THE EFFECTS OF ODD-CORRELATION AND BAND-LIMITATION IN DIRECT-WAVE RECEPTION SYSTEMS USING BROAD-BAND SPREAD-SPECTRUM TECHNIQUES

In this paper, we describe effects of odd-correlation functions and ba nd-limitation filters for direct-wave reception systems using broadban d spread-spectrum (B-SS) techniques. The receiver of this system is sy nchronized to the direct-wave. First, the effects of odd-correlation f unctions are investigated by using M-sequences and random sequences. T he effects of even-correlation functions for those sequences can be ea sily obtained by using results of effects of odd-correlation functions for random sequences. Here we derive a novel function of odd-correlat ion variance for M-sequence, which is obtained theoretically. Conseque ntly, we shaw the advantage of M-sequence which is used as spreading s equence. As a reason, in the odd-correlation function of M-sequence, s mall values are taken near the synchronous phase where harmful scatter ed-waves exist, strongly. Next, the effects of both odd-correlation fu nction and band-limitation filter are studied by using several kinds o f filters. Here we discuss the difference of characteristics in case t hat despreading sequence of bandlimited pulse or that of rectangular p ulse is used in the correlator of the receiver. The technique despread ing by rectangular pulse can be achieved a high speed signal processin g and equipment miniaturizing because of utilization of switching circ uit. We show the advantage of despreading sequence of rectangular puls e, 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 o f rectangular pulse can be kept better than that between the transmitt ing sequence and despreading sequence of bandlimited pulse. As these r esults, in severe bandlimited direct-wave reception systems using B-SS techniques, M-sequence of rectangular pulse as despreading sequence i s most suitable.