Cooperative Wireless System Research Articles

A smart scheme for relay selection in cooperative wireless communication systems

The performance of multiple-input multiple-output systems using spatial multiplexing can be degraded when the spatial information channels are correlated. This work proposes a solution to this problem, which is based on a cooperative wireless communication system. Within the cooperative system, the relay is selected either randomly or using the smart selection scheme, a simple and distributed approach proposed herein. These relay selection schemes are evaluated for several situations within a small cell environment, using a simulator that generates frequency-selective channel realizations. The simulation results show that the smart selection scheme yields high capacity gains close to the theoretical maximum gain.

Concatenated RS-Convolutional Codes for Cooperative Wireless Communication

In the last few years, several works have investigated the performance of cooperative wireless systems with various types of channel codes such as Low Density Parity Check (LDPC), Turbo, CRC, convolutional and recently Reed Solomon (RS) codes. These cooperative schemes give power to single antenna mobiles to originate virtual multiple antennas transmitter, MIMO system, by sharing their antennas so that diversity gain is achieved. The most common cooperative schemes are decode and forward (DF) and coded cooperation (CC). Concatenated Reed Solomon and convolutional codes have been used by several wireless communication standards like digital video broadcasting (DVB) standards and IEEE 802.16e WiMAX standard. In this paper, we develop two different coded cooperation schemes and apply them to the mandatory structure of physical layer specifications of IEEE 802.16e WiMAX. The results attained for both coded cooperation schemes present magnificent diversity gains over non-cooperative scheme.

Cooperative communication with asymmetric channel state information: A contract theoretic modeling approach

In relay-assisted cooperative communication, relay nodes help forwarding the information of a source node in case of link failure between the source and a destination. Although user cooperation improves the overall efficiency of the network, it requires incentive to stimulate potential relay nodes to assist the source by forwarding its data to the destination. Moreover, the potential relays are better informed than the source about their channel conditions to destination, which results in asymmetric information between the source and the relays. In this paper, we study the problem of lack of forwarding incentive in cooperative communication when channel state information of relays is private information and not known by the source. To tackle this problem, we apply the principle of contract theory to a cooperative wireless system. Source first designs incentive compatible and individually rational contract, consisting of a set of power-credit pairs. Then it broadcasts contract items to nearby nodes. Once the source node receives reply messages from the volunteer relays, it chooses one or more relays based on its requirements and communication starts. Simulation results show how credit assignment works in order to stimulate relays to cooperate and prevents relays from cheating behavior.

Power Allocation in Two-Dimensional Superposition Modulation Based Cooperative Wireless Communication System

Superposition modulation makes it possible for transmitting a node's own data along with its neighbors' relay data in a single time-slot and frequency, which can improve spectral efficiency of cooperative wireless communication system. First, we consider a two-user scenario and propose a design criterion for two-dimensional superposition modulation based cooperative transmission where the users cooperate to transmit their data to a base station. We investigate M-PSK superposition modulation based cooperative scenario for Rayleigh fading channels and thoroughly derive the average symbol error rate (SER) of such system with decode-and-forward relaying. Furthermore, we introduce a design parameter called power allocation ratio (PAR) which can be adaptively changed within the derived limits. We derive SER expressions in terms of the PAR and demonstrate its effect on average SER. Based on analytical and simulation results, we show that the proposed scheme provides reduced SER and increased spectral efficiency per link compared to existing schemes in practical scenarios. Finally, we investigate multi-user scenario, propose an adaptive power allocation scheme for superposition modulation, and confirm that SER is decreased with our proposed scheme.

Diversity-Multiplexing Tradeoff Analysis of Wireless Multiple-Antenna Cooperative Systems in General Fading Channels

Diversity-Multiplexing Tradeoff Analysis of Wireless Multiple-Antenna Cooperative Systems in General Fading Channels

Moments-based analysis of dual-hop amplify-and-forward relaying communications systems over generalised fading channels

The authors present an alternative moments-based approach for the performance analysis of dual-hop relaying communications systems over generalised fading channels. A unified analytical approach for the computation of the nth moment of the harmonic mean of N≥2 arbitrarily distributed random variables (RVs) is proposed. On the basis of this statistical result, we analyse the outage and the average error rate performance of dual-hop cooperative wireless systems employing amplify-and-forward (AF) relays. Moreover, our newly derived results can be applied to evaluate the average sum rate of AF relaying systems. Extensive numerical and simulation results are presented to substantiate the proposed analysis.

Cross Layer AMC Scheduling for a Cooperative Wireless Communication System over Nakagami-m Fading Channels

We study a single-source single-destination cooperative wireless communication system with multiple relays operating in a modified decode-and-forward mode. Nakagami-m fading with additive white Gaussian noise is assumed for all inter-node channels. The bursty data packet arrival is modeled by a Markov-modulated Poisson process (MMPP). A packet feedback model is proposed to characterize packet loss in the wireless channel. An approximation to the steady state distribution of the proposed generalized discrete time M/G/1-type queue at the source is obtained by state truncation. Packet level performance of four transmission modes adopting different modulation and coding schemes is analyzed under a variety of channel and traffic conditions using the truncated queueing analysis. The network power is used as a criterion to find boundary curves of adaptive modulation and coding (AMC) scheduling for the cooperative wireless system. Two source node transmission protocols, namely the transmit-every-clock-tick (TREC) and the LAZY protocols, are examined for both the AMC scheduling and channel utilization analysis.

Co-operative Wireless Intrusion Detection System Using MIBs From SNMP

In emerging technology of Internet, security issues are becoming more challenging. In case of wired LAN it is somewhat in control, but in case of wireless networks due to exponential growth in attacks, it has made difficult to detect such security loopholes. Wireless network security is being addressed using firewalls, encryption techniques and wired IDS (Intrusion Detection System) methods. But the approaches which were used in wired network were not successful in producing effective results for wireless networks. It is so because of features of wireless network such as open medium, dynamic changing topology, cooperative algorithms, lack of centralized monitoring and management point, and lack of a clear line of defense etc. So, there is need for new approach which will efficiently detect intrusion in wireless network. Efficiency can be achieved by implementing distributive, co-operative based, multi-agent IDS. The proposed system supports all these three features. It includes mobile agents for intrusion detection which uses SNMP (Simple network Management Protocol) and MIB (Management Information Base) variables for mobile wireless networks.

Co-operative Wireless Intrusion Detection System Using MIBs From SNMP

Co-operative Wireless Intrusion Detection System Using MIBs From SNMP

Performance analysis of decode-and-forward relaying schemes with adaptive quadrature amplitude modulation (QAM)

In this study, the authors propose two schemes to enhance the spectral efficiency of the decode-and-forward adaptive relaying with adaptive modulation. The first scheme, called the minimum error rate scheme, uses cooperative transmission all the time to achieve transmit diversity whereas the second scheme, called the maximum spectral efficiency scheme, tries to avoid cooperative transmission if the spectral efficiency cannot be improved. For each scheme, the authors introduce a policy that depends on the channel state information of each link. They provide performance analysis in terms of average spectral efficiency, average bit error rate and outage probability over independent non-identically Rayleigh fading channels. Our analysis is verified by simulation results. These results show that our proposed schemes lead to an improvement in the performance of cooperative wireless systems.

Performance Analysis of Hybrid Relay Selection in Cooperative Wireless Systems

The hybrid relay selection (HRS) scheme, which adaptively chooses amplify-and-forward (AF) and decode-and-forward (DF) protocols, is very effective to achieve robust performance in wireless networks. This paper analyzes the frame error rate (FER) of the HRS scheme in general cooperative wireless networks without and with utilizing error control coding at the source node. We first develop an improved signal-to-noise ratio (SNR) threshold-based FER approximation model. Then, we derive an analytical average FER expression as well as an asymptotic expression at high SNR for the HRS scheme and generalize to other relaying schemes. Simulation results are in excellent agreement with the theoretical analysis, which validates the derived FER expressions.

Space-Time Coding Technique Based on Four-Antenna Transceiver System

Space-time block code, as one of the space-time codes, greatly improves the performance in the cooperative wireless communication systems by the use of space and time diversity. However, traditional STBC can’t enhance the overall transmission rate and there is no form of complex codes with the rate of 1 when the number of antenna is more than 2. In order to design codes with full-rate, we refer to quasi-orthogonal STBC whose generator matrix is orthogonal between its subspaces. In this paper, based on the combination of QO-STBC and Self-adaptation technology, we propose a new plan of space-time coding which dismisses the interference among symbols when decoding and advances the coding capabilities in the context of full-rate transmission, finally we justify the new plan through lots of computational simulations.

Performance of a Fast, Distributed Multiple Access Based Relay Selection Algorithm Under Imperfect Statistical Knowledge

Cooperative wireless systems can exploit spatial diversity by opportunistically selecting the best relay to forward data to a destination. However, determining the best relay is a challenging task and requires a selection algorithm because the relays are geographically separated and only have local channel knowledge. Selecting the best relay is equivalent to finding the relay with the largest metric, where each relay computes its metric using local channel knowledge. We analyze the performance of a fast, distributed, and scalable multiple access based selection algorithm when it assumes incorrect values for two fundamental parameters that it requires to operate efficiently - the number of available relays and the cumulative distribution function (CDF) of the metrics. Such imperfect knowledge will invariably arise in practice. We develop new expressions for the time required to select the best relay as a function of the assumed and actual parameters. We show that imperfect knowledge can significantly slow down the selection algorithm. Further, in a system that uses its observations to update its CDF estimate, we determine the minimum number of observations required to limit the performance degradation. We also develop a minimax formulation that makes the algorithm robust to uncertainties in the number of relays in the system.

Code-Rate-Optimized Differentially Modulated Near-Capacity Cooperation

It is widely recognized that half-duplex-relay-aided differential decode-and-forward (DDF) cooperative transmission schemes are capable of achieving a cooperative diversity gain, while circumventing the potentially excessive-complexity and yet inaccurate channel estimation, especially in mobile environments. However, when a cooperative wireless communication system is designed to approach the maximum achievable spectral efficiency by taking the cooperation-induced multiplexing loss into account, it is not obvious whether or not the relay-aided system becomes superior to its direct-transmission based counterpart, especially, when advanced channel coding techniques are employed. Furthermore, the optimization of the transmit-interval durations required by the source and relay is an open issue, which has not been well understood in the context of half-duplex relaying schemes. Hence, we first find the optimum transmission duration, which is proportional to the adaptive channel-code rate of the source and relay in the context of Code-Rate-Optimized (CRO) TDMA-based DDF-aided half-duplex systems for the sake of maximizing the achievable network throughput. Then, we investigate the benefits of introducing cooperative mechanisms into wireless networks, which may be approached in the context of the proposed CRO cooperative system both from a pure capacity perspective and from the practical perspective of approaching the Discrete-input Continuous-output Memoryless Channel (DCMC) capacity with the aid of the proposed Irregular Distributed Differential (IrDD) coding aided scheme. In order to achieve a near-capacity performance at a low-complexity, an adaptive-window-duration based Multiple-Symbol Differential Sphere Detection (MSDSD) scheme is employed in the iterative detection aided receiver. Specifically, upon using the proposed near-capacity system design, the IrDD coding scheme devised becomes capable of performing within about 1.8 dB from the corresponding single-relay-aided DDF cooperative system's DCMC capacity.

Performance Evaluation of a Cooperative OFDM System with implementation of DAF and AAF Relaying Protocols on Color image transmission

In this paper, we investigate the performance of a single-relay cooperative wireless communication system with implementation of Orthogonal Frequency division multiplexing technique under Amplifyand-Forward (AAF) and Decode-and-Forward (DAF) relaying protocols on color image transmission. The system under investigation incorporates four conventional signal combining schemes such as Equal Ratio Combining (ERC) and Fixed Ratio Combining (FRC), Signal to Noise Ratio Combining (SNRC) and Enhanced Signal to Noise Ratio Combining (ESNRC) under BPSK and QPSK digital modulations. In the present study, results of BER simulation in AWGN and Raleigh fading channels shows that the system outperforms in ERC combining scheme as compared to others (FRC, SNRC and ESNRC) under BPSK digital modulation and AAF relaying protocol. It is observed that a quite satisfactory system performance is achieved in ERC scheme under AAF relaying protocol with BPSK digital modulation. It has been anticipated from the simulation study that the performance of the cooperative OFDM communication system degrades with the increasing of noise power and level of modulation.

Interference Cancellation in Cooperative CDMA Networks

The wireless communication networks are subjected to multi access interference and multipath fading. To minimize the interference cancellation in CDMA networks, multiple user detection schemes and cooperative communication networks are used. consider the uplink of a cooperative CDMA network, where users cooperate by relaying each other’s messages to the base station. When spreading waveforms are not orthogonal, multiple access interference (MAI) exists at the relays and the destination, causing cooperative diversity gains to diminish. To overcome this problem, we integrate various multiuser detection (MUD) schemes to mitigate MAI in achieving the full advantages of cooperation. Specifically, the relay-assisted decorrelating multiuser detector (RADMUD) is proposed to separate interfering signals at the destination with the help of precoding at the relays along with pre-whitening at the destination. In this paper we examined the BER performance of various MUD schemes are analyzed and compared with cooperative system. The advantages of RAD-MUD with co-operative communication shows better BER performance compared with non co-operative wireless communication system and other existing cooperative MUD schemes are also shown through MATLAB Simulations.

Outage Probability and Power Allocation of Amplify and Forward Relaying with Channel Estimation Errors

This paper studies the statistical properties of the signal-to-noise ratio (SNR) of the dual-hop relaying link in a cooperative wireless communication system in the presence of channel estimation errors for fixed-gain (FG) and variable-gain (VG) relays. The SNR expression is derived and three different analytical approaches with different simplifying assumptions are proposed to obtain the probability distribution function of the SNR and the outage probability in each mode. All but one approach result in closed-form expressions for the outage probability. The simplest approach in each mode has been used to find an optimum power allocation scheme for pilot and data symbols transmission at the source and the relay that results in minimizing the outage probability. Numerical analysis is used to confirm the accuracy of the derived theory and to show that the analytical approaches have a good outage performance, especially as the relay-destination distance increases. It is shown that significant power savings (e.g. 6 dB in VG mode) can be obtained by using the proposed power optimization method.

Effects of Nodes Geometry and Power Allocation in Space-Time Coded Cooperative Wireless Systems

Cooperative communications are effective in improving the performance and extend the coverage of wireless networks. One issue is to find proper methods to allocate cooperative nodes. In this paper we investigate the effects of relay position and power allocation strategy in cooperative communications employing space-time codes (STCs). We consider non-ideal links between source, relay, and destination enabling the analysis of relay allocation problem based on the performance of each link in realistic scenarios. The frame error rate for various channel conditions, available diversity, relay positions, and transmitted power levels is obtained. Both the situation of balanced and unbalanced transmit power levels for source, relay, and destination are compared. Cooperative pragmatic STCs in block fading channel (BFC) are considered for our analysis. The results provide insight on how to allocate relay nodes based on geometry, link quality, and transmitted power considerations.

Cooperative MIMO Transmissions in WSN Using Threshold Based MAC Protocol

Sensor networks require robust and efficient communication protocols to maximise the network lifetime. Radio irregularity, channel fading and interference results in larger energy consumption and latency for packet transmission over wireless channel. Cooperative multi-input multi-output (MIMO) schemes when incorporated in wireless senor network (WSN) can significantly improve the communication performance. An inefficiently designed medium access control (MAC) protocol however, may diminish the performance gains of MIMO operation. Hence, this paper proposes a distributed threshold based MAC protocol for cooperative MIMO transmissions using space time block codes (STBC). The protocol uses a thresholding scheme that is updated dynamically based on the queue length at the sending node to achieve lesser energy consumption and minimise latency ensuring the stability of transmission queues at the nodes. STBC and code combining techniques are applied to utilise the inherent spatial diversity in wireless cooperative MIMO systems. Simulation results are provided to evaluate the performance of the proposed protocol and are compared with fixed group size cooperative MIMO MAC protocols with and without STBC coding. Results show that the proposed protocol outperforms point to point communication as well as cooperative MIMO MAC protocols that use fixed group sizes. STBC technique for the proposed MAC protocol provides significant energy savings and minimises the packet delay by leveraging MIMO diversity gains.

Cooperative Subcarrier Allocation for an OFDM Relaying System with Grouped Users

In this article, the problem of downlink subcarrier allocation in a cooperative wireless multiuser OFDM system is investigated. We consider a single-cell where all the users are paired in cooperative groups. The mobile users in each group amplify and forward their partner's data stream using a time division protocol. Based on the capacity contribution from the relaying terminal, a new parameter called cooperation coefficient is introduced as a function of the relaying subchannel. This parameter is used to modify the objective parameter of the subcarrier allocation procedure. Fairness-oriented and throughput-oriented algorithms are selected from the literature to test the proposed technique. Both algorithms are modified to employ the mean of cooperation coefficient in the objective parameter of the subcarrier allocation procedure and shown to have a better total throughput without any sacrifice. Using the mean of cooperation coefficient eliminates the need for the feedback of the relaying channel to the base station. It is shown that by using the mean value of the cooperation coefficient, instead of its instantaneous value, throughput of the system would still improve compared to the non-cooperative case. Using the mean of cooperation coefficient leads to an implementable cooperative subcarrier allocation algorithm.