GSM_All, WCDMA , LTE

Introduction into Communication Eng./Mohamed Tarek

Contents Communication Introduction Multiple Access Technique GSM Network Architecture Call scenario and call set up ,Hand over ,Location update Radio planning and GSM coverage GSM Network Interferences and Signaling Access to 3G and New communication systems Communication Companies and Different positions

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Lecture 1

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Introduction Any Communication system consists of :-

source

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Transmission medium

Lecture 1

Destination

3

Introduction • The kinds of transmission medium : Wired Wireless Wired transmission medium :

1- Twisted-pair 2- Coaxial cable

3-optical fibers

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4

Introduction Communication Channels’ types:Channel Type

Properties

Applications

Simplex

One-way only

FM radio, television

Half duplex

Two-way, only one at a time

Police radio, push-to-talk

Full duplex

Two-way, both at the same time

PSTN, Mobile systems

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Introduction Communication system consists of :Noise Info. SOURCE

Source

Received Transmitted Received info. signal signal Transmitter Receiver Channel User

Transmitter Source

Source encoder

Channel encoder

Modulator

Receiver Destination 2006-01-24

Source decoder

Channel decoder Lecture 1

Demodulator 6

Introduction Encoding:Encoding is the process of transforming information from one format into another. The opposite operation is called decoding.

Encoding is the process of putting a sequence of characters (letters, numbers, punctuation, and certain symbols) into a specialized format for efficient transmission or storage. Decoding is the opposite process “ Source Encoding ” conversion from analog to digital is Encoding

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Introduction • Channel encoding deals with error control during the transmission through the communication channel. • Error detection Codes

•

Parity check codes (Odd parity – Even parity)

(Frame – Protocols )??

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Introduction Data Compression is an important subject as more digital information is required to be stored and transmitted. • Compression methods: There are two main types of compression. Lossless compression Lossy compression

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Classification of signals … • Periodic and non-periodic signals

A periodic signal

A non-periodic signal

• Analog and discrete signals

Analog signals 2006-01-24

A discrete signal Lecture 1

10

Classification of signals • Deterministic and random signals – Deterministic signal: No uncertainty with respect to the signal value at any time. – Random signal: Some degree of uncertainty in signal values before it actually occurs. • Thermal noise in electronic circuits due to the random movement of electrons • Reflection of radio waves from different layers of ionosphere

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Noise

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Digital versus analog • Advantages of digital communications: – Regenerator receiver

Original pulse

Regenerated pulse Propagation distance

– Different kinds of digital signal are treated identically. Voice

Data

A bit is a bit! Media

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Analog VS Digital

Digital Communication:Advantages of Digital :Less noise effect More reliable Easy to manipulate Flexible Compatibility with other digital systems Only digitized information can be transported through a noisy channel without degradation Integrated networks

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Introduction

Disadvantages of Digital Sampling Error Digital communications require greater bandwidth than analogue to transmit the same information. We loss some of information due to sampling process

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Introduction Definition of Analogue :Analogue is a transmission standard that uses electrical impulses to emulate the audio waveform of sound. When you use a phone, the variations in your voice are transformed by a microphone into similar variations in an electrical signal and carried down the line to the exchange Advantages of Analogue Uses less bandwidth More accurate Disadvantages of Analogue The effects of random noise can make signal loss and distortion impossible to recover and more effect by noise

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Circuit Switching VS Packet Switching

Circuit Switching

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Packet Switching

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Multiple Acess Techniqe It is used because the limitation of transmission resources comparing with the number of users

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Multiple Acess Techniqe 

Three types of Multiple Access Technique are available: Frequency Division Multiple Access (FDMA)

Time Division Multiple Access (TDMA) Code Division Multiple Access (CDMA)

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Frequency Division Multiple Access (FDMA) 

Each FDMA user is assigned a specific frequency channel. No one else in the same cell or a neighboring cell can use the frequency channel while it is assigned to a user. Although this technology will reduce signal interference, it also severely limits the number of users able to transmit at a time.

Strength User 1

f1

User 2

f2

User 3

f3 Frequency

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Time Division Multiple Access (TDMA) TDMA users share a common frequency channel, but use the channel for only a very short amount of time. They are each given a time slot and only allowed to transmit during that particular time slot. When all available time slots in a given frequency are used, the next user must be assigned a time slot on another frequency. The time slices are so small that the human ear cannot perceive the time slicing, and therefore assumes that they have the entire channel to transmit their signal.

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Time Division Multiple Access (TDMA) Strength

User 2, time=t0 User 1, time=0

Frequency

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TDMA VS FDMA Strength User 1

User 2

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User 7

26

Code Division Multiple Access (CDMA) CDMA users share a common frequency channel. All users are on the same frequency at the same time. However, each pair of users is assigned a special code that reduces interferences while increasing privacy.

Strength

Frequency 2006-01-24

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TDMA VS FDMA VS CDMA

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What is the GSM? • GSM is the Global System for Mobile telecommunications. • It is the European standard for the Mobile telecommunications and it is considered as one of the most popular standard worldwide. • It is known as the second generation mobile telecommunications system “2G system”. • It is used in Egypt by the two existing operators; Mobinil and Vodafone; also it used as a part of the third operator in Egypt “Etisalat”.

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GSM Worldwide (darker areas)

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What is the GPRS? • GPRS is the General Packet Radio Service. • Within the GSM network it shares the network databases and radio access network. • It is known as the 2.5 generation mobile telecommunications system “2G system”.

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3G Systems Universal Mobile Telecommunication Service (UMTS) is the marketing name for the 3G has two standardization bodies: 1- 3GPP which uses the W-CDMA technology. 2- 3GPP2 which uses the CDMA2000 technology.

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Basic GSM Network Structure

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Basic GSM Network Structure Mobile Station (MS) • The Mobile Station (MS) is the interface between the user and the network. The MS consists of two independent parts:  Subscriber Identity Module (SIM) card  Mobile Equipment (ME)

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Basic GSM Network Structure Mobile Equipment (ME) • • • • • •

The ME is the only part of the GSM network which the subscriber will really see. Vehicle Mounted ‫تليفون السياره‬ These devices are mounted in a vehicle and the antenna is physically mounted on the outside of the vehicle. Portable Mobile Unit This equipment can be handheld when in operation, but the antenna is not connected to the handset of the unit. Handportable Unit This equipment comprises of a small telephone handset not much bigger than a calculator. The antenna is be connected to the handset.

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Basic GSM Network Structure Mobile Equipment Capabilities: RF power capability Encryption capability Frequency capability Short message service capability The ME is the hardware used by the subscriber to access the network. The hardware has an identity number associated with it, which is unique for that particular device and permanently stored in it. This identity number is called The International Mobile Equipment Identity (IMEI) “To guarantee that the mobile not to be stolen”

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Basic GSM Network Structure International Mobile Equipment Identity (IMEI) 6 Digits

2 Digits

6 Digits

TAC

FAC

SN

IMEI

TAC: Type Approval Code, The first two digits are the code for the country approval FAC: Final Assembly Code SN: Serial Number 2006-01-24

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Basic GSM Network Structure • IMEI • Short for International Mobile Equipment Identity, a unique number given to every single mobile phone, typically found behind the battery. • IMEI numbers of cellular phones connected to a GSM network are stored in a database (EIR - Equipment Identity Register) containing all valid mobile phone equipment. • When a phone is reported stolen or is not type approved, the number is marked invalid. • The number consists of four groups that looks this: • nnnnnn--nn-nnnnnn-n

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Basic GSM Network Structure • The first set of numbers is the type approval code (TAC). The first two digits represent the country code. The rest make up the final assembly code. The second group of numbers identifies the manufacturer: • 01 and 02 = AEG • 07 and 40 = Motorola • 10 and 20 = Nokia • 41and 44 = Siemens • 51= Sony, Siemens, Ericsson • The third set is the serial number and the last single digit is an additional number (usually 0).

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Basic GSM Network Structure • Subscriber Identity Module (SIM) • The SIM as mentioned previously is a “smart card” which plugs into the ME “Mobile Equipment”.

• It contains a memory that contain information about the MS subscriber hence the name Subscriber Identity Module. • This memory can store data by the user.

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Basic GSM Network Structure • The SIM contains several pieces of information: • International Mobile Subscriber Identity (IMSI) • This number identifies the MS subscriber. It is only transmitted over the air during initialization. • Temporary Mobile Subscriber Identity (TMSI) • This number identifies the subscriber, it is periodically changed by the system. • Location Area Identity (LAI) • Identifies the current location of the subscriber. • Subscriber Authentication Key (Ki) • This is used to authenticate the SIM card.

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Basic GSM Network Structure • Mobile Station International Services Digital Network (MSISDN)

20

10

1100477

44

385

196099

CC

NDC

SN

CC

NDC

SN

Vodafone Egypt MSISDN

CC NDC SN 2006-01-24

Vodafone UK MSISDN

: Country Code : National Destination Code : Subscriber Number Lecture 1

42

Basic GSM Network Structure Base Station Subsystem (BSS) BSS

BTS

BSC

MS

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• The Base Transceiver Station – BTS • The BTS contains the RF components that provide the air interface for a particular cell. This is the part of the GSM network which communicates with the MS. The antenna is included as part of the BTS. • Converts the GSM radio signals into a format that can be recognized by the BSC. • Channel coding and interleaving. • Records and passes to the BSC the Signal strength measurements.

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Basic GSM Network Structure • The BSC is the central node within a BSS and co-ordinates the actions of Base Stations. The BSC controls a major part of the radio network. • Its main functions can be divided into two types: During Call Set Up: » Finding the called mobile station by paging. » Allocate the frequency for setting the call. During Call : » Monitoring the call quality. » Controlling the transmitted power to the MS depending on the location of the MS. » Control the handover for the MS after receiving the power measurements from the MS and from the BTS.

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Basic GSM Network Structure • • • • •

One location area consists of more than one BTS. One BSC controls more than one BTS. One BTS covers 3 cells. One cell is covered by one Antenna. So, one Location Area consists of more than one cell.

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• Transcoder (XCDR) • The Transcoder (XCDR) is required to convert the speech or data output from the MSC (64 kbit/s PCM), into the form specified by GSM specifications for transmission over the air interface, that is, between the BSS and MS (64 kbit/s to 16 kbit/s and vice versa) • The 64 kbit/s Pulse Code Modulation (PCM) circuits from the MSC, if transmitted on the air interface without modification, would occupy an excessive amount of radio bandwidth. • This would use the available radio spectrum inefficiently. The required bandwidth is therefore reduced by processing the 64 kbit/s circuits so that the amount of information • required to transmit digitized voice calls to a gross rate of 16 kbit/s. • The transcoding function may be located at the MSC, BSC, or BTS.

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Network Switching Subsystem (NSS)

NSS HLR AUC BTS

BSC

MSC/VLR

BTS 2006-01-24

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Mobile Switching Center (MSC) • The primary node in a GSM network is the MSC. It is the node which controls calls establishment. The primary functions of an MSC include the following:  Switching and call routing to or from MS.  Charging.  Service providing.  Control of connected BSC’s.  Access to PSTN.  Provides the gateway functionality to other networks.  One MSC controls more than one BSC.

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Mobile Switching Center (MSC)

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Types of the MSC There are three types of the MSC, the difference just in the function.

VMSC: Visited MSC GMSC: Gateway MSC TMSC: Transit MSC

58

Visited Mobile Switching Center Its function is to switch in the level of BSCs and it is combined with a VLR.

MSC/VLR

BSC

BSC

Transit Mobile Switching Center Its function is to switch between the different VMSC. It is not combined with a VLR.

TMSC

VMSC

VMSC

Gateway Mobile Switching Center (GMSC) • Its function is to connect the PLMN to the PSTN or to the other PLMN existing in the country.

PSTN

Vodafone

Mobinil GMSC

TMSC

VMSC

TMSC

VMSC

VMSC

VMSC

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Home Location Register (HLR) • The HLR is a centralized network database that stores and manages all mobile subscriptions belonging to a specific operator. • It acts as a permanent store for a person’s subscription information until that subscription is cancelled. • The primary functions of the HLR include:  Stores for each mobile subscriber: • Basic subscriber categories. • Supplementary services. • Current location. • Allowed/barred services. • Authentication data.  Subscription database management  Controls the routing of mobile terminated calls and SMS 2006-01-24

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Home Location Register (HLR)

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Visitor Location Register (VLR) • The role of a VLR in a GSM network is to act as a temporary storage location for subscription information for MSs, which are within a particular MSC service area. • Thus, there is one VLR for each MSC service area. This means that the MSC does not have to contact the HLR (which may be located in another country) every time the subscriber uses a service or changes its status. •

The VLR is always integrated with the MSC.

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Visitor Location Register (VLR) • For the duration when the MS is within one MSC service area, then the VLR contains a complete copy of the necessary subscription details, including the following information:  Identity numbers for the subscriber  Supplementary service information (e.g. Does the subscriber has call waiting activated or not)  Activity of MS (e.g. idle or busy)  Current Location Area of MS

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Visitor Location Register (VLR)

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Authentication Center (AUC) • To protect GSM systems, the following security functions have been defined:  Subscriber authentication: by performing authentication, the network ensures that no unauthorized users can access the network, including those that are attempting to impersonate others.

 Radio information ciphering: the information sent between the network and an MS is ciphered. An MS can only decipher information intended for it.

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Equipment Identification Register(EIR) • In order to block the stolen mobiles equipments; the EIR equipment is used; also in case of the Mobile operator wants to block a certain type of Mobile phones. • Example, In Turkey all the mobile phones bought from outside Turkey are blocked and can not be used before paying fees. • The Mobile equipment is identified by a number called International Mobile Equipment Identity (IMEI). This number is uniquely identifies the MS worldwide.

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Equipment Identification Register (EIR) • Because the subscriber and equipment are separate in GSM, it is necessary to have a separate authentication process for the MS equipment. • The equipment identification procedure uses the identity of the equipment itself (IMEI) to ensure that the MS terminal equipment is valid.

1. IMEI Request

4. Access/ Barring Data

2. IMEI

3. IMEI Check EIR

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MSC / VLR

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Equipment Identification Register (EIR) International Mobile Equipment Identity 6 Digits

2 Digits

6 Digits

TAC

FAC

SN

(IMEI)

IMEI TAC: Type Approval Code, The first two digits are the code for the country approval FAC: Final Assembly Code SN: Serial Number

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Equipment Identification Register (EIR)

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Interworking Function (IWF) Interworking Function (IWF)

The IWF provides the function to enable the GSM system to interface with the various forms of public and private data networks currently available. The basic features of the IWF are listed below. Data rate adaption. Protocol conversion.

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Echo Canceller (EC) • An EC is used on the PSTN side of the MSC for all voice circuits. Echo control is required at the switch because the incoherent GSM system delay can cause an unacceptable echo condition, even on short distance PSTN circuit connections.

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OSS • The operation and Maintenance center (OMC) is connected to all equipment (the GMSC, MSC, HLR, VLR, AUC, EIR and the BSC). • It can be viewed as a computerized monitoring center were staff can monitor and control the network remotely.

MSC OMC LAN

HLR

BSC

SMSC

Operation and Support Subsystem (OSS)

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Operations and maintenance center (OMC) • (OMC) is connected to all equipment in the switching system and to the BSC. The implementation of OMC is called the operation and support system (OSS). The OSS is the functional entity from which the network operator monitors and controls the system. The purpose of OSS is to offer the customer cost-effective support for centralized, regional, and local operational and maintenance activities that are required for a GSM network. An important function of OSS is to provide a network overview and support the maintenance activities of different operation and maintenance organizations

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Mobile Originated Call

PSTN

MSC

BSC

1. The MS ask for a signaling channel. 2. The BSC/TRC allocates a signaling channel. 3. The MS sends a call set-up request via MSC/VLR. all signaling preceding a call takes place. This includes: • Marking the MS as “active” in the VLR • The authentication procedure • Equipment identification • Sending the B-subscriber’s number to the network • Checking if the subscriber has the service “Barring of outgoing calls” activated 4. The MSC/VLR instructs the BSC/TRC to allocate . The BTS and MS. 5. The MSC/VLR forwards the B–number to an exchange in the PSTN, which establishes a connection to the subscriber. 6. If the B-subscriber answers, the connection is established.

Mobile Terminating call 1 HLR

3

PSTN

5 2

4

6 GMSC

7

MSC

BSC

8

9

Roaming: Location Update IMSI

Copy of the HLR Profile will be stored in Stock. VLR

calls allowed ?

MSC/VLR

Is roaming and Int.

60202..

Is a roaming agreement present ?

Attached Detached VLR ADD=

HLR

Stock. Egypt Airport Roaming & Int. Roaming & Int. Allowed Allowed

82

Roaming: Call to HPLMN “Home Public Location Mobile Network” MSISDN +2010….

MSC/VLR

Attached

HLR GWMSC

VLR ADD= xyz

Roaming: Call from HPLMN

MSC/VLR

Attached VLR ADD= Stock. Airport

MSISDN 010…

HLR GWMSC

Roaming & Int. Allowed

Roaming: Call from another Roamer MSISDN +2010….

MSC/VLR A

MSC/VLR B

Attached VLR ADD= Stock. B

HLR GWMSC

Roaming & Int. Allowed

Location Update Why do we need to update our location data ?  Actually, the location update process is done in aim to exactly identify the location of the subscribers within the network so that any incoming call goes directly to the called subscriber. – To fulfill this aim, one can say that we may update the system with the cell ID each time the subscriber changes his serving cell. The MSC/VLR will now know the exact cell you are roaming in. This will result in a huge amount of location update messages.



An extreme is never to make a location update and to be paged in all the network. This will cause huge amount of paging messages.

Location Update

Types of Location Update 1. Normal Location update within same MSC/VLR service area 2. Normal Location update between 2 different MSC/VLR service areas 3. IMSI attach/detach 4. Periodic Location Update

Normal Location within the same MSC/VLR Service area

4 MSC/VLR

Updates LA Record

1. The Mobile sends an allocation request message to the BTS 2. The BTS responds with the allocation message

BSC

3. The mobile sends a location update request message with its IMSI to the MSC/VLR 4. The MSC/VLR updates the location information and sends a Location Update confirmation message

Normal Location Update between 2 different MSC/VLR service areas

1. The mobile sends a location update request to the MSC.

VLR Address = New Old MSC VLR

HLR

2. The new MSC/VLR receives the IMSI and conclude the its HLR address. 3. The MSC/VLR sends a subscriber information request with the IMSI to the proper HLR

Old MSC/VLR

New MSC/VLR

Old BSC

NEW BSC

4. The HLR stores the address of the new MSC/VLR 5. The HLR sends the data to the new MSC/VLR and it is kept there 6. The HLR sends a location cancellation message to the old MSC/VLR to remove the data 7. The new MSC/VLR sends a location updating confirmation message to the mobile

LA 2 LA 1

IMSI Attach IMSI attach is a complement to the IMSI detach procedure. It is used by the mobile subscriber to inform the network that it has re-entered an active state and is still in the same location area. If the MS changes location area while being switched off, a normal location update takes place. 1. The MS requests a signaling channel.

2. The MSC/VLR receives the IMSI attach message from the MS. 3. The MSC/VLR sets the IMSI attach in the VLR. The mobile is now ready for normal call handling. 4. The VLR returns an acknowledgment to the MS.

1

BSC

2

MSC/VLR

3 4

Periodic Location Update  Periodic location update is a routine task performed by the network if

the MS doesn’t make any network action SMS, location update, receives a call,…. etc)

(sets a call, sends

 If the MS doesn’t respond to this periodic location update, it will be marked as implicitly detached. ( Temporarily out of service )

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Handover 

Handover is to keep continuity of the call when the subscriber is roaming along the network moving from one cell to another and moving between different nodes in the network.



During call, the MS is continuously measuring transmission quality of neighboring cells and reports this results to the BSC through the BTS.



The BSC, being responsible on supervising the cells, is responsible of handover initiation.



Good neighbor relations between cells is an important factor in keeping the network performance in the accepted level.

93

Types of Handover 1. Intra BSC Handover: When the cell to which the call will be handed over belongs to the same BSC of the serving cell.

2. Inter BSC / Intra MSC Handover: When the cell to which the call will be handed over belongs to the different BSCs but to the same serving MSC.

3. Inter MSC When the cell to which the call will be handed over belongs to the different BSC and different MSC.

94

Intra BSC Handover 1.

BSC

The BSC decides from the power measurement reports that the call must be handed over to another cell

2. The BSC checks the new cell and orders this cell to activate the TCH

7 8

3. The BSC orders the serving cell to send

2

a message to the MS telling the information of new TCH

4. The MS tunes to the new frequency and Serving Cell 3

4

New Cell

6 5

Sends handover access burst

5. The new cell detects the handover burst and sends information about the suitable timing advance to the MS

6. The MS sends complete message to the new cell 7. The new cell sends a message to the BSC that the handover is successful

8. The BSC orders the old Cell to release the TCH

Inter BSC /Intra MSC Handover

MSC/VLR

Old BSC

New BSC

96

Inter MSC Handover

Old MSC

Old BSC

New MSC

New BSC

Air Interface Layers Messages

Layer 3 Messages

Messages

Logical Channels

Layer 2 Packets

Logical Channels

Radio Transmission Terminal

Layer 1 Bits

Radio Transmission Base Station

Frequency Allocation system GSM

900

GSM 1800

GSM 1900

space Uplink

890 -915 MHz

1710-1785 MHz

1850-1910 MHz

Downlink

935-960 MHz

1805-1880 MHz

1930-1990 MHz

Bandwidth

25 MHz

75 MHz

60 MHz

Duplex Distance

45 MHz

95 MHz

80 MHz

Carrier Separation

200 KHz

200 KHz

200 KHz

Radio Channels

124

374

299

Frequency

99

Spectrum Allocation (GSM 900) Downlink 935 – 960 MHz

Uplink 890 – 915 MHz 200 KHz 890.2 1

2

890

890.6 3

935

121 121 122 123 124

915

890.4

935.2 1

Uplink

4

2

935.6 3

F (MHz)

Downlink 121 122 123 124 121

4

960

935.4

GSM 900 Frequency Allocation

F (MHz)

FDMA in GSM • Separation between carriers “Frequency gap” must be sufficient to eliminate interference between adjacent channels. • Where The more the separation the less the co-channel interference but the less the available channels suited in the bandwidth. • It is found that a 200 kHz channel separation is suitable for all systems.

101

TDMA in GSM • With TDMA, one carrier is used to carry a number of calls, each call using that carrier at designated periods in time . • These periods of time are referred to as time slots .

• Each MS on a call is assigned one time slot on the uplink frequency and one on the downlink frequency, and both the same. • It is found that a 8 Time Slots per carrier, called “physical channels” is suitable for all systems. • Information sent during one time slot is called a burst, and depending on information sent we named what called “logical Channels”

102

Channel Type

Traffic Channel

Transmit voice and data

Signaling Channel transmit the signaling and synchronous data between BTS and MS.

Channels • Physical Channels “Traffic ” – Associated with frequency bands, time slots, codes – Physical channels transfer bits from one network element to another

• Logical Channels “Control” – Distinguished by the nature of carried information and the way to assemble bits into data units – Three types • one-to-one: traffic channels between a BTS and a MS • one-to-many: synchronization signals from BTS to MSs in a cell • many-to-one: from MSs to the same BTS

Physical Channels

 GSM band is divided into 124 RF channels, and each channel is divided into 8 time slots using TDMA.  These time slots are called “physical channels”. CH 124

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

CH 3

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

CH 2

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

CH 1

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

Traffic Channel • Carries either encoded speech or user data up and down link between a single mobile and a single BTS. • Types of traffic channel: – Full rate (TCH) • Transmits full rate speech (13 Kbits/s). A full rate TCH occupies one physical channel. – Half rate (TCH/2) • Transmits half rate speech (6.5 Kbits/s). • Two half rate TCHs can share one physical channel, thus doubling the capacity of a cell.

106

Traffic Channel

Control Channels • These are used to carry signaling or synchronization data. They are divided into three types:– Broadcast CHannels (BCH) – Common Control CHannels (CCCH) – Dedicated Control CHannels (DCCH)

1.Broadcast Channels

• From Single BTS to all the mobiles in the area



Frequency Correction Control CHannel (FCCH)



Synchronization CHannel (SCH)

 Carries information for frequency correction of the mobile  Carries 2 important pieces of information  TDMA frame number (max = 2715684 )  Base station identity Code (BSIC)

 Broadcast Control CHannel (BCCH)

 Broadcasts some general cell information such as:  Location Area Identity (LAI),  maximum output power allowed in the cell  and the identity of BCCH carriers for neighboring cells.

109

2.Common Control Channels • To or from a certain BTS to a single mobile

• Paging CHannel (PCH) – BTS Transmits a paging message to indicate an incoming call or short message. The paging message contains the identity number of the mobile subscriber that the network wishes to contact.

• Random Access CHannel (RACH) – MS Answers paging message on the RACH by requesting a signaling channel of SDCCH.

• Access Grant CHannel (AGCH) – Assigns a signaling channel (SDCCH) to the MS.

110

3.Dedicated Control Channels • Stand alone Dedicated Control Channel (SDCCH) – The BTS switches to the assigned SDCCH. The call set-up procedure is performed in idle mode. The BSC assigns a TCH (carrier and time slot) and the MS switches to the assigned SDCCH. – SDCCH is also used to Registration & Authentication

• Slow Associated Control Channel (SACCH) – BTS Instructs the MS the transmitting power to use and gives instructions on timing advance (TA). – MS Sends averaged measurements on its own BTS (signal strength and quality) and neighboring BTS’s (signal strength). The MS continues to use SACCH for this purpose during a call.

• Fast Associated Control Channel (FACCH) – Transmits handover information. – Transmits necessary handover information

111

Control Channels

Channel Type-Summary 14.4Kbit/s FR TCH (TCH/F14.4) 9.6Kbit/s FR TCH(TCH/F9.6) Data CH TCH Voice CH

4.8Kbit/s FR TCH (TCH/F4.8) 4.8Kbit/s HR TCH (TCH/H4.8) FR Voice Traffic Channel (TCH/FS) Enhanced FR Traffic Channel (TCH/EFR) HR Traffic Channel (TCH/HS)

channel BCH CCH

CCCH

DCCH

FCCH (down) SCH (down) BCCH (down) RACH (up) AGCH (down) PCH (down) SDCCH FACCH SACCH

Power Measurements Performed by the Mobile • Power measurements represent one of the important functions carried out by a mobile station in both of its modes: – idle mode – active mode • in order for the mobile to tune to the best cell.

114

Power Measurements in Active Mode 1.

2. 3.

4.

To enable the mobile from making power measurements during a call, the uplink time slot will be delayed by an offset of three time slots from the down link time slot. (The mobile will try to measure the signal strength of these carriers one by one during the time between transmission and reception of the allocated traffic channel) The mobile is informed on the SACCH channel which BCCH frequencies to be measured. To make sure that the measured carriers do not belong to co-channel cells, the mobile will have to check the identity of the adjacent cells by reading the BSIC value sent on the SCH of each cell. This will take place during the idle frame number 26. – (Note) The signal strength of the serving cell is measured during reception of the allocated traffic channel. The mobile will make a list of the strongest six carriers and their BSIC values along with the signal strength of its cell, and reports this list to the BSC via the uplink SACCH channel which is repeated once every 26 frame.

GSM Coverage Plan •

To provide coverage for a large service area of a mobile network we have two Options: (A) Install one transceiver with high radio power at the center of the service area

– Drawbacks: • The mobile equipments used in this network should have high output power in order to be able to transmit signals across the coverage area. • The usage of the radio resources would be limited.

116

GSM Coverage Plan (B) Divide the service area into smaller areas (cells) – Advantages: • Each cell as well as the mobile handsets will have relatively small power transceivers. • The frequency spectrum might be “reused” in two far separated cells. This yields: 1- Unlimited capacity of the system.

2- Good interference characteristics

117

Cell Geometry Problem of omni directional antennas

Dead Spots

118

Cell Geometrical Shape • Differentiation between these three shapes will be in order to optimize the number of cells required to cover a given service area against the cell transceiver power. By some calculations, you will find that using hexagonal shaped cells achieves the optimum.

R

R

R

Cell Geometrical Shape Umbrella Cell

Normal Cell

Normal Cell

Macro Cell

Cell Geometrical Shape Umbrella cell

Fast moving subscribers

Pico cell In building coverage

Macro cell Slow moving subscribers

Clusters • Cluster is a set of cells where the frequency is not being reused within this cluster. • Cluster can be 3, 4, 7 and 9 cells.

122

Sectorization

Omni-Directional Cell

sectroized Cells

123

3/9 Cluster A3

B3 A2

A1 A3

B3 A2

A1

C1 A3

A2

B3 A2

A1

C3

B1

C1 A3

C2 C1

A2 A1 C3 C2 C1

C3 C2

C1

B2 B1

C3 B2

B1

B2 B1

A2

B3

A1

B3

A1

A2

B3

C1

C2

A3

C2

A3

C1

C2

C3

B1

B2

B2 B1

B2

C3

B1

B2

C3

A1 B3

A1

B3 A2

C2

A3 C2

A1 A3

C1

B3 A2

B1

B2

C3

B2

C3

B1

A3

C2 C1

4 / 12 Cluster A3

B3 A2

A1

A3 B2

B1 C3

A1

C2 A3

B3 A2

A1

A3 B2

B1 C3

C1 B3

A1

A3 B2

B1 C3

A2 B1

C1

D2 D1

B2 B1

C3

D3 C2

D2 D1

D1

A2

D3

D2

B3

A1

C2

C1

C2

A3

B1

D3

C1

B2

C3

D3

C3

D1

A2

B2 B1

D2

B3

A1

C2

D2 D1

A3 B2

C3

D3

C1

D1 B3

A1

C2 C1

C1

D1

A2

D3

D2

B3

A1

C2

D2

C2

A3

B1

D3

C1

B2

C3

D3

C3

D1

A2

B2 B1

D2

B3

A1

C2

D2 D1

A2

B1

A1

C2

A3

B3 A2

D3

C1

B2

C3

D3 C2

A3

A2

B2

C3

D1

A3

B1

D2

B3

A1

A2

D3

C1

B3

C1

D2 D1

A3 A2 A1 B3

E2 E1

D3 B2

B1

7 / 21 Cluster

E3

D2 D1

C3

B3

A3 A2 A1

B1

D1

F1

C2 C1

A1

B2

G2 G1

B1

D2

C3

F2

F1 G3

C2 C1

C1

G2 G1

F2 F1

G3 C2

F3

D1

D2

C3

E1

F3

D1

E2

D3

E1

B2

E3

E2

D3

B1

A2

B3

A1

G2

A3

E3

A2

B3

G1

F2

G3

F1

C2

F3

A3 F2

G3

C1

D2

C3

D1

E2

D3

F3 D2

C3

E1

B2

D3

B1

E3

E2 E1

B2

G2 G1

B3

A1

F1

C2

E3 A2

F2

G3

C1

A3

F3

G2 G1

Frequency Reuse  If the GSM900 system has 124 Absolute Radio Frequency Traffic Channels, and if we are using only in our network 60 of them, then we can only serve 8 x 60 = 480 Calls if we only use the frequency once.  However, a cellular network overcome this constraint and maximizes the number of subscribers that it can serve by using frequency re-use.

 The frequency reuse is performed by dividing the whole available frequencies between a group of neighboring cells which is called frequency reuse pattern or a “Cluster”, and then repeat this cluster over the whole network

127

Frequency Reuse  3/9 cluster in which the available frequencies are divided into 9 groups and distributed between 3 sites  4/12 cluster in which the available frequencies are divided into 12 groups and distributed between 4 sites  7 / 21 cluster in which the available frequencies are divided into 21 groups and distributed between 7 sites  But we must take into consideration two types of interference: 1- Co- Channel Interference 2- Adjacent Channel Interference

128

Co- Channel Interference •

Co-channel interference is caused by short distance between the cell and other cell that use the same frequency.

 To overcome this type of interference. Each frequency is reused after the same distance “D”  Reuse Plan = (D/R)2 = 3N. Where N is the number of cells per cluster

129

Adjacent Channel Interference • Adjacent frequencies, that are frequencies shifted 200kHz from the carrier frequency, must be avoided in the same cell and preferably in neighboring cells also .

• To overcome this type we must make good planning for the frequencies in the cluster

130

Frequency Planning A3

B3 A2

A3

B3 A2

A1

A1 B2

B1 C3

B1

C3

A3

C1

A3 C2

C1

C2

B2

B3

A2

A1

B3 A2

A1

B2

B1 C3

B2

C2

B1

C1

C3

C2 C1

Frequency group

Channels

A1

B1

C1

A2

B2

C2

A3

B3

C3

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87 131

Frequency Planning • In a real network the allocation of channels to cells will not be as uniform as in table, as some cells will require more channels and some will require less. • In this case, a channel may be taken from a cell with low traffic load and moved to one with a higher traffic load. • However, if doing so, it is important to ensure that interference is still minimized.

132

Which Cluster Size to use?

• •

Carrier to interference ratio It’s the difference in power level between the carrier in a given cell and the same carrier received from the nearest cell that reuses the same frequency.

Number of frequencies per site

Traffic Channels

3/9

High

High

Low

4/12

Medium

Medium

Medium

7/21

Low

Low

High

C/I Ratio

133

Introduction to Cell Planning

134

2006-01-24

Lecture 1

135

Radio Transmission problems • As it was stated before that the mobile telecommunications will use

radio transmission as the transmission technique; the radio transmission is suffering from many problems which causing unacceptable degradation of the service quality. • We will discuss these problems in details during our course.

1

Radio Transmission problems 1.

Path Loss

2.

Multipath Fading a. Rayleigh Fading b. Time Dispersion

3.

Time Alignment

2

Radio Transmission problems 1. Path Loss Cause Due to Increasing distance between MS, and BTS. Solution Handover

3

Radio Transmission problems 2. Multipath Fading Cause Due to different paths of signals between MS, and BTS. Which cause fading dips as a result of different in phase and amplitude Solution Diversity a. Space Diversity b. Polarization Diversity c. Frequency Diversity ( Frequency Hopping)

5

Radio Transmission problems 3. Time Alignment Cause

Due to different distance of different MSs from BTS (Near-Far) Solution Time Advance

7

Home Location Register (HLR)

2006-01-24

Lecture 1

141

GSM Terrestrial Interfaces • The standard interfaces used are as follows: • 2 Mbit/s. • Signaling System ITU-TSS #7 (“C7” or ‘‘SS#7”). • X.25 (packet switched data); (LAPB). • Abis using the LAPD protocol (Link Access Procedure “D”). • Whatever the interfaces and whatever their function, they will often share a common • physical bearer (cable) between two points, for example, the MSC and a BSS.

142

GSM Terrestrial Interfaces


GSM Terrestrial Interfaces • 2 Mbit/s Trunk 30-channel PCM This diagram opposite shows the logical GSM system with the 2 Mbit/s interfaces highlighted. They carry traffic from the PSTN to the MSC, between MSCs, from an MSC to a BSC and from a BSC to remotely sited BTSs. These links are also used between the MSC and IWF. Each 2.048 Mbit/s link provides thirty 64 kbit/s channels available to carry speech, data, or control information. The control information may contain C7, LAPD or X.25 formatted information. These 2 Mbit/s links commonly act as the physical bearer for the interfaces used between the GSM system entities.

145


146

X.25 Interfaces • The X.25 packets provide the OMC with communications to all the entities over which it has control and oversight. • Note that the X.25 connection from the OMC to the BSS may be “nailed through” or (permanently connected by software) at the MSC, or may be supported by a completely independent physical route.

147

X.25 Interfaces

Signaling System #7 C7 Interfaces

SS7

Signaling System #7

• The diagram opposite illustrates the use of C7 in the GSM system; carrying signaling and control information between most major entities, and to and from the PSTN. • Used to communicate between the different GSM network entities. • Between the MSC and the BSC, the Base Station System Management • Is used between the MSC and the VLR, EIR, and HLR.

Signaling System #7

A-bis (LAPD) Interfaces • a different type of interface is required. To Communicate between BTS and BSC GSM has specified the use of LAPD “A-bis”. • The GSM specifications for this interface (termed “A-bis”) are not very specific and therefore interpretations of the interface vary. This means that one manufacturers BTS will not work with another manufacturer’s BSC. • As we have already mentioned, the functionality split between the BTS and BSC is also largely in the hands of the manufacturer and therefore it is unlikely that they would operate together, even if this interface were rigidly enforced by the specifications.

151

A-bis (LAPD) Interfaces

Interface Names

The GSM System Interface Names

154

GSM Transmission Process

A/D Conversion

Segmentation Speech Coding Channel Coding Interleaving Encryption Burst Formatting

Modulation and Transmission

Analog to Digital Conversion •

Analog to digital conversion takes place in 3 steps:

1. Sampling 2. Quantization 3. Coding 1.

Sampling

Telecommunication systems use Sampling rate = 8 Ksample/s

Segmentation Segmentation refers to the process of partitioning a digital information into multiple regions . The goal of segmentation is to simplify and/or change the representation of an image into something that is more meaningful and easier to analyze.

160 sample in 20 ms = 1 Segment

1

2

3

4

.

.

.

.

.

.

.

.

.

.

.

1 2 3 4 5 6 7 8 9 10 11 12 13 0 1 2 3 4 5 6 7 8 9 10

.

.

.

.

160

Interleaving • Interleaving in computer science is a way to arrange data in a non-contiguous way in order to increase performance. It is used in: • time-division multiplexing (TDM) in telecommunications . • computer memory. • disk storage.

158

Interleaving 

Second Level Interleaving 20 ms Block A 1 2 3 4 5 6 7 8

20 ms Block B 1 2 3 4 5 6 7 8

20 ms Block c 1 2 3 4 5 6 7 8

20 ms Block D 1 2 3 4 5 6 7 8

1A

T

2A

T

3A

T

4A

T

1B

T

5A

2B

T

6A

3B

T

7A

4B

T

8A

1C

T

5B

2C

T

6B

3C

T

7B

4C

T

8B

1D

T

5C

2D

T

6C

3D

T

7C

4D

T

8C

Modulation / Demodulation in GSM • GSM uses the Gaussian Minimum Shift Keying (GMSK) • Gaussian minimum-shift keying

Modulation / Demodulation in GSM • Gaussian minimum shift keying or GMSK is a continuous-phase frequency-shift keying modulation scheme. It is similar to standard minimum-shift keying (MSK); however the digital data stream is first shaped with a Gaussian filter before being applied to a frequency modulator. This has the advantage of reducing sideband power, which in turn reduces out-of-band interference between signal carriers in adjacent frequency channels.

Open Discussion

Communication Companies Vendors :-

Communication Companies Services and subcontractors

CIVIL

Telecom

Different kinds of engineers Civil

Telecom

Target Job

Power

Mechanical

Good Luck Eng / Mohamed Tarek [email protected] 01004758147

GSM_All, WCDMA , LTE

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