Optimal throughput performance in full-duplex relay assisted cognitive networks

Wireless Networks - In this paper, we study a full-duplex cooperative cognitive radio network with multiple full-duplex secondary users acting as potential relays for transmitting the packets of a...     

Generalized diversity combining of energy harvesting multiple antenna relay networks: outage and throughput performance analysis

In this paper, the generalized diversity combining of an energy constrained multiple antenna decode-and-forward relay network is considered. Using power splitting and time switching architectures in consort with diversity combining at the relay, six protocols are proposed, i.e., power splitting with selection combining (PSSC), power splitting with maximum ratio combining (PSMRC), power splitting with generalized selection combining (PSGSC), time switching with selection combining (TSSC), time switching with maximum ratio combining (TSMRC), and time switching with generalized selection combining (TSGSC). The outage probability and throughput performance of each protocol is analyzed by first developing the closed form analytical expressions and then verifying these through the Monte Carlo simulation method. Simulation results show that system performance improves both with increasing the number of antennas and decreasing the distance between the source and relay. The TSSC/TSMRC/TSGSC protocols yield better outage performance whereas the PSSC/PSMRC/PSGSC protocols achieve relatively higher throughput performance. Finally, the effects of power splitting ratio, energy harvesting time ratio, energy conversion efficiency, sample down conversion noise, and the target signal-to-noise ratio on system performance are analyzed and presented.     

Downlink data rate,energy and spectral efficiency distribution in heterogeneous networks with cell-edge located small cells

Wireless Networks - In this paper, the probability distributions of per user downlink data rate, spectral efficiency (SE) and energy efficiency (EE) are analytically derived for a heterogeneous...     

Joint optimization of energy harvesting and information transmission for trapped user

Wireless Networks - Energy harvesting technology can solve the problem of users’ energy consumption in disaster areas. When disasters occur, some users are trapped and unable to recharge and...     

Secure communication in untrusted relay selection networks with wireless energy harvesting

In this paper, we consider the secrecy performance of an energy-harvesting relaying system with Kth best partial relay selection where the communication of a multi-antenna source-destination pair is assisted via single-antenna untrusted relays. To protect confidential source messages from untrusted relays, transmit beamforming and destination jamming signals are used. The relays are energy-constrained nodes that use the power-splitting policy to harvest energy through the wireless signals from both the source and destination. For performance evaluation, closed-form expressions of the secrecy outage probability and average secrecy capacity (ASC) are derived for Nakagami-m fading channels. The analytical results are confirmed via Monte Carlo simulations. Numerical results provide valuable insights into the effect of various system parameters, such as relay location, number of relays, and power splitting ratio, on the secrecy performance. Specifically, the maximum ASC is achieved when the relay is located between the source and destination.

     

Performance analysis of energy harvesting cognitive relay networks with primary interference

This paper investigates the outage performance of multihop energy harvesting cognitive relay network (EH-CRN), in which the secondary nodes are powered by dedicated power beacons based on the time splitting strategy. Assuming a multihop secondary network, we derive an analytical expression for the outage probability experienced by a secondary user by taking into account the effect of interference power from primary source. The developed outage probability model can be used to assess the impact of some key parameters on the reliability of the secondary user’s link in an EH-CRN. We then investigate the optimal location of the relay node in a one dimensional two-hop secondary network that minimizes the outage probability. Next, we study how the various system parameters such as energy harvesting efficiency, path loss exponent, harvest-to-transmit time duration ratio and transmit power from primary source affect the optimal relay location. The outage improvement achieved when the relay is placed at the optimum location is also investigated. Furthermore, the sensitivity of optimal relay location to the variations in position of the primary receiver is examined. Extensive simulation results are used to corroborate the analytical findings.     

Combined spatial-temporal energy harvesting and relay selection for cognitive wireless powered networks

In order to improve the Energy Efficiency (EE) and spectrum utilization of Cognitive Wireless Powered Networks (CWPNs), a combined spatial-temporal Energy Harvesting (EH) and relay selection scheme is proposed. In the proposed scheme, for protecting the Primary User (PU), a two-layer guard zone is set outside the PU based on the outage probability threshold of the PU. Moreover, to increase the energy of the CWPNs, the EH zone in the two-layer guard zone allows the Secondary Users (SUs) to spatially harvest energy from the Radio Frequency (RF) signals of temporally active PUs. To improve the utilization of the PU spectrum, the guard zone outside the EH zone allows for the constrained power transmission of SUs. Moreover, the relay selection transmission is designed in the transmission zone of the SU to improve the EE of the CWPNs. In addition to the EE of the CWPNs, the outage probabilities of the SU and PU are derived. The results reveal that the setting of a two-layer guard zone can effectively reduce the outage probability of the PU and improve the EE of CWPNs. Furthermore, the relay selection transmission decreases the outage probabilities of the SUs.     

Impact of loop-back interference and channel estimation errors on full-duplex relay networks

This paper investigates the rate performance of full-duplex (FD) relay systems under the effect of channel estimation error and residual loop-back interference. The study considers both one-way and two-way amplify and forward (AF) relaying schemes. Power allocation techniques, applied at the sources and the relay, are proposed and shown to be effective that leads to near optimal solution. Comparison between the half-duplex (HD) and FD systems using optimum power allocation are made. Also, the impact of channel estimation error and loop-back interference on the rate of FD transmission are compared. It is shown that the destructive effect of loop-back interference dominates the effect of channel estimation error. Finally, assuming a bidirectional network, the performance of two-way analog network coding (ANC) scheme is compared to the plan of using two one-way AF relaying connections. The results show that it is better to use FD ANC for low transmission power and HD one for high power than using two one-way relaying schemes.     

Machine learning-based approaches for user association and access point selection in heterogeneous fixed wireless networks

Wireless Networks - Fixed Wireless Networks (FWNs) provide an alternative means for internet connectivity in rural and harsh propagation environments. Intensive technical expertise is therefore...     

On the error performance of network-coded error-prone DF-relaying in multiple access relay channel

This paper deals with bit error performance analysis of network-coded (NC) multiple access relay channels that operate in the decode and forward mode with error-prone relaying under quasi-static Rayleigh fading channels. It shows that the combination of channel coding and NC relaying can be regarded as a distributed coding scheme (DCS) if the error propagation problem is adequately addressed. For this purpose, methods based on NC soft information relaying (NC-SIR) and NC hard information relaying (NC-HIR) are investigated. In the framework of NC-SIR, the recently proposed Rayleigh-Gaussian log-likelihood-ratio-based Model is used for modelling the soft estimated symbols at the output of the relay soft encoder. The resulting scheme is referred to as NC-SIR-DCS. On the other hand, two NC-HIR-based schemes are studied and analyzed. The first employs automatic repeat request (ARQ) protocols between the relay node and each source node to ensure error-free propagation and is referred to as NC-ARQ-DCS, while the second performs a limiter function at the destination during iterative decoding as introduced in Thobaben (1) distributed and is referred to as NC-LFD-DCS. The SNR of the one-hop link, the equivalent to the sources-relay-destination links, is estimated in the case of NC-SIR-DCS and is lower bounded in the case of NC-LFD-DCS, while in the case of NC-ARQ-DCS, the average SNR cost per information bit due to the ARQ protocol is estimated. These processes allow tractable analysis of the bit error rate performances of the presented network-coded DCSs. Simulation results are carried out to assess the accuracy of the proposed bounds for different relay positions between source nodes and destination.     

Optimal channel access for TCP performance improvement in cognitive radio networks

Cognitive radio (CR) is a promising technology to improve spectrum utilization. Most of previous work on CR networks concentrates on maximizing transmission rate in the physical layer. However, the end-to-end transmission control protocol (TCP) performance perceived by secondary users is also a very important factor in CR networks. In this paper, we propose a novel multi-channel access scheme in CR networks, where the channel access is based on the TCP throughput in the transport layer. Specifically, we formulate the channel access process in CR network as a restless bandit system. With this stochastic optimization formulation, the optimal channel access policy is indexable, meaning that the channels with highest indices should be selected to transmit TCP traffic. In addition, we exploit cross-layer design methodology to improve TCP throughput, where modulation and coding at the physical layer and frame size at the data-link layer are considered together with TCP throughput in the transport layer to improve TCP performance. Simulation results show the effectiveness of the proposed scheme.     

认知中继网络中认知用户基于频谱感知机会中继的中断性能分析

认知无线电中继网络中,认知用户需要成功感知到其所在簇内的主用户频谱空穴后才能成为认知中继节点,且各认知中继节点发射功率受到各自主用户干扰温度限制(ITC)。该文对认知中继节点采用分布式空时编码和解码转发协议时认知用户的中断性能进行了分析;给出了认知用户在干扰温度限制下中断概率的上下界,得出中断概率的上下界在不同干扰温度限下与认知用户归一化数据速率、中继数量和其对主用户检测概率的关系。给出了源节点和频谱感知中继节点在相同干扰温度限下的数值仿真,并对仿真结果进行了分析。     

Joint relay selection and power allocation algorithm in two-way relay networks with proportional fair constraint

In this paper,we consider the joint relay selection and power allocation problem for two-way relay systems with multiple relay nodes.Traditionally,relay selection schemes are primarily focused on selecting one relay node to maximize the transmission sum rate or minimize the outage probability.If so,it is possible to cause certain relay nodes overloaded.In addition,the joint relay selection and power allocation problem is a mixed integer program problem and prohibitive in terms of complexity.Therefore,we pro...     

Joint optimization of relay strategies and resource allocations in cooperative cellular networks

This paper considers a wireless cooperative cellular data network with a base station and many subscribers in which the subscribers have the ability to relay information for each other to improve the overall network performance. For a wireless network operating in a frequency-selective slow-fading environment, the choices of relay node, relay strategy, and the allocation of power and bandwidth for each user are important design parameters. The design challenge is compounded further by the need to take user traffic demands into consideration. This paper proposes a centralized utility maximization framework for such a network. We show that for a cellular system employing orthogonal frequency-division multiple-access (OFDMA), the optimization of physical-layer transmission strategies can be done efficiently by introducing a set of pricing variables as weighting factors. The proposed solution incorporates both user traffic demands and the physical channel realizations in a cross-layer design that not only allocates power and bandwidth optimally for each user, but also selects the best relay node and best relay strategy (i.e. decode-and-forward vs. amplify-and-forward) for each source-destination pair     

异构无线网络混合接入与优化机制

在LTE与WSN异构无线网络架构中,有效降低信道接入时的碰撞概率从而提高网络容量吞吐量是影响异构无线网络性能的关键因素。文中建立混合接入模型及超帧结构,完成时分复用结构下的冲突避免,降低了WSN网络的能量消耗。通过时隙优化机制,解决当接入簇首的LTE UE数量变化频繁时竞争时隙配置不合理所导致的网络资源浪费。仿真结果表明,随着LTE UE的数量的增加,协作机制的性能优于传统的随机竞争接入机制,且协作机制的吞吐量性能呈现线性增长。当接入时隙相对充足簇资源利用趋向饱和时,接入概率和网络吞吐量性能均可保持稳定。     

Energy-efficient placement and sleep control of relay nodes in heterogeneous small cell networks

Small cell (SC) provides low-power radio access with a relatively smaller coverage range than a macrocell. It has been regarded as a key solution for offloading traffic in the future 5G system. Previous works on energy-efficient placement of base stations (BSs) in cellular networks introduced placement and sleep control of low-power relay stations (RSs) to reduce the total power consumption for downlink transmission from BSs to users. As compared with legacy RSs, SC can serve as an RS with a larger coverage range though consuming a bit more circuit power. Hence, this work additionally considers to deploy small cells (SCs) in a one-dimensional highway cellular network with BSs and legacy RSs, and further models the power consumption minimization problem for placement and sleep control of legacy RSs and SCs in this network. Since the problem is hard to be solved analytically, a genetic algorithm with dynamic operator-selection mechanism is further proposed to resolve this problem. Performance of the proposed algorithm is evaluated via simulation with a practical experimental parameter setting.     

Alternate energy harvesting and information relaying in cooperative AF networks

This paper studies an energy harvesting (EH) based cooperative relaying system, where two half-duplex relays operate with EH and alternately amplify and forward source data to the destination. When one relay joins in the cooperative data transmission, the other relay will harvest wireless energy by overhearing the transmissions from both the source and the transmitting relay. Both the time-switching and power-splitting architectures are considered for the EH and data reception at relays. Since the EH can be implicitly performed by each relay through listening the ongoing transmissions, more energy can be harvested for the cooperative data transmission. The outage probability and throughput of the proposed scheme are derived. Simulation results are provided to verify the correctness of our theoretical analysis and show that our scheme can significantly outperform the single-relay system in terms of throughput.     

Performance evaluation of a two-way relay network with energy harvesting and hardware noises

In this paper, we propose a Two-Way Cognitive Relay Network (TWCRN) where the secondary users operate on an underlay mode to access the licensed bands. In the proposed protocols, two secondary sources transmit their data to a relay in the first time slot, and then the relay would forward the received information to both sources in the remaining time. Moreover, the relay is self-powered by harvesting energy from ambient Radio Frequency (RF) signals, using the Time Switching (TS) and the Power Switching (PS) method. This paper concentrates on evaluating the performance of the secondary networks under the impact of hardware impairments and co-channel interference from the primary networks. In particular, based on the secondary transmitters’ constraint power, we derive the closed-form expressions of the outage probability and the throughput over Rayleigh fading channels in two cases: TS and PS. We also investigate the energy efficiency issue and the locally optimal position of the relay to maximize the system throughput, which provides much information to install the relay location. Finally, our derivations are verified by Monte Carlo simulation.     

Performance analysis of decode-and-forward partial relay selection in NOMA systems with RF energy harvesting

Wireless Networks - In this paper, we investigate a dual hop communication decode-and-forward scheme relay system where a source node wants to transmit simultaneously two symbols to two desired...     

Design and operation of energy efficient heterogeneous mobile networks

During the last two decades we have witnessed a rapid growth in wireless communication services, which has dramatically increased the number of necessary radio access components to provide the adequate capacity and acceptable quality of service. The power cost for operating this huge number of radio Base Stations (BSs) is under serious consideration by the mobile communication industry and recent research efforts have focused on energy efficient design and optimization of the radio access network in order to alleviate the energy consumption and mobile network operators OPEX. In this work, we consider a deployment of heterogeneous BSs to serve a given geographical area and propose two energy-aware algorithms to optimally determine the operational mode of those BSs under various traffic load conditions. Performance evaluation results show that the proposed algorithms can provide near optimal solutions and achieve substantial network energy consumption reduction without compromising the efficient operation of the mobile network. We further benefit from the outcome of this formulation framework and propose BS activation schemes that yield proper BS activation profiles for continuous-time operation in the same network deployment. Various traffic loads are investigated in several simulation campaigns and our proposed schemes yield quite satisfactory energy saving gains compared to fully operational topology networks in all scenarios of interest examined.