GSM Specifications

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Introduction: The Evolution Of Mobile Telephone Systems

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Before looking at the GSM specifications, it is important to understand the following basic terms:

	bandwidth - the range of a channel's limits; the broader the bandwidth, the
	faster data can be sent
	fbits per second (bps) - a single on-off pulse of data; eight bits are
	equivalent to one byte
	frequency - the number of cycles per unit of time; frequency is measured in
	hertz (Hz)
	kilo (k) - kilo is the designation for 1,000; the abbreviation kbps represents
	1,000 bits per second
	megahertz (MHz) - 1,000,000 hertz (cycles per second)
	milliseconds (ms) - one-thousandth of a second
	watt (W) - a measure of power of a transmitter

Specifications for different personal communication services (PCS) systems vary among the different PCS networks. Listed below is a description of the specifications and characteristics for GSM.

	frequency band - The frequency range specified for GSM is 1,850 to 1,990
	MHz (mobile station to base station).
	duplex distance - The duplex distance is 80 MHz. Duplex distance is the
	distance between the uplink and downlink frequencies. A channel has two frequencies, 80 MHz apart.
	channel separation - The separation between adjacent carrier frequencies. I
	n GSM, this is 200 kHz.
	modulation - Modulation is the process of sending a signal by changing the
	characteristics of a carrier frequency. This is done in GSM via Gaussian minimum shift keying (GMSK).
	transmission rate - GSM is a digital system with an over-the-air bit rate of
	270 kbps.
	access method - GSM utilizes the time division multiple access (TDMA)
	concept. TDMA is a technique in which several different calls may share the same carrier. Each call is assigned a particular time slot.
	speech coder - GSM uses linear predictive coding (LPC). The purpose of
	LPC is to reduce the bit rate. The LPC provides parameters for a filter that mimics the vocal tract. The signal passes through this filter, leaving behind a residual signal. Speech is encoded at 13 kbps.