We consider a two-hop infrastructure-based relay link with three transmit power allocation methods. Both amplify-andforward and decode-and-forward protocols are studied. Fundamentally, a relay can operate either in a full-duplex or in a half-duplex mode. The performance in full-duplex relaying is degraded due to loop interference from the relay output to the relay input. On the other hand, the half-duplex mode eliminates the loop interference, but this reduces the end-to-end rate. In this paper, we study the feasibility of the full-duplex mode in terms of end-to-end capacity. In particular, we evaluate break-even loop interference levels, below which the fullduplex mode outperforms the half-duplex mode. The analysis shows that the full-duplex mode is feasible in the presence of reasonably high loop interference power and can offer higher capacity than the half-duplex mode.

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This work presents limited feedback schemes for closed-loop multiple-input multiple-output systems using frequency division duplex. The proposed methods employ compact feedback messages in order to (a) feed back and track a complete frequencyflat channel matrix, to be used as input to multiuser multiplexing methods designed for full channel side information (CSI) at the transmitter, and (b) enable the receiver to command the transmit weight adaptation, in order to maximize the link reliability under strong intercell interference. Simulations show that the channel feedback accuracy provided by the proposed algorithms produces a negligible bit error probability (BEP) performance loss in low mobility scenarios compared to the full CSI performance, and that the proposed interference rejection techniques can effectively exploit an estimate of the interference statistics in order to enable multiple-stream communications under the permanent presence of intercell interference signals.

This paper proposes a novel multiuser (MU) multiplexing scheme for temporally correlated multiple-input, multiple-output (MIMO) channels, suitable for systems employing low-rate feedback links. A decentralized solution is obtained by the mobile receivers, which employ interference rejection combiner (IRC) linear filters and command the update of the corresponding per-user antenna transmit weights through compact feedback messages, thus avoiding explicit transmission of channel information. The proposed limited-feedback algorithm outperforms existing MU-MIMO solutions employing quantized matrices, operating at the same feedback overhead. A compensation mechanism is presented, which enables the proposed solution to operate under moderate probabilities of feedback errors, at the expense of a small downlink overhead.

This paper proposes a closed-loop beamforming algorithm for MIMO systems employing quasi-orthogonal space-time block codes (QOSTCB) and low rate feedback channels over slowly fading channels. A recursion is formulated using a stochastic signed gradient approximation, where the receiver employs a single feedback bit to command the transmit antenna weights adaptation, at a frequency much lower than that of the data rate. The algorithm tracks the weight vector that optimizes a link performance measure, which takes into account both the self-interference properties of the space-time code and the channel conditions. Simulations show that the proposed algorithm can effectively exploit the channel temporal correlation, and outperform existing single-bit feedback schemes in low mobility scenarios.