Delay-Tolerant Multiplexed Stimulation and Its Processing Method for Multi-Channel Active Sensors

A sensing signal for an active sensor generally embeds a modulating product to ensure various noise immunity. The signal acquisition and the capacity of sensor arrays can be further improved through multiplexing techniques using orthogonal sequences. However, multi-channel and multi-user interferences degrade the performance by introducing a variety of channel delays. In this paper, we construct delay-tolerant and perfectly orthogonal codes and their decoding methods using multi-level Hadamard matrices. The stimulating codes for multi-channel sensors are re-constructed using groups of the circulant Hadamard matrix. To decode an individual channel signal, a pivot code is chosen from the group of codes. The structure of the pivot and its group code offers a pre-defined delay tolerance for the decoded channel signal at the multiplexing stage. We conducted numerical simulations where channel models are refined by the practical measurement. The results show that the proposed code and its decoding method perform better signal acquisition in the presence of channel delays and noises compared with results from existing multiplexing sequences. In both optical and capacitive channels, more than 98% of the sensing signal distortions induced from the delay variation could be removed with the designated delay tolerance.