Convolutional coding for direct sequence multicarrier CDMA

This paper presents a multicarrier asynchronous direct sequence (DS) code division multiple access (CDMA) system which, through the use of linear convolutional codes, achieves frequency diversity of an order above and beyond that realized by path diversity in a conventional RAKE DS-CDMA system. A frequency selective Rayleigh fading channel is decomposed into M frequency non-selective channels, based on the channel coherence bandwidth. Then, a rate 1/M convolutional code is used to modulate the M DS-CDMA waveforms. Diversity gains on the order of the code free distance may now be achieved. This system exhibits robust performance in the presence of narrowband interference and jamming, yet preserves the natural multiple access interference rejection properties inherent in the standard DS-CDMA model. Significant capacity gains over the single carrier system are demonstrated, while holding overall system bandwidth and information rates constant