The effects of odd-correlation and band-limitation in direct-wave reception systems using broadband spread-spectrum techniques
In this paper, we describe effects of odd-correlation functions and band-limitation filters for direct-wave reception systems using broadband spread-spectrum (B-SS) techniques. The receiver of this system is synchronized to the direct-wave. First, the effects of odd-correlation functions are investigated by using M-sequences and random sequences. The effects of even-correlation functions for those sequences can be easily obtained by using results of effects of odd-correlation functions for random sequences. Here we derive a novel function of odd-correlation variance for M-sequence, which is obtained theoretically. Consequently, we shaw the advantage of M-sequence which is used as spreading sequence. As a reason, in the odd-correlation function of M-sequence, small values are taken near the synchronous phase where harmful scattered-waves exist, strongly. Next, the effects of both odd-correlation function and band-limitation filter are studied by using several kinds of filters. Here we discuss the difference of characteristics in case that despreading sequence of bandlimited pulse or that of rectangular pulse is used in the correlator of the receiver. The technique despreading by rectangular pulse can be achieved a high speed signal processing and equipment miniaturizing because of utilization of switching circuit. We show the advantage of despreading sequence of rectangular pulse, when the limitation bandwidth of transmitting signal takes a small value. Because the characteristics of the correlation function between transmitting sequence of bandlimited pulse and despreading sequence of rectangular pulse can be kept better than that between the transmitting sequence and despreading sequence of bandlimited pulse. As these results, in severe bandlimited direct-wave reception systems using B-SS techniques, M-sequence of rectangular pulse as despreading sequence is most suitable.
band-limitation direct-wave reception system broadband spread-spectrum odd-correlation function land mobile radio communication