跳頻多址聯接╱複頻移鍵系統的多用者檢測

Abstract

跳頻多址聯接╱複頻移鍵系統的使用者容量是取決於以下兩個主要的考量 ：跳頻的方式及接收器的結構。這二者因素所造成的影響均將在此篇論文 中予以討論。我們提出了非同步跳頻多址聯接系統的最佳分集混合器，同 時分析一個非常近似於此混合器之接收器性能。我們比較了使用隨機跳頻 方式和最佳跳頻方式的系統，而且同步和非同步系統的性能表現也一併展 示出來。另一方面，通常跳頻多址聯接╱複頻移鍵系統的多用者檢測包含 二階段；第一階段是初始的判定而第二階段則是試著解決前者所留下的不 確定性及減少同頻道干擾。在分析了使用適當分集混合方式的第一階段檢 測器性能之後，我們檢視一個第二階段檢測器的效能；它是早期被發展出 來並經我們所稍加修改的一個結構。這個複雜度適中的接收器可以消除大 部分的同頻道干擾而且對於系統使用者功率準位的變異是不太靈敏的。 The capacity of a multilevel FSK (MFSK), frequency-hopped multiple access (FHMA) system is dictated by two major design concerns: the hopping pattern and the receiver structure. This paper studies the impacts of both factors. We present a maximum likelihood (ML) diversity combiner for asynchronous FHMA system, analyzes the performance of a close approximation of the ML receiver. We compare systems using random hopping patterns and those that use a set of optimal hopping patterns. Performance between synchronous and asynchronous systems are made as well. On the other hand, a multiuser detector for an FHMA/MFSK system usually consist of two stages. The first stage makes an initial decision while the second stage tries to resolve the ambiguity and reduce the cochannel interference (CCI) left by the first stage detector. After analyze the performance of the first stage detector that uses appropriate diversity combining, we then examine the effectiveness of a second stage detector which is a modification of an earlier structure developed by Timor. This receiver is of modest complexity and is capable of removing most of the CCI. Moreover, we also find that it is insensitive to power variations of the system users.