一种支持OVSF码重分配的下行带宽分配算法

WCDMA的下行链路中，OVSF码被用作区分不同物理信道的信道化码，以最大程度降低UE的多址接入干扰(MAI)，并提供对可变速率的支持。所以OVSF码的分配策略及算法直接影响网络的整体性能。该文分析了DCA算法的不足之处并提出了一种支持重分配的多码分配算法。仿真结果表明，该算法能在保持下行链路带宽利用率的同时，有效地减少OVSF码树的碎片并减轻重分配给系统带来的影响。     

可并行识别的UHF RFID防碰撞算法研究

针对传统的动态帧时隙ALOHA多标签防碰撞算法（DFSA）的系统吞吐率低、系统识别率低等问题进行了研究,提出一种可并行识别的UHF RFID防碰撞算法（OVSF-DFSA）。该算法通过基于正交可变扩频因子（OVSF）码作为扩频码的码分多址技术和DFSA协议相结合,突破了传统算法中单一时隙中只能识别一个标签的局限性,实现了标签碰撞到码碰撞的转变。以理论分析和仿真实验为基础,探究了该算法下的系统吞吐率、系统总时隙数及系统识别率等方面的性能。仿真结果表明,当帧长◢fs◣>2且OVSF码长◢m◣>2,当标签数目大于200时,OVSF-DFSA算法下系统吞吐率是DFSA算法的◢m◣倍,且与DFSA、MS-DFSA、PIGDFSA算法相比,OVSF-DFSA算法在上述性能方面效果更佳。     

基于OVSF码动态有序分配算法的呼叫公平性研究

文章通过研究W-CDMA系统OVSF码的特性,针对随机动态分配算法存在码阻塞的问题,提出了动态有序分配算法,并对该算法的流程给予了详细的描述。文章最后通过对系统性能的仿真,证明该算法在系统负荷有余量的条件下保证了用户呼叫的公平性。     

GPRS/GSM网络中的无线信道分配算法研究

随着GPRS/GSM移动接入网的广泛应用,有效的信道分配算法在保证网络服务质量中的重要性开始凸现。该文描述了GPRS/GSM移动接入网的信道分配过程,对固定信道分配算法和动态信道分配算法进行了详细分析,并采用自行开发的GPRS/GSM网络仿真软件模拟语音业务与分组数据业务动态共享信道资源的过程,从而比较了不同的信道分配算法对接入网服务质量的影响,结果显示动态信道分配方案在增加系统运算量的同时可以很好地支持网络通信的质量。     

基于效用函数的无线数据网络资源管理策略

针对可变速率的无线数据网络,提出了一种基于效用函数的资源管理策略。该策略兼顾了数据业务对吞吐量和速率波动的要求,并且综合考虑了速率分配和功率控制对系统性能的影响。仿真结果显示,该策略能够有效地抑制终端的传输速率波动;在信道环境较差时,改进后的算法可以进一步提高系统的性能。     

电力线通信中动态子载波组分配

针对电力线通信自适应OFDM系统的限制条件,探讨在每OFDM符号内各RT用户要求的约束下,研究系统总功率地窖注水分配后多子载波上的速率自适应子载波分配模型,提出一种新的动态子载波组分配算法。在典型电力线信道环境下对其仿真,并与另外两种分配算法进行比较,结果表明,本文动态子载波组分配算法的复杂度大大减小,能满足多用户资源分配的多目标要求。     

认知中基于业务和信道分级的分布式信道分配

为了支持更多的认知业务,提高认知系统的总体性能,提出了基于业务和信道分级的分布式信道分配算法.根据数据速率的不同,将认知用户的业务需求和可用信道分别分为不同等级,优先分配对应等级的空闲信道给干扰邻居数最小的认知用户,以保证更多的认知业务有机会获得空闲信道.仿真结果表明,算法能满足更多认知业务的需求,符合理论分析的结果.     

一种多径信道直扩信号伪码序列盲估计方法

针对多径信道下直接序列扩频信号伪码序列盲估计的难题,拓展了基于加性高斯白噪声信道提出的子空间法,提出了一种基于子空间法和三阶相关函数法相结合的多径信道直扩信号伪码序列盲估计的新算法,进行了理论推导。该算法对接收到的多径直扩信号按照伪码周期的两倍进行分段形成数据向量,构造自相关矩阵并进行特征值分解得到不同增益伪码序列的延迟叠加,运用m序列的三阶相关特性估计生成多项式进而估计伪码序列。计算机仿真结果验证了该算法的有效性。     

高速全数字解调器的并行码元同步设计

针对高速和宽码速率的要求,在Gardner算法的基础上设计了并行码元同步模块.该模块可以满足960MHz中频采样的全数字解调器要求,适应码速率40Mbps-320Mbps,并通过了仿真验证.     

OFDMA系统中的多用户自适应资源分配算法

正交频分复用接入具有传输速率高,带宽分配灵活等特点.在对与多天线STBC等效的单发单收模型进行研究的基础上,结合OFDMA的动态资源分配策略,提出了一种多用户多速率自适应子载波资源分配算法.仿真实验表明,自适应系统由于采用了多用户多速率自适应子载波资源分配策略,不仅可以灵活地支持多速率业务,而且能降低系统的发射总功率,进一步改善了系统性能.     

Genetic approach for dynamic OVSF code allocation in 3G wireless networks

Orthogonal variable spreading factor (OVSF) codes provide variable data rate transmissions for different bandwidth requirements in 3G WCDMA networks. In order to effectively utilize limited OVSF resources, many works in the literature have focused on dynamic code assignment (DCA) schemes. This paper investigates genetic algorithm (GA) based approach for dynamic OVSF code assignment in WCDMA networks. Different from existing conventional code assignment (CCA) and dynamic code assignment schemes, population is adaptively constructed according to existing traffic density in the OVSF code-tree. In order to improve the ability of the GA, we employ so-called “dominance & diploidy” structure to adapt to changing traffic conditions. Performances of these two methods are evaluated in terms of blocking probability and spectral efficiency, and also compared with CCA and DCA. The simulation results show that the GA, especially with diploid structure, provides reduced code blocking probability and improved spectral efficiency in the system when compared to the CCA and DCA schemes. In addition to these, different GA operators are also tested under varying traffic loads to increase the overall system performance.     

OVSF code assignment strategies with minimal fragmentations for WCDMA systems

This paper handles the internal and external fragmentation problems of WCDMA systems using Orthogonal Variable Spreading Factor (OVSF) codes. Internal fragmentation occurs when the allocated data rate is larger than what is requested, while external fragmentation occurs when the OVSF code tree is too fragmented to support a call even if there is sufficient capacity remaining in the code tree. The key factor in solving these two problems is the OVSF code assignment strategy. Most works in the literature do not consider the time-varying and location-dependent channel conditions. In this paper, we formulate the fragmentation problem as a multiple knapsack problem where each OVSF code is considered as a knapsack. We propose single-code, time-shared strategies that consider channel conditions while solving these fragmentation problems.Simulation results verify that our strategies efficiently use the precious wireless bandwidth.     

A Constant-Competitive Algorithm for Online OVSF Code Assignment

Orthogonal Variable Spreading Factor (OVSF) code assignment is a fundamental problem in Wideband Code-Division Multiple-Access (W-CDMA) systems, which plays an important role in third generation mobile communications. In the OVSF problem, codes must be assigned to incoming call requests with different data rate requirements, in such a way that they are mutually orthogonal with respect to an OVSF code tree. An OVSF code tree is a complete binary tree in which each node represents a code associated with the combined bandwidths of its two children. To be mutually orthogonal, each leaf-to-root path must contain at most one assigned code. In this paper, we focus on the online version of the OVSF code assignment problem and give a 10-competitive algorithm (where the cost is measured by the total number of assignments and reassignments used). Our algorithm improves the previous O(h)-competitive result, where h is the height of the code tree, and also another recent constant-competitive result, where the competitive ratio is only constant under amortized analysis and the constant is not determined. We also improve the lower bound of the problem from 3/2 to 5/3.     

An Algorithmic View on OVSF Code Assignment

Orthogonal Variable Spreading Factor (OVSF) codes are used in UMTS to share the radio spectrum among several connections of possibly different bandwidth requirements. The combinatorial core of the OVSF code assignment problem is to assign some nodes of a complete binary tree of height h (the code tree) to n simultaneous connections, such that no two assigned nodes (codes) are on the same root-to-leaf path. A connection that uses a 2^-d fraction of the total bandwidth requires some code at depth d in the tree, but this code assignment is allowed to change over time. Requests for connections that would exceed the total available bandwidth are rejected. We consider the one-step code assignment problem: Given an assignment, move the minimum number of codes to serve a new request. Minn and Siu propose the so-called DCA algorithm to solve the problem optimally. In contrast, we show that DCA does not always return an optimal solution, and that the problem is NP-hard. We give an exact n^O(h)-time algorithm, and a polynomial-time greedy algorithm that achieves approximation ratio Θ(h). A more practically relevant version is the online code assignment problem, where future requests are not known in advance. Our objective is to minimize the overall number of code reassignments. We present a Θ(h)-competitive online algorithm, and show that no deterministic online algorithm can achieve a competitive ratio better than 1.5. We show that the greedy strategy (minimizing the number of reassignments in every step) is not better than Ω(h) competitive. We give a 2-resource augmented online algorithm that achieves an amortized constant number of (re-)assignments. Finally, we show that the problem is fixed-parameter tractable.     

基于概率的水下传感器网络CDMA编码分配算法

水下传感器网络采用声波进行通信,具有高时延、低带宽、高误码率等特点,使得适用于无线电信道的MAC协议无法直接应用于水声信道,给水下传感器网络协议的设计带来了很大的挑战．因此,我们提出了一种可以较高概率避免扩频码冲突的分布式的基于概率的水下传感器网络CDMA编码动态分配算法．该算法不需要精确的时间同步,并且能够动态适应水下传感器网络拓扑结构的变化,适用于基于发送端的编码分配和基于接收端的编码分配．仿真实验表明,与传统的编码分配方式相比,我们的算法突出了节点的个性化,进一步降低了冲突的风险．     

OVSF-CDMA Code Assignment in Wireless Ad Hoc Networks

Orthogonal Variable Spreading Factor (OVSF) CDMA code consists of an infinite number of codewords with variable rates, in contrast to the conventional orthogonal fixed-spreading-factor CDMA code. Thus, it provides a means of supporting of variable rate data service at low hardware cost. However, assigning OVSF-CDMA codes to wireless ad hoc nodes posts a new challenge since not every pair of OVSF-CDMA codewords are orthogonal to each other. In an OVSF-CDMA wireless ad hoc network, a code assignment has to be conflict-free, i.e., two nodes can be assigned the same codeword or two non-orthogonal codewords if and only if their transmission will not interfere with each other. The throughput (resp., bottleneck) of a code assignment is the sum (resp., minimum) of the rates of the assigned codewords. The max-throughput (resp., max-bottleneck) conflict-free code assignment problem seeks a conflict-free code assignment which achieves the maximum throughput (resp., bottleneck). In this paper, we present several efficient methods for conflict-free code assignment in OVSF-CDMA wireless ad hoc networks. Each method is proved to be either a constant-approximation for max-throughput conflict-free code assignment problem, or a constant-approximation for max-bottleneck conflict-free code assignment problem, or constant-approximations for both problems simultaneously. The work of Peng-Jun Wan and Xiang-Yang Li is partially supported by NSF CCR-0311174. The preliminary version of the paper first appeared in ACM DIAL M-POMC 2004, workshop of ACM MobiCom 2004.     

A gradual neural-network algorithm for jointly time-slot/code assignment problems in packet radio networks

A gradual neural network (GNN) algorithm is presented for the jointly time-slot/code assignment problem (JTCAP) in a packet radio network in this paper. The goal of this newly defined problem is to find a simultaneous assignment of a time-slot and a code to each communication link, whereas time-slots and codes have been independently assigned in existing algorithms. A time/code division multiple access protocol is adopted for conflict-free communications, where packets are transmitted in repetition of fixed-length time-slots with specific codes. GNN seeks the time-slot/code assignment with the minimum number of time-slots subject to two constraints: (1) the number of codes must not exceed its upper limit and (2) any couple of links within conflict distance must not be assigned to the same time-slot/code pair. The restricted problem for only one code is known to be NP-complete. The performance of GNN is verified through solving 3000 instances with 100-500 nodes and 100-1000 links. The comparison with the lower bound and a greedy algorithm shows the superiority of GNN in terms of the solution quality with the comparable computation time.     

基于动态二进制转换技术的DOS环境模拟器的实现

二进制翻译技术是从一种指令集到其他指令集的代码转换技术,可用以解决移植代码到新硬件平台时的重编译问题。旨在设计和实现一种DOS环境模拟器。该模拟器基于动态二进制指令转换技术,通过对X86指令的动态翻译,结合对外设模拟技术、系统中断模拟方案等一些关键技术的研究,最终使得原先在DOS系统中运行的应用程序无需重新编译,就能在多种异构体系平台上正确地运行。通过对翻译块进行有效的组织管理,使得该动态翻译得到很好的运行性能。