GSM Um signalling & radio optimisation
GSM radio optimisation . Figure 1
Course Outline GSM system overview Radio optimisation
1
2
Um interface
GSM radio optimisation . Figure 2
3
Section A
GSM GSM system system overview overview
GSM radio optimisation . Figure 3
Topic Outline
Bursts & frames
1
System architecture
2
Channels & channel organisation
GSM radio optimisation . Figure 4
3
GSM Frequency Bands Uplink
Absolute Radio Frequency Channel Number (ARFCN) Carrier spacing 200 kHz
876 MHz 915 MHz 880 MHz 876 MHz
P-GSM E-GSM
Downlink
Primary-GSM : 1-124 Extended-GSM : 0-124, 975-1023
R-GSM
Railway-GSM : 0-124, 955-1023
Uplink
+45 MHz +45 MHz +45 MHz
Downlink 1785 MHz
1710MHz
DCS-1800
DCS-1800 : 512-885 GSM radio optimisation . Figure 5
+95 MHz
GSM Channel Coding: Normal TDMA Burst Structure Stealing flags for FACCH
Data
TSC
Data
57
1 26 1
57
3
Guard bits
3 8.25
156.25 bits, 577 µs 114 bits payload
0
1
2
3
4 4
5
6
7
TDMA frame, 8 timeslots = 4.615 ms
*TSC: Training Sequence GSM radio optimisation . Figure 6
GSM Channel Structure: Multi-Frame and Burst Types
GSM radio optimisation . Figure 7
GSM Channel Structure: Logical channels RACH (UL)
BCCH (DL)
PCH (DL)
CCCH
AGCH (DL)
TCH/F TCH/H FACCH
Dedicated Channels Signalling & Control Channels
SACCH SDCCH
GSM radio optimisation . Figure 8
Mapping onto physical channels 0 1 2 3 4 5 6 7
GSM channel coding: Block structure SDCCH or SACCH Channel Coding
TCH Channel Coding
SDCCH block
20 ms Speech Frame 456 coded bits
Data 184
BCS 40
Data 4
FR:260, EFR 244
Rate 1/2 Convolutional coding 114
114
114 114
114
Mapped on 4 TDMA TS 01234567
01234567
01234567
114
114
114
57 57 57 57 57 57 57 57
Mapped on 8 HALF TDMA TS
01234567
GSM radio optimisation . Figure 9
SACCH Channel SACCH DOWNLINK Block Rsvd
Ordered MS power (5 bits)
Rsvd Ordered timing advance (7 bits) Payload (21 octets)
SACCH UPLINK Block Rsvd
Typical message sequence on SACCH
Actual MS power (5 bits)
Rsvd Actual timing advance (7 bits) Payload (21 octets)
3.270 DL RR System Info 5 3.320 UL RR Measurement Report 3.750 DL RR System Info 5 3.800 UL RR Measurement Report 4.210 DL RR System Info 6 4.260 UL RR Measurement Report 4.700 DL RR System Info 5 4.750 UL RR Measurement Report 5.170 DL RR System Info 5 5.220 UL RR Measurement Report 5.660 DL RR System Info 6 5.700 UL RR Measurement Report 6.120 DL RR System Info 5 6.190 UL RR Measurement Report
GSM radio optimisation . Figure 10
Channel Organization Most important combinations TS0 TS0
TS0 TS0
Example: cell with only 1 TRX
01234567
GSM radio optimisation . Figure 11
Logical Channels Mapping on TS 0 FCCH + SCH + BCCH + CCCH Cycle of 51 TDMA Frames TDMA Frame
012345670123456701234567
BCCH+CCCH (Downlink) 9 Paging Blocks
In 51-TDMA Frame we have 9 paging Blocks (DL) In a complete paging cycle the maximum number of 51-TDMA frames is 9 In Uplink only RACH is used GSM radio optimisation . Figure 12
Alternative Mapping on TS 0 Used in Low Signaling Traffic Cells
1st 51-TDMA-frames
2nd 51-TDMA-frames
Paging Blocks reduced to 3 in one 51-TDMAframes cycle. GSM radio optimisation . Figure 13
Mapping of SDCCH/8 + SACCH
01234567 0123456 701234567
TDMA Frame
Used on TS1-7
GSM radio optimisation . Figure 14
Mapping of TCH (FACCH) + SACCH
0123456701234 567012 34567
TDMA Frame
GSM radio optimisation . Figure 15
Overview of GSM radio subsystem Um Protocol Stack
Abis Protocol Stack
A Protocol Stack
(OSI model)
(OSI model)
(SS7 model)
Upper Layers
Upper Layers
Upper Layers
Layer 3
Layer 3
Layer 3
Layer 2
Layer 2
Layer 2
Layer 1
Layer 1 BTS
Um interface
Layer 1 BSC
Abis interface
GSM radio optimisation . Figure 16
A interface
MSC
OSI Model
GSM radio optimisation . Figure 17
Section B
UM UM interface interface
GSM radio optimisation . Figure 18
Topic Outline
Um Protocol Stack
1
MS in Dedicated Mode
4
3
2
MS in Idle Mode
GSM radio optimisation . Figure 19
Exercises
Q&A
Um Protocol Stack
Upper Layers
User
MM
CC
Layer 3
RR
Layer 1 & 2
Transmission
GSM radio optimisation . Figure 20
Um Protocol Stack – Layer 1 & 2
Layer 2
LAPDm Protocol
Transmission
Layer 1
Radio
GSM radio optimisation . Figure 21
Derived from LAPD (ISDN) Optimized for AirInterface Limited Resources Propagation Characteristics of Radio Link
Um Protocol Stack – Layer 3 Mobility Management (MM)
Connection Management (CM) MM
Inform network about current location of mobile, privacy of MS location update identity check authentication
CC
RR
Radio Resource Management (RR)
Call Control (CC), connection between users call setup, alerting, connection & disconnection
Manage logical & physical radio channels on the air interface cell selection/reselection, Handover measurement reports channel release GSM radio optimisation . Figure 22
Layer 3: Connection Management Short Message Services SMS
Call Control and call related Supplementary services Call Establishment CC Procedures Active State Procedures Call Clearing Miscellaneous procedures
CM SS
GSM radio optimisation . Figure 23
Non Call Related Supplementary Services
Layer 3: CM-CC Messages BTS
MS
Release
Active State
Establishment
CC Setup CC Call Proceeding CC Alerting
Call Establishment Messages
CC Connect CC Connect Ack Modify, Modify Reject, Modify Complete… Hold, Hold Ack, Hold Reject Retrieve, Retrieve Ack, Retrieve Reject…
Disconnect, Release, Release Complete…
Call Information Phase Call Related Supplementary messages
Call Clearing Messages
GSM radio optimisation . Figure 24
Layer 3: Mobility Management Support CM upper sublayer CM Messages (CM service Accept/Reject/Abort/Request)
CM support
Support MS mobility Location Update (normal, periodic, IMSI attach) Registration messages (IMSI detach, LA Update Accept, LA Update Reject, LA Update Request)
MM MS
Support User User Confidentiality Authentication Security messages (Authentication Reject /Request/Response, Identity Request/Response)
GSM radio optimisation . Figure 25
Layer 3: RR Management
MOC
RR
Layer 2 service
Layer 1 Measurement Control Channel Management
Release
MM
Dedicated Mode
Idle Mode
MS
BTS
Receives/transmits system info (BCCH) and paging (CCCH) …
Establishes, maintains and releases a RR connection …
MOC: Establishment of RR connection initiates via MM MTC: by the peer entity on the NS via the paging channel
Normal release procedure or RLTimeout…
GSM radio optimisation . Figure 26
Um Layer 3 GSM Signaling Abis
Um MS
BTS
A BSC
MSC
CM
CM
MM RR
MM RR
RR
CM MM RR
RR
Connection Management Sub-layer Mobility Management Sub-layer Radio Resource Management Sub-layer
GSM radio optimisation . Figure 27
Layer 3
Layer 2
MS Tasks in Idle Mode MS
BTS Perform cell selection Perform cell re-selection LA update Listen to paging subgroup Read system information
GSM radio optimisation . Figure 28
MS Tasks in Idle Mode: Cell Selection MS selects a PLMN
MS scans for BCCH frequencies stop scanning the selected PLMN MS tries cells by Rx level
No Suitable cells Found?
MS must scan at least 30 frequencies in the GSM900 and 40 frequencies in the GSM1800 band. MS will perform ‘normal’ or ‘storedlist’ cell selection.
Suitable cells are not barred and have C1>0 (with some other criteria).
Yes Camp on a “suitable cell” GSM radio optimisation . Figure 29
MS Tasks in Idle Mode: Cell Reselection Cell Reselection Triggers path loss criterion C1 becomes negative A downlink signaling failure occurs The camped-on cell by the MS is barred A cell w/ better C1 in the same LA A cell w/ much better C1 in a different LA Random access (RR Channel Request) is still unsuccessful after Max_Retrans repetitions
GSM radio optimisation . Figure 30
Cell Reselection
MS Measurements in Idle Mode MS reads the BCCH Allocation (BA) in the neighbour cells from the Sys Info 2 messages on the BCCH channel Mobile in idle mode
0.390 DL RR System Information Type 2 - BCCH BA-IND: 1, EXT-IND: 0 BA List: 41 43 66 68 71 73 77 79 85 (Bit Map 0) 0.540 DL RR System Information Type 2ter - BCCH BA-IND: 1, EXT-IND: 0 BA List: 547 (Variable Bit Map)
BA-IND: allows to differentiate between different BCCH Allocations, i.e. BA(BCCH, idle mode) and BA(SACCH, dedicated mode) EXT-IND (only valid in 2 & 2bis): indicates whether this is the complete message or extension (e.g. for E-GSM band)
The mobile performs measurements in idle mode for cell (re)selection GSM radio optimisation . Figure 31
MS Tasks in Idle Mode: Path loss criterion C1 Path loss criterion C1 is used for cell selection C1 = RLA_C – RXLEV_ACCESS_MIN - MAX(B,0) Rx level in idle mode Minimum Ms Rx level for network access MS_TXPWR_MAX_CCH - P (P = maximum output power of MS)
C1>0?
No
Yes
Highest C1?
Yes
No GSM radio optimisation . Figure 32
Cell Selection
MS Tasks in Idle Mode Re-selection criterion C2 Cell re-selection criterion C2 and Rxlev_Access_Min are typically used in multi-layer and multi-band networks to control cell re-selection. The MS will reselect the cell with the highest C2 value. Penalty Time
C2 Serving Cell
<>11111 (Encourage)
C1 + CELL_RESELECT_OFFSET
=11111 (Discourage)
C1 CELL_RESELECT_OFFSET
C2 Non-Serving Cell For T < PENALTY_TIME C1 + CELL_RESELECT_OFFSET - TEMPORARY_OFFSET For T >= PENALTY_TIME C1 + CELL_RESELECT_OFFSET C1 - CELL_RESELECT_OFFSET
Timer T starts once a cell is placed on the list of 6 strongest neighbour. GSM radio optimisation . Figure 33
MS Tasks in Idle Mode: Cell Reselection No Calculate C2 (every 5 s)
New GSM LA?
Yes
C2(n) > C2(s) + Cell_Reselect_Hyst? And optional C2(n)>C2(s)+5
C2(n) > C2(s)? or C2(n)>C2(s)+5 Yes
For reselections within 15s, a minimum offset of 5 dB is required
Yes
Cell Reselection LA updates generate a significant amount of load on MSCs. LA borders should be put in areas with clear cell borders GSM radio optimisation . Figure 34
Cell Re-selection Responsiveness Cell Reselection Speed Factors
Response Time
① Mobile capabilities to detect new carriers C2 measurements time interval Max {5 , ((5 * N + 6) DIV 7) * BS_PA_MFRMS / 4} Number of neighbour cells Number of paging groups
Note
Up to 10s+ For 4 multi-frames paging groups
Neighbors
10 20
Interval
8s 15s
Compare
MS may select “wrong” cell: Fast moving users, long neighbor lists, high BS_PA_MFRMS
Handover measurements typically in a sliding window of 3-5s
GSM radio optimisation . Figure 35
MS Tasks in Idle Mode: Downlink signaling Failure DSC initialised to 90/BS_PA_MFRMS
decode of paging sub-channel successful?
No DSC - 4
Yes Downlink signaling Counter
DSC +1
DSC<=0? Yes
Up to 90/BS_PA_MRFMS
DL signaling Failure
Cell Reselection GSM radio optimisation . Figure 36
MS Tasks in Idle Mode: Listen to Paging Group The mobile will only listen to a limited number of paging blocks according to its IMSI. BS_PA_MFRMS indicates the number of 51-multiframes between transmission of paging messages to mobiles of the same paging group. Range: 2 to 9. Higher value means increased call setup time for MTC (it takes longer before the paging can be sent). DRX: discontinuous reception mode of operation: MS powering itself down when it is not expecting paging messages from the network. Improves battery life in idle mode. Higher value for BS_PA_MFRMS will increase the mobile battery life in idle mode. GSM radio optimisation . Figure 37
MS Tasks in Idle Mode: System Information Two examples of system info Type 3, note the difference: RR System Information Type 3 MCC-MNC-LAC-CI: 123-45-401-00001 BS-AG-BLKS-RES: 1 blocks rsvd for access grant CCCH-CONF: one basic physical channel, combined with SDCCHs BS-PA-MFRMS: 4 multiframes period T3212 Time-out: 10 decihours MaxRadioLinkTimeout: 16 multiframes CellReselHyst: 4 dB MsTxPowerMaxCCH: (0) 30 dBm Additional Reselect Param Ind (ACS): 0 RxLevAccessMin: (5) -105 dBm MaxRetransmissions: 4 TxInt: 12 slots
RR System Information Type 3 MCC-MNC-LAC-CI: 123-45-702-00002 BS-AG-BLKS-RES: 1 blocks rsvd for access grant CCCH-CONF: one basic physical channel, combined with SDCCHs BS-PA-MFRMS: 4 multiframes period T3212 Time-out: 30 decihours MaxRadioLinkTimeout: 20 multiframes CellReselHyst: 10 dB RXLEV MsTxPowerMaxCCH: (5) 33 dBm Additional Reselect Param Ind (ACS): 0 RxLevAccessMin: (8) -102 dBm MaxRetransmissions: 2 TxInt: 32 slots
GSM radio optimisation . Figure 38
MS in Dedicated Mode Measurements MS Measurements in dedicate mode
BA-IND: Differentiate between different BA lists EXT-IND (for 5 & 5bis only): Indicates complete message or extension
DL RR System Info Type 5 - SACCH BA-IND: 0, EXT-IND: 0 BA List: 43 44 67 68 69 71 75 77 79 81 85 UL RR Measurement Report - SACCH RxLevFull: -86 dBm, RxQualFull: 0 RxLevSub: -86 dBm, RxQualSub: 0 BA Used: 0, UL DTX: Not Used Measurements are valid N1: Freq list [ 10 ] Level -89 dBm BSIC 34 N2: Freq list [ 1 ] Level -98 dBm BSIC 11 N3: Freq list [ 5 ] Level -95 dBm BSIC 45 N4: Freq list [ 0 ] Level -97 dBm BSIC 70 N5: Freq list [ 8 ] Level -98 dBm BSIC 34 N6: Freq list [ 2 ] Level -104 dBm BSIC 42
MS reports measurements to the network every 480 ms
RxLev 6 strongest neighbour cells
GSM radio optimisation . Figure 39
SACCH info Layer 3 field Identifies the L3 Protocol
For RR and MM = 0000 (Skip Indicator) For CM = Transaction identifier for parallel connections
GSM radio optimisation . Figure 40
Measurements in Dedicated Mode 25
24 0 1
23
4 5 6 7 0 1
4 5 6 7 0 1 2 3 4 5 6 7 0 1
Tx 0 1
Tx 23
4 5 6 7 0 1
24
23
4 5 6 7
DL
Rx
Rx
Rx MS MS measures measures at at least least 25 25 Nbor Nbor SS SS measureme measureme nt nt samples samples in in 26 26 TDMA TDMA frame frame Multiframe Multiframe
23
Idle
Measures BSIC
23 25
Tx
4 5 6 7 0 1 2 3 4 5 6 7 0 1
23
4 5 6 7
Idle
Nbor Nbor BSIC BSIC is is measured measured during during the the Idle Idle frame frame using using the the sliding sliding window window technique technique
Full Measurement report needs 4 SACCH bursts: 4x25=100 Nbor SS samples
GSM radio optimisation . Figure 41
UL
Radio link failure Principles Ensure that calls with unacceptable quality are either reestablished or released in a defined manner. Known as “Radio link timeout”, or in general, dropped call. Parameter RADIO_LINK_TIMEOUT GSM 05.08: “The parameters that control radio link failure should be set such that the forced release will not occur until the call has degraded to a quality below that at which the majority of subscribers would have manually released. This ensures that a call on the edge of a radio coverage area, although of bad quality, can usually be completed if the subscriber wishes.”
Sent on SACCH to MS in System Information type 6 messages.
Implementation MS-implementation is specified in GSM 05.08. Based on the successful decoding of messages on the downlink SACCH. BTS-implementation is manufacturer-specific. Based on successful SACCH decoding and/or RxLev/RxQual measurements. GSM radio optimisation . Figure 42
Radio link failure Implementation Higher Radio-Link-Timeout values will “trick” the number of dropped calls: User will terminate the call (due to unacceptable quality), but the release will be classified as normal release. Typical values for Radio-Link-Timeout: 16 to 40 (or roughly 8 to 20 s).
R adio Link C ounter S
Radio Link Failure (MS Side) 18 16 14 12 10 8 6 4 2 0
S is initialised on every channel change (SDCCHTCH, intra-cell HO, HO failure with return, etc.)
Smax=RADIO_LINK_TIMEOUT SACCH decoded = +2 SACCH missed = -1 Radio Link Time Out
SACCH Multiframes GSM radio optimisation . Figure 43
RR System Info Type 6 Downlink SACCH Cell Id: MCC-MNC-LAC-CI: 123-20-401-15243 MaxRadioLinkTimeout: 16 multi-frames
Mobile originating call (MOC) signaling messages BTS
CCCH
MS Channel Request - RACH
Immediate Assignment - AGCH CM Service Request
Radio resource (RR) establishment. Request and assign a radio resource for signaling (SDCCH) Service request
SDCCH
(Authent.) (Ciphering) (Identity Check) CC Setup CC Call Proceeding
Call initiation
RR Assignment Command Assign a traffic channel (TCH)
TCH
RR Assignment Complete CC Alerting
User alerting
CC Connect CC Connect Ack
Call accepted
GSM radio optimisation . Figure 44
Mobile originating call (MOC) Message content Channel Request
establishment cause, random reference
Immediate Assignment
establish cause & random reference; assigns dedicated resource (ARFCN or hopping parameters, timeslot, sub-timeslot) or GPRS resource (TBF).
CM-Service Request
service type, ciphering key, mobile classmark (MS capabilities), mobile identity (TMSI, IMSI, IMEI)
CC Setup (MS to NW) bearer capability, BCD called party number CC Call Proceeding
bearer capability, Progress indicator
RR Assignment Command
channel description, power command
RR Assignment Complete
RR cause
CC Alerting CC Connect
Connected number, Connected subaddress
CC Connect Ack
Connect acknowledge GSM radio optimisation . Figure 45
RR establishment Contention resolution MS
Channel Request (RACH)
BTS
Immediate Assignment (AGCH)
RR Channel Request (RACH) Establishment Cause: Mobile originating call Random Reference: 3 RR Immediate Assignment (AGCH) Establishment Cause: Mobile originating call Random Reference: 3 Time: T1': 29, T2: 19, T3: 46
GSM radio optimisation . Figure 46
RR establishment Contention resolution Contention resolution
...
Random Access Channel 4.6 ms RACH ...
MS1 Establishment cause + random reference (8 bits in total)
MS3
①Use of time stamping, e.g. MS1 and MS2
②Use of random reference ③MS3 & MS4 . RxLev
Resolution
Similar
invalid RACH due to interference. both mobiles must re-attempt
MS4
MS2 Establishment cause + random reference
different random reference: Strongest MS will get channel (with correct random reference in Imm. Assign) MS3>>MS4
same random reference: both MS seize the channel. The weakest MS will fail to establish a layer-2 link with the network due to interference from strongest MS
GSM radio optimisation . Figure 47
Entering the Dedicated Mode Immediate Assignment procedure T3120
MS
BTS Paging Request - PCH
starts 0,1,…max(8, Tx) -1 TDMA frames Channel Request - RACH S is depended on Tx number and Channel Combination of TS0
restarted S+Tx TDMA frames
restarted
Channel Request (resent, IA not received)
Up to MaxRetransmissions Times Immediate Assignment - AGCH
Stopped
GSM radio optimisation . Figure 48
Mobile terminating call (MTC) signaling messages CCCH
MS
BTS Paging Request - PCH Channel Request - RACH
RR establishment
Immediate Assignment - AGCH Paging Response
Service request
SDCCH
(Authent.) (Ciphering) (Identity Check) CC Setup CC Call Confirmed
Call initiation
RR Assignment Command Assign a traffic channel (TCH)
TCH
RR Assignment Complete CC Alerting
User alerting
CC Connect CC Connect Ack
Call accepted
GSM radio optimisation . Figure 49
Um inter-cell handover Non-sync HO success Old TCH
MS
BTS
(… Measurement Reports ...) Handover Command
BSC starts T3103 (network specific)
Handover Access ...
...Handover Access
New TCH
Physical Information
Physical Information
Handover Complete
MS starts T3124 (320 ms for TCH, 675 ms for SDCCH) and repeats Handover Access until Phys. Info is received BSC starts T3105 (network specific). On expiry, repeat Phys. Info maximum of Ny1 times (network specific). On receipt Phys. Info, MS stops T3124 and switches to new channel. RR establishment on new cell complete. Data transfer is resumed on new cell. BSC stops T3103 and releases old channel.
GSM radio optimisation . Figure 50
Um inter-cell handover Non-sync HO failure HO failure, return to old channel
Handover Access …. MS starts T3124 MS timer T3124 expires, or lower layer failure
Handover Failure
Old TCH New TCH
Handover Command BSC starts T3103
Old TCH
Old TCH New TCH
MS
BTS
MS
Old TCH
HO failure, MS lost during HO
GSM radio optimisation . Figure 51
BTS
Handover Command BSC starts T3103
Handover Access …. MS starts T3124 MS timer T3124 expires, or lower layer failure BSC timer T3103 expires, or lower layer failure MS and BSC release all radio resources
Um inter-cell handover Message content Handover Command contains
BCCH/BSIC to identify neighbour cell Details of new channel: ARFCN, timeslot, training sequence Handover reference
Handover Access burst contains the Handover reference Note Handover algorithms are proprietary to network equipment manufacturers (although often based on the same principles). The handover algorithm at the origin of a handover preparation and execution doesn’t impact the handover message flow.
DL RR System Info Type 5 BA-IND: 0, EXT-IND: 0 BA List: 777 780 782 784 787 790 UL RR Measurement Report RxLevFull: -86 dBm, RxQualFull: 0 RxLevSub: -86 dBm, RxQualSub: 0 BA Used: 0, UL DTX: Not Used Measurements are valid N1: Freq list [ 3 ] Level -79 dBm BSIC 20 N2: Freq list [ 1 ] Level -98 dBm BSIC 11 Downlink RR Handover Command BCCH: 784 BSIC: 20 TimeSlot: 7 TrainingSeq: 0 Hopping: No, ARFCN: 838 HandoverRef: 127 OrderedPowerLevel: 0 Synchronized: No
GSM radio optimisation . Figure 52
Um intra-cell handover Intra-cell TCH-TCH handovers are initiated by the RR Assignment Command Success
Note In general, the Assignment Command is used to instruct the mobile to change dedicated channel within a cell, whereas the Handover Command is used to change channel across cells.
Assignment Complete message is sent on new channel
Failure, return Assignment Failure is sent on old channel to old channel MS lost during none of these messages are sent. The MS channel doesn’t manage to seize the new channel, change and fails to return to the old channel. The MS will return to idle mode GSM radio optimisation . Figure 53
Um call clearing Initiated by MS MS
Initiated by network BTS
MS
CC Disconnect
CC Disconnect
CC Release
Call clearing
CC Release Complete RR Channel Release Messages CC Disconnect
BTS CC Release
CC Release Complete Release of RR
RR Channel Release
Causes (Note abnormal releases in CAUSE analysis) Normal call clearing, User busy, No user responding, User alerting - no answer, Call rejected, Pre-emption, Invalid number format (incomplete number), Normal - unspecified, No circuit/channel available, Network out of order, Temporary failure, switching equipment, congestion, etc.
CC Release & CC Release Complete: optional information element ‘cause’ RR Channel Release
normal release, abnormal release - unspecified, abnormal release - timer expired, etc. GSM radio optimisation . Figure 54
Um dropped call
DL_RxQual
Normally the cause for dropped calls cannot be inferred from drive test data. Typical dropped calls: Radio link timeout at MS MS goes to idle mode and starts analysing Sys Info (type 3)
DL_Lev
DL RR Channel Release Cause: Abnormal release, unspecified
Cause in RR channel release message Cause in CC Disconnect, CC Release, CC Release Complete message.
GSM radio optimisation . Figure 55
Section C
GSM GSM radio radio optimisation optimisation
GSM radio optimisation . Figure 56
Topic Outline CS call benchmarking analysis
CS call analysis
1
GSM radio optimisation . Figure 57
2
CS Call Analysis Identify Problems Negative Events Dropped Call Setup Failure Handover Failure
Poor Level Rx Lev Analysis Missing Handover Missing Neighbour
Poor Quality Poor Rx Qual in poor Level Interference Poor RX Qual in good level Excessive or ping-pong handover
GSM radio optimisation . Figure 58
Add Cell Refs Please ensure your cell refs
Is pointed to the following file Please load the logfile: Nemo Drive test 1. dt1 GSM radio optimisation . Figure 59
RX Lev Analysis We analyse the DL Rx level to indicate the coverage Right click the level from GSM-Downlink measurements & place on the Map
We can see from the map that generally the level is good but in the area circled the level is bad. Let’s look into this in more detail
GSM radio optimisation . Figure 60
RX Lev Analysis-Using Filter Create the following filter
GSM radio optimisation . Figure 61
Rx Lev Analysis
GSM radio optimisation . Figure 62
Serving Cell Analysis Press the layers button layer to be BCCH
on the map and change the labelling of the “GSM Cell Beam-width”
GSM radio optimisation . Figure 63
Serving Cell Analysis Press the layers icon again Also for the “GSM_Cell_Beamwidth” layer, click lines & change the
GSM radio optimisation . Figure 64
Serving Cell Analysis Before clicking OK click on the neighbour tab click disable then click OK
GSM radio optimisation . Figure 65
Serving Cell Analysis Now click the “area control” icon and draw a box around the area circled earlier.
GSM radio optimisation . Figure 66
Serving Cell Analysis We can see that some areas are being served by a distant server. This may be due to Variable Terrain Cells off air Neighbour definitions and parameters
GSM radio optimisation . Figure 67
Serving Cell Analysis-TA Display Timing Advance from Dedicated Radio Link Attributes
GSM radio optimisation . Figure 68
Turn off Filter
GSM radio optimisation . Figure 69
RX Qual Analysis Right click the DL Serving Rxqual & put on the map
GSM radio optimisation . Figure 70
Rx Qual Analysis Correlation between areas of poor level and poor quality This is expected, and is more pronounced as traffic volumes increase
We can see other areas of poor quality where coverage was good Interference? Excessive or ping-pong handover?
We are interested in further analysis of these areas GSM radio optimisation . Figure 71
Rx Qual Analysis-Binned Queries From the tools menu choose Analysis Manager, choose a binned query & click new Enter the expression: if(((ServRxLevSub > -85) AND (ServRxQualSub >= 4)) , ServCI, null)
GSM radio optimisation . Figure 72
Rx Qual Analysis- Binned Queries Right click the query & display this on the map
GSM radio optimisation . Figure 73
Negative Events Analysis Dropped Calls From the events menu drag the dropped calls on to the map
GSM radio optimisation . Figure 74
Dropped Call Analysis-Event Query We are interested in the general conditions prior to a call drop We use the Event Query to build a picture of the conditions prior to the drop From the tools menu open the Analysis manager & choose a new Event query
GSM radio optimisation . Figure 75
Dropped Call Analysis-Event Query Choose “event dropped call” as the trigger & a 5 second window before event & then click next
GSM radio optimisation . Figure 76
Dropped Call Analysis-Event Query Select the statistics that we want to analyse
GSM radio optimisation . Figure 77
Dropped Call Analysis-Event Query Average Level
Last CI
Average quality last BCCH
Interference
Timing Advance
GSM radio optimisation . Figure 78
Dropped Call Analysis-Event Query Once all statistics are entered OK and then view the query results in the statistic explorer
GSM radio optimisation . Figure 79
Dropped Call Analysis-Event Query Save/export your Query for Future use
GSM radio optimisation . Figure 80
Handover Analysis Import the HO OK Event query & display on the statistics explorer
GSM radio optimisation . Figure 81
Handover Analysis Using a map we can look into handovers in more detail
GSM radio optimisation . Figure 82
Handover Analysis The following Analysis pack gives some useful over view figures regarding handovers & call set up.
GSM radio optimisation . Figure 83
Handover Analysis
GSM radio optimisation . Figure 84
Call Setup Analysis Call Setup Flow Diagram
GSM radio optimisation . Figure 85
Call Setup Analysis We can use the protocol stack browser to check the flow of messages around call set up
GSM radio optimisation . Figure 86
CS Call Benchmarking Why Benchmark? Overview of Performance on certain routes KPI performance can give picture of “user perception” High Level Analysis can help distinguish between area-specific and network-level problems
It is useful to run benchmark reports prior to detailed analysis to get a feel for the problems on the route GSM radio optimisation . Figure 87
CS Call Benchmarking Actix design validation & quick analysis application pack provides a series of reports & statistics that can be used to bench mark your network Right click the “stream” & open the design validation & quick analysis application pack The statistics window displays a count of various KPI’s per Cell this can then be used to start to identify problem cells
GSM radio optimisation . Figure 88
CS Call Benchmarking Call details Report This gives details of the of the main call events such as call set up & call drops negative events are highlighted in red.
GSM radio optimisation . Figure 89
CS Call Benchmarking The Design Validation report This report looks at the level quality & interference with your network & compares to a series of Matrix to decide if the area driven is of good or bad design
GSM radio optimisation . Figure 90
CS Call Benchmarking Measurement Charts report Shows distribution of Level, Quality and Timing Advance
GSM radio optimisation . Figure 91
CS Call Benchmarking Neighbor level This report looks into the dominance of your server
GSM radio optimisation . Figure 92