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Issues in Optical Wireless Communications

This document introduces some issues in optical wireless communications (OWC), including mobility enhancement, range increase, modulation schemes, and factors to consider for specific applications.

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Issues in Optical Wireless Communications

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  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title:Some Issues for OWC Date Submitted: Jan.15, 2015 Source: Soo-Young Chang (CSUS) and Jaesang Cha (Seoul National Univ. of Science & Technology) Company: CSUS and Seoul National Univ. of Science & Technology Address: Voice: +1-530-574-2741, E-Mail: sychang@ecs.csus.edu Re: Abstract: Some issues for optical wireless communications are introduced in this document. Purpose: To suggest some issues which can be raised for future OWC Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15. Slide 1

  2. OWC FEATURES • Larger bandwidth • Low probability of intercept: security • The light beam can be very narrow, which makes FSO (Free Space Optics) hard to intercept, improving security: High directivity and narrow beamwidth • Immunity from interference or jamming • Relief from frequency spectrum allocation issue : • License-free operation • Smaller, lighter, lower power, lower complexity

  3. ISSUES TO BE SOLVED (1) • Enhance mobility for OWC: • How to enhance mobility when OWC is applied? • Doppler effect. • Doppler shifts due to mobility are relatively small comparing the frequency band used. • If intensity modulation is used, this effect may affect less to information recovery. • Non-line-of-sight problem • Deploy multiple access points in various directions/areas to have higher probability of transmit/reception. • An OWC device processes signals from multiple access points and selects one (best) signal if needed. • Multi-hop OWC can be a solution because a unit can reach at least one base station or relay/repeater.

  4. ISSUES TO BE SOLVED (2) • Increase range for OWC? • So short range (up to 10 m) and narrow coverage • Various diversity schemes can be considered to increase ranges and/or data rates. • Spatial diversity, Temporal diversity (time diversity), Wavelength diversity • Duplexing between infra and units • How to implement two way communications between infra and units? Full duplex? Half duplex? TDM? FDM? • Uni-direction • Bi-direction • Hybrid: combine VLC and RF • Hot spot: combine VLC and Wi-Fi: both down links • OWC mainly relies on intensity modulation.

  5. ISSUES TO BE SOLVED (3) • Abrupt blocking problem to be solved. • Short period blocking • Long period blocking • Eye safety issue for coherent lights

  6. MODULATION FOR OWC (1) • Consider all modulation schemes which are used for RF comm. including UWB • LED emits incoherent light over a wide spectrum. • Ambient noise source is serious. • Sunlight, fluorescent, incandescent light etc. • Phase detection is impossible. • One possible way is utilization of color space models • Adaptive modulation applied • Lower data rate: • lower power or • Less sophisticated modulation scheme applied • Longer range • Adaptively change modulation schemes according to data rate and range

  7. MODULATION FOR OWC (2) • One possible way is utilization of color space models

  8. Range Speed High or low Symmetric or asymmetric One way or two way uplink and/or downlink Single channel or multiple channels contents Voice Data Video Reliability Power consumption Latency/delay Interference handling Ambient lights: sun light, incandescent, fluorescent light Divergence, FOV (field of view) Device discovery/alignment Mobility Quality of service (QoS) Power control FACTORS CONSIDERED FOR ANY SPECIFIC APPLICATIONS (1) ETRI Submission Slide 8

  9. FACTORS CONSIDERED FOR ANY SPECIFIC APPLICATIONS (2) • Topology • Do we want to support connections among multiple devices? • If so, how to switch the light direction between devices? • Blockage recovery • If the light is blocked, how to recover the communications between two devices? • Multiple hops • Do we allow the signal go through multiple hops of OWC links? • Hybrid network • Inter-working between PLC/Ethernet and OWC? • Coexistence/interoperability with • Infrared • laser

  10. FACTORS CONSIDERED FOR ANY SPECIFIC APPLICATIONS (3) Silicon PD spectral response

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