Implementation of a High-Performance Assignment Scheme for Orthogonal Variable-Spreading-Factor Codes in WCDMA Networks

[[abstract]]In WCDMA, channelization is achieved by assigning OVSF codes to different users. The codes in a Node-B are valuable and limited. Much research has been devoted to devising OVSF code-assignment strategies to support as many users as possible. A number of the strategies suffer from a “code-set fragmentation” problem, which increases the call blocking probability (CBP) on the Node-B. In order to resolve this issue some strategies have applied code-exchange and reassignment policies but increased the corresponding complexity. This paper proposes a Best-fit Least Recently Used (BLRU) code-assignment scheme without reassignment to approach an optimal method. Furthermore, we devise a revised version, Queue-assist BLRU (QBLRU), to improve system utilization and to obtain an even lower CBP than the optimal method does. Consequently, code-assignment simulation results present a QBLRU scheme that has a low CBP and the highest utilization, which is a high performance OVSF code-assignment scheme which should be useful for WCDMA networks

Maximally Flexible Assignment of Orthogonal Variable Spreading Factor Codes for Multi-Rate Traffic

In universal terrestrial radio access (UTRA) systems, orthogonal variable spreading factor (OVSF) codes are used to support different transmission rates for different users. In this paper, we first define the flexibility index to measure the capability of an assignable code set in supporting multirate traffic classes. Based on this index, two single-code assignment schemes, nonrearrangeable and rearrangeable compact assignments, are proposed. Both schemes can offer maximal flexibility for the resulting code tree after each code assignment. We then present an analytical model and derive the call blocking probability, system throughput and fairness index. Analytical and simulation results show that the proposed schemes are efficient, stable and fair

An Algorithmic View on OVSF Code Assignment

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 tractabl

Bandwidth allocation for wireless multimedia systems.

Chen Chung-Shue.Thesis (M.Phil.)--Chinese University of Hong Kong, 2001.Includes bibliographical references (leaves 100-102).Abstracts in English and Chinese.Chapter 1. --- Introduction --- p.1Chapter 1.1 --- Evolution to 3G Mobile --- p.2Chapter 1.1.1 --- First Generation --- p.2Chapter 1.1.2 --- Second Generation --- p.3Chapter 1.1.3 --- Third Generation --- p.3Chapter 1.2 --- UTRA Framework --- p.5Chapter 1.2.1 --- FDD and TDD --- p.6Chapter 1.2.2 --- Channel Spreading --- p.6Chapter 1.2.3 --- OVSF Code Tree --- p.8Chapter 1.3 --- Cellular Concepts --- p.10Chapter 1.3.1 --- System Capacity --- p.10Chapter 1.3.2 --- Multiple Access --- p.11Chapter 1.3.3 --- Resource Management --- p.15Chapter 1.4 --- Organization of the Thesis --- p.16Chapter 2. --- Analysis on Multi-rate Operations --- p.18Chapter 2.1 --- Related Works in Multi-rate Operations --- p.18Chapter 2.1.1 --- Variable Spreading Factor --- p.19Chapter 2.1.2 --- Data Time-multiplexing --- p.20Chapter 2.1.3 --- Multi-carrier Transmission --- p.21Chapter 2.1.4 --- Hybrid TDMA/CDMA --- p.23Chapter 2.2 --- Problems in Multi-rate Operations --- p.24Chapter 2.2.1 --- Conventional CDMA --- p.24Chapter 2.2.2 --- Data Time-multiplexing --- p.25Chapter 2.2.3 --- MC-CDMA --- p.25Chapter 2.2.4 --- TD-CDMA --- p.27Chapter 2.3 --- Multi-user multi-rate Operations --- p.28Chapter 3. --- Bandwidth Allocation --- p.29Chapter 3.1 --- Most Regular Binary Sequence --- p.30Chapter 3.1.1 --- Properties of MRBS --- p.31Chapter 3.1.2 --- Construction of MRCS --- p.32Chapter 3.1.3 --- Zero-one Sequence under MRBS --- p.33Chapter 3.2 --- MRBS in TD-CDMA --- p.35Chapter 3.2.1 --- Time Slot Optimization --- p.36Chapter 3.2.2 --- Sequence Generator --- p.37Chapter 3.3 --- Most Regular Code Sequence --- p.38Chapter 3.3.1 --- Properties of MRCS --- p.38Chapter 3.2.2 --- Construction of MRCS --- p.41Chapter 3.3.3 --- Fraction-valued Sequence under MRCS --- p.42Chapter 3.3.4 --- LCC and UCC --- p.45Chapter 3.4 --- MRCS in WCDMA --- p.46Chapter 3.4.1 --- Spreading Factor Optimization --- p.46Chapter 3.4.2 --- Code Generator --- p.48Chapter 3.4.3 --- Uplink and Downlink --- p.50Chapter 4. --- Multi-access Control --- p.52Chapter 4.1 --- Conflict and Resolution --- p.53Chapter 4.1.1 --- Conflicts in MRBS and MRCS --- p.53Chapter 4.1.2 --- Resolution with Buffering --- p.55Chapter 4.2 --- MRBS Transmission Scheduling --- p.56Chapter 4.2.1 --- Slot Scheduling on MRBS --- p.56Chapter 4.2.2 --- Properties of Scheduling Algorithm --- p.59Chapter 4.2.3 --- Scheduled MRBS --- p.71Chapter 4.3 --- MRCS Transmission Scheduling --- p.73Chapter 4.3.1 --- Slot Scheduling on MRCS --- p.73Chapter 4.3.2 --- Properties of Scheduling Algorithm --- p.75Chapter 4.3.3 --- Scheduled MRBS --- p.76Chapter 4.4 --- Performance Evaluation --- p.78Chapter 4.4.1 --- Simulation on Algorithm --- p.78Chapter 4.4.2 --- Resource Utilization and Delay Bound --- p.79Chapter 4.4.3 --- Blocking Model and System Capacity --- p.80Chapter 4.4.4 --- Numerical Analysis --- p.86Chapter 5. --- Conclusions and Future works --- p.92Appendix A --- p.94Appendix B --- p.98Bibliography --- p.10

Improving 3G network throughput by new service and joint design.

Li Ning.Thesis (M.Phil.)--Chinese University of Hong Kong, 2004.Includes bibliographical references (leaves 52-55).Abstracts in English and Chinese.Acknowledgments --- p.iiAbstract --- p.iii哲學碩士論文摘要 --- p.ivChapter Chapter 1 --- Introduction --- p.1Chapter 1.1 --- Research Background --- p.2Chapter 1.2 --- Contributions of the Thesis --- p.5Chapter 1.3 --- Organization of the Thesis --- p.6Chapter Chapter 2 --- Properties of OVSF Codes --- p.7Chapter 2.1 --- Tree-Structured Generation of OVSF Codes --- p.7Chapter 2.2 --- OVSF Codes Assignment --- p.10Chapter Chapter 3 --- Support Delayable Traffic in Wireless Networks --- p.14Chapter 3.1 --- System Model --- p.15Chapter 3.2 --- Scheduling Algorithm with Burst Adaptation --- p.17Chapter 3.3 --- Performance Analysis --- p.22Chapter 3.4 --- Simulation Results --- p.24Chapter Chapter 4 --- Allocate OVSF Codes with Joint Design --- p.30Chapter 4.1 --- Combine Number of Active Users and Error-Control Coding Scheme --- p.31Chapter 4.1.1 --- System Model --- p.31Chapter 4.1.2 --- Scheduling Algorithm Description --- p.33Chapter 4.1.3 --- Simulation Results --- p.35Chapter 4.2 --- Combine Power Adaptation and Error-Control Coding Scheme --- p.39Chapter 4.2.1 --- System Model --- p.39Chapter 4.2.2 --- Scheduling Algorithm Description --- p.41Chapter 4.2.3 --- Simulation Results --- p.44Chapter Chapter 5 --- Conclusion --- p.50Bibliography --- p.5

Efficient Radio Resource Allocation Schemes and Code Optimizations for High Speed Downlink Packet Access Transmission

An important enhancement on the Wideband Code Division Multiple Access (WCDMA) air interface of the 3G mobile communications, High Speed Downlink Packet Access (HSDPA) standard has been launched to realize higher spectral utilization efficiency. It introduces the features of multicode CDMA transmission and Adaptive Modulation and Coding (AMC) technique, which makes radio resource allocation feasible and essential. This thesis studies channel-aware resource allocation schemes, coupled with fast power adjustment and spreading code optimization techniques, for the HSDPA standard operating over frequency selective channel. A two-group resource allocation scheme is developed in order to achieve a promising balance between performance enhancement and time efficiency. It only requires calculating two parameters to specify the allocations of discrete bit rates and transmitted symbol energies in all channels. The thesis develops the calculation methods of the two parameters for interference-free and interference-present channels, respectively. For the interference-present channels, the performance of two-group allocation can be further enhanced by applying a clustering-based channel removal scheme. In order to make the two-group approach more time-efficient, reduction in matrix inversions in optimum energy calculation is then discussed. When the Minimum Mean Square Error (MMSE) equalizer is applied, optimum energy allocation can be calculated by iterating a set of eigenvalues and eigenvectors. By using the MMSE Successive Interference Cancellation (SIC) receiver, the optimum energies are calculated recursively combined with an optimum channel ordering scheme for enhancement in both system performance and time efficiency. This thesis then studies the signature optimization methods with multipath channel and examines their system performances when combined with different resource allocation methods. Two multipath-aware signature optimization methods are developed by applying iterative optimization techniques, for the system using MMSE equalizer and MMSE precoder respectively. A PAM system using complex signature sequences is also examined for improving resource utilization efficiency, where two receiving schemes are proposed to fully take advantage of PAM features. In addition by applying a short chip sampling window, a Singular Value Decomposition (SVD) based interference-free signature design method is presented