Cellular NetworkCellular Network

Wireless Computer CommunicationsWireless Computer Communications

Min-Xiou ChenMin-Xiou Chen

BTS

HLR

VLRPSTN

MSC

BTS

BSCBSC

MSC

BTS

BTS

BTS

BTS

BSC

BTS BTS

Cellular SystemCellular System

Why Cellular Mobile Why Cellular Mobile Telephone Systems?Telephone Systems?

Operational limitations of conventional Operational limitations of conventional mobile telephone systemsmobile telephone systems limited service capabilitylimited service capability poor service performancepoor service performance inefficient frequency spectrum utilizationinefficient frequency spectrum utilization

Mobility ManagementMobility Management

Mobility management enables Mobility management enables telecommunications networks totelecommunications networks to locate roaming mobile terminals (MTs) for locate roaming mobile terminals (MTs) for

call delivery call delivery ((location managementlocation management)) maintain connections with MTs that change maintain connections with MTs that change

their point of attachment their point of attachment ((handoff/handover handoff/handover managementmanagement))

Location ManagementLocation Management

MT periodically performs location MT periodically performs location registration (i.e., registration (i.e., location updatelocation update)) explicitly notify the network of its new access explicitly notify the network of its new access

point and store changes to its user location point and store changes to its user location profileprofile

when incoming calls arrive, the network when incoming calls arrive, the network performs performs call deliverycall delivery querying the user profile to deliver the calls to querying the user profile to deliver the calls to

the current cell location of the MTthe current cell location of the MT

IMSI ( International Mobile Subscriber Identity )IMSI ( International Mobile Subscriber Identity ) 行動用戶之全球唯一識別碼，作為驗證使用者身份行動用戶之全球唯一識別碼，作為驗證使用者身份 存於存於 HLR/AUCHLR/AUC 及燒錄於 及燒錄於 SIM SIM 卡中，卡中， 由由 MCC (Mobile Country Code )+MNC (Mobile Network MCC (Mobile Country Code )+MNC (Mobile Network

Code)+MSIN (Mobile Subscriber Identity Number)Code)+MSIN (Mobile Subscriber Identity Number) 所組成，所組成，長度不超過 長度不超過 15 15 碼，我國用 碼，我國用 15 15 碼，即 碼，即 IMSI = IMSI =

TMSI ( Temporary Mobile Subscriber Identity )TMSI ( Temporary Mobile Subscriber Identity ) 行動台行動台 中 中 SIM SIM 卡之區域性臨時識別碼卡之區域性臨時識別碼 長度不超過 長度不超過 32 32 位元。位元。 由 由 VLR VLR 產生，只在同一產生，只在同一 VLR VLR 服務區內有效。服務區內有效。

GSMGSM 身分之各種識別碼身分之各種識別碼 (Identity)(Identity)參數參數

GSMGSM 身分之各種識別碼身分之各種識別碼 (Identity)(Identity)參數參數

MSISDN ( Mobile Station ISDN )MSISDN ( Mobile Station ISDN ) 為行動台為行動台 (MS) (MS) 之全球唯一電話號碼之全球唯一電話號碼 長度不超過 長度不超過 15 15 碼，由碼，由 CC (Country Code)+NDC(National Destination CC (Country Code)+NDC(National Destination

Code)+SN(Subscriber Number)Code)+SN(Subscriber Number) 所組成，即 所組成，即 IMSI = 886-920-IMSI = 886-920-xxxxxxxxxxxx 。。

IMEI ( International Mobile Equipment Identity )IMEI ( International Mobile Equipment Identity ) 為行動台為行動台 設備之全球唯一識別碼，即手機製造產品序號設備之全球唯一識別碼，即手機製造產品序號 由由 TAC(Type Approval Code)+FAC(Final Assemble Code)+SNR(Serial TAC(Type Approval Code)+FAC(Final Assemble Code)+SNR(Serial

Number)+SP(Spare)Number)+SP(Spare) 所組成，長度 所組成，長度 15 15 碼。碼。 PIN ( Personal Identity Number ) PIN ( Personal Identity Number )

SIM SIM 卡之密碼，長度 卡之密碼，長度 4-6 4-6 碼碼 行動電話在插入 行動電話在插入 SIM SIM 卡後，需輸入正確之 卡後，需輸入正確之 PIN PIN 才能使用。 才能使用。

GSM Registration GSM Registration ProcedureProcedure

1: old TMSI + old 1: old TMSI + old VLR idVLR id

2: TMSI2: TMSIIMSIIMSI

3: location update3: location update

4: new TMSI4: new TMSI

5: registration 5: registration cancellationcancellation

HLR

VLRVLR

1

2

3

4

5

Call Delivery for Mobile Call Delivery for Mobile Terminated CallTerminated Call

MSC

MS

GMSC(INTX)

otherswitches

otherswitches

1 1

1

22

3

1

request roaming number

dial MSISDNallocate MSRN

3

routing

HLR VLR

3 paging

Registration Area Registration Area PlanningPlanning

Registration/Location Area (RA/LA)Registration/Location Area (RA/LA) consists of one or more cellsconsists of one or more cells the basic unit of registration/pagingthe basic unit of registration/paging

cell RA VLR PLMN GSM

Size of RA

Location update

Cost

Paging

Total

Hand-off (Hand-over)Hand-off (Hand-over)

Cell #1 Cell #2

Switches andProcessor

Hand-off (Hand-over):switches cells

Handoff ManagementHandoff Management

Ongoing calls are modified under two Ongoing calls are modified under two conditions: signal strength deterioration conditions: signal strength deterioration and user mobilityand user mobility

intra-cellintra-cell and and inter-cellinter-cell handoffs handoffs within and between cellswithin and between cells

softsoft handoff and handoff and hardhard handoff handoff without and with interruptions in radio linkswithout and with interruptions in radio links

Who Initiates the Who Initiates the Handoff?Handoff?

NCHONCHO (Network-controlled handoff) or (Network-controlled handoff) or MAHOMAHO (Mobile-assisted Handoff) (Mobile-assisted Handoff) the networks generates a new connection, the networks generates a new connection,

finding new resources for the handoff and finding new resources for the handoff and performing any additional routing operationsperforming any additional routing operations

MCHOMCHO (Mobile-controlled handoff) (Mobile-controlled handoff) the MT finds the new resources and the the MT finds the new resources and the

network approvesnetwork approves

Three Classes of Handoffs Three Classes of Handoffs in GSMin GSM

MSC

BSC BSC

BTS BTS BTS

MSC

BSC

BTS

MS MS

MS MS

MSMS

1. different BTS, same BSC

2. different BSC, same MSC

3. different MSC, same PLMN(old MSC=anchor MSC new MSC=relay MSC)

Technical TermsTechnical Terms

Call drop rateCall drop rate The probability that an ongoing call is The probability that an ongoing call is

dropped due to handoffdropped due to handoff

Call blocking rateCall blocking rate The probability that a new call is denied due The probability that a new call is denied due

to lack of available channelto lack of available channel

Usually call drop rate is more important Usually call drop rate is more important than call blocking ratethan call blocking rate

Handoff Management:Handoff Management:Channel Reservation SchemeChannel Reservation Scheme

Reserve some channels for handoff callsReserve some channels for handoff calls Trade call blocking rate for call drop rateTrade call blocking rate for call drop rate

Channel Assignment Channel Assignment ProblemProblem

Allocate channels to cellsAllocate channels to cells should considershould consider

QoS (Quality of Service)QoS (Quality of Service) co-channel interferenceco-channel interference adjacent channel interferenceadjacent channel interference

spectrum utilizationspectrum utilization

GoalGoal ：： maximize both QoS and maximize both QoS and spectrum utilizationspectrum utilization

Co-Channel and Adjacent-Co-Channel and Adjacent-Channel InterferenceChannel Interference

Co-channel interferenceCo-channel interference Radio signals assigned to the same channel Radio signals assigned to the same channel

will interfere with each otherwill interfere with each other

Adjacent channel interferenceAdjacent channel interference Two frequencies of wavelength close to Two frequencies of wavelength close to

each other will interfere with each other and each other will interfere with each other and should not be assigned to neighboring cellsshould not be assigned to neighboring cells

Co-channel interferenceCo-channel interference

A

BC

D

A channel assignedto A should not beassigned to B nor Cat the same time

However, it can beassigned to D withoutco-channel interference

Adjacent channel Adjacent channel interferenceinterference

Classification of Channel Classification of Channel Assignment SchemesAssignment Schemes

Fixed Channel AssignmentFixed Channel Assignment Each cell is assigned a fixed subset of Each cell is assigned a fixed subset of

frequenciesfrequencies low response time with low utilizationlow response time with low utilization

Dynamic Channel AssignmentDynamic Channel Assignment Does not give any frequency to any cell a Does not give any frequency to any cell a

prioripriori high response time with high utilizationhigh response time with high utilization

A Typical Fixed Channel A Typical Fixed Channel Assignment SchemeAssignment Scheme

All channels are dividedAll channels are dividedinto 7 disjoint setsinto 7 disjoint sets

23

456

71

23

456

71

23

456

71 2

345

67

12

345

67

12

345

67

1 23

456

71

23

456

71

Generations of Cellular Generations of Cellular SystemsSystems

The first generationThe first generation AMPSAMPS Analog system, circuit-switched serviceAnalog system, circuit-switched service

The second generationThe second generation GSM, IS-136, PDC, IS-95GSM, IS-136, PDC, IS-95 Digital system, circuit-switched serviceDigital system, circuit-switched service

2.5 G2.5 G GPRSGPRS Digital system, packet-switched serviceDigital system, packet-switched service

3 G3 G IMT-2000IMT-2000 Digital system, multimedia serviceDigital system, multimedia service

Advanced Mobile Phone Advanced Mobile Phone Service (AMPS)Service (AMPS)

Analog cellular system (1983)Analog cellular system (1983) Frequency Division Multiple Access (FDMA)Frequency Division Multiple Access (FDMA) 50 channels per cell50 channels per cell

BS

MTSOLE

MS

PSTN

AMPS (1/2)AMPS (1/2)

The first cellular systemThe first cellular system Developed during 1970s in Bell Lab.Developed during 1970s in Bell Lab. 10 years to generate the AMPS specification10 years to generate the AMPS specification 1974—1978 field trial in Chicago1974—1978 field trial in Chicago Commercial service has been available since Commercial service has been available since

19831983 FDMA (Frequency Division multiple Access) / FDMA (Frequency Division multiple Access) /

FDD (Frequency Division Duplex)FDD (Frequency Division Duplex) technology technology

AMPS (2/2)AMPS (2/2)

Channel spacing: 30 KHzChannel spacing: 30 KHz Frequency bandsFrequency bands

Forward link (BS Forward link (BS MS): 869 MHz – 894 MHz MS): 869 MHz – 894 MHz Reverse link (MS Reverse link (MS BS): 824 MHz – 849 MHz BS): 824 MHz – 849 MHz Total 832 full-duplex channelsTotal 832 full-duplex channels

Roaming management standard: Roaming management standard: EIA/TIA IS-41EIA/TIA IS-41

Service area: North America, TaiwanService area: North America, Taiwan

Digital Cellular Phone Digital Cellular Phone SystemsSystemsStandard

Frequency band

Multiple access

Duplex method

No. of channels

Channel spacing

Modulation

Channel bit rate

GSM 900 GSM1800 IS-54/-136 IS-95

270.83 kb/s 270.83 kb/s 48.6 kb/s 1.2288 Mb/s

GMSK GMSK p/4 DQPSK QPSK/DQPSK

200 kHz 200 kHz 30 kHz 1250 kHz

1248 users/channel

3748 users/channel

8323 users/channel

20798 users/channel

FDD FDD FDD FDD

CDMA/FDMATDMA/FDMATDMA/FDMATDMA/FDMA

down 935-960 up 880-915

down 1805-1880 up 1710-1785

down 869-894 up 824-849

down 869-894 up 824-849

Digital Cellular Phone Digital Cellular Phone Systems (Cont.)Systems (Cont.)

System IS-54 IS-95(DS) GSM 900/1800Portable txmit powerMax/avg.

600 mW/200mW

600 mW/600 mW

1W/125 mW

Speech coding VSELP QCELP RPE-LTPSpeech rate (Kbps) 7.95 8 (var.) 13Ch. coding 1/2 rate conv. 1/2 rate fwd

1/3 rate rev.1/2 rate conv.

Frame (ms) 40 20 4.615

IS-136 DAMPS (1/2)IS-136 DAMPS (1/2)

Also referred to as digital AMPS (DAMPS), Also referred to as digital AMPS (DAMPS), American Digital Cellular (ADC), North American Digital Cellular (ADC), North American TDMA (NA-TDMA), or even TDMA.American TDMA (NA-TDMA), or even TDMA.

The successor of IS-54 (IS-54c == IS-136)The successor of IS-54 (IS-54c == IS-136) About four months to create the IS-54 About four months to create the IS-54

specifications.specifications. The same frequency spectrum as AMPS.The same frequency spectrum as AMPS. Also defined for 1850 – 1990 PCS spectrum.Also defined for 1850 – 1990 PCS spectrum.

IS-136 DAMPS (2/2)IS-136 DAMPS (2/2)

FDMA – TDMA (Time Division multiple Access) / FDD FDMA – TDMA (Time Division multiple Access) / FDD (Frequency Division Duplex) technology(Frequency Division Duplex) technology

Carrier spacing = 30kHz.Carrier spacing = 30kHz. 3 channels (time slots) per frequency carrier3 channels (time slots) per frequency carrier Speech coding rate: 7.95 kbpsSpeech coding rate: 7.95 kbps Capacity: about 3 times that of AMPSCapacity: about 3 times that of AMPS Roaming management standard: EIA/TIA IS-41Roaming management standard: EIA/TIA IS-41 Service area: North AmericaService area: North America

IS-95 cdmaOne (1/2)IS-95 cdmaOne (1/2)

Developed by QualcommDeveloped by Qualcomm Operating in US and Korea since 1996.Operating in US and Korea since 1996. DS-CDMA (Direct Sequence Code Division DS-CDMA (Direct Sequence Code Division

multiple Access) / FDD (Frequency Division multiple Access) / FDD (Frequency Division Duplex) technologyDuplex) technology

About two years to create the IS-95 specifications.About two years to create the IS-95 specifications. Frequency bandsFrequency bands

AMPS (824 – 894 MHz)AMPS (824 – 894 MHz) PCS (1850 – 1990 MHz)PCS (1850 – 1990 MHz)

IS-95 cdmaOne (2/2)IS-95 cdmaOne (2/2)

Carrier Spacing: 1.25 MHzCarrier Spacing: 1.25 MHz Capacity: 3 – 6 times than that of TDMA, 10 Capacity: 3 – 6 times than that of TDMA, 10

times than that of AMPS. (4 – 5 times than that times than that of AMPS. (4 – 5 times than that of GSM, 8 – 10 times than that of AMPS).of GSM, 8 – 10 times than that of AMPS).

Speech coding rate: 13 or 8 kbpsSpeech coding rate: 13 or 8 kbps Roaming management standard:Roaming management standard:

EIA/TIA IS-41EIA/TIA IS-41 Service area: North America, South Korea, Service area: North America, South Korea,

ChinaChina

Cordless Phone SystemsCordless Phone Systems

System CT2 CT2+ DECT PHS PACSDuplexing TDD TDD TDD FDDFrequency band(MHz)

864-868944-948

1880-1900

1895-1918

1850-1910/1930-1990

Carrier spacing(KHz)

100 1728 300 300/300

Number ofcarriers

40 10 77 16 pairs/10 MHz

Bearer channel/carrier

1 12 4 8/pair

Channel bit rate(kbps)

72 1152 384 384

Modulation GFSK GFSK /4 QPSK /4 QPSKSpeech coding 32 kbps 32 kbps 32 kbps 32 kbpsAverage handsetTX power (mW)

5 10 10 25

Peak handsetTX power (mW)

10 250 80 200

Frame duration(ms)

2 10 5 2.5

CT2CT2

Developed in EuropeDeveloped in Europe Available since 1989Available since 1989 FDMA / TDD (Time Division Duplexing) technologyFDMA / TDD (Time Division Duplexing) technology Speech coding rate: 32kbpsSpeech coding rate: 32kbps Data rate: 2.4 – 4.8 kbpsData rate: 2.4 – 4.8 kbps Max Tx power: 10mW.Max Tx power: 10mW. Do not support handoffDo not support handoff Do not support call-delivery (call-termination)Do not support call-delivery (call-termination) CT2+ supports call-deliveryCT2+ supports call-delivery

DECT (1/2)DECT (1/2)

DECT specifications were published in 1992DECT specifications were published in 1992 Pico-cell designPico-cell design Digital system; TDMA/TDD technologyDigital system; TDMA/TDD technology 12 frequency channels/frequency carrier12 frequency channels/frequency carrier Sleep mode is employed to conserve the power Sleep mode is employed to conserve the power

of MSs.of MSs. Time slot transfer: DECT may move a Time slot transfer: DECT may move a

conversation from one time slot to another to conversation from one time slot to another to avoid interferenceavoid interference

DECT (2/2)DECT (2/2)

Supports seamless handoffSupports seamless handoff Speech coding rate: 32 kbpsSpeech coding rate: 32 kbps Supports dynamic channel allocationSupports dynamic channel allocation Typically implemented as a wireless-PBX Typically implemented as a wireless-PBX

connected to the PSTNconnected to the PSTN Can interwork with GSM to allow users Can interwork with GSM to allow users

mobility, where the GSM handsets provide mobility, where the GSM handsets provide DECT connection capability.DECT connection capability.

PHS (1/2)PHS (1/2)

Developed by the Research and Development Developed by the Research and Development Center for Radio System (RCR) in JapanCenter for Radio System (RCR) in Japan

Digital systemDigital system Offer services for homes, offices (1895 – Offer services for homes, offices (1895 –

1906.1 MHz), and outdoor (1906.1– 1918.1 1906.1 MHz), and outdoor (1906.1– 1918.1 MHz) environmentsMHz) environments

TDMA / TDD technologyTDMA / TDD technology Carrier spacing: 300 kHzCarrier spacing: 300 kHz 4 time slots/frequency carrier4 time slots/frequency carrier

PHS (2/2)PHS (2/2)

Supports sleep modeSupports sleep mode Supports dynamic channel allocationSupports dynamic channel allocation PHS utilizes dedicated control channels to PHS utilizes dedicated control channels to

carry system and signaling informationcarry system and signaling information Speech coding rate: 32 kbpsSpeech coding rate: 32 kbps User mobility: up to 100 km/hrUser mobility: up to 100 km/hr Data rateData rate

Current stage: up to 64 kbps Current stage: up to 64 kbps (( 大眾電信，大眾電信， Taiwan)Taiwan) Future: 128 kbsp Future: 128 kbsp 512 kbps 512 kbps 3G 3G

PACSPACS

Developed at Telcordia (formerly Bellcore)Developed at Telcordia (formerly Bellcore) Designed for Wireless Local Loop (WLL) and PCSDesigned for Wireless Local Loop (WLL) and PCS TDMA/FDD or TDMA/TDD technologyTDMA/FDD or TDMA/TDD technology 8 voice channels/frequency carrier8 voice channels/frequency carrier Speech coding rate: 32 kbpsSpeech coding rate: 32 kbps Mobile-controlled handoff (MCHO)Mobile-controlled handoff (MCHO) Roaming management: IS-41-like protocolRoaming management: IS-41-like protocol Supports both circuit-based and packet-based access Supports both circuit-based and packet-based access

protocolprotocol User mobility: up to 38 miles/hrUser mobility: up to 38 miles/hr

Data Services in DECTData Services in DECT

DECT data link layer is designed for DECT data link layer is designed for circuit and packer mode servicescircuit and packer mode services in the packet mode, it is possible to allocate in the packet mode, it is possible to allocate

multiple time slots to SUsmultiple time slots to SUs

Mobile Data SystemsMobile Data Systems

DataTAC/Ardis: IBM, Motorola -1983DataTAC/Ardis: IBM, Motorola -1983 MobiTex/RAM: Ericsson, Bellsouth -1989MobiTex/RAM: Ericsson, Bellsouth -1989 CDPD: Open System (IBM, AT&T) -1993CDPD: Open System (IBM, AT&T) -1993 GPRS: ETSIGPRS: ETSI

Mobile Data Systems Mobile Data Systems (cont.)(cont.)

System DataTAC MobiTex CDPDFreq. Band (MHz) 800 900, 400 800Channel spacing (KHz) 12.5/25 12.5/25 30Protocol RD-LAP MPAKS TCP/IPData rate (Kbps) 4.8/19.2 8/16 19.2Throughput (Kbps) 2.2/12.0 4-5 9.6-14.4Specification Closed Closed Open

GPRS (1/2)GPRS (1/2)

GSM data servicesGSM data services Short Message Services (SMS)Short Message Services (SMS) Bearer Services: 9.6 kbps (14.4 kbps for Phase 2+, 1996) Bearer Services: 9.6 kbps (14.4 kbps for Phase 2+, 1996)

circuit-switched datacircuit-switched data High Speed Circuit-Switched Data (HSCSD): 9.6 - 115.2 kbps High Speed Circuit-Switched Data (HSCSD): 9.6 - 115.2 kbps

(Phase 2+, 1997)(Phase 2+, 1997) GPRSGPRS

GSM Phase 2 + for GPRS is completed in 1998.GSM Phase 2 + for GPRS is completed in 1998. Provides best-effort packet-switched serviceProvides best-effort packet-switched service External Network: X.25, Internet (TCP/IP)External Network: X.25, Internet (TCP/IP)

GPRS (2/2)GPRS (2/2)

Up to 8 time slots can be assigned to a single userUp to 8 time slots can be assigned to a single user Coding schemes:Coding schemes:

CS-1: 9.06CS-1: 9.06 CS-2: 13.4CS-2: 13.4 CS-3: 13.6CS-3: 13.6 CS-4: 21.4 (no channel coding)CS-4: 21.4 (no channel coding)

Data rate: (9.06, 13.4, 15.6, 21.4, depends on channel Data rate: (9.06, 13.4, 15.6, 21.4, depends on channel coding) x (1 to 8) ==> 171.2 kbps (max)coding) x (1 to 8) ==> 171.2 kbps (max)

Additional equipments are introduced in GPRSAdditional equipments are introduced in GPRS Gateway GPRS Support Node (GGSN)Gateway GPRS Support Node (GGSN) Serving GPRS Support Node (SGSN)Serving GPRS Support Node (SGSN) Packet Control Unit (PCU)Packet Control Unit (PCU)