Conventional Cooperative Scheme Research Articles

Cooperative NOMA-Based Spectrum Leasing With Multiple Secondary Users

This paper proposes a new cooperative nonorthogonal multiple access-based spectrum leasing (CNOMA-SL) framework for enhanced network performance. Herein, the system is comprised of a primary network and a secondary network with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n$</tex-math></inline-formula> -transmitting users. Primary and secondary users exploit an underlay spectrum leasing scheme to transmit signals to a relay station (RS), which forwards the signals to the corresponding receivers. Two phases of data transmission are assumed. In Phase I, the secondary transmitters employ uplink NOMA to transmit the symbols. The RS then uses downlink NOMA to broadcast the received symbols in Phase II. We employ the maximum ratio combining decoding scheme and propose a successive-interference-cancellation concept with ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n+1$</tex-math></inline-formula> ) stages to decode the symbols at the primary and secondary receiving ends, respectively. Considering a transmission power constraint imposed at the secondary transmitters, we derive the closed-form expressions for achievable rate and outage probability for both primary and secondary users. Simulation results manifest that, compared with the conventional cooperative orthogonal multiple access-based spectrum leasing scheme, the proposed CNOMA-SL exhibits improved performance in terms of both achievable rate and outage probability. It is also revealed that the system performs better when the RS takes the lease of the whole spectrum. Furthermore, if more interference power is allowed to the primary receiver, the secondary users reach higher achievable rates.

Secrecy Outage Probability Analysis for Downlink RIS-NOMA Networks With On-Off Control

Reconfigurable intelligent surface (RIS) has been regarded as a promising technology since it has ability to create the favorable channel conditions. This paper investigates the secure communications of RIS assisted non-orthogonal multiple access (NOMA) networks, where both external and internal eavesdropping scenarios are taken into consideration. More specifically, novel approximate and asymptotic expressions of secrecy outage probability (SOP) for the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> -th legitimate user (LU) are derived by invoking imperfect successive interference cancellation (ipSIC) and perfect successive interference cancellation (pSIC). To characterize the secrecy performance of RIS-NOMA networks, the diversity order of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> -th LU with ipSIC/pSIC is obtained in the high signal-to-noise ratio region. The secrecy system throughput of RIS-NOMA networks is discussed in delay-limited transmission mode. Numerical results are presented to verify theoretical analysis that: i) The SOP of RIS-NOMA networks is superior to that of RIS assisted orthogonal multiple access (OMA) and conventional cooperative communication schemes; ii) As the number of reflecting elements increases, the RIS-NOMA networks are capable of achieving the enhanced secrecy performance; and iii) The RIS-NOMA networks have better secrecy system throughput than that of RIS-OMA networks and conventional cooperative communication schemes.

A Profit-Aware Coalition Game for Cooperative Content Caching at the Network Edge

The user demands to delay-sensitive applications have put forward new requirements for the mobile networks. Edge caching as a promising way is proposed to enhance the Quality of Service (QoS) for end users at the network edge. Given the widely distributed edge nodes, the content providers (CPs) usually prefer to integrate them with cooperative caching services, by forming a cache coalition. Although such a coalition could be beneficial as a whole, it neglects the profits of individual members, which is one major concern in forming the coalition itself. Besides, due to the poor scalability, the conventional cooperation scheme, which only considers fixed edge nodes, cannot adapt to the spatial and temporal imbalance of user requests. In this article, we tackle the problems of coalition establishment and profit allocation among the coalition members. Particularly, by adopting both fixed edge nodes and mobile vehicles as caching nodes, we propose a hybrid service provisioning framework and cooperative service caching and workload scheduling methods. To maximize the profits in managing the caching resources in the established coalition, we devise an optimization model with a mixed-integer programming (MIP), in which the QoS requirements of end users and caching capacities of each coalition member are also considered as constraints. In addition, based on the Hedonic game theory, we propose a dynamic coalition algorithm to guide each member to join or leave the coalition at each time slot out of its own profits. The experimental results demonstrate that compared to the cases only considering fixed caching nodes, our hybrid caching scheme can improve: 1) the overall profit of the coalition by 53% and 2) the average profit of individual participants by 42%, respectively.

Improving Physical Layer Security of Cooperative NOMA System with Wireless-Powered Full-Duplex Relaying

Non-orthogonal multiple access (NOMA) and wireless energy harvesting are two promising technologies for improving spectral efficiency and energy efficiency, respectively. In this paper, we study the physical layer security of a wireless-powered full-duplex (FD) relay-aided cooperative NOMA system. In particular, the source is wiretapped by an eavesdropper, and the FD relay assists the transmission from the source to a near user and a far user with self-energy recycling. To enhance the security performance of the system, we propose an artificial noise (AN)-aided cooperative transmission scheme, in which the relay emits a jamming signal to confuse the eavesdropper while receiving the signal from the source. For the proposed scheme, the ergodic secrecy sum rate (ESSR) is derived to characterize the secrecy performance and a lower bound of ESSR is obtained. Finally, numerical results verify the accuracy of the theoretical analysis of the proposed AN-aided secure transmission scheme. The superiority of the proposed scheme is also demonstrated since this scheme can achieve better secrecy performance, compared to the conventional cooperative NOMA scheme.

Hybrid NOMA/OMA Broadcasting-and-Buffer-State-Based Relay Selection

In this paper, we propose a novel buffer-aided relay selection scheme that is capable of amalgamating the concepts of non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA) in the context of two-hop cooperative networks supporting multiple relays. This is enabled by allowing relay nodes to share a common information packet in their buffers with the aid of a source-to-relay broadcasting mode. Hence, the proposed relay selection scheme switches between diverse modes of uplink NOMA, downlink NOMA, unicast, source broadcasting, and cooperative beamforming. The theoretical bounds of the outage probability, throughput, average delay, and diversity order are derived for the proposed scheme, based on a Markov chain model. Through our analytical and numerical results, it is demonstrated that the proposed scheme is capable of switching to one of the best modes in an adaptive manner while outperforming the conventional buffer-aided cooperative schemes.

Underlay Cognitive NOMA-Based Coordinated Direct and Relay Transmission

In this letter, a cooperative underlay cognitive non-orthogonal multiple access (NOMA)-based coordinated direct and relay transmission is investigated. Specifically, exact closed-form expressions for the outage probabilities (OPs) of the primary and SNs are derived, based on which the respective asymptotic analysis are carried out. Our results show the superiority of the proposed system when compared with conventional cooperative schemes. Also, it is shown that there exists an optimal point where the transmit powers of the primary and STs can be set in order to ensure a good performance for both networks.

Deep Multi-Task Learning for Cooperative NOMA: System Design and Principles

Envisioned as a promising component of the future wireless Internet-of-Things (IoT) networks, the non-orthogonal multiple access (NOMA) technique can support massive connectivity with a significantly increased spectral efficiency. Cooperative NOMA is able to further improve the communication reliability of users under poor channel conditions. However, the conventional system design suffers from several inherent limitations and is not optimized from the bit error rate (BER) perspective. In this article, we develop a novel deep cooperative NOMA scheme, drawing upon the recent advances in deep learning (DL). We develop a novel hybrid-cascaded deep neural network (DNN) architecture such that the entire system can be optimized in a holistic manner. On this basis, we construct multiple loss functions to quantify the BER performance and propose a novel multi-task oriented two-stage training method to solve the end-to-end training problem in a self-supervised manner. The learning mechanism of each DNN module is then analyzed based on information theory, offering insights into the explainable DNN architecture and its corresponding training method. We also adapt the proposed scheme to handle the power allocation (PA) mismatch between training and inference and incorporate it with channel coding to combat signal deterioration. Simulation results verify its advantages over orthogonal multiple access (OMA) and the conventional cooperative NOMA scheme in various scenarios.

Layered Inter-Cluster Cooperation Scheme for Backhaul-Constrained C-RAN Uplink Systems in the Presence of Inter-Cluster Interference.

Despite the potential benefits of reducing system costs and improving spectral efficiency, it is challenging to implement cloud radio access network (C-RAN) systems due to the performance degradation caused by finite-capacity fronthaul links and inter-cluster interference signals. This work studies inter-cluster cooperative reception for the uplink of a two-cluster C-RAN system, where two nearby clusters interfere with each other on the uplink access channel. The radio units (RUs) of two clusters forward quantized and compressed version of the uplink received signals to the serving baseband processing units (BBUs) via finite-capacity fronthaul links. The BBUs of the clusters exchange the received fronthaul signals via finite-capacity backhaul links with the purpose of mitigating inter-cluster interference signals. Optimization of conventional cooperation scheme, in which each RU produces a single quantized signal, requires an exhaustive discrete search of exponentially increasing search size with respect to the number of RUs. To resolve this issue, we propose an improved inter-BBU, or inter-cluster, cooperation strategy based on layered compression, where each RU produces two descriptions, of which only one description is forwarded to the neighboring BBU on the backhaul links. We discuss the optimization of the proposed inter-cluster cooperation scheme, and validate the performance gains of the proposed scheme via numerical results.

Efficient relay selection scheme utilizing superposition modulation in cooperative communication

In this paper, a cooperative communication scheme is proposed utilizing superposition modulation (SM) in orthogonal frequency division multiplexing (OFDM). The proposed relay selection scheme selects an optimal relay and improves the BER performance by utilizing SM in cooperative communication. Also, the proposed cooperative communication scheme transmits the signal of source and relay at the same time by utilizing SM. As a result, the proposed schemes select the optimal relay and improve the reliability and throughput compared with the conventional cooperative communication scheme.

Signal Space Cognitive Cooperation

In this work, a new transmission scheme, signal space cognitive cooperation, is introduced by applying the idea of signal space diversity in an underlay spectrum sharing decode-and-forward multi-relay cooperative network. In the proposed structure, the secondary source signal is rotated by a certain angle and then the source and the secondary best relay transmit the in-phase and the quadrature components of the rotated signal. As a consequence, two source signals, rather than one, are transmitted in two-time slots which improves data rates considerably, compared to the conventional cognitive cooperative schemes. In this work, proactive relaying mode is used in which the best relay is selected based on the max-min selection criterion before executing the transmission. Considering both statistical and the instantaneous channel state information of the feedback channel between the primary receiver and the secondary network, two power allocation methods are adopted at the source. For both methods, closed-form expressions of error probability are derived. Moreover, asymptotic analysis is performed and diversity gain is obtained to provide further insights about the system performance. Finally, analytical expressions are verified by Monte-Carlo simulations.

Non-Orthogonal Multiple Access Assisted Device-to-Device Communication: Best Helping Base Station Approach

&lt;span&gt;It can be studied in this paper that a cooperative non-orthogonal multiple access (NOMA) helps device-to-device (D2D) communication system through base station (BS). In particular, we investigate BS selection scheme as a best channel condition for dedicated devices where a different data transmission demand on each device is resolved. The analysis on amplifying-and forward (AF) relay is proposed to evaluate system performance of the conventional cooperative NOMA scheme. Under the realistic assumption of perfect channel estimation, the achievable outage probability of both devices is investigated, and several impacts on system performance are presented. The mathematical formula in closed form related to probability has also been found. By implementing Monte-Carlo simulation, the simulation results confirm the accuracy of the derived analytical results. Also, the proposed D2D cooperative NOMA system introduces expected performance on reasonable selected parameters in the moderate signal to noise ratio (SNR) regime.&lt;/span&gt;

Distributed polar-coded OFDM based on Plotkin’s construction for half duplex wireless communication

ABSTRACTA Plotkin-based polar-coded orthogonal frequency division multiplexing (P-PC-OFDM) scheme is proposed and its bit error rate (BER) performance over additive white gaussian noise (AWGN), frequency selective Rayleigh, Rician and Nakagami-m fading channels has been evaluated. The considered Plotkin’s construction possesses a parallel split in its structure, which motivated us to extend the proposed P-PC-OFDM scheme in a coded cooperative scenario. As the relay’s effective collaboration has always been pivotal in the design of cooperative communication therefore, an efficient selection criterion for choosing the information bits has been inculcated at the relay node. To assess the BER performance of the proposed cooperative scheme, we have also upgraded conventional polar-coded cooperative scheme in the context of OFDM as an appropriate bench marker. The Monte Carlo simulated results revealed that the proposed Plotkin-based polar-coded cooperative OFDM scheme convincingly outperforms the conventional polar-coded cooperative OFDM scheme by 0.5 ~ 0.6 dBs over AWGN channel. This prominent gain in BER performance is made possible due to the bit-selection criteria and the joint successive cancellation decoding adopted at the relay and the destination nodes, respectively. Furthermore, the proposed coded cooperative schemes outperform their corresponding non-cooperative schemes by a gain of 1 dB under an identical condition.

A Proposed H-STCDD Scheme in Cooperative Communication System

In this paper, the hierarchical space time cyclic delay diversity (H-STCDD) scheme is proposed. Proposed scheme uses hierarchical modulation and achieves approximately full rate. It also uses a cyclic delay diversity scheme, which improves the benefit of channel coding particularly in high SNR environment between source to relay and source to destination. According to simulation result, proposed scheme has up to 2.2 dB better BER performance than conventional cooperative scheme at BER of 10ź3 and has similar BER performance with the STCDD scheme particularly in high SNR environment between source to relay and source to destination. Throughput of the proposed scheme is better than those of other cooperative schemes. Therefore proposed scheme is more efficient than other cooperative scheme and can be efficiently used in high SNR environment between source to relay and source to destination.

Degrees of Freedom in Cached MIMO Relay Networks

It is well known that conventional cooperative relay schemes cannot provide Degrees of Freedom (DoF) gains due to the cut-set bound. In this paper, we propose a physical layer (PHY) caching scheme for relay networks to achieve DoF gains over conventional relay schemes. By properly caching some popular content at the relay station (RS), the proposed PHY caching can opportunistically transform the unfavorable relay channel topology into a more favorable MIMO broadcast channel topology (cache-induced MIMO cooperation opportunity) and enjoy a large DoF gain. Specifically, we first propose a maximum distance separable (MDS) coded PHY caching scheme to significantly improve the MIMO cooperation opportunity induced by PHY caching. Then we propose a global optimal cache content placement solution to maximize the DoF gain. We also propose a low complexity cache content placement algorithm to find a near-optimal solution without explicit knowledge of the popularity of the content files. Finally, we quantify the DoF gain w.r.t. some important system parameters. Simulations show that the proposed scheme can achieve significant throughput gains over various baselines.

Cooperative Stepwise Relaying and Combining for Multihop Vehicular Wireless Communication

Vehicular ad hoc networks (VANETs) require cooperation among vehicles in exchanging information, which improves traffic efficiency and safety. Cooperative communication among these vehicles can significantly improve wireless communication performance. This paper proposes a novel cooperative scheme named cooperative stepwise relaying and combining (CSRC) for multihop VANETs, which utilizes low-order demodulations to partially demodulate high-order modulated signals cooperatively at intermediate relay vehicular nodes. Bit error rate (BER) probability is analyzed. The performance comparison among the proposed CSRC and conventional cooperative schemes is conducted through simulation and a software-defined radio testbed. The experiment results show that CSRC significantly improves the multihop VANETs' performance with cooperative communication.

Smart Cooperative System Using Orthogonal Signaling with Signal Space Diversity

In this paper, an efficient cooperative transmission scheme with signal space diversity is proposed for two-user cooperative systems. In contrast with the conventional cooperative scheme based on orthogonal signaling, the proposed scheme obtains signal space diversity by utilizing rotated constellation. Because the proposed scheme provides much information to receiver in decoding process, a receiver can decode information more accurately. Therefore, the proposed scheme improves the bit error rate performance in severe fading channel environments. Simulation results demonstrate that the performance of the proposed scheme is especially superior to the performance of the conventional scheme in low inter-user channel quality.

Interference Alignment in Two-Cell LTE-Advanced Heterogeneous Networks

In this paper, we address the issue of interference alignment (IA) in a two-cell network and consider both inter-cell and intra-cell interferences. For cell one, a linear processing scheme is proposed to align the inter-cell interference to the same signal dimension space of intra-cell interference. For cell two, we propose a distributed interference alignment scheme to manage the interference from the nearby cell. We assume that the relay works in an amplify-and-forward (AF) mode with a half-duplex and MIMO relaying. We show that the composite desired and interfering signals aggregated over two time slots can be aligned such that the interfering signal is eliminated completely by applying a linear filter at the receiver. The precoding matrix of the relay is optimized jointly with the precoding matrix of the base station (BS). The number of data streams is optimized jointly for every user terminal (UT). The degree of freedom (DoF) performance of the proposed scheme as well as the conventional cooperation scheme are derived for multiple antennas at both base stations, relay station and user terminals. Simulation results show that the proposed alignment scheme can achieve a better DoF performance.

Reciprocally Benefited Spectrum Access Scheme With Joint Power and Subcarrier Allocation in a Software-Defined Network

Aiming at realizing ubiquitous spectrum access and improving the spectrum efficiency in a software-defined network, in this paper, we adopt the concept of cognitive radio and propose a joint subcarrier and power allocation (JSPA) scheme for reciprocally benefited spectrum access with secondary users (SUs) cooperating with primary users (PUs). In our proposed JSPA scheme, SUs adopt the decode-and-forward relaying protocol to help PUs in a two-stage way. Meanwhile, a fraction of unallocated licensed spectrum is allocated for the secondary transmission in every stage. However, if the two-stage cooperation still cannot satisfy the PUs’ outage quality-of-service (QoS) requirement, SUs then switch to the access mode and entirely capture the licensed spectrum. Our proposed scheme is to maximize the average transmission rate of SUs through joint optimal subcarriers and power allocation under the constraint of PUs’ outage QoS requirement. The closed-form expressions about the outage probability and average transmission of both PUs and SUs are derived, and we prove the optimality of our scheme. Simulation results show that, compared with the conventional cognitive cooperation scheme, the average transmission rate of SUs is improved.

디코딩 후 전달 중계 시스템에서 부분 중계 노드 선택 기법 기반 기회적 협력 방식의 아웃티지 성능 분석

In this paper, we study the opportunistic cooperation scheme that improves the outage performance through the efficient selection between a cooperative mode and a non-cooperative mode. Especially, in decode-and-forward relaying systems, we analyze the outage performance for the opportunistic cooperation using partial relay selection, where closed-form expressions of exact and asymptotic outage probabilities are derived assuming independent and identically distributed Rayleigh fading channels. In the numerical results, we verify the derived expressions, and investigate the outage performances for various target data rates and different numbers of relays. Also, we compare the outage performances of the conventional cooperation scheme and the opportunistic cooperation scheme.

A Lightweight Selection Cooperation Protocol with Multiple Available Best Relays

Selection cooperation has shown to be a practical cooperative strategy for wireless networks. In order to obtain full diversity gain, conventional selection cooperation schemes must select the node with the maximum relay-destination channel as the best relay, which restricts the choice of relay selection for the system. To overcome this limitation, we propose a lightweight selection cooperation protocol without requiring the radio of nodes to perform combining reception. Through outage probability and diversity-multiplexing tradeoff (DMT) analysis, we reveal an interesting fact that choosing any node that successfully receives the message from the source and the feedback frame from the destination as the best relay, the protocol always achieves the full diversity order and the optimal DMT. This result establishes a framework for obtaining multiple optimization objectives in selection cooperation networks. As an illustrative example, we then develop two best relay selection methods for relay balance without sacrificing the full diversity order. Simulation results demonstrate the remarkable performance and balance effect of the proposed protocol and selection methods.