Relay Network

Multipath fading degrades the performance of wireless communication system significantly as data rate increases. In-order to combat with multipath fading, orthogonal frequency division multiplexing (OFDM) have been used in existing systems. Another effective method is a code division multiple access (CDMA) scheme. It has used extensively for relay network communication systems. In this paper consists of uplink CDMA relay networks and downlink CDMA relay networks. The uplink CDMA relay networks consist of multiple sources, multiple relays and a single destination. In downlink CDMA relay networks consist of a single source, multiple relays and multiple destinations. The objective of the paper is to propose a unique, simple method of finding optimum non-binary pseudo noise (PN) spreading and de-spreading sequences. This employs maximum signal to interference plus noise ratio (SINR) criterion and channel state information (CSI). The use of SIC helps to reduce multiuser interference caused. Effective encoding and decoding scheme is used compared to existing works. Also examines the sensitivity of the schemes to 1-bit quantization, wideband jamming, mistiming alignment. Simulation results shows that the proposed method converges much faster in finding optimum PN sequences compared to existing systems.

This paper provides a comprehensive review of the domain of physical layer security in multiuser wireless networks. The essential premise of physical-layer security is to enable the exchange of confidential messages over a wireless medium in the presence of unauthorized eavesdroppers without relying on higher-layer encryption. This can be achieved primarily in two ways: without the need for a secret key by intelligently designing transmit coding strategies, or by exploiting the wireless communication medium to develop secret keys over public channels. The survey begins with an overview of the foundations dating back to the pioneering work of Shannon and Wyner on information-theoretic security. We then describe the evolution of secure transmission strategies from point-to-point channels to multiple-antenna systems, followed by generalizations to multiuser broadcast, multiple-access, interference, and relay networks. Secret-key generation and establishment protocols based on physical layer mechanisms are subsequently covered. Approaches for secrecy based on channel coding design are then examined, along with a description of inter-disciplinary approaches based on game theory and stochastic geometry. The associated problem of physical-layer message authentication is also introduced briefly. The survey concludes with observations on potential research directions in this area.

This paper investigates the problem of interference minimization which restricts the secondary users (SUs) quality of service (QoS) while coexisting the primary users (PUs), using distributed beamforming for a bidirectional cognitive relay network. We consider a network which consists of two secondary transceivers and K cognitive relay nodes and a primary network with a transmitter and receiver, all equipped with single-antenna. For effective use of spectrum we propose a two-step two-way relaying for cognitive relay networks. Our aim is to design the beamforming coefficients for a bidirectional cognitive relay network through interference minimization approach subject to two constraints on each transceiver QoS which is solved using convex optimization. Our simulation results demonstrate that our distributed relay beamforming scheme improve network performance significantly so that the interference power is decreased by increasing the number of relay nodes while QoS of the secondary network is guaranteed.

The provision of very high data rates in a ubiquitous manner throughout the service area is a great challenge for 4G and beyond-4G wireless networks. Towards that end, the deployment of fixed relays by the operators has become an accepted radio access network concept in various standardization activities including LTE-A and 802.16j. It is envisaged that next-generation networks will comprise a plethora of wireless relay stations. Worthy of mention is the plug-and-play type of relay known as nomadic relay. We devise novel radio resource management (RRM) schemes to facilitate the operation of fixed relay stations (FRSs) and nomadic relay stations (NRSs) in OFDMA-based multicellular networks. Two schemes of different decentralization levels are devised and classified as distributed and semi-centralized. A novel user-based dynamic routing or link selection that significantly reduces the feedback overhead is employed. We develop methods by which the NRSs act autonomously to acquire radio resources without relying on a central entity. NRS operation is the same in the two schemes and can be extended to any other OFDMA-based RRM scheme. Through the asynchronous opportunistic medium access of the NRSs, smart and opportunistic intra-cell channel reuse is attained. This is different from the static intra-cell reuse patterns often adopted in literature. Furthermore, we introduce a method to enable the cooperation between an NRS and a serving FRS to assist a troubled wireless terminal (WT). We thus establish the concept of nomadic relay-augmented fixed relay networks. To the extent of our knowledge of the literature, no other work has undertaken this task so far.

In this work, we introduce a new spectrum leasing based cognitive radio for OFDM-based primary/secondary networks. More precisely, we propose a new leasing scheme both in time and frequency domains in a network composed of a primary transmission and some secondary (cognitive) users forming a cooperative relay network. In the proposed scheme, the primary user decides to lease a part

In this paper we propose a new algorithm for selective relay strategies with Amplify-and-Forward (AF) relays which improves the relay network lifetime. The lifetime of the relay network is defined as the maximum number of messages which can be received with the desired SNR at the destination while the system Probability of Outage (P-outage) requirement is satisfied. The improvement in lifetime increases with the number of relays. When the number of relays is small, the method improves the lifetime under the condition ...

In this paper, we present the performance of fixed decode-and-forward cooperative networks with relay selection over independent but not identically distributed Nakagami-m fading channels, with integer values of the fading severity parameter m. Specifically, closed-form expressions for the symbol error probability and the outage probability are derived using the statistical characteristic of the signal-to-noise ratio. We also perform Monte-Carlo simulations to verify the analytical results.

Abstract—In this paper, we study the zero-forcing (ZF) and minimum mean-squared error (MMSE) algorithms for a multiple-input multiple-output (MIMO) relay network and compare their performance in terms of bit-error-rate (BER). In particular, we investigate their performance with and without using the successive interference cancellation (SIC) at the receiver. Our results demonstrate that the system performance can be significantly improved by using the SIC technique. Index Terms—multiple-input multiple-output (MIMO), relay networks, zero-forcing (ZF), minimum mean-squared error (MMSE), successive-interference-cancellation (SIC). I.

In this article, a new game theoretical method is proposed to model packet forwarding in relay networks. A simple case of relay network that consists of a source, a relay and a destination node communicating on a common channel is considered. A stationary Markovian game model is utilized to optimize the system performance in terms of throughput, delay and power consumption cost. Both cooperative and non-cooperative solutions are provided for this model. Best strategy set taken by players as well as system performance is studied for different system parameters. Also, the proposed method is extended to model a more general case of Ad-hoc networks considering different packet error rates in case of collision occurrence that improves the system performance further. Simulation results show that performance of the non-cooperative solution, in which players do not require to know each other’s selected strategy, asymptotically approaches the cooperative system performance. Hence, the proposed model with non-cooperative solution is an appropriate method to apply in practical Ad-hoc networks.

Cognitive radio (CR) has been considered a key technology to enhance overall spectrum utilization by opportunistic transmissions in CR transmitter-receiver link(s). However, CRs must form a cognitive radio network (CRN) so that the messages can be forwarded from source to destination, on top of a number of opportunistic links from co-existing multi-radio systems. Unfortunately, appropriate routing in CRN of coexisting

SUMMARY Functional standardization activities in ISO and in regional workshops are currently addressing end-system profiles and network layer relay profiles for the interconnection of several types of subnetworks. In order to achieve end-system interconnectivity, connection-mode network layer relays appear as one of the key pieces of the Open Systems Interconnection puzzle. In this paper the authors present a proposal for a connection-mode relay profile that is being input to the European Workshop for Open ...

In this paper, we investigate joint relay and jammer selection in two-way cooperative networks, consisting of two sources, a number of intermediate nodes, and one eavesdropper, with the constraints of physical-layer security. Specifically, the proposed algorithms select two or three intermediate nodes to enhance security against the malicious eavesdropper. The first selected node operates in the conventional relay mode and

In this paper, we consider two-way amplify-and-forward relaying communication over a multiple relays network in which the best relay node is selected among others. Our proposed scheme picks for duplex communication between the source and the destination only the relay which provides the best end-to-end performance based on the instantaneous channel information. Similar to the relay selection method proposed, our scheme also does not require any explicit communications among the relays. Based on the proposed relay selection criterion, we offer the performance bounds on the average sum-rate, average symbol error rate, outage probability over identically, independent distributed Rayleigh fading channels. Further, our numerical examples show that our proposed scheme provides considerable sum-rate gains and offers an increasing a diversity order as the number of relay candidates increases.