Sattar Hussain

Cognitive Wireless Sensor Networks: Emerging topics and recent challenges

Adding cognition to the existing Wireless Sensor Networks (WSNs), or using numerous tiny sensors, similar to the idea presented in WSNs, in a Cognitive Radio Network (CRN) bring about many benefits. In this paper, we present an overview of Cognitive Wireless Sensor Networks (CWSNs), and discuss the emerging topics and recent challenges in the area. We discuss the main advantages, and suggest possible remedies to overcome the challenges. CWSNs enable current WSNs to overcome the scarcity problem of spectrum which is shared with many other successful systems such as Wi-Fi and Bluetooth. It has been shown that the coexistence of such networks can significantly degrade a WSNs performance. In addition, cognitive technology could provide access not only to new spectrum, but also to spectrum with better propagation characteristics. Moreover, by the adaptive change of system parameters such as modulation type and constellation size, different data rates can be achieved which in turn can directly influence the power consumption and the network lifetime. Furthermore, sensor measurements obtained within the network can provide the needed diversity to cope with spectrum fading at the physical layer.

Spectrum sensing in cognitive radio networks: Up-to-date techniques and future challenges

Spectrum sensing is essential to secondary cognitive radio users to operate without interference to primary users. Secondary users can perform the spectrum sensing either individually or cooperatively by exchanging local observations among them. This paper presents individual spectrum sensing challenges such as hidden terminal problem, shadowing, fading, and hardware limitations. The study also discusses the benefits gained by cooperative spectrum sensing. A detailed review of up-to-date cooperative spectrum sensing techniques is given in this work along with the various sensing schemes that implement these techniques. Out review shows that cooperative spectrum sensing can improve the cognitive radio network performance by increasing spectrum efficiency and providing a better detection accuracy. However, the benefits come at the cost of increased overhead traffic, power consumption, complexity, and the need for control channels. We believe that challenges of the cooperative sensing will be the subject of many future studies yet to be done.

LASA: Low-energy adaptive slot allocation scheduling algorithm for wireless sensor networks

The wide range of wireless sensor network (WSN) applications makes it necessary to design MAC protocols that not only save energy and extend network life, but also improve network throughput, bandwidth utilization, and latency performance. In this paper we propose LASA (Low-energy Adaptive Slot Allocation) to replace the fix slot size in classical Time Division Multiple Access (TDMA) schemes by a variable slot size that dynamically adapts to the data size generated at sensor nodes. The proposed scheme eliminates slot idle time when nodes remain unnecessarily active with no data to transmit or receive. This approach outperforms the static slot size TDMA scheme, especially when there is a high traffic fluctuation and a big variance in the sensor data length. Our results show that this scheme significantly enhances network throughput, reduces bandwidth utilization, saves energy and extends network lifetime.

EPON: An extensive review for up-to-date dynamic bandwidth allocation schemes

Ethernet passive optical network (EPON) has been widely studied in literatures in the past few years. Researchers from all around the world are investigating EPON main challenges and dynamic bandwidth allocation (DBA) problems. This paper, reviews the most recent studies conducted in EPON networks and presents the new proposed DBA schemes. The reviewed schemes are classified according to the main challenge addressed by the investigator. A brief outline is given for each one along with a discussion of its performance and possible contribution to enhance EPON efficiency. Generally, the main purpose of this article is to review EPON problems and presents the up-to-date suggested solutions. Also to indicate that further studies need to be carried out if a single scheme that incorporates excellent bandwidth utilization with effective QoS support and guaranteed fairness is required.

Closed-Form Analysis of Relay-Based Cognitive Radio Networks Over Nakagami-

We propose a general framework for a comprehensive performance analysis of cooperative spectrum sensing (CSS) in cognitive radio (CR) networks. Specifically, we investigate the detection accuracy of a relay-based CR network over independent nonidentical Nakagami- m fading channels. Based on the probability density function (pdf) approach, we derive new exact and approximated closed-form expressions for the average detection probability and the average false alarm probability employing two diversity combining techniques, namely, the maximal ratio combining (MRC) scheme and the selection combining (SC) scheme. We also investigate the convergence rate of infinite series that appears in the derived exact closed-form expressions and propose to use a powerful acceleration algorithm that allows for the series termination with a finite number of terms. The results obtained reveal the importance of including the relaying link statistics and the combination techniques in the performance analysis of CR networks. The derived closed-form expression can be used to determine the energy threshold and the relaying power constraint that meet a given detection accuracy value over nonidentically distributed Nakagami- m fading.

m

In this study, the authors address the problem of bandwidth limitations of the reporting channels in cognitive radio (CR) networks. They propose a cluster-based spectrum-sensing approach that minimizes the bandwidth requirements by reducing the number of terminals reporting to the fusion centre to a minimal reporting set. The approach replaces the secondary base station by a local fusion centre and combats the destructive channel conditions by replacing the global reporting channels with local channels. They also propose a new approach to select the location of the local fusion centre using the general centre scheme in graph theory. The minimal dominating set (MDS) clustering algorithm is used to obtain the minimal set of clusters that keep the network connected. This study investigates how the sensing efficiency, the sensing accuracy, and the per-node throughput are affected by the cluster size, the number of clusters, and the reporting channels error. The results obtained reveal that the cluster-based cooperative sensing system outperforms the conventuional cooperative sensing system in terms of throughout capacity especially when the reporting channels are subjected to a high probability of error. A systematic way to find the optimal number of cooperative clusters that gives a minimum probability of false alarm is presented.

Fading Channels

This paper provides performance analysis of relay-based cognitive radio (CR) networks and presents a detect-amplify-and-forward (DAF) relaying strategy for cooperative spectrum sensing over non-identical Nakagami-m fading channels. An advanced statistical approach is introduced to derive new exact closed-form expressions for average false alarm probability and average detection probability. We also introduce a novel approximation to alleviate the computational complexity of the proposed models. This paper points out the inconsistency of several assumptions that are typically used for performance analysis of CR networks and reveals that channel fading on the relaying links yields similar performance degradations as on the sensing channel. The study also shows that it is not necessary to incorporate all CRs in the cooperative process and that a small number of reliable radios are enough to achieve practical detection level. Compared with the amplify-and-forward strategy, refraining the heavily faded relays in the DAF strategy improves the detection accuracy and reduces the bandwidth requirement of the relaying links. The presented analysis could lead to intuitive system design guidelines for CR networks impaired with non-identical faded channels.

Approach for cluster-based spectrum sensing over band-limited reporting channels

The quality of the reporting channel and the relaying mechanism play a significant role in cooperative spectrum sensing (CSS). However, these factors are frequently overlooked when it comes to discussing the performance of CSS in cognitive radio (CR) networks. In this work we investigate the performance of a relay-based CSS approach proposed for CR applications. Specifically, we analyze the detection accuracy of a CR network considering channel impairments, amplify-and-forward relying protocol, and a selection combining scheme. First, a closed form expression for the average false alarm probability is derived. Then, the probability density function (PDF) of the end-to-end signal-to-noise ratio (SNR) is obtained and a closed-form expression for the average detection probability at high SNR applications is derived. The sensing and the reporting channels are assumed to be subjected to independent and identically distributed Rayleigh fading. The PDF approach is used in our analysis. This approach is not easily tractable as it involves higher orders of Bessel functions. However, an approximated polynomial representation of a first-order modified Bessel function of the second kind makes this task possible. The results obtained validate the derived closed form expressions and show the importance of considering reporting channel statistics and relaying mechanism for accurate performance analysis of the CSS in CR networks.

Performance Analysis of Relay-Based Cooperative Spectrum Sensing in Cognitive Radio Networks Over Non-Identical Nakagami-

This paper addresses effect of reporting channel bandwidth on cognitive radio (CR) networks. A cluster based approach is considered where the secondary base station is replaced by a fusion center and a global reporting channel is used instead of local ones. A new approach to select the fusion center based on the general centre scheme in graph theory is proposed. The minimal dominating set (MDS) clustering approach is used to minimise the set of clusters that keeps the network connected. The effect of various parameters such as cluster size and number, quality of the reporting channel and sensing time on sensing efficiency, accuracy and per node throughput are investigated. Results show cluster based cooperative sensing throughput outperforms conventional cooperative sensing especially when the reporting channel has high probability of error. Systematic ways to determine optimum number of clusters and optimum sensing time are developed.

m

There have been several burgeoning research efforts found in the literature on the resource allocation schemes for CRNs. On the other hand, due to the benefit of D2D communication, International Mobile Telecommunications (IMT)—Advanced Standard systems, such as Long Term Evolution (LTE) and WiMax, allow D2D communication sharing the same radio resources with the cellular network to increase the spectral efficiency.