許多的研究說明了，在WCDMA系統當中，利用正交可變展頻係數(Orthogonal Variable Spreading Factor, OVSF)可以提供可即時變動的使用者傳輸速率。但過去大多數的研究都著重於降低展頻碼的分配次數，而並沒有提到如何將其使用在實際的系統當中。在本研究中，我們提出了一個在WCDMA系統中，以正交可變展頻係數為基礎，採用頻寬借用演算法，提供服務品質保證的動態頻寬管理方法，當有新的使用者想要進入系統或是目前現有的使用者想要提高傳輸速率，而系統沒有足夠的可用頻寬可支援時，我們所提出的頻寬借用演算法可以用來向其他在系統當中的使用者借用部分的頻寬來使用。此外，我們亦提出一個動態頻寬保留演算法來避免因為突然增加的頻寬需求，而導致的連線強迫中斷。根據我們所模擬出來的結果顯示，系統的服務品質保持在一定的水準之上。

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.

1. Introduction
2. OVSF codes
3. The Proposed Algorithm
3.1 Bandwidth borrowing algorithm (BBA)
3.1.1 Candidate selection
3.1.2 Bandwidth utilization computation
3.1.3 Load prediction
3.1.4 Priority computation
3.1.5 Call set selection
3.1.6 Reducing procedure
3.2 Bandwidth reservation algorithm (BRA)
4. Simulation
5. Conclusions
6. References

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