تجزیه و تحلیل عملکرد پروتکل دسترسی فرصت طلبانه به رسانه مبتنی بر CSMA در شبکه های حسگر رادیو های شناختی

Given the highly variable physical layer characteristics in cognitive radio sensor networks (CRSN), it is indispensable to provide the performance analysis for cognitive radio users for smooth operations of the higher layer protocols. Taking into account the dynamic spectrum access, this paper formulates the two fundamental performance metrics in CRSN; bandwidth and delay. The performance is analyzed for a CSMA-based medium access control protocol that uses a common control channel for secondary users (SUs) to negotiate the wideband data traffic channel. The two performance metrics are derived based on the fact that SUs can exploit the cognitive radio to simultaneously access distinct traffic channels in the common interference region. This feature has not been exploited in previous studies in estimating the achievable throughput and delay in cognitive radio networks. Performance analysis reveals that dedicating a common control channel for SUs enhances their aggregated bandwidth approximately five times through the possibility of concurrent transmissions on different traffic channels and reduces the packet delay significantly.

In the recent past, cognitive radio network (CRN) has gained overwhelming recognition in a great deal of wireless networks, which are not limited to the envisioned infrastructure based networks but also infrastructureless ad hoc networks. This is mainly realized due to the challenges faced by the pervasive wireless networks, which are primarily the spectrum scarcity and hostile propagation environment. Wireless sensor networks (WSNs), which are supposed to operate in the saturated free ISM bands and deployed in usually harsh environment, are the potential candidates to benefit from the dynamic spectrum access technique devised in CRN, thus effectively presenting WSNs as cognitive radio sensor networks (CRSN) [2]. Cognitive radio exploits the temporally unused spectrum defined as the spectrum hole or white space of the licensed users, known as primary users (PU) [1]. If the cognitive radio, or secondary user (SU), encounters the primary user at the licensed spectrum band, it performs spectrum handoff or stays in the same band without interfering with the licensed user by adapting its communication parameters such as transmission power or modulation scheme. As for the unlicensed spectrum bands in which the PUs cannot exist and all users have the same priority to access the spectrum, dynamic spectrum access allows the user to utilize the spectrum more efficiently. Hence, the cognitive radio technology enables the users to opportunistically access the available licensed or unlicensed spectrum bands. Due to the lack of dedicated spectrum bands in CRSN, the opportunity of accessing the spectrum is always sensed dynamically that prohibits the SUs to stipulate performance guarantees. Thus, due to the continuously changing physical layer characteristics, estimating the performance of the cognitive radio user is of paramount importance since the performance of the overlying protocols depends on some close estimate of the realized bandwidth and delay. For example, if the flow admission control at the transport or routing layer allows the large number of flows based on spontaneous increase in bandwidth that diminishes soon, QoS might be deteriorated awfully. Hence, it is indispensable to provide throughput and delay estimation of SUs that persists over the long period of time to maintain the performance of communication protocols, eventually mitigating the shortcoming of dynamic spectrum access. Performance analysis has been conducted in terms of the delay estimation [13], [14], [15], [16] and [17] and also the throughput [4], [8] and [9]. However, it has not been fairly investigated so far with little attention on the potential capacity of cognitive radio operated through common control channel. Generally, the existing studies [6] and [7] investigate the bandwidth by means of spectrum sensing efficiency, which does not reflect the bandwidth practically achievable by the SUs. Similarly throughput is analyzed for a single channel access in the common interference region where the potential of cognitive radio can be exploited to utilize multiple channels. Hence, this is the first study that investigates the performance of dynamic spectrum access for CRSN in terms of both metrics bandwidth and delay by incorporating multiple channels access. In this paper, we conduct performance analysis of secondary users in terms of the two fundamental metrics bandwidth and delay under the given PU traffic model and investigate its relationship with different factors, such as, PU idle time, PU access time, number of PUs and also the number of traffic channels that cause variations dynamically. We employ a CSMA based MAC protocol that uses a dedicated control channel to negotiate the use of a traffic channel between a pair of SU sender and receiver. The two performance metrics are derived based on the fact that SUs can exploit the cognitive radio to simultaneously access distinct traffic channels in the common interference region. The delay estimation is based on the priority queuing model M/G/C in which PUs belong to a high priority queue while SUs are grouped into a low priority queue. The queues are served through C servers or channels such that the low priority queue is served only if the number of PUs in the queue are lesser than the number of channels. It is shown that, though, the bandwidth of a SU is limited due to the PU traffic, the aggregated throughput can be enhanced significantly up to five times by enabling concurrent transmissions of SUs through distributed coordination incorporated with the CSMA scheme and the delay is also minimized significantly. The remainder of the paper is organized as follows. The existing work on performance analysis of cognitive radio network is reviewed in Section 2. In Section 3, we describe the PU and SU network model. Section 4 provides an overview of the CSMA based MAC protocol along with the bandwidth formulation for SUs. Numerical results are provided in Section 5 and finally the paper is summarized in Section 6.

This paper investigates the potential of cognitive radio by realizing simultaneous use of distinct available channels in CRSN due to their high density. Such an effort does not exist for the cognitive radio network in the literature. Therefore, the study lays down a fundamental work on two performance metrics and opens up new dimensions to investigate other QoS metrics or application specific requirements. Moreover, the performance analysis can also be exploited in many other studies such that it helps readers to investigate the performance of other MAC protocols from the CSMA class. We formulate the performance metrics bandwidth and delay for SUs under the given PU traffic model and investigate its relationship with different parameters changing dynamically. A CSMA based MAC protocol is employed with the support of a dedicated control channel to negotiate the use of a traffic channel between a SU’s sender and receiver. It is shown that the aggregated bandwidth can be enhanced significantly up to five times by enabling concurrent transmissions through distributed channel coordination incorporated with the CSMA. Moreover, the packet delay of SUs is significantly lower under higher PU activity that can be controlled by varying different network parameters such as frame period, number of SUs and PUs activity.