How 26 and 51 Multiframes in GSM GSM is very complicated when we talk about its rf side and in it very complicated to understand the structure of 26 and 51 Multiframes, here my try to make you understand simply. The 26-frame Traffic Channel Multiframe in GSM The Below Figure shows the time relationship between … Read more
BCH,CCCH and DCCH Channel of GSM BCH (Broadcast Channels) BCCH(Broadcast Control Channels) Downlink Only. Broadcast information of the serving cell (System Information). Transmitted on timeslot zero of BCCH carrier. Read only by idle mobile at least once every 30 secs. SCH (Synchronization Channels) Downlink Only Carries information for frame synchronization. Contains frame number and BSIC … Read more
Dedicated Control Channel (DCCH) in GSM SDCCH (Stand-alone Dedicated Control Channel) Uplink and Downlink. Used for call setup, authentication, ciphering location update and SMS. SACCH (Slow Associated Control Channel) Downlink and Uplink. Used to transfer signal while MS have ongoing conversation on traffic or while SDCCH is being used. On the forward link, the SACCH … Read more
Broadcast Channels (BCH) Frequency correction channel (FCCH) the “lighthouse” of a BTS Synchronization channel (SCH) PLMN/base identifier of a BTS plus synchronization information (frame number) Broadcast control channel (BCCH) to transmit system information 1-4, 7-8 (differs in GSM 900, GSM 1800, and PCS 1900) CBCH and CCCH CBCH (Cell Broadcast Channel) transmits cell broadcast messages … Read more
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 … Read more
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. … Read more
When using close frequency reuse technique, system interference is the most important factor for frequency reuse ratio. Usually, power control and discontinuous transmission technologies are adopted to lower system interference. To prevent interference and improve system communication quality under the same interference condition, frequency hopping technology is used. Therefore, frequency hopping is a very important … Read more
Effect in Cell Coverage Area In coverage limited cells the frequency hopping may increase the cell coverage area because of the frequency diversity gain, but since the BCCH time slot doesn’t hop, the increased coverage area is relevant only for the ongoing calls that have been successfully established and are allocated a hopping TCH. According … Read more
Cyclic vs. Random Hopping Sequences Both cyclic and random hopping modes are available in GSM. In the cyclic mode the frequencies are changed sequentially from the lowest frequency to the highest as defined in the MA-list. In random mode the frequency to be used for each burst is selected from the MA-list by a predefined … Read more