Modulation:
The GSM uses 0.3 GMSK modulation. 0.3 describes the 3 dB bandwidth of the Gaussian pulse shaping filler in relation to the bit rate. (e.g. BT = 0.3).
GMSK is a type of digital FM modulation. The binary ones and zeros are represented in GSM by shifting the RF carrier by ± 67.708 KHz.
The GSM channel data rate is 270.833 Kbps. It is four times that of the RF carrier shift. This minimizes the bandwidth occupied by the modulation spectrum. Also, it improves the capacity of the channel.
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The MSK modulated signal is passed through the Gaussian filter in order to smoothen the rapid frequency transitions that will spread the energy to the adjacent channels.
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