Abstract
In this article, the performance of a new time domain signal pre-equalization method for use with optical orthogonal frequency division multiplexing (OFDM) and a silicon photomultiplier (SiPM) based receiver is studied. A SiPM contains a large array of microcells and each microcell is able to detect single photons. Therefore, a SiPM can be used to create arguably the most sensitive optical receiver, which can detect light intensity signals by counting the number of arriving photons within each signal sampling period. However, each photon detection triggers an avalanche-and-quenching process and the related microcell becomes inactive for a recovery time of several nanoseconds. Consequently, any photons arriving during this period cannot be detected. This effect can cause a non-linear distortion of the received signal and, when the OFDM sampling period is short, also introduces interference between signal samples. In this article, a new signal pre-equalization method is specifically designed to compensate for the impact of the finite recovery time. In this method, the number of active microcells during the transmission of each OFDM signal sample is first estimated. Then, the amplitude of the time domain signal sample is pre-adjusted based on the predicted fraction of microcells that are active. Using this approach, the negative impacts of the recovery time of the microcells are significantly reduced. The results that are presented show that when this new form of pre-equalization is used the bit error rate (BER) performance of the system is improved for a wide range of irradiance levels.
Highlights
Indoor visible light communication (VLC) is emerging as a cutting-edge technology for high-speed wireless data transmission [1]–[5], whose achievable data rate depends on the sensitivity of the optical receiver [6]
The receiver is a critical component of any VLC system and one promising approach to creating a very sensitive VLC receiver is to use a silicon photo-multiplier (SiPM)
In each microcell, which is known as a single photon avalanche diode (SPAD), an avalanche photodiode (APD) is biased above its breakdown voltage and placed in series with a quenching device
Summary
Indoor visible light communication (VLC) is emerging as a cutting-edge technology for high-speed wireless data transmission [1]–[5], whose achievable data rate depends on the sensitivity of the optical receiver [6]. When the transmission data rate is further increased to several hundred Mbps or above, the sampling period of the signal needs to be shorter than the width of the output pulse generated from the avalanche-and-quenching process In this case, the bandlimited channel creates a conventional form of interference [20]. In this article a new pre-equalization method, which is specially designed to mitigate the interference caused by the recovery period of SiPM microcells is described and its performance with optical OFDM modulation is simulated. In this method, the amplitudes of the transmitted signal samples are pre-adjusted based on the estimated fraction of active microcells within each sampling period. By taking the microcell’s recovery period into account, the number of detected photons can be simulated
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