載波干涉編碼多載波碼域多工應用於各式上傳系統之研究

Carrier-Interferometry Coded Multi-Carrier CDMA in Various Uplink Scenarios

林昱蓮(Yu-Lien Lin)

指導教授 ： 蘇育德

國立交通大學/電機學院/電信工程系所/碩士(2018年)

摘要

本論文研究使用載波干涉編碼(Carrier-Interferometry Code)多載波碼域多工(Multi-Carrier Code Division Multiple Access)的傳收系統架構和性能分析。該系統可適用於上行傳輸及下行傳輸，惟本文只探討上行傳輸之情境。由於長度為N 之載波干涉碼可產生 2N 組載波干涉碼，載波干涉碼之間具有偽正交的互相關(Cross Correlation)特性，並且它對序列長度沒有限制，故非常適合用於過載(Overloaded)多使用者系統。也因此，我們設定系統過載率為200％，可允許K 個用戶同時傳輸，亦可讓單個用戶平行傳送K 個數據流，展頻後的符元載在N (N=K/2) 個正交子載波上。我們根據傳送端通道狀態信息(Channel State Information at the transmitter, CSI-T)之有無將系統分為常規系統及預編碼系統。常規系統中我們推導多種向度合併(diversity-combining)法則並進行性能分析。在本文研究的各種向度組合策略中，軟性最小均方誤差(soft-minimum mean square error)的方式雖有最佳性能卻有較高的計算複雜度。預編碼系統可利用CSI-T 對子載波
做適當的功率分配(Power allocation)來改善性能。CSI-T 亦可用來做資源分配(resource allocation)，避免產生嚴重衰減而提升性能。我們發現，只要簡單的CSI 將子載波分成兩類即可獲致相當大的改善。傳送端的資源與功率分配加上接收端的遞迴式軟性最小均方誤差向度合併與干擾消除可提供相當優良的系統效能表現。
最後，我們考慮兩種通道估計法，比較兩者的均方誤差表現並推導了有考慮CSI 誤差的信號偵測架構。另外，我們也研究使用軟性判決反饋(soft-decision feedback)作為偽前導信號來增加通道估計精確度的效果，並提出一個停走(stop-and-go)準則作為是否反饋之依據，此方法能避免誤差傳播並得到更好的性能。

關鍵字

載波干涉編碼 ； 多載波碼域多工 ； 軟性最小均方誤差 ； 功率分配 ； 軟性判決反饋

並列摘要

This thesis studies the architecture and performance of a multi-carrier code division multiple access (MC-CDMA) system using carrier-interferometry (CI) sequences. The
system is overloaded by allowing K users to transmit their own data streams, or, a single user to transmit K data streams over N < K orthogonal sub-carriers or time-frequency units. The overloaded rate is set to be 200% in our simulation. CI sequences are selected because of their outstanding cross-correlation property, and it does not impose a constraint on the sequence length. Our emphasis is on analyzing the performance of different multi-user detectors with different power allocation schemes in such an overloaded system. Also, resource allocation is suggested to improve the performance. Among those
diversity combining strategies introduced in this thesis, the soft minimum-mean-square error MUD is the best tradeoff between performance and computational complexity.
In the second stage of this thesis, the receiver takes the pilot-assisted channel estimation structure and imperfect channel state information (CSI) into account. We also
investigate the effect of using soft decision feedback as pseudo-pilots for enhancing channel estimation accuracy. Numerical results are provided to quantify the improvements brought about by CSI awareness and decision feedback aided channel estimation.

並列關鍵字

carrier-interferometry sequences ； multi-carrier code division multiple access ； overloaded system ； soft minimum mean- square-error ； power allocation ； soft-decision feedback

參考文獻

[1] Y. Saito, et al., “Non-orthogonal multiple access (NOMA) for future radio access,” in Proc. IEEE VTC Spring 2013, pp. 1-5, Jun. 2013.

[2] P. Li, L. Liu, K. Wu and W. K. Leung, “Interleave division multiple access,” IEEE Trans. Wireless Commun. ,vol. 5, no. 4, pp. 938-947, Apr. 2006.

[3] R. Hoshyar, F. P. Wathan, and R. Tafazolli, “Novel low-density signature for synchronous CDMA systems over AWGN channel,” IEEE Trans. Sig. Proc., vol. 56, no.

4,pp. 1616-1626, Apr. 2008.

[4] N. Yee, J. P. Linnartz, and G. Fettweis, “Multi-carrier CDMA in indoor wireless radio networks,” in Proc. IEEE Int. Symp. Pers., Indoor, Mobile Radio Commun.,