Efficient Power Allocation Schemes for Hybrid Decode-Amplify-Forward Relay Based Wireless Cooperative Network

Cooperative communication in various wireless domains, such as cellular networks, sensor networks and wireless ad hoc networks, has gained significant interest recently. In cooperative network, relays between the source and the destination, form a virtual MIMO that creates spatial diversity at the destination, which overcomes the fading effect of wireless channels. Such relay assisted schemes have potential to increase the channel capacity and network coverage. Most current research on cooperative communication are focused broadly on efficient protocol design and analysis, resource allocation, relay selection and cross layer optimization. The first part of this research aims at introducing hybrid decode-amplify-forward (HDAF) relaying in a distributed Alamouti coded cooperative network. Performance of such adaptive relaying scheme in terms of symbol error rate (SER), outage probability and average channel capacity is derived theoretically and verified through simulation based study. This work is further extended to a generalized multi HDAF relaying cooperative frame work. Various efficient power allocation schemes such as maximized channel capacity based, minimized SER based and total power minimization based are proposed and their superiority in performance over the existing equal power allocation scheme is demonstrated in the simulation results. Due to the broadcast nature of wireless transmission, information privacy in wireless networks becomes a critical issue. In the context of physical layer security, the role of multi HDAF relaying based cooperative model with control jamming and multiple eavesdroppers is explored in the second part of the research. Performance evaluation parameters such as secrecy rate, secrecy outage and intercept probability are derived theoretically. Further the importance of the proposed power allocation schemes in enhancing the secrecy performance of the network in the presence of multiple eavesdroppers is studied in detail through simulation based study and analysis. For all the proposed power allocation schemes in this research, the optimization problems are defined under total power constraint and are solved using Lagrange multiplier method and also evolutionary algorithms such as Differential evolution and Invasive Weed Optimization are employed. Monte Carlo simulation based study is adopted throughout the research. It is concluded that HDAF relaying based wireless cooperative network with optimal power allocation schemes offers improved and reliable performance compared to conventional amplify forward and decode forward relaying schemes. Above research contributions will be applicable for future generation wireless cooperative networks

Outage Probability in Multimodal Networks

In the mid 1990\u27s wireless researchers discovered that additional antennas located at the transmitter, receiver or both could help combat the unpredictable nature of the wireless channel. This field of research, known as MIMO (Multiple-Input Multiple-Output), became very active and has been thoroughly studied. Manufacturers have sought to incorporate these performance gains into their devices by including multiple transmit and receive antennas. However, as wireless devices such as mobile phones become smaller it becomes impractical to design a handset with multiple antennas.;Cooperative diversity is a technique that may be employed when device sizes are too small to incorporate a local antenna array. Using cooperative diversity, multiple wireless nodes cooperate to pass a message from a source to a destination. This leads to a virtual antenna array, allowing single-antenna devices to enjoy the benefits of a MIMO system. While cooperative diversity offers benefits, it motivates additional wireless nodes in the network. Even without cooperative diversity, our lives are increasingly dependent on a growing number of wireless devices. It\u27s obvious that the density of wireless devices in daily use will increase, and that rise in popularity demands the most optimal use of node resources.;Unfortunately, it has been shown that as the density of wireless devices for a given area increases, in the limit, the capacity of the network goes to zero. Even with advances such as MIMO and cooperative diversity, it\u27s obvious that a wireless-only future is impossible. For non-diminishing throughput, as wireless networks continue to grow in size, networks of the future will continue to incorporate additional modes of communication; wired, infrared, ultrasonic or other. In our work, we provide a strategy for harnessing these additional modes and optimizing across all the available modes of communication.;In this thesis, we present a protocol for wireless relay networks with an additional non- fading mode of communication available. As an example, we assume the presence of an additional wired channel in a relay network operating under the Laneman protocol, and we find analytical expressions for outage probability assuming communications over the wired and wireless channels are jointly optimized. We consider two cases: adding a channel between the source and a relay, and adding a channel between a relay and the destination. We show that a channel placed between the source and a relay separated by a poor wireless channel improves performance with few assumptions on the characteristics of the wire and over a wide range of wire channel transmit powers

Intercept Probability Analysis of Cooperative Wireless Networks with Best Relay Selection in the Presence of Eavesdropping Attack

Due to the broadcast nature of wireless medium, wireless communication is extremely vulnerable to eavesdropping attack. Physical-layer security is emerging as a new paradigm to prevent the eavesdropper from interception by exploiting the physical characteristics of wireless channels, which has recently attracted a lot of research attentions. In this paper, we consider the physical-layer security in cooperative wireless networks with multiple decode-and-forward (DF) relays and investigate the best relay selection in the presence of eavesdropping attack. For the comparison purpose, we also examine the conventional direct transmission without relay and traditional max-min relay selection. We derive closed-form intercept probability expressions of the direct transmission, traditional max-min relay selection, and proposed best relay selection schemes in Rayleigh fading channels. Numerical results show that the proposed best relay selection scheme strictly outperforms the traditional direct transmission and max-min relay selection schemes in terms of intercept probability. In addition, as the number of relays increases, the intercept probabilities of both traditional max-min relay selection and proposed best relay selection schemes decrease significantly, showing the advantage of exploiting multiple relays against eavesdropping attack.Comment: 5 pages. arXiv admin note: substantial text overlap with arXiv:1305.081

Full-Duplex Cloud Radio Access Network: Stochastic Design and Analysis

Full-duplex (FD) has emerged as a disruptive communications paradigm for enhancing the achievable spectral efficiency (SE), thanks to the recent major breakthroughs in self-interference (SI) mitigation. The FD versus half-duplex (HD) SE gain, in cellular networks, is however largely limited by the mutual-interference (MI) between the downlink (DL) and the uplink (UL). A potential remedy for tackling the MI bottleneck is through cooperative communications. This paper provides a stochastic design and analysis of FD enabled cloud radio access network (C-RAN) under the Poisson point process (PPP)-based abstraction model of multi-antenna radio units (RUs) and user equipments (UEs). We consider different disjoint and user-centric approaches towards the formation of finite clusters in the C-RAN. Contrary to most existing studies, we explicitly take into consideration non-isotropic fading channel conditions and finite-capacity fronthaul links. Accordingly, upper-bound expressions for the C-RAN DL and UL SEs, involving the statistics of all intended and interfering signals, are derived. The performance of the FD C-RAN is investigated through the proposed theoretical framework and Monte-Carlo (MC) simulations. The results indicate that significant FD versus HD C-RAN SE gains can be achieved, particularly in the presence of sufficient-capacity fronthaul links and advanced interference cancellation capabilities