Random Unitary Coding for Low-Complexity Cross-Domain Detection
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Solution Overview
Problem
Existing multi-carrier modulation techniques like OFDM, OTFS, and AFDM face challenges in high mobility scenarios due to Doppler shift-induced inter-carrier interference, leading to high complexity in signal detection and limited channel diversity gain, especially with sparse channel matrices.
Innovation Solution
A signal transmission method using random unitary coding modulation and cross-domain iterative detection, employing random unitary transformations to ensure channel matrix invariance and leveraging sparsity in the time-domain channel for low-complexity detection through Bayesian optimal receivers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If maximum likelihood (ML) receivers are used to achieve diversity gain in OTFS and AFDM, then signal transmission reliability is improved, but receiver complexity increases severely
Solution Approach 1:
The patent transforms the detection problem by changing the domain parameters - performing detection in both time domain and delay-Doppler domain iteratively rather than directly in one domain. This cross-domain iterative detection approach maintains ML performance while reducing computational complexity through domain transformation and iterative refinement.
Solution Approach 2:
The detection process is segmented into multiple iterative steps between time domain and delay-Doppler domain. Each iteration performs partial detection and passes results to the other domain, dividing the complex single-step ML detection into manageable sequential operations that reduce overall computational burden.
2Device complexity
If cross domain orthogonal approximate message passing (CD-OAMP) receiver is used for low-complexity detection, then receiver complexity is reduced, but channel sparsity is not fully exploited resulting in high complexity
Solution Approach 1:
The patent applies different detection strategies to different domains based on their local characteristics. In the time domain where channel sparsity exists, a matched filter approach is used to exploit sparsity. In the delay-Doppler domain, orthogonal approximate message passing is applied. This localized optimization maintains low complexity while improving detection performance.
3Device complexity
If delay-Doppler domain memory approximate message passing (DD-MAMP) receiver is used to exploit DD domain channel sparsity, then detection complexity is reduced, but time domain channel sparsity is neglected
Solution Approach 1:
The patent adds another dimension to the detection process by operating in both time domain and delay-Doppler domain. Instead of relying solely on DD domain sparsity, the method transforms signals between domains and exploits sparsity in both dimensions iteratively, thereby achieving better performance without significant complexity increase.
4Device complexity
If existing multi-carrier modulation techniques minimize inter-symbol interference to obtain sparse channel matrix, then receiver complexity is reduced, but channel diversity gain is limited
Solution Approach 1:
The patent performs preliminary channel estimation and sparsity exploitation in the time domain before main detection in the delay-Doppler domain. By pre-processing the signal to exploit time domain sparsity and prepare appropriate initial conditions, the subsequent detection achieves both low complexity and full channel diversity gain.
Data Source
AI summary
The present application provides a signal transmission method based on random unitary coding modulation and cross-domain iterative detection, including random unitary coding modulation at a signal transmitting end and cross-domain iterative detection at a receiving end. The random unitary coding modulation includes random unitary modulation or random unitary precoding, utilizing random unitary transformations to ensure that an equivalent channel matrix satisfies the correct right unitary invariance assumption. The cross-domain iterative detection includes using a cross-domain iterative receiver to receive a signal obtained after the random unitary coding modulation. The random unitary coding modulation ensures that general OAMP/VAMP, UAMP, and MAMP-type receivers achieve Bayesian optimal performance. The cross-domain iterative detection allows, through cross-domain detection, the receiver to utilize ultra-sparse time-domain channels, including low-complexity MAMP, OAMP/VAMP, and UAMP-type receivers.