Low Complexity Iterative Rake Detector for Orthogonal Time Frequency Space Modulation

TL;DR

This paper introduces a low complexity iterative rake detector for OTFS modulation that enhances SNR by combining multipath components using diversity schemes, reformulating the input-output relation for improved detection.

Contribution

It proposes a novel low complexity iterative detector based on MRC for OTFS, exploiting the channel matrix's block circulant property for improved performance.

Findings

BER performance surpasses state-of-the-art message passing detector

FER can be improved with turbo DFE and error correcting codes

Reformulated OTFS input-output relation enables efficient detection

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 combine the received multipath components of the transmitted symbols in the delay-Doppler grid using linear diversity combining schemes like maximal ratio combining (MRC), equal gain combining and selection combining to improve the SNR of the combined signal. We reformulate the OTFS input-output relation in the vector form by placing some null symbols in the delay-Doppler grid thereby exploiting the block circulant property of the channel matrix. Using the new input-output relation we propose a low complexity iterative detector based on the MRC scheme. The bit error rate (BER) performance of the proposed detector will be compared with the state of the art message passing detector and orthogonal frequency division multiplexing (OFDM) scheme employing a single tap minimum mean square error (MMSE) equalizer. We also show that the frame error rate (FER) performance of the MRC detector can be improved by employing error correcting codes operating in the form of a turbo decision feedback equalizer (DFE).