Abstract
In this paper, a comprehensive comparison analysis in terms of outage probability and average symbol error ratio (SER) is presented for cooperative cognitive multiple-input and multiple-output (CC-MIMO) multiuser systems with amplify-and-forward (AF) protocol. Specially, we consider two scenarios where the CC-MIMO multiuser systems have the perfect and imperfect channel state information (CSI). The CC-MIMO multiuser systems consist of one multi-antenna source, one single-antenna relay, and multiple multi-antenna destinations. At the secondary source and destinations, the maximal ratio transmission (MRT) and maximal ratio combining (MRC) are employed, respectively. For such CC-MIMO multiuser systems, we first obtain the exact closed-form expressions of outage probability under the two cases where the CC-MIMO multiuser systems have the perfect and imperfect CSI. Then, to reduce the implementation complexity, the tight lower bounds of outage probability and average SER are derived. Finally, to obtain insight, by using the high signal-to-noise ratio (SNR) approximation, the asymptotic estimations of outage probability are achieved. The numerical results show that the derivations are agreed with the simulations, which validate our derivations. At the same time, the results show that, for the systems without perfect CSI, the achievable diversity order reduces to one, regardless of the number of antennas at the cognitive source and destinations as well as the number of the cognitive destinations. Nevertheless, these key parameters affect the coding gain of the CC-MIMO multiuser systems. When the systems have the perfect CSI (or without feedback delay), the achievable diversity gain is determined by the minimum between the number of source’s antennas and the product of the number of destinations and the number of destination’s antennas. For the effect of PU’s parameters, our results indicate that primary systems only affect the coding gain but not the diversity gain.
Highlights
In recent years, due to the dramatic growth of wireless applications, the spectrum scarcity is becoming a major issue in future cellular mobile communications, which has drawn a lot of attention in academia and industry [1]
From Theorem 2, we can obtain the tight lower bound of outage probability for the cooperative cognitive multiple-input and multiple-output (CC-multiple-input and multiple-output (MIMO)) systems with perfect channel state information (CSI), which is given by Corollary 2
By using the similar approach and the result in (38), we can obtain the average symbol error ratio (SER) of the CC-MIMO multiuser systems with perfect CSI for all links, which is given by Corollary 3
Summary
Due to the dramatic growth of wireless applications, the spectrum scarcity is becoming a major issue in future cellular mobile communications, which has drawn a lot of attention in academia and industry [1]. For multiuser uplink cognitive relaying schemes, in [8], authors have presented an optimal solution for secondary multiuser scheduling by selecting the optimal secondary source which maximizes the received SNR at the secondary destination. For such multiuser cognitive relaying scheme, though the works [8,9,10,11] are of significance, the key limitation of these works is that all terminals are equipped with single antenna. The impact of different antenna configurations, feedback delay, and SNR imbalance on the performance is illustrated
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