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MPhil thesis of Lo Chi Wa - Department of Electronic & Computer ...

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and the time slot for system monitor, in which case the frequency switching has to befinished with 1.5 time slots which is 870µs. The corresponding minimum loopbandwidth for the settling time within 870µs is around 3kHz.577µs870µsRX onR1 R2 R3 R4 R5 R6 R7 R8R1receivesystemmonitorreceiveTX onT6 T7 T8 T1 T2 T3 T4 T5transmitFig. 11 GSM Receive and transmit time slotsT6When the wireless signals are transmitted between the base station and the handsets, thesignals will undergo different paths due to multi-reflection in order to reach thedestination. Different paths will have different delays. The signals with different delayswill interference each other constructively or destructively depended on the frequency<strong>of</strong> the signals. In this case, the wireless signals will undergo frequency selective channelas shown in Fig. 12. Signals at different frequencies will have different fading.Moreover, there are some narrowband fixed-frequency interference signals due to somenear-by electronic applications.Under the frequency selective fading and narrowband interference, some frequencyslots are in deep fades or subject to large interference. One <strong>of</strong> the solutions is frequencydiversity which can avoid deep-fade and narrowband interference. It is because deepfadingand interference occurs only when all the paths are in deep fades and jammed byinterference.16

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