本論文對於DS-CDMA行動通訊系統之誤碼率有一整體及連貫之分析。先從接收信號振幅之觀點出發，在非同步傳輸無衰減通道下，推導出以鞍點法計算的誤碼率表示式；再進一步計算在具有多路徑衰減特性的通道環境下，以空間分集式接收的效能﹔衰減通道統計模型方面，以較具有彈性的Nakagami-m機率分布討論之；數值積分結果顯示接收機輸出分布的非高斯特性，特別是在嚴重衰減環境下，鞍點近似有令人滿意的精確度，可快速精確地評估系統之各參數。系統採用最大長度碼和金碼做為例子。 以接收信號功率的統計特性，推導出訊號對干擾加上白雜訊之比(SIR)，分析蜂巢式CDMA行動通訊系統在Rayleigh 衰減通道中之上傳鏈結和下傳鏈結之效能。分析中對於傳輸距離損失，屏蔽效應，多路徑衰減以及多數使用者所造成的干擾和白雜訊等均加以考慮。當傳輸通道考慮具有指數衰減形式之多路徑強度廓面時，以無限多條路徑取代事先決定之有限條路徑來加以分析。對於寬頻服務CDMA系統，為了達到可變的多重傳輸速率，在下傳鏈結環境下，所採用的短正交碼結合長隨機碼，以及上傳鏈結採長隨機碼，本文亦分別推導其SIR的機率分布及誤碼率的表示式。兩種RAKE接收機─等增益合併和選擇性合併，於此加以討論。 The performance of a direct sequence code-division multiple-access (DS-CDMA) communication system is analyzed from two perspectives: received signal envelope and received power. With the envelope viewpoint, the BER can be accurately computed by using the saddlepoint method and the accuracy of Gaussian approximation (GA) can be assessed. The channel model is an additive white Gaussian noise (AWGN) channel subject to Nakagami fading, which can be characterized by the parameter m for various physical environments, i.e. urban, suburban, or rural areas. The effects of the multiple access interference (MAI), self-interference (SFI), path fading, and AWGN are investigated. For diversity receptions, the Mth order selective combining is considered. Results of the numerical integration illustrate the non-Gaussian property of the receiver output distribution. Examples using maximal-length sequences and Gold codes are considered. With the analysis of received power, detailed formulas in closed or approximate forms are presented for calculating the distribution of the received bit energy-to-total- noise ratio. Both downlink and uplink are considered. No predetermined number of effective multipaths is required. It is decided during computation. The saddlepoint method can greatly reduce the calculation complexity to be linear with the number of interferers. Approximations are derived for a large processing gain and a MAI limited environment respective. Methods for computing the BER are shown for receivers with equal gain or selective combiners.
