Buffer-Aided Cooperative Research Articles

Deep Learning Driven Buffer-Aided Cooperative Networks for B5G/6G: Challenges, Solutions, and Future Opportunities

Deep Learning Driven Buffer-Aided Cooperative Networks for B5G/6G: Challenges, Solutions, and Future Opportunities

Buffer-Aided Cooperative Relays in Orbital Angular Momentum Based IoT Networks

Buffer-Aided Cooperative Relays in Orbital Angular Momentum Based IoT Networks

A Low-Delay Lyapunov-Based Relay Selection Scheme in Buffer-Aided Cooperative Networks

A Low-Delay Lyapunov-Based Relay Selection Scheme in Buffer-Aided Cooperative Networks

Differential Modulation-Based Buffer-Aided Cooperative Relaying Network

In this article, we consider a multirelay cooperative network using a differential modulation technique. The given set-up consists of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$K$</tex-math></inline-formula> decode-and-forward (DF) relays, each equipped with a buffer of size <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$L$</tex-math></inline-formula> . All transceiver nodes in the considered cooperative network apply differential modulation for the transmission of data, hence, channel-state information is not required for decoding of the data at the receiving nodes. A priority-based max link selection approach is used for the selection of the best links for the transmission and reception of data. The Markov chain approach is used to derive the state-transition matrix of the system, which is then further used to model the evolution of buffer status. Analytical expressions of the outage probability and average bit error rate are obtained with the help of the state-transition matrix. The performance of the considered system is analyzed for different buffer sizes and a number of relays. The performance is then further compared with that of a coherent buffer-aided network and also with the nonbuffer-aided differential amplify-and-forward and DF systems. As compared to the coherent buffer-aided network, the considered buffer-aided differential system suffers a negligible signal-to-noise ratio penalty in the scenario when more than one buffer-aided relay is present in the network, which is a significant improvement when compared with the nonbuffer-aided differential cooperative systems, which suffer a performance penalty of approximately 3 dB as compared to their coherent counterpart.

Novel Mode Selection Schemes for Buffer-Aided Cooperative NOMA System

This paper investigates a cooperative non-orthogonal multiple access (C-NOMA) system, where the NOMA and buffer-aided cooperative transmission modes between the users are integrated. Two novel mode selection schemes are proposed, which adaptively select the NOMA and cooperative modes according to different buffer states and communication environments. These two proposed schemes are termed single-core state (SCS) and dual-core state (DCS) schemes since they correspond to single and dual-core buffer states. These core states are carefully chosen, which ensure not only a sufficient amount of available transmission modes or links but also a small number of stored packets at each buffer. The closed-form expressions of the outage probabilities and average delays of the proposed schemes are derived and verified by simulation results. Asymptotic performance analysis is also performed, revealing that both proposed schemes achieve the full diversity within the minimum required buffer size of two. Analytical and simulation results show that the proposed SCS and DCS schemes ensure favourable outage performance and the lowest delay, respectively.

Threshold Based Relay Selection for Buffer-Aided Cooperative Relaying Systems

In this paper, we propose a novel relay selection strategy for half-duplex decode-and-forward cooperative networks with an arbitrary number of buffer-aided (BA) relays. Unlike most of the existing predetermined relaying protocols, the proposed strategy is adjustable in the sense that it is controlled by K threshold levels. A Markov chain (MC) analysis is adopted for evaluating the outage probability (OP) and average packet delay (APD) of the proposed scheme. Through an asymptotic analysis, we highlight on the impact of the K controlling parameters on the triad of OP, APD and diversity order that can be contemplated. While most of the existing schemes are designed to achieve fixed APD and diversity order values, the proposed scheme can achieve all diversity orders ranging from K to 2K while compromising the asymptotic APD that will range from 2 to 2K+2. We also target the optimization of the buffer size and we prove that a buffer size of three is sufficient for extracting the full capabilities of the BA network. Simulations over Rayleigh fading channels demonstrate the performance gains and the OP-APD tradeoffs that can be attained.

Quality-of-Service Differentiation in Buffer-Aided Cooperative Free Space Optical Communication Systems

In this paper, the problem of Quality-of-Service (QoS) differentiation is studied in the context of Buffer-Aided (BA) cooperative Free Space Optical (FSO) communication systems. This is particularly true since the existing relevant literature overlooked the possibility of preferential treatment of data packets based on their delay requirements. Inspired by this observation, this paper proposes to classify the data packets emanating from the source node into either Delay Tolerant (DT) packets or Non Delay Tolerant (NDT) ones and to service these packets according to this classification at the relay node. Priority queueing is first introduced in the relay's buffer with a view to improving the delay experienced by NDT packets. Class of service mutation is then proposed as a starvation mitigation strategy to better manage the interesting dynamics resulting from the co-existence of packets having different QoS requirements in the same buffer. The various performance measures of interest for the explored QoS-aware communication system are both evaluated mathematically based on a Markov chain analysis and validated through extensive simulations. An asymptotic analysis is also carried out highlighting the dependence of the performance on the system parameters in an intuitive manner.

Optimization Analysis of Max-Link Secure Relay Selection in Buffer-Aided Cooperative Networks

Cooperative communication technology has been proved to be an useful approach to accomplish physical layer security. In recent years, more and more attention has been paid to the collaboration network with buffer relay. This paper studies the safety performance of the maximum link level options. Compared with the existing buffer-assisted cooperative security schemes, max-Link secure relay selection (Max-Link-SRS) does not require the eavesdropper’s channel state information (CSI) and has a lower complexity. Based on markov chain theory, a new closed form expression of secure interrupt probability (SOP) is derived. Numerical simulation results confirm our analysis and demonstrate that the functioning of max-Link-SRS is superior to the previously reported buffer-less aided cooperative security scheme. It provides a significant coding obtain at a smaller buffer size, while ensuring diversity gain is close to the upper limit of the double number of relays at a bigger buffer zone.

Design and Evaluation of Buffer-Aided Cooperative NOMA With Direct Transmission in IoT

The high spectrum efficiency of nonorthogonal multiple access (NOMA) is attractive to solve the massive number of connections in the Internet of Things (IoT). This article investigates a buffer-aided cooperative NOMA (C-NOMA) system in the IoT, where the intended users are equipped with buffers for cooperation. The direct transmission from the access point to the users and the buffer-aided cooperative transmission between the intended users are coordinated. In particular, a novel buffer-aided C-NOMA scheme is proposed to adaptively select a direct or cooperative transmission mode, based on the instantaneous channel state information and the buffer state. Then, the performance of the proposed scheme, in terms of the system outage probability and average delay, is theoretically derived with closed-form expressions. Furthermore, the full diversity order of three is demonstrated to be achieved for each user pair if the buffer size is not less than three, which is larger than conventional nonbuffer-aided C-NOMA schemes whose diversity order is only two in the considered C-NOMA system in the IoT.

Resource Allocation in Buffer-Aided Cooperative Non-Orthogonal Multiple Access Systems

Cooperative non-orthogonal multiple access (C-NOMA) and buffering are promising techniques to improve spectrum efficiency in the next generation of wireless networks. In this article, a buffer-aided cooperative NOMA network with direct links is studied. The throughput maximization problem is firstly formulated under the assumption of fixed power allocation and optimally solved by designing a mode selection policy. In order to further improve system throughput, the problem is extended into the case that power allocation and mode selection are jointly optimized. An optimal solution is obtained, while a sub-optimal one is also provided in order to decrease the implementation complexity. Furthermore, considering the case where the buffer has finite size and the users are delay-sensitive, a throughput-delay aware strategy is also presented. Moreover, it is shown that the proposed schemes outperform the baseline one in terms of throughput. Finally, simulations demonstrate that the sub-optimal solution achieves similar performance to the optimal one, while significantly reduces the implementation complexity.

Link Selection in Buffer-Aided Cooperative Networks for Green IoT

In this paper, the link selection algorithm in buffer-aided cooperative networks with multiple co-channel interferers for green internet of things (IoT) is investigated. In the considered system, the relay node selects the better link from the first and the second hop with the help of buffers. We evaluate the effects of the system parameters by deriving the analytical analysis as well as the asymptotic results on the exact expressions of the outage probability. The impacts of system parameters, such as the predefined target rate, the priority-outage tradeoff parameter, the buffer length and the number of interferers are evaluated in different setup scenarios. Considerable performance gains can be obtained compared with the classical decode-and-forward relaying networks. Simulation results are provided to verify the theoretical analysis.

Theoretical Analysis of Hybrid Buffer-Aided Cooperative Protocol Based on Max–Max and Max–Link Relay Selections

Motivated by the recent max–link protocol and the max–max protocol, both of which were developed for a simple dual-hop buffer-aided cooperative network, we present a novel hybrid buffer-aided cooperative protocol that attains the benefits of high reliability and reduced packet delay. More specifically, we incorporate a two-stage relay selection strategy, which is capable of attaining a low outage probability comparable to the max–link protocol. In addition, the proposed protocol maintains a beneficial end-to-end packet delay, which is lower than that of the max–link protocol in the realistic scenario supporting finite source-packet transmissions. Furthermore, by introducing a periodic Markov chain model, we derive the theoretical outage probability of our hybrid buffer-aided scheme under the realistic assumption of finite-buffer relays. Our analytical and simulation results demonstrate that the proposed protocol benefits from the aforementioned high-diversity reliable performance and the reduced end-to-end packet delay.

Throughput Maximization for Wireless-Powered Buffer-Aided Cooperative Relaying Systems

We consider a wireless-powered relaying system in which the relay nodes (RNs) that have no embedded power supply are charged by the radio frequency signal transmitted by a power beacon. Each RN is assumed to possess a buffer and can temporarily store the information received from the source node. Based on this assumption, we propose an adaptive transmission scheme, in which each RN adaptively switches between two transmission modes. To maximize the system throughput, a joint node-and-mode selection scheme in which the RN and its transmission mode are jointly selected in each time slot is investigated. For the general system setup, some analytical results are obtained, which provide useful insights in finding the optimal joint node-and-mode selection scheme. Following this, the analysis is applied to two specific systems, the single RN system and the multiple RNs system with a symmetric channel. For these system setups, the system throughput and the corresponding optimal transmission scheme are obtained in the closed-form expressions. Numerical results show that the throughput of the wireless-powered relaying system can be improved by using the proposed transmission schemes.

Buffer State Based Relay Selection for Buffer-Aided Cooperative Relaying Systems

In this paper, we propose a buffer state based relay selection scheme for a finite buffer-aided cooperative relaying system. Our proposed relay selection scheme selects a relay node based on both the channel quality and the buffer state of the relay nodes. The Markov chain model is adopted to analyze the buffer state transition properties and the outage probability of the proposed relay selection scheme is obtained in a closed-form expression. Our analytical results show that if the buffer size of each relay node is greater than 2, the proposed relay selection scheme can achieve full diversity. Furthermore, it is shown that our proposed relay selection scheme has lower average packet delay compared with the max-link relay selection scheme. In addition, the average packet delay of the proposed relay selection scheme does not increase as the buffer size increases.