多躍式細胞系統之最佳中繼站位置設計

Abstract

近年來，IEEE 802.16e 無線都會網路(wireless metropolitan area networks, WMANs) 變得非常的受歡迎，這是因為此網路有比IEEE 802.11 無線區域網路 (wireless local area networks, WLANs) 還要大很多的覆蓋面積，然而過大的覆蓋面積，很容易受到地形和距離的影響，因而造成使用者接收到的訊號強度太低;因此為了克服這個問題，許多的文章提出了訊號轉傳的概念來解決這一方面的間題，而由於中繼站(Relay Stations, RSs) 具有轉傳訊號的功能，所以在現今的無線網路中，中繼站被廣泛地使用在其中。 在現今的文章中，中繼站通常被應用在提升細胞系統邊界使用者的訊號強度，然而在一個細胞系統中，基地台(Base Station, BS) 透過一個中繼站在去做轉傳的工作需要經過兩個傳輸程序的時間，即是一個從基地台到中繼站的時間，另一個是從中繼站到使用者的時間，因此如果這兩個傳輸程序所經過的時間被考慮進去的話，那麼增加中繼站有可能會降低整個系統的容量，所以決定一個資料的傳送是經由直接傳送或是經過轉傳可由訊號的強度或是傳送量來做選取。 在這篇論文，我們主要的研究方向是要在細胞系統裡尋找一個最佳的中繼站放置的位置，讓整個系統的容量能夠達到最高的狀態。我們考量兩個中繼站選取的方法去決定是否這個轉傳的時機是必需和正確的;一個是以訊號強度來做選取，而另一個是以傳送量來做選取的動作。在這篇論文的結果中，我們可以發現以訊號強度來做選取的方法，可能有一些中繼站放置位置的系統容量會低於沒有加中繼站的情況產生;另外以傳送量來做選取的方法，我們可發現應用此方法去 做選取能夠確保中站繼放置在任何位置都能產生不低於沒有加中繼站的情況。我們也確認了一個最佳的中繼站放置位置能夠達到最高的系統容量。此外增加中繼站的另一個優點就是能讓更多的使用者能夠達到最低的通訊可靠度，以及降低佈建成本，所以我們還做了一個研究是當中繼站被佈建在最佳的位置時，這整個細胞系統所能達到的最大覆蓋面積。

In recent years, the IEEE 802.16e wireless metropolitan area networks (WMANs) is becoming very popular. Due to larger coverage compared to the IEEE 802.11 wireless local area networks (WLAN). However, the larger coverage is easy to be influenced by terrain and distance e®ects. In order to overcome those issues, the concept of relay stations (RSs) is suggested. Relay stations are usually used to enhance the signal strength for the users close to the cell boundary. However, transmission through a relay station needs two transmission phases, i.e., one is from the base station (BS) to the relay station and the other is from relay station to mobile stations (MSs). Thus, relay may also decrease system capacity if two-phase transmission time is considered. As a result, whether or not data are transmitted by one-hop or two-hop phases should be determined based on both signal strength and throughput. In this paper, we investigate the optimal relay location aiming to maximize system capacity. We consider two relay selection rules for determining whether a two-hop transmission is necessary: signal strength-oriented and throughput-oriented. We ‾nd that the signal strength-oriented two-hop transmission may yield even lower system capacity than the one-hop transmission. Based on the throughput-oriented rule, we find that the throughput in the two-hop transmission can be higher than that in the one-hop transmission at some locations. We also identify the optimal relay location that can achieve the highest system capacity, In addition, we also investigate the maximal coverage of the radio after placing RS at the optimal location.