User Cooperation Scheme Research Articles

Ambient Backscatter-Based User Cooperation for mmWave Wireless-Powered Communication Networks with Lens Antenna Arrays

With the rapid consumer adoption of mobile devices such as tablets and smart phones, tele-traffic has experienced a tremendous growth, making low-power technologies highly desirable for future communication networks. In this paper, we consider an ambient backscatter (AB)-based user cooperation (UC) scheme for mmWave wireless-powered communication networks (WPCNs) with lens antenna arrays. Firstly, we formulate an optimization problem to maximize the minimum rate of two users by jointly designing power and time allocation. Then, we introduce auxiliary variables and transform the original problem into a convex form. Finally, we propose an efficient algorithm to solve the transformed problem. Simulation results demonstrate that the proposed AB-based UC scheme outperforms the competing schemes, thus improving the fairness performance of throughput in WPCNs.

Energy Efficiency Maximization of Backscatter-Assisted Wireless-Powered MEC With User Cooperation

The integrated backscatter communication (BackCom) and active communication (AC) scheme can improve wireless powered mobile edge computing (WPMEC) system performance in general single-user and multi-user scenarios. However, there is little research in the cooperation-assisted WPMEC scenario. In this paper, we consider a cooperation-assisted WPMEC system consisting of a source node (SN), a helper and a hybrid access point (HAP) integrated with MEC servers. An innovative user cooperation (UC) scheme with integrated BackCom and AC is proposed to enhance the system performance. As a relay, the helper can help the SN to transmit its computing tasks due to the poor communication link between the SN and the HAP. To be specific, we aim at maximizing the user energy efficiency (EE) by jointly optimizing backscatter reflection coefficient for BackCom, transmission power for AC, system time and tasks allocation while considering the minimum computation bits requirement, the channel capacity and energy constraints. Based on a fractional program, the EE maximization problem first is transformed to an equivalent one. Then, we exploit variable substitution and convex optimization to transform this non-convex problem into a convex problem. In addition, semi-closed form expressions of the optimal solution are deduced. An energy efficiency maximization algorithm is proposed to solve this problem. Simulation results demonstrate that the proposed scheme significantly improves the user EE than the existing schemes.

Optimizing Computation Efficiency for NOMA-Assisted Mobile Edge Computing With User Cooperation

In this article, we investigate the application of user cooperation (UC) and non-orthogonal multiple access (NOMA) schemes for a wireless powered mobile edge computing (MEC) system under the non-linear energy harvesting model, in which two single-antenna mobile users first harvest energy from a multi-antenna access point (AP) integrated with an MEC server. Then, during the computation offloading phase, both mobile users simultaneously offload tasks to the MEC server with the harvested energy, by performing NOMA protocol. To better enhance the system performance, UC scheme is carried out, where the near user acts as a relay to help the far user offload computation tasks to the AP. To obtain energy efficient MEC design, our objective is to maximize the computation efficiency (i.e., the total computation bits divided by the consumed energy) by jointly designing the energy beamforming, time and power allocations, which yields a challenging nonconvex optimization problem. To deal with it, the original problem is first transformed into a more tractable formulation by applying the semidefinite relaxation (SDR) technique and then solved by utilizing the sequential convex approximation (SCA) method. Numerical results demonstrate that UC has a great impact when two users are close, while NOMA makes effect when two users are relatively far. Combining both NOMA and UC, the proposed scheme, named NOMA-UC MEC, yields better system performance than the benchmark schemes.

Angle Aware User Cooperation for Secure Massive MIMO in Rician Fading Channel

Massive multiple-input multiple-output communications can achieve high-level security by concentrating radio frequency signals towards the legitimate users. However, this system is vulnerable in a Rician fading environment if the eavesdropper positions itself such that its channel is highly “similar” to the channel of a legitimate user. To address this problem, this paper proposes an angle aware user cooperation (AAUC) scheme, which avoids direct transmission to the attacked user and relies on other users for cooperative relaying. The proposed scheme only requires the eavesdropper’s angle information, and adopts an angular secrecy model to represent the average secrecy rate of the attacked system. With this angular model, the AAUC problem turns out to be nonconvex, and a successive convex optimization algorithm, which converges to a Karush-Kuhn-Tucker solution, is proposed. Furthermore, a closed-form solution and a Bregman first-order method are derived for the cases of large-scale antennas and large-scale users, respectively. Extension to the intelligent reflecting surfaces based scheme is also discussed. Simulation results demonstrate the effectiveness of the proposed successive convex optimization based AAUC scheme, and also validate the low-complexity nature of the proposed large-scale optimization algorithms.

Multicast Transmissions With Full-Duplex Amplify-and-Forward User Cooperation

In order to improve the multicast transmissions, a full-duplex (FD) user cooperation scheme is proposed. In this paper, the transmitter sends the common messages to two FD users, and each user forwards its received signals to its counterpart by amplify-and-forward (AF) scheme. Considering the imperfect self-interference (SI) cancellation at the users and the AF scheme, the residual self-interference and the additive noise (RIAN) is shown to be accumulated over time. This paper first analyzes the equivalent channel model of the considered system, as well as the asymptotic statistics of the accumulated RIAN. Then, with the forward and backward decoding schemes, the corresponding achievable rates are derived, and the optimal power allocation is obtained via solving a max-min problem. In particular, one-side cooperation scheme (i.e., only one user forwards its received signal to its counterpart) is shown to be optimal to achieve the best system performance.

D2D-Enabled User Cooperation in Massive MIMO

In this article, we investigate device-to-device (D2D) communication-enabled user cooperation in massive multiple-input multiple-output (MIMO) systems. In frequency-division duplexing massive MIMO systems, cascaded precoding has been adopted to reduce the overhead of channel estimation and limited feedback. The inner precoder in cascaded precoding depends on the spatial covariance matrix of the massive MIMO channel and can be the same for the users that are close to each other. When the users are close to each other, high-quality D2D links can be expected among the users and the users can form a virtual MIMO receiver via D2D links. Since the users may require different services, the required transmission rates of those users can also be different. To improve the overall user experience, utility functions are adopted in this article and two D2D-enabled user cooperation schemes, including the data-symbol-information exchanging and receive-signal-information exchanging, are proposed, which can allocate the overall transmission rate among the users adaptively in terms of the required transmission rates of different users. In this way, the overall utility function can be maximized.

User Cooperation in Wireless-Powered Backscatter Communication Networks

In this letter, we introduce new user-cooperation schemes for wireless devices in a wireless-powered backscatter communication network with the aim to improve communication and energy efficiency for the whole network. In particular, we consider two types of wireless devices which can support different communication modes, i.e., backscatter and harvest-then-transmit, and they can cooperate to deliver the information to the access point. To improve energy transmission efficiency for the devices, energy beamforming is deployed at the power beacon. We then formulate the weighted sum-rate maximization problem by jointly optimizing time schedule, power allocation, and energy beamforming. Due to the non-convex issue of the optimization problem, we employ the variable substitutions and semidefinite relaxation techniques to obtain the optimal solution. Simulation results show that the proposed cooperation framework can significantly improve the communication efficiency compared with non-cooperation approach.

Cooperative Multi-Path Routing Solution With Real-Time Optimization for Streaming Application Using Auction Theory

Cooperation among network devices is a promising approach to improve network throughput and network service quality. In addition, it can be used to enhance network survivability against failures. In this paper, we study a cooperative multi-path routing solution for wireless Users Equipment (UEs)’ streaming applications. We assume that UEs use multi-path transport layer service, and establish two paths for streaming, one path goes through its cellular link, and the other path is established using a Wi-Fi connection with a neighbor UE. We study a user coordinated multi-path routing solution with two different energy cost functions, a Linear Cost Function (LCF) and Energy As the Cost (EAC) and design user cooperative real-time optimization and failure protection operations for the streaming application. To stimulate UEs to participate in the user cooperation operation, we design a credit system enabled by an auction mechanism. We compare the performance of user cooperation schemes to the non-cooperative scheme, and using simulation results show that applying the proposed user cooperation scheme and establishing multi-path connections for streaming has an advantage in improving the service rate and streaming success rate, and reduces energy consumption compared to non-cooperation solutions. User cooperation scheme with LCF energy cost function can also help balance the energy consumption among UEs in the system compared to user cooperation scheme with EAC energy cost function.

Physical Layer Security for Land Mobile Satellite Communication Networks With User Cooperation

In this paper, we investigate the physical layer security of land mobile satellite (LMS) communication networks, where the multiple legitimate users and eavesdroppers are considered in the system. In order to obtain the best system performance, we propose the cooperating scheme for legitimate users to receive the main signal. Besides, we design two representative eavesdropping scenes for the eavesdroppers, namely, Scene I, colluding scene: the eavesdroppers cooperate with each other and wiretap the information of the main channel together, and the Scene II, non-colluding scene which is the best eavesdropping scene, namely, the most harmful eavesdropper will be selected to overhear the information channel. Furthermore, we obtain the closed-form expressions for the non-zero probability of secrecy capacity, the secrecy outage probability (SOP), and average secrecy capacity (ASC) based on the proposed user cooperation scheme in the presence of two eavesdropping scenes. In order to obtain more insights at the high signal-to-noise-ratios, the asymptotic expressions for the SOP and ASC are also derived under two scenes, from which we can derive the effect of different parameters on the system performance conveniently. Finally, some representative Monte Carlo simulation results are provided to verify the correctness of the obtained analytical results.

Energy Beamforming Design and User Cooperation for Wireless Powered Communication Networks

We investigate user cooperation (UC) for wireless powered communication networks, where two single-antenna users are first wirelessly powered by a multi-antenna hybrid access point (H-AP), and then cooperatively transmit information signals to this H-AP via the harvested energy. To incorporate user fairness in the system performance, we formulate the weighted sum-rate maximization problem for both users to jointly optimize the energy beamforming vector, time allocation, and power allocation. Due to the non-convexity of this problem, we propose two UC schemes by employing a series of efficient variable substitutions and semidefinite programming relaxation to solve this problem. In addition, we show that the solution of the proposed schemes can achieve the global optimum by exploiting the rank-one characteristic of the energy beamforming matrix. Finally, numerical results are provided to validate our proposed schemes, which quantifies the impact of UC schemes by comparing them with the non-cooperative scheme.

Optimal Resource Allocation in Wireless Powered Communication Networks With User Cooperation

This paper investigates the optimal resource allocation in wireless powered communication network with user cooperation, where two single-antenna users first harvest energy from the signals transmitted by a multi-antenna hybrid access point (H-AP) and then cooperatively send information to the H-AP using their harvested energy. To explore the system information transmission performance limit, an optimization problem is formulated to maximize the weighted sum-rate (WSR) by jointly optimizing energy beamforming vector, time assignment, and power allocation. Besides, another optimization problem is also formulated to minimize the total transmission time for given amount of data required to be transmitted at the two sources. Because both problems are non-convex, we first transform them to be convex by using proper variable substitutions and then apply semi-definite relaxation to solve them. We theoretically prove that our proposed methods guarantee the global optimum of both problems. Simulation results show that system WSR and transmission time can be significantly enhanced by using energy beamforming and user cooperation. It is observed that when the total amount of information of two users is fixed, with the increase of the information amount of the user relatively farther away from the H-AP, the transmission time of the user cooperation scheme decreases while that of the direct transmission increases. Besides, the effects of user position on the system performances are also discussed, which provides some useful insights.

On Physical Layer Security: Weighted Fractional Fourier Transform Based User Cooperation

In this paper, we propose a novel user cooperation scheme based on weighted fractional Fourier transform (WFRFT), to enhance the physical (PHY) layer security of wireless transmissions against eavesdropping. Specifically, instead of dissipating additional transmission power for friendly jamming, by leveraging the features of WFRFT, the information bearing signal of cooperators can create an identical artificial noise effect at the eavesdropper while causing no performance degradation on the legitimate receiver. Furthermore, to form the cooperation set in an autonomous and distributed manner, we model WFRFT-based PHY-layer security cooperation problem as a coalitional game with non-transferable utility. A distributed merge-and-split algorithm is devised to facilitate the autonomous coalition formation to maximize the security capacity while accounting for the cooperation cost in terms of power consumption. We analyze the stability of the proposed algorithm and also investigate how the network topology efficiently adapts to the mobility of intermediate nodes. Simulation results demonstrate that the WFRFT-based user cooperation scheme leads to a significant performance advantage, in terms of secrecy ergodic capacity, compared with the conventional security-oriented user cooperation schemes, such as relay-jamming and cluster-beamforming.

Optimal Pricing and User Cooperation for Utility-Efficient Wireless Powered Communications

In this study, optimal pricing and user cooperation schemes are considered in a wireless powered communication network (WPCN), where multiple users harvest energy from a dedicated hybrid access point (HAP, as a power station in the downlink) and transmit their independent information to HAP (as an information receiving station in the uplink) by using the harvested energy. Due to the doubly near-far problem, best cooperation-user selection scheme where the dedicated helping user which is nearer to the H-AP and in general has better channel condition both for DL energy harvesting as well as UL information transmission from source user uses its harvested energy to help forward the source user’s information to H-AP is proposed. Moreover, in the WPCN, the energy is scarce, users have incentive to refuse to cooperate in order to conserve resource. We propose a pricing mechanism to incentivize the helping user to cooperate the uplink transmission. Two transmission protocols for source-user centric and helping-user centric with pricing mechanism are investigated. We formulate the pricing and resource allocation problem as optimization problem and propose efficient algorithms by jointly user-selection and resource allocation to maximize the energy efficient and price-performance ratio. Numerical results show that the proposed scheme with pricing can enhance the source user’s performance with lower cost. Moreover, the pricing mechanisms can incentivize the helping user to cooperate other users’ to decrease the system energy cost.

Security-embedded opportunistic user cooperation with full diversity

As a promising technique for wireless networks, cooperative communications is coming to maturity in both theory and practice. The main merit of the cooperation technique is its capability in providing additional transmission links to harvest the spatial diversity gain at the physical layer. However, due to the broadcast nature of wireless medium, the diversity gain can be also freely achieved at the potential eavesdropper if the cooperation is performed blindly. To solve this problem, we propose a security-embedded opportunistic user cooperation scheme (OUCS) in this paper. The OUCS first defines a concept called secrecy-providing capability (SPC) for both the source and the cooperative relays. By comparing the values of SPC of these nodes, the OUCS jointly decides whether to cooperate and with whom to cooperate from the perspective of physical layer security. The secrecy outage performance of the OUCS is then derived. From the results we prove that full diversity can be achieved (i.e., the diversity order is N + 1 for N cooperative relays), which outperforms existing alternatives. Finally, numerical results are provided to validate the theoretical analysis.

Distributed source-relay selection scheme for vehicular relaying networks under eavesdropping attacks

Abstract The recent development of vehicular networking technologies brings the promise of improved driving safety and traffic efficiency. Cooperative communication is recognized as a low-complexity solution for enhancing both the reliability and the throughput of vehicular networks. However, due to the openness of wireless medium, the vehicular wireless communications (VWC) is also vulnerable to potential eavesdropping attacks. To tackle with this issue, we in this paper propose a novel user-cooperation scheme with anti-eavesdropping capabilities. Specifically, prior to any frame transmission, a source-relay pair is jointly selected to maximize the achievable secrecy rate. After that, the selected relay assists the source to deliver its data to the destination. The proposed selection scheme can be realized in a fully distributed manner, and the security is guaranteed without using any encryption techniques at the upper layers. The closed-form expressions for the secrecy outage probability and the intercept probability are derived, and the achievable diversity order is also analyzed. Simulation results show that the proposed scheme outperforms the competing counterparts in terms of both the secrecy outage probability and the average secrecy rate.

Realizing high-accuracy transmission in high-rate data broadcasting networks with heterogeneous users via cooperative communication

This paper considers a broadcasting network in which multiple single-antenna (weak) and multiantenna (strong) users are receiving simultaneously spatial-multiplexed data streams from the multiantenna base station (BS). In order to improve the received data quality for the single-antenna users while preserving the transmission rates of the multiantenna users, we propose user cooperation schemes without the employment of space–time codes or retransmission from the BS which reduce the data rates and the spectral efficiency. Three cooperation schemes among single-antenna users, namely, decode-and-forward (DF), amplify-and-forward (AF), and hybrid cooperation, are examined and compared. Simulation results demonstrate that single-antenna users through cooperation can achieve comparable or superior error-rate performance as compared with noncooperative multiantenna users. Various configurations of the proposed cooperation schemes are studied to show the tradeoff in terms of cooperation overhead, receiver complexity, and system performance. The acquisition of the channel information and the effect of channel estimation errors on the system performance are also investigated for practical implementation of the proposed schemes. The proposed schemes are capable of avoiding modification to the multiple-input multiple-output (MIMO) transceivers, and are readily applicable to existing MIMO broadcasting networks.

네트워크 코딩 기반의 협력통신에서 Hybrid AF and DF 방식의 아웃티지 성능 분석 및 최적 파워 할당 기법

네트워크 코딩은 멀티캐스트 네트워크에서 전송량을 증가시키기 위해 제안된 기법으로 최근에는 다수의 사용자가 성능 향상을 위해서로의 자원을 공유하는 협력통신에 네트워크 코딩을 적용하는 연구가 활발히 진행 중이다. 네트워크 코딩 기반의 협력통신에서 사용자는 자기 자신의 데이터와 다른 사용자의 데이터를 네트워크 코딩 연산을 통해 결합하여 전송한다. 기존의 연구에서는 네트워크 코딩을 기반으로 한 적응형 복호 후 전송(Network-Coding-based Adaptive Decode-and-Forward, NC-ADF) 방식이 다이버시티(diversity) 이득과 추가적인 전송량 증대를 가져올 수 있음을 보였다. 본 논문에서는 기존 프로토콜의 성능 증대와 네트워크 코딩의 이득을 극대화 하기 위해 사용자간 채널의 상태에 따라 증폭 후 전송(Amplify-and-Forward, AF) 방식과 복호 후 전송(Decode-and-Forward, DF) 방식을 적응적으로 적용한 새로운 네트워크 코딩 기반의 협력통신 기법을 제안하였다. 또한 제안한 기법의 아웃티지 확률을 구하고 높은 SNR 영역에서 최대 다이버시티 차수(full diversity order)를 가짐을 보였다. 나아가 추가적인 성능 향상을 위해 본 논문에서 제안된 기법에 의한 아웃티지 확률을 기반으로 최적의 전송 파워 비율을 구하였다. Network coding was proposed to increase the achievable throughput of multicast in a network. Recently, combining network coding into user cooperation has attracted research attention. For cooperative transmission schemes with network coding, users combine their own and their partners messages by network coding. In previous works, it was shown that adaptive DF with network coding can achieve diversity gain and additional throughput gain. In this paper, to improve performance of conventional protocols and maximize advantage of using network coding, we propose a new network coding based user cooperation scheme which uses adaptively amplify-and-forward and decode-and-forward according to interuser channel status. We derive outage probability bound of proposed scheme and prove that it has full diversity order in the high SNR regime. Moreover, based on the outage bound, we compute optimal power allocation for the proposed scheme.

Network-coding-based coded cooperation

Coded cooperation is a promising user cooperation scheme. In this paper, we first propose a novel network-coding-based coded cooperation scheme. When a user decodes its partner's information correctly in the first frame, it transmits the combination of the partner's parity bits and its own parity bits through network coding in the second frame. This is distinct from the classical scheme, where the user only transmits the partner's parity bits during cooperation. We analyze the outage probability of the proposed scheme, and show that it achieves a full diversity order. Numerical evaluations reveal that the proposed scheme outperforms the classical scheme when the inter-user channel is poor, yet is worse when the inter-user channel is strong. Also, the results show that the proposed scheme always outperforms that of no cooperation in various channel conditions while the performance of classical scheme is worse than that of no cooperation with the poor inter-user channels. This means that the performance of the proposed scheme is more stable than the classical scheme and the proposed scheme is more tolerant to the poor inter-user channels. To combine the advantages of the proposed scheme and the classical scheme under different inter-user channel conditions, we propose an adaptive solution. This adaptive scheme enhances the system performance considerably in all channel conditions in spite of the inter-user channel quality, at the expense of only one acknowledgement or non-acknowledgement bit.

Quality of Service Analysis for Wireless User-Cooperation Networks

A wireless communication system in which multiple users cooperate to transmit information to a common destination is considered. The traffic generated by the users is subject to a stringent quality of service requirement, which is defined in terms of the asymptotic decay-rate of buffer occupancy. The performance of this communication system is analyzed, and the corresponding achievable rate-region for the two-user scenario is identified. A simple user-cooperation scheme that improves performance is proposed. This cooperative scheme is shown to significantly enlarge the achievable rate-region of the service constrained communication system, provided that the quality of the wireless link between cooperating users is better than the individual connections from the users to the intended destination. Numerical results further indicate that the gains of cooperative strategies can be substantial. This suggests that cooperation allows for a fair distribution of the wireless resources among active users.

Power efficiency of user cooperation in multihop wireless networks

In this paper we analyze the power efficiency of a user cooperation scheme for multihop wireless networks. In this scheme, the signals are jointly transmitted by two mobile terminals (MTs), emulating transmit macro diversity. We derive the optimal transmit power assignments for the two transmitting MTs and quantify the power efficiency of the scheme. The results indicate that macro diversity by way of user cooperation can substantially reduce the total consumed power in multihop wireless networks for wide range of topologies of MTs and their distances.