Reduced-complexity bandwidth efficient multitone direct sequence spread spectrum

We consider modifications to conventional MT-DS-SS signaling to both improve spectral efficiency and reduce receiver RF complexity. The first modification to the conventional MT scheme is a simple reduction in subcarrier frequency spacing, which provides a small improvement in bandwidth efficiency at no cost in complexity or performance. The second modification entails the use of fewer receiver local oscillators (LOs) than the number of subcarriers, in addition to reduced subcarrier spacing. We employ known (training) symbols to completely recover the performance loss inherent in this approach, using a single stage of inter-subcarrier interference cancellation (ISIC). This ISIC requires a very modest number of baseband processing operations. We provide the relationships between the amount of training required and the number of subcarriers and receiver LOs. Via both analysis and computer simulations, we provide example performance results, and also provide a second example reduced-RF-complexity receiver with higher data throughput, which employs an additional stage of ISIC.