Performance Of Cooperative Networks Research Articles

Research on Energy Efficiency of NOMA-SWIPT Cooperative Relay Network Using GS-DinkelBach Algorithm.

In order to improve the energy efficiency (EE) performance of cooperative networks, this study combines non-orthogonal multiple access (NOMA) with simultaneous wireless information and power transfer (SWIPT) technologies to construct a cooperative relay network composed of one base station (BS), multiple near users, and one far user. Based on the network characteristics, a time-division resource allocation rule is proposed, and EE formulas regarding direct-link mode and cooperative mode are derived. Considering user selection and decoding performance, to obtain the optimal EE, this study utilizes a DinkelBach iterative algorithm based on the golden section (GS-DinkelBach) to solve the EE optimization problem, which is affected by power transmitted from the BS, achievable rates under three communication links, and quality of service (QoS) constraints of users. The simulation results show that the GS-DinkelBach algorithm can obtain precise EE gains with low computational complexity. Compared with the traditional NOMA–SWIPT direct-link network model and the relay network model, the optimal EE of the established network model could be increased by 0.54 dB and 1.66 dB, respectively.

Adaptive Power Factor Allocation for Cooperative Full-Duplex NOMA Systems With Imperfect SIC and Rate Fairness

This paper investigates the performance of cooperative networks based on non-orthogonal multiple access (NOMA) with multiple full-duplex decode-and-forward relays. Taking into account rate fairness between the users and assuming imperfect successive interference cancellation (SIC), the problem is formulated so that power allocation is performed adaptively by the multiple relays in order to maximize the minimum users’ achievable rate. We demonstrate that the proposed optimization problem is convex and a closed-form expression for the power allocation factor is derived. The attained results show that the proposed scheme achieves satisfactory results in terms of achievable rate, fairness, and outage probability when compared to other adaptive power allocation strategies.

A Novel Relay Selection Strategy of Cooperative Network Impaired by Bursty Impulsive Noise

Best relay selection (BRS) is crucial in enhancing the performance of cooperative networks. In contrast to most previous works, where the guidelines for BRS are limited to Gaussian noise, in this paper, we propose a novel relay selection protocol for a decode-and-forward cooperative network taking into account the bursty impulsive noise (IN). The proposed protocol chooses the $N$ th best relay considering both the channel gains and the states of the IN of the source-relay and relay-destination links. For this scheme, to obtain the state of IN, we propose a state detection algorithm using maximum a posteriori (MAP) detection. To analyze the performance of the proposed protocol, we first derive closed-form expressions for the probability density function (PDF) of the received signal-to-noise ratio assuming all the relays know the state of IN perfectly (genie-condition). Then, these PDFs are used to derive closed-form expressions for the bit error rate (BER) and the outage probability. Finally, we also derive the asymptotic BER and outage expressions to quantify the diversity benefits. We show that the proposed MAP-based $N$ th BRS protocol attains the derived genie-aided analytical results and outperforms the conventional relay selection protocol, optimized for the Gaussian case, and which does not take into account the IN memory.

Relay Selection in Adaptive Buffer-Aided Space-Time Coding with TAS for Cooperative Wireless Networks

In this work, we propose an adaptive buffer-aided space-time coding scheme for cooperative wireless networks. A maximum likelihood receiver and adjustable code vectors are considered subject to a power constraint with an amplify-and forward cooperation strategy. Each relay is equipped with a buffer and is capable of storing the received symbols before forwarding them to the destination. We also present an adaptive relay selection and a new hybrid relay selection protocol, in which the instantaneous signal to noise ratio in each link is calculated and compared at the destination. The transmit antenna selection (TAS) is adopted at the destination where a single transmit antenna at the transmitter and relay that maximizes the instantaneous received signal-to-noise ratio is selected for further transmissions to improve the performance of co-operative network. A stochastic gradient algorithm is then developed to compute the parameters of the adjustable code vector with reduced computational complexity. Simulation results show that the proposed buffer-aided schemes with TAS obtain performance gains over existing schemes.

Cooperative Transmission in Simultaneous Wireless Information and Power Transfer Networks

In this paper, we consider a cooperative simultaneous wireless information and power transfer (SWIPT) network with one source–destination pair and multiple energy harvesting relays. How to efficiently use these relays has been addressed in conventional cooperative networks, and this paper investigates the impact of SWIPT on the performance of such multirelay cooperative networks. In particular, the main contribution of this paper is that a closed-form expression of the outage probability achieved by the multirelay cooperative protocol is obtained, as well as its approximation at high SNR. In addition, the performance of the cooperative network with the SWIPT relays is compared with that in conventional systems with self-powered relays.

State‐based potential power allocation game in a cooperative multiuser network

Multiuser cooperative communications represent a research area of great interest constituting a key technology for future wireless networks. In this study, the authors consider a scenario of multi-user, single-relay network, where each user employs a part of the relay's transmission power taking into account the constraint of the total transmission power of the relay. The problem of relay power allocation to individual users with a view to optimising the long-term network performance is investigated. An adequate utility function is defined, in terms of outage probability, evaluating the cooperative network's performance due to the relay's cooperation. Taking into consideration the distributed nature of cooperative networks along with the coupled constraint of relay's total transmission power, the specific problem is transformed from a network-level to a user-level optimisation problem using a modern game-theoretic tool. More specifically, the initial power allocation problem is formulated as a state-based potential game for which the corresponding Nash equilibrium exists. Finally, a gradient learning mechanism is proposed to achieve the stationary state Nash equilibrium of the game that constitutes also the global optimal solution of the initial problem. The performance of the new proposed scheme is investigated through numerical simulations for various network parameters.

Efficient Relay Selection Scheme based on Fuzzy Logic for Cooperative Communication

The performance of cooperative network can be increased by using relay selection technique. Therefore, interest in relay selection is sloping upward. We proposed two new relay selection schemes based on fuzzy logic for dual hop cooperative communication. These relay selection schemes require SNR (signal to noise ratio), cooperative gain and channel gain as input fuzzy parameters for selection of best relay. The performance of first proposed relay selection scheme is evaluated in term of BER (bit error rate) in Nakagami, Rician and Rayleigh fading channels. In second proposed relay selection scheme, threshold is used with the objective to minimize the power consumption and channel estimation load. Its performance is analyzed in term of BER, number of active relays and load of number of channel estimations.

부분차등변조 방식을 이용한 협력네트워크에서의 중계기 위치의 영향

협력네트워크는 중계기를 이용하여 데이터를 전송함으로서 음영지역을 해소하고 가상의 다중입출력 구성을 통해 통신성능을 향상시킬 수 있다. 본 논문에서는 송신기와 중계기 사이에서는 동기변조 방식을 이용하고 중계기와 수신기 사이에서는 차등변조 방식을 이용하는 부분차등변조 방식을 적용한 협력네트워크의 성능을 중계기의 위치에 따라 분석한다. 성능분석은 송신기와 수신기사이의 직접파가 존재하는 시스템과 존재하지 않는 시스템 두 가지를 고려하는데, 직접파는 차등변조 방식을 적용한다. 또한 전체시스템이 차등변조 방식을 이용했을 경우에 중계기 위치에 따른 성능을 부분차등변조 방식과 비교한다. 시스템의 성능은 송신기와 수신기 사이의 심벌오류율을 이용한다. Cooperative networks eliminate shadow area using relay and enhance communication performance by creating virtual multi input multi output (MIMO) system. In this paper, we analyze the performance of cooperative networks which use coherent modulation scheme in source-relay nodes and differential modulation scheme in relay-destination nodes depending on the relay location. We consider the performance analysis of systems with and without the direct transmission between source and destination node where the direct transmission adopts differential modulation scheme. In addition, the performance of the system with fully differential modulation scheme is compared with the system using partially differential modulation scheme. The performance of system is based on the symbol error rate between source and destination node.

Adaptive limited feedback links for cooperative multi-antenna multicell networks

The overall performance of cooperative networks is quite sensitive to channel state information (CSI) of serving and interfering base stations (BSs) and affected strongly by quality of limited feedback links. In this paper, we propose two adaptive limited feedback strategies for intercell interference cancelation in multi-antenna multicell networks. The first proposed strategy is developed to improve average multicell capacity assuming a fixed rate feedback link. This algorithm is based on adaptation of the number of bits to quantize CSI of serving and interfering BSs according to transmitter power and location of the user in its own cell. The second proposed strategy is designed in a way to increase average capacity of cell-edge users assuming an adaptive rate feedback link. This algorithm is based on the idea of allocating more bits to quantize CSI of users at cell-edge regions while allocating less bits for users near the serving BS. We illustrate performance of the proposed feedback links for downlink cooperative multi-antenna multicell networks in wireless channels.

On performance of cooperative network based on OFDM combined with TDM using MMSE-FDC in the presence of nonlinear HPA

In this paper, we analyze the impact of nonlinear high-power amplifier (HPA) on the performance of cooperative network based on orthogonal frequency division multiplexing combined with time-division multiplexing (OFDM/TDM) using minimum mean-square-error frequency-domain combining (MMSE-FDC) in a frequency-selective fading channel. We design a novel MMSE-FDC weights while taking into account the nonlinearity of HPA at source and relay. Closed-form symbol error rate and outage probability expressions are derived while approximating the residual inter-slot interference after the MMSE-FDC as a random Gaussian variable. We discuss and address the nonlinear OFDM/TDM system design issues in cooperative network using the obtained simulation and theoretical results. We show that the OFDM/TDM with MMSE-FDC can be used to reduce the impact of nonlinear HPA on overall performance of cooperative network in comparison to OFDM while providing the target quality-of-service for reduced required signal-to-noise ratio. This is because OFDM/TDM with MMSE-FDC achieves frequency diversity in addition to cooperative diversity, while reduced peak-to-average power ratio makes it more robust on nonlinear degradation due to HPA saturation in comparison to conventional OFDM.

The Affecting Factors in Resource Optimization for Cooperative Communications: A Case Study

Cooperative networks provide enhanced system performance by exploiting spatial diversity in a distributed manner. Optimum resource allocation can help improve the performance of cooperative networks and increase the efficiency of resource usage. In the literature, various system performance and optimization results have been reported for different systems and with different optimization metrics. However, there lacks a unifying framework delineating the effects of different factors on resource optimization and the resultant benefit. In this paper, we investigate the relative effects of optimization metric (error rate versus outage probability), modulation type (coherent versus differential) and relaying protocol (amplify-and-forward (AF) versus decode-and-forward (DF)). To facilitate such a case study, we provide a comprehensive set of system performance for four commonly adopted cooperative systems: coherent amplify-and-forward (CAF), coherent decode-and-forward (CDF), differential amplify-and-forward (DAF), and differential decode-and-forward (DDF). A resource optimization problem that minimizes the total transmit energy is formulated. Since energy optimization has been intensively studied in the literature, location optimization will be investigated. The analyses and simulations suggest that: i) The error rate and outage probability metrics yield similar optimization results for AF relaying systems; ii) The relaying protocol determines the optimization results while the modulation type has no effect; and iii) The difference between different relaying protocols diminishes when the number of relays increases.

Energy efficient smart-relay-based cooperative MAC for wireless networks

An enormous number of papers investigated wireless cooperative networks over the last few years. Almost all have shown that cooperative transmission improves network performance significantly. However, none of these studies have considered the hidden and exposed terminal problems which appear due to the cooperative mechanisms of relay selection and transmission processes. The hidden terminal problems increase collisions and the exposed terminal problems increase bandwidth wastage, degrading the expected performance of cooperative networks. This paper addresses these problems of traditional wireless cooperative networks. We also propose a protocol called smart-relay-based-cooperative (SRcoop) MAC to optimally reduce the impacts of hidden and exposed terminal problems. We also illustrate an efficient relay selection mechanism that uses a back-up relay to increase transmission reliability. Our innovative model significantly improves the network throughput, end-to-end delay and energy efficiency over traditional cooperative MAC, 2rcMAC, LC-MAC, C-ARQ and Adere et al. protocols.

Relay Optimization for ANC and PNC over Rician Fading Channels

Co-operation and network coding are two such powerful techniques that heightened the proficiency of wireless Networks. This paper mainly focuses on Physical-layer Network Coding (PNC) and Analog Network Coding (ANC), as they are the most studied variants of network coding in literature and represent radically different strategies between themselves, thus shedding light into which problems may hinder the scalability of network coding to more better wireless network topologies. Also, performance of cooperative networks can be enhanced with optimum relay selection. In this paper, we present the simulation results for both Analog Network Coding and Physical-layer Network Coding. We have evaluated the bit error rate (BER) over Rician fading channelsfor ANC and PNC with relay optimization by taking path loss in our system model. BPSK modulation is used for simulation results.

Effect of Feedback Delay on the Performance of Cooperative Networks with Relay Selection

In this paper, we analyze the effect of feedback delay and channel estimation errors on the performance of a decode-and-forward (DF) cooperative transmission scenario with relay selection. In our relay selection scheme, only one relay with the best relay-to-destination (R → D) channel quality is selected among the set of relays that decode the source information correctly. Specifically, the destination terminal first estimates the channel state information (CSI) of all active R → D links and then sends the index of the best relay to the relay terminals via a delayed feedback link. Due to the time varying nature of the fading channels, selection is performed based on the old version of the channel estimate. Closed-form expressions for the outage probability, average capacity and average symbol error rate (ASER) are derived. Through asymptotic diversity order analysis, we show that the presence of feedback delay reduces the asymptotic diversity order to one, while the effect of channel estimation errors reduces it to zero. Finally, simulation results are presented to corroborate the analytical results.

Time of arrival-based location estimation for cooperativerelay networks

Cooperative communications is a technique to create a virtual antenna array using several distributed single antenna nodes in the system. It helps in increasing the area of coverage without the need of increased transmission power. As the destination receives multiple copies of the source's signal, it also improves the diversity order. The performance of cooperative networks has been thoroughly investigated in the past for various system models, protocols, forwarding techniques and fading environments. Location estimation is another crucial process in cooperative relay networks, as it is for the other types of wireless communications networks. For instance, the range and location information can be used for network authentication, localization or cluster forming in cooperative networks. However, to the best of our knowledge, there is no study in the literature that addresses the location estimation problem in cooperative relay networks. In this study, we investigate the performance of a cooperative relay network performing location estimation through time of arrival (TOA). We derive Cramer-Rao lower bound (CRLB) for the location estimates made using the relay network. The analysis is extended to obtain average CRLB considering the signal fluctuations in both relay and direct links. The effects of the channel fading of both relay and direct links and amplification factor and location of the relay node on average CRLB are investigated. Simulation results show that the channel fading of both relay and direct links and amplification factor and location of relay node affect the accuracy of TOA-based location estimation.

Performance of amplify-and-forward cooperative networks with differential unitary space time coding

In wireless communications, multi-input multi-output technology has been appreciated for its high transmission rate and diversity gain. These can also be exploited in cooperative networks by using network nodes as virtual antenna arrays. In this paper, we analyze the performance of cooperative networks with differential unitary space-time modulation under high signal-to-noise ratio. Relaying protocol is based on amplify-and-forward. The effect of relay location and energy allocation as well as the comparison with a conventional cooperative network is also addressed.

Performance Analysis of Amplify-and- Forward Opportunistic Relaying in Rician Fading

This letter analyzes the performance of single relay selection cooperative wireless networks using <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">amplify-and</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">forward</i> relaying. The network channels are modeled as independent, nonidentical, Rician distributed coefficients. We derive approximate formulas for the symbol error rate (SER) of the opportunistic relaying cooperative network. We first derive the PDF of the approximate value of the total SNR. Then, assuming <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -PSK or <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -QAM modulations, the PDF is used to determine the SER. For sufficiently large SNR, this letter derives the close-form average SER. The simplicity of the asymptotic results provides valuable insights into the performance of cooperative networks and suggests means of optimizing them. We also use simulation to verify the analytical results. Results show that the derived error rates are tight bounds particularly at medium and high SNR.

Asymptotic performance analysis of amplify-and-forward cooperative networks in a nakagami-m fading environment

This letter analyzes the performance of repetition-based cooperative wireless networks using amplify-and forward relaying. The network consists of a source, R parallel relays, and a destination, and the channel coefficients are distributed as independent, non-identical, Nakagami-m. The approximated average symbol error rate (SER) is investigated. For sufficiently large SNR, this letter derives a close-form average SER when m is an integer. The simplicity of the asymptotic results provides valuable insights into the performance of cooperative networks and suggests means of optimizing them. We also use simulation to verify the analytical results. Results show that the derived error rates are tight approximations particularly at medium and high SNR.

The Influence of LOS Components on the Statistical Properties of the Capacity of Amplify-and-Forward Channels

Amplify-and-forward channels in cooperative networks provide a promising improvement in the network coverage and system throughput. Under line-of-sight (LOS) propagation conditions in such cooperative networks, the overall fading channel can be modeled by a double Rice process. In this article, we have studied the statistical properties of the capacity of double Rice fading channels. We have derived the analytical expressions for the probability density function (PDF), cumulative distribution function (CDF), levelcrossing rate (LCR), and average duration of fades (ADF) of the channel capacity. The obtained results are studied for different values of the amplitudes of the LOS components in the two links of double Rice fading channels. It has been observed that the statistics of the capacity of double Rice fading channels are quite different from those of double Rayleigh and classical Rice fading channels. Moreover, the presence of an LOS component in any of the two links increases the mean channel capacity and the LCR of the channel capacity. The validity of the theoretical results is confirmed by simulations. The results presented in this article can be very useful for communication system designers to optimize the performance of cooperative networks in wireless communication systems.

A Unified Cross-Layer Framework for Resource Allocation in Cooperative Networks

Node cooperation is an emerging and powerful solution that can overcome the limitation of wireless systems as well as improve the capacity of the next generation wireless networks. By forming a virtual antenna array, node cooperation can achieve high antenna and diversity gains by using several partners to relay the transmitted signals. There has been a lot of work on improving the link performance in cooperative networks by using advanced signal processing or power allocation methods among a single source node and its relays. However, the resource allocation among multiple nodes has not received much attention yet. In this paper, we present a unified cross- layer framework for resource allocation in cooperative networks, which considers the physical and network layers jointly and can be applied for any cooperative transmission scheme. It is found that the fairness and energy constraint cannot be satisfied simultaneously if each node uses a fixed set of relays. To solve this problem, a multi-state cooperation methodology is proposed, where the energy is allocated among the nodes state-by-state via a geometric and network decomposition approach. Given the energy allocation, the duration of each state is then optimized so as to maximize the nodes utility. Numerical results will compare the performance of cooperative networks with and without resource allocation for cooperative beamforming and selection relaying. It is shown that without resource allocation, cooperation will result in a poor lifetime of the heavily-used nodes. In contrast, the proposed framework will not only guarantee fairness, but will also provide significant throughput and diversity gain over conventional cooperation schemes.