Inphase and Quadrature Utilization for Pairing Diversity and Interference Exploitation in Uplink OFDMA

This paper proposes a new pairing cooperative technique to achieve spatial diversity and constructive interference exploitation in uplink orthogonal frequency-division multiple access (OFDMA) systems. The underlying principle is to pair users such that their symbols are combined into a single constellation, according to a predefined rule, so that the same symbol is transmitted by each pair of users so their signals can be coherently summed at the receiver, hence maximizing the received signal power. To achieve such constructive combination of both signal copies, single-dimensional OFDMA is utilized in the inphase and quadrature dimensions. It will be shown that such transmission method not only maximizes the received power but also greatly reduces sensitivity to timing misalignment between the cooperating users. Both time synchronous and asynchronous transmission scenarios will be considered. In the asynchronous case, interference reduction will be applied at the base station to reinstate the pairs´ orthogonality and hence minimize co-channel interference. The performance of this technique is evaluated through simulations and mathematical analysis. It will be shown that the results from both models closely match and that the proposed technique provides significant bit-error-rate reductions, particularly at low signal-to-noise ratio, and throughput improvements relative to existing cooperative transmission techniques.