Question

Which is the following is NOT true for GSM? Check all what can apply: a) The uplink and the downlink channels are separated by 45 MHz. b) There are eight half rate users in one time slot. c) The peak frequency deviation of the GSM modulator is an integer multiple of the GSM data rate. d) GSM uses a constant envelop modulation.

Answer 1

a) The uplink and the downlink channels are separated by 45 MHz. - TRUE

b) There are eight half rate users in one time slot. - TRUE

c) The peak frequency deviation of the GSM modulator is an integer multiple of the GSM data rate. - TRUE

d) GSM uses a constant envelop modulation - NOT TRUE

The uplink and downlink channels in GSM are indeed separated by 45 MHz. This frequency division allows for simultaneous transmission and reception without interference.

Each GSM time slot accommodate eight half-rate users. GSM uses a time-division multiple access (TDMA) scheme where each time slot is divided into eight equal parts and each part can carry a half-rate voice channel.

The peak frequency deviation of the GSM modulator is indeed an integer multiple of the GSM data rate. In GSM, a Gaussian Minimum Shift Keying (GMSK) modulation is used which has a modulation index of 0.3, ensuring that the peak frequency deviation is an integer multiple of the data rate.

GSM uses GMSK modulation which is a constant envelope modulation. Constant envelope modulation techniques ensure that the amplitude of the modulated signal remains constant which helps reduce nonlinear distortion in the transmitter and is more power-efficient.