07 Tm2100eu02tm 0001 Radio Interface

8/13/2019 07 Tm2100eu02tm 0001 Radio Interface

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Radio Interface Siemens

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Contents

1 Physics of Layer 1 32 Logic of L1 233 MOC / MTC 35

Radio Interface


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Siemens Radio Interface

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1 Physics of Layer 1

Physics of Layer 1

TDMAframe4.615

ms

time

TS4

TS5

TS6

TS7

TS0

TS1

TS2

TS3

Frequency[MHz]

Duplex distance: 45 MHz

200 kHz

Example:GSM900

890 915 935 960

UL DL

TS577

s

Physical channel (Um)Physical channel (Um)

Radio Interface (Layer 1)

Fig. 1


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The Radio Interface: Physics of Layer 1

The Layer 1 of Um is described in GSM Rec. 04.04. In the following, L1 is separated

for didactical reasons in the Physics of L1 transmission and the Logic of L1transmission.

For the transmission of user data / signaling physical channels are allocated to theusers. A physical channel in GSM is defined by a frequency pair for UL/DL and aTime Slot TS of the TDMA frame. The frequency bandwidth in GSM is 200 kHz. ATime Slot TS has a duration of 0.577 ms. 8 TS form a TDMA frame; the duration of aTDMA frame is 4.615 ms.

The Burst

In GSM, using FDMA & TDMA for multiple access, the transmission of data is notcontinuously. In every Time Slot TS the HF has to be switched on, the data aretransmitted briefly and then the HF transmission is switched off again. This type of HF transmission is called pulse or bursty operation. Therefore, the content of a TSis called Burst.

The transmitter is only allowed to transmit the HF Burst within the duration of the TS.If the HF transmission exceeds the duration of the TS, the transmission mightinterfere with the transmission of the succeeding user. In this case, strongdisturbances of both connections follow. For this reason, the transmission must betimed exactly. Furthermore, it is not possible to switch on / off immediately. Toprevent interference between neighboring TS, the GSM Rec. define a duration during

which the switching process must be closed. The BS and MS must be able to switchthe HF power on / off within 0.028 ms over a wide dynamic range. This range is 70dB for BS and 36 dB for MS.

So the burst transmission can be explained as a maximum of 0.028 ms for switchingon HF to the necessary power level, 0.5428 ms for the HF transmission of the so-called useful part (corresponding with 147 bit) and 0.028 ms for switching off the HFpower level down to background noise level. Note: This useful part + flanksexceeds the duration of a TS (0.577 ms) and often irritate readers of GSM literature.The 0.028 ms are however only time maximum limits for the flanks. They carry novaluable information and so they are allowed to interfere with the succeeding Burstsin a negligible way.


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Power

Time

28 s 28 s542,8 s

The Burst

Useful partUseful part

Fig. 2


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Burst: Content

A Time Slot is defined as a duration of 0.577 ms (to be precise: 0.576923 ms). This

duration is divided per definition into 156.25 bit. This means an individual bit has aduration of 3692.3 ns.

The 156.25 bit are used / defined as follows:

142 bit for the transmission of Information (not only users data / signaling but alsocontrol information necessary for maintenance of the connection)

3 bit as Tail Bits TB for edge limitations of the TS. They are preventing, that usefulinformation are falling into the flanks of the burst. TB contain no useful information.They are modulated as content 0.

8.25 bit as Guard Period GP. The GP is not part of the HF transmission. It is used to

compensate run-time effects in the cells. Note: There is one exception of GPs: Thefirst MS transmissions of the MS toward the network use special bursts (AccessBurst) with an extended GP of 68.25 bit.


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Burst: Content

7 0 1 2 3 4 5 6 7

TBTail Bits

3 bit

Information142 bit

TBTail Bits

3 bit

GPGuard Period

8.25 bit

HF transmission

TS = 576 12/13 s= 156.25 bit

1 bit = 3.6923 s

Fig. 3


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Example: Normal Burst NB

The Normal Burst is part of the Logic of Layer 1 and will be explained together with

the four other Burst Types later-on in detail. It is shown here for didactical reasons toget an idea of the content of what has been determined as Information.

The 142 bit of Information (content: 0 or 1) are realized in the middle of the burstto enable reliable transmission. The 3 TB (content: 0) on the edge provide buffer against data loss at the flanks of the burst.

The Normal Burst NB contains: 2 x 3 bit as Tail Bits TB 2 x 57 bit as Information (User Data / Signaling) 2 x 1 bit as Stealing Flags which inform the receiving side if user data or user

related signaling is transmitted 26 bit as Training Sequence for time synchronization and transmission quality

analysis

Now the structure of a TS / burst is explained, the content has been described downto bit level, but the question is now:

How are the 0 and 1 physically presented on the radio interface?


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TB Information-Bits S TrainingSequence S TB GPInformation-Bits

156.25 Bit = 576.9 s

3 57 1 26 1 57 3 8.25

Normal Burst 5 Burst Types with different logical content(discussed later-on)

5 Burst Types with different logical content(discussed later-on)

Example:Normal Burst

Bit

S: Stealing flagTB: Tail BitsGP: Guard Period

142 bit Information

Fig. 4


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GSM Modulation: Gaussian Minimum Shift Keying

For transmission of the binary data 0 and 1 in GSM a frequency modulation

method has been chosen. It is known as Gaussian Minimum Shift Keying GMSK.

Minimum Shift Keying MSK

The GMSK is based on Minimum Shift Keying MSK. MSK is a modulation principle, where the information is transmitted in the instantaneous frequency of the HF signal.

The carrier frequency f T is shifted by the frequency difference f = 67.7 kHz toindicate "1" or "0". This is achieved not by shifting the frequency directly, but by achange of the phase velocity. This results in a frequency and phase variation.

Gaussian MSK

In GMSK, the phase transitions are smoothed by filtering the data with a gaussiancurve. This enables smooth phase shifts, keeping the bandwidth comparable narrow.Thus, a bandwidth of only 200 kHz can be achieved.


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1

0f T - f

f T + f

f T

+ 180+ 90

t

- 180

- 90

phase

binarysignal

frequency

Minimum ShiftKeying MSK

GMSK: Gaussian MSK MSK signal x Gaussian curve smaller band-width

Fig. 5


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Frames

TDMA frames

A single frequency band in TDMA systems is subdivided into several Time Slots TS, which can be used by different users. In GSM 8 TS form one TDMA frame (4.615ms), i.e. 8 physical channels are using the same frequency band being cyclically(every 4.615 ms) allocated to a certain user / application.

So the TDMA frame is a repetition cycle with a duration of 4.615 ms.

The TDMA frames themselves are again part of a repetition cycle of a larger duration.Certain contains are always repeated after a certain duration. This repetition cycle iscalled: Multiframe.

Multiframes

Here a separation has to be done according to the type of information a physicalchannel is transmitting. The physical channels can be used to transmit either user data or signaling.

Multiframes of physical channels allocated for user traffic (Traffic Channels TCH) arerepetition cycles of 26 TDMA frames.

Multiframes of physical channels allocated for signaling data (mostly on one / severalof the TS0 of the carrier of one cell) are repetition cycles of 51 TDMA frames.

Certain logical contents are repeated on certain TDMA frames of the 26 TDMAframes of the TCH Multiframes or on the 51 TDMA frames of the signalingMultiframe.


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Example: Traffic Channel TCH Multiframe

The TCH Multiframe consists of 26 TDMA frames with user data. Every one of this 26

TDMA frames contains a certain logical content. So certain contents are repeatedevery 120 ms. This is necessary because the user data which are transmitted onthis Traffic Channel are not only the user information (Traffic Channel TCH = user speech, fax, data) which he likes to transmit. Also user related control information(so-called Slow Associated Control Channel SACCH) which are necessary tomaintain the connection are transmitted on the same physical channel. They aretransmitted every TCH Multiframe, i.e. every 120 ms on the 13th TDMA frame (FullRate TCH), respectively at Half Rate transmission for the first user of this physicalchannel on the 13th and for the second user on the 26th TDMA frame.

In Full Rate transmission the 26th TDMA frame is empty (Idle I).

A general overview and description of the different logical contents which aredefined in GSM and the content of the Signaling Multiframes is given later-on inLogic of L1.


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26 TDMA frame = 120 ms

Full Rate (FR) TCH

T/t = TDMA frame for TCHA/a = TDMA frame for SACCH/TI = Idle

2 Half Rate (HR) TCH

Example:TCH Multiframe

T T T T T T T T T T T T A T T T T T T T T T T T T I

T t T t T t T t T t T t A t T t T t T t T t T t T a

Signaling Multiframe Logic of L1

User related control datato maintain connection

TCH: Traffic ChannelSACCH: Slow Associated Control C hannel

Fig. 7


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Time Structure of the Radio Interface:

Bit : The shortest unit of the GSM radio interface is one bit. Its information is GMSK

modulated onto the HF. Its duration is 3692.3 ns.Time Slot TS : The TS consists of 156.25 bit. It is the shortest possible transmissiontime in GSM with a duration of 0.57688 ms.

TDMA frames: 8 TS form 1 TDMA frame with a duration of 4.615 ms. 8 physicalchannels are using the same frequency band being cyclically (every 4.615 ms)allocated to a certain user / application.

Multiframes : The TDMA frames themselves are again part of a repetition cycle of alarger duration, the Multiframe. Certain contains are always repeated after a certainduration. Multiframes for user traffic (Traffic Channels TCH) are repetition cycles of 26 TDMA frames with a duration of 120 ms. Multiframes for signaling are repetitioncycles of 51 TDMA frames with a duration of 235.4 ms.

Superframe : The TCH / Signaling Multiframes are summarized in longer repetitioncycles to Superframes. Superframes consist of 51 TCH / 26 Signaling Multiframes. ASuperframe (1326 TDMA frames) is the smallest common multiple of TCH andsignaling Multiframes with a duration of 6.12 s.

Hyperframe : The Hyperframe is the GSM numbering period. It comprises 2048Superframes and is exactly 12,533.76 s or 3 h 28 min 56.76 s long. It is a multiple of all cycles described up to now and determines all transmission cycles / periods onthe radio interface. The Hyperframe is the shortest cycle for repetition of thefrequency hopping algorithm and for ciphering.


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1 Signalling Multiframe =51 TDMA frames 235,4 ms

1 TCH Multiframe =26 TDMA frames = 120 ms

Time

StructureHyperframe =

2048 Superframes 3h 29 min

0 1 2 3 4 5 6 7

0 1 2 3 24 25 0 1 2 3 49 50

0 1 2 3 4950

0 1 2 3 24 25

1 Superframe =51 x 26

TDMA frames 6.12 ms

Numbering Periode.g. repetition of frequency hopping ciphering

Channel organisationscheme

Repetition schemefor TCH / Signaling

BURST = TS content

1 TDMA frame= 8 TS = 4,615 ms

1 Burst = 156,25 bit = 576,88 us(1 bit = 3,6923 us)

Fig. 8


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Adaptive Frame Alignment

In GSM the numbering of the Uplink UL and Downlink DL Time Slots TS is shifted by

three TS against each other. This prevents simultaneous transmission and receptionin GSM and enables to create simpler and cheaper Mobile Stations MS. Narrowbandfilters are not necessary. This enabled to built GSM handhelds directly fromcommercial start of GSM in the early 90th.

Timing Advance TA

The Guard Periods GP of the Normal Bursts are not able to compensate signaldelays in larger GSM cells. The MS receives synchronization signals from the BS,synchronizes their transmission based on this signals, but it cannot recognize itsdistance from the BS. The distance can be up to 35 km in a normal GSM cell. Atransmission without special compensation of this run-time delay would result ininterference with the succeeding TS.

Therefore, the BS analyses the delay of the MS transmission using the very first MSburst (which has an extended GP). The BS adjusts its transmission in the DL andinforms the MS with the Timing Advance TA information how to adjust the ULtransmission (i.e. how much earlier the transmission has to start). Over the totalconnection, the delay is analyzed by the BS and new TA values set for the MS. 64TA values (difference: plus/minus 1 bit period) can be used to compensate run-timeeffects.


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Adaptive frame alignment:preventing simultaneous transmission / receiving

UL/DL shifted by 3 TS

Adaptive frame alignment /Timing Advance TA

76543210

76543210 DL

UL

Timing Advance TA :compensation of propagation delays

BTS commands MS to transmit earlier:2 x propagation time MS - BTS

Fig. 9


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Frequency Hopping

Frequency Hopping means to change the frequency used for transmission is

consequently changed every TDMA frame following a certain frequency hoppingalgorithm. The Time Slot of the physical channel is still fixed.

The logic behind frequency hopping is to guarantee that all channels have the samehigh degree of transmission quality by dividing possible short term interference over all channels of the cell.

So a narrow-band interference does not disrupt the total transmission on one carrier,i.e. on one frequency band, because the transmission is hopping from TDMA frameto TDMA frame to other frequencies.

Nevertheless, now interference occurs for all the carrier of the cell from time to time when transmitting on the disturbed frequency band. But this can be compensated inGSM, because in classical GSM there is always redundancy on the transmitted data.The redundant information is delivered in the next TS of the succeeding TDMAframe, i.e. on another frequency (which is not disturbed).

Frequency hopping is optional in GSM. It is on the PLMN operators decision to usefrequency hopping or not. Frequency hopping significantly improves the quality / reliability of transmission.

The carrier transmitting the Broadcast Control Channel BCCH (carrying informationnecessary for MS synchronization to the network) does not participate in frequencyhopping.

Frequency hopping is done in the MS and BS, managed from the BSC. Thefrequency hopping algorithm can be configured from an OMC.


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Frequency Hopping

frame 0 frame 1 frame 2 frame 3 frame 4 frame 5

RFC 1

RFC2

RFC 3

RFC 4

RFC 5

TCH

Compensation of narrow-band interference

stable & reliable transmission(redundant bits on different TDMA frames)

Fig. 10


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2 Logic of L1

Signaling

TrafficUser Data

DL

DL

UL

UL + DL

DL

UL+

BCCH

FCCH

SCH

PCH

AGCH

RACH

SDCCH

SACCH

FACCH

TCH/FTCH/H

BCHBroadcast Channel

CCCHCommon Control

Channel

DCCHDedicated Control

Channel

Logic of L1

Radio Interface (Layer 1)

Fig. 11


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Logical Channels

Different signaling and user data contents determine different Logical Channels in

GSM.For user data transmission two different Logical Channels are used:

TCH/F Traffic Channels, Full rate (FR/EFR speech: 13 / 12.2 kbit/s; data: 9.6kbit/s)

TCH/H Traffic Channels, Half rate (HR speech: 5.6 kbit/s; data: 4.8/2.4/1.2/0.6/0.3kbit/s)

For signaling 3 types of Logical Channels are used: BCHs, CCCHs and DCCHs.

Broadcast Channels BCH are used DL only for MS synchronization & information: FCCH Frequency Correction Channel: for MS frequency synchronization SCH Synchronization Channel: for MS time synchronization; contains additionally

TDMA frame no., BSIC BCCH Broadcast Control Channel: contains system & cell parameters, e.g. CGI

(i.e. PLMN, LAI), channel combining, frequency hopping algorithm, cipher mode,cell capabilities: e.g. EFR/FR/HR, VAD/DTX, ASCI, HSCSD, GPRS, EDGE,..)

Common Control Channels CCCH are used uni-directional UL & DL for initialaccess:

PCH Paging Channel: to search the MS in the LAI in case of an MTC RACH Random Access Channel: MS request for dedicated signaling resources AGCH Access Grant Channel: to grant a dedicated channel to the MS

Dedicated Control Channels DCCH are used bi-directional for dedicated signaling: SDCCH Stand-alone Dedicated Control Channel: dedicated signaling between MS

& BS for Call Setup (Authentication, Cipher start, IMEI check, TMSI-Reallocation,Setup,..) LUP procedures, SMS

SACCH Slow Associated Control Channel: allocated together with SDCCH or TCH; control information to maintain connection (e.g. DL: Power Control, Timing

Advance, Comfort Noise; UL: Measurement Reports for Handover,..) FACCH Fast Associated Control Channel: allocated instead of TCH in case of

enhanced demand for signaling resources (Handover, Call Release, IMSI-Detach,OACSU..)


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Allocation of signaling channel

Signaling MS BTSE for e.g. Call Setup (Authentication, Cipher start, IMEI check,Setup info,..) LUP, SMS,...

Signaling

TrafficUser Data

DL

DL

UL

UL + DL

DL

UL+

FCCH

SCH

PCH

AGCH

SDCCH

SACCH

FACCH

TCH/F

TCH/H

Frequency synchronization

Time synchronization + BSIC, TDMA-No.

Paging / Searching (MTC)

Measurement Report,TA, PC, cell parameters,...

Signalling instead of TCH(e.g. for HOV, IMSI Detach, Call Release)

BCHBroadcast Channel

CCCHCommon Control

Channel

DCCHDedicated Control

Channel

User data Full Rate

Logical channels

User data Half Rate

BCCH: Broadcast Control ChannelFCCH: Frequency Correction ChannelSCH: Synchronisation ChannelPCH: Paging Channel

AGCH: Access Grant ChannelRACH: Random Access ChannelSDCCH: Stand-alone Dedicated Control Channel

SACCH: Slow Associated Control ChannelFACCH: Fast Associated Control ChannelTCH: Traffic Channel

BCCHCGI, FR/EFR/HR, VAD/DTX, HSCSD,frequency hopping, channel combinations

RACH Request for signaling channel

Fig. 12


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Burst Types

The HF transmission, which is transmitted in a Time Slot with a pre-defined bit

sequence is call Burst. In GSM there are 5 different Burst types defined:

Normal Burst NB : The NB is used for most of the Logical Channels (TCH, BCCH,PCH, AGCH, SDCCH, SACCH, FACCH). It consists of the following bit sequence:

2 x 3 bit as Tail Bits TB for edge limitation of the HF burst (content: 0), 2 x 57 bit as Data Bits (Information), which carry the users data or signaling

information. 2 x 1 bit as Stealing Flags S, which indicate whether user data (TCH) or user

related signaling (FACH) is transmitted in this Burst. 26 bit as Training Sequences, which are fixed bit pattern (8 different sequences

exist for NB) for synchronization of the transmitted burst & recognition of transmission quality

8.25 bit as Guard Period GP, which is not part of the HF transmission; used asguard period between succeeding TS.

Frequency Correction Burst : It is used for the FCCH only, consisting of: 142 Fixed Bits with content 0; it is used for MS frequency synchronization

2 x 3 bit as Tail Bits 8.25 bit Guard Period

Synchronization Burst : It is used for the SCH only, consisting of: 64 bit as Training Sequence for initial precise MS time synchronization 2 x 39 bit with Information necessary for initial MS access (BSIC, TDMA frame

number, NB training sequence used in this cell,..)

Random Access Burst : It is used for RACH only, consisting of: 36 bits Information for initial access (BSIC, MS random no., access reason) 41 bits as Synchronization Sequence 8 + 3 bits as Tail Bits 68.25 bits Guard Period GP; the extended GP prevents interference with the

succeeding TS occurring due to the run-time problem (the MS lacks of informationabout its distance to the BS before starting access)


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Dummy Burst : The Dummy Burst has NB structure; it is transmitted in special casesif nothing else (useful) is to be transmitted (e.g. at the BCCH carrier, which has to betransmitted continuously because it is the cell beacon).

TB3bit

Information57 bit

S1bit

TrainingSequence

26 bit

S1bit

TB3bit

GP8.25

bit

Information57 bit

156.25 Bit = 576.9 s

Normal Burst TCH, BCCH, PCH, AGCH,SDCCH, SACCH, FACCH

Burst Types

TB3bit

Fixed bits142 bit

TB3bit

GP8.25

bit

Frequency Correction Burst: FCCH

TB3bit

Information39 bit

TrainingSequence

64 bit

TB3bit

GP8.25

bit

Synchronization Burst: SCH

TB8bit

SynchronizationSequence41 bit

TB3bit

GP68.25bit

Information36 bit

Random Access Burst: RACH

Information39 bit

Dummy Burst: Structure Normal Burst

Fig. 13


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Multiframe: Channel Combinations

There are seven different schemes to co-ordinate the logical channels in multiframes.

Three schemes are used for the co-ordination of Full rate and Half rate TrafficChannels. Four schemes are used to co-ordinate signaling, depending on therequirements of the individual cell. The network operator has do decide, whichchannel combinations are used for a cell.

Combination I III are used for TCH Multiframe co-ordination (Full rate / Half rate).

Combination IV VII are used for Signaling Multiframe co-ordination.

Combination I: TCH/F + FACCH/F + SACCH/F

Combination I is used to transmit Full rate user data & speech. The frames 011and 13-24 are used for user data, frame 12 is used for SACCH (user relatedcontrol data) and frame 25 is not used (I: Idle).

Combination II & III: TCH(0,1) + FACCH/H(0,1) + SACCH/H(0,1) respectivelyTCH/H(0) + FACCH/H(0) + SACCH/H(0) + TCH/H(1) + FACCH/H(1) + SACCH/H(1)

Combination II & III are used to transmit Half rate user data & speech. 2 TCH/Huser have to share the 26 multiframes. Data from user 1 or user 2 are filledalternately into the frames. The SACCH of user 1 is on frame 12, the SACCH of user 2 is on frame 25.

Combination IV: FCCH +SCH + CCCH (PCH & AGCH) + BCCH

Combination IV offers much space for the Common Control Channels CCCH.Therefore, this combination is used often for cells with many carrier. As BCCHcarrier it is the cell beacon and so it must be used exactly only on one carrier of the cell. It is allocated on TS 0 of this carrier and has to be transmittedcontinuously. If no useful information is to be transmitted, Dummy Bursts have tobe used. There is no Power Control used on the cells beacon. Combination IV lacks of dedicated signaling channels (SDCCH and SACCH). Therefore, it has tobe used together with combination VII.


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I) TCH/F + FACCH/F + SACCH/F

II) TCH/H(0,1) + FACCH/H(O,1) + SACCH/H(0,1)

III) TCH/H(0) + FACCH/H(0) + SACCH/H(0) +

TCH/H(1) + FACCH/H(1) + SACCH/H(1)

IV) FCCH + SCH + CCCH + BCCH

V) FCCH + SCH + CCCH + BCCH + SDCCH/4 + SACCH/4

VI) CCCH + BCCH

VII) SDCCH/8 + SACCH/8

Multiframe: Channel Combinations

F0

S1

BCCH2 - 5

CCCH6 - 9

F10

S11

CCCH12 - 19

F20

S21

CCCH22 - 29

F30

S31

CCCH32 - 39

F40

S41

CCCH42 - 49

I50

F:FCCHS:SCHB: BCCH

R0

R1

R10

R11

R20

R21

R30

R31

R40

R41

R50

DL

UL

Combination IV

C: CCCH (PCH, AGCH)I: IdleR: RACH

TCH-Combinationsshown before

TCH-Combinationsshown before

Fig. 14


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Combination V: FCCH + SCH + CCCH + BCCH + SDCCH/4 + SACCH/4

Combination V is the minimum configuration for a cell, because is contains alllogical channels necessary for signaling in a cell. It is often used for cells with onlyone or two carrier. For combination V the same is valid as for combination IV: It isthe cell beacon, it must be allocated on TS 0 of exactly one carrier of the cell. Ithas to be transmitted continuously. SDCCH/4 and SACCH/4 means that thiscombination offers the capacity for 4 simultaneous dedicated signalingconnections.

Combination VI: CCCH + BCCH

Combination VI can be used together with combination IV and VII for cells withvery much traffic and many carriers (up to 16 carriers). This means to be an

increased demand for Common Control Channels, which are offered bycombination VI. The multiframe structure of combination VI is similar as thestructure of combination IV, without FCCHs and SCHs. In combination with IV,combination IV is allocated on TS0 on the carrier and VI combinations can beallocated at TS 2 / 4 / 6 depending on the traffic volume of the cell.

Combination VII: SDCCH/8 + SACCH/8

Combination IV and VI offer no dedicated signaling channels. Therefore, they haveto be used together with combination VII. Combination VII offers up to 8simultaneous dedicated signaling channels. Combination VII can be allocated onTS 0 of other carrier than the BCCH carrier. The BCCH indicates the allocation of combination VII.


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Signaling Multiframe: Combination V

F S F S F S IBCCH CCCH CCCH CCCH SDCCH

0SDCCH

1 F S SDCCH

2SDCCH

3 F S SACCH

0SACCH

1

F S F S F S IBCCH CCCH CCCH CCCH SDCCH

0SDCCH

1 F S SDCCH

2SDCCH

3 F S SACCH

2SACCH

3

SDCCH

0SDCCH

1SDCCH

2SDCCH

0SDCCH

1SDCCH

2

SACCH

2SACCH

0

SDCCH

3SDCCH

3

R R

R R

SACCH

3SACCH

1

R R

R R

R R

R R

R R

R R

R R

R R

R R

R R

R R

R R

R R

R R

R R

R R

R R

R R

R

R

R R

R R

R R

R R

R R

R R

DL: BCCH + CCCH + 4 SDCCH (SDCCH/4) + 4 SACCH (SACCH/4)

UL: CCCH + SDCCH/4 + SACCH/4

ISDCCH

0SDCCH

1SACCH

4SACCH

5

ISDCCH

0SDCCH

1SACCH

0SACCH

1

SDCCH/8 + SACCH/8

UL

Combination VIIDLSDCCH

2SDCCH

3SDCCH

2SDCCH

3

SDCCH

4SDCCH

5SDCCH

4SDCCH

5

SDCCH

6SDCCH

7SDCCH

6SDCCH

7

SACCH

6SACCH

7SACCH

2SACCH

3

I

I

I

I

SACCH

5SACCH

6SACCH

0SACCH

1

SACCH

7SACCH

2

I

I

I

I

I

I

SDCCH

0SDCCH

1SDCCH

0SDCCH

1

SDCCH

2SDCCH

3SDCCH

2SDCCH

3

SDCCH

4SDCCH

5SDCCH

4SDCCH

5

SDCCH

6SDCCH

7SDCCH

6SDCCH

7

SACCH

4SACCH

0

Fig. 15


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L1 Summary: Physical Channels & GSM Data Rates

GSM uses combined TDMA and FDMA for multiple access.

GMSK has been chosen as modulation principle. The GSM channel bandwidth is 200kHz, the modulation rate 270.833 kbit/s (derived from the GSM frequency normal 13MHz: 13 MHz/48).

According to the GSM TDMA principle chosen with 8 physical channels on onecarrier the total gross data rate for 1 physical channel is 270,833 / 8 = 33,85 kbit/s.

1 physical channel consists of 1 TS (UL/DL) on 1 carrier. 1 TS consists of 156.25 bit.

In the Normal Burst, used for TCH transmission, only 114 bit of these 156.25 bit areinformation bits (user data & user related signaling). Therefore, only 24.7 kbit/s of the33.85 kbit/s are information.

In a TCH Multiframe, only 24 of the 26 frames are filled with TCH, i.e. user data. Theother frames are filled with SACCH (frame 12) or Idle (frame 25). Therefore, the realgross rate of user data in GSM is 22.8 kbit/s.

The net rate in GSM is 13 kbit/s for FR speech, 12.2 kbit/s for EFR, 9.6 kbit/s for datatransmission (+ different other rates for HSCSD and GPRS). The difference betweenthe GSM net rate of user data and the gross rate of 22.8 kbit/s is used for dataredundancy to enable a reliable transmission.

The GSM modulation rate is 270,833 kbit/s. I.e. one single bit has a duration of

3692.3 ns.156.25 bit form one Time Slot TS, i.e. the duration of one TS is 0.5769 ms.

8 TS form one TDMA frame, i.e. the duration of one TDMA frame is 4.615 ms; itcontains 1250 bit.


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L1 Summary: Physical Channel / GSM Data Rates

TB3

Information57

S1

Training Seq.26

S1

TB3

GP8.25

Information57

0 1 2 3 4 5 6 7

RFC1

RFC2

RFC3

RFCi

RFC123

RFC124

UL: 890 MHz 915 MHz

FDMA

GMSK Modulation 200 kHz

270.833kbit/s

TDMA1 TDMA Frame: 4.615 ms / 1250 bit

1 TS: 33.85 kbit/s

1 Normal Burst: 576.9 s / 156.25 bit

1 Bit = 3.6923 s

24.7 kbit/s = 22.8 kbit/s TCH data (incl. redundancy)+ 0.95 kbit/s SACCH + 0.95 kbit/s Idle

Fig. 16


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Mobile Originating Call MOC

The MOC is defined as an MS initiated call setup. Several procedures are necessary

between the MS and the BSS respectively the CN to set up a call. In the following theL1 messages on Um necessary for a normal MOC (without Off Air Call SetupOACSU; no emergency call) are shown:

Channel Request (RACH):MS requests the assignment of a dedicated signalingchannel

Immediate Assignment (AGCH): the network assigns a dedicated signalingchannel (SDCCH & SACCH). Additionally, a first TA information and Power Control PC is included.

CM Service Request (SDCCH): the MS provides information on the requestedservice (Basic Call, Emergency Call, SMS,...) and transmits the subscribersidentity (TMSI / IMSI).

Authentication Request (SDCCH): the networks checks the real identity (Ki) of theSIM transmitting RAND.

Authentication Response (SDCCH): the MS answers with the SRES on the Authentication Request

Cipher Mode Command (SDCCH): the network commands the MS to startciphering

Cipher Mode Complete (SDCCH): the MS acknowledges the cipher start (firstciphered message)

Setup (SDCCH): the MS transmits the Setup information including the desired TS / BS and number of the B-subscriber.

Call Proceeding (SDCCH): the network acknowledges the authorization for therequested service and confirms the call proceeding.

Assign Command (SDCCH): a TCH is allocated to the MS Assign Complete (FACCH): the MS confirms the TCH allocation (using TCH

resources) Alerting (FACCH): the network informs the MS on successful call setup (i.e. the

phone of the B subscriber rings). This starts generation of the ringing signals in theMS, too. Connect (FACCH): the MS is informed, that the B subscriber accepted the call Connect Acknowledge (FACCH): the MS confirms the Connect message TCH: now network switch over to data transfer; the communication is able to start


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Mobile Originating Call MOC

The basic MOC includes at least 14 messages. As a rule, this signaling requires less

than 2 s.Optional further messages are:

IMEI Request, IMEI Response to check the equipment identity

TMSI Reallocation: to allocate a new TMSI to the MS

IMEI check and TMSI reallocation are proceeded after start of ciphering

OACSU:

In case of (TCH) overload on Um OACSU can be used. In this case, the AssignCommand / Assign Complete messages are sent after the Alert message, wasting noTCH resources during this time (only SDCCH resources).

Emergency Call

In case of an Emergency Call, Authentication and Cipher are skipped. Call setup isfaster and allows usage of every Mobile Equipment (even without valid SIM card;IMEI on black list).

MOC Part I & Part II

The two slides MOC Part I & Part II are optional for the TM2100 GSM Introductioncourse. They show the full message flow for a Basic MOC between MS and BSS / NSS, including IMEI check and TMSI reallocation as well as the Call Release.

The SS7 message flow using L4 protocols MAP & BSSAP and L3 Radio Interfacemessages of RR, MM and CM can be used for self-study.


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MOCPart I

Channel Request CHAN_REQ

MS BSS MSC VLRISDN

Immediate Assign IMM_ASS_CMD)

CM Service Request CM_SERV_REQCM_SERV_REQ

Authentication Request AUTH_REQ AUTH_REQ

Authentication Response AUTH_RSP AUTH_RSP

Cipher Mode Command CIPH_CMDCIPH_CMD

Cipher Mode Complete CIPH_MOD _COMCIPH_MOD_COM

Check IMEI

TMSI Re-allocation TMSI_REAL_COMTMSI-REAL-CMD

TMSI_REAL_COMTMSI_REAL_COM

SETUPSETUP

Process Access RequestPROC_ACCESS_REQ

AUTH_RSP

Set Cipher ModeSET_CIPH_MODE

Forward New TMSIFORW_NEW_TMSI

TSMI AcknowledgedTMSI_ACK

SEND INFO

EIR

Fig. 19


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MS BSS MSC VLRISDN

Call Proceeding CALL_PROCCALL_PROC

ALERT ALERT

MOCPart II

Assign Command ASS_CMD Assign Request ASS_REQ

ASS_COM Assign Complete ASS_COM

Connect CONCON

CON_ACKConnect Acknowledged CON_ACK

Initial Address Message IAM

Address Complete Message ACM

Answer Message ANM

User data

Release RELREL

DISCDisconnect DISC

Clear Command CLR_CMDRelease phys. Channel CHAN_REL

REL_COMRelease Command REL_COM

Clear Complete CLR_CMPDisconnect DISC

Release REL

Release Complete RLC

Complete Call CALL_CMP

Fig. 20


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TM2100EU02TM_000142

Mobile Terminating Call MTC

The MTC is initiated by the network if there is a call for the subscriber. The MTC

message flow is very similar to the MOC message flow. The most importantdifference on Um is the start. The MS has to paged in all cells of a Location Area LA,using the Paging message.

Paging (PCH): The MS is paged in all LA cells using the TMSI / IMSI.

Setup (SDCCH): Another difference between MTC and MOC is the Setup message.In an MTC it is transmitted from the network to the MS, giving information on therequested service (TS, BS) and the ISDN / MSISDN number of the calling party.

Call Confirmed (SDCCH): After checking its capabilities to support the requestedservice, the MS acknowledges the Setup message with Call Confirmed.

Alerting (FACCH): Different to the MOC, in the MTC the Alerting message istransmitted from the MS to the network, to indicate the start of ringing in the MS.

Connect (FACCH) & Connection Acknowledge: Different to the MOC, in the MTCboth messages have opposite direction, too.


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MS requests for signaling channel

Signalling channel allocation [SDCCH x, TA]

Request MOC (SMS, Emergency Call,..)[TMSI/IMSI]

Request Authentication [RAND]

Authentication Response [SRES]

Start Ciphering

Acknowledgement; 1st ciphered message

Setup Message[Bearer Service, Calling No.]

Requested Service possible in MS

TCH-Allocation [frequency, TS]

Acknowledgement (on TCH resource)

Ringing signal started in MS

Mobile subscriber accept call

AcknowledgementStart of user data transmission & charging

MTCMobile

TerminatingCall

RACH: Channel Request

AGCH: Immediate Assign

SDCCH: CM Service Request

SDCCH: Authentication Request

SDCCH: Authentication Response

SDCCH: Cipher Mode Command

SDCCH: Cipher Mode Complete

SDCCH: Setup

SDCCH: Call Confirmed

SDCCH: Assign Command

FACCH: Assign Complete

FACCH: Alerting

FACCH: Connect

FACCH: Connection Ackn.

TCH

PCH: Paging Request Searching MS in Location Area

Fig. 21


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Documents

07 Tm2100eu02tm 0001 Radio Interface