Distributed Space-time Coding Research Articles

Selective-Fading Multiple-Access MIMO Channels: Diversity-MultiplexingTradeoff and Dominant Outage Event Regions

We establish the optimal diversity-multiplexing (DM) tradeoff for coherent selective-fading multiple-access MIMO channels and provide corresponding code design criteria. As a byproduct, on the conceptual level, we find an interesting relation between the DM tradeoff framework and the notion of dominant error event regions, first introduced in the AWGN case by Gallager, IEEE Trans. IT, 1985. This relation allows us to accurately characterize the error mechanisms in MIMO fading multiple-access channels. In particular, we find that, for a given rate tuple, the maximum achievable diversity order is determined by a single outage event that dominates the total error probability exponentially in SNR. Finally, we examine the distributed space-time code construction proposed by Badr and Belfiore, Int. Zurich Seminar on Commun., 2008, using the code design criteria derived in the present paper.

Generalized UAV Selection With Distributed Transmission Policies

Unmanned aerial vehicle (UAV)-aided communications is a promising emerging technology that will be adopted in the next generation communication networks. In this paper, a number of advanced cooperative UAV-aided communication solutions is proposed and evaluated, which considerably improve the performance of traditional terrestrial networks. Specifically, two generalized multi-UAV-selection schemes are introduced, depending on whether a direct link between the source and the destination is available or not. Once the UAVs have been selected, they may retransmit the source message to the destination using distributed space-time coding, or, in the presence of channel state information, distributed beamforming. A number of metrics to evaluate the performance on a realistic channel model was adopted, including the end-to-end outage probability (OP), the so-called goodput, and the average number of path estimations, as well as the total UAV communications power consumption. Exact expressions for the OP were obtained in terms of finite sums. Moreover, convenient closed-form expressions for the asymptotic OP were derived, valid for large numbers of UAVs, which are also very accurate for few UAVs. All results were compared with numerical simulations, which clearly depict the performance improvement induced by the proposed schemes as well as the impact of various system and channel parameters to the performance.

Regional Financial Economic Data Processing Based on Distributed Decoding Technology

To improve the effect of regional financial and economic data processing, this study combines the distributed decoding technology to construct the regional financial data processing system. Furthermore, this study combines the technical characteristics of cooperative communication and unitary space-time codes to design a non-differential distributed space-time code based on cyclic unitary matrix groups. In addition, this study uses the particularity of trigonometric functions to design a non-differential distributed space-time code based on trigonometric functions. Finally, according to the characteristics of the distributed space-time code of trigonometric functions, this study obtains a decoding algorithm with low decoding complexity and uses MATLAB to conduct simulation experiments to verify the financial data processing and economic analysis effect of the system in this study. The experimental analysis results show that the regional financial and economic data processing system based on distributed decoding technology proposed in this study can play an important role in the analysis of financial and economic data.

Power Allocation for Self-Coded Distributed Space-Time Codes in FD Two-Way Relaying Networks

In this paper, a power allocation space-time coding scheme based on the self-coding property of residual loop interference (RLI) for two-way full-duplex (FD) amplify-and-forward (AF) relaying networks is proposed. The relay and direct link cooperate to forward the received signals to destination node, forming the self-coded distributed space-time code, in which the relay performs self-coding using the RLI after implementing some self-interference cancellation techniques. Then, an iterative power allocation algorithm is presented. With the proposed power allocation algorithm, both amplifying factor and transmit powers of terminal nodes are jointly optimized to maximize the smaller signal-to-interference-plus-noise ratio (SINR) of terminal nodes under a total power constraint when estimated instantaneous channel state information is available. We theoretically demonstrate the benefits of the proposed power allocation algorithm compared to equal power allocation. Simulation results show that the proposed scheme achieves significant improvement in performance compared with existing schemes for FD relaying systems and half-duplex relaying systems.

Joint design of beamforming and time switching/power splitting for wireless-powered multi-antenna dual-relay network

In this paper, we consider a wireless-powered dual-relay network consisting of one multi-antenna source, two single-antenna energy-constrained relays and one single-antenna destination without direct source to destination link. In order to establish the communication flow, the energy-constrained relays harvest energy from the radio frequency transmitted by the source firstly, then exploit the harvested energy to forward the source information to the destination based on distributed space time coding (DSTC). Under this network architecture, three decode-and-forward (DF) technique-based relaying protocols, i.e., time switching-based relaying (TSR) protocol, power splitting-based relaying (PSR) protocol, and hybrid relaying (HR) protocol, are considered to drive the energy transfer and information transmission. To maximize the network throughput, the joint design for the optimal energy and information beamforming vectors employed at the source, the optimal time switching, and power splitting ratios under these three protocols are investigated and solved efficiently by employing simple sequential optimization approach or alternating optimization approach. Simulations are conducted to show the superior performance achieved by our proposed scheme. Moreover, we find that the TSR protocol outperforms the PSR protocol in the low signal-to-noise ratio (SNR) region, while the latter outperforms the former in the high SNR region. And the HR protocol achieves the best performance in any SNR region. At the same time, the effect of the relays’ locations on the throughput performance of these three protocols is also investigated.

Diversity‐multiplexing tradeoff analysis in cooperative wireless networks with a multiple‐antenna relay

Multiple antennas can be used for increasing the amount of diversity or number of degrees of freedom in wireless communication systems. In this study, the authors consider a wireless half-duplex relay network consisting of one source–destination pair each with a single antenna and one relay with multiple antennas. They assume an approach where cooperation of the relay in the transmission depends on the decoding status at the relay. If the relay participates in transmission, the source and the relay use the distributed space-time code simultaneously. They derive the outage probability and the diversity-multiplexing tradeoff for the proposed protocol at high SNR. They have shown that the use of the centralised antennas with simultaneously decoding compared to the distributed antennas with independently decoding can improve the system performance.

New beamforming and space‐time coding for two‐path successive decode and forward relaying

Successive relaying is a bandwidth-efficient scheme in cooperative networks. In this study, a novel distributed space-time coding (DSTC) transmission scheme for a two-path successive relay network is proposed that enjoys threshold-based selection relaying protocol. A new beamforming method is also employed alongside the proposed DSTC transmission scheme. Three scenarios are considered in this study. In the first scenario, single-input–single-output (SISO) relays are considered. In the second and third scenarios, multiple-input–multiple-output (MIMO) relays are used, but in the second case a transmission scheme named as quasi-DSTC scheme alongside employing space-time coding at each relay is proposed. A closed-form expression for the end-to-end bit error rate (BER) of the system is derived and it is shown that regardless of the fading in inter-relay channel, the proposed scheme achieves full diversity order even when there are decoding errors at the relay nodes. Simulation results show a significant saving in power of about 2.5, 3, and 4 dB at BER ( 10 − 4 ) compared with other conventional methods in the case of using SISO relays, MIMO relays in the second and third scenarios, respectively.

Delay-tolerant distributed space-time coding with feedback for cooperative MIMO relaying systems

An adaptive delay-tolerant distributed space-time coding (DSTC) scheme equipped with a feedback channel is proposed for two-hop cooperative multiple-input multiple-output (MIMO) networks. A maximum likelihood receiver and adjustable code matrices subject to a power constraint with a decode-and-forward cooperation strategy are considered with different DSTC antenna configurations. In the proposed delay-tolerant DSTC schemes, an adjustable code matrix is employed to transform the space-time coded matrices at the relay nodes. Stochastic gradient and least squares algorithms are also developed with reduced computational complexity. The proposed algorithms are then extended to a cooperative MIMO system using amplify-and-forward strategy and opportunistic relaying algorithms in order to develop a delay-tolerant coding scheme combined with optimal relay selection strategies. An upper bound on the pairwise error probability and a rank criterion analysis are derived which indicate the advantage of the proposed algorithms. Simulation results show that the proposed algorithms obtain significant performance gains and address the delay issue in cooperative MIMO systems as compared to existing DSTC schemes.

Dual Relay Selection for Cooperative NOMA With Distributed Space Time Coding

We consider a two-user multi-relay cooperative non-orthogonal multiple access (NOMA) network with distributed space–time coding. Two dual-relay selection strategies are proposed for cooperative NOMA, namely, two-stage dual relay selection with fixed power allocation (DRS-FPA) and two-stage dual relay selection with dynamic power allocation (DRS-DPA). Furthermore, lower and upper bounds on the outage probability for the DRS-FPA scheme and the exact outage probability for the DRS-DPA scheme are obtained in closed-form, respectively. Numerical results show that the proposed two-stage DRS schemes not only yield better outage performance than the existing single relay selection schemes without sacrificing spectral efficiency, but can also achieve full diversity gain.

Distributed Space-Time Coding Based on the Self-Coding of RLI for Full-Duplex Two-Way Relay Cooperative Networks

In this paper, we consider full-duplex two-way relay cooperative networks, which allow the relaying of communications in both directions simultaneously and over the same frequency band. We propose a self-coded distributed space-time coding (SC-DSTC) scheme, in which the relay node performs a self-convolutional encoding and forms a distributed linear convolutional space-time code together with the direct link. The self-convolutional code at the relay is realized by using the stronger part of residual loop interference. The encoding process is implemented for both directions simultaneously through the local loop channel by a single amplifying factor, which is optimized when the loop channel information is imperfect. The simulation results show that the proposed SC-DSTC scheme can achieve asynchronous full cooperative diversity and is robust to the loop channel state information error at the relay when it is dominant among the interference and noise.

Effectiveness and Relay Efficiency of Opportunistic Multipoint Relaying on Cooperative ARQ

This paper studies the effectiveness and relay efficiency of using opportunistic multipoint relaying and distributed space-time coding (ODSTC) for cooperative Automatic Repeat reQuest (ARQ). According to the complexities for diversity exploration in retransmissions, three types of ARQ protocols are studied herein, allowing us to examine the effectiveness of the protocols and the efficiencies of using ODSTC relaying for ARQ. The efficiency is studied from the viewpoint of the signal quality enhancement per active relay, while the effectiveness is investigated from the perspectives of diversity and throughput improvements with the different protocols. The results show that both are closely related to the link qualities of the forwarding channels. When the link quality between the source and relays is considerably higher than the quality between the relays and the destination, a simple protocol that opportunistically chooses two active relays for ODSTC (ODSTC2) at the beginning of retransmissions is good enough to yield a significant throughput improvement. Otherwise, when the performance is limited by the number of successfully decoding relays, then having relays of unsuccessful decoding to overhear the signals sent by active relays plays a crucial role in resolving the limitation. By having the new successfully decoding relays to participate in the subsequent retransmissions, both diversity and throughput can be significantly improved. According to our analysis and simulation studies, an appropriate protocol with ODSTC2 in general can provide effective throughput improvements in two times retransmissions.

Distributed space-time coding scheme with differential detection and power allocation for cooperative relay network

By introducing orthogonal space-time coding (STC) scheme in wireless cooperative relay network, two distributed differential STC (DSTC) schemes based on the amplify-and-forward (AF) and decode-and- forward (DF) methods are, respectively, developed. The scheme performance is investigated in symmetric and asymmetric wireless relay networks. The presented schemes require no channel information at both relay terminals and destination terminal, and have linear decoding complexity when compared with the existing scheme. Moreover, they are suitable for the application of different constellation modulations and DSTC schemes, and thus provide more freedoms of design. Besides, the power allocations between source and relay terminals are jointly optimized to minimize the system pairwise error probability for symmetric and asymmetric networks, and two practical methods are presented to solve the complicated optimized problem from asymmetric network. Simulation results show that the scheme with DF method has better performance than that with AF method due to no amplification of noise power, but the performance superiority will decrease at high SNR due to the error propagation of decoding at the relays. Furthermore, the distributed DSTC schemes with optimal power allocation have better performance than those with conventional fixed power allocation.

Diversity-multiplexing Tradeoff of Opportunistic Relaying Coded Cooperation and Distributed Space-time Coding Coded Cooperation

In this paper, we analyze the diversity-multiplexing tradeoff (DMT) performance of opportunistic relaying coded cooperation (ORCC) and distributed space-time coding coded cooperation (DSTCCC) with arbitrary number of relays. Exact DMT curves are derived for two scenarios, i.e., when the source is included in cooperation (denoted by S1) or not (denoted by S2), by formulating the problem as linear optimization problem. The DMT curves of ORCC and DSTCCC are found to be identical for S1 (or S2), and S1 has better DMT performance than S2. Numerical results are provided to illustrate the analysis as well.

Buffer-aided distributed space-time coding schemes and algorithms for cooperative DS-CDMA systems

In this work, we propose buffer-aided distributed space-time coding (DSTC) schemes and relay selection algorithms for cooperative direct-sequence code-division multiple access (DS-CDMA) systems. We first devise a relay pair selection algorithm that can exploit all possible relay pairs and then select the optimum set of relays among both the source-relay phase and the relay-destination phase according to the signal-to-interference-plus-noise ratio (SINR) criterion. Multiple relays equipped with dynamic buffers are then introduced in the network, which allows the relays to store data received from the sources and wait until the most appropriate time for transmission. A greedy relay pair selection algorithm is then developed to reduce the high cost brought by the exhaustive search that is required when a large number of relays are involved in the transmission. The proposed techniques effectively improve the quality of the transmission with an acceptable delay as the buffer size is adjustable. An analysis of the computational complexity of the proposed algorithms and the delay and a study of the greedy algorithm are then carried out. Simulation results show that the proposed dynamic buffer-aided DSTC schemes and algorithms outperform prior art.

Adaptive Buffer-Aided Distributed Space-Time Coding for Cooperative Wireless Networks

This work proposes adaptive buffer-aided distributed space-time coding schemes and algorithms with feedback for wireless networks equipped with buffer-aided relays. The proposed schemes employ a maximum likelihood receiver at the destination, and adjustable codes subject to a power constraint with an amplify-and-forward cooperative strategy at the relays. The adjustable codes are part of the proposed space-time coding schemes and the codes are sent back to relays after being updated at the destination via feedback channels. Each relay is equipped with a buffer and is capable of storing blocks of received symbols and forwarding the data to the destination if selected. Different antenna configurations and wireless channels, such as static block fading channels, are considered. The effects of using buffer-aided relays to improve the bit error rate (BER) performance are also studied. Adjustable relay selection and optimization algorithms that exploit the extra degrees of freedom of relays equipped with buffers are developed to improve the BER performance. We also analyze the pairwise error probability and diversity of the system when using the proposed schemes and algorithms in a cooperative network. Simulation results show that the proposed schemes and algorithms obtain performance gains over previously reported techniques.

Wireless Information and Power Transfer for Multirelay-Assisted Cooperative Communication

In this paper, we consider simultaneous wireless information and power transfer (SWIPT) in multi-relay assisted two-hop relay system, where multiple relay nodes simultaneously assist the transmission from source to destination using the concept of distributed space-time coding. Each relay applies power splitting protocol to coordinate the received signal energy for information decoding and energy harvesting. The optimization problems of power splitting ratios at the relays are formulated for both decode-and-forward (DF) and amplify-and-forward (AF) relaying protocols. Efficient algorithms are proposed to find the optimal solutions. Simulations verify the effectiveness of the proposed schemes.

A Strategy for Improvement of Distributed Space Time Coding Gain in Cooperative Wireless Networks

A Strategy for Improvement of Distributed Space Time Coding Gain in Cooperative Wireless Networks

ML and MAP channel estimation for distributed one-way relay networks with orthogonal training

In this letter, we investigate the individual channel estimation for the classical distributed-space-time-coding (DSTC) based one-way relay network (OWRN) under the superimposed training framework. Without resorting to the composite channel estimation, as did in traditional work, we directly estimate the individual channels from the maximum likelihood (ML) and the maximum a posteriori (MAP) estimators. We derive the closed-form ML estimators with the orthogonal training designing. Due to the complicated structure of the MAP in-channel estimator, we design an iterative gradient descent estimation process to find the optimal solutions. Numerical results are provided to corroborate our studies.

Time Varying Channel Estimation for DSTC-Based Relay Networks: Tracking, Smoothing and BCRBs

In this paper, we examine the channel estimation in an amplify-and-forward (AF) one-way relay network (OWRN) under time selective flat fading scenario, where the distributed space-time coding (DSTC) is adopted at relay nodes. Different from most existing works, our target is to estimate and track the individual channels of each relay hop instead of the composite channels. To reduce the number of the channel parameters to be estimated, we apply the polynomial basis-expansion-model (P-BEM) and convert the problem to estimating the channel coefficient-vectors (called in-BEM-CVs) of each relay hop. With the aid of the autoregressive (AR) model, we formulate the dynamic state space for the in-BEM-CV estimation. Specifically, we adopt the unscented Kalman filter (UKF) to track the in-BEM-CV dynamic variations in an forward manner, and utilize the unscented Rauch-Tung-Striebel smoother (URTSS) to smooth the UKF's estimations in an backward manner. To make the study complete, we also derive Bayesian Cramer lower bounds (BCRBs) for the in-BEM-CV estimation. Finally, numerical results are provided to corroborate the proposed studies.

Wireless Video Multicast With Cooperative and Incremental Transmission of Parity Packets

In this paper, a cooperative multicast scheme that uses Randomized Distributed Space Time Codes (R-DSTC), along with packet level Forward Error Correction (FEC), is studied. Instead of sending source packets and/or parity packets through two hops using R-DSTC as proposed in our prior work, the new scheme delivers both source packets and parity packets using only one hop. After the source station (access point, AP) first sends all the source packets, the AP as well as all nodes that have received all source packets together send the parity packets using R-DSTC. As more parity packets are transmitted, more nodes can recover all source packets and join the parity packet transmission. The process continues until all nodes acknowledge the receipt of enough packets for recovering the source packets. For each given node distribution, the optimum transmission rates for source and parity packets are determined such that the video rate that can be sustained at all nodes is maximized. This new scheme can support significantly higher video rates, and correspondingly higher PSNR of decoded video, than the prior approaches. Three suboptimal approaches, which do not require full information about user distribution or the feedback, and hence are more feasible in practice are also presented. The proposed suboptimal scheme with only the node count information and without feedback still outperforms our prior approach that assumes full channel information and no feedback.