多通道隨機接取之設計與分析：透過隨機幾何之方法

Design and Analysis of Multi-Channel Random Access: A Stochastic Geometry Approach

高靖越(Ching-Yueh Kao)

指導教授 ： 陳光禎

國立臺灣大學/電機資訊學院/電信工程學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.00909

摘要

在這份論文中，我們研究使用者在多個正交頻率通道環境下之分散式無線隨意網路中的效能，並提出合適的隨機接取策略。在這類問題中，無線網路的空間分布特性通常是被忽略的；而我們透過來自隨機幾何理論的數學工具，對於這樣的問題推導出了其效能指標的解析解。藉由賽局理論的觀點，我們建構了具有利己特性、在網路中共享頻譜資源之使用者的互動模型；並且，我們將這樣情境下的效能結果，與當網路中具有一特定中央控管者或是當使用者具有合作性時之效能解析解進行比較。此外，我們也對利用通道旁消息於接取決策之影響進行探討。其中，我們發現若傳送端擁有通道狀態資訊，通道的多樣性可以被利用，並將有助於使用者效能之提升；但是，當使用者的密度高，並且使用者知道所有通道的可用性時，效能反而會因此降低，也就是產生了類似布雷斯悖論的現象。最後，我們提出幾個能更進一步提升網路效能的機制。藉著利用時域上的資源，我們提出一個接取控制方法以減輕高使用者密度時的干擾問題。另一方面，在無線電裝置具有同時接取多個通道的能力、並使用者密度低時，可透過最大比率合成來利用頻率之多樣性以增進效能。

關鍵字

多通道 ； 隨機接取 ； 無線隨意網路 ； 隨機幾何 ； 賽局理論 ； 通道旁消息

並列摘要

In this thesis, we study the performance of and devise appropriate random access strategies for users in a decentralized wireless ad hoc network operating on multiple orthogonal frequency channels. The spatial factor of such problems which is still lack of study is considered with the help of tools from stochastic geometry, from which we derived closed-form expressions for performance metric. The interactions between selfish users sharing the radio resources are modeled with a game-theoretic point of view, and the performance are compared with that in the case when there's a central entity or when the users are cooperative, where we also provide explicit characterizations. The impacts of utilizing channel side information when making access decisions are also explored, where with local channel state information (CSI) available at the transmitter, channel diversity can be exploited and user performance can be improved; but when channel availability information are known by users, a Braess-like paradox, where when more information is provided the performance however degrades, can occur when the user density of the network is high. Finally, mechanisms that may further improve the network performance are introduced. Taking advantage of the time domain resource, an access barring method is proposed to alleviate the interference problem with high user density. On the other hand, frequency diversity can be exploited at low user density with Maximal Ratio Combining (MRC) to improve the performance when the radio devices are capable of accessing multiple channels simultaneously.

並列關鍵字

Multiple channels ； random access ； wireless ad hoc networks ； stochastic geometry ； game theory ； channel side information

參考文獻

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