BROADCAST CAPABILITY OF DIRECT SEQUENCE AND HYBRID SPREAD SPECTRUM

Two forms of spread-spectrum 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 messages that can be transmitted 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 multiple-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 for broadcasting the different messages. Systems with chip-synchronous signals and systems with random delays 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. © 1990 IEEE