共查询到20条相似文献,搜索用时 656 毫秒
1.
Capacity gain of beamforming techniques in a WCDMA system under channelization code constraints 总被引:1,自引:0,他引:1
Ramiro-Moreno J. Pedersen K.I. Mogensen P.E. 《Wireless Communications, IEEE Transactions on》2004,3(4):1199-1208
This study addresses the performance of a wideband code-division multiple-access mobile communications system with beamforming antenna arrays (AAs) at the base station, synthesizing a grid of beams. In order to fully exploit the capacity gain from beamforming without jeopardizing the stability of the system, a directional power-based admission control (AC) scheme is applied. Due to the higher capacity offered by beamforming techniques, shortage of orthogonal channelization codes in the downlink becomes an increasingly important factor, which may result in blocking of users before the interference power limit is reached. The problem of channelization code shortage is addressed, and a solution based on splitting the cell into several code regions is proposed. For a network with circuit switched data services operated at 64 kb/s, the capacity gain for an eight-element AA is found to equal a factor of 2.5 for a universal mobile telecommunications equivalent system, with one channelization code set per cell. The capacity gain is limited by severe channelization code shortage under these circumstances. This problem is solved by deploying a cell splitting strategy with multiple code regions, which subsequently results in a capacity gain increase to a factor of 3.4. Furthermore, the soft capacity mechanism associated with partial deployment of AAs in a subset of the cells in the network is also addressed. It is demonstrated that a hot spot cell with AAs also helps increase the capacity of the surrounding cells with conventional sector antennas when using a power-based AC strategy. 相似文献
2.
3.
Ben-Jye Chang 《Wireless Personal Communications》2007,41(3):325-344
For achieving high transmission rate in mobile multimedia communications, 3G WCDMA systems adopt the Orthogonal Variable Spreading
Factor (OVSF) code tree to assign a single channelization code for each accepted connection. Based on the orthogonal characteristic
of an OVSF code tree, an allocated code blocks the channelization codes that are on the descendant branches and the ancestral
codes of the allocated code. Several researches have been proposed to overcome the code-blocking problem for maximizing system
utilization. By using both the code assignment and reassignment mechanisms, the system utilization and code blocking can be
improved. Nevertheless, the data rate of traffic classes in such single code assignment system should be powers of two of
the basic rate, which is impractical and wastes the system capacity when the required rate is not powers of two of the basic
rate. A good solution is to assign multiple codes to a new connection, but causes two drawbacks: high complexity of handling
multiple codes and high cost from using more number of rake combiners. Consequently, there is a trade-off between waste rate
and complexity of handling multiple codes assignments. In previous researches, high computation complexity of assigning multiple
codes for a connection and large number of reassignment codes suppressed the advantage of reducing waste rate. Therefore,
we propose an adaptive efficient partition algorithm with the Markov Decision Process (MDP) analysis approach to reduce the
large number of reassignment codes while improving waste rate. There are two main motivations in the proposed approach. First,
we propose an adaptive efficient partition algorithm to determine multiple codes based on the current state of the OVSF code
tree for the new incoming connection. Second, after determining the multiple codes, we adopt the MDP analysis to assign the
least-cost code for each determined code. Numerical results demonstrate that the proposed MDP approach yields the least number
of reassignments and the least number of codes per connection while reducing waste rate significantly, as compared to other
approaches. 相似文献
4.
谢良平 《电信工程技术与标准化》2005,(12):36-38
本文概述了WCDMA无线网络多业务多速率、软切换因子、小区呼吸、导频污染、自干扰特性等特点,分析和探讨了WCDMA与GSM无线网络规划的区别. 相似文献
5.
This letter investigates the performance of a mixed diversity-spatial multiplexing transmission strategy for multiple input-multiple output (MIMO) networks based on dual code transmission with antenna selection. The wideband code division multiple access (WCDMA) physical layer protocol has been used to demonstrate that for eight transmit and four receive antennas per user, 2.4Mbps more capacity is provided compared to single code spatial multiplexing transmission and 100% code allocation gain, compared to diversity combining and four codes per user. 相似文献
6.
《Vehicular Technology, IEEE Transactions on》2009,58(7):3361-3370
7.
OVSF codes are used as channelization codes in WCDMA. Due to code blocking property of OVSF codes, the bandwidth available in the system is severely limited. Code reassignments mitigate the impact of the blocking property at the expense of causing delays and decreasing the throughput of the system. Nonblocking OVSF (NOVSF) codes have been proposed to alleviate the adverse effect of code reassignments. This paper presents a code assignment algorithm for NOVSF codes, which does not require any code reassignments. Simulation results show that NOVSF codes achieve better throughput than OVSF codes, even though code reassignments are allowed in the assignments of OVSF codes. 相似文献
8.
9.
Uplink capacity improvement through orthogonal code hopping in uplink-synchronized CDMA systems 总被引:1,自引:0,他引:1
We propose an orthogonal code hopping multiple access (OCHMA) scheme in order to improve the capacity of an uplink-synchronized code division multiple access (CDMA) systems. When orthogonal codes (OCs) are used for channelization in uplink-synchronized CDMA systems, a finite set of OCs tends to severely limit the capacity gain of the uplink-synchronized CDMA systems. The OCHMA system allows each user to use a different OC for each symbol according to an allocated hopping pattern (HP). It also allows multiple users to use the same OC at a specific symbol time, which is called an HP collision. Thus, the proposed OCHMA scheme can accommodate more users than the number of available OCs. We analyze the capacity of the OCHMA scheme and compare the performance of the OCHMA with that of conventional schemes including the system using multi-scrambling codes (MSC) which have also been proposed to overcome a code-limited situation. 相似文献
10.
在WCDMA无线网络中,由于新业务的非对称性,下行链路更有可能成为系统容量的瓶颈。研究了在理想功率控制下路径损耗因子、阴影标准方差等不同无线参数对下行链路软切换容量增益的影响,为无线网络规划提供了一定的依据。 相似文献
11.
12.
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. 相似文献
13.
This paper validates the feasibility of automated optimization of key wideband code division multiple access (WCDMA) radio resource management parameters using control methods. The parameters are regularly adjusted in order to improve performance. The parameters examined in this study include the total cell transmission power target, the received total interference target, the downlink radio link power maximums, the handover windows and the pilot channel powers. The control was based on expert‐defined rules, which applied specific trade‐off policies and statistics of poor quality calls, blocking, packet queuing, power and interference levels and terminal measurements to qualify the parameter values. The approach was validated using a dynamic WCDMA system simulator with a deployment of macro and micro cells on a city region. Results on automated optimization of single parameters on cell level and results on simultaneous multi‐parameter optimization on cell‐cluster level are presented in this paper. The use of the automated parameter optimization methods was shown to result in a significant increase of capacity in comparison to the default parameter settings. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
14.
Yuh-Shyan Chen Ting-Lung Lin 《Mobile Computing, IEEE Transactions on》2006,5(3):224-239
Orthogonal variable spreading factor (OVSF) channelization codes are widely used to provide variable data rates for supporting different bandwidth requirements in wideband code division multiple access (WCDMA) systems. Many novel works in the literature have intensively investigated code placement and replacement schemes in OVSF code trees to reduce the code blocking probability and the code reassignment cost. In this paper, we introduce a new code tree structure, namely, a rotated-orthogonal variable spreading factor (ROVSF) code tree, whose code capacity is the same as that of the traditional OVSF code tree. This work addresses both code placement and replacement schemes in the ROVSF code tree system, where ROVSF codes can be used at the forward link of WCDMA systems. Some valuable properties of the developed ROVSF code tree are presented to develop code placement/replacement schemes with lower code blocking probability and less code reassignment cost. The main contribution of our scheme is to identify linear-code chains (LCCs) and nonlinear-code trees (NCTs) in the ROVSF code tree. This work exploits the unsequence property of linear-code chains to design a new code placement and replacement mechanism. Our code placement/ replacement schemes initially attempt to allocate request codes on LCCs and, then, to allocate them to NCTs. Using LCCs with the unsequence property allows us to efficiently reduce the code blocking probability and the code reassignment cost. Extensive simulations are conducted to illustrate that our code placement/replacement results based on the ROVSF code tree actually improve the code blocking probability and the code reassignment cost. 相似文献
15.
对多输入多输出(MIMO)相关衰落信道上宽带码分多址接入(WCDMA)的安全性能进行评估,一种省时高效的解决方案是理论分析法。推导了相关 Nakagami 衰落信道上采用空时分组码和二维瑞克接收机(2D-Rake)的 WCDMA 系统的非零安全容量概率和安全中断概率的精确解析表达式。利用上述表达式,可以快速地评估收发天线数、天线相关系数、Nakagami衰落系数、平均路径衰减系数等参数对WCDMA系统安全性能造成的影响。数值计算和仿真结果相吻合,证明了以上理论分析的正确性。推导了WCDMA系统渐近安全中断概率的解析表达式。结果表明,WCDMA 系统的安全分集增益为主信道各个可分离路径上的分集增益之和,与窃听信道无关;对于恒定多径强度轮廓的同分布Nakagami衰落信道,WCDMA系统的安全分集增益为主信道的收/发天线数、多径个数以及Nakagami衰落系数四者之积。 相似文献
16.
WCDMA与GSM系统间切换浅析 总被引:1,自引:0,他引:1
本文介绍了WCDMA系统和GSM系统间切换和小区重选的操作过程,分析了压缩模式对网络质量的影响,并对提高切换成功率提出了几点建议.另外,本文对切换相关的GSM网络升级和测量控制参数的设置也进行了讨论. 相似文献
17.
The opportunities and constraints for application of beamforming techniques in UMTS are reviewed and compared by means of extensive dynamic network-level simulations. We start by reviewing the physical layer specifications for UMTS in order to clarify which channels are allowed to use beamforming. Second, radio resource management for cells with beamforming capabilities are addressed from a standardization and algorithmic point of view. The exchange of beamforming specific measurement reports between the base station (Node-B) and the radio network controller is discussed as well as beam switching mechanisms, directional power-based admission control, and more. In addition to implementation of beamforming within logical cells, options for exploiting the antenna array to synthesize independent sector beams are also investigated (i.e., higher order sectorization via beamforming). The presented results show that beamforming within logical cells is an effective enabler for higher system capacity, while the use of beamforming for creation of many logical cells is less attractive due to significantly larger soft handover overhead and somewhat reduced capacity gain. 相似文献
18.
Ben-Jye Chang 《Telecommunication Systems》2006,33(4):333-352
3G Wideband CDMA systems adopt the Orthogonal Variable Spreading Factor code tree as the channelization codes management for
achieving high data rate transmission in personal multimedia communications. It assigns a single channelization code for each
accepted connection. Nevertheless, it wastes the system capacity when the required rate is not powers of two of the basic
rate. One good solution is to assign multiple codes for each accepted connection but it causes two inevitable drawbacks: long
handoff delay and new call setup delay due to high complexity of processing with multiple channelization codes, and high cost
of using more number of rake combiners. Especially, long handoff delay may result in more call dropping probability and higher
Grade of Service, which will degrade significantly the utilization and revenue of the 3G cellular systems. Therefore, we propose
herein an adaptive efficient codes determination algorithm based on the Markov Decision Process analysis approach to reduce
the waste rate and reassignments significantly while providing fast handoff. Numerical results demonstrate that the proposed
approach yields several advantages, including the lowest GOS, the least waste rate, and the least number of reassignments.
Meanwhile, the optimal number of rake combiners is also analyzed in this paper.
This research was supported in part by the National Science Council of Taiwan, ROC, under contract NSC-93-2213-E-324-018. 相似文献
19.
The traffic performance of integrated 3G wide-band code division multiple access (WCDMA) and GSM/GPRS network is evaluated.
This type of network links two cellular radio systems which have different set of frequency bands and the same coverage size.
The base station of 3G WCDMA is installed on an existing GSM/GPRS site. Dual-mode mobile terminals use handoff to establish
calls on the better system. The soft handoff or inter-frequency hard handoff occurs when mobile terminals of 3G WCDMA or GSM/GPRS
move between two adjacent cells, respectively. The inter-system hard handoffs are used between 3G WCDMA and GSM/GPRS systems.
The data rate conversions between different systems, soft handoff region size, multiple data rate multimedia services, and
the effect of the mobile terminal mobility on the user mean dwell time in each system are considered in the study. The simulation
results demonstrate that a great traffic performance improvement on the complementary use of 3G WCDMA and GSM/GPRS cellular
radio networks compared with the use of GSM/GPRS cellular radio networks. When high-data rate transmission is chosen for low-mobility
subscribers, both the handoff failure probability, and carried traffic rates increase with the new call generation rate. However,
both rates decrease conversely with the increasing new call generation rate as soon as the new call generation rate exceeds
a critical value. This causes the integrated networks saturation. The higher mean speed for the mobile terminals produces
lower new call blocking probabilities and total carried traffic. The new call blocking probabilities and total carried traffic
increase with the size of the soft handoff region. 相似文献
20.
HISAKAZUKikuchi 《中国邮电高校学报(英文版)》2004,11(4)
Next generation wireless communication is based on a global system of fixed and wireless mobile services thatare transportable across different network back-bones,network service providers and network geographical boundaries.This paper presents an approach to investigate the effects of soft handover and perfect power control on the forward link ina DS-CDMA cellular system.Especially,the relationships between the size ofhandover zone and the capacity gain are e-valuated under the log-normal shadow channel.Then the optimization of maximum forward capacity is very necessary tobe done with the maximum size of soft handover zone to the various system characteristics. 相似文献