應用於正交頻分多工與正交頻分多重存取系統之頻域預編碼技術

Abstract

因為提供了好的頻譜緊密度及能有效提供頻率分集能力，頻域預編碼式正交分頻多工與正交分頻多重存取系統是有效率的方波成形正交分頻多工與正交分頻多重存取系統。本論文旨在更進一步地探討頻域預編碼式正交分頻多工與正交分頻多重存取系統。在本論文的第一部分中，我們針對使用交織子載波分配之正交分頻多重存取系統與零插入正交分頻多工系統做探討，並提出兩種新的頻域預編編碼器，以用來改善頻譜緊密度與降低實現複雜度。明確地說，藉由最小化統治性頻譜係數，本研究建構出一可提供更高頻譜緊密度之相關性預編碼器。此外，我們也提出一多階式頻域預編碼技術以建構出一可提供f−2L−2 速度衰減之頻譜旁波並具有低實現複雜度之正交式預編碼器。此新正交式預編碼器建構之正交分頻多重存取信號或零插入正交分頻多工信號和原正交式預編碼器建構之正交分頻多重存取信號或零插入正交分頻多工信號有一樣的頻譜但只需要較低的實現複雜度。在本論文的第二部分中，我們提出了一種針對使用消除子載波之正交分頻多重存取系統的頻譜預編碼技術。在使用消除子載波之正交分頻多重存取系統中，分配給用戶的子載波被分為兩類，即資料子載波和消除子載波。資料子載波被用於發送資料符元而消除子載波被用於發送預編碼的符元，並賦予傳送之正交分頻多重存取信號非常小的功率頻譜的旁瓣衰減。我們設計了用於此系統之頻譜預編碼器並分析了用在消除子載波上的平均冗餘能量。在消除子載波的數量是固定的狀況下，所提出之頻譜預編碼式使用消除子載波之正交分頻多重存取信號可提供與現有的使用消除子載波之正交分頻多重存取信號等量的功率譜緊密度，同時消耗同等或更小的平均冗餘能量在消除子載波上。

Spectrally precoded orthogonal frequency-division multiplexing (OFDM) and its multiple access extension (OFDMA) are useful rectangularly pulsed OFDM and OFDMA signaling formats for they exploit high spectral compactness and frequency diversity characteristics. This thesis aims at exploring more on spectrally precoded OFDM and OFDMA. In the first part of the thesis, two new spectral precoders of the largest precoding rate are developed in order to provide improved spectral compactness and reduce implementation complexity, respectively, for OFDMA using cyclic prefix and interleaved subcarrier allocation (IOFDMA) and OFDM using zero padding (ZP-OFDM). Specifically, a new correlative precoder is developed and shown to minimize the dominant spectral coefficient among all correlative precoders of the largest precoding rate and thus can construct IOFDMA and ZP-OFDM signals providing extremely high spectral compactness. Besides, a multiple-stage spectral precoding technique is proposed to construct low-complexity orthogonally precoded IOFDMA and ZP-OFDM with power spectral sidelobes decaying as f^{-2L-2} for L>1, where L is the number of stages. The corresponding orthogonally precoded IOFDMA and ZP-OFDM signals conveying independent zero-mean data are respectively shown to provide the same power spectrum as existing orthogonally precoded IOFDMA and ZP-OFDM signals of the largest precoding rate, while requiring much less complexity. In the second part of this thesis, the cancellation-subcarrier-based (CS-based) spectral precoding scheme is proposed for OFDMA. In the scheme, the subcarriers allocated to a user are divided into two parts, namely, data subcarriers and cancellation subcarriers. The data subcarriers are used to transmit data symbols and the cancellation subcarriers are used to transmit precoded symbols and endow the resulting OFDMA signals with extremely small power spectral sidelobes decaying as f^{-2L-2} for L>1. When the number of cancellation subcarriers is assigned, the proposed CS-based spectrally precoded OFDMA signals are shown to provide comparable power spectral compactness to existing CS-based OFDMA signals while giving comparable or much smaller average redundant power on cancellation subcarriers.