SPAD-Based Optical Wireless Communication With Signal Pre-Distortion and Noise Normalization

Abstract

In recent years, there has been a growing interest in exploring the application of single-photon avalanche diode (SPAD) in optical wireless communication (OWC). As a photon counting detector, SPAD can provide much higher sensitivity compared to the other commonly used photodetectors. However, SPAD-based receivers suffer from significant dead-time-induced non-linear distortion and signal dependent noise. In this work, we propose a novel SPAD-based OWC system in which the non-linear distortion caused by dead time can be successfully eliminated by the pre-distortion of the signal at the transmitter. In addition, another system with joint pre-distortion and noise normalization functionality is proposed. Thanks to the additional noise normalization process, for the transformed signal at the receiver, the originally signal dependent noise becomes signal independent so that the conventional signal detection techniques designed for AWGN channels can be employed to decode the signal. Our numerical results demonstrate the superiority of the proposed SPAD-based systems compared to the existing systems in terms of BER performance and achievable data rate.

Performance analysis of SPAD-based optical wireless communication with OFDM

“…The regimes with power less and higher than this power are denoted as low-and high-power regime, respectively. In addition, the variance of the photon count is signal dependent and is less than the mean value, which shows the sub-Poisson property of the SPAD receiver [10]. This is different from the ideal photon counting receiver, i.e., when τ d = 0, whose mean and variance of the detected photon count are identical and both increase linearly with the received optical power, as also plotted in Fig.…”

“…However, the performance of a practical SPAD-based receivers depends on non-ideal effects such as dead time, photon detection efficiency (PDE), dark count rate (DCR), afterpulsing and crosstalk. In particular, due to the existence of dead time, significant nonlinearity is introduced which causes the deviation of the detected photon count of SPAD receivers from the Poisson distribution [10]. In order to mitigate the dead time effect and hence improve the photon counting capability, an array of SPADs whose output is the superposition of the photon counts of the individual SPADs is commonly utilized [9], [20].…”

“…To improve the performance of SPAD-based receivers, a detection scheme which uses not only the photon count information but also the photon arrival information is proposed in [9]. In addition, a SPAD-based OWC system with joint pre-distortion and noise normalization functionality is proposed to mitigate the SPAD nonlinear distortion [10]. Although most of the SPAD-based OWC works focus on simple on-off keying (OOK), optical orthogonal frequency division multiplexing (OFDM) has also been employed in SPAD-based systems to improve the spectral efficiency (SE) [11]- [13].…”

Highly Sensitive SPAD-Based Receiver for Dimming Control in LiFi Networks

“…For an array of PQ SPADs with SPAD pixels and each with a dead time, the average detected photon count during the time-domain OFDM sample duration, , can be expressed as [ 32 , 37 ] Assuming the sample duration is larger than the dead time, i.e., , the variance of the detected photon count of the array is given by [ 39 , 40 ] VLCs employ intensity modulation and direct detection (IM/DD), wherein a direct-detection receiver generates a photocurrent proportionate to the incident optical power. In contrast to standard VLC systems employing linear PDs, which assume a simple additive white Gaussian noise (AWGN) channel, the dead time of SPAD introduces non-linear signal distortion and complicated signal-dependent shot noise, which must be accounted for in the performance analysis [ 11 ].…”

“…Dead time is the period during which the SPAD is insensitive to incoming photons and unable to detect any subsequent events. In particular, because of the nonlinearity induced by dead time, SPAD receivers’ observed photon counts deviate significantly from the Poisson distribution [ 11 ]. As a way to reduce the dead time effect and hence increase photon-counting capabilities, a SPAD array is widely used that outputs the superposition of the photon counts of each individual SPAD, and the overall photon counts can be further approximated as Gaussian [ 12 ].…”