A Design Framework That Unifies 6G Modulation Schemes for Double Selectivity

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Abstract
There is significant recent interest in designing new modulation schemes for doubly-selective channels with large delay and Doppler spreads, where legacy modulation schemes based on time-frequency signal representations underperform. Multiple modulation schemes, e.g., in the delay-Doppler, chirp, time-sequency, and other domains, have been proposed in the literature for this purpose, with varying implementation details. In this letter, we establish that all previously proposed modulation schemes for doubly-selective signaling are instances of a single family of complex Hadamard-modulated pulse trains. When the delay and Doppler spread of the doubly-selective channel is limited to a certain support, all modulation schemes in this waveform family offer equivalent, full diversity achieving performance with no symbol fading and low channel estimation overhead. The existence of this waveform family also enables flexible, multi-waveform co-existence – allowing a common transceiver architecture to generate multiple waveforms in the family, that may each be flexibly allocated to different users and services.
Funding Information
  • National Science Foundation (2342690)
  • National Science Foundation (2148212)
  • federal agency and industry partners as specified in the Resilient and Intelligent NextG Systems Program
  • Air Force Office of Scientific Research (FA 8750-20-2-0504)
  • Air Force Office of Scientific Research (FA 9550-23-1-0249)

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