Abstract
The cognitive radio (CR) paradigm has the potential of improving the exploitation of the electromagnetic spectrum by detecting instantaneously unoccupied spectrum slots allocated to primary users (PUs). In order to support the process of spectrum reuse, we consider a CR scheme, which senses and opportunistically accesses a PU’s spectrum for communication between a pair of nodes relying on the stop-and-wait hybrid automatic repeat request (SW-HARQ) protocol. This arrangement is represented by the cognitive SW-HARQ (CSW-HARQ), where the availability/unavailability of the PU’s channel is modeled as a two-state Markov chain having OFF and ON states, respectively. Once the cognitive user (CU) finds that the PU’s channel is available (i.e., in the OFF state), the CU transmits data over the PU channel’s spectrum, while relying on the principles of SW-HARQ. We investigate both the throughput and the delay of CSW-HARQ, with a special emphasis on the impact of the various system parameters involved in the scenarios of both perfect and imperfect spectrum sensing. Furthermore, we analyze both the throughput as well as the average packet delay and end-to-end packet delay of the CSW-HARQ system. We propose a pair of analytical approaches: 1) the probability-based and 2) the discrete time Markov chain-based. Closed-form expressions are derived for both the throughput and the delay under the perfect and imperfect sensing environments that are validated by simulation. We demonstrate that the activity of PUs, the transmission reliability of the CU, and the sensing environment have a significant impact on both the throughput and the delay of the CR system.
Highlights
The 21st century has witnessed an exponential growth in wireless applications, which has significantly increased the electromagnetic spectrum demand and led to spectrum scarcity in the most desirable low-attention frequency bands [1]
PERFORMANCE RESULTS we demonstrate the performance of the CSW-HARQ system in terms of three performance metrics, namely, 1) throughput 2) average packet delay and 3) endto-end packet delay, when both idealized perfect sensing and practical imperfect sensing environments are considered
In this paper, we have investigated the performance of the CSW-HARQ transmission scheme both in the perfect and imperfect sensing scenarios
Summary
The 21st century has witnessed an exponential growth in wireless applications, which has significantly increased the electromagnetic spectrum demand and led to spectrum scarcity in the most desirable low-attention frequency bands [1]. In [22] a simulation based study was provided for characterizing the performance of CGBN-HARQ in both perfect and in imperfect sensing environments In this contribution, we extend the work presented in [21] to the imperfect sensing environment and derived closed-form analytical expressions. (a) The proposed CSW-HARQ scheme intrinsically amalgamates the CR capability with the conventional SW-HARQ protocol in order to achieve reliable data transmission in realistic imperfect sensing. (b) Firstly, the CSW-HARQ scheme is modelled and theoretically analysed using a probability-based approach considering both perfect and imperfect reusing Using this approach, closed-form expressions are derived for the a) average packet delay, b) for the throughput of the CU system and c) for the end-to-end packet delay. The basic principles of the proposed CSW-HARQ transmission scheme are discussed, followed by the operation of the CU transmitter and receiver in Sections III-A and III-B, respectively.
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