共查询到19条相似文献,搜索用时 164 毫秒
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文章通过对cDMA20001×数据吞吐量相关理论的研究,综合了基于用户数呼叫准入控制与基于干扰呼叫准入控制的优点,对M/M/m排队系统进行了修正,提出了新的M/M/m变速率自适应优先服务排队系统(M/M/m/VRAP)模型,并从模型的基本原理和系统性能两方面进行了详细分析。该模型可大大提高CDMA20001X数据业务物理层的吞吐量。 相似文献
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一种新型的OFDMA系统调度算法 总被引:1,自引:0,他引:1
近年来正交频分多址接入(OFDMA,Orthogonal Frequency Division Multiplexing Access)技术在无线通信中的应用越来越广泛。针对OFDMA系统中的资源调度问题,介绍和分析了OFDMA系统中常见的分组调度算法-轮询算法、最大载干比算法和比例公平算法,并且提出了一种结合了遗传搜索的自适应调度算法。最后在此基础上对这四种分组调度算法进行了仿真和分析,仿真结果表明,不管是系统吞吐量还是公平性,自适应调度算法都有较好的性能提升。 相似文献
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在自适应调制和调度的无线通信系统,特别是OFDMA系统中,反馈信息压缩技术已成为研究热点。文中研究了随机波束成形OFDMA系统中分簇反馈压缩技术以及门限信噪比压缩技术,结合二者的优点提出了一种改进方案——分簇门限信噪比压缩技术。仿真证明,采用分簇门限信噪比技术与分簇技术、门限信噪比技术相比,明显降低了反馈量,且在用户较多时系统容量损失很少。 相似文献
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在OFDMA系统中,采用交织子载波分配方法可以提高频率分集和系统容量,但是发射机和接收机之间的载波频率偏移会破坏子载波间的正交性,从而导致本用户的载波间干扰以及用户间干扰。该文分析了交织OFDMA上行链路的信号结构,提出了一种采用自适应波束形成器的载波频偏补偿方法,并给出了两种自适应波束形成器:匹配滤波器和MMSE方法。仿真结果验证了MMSE自适应波束形成器的误比特率性能优于匹配滤波器以及传统的循环卷积方法。 相似文献
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针对正交频分多址(OFDMA)系统下行链路多业务自适应调度的问题,该文首先以最大化系统吞吐量为优化目标、每种业务的服务质量(QoS)保证为约束条件,建立了一种通用的多业务自适应资源分配模型。为解决此优化问题,提出了一种具体的自适应资源调度算法。该算法对实时业务按照用户选择最好的信道的原则分配尽可能少的资源以保证其QoS,对非实时业务把尽可能多的剩余资源按照信道选择最好的用户的原则进行分配,充分利用信道资源,提升系统容量。仿真结果表明,该算法保证了下行OFDMA系统吞吐量的同时,在实时业务的延时和丢包率等方面有一定的优越性。 相似文献
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协作空分复用CSM系统中的信道估计算法研究 总被引:1,自引:0,他引:1
文章就当前MIMO应用过程中终端多天线受限制问题,阐述了单天线终端协作与基站组成虚拟MIMO多天线阵列——基于OFDMA的CSM协作空分复用系统结构。同时,提出对OFDMA系统中时频二维的资源进行分“块”独立进行信道估计,简化了OFDMA系统信道估计模型的复杂度。然后从应用的角度对比分析了基于OFDMA的CSM系统的信道估计算法LS和MMSE两种算法性能与优缺点。通过在PB3信道模型中仿真,得出适用于慢变信道的平滑滤波后的LS信道估计算法。 相似文献
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A Mobility Model and Performance Analysis in Wireless Cellular Network with General Distribution and Multi-Cell Model 总被引:1,自引:0,他引:1
Multi-cell mobility model and performance analysis for wireless cellular networks are presented. The mobility model plays
an important role in characterizing different mobility-related parameters such as handoff call arrival rate, blocking or dropping
probability, and channel holding time. We present a novel tractable multi-cell mobility model for wireless cellular networks
under the general assumptions that the cell dwell times induced by mobiles’ mobility and call holding times are modeled by
using a general distribution instead of exponential distribution. We propose a novel generalized closed-form matrix formula
to support the multi-cell mobility model and call holding time with general distributions. This allows us to develop a fixed
point algorithm to compute loss probabilities, and handoff call arrival rate under the given assumptions. In order to reduce
computational complexity of the fixed point algorithm, the channel holding time of each cell is down-modeled into an exponentially
distributed one for purposes of simplification, since the service time is insensitive in computing loss probabilities of each
cell due to Erlang insensitivity. The accuracy of the multi-cell analytic mobility model is supported by the comparison of
the simulation results and the analytic ones. 相似文献
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The concept of adaptive admission control in cellular wireless networks ensures quality of service by reserving bandwidth for handoff calls. It is equally important in current second generation wireless systems as well as in the future IMT-2000 and UMTS systems. In order to ensure bounded call level QoS we propose to track the changes of the handoff call arrival rate and integrate this information in the admission algorithm. However, the handoff call arrival rate can vary when the new call arrival rate and/or user mobility vary. In our previous work we have analysed bandwidth reservation techniques needed to maintain a stable call level QoS when new call arrival rate is changing in a group, or groups, of wireless cells. This paper analyses bandwidth reservation techniques that are adaptive to the user mobility as well as to the changing new call arrival rate, and which can ensure stable call level QoS over a range of user mobilities. We also propose the technique to derive bandwidth reservation policy when the QoS characteristics over a range of user mobilities are given. 相似文献
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This paper proposes a prioritized call admission control (CAC) model to support soft handoff calls with quality of service (QoS) assurances for both the uplink and downlink connections in a CDMA system. CAC is formulated as a combinatorial optimization problem in which the problem objective is to minimize the handoff forced termination rate. The model, which is based on the adaptive channel reservation (ACR) scheme for prioritized calls, adapts to changes in handoff traffic where the associated parameters (reserved channels, and new and handoff call arrival rates) can be varied. To solve the optimization model, iteration-based Lagrangean relaxation is applied by allocating a time budget. We express our achievements in terms of the problem formulation and performance improvement. Computational experiments demonstrate that the proposed ACR scheme outperforms other approaches when there are fewer rather than more channels, and it reduces the handoff call blocking rate more efficiently when the handoff traffic is heavily loaded. Moreover, the model can be adapted to any kind of reservation service. 相似文献
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ZHANG Qi-zhi LIAO Jian-xin ZHU Xiao-min State Key Laboratory of Networking Switching Beijing University of Posts Telecommunications Beijing P.R. China 《中国邮电高校学报(英文版)》2005,12(2)
1IntroductionIntelligent network,an affiliated network over com-munication network,is introduced for the quick provi-sion of newservices[1 ~2].In the structure of intelligentnetwork,a Service Control Point(SCP) serves a lot ofService Switch Point(SSPs)[3 ~4].It is a veryi mportanttopic that howto guarantee the Qos of SCP (e .g.thenumber of successfully processed calls per unit ti me)whenthe network becomes overloadedinthis centralizednetwork structure . There were many studies about the… 相似文献
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Comparing the PCS location tracking strategies 总被引:1,自引:0,他引:1
Yi-Bing Lin Shu-Yuen Hwang 《Vehicular Technology, IEEE Transactions on》1996,45(1):114-121
The cache scheme has been proposed to reduce the location tracking overhead of a personal communications services (PCS) network. In the previous papers, we studied the cache scheme under the assumptions that the home location register (HLR) access time is constant and the portable residence times have an exponential distribution. This paper compares the cache scheme with a basic scheme (such as IS-41). We generalize the previous models by considering the queueing effect of the HLR (i.e., we model the HLR by an M/G/1 queue) and by considering an arbitrary distribution for the portable residence times. Our study shows that the cache scheme is likely to outperform the basic scheme when (1) the net traffic to the HLR in the basic scheme saturates and the hit ratio in the cache scheme is larger than zero, (2) the portable mobility is low with respect to the call arrival rate, and (3) the variance of the HLR service time distribution is large (for a fixed mean service time). We also indicate an intuitive result that the cache hit ratio is high for a high call arrival rate and low portable mobility. For a fixed mean portable residence time, we show that a higher cache hit ratio is expected for a portable residence distribution with larger variance 相似文献
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Yu-Jung Chang Feng-Tsun Chien Kuo C.-C.J. 《Selected Areas in Communications, IEEE Journal on》2007,25(4):657-666
Performance analysis of multiuser orthogonal frequency division multiplexing (OFDM-TDMA) and orthogonal frequency division multiple access (OFDMA) networks in support of multimedia transmission is conducted in this work. We take a cross-layer approach and analyze several quality-of-service (QoS) measures that incilude the bit rate and the bit error rate (BER) in the physical layer, and packet average throughput/delay and packet maximum delay in the link layer. The authors adopt a cross-layer QoS framework similar to that in IEEE 802.16, where service classification, flow control and opportunistic scheduling with different subcarrier/bit allocation schemes are implemented. In the analysis, the Rayleigh fading channel in the link layer is modeled by a finite-state Markov chain, and the channel state information (CSI) is assumed to be available at the base station. With the M/G/1 queueing model and flow control results, the analysis provides important insights into the performance difference of these two multiaccess systems. The derived analytical results are verified by extensive computer simulation. It is demonstrated by analysis and simulation that OFDMA outperforms OFDM-TDMA in QoS metrics of interest. Thus, OFDMA has higher potential than OFDM-TDMA in supporting multimedia services. 相似文献
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As the system performance is obviously improved by introducing the concept of relay into the traditional orthogonal frequency division multiple access(OFDMA)systems,resource scheduling in relay-enhanced OFDMA systems is worthy of being studied carefully.To solve the optimization problem of achieving the maximum throughput while satisfying the quality of service(QoS)and guaranteeing the fairness of users,a novel resource scheduling scheme with QoS support for the downlink of two-hop relay-enhanced OFDMA systems is proposed.The proposed scheme,which is considered both in the first time sub-slot between direct link users and relay stations,and the second time sub-slot among relay link users,takes QoS support into consideration,as well as the system throughput and the fairness for users.Simulation results show that the proposed scheme has good performance in maximizing system throughput and guaranteeing the performance in the service delay and the data loss rate. 相似文献
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Cognitive Radio (CR) system based on Orthogonal Frequency Division Multiple Access (OFDMA), such as Wireless Regional Area
Networks (WRAN) and Worldwide Interoperability for Microwave Access (WiMAX), often attempt to improve performance via dynamic
radio resource management, which is characterized as concurrent processing of different traffic and nondeterministic system
capacity. It is essential to design and evaluate such complex system using proper modeling and analysis tools. In the previous
work, most of the communication systems were modeled as Markov Chain (MC) and Stochastic Petri Nets (SPN), which have the
explicit limitation in evaluating adaptive OFDMA CR system with wide area traffic. In this paper, we develop an executable
top-down hierarchical Colored Petri Net (CPN) model for adaptive OFDMA CR system, and analyze its performance using CPN tools.
The results demonstrate that the CPN can model different radio resource management algorithms in CR Systems, and the CPN tools
require less computational effort than Markov model using Matlab, with its flexibility and adaptability to the traffics which
arrival interval and processing time are not exponentially distributed. 相似文献