Wireless infrared indoor communications: how to combat the multi-path distortion S. Jivkova and M.Kavehrad Center for Information & Communications Technology Research (CICTR) Department of Electrical Engineering The Pennsylvania State University Photonic EAST 2000

Outline Multi-Spot Diffusing Configuration (MSDC): characteristic features Multi-path distortion Receiver geometrical configuration Channel parameters Novel receiver optical front-end design Conclusions Photonic East 2000

Characteristic features One-to-many and many-to-one communications Lack of alignment requirement Roaming possible Can be virtually free from multipath induced temporal distortion Relatively large cell size Tolerance to shadowing and blockage Quasi non-directed non-LOS configuration

Element T R Multipath distortion Multi-spot diffusing configuration

At least one diffusing spot lies within each branch field-of-view At most one diffusing spot lies within each branch field-of-view FOV1FOV2 Multi-spot diffusing configuration

Circle areas on the ceiling covered by the central receiver branch for a receiver position (0.3m, 05m) measured from the room corner Room size: 6m x 6m x 3m Reflectivity of room surfaces: 0.7 (walls and ceiling), 0.3 (floor) Number of reflections considered: 3 Transmitter position: center of the room, 0.9m above the floor

FOV1 (two diffusing spots within receiver branch FOV) FOV2 (one diffusing spot within receiver branch FOV) Multi-spot diffusing configuration: Channel characteristics

Field-of-view of a 7-branch composite receiver Number of spots covered by each branch: - At least one: - At most one: SS DD FOV2 FOV1 central side central Multi-spot diffusing configuration

Receiver optical subsystem Major factors in receiver optical subsystem design: Signal gain Ambient light rejection Physical weight, size and cost

wave 1, wave 2, hologram two plane waves, plane substrate (plane holographic mirror) wave 2, wave 1, hologram two spherical waves, curved substrate (spherical holographic mirror) two spherical waves, plane substrate (spherical holographic mirror) wave 2, wave 1, hologram Recording of Reflection Holograms Multi-spot diffusing configuration Receiver optical subsystem

Holographic curved mirror as a receiver optical front-end Multi-spot diffusing configuration Receiver optical subsystem photodetector holographic curved mirror 22 dielectric filling

Multi-spot diffusing configuration Receiver optical subsystem

Angular and spectral selectivity of a reflection hologram Multi-spot diffusing configuration Receiver optical subsystem   =0,   = , =850nm, n=1.5,  n=0.01, d=60  m

HSM HPM Multi-spot diffusing configuration Receiver optical subsystem

HSM HPM Multi-spot diffusing configuration Receiver optical subsystem

Diffuse configuration: Channel characteristics FOV=70deg FOV=10deg

Diffuse configuration: Diffuse configuration:Channel characteristics Room size: 8m x 8m x 4m Reflectivity of room surfaces: 0.7 Number of reflections considered: 5 Transmitter position: center of the room, 1m above the floor Lomba, Valadas and Duarte, 6 th IEEE Intl. Symp. On Personal, Indoor and Mobile Radio Communications, Sept , 1995, Toronto, Canada, Proc., pp

Comparison between Pure-Diffuse and Multi-Spot Diffuse (MIMO) in terms of 3-dB Optical Channel Bandwidth for a Sample Receiver Position 3.7m away from Transmitter 3-dB BandwidthArchitecture TypeField-of-View Diffuse Multi-Spot- Diffuse 70 deg 10 deg FOV1 FOV2 19MHz 23MHz 190MHz 2.4GHz Photonic East 2000

Conclusions Major factors causing channel distortion - Higher order reflections - Number of diffusing spots - Diffusing spot size Virtually ideal channel: conditions - FOV1 (3dB < 200MHz) - FOV2 (3dB > 2GHz) Holographic curved mirror as a receiver optical front-end - Multi-functionality - Insignificant physical weight Photonic East 2000