Multi-Element Optical Wireless Modules for Mobile Networking and - PowerPoint PPT Presentation

Multi-Element Optical Wireless Modules for Mobile Networking and Lighting Murat Yuksel murat.yuksel@ucf.edu Networking and Wireless Systems Lab (NWSL) Electrical and Computer Engineering University of Central Florida Project Websites https://sites.google.com/site/nsfvlc http://www.ece.ucf.edu/~yuksem/fso-manet.htm CoNEXT Student Workshop, December 9, 2019

Outline Part I: Multi-Element FSO (Optical Wireless) Modules n Motivation n FSO Modules w/ Electronic Steering n Multi-Transceiver FSO Spheres n LOS Alignment Protocol n FSO Packet Simulations n FSO Modules w/ Mechanical Steering n In-Band LOS Alignment n 2D vs. 3D n Multi-Element VLC n Future Directions Part II: Career Advice CoNEXT Student Workshop, December 9, 2019

Part I Multi-Element FSO (Optical Wireless) Modules CoNEXT Student Workshop, December 9, 2019

Wireless Capacity – NOW! n Scary trends in mobile wireless demand n Grown 4K-fold in 10 years and almost 400M-fold in 15 years. 2017-2022 predictions: > 1.5 times increase per year Cisco VNI Report 2018 CoNEXT Student Workshop, December 9, 2019

Seems Inescapable by the Internet n Wireless node count > wireline in 2015! n Mobile node count will surpass fixed node count too.. n Mobile nodes and M2M will dominate wireless traffic The RF spectrum is getting saturated.. We need alternative communication spectrum resources for opportunistic usage. CoNEXT Student Workshop, December 9, 2019

Wireless Spectrum Tradeoffs: 6 Rate/Mobility/Range Rate More Redundancy & Spatial Reuse We study this mostly (e.g. MIMO for LTE Advanced, unexplored region femtocells) for directional high frequency bands (e.g., FSO and mmWave) Recent 4G designs with a focus on are mostly exploring Designs directionality, Designs this region w/ high spatial reuse and w/ high Rate & software-control. Rate & Range Mobility while trying to while trying to mmWave? increase Mobility. increase Range. More Directionality (e.g. WiMAX) Designs w/ high Mobility & Range while 3G, 4G trying to increase Rate. Range Mobility More More Directionality Most 3G and 4G Coding (e.g., UMTS, designs explored (e.g., GSM) WiFi, Mobile this region WiMAX) CoNEXT Student Workshop, December 9, 2019

7 Wireless Spectrum Tradeoffs (cont’d) n Mostly unlicensed bandwidth available at higher frequency EM spectrum Higher rate even with modest spectral n efficiency High spatial reuse due to highly directional n signal propagation FSO n But, these EM regions are poorly suited for mmWave range : small wavelength is absorbed too n 802.11-16 easily Cellular (2G-4G) mobility : line-of-sight alignment n KEY INSIGHT Give up on range goals, focus on rate instead! HOW? Develop low-cost multi-element designs for opportunistic (ad-hoc) use. Handle mobility at higher layers with limited support from PHY/MAC. CoNEXT Student Workshop, December 9, 2019

8 Free-Space-Optical (FSO): Open spectrum n Open spectrum : n > 300 GHz n FSO usage: n point-to-point links n interconnects n indoor infrared/visible communications n DoD use of FSO: n satellite communications n air-to-ground, air-to-air, air-to- satellite n Recent civilian uses: n VLC CoNEXT Student Workshop, December 9, 2019

Optical Wireless: Commodity components Receiver Transmitter (Photo Diode/ Transistor) (Laser/VCSEL/LED) ON-OFF Keyed Light Pulses Digital Data IrDAs… Lasers… LEDs… VCSELs… Many FSO components are low cost & available for mass production. CoNEXT Student Workshop, December 9, 2019

Opportunistic FSO (Optical Wireless) Channel Complements always-on, lower-rate, Available Capacity higher range wireless. Optical wireless opportunistic channel RF opportunistic channel Basic RF channel Delay-tolerant applications (e.g. email, FTP, Video-on-demand) Real-time, interactive Basic RF channel (e.g. 3G, 4G, 5G/WiMAX) applications (e.g. chat, VoIP) Time We consider a specific PHY technology, free-space-optics (FSO), that could be useful in this context, and its implications on higher-layer protocols. CoNEXT Student Workshop, December 9, 2019

Optical Wireless: Why? n More secure: Highly directional => low probability of interception n Small size and weight: Dense packaging is possible n Very low cost and reliable components n <60 cents a piece and <$5 per LED transceiver package + up to 10 years lifetime n Very low power consumption (100 microwatts for 10-100 Mbps!) n Even lower power for 1-10 Mbps n 4-5 orders of magnitude improvement over RF n Huge spatial reuse => multiple parallel channels for bandwidth increases CoNEXT Student Workshop, December 9, 2019

FSO Issues/Disadvantages n Limited range (no waveguide, unlike fiber optics) n Need line-of-sight (LOS) n Any obstruction or poor weather (fog, heavy rain/snow) can increase BER in a bursty manner n Bigger issue: Need tight LOS alignment: n LOS alignment must be maintained with mobility or sway! n Effects of relative distance and mobility Received power Spatial profile: ~ Gaussian drop off Can we reap FSO’s benefits while solving these issues? CoNEXT Student Workshop, December 9, 2019

13 Software-Defined FSO Modules: Spherical Designs How to handle mobility under LOS alignment requirement? n Software-Defined Mobile FSO = Directionality + Angular Diversity + Electronic Steering Multi-transceiver spherical FSO designs. Need a distributed protocol for this! A B Bidirectional LOS • Multi-element spherical Spherical Modules Tessellated w/ modules B’ Many FSO • Angular diversity due to Transceivers spherical packaging • Designs conformal to surfaces • Electronic steering of LOS alignment across many redundant FSO transceiver elements CoNEXT Student Workshop, December 9, 2019

3-Transceiver Prototype The design consists of 3 FSO Circular 3 transceivers connected to a Transceiver circuit board with a Design microcontroller. PIC 12f615 Transceiver Modulator Microcontroller Header Programming Line Interface Transceiver CoNEXT Student Workshop, December 9, 2019

FSO Prototype: Mobility Experiment C A B Node-A A Node-B C ~19Kb/s ~20m frame size 50B B alignment timer 500ms Ad Hoc Networks 2013 CoNEXT Student Workshop, December 9, 2019

Worth It? OK. It works.. But, does it really worth the effort? Can we really scale wireless capacity via these multi- transceiver FSO modules? What are the limits? How to tune the LOS alignment protocol? How about power consumption of all these transceivers? … CoNEXT Student Workshop, December 9, 2019

FSO Packet Simulations: Propagation & Interference n FSO Propagation n Geometric Attenuation n divergence angle n receiver’s surface n Atmospheric Attenuation n visibility ! "# = % + 1 2) cos - . "# Lambertian law CoNEXT Student Workshop, December 9, 2019

TCP Throughput over FSO Modules For high mobility, need to Spatial reuse exploited: increase/tune search frequency or > 100-fold improvement in use buffering at layers 2 or 3. dense networks Ad Hoc Networks 2014 CoNEXT Student Workshop, December 9, 2019

FSO Modules: Buffering End-to-end transport like TCP is extremely sensitive to intermittency è n Need to smoothen the opportunistic FSO channel. Buffer the layer 2 frames during Available intermittent disconnections Capacity Optical wireless opportunistic channel RF opportunistic channel Basic RF channel Basic RF channel (e.g. 2G, 3G, 4G/WiMAX) Time CoNEXT Student Workshop, December 9, 2019

FSO Modules: Buffering Cross-layer buffering But, interacts with TCP makes FSO almost congestion control at independent of Buffering helps low mobility! network size! significantly at high mobility. 8 transceivers CoNEXT Student Workshop, December 9, 2019

21 FSO Modules: Mechanical Steering n Assumptions: n One transceiver on mechanically steerable head n Equipped with Inertial Measurement Unit n In-band: No radio or out-of-band channel n No GPS n Can we discover and maintain the FSO link in n 2D: PackBots, UGVs, ships n 3D: UAVs, Google Balloons, FB solar drones CoNEXT Student Workshop, December 9, 2019

(Sort of) In-Band LOS Discovery n 2D: Randomized rotation n 3D: Synch w/ RF at the start, then, rotate over a helix: 2 s for 12 0 divergence angle 0.2 s for 12 0 divergence angle 3 s for 7.5 0 divergence angle 0.4 s for 7.5 0 divergence angle 19 s for 3 0 divergence angle 0.9 s for 5 0 divergence angle 2.5 s for 3 0 divergence angle (w/ 90% conf) (w/ 90% conf) IEEE MILCOM 2016 IEEE TMC 2019 1 CDF of Discovery 0.8 0.6 Experiment: ω = 135 o /s Snapshot of 3D discovery experiments Experiment: ω = 180 o /s 0.4 Simulation: ω = 135 o /s 0.2 Simulation: ω = 180 o /s 0 0 1 2 3 4 5 6 Time Spent (s) Discovery within a few seconds: IEEE MILCOM 2016 No GPS, only initial synchronization via a Ad Hoc Nets 2019 beacon (patent pending) 3D: Still evaluating a totally in-band solution CoNEXT Student Workshop, December 9, 2019

23 In-Band LOS Link Maintenance in 3D Key Idea: Use the link itself to exchange n Laser at Long Range LED at Short Range at every t x Speed 25 m/s 5 m/s <Direction, Speed, Orientation of the head> Range 2.5km 100m Then, each node can autonomously n 3 o , 5 o , 7.5 o θ 2, 2.25, 2.5 mrad determine Angular Velocity of head n Direction of Rotation n IEEE TMC 2017 IEEE MILCOM 2016 IEEE ICC OWC 2016 ACM MOBICOM HotWireless 2015 Smaller tolerance to deviation à Smaller t x IEEE WCNC 2014 CoNEXT Student Workshop, December 9, 2019