DFT-s-OTFS Modulation for Terahertz Link Robustness
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Solution Overview
Problem
Existing orthogonal frequency division multiplexing (OFDM) and discrete Fourier transform spread OFDM (DFT-s-OFDM) are not robust to fast time-varying channels with high Doppler spread, leading to inter-carrier interference and degraded link performance in the Terahertz frequency band, where the peak-to-average power ratio (PAPR) of power amplifiers also decreases, affecting data rate and bit error rate.
Innovation Solution
The implementation of a discrete Fourier transform spread orthogonal time frequency space modulation method, which includes DFT precoding, delay-Doppler domain mapping, OTFS modulation, and IDFT decoding, reduces the PAPR and improves robustness to Doppler channels by using DFT precoding, delay-Doppler domain processing, and single-tap equalization with a gradient descent algorithm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If OFDM or DFT-S-OFDM is used for Terahertz communication, then the system can operate at high carrier frequencies, but the Doppler spread effect becomes severe causing inter-carrier interference and degraded link performance
Solution Approach 1:
The patent introduces a delay-Doppler domain as an additional dimension for signal processing. By mapping signals from the traditional time-frequency domain to the delay-Doppler domain, the system can separately process and compensate for Doppler effects, thereby maintaining link performance at Terahertz frequencies where Doppler spread is severe.
Solution Approach 2:
The patent changes the fundamental processing parameters by applying DFT precoding in the delay-Doppler domain rather than in the time domain. This parameter change transforms how the system handles Doppler spread, converting it from a harmful effect into a manageable dimension for signal processing and compensation.
2Productivity
If the operating frequency is increased to Terahertz band, then the data rate can be improved, but the saturation output power of the power amplifier rapidly decreases to less than 10 dBm
Solution Approach 1:
The patent changes the signal waveform parameters and processing methods to achieve lower PAPR. By using DFT precoding in the delay-Doppler domain and OTFS modulation, the signal characteristics are transformed to have more favorable power distribution, enabling the power amplifier to operate closer to its saturation point and thereby improving the available output power at Terahertz frequencies.
3Device complexity
If traditional OFDM waveform is maintained for THz mobile communications, then the system structure remains simple, but the data rate and bit error rate performance will be severely deteriorated
Solution Approach 1:
The patent adds the delay-Doppler domain processing dimension while maintaining compatibility with existing OFDM frameworks. The DFT precoding and OTFS modulation can be integrated into current system architectures, providing improved BER performance without requiring complete system redesign.
4Reliability
If DFT precoding and delay-Doppler domain processing are applied, then the robustness to Doppler channel is improved, but the device complexity increases
Solution Approach 1:
The patent segments the signal processing into distinct functional blocks: DFT precoding stage, delay-Doppler domain mapping stage, OTFS modulation stage, and corresponding demodulation stages. This segmentation allows each component to be optimized independently and facilitates implementation using existing signal processing hardware with minimal modifications.
Data Source
AI summary
A discrete Fourier transform spread orthogonal time frequency space modulation method comprises the steps of performing DFT preceding processing and delay-Doppler domain mapping processing on the transmit data symbols, OTFS modulator, and performing delay-Doppler domain demapping processing and IDFT decoding processing on a received signal to realize demodulation; compared with the existing waveforms, including OFDM and DFT-s-OFDM, the proposed DFT-s-OTFS can reduce the bit error rate under high Doppler spread and the peak-to-average power ratio of the transmitted signal at the same time.