Mohamed Hossam Ahmed

Performance Analysis of Cooperative Diversity Wireless Networks over Nakagami-m Fading Channel

This letter analyzes the performance of cooperative diversity wireless networks using amplify-and-forward relaying over independent, non-identical, Nakagami-m fading channels. The error rate and the outage probability are determined using the moment generating function (MGF) of the total signal-to-noise-ratio (SNR) at the destination. Since it is hard to find a closed form for the probability density function (PDF) of the total SNR, we use an approximate value instead. We first derive the PDF and the MGF of the approximate value of the total SNR. Then, the MGF is used to determine the error rate and the outage probability. We also use simulation to verify the analytical results. Results show that the derived error rate and outage probability are tight lower bounds particularly at medium and high SNR

Call admission control in wireless networks: a comprehensive survey

Radio resource management (RRM) plays a major role in Quality of Service (QoS) provisioning for wireless communication systems. The performance of RRM techniques has a direct impact on each users individual performance and on the overall network performance. Arriving (new and handoff) calls are granted/denied access to the network by the call admission scheme (CAC) based on predefined criteria, taking the network loading conditions into consideration. CAC in wireless networks has been receiving a great deal of attention during the last two decades due to the growing popularity of wireless communications and the central role that CAC plays in QoS provisioning in terms of the signal quality, call blocking and dropping probabilities, packet delay and loss rate, and transmission rate. In the first and second generation of wireless systems, CAC has been developed for a single service environment. In the third generation and beyond wireless systems, multimedia services such as voice, video, data, and audio are to be offered with various QoS profiles. Hence, more sophisticated CAC schemes are developed to cope with these changes. This article provides a comprehensive survey of CAC schemes in modern wireless networks.

On the Performance of Cooperative-Diversity Networks with the Nth Best-Relay Selection Scheme

In this letter, we consider the adaptive decode-and-forward (DF) and amplify-and-forward (AF) cooperative-diversity systems with the Nth best-relay selection scheme. In the best-relay selection scheme, from the set of M relays the best relay only forwards the source signal to the destination. However, the best relay might be unavailable; hence we might resort to the second, third or generally the Nth best relay. We derive closed-form expressions for the symbol error probability, outage probability and asymptotic error probability. In particular, we derive a closed-form expression for the probability density function (PDF) of the signal-to-noise ratio (SNR) of the relayed signal at the destination node. Then, we find a closed-form expression for the moment generating function (MGF) of the output SNR at the destination. This MGF is used to derive the closed-form expressions of the performance metrics. All these expressions are derived over identical and non-identical Rayleigh fading channels. Results show that with the Nth best relay the diversity order is equal to (M - N + 2) where M is the number of relays.

Exact Error Probability and Channel Capacity of the Best-Relay Cooperative-Diversity Networks

Cooperative diversity networks have recently been proposed as a way to form virtual antenna arrays without using collocated multiple antennas. In this paper, we consider adaptive decode-and-forward cooperative diversity system where a source node communicates with a destination node directly and indirectly (through multiple relays). In this letter, we investigate the performance of the best-relay selection scheme where the best relay only participates in the relaying. Therefore, two channels only are needed in this case (one for the direct link and the other one for the best indirect link) regardless of the total number of relays. The best relay is selected as the relay node that can achieve the highest signal-to-noise ratio at the destination node. We developed a general analytical model to analyze the performance of the adaptive decode-and-forward cooperative networks with best-relay selection. In particular, exact closed-form expressions for the error probability and Shannon capacity are derived over independent and nonidentical Rayleigh fading channels. Results show that the best-relay selection not only reduces the number of required channels but also can maintain a full diversity order.

Performance analysis of incremental-relaying cooperative-diversity networks over rayleigh fading channels

Cooperative diversity networks have recently been proposed as a way to form virtual antenna arrays without using collocated multiple antennas. Cooperative diversity networks use the neighbor nodes to assist the source by sending the source information to the destination for achieving spatial diversity. Regular cooperative diversity networks make an inefficient use of the channel resources because relays forward the source signal to the destination every time regardless of the channel conditions. Incremental relaying cooperative diversity has been proposed to save the channel resources by restricting the relaying process to the bad channel conditions only [1]. Incremental relaying cooperative relaying networks exploit limited feedback from the destination terminal, e.g., a single bit indicating the success or failure of the direct transmission. If the destination provides a negative acknowledgment via feedback; in this case only, the relay retransmits in an attempt to exploit spatial diversity by combining the signals that the destination receives from the source and the relay. In this paper, we study the end-to-end performance of incremental relaying cooperative diversity networks using amplify-and-forward relays over independent non-identical Rayleigh fading channels. Closed-form expressions for the bit error rate and the signal-to-noise ratio (SNR) outage probability are determined. Results show that the incremental relaying cooperative diversity can achieve the maximum possible diversity, compared with the regular cooperative diversity networks, with higher channel utilization.

Performance Analysis of Cooperative Diversity with Incremental-Best-Relay Technique over Rayleigh Fading Channels

In this paper, we introduce a comprehensive analysis of the incremental-best-relay cooperative diversity, in which we exploit limited feedback from the destination terminal, e.g., a single bit indicating the success or failure of the direct transmission. If the destination provides a negative acknowledgment via feedback; in this case only, the best relay among M available relays retransmits the source signal in an attempt to exploit spatial diversity by combining the signals received at the destination from the source and the best relay. Furthermore, we study the end-to-end performance of the incremental-best-relay cooperative-diversity networks using decode-and-forward and amplify-and-forward relaying over independent non-identical Rayleigh fading channels. Closed-form expressions for the bit error rate, the outage probability and average channel capacity are determined. Results show that the incremental-best-relay cooperative diversity can achieve the maximum possible diversity order, compared with the regular cooperative-diversity networks, with higher channel utilization. In particular, the incremental-best-relay technique can achieve M+1 diversity order at low signal-to noise ratio (SNR) and considerable virtual array gain at high SNR.

On the Performance of Amplify-and-Forward Cooperative Diversity with the Nth Best-Relay Selection Scheme

Cooperative-diversity networks have recently been proposed as a way to form virtual antenna arrays without using collocated multiple antennas. In this paper, we consider the amplify-and-forward cooperative-diversity system with the Nth best-relay selection scheme. In the best-relay selection scheme, the best relay only forwards the source signal to the destination. However, the best relay might be unavailable; hence we might resort to the second, third or generally the Nth best relay. We derive closed-form expressions for the symbol error probability, outage probability and channel capacity. In particular, we derive a closed-form expression for the probability density function of the signal-to-noise ratio of the relayed signal at the destination node. Then, we find a closed-form expression for the moment generating function of the total SNR at the destination. This MGF is used to derive the closed-form expressions of the performance metrics. Results show that with the Nth best relay the diversity order is equal to (M - N +2) where M is the number of relays. Simulation results are also given to verify the analytical results.

Performance of cooperative diversity using Equal Gain Combining (EGC) over Nakagami-m fading channels

Cooperative diversity is a promising technology for future wireless networks. In this paper, we derive exact closed-form expressions for the average bit error rate (BER) and outage probability (Pout) for differential equal gain combining (EGC) in cooperative diversity networks. The considered network uses amplify-and-forward relaying over independent non-identical Nakagami-m fading channels. The performance metrics (BER and Pout) are derived using the moment generating function (MGF) method. Furthermore, we found (in terms of MGF) the SNR moments, the average signal-to-noise ratio (SNR) and amount of fading. Numerical results show that the differential EGC can benefit from the path-loss reduction and outperform the traditional multiple-input single output (MISO) system. Also, numerical results show that the performance of the differential EGC is comparable to the maximum ratio combining (MRC) performance.

Performance Analysis of Generalized Selection Combining for Amplify-and-Forward Cooperative-Diversity Networks

We consider an amplify-and-forward (AF) cooperative-diversity system where a source node communicates with a destination node directly and indirectly (through multiple relays). in this paper, we analyze the system where N multiple relays that have the strongest signal strength at the destination are selected out of M relays and forward their received data from the source node to the destination node. We derive closed-form expressions for the average symbol error probability, the outage probability, the average channel capacity, the average signal-to-noise ratio (SNR), the amount of fading, and the SNR moments. In particular, closed-form expression for the moment generating function of the SNR at the destination node is determined. Then, we find a closed-form expression for the probability density function (PDF) of the total SNR at the destination. This PDF is used to derive the closed-form expressions of the performance metrics. Simulation results are also given to verify the analytical results. Results show that increasing N will slightly improves the error performance and degrade the outage probability and average channel capacity. In particular, N = M gives the best performance in terms of error performance and N = 1 (the best relay) gives the best performance in terms of outage probability and average channel capacity.

Radio Resource Allocation Techniques for Efficient Spectrum Access in Cognitive Radio Networks

This paper provides an overview of cognitive radio (CR) networks, with focus on the recent advances in resource allocation techniques and the CR networks architectural design. The contribution of this work is threefold. First, a systematic way to study the resource allocation problem is presented; various design approaches are introduced, such as signal-to-interference-and-noise ratio (SINR) or transmission power-based, and centralized or distributed methods. Second, CR optimization methods are presented, accompanied by a comprehensive study of the resource allocation problem formulations. Furthermore, quality of service criteria of the physical or/and the medium access control layers are investigated. Third, challenges in spectrum assignment are discussed, focusing on dynamic spectrum allocation, spectrum aggregation and frequency mobility. Such approaches constitute an emerging trend in efficient spectrum sharing and affect the performance of resource allocation techniques. The open issues for future research in this area are finally discussed, including adaptability-reconfigurability, dual accessibility, and energy efficiency.