Active interference cancellation-aided QoS-aware distributed ARQ for cognitive radios with heterogeneous traffics
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RESEARCH
Open Access
Active interference cancellation-aided QoS-aware distributed ARQ for cognitive radios with heterogeneous traffics Juan Liu1 , Wei Chen1* , Zhigang Cao1 and Ying Jun (Angela) Zhang2
Abstract Relay-assisted Automatic Repeat reQuest (ARQ), which allows the relays instead of the source to carry out retransmissions of packets erroneously received at the destination, is an efficient cooperative transmission technique to improve link reliability with high spectrum efficiency in wireless networks. In cognitive radio (CR) systems, however, this relay-assisted ARQ could induce large latency, since a successful transmission of a packet may consume two idle timeslot or temporal spectrum holes. To overcome this limitation, an active interference cancellation (IC)-aided distributed relay-assisted ARQ method is proposed in this article to serve heterogeneous elastic traffics with diverse quality of service (QoS) demands in CR systems. Specifically, by applying our recently proposed distributed beamforming-based IC method in the physical layer, cognitive relays can exploit spatial spectrum holes (SSHs) to retransmit while keeping the interference to primary users at a tolerable level. Meanwhile, at the MAC layer, two scheduling policies, namely probabilistic and queue-length-based scheduling, are proposed to obtain an efficient allocation of temporal and SSHs to direct transmissions and retransmissions. The performance of the proposed schemes are analyzed and optimized by adjusting the scheduling parameters. As a result, the secondary users can obtain significant QoS gains, as validated by theoretical and simulation results. Keywords: Cognitive radio, Distributed ARQ, Interference cancellation, Opportunistic scheduling, Markov chain
1 Introduction As an efficient cooperative transmission technique, distributed relay-assisted Automatic Repeat reQuest (ARQ) can improve the link reliability of wireless links in wireless relay networks [1-4]. In contrast to traditional ARQ where the source is responsible of retransmitting packets erroneously received at the destination [5], distributed relay-assisted ARQ allows the relays of the source-todestination (S–D) link to retransmit erroneous packets in a distributed way. Here, the relays are involved only when they receive Negative ACKnowledgement (NACK) packets sent by the destination, indicating it cannot successfully decode the source packet. In this way, high cooperative diversity gain can be achieved at the cost of little spectral efficiency loss. *Correspondence: [email protected] 1 State Key Laboratory on Microwave and Digital Communications, Tsinghua National Laboratory for Information Science and Technology (TNList) and Department of Electronic Engineering, Tsinghua University, Beijing, China Full list of author information is available at the end of the article
Recently, some efforts have been devoted to applying distributed ARQ in cognitive radio (CR) systems [6-8] to improve the reliability of secondary links, and thus the utilization of scarce and valuable spectrum b
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