Abstract-We evaluate the Energy Efficiency-Spectral Efficiency (EE-SE) trade-off of Multiple-Input Multiple-Output (MIMO) and Transmit Antenna Selection/Maximum Ratio Combining (TAS/MRC) schemes. A realistic power consumption model (PCM) is considered, and it is shown that using TAS/MRC can provide significant energy savings when compared to MIMO in the low to medium spectral efficiency region, regardless the number of antenna elements. If the number of receive antennas is fixed, the energy efficiency gain of using TAS/MRC becomes even greater with the increasing number of transmit antennas. The optimal value of spectral efficiency that minimizes the energy consumption is obtained in closed-form, and confirmed by numerical results. Moreover, it is also shown that considering a non-realistic PCM can lead to mistakes when analyzing the gain obtained by using TAS/MRC instead of MIMO.

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We evaluate the performance of a network‐coded cooperative secondary network in a cognitive radio system under spectrum sharing constraints. The secondary network is composed of multiple sources that cooperate to transmit their own information to a common secondary destination. The outage probability is analysed under a given maximum interference constraint set by the primary network as well as to the maximum transmit power limit of the secondary sources. Moreover, we also obtain a closed‐form equation for the ϵ‐outage capacity, that is, the maximum information rate achieved by the secondary sources given a target outage probability. Also, we resort to the Dinkelbach algorithm in order to find the optimum number of parity packets that maximises the ϵ‐outage capacity. The influence of the number of source nodes and another system parameters in the secondary's performance is also evaluated, and we show through theoretical and numerical results that cooperative communication with network coding can provide significant gains in terms of outage probability and diversity order when compared with non‐cooperative or traditional cooperative. Copyright © 2015 John Wiley & Sons, Ltd.

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