摘要：近年來,正交分頻多工系統(OFDM)在多媒體信號通訊中扮演愈來愈重要的 角色。這是因為 OFDM 系統可以對抗來自多重路徑通道的干擾。由於直接 降頻架構的低成本優點,近來探討使用此架構來實現 OFDM 系統的研究有 愈來愈多的趨勢。雖然它們有低成本的優點,此類接收器也有不少非理想 性效應的缺點。這些缺點主要有兩項:實虛部不協調以及載波頻率位移。 如果我們在接收端沒有將這些非理想性效應加以補償,它們會對 OFDM 系 統的效能造成很大的影響。過去專家學者提出過很多資料輔助的方法來解 決這些非理想性效應的參數估測問題。但是資料輔助的方法需要用到訓練 序列而傳送訓練序列會造成頻寬的浪費。由於盲蔽估測方法俱有節省頻寬 的優點,近年來有越來越多的專家學者探討如何盲蔽估測實虛部不協調, 載波頻率位移以及通道響應的問題。本三年期計畫的目標是要提出一些盲 蔽方法來有效且準確的估測這些非理想性效應及通道響應。第一年,我們 將研究 SISO OFDM 系統中的盲蔽估測問題。第二年,我們將探討如何在 OSTBC MIMO OFDM 系統中來盲蔽估測這些系統參數。第三年,我們將研究 雙向中繼網路系統中的盲蔽估測問題。
Abstract: In recent years, the orthogonal frequency division multiplexing (OFDM) systems have been playing an increasingly important role in the transmission of multimedia signals because they are robust to multipath channels. Recently there is a lot of interest in using the direct-conversion architecture for the implementation of the OFDM systems due to its low cost. However a direct-conversion receiver suffers from many non-idealities. The two main non-ideal effects are in-phase quadrature-phase (IQ) imbalance and carrier frequency offset (CFO). If these effects are not properly compensated at the receiver, the system can suffer from severe intersymbol interference and the system performance degrades significantly. In the past, many data-aided algorithms have been introduced for the estimation and compensation of these non-idealities. However in these data-aided methods, there is a need to transmit training sequences and as a result, there is a loss of bandwidth. Recently there is a growing interest in blind estimation of IQ imbalance, CFO and channel impulse response due to its bandwidth efficiency. It is the goal of this three-year project to develop efficient and accurate blind methods for the joint estimation of these non-idealities and channel response. In this first year, we will address the blind estimation problems in SISO OFDM systems. In the second year, we will explore these issues in OSTBC (orthogonally space-time block coded) MIMO OFDM systems. In the third year, we will study the blind estimation of system parameters in two-way relay networks (TWRN).