WCDMA系统的信道码分配策略

第三代移动通信系统WCDMA支持多业务、多QoS的传输,能更好地利用信道码的分配策略。3GPPWCD-MA标准采用的正交可变长扩频码(OVSF)支持变速率业务,举例说明了一种可行的信道码动态分配方案。     

Region Division Assignment: A New OVSF Code Reservation and Assignment Scheme for Downlink Capacity in W-CDMA Systems

This work focuses on the efficient management of orthogonal-variable-spreading-factor (OVSF) codes for multimedia communications in the W-CDMA systems. Because these systems must assign only OVSF codes that are mutually orthogonal, even if they have sufficient transmission capacity they block connections for which no orthogonal OVSF codes are available. This code blocking can, with extra overhead, be eliminated by reassigning codes, but in this paper we propose an OVSF code management scheme designed to not reassign codes. This scheme, called Region Division Assignment, cannot eliminate code blocking but can reduce the overhead for code assignment. Computer simulations based on the multiple access protocol in UMTS/IMT-2000 show that the proposed scheme can efficiently provide variable-rate services as well as low-rate services. This paper was presented in part at the IEEE Vehicular Technology Conference Fall 2001, October 7-11, 2001, Atlantic City, NJ USA. Rujipun Assarut received his BE from Chularongkorn University, Thailand, in 1997 and his MS from Gunma University, Japan, in 2002. Currently, he is working as a software engineer for NEC communication systems. His current project is the development of IP phone for enterprise applications. Ken’ichi Kawanishi is a research associate with Gunma University, Japan. His current research interests include queueing theory and stochastic processes. He is a member of ORSJ, JSIAM and IEICE. Ushio Yamamoto received a bachelor’s degree in information engineering, and a master’s degree and Ph.D. degree in information science from Tohoku University in 1992, 1994 and 1997, respectively. He is now an associate professor in Dept. of Computer Science, Gunma University. He has been engaged in research on wireless ad hoc networks, multimedia communication networks, load balancing on computer networks and intelligent agents. He is a member of IPSJ and JSAI. Yoshikuni Onozato is a Professor with Gunma University. His research interests are in satellite systems, computer communication networks and distributed computing systems and span the entire spectrum from the design and performance evaluation of these systems to their implementation. He is a member of IEEE, ACM, IPSJ, ORSJ and IEICE.     

Markov-Based OVSF Code Assignment Scheme and Call Admission Control for Wideband-CDMA Communication Systems

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.     

An Efficient Adaptive Grouping for Single Code Assignment in WCDMA Mobile Networks

For achieving high utilization and efficient code management of the OVSF code tree in 3G WCDMA networks, several researches have extensively studied. Based on combining both the code assignment and the reassignment mechanisms, it increases obviously high utilization and reduces completely the code blocking. Nevertheless, the required rate of traffic should be powers of two of the basic rate, i.e. 1R, 2R, 4R, …, etc., which is impractical and results in wasting the system bandwidth while the required rate is not powers of two of the basic rate. Several multi-code assignment mechanisms have proposed to reduce the waste rate. Nevertheless, these methods bring two inevitable drawbacks including, high complexity of handling multiple codes, and increasing the cost of using more rake combiners at both the base stations and mobile nodes. Therefore, we propose an adaptive grouping code assignment herein to provide a single channelization code for any possible rate of traffic, even though the required rate is not powers of two of the basic rate. Based on the dynamic programming algorithm, the adaptive grouping approach forms several calls into a group. Then it allocates a subtree to the group and adaptively shares the subtree codes for these calls in the concept of time-sharing of slots during a group cycle time. Therefore, the waste rate and code blocking are thus reduced obviously while using a single rake combiner. Since the delay problem may be occurred in such a time-sharing approach, we propose two schemes of cycle interleaving methods to reduce delay. Numerical results indicate that the proposed adaptive grouping approach reduces significantly the waste rate and thus increases the system utilization. Moreover, the proposed cycle interleaving scheme reduces data delay significantly. 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. 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 wirless networking, resource management for wireless networks and mobile cellular networks, and performance evaluation of networks. Min-Xiou Chen received the BS degree in computer science and information engineering from Tung Hai University, Tai-Chung, Taiwan, in 1996, and the MS and PhD degrees in computer science and information engineering from National Chung Cheng University, Chia-Yi, Taiwan, in 1998 and 2005, respectively. He is now an assistant professor at the Department of Computer Science and Information Engineering, Chung Hua University, Hsin-Chu, Taiwan. His research interests include wireless communication, SIP, sensor network and resource management in WCDMA systems. He is a member of the IEEE. Kun-Chan Tsai received the BS degree in information engineering and computer science from Feng Chia University, Taichung, Taiwan, in 2001, and the MS degree in computer science and information engineering from National Chung Cheng University, Chia-Yi, Taiwan, in 2003. His research interests include wireless communications and resource management in WCDMA systems.     

A Fast Code-Assignment Strategy for a WCDMA Rotated-OVSF Tree with Code-Locality Capability

In this paper, a new channelization code tree structure, namely an ROVSF (rotated-orthogonal variable spreading factor) code tree, is defined and investigated. Most existing code assignment schemes are investigated on the OVSF (orthogonal variable spreading factor) code tree in WCDMA systems. The main work of this investigation is to exploit and justify the new properties of the ROVSF code tree. We show that the ROVSF code tree offers the same code capability to that of the conventional OVSF code tree, but our ROVSF code tree additionally has the code-locality capability. With the code-locality capability, a fast code-assignment strategy is developed on the ROVSF code tree. Compared to existing code assignment schemes on OVSF code trees, a fast code assignment scheme is developed with lower search costs and a low blocking rate, due to its code-locality capability. Finally, the simulation results illustrate that our proposed scheme on the ROVSF code tree actually has lower search costs and a better blocking rate.This work was supported by the National Science Council of the R.O.C. under grant nos. NSC91-2213-E-194-041 and NSC91-2213-E-194-042.     

业务非均匀分布CDMA系统中一种基于公平性保证的贪婪呼叫接纳控制策略

呼叫接纳控制(Call Admission Control,CAC)是移动通信系统资源管理的主要内容之一。它通过接纳或者拒绝一种用户服务请求,来保持系统的正常运行,是平衡用户服务满意度与系统资源最大化利用矛盾的主要手段。该文主要研究小区间业务非均匀分布时基于公平性保证的动态CAC策略,提出了一种新的CAC策略,可适用于多业务且有变速率(Variable BitRate,VBR)业务的情况。该策略采用贪婪算法,用户请求接入以全系统的预期信干比作为判决条件,从而实现了不同到达率小区之间阻塞率的均衡,保证了用户接入的公平性,对于实际系统的应用具有重要的意义。     

基于GoS的功率控制WCDMA系统呼叫准入控制算法

该文提出的基于GoS的呼叫准入控制(GoS-CAC)算法的判决门限综合了多种因素:系统负荷、各业务服务质量(QoS)要求、信道质量、干扰水平、系统服务等级(GoS)以及用户的切换等等。GoS-CAC算法与功率/ 数据速率调节机制巧妙结合,具有判决速度快、精度高、门限自适应和简单易行等特点。仿真结果表明,与传统CAC算法相比,GoS-CAC算法的切换用户业务阻塞性能优约10%,系统GoS优50%左右,而中断性能优57%以上。     

网格空时码在WCDMA中的解决方案

本文根据STTD向下兼容的特点,提出一种网格空时码在WCDMA中的解决方案,并给出一组适用于该方案的STTC编码.研究表明,在WCDMA系统中采用本文给出的编码方式,不仅能够具有与空时传输分集(STTD:Space-Time Transmit Diversity)相同的向下兼容特性,而且能够获得更好的抗衰落性能.     

Optimization of Handover Parameters for Traffic Sharing in GERAN

Cellular network traffic is unevenly distributed both in time and space, which greatly complicates network dimensioning. As a result, some cells in the network are permanently congested, while others are underutilized. In a previous paper, the authors showed that this problem can be effectively solved in GSM/EDGE Radio Access Networks (GERAN) by modifying handover boundaries. However, several drawbacks prevent operators from fully exploiting the potential of this technique. This paper investigates the limitations of current traffic-sharing approaches with tight frequency reuses in GERAN. To deal with such limitations, an algorithm is proposed to jointly optimize handover margins and signal-level constraints based on network statistics for traffic sharing in GERAN. A complementary algorithm is proposed to adjust cell (re)selection offsets to minimize the number of handovers. Simulation results show that the proposed method achieves a significant reduction in call blocking without excessive call quality impairment or increase of network signaling load when compared to the current approaches. More traffic can thus be handled without the need for any hardware upgrades, providing a cost-effective means to increase network capacity.

Performance of Reservation in Call Admission Control Schemes for Code-Division Multiple Access Systems with Nonuniform Traffic Distribution Among Cells

In this paper, we propose the reservation type call admission control (CAC) scheme to resolve the intercell unbalanced traffic problem. Differently from a conventional CAC scheme where the system resource is fully allocated to the local users in the home cell, the proposed CAC scheme reserves a small portion of the system resource for new calls occurring in the neighboring cells instead of fully allowing the local users in the home cell to occupy the system resource. As a result, the proposed CAC scheme improves the overall call blocking probability when the traffic is nonuniformly distributed among cells. More specifically, the proposed CAC scheme improves the overall call blocking probability by 15% when one cell has 67% more traffic than its surrounding cells.     

MIMO系统中的一种码距分配矩阵构造方案

针对多输入多输出(MIMO)系统采用奇异值分解(SVD)预编码时最优码距分配矩阵的构造无闭式解且搜索复杂度高的问题,基于变形的Hadamard矩阵,以接收端成对错误概率最小化为准则,给出了一种易求解且为闭式构造的码距分配方案。同时,给出了与之相应的功率分配方案,进一步提高了系统的性能。仿真结果表明,该算法性能与现有方法近似,但复杂度降低。当推广到具有发射相关性的MIMO系统时,仍具有较好的性能。     

Fixed and dynamic bandwidth allocation strategies for wireless mobile integrated services networks

Performance evaluation of two bandwidth allocation strategies in wireless mobile integrated services networks is carried out. Performances of the proposed strategies are compared with those of the traditional guard channels and threshold strategies. In the study, a single wireless cell which is accessed by voice and non-voice traffic types producing, respectively narrowband and wideband calls is considered. In the proposed strategies a number of channels are reserved in a fixed or dynamic fashion for the use of originating wideband calls in addition to the guard channels allocated for the handoff calls. The results indicate that the two strategies have comparable advantages and by manipulating the number of reserved channels, desired performance levels can be achieved. The dynamic reservation based strategy makes the system fairer for the originating wideband calls while maintaining low handoff dropping probability and acceptable channel utilization levels. On the other hand, the fixed reservation strategy provides a lower handoff call dropping at comparable channel utilization levels. The tradeoff is between improving the handoff call dropping versus the originating wideband call blocking. Both strategies provide better performance for the originating wideband calls compared with that provided by the traditional guard channels strategy.

A Rapid Code Acquisition Scheme for DS/SS Systems

In this paper, we propose a rapid code acquisition scheme for direct-sequence spread-spectrum (DS/SS) system basing on the improved seed accumulation of sequential estimation (ISASE). This method solves the problem that SASE scheme cannot work in the presence of carrier-frequency offset. The mean acquisition time of the ISASE scheme is derived by the generating function flow graph technique, and the tolerance of carrier-frequency offset is obtained in a closed-form expression. The performance of the proposed acquisition scheme is analytically evaluated in terms of the mean acquisition time. Analysis in theory and numerical results show that the proposed scheme yields improvement of the mean acquisition time over the RASE scheme by a factor of 2–15 times for the PN} period more than 255 in normal operating condition. For the important parameter-accumulating number m, we recommend to choose from 5 to 20 through the tradeoff of the tolerance of carrier-frequency offset and acquisition speed. Jiachi Wang was born in September, 1971. He is a Phd candidate in department Electronics and Information Engineering, Huazhong University of Science and Technology. His research areas include spread spectrum and digital communication, and digital signal processing. Xiulin Hu was born in 1945. He is a professor and Phd advisor in department Electronics and Information Engineering, Huazhong University of Science and Technology. His research areas include spread spectrum and digital communication. Yunyu Zhang was born in 1948. She is a professor in department Electronics and Information Engineering, Huazhong University of Science and Technology. Her research areas include software radio and digital communication. Qingyun Dai was born in 1977. She is a Phd candidate in department of Electronics and Information Engineering, Huazhong University of Science and Technology. Her research areas is wireless network.     

低轨星座卫星通信系统中多业务条件下的非充分保证切换策略

该文提出了一种适用于低轨星座卫星通信系统多业务条件下的非充分保证切换策略。该策略在小于一个小区最大驻留时间的时间间隔内为到达小区的呼叫安排和预定信道,在呼叫结束环节作为补充策略对存在切换失败风险的信道进行调整。提出了策略在多业务条件下具体的实施方法,根据实时的切换呼叫性能调整策略的非充分程度。通过仿真,分析比较了不同程度非充分保证切换策略的QoS性能,验证了动态自适应调整非充分程度值的IGH策略的有效性。仿真结果表明,相对于保证切换策略,新策略以存在微小切换失败概率为代价,换取了新呼叫阻塞概率的显著降低,是一种适用于多业务低轨卫星通信系统的信道分配策略。     

一种用于HAPS WCDMA系统的嵌入式多波束覆盖方案

该文提出了一种用于平流层平台WCDMA系统的固定波束加可控波束天线覆盖方案。该方案根据不同用户分布,在原有固定波束中合理嵌入可控波束,并有效调整嵌入波束的位置和大小,来优化系统容量。仿真结果表明该方案能够有效地提高平流层通信系统容量,节省波束资源,并且在变化的用户分布情况下保持容量的稳定性。该方案的这种优越性尤其体现在通信热点问题的解决中。     

用于WCDMA系统的MMSE接收机的功率与数据速率相结合的分配算法

该文针对3GPP WCDMA系统的反向链路,提出了一种基于MMSE接收机的功率和数据速率相结合的控制算法。该算法可以保证用户在达到目标信干比的同时,减小平均发射功率、加快收敛速度,从而提高系统的整体性能。仿真结果验证了所提出方案的正确性和优化算法的有效性。采用该文提出的算法,与MMSE功率控制算法比较,系统容量可增加近10％,而收敛速度可提高30％左右。     

A New Call Admission Control Scheme Based on Mobile Position Estimation in DS-CDMA Systems

Call dropping is considered more annoying than call blocking in wireless cellular networks. The cost of the classical method of employing guard channels to decrease the call dropping rate is the increase in call blocking rate. Since subscriber mobility changes in time, the number of handoff attempts in each cell is subject to fluctuations, making static assignments (or periodical update) of a given number of guard channels inefficient. In this paper, we propose an adaptive scheme that employs reservations, instead of static assignments, to adaptively adjust the number of guard channels in each cell according to the current requirements. Thus, unnecessary allocation of guard channels is avoided resulting in a lower cost in terms of call dropping. The reservation requests are made according to the recent mobility pattern of the subscriber. A likelihood value is associated with each reservation request so that fewer channels are reserved by benefiting from the statistical accumulation of the requests. The channels are reserved by considering the interference that would be created once they are in use. The proposed scheme is evaluated against the classical guard channel scheme with a realistic mobility model.This author is currently associated with Georgia Institute of Technology-Regional Engineering Program (GTREP).Tuna Tugcu received his B.S. and Ph.D. degrees in computer engineering from Bogazici University in 1993 and 2001, respectively, M.S. degree from New Jersey Institute of Technology in 1994. He pursued post-doctorate study in Broadband and Wireless Networking Lab at Georgia Institute of Technology until July 2002. Currently, he is a visiting assistant professor at Georgia Institute of Technology-Regional Engineering Program. His research interests include real-time systems, communication networks, and wireless communications. Dr. Tugcu is a member of the IEEE.Cem Ersoy received his B.S. and M.S. degrees in electrical engineering from Bogazici University in 1984 and 1986, respectively. He worked as an R&D engineer in NETAS A.S. between 1984 and 1986. He received his PhD in electrical engineering from Polytechnic University in 1992. Currently, he is a professor in the Computer Engineering Department of Bogazici University. His research interests include performance evaluation and topological design of communication networks, wireless communications and mobile applications. Dr. Ersoy is a Senior Member of the IEEE.     

Downlink traffic control for multiple classes of services in MC-CDMA cellular systems

We consider the problem of downlink traffic control in Multi-code Code Division Multiple Access (MC-CDMA) systems, which support multiple classes of services with diverse QoS requirements. Prior solutions proposed for this problem have largely focused on call admission control at the connection level while neglecting the stochastic behavior of mobile subscribers and channel conditions. We quantitatively demonstrate that these statistical factors, in particular log-normal shadowing in propagation and voice activity factors, have a significant impact on the connection-level performance. Furthermore, we show that conventional data services can be best handled at the packet level as background transmissions by taking advantage of these statistical variations, which leads to significantly better utilization of the scarce wireless spectrum. The research was supported in part by grants from RGC under the contracts HKUST6104/04E and HKUST6165/05E, a grant from NSFC/RGC under the contract N_HKUST605/02, a grant from NSF China under the contract 60429202. Jihui Zhang’s work was partially supported by Microsoft fellowship. Jihui Zhang (S’02) received her B.S. degree from Fudan University, China in 2001, and the Ph.D. degree from the Hong Kong University of Science and Technology in 2005, both in the Computer Science. Her research interests include CDMA cellular networks and wireless ad-hoc networks. Bo Li (S’89-M’92-SM’99) received his B. Eng. and M. Eng. degrees in the Computer Science from Tsinghua University, Beijing in 1987 and 1989, respectively, and the Ph.D. degree in the Electrical and Computer Engineering from University of Massachusetts at Amherst in 1993. Between 1993 and 1996, he worked on high performance routers and ATM switches in IBM Networking System Division, Research Triangle Park, North Carolina. Since 1996, he has been with the Department of Computer Science, Hong Kong University of Science and Technology, where he is now an associated professor and Co-Director for the ATM/IP Cooperate Research Center, a government sponsored research center. He also holds an adjunct researcher position at the Microsoft Research Asia (MSRA), Beijing, China, and adjunct professorship in several universities. His recent research interests are on adaptive video multicast, packet scheduling and dynamic routing in optical networks, resource management in mobile wireless systems, scheduling and energy efficient routing in ad hoc networks, across layer design for sensor networks, and content distribution and replication. He has published 150 papers and held several patents in above areas. He has been on editorial board for 16 journals, mainly in IEEE and ACM. He has been involved in organizing over 40 conferences, esp. IEEE Infocom since 1996. He was the Co-TPC Chair for IEEE Infocom 2004.     

A New Connection Admission Control for Spotbeam Handover in LEO Satellite Networks

Frequent spotbeam handovers in low earth orbit (LEO) satellite networks require a technique to decrease the handover blocking probabilities. A large variety of schemes have been proposed to achieve this goal in terrestrial mobile cellular networks. Most of them focus on the notion of prioritized channel allocation algorithms. However, these schemes cannot provide the connection-level quality of service (QoS) guarantees. Due to the scarcity of resources in LEO satellite networks, a connection admission control (CAC) technique becomes important to achieve this connection-level QoS for the spotbeam handovers. In this paper, a geographical connection admission control (GCAC) algorithm is introduced, which estimates the future handover blocking performance of a new call attempt based on the user location database, in order to decrease the handover blocking. Also, for its channel allocation scheme, an adaptive dynamic channel allocation (ADCA) scheme is introduced. By simulation, it is shown that the proposed GCAC with ADCA scheme guarantees the handover blocking probability to a predefined target level of QoS. Since GCAC algorithm utilizes the user location information, performance evaluation indicates that the quality of service (QoS) is also guaranteed in the non-uniform traffic pattern.     

多业务LEO卫星网络中最优呼叫允许控制及切换管理策略

该文针对多业务条件下的LEO(Low-Earth-Orbit)卫星网络,提出了一种新的基于最优多门限信道预留(OMTCR)的呼叫允许控制(CAC)及切换管理策略,建立了评价LEO卫星网络连接级QoS性能的理论分析模型框架。借鉴经济学收益函数的概念分别建立了无QoS约束和有QoS约束的系统收益目标优化模型,求解在给定系统参数和输入业务条件下OMTCR的最优门限参数矢量。仿真结果表明OMTCR能够在不同用户QoS要求和系统收益目标的多业务环境下获得比传统CS(Completely Sharing)策略及GC(Guard Channel)策略更好的性能。