GSM

Structure of Combined BCCH in GSM

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: FCCH?SCH?BCCH?CCCH+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 […]

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Structure of Combined BCCH in GSM

Structure of Main BCCH in GSM

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 […]

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synchronization, sch, timeslots, information, frequency

Physical Combination of Logical Channel in GSM

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, […]

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Physical Combination of Logical Channel in GSM

Uplink Logical Channel in GSM

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. […]

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Uplink Logical Channel in GSM

Logical Channel Type in GSM

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, […]

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traffic channel, control channel, physical channels, channel, logical, information, frequency

Burst in GSM

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 […]

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same frequency, training, different, sequence, channels, logical, transmission

Definition of Logical Channel in GSM

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 […]

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messages, information, channel, physical, logical

What is Frame and Channel in GSM

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 […]

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frequency, transmission, brust

DTX: Discontinuous Transmission

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. […]

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discontinuous transmission, transmission, voice, system, signal, mobile

Frequency Hopping

When the voice signal is transmitted after being processed and modulated, the frequency hopping technique will be used too, i.e. the transmission carrier varies constantly at different timeslots (of course, the variation should comply with the frequency planning principles). The following two factors are considered in introduction of the frequency hopping technology: 1. For the […]

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frequency, system, hopping, interference, gsm

What is Interleaving

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 […]

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second interleaving, channel coding, interleaving, successive, burst, block

What is Channel Coding

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 […]

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redundancy, stream, coding, stream, coder, voice

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