OVSF码在WCDMA中的应用

随着移动通信技术的发展,多媒体信息的传输是必然的趋势。WCDMA是第三代移动通信IMT 2000中的主流技术,他支持多媒体从低速率到高速率的多种业务。每种业务有不同的地址码,为了防止各种数据业务的干扰,地址码必须具有正交的特性。由于速率不同,而扩频后的带宽是固定的,为了满足信道的传输,就采用了不同长度的正交码(OVSF)。介绍了OVSF码在WCDMA中的使用,并讨论了OVSF码在WCDMA下行链路分配的几种算法,容量门限法更接近实际情形,能有效降低码阻塞率,保证实时传输。     

OVSF Code Sharing and Reducing the Code Wastage Capacity in WCDMA

The non quantized nature of user rate wastes the code capacity in Orthogonal Variable Spreading Factor Codes (OVSF) based Code Division Multiple Access (CDMA) systems. The code sharing scheme in multi code CDMA is proposed to minimize the code rate wastage. The scheme combines the unused (wastage) capacity of already occupied codes to reduce the code blocking problem. Simulation results are presented to show the superiority of the proposed code assignment scheme as compared to existing schemes.

An Efficient Adaptive Grouping for Single Code Assignment in WCDMA Mobile Networks

For achieving high utilization and efficient code management of the OVSF code tree in 3G WCDMA networks, several researches have extensively studied. Based on combining both the code assignment and the reassignment mechanisms, it increases obviously high utilization and reduces completely the code blocking. Nevertheless, the required rate of traffic should be powers of two of the basic rate, i.e. 1R, 2R, 4R, …, etc., which is impractical and results in wasting the system bandwidth while the required rate is not powers of two of the basic rate. Several multi-code assignment mechanisms have proposed to reduce the waste rate. Nevertheless, these methods bring two inevitable drawbacks including, high complexity of handling multiple codes, and increasing the cost of using more rake combiners at both the base stations and mobile nodes. Therefore, we propose an adaptive grouping code assignment herein to provide a single channelization code for any possible rate of traffic, even though the required rate is not powers of two of the basic rate. Based on the dynamic programming algorithm, the adaptive grouping approach forms several calls into a group. Then it allocates a subtree to the group and adaptively shares the subtree codes for these calls in the concept of time-sharing of slots during a group cycle time. Therefore, the waste rate and code blocking are thus reduced obviously while using a single rake combiner. Since the delay problem may be occurred in such a time-sharing approach, we propose two schemes of cycle interleaving methods to reduce delay. Numerical results indicate that the proposed adaptive grouping approach reduces significantly the waste rate and thus increases the system utilization. Moreover, the proposed cycle interleaving scheme reduces data delay significantly. Ren-Hung Hwang received his M.S. and Ph.D. degrees in computer science from University of Massachusetts, Amherst, Massachusetts, USA, in 1989 and 1993, respectively. He joined the Department of Computer Science and Information Engineering, National Chung Cheng University, Chia-Yi, Taiwan, in 1993, where he is now a full Professor and the Chair of the Department of Communication Engineering. His research interests include Internet QoS, peer-to-peer infrastructure design, and 3G QoS. Ben-Jye Chang received his M.S. degree in computer engineering from University of Massachusetts, Lowell, in 1991 and the Ph.D. degree in computer science and information engineering from National Chung-Cheng University, Taiwan, in 2001. He joined the Department of Computer Science and Information Engineering faculty at Chaoyang University of Technology, Taiwan, in 2002, where he is currently an Associate Professor. His research interests include QoS-based networks, QoS wirless networking, resource management for wireless networks and mobile cellular networks, and performance evaluation of networks. Min-Xiou Chen received the BS degree in computer science and information engineering from Tung Hai University, Tai-Chung, Taiwan, in 1996, and the MS and PhD degrees in computer science and information engineering from National Chung Cheng University, Chia-Yi, Taiwan, in 1998 and 2005, respectively. He is now an assistant professor at the Department of Computer Science and Information Engineering, Chung Hua University, Hsin-Chu, Taiwan. His research interests include wireless communication, SIP, sensor network and resource management in WCDMA systems. He is a member of the IEEE. Kun-Chan Tsai received the BS degree in information engineering and computer science from Feng Chia University, Taichung, Taiwan, in 2001, and the MS degree in computer science and information engineering from National Chung Cheng University, Chia-Yi, Taiwan, in 2003. His research interests include wireless communications and resource management in WCDMA systems.     

Enhancing the high speed downlink packet access operation of 3G WCDMA systems

In high‐speed downlink packet access (HSDPA), the combination of adaptive modulation and coding, hybrid automatic repeat request, and an extended multicode operation has replaced two fundamental aspects of wideband code division multiple access systems, namely, variable spreading factor and fast power control. Despite its enhanced characteristics, the HSDPA operation can be problematic when the majority of incoming traffic load consists of low data rate delay‐sensitive services such as mobile voice‐over‐Internet Protocol. To tackle this case, we propose an enhanced HSDPA operation that exploits multiple layers of the channelization code tree through a specifically designed packet scheduling and code allocation process. Enhanced HSDPA, when compared with the conventional HSDPA, provides a more flexible sharing of the available capacity and is able to increase the number of users that can be served with the required quality of service in terms of packet delay. The efficiency of the proposed scheme is confirmed by simulation results. Copyright © 2011 John Wiley & Sons, Ltd.     

Region Division Assignment: A New OVSF Code Reservation and Assignment Scheme for Downlink Capacity in W-CDMA Systems

This work focuses on the efficient management of orthogonal-variable-spreading-factor (OVSF) codes for multimedia communications in the W-CDMA systems. Because these systems must assign only OVSF codes that are mutually orthogonal, even if they have sufficient transmission capacity they block connections for which no orthogonal OVSF codes are available. This code blocking can, with extra overhead, be eliminated by reassigning codes, but in this paper we propose an OVSF code management scheme designed to not reassign codes. This scheme, called Region Division Assignment, cannot eliminate code blocking but can reduce the overhead for code assignment. Computer simulations based on the multiple access protocol in UMTS/IMT-2000 show that the proposed scheme can efficiently provide variable-rate services as well as low-rate services. This paper was presented in part at the IEEE Vehicular Technology Conference Fall 2001, October 7-11, 2001, Atlantic City, NJ USA. Rujipun Assarut received his BE from Chularongkorn University, Thailand, in 1997 and his MS from Gunma University, Japan, in 2002. Currently, he is working as a software engineer for NEC communication systems. His current project is the development of IP phone for enterprise applications. Ken’ichi Kawanishi is a research associate with Gunma University, Japan. His current research interests include queueing theory and stochastic processes. He is a member of ORSJ, JSIAM and IEICE. Ushio Yamamoto received a bachelor’s degree in information engineering, and a master’s degree and Ph.D. degree in information science from Tohoku University in 1992, 1994 and 1997, respectively. He is now an associate professor in Dept. of Computer Science, Gunma University. He has been engaged in research on wireless ad hoc networks, multimedia communication networks, load balancing on computer networks and intelligent agents. He is a member of IPSJ and JSAI. Yoshikuni Onozato is a Professor with Gunma University. His research interests are in satellite systems, computer communication networks and distributed computing systems and span the entire spectrum from the design and performance evaluation of these systems to their implementation. He is a member of IEEE, ACM, IPSJ, ORSJ and IEICE.     

Markov-Based OVSF Code Assignment Scheme and Call Admission Control for Wideband-CDMA Communication Systems

For the reason of the orthogonal characteristic of the Orthogonal Variable Spreading Factor (OVSF) code tree in Wideband CDMA (WCDMA) systems, code blocking increases as traffic load (i.e. Erlang load) or the required rate increases. This causes inefficient utilization of channelization codes. Hence, how to efficiently manage the resource of channelization codes of the OVSF code tree in WCDMA systems is an important issue and has been studied extensively. There are two aspects to achieve efficiency including code assignment and code reassignment. In the aspect of code assignment, an efficient code assignment scheme reduces code blocking probability significantly. In the aspect of code reassignment, code reassignment results in several drawbacks, such as large overhead of computation, high complexity of codes moving, and long call setup time for a new request call, etc. Therefore, in this paper we focus on the first aspect of how to efficiently assign the channelization codes. Additionally, most researches did not consider the analysis of tree state with dynamic traffic load and their analysis lack of systematic call admission control (CAC) mechanism. Therefore, in this paper, we first propose the Markov decision process (MDP) based analysis to assign channelization codes efficiently. Next, we extend the MDP-based approach as the call admission control mechanism to maximize the system revenue while reducing blocking probability. Furthermore, a bit string masking algorithm is proposed to reduce the time complexity of tree managing and searching for available channelization codes. Numerical results indicate that the proposed MDP approach yields the best fractional reward loss, code blocking reward loss, and code blocking ratio as compared to that of other schemes, including the random, left most, and crowded first schemes. Ben-Jye Chang received his M.S. degree in computer engineering from University of Massachusetts, Lowell, in 1991 and the Ph.D. degree in computer science and information engineering from National Chung-Cheng University, Taiwan, in 2001. He joined the Department of Computer Science and Information Engineering faculty at Chaoyang University of Technology, Taiwan, in 2002, where he is currently an associate professor. His research interests include QoS-based networks, QoS wireless networking, resource management for wireless networks and mobile cellular networks, and performance evaluation of networks. Min-Xiou Chen received the B.S. and M.S. degrees in computer science and information engineering from Tung Hai University and National Chung Cheng University in 1996, and 1998, respectively. He is currently a Ph.D. candidate in the Department of Computer Science and Information Engineering, National Chung Cheng University. His research interests include wireless communication, SIP, and resource management in WCDMA systems. Ren-Hung Hwang received his M.S. and Ph.D. degrees in computer science from University of Massachusetts, Amherst, Massachusetts, USA, in 1989 and 1993, respectively. He joined the Department of Computer Science and Information Engineering, National Chung Cheng University, Chia-Yi, Taiwan, in 1993, where he is now a full professor and the Chair of the Department of Communication Engineering. His research interests include Internet QoS, peer-to-peer infrastructure design, and 3G QoS. Chun-Huan Chuang received the B.S. and M.S. degrees in computer science and information engineering from National Chung Cheng University, Taiwan, in 2001 and 2003, respectively. His research interests include wireless communication and resource management in WCDMA systems.     

WCDMA系统的信道码分配策略

第三代移动通信系统WCDMA支持多业务、多QoS的传输,能更好地利用信道码的分配策略。3GPPWCD-MA标准采用的正交可变长扩频码(OVSF)支持变速率业务,举例说明了一种可行的信道码动态分配方案。     

Dynamic bandwidth recycle algorithm for OVSF–CDMA systems

This paper presents a dynamic bandwidth recycle algorithm in the downlink of a WCDMA system using orthogonal variable spreading factor codes (OVSF). It consists of a bandwidth recycle algorithm and a bandwidth reservation algorithm. The bandwidth recycle algorithm is used to recycle bandwidth from current serviced connections when the system does not have enough available bandwidth to support a bandwidth request. The bandwidth reservation algorithm is used to reduce transmission delay caused by suddenly increasing bandwidth requests. Four traffic classes, conversational, streaming, interactive, and background classes, defined by universal mobile telecommunication system (UMTS) are considered. Simulation results show that the bandwidth utilization and block rate are improved, the bandwidth guaranteed to conversational and streaming classes are protected, and the delay time of interactive and background classes are kept under an acceptable value even when the traffic load is heavy. Copyright © 2005 John Wiley & Sons, Ltd.     

A Guard Code Scheme for Handover Traffic Management in WCDMA Systems

A key performance indicator of mobile wireless networks is failure probability of handover calls. In this paper, we propose a Call Admission Control policy which prioritizes handover calls over new calls in WCDMA systems. The OVSF code occupancy of the system is modeled by a Markov chain and the differentiation between handover and new calls is performed at the code level by introducing a “guard code” scheme. The scheme belongs to the well-known family of guard channel schemes and reserves some code capacity to favor the continuation of handover calls over the new calls. As the management of the general case is intractable, we solve certain numerical instances of the problem and manage to calculate several performance metrics like new call blocking and handover failure probabilities and code utilization. We complete our study with simulation results in the case of higher OVSF code tree capacity.

浅析WCDMA切换策略的应用

简单地介绍了WCDMA切换算法,通过与CDMA 2000切换的比较,较详细地论述了在十字路口拐弯处、室内外、电梯、大桥、高速铁路及隧道等场景下的WCDMA切换策略应用,希望能对WCDMA网络的规划与优化提供一些帮助。     

Smart Antenna Based OVSF Code Assignment for WCDMA Networks

This paper presents a new method for dynamic allocation of orthogonal variable spreading factor (OVSF) codes in WCDMA networks where each base station is equipped with an adaptive antenna array (AAA). Previous works about OVSF code assignment problem deal with the code limited case. Here, we investigate the feasibility to turn the problem into the SIR limited case. With our scheme, the new call request is allocated an OVSF code that may be currently used by an active user whose downlink beam has the smallest spatial correlation with the channel vector of the requesting user, as long as desired SIR level is achieved. The performance of the new scheme is justified through computer simulations under different traffic load conditions.     

A Study of the Simulation Platform of WCDMA

1　IntroductionAtpresent,manydifferentsystemshavecoex istedinthedevelopmentofmobilecommunication .Thingshavegotmorecomplexinthedevelopmentof3Gthanever.Inadditiontothecoexistenceofmul tiplemobileschemes,anothercomplexityisthatthe3Gmustbecompatiblewiththe 2Gsystems.Soft wareDefinedRadio (SDR )orSoftWareRadio(SWR)isakindofnewwirelesscommunicationtechnology .Ithasbeenrecognizedasthenextmajorleapforwardinmobilecommunications.Particular ly ,itisabletoprovidetheseamlessconnectionbe tweenmanyex…     

WCDMA无线网络码资源优化

中国联通WCDMA网络经过两年多的大规模建设与发展,用户数量不断增加,网络负荷也逐渐增高,与用户感知密切相关的码资源也开始不足的现象,导致网络性出现波动甚至恶化,比如无线接通率降低,单用户速率下降等。通过对长沙WCDMA无线网络码资源利用情况的分析研究,从覆盖控制、双载波方案、参数优化等方面来优化解决。     

宽带码分多址系统仿真研究

在分析第三代移动通信系统的基础上,使用ＥＤＡ工具Ｃｏｓｓａｐ,自行开发了ＷＣＤＭＡ完整的函数库,重点对ＷＣＤＭＡ系统的物理链路层结构进行了系统仿真,建立了上行链路（ＵＬ）和下行链路（ＤＬ）的仿真平台。本文根据ＩＴＵ－Ｒ Ｍ．１２２５建议的多径衰落环境,分别根据１９９８年９月ＥＴＳＩ的ＷＣＤＭＡ草案和１９９９年１１月“ＩＭＴ－２０００无线接口技术规范”建议,对话音信道和数据信道进行了全面的仿真测试。     

OVSF码分配算法研究

提出1种优先选择极左碎片的信道化码分配算法,该算法用很简单的方式降低了码阻塞率。将新算法与已有的极左法和权重法进行比较,理论分析和计算机仿真表明,极左碎片法具有与极左法相近的简单性,在码阻塞率和公平性方面几乎与权重法一样好,是简单、高效和公平的综合性能最好的算法。该算法可应用于以OVSF码作为信道化码的各种DS-CDMA系统。     

Reducing code wastage in orthogonal variable spreading factor‐based wideband code division multiple access networks

Most third‐generation and beyond wideband code division multiple access networks use the orthogonal variable spreading factor code tree for channelization codes. The codes in this code tree are limited and the performance of a wireless network depends upon the code assignment for new calls. In this paper, we introduce a term called ‘wastage capacity’, which gives us the amount of wastage caused when a code (single or multiple) with a data rate higher than the rate of the incoming call is assigned to it. We suggest two methods to keep wastage capacity below an arbitrary threshold value or zero. In the first method, we devised an algorithm in which wastage up to a certain threshold would be tolerated and the minimum rakes to get this wastage capacity were identified. In the second approach, we reduced the wastage capacity to zero irrespective of the number of rakes at the expense of higher cost and complexity. Copyright © 2011 John Wiley & Sons, Ltd.     

TD-SCDMA与WCDMA扰码规划比较

由于WCDMA和TD-SCDMA的扰码组成有着根本性的区别,本文对两个系统扰码规划考虑的主要因素进行了深入的研究。在对码资源分析的基础上,对比了WCDMA和TD-SCDMA规划特点的区别,得出了WCDMA和TD-SCDMA系统扰码规划应该遵循的不同原则。     

基于Kalman滤波的WCDMA上行链路衰落信道跟踪

针对WCDMA上行链路的结构,介绍了一种基于卡尔曼滤波和线性内插的信道跟踪方法。Kalman滤波器通过线性内插所提供的粗略的数据估计值来准确地获得信道参数的LMMSE解,跟踪信道的变化。仿真结果表明该方法能有效跟踪快速衰落信道,改善系统的性能。     

WCDMA系统的迭代信道估计研究

本文针对WCDMA系统非连续导频情况,研究了采用Turbo编码的迭代信道估计技术,提出了一种基于LMS算法自适应滤波的信道估计方法.对信道估计值采用不同滤波器方法:维纳滤波、滑动平均滤波、FIR滤波、LMS自适应滤波的性能进行了比较,同时采用基于代价函数的方法对迭代信道估计进行了分析.理论分析和仿真结果表明对迭代信道估计所得信道估计值进行滤波的方法能够提高信道估计的精度,从而降低接收机的误比特率.     

WCDMA上行链路一种新的参数优化方法

本文在研究了WCDMA上行链路导频信道辅助相干解调的基础上,提出了参数优化的一种新方法.根据给定信噪比下误码概率最小的准则,本文得到了理论上信道估计器最佳的平均长度和导频信道相对数据信道最优的功率比.