具中繼站輔助之4G行動通訊系統設計

Abstract

4G 系統需要具中繼站(relays)的網路架構以增加通訊維度、提高傳輸率與頻譜效率。除 外，中繼站亦能縮短用戶與其接取點(access station)的距離，減低傳播損失(propagation loss)及遮敝(shadowing)效應，進而減少手機的電池消耗，亦可提供較平均的數據含蓋範 圍(uniform data-rate coverage )；在現有的3G 系統中，細胞邊緣的用戶僅能使用較低的 傳輸速率。另外，設計4G 系統使其具有與3G 一樣的細胞含蓋範圍(cell coverage)是重 要的考量，太小的含蓋範圍將造成太頻繁的換手(hand-off)，降低系統品質。利用傳統的 網路架構，因高傳輸率的關係，4G 的含蓋範圍勢必縮小。 目前IEEE 802.16j 已針對如何在IEEE 802.16e 的系統中使用中繼站訂定規格；重點 在於不改變現有手機規格的條件下，設計完整可行MAC 協定，預定可在2008 年中完成。 然而，如何在實際系統中佈放中繼站、如何選擇中繼站路徑(relay path)、如何善用中繼 站所提供的Cooperative Communication 機會以達到最佳系統品質等等卻仍是未解的議 題，本計畫之目標即試著針對這些重要議題提出解答，包括中繼站的最佳佈放設計，中 繼站最佳路徑選擇及中繼器系統的線性預編碼器設計等。

Relay-assisted cellular architecture is an important enabling technology for 4G systems to increase degree-of-freedom, user throughput, and spectral efficiency. Use of relay stations can also shorten the distance between a mobile station and its serving station that leads to a reduced path-loss and effects of shadowing; in turns, it provides a more uniform data coverage and saves the transmit power of the mobile stations. Currently, IEEE 802.6j is finishing the specification of relay operations within the existing IEEE 802.16e systems: a complete set of MAC protocol has been defined under the assumption of no change in the mobile stations. Nevertheless, the important issues such as how to deploy the relay stations in practical systems to achieve the best performance, how to select the best relay path for a mobile station, and how to best utilize the cooperative communication opportunity inherent in the relay-assisted network are still remained unsolved. The project aims to provide answers for these important issues.