IEEE 802.16e OFDMA 多輸入輸出通道估測技術之探討與數位訊號處理器實現

Abstract

正交分頻多重進接(OFDMA)技術近來在行動環境中廣受注目且已經應用在許多數位通訊應用中。如果利用多通道傳輸(MIMO)更可提高其傳輸效率以及抵抗通道衰減的能力。本篇論文介紹IEEE 802.16e正交分頻多工存取(OFDMA)裡，多通道傳輸通道估計的問題、演算法、分析、以及實作方面的議題。 在通道估測當中，我們實做了兩個方法並去比較其效能。第一個是線性內插，首先我們使用最小平方差的估測器來估計在導訊上的通道頻率響應，之後我們分別在頻域以及時域上使用線性內插法來得到資料載波上的平率響應。第二個方法是 Wiener filter，由於此方法需要知道導訊載波以及資料載波通道的互相關，因此第一步是先用線性內插求得資料載波上的頻率響應，之後利用此結果去估測我們需要的互相關。最後我們利用其互相關以及導訊載波頻率響應的自相關求得Wiener filter在各個導訊載波的權重，以求得資料載波上更精確的頻率響應。其中Wiener filter的準確度和我們統計的通道範圍有關，因此對於不同的通道範圍我們也做了模擬。 在模擬當中，我們先在AWGN通道上驗證我們的模擬模型，然後再放置於多重路徑的SUI-2和SUI-3通道上模擬。 為了增進程式在數位處理器上的實行效率，我們將原始的浮點運算C程式修改為定點運算的程式版本。並做模擬以觀察其效能。 在本篇論文中，我們首先簡介IEEE802.16e OFDMA上行以及下行多通道傳輸的標準機制，以及各種通道估測的技術。接著是模擬多通道傳輸上使用不同通道估測技術的方式，最後介紹DSP的實現環境以及定點數的模擬結果。

OFDMA (orthogonal frequency division multiple access) technique has drawn much interest recently in the mobile transmission environment and been successfully applied to a wide variety in the mobile transmission environment and been successfully applied to a wide variety of digital communications applications over the past several years. If we applied MIMO (multiple input and multiple output) technique it can enhance the performance of the transmission and the capability of the resistance the channel fading. In this thesis, we introduce the MIMO channel estimation problems, algorithms, analyses and implementation issues for IEEE 802.16e OFDMA PHY system. In the channel estimation, we have implemented two methods to compare the performance. The first is linear interpolation. First we use LS estimator to estimate the channel response on pilot subcarriers, and then we use linear interpolation in time domain and frequency domain separately to get the frequency response on data subcarriers. The second method is Wiener filter. Because of using this method we need to know the cross-correlation of pilot and data subcarriers’ channel responses, the first step is using the linear interpolation to get the frequency responses on data subcarriers and then using this result to estimate the cross-correlation we want. Finally we use the cross-correlation and the autocorrelation of pilot subcarrier channel responses to get the weight of pilot subcarriers, and get the more accurate channel response on data subcarriers. Meanwhile, the accuracy of Wiener filter is related to the rang of channel responses we use to average, so we also simulate in different channel range. In the simulation, we verify our simulation model on AWGN channel and then do the simulation on SUI-2 and SUI-3 multipath channel. In order to increase the efficiency on DSP, we rewrite the floating-point C program to fixed-point version, and do the simulation to see the performance. In the thesis, we first introduce the standard of the IEEE 802.16e OFDMA MIMO transmission and variant channel estimation methods. Then we simulate MIMO transmission using different channel estimation techniques. Finally we introduce the DSP implementation environment and fixed-point simulation result.