| 摘要: | 在無線細胞系統中,同頻干擾效應對於系統效能來說是一個限制的因素,區域性點對多點傳輸系統 Local Multipoint Distribution System (LMDS) 這種固定的無線傳輸系統也不例外。在 LMDS 中 下鏈通常是較高容量的,而且較窄的用戶端天線的波束也是排拒同頻干擾的一項因素,所以下鏈的同頻干擾是較嚴重的。因此對LMDS中的下鏈同頻干擾的評估是本篇論文的主旨。 LMDS操作在Ka 波段,而操作在這個頻帶範圍內具有一些限制, 像是雨衰會造成通訊品質的下降且限制無線通訊系統的傳輸路徑長度,植物的葉片也會對信號強度造成衰減並造成信號的退極化,因此在本篇論文中我們將降雨和樹葉所造成的衰減視為多餘路徑衰減的主要來源。 由於在LMDS中用戶端是使用高指向性的天線,因此在天線主波束方向上的干擾源影響較其他者嚴重,所以我們提出一個新的細胞架構來減少這些干擾源的影響。我們只改變其頻帶配置及極化交錯,所以我們可以不必在設備方面作多餘的投資而得到較好的系統效能。 In wireless cellular systems, cochannel interference is the limiting factor to system performance. Fixed wireless systems such as Local Multipoint Distribution Systems (LMDS) is no exception to this rule. In LMDS, because the downlink is usually higher-capacity and the narrow beam of subscribers’ antenna is an interference-limiting factor, the downlink interference is more serious. Consequently, assessment of cochannel interference on the downlink direction of LMDS is the subject of this thesis. LMDS is operated at Ka band, and operation in the millimeter range imposes some restrictions. Attenuation due to rainfall can cause degradation of the quality of communication and restrict the path length of radio communication systems. The attenuation caused by transmission through vegetation is another restriction, and depolarization caused by foliage is taken into consideration, too. The excess path loss considered in this thesis is mainly come from the attenuation caused by rainfall and foliage. In LMDS, the use of high-directivity antenna makes the influence of those interfering sources in the direction of the antenna’s main beam more serious than others, so we propose a new cellular architecture to try to reduce those sources. We only change the frequency allocation and polarization interleaving. In this situation, we don’t have to make extra investment in equipment and then we can get better system performance. |
