Recent Progress in Optical Wireless Communication Giulio Cossu, Wajahat Ali, Raffaele Corsini, Ernesto Ciaramella INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva

Summary Overlook on Optical Wireless Communication (OWC) – Motivations and applications – Devices Visible Light Communication (VLC) experiments – Indoor applications – Vehicle to vehicle communication – Underwater communication OW for HEP and medical imaging – Preliminary results INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva

Introduction INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva Optical Wireless (OW): Wavelengths from infrared to ultraviolet Free-space as optical medium Visible Light Communication (VLC): e.g. synergy between illumination and data transmission

Light Emitting Diodes (LEDs) INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva Phosphorescent white LED Blue chips + phosphorus layer Limited bandwidth due to the slow phosphor layer (2-3 MHz) Original frequency response restored with blue filter (10-15 MHz) RGB white LED Mix of Red + Green + Blue chips Full bandwidth without optical filter Allows Wavelength Division Multiplexing (WDM) Lower power consumption, lower voltage, longer lifetime, smaller size, cooler operation and faster response

Differences between OW and RF technologies INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva Property of mediumRadioOptical Bandwidth regulationYesNo Electromagnetic interf.YesNo Power limitationRadio lawEye safety/illumination Multipath fadingYesNo Passes though wallsYesNo Physical securityLowHigh Input x(t)AmplitudePower (always positive) Detection typeCoherent/IncoherentIncoherent

Link Configuration INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva

Modulation format INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva  Single-carrier modulation (power efficiency) o On-Off Keying (OOK) DC-balanced coding  Multi-carrier modulation (High speed) o Orthogonal Frequency Division Multiplexing (OFDM) Discrete Multi-Tone (DMT) IM/DD scheme x(t) > 0 Power efficiency High speed

Discrete Multi-tone – Advantages Advantages Spectral efficiency: bit-power loading Easy frequency equalization Able to contrast the multipath

VLC Applications INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva

High-speed OWC link – Introduction INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva Achieved results (2012) 1 15 cm – Phosphorescent LED (single channel) [Photonics journal] (2012) cm – RGB LED (WDM channel) [ECOC] (2012) cm – RGB LED (WDM channel) [Optics Express] (2014) m – RGBY LED (WDM channel) [ECOC] Goal : Highest speed operation (with low-cost components) Minimization of power losses -> Directed Line-of-sight configuration Narrow emission beam Narrow acceptance angle WDM operation (different colors transmit different data)

High-speed OWC link – Experimental Setup INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva Downlink: 12 chips (3 for each color). 22° Lambertian emission Uplink: IR-LED emitting at 850 nm, 130° Lambertian emission DMT signals N=512 subcarriers BW=220 MHz

High-speed OWC link – Experiment INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva Summary: ≥ 5 Gbit/s with distance ≤ 3.5 m (downlink) Uplink ranges from 1.1 to 1.5 Gbit/s (4 -> 1.5 m)

High-mobility OWC link – Introduction INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva Achieved results (2013) m – Phosphorescent LED (uni-directional) (2014) m – Phosphorescent LED/IR-LED (bi-directional) (2014) m – RGB LED/IR-LED (bi-directional) Goal : High speed operation in high mobility Non Directed Line-of-sight scheme Trade-off between diffuse links and high speed of LOS links. Scenario closer to typical indoor topology: synergy illumination and data Robust to indoor ambient light

Custom RGB LED: 470 nm (local minimum of the Ph-LED) Aux LED: Cool white phosphoroscent LED (to emulate ambient light) 120° Lambertian emission DMT signals N=512 subcarriers BW=75 MHz Tx Downlink High-mobility OWC link – Experimental setup

High-mobility OWC link – Experiment INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva Measurement conditions Vertical distance between ceiling and desktop: h = 2 m Fixed 500 Rx BER < 1,48∙10 -3 (error-free after FEC decoding) Measurements for downlink and uplink: Maximum data rate a)φ=ψ=0° (R=0 m), Data rates: 400 Mbit/s (downlink) – 380 Mbit/s (uplink) a)φ=ψ =45° (R=2 m) Data rates: 200 Mbit/s (downlink and uplink) Hot spot having r ≤ 2 m (≈12 m 2 ) with a maximum of 400 Mbit/s (at the center) and a guaranteed data rate of 200 Mbit/s.

INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva Intelligent Transport System (ITS) Increase safety, reduce congestion, enhancing mobility Vehicle-to-Infrastructure (V2I): roadside sensor, traffic lights Vehicle-to-Vehicle (V2V): safety-critical communication Common Radio Frequency (RF) solution IEEE based protocols: 5.9 GHz bandwidth Network congestion because of isotropic nature of the radio-waves «Broadcast storm» Optical Wireless Low cost and limited impact: LEDs already present on the cars Free from broadcast storm: strong directionality

Car-to-Car communication – Preliminary results INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva CONFIDENTIAL «Broadcast storm»

Car-to-Car communication – Preliminary results INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva

Car-to-Car communication – Preliminary results INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva Step-like behavior: No error until the distance is such that the signal is higher than the serial port sensitivity Maximum distance (m) 1No lens Tx – No lens Rx0,25 218° lens Tx – No lens Rx0,5 3No lens Tx – Lens Rx2,6 444° lens Tx – Lens Rx14,5 518° lens Tx – Lens Rx 31

Underwater communication - Introduction INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva Underwater monitoring exploiting vehicles in cooperation needs of data exchange among vehicles Radio waves extremely attenuated in water Acoustic modems for long distance suffer low data rate (hundreds bit/s) latency (v=1500 m/s) high cost Optical Underwater Communication

Underwater communication – Preliminary results INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva Almost 7 hours BER monitoring Up to 100 Mbit/s Error free after FEC decoding

OWC for INFIERI applications OWC for Medical Imaging: – To avoid strong electromagnetic interference in PET detectors We performed some preliminary results for the joint project with University Carlos 3 of Madrid. INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva

Board-to-Board communication – Introduction OWC for HEP Design a Multi Gigabit OWC system for particles detectors (CMS used as a case study) Requirements: – Transmission distance: 10 cm – Transmission bitrate: 2.5 Gbit/s – Target bit error rate (BER): – HEP environment INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva

Board-to-Board communication – Preliminary results INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva Preliminary experimental results: o Tx: Vertical Cavity Surface Emitting Laser (VCSEL) –Relatively high output optical power: 0 dBm (1 mW) –Medium divergence angle: 16° –Emission wavelength: 1550 nm (no absorption with silica material) o Rx: Photodiode –Active area: 60 µm diameter –Ball lens: 1.5 mm diameter Transmission link up to 1 cm approx. Ray-tracing simulation (TracePro) in order to optimize the receiver

Board-to-Board communication – Preliminary results INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva Target distance: 10 cm Target bitrate: 2.5 Gbit/s Target bit error rate (BER): Simulation shows 2 dB power margin respect to our transmitted power As expected, margin increases with bigger ball lens (together with tolerance to misalignment) Simulation shows 2 dB power margin respect to our transmitted power As expected, margin increases with bigger ball lens (together with tolerance to misalignment)

Board-to-Board communication – Preliminary results INFIERI 5th Workshop: April 27-29, 2015, CERN Geneva Ball lens Photodiode misalignment Current condition 22 dB power penalty (~150 times)

Conclusions Optical wireless system as new technology alternative to RF Main application: communication -> Visible Light Communication High-speed indoor communication 5.2 Gbit/s WDM approach in 3 m (RECORD) 400 Mbit/s in Non-directed 2 m (RECORD) Vehicles to vehicles communication Security message up to 31 m exploiting 1 LED Underwater communication Up to 100 Mbit/s error-free in 2.5 m underwater Medical Imaging Preliminary results: tolerance measurement at m distance High Energy Physics Preliminary results: 1 cm transmission. Simulated: 10 cm feasible

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