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Abstract This thesis discusses channel estimation process in wireless communications systems; our main concerns are on channel estimation techniques based on the superimposed pilots, because these techniques increase the spectral efficiency of the communication systems compared to traditional techniques that are usually based on pilot signals transmission. Our main contribution in this thesis are as follows: firstly, we introduce a joint channel estimation algorithm for single-input-single-output (SISO) time domain synchronous-orthogonal frequency division multiplexing (TDS-OFDM) system based on superimposed pilots transmission. Secondly, we introduce a new channel estimation algorithm based on superimposed pilots for the spatial multiplexing multiple-inputs-multiple-outputs (MIMO) OFDM systems. Finally, we propose a channel estimation algorithm for multiuser massive MIMO system based on superimposed pilots then we modify it for sparse channel estimation with the aid of compressive sensing techniques, particularly the orthogonal matching pursuit algorithm. The thesis is divided into six chapters as listed below: Chapter 1: This chapter gives a brief introduction to the objectives, major contribution and organization of the thesis. Also, it gives a review on the wireless communications channel, OFDM systems and channel estimation in OFDM system. Chapter 2: This chapter introduces a channel estimation algorithm for TDS-OFDM system based on the use of particular type of superimposed pilots wherein no mutual interference between superimposed pilots signals and data signals to improve the channel estimation accuracy. Chapter 3: This chapter presents a review on the MIMO wireless communications systems and the benefits of employing the transmitter and/or the receiver with multiple antennas. Also, it gives a review on detection algorithms for MIMO systems. Chapter 4: This chapter introduces a channel estimation algorithm for spatial multiplexing MIMO-OFDM systems based on the use of particular type of superimposed pilots wherein no mutual interference between superimposed pilots signals and data signals. Chapter 5: This chapter introduces a review on multiuser massive MIMO systems then it proposes a channel estimation algorithm for multiuser massive MIMO based on superimposed pilot signal transmission after that it modifies the proposed algorithm for sparse channel estimation. Chapter 6: This chapter gives the conclusion of this thesis and introduces some suggestions for the future work. |