近年來由於超寬頻通信系統的短距離、低功率的寬頻傳輸特性使其成為目前無線通訊中的新寵。已有許多超寬頻通訊在室內傳輸的相關文獻已經被發表，其大多研究是以量測方式找出影響通道的統計參數後，並分析在此通道統計模型下的系統傳輸錯誤率。本研究的目標是希望利用天線場型的調整，使得系統傳輸位元錯誤率能夠最低。其中的要件除了通訊系統的參數之外，還包括室內環境多路徑傳輸效應的影響，因此要解決這樣的問題可以看成一種求解最佳化的問題。由於基因法則的好處在於不須列出變數和因變數的明顯數學關係亦能找出最佳解，因此本研究使用基因法則作為最佳化的工具。和一般以天線場型為目標函數所不同的地方是，本研究擬以降低室內通信傳輸位元錯誤率為目標函數，再利用基因法則作最佳化的調整，尋找出滿足最低傳輸位元錯誤率時的天線場型，此種場型最能滿足室內無線通訊的需求。 本研究首先利用射線追蹤法計算出任意給定室內環境之脈衝響應，根據已知的天線陣列以及考慮具同步電路的脈衝無線電超寬頻通訊系統，利用基因法則做最佳化的運算，尋找出當傳輸位元錯誤率最低時的天線場型以及系統的效能分析。並且將此結果應用在室內無線區域迴路的通訊上。 模擬結果顯示，透過基因演算法分別地調整天線陣列中每一個天線元件的信號聵入線長度，確實能在3GHz-6GHz合成出具有指向性的輻射場型。此一指向性輻射場型能提供以下優點。(1) 在接收端能有效地接收到每根天線所幅射出的能量，並進而提高接收端的訊雜比。(2) 此指向性輻射場型能有效地減少多路徑效應的發生，使得信號在通道中傳輸的延遲擴散降低。 (3) 可大幅降低位元錯誤率，提高通訊品質。 In this paper, a new ultra wideband circular antenna array(UCAA) combining genetic algorithm to minimize the bit error rate (BER) is proposed. The ultra wideband(UWB) impulse responses of the indoor channel for any transmitter-receiver location are computed by SBR/Image techniques, inverse fast Fourier transform and Hermitian processing. By using the impulse response of multipath channel, the performance of the binary pulse amplitude modulation (B-PAM) impulse radio (IR) UWB system with circular antenna array can be calculated. Based on the topography of the antenna and the BER formula, the array pattern synthesis problem can be reformulated into an optimization problem and solved by the genetic algorithm. The novelties of our approach is not only choosing BER as the object function instead of sidelobe level of the antenna pattern, but also consider the antenna feed length effect of each array element. The strong point of the genetic algorithm is that it can find out the solution even if the performance index cannot be formulated by simple equations. Simulation results show that the synthesized antenna array pattern is effective to focus maximum gain to the LOS path which scales as the number of array elements. In other words, the receiver can increase the received signal energy to noise ratio. The synthesized array pattern also can mitigate severe multipath fading in complex propagation environment. As a result, the BER can be reduced substantially in indoor UWB communication system.
