Cooperative Wireless Communication System Research Articles

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.

Optimal power allocation for complex field network coding scheme with the K- th best relay selection

Wireless relay and network coding are two critical techniques to increase the reliability and throughput of wireless cooperative communication systems. In this paper, a complex field network coding (CFNC) scheme with the K-th best relay selection (KBS) is proposed and investigated, wherein the K-th best relay is selected to forward the multiplexed signal to the destination. First, the upper bound of the symbol error probability (SEP), the diversity order, and the coding gain are derived for the CFNC scheme with KBS. Then, the coding gain is utilized as the optimized criterion to determine the optimal power allocation. It is validated through analysis and simulation that the CFNC scheme with KBS can achieve full diversity only when K=1, while the diversity order decreases with increasing parameter K, and the optimal power allocation can significantly improve the performance of the CFNC scheme with KBS.

Distributed Power Allocation Scheme for Multi-Relay Shared-Bandwidth (MRSB) Wireless Cooperative Communication

In multi-relay shared-bandwidth (MRSB) wireless cooperative communication systems, it generally needs destination node to determine the optimal relay subset and broadcast the information to the candidate relays. One drawback to this central scheme is its high complexity and time consumption. In this letter, we propose a distributed power allocation strategy that makes the system's Signal-Noise-Ratio (SNR) performance improve monotonically in the number of the relays. Each terminal can relay its overheard information with specified transmission power according to its own channel information separately. Consequently, the NP problem of solving the optimal relay subset in previous central mode is transformed into the problem of power allocation and distributed relay scheduling is realized in a simple way. Through Monte Carlo simulations being carried out under Rayleigh fading channel condition, the performance of the proposed scheme is highlighted by comparing with previous central mode schemes.

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.

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.

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.

Bandwidth Resource Competition in Cooperative Cognitive Wireless Communications

In this paper, we analyze the behavior of Cooperative Cognitive Wireless nodes for the bandwidth resource competition using the ecological models of mutualism. We transform our cooperative cognitive wireless communication (CCWC) system as mutually interacting species. The two types of species are primary and secondary users. The Primary users have under-utilized licensed bandwidth to be shared with the secondary users. On the other hand, secondary users are willing to behave as possible relays for cognitive primary users, in exchange of shared licensed bandwidth. So, instead of pricing model, the proposed system is analyzed with the traditional barter system (exchange of commodities). We analyzed our proposed system based on three ecological models. Our first model is based on the coalitional form of Lotka–Volterra equations, where predator-prey role of mobile nodes are replaced with cooperation as in symbiosis. The second model deals with the population dynamism of strategically interacting partner for conflicting bandwidth resource. The third model adds the dynamism for the varying amount of bandwidth to be shared among the individual mobile users. For each type, a mathematical model is derived and then simulated for the equilibrium position analysis. The obtained results show that sharing of bandwidth resource is essential for the existence of CCWC systems.

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.

Cooperative Signaling with Soft Information Combining

We propose a Decode‐and‐Forward (DF) scheme using distributed Turbo code (DTC) for a three‐node (source, relay, and destination) wireless cooperative communication system. The relay decodes, then interleaves, and reencodes the decoded data. It then forwards the reencoded packet and its instantaneous receive SNR to the destination. The performances using both ideal and quantized SNR are studied. The destination uses a modified metric within a Turbo decoding algorithm to scale the soft information calculated for the relay code. The proposed scheme is simple to implement and performs well.

A utility‐based capacity optimization framework for achieving cooperative diversity in the hierarchical converged heterogeneous wireless networks

AbstractA hierarchical convergence mechanism for the heterogeneous wireless communication system via the heterogeneous cooperative relay node is presented in this paper, in which the techniques of cooperative communication and wireless relay are utilized to improve performances of the individual user and the overall converged networks. In order to evaluate the benefits of the proposal, a utility‐based capacity optimization framework for achieving the heterogeneous cooperative diversity gain is proposed. The heterogeneous cooperative capacity, relay selection and power allocation theoretical models are derived individually. The joint optimization model for relay selection and power allocation is presented as well. Owing to the computation complexity, the sub‐optimal cooperative relay selection algorithm, the sub‐optimal power allocation algorithm and the sub‐optimal joint algorithm are determined to approach the maximum overall networks' spectrum efficiency. These proposed algorithms are designed in conformance to guarantee the equivalent transmission rates of the different wireless access networks. The simulation results demonstrate that the utility‐based capacity model is available for the heterogeneous cooperative wireless communication system, and the proposed algorithms can improve performances by achieving the cooperative gain and taking full advantage of the cross‐layer design. Copyright © 2008 John Wiley & Sons, Ltd.

Radio resource management for cooperative wireless communication systems with organized beam-hopping techniques

Readiness in deployment and flexibility in radio resource configuration are the main features of future wireless communication systems. A cooperative wireless communication system (CWCS) is proposed to follow the same principle, aiming at improving the overall performance of a wireless system with the support of advanced beam-hopping techniques. In this article, we propose a multiloop radio resource management mechanism for the CWCS based on the organized beam-hopping (OBH) technique. The proposed RRM mechanism enhances the robustness of the CWCS, based on the OBH technique working with fast temporal-spatial variant traffic. The results show that the system performance can be further improved by hybrid transmission and event- driven access management techniques.

Modulation and demodulation for cooperative diversity in wireless systems

This paper develops a general framework for maximum likelihood (ML) demodulation in cooperative wireless communication systems. Demodulators with piecewise-linear combining are proposed as an accurate approximation of the nonlinear ML detectors for coherent and noncoherent decode-and-forward (DF). The detectors with piecewise-linear combiner not only have certain implementation advantages over the nonlinear ML detectors, but also can lead to tight closed-form approximations for their error probabilities. High SNR approximations are derived based on the closed-form BER expressions. For noncoherent DF, the approximation suggests a different optimal location for the relay in DF than for the relay in amplify-and-forward (AF). A set of tight bounds of diversity order for coherent and noncoherent DF with multiple relays is also provided, and comparison between DF and AF suggests that DF with more than one relay loses about half of the diversity order of AF