A Cross-Layering Design for IPv6 Fast Handover Support in an IEEE 802.16e Wireless MAN

Broadband wireless access networks, such as the IEEE 802.16 standard for wireless metropolitan area networks (WMANs), aim to provide high bandwidth, low-cost, scalable solutions that extend multimedia services from backbone networks to wireless users. Because of a larger coverage area, portability and mobility have become significant issues for providing high quality mobile services, as it is crucial to minimize handover latency and maintain IP session continuity. As a result, such issues were addressed by the IEEE 802.16e task group on the mobile WMAN. However, the scope of the IEEE 802.16e standard did not include cross-layering approaches for the enhancement of upper layer handover performance. This article proposes a new cross-layering design for fast IPv6 handover support over IEEE 802.16e. First, we describe the IEEE 802.16 deployment architectures, as well as the link layer, handover procedures in IEEE 802.16e. Next, we describe the operation of fast IPv6 handover and point out the need for interaction between the network layer and the link layer for proper performance. Then, we propose a new cross-layering design to achieve a proper behavior of the fast IPv6 handover over IEEE 802.16e. Finally, we present handover scenarios for the proposed techniques and discuss the major factors that contribute to the handover latency.     

IEEE 802.16j切换模型研究

终端移动性是移动通信的重要特征。本文介绍了IEEE 802.16j标准中移动台切换的场景,并对其中的特殊情况——中继站内部切换进行了分析,并采用数学方法建立了移动台的切换模型。最后进行了网络仿真并对仿真结果进行了分析。     

一种基于IEEE 802.16e的新型切换算法研究

提出一种基于IEEE 802.16e无线网络的新型切换算法。算法充分考虑了IEEE 802.16e的测距、认证、注册等主要使用行为,通过引入业务流(Service Flow)认知,使基于业务流的移动终端处的切换时间达到最小。仿真分析表明,利用标准提出的多种不同能力的交互,算法能够有效降低切换时间。     

Mobility using IEEE 802.21 in a heterogeneous IEEE 802.16/802.11-based, IMT-advanced (4g) network

Industry is defining a new generation of mobile wireless technologies, called in cellular terminology "fourth generation" or "4G." This article shows that a system combining extensions of two radio access technologies, IEEE 802.11 and IEEE 802.16, meets the ITU-R's "IMT-Advanced" or 4G requirements. The extensions are 802.16 m (100 Mb/s, 250 km/h) and 802.11VHT (1 Gb/s, low velocity). The focus of this article is to show how IEEE 802.21 (the emerging IEEE standard for media-independent handover services) supports ";seamless"; mobility between these two radio access technologies. This mobility integrates the two radio access technologies into one system. We conclude that an 802.11VHT + 802.16 m + 802.21 system is likely to be proposed to the ITU-R for IMT- Advanced 4G.     

Successive multiuser detection and interference cancelation for contention based OFDMA ranging channel [transactions letters]

In this letter, we propose a successive multiuser detector (SMUD) for contention based OFDMA ranging channel compliant to the IEEE 802.16 (WiMAX) standard. A ranging channel consists of a set of subcarriers in specific time slots shared by multiple users, so the multiple access interference (MAI) limits the performance of ranging detectors. Different from existing methods that treat the MAI as noise, the proposed SMUD successively detects the channel paths of active ranging signals and cancels their interference for further detection. This approach significantly suppresses the MAI and improves both user detection and parameter estimation performance.     

Handover of relay stations for load balancing in IEEE 802.16

The load balancing in wireless networks is a very effective way for maximization of a system throughput. The paper proposes a new load balancing scheme in order to avoid a congestion of base stations (BSs) in IEEE 802.16 standards. While in many technical studies the load balancing is achieved by a handover (HO) of mobile stations (MSs), the novelty of our approach lies in the utilization of the HO of relay stations (RSs). Hence, the algorithm enabling load balancing via RSs is developed and optimized. Furthermore, the paper contemplates the implementation of the proposed mechanism to networks based on IEEE 802.16 standards. The performance of the mechanism is evaluated in terms of achieved system throughput and signaling overhead both at the air interface and over the wired backbone. The obtained results indicate that the load balancing mechanism through the HO of RSs outperforms existing load balancing mechanisms exploiting conventional HO of MSs. Copyright © 2011 John Wiley & Sons, Ltd.     

Adaptive load‐balancing association handoff approach for increasing utilization and improving GoS in mobile WiMAX networks

The IEEE 802.16e standard is thus proposed for supporting high data rate and dynamic mobility in WiMAX. IEEE 802.16e specifies the association handoff mechanism in the MAC layer, i.e., providing contention‐free‐based initial ranging, and thus mobile stations can perform the initial ranging early during the handoff period. An MS executing the association handoff during a scan duration is disallowed to send/receive any packets to/from the serving BS. IEEE 802.16e suffers from not determining a precision scan duration period because of losing the transmission opportunity or the response status of the received ranging response (RNG‐RSP) message. Although the MS can set a longer scan duration to complete the initial ranging procedure, it significantly degrades handoff delay and delay jitter of real‐time service flows. In addition, most handoff studies seldom considered balancing traffic load among neighbor base stations (BSs). This paper thus proposes an efficient Adaptive Load‐balancing Association handoff approach (ALA) consisting of two phases: (1) the Adaptive Association Handoff phase (AAH) and (2) the Predictive Direction‐based Load Balancing phase (PDLB), to overcome above mentioned problems. AAH proposes an adaptive re‐association mechanism to reduce lost synchronizations, and thus improve the grade of service. PDLB adopts the Polynomial Regression‐based RSS prediction algorithm to accurately predict the moving direction of mobile nodes. Numerical results demonstrate that ALA significantly outperform IEEE 802.16e and others in average handoff delay, number of handoffs, dropping probability, GoS, network utilization, and number of lost synchronizations. Copyright © 2011 John Wiley & Sons, Ltd.     

LDPC码在802.16a OFDM系统 衰落信道中的性能分析

本文通过对802.16a OFDM系统信道的分析,权衡估计的性能和算法复杂度两个因素,针对不同的传输环境,提出了动态的OFDM信道估计方案.另外我们找到了一组优秀的非正则LDPC码,将其应用于IEEE 802.16a OFDM环境中,仿真验证了它们在SUI-3和SUI-5多径衰落信道环境下具有良好的性能,并和协议中提出的卷积Turbo码进行了比较,结果证明在相同条件下,本文的LDPC码可以取得比协议提出的卷积Turbo码更优越的性能,具有更好的抗多径衰落的能力.     

Design and analysis of cellular mobile communications system basedon DQRAP/CDMA MAC protocol

Future third-generation mobile communication systems will need multi-access control (MAC) protocols suitable for multimedia code division multiple access (CDMA) radio communications. Distributed queueing random access protocol (DQRAP)/CDMA is a general purpose MAC protocol oriented to the CDMA environment. Analytical model expressions and computer simulations have shown its capacity to achieve near-optimum performance under heterogeneous traffic scenarios in a unicellular environment. A cellular environment has been designed to verify that DQPAP/CDMA maintains its near-optimum performance in a packet switched mobile communication system. A new handover technique based on the protocol is proposed to further improve the system performance     

Performance analysis of channel estimation for LDPC-coded OFDM system in multipath fading channel

In this paper, the channel estimation techniques for Orthogonal Frequency Division Multiplexing （OFDM） systems based on pilot arrangement are studied and we apply Low Density Parity Check （LDPC） codes to the system of IEEE 802.16a with OFDM modulation. First investigated is the influence of channel cstimation schemes on LDPC-code based OFDM system in static and multipath fading channels. According to the different propagation environments in 802.16a system, a dynamic channel estimation scheme is proposed. A good irregular LDPC code is designed with code rate of 1/2 and code length of 1200. Simulation results show that the performance of LDPC coded OFDM system proposed in this paper is better than that of the convolution Turbo coded OFDM system proposed in IEEE standard 802.16a.     

Limits of digital unit–remote radio unit distance and cell coverage induced by time division duplex profile in mobile WiMAX systems

We analyze the theoretical limits of three characteristics in the mobile WiMAX base station composed of DU (digital unit) and RU (remote radio unit): (i) the maximum distance between DU and RU; (ii) the maximum number of cascading RUs that can be connected to a DU; and (iii) cell coverage from RU. These theoretical limits are induced by the time division duplex profile of the IEEE802.16 standard. With the typical parameters of the mobile WiMAX system, the maximum allowable distance between DU and RU is 7.4 km and the cell coverage from RU is 8.3 km for 10‐MHz channel BW. This analysis will be a helpful practical guideline for designing mobile WiMAX base stations and planning mobile WiMAX cells. Copyright © 2011 John Wiley & Sons, Ltd.     

Modeling Contention Based Bandwidth Request Scheme for IEEE 802.16 Networks

IEEE 802.16 standard specifies a contention based bandwidth request scheme for best-effort and non-real time polling services in point-to-multipoint (PMP) architecture. In this letter we propose an analytical model for the scheme and study how the performances of bandwidth efficiency and channel access delay change with the contention window size, the number of contending subscriber stations, the number of slots allocated for bandwidth request and data transmission. Simulations validate its high accuracy.     

GHAP: An Efficient Group-based Handover Authentication Mechanism for IEEE 802.16m Networks

IEEE 802.16m is now under consideration by the International Telecommunication Union (ITU) to become the International Mobile Telecommunications (IMT)-Advanced standard. However, handover authentication is a critical issue in this area. In this paper, we propose an efficient group-based handover authentication mechanism, named as GHAP, for correlated mobile stations (MSs) in IEEE 802.16m networks. In our scheme, the correlated MSs who have the similar Signal to Interference-plus-Noise Ratio and history handover information etc. are divided into the same handover group. When the first MS of the handover group members moves from the service base station (BS) to a target BS, the service BS transmits all the handover group members’ security context to the target BS utilizing the security context transfer (SCT) method and then all these MSs in the same handover group can easily perform the handover authentication with the target BS. Different from the conventional SCT schemes, our scheme uses the MSs’ security context as a symmetric key of Cipher-based message authentication code (CMAC) but not the key material of deriving new session key. Therefore, the proposed scheme can effectively resist the domino effect existing in the previous SCT schemes. Moreover, security analysis shows that the proposed scheme also meets the other security requirements in handover authentication semantics. Furthermore, performance analysis demonstrates that the proposed scheme is very efficient in reducing average handover latency.     

Capacity estimation and TCP performance enhancement over mobile WiMAX networks - [WiMAX update]

The mobile WiMAX system is based on IEEE 802.16e, which defines radio interface supporting several classes of Internet Protocol applications and services. While the mobile WiMAX system is being deployed, IEEE 802.16m TG is developing an amendment to the IEEE 802.16e to greatly improve the system performance, and it is focusing not only on the PHY and MAC performance but also on a level of end-to-end performance improvement that includes the scope of the network and application to embrace the strong market request and interest. To evaluate the mobile WiMAX system capacity and performance, all the aspects of performance evaluation ? from air link to application ? are required. For the network and application-level capacity and performance analysis, we first provide an overview of mobile WiMAX systems, especially of the OFDMA/TDD systems of IEEE 802.16e and then describe subscriber and application profiles that include traffic-mix ratio, data-session attempts for applications, diurnal-application traffic distribution, and the application-traffic model. Afterward, the simulation results of network- traffic characteristics and demand estimation are provided. Finally, in the last section, we provide simulation results of end-to-end application performance evaluation using the examples of VoIP and a TCP/IP performance-enhancement method that can be implemented in the mobile WiMAX MAC or MAC/IP cross layer.     

Design of spread spectrum multicode CDMA transport architecture formultimedia services

We investigate a new application of the well-known spread spectrum code division multiple access (SS-CDMA) techniques to multimedia services related to the development of the next-generation wireless mobile networks interconnecting with a wireline ATM-based broadband network. Such services allow users to share novel multimedia applications without any geographical restrictions. However, since the mobile radio channel has a fixed limited bandwidth, the traditional SS-CDMA system may not be sufficient to accommodate the variable bit rate (VBR) multimedia services requested by multiple mobile users simultaneously. Moreover, the traffic load at the base station can change dynamically due to the time-varying throughput requirement of these requested multimedia services. To tackle this difficulty, a multicode CDMA (MC-CDMA) technique is proposed to provide multirate multimedia services by varying the number of spreading codes assigned to each user in order to meet its throughput requirement. In MC-CDMA, a spreading code can be used to transmit information at a basic bit rate. Users (video or data) who need higher transmission rates can use multiple codes in parallel. Meanwhile, the maximum available number of codes in the MC-CDMA system is still limited. Hence, a cost-effective dynamic code allocation scheme has then been proposed to dynamically assign an appropriate number of codes to each user for achieving the maximum resource utilization for multiuser multimedia services via the mobile radio channel. Finally, a number of real multimedia titles generated from the well-known MacroMind Director are conducted to evaluate performance     

Analysis of IPv6 handovers in IEEE 802.16 environment

The second generation of WiMAX solutions, based on IEEE 802.16-2005 standard, offers limited mobility support. Unfortunately, after quickly changing the point of attachment on the WiMAX data link layer (DLL), very slow and inefficient IPv6 reconfiguration takes place. Delays introduced by automatic configuration (DHCPv6 and IPv6 protocols) and Mobile IPv6 can easily diminish or even render useless all benefits gained using the efficient handover performed on DLL. As handover is a crucial process in mobile cellular environments, reasons behind delays introduced by IPv6 layer mechanisms have to be analyzed and appropriate countermeasures applied. In order to analyse influence of different factors on the handover delay a simulation environment modelling the full handover procedure in a WiMAX environment has been developed. It allows simulation and analysis of various mobility related issues, offering support for multiple base stations with groups of subscribers, both fixed and mobile, with various mobility models. Also support for tight integration with higher layers (IPv6, DHCPv6, and Mobile IPv6) is fully implemented. All stages of full IPv6 handover in IEEE 802.16 environment, focusing on major reasons of reconfiguration delays are described. The paper presents components, functional requirements and architecture of the simulation environment, together with example simulation results. The obtained results clearly show that most significant delays are caused by the IPv6 layer. The areas of improvement in several autoconfiguration mechanisms are identified. Proposals include novel use of DHCPv6 relays for remote configuration, solving DAD delays, limiting Binding Update procedure in Mobile IPv6, and configuring routing through DHCPv6 communication. A universal metric for assessing impact of every stage on handover efficiency is also defined. Several proposed improvements to the IPv6 handover process are evaluated. Discussion regarding possible generalization of best improvement proposals and remarks on further research areas conclude this paper.     

Relay Technologies for WiMAX and LTE-Advanced Mobile Systems

Relay technologies have been actively studied and considered in the standardization process of next-generation mobile broadband communication systems such as 3GPP LTE-Advanced, IEEE 802.16j, and IEEE 802.16m. This article first introduces and compares different relay types in LTE-Advanced and WiMAX standards. Simulation results show that relay technologies can effectively improve service coverage and system throughput. Three relay transmission schemes are then summarized and evaluated in terms of transmission efficiency under different radio channel conditions. Finally, a centralized pairing scheme and a distributed pairing scheme are developed for effective relay selection. Simulation results show that the proposed schemes can maximize the number of served UE units and the overall throughput of a cell in a realistic multiple-RS-multiple-UE scenario.     

Performance comparison of OFDM bandwidth request schemes in fixed IEEE 802.16 networks

IEEE 802.16 standard specifies two contention based bandwidth request schemes working with OFDM physical layer specification in point-to-multipoint (PMP) architecture, the mandatory one used in region-full and the optional one used in region-focused. This letter presents a unified analytical model to study the bandwidth efficiency and channel access delay performance of the two schemes. The impacts of access parameters, available bandwidth and subchannelization have been taken into account. The model is validated by simulations. The mandatory scheme is observed to perform closely to the optional one when subchannelization is active for both schemes.     

WiMAX移动性的改进与增强

基于IEEE 802.16协议族的WiMAX网络将按照固定、游牧、移动的趋势发展,其中802.16e协议是面向全面移动性的。分析了802.16e协议空中接口媒体接入控制层(MAC)在切换方面的改进和物理层(PHY)针对移动性的改进并进行参数选择。针对802.16e网络架构对移动场景支持的不足,提出一种新的适合移动性的WiMAX网络增强型体系架构。     

Achieving Faster Handovers in Mobile WiMAX Networks

WiMAX is a wireless metropolitan area network (WMAN) specified by IEEE 802.16. It provides the broadband wireless access for mobile devices. In such a system, to enable the mobility, the handover is supported to maintain the connectivity of the mobile station (MS) when it moves from the coverage of the serving base station (BS) to the coverage of a neighbor BS. In the handover process, scanning is required to find a suitable target BS, and network re-entry is needed to establish the new connection. However, in the standard handover process, a long latency to data transmissions is caused resulting in the serious interruption to ongoing services. In this paper, an improved handover scheme is proposed to reduce the latency introduced in the handover process by shortening the scanning and enhancing the network re-entry. The proposed scanning strategy reduces the latency by reducing the number of neighbor BSs to be scanned through estimating the rough location of the MS. The enhanced network re-entry reduces the delay by updating transport connection identifiers (CIDs) early to allow the fast resumption of active applications. Simulations were conducted to evaluate the performance of the proposed handover scheme. The results show that the proposed handover scheme reduces the data transmission latency during handover significantly.