Orthogonal variable spreading factor (OVSF) code is used in WCDMA system to provide variable service data rates. However, most researches focus on decreasing the number of code assignment without considering how to manage bandwidth with properties of OVSF code. In this research, we propose a dynamic bandwidth borrowing algorithm for quality of service (QoS) supported in the OVSF-CDMA system. When a new call arrives or a current serviced call requests a higher data rate, but the system can not provide the required bandwidth, the borrowing algorithm can be activated to borrow bandwidth from current serviced calls. Also, a dynamic bandwidth reserved algorithm is proposed to avoid forced termination caused by the suddenly increasing bandwidth requirements of current serviced calls. Simulation results show that the value of throughput increases and the QoS of current serviced calls can be maintained.

In thesis, we design a new orthogonal complementary codes- columnwise complementary codes. Its advantage is: (1)As traditional orthogonal complementary codes, it has perfect orthogonal complementary property of auto-correlation and cross-correlation. (2)We can choose different type of columnwise complementary codes to restrain frequency selective fading and time selective fading. (3)Compared with complete complementary codes, it can support more users. (4)The generating method of columnwise complementary codes is easy to understand. (5)It can be used in multi-rate transmission system. (6)The generality: complete complementary codes and 2D OVSF codes are subsets of columnwise complementary codes. We also discuss its bit error rate in a frequency selective Rayleigh fading channel and a time selective fading channel by computer simulation.

This research investigated the efficient utilization of wireless bandwidth in Code Division Multiple Access (CDMA)systems that support multiple data rates with Orthogonal Variable Spreading Factor (OVSF)codes. The specific problem being addressed was that currently proposed public-domain algorithms for assigning OVSF codes make inefficient use of wireless bandwidth for bursty data traffic sources with different Quality of Service (QoS) requirements. The purpose of this research was to develop an algorithm for the assignment of OVSF spreading codes in a Third-Generation (3G)Wideband CDMA (WCDMA)system. The goal of this algorithm was to efficiently utilize limited, wireless resources for bursty data traffic sources with different QoS requirements. The key contribution of this research was the implementation and testing of two code sharing techniques which are not implemented in existing OVSF code assignment algorithms. These techniques were termed statistical multiplexing and dynamic code sharing. The statistical multiplexing technique used a shared channel to support multiple bursty traffic sources. The dynamic code sharing technique supported multiple data users by temporarily granting access to dedicated channels. These techniques differed in terms of both complexity and performance guarantees. / Ph. D.

WCDMA是一個寬頻直接序列分碼多工存取(DS-CDMA)系統，使用正交可變展頻係數(Orthogonal Variable Spreading Factor，OVSF)碼以支援多樣化的資料傳輸速率，提供可變動位元速率和服務品質(Quality of Service，QoS)保障，以滿足使用者對多媒體應用服務的需求。在本研究中我們將訊務分群並配置符合的正交變數展頻係數碼的方式，來處理資源分配的問題，期讓每位使用者都能有滿意的服務品質。在論文中，為提供不同等級的差別服務以兼顧QoS和避免頻寬浪費，我們提出以動態群組配置的方式，從所有提出服務要求的訊務中，依其服務優先等級順序，挑選適合的訊務，將其放置於同一群組。系統會配置一OVSF碼給此群組，透過分時共用來進行資料傳輸，使其能提供多樣化的資料傳輸速率，減少碼阻斷，提高系統頻寬的使用率，並滿足使用者對服務品質的需求。實驗模擬顯示，本研究所提出的方法能提供多樣化的資料傳輸速率，並能有效減少碼阻斷，提高頻寬及系統使用率，並達到QoS的要求。 / WCDMA is a wideband Direct-Sequence Code Division Multiple Access (DS-CDMA) system, it uses Orthogonal Variable Spreading Factor (OVSF) codes to support diverse data transmission rates. Orthogonal variable spreading factor codes have the ability to provide variable bit rates and QoS to meet different multimedia application requirements. In this research, we group the traffic and use Orthogonal Variable Spreading Factor (OVSF) technique to deal with resource allocation problem in order to offer satisfactory quality of service to the users. We propose dynamic group allocation method to provide differentiated services in order to meet the QoS requirement and avoid bandwidth wasting. From all those requested services, we move all those services of the same service priority to the same group. The system will subsequently assign OVSF code to each group. Data transmission of each group is based on time-sharing mechanism. Simulations show that the proposed method can provide diverse data transmission rates, and is able to reduce code blocking rate, increase bandwidth and system utilization, and meet the QoS requirement.