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Frequency-hopping spread spectrum (FHSS) is a method of transmitting radio signals by rapidly changing the carrier frequency among many frequencies occupying a large spectral band. The changes are controlled by a code known to both transmitter and receiver .
For mobile phone technology, a mobile allocation index offset (MAIO) refers a time delay separating traffic channels.When a GSM (Global System for Mobile Communications) mobile phone is served by a cell that is hopping over a set of frequencies, the separate traffic channels hop over the allocated frequencies according to a hopping sequence number (HSN).
This is the case in both GSM and IS-136 for example. Exceptions to this include the DECT and Personal Handy-phone System (PHS) micro-cellular systems, UMTS-TDD UMTS variant, and China's TD-SCDMA, which use time-division duplexing, where different time slots are allocated for the base station and handsets on the same frequency.
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 frequency.
Um also supports frequency hopping (GSM 05.01 Section 6), which is not specifically intended as a security feature but has the practical effect of adding significant complexity to passive interception of the Um link. Authentication and encryption both rely on a secret key, Ki, that is unique to the subscriber.
Practical synchronous digital systems radiate electromagnetic energy on a number of narrow bands spread on the clock frequency and its harmonics, resulting in a frequency spectrum that, at certain frequencies, can exceed the regulatory limits for electromagnetic interference (e.g. those of the FCC in the United States, JEITA in Japan and the ...
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.
Binary constant-weight codes have several applications, including frequency hopping in GSM networks. [1] Most barcodes use a binary constant-weight code to simplify automatically setting the brightness threshold that distinguishes black and white stripes.