Throughput Analysis for Code Division Multiple Accessing of the Spread Spectrum Channel

We consider the use of error correction codes of rate
r
on top of pseudonoise (PN) sequence coding for code division multiple accessing of the spread spectrum channel. The channel is found to have a maximum throughput of 0.72 and 0.36 based on the evaluation of channel capacity and cutoff rate, respectively. More generally, these two values are derived for given bandwidth expanding
n/r
versus
n/N
where
n
is the length of the PN sequence and
N
is the number of simultaneous users. It is found that to achieve the maximum throughput,
n
should be small. This implies that coding schemes with short PN sequences and low rate codes are superior in terms of throughput or antijam capability. The extreme case of
n = 1
corresponds to using a very low rate code with no PN sequence coding. Convolutional codes are recommended and analyzed for their error rate and decoding complexity.