The first tests of smartphone camera exposure effect on optical camera communication links

In this paper, we study the effect of smartphone camera exposure on the performance of optical camera communications (OCC) link. The exposure parameters of image sensor sensitivity (ISO), aperture and shutter speed are included. A static OCC link with a 8×8 red, green and blue (RGB) LED array employed as the transmitter and a smartphone camera as the receiver is demonstrated to verify the study. Signal-to-noise ratio (SNR) analysis at different ISO values, the effect of aperture and shutter speed on communication link quality is performed. While SNRs of 20.6 dB and 16.9 dB are measured at 1 m and 2 m transmission distance, respectively for a ISO value of 100, they are decreased to 17.4 dB and 13.32 dB for a ISO of 800. The bit error rate (BER) of a 1 m long OCC link with a camera’s shutter speed of 1/6000 s is 1.3×10 −3 (i.e., below the forward error correction BER limit of 3.8×10 −3 ) and is dropped to 0.0125 at a shutter speed of 1/20 s. This study provides insight of the basic smartphone settings and the exposure adjustment for further complex OCC links

Experimental and Analytical Investigations of an Optically Pre-Amplified FSO-MIMO System With Repetition Coding Over Non-Identically Distributed Correlated Channels

This paper presents theoretical and experimental bit error rate (BER) results for a freespace optical (FSO) multiple-input-multiple-output system over an arbitrarily correlated turbulence channel. We employ an erbium-doped fiber amplifier at the receiver (Rx), which results in an improved Rx’s sensitivity at the cost of an additional non-Gaussian amplified spontaneous emission noise. Repetition coding is used to combat turbulence and to improve the BER performance of the FSO links. A mathematical framework is provided for the considered FSO system over a correlated non-identically distributed Gamma-Gamma channel; and analytical BER results are derived with and without the pre-amplifier for a comparative study. Moreover, novel closed-form expressions for the asymptotic BER are derived; a comprehensive discussion about the diversity order and coding gain is presented by performing asymptotic analysis at high signal-tonoise ratio (SNR). To verify the analytical results, an experimental set-up of a 2 × 1 FSO-multiple-inputsingle-output (MISO) system with pre-amplifier at the Rx is developed. It is shown analytically that, both correlation and pre-amplification do not affect the diversity order of the system, however, both factors have contrasting behaviour with respect to coding gain. Further, to achieve the target forward error correction BER limit of 3.8 × 10−3 , a 2 × 1 FSO-MISO system with a pre-amplifier requires 6.5 dB lower SNR compared with the system with no pre-amplifier. Moreover, an SNR penalty of 2.5 dB is incurred at a higher correlation level for the developed 2×1 experimental FSO set-up, which is in agreement with the analytical findings

Performance evaluation of neural network assisted motion detection schemes implemented within indoor optical camera based communications

This paper investigates the performance of the neural network (NN) assisted motion detection (MD) over an indoor optical camera communication (OCC) link. The proposed study is based on the performance evaluation of various NN training algorithms, which provide efficient and reliable MD functionality along with vision, illumination, data communications and sensing in indoor OCC. To evaluate the proposed scheme, we have carried out an experimental investigation of a static indoor downlink OCC link employing a mobile phone front camera as the receiver and an 8 x000D7; 8 red, green and blue light-emitting diodes array as the transmitter. In addition to data transmission, MD is achieved using a camera to observe userx02019;s finger movement in the form of centroids via the OCC link. The captured motion is applied to the NN and is evaluated for a number of MD schemes. The results show that, resilient backpropagation based NN offers the fastest convergence with a minimum error of 10x02212;5 within the processing time window of 0.67 s and a success probability of 100 x00025; for MD compared to other algorithms. We demonstrate that, the proposed system with motion offers a bit error rate which is below the forward error correction limit of 3.8 x000D7; 10x02212;3, over a transmission distance of 1.17 m

Impact of Channel Correlation on Different Performance Metrics of OSSK-Based FSO System

In this paper, we study the impact of correlation on the bit error rate (BER) and the channel capacity of a free-space optical (FSO) multiple-input-multiple-output (MIMO) system employing optical space shift keying (OSSK) over a fading channel. In order to study a practical correlated channel, we consider the effect of channel correlation due to both small-and large-scale eddies and show that the use of OSSK over correlated FSO channel can lead to an improved system performance with increasing correlation level of upto 0.9. In this work, we first develop an analytical framework for different performance metrics of the OSSK multiple-input single-output system with correlation and then extend our investigation by proposing an asymptotically accurate mathematical framework for MIMO. We also validate all the analytical results using MATLAB simulations. Finally, we develop an experimental setup of FSO with two correlated links to study the throughput and latency of the links at different turbulence levels

A Flexible OLED based VLC Link with m-CAP Modulation

In recent years there has been a growing interest in using organic light emitting diodes (OLEDs) for illumination in indoor environments. They offer attractive features such as flexibility and large active areas at a low cost; they are energy efficient and have higher illumination levels compared to silicone based LEDs. In addition, the utilization of OLEDs have increased in devices such as smart mobile phones and TVs because of their low thickness. This paper investigates the performance of an OLED based visible light communications (OVLC) system, using a curved and flat OLED with multiband carrierless amplitude and phase (m-CAP) modulation for m = 2 at different angles of incidence on the optical receiver. It is shown that the BER performance is improved (i.e., below the forward error correction (FEC) limit of 3.8×10 −3 ) with the curved OLED when the optical receiver moving along a circular path for the viewing angles greater 40° compared to the flat OLED, which is advantageous in device to device communications

A Flexible OLED based VLC Link with m-CAP Modulation

In recent years there has been a growing interest in using organic light emitting diodes (OLEDs) for illumination in indoor environments. They offer attractive features such as flexibility and large active areas at a low cost; they are energy efficient and have higher illumination levels compared to silicone based LEDs. In addition, the utilization of OLEDs have increased in devices such as smart mobile phones and TVs because of their low thickness. This paper investigates the performance of an OLED based visible light communications (OVLC) system, using a curved and flat OLED with multiband carrierless amplitude and phase (m-CAP) modulation for m = 2 at different angles of incidence on the optical receiver. It is shown that the BER performance is improved (i.e., below the forward error correction (FEC) limit of 3.8×10 −3 ) with the curved OLED when the optical receiver moving along a circular path for the viewing angles greater 40° compared to the flat OLED, which is advantageous in device to device communications

Optical CS-DSB Schemes for 5G mmW Fronthaul Seamless Transmission

[EN] This paper describes the experimental demonstration of the hybrid optical/millimeter wave signal generation and transmission over combined optical fiber and free space optics fronthaul network with a seamless antenna link. An electrical bandpass filter is used to filter out the spectrum after photodetection in order to realize the seamless antenna transmission. The successful transmission of 64/256-quadrature amplitude modulation (QAM) 5G signal with up to 200 MHz bandwidth is presented by using two different setups: one is based on two Mach-Zehnder modulators (MZM) and the other employs a directly modulated laser (DML) to provide more cost efficient fronthaul solution. The DML based approach reveals mildly better performance in comparison to the MZMs in terms of higher achieved signal-to-noise ratio and lower error vector magnitude (EVM). More specifically, the best signal-to-noise ratio and EVM achieved with the DML based setup has been 31.5 dB and 3. 3%, respectively, compared to 30.3 dB and 3.8% with the MZMs based setup while transmitting 256-QAM signal with 100 MHz bandwidth. However, both setups kept the EVM well below the given 9% and 4.5% limit for 64- and 256-QAM, respectively.This work was supported in part by the Ministry of Industry and Trade in Czech Republic under Grant FV40089, in part by EU COST Action NEWFOCUS under Grant CA19111, and in part by the Ministerio de Ciencia, Innovacion y Universidades under Grant FOCAL RTI2018-101658-B-I00.Bohata, J.; Vallejo-Castro, L.; Ortega Tamarit, B.; Zvanovec, S. (2022). Optical CS-DSB Schemes for 5G mmW Fronthaul Seamless Transmission. IEEE Photonics Journal. 14(2):1-7. https://doi.org/10.1109/JPHOT.2022.31610871714

Duobinary Modulation for Visible Light Communications

The paper proposes and experimentally investigates the performance of the duobinary transmission technique for a highly bandlimited VLC system. By adding a controlled amount of inter-symbol interference (ISI) into the transmitted signals through the use of pulse shaping filters, data rate can be doubled within the same signal bandwidth. To gain full insight into duobinary signalling, the so-called modified binary scheme is also tested. Bit error rate (BER) performance of both systems is measured for a range of data rates and compared to BERs for ideal binary and traditional on-off keying non-return to zero (OOK-NRZ) formats, across the same physical link. We show the duobinary system can support higher bit rates and lower BER than OOK-NRZ while requiring half the bandwidth of the binary scheme