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The transmitter and receiver can use fixed tables of frequency-hopping patterns, so that once synchronized they can maintain communication by following the table. In the US, FCC part 15 on unlicensed spread spectrum systems in the 902–928 MHz and 2.4 GHz bands permits more power than is allowed for non-spread-spectrum systems.
Techniques known since the 1940s and used in military communication systems since the 1950s "spread" a radio signal over a wide frequency range several magnitudes higher than minimum requirement. The core principle of spread spectrum is the use of noise-like carrier waves, and, as the name implies, bandwidths much wider than that required for ...
GSM radio frequency optimization (GSM RF optimisation) is the optimization of GSM radio frequencies. GSM networks consist of different cells and each cell transmit signals to and receive signals from the mobile station, for proper working of base station many parameters are defined before functioning the base station such as the coverage area of a cell depends on different factors including ...
LE-ACL employs a spread spectrum scheme known as adaptive frequency hopping. At the start of each connection event, frequency hopping occurs, with one of the 37 general purpose Bluetooth LE radio channels being selected from the set of available channels using a channel selection algorithm. Each device in the connection will then switch to the ...
A hopping sequence is followed by the TRXs and handsets using the sector. Several hopping sequences are available, and the sequence in use for a particular cell is continually broadcast by that cell so that it is known to the handsets. A TRX transmits and receives according to the GSM standards, which specify eight TDMA timeslots per radio ...
Most 2G cellular systems, with the notable exception of IS-95, are based on TDMA. GSM, D-AMPS, PDC, iDEN, and PHS are examples of TDMA cellular systems.. In the GSM system, the synchronization of the mobile phones is achieved by sending timing advance commands from the base station which instruct the mobile phone to transmit earlier and by how much.
An advanced form of FDMA is the orthogonal frequency-division multiple access (OFDMA) scheme, for example, used in 4G cellular communication systems. In OFDMA, each node may use several sub-carriers, making it possible to provide different quality of service (different data rates) to different users.
GSM combines short packet sizes, frequency hopping, redundancy, power control, digital encoding, and DTX to minimize interference and the effects of interference on a conversation. In this respect, DTX indirectly improves the over-all capacity of a network.