頻率選擇衰減通道下對展頻系統接收機之設計

論文中，展頻通訊系統之接收機設計將在無線衰減環境中，討論與分析。其內容，包含數位碼追蹤迴路部分以及對於複碼直序分碼多重存取系統之連續消減干擾技術之研究。論文第一部分，主要討論帶限偽雜訊之訊號，在頻率選擇衰減通道下，以耙式為接收架構，對於數位延遲鎖相迴路嵌入一離散自動增益控制演算機制之系統的探討與效能分析。相關統計特性亦在Nakagami-m隨機程序中，探究。穩態時差之最後封閉解描述是從基於Chapman-Kolmogorov方程式所表示出的暫態時差機率密度函數而推導出的。主要系統統計特性，平均失鎖時間、時均方偵測誤差以及系統特性極限Cramér-Rao lower bound，都將在頻率選擇Nakagami-m衰減通道中，討論、分析與模擬。而上述之數值分析結果，將在時域電腦模擬中，得到驗證。此外，數位延遲鎖相迴路裝置沉浸在都普勒飄移效應中，其追蹤效能分析亦被探究。論文另一部分，主要在逆向鏈結之頻率選擇衰減通道中，對於具有連續消減干擾機制之非同調與同調複碼直序分碼多重存取通訊系統，進行探討。以耙式為接收架構，採用連續消減干擾方案後，多重存取干擾因素將有效抑制。採用連續消減干擾技術的系統之最後封閉解，在Nakagami-m衰減通道中，將被推導、求得。從電腦模擬結果證明，在多重路徑衰減環境中，複碼直序分碼多重存取通訊系統採用連續消減干擾機制後的確具有較佳的系統表現。從理論分析而來的數值分析結果，亦得到驗證。此外，在同步因素考量下，採用同調接收機比使用非同調接收機，更能得到令人滿意的錯誤率。

關鍵字

偽雜訊碼追蹤；連續消減干擾； Nakagami-m衰減通道；頻率選擇；平均失鎖時間；多重存取干擾；離散自動增益控制；複碼直序分碼多重存取；數位延遲鎖相迴路；耙式； Cramér–Rao下界

並列摘要

In this thesis, the receiver design of the spread spectrum (SS) communications system over wireless fading environments, including the digital code tracking loop and the successive interference cancellation for multicode direct-sequence code-division multiple access systems, is evaluated. 1. For band-limited pseudo-noise signals, a non-coherent digital delay-lock loop (DDLL) equipped with a discrete automatic gain control algorithm under a RAKE scheme over frequency-selective fading channels is studied. Its associated statistical characteristics are analyzed based on the Nakagami-m stochastic process. The transition timing error probability density function (pdf) of the Chapman-Kolmogorov equation is evaluated to drive an analytical expression for the steady-state timing error pdf. The mean time to lose lock and the mean square tracking error with its corresponding Cram’er-Rao lower bound under frequency-selective Nakagami-m fading environments are scrutinized, while their numerical results are confirmed by time-domain computer simulations. Moreover, the tracking performance of the DDLL in the presence of Doppler shifts is also examined. 2. Noncoherent and coherent multicode direct-sequence code-division multiple access (DS-CDMA) systems with successive interference cancellation (SIC) for multimedia reverse links over frequency-selective fading channels are studied. Followed by a RAKE receiver, the SIC scheme is applied for combating the multiple access interference. The bit error rate (BER) using the SIC technique over Nakagami-m fading channels is derived. Simulation results show that the multicode DS-CDMA system with SIC has demonstrated better performance than that without SIC under the multipath fading environment, while their corresponding numerical results from performance analyses are also provided for verifications. Furthermore, the coherent receiver could achieve a more satisfactory BER than the noncoherent counterpart at the expense of synchronization.

並列關鍵字

RAKE ； successive interference cancellation ； pseudonoise code tracking ； Nakagami-m fading channel ； mean time to lose lock ； multiple-access interference ； multicode DS-CDMA ； frequency-selective ； discrete automatic gain control ； Cramér–Rao lower bound ； digital delay-lock loop

參考文獻

[3] G. L. St‥uber, Principles of Mobile Communication, 2nd ed., Boston, MA: Kluwer Academic, 2001.

[4] H. B. James and P. I. Wells, “Some tropospheric scatter propagation measurements near the radio-horizon,” Proc. IRE, pp. 1336–1340, Oct. 1955.

[5] G. R. Sugar, “Some fading characteristics of regular VHF ionospheric propagation,”Proc. IRE, pp. 1432–1436, Oct. 1955.

[6] T. L. Staley, R. C. North, W. H. Ku, and J. R. Zeidler, “Performance of coherent MPSK on frequency selective slowly fading channels,” Proc. IEEE Veh. Technol. Conf., Atlanta, GA, pp. 784–788, April 1996.

[7] M. Nakagami, “The m-distribution: a general formula of intensity distribution of rapid fading,” in Statistical Method in Radio Wave Propagation, Oxford: Pergamon Press 1960, pp. 3–36.

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頻率選擇衰減通道下對展頻系統接收機之設計

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