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1.
CDMA EVDO系统是一种高速数据传输系统,数据传输本身具有传输突发性和传输速率波动大的特点.同时,由于CDMA EVDO系统前向采用满功率时分复用方式,只有反向采用码分复用方式,所以对于链路负荷的控制只集中在反向链路过载控制上面.针对数据系统,负荷控制算法的难点在于反向链路数据的突发性对系统造成的干扰,以及如何平衡系统吞吐量与抑制反向干扰.针对现有负荷算法自身的特点,文中设计了多条件下的对比测试实验,通过对测试数据进行分析,结合现有算法设计文中提出了一种切实可行的优化负荷算法,能够弥补现有负荷控制算法的不足. 相似文献
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CDMA系统中的功率控制 总被引:1,自引:1,他引:0
功率控制是CDMA移动通信系统中最为重要的核心技术之一。该文主要介绍CDMA系统反向链路和前向链路的各种功率控制技术。首先介绍功率控制对于CDMA系统的重要性及功率控制的分类,然后分别介绍CDMA系统反向链路和前向链路的功率控制算法。 相似文献
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Soft handoff has a special importance to power controlled code division multiple access (CDMA) systems. We introduce a new analytical model for CDMA soft handoff with emphasis on interference statistics at a system level. The relationship between soft handoff and power control is further explored by integrating power control error and shadowing correlation into the model. A new forward link model is also devised to study the effects of soft handoff on forward link performance. It is observed that the performance degradation due to power control error increases with increase in soft handoff region and higher shadowing correlation lowers the interference contribution from nonhandoff mobile stations (MS). It is also found that, unlike the reverse link, the forward performance depends on both given soft handoff setting and system load 相似文献
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研究了码分多址反向链路数据传输采用不同的调度算法受系统处理时延影响的程度,这种影响与信道估计误差有关,也与传输速率的更新时间有关。通过对CDMA2000的动态系统级仿真,其结果显示反向链路上的最大速率与轮询结合的算法、最小路径损耗算法、以及轮询算法在有处理时延时吞吐量性能都会降低,其中最大速率与轮询结合的算法降低的程度最小,轮询算法降低程度最大,最小路径损耗算法介于中间。性能降低也与快衰信道类型相关,信道变化越快算法性能受到的影响越大。提出了一种对调度算法的改进方法,即根据移动台处理时延的变化,为近期处理时延较小的移动台分配更多的资源,结果表明该方法改善了系统吞吐量。 相似文献
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CDMA2000 1xEV-DO是基于3G 技术中的一种高速数据传输系统,其反向链路采用码分复用方式.由于数据传输系统具有数据传输突发性和速率波动大的特点,因此需要在反向链路进行负荷控制,防止出现热噪声超标导致信号崩溃.为解决系统反向链路数据吞吐量的最大化和 反向链路的稳定性问题,本文引入了比例积分微分控制算法.通过模糊控制方法自动实时整定算法中的控制参数,结合增量型比例积分微分控制算法,降低了计算资源损耗,实现反向链路稳定性和反向链路数据吞吐量最大化的平衡. 相似文献
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CDMA2000 1xEV-DO中的分组调度算法 总被引:1,自引:0,他引:1
移动通信系统需要更好地支持分组数据业务,并满足高速分组数据业务的服务质置要求。这可以通过采用好的调度算法提高平均业务速率和系统整体稳定性实现。针对CDMA2000 1x EV-DO系统的有代表性的调度算法有3种:正比公平算法、速率受限的最大载干比算法、加权公平排队-正比公平(WFQ-PF)联合算法。正比公平调度算法是一种算法简单实用的调度方案,但不能满足用户的服务质景保证;速率受限的最大载干比算法具有比正比公平算法更高的平均吞吐量,可方便地在吞吐量和公平性之间获得很好的折衷;WFQ-PF联合算法具有良好的综合性能,但算法较复杂。 相似文献
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Third-generation (3G) cellular code division multiple access (CDMA,) systems can provide an increase in capacity for system operators over existing second-generation (CDMA) systems. The gain in capacity for the base station to mobile (forward) link can be attributed to improvements in coding techniques, fast power control, and transmit diversity techniques. Additional gains in the mobile to base station (reverse) link can be attributed to the use of coherent quadrature phase shift keyed (QPSK) modulation and better coding techniques. While these enhancements can improve the performance of the system, system operators expect that with increased demand for data services, even greater capacity enhancements may be desired. There are essentially three methods, which we describe, based on diversity, spatial beamforming, and a combination of diversity and beamforming, to improve the performance of system through the use of additional antennas at the base station transmitter and receiver. The performance improvements are a function of the antenna spacings and the algorithms used to weight the antenna signals. We focus on the possibilities for the cdma2000 3G system that do not require standards changes. We highlight the performance enhancements that can be obtained on both the reverse and forward links through use of an antenna array architecture that supports a combination of beamforming and transmit diversity. We focus on the performance enhancements for the forward link 相似文献
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This thesis is based on the design and development of ADSL access networks. We h
ave completed the hardware and software functions in two main ADSL equipments: A
TU C and ATU R. With the system design, we carry out researches to find out ef
fective methods to improved performance in the following aspects: (a) how to all
ocate limited bandwith among services with different QoS requirements and
(b) what is the effect of asymmetric links on TCP end to end flow control mech
anism. We make detailed analyses and propose useful solutions to those problems
we find. The main contents of this thesis are as follows: (1) the design and rea
l
ization of ADSL access system. This part includes the principles of ADSL access
technology, ADSL broadband access network architecture, and ATM over ADSL protoc
ol models that we use in our system. We give detailed hardware and software desi
gn steps in this part, and list system testing results to show the system perfor
mance. In our hardware, the CPU is a RISC microprocessor. Combined with a high
speed digital signal processor, the whole system can hold high reliability. Our
software design platform is a Psos multi task real time operation system. We h
ave developed a series of hardware drivers besides other tasks for high level co
ntrol and interruption processing. Currently, our system has reached the expecte
d performance under test environment. Our next step is the development of DSLAM
and in this part we give a feasible design scheme. (2) Packet scheduling policy
I
n ADSL system. In order to optimize ATU R performance, we need a scheduling pol
icy to regulate the order and number of packet output to the uplink. For this pu
rpose, we study the scheduling algorithm design methods in a single network node
and their performance. After studying the existing algorithms carefully, we fir
st conclude certain important design principles and criterions for scheduling po
licy evaluation. And then by using service curve function, we make detailed perf
ormance analysis of a typical scheduling policy — the earliest deadline first.
The advantage of characterizing service by using a function is that the service
curve can provide a wide spectrum of service characterization. With this method,
we first develop a generalized algorithm for calculating the deadlines used in
the service curve based on the earliest deadline first policy, and then design a
simplified computing program for an important curve. After that, holding fair b
andwidth allocation and packet deadline guarantee as policy evaluation standards
, we analyze this scheduling policy performance and propose solutions to those p
roblems that we find. Finally, we, in theory, prove these improving algorithms.
All these solutions and algorithms we design in this part are now under developm
ent in real systems and will enhance system performance. (3) Effects of asymmetr
I
c links on TCP performance and solutions. TCP is a widely used transmission cont
rol protocol. It regulates its forward data sending through reverse ACKs. What a
re the new problems to its flow control mechanism on asymmetric links and how to
solve them are the two main points of this part. We first study the relationshi
p between normalized bandwidth ratio, link buffer capacity and TCP link throughp
ut under asymmetric link models. We find that TCP ack transportation on slow bac
kward link is a key reason that causes the problems in TCP asymmetric links. Ser
ving this as a start point, we present several improving solutions to TCP flow c
ontrol algorithm and test them through simulation. Besides, TCP has been widely
implemented in many networks. To give compatibility with current TCP end users,
we use scheduling solutions to regulate data packet and ack packet transmission
ratio onto uplinks. In the theoretical analysis of several typical scheduling po
licies, we find a feasible algorithm to control TCP data efficiency on asymmetri
c links. Finally, we prove those analyses and propose algorithm through simulati
on. 相似文献
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EV—DO是CDMA3G的一种高速数据传输技术,它具有独特的反向链路媒体介入控制算法机制,可以参与调整基站反向链路的状况.以优化小区的反向链路情况。除此之外,EV—DO仍然支持反向功率控制。结合两者的特点,共同优化小区反向链路、提高服务质量,是一个需要研究的方向。 相似文献
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The base station transceiver subsystem (BTS) of the CDMA Mobile System is interfaced to mobile stations over the air and to the wired network through a packet switched interconnection network. The potential benefits of CDMA technology are achieved when the transmitter and the receiver are properly designed and implemented. The physical layer of the air interface at the base station is implemented with the CDMA ASICs and control circuits in the channel card of the BTS. We present the design perspectives and structural illustration of the BTS. Base station modem ASICs and their control to implement the CDMA receiver, baseband and RF signal processing blocks, and BTS controller are described. Elaborate power control is essential to ensure the high capacity which is one of advantages of the CDMA technology. The closed loop reverse link power control and the forward link power control operated in the BTS are described. 相似文献
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Moh Lim Sim Gunawan E. Boon-Hee Soong Cheong-Boon Soh 《Vehicular Technology, IEEE Transactions on》1999,48(3):911-921
Performance of a reverse link code-division multiple-access (CDMA) system with fast close-loop power control algorithms is studied. It is found that if the fast close-loop power control algorithm functions effectively, the speed of the mobile unit is in the range such that its Doppler frequency is less than one tenth of the power control updating rate. This paper also proposes a new predictive power control algorithm with better performance in terms of system capacity than the conventional and adaptive step size algorithms. An increase in system capacity as high as 22% compared with the conventional algorithm can be achieved depending on the mobile velocity 相似文献
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Kim J.Y. Stuber G.L. Akyildiz I.F. 《Selected Areas in Communications, IEEE Journal on》2001,19(2):266-276
Hierarchical code division multiple access (CDMA) cellular systems, consisting of macrocells with underlying microcells, are studied. We seek power control schemes which will allow both hierarchical layers to share the same spectrum. For the reverse link, hierarchical maximal ratio combining (HMRC) is applied where each mobile station (MSs) is received and coherently combined by base stations (BSs) in both layers. For the forward link, selective transmit diversity (STD) is applied where each BS provides multiple transmit paths for MSs to choose. We show that both HMRC and STD are effective in hierarchical CDMA architectures. We conclude that hierarchical architectures are a viable solution for improving CDMA cellular system capacity, and a significant performance gain can be achieved without assigning disjoint spectrum between the layers, by utilizing macrodiversity schemes such as HMRC and STD 相似文献
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In this paper, we study the performance of a simple and easy‐to‐implement distributed power control strategy applicable to direct sequence code division multiple access (DS‐CDMA) networks. The scheme makes use of the received power measurements made on the forward link at individual mobile units to control the transmit powers on their reverse links. The algorithm, which effectively compensates for the slowly varying distance and shadow losses (due to their high correlation on both forward and reverse links), attempts to minimize the effect of fast multipath fading by averaging it out. We adopt a quasi‐analytic approach to estimate the reverse link capacity performance of an open‐loop power control scheme in both a single cell and a multi‐cell environment, and we do this for both a fixed base station and a moving base station scenario. Non‐stationary base stations are typical in tactical and emergency communications scenarios where the base stations could be mounted on moving platforms (e.g., tanks, jeeps, unmanned airborne vehicles). We estimate the capacity degradation, when base stations move relative to other cells, as a function of the amount of cell overlap and the standard deviation of the power control error. We also provide a comparison of the performance of the open‐loop power control strategy with that of a closed‐loop power control strategy. 相似文献
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Wan Choi Jin Young Kim 《Vehicular Technology, IEEE Transactions on》2001,50(3):737-749
Some studies have been done on capacity of a code division multiple access (CDMA) system with mixed multirate sources. However, a vast majority of these studies have concentrated on the reverse-link. This trend comes from the fact that the capacity of a CDMA system is reverse-link limited. However, the forward-link can be a limiting link because emerging data services are likely to require higher data rates in the forward-link than in the reverse-link. In this paper, we analyze and simulate the forward-link capacity of a CDMA system with mixed multirate sources in a multipath fading channel. The outage probability of the forward-link is derived for a CDMA system with mixed multirate sources. By introducing a forward-link power factor, the forward-link Erlang capacity is obtained in a closed form. The forward-link capacity is analyzed in terms of the number of multipaths, the number of RAKE fingers in a mobile station, closed-loop power control, and impact of soft handoff. The results in this paper can be applied to overall system design of a CDMA system with multimedia services in future mobile communication systems 相似文献
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The forward and reverse link capacities of code division multiple access (CDMA) and analog cellular system in North America (AMPS) are derived when they are overlaid. Formulas that describe the relationship between the number of CDMA and AMPS users for a given carrier to interference ratio (C/I) of each are presented. A nonlinear system that reduces the power of narrow-band interference is introduced. Simulation results are presented for one narrow-band interferer 相似文献