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Flexible Synchronization for Multi-User Uplink Communication Based on DDAM-OFDMA
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DOI：10.1109/TCOMM.2026.3664440.png)
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Abstract
En 中文
The classic orthogonal frequency division multiple access (OFDMA) faces critical challenges in doubly-selective millimeter-wave (mmWave) massive multiple-input multiple-output (MIMO) systems, and excessive cyclic prefix (CP) overhead and stringent synchronization requirements substantially degrade spectral efficiency. To address these challenges, recent studies have explored delay alignment modulation (DAM), which exploits joint spatial-delay processing to mitigate inter-symbol interference (ISI) and reduce CP overhead without relying on conventional channel equalization structure in single-user systems. Building upon this concept, we leverage delay-Doppler alignment modulation (DDAM), which is a generalization of DAM suitable for doubly-selective channels, to enhance multi-user uplink OFDMA performance. Specifically, we propose a novel flexible synchronization multi-user uplink transmission framework based on DDAM-OFDMA, which integrates DDAM with OFDMA to jointly reduce CP overhead and relax synchronization constraints. First, we analyze the synchronization and CP overhead limitations of uplink OFDMA and highlight the potential of DDAM at the BS to mitigate these issues. To gain further insights, we first consider a DDAM-OFDMA system under the special case of a single-path channel model and derive its input-output relationship, illustrating how DDAM reduces CP overhead while enhancing synchronization robustness. We then formulate a joint optimization problem for time-domain and frequency-domain beamforming to maximize the sum rate and derive the closed-form expression. The proposed framework is then extended to multi-path scenarios by designing the perfect synchronization and the flexible synchronization. Specifically, the perfect synchronization is the extension of the single-path model. Then, the flexible synchronization additionally achieves the controllable channel delay spread, which is achieved through DDAM’s delay compensation and path-based beamforming. Simulation results validate that the proposed DDAM-OFDMA scheme outperforms various benchmark schemes in terms of spectral efficiency and bit error rate (BER).
Keywords:
Delay-Doppler alignment modulation
delay-Doppler post-compensation
path-based beamforming
flexible synchronization
OFDMA
Journal
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3.6W