An ADC-Aware Receiver Design for Multi-User MIMO Underlay System With Strong Cyclostationary Legacy Signal

In this paper, we design a receiver (RX) for a multi-user multiple-input multiple-output (MU-MIMO) underlay system in the presence of a strong cyclostationary legacy signal. Each desired signal is chosen to be a single-carrier signal that exhibits cyclostationarity with the same cycle period as the legacy signal. If a conventional RX is used that does not take into account the effect of the analog-to-digital converter (ADC), then the strong interference from the legacy transmitter (TX) may cause quantization noise to dominate the desired signals from the underlay TXs and severely degrade the reception performance. To address this issue together with the cyclostationarity of the signals, we propose an ADC-aware RX that adopts an analog-digital hybrid combiner structure. The analog combiner first suppresses the interference power to a negligible level through the projection onto an approximate null space of the interference correlation matrix. Then, it enhances the total power of desired signals by applying the principal component analysis on the signal correlation matrix. After the output of the analog combiner is sampled and quantized at the ADCs, the digital combiner generates the linear minimum mean-squared error estimates of the symbols transmitted by the underlay TXs. During the symbol estimation, it fully exploits the periodic spectral correlation induced by the cyclostationarity of signals. Simulation results show that our proposed RX effectively maximizes signal-to-interference-plus-noise ratio and, under certain conditions, approaches the performance achievable in the absence of the legacy TX.