單載波適應性調變系統中模式邊界值之決定

Abstract

在有衰減變化的通道(fading channel)環境下，適應性調變是一種能有效改善頻寬效率的技術。本論文中，討論根據不同的訊雜比(SNR)來變化使用的調變模式。其中模式邊界(switching level)的決定是影響整個系統效能的一個重要關鍵。我們將先針對平坦衰落通道(flat fading channel),討論幾種不同的決定模式邊界的方法，並分析比較他們的優劣。 我們會介紹IEEE 802.16a無線都會網路中單載波傳輸部分的實體層。適應性調變技術將被使用在802.16a系統中。將原先的模式邊界加上適當的調整後，新的模式邊界便可用於多重路徑衰落通道 (multi-path fading channel)。

Adaptive modulation is a powerful technique to improve the bandwidth efficiency over a fading channel. In this thesis, adaptation of modulation mode according to different SNR condition is considered. In such a communication system, determination of the switching levels between modulation modes is very important because it makes a great impact on the system performance. Several methods to determine the switching level in flat fading channel are discussed in this thesis, each having its own advantages and disadvantages. The switching level optimization algorithms are used in 802.16a system. Considering the performance degradation introduced by the multi-path effect, the switching levels are adjusted by adding some suitable margins.