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Title: DS/CDMA行動通訊系統使用模糊理論之功率控制
Fuzzy-Based Power Control for DS/CDMA Cellular Mobile Communication
Authors: 王益慧
Yi-Hui Wang
Contributors: Yih-Chuan Lin;Nan-Yuan Yen
電腦與通訊研究所
Keywords: 直序序列分碼多工擷取;回饋式功率控制演算法;模糊規則庫
DS/CDMA;lots of researches on power control;fuzzy-rule base
Date: 2003
Issue Date: 2011-05-24 14:36:17 (UTC+8)
Publisher: 高雄市:[樹德科技大學電腦與通訊研究所]
Abstract: DS/CDMA行動通訊系統使用模糊理論之功率控制
學生:王益慧指導教授:林易泉博士
顏楠源博士
樹德科技大學電腦與通訊系碩士班
摘要
直序序列分碼多工擷取(DS/CDMA)技術在近年來蜂巢式行動電話系統中被廣泛地研究,通道特性例如多路徑衰減、遮蔽效應和路徑損失將會造成干擾甚至更糟。
功率控制在DS/CDMA系統對抗近遠問題是必要的且在許多文獻上也有針對功率控制設計之研究,在傳統回饋式功率控制演算法中允許基地台不管是傳送增加或減少之功率控制命令給每一個使用者,所傳送的功率都是透過固定步階大小來調整,使得所接收之功率幾乎相同。然而這樣的系統仍有穩定度差、大幅度的功率超出(overshoot)及比較長的上升時間(rise time)等問題。為了解決這個問題,利用模糊積分器(PI),將所接收的功率錯誤(power error) 和錯誤變化(error change)這些變數輸入以決定每一個使用者所傳輸的功率,這樣的作法無非是讓基地台接收所有的使用者的信號時幾乎能維持同樣的功率強度,使系統達到比較好的穩定度和控制性能。
為了決定控制的行為,我們使用了模糊規則庫,它是由推論機制結合了一些處理敘述的知識,這些控制行為能導致快速的上升時間,使功率超出的部份減少且使平均平方根(rms)的追蹤錯誤降低。我們將[15] 的歸屬函數修正成半圓形的形狀,這樣可以達成比較好的性能,從模擬的結果可以發現經過修正後之模糊架構為基礎的功率控制在性能上會比傳統的乒乓功率控制來得好。
Fuzzy-Based Power Control for DS/CDMA Cellular Mobile Communication
Student : Yi-Hui Wang Advisors : Dr. Yih-Chuan Lin
Dr. Nan-Yuan Yen
Institute of Shu-Te University of
Computer & Communication Department
ABSTRACT
Direct Sequence Code Division Multiple Access (DS/CDMA) techniques have been investigated for cellular mobile radio system recently. The channel characteristics such as the multipath fading, the shadowing effect, and the path loss will make the interference even worse.
Power control is essential for DS/CDMA system to combat the near-far problem and there are lots of researches on power control schemes in the literatures. The conventional feedback power control algorithms allow the base station to send a power command to either raise or lower each user transmitting signal power level by a fixed power step and then keep the received powers almost equal. However, this control scheme suffers from poor system stability, large overshoot, and long rise time. To tackle this difficulty, a fuzzy Proportional-plus-Integral (PI) control, whose input variables are the received power error and error change, is introduced to determine each user’s transmitting power in order to maintain simultaneously all users’ signal power received at the base station nearly equal and to achieve better system stability and control performance.
The fuzzy-rule base is used by an inference mechanism in conjunction with some knowledge of the states of process in order to determine control actions. These control actions would lead to the fast rise time, minimum overshoot, and small root-mean-squared (rms) tracking error. We modified the membership function of [15] to improve the performance by the semicircle shape. From the simulation results, we found the modified fuzzy based scheme performed better than the tradition scheme performed of ping-pong power control.
Appears in Collections:[電腦與通訊系(所)] 博碩士論文

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