排程技術對正交分頻多工多天線系統涵蓋範圍影響之研究

Abstract

這篇論文主要在研究如何在以正交分頻多工多天線系統(OFDM-Based Spatial Multiplexing Systems)下有效的分配子通道(Subchannel)以增加可靠涵蓋範圍(Coverage)，首先討論單一使用者的情況，我們推出在頻率選擇通道環境中之正交分頻多工多天線系統下的連結中斷機率(Link Outage Probability)之數學表示式，為了能從連結中斷機率來求得可靠涵蓋範圍的數學表示式，我們另外推出了另一個連結中斷機率的近似數學表示式。從我們的模擬分析結果中，證明了所推出的連結中斷機率與可靠涵蓋範圍之數學模型是非常精確的，此外我們也呈現了傳送與接收天線之個數、頻率選擇多樣性之程度(Degree of Frequency Selectivity)、以及路徑衰減因子(Pass Loss Exponent)是如何的在正交分頻多工多天線系統下影響連結中斷機率與可靠涵蓋範圍。 在多重使用者的環境下，我們首先把用於單一傳送接收天線正交分頻多工系統(SISO OFDM)下的公平性導向子通道分配演算法(FOSA)拓展至多重傳送接收天線正交分頻多工系統(MIMO OFDM)中，接著提出了簡易且可以增加更多可靠涵蓋範圍之涵蓋可靠度導向子通道演算法(COSA)。既然COSA可以在與FOSA差不多公平性下同時增大更多可靠涵蓋範圍，我們把重心放在SOSA演算法上，並且利用順序統計學(Order statistics)以及Glivenko- Cantelli定理推導出在使用COSA演算法下之連結可靠機率與可靠涵蓋範圍的數學表示式。模擬結果中證明了在使用COSA演算法時我們所推出的可靠涵蓋範圍之數學模型是非常精確的，此外我們也呈現了整體傳送功率、傳送與接收天線之個數、使用者數量、以及路徑衰減因子是如何的在各種不同演算法下影響頻率選擇通道環境下之可靠涵蓋範圍，同時我們也解釋了各種影響因子的物理現象。

In this thesis we investigate how to efficiently assign the subchannels to enhance the coverage performance of orthogonal frequency division multiplexing (OFDM)-based spatial multiplexing systems. For the single user case, we present an analytical formula that can evaluate the link outage probability for spatial multiplexing multi-input multi-output (MIMO)-OFDM system. We also provide another simplified approximation of the exact link outage probability that can apply to calculated the cell coverage associated a certain link outage probability. From our numerical results, we validate the accuracy of the analytical model and approximation method by simulation. We also present some results to illustrate how and to what extend the number of antennas, frequency selectivity order, and the pass loss exponent affect the link outage and the cell coverage for the spatial multiplexing MIMO-OFDM system.

In multi-user case, we first extend the fairness-oriented subcarriers assignment algorithm (FOSA) from SISO OFDM to MIMO OFDM. Next we propose another low-complexity coverage-oriented subcarriers assignment algorithm (COSA) which can achieve larger cell coverage of OFDM-based spatial multiplexing systems than FOSA. Since COSA can achieve almost the same fairness performance as FOSA and have larger cell coverage than FOSA, we focus on COSA and derive an analytical expression form for link outage probability and cell coverage reliability by means of order statistics and Glivenko- Cantelli Theorem. From our numerical results, we validate the accuracy of the analytical model and approximation method by simulations. We also present some results to illustrate how the total transmit power, the number of antennas, the number of users and pass loss exponents affect the cell coverage reliability under various subcarriers assignment algorithms for the spatial multiplexing-based MIMO-OFDM system. Explanations for this physical phenomenon are also included.