基於使用者移動資訊之跨層無線快取設計

Abstract

如今，行動載具數量的快速增長和網絡基礎建設如基地台密度的增加正在發生。攀升的存取速率往往會導致行動網絡回載線路的擁塞。因此，基地台級別的無線快取設置被提出以減輕回載線路負擔。此外，由於基地台數量的增加，協調基地台間干擾之技術的重要性也逐漸增加。多點協作（Cooperative Multipoint Operation）被視為一種有效的干擾協調方式，其可動態協調多個基地台進行傳輸和接收。 多點協作將基地台間的交叉干擾轉換為有用信號，提高網絡利用率，從而提高用戶的整體服務質量，效果對位於基地台服務區域邊緣的用戶尤為明顯。但是，多點協作的實作將造成大量回載流量。通過在基地台無線快取儲存資料，多點協作將享有改善的通信質量而同時不對回載造成沈重負擔。本論文提出了基於使用者移動資訊之跨層快取設計，利用用戶移動資訊以估測當下不同檔案之受歡迎度並基於估側之檔案受歡迎度實行快取內容擺置。本快取內容擺置旨在最小化傳輸功率和回載流量消耗。由於考慮了用戶移動性，所提出的算法進一步提高了基地台無線快取之命中率，從而降低了整個系統的功率和回程消耗。

These days we are witnessing the rapid growth in the number of mobile devices and the increased densification of network infrastructure. Explosion of access rates tends to cause the congestion in the backhaul of wireless networks. Therefore, wireless caching at base station level has been proposed to relieve the burden on backhaul. Also, due to the growing number of base stations, techniques leverageing on the inter-cell interference has gained support. Cooperative Multipoint Operations (CoMP), seen as a promising way for interference mitigation, dynamically coordinate multiple geographically separate base stations for transmission and reception. CoMP turns the crosslink interference into useful signals, improve the utilization of the network, and thus raise the overall quality for users, especially users at cell edges. However, the implementation of CoMP sets a strict backhaul requirement. By caching a portion of popular data at base stations, cache-induced CoMP has been proposed, enjoying the improved communication quality without taxing the backhaul links. With the knowledge of users mobility, the variations in content popularity from time to time are captured. We then proposed a user-mobility-aware cross-layer design of cache content based on the estimated content popularity. The cache design aims at minimizing the transmit power and backhaul consumption. Due to the consideration of user mobility, the proposed algorithm further improves the hit rate of base station cache and thus lowers the power and backhaul consumption of the whole system.