Massive Random Access with Tensor-based Modulation in the Presence of Timing Offsets

Tensor-based modulation (TBM) [1] is a novel waveform design allowing massive random access in future wireless networks. In this article, we study the sensitivity of TBM to timing offsets when using orthogonal frequency division multiplexing (OFDM) transmissions. We show that as long as some mild conditions are met with respect to the mapping of the tensor elements on the OFDM time-frequency grid, it is still possible to separate the users, and to estimate and compensate their timing offsets on a per-user basis. We demonstrate the effectiveness of the estimator with both coherent and non-coherent modulation schemes.