Ladas & Parry
Method and apparatus for implementing a direct-sequence code division multiple access communication system with an M-ary pulse-position modulated spreading-sequence signal
 A BPSK-MPP-DS-CDMA system is devised based on an M-ary pulse position modulated spreading-sequence signal. Under same bandwidth, same amount of energy used for one decision, and same bit error rate comparison conditions, if the number of users is less than the number N.sub.u of available sequence signals in the spreading sequence signal set {S.sub.p (t)} used in the BPSK-MPP-DS-CDMA system, the multiple access capacities of the BPSK-MPP-DS-CDMA system according to the present invention for M=4, M=8, and M=16 are improved by factors of at least 1.335, 1.66, and 1.65 over conventional BPSK-DS-CDMA systems. On the other hand, if the number of users reaches N.sub.u, the multiple access capacity can not be increased futher, however, the bit error rate of the system still be reduced. Furthermore, significant amount of transmission energy is saved. 
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Chen-Yi
Chang