浅析OVSF码多码分配算法

介绍了现有的两种OVSF多码分配算法,并通过计算机仿真考察了它们在吞吐量、和阻塞率等指标上的性能。仿真结果表明,快速算法和传输所专利算法在吞吐量和阻塞率上的表现一样,但是快速算法更加快速、简单。因此快速算法可广泛应用于以OVSF码作为信道化码的各种DS-CDMA系统中。     

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码保留分配算法研究

提出1种为每类呼叫预留资源的信道化码分配算法。将新算法与已有的单一分区法、混合分区法1、混合分区法2等保留算法进行比较,计算机仿真表明,分区借码法在公平性和码阻塞率方面最好,是公平和吞吐量最好的保留算法。该算法简单、有效和公平,可应用于以OVSF码作为信道化码的各种DS-CDMA系统。     

一种新的OVSF码动态有序分配算法

该文通过研究W-CDMA系统下行链路OVSF码的特性,针对传统的随机动态分配算法存 在码阻塞的问题,提出了一种动态有序分配算法,采用先分配低速用户,相同层从低序号码字向高序号码字 顺序分配的原则。并对该算法的流程和系统实现给予了详细的描述。最后通过系统性能的理论分析和数值仿 真,证明该算法大大降低了码字阻塞概率,减少了系统开销,对于工程应用具有重要价值。     

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。     

一种新的OVSF码快速生成分配算法研究

本文利用复制方法提出一种新的OVSF码复制生成算法,并在此基础上,研究了非可重排和可重排两种情况下的OVSF码快速分配问题.利用复制生成的OVSF码字具有明显的异前置性特点,从而可以提高码字分配效率和减小硬件实现复杂度和降低呼叫阻塞率.     

cdma2000系统中Walsh码的优化分配算法

Walsh码是码分多址系统中一种重要的正交扩频码。随着 3G系统的发展 ,高速率数据业务的引入 ,对有限Walsh码资源的需求日益增加 ,因此合理的管理和分配成为必然。本文以cdma2 0 0 0系统中Walsh码的使用为例 ,分析了Walsh码的工作原理和使用现状 ,提出了一种动态分配的优化算法。     

一种生成OVSF码树的新方法

在第三代移动通信技术中，直接序列扩展频谱技术是其核心技术之一，通信系统的带宽是固定的，某些业务需要以很高的速率进行传输，因此对以不同速率传输的业务码流必须采用不同的扩频比进行频谱的扩展。在同一个小区当中，多个移动用户可以同时发送不同的多媒体数据，为了防止多个用户不同业务之间的干扰，必须设计出一类适合于满足不同速率多媒体业务，即3GPP标准中的正交可变扩频因子（OVSF）码。[第一段]     

低信噪比WCDMA信号扩频码的盲估计方法

针对低SNR(信噪比)下WCDMA(宽带码分多址)上行链路信号OVSF(正交可变扩频因子)码难检测的问题,提出了一种利用WCDMA信号的相关矩阵累加平均与其奇异值分解相结合的方法。该方法是在WCDMA信号的OVSF码周期、码速率等参数已知的前提下,将接收到的信号以一随机固定值为起点进行周期分段,形成多个连续观察向量,求相关矩阵并累加平均,并对相关矩阵进行奇异值分解,由相关矩阵的主特征向量估计出WCDMA信号的OVSF码序列,从而对接收的信号实行盲解扩处理。仿真结果表明,该方法在较低SNR条件下也能取得良好的效果。     

一种改进的DSSS信号扩频码估计算法研究

在低信噪比条件下检测出直接序列扩频(DSSS)信号后,要恢复出原始信息,估计出扩频码序列是非常关键的,因此有必要研究DSSS信号的扩频码序列估计算法。提出了一种基于改进的协方差矩阵迭代算法应用于估计扩频码序列。理论分析和计算机仿真实验都表明了该算法能在低信噪比下估计出扩频码序列,与其他一些扩频码序列估计算法如基于投影子空间的算法、基于神经网络的算法相比,具有运算量更小等优势。     

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.     

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.     

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.

针对业务变化的TD-SCDMA信道码分配算法探讨

在三代移动通信TD—SCDMA系统信道的分配是载波、时隙、信道码（扩频码）的分配。本文针对用户使用的业务不断变化的TD—SCDMA系统提出一种新的信道码分配算法，对算法的流程进行详细的描述，并且通过仿真证明新算法在呼叫阻塞率方面强与原有信道码分配算法，对于工程的应用有重要的价值。     

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.     

LDPC code reconstruction based on algorithm of finding low weight code-words

LDPC code reconstruction without a candidate set is one of the tough problems in channel code reconstruction.First,theoretical analysis was provided for the number of received code-vectors needed for the reconstruction,and a lower bound was derived.Then,according to the lower bound,and based on an algorithm for finding low weight code-words,a new reconstruction method was proposed.It looked for low weight vectors one by one from the dual space of the received code-vector space and used them to reconstruct the sparse parity-check matrices.Number of iterations and the computational complexity of the method were analyzed based on exponential distribution theory.Under noise-free conditions,drawbacks of the existing method,including limited applicable range and large quantity of required data,have been overcame.Under noisy conditions,the proposed method has higher robustness against noise and relatively low complexity,compared to existing methods.For QC-LDPC codes,the reconstruction performance can be further improved using the quasi-cyclic property of their sparse parity-check matrices.     

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.