it802 d mobilecommunicationspart4

IT 802DMobile Communications

Part 4Debasis Das

04/08/2023 Debasis Das Mallabhum Institute of Technology

2

Radio Interface-1890 MHz to 915 MHz, 200 KHz each

935 to 960 MHz, 200 KHz each

MS to BTS , reverse links

BTS to MS, forward links

45 MHz gap125Possible channels,124 are used

Channels assignedIn pairs, 45 MHz gap

Absolute Radio Frequency Channel number (ARFCN) – 0 to 124 and 975 to 1023

04/08/2023 3

Radio Interface-2Physical Channel

Debasis Das Mallabhum Institute of Technology

124 channels, 935-960 MHz

124 channels, 890-915 MHz

TS0

Guard

space

TS1

TS2

. . . .TS7

tUserdata

Userdata

SS Training t

Guard

space

Time

3 57 57 31 126546.5 micro S

577 micro S

4.615 ms

GSM TDMA Frame

GSM time slot. Normal burst


4

Up/Down linksChannels 1 & 124 not used in GSM 90032channels for organizational data90 channels for usersOne BTS handles 1 organizational channel

and up to 10 user data channels.Each of 248 (124 x 2 Up and down),

separated by GSM time frameEach GSM time frame slot has a fixed pattern


5

GSM Time SlotData transmitted in small portions, burstsBurst is 546.5 micro sec long and contains 148 bitsRemaining 30.5 micro sec slot is used as guard spaces

Avoids multipath overlaps, gives transmitter time to switch on and off

156.25 bits in 577 micro sec leads to a data rate of 33.8 Kbps, 270 kbps over a radio carrier

All 3 bits of tail is set to 0Training sequence adapts receiver to current propagation

conditions and select the strongest signal in multipath situation

S- flag indicating user data or network control data4 more busts are defined


6

Types of burstsFrequency correction bursts, helps MS to

correct the LO frequency

Synchronization burst wit extended training

sequence, help sync MS with BTS

Access burst set up initial connection with

BTS

Dummy burst, when no data is available for a

slot


7

Simplification of Transmitter Hardware

Up and downlinks are separated in frequency by 45

MHz in GSM 900 and 95 MHz in GSM 1800

TDM frames are shifted in time by three slots. If BTS

send data on t0 in slot 1 on the downlink then the

MS will access slot 1 of uplink in t0+3.577 micro sec

Thus MS does not need a full duplex transmitter


8

Point to NoteAs solution to frequency selective fading,

sometimes a slow frequency hopping

sequence is sometimes prescribed

MS and BTS may change carrier frequency

after each frame based on a common hopping

sequence


9

Logical Channels & Frame HierarchyPhysical & logical Channels

1

2

7

3

4

8

5

6

4.615 ms8*124 Duplex channels

C1C2xC2C1C2xC2C1


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Logical Channels & Frame HierarchyTraffic & Control Channels-1Traffic Channels (TCH)

Available Full rate TCH (TCH/F), 22.8 kbps data rate Half rate TCH (TCH/H), 11.4 kbps data rate

Beginning of GSM TCH/F- 13 kbps, TCH/FS (22.8-13=9.8 kbps) TCH/H + TCH/HS may not give the right voice quality

Full rate codecs FR-13 kbps, HR-5,6 kbps

Enhanced full rate (EFR), better voice quality at 12.2 kbps, given low transmission errors

Adaptive multi rate (AMR) is used in 3GOther TCH/F4.8 and TCH/F14,4,coding, error correction differ


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Logical Channels & Frame HierarchyTraffic & Control Channels-2

Control Channel Broadcast control channel (BCCH) ( info carried are cell id, options

available, frequencies in the cell and neighboring cells) Frequency control channel (FCCH) , Synchronization channel

(SCCH) Common control channels ( CCCH)(info regarding MS and BS; BTS to

MS uses paging channel (PCH), MS to BTS uses random access channel (RACH). MS uses access grant channel (AGCH) to tell MS that it can use a TCH or a SCCH for further set up.

Dedicated control channel (DCCH) (bi directional) Stand alone dedicated control channel ( SDCCH), low rate, 782 bps

for signaling, authentication, registration, etc. data Slow associated dedicated control channel (SACCH), associated

with each TCH and SDCCH Fast associated dedicated control channel ( FACCS), uses TCH time

channel for fast data transfer, such as handover time


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Logical Channels & Frame HierarchyTraffic & Control Channels-3

No arbitrary transmission of channels, fixed patternsSpeech multi-frame, 26 TDMA frames

Slow signaling slot

Blank slot/S

Pattern repeats

Normal burst-114 bits every 4.615 ms=24.7 kbps24 of 26 TCH is used, effective rate then= 22.8 kbps

TCH frames


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GSM Logical Channel TypesTraffic channels (TCH)

Carries digital user speech or data, identical

on both forward and reverse links

Control channels (CCH)

Carries signaling and synchronizing commands

between base station and mobile station, some

CCH may defined for only the forward or the

reverse links


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Traffic Channels (TCH)Full rate TCH (22.8 kbps)

Full rate speech channel (TCH/FS)Full rate data channel ,9600 bps (TCH/F9.6)Full rate data channel, 4800 bps (TCH/F4.8)Full rate data channel, 2400 bps (TCH/F2.4)

Half rate TCH (11.4 kbps)Half rate speech channel (TCH/HS)Half rate data channel, 4800 bps (TCH/H4.8)Half rate data channel, 2400 bps (TCH/H2.4)


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Control Channels(CCH)Each control channel consists of several logical

channels, distributed in timeControl channel types

Broadcast channel (BCH)Common control channel (CCCH)Dedicated control channel (DCCH)

BCH and CCCH are allocated in TS0 slots only, broadcast only during certain frames in the 51 frame control Superframe and designated ARFCNs (34).

DCCH can be sent any time slot, frame


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Control Channel Types- BCHBroadcast channels (BCH)

Broadcast control channel (BCCH) Works as a TDMA beacon, helps synchronize MSs in a cell,

broadcasts on TS0 only Broadcast control channel (BCCH): cell & network id,

operating characteristics of cell (current control channel structure, channel availability, congestion, etc.), list of channels in use during frames 2 to 5 of control multi frame

Frequency control channel (FCCH): special pattern every 10th frame for synchronizing LO frequency in MS

Synchronization channel (SCH): serving base station is identified by base station identity code(BSIC) and frame number (FN), following FCCH and repeated every 10th frame


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Control Multi-frame

F BS B B B C C C C F S C C C F S C C F S C C I

Control channel multi-frame, forward link, TS0

0R

2R

1R

49R

50R

Control channel multi-frame, reverse link, TS0R: Reverse RACH burst (CCCH)

F: FCCH burst, S: SCH burst, B: BCCH burst, all three BCHC: PCH/AGCH burst (CCCH), I: idle

C


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Control Channel Types- CCCHUses TS0 if BCH is not using it or the idle frame

Paging channel (PCH), forward link only Broadcasts IMSI number of incoming call, request to

acknowledge on RACH, used to broadcast text messages as part of SMS feature of the GSM

Random access channel (RACH), a slotted ALOHA channel, reverse link only, Acknowledge a call, initiate a call by MS, during TS0,

base assigns a SDCCH for call establishment, connection confirmed over AGCH

Access grant channel (AGCH), forward link only Instructs a MS to operate in a physical link and ARFCN


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Control Channel Types- DCCHBi directional, any TDM slot & ARFCN except

TS0Standalone dedicated control channel (SDCCH)

Carries signaling data after a connection is made with base station and before a TCH assignment is made, lets MS and base remain connected as MSC verifies subscriber and allocates resources

Slow associated control channel (SACCH) Sends & receives regular control information such as

transmit power level instruction and specific timingFast associated control channel (FACCH)

Fast control requirements such as handover, steal frames from TCH


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Call From Within GSM-1Subscriber should be synchronized to the local baseAfter receiving FCCH, SCH and BCCH, subscriber

will get on to appropriate BCHSubscriber dials the number and hits sendSends a RACH using the same ARFCN on which it

was lockedBase sends AGCH on CCCH and assigns a SDCCHMobile unit gets time slot and ARFCN assignment

through AGCH and tune to it, wait for SACCH for time advance and transmitter power commands


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Call From Within GSM-2While MS and base finish authentication and

user validation, MSC locates and establishes a connection with th4 called party in the PSTN, MSC switches the speech path to the serving base station.

Base station command via SDCCH about TS and ARFCN assignments for a specific TCH

Transferred to TCH to and fro transfers start and SDCCH is vacated


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Call from PSTNPage is responded by the MS, replies with

RACH

Base uses AGCH and CCCH to assign a new

SDCCH and a SACCH while network and

base are connected

MS does timing advance and authentication

on SDCCH, base issues a new physical

channel assignment and the TCH assignment

is made


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Traffic Multi-frame

Burst

Slot

0 1 2 …….. 7

577 micro sec4.615 ms

0 1 2 …….. 25traffic multi-frame, 120 ms

0 1 2 …….. 51

6.12 secSuperframe

0 1 2 …….. 2045 2046 2047

Hyperframe3 h, 28 m, 53.76 s2,715,647 frames

it802 d mobilecommunicationspart4

Education

rate data channel

tch time channel

user data channels

organizational channel

gappossible channels

mhz124 channels

low rate

rate efr