在裝置對裝置通訊網路下鄰近搜尋及自我連結建立之設計與分析

Abstract

在傳統的蜂巢式網路底下，連結的建立必須經由基地台和核心網路的幫助。假如裝置對裝置(D2D)具有相對近距離的情況下，蜂巢式網路在多節點跳躍、路由、網路負載或延遲及功率的效能上可能會比D2D連結不具效率。對於在蜂巢式網路底下自動的D2D通訊可以減輕基地台和核心網路的負載並且藉由好的直接連結，可以增強頻譜使用效率和網路吞吐量。

對有效率的D2D通訊來說，裝置必須可以追蹤它的周遭環境和尋找適合可以做連結的裝置，在論文中，我們提出了一個裝置對裝置連結建立的流程可以促使裝置建立可靠D2D的連結並且在傳送訊號時不能對蜂巢式網路造成過大的干擾。基於提出的流程及相關的訊號品質要求，假設裝置分別由泊松點過程 (PPPs)模型下產生，我們分析成功的D2D連結建立(SDLS)機率。一個精確的干擾表示式是非常複雜的，因此我們分別利用近似和上限的情況，用PPP去描述對蜂巢式使用者所造成的干擾源位置並計算相對應蜂巢式使用者的訊號與干擾加雜訊比，在這兩種情況下，SDLS機率對於傳送功率是一擬凹 (quasiconcave)函數，同時也提出二分法搜尋的上下界，這可以使我們加快演算法的收斂速度並證明在我們所搜尋的區間存在著唯一的最佳探詢訊號的功率。

Conventional cellular networks require that a link be setup through the aids of base stations and the associated core network. It is very inefficient either in terms of required multi-hop link setup, routing and other network overheads or from the viewpoint of delay and power performance if the associated physical device-to-device (D2D) link is in relatively good condition. Autonomous D2D communication as an underlay to an existing cellular network reduces the base stations (eNBs) and core network's loadings while enhancing the spectral efficiency and network throughput by taking the advantage of good direct link qualities.

For efficient D2D communications, a device must be able to track its local environment and discover suitable connecting devices within a short time span. In this thesis, we propose a D2D link setup protocol that enables a device to establish a reliable D2D link using proper radio resources while causing only tolerable interference to the underlaid cellular network. We analyze the success D2D link setup (SDLS) probability based on the proposed protocol and related signal quality requirements, assuming devices are distributed according to some two dimensional Poisson point processes (PPPs). As the exact expression for the sum interference is very complicated, we use an approximation model and an upper bound to describe the active devices' location distribution in evaluating the signal-to-noise-plus-interference ratio of a macrocellular terminal. Using either one in computing the SDLS probability, we show that it is a quasiconcave function of the device' transmit power. We apply a bisection search with the help of the derived upper and lower search bounds to accelerate the search and prove that the existence of the optimal solution.