Adaptive Interference Tolerant Receivers for Asynchronous Cooperative MIMO Communications

Adaptive single user receivers are demonstrated in this paper for a Cooperative Virtual MIMO network applying Spread Spectrum Sequences. In asynchronous decentralized cooperative systems, it is expected that, for typical wireless environments, user transmissions from adjacent relaying nodes (and other cells) will create interference. Large scale MIMO antenna arrays can mitigate interference with sufficient degrees of freedom but they can be underdetermined in decentralized non orthogonal multiple access (NOMA). In this paper we use Spread Spectrum CDMA sequences when user cooperation and relaying is necessitated and correspondingly apply decentralized single user algorithms utilizing an adaptive multiuser detection approach. The approach does not require Channel State Information (CSI) and operates in a decentralized manner without requiring knowledge of the transmissions from other users (i.e. power, channel gain and phase, and multiuser chips). This yields a low interference cooperative MIMO communication network that is useful for communication in areas with poor coverage or to temporarily increase spectral efficiency to enable a high throughput uplink or downlink channel. The adaptive algorithm utilized in this paper is investigated for both chip-level and symbol-level optimization where it noted that when applying chip-level optimization, a more interference robust receiver can be built when utilizing processing gain (rather than receiver dimensionality) as a metric to combat interference when the number of transmitter antennas used are fixed.