Abstract
We consider optical camera communication (OCC) between a camera receiver with optical lenses and distributed transmitters. This article investigates the features of an OCC system when the periods of reception and transmission are slightly different from each other. We describe a received light signal model for the OCC system with on-off keying and regard the received signals generated from a probability distribution of a Gaussian mixture model. We obtain the parameters of the probability distributions by applying a variational Bayesian inference method and utilize them for channel estimation. In addition, we define cost functions and minimize them to demodulate the transmitted bit sequences. The demodulation procedure uses a maximum-likelihood sequence detection method, which can be implemented by the Viterbi algorithm and estimates a synchronization parameter by minimizing the cost functions. Our new demodulation method requires neither synchronization devices nor training sequences for estimating the parameters. Moreover, the receiver does not need the precise transmission period, which is difficult to know in advance in practical situations because of the frequency tolerance of the clock generator in the transmitter. To validate our developed method, we conducted numerical simulations and compared the results with those from an oracle estimator that knows the parameters other than the bit sequence in advance. We also experimented in a real setup situation, and the results show the efficiency of our developed method.
Highlights
V ISIBLE light communication (VLC) is a research area that has emerged mainly due to the widespread use of Manuscript received February 26, 2020; revised June 24, 2020; accepted July 18, 2020
Whether the sampling period TRX is longer than the transmission period TTX or not, the bit error rate (BER) stay in the low range, signals in the TRX > TTX cases resemble undersampling situation and should be more difficult to demodulate than that in the opposite case
To demodulate the bit sequence from the light signals, we introduced a received signal model and a cost function that should be minimized
Summary
V ISIBLE light communication (VLC) is a research area that has emerged mainly due to the widespread use of Manuscript received February 26, 2020; revised June 24, 2020; accepted July 18, 2020. Thanks to the receiver’s optical lenses, emitted lights are spatially separated on the IS and the massive number of pixels enables the camera receiver to detect the positions of objects This enables the receiver to trace moving transmitters and communicate with multiple transmitters simultaneously. To estimate the background noise and the synchronization parameter, the method needs a training sequence This additional noninformational sequence reduces the bit transmission efficiency. Taking into account these issues, we suggested a method that requires neither synchronization devices nor training sequences [23]. We developed a demodulation method for an OCC system that can estimate the background noise level and synchronization parameters without any synchronization devices and training sequences.
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