前置編碼對於正交頻率分割多工系統使用位元負載之分析

Abstract

傳統的正交頻率分割多工系統使用離散複立葉轉換的前置編碼矩陣是被大家所廣泛的認知為前置迴旋碼單載波系統。然而，在這個系統下，位元必須一致的被指派到每個子通道中。現在我們嘗試利用前置編碼矩陣將子通道分割成若干群。接著，我們可以用不同的位元配置到每個群。

The OFDM system has been successfully applied to wireless digital communications over the past several years. It is well-known that OFDM systems suffer from the noise enhancement problem due to channel spectral nulls and the PAPR problem. Recently, a new system called SC-CP (single carrier with cyclic prefix) system is receiving growing attention as another wireless transmission technique. This is because the SC-CP system can mitigate the noise enhancement problem and it doesn’t suffer from PAPR problem. Bit-loading algorithm is a powerful technique to improve BER performance in time-invariant channel. However, this technique can’t be applied to the SC-CP system which is a special kind of precoded OFDM systems. In this thesis, we propose a precoded OFDM system which can enjoy the advantage of the bit-loading algorithm. We will study the BER performance, PAPR reduction and the implementation complexity of the transmitter in our proposed system. We also carry out some simulations in time-invariant and time-variant channels. Besides, we also compare those systems with FEC and interleaving. Our simulation results validate that our proposed system can provide better BER performance than the OFDM and the SC-CP systems.