低重分配概率的OVSF码重分配算法

在采用正交可变长扩频因子(OVSF)码作为信道化码的直接序列扩频码分多址系统中,提出用重分配概率作为重分配算法的一个新的评价指标,重分配概率越小,系统的计算复杂度越低。进而提出一种低重分配概率的、基于空码容量的重分配算法,在解决本次码阻塞的同时,兼顾对未来高数据速率的呼叫的支持能力,减少未来码阻塞发生。仿真证实,重分配概率比已有2种重分配算法都小。     

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。     

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.

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.

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.     

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.     

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.     

A Fast Code-Assignment Strategy for a WCDMA Rotated-OVSF Tree with Code-Locality Capability

In this paper, a new channelization code tree structure, namely an ROVSF (rotated-orthogonal variable spreading factor) code tree, is defined and investigated. Most existing code assignment schemes are investigated on the OVSF (orthogonal variable spreading factor) code tree in WCDMA systems. The main work of this investigation is to exploit and justify the new properties of the ROVSF code tree. We show that the ROVSF code tree offers the same code capability to that of the conventional OVSF code tree, but our ROVSF code tree additionally has the code-locality capability. With the code-locality capability, a fast code-assignment strategy is developed on the ROVSF code tree. Compared to existing code assignment schemes on OVSF code trees, a fast code assignment scheme is developed with lower search costs and a low blocking rate, due to its code-locality capability. Finally, the simulation results illustrate that our proposed scheme on the ROVSF code tree actually has lower search costs and a better blocking rate.This work was supported by the National Science Council of the R.O.C. under grant nos. NSC91-2213-E-194-041 and NSC91-2213-E-194-042.     

OFDM移动通信系统中的最大多普勒估计

提出了一种基于信道估计自相关函数的多普勒频移估计算法.在OFDM符号数据段前插入正交可变扩频因子(OVSF)序列,求出时域的信道冲激响应,利用信道冲激响应的自相关实现多普勒频移估计.仿真结果表明,该算法可以在较大多普勒频移范围内有效地估计出多普勒频移.     

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。