Cooperative AF Relaying in Spectrum-Sharing Systems: Outage Probability Analysis under Co-Channel Interferences and Relay Selection

Abstract

Abstract-For cooperative amplify-and-forward (AF) relaying in spectrum-sharing wireless systems, secondary users share spectrum resources originally licensed to primary users to communicate with each other and, thus, the transmit power of secondary transmitters is strictly limited by the tolerable interference powers at primary receivers. Furthermore, the received signals at a relay and at a secondary receiver are inevitably interfered by the signals from primary transmitters. These co-channel interferences (CCIs) from concurrent primary transmission can significantly degrade the performance of secondary transmission. This paper studies the effect of CCIs on outage probability of the secondary link in a spectrum-sharing environment. In particular, in order to compensate the performance loss due to CCIs, the transmit powers of a secondary transmitter and its relaying node are respectively optimized with respect to both the tolerable interference powers at the primary receivers and the CCIs from the primary transmitters. Moreover, when multiple relays are available, the technique of opportunistic relay selection is exploited to further improve system performance with low implementation complexity. By analyzing lower and upper bounds on the outage probability of the secondary system, this study reveals that it is the tolerable interference powers at primary receivers that dominate the system performance, rather than the CCIs from primary transmitters. System designers will benefit from this result in planning and designing next-generation broadband spectrum-sharing systems.Index Terms-Amplify-and-forward (AF) relaying, co-channel interference (CCI), interference power constraints, outage probability, relay selection, spectrum sharing.

An Adaptive Transmission Scheme for Amplify-and-Forward Relaying Networks

“…The approximation of the harmonic mean by the minimum leads to a tight approximation at medium-to-high SNR, which has been largely used in the literature to handle similar problems in which exact calculations prove very intricate or infeasible, so that bound or approximate calculations become necessary (see, for instance, [32], [39,Eq. (29)], and [40], and references therein).…”

Direct Link-Aware Optimal Relay Selection and a Low Feedback Variant for Underlay CR

“…Instead, [14] focuses on maximizing the average rate of the secondary network, and proposes a transmit power allocation strategy for the source and AF relays, which are subject to the average interference constraint. However, in both [13], [14], the conventional RS rule that selects the relay with the highest endto-end SINR at D is employed.…”

“…(iii) We study the average interference constraint because it is less restrictive than the conservative peak interference constraint, and is well motivated when the packet transmitted by P Tx spans multiple channel coherence times. It has also been studied in the CR literature [13], [14], [22]. (iv) We assume that each node has one antenna because reducing the hardware complexity and cost of multiple-input multiple-output (MIMO) systems is one of the motivations for cooperative relaying.…”

“…2 The interference caused to P Rx due to transmissions by S can also be accounted for in our model as follows. In the per slot constraint [14], the average interference in slot 1 due to transmissions by S and that in slot 2 due to transmissions by the selected relay β are considered separately. Here,…”

Full-Duplex opportunistic relay selection in future spectrum-sharing networks

“…To tackle such a challenge, relay selection was introduced to underlay networks, and it was shown to offer remarkable performance gains relative to its fixed relaying counterpart [3]. Cognitive relay selection was fairly investigated in the literature under the relaying strategies of amplifyand-forward (AF) and decode-and-forward (DF) [3]- [6].…”