The technology of tomorrow is expanding in al directions and new technologies are leaving humans with endless possibilities The communication computer are the technologies of future which will change this universe into one globe logically, not physically, The revolution of cell technology is expanding day by day. I am going to discuss on the topic which is GSM communication system, which is used in cell technology GSM is a cellular network, which means that mobile connects to it by searching for cells in the immediate vicinity GSM networks operate in four different frequency range Most GSM networks operate in the 900 MHz or 1800 MHz bands Some countnes like Canada and US use 850 MHz and 1900 MHz bands because 900 and 1800 MHz frequency bands were already allocated The rarer 400 and 450 MHz frequency bands are assigned i some countres where these
frequencies were previously used for first-generation systems 900 uses 890-915 MHz to send information from the mobile station to the base station (uplink) MHz for the other direction (downlink), providing 124 RF channels numbers 1 to 124) spaced at 200 kHz Duplex spacing of used GSM-900 In some countries the range band has been extended to cover a larger frequency This extended GSM, E-GSM, uses 880-915 uplink) and MHz (downlink), adding 50 channels channel numbers 975 to 1023 and 0) to the onganal GSM 900 band Time Division Multiplexing is used to allow eight full-rate or sixteen half rate speech per radio frequency channel. There are eight radio timeslots eight burst periods) grouped into what is called a TDMA frame Half rate channels use alternate frames in the same timeslot. The channel data rate for all 8 channels is 270 833 kbit/s, and the frame duration is 4,615 ms The transmission power in the handset is limited to a maximum of 2 watts in GSME50/900 and I watt in GSM1800/ 1900 GSM has used a variety of voice codec to squeeze 3 1 kuu audio into between 5 6 and 13 kbil s Onginally, two codec. named after the types of data channel they were alloca were used, called hall rate (5.6 khit s) and full rate (13 kbit/s These used a system based upon linear predictive coding LPC) In addition to being effichent with bit rates, these codec also made it casier to identity more important parts of the audio, allowing the aur interface layer to prioritize and better protect these parts of the signal GSM was further enhanced in 1997 with the Enhanced he Full Rate (EFR) codec, a 12 2 kbit/s codec that uses a full im rate channel Finally, with the development of UMTS, EFR was refactored into a variable rate codec called AMR Namowband, which u high quality and robust against interference when used on full rate channels, and less robust but still relatively high quality when used in good radio conditions on half-rate channels There are five diTerenu cell sizes in a GSM nerwork- Macro, Micro, Pico, Femo and umbrella cells The coverage area of each cell vanes according to the implementation environment Macro cells can be regarded as cells where the base station antenna is installed on a mast on a building above average roof top level Micro cells are cells whose antenna height is under average roof top level, they are typically used in urban areas Pico cells are small cells whose cov diameter is a few dozen meters,
they are mainly used indoors. Femto cells are cells designed for use in residential or small business environments and connect to the service provder’s network va a broadband intermet connection Umbrella cells are used to cover shadowed regaons of smaller cells and fill in gaps in coverage berween those cells Cell horizontal radius vanes depending on antenna height, antenna gaun and propagation conditions from a couple of hundred meters to several tens of kilometers The longest the GSM fication supports in B specifi 35 kilometers (22 mi There are also several implementations of the concept of an extended cell, where the cell radius could be double or even more, depending on the antenna system, the type of terrain and the timing advance be Indoor coverage is also supported by GSM and may be Science Simplified achieved by using an indoor pico cell base station, or an indoor repeater with distributed indoor antennas fed through power splitters, to deliver the radio signals from an antenna outdoors to the separate indoor distributed antenna system. These are typically deployed when a lot of call capacity is needed indoors, for example in shopping centers or airports However, this is not a prerequisite, since indoor coverage is also provided by in-building penetration of the radio signals from nearby cells The modulation used in GSM is Gaussian minimum shift keying (GMSK), a kind of continuous-phase frequency shift keying. In GMSK, the signal to be modulated onto the carrier is first smoothed with a Gaussian low-pass filter pnor to being fed to a frequency modulator, which greatly reduces the interference to neighboring channels.