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1.
WCDMA中的OVSF码分配算法① 总被引:1,自引:1,他引:0
作为第三代移动通信IMT-2000中三大主流技术之一的WCDMA,采用长度可变的正交码序列OVSF作为信道化扩频序列,可支持多种速率请求。OVSF码的可变长特性可以满足通信中的多速率业务要求,而其正交性质则可以减小信道间的相互干扰。对OVSF码进行了研究,通过理论及MATLAB仿真验证了其正交性,分阶段对单码分配、动态码分配及满足不同QoS业务要求的动态码分配进行了介绍。并分别针对系统吞吐量和码阻塞率对各单码分配算法进行了仿真比较,验证了各种算法之间的性能优劣。 相似文献
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为了提高无线网状网络的链路容量,提出一种在网络中配置节点多射频多信道的混合信道分配算法.通过配置默认信道并优化默认信道的使用,该算法基于启发式信道分配策略来减小链路干扰提升链路容量.基于网络物理拓扑,该算法生成简化的网络逻辑拓扑,使得信道分配方案能够结合路由优化网络性能.对信道分配的动态调整,确保了网络容量的实时优化.仿真结果显示,本信道分配算法可以有效地提升网络性能. 相似文献
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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。 相似文献
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考虑信道频宽对链路传输距离和链路间干扰的影响,对可变频宽无线网络现有的累积干扰模型进行了改进,并基于改进的干扰模型对可变频宽无线网络的信道频谱分配和链路调度问题进行了建模分析。设计了一种两层优化算法对信道频谱分配和链路调度问题进行解耦,提出了一种考虑链路负载需求满足程度的链路优先级指标,启发式地构建并发传输信道分配矩阵的方法。仿真结果表明,两层优化算法能够在合理时间内收敛,启发式方法能够高效地构建并发传输信道分配矩阵。 相似文献
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IEEE 802.11物理层和MAC具有支持多信道和多速率的能力。在多速率情况下,IEEE 802.11网络产生性能异常问题,低速率链路严重降低了高速率链路的性能,导致系统性能下降。针对该问题,设计了基于均衡算法的协作信道分配(CCA)协议,以解决无线网络中的性能异常问题。CCA的主要思想是通过预估传输时间(ETT)标准和均衡算法来解决信道分配问题。在预估传输时间标准下,CCA通过多信道来分离不同速率链路。通过使用均衡算法,CCA还能增加吞吐量的公平性。仿真结果表明,在无线网状网中,CCA能有效改善网络性能。 相似文献
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针对无线网络链路干扰问题,综合借鉴多处理器任务调度算法提出了一种贪婪信道分配算法,为所访问的无线网链路甄选出干扰最小的信道,并且证明了本算法的近似比率为2-1/k,其中为k为可用的正交信道数,算法复杂度为O(|E|2)。为了验证本文算法的可行性和有效性,将本文所提出的贪婪算法与随机信道分配算法和按序信道分配算法进行了实验对比。仿真结果表明:本文所提出的贪婪算法的整体性能优于其他两种算法,并且贪婪算法得到的最大干扰和平均干扰归一化值随着可用正交信道数的变化趋势较其他两种算法稳定。从而验证了本文算法能有效的降低链路干扰,一定程度上可以提升网络吞吐量。 相似文献
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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. 相似文献
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A Constant-Competitive Algorithm for Online OVSF Code Assignment 总被引:1,自引:0,他引:1
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. 相似文献
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An Algorithmic View on OVSF Code Assignment 总被引:2,自引:0,他引:2
Thomas Erlebach Riko Jacob Matus Mihalak Marc Nunkesser Gabor Szabo Peter Widmayer 《Algorithmica》2007,47(3):269-298
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 nO(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. 相似文献
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《Computer Networks》2008,52(12):2331-2343
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. 相似文献
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OVSF-CDMA Code Assignment in Wireless Ad Hoc Networks 总被引:1,自引:0,他引:1
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. 相似文献
16.
基于离散无记忆信源模型,分析了变长码的抗误码扩散概率。利用在理想条件下的概率分布,计算了同步变长码的抗误码扩散概率。分析发现同步变长码的抗误码扩散概率与其码距分布有关。给出了一种计算同步变长码玛距分布的迭代算法。数值计算结果显示同步变长码的抗误码扩散概率随其移位对称数的增加而减少。 相似文献
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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. 相似文献
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《International Journal of Parallel, Emergent and Distributed Systems》2012,27(1-3):143-163
Transformation to single assignment form is presented as a technique enabling the exploitation of fine-grain parallelism in programs. An efficient algorithm is presented for the creation of Single Assignment and Static Single Assignment code from unstructured FORTRAN codes, including programs with irreducible flow graphs. The algorithm transforms code directly without requiring conversion to flow graph form. The algorithm creates code of near optimal quality with respect to both the number of names and assignment statements added to the code. Experimental results show the degree of enlargement of storage and program length when creating single assignment code, and the containment of enlargement using name reclamation. Other results show the extent of improved parallelizalion using single assignment code. 相似文献
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给出了一种用于预估分组业务(PS)的DS-CDMA网络单小区下行链路容量和基站(NodeB)功率需求的分析方法。并在不同的网络条件下给出了吞吐量的计算结果以及下行链路BLER与Eb/N0的关系。对有关影响网络性能的BLER、码资源和其他方面的因素给予了分析。基于公司实际外场数据,对小区容量的理论公式给予了说明和验证。在使用主扰码和理想的功率控制下,通过计算机仿真得到了下行链路的384 Kb/s分组业务容量能够到达310 KB/s的结论。并且随着无线信道的波动该容量会有变动。 相似文献