A novel approach to managing a fully distributed cognitive radio network (CRN) is presented. This approach builds on the concept of history‐based spectrum access, in which cognitive base stations (BSs) independently estimate the system load using history records and adaptively swap their occupied spectrum bands to ensure allocation fairness and high overall throughput. In addition, cognitive BSs monitor primary user (PU) behavior in order to avoid interfering with active PUs. In this work, we address two issues that afflict history‐based access: the first is the high cost of the sensing devices needed at each cognitive BS to be able to independently draw conclusions about the status of the CRN and the second is the unreliability inherent in practical sensing hardware (such as energy detectors). Simulation results show that the proposed technique manages to solve the two abovementioned issues without any noticeable drop in performance and without sacrificing the distributed nature of the protocol.

Reversible data hiding (RDH) algorithms are concerned with the recovery of the original cover image upon the extraction of the secret data. In some RDH algorithms, embedding and extraction are performed through modifying the histogram of prediction errors that are computed using certain predictors. However, the embedding capacity and image quality in these algorithms are dependent on the characteristics of a single predictor. In this paper, we propose the idea of employing multiple predictors in order to increase the embedding capacity. The idea of multiple predictors is integrated in the modification of prediction errors algorithm without adding any overhead regarding the predictor that is used for embedding at each pixel in the image. The selection of the accurate predictor depends on the polarity of the prediction errors from all predictors. Experimental results proved the efficiency of the proposed algorithm in terms of increasing the embedding capacity and producing competitive quantitative and qualitative quality of the stego image when compared with recent algorithms.

One of the crucial and inherent issues in a practical iris recognition system is the occlusion that happens due to eyelids and eyelashes. This occlusion increases the complexity and degrades the performance of matching and feature extraction processes. Generally, two types of approaches have been proposed to solve this issue. The first approach requires generating an iris mask that indicates which part of the iris is useful and which others are occluded. However, in the second approach, a fixed region of interest (ROI) within the iris area is selected to avoid the regions of occlusion. In this paper, we experimentally study both approaches but due to the latter characteristic, which is its ability to simplify the matching and feature extraction processes, it has been adopted in our techniques used, specifically for iris segmentation, iris normalization, and feature extraction. Accordingly, for matching and feature extraction, the lower side of the pupillary region (i.e. the innermost 25% of the lower half of the iris ring) is found to be the best ROI. This small area of iris is almost free of eyelids and eyelashes and it contains abundant texture information. Interestingly, this selection of small area helps us in proposing a simple yet efficient technique for feature extraction, called mean-based feature extraction technique (MB-FET). This technique is based on analyzing the local intensity variations. The proposed technique achieves a lower processing burden than other traditional methods such as Fourier or wavelet decompositions (e.g. Gabor wavelet). In most traditional techniques, many parameters (e.g. five parameters for 2D-Gabor filter) must be optimally determined in advance to achieve an accurate feature extraction process. Unfortunately, these parameters may not match various variations in image capturing conditions (e.g. variations in illumination due to change in image capturing distance). Moreover, the basic functions of the traditional methods are fixed in advance (off-line) and do not necessarily match the texture of all irises in the database. However, for our proposed technique MB-FET, there is no need to determine in advance any parameter or basic function. MB-FET dynamically adapts its parameter (only one parameter) with intensity variations. The proposed technique generates a binary iris code, hence a simple and fast matching process is done using the Hamming distance. The experimental results using the CASIA iris database show that the proposed technique achieves promising results for a robust and reliable iris recognition.

IEEE 802.22 wireless regional area network (WRAN) is a cognitive radio-based network. WRANs are intended to be deployed by different service providers and designed to opportunistically utilize the unused TV bands. WRANs have to self-coexist with other overlapped WRANs in a distributed manner. Therefore, every service provider tries to acquire a band free of interference from others to satisfy a required quality of service. This self-coexistence problem is one of the major challenges in WRAN. In this paper, we propose a Markov-based distributed approach for mitigating this problem. We model the problem as an absorbing discrete-time Markov chain. In this model, if two or more overlapped WRANs select the same band, then each one should either stay or switch to another band according to a certain switching probability. This process continues until each one of the WRANs finds an interference-free band. In this case, the Markov chain reaches the absorbing state. This model is employed to find the optimal switching probability, which in turn minimizes the time required to reach the absorbing state. The switching probability is numerically found as a function of the number of overlapped WRANs and available bands. Extensive simulation has been conducted to validate our numerical results.

Opportunistic routing has recently been proposed for ad hoc networks. Several works showed that opportunistic routing improves network performance. None of these works, however, studied the integration of opportunistic routing into multi-rate ad hoc networks. In this paper, we study this integration. Specifically, we consider the problem of determining the required number of retransmissions in opportunistic routing and the transmission rate in each retransmission such that the required (re)transmission time for a sent packet is minimized while at the same time a target end-to-end PER is satisfied. We show that this problem is NP-hard. Accordingly, we propose an approximate solution called Opportunistic routing Over Multi-rate Multi-hop ad hoc networks (OOMM). Extensive simulations over a multi-rate OFDM-based UWB network show that OOMM achieves high performance relative to different routing techniques (21%-48% throughput improvement).

The convolutional coding is a very popular channel coding technique for the major reason of mitigating the probability of having many retransmissions because of difficult (noisy) communication channels. Sequential decoding is a type of convolutional codes that becomes of interest in wireless communication since it affords a decoding time that can be adaptive to channel state. In this study, the authors propose an improved queuing model, using discrete-time semi-Markov chain, which represents a modified packet retransmission policy over previously proposed queuing model. The authors queuing model mainly describes the behaviour of the buffer, which belongs to intermediate hops, when sequential decoding is implemented and concerns also about packets being transmitted over erroneous channels. The authors aim after conducting queuing analysis to find a real mathematical form for the average buffer occupancy as a network performance metric. Although the improved queuing model when incorporating the new policy for retransmission is very complicated, we are finally able to derive an expression for that performance metric considering practical assumptions. They further illustrate how the modified queuing model has a better impact on the end-to-end delay of messages, being transmitted without any extra buffering requirements needed, than the other relevant proposed queuing model. They conduct a simulation study using computer programming with the same assumptions used for queuing analysis to validate their analytical explanations and results. Furthermore, they validate the correctness of their closed-form expression through comparing its results with those obtained from expression related to a queuing model which discarded employing any retransmission policy.

Ultra-wideband (UWB) communications has emerged as a burgeoning technology for high data rate wireless personal area networks (WPANs). In this paper, we propose a novel resource utilization mechanism (RUM) for improving the throughput in multi-rate UWB-based WPANs. RUM is intended to remedy a critical issue in both unicast and multicast transmissions. In unicast (single- and multi-hop), the connectivity of a source-destination pair is defined by the ability to overhead control messages (e.g., route requests, request-to-send/clear-to-send, etc.). These messages are usually sent at a low transmission rate to extend their reachability, hence a node can directly communicate with faraway destinations. Such destinations cannot be reliably reached by high transmission rates. This leads to a long channel reservation time and hence a high blocking probability for prospective reservations and low network throughput. In the case of multicast, the maximum transmission rate is bottlenecked by the farthest destination. RUM exploits opportunistic-relaying and time-spreading techniques to improve link reliability and increase the transmission rate, and hence network throughput. Simulations are used to demonstrate the performance gain of RUM.

Ultra-wideband (UWB) communications has emerged as a promising technology for high data rate wireless personal area networks (WPANs). In this paper, we address a key issue that impacts the performance of multi-hop, multi-rate UWB-based WPANs, namely joint routing and rate selection. Arbitrary selection of routes (including direct links) and transmission rates along these routes results in unnecessarily long channel reservation time and high blocking rate for prospective reservations, and leads to low network throughput. To remedy this situation, we propose a novel overhearing-aware joint routing and rate selection (ORRS) scheme, which improves the network throughput by exploiting the dependence between the channel reservation time and the multi-rate capability of an UWB system. At the same time, ORRS takes advantage of packet overhearing, a typical characteristic of broadcast communications. For a given source-destination pair, ORRS aims at selecting a path and its transmission rates that achieve the minimum reservation time, leading to low blocking rate for prospective reservations and high network throughput. We show that achieving this goal while simultaneously exploiting packet overhearing and satisfying a target packet delivery probability over the selected route leads to an NP-hard problem. Accordingly, ORRS resorts to approximate solutions (proactive and reactive) to find a near-optimal result with reasonable computational/communication overhead. We further propose other variants that exploit packet overhearing in different ways to improve ORRS performance.

Ultrawideband (UWB) communications has emerged as a promising technology for high data rate wireless personal area networks (WPANs). Several proposals for UWB-based WPANs have been made. One widely popular proposal was standardized by ECMA-368, and is based on OFDM. In this paper, we address one of the important aspects that impact the performance of this standard, namely interference management between different uncooperative beacon groups that operate simultaneously over the same area. We first propose an interference management distributed reservation protocol (IM-DRP) for OFDM-based UWB communications. IM-DRP aims at improving the throughput of an UWB WPAN by reducing interference between uncooperative beacon groups. We then integrate IM-DRP into the design of a rate adaptation strategy that exploits the multirate capability of OFDM-based UWB systems. Besides maintaining a target packet error rate, our proposed strategy attempts to reduce the required reservation time over a link, hence allowing more links to be simultaneously activated. This improves the overall network throughput. Simulations are used to demonstrate the performance gain of our proposed schemes.

IEEE 802.22 wireless regional area network (WRAN) is an emerging cognitive radio-based system. One of the major challenges for WRANs is how to efficiently schedule both channel sensing and data transmission for multiple adjacent WRAN cells. This challenge is known as coexistence problem. In this paper, we propose four schemes that aim at reducing the coexistence-problem effect. These schemes are based on a well-known operation mode of IEEE 802.22, namely dynamic frequency hopping (DFH). The first and second schemes are based on using omni-directional antennas at the base stations (BSs), whereas the BSs in the other two schemes use directional antennas. The first scheme, coined fixed-scheduling DFH (FDFH), bases upon a fixed scheduling of working channels for adjacent WRAN cells. The second scheme, called cooperative DFH (CDFH), cooperatively selects working channels. The third scheme, namely sectoral DFH (SDFH), is proposed to reduce the coordination overhead of CDFH via dividing a WRAN cell into sectors to decrease the chances of collisions between adjacent cells. Finally, we integrate FDFH and SDFH into a new scheme, called fixed-scheduling sectoral DFH (FSDFH), which exploits the advantages of both schemes with no additional overhead. Computer simulations are used to demonstrate the performance gain of the proposed schemes.

Ultra-wideband (UWB) communications has emerged as a promising technology for high data rate wireless personal area networks (WPANs). Several proposals for UWB- based WPANs have been made. One widely popular proposal was standardized by ECMA-368, and is based on OFDM. In this paper, we address one of the important aspects that impact the performance of this standard, namely interference management between different uncooperative beacon groups operating simultaneously over the same area. We propose an interference management distributed reservation protocol (IM-DRP) for OFDM-based UWB communications. IM-DRP aims at improving the throughput achieved by WPANs by reducing interference between uncooperative beacon groups. Computer simulations are used to demonstrate the performance gain of the proposed protocol.