Amplify-And-Forward

We consider the remote estimation of a timecorrelated field using an energy harvesting (EH) sensor. The sensor observes the unknown field and communicates its observations to a remote fusion center using an amplify-forward strategy. We consider the design of optimal transmission strategies in order to minimize the mean-square error (MSE) at the fusion center. Contrary to traditional approaches, the degree of correlation between the field values constitutes an important aspect of our formulation. We provide the optimal power allocation strategies for a number of illustrative scenarios, including the circularly wide-sense stationary (c.w.s.s.) signals with static correlation coefficient and the sampled low-pass c.w.s.s. signals. Based on these results, we propose low-complexity policies for the general case. Numerical evaluations illustrate the performance of the optimal and the low-complexity policies.

Two driving goals for cognitive radio (CR) technique are maximizing spectrum utilization and avoiding interference to primary users. In this paper, we deal with the CR concept for legacy primary links optimized for non-interference surroundings. In this type of network, primary destinations are not able to deal with possible interference and a missed cognitive detection significantly reduces the system performance. The enhancement of the primary network with cooperative diversity in addition to the well-known diversity gain for the primary link improves the sensing ability of the system and protects the primary user from possible interference. Both Amplify-Forward (AF) and Decode-Forward (DF) cooperative schemes are studied for the problem under consideration and a new DF policy which introduces a cognitive relay behavior is investigated. The proposed technique provides CR benefits without complicated network modifications and seems to be an attractive solution for future legacy networks with flexibility limitations.

We investigate the performance of the protocols for cooperative communications, such as amplify-forward and decode-forward, in correlated fading channels. Our analytical and simulation results show that correlation can have varied effects on the capacity, compared to the uncorrelated cases. If the quality of the source-destination channel is better, in terms of the variances of the fading coefficients, than that of the source-relay channel, correlation may cause degradation in the capacity. Otherwise, cooperation between terminals in correlated fading channels could offer more capacity than in the uncorrelated scenarios.

We investigate the performance of the protocols for cooperative communications, such as amplify-forward and decode-forward, in correlated fading channels. Our analytical and simulation results show that correlation can have varied effects on the capacity, compared to the uncorrelated cases. If the quality of the source-destination channel is better, in terms of the variances of the fading coefficients, than that of the source-relay channel, correlation may cause degradation in the capacity. Otherwise, cooperation between terminals in correlated fading channels could offer more capacity than in the uncorrelated scenarios.

In this work, joint routing and power allocation problem is formulated in an optimization framework for end-to-end outage minimization under the constraint of total permissible transmission power. A closed form solution for optimal transmission power is obtained following the extraction of routing metric. The scheme is referred as minimum end-to-end outage probability (MEO) strategy. A distributed implementation of the proposed strategy is also presented. Simulation results prove that our proposed MEO routing and power allocation strategy succeeds in achieving significant improvement of end-to-end outage probability over MEO routing and equal power allocation scheme.

The orthogonal space-time block code (OSTBC) and cooperative relaying schemes are the two major spatial diversity techniques to achieve high link reliability in any wireless communication system. Typically, the OSTBC based cooperative amplify-and-forward relaying system achieves optimal diversity gain with simple linear decoding by assuming that the channels remain quasi-static during the length of the Alamouti code-word symbol periods. However, due to time selective fading or relay node's mobility, the quasi-static assumptions does not hold good and causes severe error floor in the system. In this paper, at first, we have investigated various conventional signal detection methods to improve the system performance which include Alamouti and quasi-ML detection (QMLD) methods. Then, we derive the exact closed-form signal-to-interference-plus-noise ratio expression for the Alamouti method and signal-to-noise ratio for the QMLD method. Based on this performance analysis, we propose a decision feedback detection (DFD) which is a hybrid of Alamouti and QMLD methods. The simulation results show that the proposed DFD method significantly outperforms the conventional QMLD method under high mobility channel environment.

The orthogonal space-time block code (OSTBC) and cooperative relaying schemes are the two major spatial diversity techniques to achieve high link reliability in any wireless communication system. Typically, the OSTBC based cooperative amplify-and-forward relaying system achieves optimal diversity gain with simple linear decoding by assuming that the channels remain quasi-static during the length of the Alamouti code-word symbol periods. However, due to time selective fading or relay node's mobility, the quasi-static assumptions does not hold good and causes severe error floor in the system. In this paper, at first, we have investigated various conventional signal detection methods to improve the system performance which include Alamouti and quasi-ML detection (QMLD) methods. Then, we derive the exact closed-form signal-to-interference-plus-noise ratio expression for the Alamouti method and signal-to-noise ratio for the QMLD method. Based on this performance analysis, we propose a decision feedback detection (DFD) which is a hybrid of Alamouti and QMLD methods. The simulation results show that the proposed DFD method significantly outperforms the conventional QMLD method under high mobility channel environment.

A low complexity massive multiple-input multipleoutput (MIMO) technique is studied with a geometry-based stochastic channel model, called COST 2100 model. We propose to exploit the discrete-time Fourier transform of the antenna correlation function to perform user scheduling. The proposed algorithm relies on a trade off between the number of occupied bins of the eigenvalue spectrum of the channel covariance matrix for each user and spectral overlap among the selected users. We next show that linear precoding design can be performed based only on the channel correlation matrix. The proposed scheme exploits the angular bins of the eigenvalue spectrum of the channel covariance matrix to build up an "approximate eigenchannels" for the users. We investigate the reduction of average system throughput with no channel state information at the transmitter (CSIT). Analysis and numerical results show that while the throughput slightly decreases due to the absence of CSIT, the complexity of the system is reduced significantly. cc Index terms-COST 2100 channel model, massive MIMO, MMSE estimation, spatial correlation, user scheduling. I. INTRODUCTION Massive multiple-input multiple-output (MIMO) is a technology which involves an increased number of base station (BS) antennas and users in a multiuser (MU)-MIMO system. To investigate the performance of massive MIMO systems, an accurate multiuser channel model is necessary. Most standardized MIMO channel models such as IEEE 802.11, the 3GPP spatial model, and the COST 273 model rely on clustering [1]. Geometry-based stochastic channel models (GSCMs) consider the physical reality of channels to investigate the performance of MIMO systems using the concept of clusters [2]. The COST 2100 model is a well known GSCM [2], [3].

A low complexity massive multiple-input multipleoutput (MIMO) technique is studied with a geometry-based stochastic channel model, called COST 2100 model. We propose to exploit the discrete-time Fourier transform of the antenna correlation function to perform user scheduling. The proposed algorithm relies on a trade off between the number of occupied bins of the eigenvalue spectrum of the channel covariance matrix for each user and spectral overlap among the selected users. We next show that linear precoding design can be performed based only on the channel correlation matrix. The proposed scheme exploits the angular bins of the eigenvalue spectrum of the channel covariance matrix to build up an "approximate eigenchannels" for the users. We investigate the reduction of average system throughput with no channel state information at the transmitter (CSIT). Analysis and numerical results show that while the throughput slightly decreases due to the absence of CSIT, the complexity of the system is reduced significantly. cc Index terms-COST 2100 channel model, massive MIMO, MMSE estimation, spatial correlation, user scheduling. I. INTRODUCTION Massive multiple-input multiple-output (MIMO) is a technology which involves an increased number of base station (BS) antennas and users in a multiuser (MU)-MIMO system. To investigate the performance of massive MIMO systems, an accurate multiuser channel model is necessary. Most standardized MIMO channel models such as IEEE 802.11, the 3GPP spatial model, and the COST 273 model rely on clustering [1]. Geometry-based stochastic channel models (GSCMs) consider the physical reality of channels to investigate the performance M. Bashar, A. G. Burr, and K. Cumanan are with the

A low complexity massive multiple-input multipleoutput (MIMO) technique is studied with a geometry-based stochastic channel model, called COST 2100 model. We propose to exploit the discrete-time Fourier transform of the antenna correlation function to perform user scheduling. The proposed algorithm relies on a trade off between the number of occupied bins of the eigenvalue spectrum of the channel covariance matrix for each user and spectral overlap among the selected users. We next show that linear precoding design can be performed based only on the channel correlation matrix. The proposed scheme exploits the angular bins of the eigenvalue spectrum of the channel covariance matrix to build up an "approximate eigenchannels" for the users. We investigate the reduction of average system throughput with no channel state information at the transmitter (CSIT). Analysis and numerical results show that while the throughput slightly decreases due to the absence of CSIT, the complexity of the system is reduced significantly. cc Index terms-COST 2100 channel model, massive MIMO, MMSE estimation, spatial correlation, user scheduling. I. INTRODUCTION Massive multiple-input multiple-output (MIMO) is a technology which involves an increased number of base station (BS) antennas and users in a multiuser (MU)-MIMO system. To investigate the performance of massive MIMO systems, an accurate multiuser channel model is necessary. Most standardized MIMO channel models such as IEEE 802.11, the 3GPP spatial model, and the COST 273 model rely on clustering [1]. Geometry-based stochastic channel models (GSCMs) consider the physical reality of channels to investigate the performance of MIMO systems using the concept of clusters [2]. The COST 2100 model is a well known GSCM [2], [3].

Power management strategies are extremely important in Wireless Sensor Networks (WSNs). The objective is to make the nodes operate as long as possible. In the same context, in this article, our aim is to provide the optimal transmission power to maximize the network lifetime using the Orthogonal Multiple Access Channel (OMAC) in Harvesting System (HS). We consider that the nodes have direct communication with a Fusion Center (FC) with causal Channel Side Information (CSI) at the sender and receiver. We begin the analysis by considering a single transmitter node powered by a rechargeable battery with limited capacity energy. Afterward, we generalize the analysis with M transmitter nodes. In both cases, the transmitters are able to harvest energy from nature. Eventually, we show the viability of our approach in simulations results.

This paper addresses the maximizing network lifetime problem in wireless sensor networks (WSNs) taking into account the total Symbol Error rate (SER) at destination. Therefore, efficient power management is needed for extend network lifetime. Our approach consists to provide the optimal transmission power using the orthogonal multiple access channels between each sensor. In order to deeply study the properties of our approach, firstly, the simple case is considered; the information sensed by the source node passes by a single relay before reaching the destination node. Secondly, global case is studied; the information passes by several relays. We consider, in the previous both cases, that the batteries are nonrechargeable. Thirdly, we spread our work the case where the batteries are rechargeable with unlimited storage capacity. In all three cases, we suppose that Maximum Ratio Combining (MRC) is used as a detector, and Amplify and Forward (AF) as a relaying strategy. Simulation resu...

We examine the performance of a dual-hop nonregenerative system with adjustable relay gain, subject to power constraints. An optimization problem is formulated and solved algorithmically for the binary phase-shift keying bit-error rate utility. The model allows for arbitrary channel statistics. Emphasis is placed on the relation between the optimal solutions obtained when observing the channels of either the first or both hops, as well as the comparison with easily implementable heuristic policies. Numerical results indicate that simple heuristics perform well for a wide range of signal-to-noise ratio (SNR), except for certain high-SNR cases. Finally, the effect of independent channel assumption on system performance is evaluated.

This paper analyzes the performance of clustered decode-and-forward multi-hop relaying (CDFMR) wireless Rayleigh fading networks, and sheds light on their design principles for energy and spectral efficiency. The focus is on a general performance analysis (over all SNR range) of heterogeneous wireless networks with possibly different numbers of relays in clusters of various separations. For clustered multi-hop relaying systems, ad-hoc routing is known as an efficient decentralized routing algorithm which selects the best relay node on a hop-by-hop basis using local channel state information. In this article, we combine ad-hoc routing and cooperative diversity in CDFMR systems, and we derive (i) a closed-form expression for the probability distribution of the end-to-end SNR at the destination node; (ii) the system symbol error rate (SER) performance for a wide class of modulation schemes; and (iii) exact analytical expressions for the system ergodic capacity, the outage probability and the achievable probability of the SNR (power) gain. We also provide simple analytical asymptotic expressions for SER and the outage probability in high SNR regime. Simulation results are provided to validate the correctness of the presented analyses.

In this paper, we propose a Cooperative Transmission Strategy using Entropy-based Relay Selection in Mobile Ad-hoc Wireless Sensor Networks (MAWSN) with Rayleigh Fading Environments. The main features and contributions of the proposed cooperative transmission strategy are as follows. First, entropy-based relay selection is used to improve data transmission reliability from a source node to a destination node. Second, we present a theoretical analysis model for the proposed cooperative transmission strategy with the outage probability of the end-to-end performance. The performance of our protocol is evaluated using analysis and simulation.

Systematic Luby Transform (SLT) codes constitute rateless codes, which are capable of adaptively adjusting their code rate depending on the channel quality without explicit channel state information (CSI) at the transmitters. SLTs are also suitable for space-time collaboration aided relay networks. In this paper, an iterative decoding aided SLT scheme is combined with 16-QAM transmission in a wireless relay aided network. The Bit Error Ratio (BER) results and Extrinsic Information Transfer (EXIT) charts are provided to evaluate the performance of the proposed scheme. The simulation results show that the proposed scheme using amplify-and-forward (AF) relaying achieves a 2.5dB gain at a BER of 10 −5 , while the attainable improvement is nearly 6dB for decode-andforward (DF) relaying, compared to the non-cooperative scheme, where the 16-QAM and the SLT decoder work independently. Moreover, the AF relaying aided SLT coded 16-QAM scheme is more beneficial, when the relay station is close to the source. By contrast, the DF relaying performs best near the mid-point between the source and destination. In addition, a modified Hybrid Automatic-Repeat-reQuest (HARQ) protocol using incremental redundancy is applied along with the SLT coded 16-QAM scheme to enhance the achievable throughput and energy efficiency of cooperative networks. This arrangement reduces the total transmit power by about 8%, compared to the classic HARQ scheme.

Hybrid-Automatic-Repeat-reQuest (H-ARQ) has become an indispensable technique in reliable communication systems. Hence, in this paper we review the state-of-art and investigate the performance of H-ARQ in the context of cooperative wireless communications. As a novel advance, we also propose a relay-switching regime based H-ARQ scheme, which is capable of increasing the achievable system throughput as confirmed by both theory and practice. Furthermore, we evaluate the achievable upper-bound performance in the context of perfect Channel State Information (CSI). Then we proceed to quantify the performance erosion imposed by realistic CSIbased-coherent detection as well as low complexity non-coherent detection assisted cooperative H-ARQ. Finally, we propose a general design guidelines for H-ARQ aided cooperative systems.

In a tactical wireless communication environment, it is common for device-to-device communication to occur without a base station, but this can be problematic when the distance between the source and destination is too far. Relays are often used to improve transmission distance and reliability, but amplification-based relaying can result in lower communication performance compared to other methods. This paper proposes a method for obtaining diversity gain through the application of time delay during relaying. The proposed method is compared to a conventional method that uses phase rotation to obtain diversity gain. Simulation results show that the proposed method has slightly lower or similar performance improvement compared to the conventional relay method.

This paper proposes an iterative spatial demapping (ISM) scheme for simultaneous data exchange in three-way relaying systems where each user does not have direct links to the other users. Based on a priori knowledge provided by the decoders, ISM demapper makes the simultaneous data exchange only within two transmission phases by the help of a relay. The proposed structure is very simple since only two 2-state (memory 1) convolutional codes (CC) are used by each user: first CC is with rate-1 as doped accumulator (inner encoder) and the other is with rate-1/2 (outer encoder). The performances are evaluated by computer simulations in additive white Gaussian noise (AWGN) and two cascaded frequency-flat block Rayleigh fading channels. Bit-error-rate (BER) performance results show that clear turbo cliff can be achieved, with a transmit power close enough to the theoretical limit, for each user in AWGN channels. Extrinsic information transfer (EXIT) chart analysis is also presented to evaluate the convergence property of the iterative decoding algorithm. Since the proposed technique is spectrally efficient, it has a plenty of potential applications for future multi-way relaying systems where power and spectrum efficiency as well as energy consumption due to signal processing are of significant importance.

This paper proposes an iterative spatial demapping (ISM) scheme for simultaneous data exchange in three-way relaying systems where each user does not have direct links to the other users. Based on a priori knowledge provided by the decoders, ISM demapper makes the simultaneous data exchange only within two transmission phases by the help of a relay. The proposed structure is very simple since only two 2-state (memory 1) convolutional codes (CC) are used by each user: first CC is with rate-1 as doped accumulator (inner encoder) and the other is with rate-1/2 (outer encoder). The performances are evaluated by computer simulations in additive white Gaussian noise (AWGN) and two cascaded frequency-flat block Rayleigh fading channels. Bit-error-rate (BER) performance results show that clear turbo cliff can be achieved, with a transmit power close enough to the theoretical limit, for each user in AWGN channels. Extrinsic information transfer (EXIT) chart analysis is also presented to evaluate the convergence property of the iterative decoding algorithm. Since the proposed technique is spectrally efficient, it has a plenty of potential applications for future multi-way relaying systems where power and spectrum efficiency as well as energy consumption due to signal processing are of significant importance.

In this paper, we propose a distributed Alamouti space-time code (DASTC) for two-way relay networks employing a single amplify-and-forward (AF) relay. We first derive closedform expressions for the approximated average sum-rate of the proposed DASTC scheme. Our analysis is validated by a comparison against the results of Monte-Carlo simulations. Numerical results verify the effectiveness of our proposed scheme over the conventional DASTC with one-way communication.

Systematic Luby Transform (SLT) codes constitute rateless codes, which are capable of adaptively adjusting their code rate depending on the channel quality without explicit channel state information (CSI) at the transmitters. SLTs are also suitable for space-time collaboration aided relay networks. In this paper, an iterative decoding aided SLT scheme is combined with 16-QAM transmission in a wireless relay aided network. The Bit Error Ratio (BER) results and Extrinsic Information Transfer (EXIT) charts are provided to evaluate the performance of the proposed scheme. The simulation results show that the proposed scheme using amplify-and-forward (AF) relaying achieves a 2.5dB gain at a BER of 10 −5 , while the attainable improvement is nearly 6dB for decode-andforward (DF) relaying, compared to the non-cooperative scheme, where the 16-QAM and the SLT decoder work independently. Moreover, the AF relaying aided SLT coded 16-QAM scheme is more beneficial, when the relay station is close to the source. By contrast, the DF relaying performs best near the mid-point between the source and destination. In addition, a modified Hybrid Automatic-Repeat-reQuest (HARQ) protocol using incremental redundancy is applied along with the SLT coded 16-QAM scheme to enhance the achievable throughput and energy efficiency of cooperative networks. This arrangement reduces the total transmit power by about 8%, compared to the classic HARQ scheme.

Hybrid-Automatic-Repeat-reQuest (H-ARQ) has become an indispensable technique in reliable communication systems. Hence, in this paper we review the state-of-art and investigate the performance of H-ARQ in the context of cooperative wireless communications. As a novel advance, we also propose a relay-switching regime based H-ARQ scheme, which is capable of increasing the achievable system throughput as confirmed by both theory and practice. Furthermore, we evaluate the achievable upper-bound performance in the context of perfect Channel State Information (CSI). Then we proceed to quantify the performance erosion imposed by realistic CSIbased-coherent detection as well as low complexity non-coherent detection assisted cooperative H-ARQ. Finally, we propose a general design guidelines for H-ARQ aided cooperative systems.

In this study, a new energy-efficient hybrid opportunistic cooperative (HOC) transmission protocol is proposed for single-carrier frequency division multiple access (SC-FDMA)-based cooperative networks. The author considers a single source-destination pair and multiple relays network. The proposed protocol improves the energy efficiency of SC-FDMAbased networks by selecting the most energy-efficient cooperative transmission protocol from a set of available protocols according to the current channel state information. The protocols considered in the development of the HOC protocol are amplify-and-forward, decode-and-forward, compress-and-forward and estimate-and-forward. Computer simulation is done over four different scenarios of channel conditions. The obtained results show that the proposed HOC protocol significantly improves the delay-limited capacity and minimises the outage probability of SC-FDMA-based cooperative networks. The results also show that the minimum required average total power in the proposed HOC protocol is less than that of opportunistic decode-and-forward by 0.55 dB.

The symbol error probability (SEP) of amplify-and-forward (AF) multiple-input multiple-output (MIMO) cooperative networks where beamforming is adopted at both the source and destination is investigated. In particular, the tight lower bound for SEP of AF MIMO relay systems is presented with hop-by-hop beamforming over independent, but not necessarily identically distributed, Nakagami-m fading channels. Furthermore, assessing the high SNR, an asymptotic SEP expression is derived which reveals the array and diversity gain. Numerical results are shown to verify the analysis in some representative scenarios.