國立臺灣大學電信工程學研究所陳光禎2006-07-262018-07-052006-07-262018-07-052003-07-31http://ntur.lib.ntu.edu.tw//handle/246246/20259在後三代的行動通訊系統中，主要的 任務是藉由更有效率的使用有限的頻 寬，以提供比第三代行動通訊系統 (IMT-2000)更大量、更高品質的多媒 體資訊傳輸。另外，透過可程式化的 通訊系統設計，使得後三代的通訊系 統不但能與其它世代的行動電話相通 訊，更能與其它無線網路系統（例如： 無線區域網路IEEE 802.11a, IEEE 802.11g）或是無線個人通訊系統（例 如：藍芽通訊系統等）相連接，以實 現個人全域通訊系統。 在第一年的計畫中，藉由保持頻域上 不同使用者的訊號正交來避免使用者 之間訊號的干擾（MAI，multiple access interference） [2]；以及學習正交頻域 多工（OFDM）避免相鄰訊號干擾 （ISI，inter-symbol interference）的方 法，我們首先提出一個既無多人訊號 干擾，也無相鄰訊號干擾的一個多人 通訊系統（ FDOMC-IT ， frequency-domain orthogonal multiuser communications with inverse transformation）。這個多人的通訊系統 適用於非同步傳輸（ asynchronous transmission）的情況，並且適用於真 實的選頻衰退通道（frequency-selective slowly fading channels）中。更值得一 提的是，這個通訊系統最佳解調的複 雜度，無視於多人通訊與選頻衰退通 道的情況， 跟單人點對點 （point-to-point）的傳輸系統在最簡單 的通道中的最佳解調的複雜度一樣 低。此外，我們進一步的提出一個能 充份使用選頻通道（frequency-selective channels）的相異增益（diversity gain） 的通訊系統（ FDOMC-DS ， frequency-domain orthogonal multiuser communications with direct spreading） 來改進因為處於衰退通道（ fading channels）的系統效能。這兩個提出的 通訊系統不但複雜度低、製造的成本 低，更能提供可變資訊傳輸量的服 務，使得它們成為後三代通訊系統中 的最佳後選者。 我們還更進一步的根據最大事後機率 的規則（ maximal a posteriori probability），設計出最佳效能的時序估 測法（timing estimation）。這個時序估 測法考慮到了在選頻衰退通道中所可 能產生的相鄰訊號間的干擾，並且有 效的利用選頻通道的相異增益來正確 地估計訊號的時序。更值得一提的 是，這個估測法不需要知道選頻衰退 通道的資訊即可操作。我們不但用數 學分析的方法，找出此估測法有效的 充份條件，更以實驗數據來驗證此估 測法的良好表現。最後，我們還推導 出不需要訊號資訊即可估計的設計。 這個時序估測法考慮到了真實通道上 的各種複雜問題，因此可適用於許多 真實的通訊系統的設計中。 藉由我們提出的通訊系統以及其所需 的時序估測法，我們完成了絕大部份 的系統設計。而這些設計的良好特性 （例如其高效能與低複雜度）使得後 三代的行動通訊系統的設計得以完 成。In the communications systems beyond the third generation (B3G) mobile communications, the primary concept leads to develop the efficiently utilization of spectrum to provide the higher data rate services than IMT-2000 and to develop the programmable systems adaptive to multiple communications systems, such as the wide-band CDMA in IMT-2000, OFDM in IEEE 802.11a [1] and IEEE 802.11g, the Bluetooth technologies. In the first year of the project, by inheriting the properties of the frequency-domain approach [2] to avoid MAI in the asynchronous multiuser communications and sharing the rationale behind OFDM systems to mitigate ISI, we propose an asynchronous multiuser communications system (i.e. the frequency-domain orthogonal multiuser communications with inverse transformation (FDOMC-IT)) over frequency-selective slowly fading channels such that the optimal demodulation with similar complexity to point-to-point communications is possible. In addition, by spreading the symbol energies to the whole transmission frequency band, we further introduce another asynchronous multiuser communications system (i.e. the frequency-domain orthogonal multiuser communications with direct spreading (FDOMC-DS)) to utilize the frequency diversity gain. These proposed systems not only mitigate MAI and ISI efficiently with simple complexity but also are flexible for variable rates transmission to suggest their applications to practical multimedia services. Applying the composite hypothesis testing procedure, we further introduce the maximum a posteriori probability (MAP) symbol synchronization in the wireless communications systems with statistical channel information over frequency-selective slowly fading channels. This proposed estimation takes the presence of interference due to frequency-selective channels into account and efficiently utilizes the inherited frequency-diversity to combat the channel fading impairment. By mathematical analysis, we prove the fundamental condition to have a consistent symbol synchronizer over frequency-selective slowly fading channels when the channel impulse response is unknown. We further conduct simulations to justify its performance considering the practical implementation with a finite number of timing candidates and extend its applications to the case without training symbols. This proposed timing estimation considers more generalized scenarios with feasible complexity and therefore could be extensively applied in many practical communications systems. With the introduction of the frequency-domain orthogonal multiuser communications systems (FDOMC) and the optimal timing estimation over frequency-selective slowly fading channels, it is promised to design the high-rate B3G systems for multi-media services with simple complexity.application/pdf242513 bytesapplication/pdfzh-TW國立臺灣大學電信工程學研究所後三代行動通訊系統頻域 正交多工通訊系統最佳時序估測選頻衰退通道B3GFDOMCOptimal Timing Estimationand Frequency-selective slowly fading channelsreporthttp://ntur.lib.ntu.edu.tw/bitstream/246246/20259/1/912213E002102.pdf