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In this work, we provide a comprehensive analysis of stability properties and delay gains that wireless multicasting capabilities, as opposed to more traditional unicast transmissions, can provide for content distribution in mobile networks. In particular, we propose a model and characterize the average queue-length (and hence average delay) performance of unicasting and various multicasting strategies for serving a dynamic user population at the wireless edge. First, we show that optimized static randomized multicasting (we call it ‘blind multicasting’) leads to stable-everywhere operation irrespective of the network loading factor (given by the ratio of the demand rate to the service rate) and the content popularity distribution. In contrast, traditional unicasting suffers from unstable operation when the loading factor approaches one, although it outperforms blind multicasting at small loading factor levels. This motivates us to study ‘work-conserving multicast’ policies next that always outperform unicasting while still offering stable-everywhere operation. Then, in the worst-case of uniformly-distributed content popularity, we explicitly characterize the scaling of the average queue-length (and hence delay) under a first-come-first-serve multicast strategy as a function of the database size and the loading factor. Consequently, this work provides the fundamental limits, as well as the guidelines, for the design and performance analysis of efficient multicasting strategies for wireless content distribution.

Video content streaming between two vehicles has various applications in vehicular ad-hoc networks (VANETs). Due to the highly dynamic nature of VANETs, video contents are usually transferred via multiple discovered routes to increase the chance of error-free packet delivery. However, vehicular routes suffer from limited lifetimes and low connectivity probabilities, which result in increasing packet loss ratio (PLR) and frequent video playback freezing. In this paper, PLR is minimized by optimally distributing video packets in multiple routes while meeting quality of service (QoS) parameters (meeting freezing delay and number of transferred video packets constraints). By doing so, reconstruction and playback of the video are achieved with guaranteed QoS. Performance evaluation of our proposed scheme shows enhancements in terms of average PLR (63.3%), average freezing delay (6%), average packet end-to-end delay (66.6%) and average number of delivered video packets (8%) after 10 seconds simulation.

Internet of Things (IoT) paradigm with strong impact on future life will be interconnected through Cognitive Radio Networks (CRNs). CRNs with Ubiquitous trait are highly promising to achieve interference-free and on-demand services. CRs are able to sense the spectral environment, to detect unoccupied bands, and to use them for signal transmissions. This opportunity encourages malicious Users to surpass CRs by Primary User Emulation (PUE) attack and use vacant spectrums. This paper proposes an unsupervised algorithm to distinguish CRs from PUs regardless of static and mobile user. Employing K-means and graph theory are coincident in our algorithm to improve detection outcomes. The edge of graph corresponding to the relation between signals is used and the result of comparison the signal properties is exposed to different clusters. The Receiver Operating Characteristic (ROC) and Detection Error Tradeoff (DET) of our proposed algorithm prove our claim.

In this work, we provide a comprehensive analysis of stability properties and delay gains that wireless multicasting capabilities, as opposed to more traditional unicast transmissions, can provide for content distribution in mobile networks. In particular, we propose a model and characterize the average queue-length (and hence average delay) performance of unicasting and various multicasting strategies for serving a dynamic user population at the wireless edge. First, we show that optimized static randomized multicasting (we call it ‘blind multicasting’) leads to stable-everywhere operation irrespective of the network loading factor (given by the ratio of the demand rate to the service rate) and the content popularity distribution. In contrast, traditional unicasting suffers from unstable operation when the loading factor approaches one, although it outperforms blind multicasting at small loading factor levels. This motivates us to study ‘work-conserving multicast’ policies next that always outperform unicasting while still offering stable-everywhere operation. Then, in the worst-case of uniformly-distributed content popularity, we explicitly characterize the scaling of the average queue-length (and hence delay) under a first-come-first-serve multicast strategy as a function of the database size and the loading factor. Consequently, this work provides the fundamental limits, as well as the guidelines, for the design and performance analysis of efficient multicasting strategies for wireless content distribution.

Vehicular ad hoc networks (VANETs) have attracted many researchers' attention in recent years. Due to the highly dynamic nature of these networks, providing guaranteed quality-of-service (QoS) video-on-demand (VOD) sessions is a challenging problem. In this paper, a new adaptive geographic routing scheme is proposed for establishing a simplex VOD transmission in urban environments. In this scheme, rather than one route, a number of independent routes are discovered between source and destination vehicles whose number of routes depends on the volume of the requested video and lifetime (span of time in which a route is almost fixed) for each route. A closed-form equation is derived for estimating the connectivity probability of a route, which is used to select best connected routes. Simulation results show the QoS parameters: packet loss ratio is decreased by 40.79% and freezing delay is significantly improved by 25 ms compared with those of junction-based multipath source routing at the cost of 2-ms degradation in the end-to-end delay.

A cooperative multiple-input multiple-output wireless communication has two phases: data exchange (information sharing) among source nodes, and cooperative transmission to the base station by these nodes. A bandwidth efficient method for implementing such a communication link is orthogonal distributed space---time Block Codes (ODSTBCs). It can provide full diversity with low decoding complexity, when all exchanged data correctly received by the cooperative nodes. However, in this paper, we consider that the data exchange is not error-free, and in this case, we derive a closed-form expression for the upper bound of ODSTBC bit error rate (BER). Moreover, we show that for achieving a desired BER, without sacrificing throughput or increasing complexity, it's sufficient that the number of cooperative nodes is kept in a specific range, which can be obtained by using this BER upper bound. Numerical and simulation results prove the accuracy of the ODSTBC BER upper bound, and the validity of the proposed method for calculating number of cooperative nodes required to achieve a desired BER.

Green communications has been paid much attention recently, to provide energy efficient networks with a high level of quality of service (QoS). In this study, the authors propose a cross-layer scheduling scheme for the downlink of long-term evolution networks, considering the buffer state which may be empty in some times. Their target is to minimise energy consumption under the constraints of limited average transmitting power in the base station, and maximum tolerable delay as QoS of heterogeneous users. In the proposed scheme, the authors use an effective capacity link layer model to consider the data link layer characteristics, such as probability of non-empty buffer and probability of maximum delay, along with the physical layer parameters. Simulation results show more than 48% reduction of energy consumption in peak traffic loads.

In this paper, a two-phase algorithm for the spectrum sensing and power/rate control of a secondary user (S-user) or cognitive radio is proposed. In the first phase, the primary base station (P-BS), which is conscious of both the number and the data rate of primary active users (P-user), broadcasts theitusage capacity percentage (UCP) of its cell. Since knowing only the UCP is not enough to guarantee that the total load (of P-users and S-users) is less than a maximum permissible load, the S-user must measure the total interference received from both the P-users and other S-users. In this direction, using both the UCP and measurement of the interference received from the P-users and the S-users by the S-user or secondary base station (S-BS), we mathematically derive an equation for issuing data transmission permission, which if it is held then the second phase of the algorithm: the transmit power/rate control starts. In this phase, the S-user and the S-BS look for feasible values for the transmit power level and transmission rate. If there are feasible values, it starts its transmission at these feasible transmit power and rate. Since both the location of the S-user and the channel condition vary in time, the whole algorithm is iterated periodically with a period faster than the coherence time of the channel. Furthermore, we consider the down link of the above system with cooperation among neighboring S-users to overcome fading channels and we investigate the amount of improvement in the reliability of the issuing data transmission permission. As well, we consider the uplink of the system with multiple antennas in the S-BS to investigate the improvement in the same parameter over spatially correlated and independent fading channels. Theoretical analysis is validated using computer simulations. Both theoretical analysis and computer simulations show that the proposed cooperative spectrum sensing algorithm performs properly at SNR = −5dB in flat Nakagami-m fading channels with m = 1 even in correlated fading channels. We also address the improvement of the reliability of the issuing data transmission permission in the uplink in case of using multiple antennas only in the S-BS. Copyright © 2011 John Wiley & Sons, Ltd.

Employing cooperative communication in multihop wireless sensor networks provides the network with significant energy efficiency. However, the lifetime of such a network is directly dependant upon the lifetime of each of its individual sections (or clusters). Ignoring the fact that those sections close to sink have to forward more data (their own data plus the data received from the previous sections) and hence die sooner with considering equal section sizes, leads to a sub-optimal lifetime. In this paper, we optimize the section sizes of a multihop cooperative WSN so that it maximizes the network lifetime. Simulation results demonstrate a significant lifetime enhancement for the proposed optimal sectoring.

In this paper, we investigate the joint spectrum sensing and resource allocation problem to maximize throughput capacity of an OFDM-based cognitive radio link with a cognitive relay. By applying a cognitive relay that uses decode and forward (D&F), we achieve more reliable communications, generating less interference (by needing less transmit power) and more diversity gain. In order to account for imperfections in spectrum sensing, the proposed schemes jointly modify energy detector thresholds and allocates transmit powers to all cognitive radio (CR) subcarriers, while simultaneously assigning subcarrier pairs for secondary users (SU) and the cognitive relay. This problem is cast as a constrained optimization problem with constraints on (1) interference introduced by the SU and the cognitive relay to the PUs; (2) miss-detection and false alarm probabilities and (3) subcarrier pairing for transmission on the SU transmitter and the cognitive relay and (4) minimum Quality of Service (QoS) for each CR subcarrier. We propose one optimal and two sub-optimal schemes all of which are compared to other schemes in the literature. Simulation results show that the proposed schemes achieve significantly higher throughput than other schemes in the literature for different relay situations., EAI Endorsed Transactions on Wireless Spectrum 14(1): e4 Published 13th Apr 2014

Recently, cross-layer relay selection methods are proposed in favor of providing QoS requirements of users in multi-user cooperative networks as a way to achieve a better performance. However, most of them have failed to achieve an acceptable level of fairness in satisfying diverse QoS requirements in a multi-media service. On the other hand, reducing consumed power is essential today in cooperative networks. In this paper, we aim to improve fairness and reduce consumed power in a multi-user cooperative network with multi-media service. For this purpose, we propose a novel algorithm based on management of relay nodes' buffer space and the priority concept during relay selection. Simulation results certify that our algorithm outperforms previous ones in terms of system spectrum efficiency, fairness, and average consumed power.

The performance of cooperative communications is highly dependent on careful resource allocation such as relay selection. Considering individual QoS requirements in a multi user system, traditional cross-layer relay selection schemes, failed to achieve an acceptable level of fairness considering limited buffer capacity of relays. To address this problem, in this paper, we propose a buffer management-based best relay selection algorithm considering both physical and MAC layer parameters. Our simulation results show that the proposed algorithm outperforms traditional ones significantly in terms of fairness, system spectrum efficiency, and average transmission time delay. Moreover, the proposed algorithm can be implemented in a distributed fashion with no need to a central processor and with minimum required signaling among the nodes.

In cognitive radio networks, secondary users can be coordinated to perform cooperative spectrum sensing to achieve higher detection accuracy. However, when the number of cooperative users increases, more overhead traffic of decision transmission introduced to network and throughput of cognitive radio network decreases. Furthermore, the performance of cooperative spectrum sensing is limited by the probability of reporting errors. In this paper, first we study optimal number of secondary users in cooperative spectrum sensing to maximize the achievable throughput for the secondary network under the constraint that the primary users are sufficiently protected. We formulate the optimization problem mathematically for cognitive radio networks over Rayleigh fading channels, which affects on decision reporting error. Then, we investigate the effect of fusion rule parameter on the throughput performance and develop the optimization model to increase the maximum achievable throughput. Numerical and simulation results will prove that the final optimization problem yields the highest throughput for the secondary network.

In Wireless Sensor Networks (WSNs), recharging node batteries may be inconvenient or impossible. There are several different approaches to overcome this problem. LEACH (Low-Energy Adaptive Clustering Hierarchy) is a well known algorithm whose best advantage is that each node makes its decision about whether to be a cluster-head independently, but it cannot guarantee an even energy load distribution. To over come this problem, we should consider the remaining energy of each node and the average residual energy of its neighboring nodes. However, this makes the nodes to be dependent on each other. For this reason, in this paper, we propose an energy efficient cluster-head selection algorithm, which is an extension to the LEACH. Our new algorithm is based on the differentiation of each node's energy. In the proposed algorithm, each node cares about its neighboring nodes, without getting any information from them. Simulation results show that our proposed algorithm could better balance the load and prolong the lifetime of the network by about 10% compared with LEACH.

Cognitive radio is a new technology for improving frequency spectrum usage in wireless networks. A pivotal issue in cognitive radio is spectrum sharing, which allows primary (licensed) users to share their licensed radio frequency spectrum with secondary (unlicensed) users. In this paper, we will model the cognitive radio environment as a quality based competition. We consider the spectrum sharing problem between multiple primary users and only one secondary user. The novelty of this paper is that we formulate this problem as an oligopoly market competition and use the Cournot game (quality-based competition) to obtain the optimal spectrum allocation for the secondary user. Nash equilibrium is considered as the solution of this game. We will consider two different cases: static game in which each user can observe the adopted strategies and the payoff of others and dynamic game in which the strategy of each user is selected based on only the information obtained during the game. At the end, the stability condition for the dynamic case of spectrum sharing is investigated. Performance evaluation shows that our model results in more profits for primary users with lower offered prices for the secondary user and larger shared spectrum sizes at the expense of some stability decrease.

In a cognitive radio network (CRN), a primary (licensed) user (PU) can share its frequency spectrum by renting this spectrum to a secondary (unlicensed) user (SU). In this paper, we propose an auction-based CRN model whose novelty is considering multiple PUs along with multiple SUs. These PUs compete with each other so that they can earn more profit while the SUs pay less and earn higher payoffs. This situation is formulated as an oligopoly market. For the SUs, we adopt Hackner utility function to obtain the demands for the frequency spectrum and according to their payoff functions the best scenario in each stage of the dynamic spectrum sharing game is selected in the case in which there is a limit on PUs to supply SUs' demands. Simulation results show that our proposed model satisfies both groups of PUs and SUs.

We study the problem of optimizing the symbol error probability (SEP) performance of cluster-based cooperative wireless sensor networks (WSNs). It is shown in the literature that an efficient relay selection protocol based on simple geographical information of the nodes to execute the cooperative diversity transmission, can significantly improve the SEP performance at the destination of such networks. Also, a similar analysis on the optimal power allocation for the source and the relay exists in the literature. However, we propose that to achieve the minimum SEP at the destination, a joint optimization of power allocation and relay selection should be accomplished. To this aim, we reformulate the SEP performance at the destination of a simple cluster-based cooperative WSN in the general form and solve the mentioned joint optimization problem efficiently for a relay deployment scenario. Simulation results demonstrate that the proposed joint optimization can effectively improve the SEP performance of the network for both 1-hop and multi-hop scenarios in comparison with the previous disjoint optimal relay deployment scheme.

We study the problem of optimizing the symbol error probability (SEP) performance of cluster-based cooperative wireless sensor networks (WSNs). We propose that to achieve the minimum SEP at the destination, a joint optimization of power allocation and relay selection should be accomplished. To this aim, we reformulate the SEP performance of a simple cluster-based cooperative WSN in the general form and solve the joint optimization problem efficiently. Simulation results demonstrate that the proposed joint optimization can efficiently improve the SEP performance of the network in comparison with the previous disjoint optimal relay selection schemes.

In this paper, we develop a single user and a multi user version of a Distributed Underlay Channel Assignment (DUCHA) algorithm for spectrum access to a downlink channel of a primary cell for a cognitive cooperative ad hoc network overlaid with the cell. We use direct sequence spread spectrum as a medium interface for cognitive links. We investigate performance of DUCHA algorithm in three spreading scenarios with regard to the bandwidth of the channel. Simulation results show that when there are 100 cognitive channel applicants and spreading factor is 100 the multi user DUCHA algorithm assigns the channel to an average 51.8 percent of channel applicants and in this case it achieves 22.57 bps/Hz spectral efficiency under high power interference from the primary base station of the cell. We show that in this condition the increased in-band and out of band interference temperatures are non-harmful and have values of respectively 22.48 dB and -0.99 dB.

Energy supply in wireless sensor networks (WSNs) is limited and non-replenishable, and energy efficiency is the most important feature in designing these networks. One way to reduce the energy consumption of WSNs and hence prolong the lifespan of these networks is to use adaptive clustering algorithms. In this paper, we use Ant Colony Optimization for Clustering (ACO-C) to propose a new energy aware clustering protocol for WSNs. By using appropriate cost functions, implemented at the base station, our algorithm minimizes and distributes the cost of long distance transmissions and data aggregating among all sensor nodes evenly. Simulation results show the effectiveness of our protocol over other well known clustering algorithms in terms of both network lifetime and data delivery to the base station.

Cellular networks are expected to change to Multi-hop Cellular Networks (MCNs). While a mobile station and the base station have a direct link in a conventional cellular network, in MCN, mobile stations with unsatisfactory path to the base station, could instead relay their data through other mobile stations with better channel conditions. This can improve coverage and capacity, and reduce the total transmission power, but its efficiency depends on the relaying strategy used. This paper investigates a new efficient relay selection method in multihop cellular networks. In our novel relay selection scheme, a mobile station chooses two relay stations which have the best in distance criterion and sends its data through these relay stations. The capacity improvement due to the proposed schemes is demonstrated through simulation results.

In a multihop cellular network, the physical layer of mobile stations is modified so that in addition to being able to transmit to base stations, mobile stations will also be able to transmit directly to other mobile stations. This will allow mobile stations to lower their maximum transmission power and use other stations as repeaters to forward their packets to the base station. Precise representation of the physical layer is required for analysis and simulation of multihop cellular networks. In this paper, the effects of correlated shadowing in multihop cellular networks will be investigated. In addition, by considering statistical model for the shadowing correlation between link pairs a new relay selection scheme for multihop cellular networks in shadow fading environments is proposed. Taking into account fluctuated SINR during the reception of long packets, especially in multimedia communications, outage probability is introduced as a QoS parameter. Finally, the results show that relay selection based on independent shadowing models underestimate the system performance.

This paper examines and analyzes the impact of correlations that exist in shadow fading between links in multihop cellular networks. Statistical moments of the total interference are derived based on two correlated shadowing models, shadowing model as functions of the spatial loss field and correlated lognormal shadowing. We apply both methods in order to evaluate performance in uplink of multihop CDMA cellular systems. Outage probability is introduced as a QoS parameter. The results show that there is no significant difference between two correlated shadowing models. But, taking into consideration independent shadowing causes an optimistic and unreal performance evaluation which may not useful for deployment of multihop cellular networks in real environments.

In this paper, a two phase algorithm for spectrum sensing and power control of a secondary user (S-user) or cognitive radio is proposed. In the first phase, the primary base station (P-BS), which is conscious of the number of primary active users, broadcasts the percentage of the spectrum usage of the cell by primary users (P-users). If the cell is not fully loaded, the S-user and/or S-BS estimates interference to check if condition for data transmission is hold. If this is so, the second phase of the algorithm, the transmit power control of S-user is started. In this paper, a new method based on fluctuations of estimated covariance matrix of the received signal is proposed for identifying the interference of secondary and P-users. Computer simulations show that the proposed algorithm performs properly in the SNR of -5 dB.

In this paper, we propose an algorithm for dynamic resource allocation in OFDM (orthogonal frequency division multiplexing) or OFDMA (OFD multiple access) based networks. We consider two groups of users consisting of group 1 called constant bit-rate (CBR) users (who are delay-sensitive and data-rate sensitive) and group 2 called best effort (BE) users. The proposed algorithm gives higher priority to the first group at the time of resource (transmitted power levels and subchannels) allocation to each user, to meet their CBR requirements. The performance of the proposed algorithm is evaluated through computer simulations, which show that the algorithm performs near optimum with the added superiority of meeting the bit requirements of the first group users.

A wireless sensor network (WSN) consists of a large number of small sensors with limited energy. Prolonged network lifetime, scalability, and load balancing are important requirements for many WSN applications. Clustering sensor nodes is an effective technique for achieving these goals. In this work, we propose a new energy-efficient approach for clustering nodes in WSNs. Based on this approach, we propose a two phase algorithm; in its first phase, cluster heads are selected according to the Sebestyen algorithm. In the second phase, nodes are allocated to the cluster heads so balanced from number of membership view. Two criteria are considered in this allocation. The first criterion is the Euclidean distance between nodes and cluster heads, and the second one is the node degree. The simulation results demonstrate that our proposed algorithm enhances the WSN lifetime significantly in comparison to the weight-based clustering protocols and original Sebestyen algorithm.

Wireless sensor networking, an emerging new field in technology, now opens a vast horizon of application scenarios including environment monitoring, home security and earthquake warning. Since the sensor nodes have limited available power, energy conservation is a critical issue and developing an energy-efficient routing protocol is one of the major issues in wireless sensor networks. In this paper, the authors propose a novel hierarchical routing protocol called efficient power management protocol with limited cluster size (EPMPLCS) which limits the size of clusters and avoids large energy consumption among cluster-heads and distant members in big clusters thus prolongs the network lifetime. Furthermore, EPMPLCS improves the assumption that the data of different sensors in one cluster are highly correlated. Simulation results show that EPMPLCS performs better than low-energy adaptive clustering hierarchy (LEACH).

In this paper we present and evaluate a low cost simple method for accurate Time Of Arrival (TOA) estimation in multipath fading channels for positioning purposes. It is well known that TOA estimations are biased in multipath propagation and non-line-of-sight (NLOS) conditions. These biases will result in poor position estimations in wireless networks. Recently supper-resolution methods have been widely used for high resolution TOA estimations. Although these methods result in accurate TOA estimates, but they need strong processors that in many cases makes them impractical. Here, using time domain properties of the estimated channel delay profile, we introduce a simple method to reduce the TOA estimation errors due to the multipath fading channels. In order to evaluate the proposed method, we simulate a UMTS network based on 3GPP standards. The positioning error using the proposed method will be compared with the ones obtained by MUSIC algorithm which is a famous and accurate supper-resolution method. Simulation results show the effectiveness of the proposed method.

This paper proposes and evaluates a simple and efficient method to mitigate the positioning error caused by Multipath fading channels. Using geometric properties of the correlated received signals and Monte Carlo simulations, a lookup table has been developed to correct the TDOA estimation error. The performance of this multipath rejection (MPR) method has been evaluated for 3GPP wireless network standards. Simulation results show that the proposed method reduces the TDOA estimation error significantly and therefore improves the accuracy of mobile position estimation.

This paper focuses on the transmission of real-time fax in IP networks. For this purpose, the best current practices, i.e., utilization of the session initiation protocol (SIP) as the signaling protocol along with ITU-T T.38 recommendation, are adopted. Two traffic engineering measures: utilization of SIP contact header and DijfServ QoS architecture, are proposed to streamline the implementation of the real-time FoIP. Network simulation results show that the proposed architecture, compared to the "best effort" service, has much less transmission time and jitter, and packets received are in correct sequence. Moreover, SIP contact header reduces load on network's specialized resources. Therefore, this layout is a viable alternative for traditional PSTN fax