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Message Passing-Based Joint Channel Estimation and Signal Detection for OTFS with Superimposed Pilots

Fupeng Huang, Qinghua Guo, Youwen Zhang, Yuriy Zakharov

TL;DR

The paper tackles the high complexity of joint CE and signal detection in OTFS with superimposed pilots by proposing SP-DD, a low-complexity MP-based receiver that leverages GCE-BEM for channel modeling; complexity per iteration scales as $O(QMN\log(MN))$ and avoids matrix inversions. To boost CE efficiency, it adds SP-DD-D, which concentrates pilot power in the frequency domain through time-domain pilot design, reducing pilot power and PAPR while preserving CE accuracy. The work provides a detailed factor-graph formulation, four-part MP algorithm, and complexity analysis, plus extensive simulations on 5G-TDL-C channels showing substantial runtime reductions with only marginal BER/NMSE loss compared to higher-complexity SP receivers. The proposed design enables practical SP OTFS in high-mobility scenarios, offering a compelling tradeoff between spectral efficiency, estimation accuracy, and computational burden. $x$

Abstract

Receivers with joint channel estimation and signal detection using superimposed pilots (SP) can achieve high transmission efficiency in orthogonal time frequency space (OTFS) systems. However, existing receivers have high computational complexity, hindering their practical applications. In this work, with SP in the delay-Doppler (DD) domain and the generalized complex exponential (GCE) basis expansion modeling (BEM) for channels, a message passing-based SP-DD iterative receiver is proposed, which drastically reduces the computational complexity while with marginal performance loss, compared to existing ones. To facilitate channel estimation (CE) in the proposed receiver, we design pilot signal to achieve pilot power concentration in the frequency domain, thereby developing an SP-DD-D receiver that can effectively reduce the power of the pilot signal and almost no loss of CE accuracy. Extensive simulation results are provided to demonstrate the superiority of the proposed SP-DD-D receiver.

Message Passing-Based Joint Channel Estimation and Signal Detection for OTFS with Superimposed Pilots

TL;DR

The paper tackles the high complexity of joint CE and signal detection in OTFS with superimposed pilots by proposing SP-DD, a low-complexity MP-based receiver that leverages GCE-BEM for channel modeling; complexity per iteration scales as and avoids matrix inversions. To boost CE efficiency, it adds SP-DD-D, which concentrates pilot power in the frequency domain through time-domain pilot design, reducing pilot power and PAPR while preserving CE accuracy. The work provides a detailed factor-graph formulation, four-part MP algorithm, and complexity analysis, plus extensive simulations on 5G-TDL-C channels showing substantial runtime reductions with only marginal BER/NMSE loss compared to higher-complexity SP receivers. The proposed design enables practical SP OTFS in high-mobility scenarios, offering a compelling tradeoff between spectral efficiency, estimation accuracy, and computational burden.

Abstract

Receivers with joint channel estimation and signal detection using superimposed pilots (SP) can achieve high transmission efficiency in orthogonal time frequency space (OTFS) systems. However, existing receivers have high computational complexity, hindering their practical applications. In this work, with SP in the delay-Doppler (DD) domain and the generalized complex exponential (GCE) basis expansion modeling (BEM) for channels, a message passing-based SP-DD iterative receiver is proposed, which drastically reduces the computational complexity while with marginal performance loss, compared to existing ones. To facilitate channel estimation (CE) in the proposed receiver, we design pilot signal to achieve pilot power concentration in the frequency domain, thereby developing an SP-DD-D receiver that can effectively reduce the power of the pilot signal and almost no loss of CE accuracy. Extensive simulation results are provided to demonstrate the superiority of the proposed SP-DD-D receiver.
Paper Structure (21 sections, 109 equations, 8 figures, 6 tables, 1 algorithm)

This paper contains 21 sections, 109 equations, 8 figures, 6 tables, 1 algorithm.

Table of Contents

  1. Introduction
  2. OTFS Transmitter and Channel Model
  3. Transmitter Structure
  4. Channel Model
  5. Proposed Message Passing Based Receivers
  6. Factor Graph Representation
  7. Message Passing Algorithm Design
  8. Message Computations in $PART$ $I$
  9. Message Computations in $PART$ $II$
  10. Message Computations in $PART$ $III$
  11. Message Computations in $PART$ $IV$
  12. Iterative Receiver with Designed Pilots
  13. Pilot Power Ratio Determination and Complexity Analysis
  14. Determining Pilot Power Ratio and Power Concentration Factor
  15. Complexity Analysis
  16. ...and 6 more sections

Figures (8)

  • Figure 1: Structure of the OTFS transmitter with the SP scheme.
  • Figure 2: Factor graph representation for developing the OTFS receivers.
  • Figure 3: Schematic diagram of time-domain pilot and frequency-domain pilot conversion
  • Figure 4: BER of the proposed SP-DD and SP-DD-D receivers versus (a) damping factor; (b) the number of iterations.
  • Figure 5: BER of the proposed SP-DD and SP-DD-D receivers versus (a) $\beta$; (b) $\rho_F$.
  • ...and 3 more figures