Lisheng Fan

A Cache-Aided Communication Scheme for Downlink Coordinated Multipoint Transmission

Content caching at the base stations (BSs) is a promising strategy that can provide improved quality-of-service (QoS) provisioning for content-centric services, and at the same time reduce instantaneous backhaul payload. This paper focuses on the applications of the caching mechanism in the downlink of coordinated multipoint (CoMP) transmission, where the collaborating BSs cooperatively serve the user equipments (UEs). A cache-aided transmission scheme for downlink CoMP with limited local cache resources at the BSs is proposed to improve QoS provisioning in terms of outage performance. In order to cache files more efficiently while guaranteeing the QoS, the contents are divided into two sets, a popular set and a less popular set, according to their popularity profile following the Zipf model. The popular files are cached at all the BSs, while the less popular files are cached only at part of the BSs in a cache cluster subject to the strategy design. Furthermore, based on the popularity of the requested files, UEs are categorized into two groups and the notion of request competition between the two groups is introduced. The corresponding request competition model and admission probabilities for transmission requests are analyzed. Based on the request competition model, the best cache placement strategy for the popular and less popular sets that minimizes the average outage probability is derived. Numerical results show that the proposed cache-aided CoMP scheme outperforms the baseline traditional caching strategies in terms of the average transmission outage.

Multiuser Energy Harvesting Relaying System with Direct Links

In this study, the authors study an energy harvesting relaying system with multiuser, in which the relay node is capable of harvesting radio-frequency energy and retransmitting data with harvested energy by employing the power splitting strategy. The joint impact of direct and relaying links is taken into account in the process of user selection, and furthermore exploited for data transmission by using the selection combing receiver. To evaluate the system performance, analytical outage probabilities regarding both amplify-and-forward (AF) and decode-and-forward (DF) relaying have been derived under Rayleigh fading channel. Furthermore, they calculate the asymptotic expressions of outage probability, and they confirm that AF relaying as well as DF relaying approaches the system diversity order of N + 1 , where N denotes the user number. Numerical results are demonstrated to validate the proposed analysis as well.

Joint User and Relay Selection for Cooperative NOMA Networks

This paper investigates the joint user and relay selection algorithm for cooperative non-orthogonal multiple access networks, where multiple users transmit messages to two destinations by utilizing multiple amplify-and-forward relays. To improve the outage performance of system, an optimal selection criterion is proposed at the user-relay pairs. We derive the closed-form analytical expressions on the outage probability, as well as the asymptotic expressions for large transmission power. Based on the derived analytical expressions, the effect of the number of relays and the target data rate on the outage performance is revealed. Results indicate that when the target data rate becomes small enough, the diversity order of the outage probability equals to the number of relays, while the target data rate grows without bound, the outage probability achieves one.

Coordinated Beamforming for Heterogeneous Small-Cell Networks with a Non-ideal Backhaul

In this article, intra- and inter-cell interference caused by the non-ideal backhaul in coordinated multipoint (CoMP) are studied. A recursive estimation-based zero-forcing beamforming (RE-ZFBF) scheme is proposed to mitigate the interference. Based on an initial value, the RE-ZFBF scheme recursively approximates the beamformer variation between two consecutive time points by exploiting the temporal channel correlation. In contrast to a previous work, the authors convert the original non-convex constraint quality-of-service problem to an unconstrained convex one, by optimising the estimation of the beamformer error, rather than the beamforming power. It is shown that the proposed scheme can mitigate at most half the intra- and inter-cell interference, enhance the ZFBF performance, and outperform the existing works for CoMP with a non-ideal backhaul in heterogeneous small-cell networks.

On the performance of three-dimensionalantenna arrays in millimetre wave propagation environments

In order to reap the full scale of benefits of millimetre wave (mmWave) massive multiple-input multiple-output (MIMO) systems, the design of antenna arrays at the transmitter or receiver becomes more critical due to the propagation characteristic at mm-frequencies. In this study, the authors investigate the performance of two types of antenna array, namely uniform rectangular planar array (URPA) and uniform cylindrical array (UCYA). The channel behaviour is presented in full-dimensional mmWave propagation conditions by considering both the azimuth and elevation dimensions. The squared inner product and singular value spread are studied for URPA and UCYA configurations, these properties reveal the effective interference and channels stability of antenna array. The authors also evaluate the achievable rate with the equal power allocation and water-pouring power allocation schemes. Simulation results show that under the same system configurations, the performance that includes the radiation pattern, the channel eigenvalue distribution, the effective interference, and the achievable rate, of UCYA configuration always outperforms that of URPA configuration. Therefore, it can be concluded that in three-dimensional propagation environments, the UCYA configuration is especially appealing for mmWave MIMO systems.

High-speed based adaptive beamforming handover scheme in LTE-R

In recent years, high-speed railways (HSRs) are being developed rapidly all over the world because of their convenience, safety, comfort, and other advantages. However, the reliability and security of HSR wireless communication systems have faced severe challenges, such as the Doppler effect, complicated wireless channel model, frequent handovers and so on. The International Union of Railways is pushing the evolution of the global system for mobile communications for railway (GSM-R) internationally. In this study, a high-speed based adaptive beamforming handover scheme is proposed to improve the handover performance for HSR wireless communication systems. When the high-speed train enters the overlapping region, the serving evolved NodeB (eNodeB) and target eNodeB are using beamforming with different gain factors to improve the received signal quality. In addition, this scheme can dynamically adjust the handover hysteresis margins of the reference signal receiving power (RSRP) and the reference signal receiving quality (RSRQ) based on the speed and position. Simulation results have demonstrated that the proposed handover scheme can improve the handover performance by increasing the handover trigger probability and success probability effectively.

DF relaying networks in randomly distributed interference environments

In this paper, we consider a two-hop cooperative relaying network in a randomly distributed interference environment, where the source communicates with the destination, assisted by N decode-and-forward (DF) relays. We consider the interference-limited environments, where the received signals at the relays and the destination are degraded by random interference nodes distributed according to homogeneous Poisson point processes (PPPs). Based on received signal-to-interference ratio (SIR), relay selection has been deployed to determine one optimal relay out of N ones. To analyze the system performance, we derive both analytical and asymptotic expressions for outage probability under Rayleigh fading channel. From the given results, we see that the system diversity order on SIR varies reversely with the path loss factor α. Additionally, the given results suggest that the system performance is mainly limited by the second hop. Numerical verifications and simulation results are presented to validate our analysis.