Relay Communication System Research Articles

Destination Assisted Jamming and Beamforming for Improving the Security of AF Relay Systems

In this paper, we propose a destination-assisted jamming and beamforming (DAJB) scheme for physical layer security in a one-way cooperative amplify-and-forward (AF) relay communication system. The system model consists of one source, one destination, one eavesdropper, and N relay nodes, with the individual power constraint of each relay node and the destination-assisted jamming node as well as unknown instantaneous channel state information (CSI) of the eavesdropper. Due to the half-duplex constraint of the relay nodes, there are two phases in our proposed DAJB scheme. In the first phase, the source node broadcasts information signal and all N relay nodes listen simultaneously. In the meantime, the destination node transmits the jamming signal to confuse the potential eavesdropper. In the second phase, all N relay nodes amplify and forward the received signals, covered by the artificial noise (AN), to the destination using the distributed beamforming technology. The optimal beamformer weights and power allocation are obtained by solving the second-order convex cone programming (SOCP) together with a linear programming (LP) problem. Furthermore, the performance of the DAJB scheme is analyzed in terms of the achievable secrecy rate. Compared with the scheme that selects a relay node as the jammer, we obtain larger power gain to achieve higher secrecy rates. Finally, the simulation results verify that the DAJB scheme greatly improves the secrecy rate of a one-way cooperative AF relay communication system.

Precoding Design of MIMO Amplify-and-Forward Communication System With an Energy Harvesting Relay and Possibly Imperfect CSI

In this paper, we investigate the simultaneous wireless information and power transfer (SWIPT) in a multiple-input multiple-output (MIMO) amplify-and-forward relay communication system, where the relay is an energy harvesting (EH) node and harvests the energy the signals transmitted from the source. The harvested energy is partially used to forward signals from the source to the destination, and the remaining energy is stored for other usages. The SWIPT in relay-assisted communication is interesting as long as the relay stores energy from the source and the destination receives successfully the data from the source. In this context, we propose to investigate the source and relay precoders that characterize the relationship between the achievable stored energy at the relay and the achievable source-to-destination rate, namely, the rate-stored energy (R-E) tradeoff region. First, we consider the ideal scheme, where there is the simultaneous operation of the EH and information decoding (ID) receivers at the relay. Then, we consider practical schemes, such as the power splitting and the time switching that separate the operation of EH and ID receivers over power domain or time domain, respectively. Moreover, we study the case of imperfect channel state information at the relay and the destination, and characterize its impact on the achievable R-E region. Through the simulation results, we show the effect of the position of the relay and the channel uncertainty on the achievable R-E regions of all the schemes when the used energy at the relay is constant or variable. We also show that, although it provides an outer bound on the achievable rate-energy region in one-hop MIMO systems, the ideal scheme provides only an upper bound on the maximum achievable end-to-end rate and not an outer bound on the R-E region.

Channel Estimation of MIMO Relay Systems With Multiple Relay Nodes

In this paper, we consider the channel estimation problem for multiple-input multiple-output wireless relay communication systems with multiple relay nodes. In particular, all individual channel matrices of the first-hop and second-hop links are estimated at the destination node by applying the superimposed channel training algorithm, where training sequences are superimposed at the relay nodes to assist the estimation of the relays-destination channel matrices. To improve the performance of channel estimation, we consider the estimation error inherited from the second-hop channel estimation and develop a new minimal mean-squared error-based algorithm to estimate the first-hop channel matrices. Furthermore, we derive the optimal power allocation and training sequences at the source and relay nodes. Numerical examples demonstrate a better performance of the proposed superimposed channel training algorithm.

Stochastic Polynomial Decomposition-Based Energy-Efficient Hybrid DLT Codes

Forward error correction codes are commonly adopted in dual-hop relay communications, among which Luby transform (LT) codes are favorable because of their low-complexity decoder and rate adaptability to erasure channels. To alleviate the high computational cost in the primitive LT-based cooperative communications, hybrid decomposed LT (h-DLT) codes are proposed recently. By dispersing the computational cost of LT codes into the source and the relay, the computational cost of both nodes can be reduced considerably. However, there are some practical limitations. First, the nonnegative decomposition algorithm developed for h-DLT codes construction has no control of decomposition accuracy. Second, the cooperative relay communication protocol based on the original h-DLT codes can induce high communication cost. In this paper, we propose a stochastic nonnegative polynomial decomposition algorithm, which achieves robust decomposition and higher decomposition accuracy for h-DLT codes construction. Based on the new algorithm, a new type of h-DLT codes is proposed for cooperative relay communications with higher energy efficiency. Simulations are conducted to manifest the performance of the new h-DLT codes and benefits of the corresponding cooperative relay communication system. In addition, multiple design factors are investigated.

Development and Testing of a Two-UAV Communication Relay System.

In the development of beyond-line-of-sight (BLOS) Unmanned Aerial Vehicle (UAV) systems, communication between the UAVs and the ground control station (GCS) is of critical importance. The commonly used economical wireless modules are restricted by the short communication range and are easily blocked by obstacles. The use of a communication relay system provides a practical way to solve these problems, improving the performance of UAV communication in BLOS and cross-obstacle operations. In this study, a communication relay system, in which a quadrotor was used to relay radio communication for another quadrotor was developed and tested. First, the UAVs used as the airborne platform were constructed, and the hardware for the communication relay system was selected and built up. Second, a set of software programs and protocol for autonomous mission control, communication relay control, and ground control were developed. Finally, the system was fully integrated into the airborne platform and tested both indoor and in-flight. The Received Signal Strength Indication (RSSI) and noise value in two typical application scenarios were recorded. The test results demonstrated the ability of this system to extend the communication range and build communication over obstacles. This system also shows the feasibility to coordinate multiple UAVs’ communication with the same relay structure.

Performance of a bi-directional relaying system with one full duplex relay

Full duplex communication system has the potential to double the spectral efficiency compared to traditional half duplex communication system. However self interference in full duplex relay is considered as the major concern to the performance of system. In this paper, performance of two way relaying communication system is studied with a full duplex relay. Specifically, the probability density function (PDF) of the signal-to-interference-plus-noise ratio (SINR) is derived. By using the derived PDF, closed form expressions for average bit error rate (BER) is derived for various binary modulation schemes such as, coherent binary phase shift keying (BPSK), differential BPSK, coherent binary frequency shift keying (BFSK), and non-coherent BFSK. Moreover, the ergodic capacity of the considered system is also analyzed.

Thỏa hiệp phẩm chất BER-độ phức tạp trong các hệ thống chuyển tiếp vô tuyến MIMO-SDM-AF sử dụng tách tín hiệu kết hợp rút gọn dàn

Relay communication systems have attracted great attention recently due to their advantages in coverage extension, improved signal quality as well as increased end-to-end throughput. In the multiple-input multiple-output (MIMO) spatial-division multiplexing (SDM) amplify-and-forward (AF) relay communication systems, the bit error rate (BER) performance of the system depends significantly on the signal detector at the destination. However, optimal detectors which provide the minimum BER often require probitive complexity. In order to make it possible for practical implementation, we propose to apply the lattice reduction (LR) to the linear detectors at the destination receiver in order to balance the trade-off between their detection performance and computational complexity. Our analysis shows that the LR-aided (LRA) linear detectors using zero forcing (ZF) and minimum mean square error (MMSE) can achieve signifcant improvement in BER performance over the linear ZF and MMSE detectors while requiring the same complexity order.

Energy-efficient antenna selection in green MIMO relaying communication systems

In existing literature on multiple-input multiple-output (MIMO) relaying communication systems, antenna selection is often implemented by maximizing the channel capacity or the output single-to-noise ratio (SNR). In this paper, we propose an energy efficient low-complexity antenna selection scheme for MIMO relaying communication systems. The proposed algorithm is based on beamforming andmaximizing the Frobenius norm to jointly optimize the transmit power, number of active antennas, and antenna subsets at the source, relaying and destination. We maximize the energy efficiency between the link of source to relay and the link of relay to destination to obtain the maximum energy efficiency of the system, subject to the SNR constraint. Compared to existing antenna selection methods forMIMO relaying communication systems, simulation results demonstrate that the proposedmethod can save more power in term of energy efficiency, while having lower computational complexity.

Discrete-time Gaussian interfere-relay channel

In practical wireless relay communication systems, nondestination nodes are assumed to be idle not receiving signals while the relay sends messages to a particular destination node, which results in reduced bandwidth efficiency. To improve the bandwidth efficiency, we relax the idle assumption of non-destination nodes and assume that non-destination nodes may receive signals from sources. We note that the message relayed to a particular node in such a system gives rise to interference to other nodes. To study such a more general relay system, we consider, in this paper, a relay system in which the relay first listens to the source, then routes the source message to the destination, and finally produces interference to the destination in sending messages for other systems. We obtain capacity upper and lower bounds and study the optimal method to deal with the interference as well as the optimal routing schemes. From analytic results obtained, we find the conditions on which the direct transmission provides higher transmission rate. Next, we find the conditions, by numerical evaluation of the theoretical results, on which it is better for the destination to cancel and decode the interference. Also we find the optimal source power allocation scheme that achieves the lower bound depending on various channel conditions. We believe that the results provided in this paper will provide useful insights to system designers in strategically choosing the optimal routing algorithms depending on the channel conditions.

Laplace Autoregressive Model for Cascaded Systems

System modeling problems, such as the channel of a single-hop relay communication system in a flat-fading environment, require a cascade of two or more autoregressive (AR) processes to capture the entire system characteristics. However, for the purpose of system simulation and parameter estimations, it is more convenient if the entire system is modeled by a single AR model. In this paper, we consider a cascade system whose statistical characteristics of its subsystems is represented by two independent ${p}$ th-order complex Gaussian AR processes, and model it by a single ${p}$ th-order Laplace AR process. In our analysis, we first demonstrate that the marginal probability distribution functions of the real and imaginary components of a system described by a cascade of the two complex Gaussian AR processes are Laplace distributed. Then, to model the cascaded system, we develop a single complex Laplace AR process whose parameters are configured to match other statistical characteristics of the cascaded system. Specifically, we show that the autocorrelation of the developed Laplace AR process satisfies Yule–Walker type of equations and derive the steps for the design of its parameters through autocorrelation matching.

A Random Channel Sounding Decision Feedback Receiver for Two-Way Relay Communication With Pilotless Orthogonal Signaling and Physical-Layer Network Coding

We propose a decision feedback (DFB) receiver at the relay of a two-phase (2P) two-way relay (TWR) communication system that employs pilotless orthogonal modulation (such as frequency-shift keying) in the uplink and physical-layer network coding over finite field in the downlink. The proposed relay receiver is able to attain a performance very close to that of an ideal coherent detector in the presence of time-selective Rayleigh fading and additive white Gaussian noise in the uplinks. It exploits the fact that when the uplink symbols from the users are different, then the fading gains affecting these symbols can be separated and individually tracked at the relay. In essence, the proposed receiver performs random channel sounding although no actual pilots are transmitted. The channel estimates obtained this way can then be subsequently used in a coherent detector to improve the reliability of the relay detected data. To ensure fast convergence, we propose to kick start the DFB receiver using a partial-coherent detector developed earlier by the authors. We compare the performance of the proposed system against a similar 2P-TWR system that employs differential phase-shift keying (DPSK) in the uplink and DFB multiple-symbol differential detection at the relay. We found that the proposed pilotless orthogonal modulation system can actually attain a significantly lower bit error rate (BER) than its DPSK counterpart. For static fading and a BER of $\mbox{10}^{-3}$ , the signal-to-noise ratio (SNR) gap between the two approaches is 1 dB in the binary case and 8 dB in the quaternary case. These gaps increase further with time-selective fading.

Nested Tucker tensor decomposition with application to MIMO relay systems using tensor space–time coding (TSTC)

The aim of this paper is twofold. In a first part, we present a new tensor decomposition that we call Tucker train decomposition or nested Tucker decomposition (NTD). NTD can be viewed as a particular case of tensor-train decomposition recently proposed for representing and approximating high-dimensional tensors in a compact way. NTD of a fourth-order tensor is more specially analysed in terms of parameter estimation and uniqueness issue. In a second part, we show that the use of a tensor space–time coding (TSTC) structure at both the source node and the relay node of a one-way two-hop multi-input multi-output (MIMO) relay communication system leads to a nested Tucker decomposition of the fourth-order tensor formed by the signals received at the destination. Two semi-blind receivers are then proposed for jointly estimating the transmitted information symbols and the two individual relay channels. The first one is iterative, based on a three-step alternating least squares (ALS) algorithm, whereas the second one, denoted 2LSKP, is a closed-form solution based on the LS estimations of two Kronecker products. Two supervised receivers are also derived by using a (short) pilot-assisted closed-form solution for calculating channel estimates. These estimates are exploited either for initializing the ALS receiver or for designing a zero-forcing (ZF) receiver. Extensive Monte Carlo simulation results are provided to demonstrate the performance of the proposed relay system.

Proposal of channel estimation method for wireless two-way relay system of using SFBC MIMO-OFDM technique

In a two-way relay communication system, two user terminals (UTs) can communicate and exchange their information data through a relay station by using two timeslots. To realize the two-way relay communication system, each UT is required to estimate channel frequency responses (CFRs) both for up and down links in two timeslots efficiently which be employed in the demodulation of the other user's information data with frequency domain equalization. To satisfy this requirement, this paper proposes a novel CFR estimation method for the wireless two-way relay communication system of using SFBC MIMO-OFDM technique. The salient feature of proposed CFR estimation method is to employ the maximum likelihood estimation method for the proposed scattered pilot subcarriers assignment which can achieve higher CFR estimation accuracy even in higher time-varying fading channel and when the transmission OFDM signal is sampled by the non-Nyquist rate. In the proposed system, the SFBC technique is also employed for the data subcarriers both for the pilot symbols including data subcarriers and data symbols consisting of all data subcarriers in the frequency axis to improve the bit error rate (BER) performance in the two-way relay system. From the computer simulation results, this paper demonstrates the effectiveness of proposed two-way relay communication system of using SFBC MIMO-OFDM technique. To demonstrate the effectiveness of proposed two-way relay communication system of using SFBC MIMO-OFDM technique, this paper conducts various computer simulations as comparing with the conventional methods in higher time-varying fading channel. From the computer simulation results, this paper confirms that the proposed method even at the non-Nyquist rate can achieve higher channel estimation accuracy evaluated by the normalized mean square error (NMSE) and better BER performances by 5 and 22 times, respectively as comparing with the conventional methods when the normalized Doppler frequency ($$f_dT_S$$fdTS) is $$10^{-2}$$10-2 and the carrier to noise power ratio (C/N) is 25 dB.

Optimal Source and Relay Design for Multiuser MIMO AF Relay Communication Systems With Direct Links and Imperfect Channel Information

In this paper, we propose statistically robust design for multiuser multiple-input multiple-output (MIMO) relay systems with direct source-destination links and imperfect channel state information (CSI). The minimum mean-squared error (MMSE) of the signal waveform estimation at the destination node is adopted as the design criterion. We develop two iterative methods to solve the nonconvex joint source, relay, and receiver optimization problem. Simulation results demonstrate the improved robustness of the proposed algorithms against CSI errors.

Reed Muller coded-cooperative diversity for multiple relays with signal space diversity and MRC reception at the destination

Recently, Reed---Muller (RM) codes have been investigated for half-duplex coded-cooperative relay communication systems. RM coded-cooperative (RMCC) diversity promised considerably low encoding and decoding complexity as compared to its predecessor channel codes. In this paper, we investigate the bit error rate (BER) performance of RMCC diversity for multiple relays operating in half-duplex mode with binary phase shift keying (BPSK) and quadrature amplitude modulation such as 4-QAM. In order to improve the BER performance of 4-QAM modulation, we use well known signal space diversity (SSD) technique in the proposed system. At the destination, maximal ratio combining is used for signal detection and joint majority logic decoding is used to recover information transmitted at the destination. Monte Carlo simulations show that the RMCC diversity gains increase manifolds with inclusion of multiple relays and for higher modulation i.e., 4-QAM, SSD provides additional diversity gains over the conventional 4-QAM system. Theoretical expressions for average BER are also derived and are validated with the help of Monte Carlo simulations.

Simplified MMSE Precoding Design in Interference Two-Way MIMO Relay Systems

We investigate the transceiver design for interference two-way amplify-and-forward multiple-input multiple-output relay communication systems. A novel algorithm with a closed-form solution is developed to optimize the relay precoding matrix based on its optimal structure and a modified transmission power constraint at the relay node. An iterative algorithm is proposed to minimize the sum mean-squared error of the signal waveform estimation. Simulation results demonstrate that the proposed algorithm achieves a better performance-complexity tradeoff compared with existing techniques.

A Novel Semi-blind Receiver Algorithm Based on PARATUCK2 Model in MIMO Relay Communication System

A Novel Semi-blind Receiver Algorithm Based on PARATUCK2 Model in MIMO Relay Communication System

Distributed Linear Constellation Precoding with BICM/BICM-ID in Two-Way Relaying Communications

This paper investigates distributed linear constellation precoding (DLCP) for two-way relaying communication systems in conjunction with the techniques of bit-interleaved coded modulation (BICM) and BICM with iterative decoding (BICM-ID). First, a decoding strategy for the relay node that is based on quaternary code representation is developed. Then, the union bounds (for the case of BICM) and error-free feedback bounds (for the case of BICM-ID) on the quaternary digit error probability and bit error probability under network coding in the multiple-access (MA) phase are obtained. Based on the obtained bounds, the impact of DLCP on the error performance is analyzed by considering three error types in the MA phase. It is shown that type-3 errors need to be carefully taken into account in the design of a DLCP scheme. By developing a performance metric related to type-3 errors, the design parameter of DLCP is optimized when BICM is used, whereas it is shown that DLCP is not needed when BICM-ID is used. Extensive simulation results are provided to corroborate the analysis and demonstrate the performance superiority of the proposed decoding strategy over the one that directly decodes the exclusive-OR ( xor ) code. For the case of BICM, the performance advantage achieved by properly designing DLCP is also illustrated.

A dynamic trajectory control algorithm for improving the communication throughput and delay in UAV-aided networks

Recently, the UAS has been extensively exploited for data collection from remote and dangerous or inaccessible areas. While most of its existing applications have been directed toward surveillance and monitoring tasks, the UAS can play a significant role as a communication network facilitator. For example, the UAS may effectively extend communication capability to disaster-affected people (who have lost cellular and Internet communication infrastructures on the ground) by quickly constructing a communication relay system among a number of UAVs. However, the distance between the centers of trajectories of two neighboring UAVs, referred to as IUD, plays an important role in the communication delay and throughput. For instance, the communication delay increases rapidly while the throughput is degraded when the IUD increases. In order to address this issue, in this article, we propose a simple but effective dynamic trajectory control algorithm for UAVs. Our proposed algorithm considers that UAVs with queue occupancy above a threshold are experiencing congestion resulting in communication delay. To alleviate the congestion at UAVs, our proposal adjusts their center coordinates and also, if needed, the radius of their trajectory. The performance of our proposal is evaluated through computer-based simulations. In addition, we conduct several field experiments in order to verify the effectiveness of UAV-aided networks.

Channel Estimation for Time-Varying MIMO Relay Systems

In this paper, we investigate the channel estimation problem for multiple-input multiple-output (MIMO) relay communication systems with time-varying channels. The time-varying characteristic of the channels is described by the complex-exponential basis expansion model (CE-BEM). We propose a superimposed channel training algorithm to estimate the individual first-hop and second-hop time-varying channel matrices for MIMO relay systems. In particular, the estimation of the second-hop time-varying channel matrix is performed by exploiting the superimposed training sequence at the relay node, while the first-hop time-varying channel matrix is estimated through the source node training sequence and the estimated second-hop channel. To improve the performance of channel estimation, we derive the optimal structure of the source and relay training sequences that minimize the mean-squared error (MSE) of channel estimation. We also optimize the relay amplification factor that governs the power allocation between the source and relay training sequences. Numerical simulations demonstrate that the proposed superimposed channel training algorithm for MIMO relay systems with time-varying channels outperforms the conventional two-stage channel estimation scheme.