Zak-OTFS
From Wikipedia, the free encyclopedia
Zak-OTFS is the primary implementation of OTFS, a 2D modulation technique that transforms the information carried in the Delay-Doppler coordinate system. Zak-OTFS is designed to integrate with the 3GPP stack so that scheduling and resource element allocation is unchanged.[1]
It is optimized for wireless communication environments applicable to 6G use cases, such as FR3, NTN and ISAC.[2][3] Zak-OTFS is supports different channel conditions in real time.[4][5]
Capabilities
Capacity Performance in Doubly Spread Channels
The transmit signals of Zak-OTFS are similar to OFDM systems, but OFDM operates in the time-frequency domain where high Doppler shifts and delay spreads cause inter-carrier interference (ICI) and inter-symbol interference (ISI), while Zak-OTFS operates in the delay-Doppler domain where the channel appears quasi-static even under high mobility.[6] Also, Zak-OTFS can achieve full diversity in time selective and frequency selective fading channels.[6]
Integrated Sensing and Communications (ISAC)
Zak-OTFS has natural applications in radar and sensing due to its delay-Doppler domain representation. The delay-Doppler grid directly corresponds to the range and velocity information of radar targets, making Zak-OTFS suited for integrated sensing and communications (ISAC) systems.[7] The self-ambiguity function of the Zak-OTFS waveform in the delay-Doppler domain is a lattice, which allows it to identify the range and velocity of multiple targets without dividing the available time-bandwidth region.[8]
In addition to direct extraction of range and velocity from the delay-Doppler grid, Zak-OTFS also demonstrates the ability to simultaneously communicate and sense using the same waveform, perform in high-mobility scenarios,[9] and efficiently separate multiple targets in delay-Doppler space.[8]
Research has demonstrated OTFS-based ISAC systems for automotive radar, aviation surveillance, and maritime monitoring applications.[6]
Non-Terrestrial Networks
Through its fundamental delay-Doppler domain operation, Zak-OTFS is able to process signals from multiple satellites at different delay-Doppler coordinates, achieve full-frequency reuse through delay-Doppler domain separation, and reduce GNSS-based pre-compensation.
Channel Equalization and Estimation
Zak-OTFS processing techniques have culminated in the creation of a Neural Receiver by Virginia Tech that is part of a development environment created by Cohere Technologies, Duke University, and Virginia Tech.[10]
Prior to the creation of the Neural Receiver, low complexity equalization had been proposed based on Message Passing (MP), Markov Chain Monte Carlo (MCMC), and Linear equalization methods.[11][12][13][14]Iterative Rake decision feedback equalization achieved equivalent performance to message passing with a lower complexity that was independent of the modulation size.[15][16][17][18]