Investigation on uplink collaborative contention-based bandwidth request for WiMAX three hop relay networks

This paper suggests a collaborative contention bandwidth request (BR) mechanism for worldwide interoperability for microwave access (WiMAX) three-hop relay networks. By complimenting message and code BR in three hops of a link, the proposed framework enables low block error rate (BLER), packet dropping and signaling overhead while preserving the connection throughput and access delay requirements of best effort (BE) services. With three hops between base station (BS) and mobile station (MS) via relay station 1 (RS1) and relay station 2 (RS2), there take place eight possible BR mechanisms with message and code BR. Among eight BR mechanisms, message-message-code (MMC) BR performs better with message dominant BR and code-message-code (CMC) BR performs better with code dominant BR. Further, with CMC BR, the BLER is reduced by 5.88%, packet dropping is reduced by 8.68%, medium access control (MAC) overhead is reduced by 7.6%, MAC wastage is reduced by 4.47%, connection delay is reduced by 28.30%, queuing delay is reduced by 8.65%, queue size is reduced by 15.25% and throughput is improved by 11.51% than MMC BR mechanism.     

Dynamic hybrid automatic repeat request (DHARQ) for WiMAX – Mobile multihop relay using adaptive power control

Wireless multihop network is currently attracting much attention as a new wireless broadband access technology due to numerous benefits. This work proposes a power control scheme for WiMAX multihop relay system. In contrast to existing power control and optimization approaches, our proposed method uses an adaptive Channel Quality Measurement for a relay station to reduce interferences to other mobile station (MS) or relay station (RS) within the same cell and hence increase the number of hops per link and consequently maximize the spatial reuse. The proposed power control is applied to a new dynamic HARQ algorithm for adaptive channel quality enhancement. Simulation results have indicated that the proposed approach achieves superior BER/PER performance enhancement in comparison to previous related works.     

An adaptive random access strategy for multi-channel relaying networks

In this paper, an adaptive random access strategy is presented for multi-channel relaying networks to address the issue of random access of the non-real-time (NRT) services. In the proposed scheme, NRT services access the base station (BS) by first accessing the nearest relay node (RN). When collision occurs, for the sake of fast and efficient access, the user will begin a frequency domain backoff rather than randomly retry in time domain. A remarkable feature of this scheme is that the RN will adaptively determine the maximum allowed frequency backoff window at each access period. This is achieved according to the new arrival rate as well as the number of available access channels. Moreover, to alleviate the interference caused by sub-channel reuse among RNs, a fractional frequency reuse scheme is also considered. The analysis and numerical results demonstrate that our scheme achieves higher throughput, lower collision probability and lower access delay than conventional slotted Aloha as well as the scheme without frequency backoff window adaptation.     

Subcarrier allocation in multi-hop orthogonal frequency division multiple access wireless networks

Orthogonal frequency division multiplexing (OFDM) has been widely considered as a key technique for next generation mobile communication systems. Meanwhile, relaying technologies can improve users’ quality of service, increase network capacity and enlarge cellular coverage at a low cost. In this paper, we focus on subcarrier allocation and utilization in multi-hop OFDM access (OFDMA) wireless networks, and propose two efficient subcarrier allocation schemes aiming to increase network throughput and subcarrier utilization. The first scheme selects suitable links for data transmission from base stations to terminals at the beginning. Then, interference-free links are included into the same group for network resource reuse. For the purpose of global optimization, we propose a Tabu-based searching algorithm as the second subcarrier allocation scheme. Simulation results demonstrate that our proposed algorithms outperform other schemes in both network throughput and subcarrier utilization.     

基于多跳中继的宽带接入网组网成本性能分析*

利用成本分析模型及等性能成本比较方法对基于多跳中继的宽带无线接入网络部署进行了量化分析,并与传统单跳网络部署进行了仿真比较。结果显示,基于中继的网络部署在保证性能的前提下能有效地降低组网成本,增强网络边缘吞吐量,扩大基站覆盖范围。进一步分析表明,无线资源配置方法也对网络的成本增益有一定的影响。复用技术能进一步改善中继网络的成本效益,并有效提升网络性能。     

改进的WiMAX中继选择算法研究

针对802.16j 的移动多跳中继网络提出一种基于路径损耗和SINR的中继选择算法。该算法通过计算每条传输链路的路径损耗,选出路径损耗之和最小的2个中继站,比较这2个中继站与移动终端之间接入链路的SINR,将具有最大接入链路SINR值的中继站作为最优中继来改善移动终端的服务质量。对系统性能指标进行仿真分析,结果表明该算法可以有效降低中断概率和提高网络的稳健性。     

Performance analysis of LTE downlink system using relay-based selective transmission

As society continues to integrate information-based technologies into daily life, there is an increased need for small, powerful mobile phones. Recently, relaying technologies have been researched for standardization of the next generation of mobile communication systems, including third-Generation Partnership Project (3GPP) LTE-Advanced, IEEE 802.16j, and IEEE 802.16m. Especially, LTE-Advanced is an evolutionary version of IMT-2000 defined by the ITU. To satisfy these requirements, relaying technology is considered as a powerful candidate scheme with carrier aggregation, MIMO, and CoMP. Relaying technology has been introduced to guarantee high data rates to multiple users. It can also extend cell coverage or effectively increase the average throughput of the cell by installing relay nodes at cell edges or in shadow areas. Thus, in this paper, we propose a method for boosting reception performance using the downlink transmission method of the LTE system, which is the next-generation mobile communication technology standard currently underway in 3GPP. At the moment, orthogonal frequency division multiplexing (OFDM), which is suitable for high-speed data transmission and multipath, is commonly used in an LTE downlink system. However, the OFDM method has a disadvantage of displaying a relatively higher PAPR at the terminal since it basically uses a multi-carrier. To this end, single carrier division multiple access (SC-FDMA) is used in an LTE uplink system in order to compensate for this defect related to high PAPR of OFDM at such an important terminal where power efficiency is important. However, when the channels in the frequency domain deteriorate signals, SC-FDMA reveals a defect in that the impact of deteriorated parts spreads and causes performance degradation. To this end, we propose that a relay be installed between the station and terminal, the distance between BS and RS be set at 500 or 1,000 m, and orthogonal frequency division multiple access (OFDMA) and SC-FDMA be chosen as transmission methods of RS. This paper found SC-FDMA to be a better choice when RS is closer to BS, whereas OFDMA is a better choice when the distance between BS and RS is farther. The system’s reception performance improved when the transmission method fit the circumstances in the middle between BS and MS.     

基于协作中继的多点广播码分多址信息系统设计

为了提高多群多点广播中继网络系统的性能,提出一种改进的协作中继多点广播码分多址(CDMA)系统设计。该方案利用协作中继辅助的分布式波束形成 实现单天线基站多播,获得了较好的空间分集增益。在该系统中,多个基站利用多个中继节点向多个目的地的各个小组传播消息;利用CDMA技术来减少中继节点以及目的地节点的多址干扰(MAI)障碍,同时每个中继节点作为线性预编码波束合成器,可以在合适的代码空间重塑基站信号;对线性波束形成矩阵进行优化,使得中继节点的功率最小化,从而满足QoS在信号干扰噪声比方面的要求。系统性能仿真对比实验的结果表明,提出的改进方案明显优于传统的正交复用方案(FDMA / TDMA)。     

LASER: A load-aware spectral-efficient routing metric for path selection in IEEE 802.16j multi-hop relay networks

For coverage extension and throughput enhancement, the IEEE 802.16j task group has developed a novel multi-hop relay network architecture to enable typical IEEE 802.16 networks to achieve data transmission between base stations and mobile stations via a multi-hop path with relay stations deployment. How to determine an effective path for throughput gain and overhead reduction is emerging and crucial in IEEE 802.16 multi-hop relay networks. This paper introduces a load-aware spectral-efficient routing metric, called LASER, to evaluate paths, and proposes an efficient scheme to determine a proper path. Based on the LASER metric, the proposed path selection scheme formulates the path cost as the summation of cost of each link, and the path with the minimum cost will be selected as the appropriate one. Simulation results show that the proposed LASER-based path selection scheme significantly outperforms existing path selection schemes in network throughput and map overhead.     

Dynamic-cost-reward connection admission control for maximizing system reward in 4G wireless multihop relaying networks

The 3GPP Long Term Evolution (LTE) Advanced and IEEE 802.16j specifications adopt the mobile multi-hop relaying (MMR) mechanism for enlarging service area and improving wireless transmission quality simultaneously. By deploying different types of Relay Stations (RSs), MMR can bring some advantages: (1) the signal fading and wireless interference of a single long wireless link is improved obviously; (2) the ranges of wireless access and relay area are extended, etc. MMR can offer a high data rate transmission for packet services and can increase system capacity. Note that MMR can be applied to the public transportation system, e.g., equipped a mobile RS on a high-speed train. A mobile RS handoff initializes a multiple handoff requests of different types of traffics. It becomes as a critical handoff issue in 4G MMR. Thus, the MMR handoff needs a new efficient Connection Admission Control (CAC) to guarantee qualities for various types of traffics and to increase system revenue. However, traditional CACs are difficult to fulfill the objectives. This paper thus proposes the Dynamic Cost-Reward-based (DCR) CAC that consists of two key mechanisms: (1) adopting a Markov decision process-based (MDP) cost function and (2) providing different reward functions for different types of nodes and various types of connection. Additionally, a mathematical analytical Markov chain is modeled for DCR. The simulation results are very close to the analysis results, which justifies the correctness of the analytical model. Numerical results demonstrate that DCA outperforms the compared CACs in the probabilities of new blocking, MS-handoff, and RS-handoff dropping, FRL, GoS, and system reward.     

一种联合D2D资源分配的中继选择算法的研究

为提高蜂窝网络中边缘用户的QoS,可在蜂窝网络中引入了D2D辅助中继技术,然而由于D2D链路复用蜂窝资源会与蜂窝链路之间产生同频干扰,为了降低这种干扰,提出了一种联合资源分配的中继选择算法,该算法首先使用一种资源分配策略,使得D2D链路对蜂窝链路产生的干扰最小,然后结合资源分配结果提出了一个中继选择方案,该方案不仅考虑了D2D链路和回程链路的信道质量,而且还同时考虑到了对蜂窝链路的干扰问题。通过仿真验证,本文所提出的算法不仅能有效提升边缘用户吞吐量,同时保证了中心用户的QoS。     

An efficient technique for integrating voice and data in wireless communications with a cellular structured environment

The need for efficient radio channel utilization in an environment of dispersed roaming terminals with adverse characterization, has encouraged new areas of research in mobile communication system. It is therefore in this vein that we propose a new multiple access technique that improves system throughput. In this paper, the performance analysis of a wireless communication system capable of integrating voice and data efficiently over radio frequency channels through the proposed scheme, multiple access with reservation after contention (MARC) is presented. Integrating packets of voice and data information onto a common channel is accomplished by placing the data within the silence gaps of the speed conversation, but after a successful contention and upon slot assignment. The scheme employs contention for uplink access to the radio channel via the base station, thus providing a means of control access.     

移动IP网络中移动性管理的指针优化

移动性管理是移动通信技术中的一个关键问题,对于移动通信网络的性能具有决定性的作用。该文提出了一种在移动IP环境下的基于分布式注册服务器的指针优化策略,通过在路由器间建立并调整指针,跟踪移动节点的位置变化,使位置更新过程局部化,仅当连接请求到达时,才进行可能的对移动数据库的更新,从而减少网络中移动性管理的开销。该文中同时给出了指针优化策略的两种实现方案。     

Competitive scheduling for OFDMA systems with guaranteed transmission rate

Next-generation broadband wireless standards use orthogonal frequency division multiple access (OFDMA) as the preferred physical layer multiple access scheme, especially for the downlink. Due to limited resources available at the base station, multi-user resource allocation is crucial for delivering the applications with various quality-of-service (QoS) demands. We study the OFDMA resource allocation problem for the adaptive modulation and coding (AMC) mode of mobile WiMAX, in which resources in the form of allocation units (AU) are to be allocated and the channel knowledge of only some good sub-channels for the users is available to the scheduler. The objective is to maximize the sum-rate for all the users while maintaining guaranteed minimum and maximum traffic rates for certain users under a total transmission power constraint. Two novel factors, band selectivity factor (BSF) and competition factor (CF), are introduced. Based on the two factors, we propose a sub-optimal approach, rate-guaranteed competitive scheduling (RCS). It is suitable to be deployed in practical systems and exploits multi-user diversity with very low complexity. Simulation results show that RCS can achieve almost 75% of throughput of the optimal solution.     

移动边缘计算技术在高铁通信网络中的应用

随着高铁的日益普及,在高铁列车与地面之间建立移动数据通道,满足车地数据传输以及旅客上网的需求,成为越来越迫切的问题.现有GSM-R和LTE-R的解决方案,还存在带宽小、时延大、传输不稳定等问题.为此,本文提出采用移动边缘计算（Mobile Edge Computing,简称为MEC）技术来优化高铁通信网络.主要思想是在车厢和基站部署MEC服务器,经过两级MEC服务器的协同配合,达到复用空口链路、提升无线传输稳定性和降低时延的目的,并最终提升用户体验.通过实际网络试验结果显示,该方案可显著提升传输速率、减小传输时延.     

Slot allocation algorithms in centralized scheduling scheme for IEEE 802.16 based wireless mesh networks

In IEEE 802.16 based wireless mesh networks (WMNs), TDMA (Time Division Multiple Access) is employed as the channel access method and only TDD (Time Division Duplex) is supported and there are no clearly separate downlink and uplink subframes in the physical frame structure. As the uplink and downlink traffic has different characteristics in that the uplink traffic decentralizes in each MSS (Mesh Subscriber Station) and the downlink traffic centralizes in the MBS (Mesh Base Station), different scheduling methods should be taken in the uplink and downlink. This paper presents a uniform slot allocation algorithm which is suitable for both uplinks and downlinks. To achieve higher spatial reuse and greater throughput and to avoid switching frequently between receiving and transmitting within two adjacent time slots when a relay node forwards traffic, different link selection criteria are taken into account when allocating slots for uplinks and downlinks. A combined uplink and downlink slot allocation algorithm is proposed for further improving the spatial reuse and network throughput. The proposed algorithms are evaluated by extensive simulations and the results show that it has good performance in terms of spatial reuse and network throughput. To the best of the authors’ knowledge, this work is the first one that considers combined uplink and downlink slot allocation on the centralized scheduling scheme in IEEE 802.16 based WMNs.     

LTE上行干扰协调技术的研究

针对LTE技术上行链路干扰问题,综合分析现存的各种小区间干扰抑制技术,提出一种新的小区间干扰协调方案,包括频带分配和能量分配2个步骤.将干扰少的频带分配给离基站远的用户,采用集中式能量分配算法分配合适的发射功率.通过计算机仿真,将该方案与现有方案在吞吐量、效能、时延方面进行对比,可取得较好的实验效果.     

传感器网络中具有负载平衡的移动协助数据收集模式

数据收集是无线传感器网络的一个基本功能.然而,现有的数据收集模式大都是基于静止基站的网络结构,导致基站周围的节点由于担负着网络内的所有负载而快速死亡,成为网络性能的瓶颈.研究如何利用移动基站收集数据来达到负载平衡.提出了一个利用移动基站协助数据收集的模式(movement-assisted data gathering,简称MADG),它将基站移动区域设置为缓冲区,首先将数据沿最短路径传输到缓冲区内,然后在基站移动的过程中进行数据收集.证明了缓冲区位置设置在距离中心时数据传输总能耗最少,并证明了存在一个缓冲区位置使得最大节点负载最小化,进而确定了同时考虑到能源消耗和负载平衡的基站移动区域.理论分析和实验结果表明,提出的数据收集模式在很大程度上降低了网络节点的最大负载,并且减少了数据传输能源中的消耗,分别比固定基站和同类工作的最大网络负载降低95%和80%以上.     

Relay technologies and technical issues in IEEE 802.16j Mobile Multi-hop Relay (MMR) networks

An amendment to the 802.16e standard namely IEEE 802.16j specifying relay station (RS) and multi-hop relay base station (MR-BS) was approved in year 2006 supports Mobile Multi-hop Relay networks. (MMR). It provides coverage extension to isolated area and throughput enhancement by specifying relay stations. The physical (PHY) layer of WiMAX IEEE 802.16j standard is based on the IEEE 802.16-2004 and IEEE 802.16e-2005 standards and was designed from IEEE 802.11a. This paper reviews the Relay technologies and technical issues in the physical and MAC layer of IEEE 802.16j such as Data forwarding schemes frame structure, Link adaptation, modulation and coding, these issues belongs to physical layer, QoS scheduling services, Bandwidth allocation and request, Network planning, MAC handover procedures, connection management, path management, interference management, all these issues belongs to MAC layer.     

Energy-efficiency-aware relay selection in distributed full duplex relay network with massive MIMO

This paper considers a distributed full duplex relay network where multiple sources simultaneously transmit their signals to multiple destinations via the cooperation of a set of relay stations (RSs). Each RS is assumed to be equipped with large antenna arrays while all sources and destinations only have a single antenna. We assume the channels are Rician fading and the RSs use linear processing to process the signals with imperfect channel state information (CSI). We derive the closed-form expressions of the end-to-end achievable rates for the maximum-ratio combining/matched-filter (MRC/MF) and the zero-forcing (ZF) processing. These results are then used to pursue a detailed analysis of the power saving of the relay network. Then we study the energy-efficiency-aware relay selection strategy since the energy efficiency affects network lifetime in future wireless network. We propose a sub-optimal strategy with low complexity that only requires the statistical CSI. Simulations show that the energy efficiency of the system can be improved with optimal power allocation and our proposed strategy performs very close to the exhaustive search algorithm which is optimal.