GSM BURSTS

GSM Bursts The Normal Burst: There are FOUR different types of bursts used for transmission in GSM. 1) The normal burst 2) The "F" or frequency correction burst 3) The "S" or synchronous burst 4) The access burst The Normal Burst: The normal burst is used to carry data and most signaling. It has a total length of 156.25 bits, made up of two 57 bit information bits, a 26 bit training sequence used for equalization, 1 stealing bit for each information block (used for FACCH), 3 tail bits at each end, and an 8.25 bit guard sequence, as shown in Figure 2. The 156.25 bits are transmitted in 0.577 ms, giving a gross bit rate of 270.833 kbps…….

GSM Bursts The Normal Burst: There are FOUR different types of bursts used for transmission in GSM. 1) The normal burst 2) The "F" or frequency correction burst 3) The "S" or synchronous burst 4) The access burst The Normal Burst: …….. This burst carries our conversation in digital form. That's what the two 57 information, message, or data bits are for. The normal burst also carries signaling information needed to manage call processing, that is, data for setting up, maintaining, and then ending a call. What then are training, tail, stealing, and guard bits? Once again we go step by step

GSM Bursts The Normal Burst: There are FOUR different types of bursts used for transmission in GSM. 1) The normal burst 2) The "F" or frequency correction burst 3) The "S" or synchronous burst 4) The access burst The Normal Burst: a.) Training sequence bits. Used for equalization. Bits which get the base station and mobile in "tune" with each other. You need some background. As John will write later on, b.) Stealing bits. Whereby a bit is stolen from message bits, just temporarily, to make way for the Fast Associated Channel. It runs in a blank and burst mode. It transmits during handovers or when the slow associated channel can't send information quickly enough

GSM Bursts The Normal Burst: There are FOUR different types of bursts used for transmission in GSM. 1) The normal burst 2) The "F" or frequency correction burst 3) The "S" or synchronous burst 4) The access burst The Normal Burst: c.) Tail bits: The tail bits clear the code that has gone before, setting everything back to 0 or a null state. d.) Guard bits: Empty time spaces separating data packets to make sure one burst does not run into another. The guard period allows "the sender some freedom to shift transmission timing to allow the receiver to receive aligned bursts." Guard bits, in other words, permit some leeway or slack.

GSM Bursts Frequency Correction Burst There are FOUR different types of bursts used for transmission in GSM. 1) The normal burst 2) The "F" or frequency correction burst 3) The "S" or synchronous burst 4) The access burst Frequency Correction Burst This is used by the MS to detect a special carrier which transmitted by every BTS in GSM network. This carrier is called BCCH, acts as a form of beacon as MS will search for BCCH carriers to detect the presence of GSM network. The FB is also used by MS as a frequency reference for their internal timebases. Every bit in FB is set to zero and after GMSK modulation, this results in a pure sinewave at a frequency around 68 KHz

GSM Bursts Synchronous Burst There are FOUR different types of bursts used for transmission in GSM. 1) The normal burst 2) The "F" or frequency correction burst 3) The "S" or synchronous burst 4) The access burst Synchronous Burst Carries 78 bits of coded data formed into two blocks of 39 bits on either side of a 64bit training sequence. This burst carries details of GSM frame structure and allows an MS to fully synchronies with BTS, this is the first burst that a MS has to demodulate. Welcome to the synchronization burst. What the base station transmits to a mobile to get in order with the rest of the digital traffic. It exists, not surprisingly, on a channel called the Synchronization Channel or SCH.

GSM Bursts Access Burst There are FOUR different types of bursts used for transmission in GSM. 1) The normal burst 2) The "F" or frequency correction burst 3) The "S" or synchronous burst 4) The access burst Access Burst This consists of a 41bit Training Sequence, followed by a 36-bit information bits. The Access burst is used by the MS to access the network initially and it is the first uplink burst that a BTS will have to demodulate from a particular MS, the training sequence is extended to ease the demodulation process. The access control burst is only broadcast on the random access channel or RACH.