在使用單載波之空間調變系統中，處理天線間訊號干擾及多重路徑所產生之符元間干擾為重要議題。其中使用線性等化器處理接收訊號所產生之複雜度很小，但錯誤率效能卻非常不理想。而最大概似偵測器具有最佳之錯誤率效能，然而在星座點數較大或區塊長度增加的情況，其複雜度會呈指數性地提升。為簡化其複雜度，使用樹狀搜尋之M演算法有助於減少大量運算，因此有文獻利用通道之區塊循環特性直接使用M演算法，但因通道呈衰減特性，所以此做法需保留大量分枝數以達成良好的錯誤率效能，但這會使樹狀搜尋之複雜度頗高。本篇論文提出使用前置頻域濾波器以提升其效能，透過適當地前置濾波器設計以改善等效通道，使得做樹狀搜尋時所需保留之分枝數降低；而前置濾波的部份，因利用頻域濾波器處理接收訊號，所產生之複雜度並不高，故整體複雜度相對較低。根據模擬結果顯示，本論文所提出之演算法與其他M演算法比較，在錯誤率效能相近的情況下，整體所需之複雜度下降許多。

Combating inter-antenna interference (IAI) and inter-symbol interference (ISI) caused by multipath channels is a very important issue in single-carrier spatial modulation (SC-SM) systems. Although using linear equalizers achieves a low complexity, the bit–error-rate (BER) performance is far from optimal. The maximum likelihood detector (MLD) gives the optimal BER performance; however, the complexity increases exponentially with a larger constellation size or a longer data block length. Taking advantage of the block circulant characteristic of the channel in the SC-SM systems, the M-algorithm can be directly applied to reduce the complexity of the MLD. Due to the fading channels, however, this method needs to retain a large number of branches to maintain a good BER performance, which results in a high complexity in tree search. In the thesis, we propose to precede the M-algorithm with an appropriately designed frequency-domain prefilter to improve the equivalent channel, so that the number of branches retained by the M-algorithm (and thus the complexity of tree search) can be significantly reduced. Since the signal processing and design of the prefilter are done in the frequency domain, the complexity overhead incurred by prefiltering is relatively small. Simulation results demonstrate that compared to the conventional M-algorithm, the proposed algorithm achieves the same BER performance with a considerably lower complexity

[1] S. Sugiura and L. Hanzo, “Single-RF spatial modulation requires single-carrier transmission: Frequency-domain turbo equalization for dispersive channels,” IEEE Trans. Veh. Technol., vol. 64, no. 10, pp. 4870–4875, Oct. 2015.
[2] J. Jeganathan, A. Ghrayeb, and L. Szczecinski, “Spatial modulation: Optimal detection and performance analysis,” IEEE Commun. Lett., vol. 12, no. 8, pp. 545–547, Aug. 2008.
[3] P. Yang, M. Di Renzo, Y. Xiao, S. Li, and L. Hanzo, “Design guidelines for spatial modulation,” IEEE Commun. Surv. Tuts., vol. 17, no. 1, pp. 6–26, Mar. 2015.
[4] B. Zhou, Y. Xiao, P. Yang, J. Wang, and S. Li, “Spatial modulation for single carrier wireless transmission systems,” in Proc. 6th Int. ICST Conf. Commun. Netw. China, Harbin, China, Aug. 2011.
[5] L. Xiao, D. Lilin, Y. Zhang, Y. Xiao, P. Yang, and S. Li, “A low complexity detection scheme for generalized spatial modulation aided single carrier systems,” IEEE Commun. Lett., vol. 19, no. 6, pp. 1069–1072, Jun. 2015.
[6] N. Benvenuto and S. Tomasin, “On the Comparison Between OFDM and Single Carrier Modulation with a DFE Using a Frequency-Domain Feedforward Filter,” IEEE Transactions on Communications, vol. 50, no. 6, pp. 947-955, Jun. 2002.
[7] J. J. Jia, S. J. Wang, and K. C. Lai, “Hybrid-domain sequence detector for training sequence-aided single-carrier block transmission signals,” IEEE Trans. Wireless Commun., vol. 14, no. 12, pp. 6565–6578, Dec. 2015.
[8] M. Di Renzo, H. Haas, A. Ghrayeb, S. Sugiura, and L. Hanzo, “Spatial modulation for generalized MIMO: Challenges, opportunities and implementation,” Proc. IEEE, vol. 102, no. 1, pp. 56–103, Jan. 2014.
[9] R. Y. Mesleh, H. Haas, C. W. Ahn, and S. Yun, “Spatial modulation-A new low complexity spectral efficiency enhancing technique,” in Proc. IEEE Int. Conf. Commun. Netw. China, Beijing, China, Oct. 2006
[10] R. Y. Mesleh, H. Haas, S. Sinanovic, C. W. Ahn, and S. Yun, “Spatial modulation,” IEEE Trans. Veh. Technol., vol. 57, no. 4, pp. 2228–2241, Jul. 2008.
[11] Chih-Heng Tsai,” An Equalizer for Single-Carrier Block Transmission System Using Frequency-Domain Preprocessing Combined with Tree Search” Institute of Computer and Communication Engineering National Cheng Kung University Thesis for Master of Science, July 2013.
[12] K. B. Petersen, M. S. Pedersen, “The Matrix Cookbook,” January 5, 2005.