The main contributions of this thesis are the development of channel estimation algorithms for single antenna Systems, single input single output OFDM (SISO-OFDM) Systems, and multiple input multiple output OFDM (MIMO-OFDM) Systems:
i. We developed low complexity adaptive algorithms (VSSNLMS and M-VSSNLMS algorithms) that are robust against both slow and fast fading channel scenarios, in comparison with other algorithms employed in literatures, to implement the proposed soft iterative channel estimator for turbo equalizer base receiver for single antenna communications Systems.
ii. A faster and low complexity subspace algorithm in comparison with other employed in literatures is proposed for parametric estimation of the channel impulse response
of the proposed decision directed channel estimation method for the SISO-OFDM and MIMO-OFDM Systems.
iii. We also developed a low complexity adaptive predictor, in comparison with other available ones in literature, for implementation of the adaptive predictor module of the proposed decision directed channel estimation method proposed for the SISO- OFDM and MIMO-OFDM Systems.
iv. Lastly, the low complexity adaptive algorithm we proposed for channel estimation in single antenna communication Systems is also proposed for use and re-derived in the context of MIMO channel for implementation of the temporary channel transfer function estimator of the decision directed channel estimation method put forward for the MIMO-OFDM Systems.
All these algorithms that we proposed for the implementation of channel estimator for single antenna Systems, SISO-OFDM Systems and MIMO-OFDM Systems are confirmed to provide near optimal performance with low complexity in comparison with some other ones in literature through computer simulations. These contributions are detailed in four chapters of this thesis as summarized below.
In Chapter 3, computationally efficient iterative channel estimation for Turbo equalizer-based communication receiver employing Variable Step Size Normalized Least Mean Square (VSSNLMS) algorithm [17] and Multiple-Variable Step Size Normalized Least Mean Square (M- VSSNLMS) algorithm are proposed for single antenna wireless communication Systems. The VSSNLMS and M-VSSNLMS algorithms employed for the implementation of the iterative channel estimation is proposed in order to address the problem of slow convergence rate associated with the Least Mean Square (LMS)-based channel estimation algorithm proposed in literature for single antenna communication system. It is also our intention to put forward a less complex algorithm compared with the well known Recursive Least Square (RLS) algorithm.
In Chapter 4, Fast Data projection Method (FDPM) subspace tracking algorithm-based Channel Impulse Response Estimator is proposed for implementation of the Decision Directed Channel Estimation (DDCE) scheme for SISO-OFDM Systems. This is carried out in the context of a more realistic Fractionally Spaced-Channel Impulse Response (FS-CIR) channel model, as against the channel characterized by a Sample Spaced- Channel Impulse Response (SS)-CIR. In this chapter, we also derive a fast convergence Variable Step Size Normalized Least Square-
based predictor, with low computational complexity in comparison with other in literature, for the implementation of the CIR predictor module of the DDCE scheme.
In Chapter 5, we designed a novel iterative receiver structure for the FDPM-based Decision Directed Channel Estimation scheme for SISO-OFDM system. The iterative design is based on Turbo iterative principle. It is shown that a significant improvement in the performance can be achieved with the iterative DDCE scheme for OFDM Systems in comparison with the non- iterative scheme presented in Chapter 4.
In Chapter 6, Iterative receiver structure for FDPM-based DDCE scheme of Chapter 5 is extended to MIMO-OFDM Systems. In addition, Variable step size Normalized Least Mean Square (VSSNLMS)-based channel transfer function estimator is derived in the context of MIMO Channel, following the idea presented in Chapter 3, for the implementation of the CTF estimator module of the iterative Decision Directed Channel Estimation scheme for MIMO-OFDM Systems.
1.8 Publications
During this research work, the following conference and journal papers have been published.
1.8.1 Journal Papers
1. Olutayo O. Oyerinde and Stanley H. Mneney, “Improved Soft Iterative Channel Estimation for Turbo Equalization of Time Varying Frequency Selective Channels,”
Wireless Personal Communication Journal, vol. 52, no.2, pp. 325-340, ISSN: 0929- 6212, January 2010.
2. Olutayo O. Oyerinde and Stanley H. Mneney, “Variable Step Size Algorithms for Network Echo Cancellation,” Ubiquitous Computing and Communication (UBICC) Journal, vol. 4, no. 3, pp. 746-757, ISSN: 1992-8424, August 2009.
1.8.2 Conference Papers
1. Olutayo O. Oyerinde and Stanley H. Mneney, “Iterative Decision Directed Channel Estimation for BICM-based MIMO-OFDM Systems,” in Proceedings IEEE International Conference on Communications, South Africa, 5 pages, 23rd - 27th May 2010.
2. Olutayo O. Oyerinde and Stanley H. Mneney, “FDPM Aided Decisison Directed Channel Estimation with VSSNLMS-based Predictor for OFDM Systems,” in Proceedings IEEE International Symposium on Broadband Multimedia System and Broadcasting, Shanghai, China, 6 pages, 24th-26th March 2010.
3. Olutayo O. Oyerinde and Stanley H. Mneney, “Iterative OFDM Receiver with Decision Directed Channel Estimation,” in Proceedings of IEEE AFRICON 2009, Nairobi, Kenya, 6 pages, 23rd -25th September 2009.
4. Olutayo O. Oyerinde and Stanley H. Mneney, “Adaptive CIR Prediction of Time- Varying Channels for OFDM System,” in Proceedings of IEEE AFRICON 2009, Nairobi, Kenya, 5 pages, 23rd -25th September 2009.
5. Olutayo O. Oyerinde and Stanley H. Mneney, “Decision Directed Channel Estimation for OFDM Systems employing Fast Data Projection Method Algorithm,”
in Proceedings of IEEE International Conference on Communication (ICC), Dresden, Germany, 5 pages. 14th -18th June 2009.
6. Olutayo O. Oyerinde and Stanley H. Mneney, “Soft Iterative Decision Directed Channel Estimation for OFDM Systems employing Adaptive Predictor,” in Proceedings of IEEE 1st International Conference on Wireless Communication Society, Vehicular Technology, Information Theory and Aerospace & Electronics Systems Technology (Wireless VITAE’09), Aalborg, Denmark, pp.857-861, 17th - 20th May 2009.
7. Olutayo O. Oyerinde and Stanley H. Mneney, “Soft Input Iterative Channel Estimation for Turbo Equalization over Time Varying Frequency Selective fading Channel,” in Proceedings of South Africa Telecommunication Networks and Applications Conference (SATNAC) 2008, Wild Coast Sun, Eastern Cape Coast, South Africa, pp. 77-82, 7th-10th September, 2008.
8. Olutayo O. Oyerinde and S. H. Mneney, “Single and Multiple - Variable Step Size Normalized Least Mean Square Algorithms for Network Echo Cancellation,” in Proceedings of the 5th International Conference on Cybernetics and Information Technologies, Systems and Applications: CISTA 2008, in the context of International Multi-Conference on Engineering and Technological Innovation: IMETI 2008, pp 1- 5, Orlando, Florida, USA, 29th June - 2nd July, 2008.