When the audio signal passes through a filter, it mimics the vocal tract. This tool compresses the bit rate and gives an estimate of the speech parameters. Speech Codingįor speech coding or processing, GSM uses Linear Predictive Coding (LPC). Channel SpacingĬhannel spacing indicates the spacing between adjacent carrier frequencies. The downlink frequency band 890 - 915 MHz (basic 900 MHz band only). The uplink frequency range specified for GSM is 933 - 960 MHz (basic 900 MHz band only). GSM is a digital system with an over-the-air bit rate of 270 kbps. The gross transmission rate of a timeslot is 22.8 Kbps. The total symbol rate for GSM at 1 bit per symbol in GMSK produces 270.833 K symbols/second. These slots are separated by time so that a mobile unit doesn’t transmit and receive data at the same time. Each of these slots are used for both transmission as well as reception of data. In this process, the FDMA part divides the frequency of the total 25 MHz bandwidth into 124 carrier frequencies of 200 kHz bandwidth.Įach BS is assigned with one or multiple frequencies, and each of this frequency is divided into eight timeslots using a TDMA scheme. Radio spectrum being a limited resource that is consumed and divided among all the users, GSM devised a combination of TDMA/FDMA as the method to divide the bandwidth among the users. The GSM uses Gaussian Minimum Shift Keying (GMSK) modulation method. The transmitted data is demodulated back to its original form at the receiving end. Modulation is the process of transforming the input data into a suitable format for the transmission medium. Vital characteristics of the GSM specification are listed below− Modulation The requirements for different Personal Communication Services (PCS) systems differ for each PCS network.
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