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Orthogonal Time-Frequency-Space (OTFS) and Related Signaling

Lie-Liang Yang

TL;DR

The paper analyzes orthogonal time-frequency-space (OTFS) signaling and shows it embeds orthogonal short-time Fourier (OSTF) as a companion scheme, framing OTFS as the 2D extension of SC-FDMA and OSTF as the 2D extension of OFDM. By mapping data between delay-Doppler and time-frequency domains via ISFFT/SFFT and employing the OSTF transmit/receive transforms, OTFS achieves a delay-Doppler domain representation of the channel that enables potential TF-diversity across resolvable paths. It also clarifies relationships to OFDM/SC-FDMA, discusses multiuser multiplexing options, and presents generalized uplink/downlink resource-allocation schemes (LOTFS-MA, IOTFS-MA) along with TF-spread and ISFFT-spread OSTF variants. The work highlights that practical deployment hinges on accurate channel estimation and complexity-aware detector designs, with pilot placement potentially in either domain depending on channel sparsity and environment.

Abstract

The principle of orthogonal time-frequency-space (OTFS) signaling is firstly analyzed, followed by explaining that OTFS embeds another signaling scheme referred to as orthogonal short-time Fourier (OSTF). Then, the relationship among OTFS, OSTF, orthogonal frequency-division multiplexing (OFDM) and single-carrier frequency-division multiple-access (SC-FDMA) is explored, demonstrating that OSTF/OTFS are fundamentally the extensions of OFDM/SC-FDMA from one-dimensional (1D) signaling to two-dimensional (2D) signaling. Hence, the characteristics and performance of OSTF/OTFS schemes can be perceived from the well-understood OFDM/SC-FDMA schemes. Accordingly, the advantages and disadvantages of OSTF/OTFS are discussed. Furthermore, from the principles of OFDM/SC-FDMA, the multiuser multiplexing in OSTF/OTFS systems is analyzed with respect to uplink and downlink, respectively. Added on this, a range of generalized multiplexing schemes are presented, whose characteristics are briefly analyzed.

Orthogonal Time-Frequency-Space (OTFS) and Related Signaling

TL;DR

The paper analyzes orthogonal time-frequency-space (OTFS) signaling and shows it embeds orthogonal short-time Fourier (OSTF) as a companion scheme, framing OTFS as the 2D extension of SC-FDMA and OSTF as the 2D extension of OFDM. By mapping data between delay-Doppler and time-frequency domains via ISFFT/SFFT and employing the OSTF transmit/receive transforms, OTFS achieves a delay-Doppler domain representation of the channel that enables potential TF-diversity across resolvable paths. It also clarifies relationships to OFDM/SC-FDMA, discusses multiuser multiplexing options, and presents generalized uplink/downlink resource-allocation schemes (LOTFS-MA, IOTFS-MA) along with TF-spread and ISFFT-spread OSTF variants. The work highlights that practical deployment hinges on accurate channel estimation and complexity-aware detector designs, with pilot placement potentially in either domain depending on channel sparsity and environment.

Abstract

The principle of orthogonal time-frequency-space (OTFS) signaling is firstly analyzed, followed by explaining that OTFS embeds another signaling scheme referred to as orthogonal short-time Fourier (OSTF). Then, the relationship among OTFS, OSTF, orthogonal frequency-division multiplexing (OFDM) and single-carrier frequency-division multiple-access (SC-FDMA) is explored, demonstrating that OSTF/OTFS are fundamentally the extensions of OFDM/SC-FDMA from one-dimensional (1D) signaling to two-dimensional (2D) signaling. Hence, the characteristics and performance of OSTF/OTFS schemes can be perceived from the well-understood OFDM/SC-FDMA schemes. Accordingly, the advantages and disadvantages of OSTF/OTFS are discussed. Furthermore, from the principles of OFDM/SC-FDMA, the multiuser multiplexing in OSTF/OTFS systems is analyzed with respect to uplink and downlink, respectively. Added on this, a range of generalized multiplexing schemes are presented, whose characteristics are briefly analyzed.
Paper Structure (7 sections, 48 equations, 6 figures)

This paper contains 7 sections, 48 equations, 6 figures.

Table of Contents

  1. Introduction
  2. Principles of Orthogonal Time-Frequency-Space (OTFS)
  3. Relationship of OTFS with OSTF, OFDM and SC-FDMA
  4. Multiuser Multiplexing and Resource-Allocation in OTFS and OSTF Systems
  5. Uplink
  6. Downlink
  7. Concluding Remarks

Figures (6)

  • Figure 1: OTFS signaling relationship between DD-domain and TF-domain.
  • Figure 2: Modulation and demodulation signaling in OTFS principles.
  • Figure 3: Diagram illustrating the relationship between OFDM and SC-FDMA signaling.
  • Figure 4: Diagram illustrating the relationship among OTFS, OSTF, OFDM and SC-FDMA.
  • Figure 5: Illustration of a time-frequency selective wireless channel.
  • ...and 1 more figures