Multiple Access Relay Networks Research Articles

Controlled Power Cooperative Non Orthogonal Multiple Access Relay Networks

Controlled Power Cooperative Non Orthogonal Multiple Access Relay Networks

Energy-Efficient Mobile Edge Computing in RIS-Aided OFDM-NOMA Relay Networks

In this paper, the design of task offloading and computing strategy in a mobile edge computing (MEC) system deployed over a reconfigurable intelligent surface (RIS)-aided orthogonal frequency division multiplexing based non-orthogonal multiple access (OFDM-NOMA) relay network is studied, where both a relay node and an MEC server located at an access point help a user terminal accomplish task computing. Our objective is to minimize energy consumption for communication and computation at the user terminal and the relay subject to a given task executing delay constraint. To this end, a novel protocol is first proposed to enable the user terminal and the relay to fully utilize the high passive beamforming gain provided by RIS and the high spectral efficiency offered by OFDM and NOMA techniques for task offloading. Then, under the newly proposed protocol, a resource allocation optimization problem is formulated, where RIS reflection coefficients, task offloading and computing time allocation, subcarrier and power allocation, task partition, and CPU frequency of the MEC server are jointly optimized. Because the numerous optimization variables are coupled with each other and integer programming is involved for subcarrier allocation optimization, the formulated problem is a mixed integer programming and highly non-convex problem that is hard to tackle. To address this problem, an efficient algorithm is devised to achieve its solution by employing alternating optimization, layer optimization, big-M formulation and successive convex approximation techniques. Simulation results validate that substantial energy savings can be achieved by employing RIS and OFDM-NOMA techniques in wireless relaying-based MEC systems.

Network-coded uplink clustered NOMA relay networks: Models and performance comparisons

In this paper, network sum-rate maximization (NSR-MAX) for network-coded (NC) uplink clustered non-orthogonal multiple-access (NOMA) relay networks is considered. In particular, the goal is to maximize network sum-rate via optimal power allocation, where the user clusters communicate with the base-station over an amplify-and-forward relay, subject to quality-of-service (QoS) constraints. Two NC-NOMA transmission models – namely NC-NOMA-I and NC-NOMA-II – are proposed, where in the first model, network-coding is applied at the relay only, while the second model applies network-coding for user clusters’ transmissions and at the relay to further minimize the transmission delay. The formulated NSR-MAX problem happens to be non-convex, and hence, is computationally-intensive. Thus, a low-complexity iterative two-layer algorithm (ITLA) is devised, which decouples the formulated problem and efficiently solves its over two-layers. Specifically, the inner-layer solves the NSR-MAX problem to obtain the optimal relay transmit power, while the outer-layer determines the optimal users’ transmit powers. Numerical results are presented, which illustrate that the proposed ITLA yields near-optimal solutions for all transmission models, in comparison to the formulated NSR-MAX problem (solved via global optimization package) as well as outperforming its OMA-based counterparts. Not only that, but the NC-NOMA-II is shown to be superior to the other NOMA and OMA schemes, while demonstrating resilience to timing offsets as well as successive interference cancellation (SIC) and channel state information (CSI) errors.

Secure and Reliable Transmission in mmWave NOMA Relay Networks With SWIPT

In this article, we consider the millimeter-wave simultaneous wireless information and power transfer nonorthogonal multiple access (NOMA) relay networks in the presence of multiple passive eavesdroppers, where the near and far Internet of Things (IoT) devices with different communication requirements are served by one source with the help of the relays, and stochastic geometry is used to characterize the distribution of multiple nodes. First, a NOMA pairing and relay selection scheme is designed. Then, the closed-form expressions for the energy-information coverage probability (EICP) and the effective secrecy throughput of the near IoT devices are derived. Finally, the EICPs of the far IoT device under random relay selection and opportunistic relay selection schemes are obtained. Moreover, the asymptotic expressions of the EICP for both the near and far IoT devices are derived, which show that the asymptotic EICP when the number of antennas at the source or relay tends to infinity is only dependent on the location distribution of nodes and blockage environment. The simulation results show that NOMA can outperform orthogonal multiple access, and the advantage of the opportunistic relay selection scheme over the random relay selection scheme is more obvious when the density of the relay is relatively large.

Energy‐efficient radio resource allocation for dual‐hop relay‐assisted orthogonal frequency division multiple access systems with quality of service provisioning

AbstractBesides the conventional spectral efficiency metric, energy efficiency (EE) has been adopted as one of the new mandatory performance metrics for green future mobile networks. In this sense, in this article we study energy‐efficient radio resource allocation for dual‐hop orthogonal frequency division multiple access relay networks considering multiple relays and users. Resource allocation in our scenario is comprised of relay selection, subcarrier pairing, subcarrier assignment, and transmit power allocation. Particularly, in the context of EE with quality of service constraints, three different problems, namely, power consumption minimization, global EE maximization, and minimum individual EE maximization are addressed. For tackling them, first, we demonstrate a property that exploits the use of the decode and forward protocol employed in the relays and we show how it can be applied to simplify the investigated problems. Although some of these problems are nonconvex due to the fractional objective functions and integer optimization domain, optimal solutions are provided using generalized fractional programming theory to transform the fractional objective functions to the subtractive forms. Then, by employing Dinkelbach or bisection methods, we propose iterative algorithms where a parametric problem is solved in each iteration until reaching convergence. By introducing a penalty function to handle integer variables and applying majorization‐minimization approach, we make the parametric problem convex and we propose suboptimal iterative solutions with reduced computational cost. Regarding obtained simulation results, we discuss the performance of the involved solutions in terms of global EE and fairness with respect to different parameters of the system.

A Novel Resource Allocation for SWIPT-NOMA Enabled AF Relay Based Cooperative Network

In this work, a novel resource allocation scheme is proposed to find the optimal time-switching and power-splitting factors in a SWIPT assisted non-orthogonal multiple access (NOMA) relay network with combined time switching and power splitting protocol. The system model consists of a source node broadcasting a multiplexed NOMA signal to the far and near user via an amplify-and-forward energy harvesting relay node in a Rayleigh-flat-fading channel environment. Here, effective SNR maximization at both the near and far users is formulated as an optimization problem under total transmit power constraint and to deal with this both the Lagrangian multiplier approach and differential-evolution algorithm have been exploited. Furthermore, performance study is presented about the comparison of proposed scheme with the fixed allocation scheme in terms of outage probability under the impact of distinct target rates, relay locations, and channel conditions. Finally, the simulation results signify the performance improvement in the system with the optimal values obtained from the proposed scheme over the fixed time and power splitting factors.

Energy Efficient Buffer-Aided Transmission Scheme in Wireless Powered Cooperative NOMA Relay Network

In this paper, we consider a wireless powered cooperative non-orthogonal multiple access (NOMA) relay network, in which one source is supposed to send independent messages to two users with the assistance of one energy-constrained relay that harvests energy from the source. Firstly, we study the minimum power consumption at the source node to fulfill the least required transmission rates by two users in both time switching relaying (TSR) strategy and power splitting relaying (PSR) one. Secondly, when the relay is provisioned with data buffer and energy storage, the long-term average power consumption minimization problem is formulated to take into account of the data and energy queue causality, peak transmit power constraint, and transmission mode selection. By using Lyapunov optimization framework, a novel buffer-aided transmission scheme (BATS) is proposed to asymptotically approach the optimal solution. Our analysis shows that, the PSR outperforms the TSR in terms of the realized energy efficiency, and BATS can be utilized to further improve the energy efficiency. It is disclosed that, there is an inherent trade-off between the long-term power consumption and the average queuing delay. In addition, larger user rates or less power consumption can be realized if a larger delay can be tolerated.

Achievable Rate Region under Linear Beamforming for Dual-Hop Multiple-Access Relay Network.

Consider a network consisting of two independent single-antenna sources, a single-antenna destination and a helping multiple-antenna relay. This network is called a dual-hop multiple access relay network (MARN). In this network, sources transmit to the relay simultaneously in the first time slot. The relay retransmits the received sum-signal to the destination using a linear beamforming scheme in the second time slot. In this paper, we characterize the achievable rate region of MARN under linear beamforming. The achievable rate region characterization problem is first transformed to an equivalent “corner point” optimization problem with respect to linear beamforming matrix at the relay. Then, we present an efficient algorithm to solve it via only semi-definite programming (SDP). We further derive the mathematical close-forms of the maximum individual rates and the sum-rate. Finally, numerical results demonstrate the performance of the proposed schemes.

On MIMO Linear Physical-Layer Network Coding: Full-Rate Full-Diversity Design and Optimization

This paper considers a multiuser communication network, where a receiver is set to compute functions of the messages from $K$ users. All user nodes and the receiver are equipped with multi-antenna. We propose a space–time (ST) coded multiple-input multiple-output (MIMO) linear physical-layer network coding (LPNC) scheme that promises full-rate and full-diversity, while achieving the maximum coding gain of LPNC. In the proposed framework, the users’ messages are encoded by the same linear dispersion ST code and transmitted simultaneously. The receiver exploits the MIMO LPNC mapping in reconstructing an arbitrary number of linearly network-coded (NC) messages. We derive the NC generator matrix that leads to the greatest coding gain and minimized error probability at the receiver. On top of that, we analytically show that the proposed ST coded LPNC scheme guarantees the full-diversity and full-rate transmission. The proposed method applies to a wide range of network configurations. Two case studies on: (1) MIMO two-way relay network and (2) MIMO multiple-access relay network are presented in this paper. For both case studies, numerical results are shown to demonstrate the performance improvement of the proposed scheme over conventional schemes by more than 4 dB, while the full-rate and full-diversity behaviors are in line with our analysis.

Distributed Decode–Forward for Relay Networks

A new coding scheme for general $N$ -node relay networks is presented for unicast, multicast, and broadcast. The proposed distributed decode–forward scheme combines and generalizes Marton coding for single-hop broadcast channels and the Cover–El Gamal partial decode–forward coding scheme for three-node relay channels. The key idea of the scheme is to precode all the codewords of the entire network at the source by multicoding over multiple blocks. This encoding step allows these codewords to carry partial information of the messages implicitly without complicated rate splitting and routing. This partial information is then recovered at the relay nodes and forwarded further. For $N$ -node Gaussian unicast, multicast, and broadcast relay networks, the scheme achieves within $0.5 N$ bits from the cutset bound, and thus from the capacity (region), regardless of the network topology, channel gains, or power constraints. Roughly speaking, distributed decode–forward is dual to noisy network coding, which generalized compress–forward to unicast, multicast, and multiple access relay networks.

Sub-Channel and Power Allocation for Non-Orthogonal Multiple Access Relay Networks With Amplify-and-Forward Protocol

In this paper, we study the resource allocation problem for a single-cell non-orthogonal multiple access (NOMA) relay network where an OFDM amplify-and-forward relay allocates the spectrum and power resources to the source–destination (SD) pairs. We aim to optimize the resource allocation to maximize the average sum-rate. The optimal approach requires an exhaustive search, leading to an NP-hard problem. To solve this problem, we propose two efficient many-to-many two-sided SD pair-subchannel matching algorithms, in which the SD pairs and sub-channels are considered as two sets of players chasing their own interests. The proposed algorithms can provide a sub-optimal solution to this resource allocation problem in affordable time. Both the static matching algorithm and the dynamic matching algorithm converge to a pair-wise stable matching after a limited number of iterations. Simulation results show that the capacity of both proposed algorithms in the NOMA scheme significantly outperforms the conventional orthogonal multiple access scheme. The proposed matching algorithms in NOMA scheme also achieve a better user-fairness performance than the conventional orthogonal multiple access.

Linear Physical-Layer Network Coding and Information Combining for the <inline-formula> <tex-math notation="LaTeX">$K$ </tex-math> </inline-formula>-User Fading Multiple-Access Relay Network

We propose a new linear physical-layer network coding (LPNC) and information combining scheme for the $K$ -user fading multiple-access relay network (MARN), which consists of $K$ users, one relay, and one destination. The relay and the destination are connected by a rate-constraint wired or wireless backhaul. In the proposed scheme, the $K$ users transmit signals simultaneously. The relay and the destination receive the superimposed signals distorted by fading and noise. The relay reconstructs $L$ linear combinations of the $K$ users’ messages, referred to as $L$ network-coded (NC) messages, and forwards them to the destination. The destination then attempts to recover all $K$ users’ messages by combining its received signals and the NC messages obtained from the relay. We develop an explicit expression on the selection of the coefficients of the NC messages at the relay that minimizes the end-to-end error probability at a high signal-to-noise ratio. We develop a channel-coded LPNC scheme by using an irregular repeat-accumulate modulation code over GF( $q$ ). An iterative belief-propagation algorithm is employed to compute the NC messages at the relay, while a new algorithm is proposed for the information combining decoding at the destination. We demonstrate that our proposed scheme outperforms benchmark schemes significantly in both un-channel-coded and channel-coded MARNs.

A generalized design of distributed rateless codes with decreasing ripple size for multiple-access relay networks

In this correspondence, the problem of existing distributed rateless codes (DRC) with inaccurate degree distributions in the sources and the relay is addressed. Based on a well-known multiple-access relay network model, a generalized design of DRC (GDRC) is proposed by using optimization theory and heuristic Jacobian iterative algorithm, in which the interaction between the degree distributions in the sources and in the relay is considered. Our GDRC can be applied to Luby transfer codes or any other rateless codes that can be described with a degree distribution. Furthermore, a novel approach of designing GDRC with decreasing ripple size is proposed by directly analysing the interaction between the ripple size revolutions in the sources and in the relay. Our proposed scheme is evaluated and compared with existing schemes. It is shown that our proposed scheme exhibits reduced overhead, memory usage, bit error rate and energy consumption compared to the existing schemes.

A chunk and power allocation algorithm for proportional fairness in OFDMA relay networks

Applying amplify-and-forward (AF) protocol to orthogonal frequency division multiple-access (OFDMA) relay networks opens questions regarding subcarrier matching and resource allocation on relay stations. In this paper we consider a chunk-based OFDMA-AF system with a single source station, single or multiple relay stations, and a single destination serving multiple users. Due to the fact that contiguous subcarriers are correlated, it is possible to group them into chunks, so as to reduce the signaling overhead and the complexity of subcarrier allocation. Another important consideration is ensuring fairness among the users of the system. We present a chunk reordering and power allocation algorithm on the relay station, with the goal of maximizing the total data rate of the system, taking proportional fairness and the modulation and coding schemes constraints into account. We use the single-subcarrier approach as a benchmark and investigate the impact of the chunk size and the number of relays on the achieved data rate, showing that the proposed algorithm achieves strong results even with large chunk sizes. The algorithm is derived for full-duplex mode and extended to multiple-relay networks by the proposed optimal relay selection strategy, which is experimentally compared to several heuristic relay selection strategies.

Joint resource allocation, routing and CAC for uplink OFDMA networks with cooperative relaying

In this paper, we propose a joint resource allocation, routing, and connection admission control (CAC) scheme for uplink transmission in orthogonal frequency division multiple access (OFDMA) relay networks with cooperative relaying. For cooperative relaying, relay station can relay uplink data from mobile station (MS) to base station with cooperation of the MS using transmit diversity. Transmit diversity can be achieved by virtual MISO via distributed space---time coding. The proposed scheme jointly allocates OFDMA resources and selects path for each user with CAC to maximize the upink throughput of cooperative OFDMA relay networks. The basic OFDMA resource unit is considered as a resource element which is one subcarrier over one OFDMA symbol. An efficient multi-choice multi-dimensional knapsack (MMKP) algorithm is presented for the proposed scheme. The proposed MMKP algorithm provides a unified framework which is applicable to OFDMA networks with and without cooperative relaying. We evaluate the performance of the proposed scheme with and without cooperative relaying in a hilly terrain with heavy tree density by using OPNET-based simulation. We show that the cooperative relaying improve the uplink system throughput compared with non-cooperative relaying, and the proposed scheme outperforms the conventional link quality-based scheme in both cooperative and non-cooperative relay networks.

Superimposed Training Based Channel Estimation for Uplink Multiple Access Relay Networks

In this paper, the channel estimation in uplink multiple access relay networks (MARNs) with analog network coding protocol has been researched. We apply the superimposed training (ST) scheme where each relay puts a separate training sequence on the top of the received one before forwarding to destination, and design a maximum likelihood based channel estimation algorithm for the composite source-relay-destination and individual relay-destination links. The optimal training sequences as well as the superimposed training power are also derived in closed forms. To make our study more complete, the channel estimation in the time-selective fading environment is further considered, and a correlation-based channel estimation (CBCE) algorithm is developed by taking advantage of time-domain channel autocorrelation nature. Simulation results show that the presented ST scheme can effectively improve the performance of multi-user detection in MARNs, and the proposed CBCE algorithm significantly outperforms the existing channel estimation methods.

A Distributed LT Code Design for Multiple-Access Relay Networks Subject to Erasures

This letter proposes a new distributed Luby transform (LT) code which is particularly suitable for the multiple-access relay network with erasure channels. We analyze the asymptotic performance of our distributed coding scheme by virtue of AND-OR tree analysis and present the simulation results of finite length comparing with existing methodologies. The proposed coding scheme is shown to be superior to conventional strategies in presence of both source-relay and relay-sink erasures.

Design of Distributed Beamforming for Dual-Hop Multiple-Access Relay Networks

This paper studies a dual-hop multiple-access relay network where two independent source nodes transmit information to a common destination node with the aid of multiple single-antenna amplify-and-forward relays. Each relay node is subject to an individual power constraint. We focus on the design of distributed beamforming schemes for the relays to support the transmission rate requirements of the two sources. To this end, we first characterize the achievable rate region for this network via solving a sequence of corner point optimization problems proposed in this paper. We also develop several low-complexity suboptimal schemes in closed form. Two inner bounds of the achievable rate region are theoretically shown to be approximately optimal in two special scenarios. Finally, numerical results demonstrate the effectiveness of our proposed approaches.

Cooperation Versus Multiplexing: Multicast Scheduling Algorithms for OFDMA Relay Networks

With the next-generation cellular networks making a transition toward smaller cells, two-hop orthogonal frequency-division multiple access (OFDMA) relay networks have become a dominant, mandatory component in the 4G standards (WiMAX 802.16j, 3GPP LTE-Adv). While unicast flows have received reasonable attention in two-hop OFDMA relay networks, not much light has been shed on the design of efficient scheduling algorithms for multicast flows. Given the growing importance of multimedia broadcast and multicast services (MBMS) in 4G networks, the latter forms the focus of this paper. We show that while relay cooperation is critical for improving multicast performance, it must be carefully balanced with the ability to multiplex multicast sessions and hence maximize aggregate multicast flow. To this end, we highlight strategies that carefully group relays for cooperation to achieve this balance. We then solve the multicast scheduling problem under two OFDMA subchannelization models. We establish the NP-hardness of the scheduling problem even for the simpler model and provide efficient algorithms with approximation guarantees under both models. Evaluation of the proposed solutions reveals the efficiency of the scheduling algorithms as well as the significant benefits obtained from the multicasting strategy.

Tradeoff Between Reliability and Security in Multiple Access Relay Networks Under Falsified Data Injection Attack

We consider a multiple access relay network where multiple sources send independent data to a single destination through multiple relays, which may inject falsified data into the network. To detect the malicious relays and discard (erase) data from them, tracing bits are embedded in the information data at each source node. In addition, parity bits are added to correct the errors caused by fading and noise. When the total amount of redundancy, tracing bits plus parity bits, is fixed, an increase in parity bits to increase the reliability requires a decrease in tracing bits, which leads to a less accurate detection of malicious behavior of relays, and vice versa. We investigate the tradeoff between the tracing bits and the parity bits in minimizing the probability of decoding error and maximizing the throughput in multisource, multirelay networks under falsified data injection attacks. The energy and throughput gains provided by the optimal allocation of redundancy and the tradeoff between reliability and security are analyzed.