1 Oma310000 Gsm Radio Interface Issue2.21

8/11/2019 1 Oma310000 Gsm Radio Interface Issue2.21

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Confidential Information of Huawei. No Spreading Without Permission


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In the Public Land Mobile communication Network (PLMN), the MS is connected with the

network via the radio channel. In this way, the subscribers can access the network and

obtain communication services. To achieve the interworking between MS and BTS, a set

of standards are needed for signal transmission through the radio channel. This set of

specifications which are related to the radio channel signal transmission, aim at Um

interface.

The Um interface is a kind of radio interface. It is responsible for the communication

between the mobile station and the BTS and provides the interworking link between the

mobile station and GSM system. Its physical connection is achieved via the radio waves.

The Um interface is the most important interface among all the interfaces in GSM system.

First of all, the complete and normative Um interface realizes full compatibility between MS

of different venders and different networks. That is fundamental conditions needed in

global roaming of the GSM system; second, the radio interface determines the rate of

frequency spectrum utilization of GSM system. The name Um is derived from the name

of the interface between the client terminal and the network in ISDN , in which the m

means mobile.


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The first layer is the physical layer, which is marked as L1 and is the lowest layer. This layer

provides the radio link needed in transmission of bit stream. It defines the radio access

capability of the GSM system and provides the most fundamental radio channel (logical

channel) for the information transmission of higher-layer , including the traffic channel

and control channel. For detailed description of logical channel, please refer to relevant

documents.

The second layer, marked as L2, is the data link layers and it is the middle layer. It applies

the LAPDm protocol. This layer includes various types of data transmission structures. It

controls the data transmission so as to ensure the reliable dedicated data links which are

set up between the mobile station and base station. The LAPDm protocol is based on the

D channel link access protocol (LAPD) in ISDN. For LAPDm, the radio transmission and

control characteristics are suitable to the signal transmission at the Um interface.

The third layer is the network application layer, which is marked as L3 and is the top layer.

It includes various types of messages and programs for control and management of the

services. That is to say, in this layer, specific messages of the mobile station and the system

control processes are packed into different protocols and mapped to logical channels. L3

includes three sub-layers: the Radio Resources management (RR), Mobility Management

(MM) and Communication Management (CM). These are the major contents of the

messages transmitted via the Um interface. The CM sub-layer includes three major parts:CC (call control service), SS (supplementary service) and SMS (short message service).


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The GSM Um interface applies the multiple access technology. With this technology, multiple

subscribers can share the same public communication connection. Basically, there are three modes

of channelization for multiple access, the frequency, time and code division multiple accessconnections respectively. They are frequency division multiple access (FDMA), time division multiple

access (TDMA) and code division multiple access (CDMA)


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FDMA-frequency division multiple access:

The frequency division is also called channelization sometimes. In this mode, thewhole assignable frequency spectrum is divided into many single radio channels.

Under the control of the system, each subscriber can be served by any one of these

channels.

The analogue cell system, AMPS, is a typical example that uses the FDMA

technology. The digital cell system can also use the FDMA. The difference is that it

only uses the frequency division mode, but the GSM system uses the FDMA also.

TDMA-time division multiple access:

The time division multiple access refers to dividing a broadband radio channel intoseveral timeslot, so that every subscriber seizes one of the timeslots; and the signal

is received (or transmitted) only in that specific timeslot. That is the reason why it is

called time division multiple access. This multiple access mode is used in digital cell

systems and GSM as well.

CDMA-Code division multiple access:

It is a multiple access mode in which the spread spectrum technique is used to

form different code sequences. It is quite different from FDMA and TDMA. In

FDMA and TDMA, the subscriber information is divided or separated based on thefrequency and time, but CDMA mode can transmit information of multiple

subscribers via the same radio channel at the same time.


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The radio channel is quite different from the wired channel. First, the radio channel has a

distinct time-change characteristic. The radio channel is exposed to the air, so it is

vulnerable to the interferences in the air. The signal is influenced by various interferences,

multi-path fading and shadow fading, so the error bit ratio is rather high. To solve the

problems mentioned above, a series of forward and backward(uplink & downlink)

transmission techniques are applied. The original subscriber data or signaling data are

transformed before being carried by the radio waves. And at the other end of the

transmission, a reverse transforming will be done. This can provide necessary protection to

the transmitting signal. The transformation methods roughly include the channel

coding/decoding, interleaving/de-interleaving, burst formatting, encryption/decryption, and

modulation/demodulation. For the voice, to pass an analog-to-digital converter is actually a

sampling process in the rate of 8KHz,after quantification each 125s contains 13bit of

code stream; then speech coding is performed with every 20ms as a segment and the

code transmission rate is reduced to 13Kbit/s, which becomes 22.8Kbit/s after the channel

coding; then the voice becomes a code stream at 33.8kbit/s after code interleaving,

encryption and burst formatting and is transmitted finally. The processing at the terminal is

just the reverse of the above procedures.


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The voice compression coding technique is widely used in the modern digital

communication systems. In this technique, a voice coder is used to set up a model to

simulate the voice and noise produced by human vocal organs. The parameters to form the

model will be transmitted through the TCH channels.

The voice coder is based on the residual excited linear prediction (REIP) coder. Moreover,

the long term predictor (LTP) is used to enhance the compression effect. LTP can make the

coding of residual data more advantageous by removing the vowels from the voice. With

20ms as the unit, the voice coder outputs 260bits after compressed coding. Therefore, the

code rate is 13kbps. According to the different classes of the importance of the

information, the output bits can be classified into three categories: 50 very important

bits,132 important bits and 78 ordinary bits.

Comparing with the traditional PCM line on which the voice is coded directly and

transmitted (64kbps), the 13kbps voice rate of the GSM system is much lower. The more

advanced voice coder in the future can further reduce the rate to 6.5kbps (half-rate voice

coding).


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To check and correct errors during the transmission, redundancy data and the information

calculated from the source data are added to the stream so as to increase the bit rate. For

the voice, the length of these codes is 456 bits every 20ms.

The bit rate of code stream output from the voice coder is 13Kbit/s, which is divided into

many 20ms continuous segments with each segment containing 260 bits. They can be

classified as:

50 very important bits;

132 important bits;

78 ordinary bits,

Redundancy processing is conducted, as shown in the above diagram.

The block coder is applied with 3 bits of redundancy code; while the excited coder applies

with 2 times redundancy and then adds 4 tail bits into the data stream.

There are three channel coding modes in the GSM system: convolution coding, block

coding and parity coding. For detailed information, please refer to related documents.


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If the voice signal is modulated and transmitted directly after channel coding, due to the

condition changes in mobile communication channel, a deep of the fading will influence a

successive string of bits and cause high bit error rate.

If the bits of a successive string are interfered or lost, the other end of the communication

can not decode the interfered or lost bits. To solve this problem, some technique or

method to separate the successive bits are required. Thus the successive bits in a message

can be transmitted dispersedly so that the bit error should be discrete. In this way, even if

errors occur, the errors are only concerned with a single or very short bit stream, which will

not lead to that the whole burst or the whole message block cannot be decoded. In this

case, the channel coding will take effect and recover the bit errors. This method is called

interleaving technique. The interleaving method is the most effective coding method for

dispersion of bit errors.

The key point of interleaving is to disperse some bits( suppose there are b bits) of the

code into some ( suppose to be n bursts) burst sequences so as to change the adjacent

relationship between bits. The higher the value of n is, the better the transmitting works.

However, the transmission delay is higher too. Therefore, a balanced consideration is

needed, the interleaving is related to the purpose of the channel. In the GSM system, the

second interleaving is applied.


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After channel coding, the extracted 456 bits are distributed into 8 groups with each group

containing 57 bits. That is the first interleaving, also called internal interleaving as shown in

the above diagram. Through the first interleaving, the successive messages in the groupsare dispersed. One burst carries two segments of voice information composed of 57 bits.

Obviously, if the two groups of 57 bits information from the first interleaving of a

successive 20ms voice blocks are inserted to the same burst sequence, the loss of the burst

will lead to loss 25% bits in the 20ms voice block. Therefore, one more interleaving is

needed between two voice blocks, which is called the inter-block interleaving or second

interleaving.

Suppose that voice block B is divided into 8 groups: perform inter-block interleaving to the

first four groups (B0, B1, B2 and B3) of block B and the last four groups (A4, A5, A6 and

A7) of the previous voice block A ; thus, four bursts are constituted: (B0, A4), (B1, A5), (B2,A6) and (B3, A7); to break the adjacency relationship between successive bits, bits of block

A occupy the even position of the burst while bits of block B occupy the odd position of

the burst. For example, B0 occupies the odd bit of the burst while A4 occupies the even bit.

Similarly, perform interleaving to the last four groups of block B and the first four groups

of the next block C. After the second interleaving, a 20ms voice block is inserted into 8

different burst sequences respectively and then transmitted one by one. Even if a whole

burst is lost during transmission process, only 12.5% of each voice block is influenced and

the errors can be corrected through channel coding at the other end. In addition, the

second interleaving for the control information is different. The interleaving mode is (B0,B4), (B1, B5), (B2, B6) and (B3, B7).


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As shown in the diagram, the front and end 3 tail bits delimit the burst; the 26 bits are

training sequence bits; and the bit at both sides of the training bits are used as bit

stealing flags.


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Transmission delay is unavoidable in the radio interface. If the mobile station moves away fromthe base station during a call, the further distance the more delay. The uplink is as the same.

If the delay is too high, the timeslots of the signal from a certain mobile station and that of the

next signal from another mobile station received by the base station will overlap each other, thuscausing inter-code interference. To avoid this, during a call, the measurement report sent fromthe mobile station to the base station carries a delay value. Moreover, the base station shouldmonitor the time when the call arrives and send an instruction to the mobile station via thedownlink channel every 480ms so as to inform the mobile station the time of advancetransmission. This time is the TA (timing advance), which ranges between 0~63 (0~233s ). TheTA value is limited by the timing advance code 0~63bit of the GSM system. Therefore, themaximum coverage distance of the GSM is 35km. Its calculation is as follows:

1/2*3.7 s/bit*63bit*c=35km


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{In the formula, 3.7s /bit is the duration per bit (577/156.25); 63bit is the maximum bitnumber of the time adjustment; c is the light speed (transmission speed of the signal); and indicates that the go and return trip of the signal.}

According to the above description, the distance corresponding to 1bit period is 554m.Influenced by the multi-path propagation and MS synchronization precision, the TA errormay reach up to about 3bit (1.6km).

When the MS is in idle mode, the time sequence within the MS can be adjusted via the SCHchannel. However, the mobile station does not know how far it is away from the basestation. If the distance between the MS and the base station is 30km, the time sequence ofthe MS will be 100s slower than that of the base station. When the mobile phone sendsits first RACH signal, it is already 100s later. For there is still another 100s oftransmission delay, when the signal reaches the base station, the total delay is 200s . It isvery possible that the signal collides with the pulse of the adjacent timeslot around the basestation. Therefore, RACH and some other channel access pulses will be shorter than otherpulses. Only after receiving the time sequence adjustment signal (TA) from the base station,MS can send pulses of normal length. In this case, the MS needs to send signals by 200sin advance.


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When the voice signal is transmitted after being processed and modulated, the frequencyhopping technique will be used too, i.e. the transmission carrier varies constantly at

different timeslots (of course, the variation should comply with the frequency planningprinciples).

The following two factors are considered in introduction of the frequency hoppingtechnology:

1. For the fading process is related to the frequency band, the application of the frequencyhopping in the system may reduce the effects of the rayleigh fading.

2. Due to the interference diversity, in areas with dense traffic, the cell capacity is restrictedby the interference caused by the frequency multiplexing. In addition, the system isdesigned to meet the demands of subscribers, the maximum capacity of the system iscalculated on the assumption that the quality of a certain number of calls is reduceddistinctly due to interference. The lower the diversity measured around the specified C/I

value, the larger the system capacity. The interference on a call is the average value of theinterference level caused by many other calls. Thus, for a specified interference intensity,the more the interference sources, the better the system performance.

The radio interface of the GSM system is designed with the slow frequency hopping (SFH)technique. The difference between SFH and the fast frequency hopping (FFH) is that thefrequency change of the latter is faster than the modulating frequency. During the wholeburst sequence transmission period of the GSM system, the transmitting frequency remainsunchanged. Therefore, it belongs to slow frequency hopping, as shown in the abovediagram.

The GSM system allows 64 types of different frequency hopping sequences. There aremainly two parameters involved in description of them: mobile allocation index offset

(MAIO) and hopping sequence number (HSN). The values for MAIO can be as many as thefrequencies in a group; and there are 64 different values available for HSN.


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Actually, during the communication process, the mobile subscriber talks only 40% of the

time and there is not much useful information transmitted during rest of the time. If all the

information is transmitted to the network, it will not only be a waste of the system

resources but also add more interference to the system. In order to overcome this problem,

the DTX technique is used in the GSM system, i.e. the transmission of radio signals is

prohibited when there is no voice signal being transmitted. This is to reduce the

interference level and increase the system efficiency. In addition, this mechanism can also

save the battery of the mobile station and prolong the standby time of the mobile station.

Note that, the DTX function is not used for data transmission.

There are two transmission modes for the GSM system: one is the normal mode. In this

case, the noise obtains the same transmission quality as the voice; the other is the

discontinuous transmission mode. In this case, the mobile station only transmits the voice

signals. The noise at the receiving end is artificial.

The artificial noise is used to inform the hearer that communication connection is ok when

none of the subscribers are speaking. And the noise is designed as a comfortable noise

which will not make the hearer uncomfortable.

The comfortable noise transmission also meets the requirements of the system

measurement. In DTX mode, only 260bit codes are transmitted per 480ms; while in normal

mode, 260bit codes are transmitted per 20ms. In the DTX mode, these 260 bits will

generate SID (Silence Descriptor) frames. These frames, like the voice frames, will be

processed via channel coding, interleaving, encryption and modulation, and then be

transmitted in 8 continuous bursts. In other time, there is no message transmitted.


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The DTX mode is optional. However, the transmission quality will be reduced a bit in the

DTX mode. Especially when both ends of the communication are mobile subscribers, the

influence on the transmission quality will be more severe because the DTX will be used

twice on the same path. In addition, to implement the DTX function, the system should be

able to indicate when to start the discontinuous transmission and when to stop it; and

when the DTX is active the coder should be able to detect whether the signal is a voice

signal or a noise signal. Thus, the VAD technique has to be used. The VAD algorithm

determines whether each output frame contains voice or background noise by comparing

the measured signal energy with the threshold defined for it. The principle of the

determination is that the noise energy should always be lower than the voice energy.


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During the process of radio transmission of signals, to reduce the interference, to increase

the utilization efficiency of the frequency spectrum, and to prolong the battery life, the

transmission power can be adjusted, that is called power control. More specifically, the

power control refers to adjust the transmission power of the mobile station or base station

in the radio mode within a certain range. Its objective is the same as that of the DTX.

When the receiving level and quality is rather strong, the transmission power at the TX

terminal can be reduced appropriately so that the communication can be kept at a certain

level. In this way, the interference on other calls around can be reduced. The specific

process will be described in the subsequent content together with Huawei power control

algorithm.


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The major basic concept concerned with the radio path transmission of the GSM system is

the burst sequence (simplified as Burst). It is a string of transmission units including more

than 100 modulation bits. The burst sequence has a restricted duration and seizes a

restricted radio frequency spectrum. They can be described as output from the time and

frequency window. This window is called Slot. In other words, within the system frequency

band, the central frequency of the slot is set every 200KHz (observed from the opinion of

FDMA); while the slot occurs cyclically as the time evolves, which seizes 15/26ms (i.e.

approximately 0.577ms) each time (observed from the opinion of TDMA). The intervals of

these slots are called Time Slots and the duration of them is called the time unit (marked

as BP, indicating the Burst Period).

We can use the time/frequency chart to draw the slot as a small rectangle with the length

of 15/26ms and width as 200KHz, as shown in the above diagram. Similarly, we can call

the 200KHz bandwidth specified in GSM as Frequency Slot, which is equivalent to the

Radio Frequency Channel (i.e. RF channel) in the GSM specifications.

The two terms: timeslot and burst sequence are different to a degree in actual application.

For example, the burst sequence is sometimes related to the time-frequency rectangular

unit and sometimes to its content. Similarly, the timeslot has the meaning of time value or

indicates that a slot in every 8 slots is used periodically.

To use a specified channel means to transmit the burst sequence at the specified moment

and frequency, i.e. the specified slot. Generally, the time of slots in a channel is

discontinuous.


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The physical channel is the medium over which the information is carried.

The logical channel consists of the information carried over the physical channels.

A Physical Channel (a TS, defined by a fixed position (0-7) on a given TDMA frame) may be

used to broadcast messages containing different kinds of information:

traffic messages for speech and data,

signaling messages for different procedures and supplementary services,

synchronization messages for temporal and logical synchronization between the mobile

stations and the BTS,

measurements messages for uplink report of the downlink measurements,

control messages to manage the access to the network.

All these kinds of messages are classified in Logical Channels. Depending on the quantity

of information to transmit and on their consistency, several logical channels may be

mapped onto one physical channel, in order to use its successive Time Slots as much as

possible (optimization of the resources number by maximizing the occupancy duration of

each).

As a conclusion:

Physical Channel = information container

Logical Channel = specification of the information global content


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The Logical Channel is used in time multiplex in a physical channel, which is categorized

according to the types of messages transmitted in the physical channel. Different logical

channels are used in transmission of different types of information between BS and MS,

such as the signaling or traffic data. In GSM system, five different types of burst sequences

are specified for different logical channels, which have different time-amplitude diagrams

as shown in the above diagrams.

The training sequence helps to discriminate radio channels with same frequency so as to

help to demodulate the signals. However, there is no training sequence for FB and DB; for

SB and AB, the training sequence is constant, i.e. the synchronous bit; for NB, there are 8

different training sequences specified in the specifications. These 8 different training

sequences of NB are numbered from 0 to 7, which are called training sequence numbers.

By allocating training sequences with distinct differences to channels of the same

frequency used in cells that are close to and may interfere with each other, the co-

frequency interference can be avoided efficiently during modulation.


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As we know, every cell has several TRX and every TRX includes 8 timeslots (i.e. providing 8

basic physical channels). In the radio subsystem, the physical channel supports the logical

channel based on the type of message transmitted . In this way, the physical channels are

mapped as different logical channels. In the GSM system, the logical channel is classified as

the dedicated channel (DCH) and the common channel (CCH). Sometimes, it can also be

classified as the traffic channel and control channel.

The traffic channel (TCH) carries voice or data, which are the full-rate traffic channel (TCH/F)

and half-rate traffic channel (TCH/H). These two types of channels carry information at the

rates of 13 kbit/s and 6.5 kbit/s respectively. The channel using half of the time slots of a

full-rate channel is the half-rate channel. Therefore, a carrier can provide 8 full-rate or 16

half-rate traffic channels.

The frequency correction channel (FCCH) carries the information for frequency correction

of MS and BTS.

The control channel (CCH) is used to transmit signaling or synchronous data. There are

mainly 3 types of control channels: Broadcast Channel (BCCH), Common Control Channel

(CCCH) and Dedicated Control Channel (DCCH).


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1. Frequency correction channel (FCCH)

It carries the information for frequency correction for the mobile station. The MS can communicate

with a cell and demodulate other information of the same cell just via FCCH. Moreover, the MS can

also know whether the carrier is a BCCH carrier via FCCH.

2. Synchronous channel (SCH)

After FCCH decoding, the MS will continue to decode the SCH channel message. This message

includes the information for MS frame synchronization and BS identification: Base Station Identifying

Code (BSIC). It seizes 6 bits, in which 3 bits are PLMN color codes ranging between 0~7; while the

remaining 3 bits are Base Station Color Codes (BCC) ranging between 0~7.

The simplified TDMA frame number (RFN) seizes 22 bits.


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3. Broadcast control channel (BCCH)

Generally, there is always a BCCH channel in every cell , which is responsible for

broadcasting system information to the mobile station. These system information enablethe MS to identify and access network at the idle mode.

4. Paging channel (PCH)

This is a downlink channel which is used to page mobile stations. When the network is to

set up communication with a certain MS, it will send paging messages via the PCH channel

to all cells in the LAC area in which the certain MS has currently registered, and indicates

TMSI or IMSI of the certain mobile.

5. Access granted channel (AGCH)

This is a downlink channel used in answering a network access request by the mobile

station, i.e. allocation of an SDCCH or a TCH directly.


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1. Random access channel (RACH)

It is an uplink channel used for MS randomly access to network by requesting for an SDCCH. The

request includes a 3bit setup reason (call request, paging response, location update request and short

message request etc.) and a 5bit random reference number for MS to differentiate the access granted

messages.

2. Stand-Alone Dedicated Control Channel (SDCCH)

It is a bi-directional dedicated channel used in transmission of signaling messages concerned with

connection setup, location update message, short message, authentication message, encryption

command, channel allocation message and various kinds of additional services etc. It can be divided

into the Stand-Alone Dedicated Control Channel (SD/8) and the Dedicated Control Channel in

combination with CCCH (SD/4).


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3. Slow associated control channel (SACCH)

It is used together with the traffic channel or SDCCH. It carries some specific informationwhile transmitting the subscriber information. At the uplink, it mainly transmits the

measurement report ; while at the downlink, it mainly transmits some system

information. These messages include the quality of communication, LAI, CELL ID, BCCH

signal strength of the adjacent cell, NCC permit, cell option, TA and power control level

etc.

4. Fast associated control channel (FACCH)

It is used together with TCH for providing signaling messages whose speed and

timeliness are much higher than the slow associated control channel (SACCH) for thesystem during the transmission process. This channel uses frames borrowed from the

traffic channel for its connection and transmits such instruction messages as handover.

For the voice decoder can repeat the voice of the last 20ms, this kind of interruption due

to frame stealing will not be detected by the subscriber. Besides the three types of

control channels described above, there is a cell broadcast control channel (CBCH). It is

used at the downlink and carries the short message service cell broadcast (SMSCB)

information. This kind of control channel uses the same physical channel as that used in

SDCCH.


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As shown above, CCCH=PCH+RACH+AGCH; downlink CCCH=PCH+AGCH; and uplink

CCCH=RACH. In the above combinations, combination 3 and 4 must be allocated to slot 0

of the BCCH carrier configured for the cell; while combination 5 must be allocated to

timeslots 2, 4 and 6 of the BCCH carrier. The FACCH works in the frame stealing mode, for

which no fixed time sequence will be allocated. In addition, the cyclic multiframe period of

SACCH/C4 and SACCH/C8 is 102 frames.


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The TDMA/FDMA multiplexing is used in GSM, the information needed in the

synchronization between MS and BTS is provided by FCCH+SCH.

The MS determines the frequency of the BCCH carrier by searching for the frequency

correction Burst transmitted via FCCH; then it finds the SCH (synchronization channel)

according to the relationship between SCH and FCCH and decodes the current frame

number and BSIC for synchronization with BTS. Furthermore, it determines whether the

cell is barred or not and decodes the system information on BCCH.

In the structure diagram of extended BCCH, except that the F and S timeslots are replaced

by Idle timeslots, the rest of the structures are the same as that of the main BCCH.


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It is used in the configuration of cells of low traffic density and small capacity. The

Combined BCCH is only configured at timeslot 0.

Channel combination: FCCHSCHBCCHCCCH+SDCCH/4+SACCH/4

SDCCH/4: Stand-alone dedicated control channel. Each TDMA multiframe with 51 frames

has 4 SDCCH;

SACCH/4: Slow SDCCH/4 associated control channel;

Compared with the main BCCH channel, 4 signaling channels are added to the 51 frames.

The functions of these 4 signaling channels are the same as those of the SDCCH8 channel.

Therefore, this channel combination can be taken as a combination of the functions of the

above two channels. This combination take effect on two aspects: first, this reduced thequantity of AGCH+PCH on CCCH and only a small-capacity system is provided; second, this

combination provides a certain quantity of signaling channels in timeslot 0. Thus, it is

unnecessary to assign SDCCH8 channels in a small-capacity system. This channel suitable

for small-capacity systems. And it is also an example of the flexible GSM network

configuration.


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Channel combination: SDCCH/8+ SACCH/C8

SDCCH/8: Stand-alone dedicated control channel. Each TDMA multiframe with 102 frameshas 8 SDCCH.

SACCH/C8: Slow SDCCH/8 associated control channel.


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Channel combination: TCH/F + FACCH/F + SACCH/F

TCH/F: Full-rate voice channel; FACCH/F: Full-rate fast associated control channel;

SACCH/F: Fast TCH/F associated control channel.


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The common control channel includes PCH, AGCH and RACH, in which AGCH and PCH are

downlink while RACH is uplink. Its purpose is to send the access granted (immediate

assignment) message, paging message and random access message. Based on the

configuration of traffic channels in the cell and the traffic model of the cell, the CCCH

channel can be borne by one or more physical channels. Moreover, the CCCH can share

the same physical channel with the SDCCH channel. The combination mode for the

common channel in the cell depends on the configuration parameter of the common

channel.

As a way for load control, the MS may be distributed to several different sub-groups by

operators for access or other operation purposes. The CCCH grouping and paging

grouping are two examples.


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1 Oma310000 Gsm Radio Interface Issue2.21