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FCCH
FCCH stands for Frequency Correction Channel. It is a downlink-only control channel in the GSM Um air interface. The FCCH burst, defined in GSM 05.02 section 5.2.4, is an all-zero sequence that produces a fixed tone in the GMSK modulator output. This tone enables the Mobile to lock its local oscillator to the BS clock as required in GSM specification 05.01 section 6. The FCCH is transmitted in frames immediately before the SCH. References * 3GPP TS 05.01 Physical layer on the radio path; General description * 3GPP TS 05.02 Multiplexing and Multiple Access on the Radio Path * http://www.3gpp.org/ftp/Specs/html-info/05-series.htm GSM standard {{telecom-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Um Air Interface
The Um interface is the air interface for the GSM mobile telephone standard. It is the interface between the mobile station (MS) and the Base transceiver station (BTS). It is called Um because it is the mobile analog to the U interface of ISDN. Um is defined in the GSM 04.xx and 05.xx series of specifications. Um can also support GPRS packet-oriented communication. Um layers The layers of GSM are initially defined in GSM 04.01 Section 7 and roughly follow the OSI model. Um is defined in the lower three layers of the model. Physical Layer (L1) The Um physical layer is defined in the GSM 05.xx series of specifications, with the introduction and overview in GSM 05.01. For most channels, Um L1 transmits and receives 184-bit control frames or 260-bit vocoder frames over the radio interface in 148-bit bursts with one burst per timeslot. There are three sublayers: # Radiomodem. This is the actual radio transceiver, defined largely in GSM 05.04 and 05.05. # Multiplexing and Timing ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Synchronization Channel
Synchronization Channel is a downlink only control channel used in GSM cellular telephone systems. It is part of the Um air interface specification. The purpose of the SCH is to allow the mobile station (handset) to quickly identify a nearby cell (a BTS) and synchronize to that BTS's TDMA structures. Each radio burst on the SCH contains: * the current frame clock of the serving BTS, * the Base station identity code (or BSIC), a truncated form of cell identity, and * an extended Training Sequence that is easily detected with a matched filter. When mobile turns on after getting FCCH it waits for getting SCCH which is to synchronise mobile's oscillator frequency with the frequency of the Base channel. The burst structure of the SCH is defined in GSM specification 05.03 section 4.7. The encoding of the frame clock is defined in GSM specification 04.08 section 9.1.30. The TDMA multiplexing pattern of the SCH is defined in GSM specification 05.02 clause 7 table 3. The GSM Synchro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
GMSK
In digital modulation, minimum-shift keying (MSK) is a type of continuous-phase frequency-shift keying that was developed in the late 1950s by Collins Radio employees Melvin L. Doelz and Earl T. Heald. Similar to OQPSK, MSK is encoded with bits alternating between quadrature components, with the Q component delayed by half the symbol period. However, instead of square pulses as OQPSK uses, MSK encodes each bit as a half sinusoid. This results in a constant-modulus signal (constant envelope signal), which reduces problems caused by non-linear distortion. In addition to being viewed as related to OQPSK, MSK can also be viewed as a continuous-phase frequency-shift keyed ( CPFSK) signal with a frequency separation of one-half the bit rate. In MSK the difference between the higher and lower frequency is identical to half the bit rate. Consequently, the waveforms used to represent a 0 and a 1 bit differ by exactly half a carrier period. Thus, the maximum frequency deviation is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
