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A Novel Precoder for Peak-to-Average Power Ratio Reduction in OTFS Systems

Saurabh Prakash, Venkatesh Khammammetti, Saif Khan Mohammed

TL;DR

OTFS signals suffer high PAPR after TD transformation, challenging PA efficiency. The paper introduces a low-complexity iterative amplitude-precoding scheme that augments the delay-Doppler alphabet to S = S_A,D ∪ S_2A,D and selects x[k,l] ∈ {u[k,l], 2u[k,l]} to minimize the PAPR of the transmit signal s = (F_N^H ⊗ I_M) x. A heuristic iterative search scales amplitudes via 2^((3 - 2|x[t]|/A)) to find a good precoder x*, with complexity O(M^2 N^2 log(MN)). The approach yields roughly 5 dB PAPR improvement over uncompensated OTFS and outperforms companding, DFT precoding, and clipping+filtering in CCDF metrics, while preserving BER performance and showing robustness to wide Doppler ranges. This makes the method a practical PAPR reduction option for OTFS in high-mobility scenarios with scalable complexity.

Abstract

We consider the issue of high peak-to-average-power ratio (PAPR) of Orthogonal time frequency space (OTFS) modulated signals. This paper proposes a low-complexity novel iterative PAPR reduction method which achieves a PAPR reduction of roughly 5 dB when compared to a OTFS modulated signal without any PAPR compensation. Simulations reveal that the PAPR achieved by the proposed method is significantly better than that achieved by other state-of-art methods. Simulations also reveal that the error rate performance of OTFS based systems with the proposed PAPR reduction is similar to that achieved with the other state-of-art methods.

A Novel Precoder for Peak-to-Average Power Ratio Reduction in OTFS Systems

TL;DR

OTFS signals suffer high PAPR after TD transformation, challenging PA efficiency. The paper introduces a low-complexity iterative amplitude-precoding scheme that augments the delay-Doppler alphabet to S = S_A,D ∪ S_2A,D and selects x[k,l] ∈ {u[k,l], 2u[k,l]} to minimize the PAPR of the transmit signal s = (F_N^H ⊗ I_M) x. A heuristic iterative search scales amplitudes via 2^((3 - 2|x[t]|/A)) to find a good precoder x*, with complexity O(M^2 N^2 log(MN)). The approach yields roughly 5 dB PAPR improvement over uncompensated OTFS and outperforms companding, DFT precoding, and clipping+filtering in CCDF metrics, while preserving BER performance and showing robustness to wide Doppler ranges. This makes the method a practical PAPR reduction option for OTFS in high-mobility scenarios with scalable complexity.

Abstract

We consider the issue of high peak-to-average-power ratio (PAPR) of Orthogonal time frequency space (OTFS) modulated signals. This paper proposes a low-complexity novel iterative PAPR reduction method which achieves a PAPR reduction of roughly 5 dB when compared to a OTFS modulated signal without any PAPR compensation. Simulations reveal that the PAPR achieved by the proposed method is significantly better than that achieved by other state-of-art methods. Simulations also reveal that the error rate performance of OTFS based systems with the proposed PAPR reduction is similar to that achieved with the other state-of-art methods.
Paper Structure (6 sections, 8 equations, 7 figures, 2 tables, 1 algorithm)

This paper contains 6 sections, 8 equations, 7 figures, 2 tables, 1 algorithm.

Table of Contents

  1. Introduction
  2. System Model
  3. Sampling the TD transmit signal
  4. Proposed novel approach for PAPR Compensation
  5. Numerical Simulations
  6. Conclusion

Figures (7)

  • Figure 1: Zak-OTFS transceiver signal processing with proposed precoding at transmitter for PAPR reduction.
  • Figure 2: $D=4$. Alphabet set ${\mathcal{S}}_{A,D}$ (black dots on the green circle) and ${\mathcal{S}}_{2A,D}$ (black dots on the blue circle). Precoded symbols belong to the extended alphabet set ${\mathcal{S}}_{A,D} \, \bigcup {\mathcal{S}}_{2A,D}$ (consisting of all eight black dots on both circles).
  • Figure 3: PAPR CCDF with BPSK.
  • Figure 4: PAPR CCDF with QPSK.
  • Figure 5: BER vs. SNR. BPSK information symbols.
  • ...and 2 more figures