Broadcast Capability of Direct-Sequence and Hybrid Spread Spectrum.

摘要

Two forms of spread spectruim signaling: direct sequence and hybrid (direct sequence/frequency hopped) are shown to provide high broadcast capability especially when used in conjunction with forward error control coding schemes. The broadcast capability is defined as the maximum number of simultaneous distinct inessages that can be tranmitted to distant receivers from a single transmitter at a given bit error rate. This quantity provides a useful measure of the capacity of hub to mobile or satellite to earth station links of communication networks. When bursty data or voice traffic is dominant in such networks, the above forms of spread spectrum code division mutliple access (CDMA) provide a viable alternative to frequency division (FDMA) or time division (TDMA) multiple access. Different ways of multiplexing the direct sequence and hybrid signals are presented which employ distinct carriers, distinct pairs of orthogonal carriers, and only two orthogonal carriers to broadcast the different messages. Systems with chip synchronous signals and systems where random delays are introduced between the signals are considered. The average error probability of all systems is evaluated using the characteristic function and Gaussian approximation techniques. Besides the uncoded systems, systems using Reed-Solomon and convolutional codes are analyzed. A comparison of the broadcast capability of the different schemes is presented.