A time-varying projection receiver for asynchronous DS/CDMA systems with narrowband interference over Multipath fading channels

In this work, the authors present a projection receiver for an asynchronous DS/CDMA System, operating over a Multipath fading channel and sharing a fraction of its bandwidth with a narrowband data-like interferer. The proposed receiver achieves narrowband interference rejection by projecting the received waveform onto the orthogonal complement of the subspace spanned by the interference: this operation is shown to entail in general a time-varying processing of the observables. In order to improve system performance, it is here exploited the possibility of considering an observation interval larger than the bit signaling time Tt,, as well as that of sampling the received waveform faster than the chip-rate. As to the performance assessment, we focus on the relevant case of Rayleigh distributed fading, and give closed-form formulas for the system Bit Error Rate (BER) and Near-Far Resistance. Results show that the system largely outperforms conventional detectors, in that it achieves a complete nullification of the interference, no matter its energy. Additionally, as expected, increasing the sampling rate and the processing window length yields a performance improvement.