2-비트 GMSK 차동복조기의 성능향샹에 관한 연구

초록

In additive white Gaussian noise (AWGN) and fast Rayleigh fading environment, the bit error rate(BER) performance of permodulation Gaussian filtered minimun shift keying(GMSK) using two-bit differential detection in conjunction with decision feedback and diversity reception is theoretically investicated. In GMSK modulation technique, a narrow output power spectrum can be obtained by means of a premodulation Gaussian low pass filter(GLPF). Howevern this narrow-band spectrum is attained at the sacifice of introducing severe intersymbol inerference(ISI) into the baseband waveform of the FM modulatior input. We introduce differential detector structure which use decision feedback to partially remove the effect of destructive ISI. In comparison to the conventional two-bit differential detection of GMSK, the proposed structures provide about 4.3dB signal to noise ratio(SNR) improvement when the premodulation filter bandwidth-time product is 0.25. Also to reduce the Rayleigh fading effects, postdetection diversity peception is considered. Thus the improvement of additive performance can is expected. Decision feedback reduces BER for all values of BtT. And error floor is lower. As a result, the BER performance of dfferential detector is brought closer to coherent detection without increasing transmitting power while avoiding the problems associated with the carrier recovery