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A DFT-based Low Complexity LMMSE Channel Estimation Technique for OFDM Systems

Patra Jyoti P., Pradhan Bibhuti Bhusan, Singh Poonam

Journal of Telecommunications and Information Technology

2022

nr 1

72--78

The linear minimum mean square error (LMMSE) channel estimation technique is often employed in orthogonal frequency division multiplexing (OFDM) systems because of its optimal performance in the mean square error (MSE) performance. However, the LMMSE method requires cubic complexity of order O(N 3 p ), where Np is the number of pilot subcarriers. To reduce the computational complexity, a discrete Fourier transform (DFT) based LMMSE method is proposed in this paper for OFDM systems in the frequency selective channel. To validate the proposed method, the closed form mean square error (MSE) expression is also derived. Finally, a computer simulation is carried out to compare the performance of the proposed LMMSE method with the classical LS and LMMSE methods in terms of bit error rate (BER) and computational complexity. Results of the simulation show that the proposed LMMSE method achieves exactly the same performance as the conventional LMMSE method, with much lower computational complexity.

Improved Signal Detection Techniques for QOSTBC System in Fast Fading Channel

Patra Jyoti P., Singh Poonam

Journal of Telecommunications and Information Technology

2020

nr 1

6--12

Most existing quasi-orthogonal space time block coding (QO-STBC) schemes have been developed relying on the assumption that the channel is ﬂat or remains static during the length of the code word symbol periods to achieve an optimal antenna diversity gain. However, in timeselective fading channels, this assumption does not hold and causes intertransmit-antenna-interferences (ITAI). Therefore, the simple pairwise maximum likelihood decoding scheme is not suﬃcient to recover original transmitted signals at the receiver side. To avoid the interferences, we have analyzed several signal detection schemes, namely zero forcing (ZF), two-step zero forcing (TS-ZF), minimum mean square error (MMSE), zero forcing – interference cancelation – decision feedback equalizer (ZF-IC-DFE) and minimum mean square error – interference cancelation – decision feedback equalizer (MMSE-IC-DFE). We have proposed two eﬃcient iterative signal detection schemes, namely zero forcing – iterative interference cancelation – zero forcing – decision feedback equalization (ZF-IIC-ZF-DFE) and minimum mean square error – parallel interference cancelation – zero forcing – decision feedback equalization (MMSE-IIC-ZF-DFE). The simulation results show that these two proposed detection schemes signiﬁcantly outperform all conventional methods for QOSTBC system over time selective channel.