Low complexity iterative rake decision feedback equalizer for zero-padded OTFS systems

Tharaj Thaj, Emanuele Viterbo

Research output: Contribution to journalArticleResearchpeer-review

Abstract

This paper presents a linear complexity iterative rake detector for the recently proposed orthogonal time frequency space (OTFS) modulation scheme. The basic idea is to extract and coherently combine the received multipath components of the transmitted symbols in the delay-Doppler grid using maximal ratio combining (MRC) to improve the SNR of the combined signal. We reformulate the OTFS input-output relation in simple vector form by placing guard null symbols or zero padding (ZP) in the delay-Doppler grid and exploiting the resulting circulant property of the blocks of the channel matrix. Using this vector input-output relation we propose a low complexity iterative decision feedback equalizer (DFE) based on MRC. The performance and complexity of the proposed detector favorably compares with the state of the art message passing detector. An alternative time domain MRC based detector is also proposed for even faster detection.We further propose a Gauss-Seidel based over-relaxation parameter in the rake detector to improve the performance and the convergence speed of the iterative detection. We also show how the MRC detector can be combined with outer error-correcting codes to operate as a turbo DFE scheme to further improve the error performance. All results are compared with a baseline orthogonal frequency division multiplexing (OFDM) scheme employing a single tap minimum mean square error (MMSE) equalizer.

Original languageEnglish
Pages (from-to)15606-15622
Number of pages17
JournalIEEE Transactions on Vehicular Technology
Volume69
Issue number12
DOIs
Publication statusPublished - Dec 2020

Keywords

  • Complexity theory
  • Decoder
  • Delay-Doppler Channel
  • Delays
  • Detector
  • Detectors
  • DFE
  • Diversity reception
  • Gauss Seidel
  • Maximal Ratio Combining
  • OTFS
  • Rake
  • Receivers
  • Successive Over-Relaxation
  • Time-domain analysis
  • Time-frequency analysis
  • Turbo

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