 LTE ASS Parameters - SM The SM Rate Gain can be refined per clutter t ype using the LTE Clutter Parameters if required.



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Figure 5-17 LTE Clutter Parameters - SM. Spatial Multiplexing does increase throughput but this comes at an expense of higher SINR requirements as shown on the LTE bearers

Figure 5-18 MIMO SINR Delta for Spatial Multiplexing We will examine how the Achievable bearers plot and data rates change with the application of SM. As shown in Figure 5-16 a combination of 1TX by 2 RX provides no improvements so we will go for 2TX by 2RX elements that should roughly provide a doubling in data rates subject to clutter parameters. I n general, the Rate Gain is equal to the minimum of TX and RX elements and is also affected by the clutter specific parameters (Figure 5-17). As shown in Figure 5-19 and Figure 5-20 coverage slightly shrinks with SM because of the higher SINR requirements but at the same time data rates almost double. Take for example eNodeB 032451 at South-West of the map. Areas providing 3-4Mbps data rate without MIMO jump up to 6-7Mbps with Spatial Multiplexing. 50% Loaded Network without MIMO

50% Loaded Network with SM (2TX by 2RX)

Figure 5-19 Achievable DL Bearer without and with SM – Minor Coverage Change



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50% Loaded Network without MIMO

50% Loaded Network with SM (2TX by 2RX)

Figure 5-20 DL Data Rate Improvement with Spatial Multiplexing Multiplexing

5.2.3

SU-MIMO – Adaptive Switching

As shown in the previous two subchapters Diversity and Spatial Multiplexing provide significant gains to the network. Both of them can be deployed at the same time in Adaptive Switching mode by eNodeBs so as to provide higher throughput to users close to the cell and extended coverage to users further away at the cell edge. Observing how the Achievable DL bearer changes with Adaptive Switching (Figure 5-21) there is an obvious difference compared to operating the network without SU-MIMO. Take for example eNodeB 032451 at South-West of the map. Starting from the vicinity of the cell and moving further away the following bearers are deployed DL-CQI-15, DL-CQI-14, DL-CQI-13, DL-CQI-12, DL-CQI-15, DLCQI-14, DL-CQI-13. The switch from DL-CQI-12 to DL-CQI-15 is the point where Diversity takes over Spatial Multiplexing. 50% Loaded Network without MIMO

50% Loaded Network with SU-MIMO (Diversity and Spatial Multiplexing in Adaptive Switching md)

Figure 5-21 Achievable DL Bearer without without and with SU-MIMO (2TX by 2RX) The DL Transmission array (Figure 5-22) is more indicative of the type of SU-MIMO that is selected for every pixel. The aim is always to provide the higher possible data rate at every pixel. This aim governs the decision of whether to choose SM or diversity and which specific bearer to deploy for every pixel.



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Figure 5-22 Transmission Modes with with adaptive switching (no user defined thresholds) thresholds) Examining the DL Data Rate (Figure 5-23) and comparing against the cases when either Diversity or SM is deployed we can convey that adaptive switching is, as expected, combining the gains from both types of MIMO by deploying the most appropriate one for every pixel. No MIMO

Spatial Multiplexing

Diversity

Adaptive Switching (Diversity - SM)

Figure 5-23 DL Data Rate with Adaptive Switching (no user defined defined thresholds)



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The user can set specific thresholds per cell to govern the switch between Diversity and SM depending on DL Reference Signal SNR. In this case the Transmission-Modes-plot changes as shown in Figure 5-25 and the achievable bearer plot changes similarly as indicated in Figure 5-26.

Figure 5-24 User Defined Threshold Threshold for Adaptive Switching Automatic Adaptive Mode

With User Def. Thresholds

Figure 5-25 Transmission Modes with with adaptive switching (with user defined defined thresholds) Automatic Adaptive Mode

With User Def. Thresholds

Figure 5-26 Achievable DL Bearer without without and with SU-MIMO with user defined thresholds thresholds



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Figure 5-27 is is the comparing all different options for SU-MIMO and how they affect Data Rates. No MIMO

Spatial Multiplexing

Diversity

Adaptive Switching (Diversity - SM)

Adaptive Switching (Diversity - SM) user defined Thresholds

Figure 5-27 DL Data Rate with Adaptive Switching



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5.2.4

MU-MIMO

MU-MIMO is used to increase the cells’ throughput. This is achieved by co-scheduling terminals on the same Resource Blocks. Applying MU-MIMO will make no obvious changes to a network unless it is overloaded. To demonstrate the use of MU-MIMO we will spread terminals and run the SIM in snapshot mode. The density of terminals will be high enough for many of them to fail due to insufficient capacity. Then we will enable MU-MIMO and observe how the network is now capable to serve more of the terminals that were previously dropped because of the eNodeBs’ resources maxing out. In order for MU-MIMO to be used there is a higher Traffic & Control SINR requirement defined

. Figure 5-28 Bearers - MU-MIMO SINR Delta

Figure 5-29 Cell AAS Settings - MU-MIMO Average Co-scheduled Terminals RSRQ changes when MU-MIMO is deployed because the number of served terminals changes. In Figure 5-30 we can observe how multiuser MI MO Improves the Data Rates. Without MIMO

MU-MIMO deployed

Figure 5-30 DL Data Rate without and with MU-MIMO Figure 5-31 depicts the actual difference of DataRate with MU-MIMO - DataRate without MU-MIMO. We can observe that when MU-MIMO is deployed everywhere, it provides small improvements close to the cell, large improvements close to the cell edge and mediocre improvements at the cell edge.



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Figure 5-31 Improvement in DL Rate with MU-MIMO MU-MIMO deployed The following figure demonstrates how total DL Cell Throughout (per cell) increases when MUMIMO is enabled. This is an effect of the eNodeB now being capable to serve a higher number of users by scheduling them on the same resources. These users would be otherwise failing to connect. connect. MU-MIMO deployed

without MIMO

Figure 5-32 DL Cell Throughput without and with MU-MIMO MU-MIMO The following table indicates how a highly loaded network can accommodate extra users by deploying MU-MIMO. Cell Composite Report On Service hidata Without MIMO

With MU-MIMO

Mean Attempted

4930.286

4889.714

Mean Served

2743.857

55.65%

3484.929

71.27%

Mean Failed

2186.429

44.35%

1404.786

28.73%

Contributions to Failure



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DL RSRP

0.37%

0.47%

RSRQ

0.16%

0.15%

DL BCH/SCH SINR

0.00%

0.00%

UL SINR

0.00%

0.00%

DL SINR

1.88%

1.89%

UL Capacity

0.00%

0.00%

DL Capacity

97.62%

97.51%

No valid connection scenarios

0.00%

0.00%

No covering cells

0.00%

0.00%

Note: Terminals can fail to connect for multiple reasons so the failure reason percentages can sum to more than 100%. Table 5-1 Composite failure report with and without MU-MIMO. Doing some further analysis to these results we observe that the MU-MIMO provides great gains to heavily loaded cells and relatively smaller gains to lightly loaded cells. Moreover, from Figure 5-31 we observe that this improvement in is mainly coming from the cell edge rather than the cell centre.

Figure 5-33 Comparative Cell Throughput Improvement Improvement with MU-MIMO versus Cell Cell Load

5.2.5

SU-MIMO and MU-MIMO

We will now enable SU-MIMO (Diversity and Spatial Multiplexing) and MU-MIMO at the same time. Our strategy will be to use SM close to the eNodeBs to increase data rates, Diversity further away from the eNodeBs to increase coverage and MU-MIMO for heavily loaded cells to reduce the number of failures due to capacity.



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Loaded Network with MIMO

Unloaded Network with MIMO

Figure 5-34 DL Transmission Mode with SU-MIMO and MU-MIMO

Figure 5-35 DL Data Rate with SU-MIMO and MU-MIMO

Figure 5-36 Achievable DL Bearer with SU MIMO and MU-MIMO

Figure 5-37 DL Transmission Mode with SU-MIMO and MU-MIMO MU-MIMO



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In this chapter the advantage of SU-MIMO and MU-MIMO over single antenna transmission were demonstrated. For the trial area examined, the deployment of MU-MIMO increased the number of served terminals by 15% and the combined deployment of SU-MIMO and MU-MIMO increased the number of served terminals by 33%.

Cell Composite Report On Service Without MIMO

With MU-MIMO

With SU-MIMO and MU-MIMO

Mean Attempted

4930

4889

4943

Mean Served

2743

55.6%

3484

71.27%

4350

88.01%

Mean Failed

2186

44.3%

1404

28.73%

592

11.99%

Contributions to Failure DL RSRP

0.37%

0.47%

1.20%

RSRQ

0.16%

0.15%

0.11%

DL BCH/SCH SINR

0.00%

0.00%

0.00%

UL SINR

0.00%

0.00%

0.00%

DL SINR

1.88%

1.89%

1.64%

UL Capacity

0.00%

0.00%

0.00%

DL Capacity

97.62%

97.51%

97.08%

No valid connection scenarios

0.00%

0.00%

0.00%

No covering cells

0.00%

0.00%

0.00%

Note: Terminals can fail to connect for multiple reasons so the failure reason percentages can sum to more than 100%. Table 5-2 Composite failure report with SU and MU-MIMO.



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5.3

ICIC

Inter-Cell Interference Coordination (ICIC) schemes aim to maximize spectral efficiency of LTE systems by re-using the available resource blocks (RBs) as often and in as many cells as possible while keeping the overall ICI in the system to an acceptable level. There are various schemes that are designed to mitigate ICI, and their implementation in the live network scenario is largely governed by the equipment vendors. The following ICIC schemes are suppo rted in ASSET: • • •

Reuse 1 (Prioritisation) Soft Frequency Reuse Reuse Partitioning

They are defined on the carrier layer (Figure 5-38). Fundamental to each of these methods is a division of the network into two areas in relation to the cell coverage, i.e. Cell Centre Users (CCUs) and Cell Edge Users (CEUs). This spatial separation of cell service area is controlled in ASSET by the Cell Edge Thresholds defined per cell in the Site Database. The available thresholds are “RSRP” and “Relative RSRP”. RSRP is self-explanatory while the latter is defined in dBs and can be expressed as the difference between the RSRPs of the serving and the strongest i nterfering cell.

Figure 5-38 ICIC Schemes

Figure 5-39 Cell Edge Thresholds For this Analysis we will use the Relative RSRP option (Figure 5-40) as it captures better the Cell Edge Edge compared to RSRP threshold that captures the Site Site Edge. The result of the two Cell Edge Threshold option is shown in the following fi gure. Based on RSRP

Based on Relative RSRP

Figure 5-40 Cell Centre / Cell Cell Edge



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5.3.1

Reuse 1 (Prioritisation)

Reuse-1 is implemented by splitting the total bandwidth in partitions and prioritising their use to different cells in a coordinated format. ICIC schemes target the improvement of Traffic and Control SINR. This will affect positively the achievable bearers and subsequently the number of served terminals and network throughput. Without ICIC

With Reuse 1 (Prioritisation)

Figure 5-41 Traffic & Control SINR without and with ICIC (Reuse-1, Prioritisation) The main factor improved by ICIC is Traffic & Control SINR which is shown in Figure 5-41. This improvement allows for a more favourable allocation of bearers (Figure 5-42) and consequently higher data rates (Figure 5-43). Without ICIC


Figure 5-42 Achievable DL bearer without without and with ICIC (Reuse-1, Prioritisation)



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Without ICIC

Figure 5-43 DL Data Rate without and with ICIC (Reuse-1, Prioritisation) Prioritisation) The improvement of Traffic & Control SINR with the deployment of Prioritisation is dependent on the Cell Loading and on the Coordination factor (Figure 5-44). The “Coordination Factor” takes into account that the modelling is probabilistic and scales the maximum theoretical gains accordingly. A coordination factor of 1 means perfect coordination and a coordination factor of 0 assumes no coordination at all. For the purpose of this tr ial a value of 0.7 is used.

Figure 5-44 Average Traffic&Control SINR Improvement Improvement with Prioritisation as a function of Cells’s Cells’s Load Level and the Coordination Factor (CF)



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As shown in Figure 5-44, irrespective of the Coordination Factor, if a Network is heavily loaded (over 70%) then gains are negligible. The gains of Prioritisation diminish as if the network load is high. To explain this, we will take the example of a 3sectored network. If the cell load is more than 1/3 or 33% then the prioritised recourses for each one of the cells is not enough to serve the load and overlapping (thus interference) is unavoidable. For an 80% loaded network the use of prioritisation doesn’t provide any gains as shown in Figure 5-45.

DL Data Rate Without ICIC

DL Traffic/Ctrl SINR Without ICIC

DL Data Rate With Reuse-1 (Prioritisation)

DL

Traffic/Ctrl

SINR

With

Figure 5-45 Highly Loaded (80%) Network Network without and with Prioritisation – Same Performance



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Reuse-1

5.3.2

Soft Frequency Reuse and Reuse Partitioning

Soft Frequency Reuse This scheme is an extension of the Reuse-1 (Prioritisation) (Prioritisation) scheme, where in addition to prioritising RBs in each cell, a power difference in the DL between cell centre users (CCUs) and cell edge users (CEUs) is also introduced. This difference in power between RBs effectively divides the cell into an inner and an outer region, and the users located in these regions can be classified as the CCUs and CEUs, respectively. Hence, by prioritising and using more power on CEUs' RBs, overall ICI mitigation in the network and performance gain in terms of coverage and cell-edge capacity can be r ealized. To define a Soft Frequency Reuse Scheme: • •

•

Split the carrier bandwidth (RBs) into two dedicated portions or zones, i.e. CC zone and CE zone, one for CCUs and the other for CEUs, usin g the “Soft “ Soft Bandwidth Ratio” Ratio” parameter. Specify a “Coordination “Coordination Factor ”. ”. The Reuse-1 (Prioritisation) scheme (as described in the previous section) is implemented within both zones; each sector has a prioritised partition in each zone, which it tries to use before the non-prioritised partitions in that zone. The “Coordination Factor ” can be used to adjust the calculated probability of collision. Specify a power difference between the DL RBs of the CEUs and CCUs, using the “ Power “ Power Ratio” Ratio” parameter. The concept is that the CCUs can be reached with the reduced power whereas the CEUs need the higher power level for successful transmission. This results in a possible performance gain for the CEUs.

This picture shows an example of the Soft Frequency Reuse scheme:

Figure 5-46 Soft Frequency Reuse Scheme (Power (Power Ratio 50%, Bandwidth Ratio 50%)

Figure 5-47 Soft Frequency Reuse Scheme – Example Example Settings



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Reuse Partitioning In addition to the prioritisation of RBs and different DL power levels, this scheme also divides the available spectrum into multiple partitions. Reuse Partitioning is similar to Soft Frequency Reuse, because it divides the available a vailable carr ier bandwidth (RBs) into two dedicated zones, one for CCUs, the other for CEUs. As in Soft Frequency Reuse, Reuse , the CC zone uses Reuse 1 (Prioritisation). (Prioritisation). However, unlike Soft Frequency Reuse, Reuse , the CE zone does not use Reuse 1 (Prioritisation), but instead employs the traditional frequency reuse of N , where N where N is is the number of sectors on the eNodeB. Each sector can only consume CE resources from its own dedicated CE partition. Restricting each sector to its own dedicated CE partition results in power concentration for the CE partition, which means that the spectral density of the power transmitted over a fraction of the CE RBs is higher than the spectral density of the same power transmitted over t he entire RBs.

Figure 5-48 Reuse Partitioning

Figure 5-49 ReUse Partitioning – Example Settings We will now compare Soft Frequency Reuse and Reuse Partitioning against no ICIC at all. The first factor to examine is DL Traffic and Control SINR (Figure 5-50). In Figure 5-51 we can see how the Achievable bearer is improved with the deployment of the ICIC schemes and finally in Figure 5-52 we can observe the obvious improvement in DL Data Rate.



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No ICIC

Soft Frequency Reuse

Reuse Partitioning

Figure 5-50 DL Traffic & Control SINR without and with ICIC ICIC



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No ICIC


Reuse Partitioning

Figure 5-51 Achievable DL bearer without and with ICIC



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No ICIC


Reuse Partitioning

Figure 5-52 DL Data Rate without and with ICIC



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Taking a closer look at the results, we have created the following graphs to prove the superiority of the aforementioned ICIC schemes:

Figure 5-53 Traffic & Control SINR without and with ICIC The above figure demonstrates how the ICIC schemes improve the SINR Cumulative distribution.

Figure 5-54 DL Data Rates without and with ICIC The above figure comprehensively demonstrates the effect of ICIC schemes on the ultimate operators’ goal; to increase the Data Rates.



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Figure 5-55 DL Data Rates without and with ICIC – Cumulative Cumulative Distribution Without any ICIC scheme only 67% of the covered area can support speeds up to 40Mbps. The deployment of Soft Frequency Reuse increases this figure by 5%, up to 72% and the deployment of Reuse Partitioning improves it by 24%, up to 91%.

5.4

Schedulers

LTE services consist of two traffic types Real Time and Non-Real Time. Real Time services have an associated Maximum Bit Rate (MBR) demand in addition to the (minimum) Guaranteed Bit Rate (GBR), whereas Non-Real Time services have only a GBR demand. When running a simulation, ASSET first attempts to serve the GBR demands of both Real Time and Non-Real Time services, taking into account the Priority values of t he different services. Resources are first allocated to the service with the highest priority, and then to the next highest priority service, and so on. Terminals are only served if there are enough resources available to satisfy their GBR demand. In the event that there are not enough resources to fulfil the GBR demand of all Real Time and NonReal Time services, then only the Priority values of the services determine the precedence of resource allocation. If resources are still available after the GBR demands have been met, then different scheduling algorithms algorithms can be employed to attempt to serve the MBR of Real Time services. To satisfy the Maximum bit rate of Real Time services (RT-MBR), there are four different scheduling algorithms available: On the General LTE Parameters Page, at the Cell layer, there exists an option of four different schedulers to select from: • • • •

Max SINR Proportional Demand Proportional Fair Round Robin



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Figure 5-56 Schedulers – LTE PArams Let’s draw a simple example. We have two services only: Real Time Service : RT_S1, GBR=100kbps, MBR=300kbps Non Real Time Service : NonRT_S1, GBR=140kbps. RT_S1 NonRT_S1

RT_S_MBR RT_S_GBR NRT_S_GBR

Now let’s assume a cell is serving five RT_S1 users and four NonRT_S1 users with that much RBs available: RT_S_GBR -1

NRT_S_GBR -1

NRT_S_GBR-2 RT_S_GBR -3

RT_S_GBR -2 NRT_S_GBR -3

NRT_S_GBR -4

RT_S_GBR -4

Unused resources, available for RT_S_MBR -1 -2 -3 -4 and -5 to be allocated according to the selected Scheduler. RT_S_GBR -5

Figure 5-57 Schedulers – LTE PArams

Round Robin The aim of this scheduler is to share the available/unused resources equally among the RT terminals (i.e. the terminals requesting RT services) in order to satisfy their RT-MBR demand. This is a recursive algorithm and continues to share resources equally among RT terminals, until all RT-MBR demands have been met or there are no more resources left to allocate.

Proportional Fair The aim of this Scheduler is to allocate the available/unused resources as fairly as possible in such a way that, on average, each terminal gets the highest possible throughput achievable under the channel conditions. This is a recursive algorithm. The remaining resources are shared between the RT terminals in proportion to their bearer data rates. Terminals with higher data rates get a larger share of the available resources. Each terminal gets either the resources it needs to satisfy its RT-MBR demand, or its weighted portion of the available/unused resources, whichever is smaller. This recursive allocation process continues until all RT-MBR demands have been met or there are no more resources left to allocate.



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Proportional Demand The aim of this scheduler is to allocate the remaining unused resources to RT terminals in proportion to their additional resource demands. This is a non-recursive allocation process and results in either satisfying the RT-MBR demands of all terminals or the consumption of all of the resources,.

Max SINR The aim of this Scheduler is to maximise the terminal throughput and in turn the average cell throughput. This is a non-recursive resource allocation process where terminals with higher bearer rates (and consequently higher SINR) are preferred over terminals with lower bearer rates (and consequently lower SINR). This means that resources are allocated first to those terminals with better SINR/channel conditions, thereby maximising the throughput.

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Figure 5-59 The effect of schedulers on a heavily loaded network It becomes obvious that Max SINR Scheduling will maximise the network throughput as terminals with the best RF conditions are served first. However this is not optimising the user experience as users with worse RF conditions are neglected. Also Max SINR approach is unfriendly to mobile users as their SINR is often changing from good to bad and they would possible get complete interruption of service when moving through bad RF conditions. The Round Robin approach is completely random as it simply allocates the same resources to all terminals in turns. Proportional Fair seems as the fairest choice because it provides resources analogous (or proportional) to the RF conditions. This is in contradiction to Max SINR where the allocation of resources is not analogous to RF conditions but absolute. In other words with Proportional Fair scheduling terminals experiencing bad RF conditions will not be cut off all together but will be simply allocated fewer resources which is important for the continuity of continuity of the service. Finally, Proportional Demand is trying to satisfy the more demanding users by allocating more resources t o them and this results in decreased overall net throughput. Proportional Demand completely ignores RF conditions and the effect of this is to totally waste resources by trying to serve very demanding users happening to be at very bad RF conditions.



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ASSET v8 - LTE Application Notes - 2.0

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