基於不規則重覆累加碼之最佳速率分集取捨時空編碼

Optimal Rate-Diversity Tradeoff Space-Time Codes Based on Irregular Repeat-Accumulate Codes

邱文賢(Wen-Hsien Chiu)

指導教授 ： 蘇炫榮

國立臺灣大學/電機資訊學院/電信工程學研究所/碩士(2006年)

https://doi.org/10.6342/NTU.2006.01205

摘要

適用於不同移動速度系統下之多輸入多輸出(MIMO)智慧貪婪式編碼的設計是一開放性的課題。基於Lu和Kumar所提出可在某分集增益下允許傳送最大速率的時空編碼，我們進一步提出新的最佳速率分集取捨(Optimal rate-diversity tradeoff)的時空碼。事實上，這些新的編碼本身是不規則重複累加碼(Irregular repeat-accumulate code)的一種，所以當通道變化增快時，此編碼擁有卓越的能力去利用額外的時間分集增益。

本文首先探討新提出的最大秩距累加碼(Maximal rank-distance accumulate code)。根據此編碼的因子圖，我們可以採用渦輪式多輸入多輸出接收器，並以有效率的信息傳遞演算法作解碼。接著我們探討適應性和積演算法，以解決在高速率編碼系統下解碼所產生的收斂性問題。

經由程式模擬，在快速變化通道下此編碼利用時間分集增益的能力和碼長呈正向關係。但此編碼碼長即為建構時所考慮的場中之不可分解多項式的階數。因此，要增大碼長長度必須在相對應場中大量搜尋更高階的不可分解多項式。基於此設計上的困難，我們進而提出另一套新的串接交錯式最大秩距累加碼 (Cascade-Interleave maximal rank-distance accumulate code)。此設計優點在於可以輕易地增長碼長，更加適用於在通道變化快速的狀況。

最後，基於前面所提的編碼架構，我們提出一個廣義完整的時空編碼結構，可擴展至一般常用的傳輸星座圖，例如，脈衝振幅調變(PAM)、正交振幅調變(QAM)、2k-相位鍵移調變(2k -PSK)。

關鍵字

時空編碼 ； 速率分集取捨 ； 不規則重覆累加碼 ； 最大秩距累加碼 ； 串接交錯式最大秩距累加碼

並列摘要

The design of smart-greedy space-time (ST) codes for multiple-input multiple-output (MIMO) wireless systems in a variety of mobility conditions is an open problem of
great interest. Motivated by the algebraic space-time constructions of Lu and Kumar, which achieve the transmit diversity gain and permit the maximum transmission rate
possible, we propose an algebraic method for constructing optimal ST codes in the sense of achieving the rate-diversity tradeoff. We also show that our codes belong to a
class of irregular repeat-accumulate codes which can provide the potential of seizing possible temporal diversity. In this thesis, we first present new space-time codes using maximal rank-distance accumulate (MRDA) codes whose encoder consists of a repeater, an edge interleaver, a single parity-check encoder, and a simple accumulator.
Based upon their factor graph representations, we employ efficient massage-passing algorithms on the combined graph of a turbo MIMO receiver composed of an inner MIMO detector and an outer MRDA decoder. We show that for rate-1 MRDA
codes, the well-known sum-product algorithm suffices. However, it does not work for high rate MRDA codes. The convergence problems are solved by introducing the
modification of the code structure and the adaptive sum-product algorithm.
From the simulation results, more temporal diversity can be obtained in fast fading channels as the block size increases. The main difficulty in increasing the block size of MRDA codes is that the block size T is the degree of primitive polynomial such that designing codes of large T needs inevitable exhaustive search. Without a exhaustive
search for primitive polynomial with large degree, a large size scheme called cascade-interleave maximal rank-distance accumulate (CIMRDA) codes is proposed.
Furthermore, based on the binary (CI)MRDA codes, a generalized unified construction which yields ST codes over commonly used constellations such as PAM, QAM, 2k-PSK is discussed.

並列關鍵字

space-time coding ； rate-diversity tradeoff ； irregular repeat-accumulate code ； maximal rank-distance accumulate code ； cascade-interleave maximal rank-distance accumulate code

參考文獻

[1] S. M. Alamouti, “A simple transmit diversity technique for wireless communication,

” IEEE J. Selected Areas in Communication, vol. 16, no. 8, pp. 1451-1458,

Oct. 1998.

[2] E. Gabidulin, “Theory of codes with maximum rank distance,” Probl. Inform.

Transm., vol. 21, pp. 3-16, Jan-Mar 1985.