Game Theoretic Approach for Enforcing Truth-Telling upon Relay Nodes

ABSTRACTUser cooperation has evolved as a popular coding technique in wireless relay networks (WRNs). Using the neighboring nodes as relays to establish a communication between a source and a destination achieves an increase of the diversity order. The relay nodes can be seen as a distributed multi‐antenna system, which can be exploited for transmit diversity by using distributed space–time block coding (STBC). In this paper, we investigate the bit error rate (BER) of multi‐hop WRNs employing distributed STBC at the relay nodes. We develop the general model of WRNs using distributed STBC, and we derive the pairwise error probability and an approximation of the BER. We examine the impact of several parameters, such as distributed STBC at the relays, the number of relays, the distances between the nodes, and the channel state information available at the receivers, on the BER performance of the multi‐hop WRN. The obtained results provide guidelines about the expected error performance and the design of channel estimation for these networks. Copyright © 2011 John Wiley & Sons, Ltd.

This paper addresses channel state information (CSI) estimation in a wireless relay network, which consists of a base station (BS), a relay station (RS), and a mobile station (MS). We propose a method for the BS to obtain the instantaneous CSIs of the three links (BS-RS, BS-MS, and RS-MS links) with minimized overhead. The CSI availability plays an important role for the BS to adapt its transmission strategies to the given channel conditions. Our proposed method exploits the fact that the link condition between fixed BS and fixed RS tends to be stable, and the frequent CSI update is not necessary for this link. In order for the BS to obtain the CSI of the distant link (i.e. RS-MS link), RS amplifies a pilot signal received from MS with a pre-defined amplification factor, and forwards it to BS. This enables the BS to obtain the CSI of the RS-MS link based on the received pilot signal and pre-knowledge on the CSI of BS-RS link. We show by computer simulation that our proposed method can reduce the required overhead for CSI estimation with little degradation on the accuracy of the obtained CSI.

In this paper, an efficient QoS aware resource allocation algorithm is proposed for wireless relay networks. This algorithm is yielded by considering G/G/1 queue for each subcarrier and using effective capacity concept to model the transmission delay in wireless relay networks. The objective is to minimize the transmission power considering support of QoS parameters. The constant user arrival rate is assumed throughout the paper. An extended Kalman filter also is used to estimate the residual times and vacation times of the relays and subcarriers. Based on the channel state information and queue state information, proposed algorithm assigns proper subcarriers to the relays. Then, the optimum subcarriers and relays are allocated for optimum power efficient transmission to the users.

In this paper, we propose a robust collaborative relay beamforming scheme in the presence of imperfect channel state information (CSI) for a multiple single-antenna two-way relays network with reciprocal channels. Many existing beamforming schemes have been investigated using perfect CSI for relay-aided systems. However, in practical communication systems the channel estimation is always inaccurate at relay nodes, leading to the deviation between the true CSI and the estimated CSI. Aiming to tackle the performance degradation caused by the CSI mismatch, a constrained optimization problem corresponding to the robust relay beamforming vector is formulated, in which the channel estimation error is characterized by the stochastic error model. Herein the commonly used performance metric, expected weighted sum mean squared error, is adopted as design objective to evaluate the overall link reliability. It is found that due to the intractable expression of the cost function, we can not resort to the traditional methods for solving the involved optimization problem. Whereas, by exploring the lower bound of the cost function using Jensen's inequality and the Taylor series expansion, the original optimization problem is recast to a convex optimization in the form of Rayleigh---Ritz ratio, which results in a closed-form robust relay beamforming solution. Numerical results verify the robustness and superiority of the proposed scheme against CSI errors in terms of system sum rate and average BER.

We consider wireless relay networks for use in industrial applications with strict requirements on both reliable and timely communications. In most cases commercially available transceivers must be used, which implies that only hard decision detector outputs are available. Since relay networks typically use retransmissions of erroneous packets, packet combining methods have the potential to increase the information reliability without excessive delay. We evaluate three different hard decision packet combining methods for different placement of the source, the relay node and the destination. Packet combining can in general be improved with knowledge of the current channel state information, which, however, is often not available. In this paper we find a packet combining method which does not use channel state information but which delivers similar performance as the scheme that has knowledge of the channel state.

Network coding has recently been applied to wireless networks and has achieved some initial success. Researches in wireless network coding have been mostly focusing on utilizing the broadcast nature of the wireless networks. In this paper, we propose a novel network coding framework for wireless relay networks that also takes into consideration the fading and error prone nature of the wireless networks. First, we extend the traditional network coding in lossless networks which operates on 0-1 bits, to a new framework which defines network coding on the posterior probability of each bit. This new framework allows an imperfect decode-recode process at a relay node and avoids possible error propagation when a hard decision is made at the relay node. It implicitly integrates decode-and-forward and estimate-and-forward strategies for wireless network coding to address the technical issues of channel fading and transmission errors. The proposed approach is validated through both theoretical analysis and extensive simulations. Both analysis and simulation confirm that this new framework is able to achieve significant gain over traditional network coding. This new framework also enables the introduction of adaptive scheme into network coding. We demonstrate a basic adaptation scheme and present some preliminary experimental results. The proposed adaptive scheme will lay down an essential foundation in this emerging field of wireless network coding in order to address issues related to link heterogeneity.

In this paper, we consider cooperative beamforming in an amplify-and-forward (AF) cooperative network with multiple relay nodes. Specially, only "appropriate" relay nodes are selected to perform cooperative beamforming. Source node can determine the relay nodes with just mean channel gain, which will reduce the complexity of obtaining instantaneous channel state information (CSI). This scheme guarantees that the energy is allocated to those "appropriate" relay nodes, and accordingly improves the energy efficiency. Therefore, it is able to provide superior diversity over the conventional cooperative beamforming. We also prove that power allocation (PA) between source and selected relay nodes is a convex problem, which can be resolved with lower computational complexity. Simulation results demonstrate that our scheme achieves an essential improvement in terms of outage performance, as well as high energy-efficiency for energy-constrained networks.

In MIMO-OFDM communications, the channel state information (CSI) of the forward link is needed for precoder design at the transmitter to achieve the maximal performance gains. In frequency division duplex (FDD) systems, the CSI estimated at the receivers needs to be fed back to the transmitters. Because of the limited network resources, there will be CSI feedback errors due to quantization, delay and clustering (where one CSI feedback is used to represent a cluster of adjacent subcarriers for feedback reduction). Consequently, the system performance degrades and the gains expected from using MIMO diminish. To mitigate this performance degradation, an adaptive codebook-based CSI prediction and interpolation scheme is proposed for multiuser MIMO-OFDM systems. In this scheme, geodesic CSI prediction is employed at the receiver to mitigate the feedback delay and geodesic CSI interpolation is performed at the transmitter to mitigate the cluster feedback effect. Since the performance gain assumed by the CSI prediction and interpolation is limited by the low resolution CSI quantization, a simplified adaptive codebook is developed to support the CSI prediction and interpolation. Simulation results show that the proposed scheme is effective in mitigating the performance loss due to quantization, feedback delay and cluster feedback.

The feasibility of implementing non-orthogonal multiple access (NOMA) in massive multiple-input multiple-output (MIMO) downlink with distributed antenna arrays is investigated. The achievable downlink rates are derived for two channel state information (CSI) cases, namely (i) estimated uplink CSI at the access points (APs) via user uplink pilots and statistical CSI at the users, and (ii) estimated uplink CSI at the APs via uplink user pilots and estimated downlink CSI at the users via downlink pilots beamformed by the APs. The trade-off between the number of served user nodes and their achievable rates is investigated. The adverse effects of imperfect successive interference cancellation (SIC) and detection uncertainty on the achievable downlink rates are quantified. We show that the achievable downlink rate of NOMA can be inferior to that of the orthogonal multiple-access (OMA) counterpart in the low-user regime. This is a direct consequence of residual interference caused by intra-cluster pilot contamination and error propagation from imperfect SIC. However, the proposed massive MIMO NOMA downlink outperforms the OMA counterpart in the highuser regime in terms of the achievable downlink rate. Moreover, the impact of downlink pilots on the sum rate is also investigated.

To rely on data transmission in low bit rate regime, more protection is required against the channel errors. In video communication over such a regime, a robust and reliable system is needed, which adapted itself matching to the variations of the channel. In this paper we propose to employ joint source and channel coding for video transmission to yield optimal channel and source code rate according to Channel State Information (CSI) at transmitter. Through the employing this technique, transmitter not only sends the video signal but also transmits side information (SI) to the receiver. Also receiver sends the CSI via feedback to the transmitter. Both CSI and SI are contained very important information therefore more protection should be applied. We propose a bi-directional relay model in which CSI and SI are available at the relay node. We evaluate the proposed scheme over Rayleigh fading channel. Results demonstrate the efficiency of the proposed scheme.

Optimal power allocation (OPA) schemes for amplify-and-forward (AAF) relay networks have been widely investigated in recent years, usually under the assumption of readily known channel state information (CSI). This paper proposes a semi-blind iterative relay node selection (SBIRS) scheme to carry out the OPA procedure when the CSI are entirely unknown at the destination. We first develop a semi-blindly weighted multiple-eigenvector (SBWMEV) solution for optimally allocating power among all the relay nodes in the network. Aided by the intrinsic salient feature of the SBWMEV eigenvector structure, we further propose an iterative relay selection algorithm to simplify the SBWMEV solution with enhanced performance. In an iterative relay node selection manner, the proposed SBIRS scheme is capable of potentially allocating more power to the relay nodes with better channel conditions. Simulations verify that the SBIRS schemes outperform the SBWMEV scheme in terms of throughput and outage probability.

The impact of channel estimation errors is investigated in two-way relay networks (TWRNs) with two different channel state information (CSI) estimation schemes, namely separate and cascaded. In the former scheme, the relay node is chosen in accordance with the CSI of the individual channels between the source nodes and the relay node. By contrast, in the latter scheme, relay node selection is performed in accordance with the CSI of the cascaded channel between the two source nodes. For both estimation schemes, the effect of the CSI estimation error on the outage probability is examined by means of the Cramer–Rao lower bound. Moreover, in contrast to previous studies, the source nodes in the TWRN are assumed to have different estimation errors. The numerical results confirm the validity of the derived expressions and show that the presence of different estimation errors at the two source nodes has a significant effect on the performance of the TWRN.

In this paper, a physical-layer network coding (PNC) method is offered for a two-way relay network with spatial modulation (SM) for source node and relay node. For this purpose, we consider a two-way relay network consists of a single relay node and two source nodes both equipped with multiple antennas. It includes two source nods for transferring the data through SM and also, the relay node for decrypting coded packet network (through the XOR) of two packets received from the source node. In the proposed method, the signal detection approach with maximum-likelihood for the PNC with SM modulation is used for relay nodes. The simulation results show that the bit error rate (BER) in the relay node of the proposed method is significantly improved compared to the conventional method PNC; while the data rate is based on the same BER. It is worth mentioning that the performance of the proposed method, when the number of antenna nodes rises, is significant. And it leads to increase in the data rate which indicates that the proposed method will be much convenient for the next generation of wireless communication systems, especially the fifth generation. It should also be said that the suggested SM-based PNC method, does not need channel state information at transmitter. So it can be easily implemented in practice.

We present a flexible class of stochastic models that are developed for cooperative wireless relay networks systems, in which the relay processing functionality is not known at the destination. The challenge is then to perform system identification in this wireless relay network. We first construct a statistical model based on a representation of the system using Gaussian Processes. We then develop a computationally efficient algorithm which is based on the Iterated Conditioning on the Modes estimation to undertake system identification for each relay in the presence of partial Channel State Information (CSI). We evaluate the identification performance for different non-linear relay functionalities.

In the last 2 years, all-optical relaying techniques for free-space optical (FSO) communications have drawn considerable attention. In this study, the outage performance of an FSO communication system with parallel all-optical relays is investigated. A composite channel is established, which includes atmospheric loss, pointing error and atmospheric turbulence. To show the impact of the channel state information (CSI) on system performance, either full CSI or semi-blind CSI at the relay nodes is considered. After that, the theoretical expressions of the outage probabilities for different scenarios are derived. Numerical results show that the derived expressions are quite accurate to evaluate the system performance. Moreover, the derived results demonstrate that the systems with semi-blind CSI relaying can provide comparable performance to systems with full CSI relaying, and also indicate that the performance over strong turbulence channels with clear weather outperforms that over weak turbulence channels with light fog.