BANDWIDTH MANAGEMENT

Any time AnywhereMobility & Roaming High capacity & subs. densityEfficient use of radio spectrumSeamless Network ArchitectureLow costFlexibilityInnovative ServicesStandard InterfacesMOBILE COMMUNICATION OBJECTIVES

Public Land Mobile NetworkINDIA has adopted GSM standard for PLMN.Digital Cellular System.Operates at 900 MHz.International Roaming facility.Power class 0.8 to 20W.Cell Radius upto 35 Kms.Maximum mobility speed 250 Km/hr.

BANDWIDTH MANAGEMENT TECHNIQUESFDMA TDMA Cellular Technology & Frequency Re-use SchemeSpeech CodingModulation

FDMAFrequency Division Multiple Access SchemeUplink Frequency Band = (890 915) MHzDownlink Frequency Band = (935 960) MHzAbsolute Radio Freq Carrier Number (ARFCN)Bandwidth = 915 890 or 960 935 = 25 MHz

GSM - MULTIPLE ACCESSGSM uses both FDMA & TDMA FDMA Access along Frequency axis Each RF carrier 200khz apart Total 124 RF Channels available. One or more carrier assigned to each base station...

GSMFDMA

TDMATime Division Multiple Access SchemeOne Radio Frequency = Eight Time SlotsOne TDMA Frame = Eight Time SlotsOne Time Slot = One Physical ChannelOne Time Slot Duration = 0.577 msec

GSMTDMA45 MHzFrequencyF2F1(Cell transmit)F2F1(Cell Rx)AmplitudeTypical TDMA/ FDMA frame structure

FDMA/TDMA Scheme FRAME

CMCCSMSSS Normal Burst3T 57 Encrypted1S 26 Training1S 57 Encrypted3T8.25 GP TIME SLOT

87654321FRAME OF 8 TIME SLOTSFRAME REPETITIONPHYSICAL CHANNELS876543211PHYSICAL CHANNELS

CELLULAR TECHNOLOGY

Cellular TechnologyCell Site

CELLULAR MOBILE CONCEPTS

WHAT IS A CELL ? A base station (transmitter) having a number of RF channels is called a cell Each cell covers a a limited number of mobile subscribers within the cell boundaries ( Coverage area) Typical Cell Radius Aprrox = 30 Km (Start up), 1 Km (Mature)

CELLEach Cell uses a specific set of radio frequenciesEach Base Station contains one or more TRXs

Types of Cells

OMNI CELLSSECTOR CELLS - Two Sector Cells - Three Sector Cells

Fundamental problemsRadio range, or coverageno. of channels, or voice circuitsFull, seamless service coverageLarge no. of subscribers in the range of millions

CELLULAR MOBILE CONCEPTSRADIO IN LOCAL LOOP LIMITED AVAILABILITY OF RF SPECTRUMINTERFERENCE PROBLEMINTERFERENCE AND SYSTEM CAPACITY FREQUENCY REUSE PATTERNCELLULAR PRINCIPLECELLULAR ENVIRONMENTCAPACITY CONSIDERATIONSFUTURE TRENDS

Frequency Re-use Scheme

ASSUMPTIONS Traffic /User = 30 mE , GOS = 1%

CELLULAR MOBILE CONCEPTS

CELL RADIUS (KM)

COVERAGE AREA(KM2)

No. Of MOBILE SUBS.

No. of CHANNELS REQD.

1

3.14

100

8

3

28.3

900

38

10

314

10,000

@ 360

25

1960

60,000

@ 2,000

360 * 25 KHz * 2 = 18 000 KHz = 18 MHz FOR A CELL OF 10 KM RADIUS ONLY THIS IS IMPOSSIBLE TO BE ALLOCATED HENCE FREQUENCY REUSE IS A MUST TO COVER THE TOTAL SERVICE AREA WITH A LIMITED AVAILABLE RF RESOURCES HENCE THE NEED FOR A CELLULAR PRINCIPLE

CELLULAR MOBILE CONCEPTS

Frequency Re-use Scheme

CLUSTER

A CLUSTER OF CELLS

4567231

CELLULAR MOBILE CONCEPTS

FREQUENCY REUSE PATTERN

1DRCELLULAR PRINCIPLE N=7

CELLULAR MOBILE CONCEPTS

CO-CHL INTERFERENCE :Interference caused by another cell/mobile using the same frequency DRCo Chl Interference is a Function of Qthe re-use ratio:

Q =D / R Lower Q Increased Co-Chl Interference Higher Q Reduced Co-Chl Interference

Co Channel Interference Q = D /R = 3N N =Cluster SizeR = Size (Radius of Cell)D = Distance between two Co- Channel Cells

LOWER Q Higher Interference Increased System Handling Capacity Co Channel Interference

CLASSIFICATION OF CELLSMICRO CELLMACRO CELLUMBRELLA CELL

GSM CAPACITY CONSIDERATIONS 8 Access Channels 1--Signaling 7- VoiceWith 2 % GoS 2.94 E 2.94E/25mE=120 Subs120 Subs/Sector 3 = 360 Subscribers

Techniques adopted in CELLULAR ENVIRONMENTPower Control Channel CodingInterleavingEqualizationSlow Frequency HoppingAntenna Diversity

Speech CodingAudio CODECRPE : LTP = Regular Pulse Excitation : Long term Prediction

ModulationGMSK = GAUSSIAN MINIMUM SHIFT KEYING

GSM Specifications GSM 900 Mobile to BS(UP-LINK) -890 to 915 MHzBS to Mobile (DOWN -LINK) - 935 to 960 MHz Bandwidth - 25 MHz GSM 1800 ( DCS ) Mobile to Cell(UP-LINK) -1710 to 1785 MHz Cell to Mobile (DOWN -LINK) - 1805 to 1880 MHz Bandwidth - 75 MHz RF Spectrum :

GSM Specifications Carrier Separation -200 kHzNo. of RF Carriers -124Access Method -TDMA/FDMAModulation Method -GMSKTransmission Rate -270.833 KbpsSpeech Coding -Full rate 13 Kbps Half rate 6.5 KbpsDuplex Distance -45 MHz

GSMDigital Voice Transmission - In GSM speech coding a block of 20 ms is encoded in one set of 260 bits. - This calculates as 50X 260 = 13 kbps. Thus GSM speech coder produces a bit rate of 13 kbps per subscriber. - This provides speech quality which is acceptable for mobile telephony and comparable with wire-line PSTN phones.Speech Coding

GSMDigital Voice Transmission - It uses 260 bits from speech coding as input and outputs 456 encoded bits. - In one burst one block of 57 bits from one sample and another block from another sample are sent together. - These 456 bits for every 20 ms of speech are interleaved forming eight blocks of 57 bits each.Channel CodingInterleaving

GSMDigital Voice Transmission - Additional bits as training sequence added to basic speech/data. - Total of 136 bits added, bringing overall total to 592 bits. - To counteract the problems encountered in radio path.Burst Formatting - Each TS of TDMA frame is 0.577 ms long and during this time 156.25 bits are transmitted. - One burst contains only 148 bits. Rest of the space, 8.25 bits time, is empty and is called Guard Period ( GP ). - GP enables MS/BTS to ramp up and ramp down.

GSMGaussian Minimum Shift Keying (GMSK)The modulation method in GSM is GMSK which facilitates the use of narrow bandwidth and coherent detection capability.Rectangular pulses are passed through a Gaussian filter prior to their passing through a modulator.The modulation scheme almost satisfies the adjacent channel power spectrum density requirements of -60dB specified by CCIR.

GSM Speech to Radio waves200kHz BW

GSM Radio Interface - CYCLES

Organisation of Speech & DataFrames 0-11 : TCHFrames 12 : SACCHFrames 13-24 : TCHFrames 25 : Unused26 frame multiframeDuration: 120 msTDMA frameDuration: 60/13 ms=4.615 msTailbitsData bitsStealingbitTraining sequenceStealingbitData bitsTailbitsGuardbitsNormal burstDuration 15/26 ms

GSM-- TDMA STRUCTURE TDMA 8 Time Slots / RF Channel Time slot duration 0.577m sec or 15 / 26 m sec Frame 8 Burst Periods ( Time Slots) = 8 15/26 = 4.615 m sec Multi Frame Traffic 26 4.615 = 120 msec Control 51 4.615 = 235.365 m sec Super Frame 51 Traffic Multi frames 26 Control Multi frames Hyper Frame 2048 Super Frames = 3 28 52.76 hr min sec

GSMLOGICAL CHANNELS USER INFORMATION( TRAFFIC) SIGNALLING INFORMATION (CONTROL)

GSM CONTOL CHHANELS OVER LOGICAL CHANNELS THREE TYPES OF CONTROL CHANNELS Intended to carry signalling and synchronisation Broadcast control channel BCCH Common control channel CCCH Dedicated control channel DCCH

OPERATIONAL CONCEPTS Hence IDLE MODE & DEDICATED MODE DEDICATED MODE -- When a full Bi -directional P to P CHL has been allocated during an established call IDLE MODE MODE -- When MS is powered on (active) without being in dedicated mode

GSM THREE TYPES OF CONTROL CHANNELS

OPERATIONAL CONCEPTS IDLE MODE -- When MS is powered on (active) without being in dedicated mode MS stays continuously in touch with BS Listens to transmissions from BS to intercept Paging Messages ( for incoming calls) Monitors Radio Environment in order to evaluate Chl Quality & choose the most suitable BS Listens to BS to avail short message broadcast service

OPERATIONAL CONCEPTS ACCESS PROCEDURE -- Access to system ( switch over from IDLE to DEDICATED Mode) MS indicates to BS that it needs a connection BS accepts the request & indicates which traffic CHL it may use For above purpose specific transmission is done over Common Channels

OPERATIONAL CONCEPTS MOBILE O/G Call MS sends access over RACH System allocates SDCCH through AGCH Lastly TCH is assigned through SDCCH when a conversation can start Set up information exchanged over SDCCH ( Authentication , Measurement Reports, Power Control)

OPERATIONAL CONCEPTS MOBILE I/C Call Paging to MS through PCH since MS is monitoring PAGCH MS responds by sending a page response over RACH Set up information exchanged over SDCCH ( Authentication, Call set-up messages , Power Control) As a result system allocates SDCCH to MS over AGCH Lastly TCH is allocated to mobile over SDCCH . Mobile starts conversation.

OPERATIONAL CONCEPTS IDLE MODE IDLE MODE ACCESS PROCDURE DEDICATED MODE MS O/G Call MS I/C Call----FCCH---- SCH----BCCH----RACH----AGCH----SDCCH----TCH----PCH----RACH----AGCH----SDCCH----TCH