OFDM無線網路之合作通訊---子計畫三：合作式正交分頻多工系統之空時編解碼與訊號處理(I)

Abstract

在此研究之中，針對正交分頻多工(orthogonal frequency division multiplexing, OFDM) 通訊系統，我們將設計與探討合作式通訊在快速衰減 通道中(fast fading channels)，不同合作模式下的非同步(non-coherent)通 道容量、通道碼編碼，與同時通道估計，符碼檢測與合作式空時碼解碼(Joint channel estimation, symbol detection and cooperative space-time channel decoding)的訊號處理機制。 在無線區域網路的帶動下，都會型寬頻行動通訊網路的研發與設計正快 速的在發展中。行動寬頻無線數據通訊是繼無線區域網路之後的重要通訊發展 里程碑。他最重要的目的是要讓使用者無論是在街上、汽車上或是在火車上等 各地方，都可以隨時享受寬頻上網之服務。要使得此項概念得以實現，則行動 寬頻無線系統在實體層的通訊技術上要面對諸如高速移動通訊、低接收端訊號 雜訊比與高通訊可靠度之嚴厲挑戰。而克服此諸多物理限制條件的有效方式， 除了借助多輸入與輸出天線(multiple input multiple output, MIMO, antennas)技術 的輔助外，更可藉由中繼式(relay)或合作(cooperative)通訊來增加訊號的接收品 質，通道容量與通訊距離。因此針對MIMO OFDM 在快速衰減通道環境下， 本計畫要探討如何藉由合作式通訊來實質的增加系統之通訊容量。如何編碼以 達成合作式通訊所賦予的空時通道容量。以及從信號處理層面上，特別是當使 用者在高速移動與訊號強度大幅衰減的情下，如何經由高適應性的訊號處理機 制來設計合作式通訊的接收機。 在此目標與原則下本計畫分為三個來執行步驟。首先我們將從通道容量 的角度來探討在來源端、目的端與中繼端均未知通道係數的情形下，非同步 (noncoherent)合作式通訊的可得通道容量與其受通道衰減速度(fading speed)與 通道估測誤差之影響。第二部份將著重在設計一個適用於快速衰減通道的合作 式通道編碼機制，並分析其可達成之通道容量與通訊可靠度。而第三部份則將 發展在快速衰減通道中的合作式同時通道追蹤，符碼檢測與通道解碼機制。目 標是希望找出在快速衰減通道中可逼近非同步合作式通訊通道容量的接收機設 計方式。

In this research, we will investigate, for the orthogonal frequency division multiplexing (OFDM) systems, the non-coherent channel capacity, effective coding schemes and the corresponding signal processing methods of joint channel estimation, symbol detection and channel decoding for cooperative communications in fast fading channels. With the great success of wireless local network, mobile broadband wireless communications emerge as the next milestone towards ubiquitous wireless communications. The goal of this ubiquitous wireless communication is to provide broadband wireless access to users almost anytime and everywhere, whether they are walking on a street, driving on a highway or even taking high speed strains. To realize this concept, the design of physical layer faces great challenges to support communications under high speed fading, low signal to noise ratio and extended transmission ranges. To overcome these many physical limitations, in addition to the use of multiple input and multiple output (MIMO) antennas, one can further resort to relay or cooperative communications to improve the quality of received signal, the effective system channel capacity and the transmission range. In view of the importance of cooperative communications to the success of ubiquitous wireless communications, in this research we propose to investigate the available noncoherent capacity of cooperative communications, the corresponding space-time channel coding schemes as well as the effective adaptive signal processing methods to achieve the noncoherent cooperative channel capacity in fast fading environments. The entire project is partitioned into three main execution phases. First we will study the noncoherent capacity for various types of cooperative transmission methods in fading channels and investigate the effects of estimation errors on the achievable cooperative channel capacity. Using this capacity study as a design guideline, in the second stage, we will search for possible space-time coding schemes that can potentially approximate the noncoherent cooperative channel capacity. Finally, in the third part of this research, we will develop effective adaptive signal processing schemes for joint channel estimation, symbol detection and cooperative space-time decoding in fast fading environments, aiming at characterizing the essential design guidelines for cooperative receivers that can approximate the noncoherent capacity promised by cooperative communications.