Mobile Relay Station Research Articles

A Decision for Throughput Optimization in UAV-Enabled Emergency Outdoor–Indoor Fairness Communication

This paper investigates the throughput optimization strategy in an unmanned aerial vehicle (UAV)-enabled emergency outdoor–indoor fairness communication scenario, with the UAV as a mobile relay station in the air, to provide outdoor–indoor communication services for users inside buildings. The occurrence of severe signal fading caused by outdoor transmission loss through wall loss as well as indoor transmission loss when the UAV forwards the information to the indoor users reduces the channel gain and degrades the system downlink throughput. To improve the downlink throughput of the system and ensure communication fairness for indoor users, we designed a joint UAV location deployment and resource allocation (JLRO) algorithm that optimized UAV three-dimensional (3D) deployment location, power and bandwidth resource allocation. The simulation results demonstrate the convergence and validity of the proposed JLRO algorithm, as well as its superiority compared to benchmark algorithms.

Optimization of mobile‐relay‐aided base station sleep mode in wireless dense small cell network

AbstractIn this paper, a novel sleep‐mode base station (BS) selection scheme, namely forced handover, is proposed using the mobile stations as mobile relay stations in order to maximize number of sleeping BSs. Forced‐handover is a concept of forcing edge mobile stations to neighbour relay stations for both energy saving and SINR improvement of the network. The proposed energy saving scheme can be applied to not only micro sleep and macro sleep mode but also turning off the BSs. The performances of BS sleep mode schemes is investigated in various environments such as small cell network and different user distributions.

A Mobility Model for a 3D Non-Stationary Geometry Cluster-Based Channel Model for High Speed Trains in MIMO Wireless Channels.

During channel modeling for high-mobility channels, such as high-speed train (HST) channels, the velocity of the mobile radio station is assumed to be constant. However, this might not be realistic due to the dynamic movement of the train along the track. Therefore, in this paper, an enhanced Gauss-Markov mobility model with a 3D non-stationary geometry based stochastic model (GBSM) for HST in MIMO Wireless Channels is proposed. The non-isotropic scatterers within a cluster are assumed to be around the sphere in which the mobile relay station (MRS) is located. The multi-path components (MPCs) are modeled with varying velocities, whereas the mobility model is a function of time. The MPCs are represented in a death-birth cluster using the Markov process. Furthermore, the channel statistics, i.e., the space-time correlation function, the root-mean-square Doppler shift, and the quasi-stationary interval, are derived from the non-stationary model. The model shows how the quasi-stationary time increases from 0.21 to 0.451 s with a decreasing acceleration of 0.6 to 0.2 m/s2 of the HST. In addition, the impact of the distribution of the angles on the channel statistics is presented. Finally, the simulated results are compared with the measured results. Therefore, there is a close relationship between the proposed model and the measured results, and the model can be used to characterize the channel's properties.

Recent Developments and Future Challenges in Channel Measurements and Models for 5G and Beyond High-Speed Train Communication Systems

The fast developments of high-speed train (HST) and growing communication demands of users pose new challenges for HST communication systems. To provide reliable communication services, key 5G communication technologies, such as millimeter-wave (mmWave) and massive multiple-input multiple-output (MIMO), and potential architectures, such as coordinated multipoint and mobile relay station, are considered in future railway communications. New technologies and architectures will bring new channel propagation characteristics. Accurate channel models that can capture these channel characteristics play a critical role in the design and test of future railway communication systems. This article reviews the HST channel measurements conducted in different scenarios and frequency bands, and the advanced HST channel models. Then a novel HST channel model incorporating the mmWave and massive MIMO propagation characteristics is presented, and its frequency non-stationarity is analyzed. Finally, some future directions are discussed.

A 3D geometry-based scattering model for vehicle-to-vehicle wideband MIMO relay-based cooperative channels

In this paper, a three-dimensional (3D) geometry-based stochastic scattering model (GBSSM) for wideband multi-input multi-output (MIMO) vehicle-to-vehicle (V2V) relay-based cooperative fading channel based on geometrical three-cylinder is proposed. Non-line-of-sight (NLOS) propagation condition is assumed in amplify-and-forward (AF) cooperative networks from the source mobile station (S) to the destination mobile station (D) via the mobile relay station (R). We extend the proposed narrowband model to wideband and also introduce the carrier frequency and bandwidth into the model. To avoid complicated procedure in deriving the analytical expressions of the channel parameters and functions, the channel is realized first. By using the realized channel matrix, the channel properties are further investigated.

Energy-efficient mobile relay deployment scheme for cellular relay networks

In this paper, an efficient mobile relay deployment scheme to select the deployment sites for mobile relay stations (MRSs) from the candidate positions is proposed, aiming at maximizing energy efficiency (EE) while guaranteeing the spectral efficiency (SE) requirement and the coverage constraints of mobile users (MUs). Firstly, an interference graph construction method is proposed to calculate the interference at MUs served by MRSs. Then, the deployment scheme at each observation time is proposed and our framework consists of three main algorithms. The first algorithm based on the extended Hungarian deployment algorithm is proposed to find the optimal solution, i.e., minimum movement distance. In addition, a greedy deployment algorithm and a static deployment algorithm are proposed to compare with the extended Hungarian deployment algorithm. Furthermore, we compare the performance of these algorithms via simulations and analyze the impact of various parameters on the performance. Simulation results demonstrate that the extended Hungarian deployment algorithm can considerably improve system EE compared to the other two algorithms. Moreover, relay switching occurs more frequently and average relay service time reduces with the increase of maximum speed of MUs.

Outage Probability Analysis of Linear MANETs in Dual-Hop AF Systems With Noisy Relay and Interference-Limited Destination

The outage performance of a dual-hop mobile ad hoc network (MANET), which employs amplify-and-forward (AF) relaying in a Rayleigh fading environment in the presence of a Poisson field of interferers at the destination, is investigated. All mobile users are assumed to follow the Poisson arrival model along the highway and can only communicate with each other via a stationary base station or a mobile relay station. Under this MANET model, a single-integral expression for the exact outage probability and a tight lower bound are both derived. The impacts of transmitting power, path-loss exponent, and spatial density of interferers on the performance of dual-hop systems are found. It is revealed that the outage probability of each hop, as a function of distance, transmitting power, etc., has a different impact on the end-to-end outage probability. The outage probability floor is derived when the transmission power at the source/relay becomes large. The optimal power allocation for the dual-hop link is obtained. The behavior of the outage probability during the communication process between the moving nodes is investigated. The analytical results are validated with Monte Carlo simulation.

A distributed virtual MIMO coalition formation framework for energy efficient wireless networks

In this paper, we consider a distributed virtual multiple-input multiple-output (MIMO) coalition formation algorithm. Energy savings are obtained in the reverse link by forming multi-antenna virtual arrays for information transmission. Virtual arrays are formed by finding a stable match between two sets of single antenna devices such as mobile stations (MSs) and relay stations (RSs) based on a game theoretic approach derived from the concept of the college admissions problem. Thus, power savings are obtained through multi-antenna arrays by implementing the concepts of spatial diversity and spatial multiplexing for reverse link transmission. We focus on optimizing the overall consumed power rather than the transmitted power of MSs and RSs. Furthermore, it is shown analytically and by simulation that when the overall consumed power is considered, the energy efficiency of the single antennas devices is not always improved by forming a virtual MIMO array. Hence, single antenna devices may prefer to transmit on their own when channel conditions are favorable. In addition, the simulation results show that the framework we propose provides comparable energy savings and a lower implementation complexity when compared to a centralized exhaustive search approach.

A Receive Beamforming Technique for an LTE-based Mobile Relay Station with Antenna Array

A mobile relay station (MRS) with soft handover experiences performance degradation because the received signal at the MRS located between two base stations (BSs) is the sum of these two signals with different carrier frequency offsets (CFOs). In this paper, two receive beamforming techniques with CFO compensation (a joint receive beamforming (JB) technique and a spatially separated receive beamforming (SB) technique) are proposed for the MRS with a uniform linear array (ULA) in orthogonal frequency-division multiplexing (OFDM) systems. The SB technique is shown to be robust against CFO errors and can be effectively used for the MRS in a multipath fading channel. The performance of the proposed techniques is evaluated via simulation in a Long Term Evolution (LTE) environment.

Air-based Multi-hop Sensor Network for the Localization of Persons

In this work an air-based sensor network for the localization of persons at extensive areas is presented. The developed network consists of a localization device which the person is wearing (BodyGuard-System), a mobile relay station in the air, and a base station. All three parts communicate with the same radio chip. The BodyGuard-System is an inertial navigation system which was developed for localization in difficult environments with high accuracy and low measurement uncertainty. To increase the range of the system, a multi-hop network was built up. The measured data of the BodyGuard-System and the mobile relay station is visualized on a PC in the base station. This multi-hop network is necessary for example for fire department missions.

A Nonstationary Wideband MIMO Channel Model for High-Mobility Intelligent Transportation Systems

The recent development of high-speed trains (HSTs), as a high-mobility intelligent transportation system, and the growing demands of broad-band services for HST users, introduce new challenges to wireless communication systems for HSTs. The deployment of mobile relay stations on top of the train carriages is one of the promising solutions for HST wireless systems. For a proper design and evaluation of HST wireless communication systems, we need accurate channel models that can mimic the underlying channel characteristics for different HST scenarios. In this paper, a novel nonstationary geometry-based stochastic model (GBSM) is proposed for wideband multiple-input multiple-output HST channels in rural macrocell scenarios. The corresponding simulation model is then developed with angle parameters calculated by the modified method of equal areas. Both channel models can also be used to model nonstationary vehicle-to-infrastructure channels in vehicular communication networks. The system functions and statistical properties of the proposed channel models are investigated based on a theoretical framework that describes nonstationary channels. Numerical and simulation results demonstrate that the proposed channel models have the capability to characterize the nonstationarity of HST channels. The statistical properties of the simulation model, verified by the simulation results, can match those of the proposed theoretical GBSM. An excellent agreement is achieved between the stationary intervals of the proposed simulation model and those of relevant measurement data, demonstrating the utility of the proposed channel models.

Navigation-based self-optimization handover mechanism for mobile relay stations in WiMAX networks

Organic Computing has similar characteristics of organism which can be self-adjustment for a variety of conditions. Moreover, during the wireless communication technological evolution progress, WiMAX (Worldwide Interoperability for Microwave Access) offers ability of high capacity and far distance transmission. WiMAX provides high-speed access and a coverage range across several kilometers, but the actual coverage range was merely a few kilometers due to the shelter of buildings or terrain. IEEE 802.16 working group designed 802.16j-based RS (Relay Station) to overcome above problem. In this paper, we present a mechanism called Self-Optimization Handover Mechanism. This mechanism is using GPS (Global Positioning System) navigation system to gather the related information for the position and combine the mobility characteristics of Mobile Relay Station. Especially, the concept of Self-Optimization of Organic Computing has been integrated into this mechanism. There are some advantages for this new mechanism, including: (1) The base station can provide advance plan and select the path. (2) The mechanism can reduce the number of possible handover and hop. (3) The mechanism can reduce the time of channel scan.

Intrusion tolerant QoS provision in mobile multihop relay networks

We propose in this article an architecture called trusted timely attacks-tolerating communication architecture (3TCA) designed for mobile multihop relay (MMR) networks. The 3TCA architecture is based on trusted components providing trusted time-related and security-related services along with an intrusion-related service while guaranteeing QoS compensation. 3TCA components are implemented at access nodes such as relay stations (RSs) and multihop relay base stations (MR-BSs) in order to achieve trusted QoS-aware handover management while guaranteeing intrusion tolerance. In particular, we provide QoS guarantees in terms of delay, bandwidth and jitter for the MMR networks while addressing group mobility through performing handover disturbance compensation for mobile RSs. Meanwhile, we tolerate particular timely-based and DoS attacks through compensating their impact on the already agreed QoS level. Simulations show that adopting compensation is suited for the MMR context although it induces additional complexity.

Cell searching and DoA estimation for a mobile relay station in a multipath environment

In this paper, a mobile relay station (MRS) for vehicles with a beamforming antenna is considered to increase the reliability of the transmission link, particularly for the MRS at the cell boundary. A cell searching and direction-of-arrival estimation method for an MRS with a uniform linear array is proposed for OFDM-based cellular systems in a multipath environment, even with the existence of the symbol timing offsets and carrier frequency offsets. The performance of the proposed method is evaluated by computer simulation using the standard profile of IEEE 802.16e.

다중 경로 채널에서의 이동 릴레이의 셀 탐색 및 DoA 추정 방법

본 논문에서는 빔포밍 안테나를 탑재한 이동 릴레이(MRS, Mobile Relay Station), 특히 셀 경계 근방에 위치한 이동 릴레이의 링크(link) 의 안정성을 향상시키는 방법에 대해 기술한다. OFDM 통신 방식 기반 시스템의 다중 경로 환경에서의 선형 어레이(Uniform Linear Array)를 이용한 셀 탐색 및 DoA(Direction of Arrival) 추정방법을 제안하였으며, 공간 상관 행렬 기반의 제 1 방법과 이중 차등 상관 행렬 기반의 제 2 방법의 성능을 모의실험을 통하여 평가하였다. 모의실험은 IEEE 802.16e 표준에 기반하였다. In this paper, a mobile relay station(MRS) for vehicles with a beamforming antenna is considered to increase the reliability of a transmission link, especially for the MRS at cell boundary. Cell searching and direction-of-arrival(DoA) estimation methods for an MRS with a uniform linear array(ULA) are proposed for a multipath environment in OFDM-based cellular systems. Performances of the proposed methods(Method1 and Method2) are evaluated by computer simulation with the standard profile of IEEE 802.16e.

A Host-based Fast Mobility Scheme (HFMS) in 802.16j Mobile RS Mode

As technologies for the high quality multimedia application and 4G WiMAX network prevail, one can easily be under services everywhere through WiMAX wireless network. However, the service disruption time (SDT) caused by handover procedure leads to an unacceptable quality of service (QoS) for mobile users, especially in IEEE 802.16j mobile relay station (MRS) mode. Therefore, we proposed a host-based fast mobility scheme (HFMS) in IEEE 802.16j MRS mode to reduce the SDT and solve the packet loss problem during handover via the cooperation between the MRS's link-layer and mobile station's (MS's) IP layer. In the proposed scheme, the MRS's link-layer will notify the MS's IP layer to perform IP layer handover procedure when the MRS performs link-layer handover. The parallel handover reduces the SDT efficiently. On the other hand, the proposed buffering mechanism can avoid packet loss. As a result, the seamless mobility and satisfactory QoE can be achieved for mobile users in IEEE 802.16j MRS mode.

Outage Performance of Cooperative Relaying with Fixed and Best-Selected Mobile Relays Over Non-Identically Distributed Links

In multi-relay cooperative networks, selecting the best relay to cooperate is known to be spectrally efficient, provided that perfect channel state information (CSI) is available for relay selection. When relays are mobile, the time-varying nature of fading channels renders the provision of accurate CSI challenging and significantly degrades the performance of best relay selection. In this paper, the joint deployment of dedicated relay station (DRS) and mobile relay stations (MRSs) is considered, whereby the MRS selected based on CSI and the stationary DRS simultaneously forward the overheard signal to the destination within the total power constraint. Closed-form expressions for exact and asymptotic outage probability over non-identically distributed links are derived, and comparisons with related schemes are conducted to demonstrate the merits of the proposed scheme.

Two-hop Relay-based Vehicular Network in WiMAX

In mobile communication, routing data through intermediate mobile node is a challenging task due to high mobility of nodes which causes rapid change in network topology and frequent disconnection between pair of nodes. To address these issues, Mobile Relay Station (MRS) is introduced into the network based on IEEE 802.16j standard. The MRS features are similar to the Fixed Relay Station (FRS), however the MRS has capability to move as Mobile Station (MS). In intermittent connection, by adapting the features of Delay Tolerant Network (DTN), the MRS can store and carry the data until it find the destination to forward the data. Assuming that MS is aware of its’ own movement as well as its closest neighbor nodes. In this paper, Dynamic Routing Algorithm (DyRA) has been proposed to select next hop node towards the destination. The forwarding decision is based on a computed metric which is a combination of Packet Reception Rate (PRR), Link Expiration Time (LET) information and Number of Slots (NoS) available at the candidate MRS nodes. Also, the proposed Relay-based Vehicular Network (RVN) in WiMAX using cross layer design (CLD) is designed to select the optimal next hop node and set new route when current routing path is no longer available. The preliminary results for system throughput performance and average end-to-end delay are analyzed. The results show that by deploying relay-based in vehicular network can enhance system throughput in terms of packet loss ratio (PLR), packet delivery ratio (PDR), and average end-to-end (ETE) delay. NCTUns simulation environment has been used to study the mobile node performance.

Cell Searching and DoA Estimation Methods for Mobile Relay Stations with a Uniform Linear Array

In this paper, cell searching and direction-of-arrival (DoA) estimation methods are proposed for mobile relay stations with a uniform linear arrays in OFDM-based cellular systems. The proposed methods can improve the performance of cell searching and DoA estimation, even when there exist symbol timing offsets among the signals received from adjacent base stations and Doppler frequency shifts caused by the movement of the mobile relay station. The performances and computational complexities of the proposed cell searching and DoA estimation methods are evaluated by computer simulation under a mobile WiMAX environment.

An Overlaid Hybrid-Division Duplex OFDMA System with Multihop Transmission

In this letter, we propose an overlaid hybrid division duplex (HDD) concept for cellular systems which divides a cell into inner and outer regions and utilizes the merits of both time division duplex (TDD) and frequency division duplex (FDD). The proposed system can take advantage of both TDD and FDD without handover between two duplex schemes. Moreover, it is shown that the proposed HDD system outperforms the conventional TDD or FDD system with mobile relay stations when the synchronization issue is considered in orthogonal frequency division multiple access systems. Thus, the proposed overlaid HDD can be considered as a new framework for future cellular systems.