Time Division Broadcast Research Articles

Joint Resource Allocation in a Two-Way Relaying Simultaneous Wireless Information and Power Transfer System

Simultaneous wireless information and power transfer (SWIPT) technology provides an efficient solution to energy-limited communication terminals in a wireless network. However, in the current application scenario of SWIPT technology, relays use all the collected energy forwarding to assist communication between source nodes, while ignoring the fact that relays can accumulate and store energy. This is of great practical significance in collaborative communication. By using a transmission scheme of a time-division broadcast for the direct transmission link, improvement of the system diversity gain through combining the technology at the receiver can be realized. Based on the above, we propose a two-way relay energy accumulation communication system, which is extended from a single relay system to a multi-relay system. The instantaneous transmission rate of the system link and the system equivalent profit are optimized by jointly optimizing the relay selection, time slot allocation factor, power splitting factor and relay transmit power. Compared with the comparison algorithm, the proposed algorithm shows a significant improvement in the performance of the system.

Sequential Doppler-Shift-Based Optimal Localization and Synchronization With TOA

Doppler shift is an important measurement for localization and synchronization (LAS), and is available in various practical systems. Existing studies on LAS techniques in a time-division broadcast LAS system (TDBS) only use sequential time-of-arrival (TOA) measurements from the broadcast signals. In this article, we develop a new optimal LAS method in the TDBS, namely, LAS-SDT, by taking advantage of the sequential Doppler shift and TOA measurements. It achieves higher accuracy compared with the conventional TOA-only method for user devices (UDs) with motion and clock drift. Another two variant methods, LAS-SDT-v for the case with UD velocity aiding and LAS-SDT-k for the case with UD clock drift aiding, are developed. We derive the Cramér–Rao lower bound (CRLB) for these different cases. We show analytically that the accuracies of the estimated UD position, clock offset, velocity, and clock drift are all significantly higher than those of the conventional LAS method using TOAs only. Numerical results corroborate the theoretical analysis and show the optimal estimation performance of the LAS-SDT.

Performance analysis and optimization of energy harvesting cognitive multi-hop relay network over mixed Rayleigh and double-Rayleigh fading channels

In this paper, we investigate the outage performance of an energy harvesting underlay cognitive multi-hop relay network. In the network, energy-constrained secondary network (SN) nodes harvest energy from radio frequency signal of a power beacon (PB) node. The source node transmits information to destination node via multiple intermediate relay nodes by using a time division broadcast protocol, and the hardware impairments of SN nodes’ transceiver are modeled. The outage performance of SN is analyzed and evaluated by accurately approximate and asymptotic closed-form expressions of outage probability (OP) over quasi-static mixed Rayleigh and double-Rayleigh fading channels. Additionally, due to the complexity of OP expression, a chaotic dragonfly algorithm (CDA) is proposed to jointly optimize energy harvesting ratio and PB node’s abscissa, which can achieve OP minimization of SN. Extensive simulations demonstrate the correctness of theoretical analysis and the effectiveness of the proposed CDA.

Optimal Localization With Sequential Pseudorange Measurements for Moving Users in a Time-Division Broadcast Positioning System

In a time division broadcast positioning system (TDBPS), a user device (UD) determines its position by obtaining sequential time-of-arrival (TOA) or pseudorange measurements from signals broadcast by multiple synchronized base stations (BSs). The existing localization method using sequential pseudorange measurements and a linear clock drift model for the TDPBS, namely LSPM-D, does not compensate the position displacement caused by the UD movement and will result in position error. In this paper, depending on the knowledge of the UD velocity, we develop a set of optimal localization methods for different cases. First, for known UD velocity, we develop the optimal localization method, namely LSPM-KVD, to compensate the movement-caused position error. We show that the LSPM-D is a special case of the LSPM-KVD when the UD is stationary with zero velocity. Second, for the case with unknown UD velocity, we develop a maximum likelihood (ML) method to jointly estimate the UD position and velocity, namely LSPM-UVD. Third, in the case that we have prior distribution information of the UD velocity, we present a maximum a posteriori (MAP) estimator for localization, namely LSPM-PVD. We derive the Cramer-Rao lower bound (CRLB) for all three estimators and analyze their localization error performance. We show that the position error of the LSPM-KVD increases as the assumed known velocity deviates from the true value. As expected, the LSPM-KVD has the smallest position error while the LSPM-PVD and the LSPM-UVD are more robust when the prior knowledge of the UD velocity is limited. Numerical results verify the theoretical analysis on the optimality and the positioning accuracy of the proposed methods.

Achievable Rate Region of Energy-Harvesting Based Secure Two-Way Buffer-Aided Relay Networks

This paper considered an energy-harvesting based secure two-way relay (EH-STWR) network, where two users exchanged information with the assistance of one buffer-aided relay that harvested energy from two users. To realize the confidential message exchange between two users in the presence of a potential eavesdropper, a secure bidirectional relaying scheme based on time division broadcast (TDBC) was proposed, where one user sent artificial noise to suppress the eavesdropper and another user transmitted data to the relay. A secure sum-rate maximization problem was formulated subject to average and peak transmit power constraints, data buffer and energy storage causality, and transmission mode constraints. By employing the Lyapunov optimization framework, a security-aware adaptive transmission scheme was proposed to jointly adapt transmission mode selection, power allocation, and security rate allocation according to channel/buffer/energy state information (CSI/BSI/ESI). Analysis results showed that the average achievable secrecy rate region can be significantly improved and there exists an inherent trade-off among transmission delay, requirement of transmit power consumption, and achievable secure sum-rate. Moreover, the channel condition between the energy-constrained relay and the potential eavesdropper is a critical factor on the achievable long-term average secrecy rate performance.

Multi-Antenna Two-Way Relay Based Cooperative NOMA

In this paper, we investigate a non-orthogonal multiple access (NOMA) assisted multi-antenna two-way relay system, where multi-antenna users apply NOMA to support bidirectional superposition transmission via multiple multi-antenna relays. Specifically, we propose two cooperative strategies, namely multiple-access broadcast NOMA and time division broadcast NOMA. For each of the two cooperative strategies, we devise a joint antenna-and-relay selection scheme to enhance the transmission reliability. Analytical expressions for the outage probability and diversity order are derived to evaluate the system performance achieved by the proposed cooperative strategies with the corresponding joint antenna-and-relay selection schemes. To further reduce the outage probability, we use the derived analytical results as objective functions to optimize the transmit power allocation under both cooperative strategies. Finally, extensive simulations are carried out to validate the accuracy of the derived analytical results. Our simulation results indicate that the proposed strategies significantly outperform existing benchmark strategies in terms of outage probability and diversity order.

Performance of Dynamic Time Division Broadcast Protocol with Rateless Coding

Two-way relaying channel (TWRC) improves the throughput of one-way relaying channel through network coding at the relay. Time division broadcast (TDBC) is one typical protocol for TWRC, but with three time slots for one round information exchange leading to throughput loss. To enhance throughput performance, incremental redundancy transmission is usually incorporated into TDBC (i.e., TDBC-IR) by one bit feedback, indicating the successful or failed transmission. Nevertheless, TDBC-IR still suffers in throughput since it cannot fully exploit and adapt to the varying channel dynamics. In the paper, we propose a dynamic TDBC protocol with incremental redundancy in the form of rateless coding (i.e., DTDBC-RC) to fully utilizing the varying channel dynamics. In DTDBC-RC, the two sources first transmit in rateless coding way with given maximum allowable transmission time, and then the relay retransmits or not based on its decoding results. To reveal the advantages of DTDBC-RC, we analyze its performance comprehensively in terms of outage probability, expected rate, and diversity-multiplexing trade-off (DMT). We also present a subslot realization scheme for DTDBC-RC (i.e., sub-DTDBC-RC) since the DMT of DTDBC-RC cannot be obtained directly. Simulation and numerical results show the performance advantage of DTDBC-RC (or sub-DTDBC-RC) over TDBC-IR in terms of both expected rate and DMT.

Security-Reliability Tradeoff Analysis for Underlay Cognitive Two-Way Relay Networks

We consider an underlay wiretap cognitive two-way relay network (CTWRN), where two secondary sources exchange their messages via multiple secondary decode-and-forward digital network coding relays in the presence of an eavesdropper by using a three-phase time division broadcast protocol and sharing the licensed spectrum of primary users. To mitigate eavesdropping attacks, an artificial noise (AN)-aided opportunistic relay selection scheme, called generalized max-min (GMM) relay selection is proposed to enhance physical layer security for the wiretap CTWRNs. The performance of the GMM scheme is analyzed, and evaluated by the exact closed-form outage probability and intercept probability. Additionally, we also provide asymptotic approximations for the outage probability and intercept probability at high signal-to-noise ratio. For comparison, we analyze the performance of the conventional max-min (MM) relay selection scheme as well. It is shown that the GMM scheme outperforms the MM scheme in terms of the security-reliability tradeoff (SRT), where the security and reliability are quantified by the intercept probability and outage probability, respectively. Moreover, the SRTs of the MM and GMM schemes can be substantially improved by increasing the number of secondary relays, while the improvement of the GMM scheme is more evident than that of the MM scheme.

Opportunistic MIMO Two-Way Relaying: Diversity-Multiplexing Tradeoff Analysis

This letter analyzes the diversity-multiplexing tradeoff (DMT) performance of an opportunistic MIMO two-way relaying (OMTWR) scheme for the time-division broadcast (TDBC) and multiple-access broadcast (MABC) protocols. The analysis reveals the following. In terms of the DMT, the MABC-based OMTWR outperforms its TDBC-based counterpart for low multiplexing gains. Interestingly, the opposite is found to be true in the high-multiplexing gain regime. In terms of the outage capacity, the MABC-based OMTWR outperforms the TDBC-based scheme in the low-SNR regime, whereas, in the high-SNR regime, the TDBC-based OMTWR achieves higher transmission rate compared with its MABC-based counterpart.

Optimal Combining and Performance Analysis for Two-Way EH Relay Systems With TDBC Protocol

In this paper, we investigate a simultaneous wireless information and power transfer (SWIPT) based two-way decode-and-forward (DF) relay network, where time switching (TS) is employed for SWIPT and time division broadcast (TDBC) is employed for two-way relaying. We focus on the design of a combining scheme that decides how the relay combines the signals received from two terminals through a power allocation ratio at the relay. We formulate an optimization problem to minimize the system outage probability and obtain the optimal power allocation ratio in closed form. For the proposed optimal combining scheme, we derive the expressions for the system outage probability and capacity. Simulation results verify our derived expressions and show that the proposed scheme achieves a higher system outage capacity than the existing schemes.

Achievable Rate-Energy Region in Two-Way Decode-and-Forward Energy Harvesting Relay Systems

At an energy harvesting relay, securing residual harvested energy, net remaining energy after each receiving and forwarding cycle, is of importance for sustainable operation. However, there exists a tradeoff between the achievable rate and residual harvested energy, whereby understanding this tradeoff concretely is crucial for energy harvesting relay system design. This paper analyzes the rate-energy (R-E) region for achievable rate and residual harvested energy in two-way decode-and-forward (DF) relay systems with a power splitting based energy harvesting relay. In particular, we characterize R-E regions for multiple access broadcast (MABC) and time division broadcast protocols. Moreover, we propose a new energy harvesting relaying protocol, namely, information and energy signals multiple access broadcasts (IEBC), to improve the achievable R-E region. The boundary of the R-E regions is obtained by optimizing a power splitting factor in each protocol. Moreover, to have better analytic comparisons and useful insights on performance, we derive approximated R-E regions of all protocols for high and low signal-to-noise ratio cases. Based on the approximated R-E region, it is shown that if the required residual energy is large, the IEBC outperforms the others, but if the required residual energy is small, either the IEBC or MABC is preferred.

Adaptive Link Utilization in Two-Way Spectrum Sharing Relay Systems Under Average Interference-Constraints

In this paper, we investigate the performance of an underlay cognitive two-way relay system with direct link using time division broadcast protocol in the presence of primary user's interference. Herein, relying on the practicability and low complexity of statistical channel state information, the secondary transmissions are in compliance with the fading-averaged interference constraints imposed by the primary receiver. For this setup, we study an adaptive link utilization scheme (ALUS) that can exploit both direct and relay links with appropriate diversity combining methods to improve the performance of secondary users. Based on ALUS, we evaluate and compare the performance of two decode-and-forward based relaying strategies viz., fixed relaying and incremental relaying. We derive the tight closed-form expressions of outage probability of the secondary communications for both the strategies over Nakagami- m fading channels. We further conduct asymptotic high signal-to-interference-plus-noise ratio analysis to examine the achievable diversity order of the considered system. In addition, we quantify the expected spectral efficiency and average transmission time for both relaying strategies. Our results illustrate that the incremental relaying strategy can significantly improve the system performance in comparison with fixed relaying. Numerical and simulation results are provided to attest our theoretical studies.

Network-Coded Cooperative Spatial Multiplexing in Two-Way Relay Channels

In this paper, for a two-way relay channel comprising two multi-antenna transceivers and $L$ single-antenna potential relay nodes, we propose three network-coded cooperative spatial multiplexing (CSM) schemes that effectively overcome the rate loss incurred due to the half-duplex limitation of the transceivers and the relay nodes and achieve high spectral efficiency. In the following, these three schemes are referred to as time-division broadcast (TDBC)-CSM , incremental (I)-TDBC-CSM and multiple-access broadcast (MABC)-CSM . We investigate these schemes in terms of the outage probability, the average transmission rate, the asymptotic behavior, and the diversity-multiplexing tradeoff. The analysis of the paper shows that, first, the I-TDBC-CSM scheme achieves the full diversity of order $L\min (M_1,M_2)+M_1M_2$ , where $M_1$ and $M_2$ are the numbers of antennas employed by the two transceivers; second, the TDBC-CSM and MABC-CSM schemes achieve the diversity of order $L\min (M_1,M_2)$ , where this quantity is the maximum achievable diversity gain in the absence of the direct link between the transceivers; third, the TDBC-CSM and I-TDBC-CSM schemes effectively overcome the rate loss incurred due to the half-duplex limitation of the relay nodes; fourth, the MABC-CSM scheme not only overcomes the half-duplex limitation of the relay nodes but also mitigates the spectral efficiency loss incurred due to the half-duplex limitation of the transceivers; and fifth, if one or both of the transceivers are equipped with a massive antenna array, the asymptotic average rate of the CSM-based schemes scales linearly with the number of potential relay nodes, as opposed to the conventional relaying schemes, in which the average rate is not scalable with $L$ . We provide extensive simulation results to confirm the theoretical analysis of the paper. The simulation results show that for a given outage probability, the proposed schemes outperform the conventional relaying schemes in terms of the average transmission rate.

A Spectrally Efficient Signal Space Diversity-Based Two-Way Relaying System

This work proposes a new transmission scheme for multirelay two-way relaying systems, where two end- sources communicate with each other via a set of relays. In the proposed scheme, we consider signal space diversity and time division broadcast protocol jointly to increase spectral efficiency without sacrificing the system reliability. The idea behind this consideration is that original data symbols are rotated before transmission, and then the in-phase and quadrature components of these rotated symbols are transmitted through the cooperation of the end-sources and the relays. By doing so, the end-sources exchange four symbols over three time slots instead of two, i.e., doubling the number of transmitted symbols. In addition, relay selection is incorporated into this scheme to achieve a further increase in spectral efficiency. For relay selection, two different strategies are discussed: reactive and proactive relay selections. These strategies differ depending on whether relay selection is performed after or before the start of transmission. Specifically, for each relay-selection strategy, we first obtain a closed-form expression for the end-to-end (E2E) error probability with an arbitrary constellation, which accounts for all the resulting nonuniform constellation cases due to constellation rotation. Subsequently, with the derived expressions, we then formulate an optimization problem that considers the joint optimization of the rotation angle and the transmit powers at the end-sources and the relays. The objective of the optimization problem is to minimize the E2E error probability of one of the end-sources, while satisfying a set of total and individual transmit power constraints and a predefined threshold for the E2E error probability of the other end-source. Numerical results verify the theoretical analysis, and show that the scheme proposed herein provides not only higher spectral efficiency, but also more reliable transmission.

Wireless Energy Harvesting Assisted Two-Way Cognitive Relay Networks: Protocol Design and Performance Analysis

This paper analyzes the effects of realistic relay transceiver on the outage probability and throughput of a two-way relay cognitive network that is equipped with an energy-harvesting relay. In this paper, we configure the network with two wireless power transfer policies and two bidirectional relaying protocols. Furthermore, the differences in receiver structure of relay node that can be time switching or power splitting structure are also considered to develop closed-form expressions of outage and throughput of the network providing that the delay of transmission is limited. Numerical results are presented to corroborate our analysis for all considered network configurations. This paper facilitates us not only to quantify the degradation of outage probability and throughput due to the impairments of realistic transceiver but also to provide an insight into practical effects of specified configuration of power transfer policy, relaying protocol, and receiver structure on outage and throughput. For instance, the system with multiple access broadcast protocol and the power splitting-based receiver architecture achieves ceiling throughout higher than that of the transmission rate of source nodes. On the contrary, a combination of dual-source energy transfer policy and the time division broadcast protocol is contributed the highest level of limiting factor in terms of transceiver hardware impairments on the network throughput.

Joint Source-Channel Coding of JPEG 2000 Image Transmission Over Two-Way Multi-Relay Networks.

In this paper, we develop a two-way multi-relay scheme for JPEG 2000 image transmission. We adopt a modified time-division broadcast cooperative protocol, and derive its power allocation and relay selection under a fairness constraint. The symbol error probability of the optimal system configuration is then derived. After that, a joint source-channel coding (JSCC) problem is formulated to find the optimal number of JPEG 2000 quality layers for the image and the number of channel coding packets for each JPEG 2000 codeblock that can minimize the reconstructed image distortion for the two users, subject to a rate constraint. Two fast algorithms based on dynamic programming and branch and bound are then developed. Simulation demonstrates that the proposed JSCC scheme achieves better performance and lower complexity than other similar transmission systems.

Two‐way relay networks with wireless power transfer: design and performance analysis

This study considers amplify-and-forward two-way relay networks, where an energy constrained relay node harvests energy from the received radio-frequency signal. Based on time switching receiver, they separate the energy harvesting (EH) phase and the information processing (IP) phase in time. In the EH phase, three practical wireless power transfer policies are proposed: (i) dual-source (DS) power transfer, where both sources transfer power to the relay; (ii) single-fixed-source power transfer, where a fixed source transfers power to the relay; and (iii) single-best-source (SBS) power transfer, where a source with the strongest channel transfers power to the relay. In the IP phase, a new comparative framework of the proposed wireless power transfer policies is presented in two bi-directional relaying protocols, known as multiple access broadcast (MABC) and time division broadcast (TDBC). To characterise the performance of the proposed policies, new analytical expressions are derived for the outage probability, the throughput, and the system energy efficiency. Numerical results corroborate the authors’ analysis and show: (i) the DS policy performs the best in terms of both outage probability and throughput among the proposed policies, (ii) the TDBC protocol achieves lower outage probability than the MABC protocol, and (iii) there exits an optimal value of EH time fraction to maximise the throughput.

Cooperative spectrum sharing in two‐way multi‐user multi‐relay networks

In this study, the authors consider a cooperative spectrum sharing network with multiple primary users (PUs) and multiple secondary users (SUs). Hereby, one end-PU communicates bidirectionally with one of the best selected other end-PUs with the cooperation of the best selected SU using time division broadcast protocol. Based on an overlay approach, the selected SU allocates its partial power to relay the PUs’ signals and utilises the remaining power to transmit its own signal. The authors devise a low-complexity distributed PU–SU selection strategy to minimise the overall outage probability of the primary system. For Nakagami-m fading, the authors derive tight expressions of outage probability for both primary and secondary systems of the considered scheme. Further, by deriving their asymptotic behaviour at high signal-to-noise ratio, the authors highlight the performance gain accrued by cooperative and multiuser diversity along with that offered by the channels under Nakagami-m fading. Besides, the authors demonstrate the effective locations for the SUs to access the spectrum. Above all, the authors illustrate that the increase of the number of SUs is more desirable than the number of PUs to explore the spectrum sharing opportunities. Numerical and simulation results substantiate the effectiveness of the proposed scheme and the theoretical analysis.

Distributed Role Selection With ANC and TDBC Protocols in Two-Way Relaying Systems

This paper advocates a distributed role selection strategy to coordinate two-way relaying transmissions among three cooperative nodes. For such, the local channel state information comparison and decision feedback mechanism are merged into classical analog network coding (ANC) and time division broadcast (TDBC) protocols such that the cooperative role of each node can be designated in a distributed fashion. We refer to this distributed role selection rule as d-ROSE. In both ANC-based and TDBC-based two-way relaying scenarios, strict proof for the equivalence of d-ROSE and optimal ROSE is given, which indicates that albeit the different form, their final role decision is essentially the same. Outage analysis for the d-ROSE strategy is carried out and the scaling law of the system outage behavior at high signal-to-noise ratio (SNR) is characterized, which manifests that d-ROSE can enhance the system diversity gain to one-order higher relative to the ANC and TDBC protocols. It is also shown that d-ROSE can reduce the signaling overhead upto 60% to perform the outage-optimal role selection. Finally, the impacts of node placement on the outage performance as well as the average signaling overhead of d-ROSE are numerically evaluated and some useful conclusions are drawn.

Energy-Aware Hybrid Cooperative Relaying with Asymmetric Traffic

In this paper, we study an asymmetric two-way relaying network where two source nodes intend to exchange information with the help of multiple relay nodes. A hybrid time-division broadcast relaying scheme with joint relay selection (RS) and power allocation (PA) is proposed to realize energy-efficient transmission. Our scheme is based on the asymmetric level of the two source nodes’ target signal-to-noise ratio indexes to minimize the total power consumed by the relay nodes. An optimization model with joint RS and PA is studied here to guarantee hybrid relaying transmissions. Next, with the aid of our proposed intelligent optimization algorithm, which combines a genetic algorithm and a simulated annealing algorithm, the formulated optimization model can be effectively solved. Theoretical analyses and numerical results verify that our proposed hybrid relaying scheme can substantially reduce the total power consumption of relays under a traffic asymmetric scenario; meanwhile, the proposed intelligent optimization algorithm can eventually converge to a better solution.