Abstract-In a spectrum sharing underlay context, we investigate the exact derivation of the outage probability for relay-aided cognitive radio communications. To give more degrees of freedom to the secondary system in acquiring a targeted quality-of-service (QoS) under the primary system interference constraint, the secondary link is assisted by a set of relays acting in a two-hop decode-and-forward selective relaying mode. By means of the cumulative distribution functions of the received signal-to-noise ratio (SNR) at the secondary receiver, we derive the end-to-end outage probability of the secondary system in its closed form. The analytical and simulation results are then compared and interestingly shown to perfectly match over the entire interference threshold region.

Abstract-This paper investigates throughput-efficient relay ARQ protocols for single carrier MIMO systems with amplify-and-forward relaying. We focus on reducing the multiplexing loss due to the half-duplex operation at the relay. We introduce two new relaying protocols where both ARQ and relaying are jointly targeted. Compared to the conventional relaying techniques, the proposed mechanisms require only one time slot duration for transmitting the entire data packet at each ARQ round. We also focus on performance evaluation, and show that the new techniques provide significant improvement in average throughput while maintaining good outage probability performance.Index Terms-Amplify-and-Forward, ARQ, MIMO, cooperative relaying, outage probability, average throughput.

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International audienceIn this paper, we carry out an exact outage analysis for a secondary (unlicensed) system operating under a strict primary (licensed) system outage constraint. We focus on single-user singleinput multiple-output (SIMO) secondary communications where the direct link is being assisted by a cluster of single-antenna decodeand-forward (DF) relay nodes acting in a half-duplex selective-andincremental relaying mode. Firstly, we derive a transmit power model for the secondary system where the source and relays adapt their transmit power based on: 1) a perfect acquisition of the underlying interference channel state information (I-CSI), and 2) an interference constraint that is either fixed or proportional to the primary system outage probability. Secondly, the cumulative distribution functions (CDF)s of the received signal-to-noise ratio (SNR) at the secondary receiving nodes are devised in a recursive and tractable closed-form expressions. These statistics are used to derive the exact end-to-end secondary system outage probability. The analytical and simulation results are then compared and interestingly shown to perfectly match, while revealing that with a moderate number of primary and secondary receive antennas, the secondary system spectral efficiency is amply enhanced as opposed to being severely degraded in the single receive antenna case

In a cost-effective implementation, we address the problem of cross-interference in cognitive multiple-input multiple-output (MIMO) spectrum sharing where mutual cochannel interference (CCI) between the primary and secondary systems is of major concern. First, we propose an optimal transmit-antenna selection (TAS) strategy that instead maximizes the received signal-to-interference-plus-noise ratio (SINR) after maximum-ratio combining (MRC). We statistically analyze the combined SINR structure and derive new expressions of its cumulative and probability distribution functions. Interestingly, we accurately show the substantial gains offered by the proposed TAS strategy in terms of the secondary system outage performance compared to the existent state-of-the-art TAS strategies. Finally, our analytical results are validated by simulations and some important insights are also underlined.