Abstract
To mitigate spectrum scarcity, the cognitive radio (CR) paradigm has been invoked for improving the overall exploitation of the licensed spectrum by identifying and filling the free spectrum holes without degrading the transmission of primary users (PUs). Hence, we conceive a CR communication scheme, which enables a cognitive user (CU) to sense the activity of the PUs over a primary radio (PR) channel, which is exploited to transmit data using the modified Go-Back-N hybrid automatic repeat request (GBN-HARQ) protocol, when PR channel is free from the PUs. This arrangement is termed as the cognitive GBN-HARQ (CGBN-HARQ), whereby the activity of the PUs on the PR channel is modeled as a two-state Markov chain having “ ON” and “ OFF” states. However, the CU may wrongly detect the “ ON”/“ OFF” activity of the PUs in the channel, hence resulting in false-alarm or misdetection. Therefore, the two-state Markov chain is extended to four states by explicitly considering all the wrong sensing decisions. In this paper, we analytically modeled the CGBN-HARQ scheme with the aid of a discrete time markov chain (DTMC). Explicitly, an algorithm is developed for deriving all the legitimate states and for eliminating the illegitimate states, which assists us in reducing both the dimensionality of the state transition matrix and the associated computational complexity. Furthermore, based on DTMC modeling, we derive closed-form expressions for evaluating the throughput, the average packet delay, and the end-to-end packet delay of CGBN-HARQ in realistic imperfect sensing environment. The results are also validated by our simulations. Our performance results demonstrate that both the achievable throughput and the delay are significantly affected by the activity of the PUs as well as by the reliability of the PR channel and by the number of packets transmitted per time-slot (TS). To attain the maximum throughput and/or the minimum transmission delay, the number of packets transmitted within the TS should be carefully adapted based on the activity level of the PUs and on the quality of the PR channel.
Highlights
Since the germination of the cognitive radio concept [1], it has been considered to be one of the favourable regimes for mitigating the spectrum shortage that resulted from the inefficient spectrum utilization
We investigated a CGBN-HARQ transmission scheme conceived for cognitive radio (CR) systems, when both reliable and unreliable sensing are considered
The CGBN-HARQ system was modelled using Discrete Time Markov Chain (DTMC)-based approach, based on which closed-form expressions have been derived both for the throughput and for the delay
Summary
Since the germination of the cognitive radio concept [1], it has been considered to be one of the favourable regimes for mitigating the spectrum shortage that resulted from the inefficient spectrum utilization. The studies in [2]–[5] show that the inefficient utilization stems from the classic static spectrum allocation policy. Based on this policy, a certain bandwidth is exclusively allocated to a network, which is only available for the primary users (PUs). The CUs have to evacuate the spectrum as soon as the PUs are reclaiming it These capabilities of CR have encouraged the regulatory bodies to officially allow the deployment of CR systems in order to maximize the overall spectrum exploitation without having to make any changes to the existing PR systems operated under the classic fixed spectrum allocation approach [2], [10], [11]. Various IEEE standards have incorporated the CR concept, including IEEE 1900, 802.11y, 802.16h, 802.22, etc., as shown in [12] and the references in it
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