BER performance of baseband DS/SSMA using FM coded M sequences in bandwidth limited channels

We discuss the bit error rate (BER) performance of asynchronous baseband DS/SSMA systems using line coded M sequences. As the line codes, we adopt FM family codes that provide M sequences with the DC free spectrum and good correlation properties. It has been already reported that some combinations of three FM coded M sequences provide a better cross-correlation property than that of the preferred pairs of noncoded M sequences. Since their quantitative evaluation in terms of the BER performance improvement due to the line coding has not been done yet, we considered it in this paper. We first derive an equation for the BER analysis, then compare the BER performance of the FM coded M sequences with that of the noncoded M sequences in two bandwidth limited channels, a band pass and a power line channel. In our scenario, the improvement of the required E_b/N₀ is 1 dB and 3 dB, respectively. Furthermore we propose a system using FM coded M sequences of different periods simultaneously. This proposed system of the different periods can achieve the channel efficiency 4/3 times better than a system using noncoded M sequences of the same period, while the required E_b/N₀ of both systems is almost the same