可應用於多天線系統快速時間同步之研究

Abstract

近幾年在無線技術發展下，新一代無線通訊系統中，正交分頻多工 (Ortho- gonal Frequency Division Multiplexing, OFDM)已經逐漸變成主流核心，在一個多路徑衰減的通道中，正交分頻多工被證明能有效的對抗由多路徑衰減所帶來的不理想因素。 本論文主要提出一個可以應用在IEEE所制定的無線區域網路標準IEEE 802.11n 上之時間同步(Timing Synchronization)。其中IEEE 802.11n 所使用的方式即為多輸入多輸出正交分頻多工(Multi-Input-Multi-Output Orthogonal Frequency Division Multiplexing), MIMO-OFDM)。 本論文所提出的同步架構著重在時間同步(Timing synchronization)中。主要在試圖解決在多路徑衰減的通道中，因為通道效應的影響，在接收端所接收到的信號能量會放大或衰減，而使時間同步產生的取樣判斷上的錯誤.。以一個時脈產生22個不同相位的時序而言，提出的方法將會使最後取樣的相位與理想的相位差距三個相位內。

DUE to the explosive growth demand for wireless communications, the next-generation wireless communication systems are expected to provide ubiquitous, high-quality, high-speed, reliable, and spectrally-efficient. However, to achieve this objective, several technical challenges have to be overcome attempt to provide high-quality service in this dynamic environment [1]. Orthogonal frequency division multiplexing (OFDM), one of the multi-carrier modulation schemes, turns out to be a strong candidate for the future wideband wireless systems because of its high spectral efficiency and simplicity in equalization. However, OFDM also has its drawbacks. The notable issues of OFDM system are more sensitive to synchronization errors than single carrier system [2], [3]. Most OFDM synchronization methods have one or some of the following limitations or drawbacks: have a limited range of operation, address only one task, have a large estimation variance, lack robust sync detection capability, and require extra overheads [4]. In this work, we introduce a timing synchronization algorithm for 4*4 MIMO-OFDM systems, and try to solve the problem which the signal power will enlarge or decade cause by multi-path channel. This problem will cause sampling phase error. Assume a multiphase generator is used to generate 22 different phases between one clock cycles, the difference between ideal sampling phase and sampling phase determined by this work is 3. Ten L-STS (Legacy Short Training Sequences) are defined in the 802.11n specification, we will perform timing synchronization by used four L-STS in multi-path channel environment and seven L-STS in time variance channel environment. Half L-STS will be used in multi-path channel, and full L-STS will be used in time variance channel.