基因演算法在直序式超寬頻多用戶偵測器之應用研究

Application of Genetic Algorithm to Multi-user Detection in DS-UWB system

林仲文(Chung-Weng Lin)

指導教授 ： 譚旦旭

國立臺北科技大學/機電學院/電機工程系所/碩士(2005年)

https://doi.org/10.6841/NTUT.2005.00034

摘要

直序式超寬頻通訊（DS-UWB）是目前IEEE 802.15.3a標準考慮的主要方案之一。超寬頻通訊技術適用於短距離（＜10公尺）環境，其中的多重路徑效應在多用戶情況下，容易影響展頻碼之間的正交特性，進而造成多重存取干擾（Multi-Access Interference, MAI）的問題。為了消除MAI，最佳多用戶偵測器雖然能達到極佳的系統效能，但因計算複雜度太高，故無法實現。為了在效能與複雜度之間取得平衡，若干研究提出了次佳的方法，基因演算法多用戶偵測器（Genetic algorithm based multi-user detector, GA-MUD）即為次佳化偵測器的一個例子。但一般GA-MUD大都以傳統偵測器（Conventional Detector, CD）產生GA之初始解，此架構在DS-UWB通道環境下，CD無法有效偵測傳送位元，使得GA無法發揮最佳效能。
為了克服傳統GA-MUD之困難，我們提出新的GA-MUD系統架構（簡稱RRGA-MUD），此架構利用耙式偵測器（Rake Receiver）產生GA之初始解。模擬結果顯示，RRGA-MUD在越惡劣通道環境中其效能愈顯著，甚至在CM4低SNR情況下，擁有優於Rake-32單一用戶之效能。除外，我們也比較RRGA-MUD與其他兩種GA-MUD之效能，由實驗證明，我們提出的RRGA-MUD架構效能最佳。

關鍵字

超寬頻 ； 直序超寬頻 ； 直序式分碼多工 ； 基因演算法 ； 多用戶偵測器

並列摘要

The DS-UWB is one major candidate of IEEE 802.15.3a standard for communication link that is below 10 meters. However, for the multi-user application the multiple access interference (MAI) due to imperfect orthogonality between spreading codes induced by UWB dense multi-path degrades system performance. Though optimum multi-user detector (OMD) can achieve remarkable performance, its computational complexity is too high to implement. Therefore, many sub-optimal multi-user detectors (MUDs) have been proposed to attain best trade-off between performance and complexity, such as the genetic-based MUD (GA-MUD). Generally, GA-MUD that applies the conventional detector (CD) to generate initial solution exhibits good performance in the DS-CDMA system. However, it has been found that the CD is unable to provide acceptable initial solution for GA optimization process in the DS-UWB system and thus the solution can easily be trapped into local optimum.
To overcome this difficulty, a novel RRGA-MUD that combines the Rake receiver and a modified GA is proposed. This MUD employs the finger-8 Rake receiver to generate initial solution for GA-based optimization. A series of simulations is conducted over the UWB channels of CM1 ~ CM4 with 1, 6, and 10 users. Experimental results show that the proposed RRGA-MUD yields notable performance under severe communication environments. Especially, it achieves better performance than the Rake-32 (single user) over the CM4 environment. We also compare the performances between RRGA-MUD and the other two GA-MUDs, and the result reveals that our proposed MUD has the best performance.

並列關鍵字

UWB ； DS-UWB ； DS-CDMA ； Genetic Algorithm ； Multi-user Detector(MUD)

參考文獻

[2]S. Stroh, “Ultra-Wideband: Multimedia Unplugged,” IEEE Spectrum, 2003.

[6]S. R. Saunders, “Antennas and Propagation for Wireless Communication Systems,” Published by John Wiley & Sons., 1999.

[14]A. Molisch, M. Win, and D. Cassioli, “The Ultra-Wide Bandwidth Indoor Channel: from Statistical Model to Simulations,” IEEE P802.15-02/284-SG3a and IEEE P802.15-02/285-SG3a.

[15]J. Cramer, R. Scholtz, and M. Win, “Evaluation of an Indoor Ultra-Wideband Propagation Channel,” IEEE P802.15-02/286-SG3a and IEEE P802.15-02/325-SG3a.

[19]A. Batra, et al., “Multi-band OFDM Physical Layer Proposal,” IEEE 802.15-03/267r6, Texas Instruments, Sep. 2003.