Optimal Communication Coverage for Free-Space-Optical MANET Building Blocks

1. Optimal Communication Coverage for Free-Space-Optical MANET Building Blocks Murat Yuksel, Jayasri Akella, Shivkumar Kalyanaraman, Partha Dutta Electrical, Computer, and Systems Engineering Department Rensselaer Polytechnic Institute, Troy, NY yuksem@ecse.rpi.edu, akellj@rpi.edu, shivkuma@ecse.rpi.edu, duttap@rpi.edu

2. Outline • Motivation • FSO MANETs Node Designs • Optimizing FSO Node Designs • FSO Node Design Recommendations • Summary Rensselaer Polytechnic Institute, Troy, NY

3. Motivation • Free-space-optical (FSO) communication requirements: • Line of sight (LOS) existence • alignment between the communicating antennas • FSO against RF: • Lower power per bit • Significantly higher transmission rates due to optical spectrum • FSO in MANETs: • Inexpensive, mobility tolerant components needed Rensselaer Polytechnic Institute, Troy, NY

4. FSO MANETs Node Designs • Traditional FSO node/component designs: • sufficient for building sways or vibrations • not sufficient for mobile ad hoc environments • To ensure uninterrupted data flow, auto-aligning transmitter and receiver modules are necessary. • FSO node designs that uses: • spherical surfaces – angular diversity • covered with multiple transmitter and receiver modules – spatial reuse Spherical surface covered (tessellated) with LED+PD pairs (transceivers) Hybrid of spherical and array: honeycombed arrays of transceivers Rensselaer Polytechnic Institute, Troy, NY

5. FSO MANETs Node Prototypes • Electronic tracking of the other mobile node • allows maintenance of the logical optical link Rensselaer Polytechnic Institute, Troy, NY

6. Optimizing FSO Node Designs • How good the node be in terms of • coverage? • range? • How many transceivers can/should be placed on the nodes? • Various factors effect optimum coverage and the designs of FSO nodes: • Visibility – weather conditions • Transmitter’s source power and detector’s sensitivity • Divergence and reception angles of devices – higher cost for smaller angles • Number of transceivers per area – packaging optimality • We focus on a 2-d circular design Rensselaer Polytechnic Institute, Troy, NY

7. Optimizing FSO Node Designs (cont’d) • Two cases are possible: overlapping or non-overlapping coverage. The interference area can be calculated if the FSO propagation lobe is approximated by a triangle and a half circle. Rensselaer Polytechnic Institute, Troy, NY

8. Optimizing FSO Node Designs (cont’d) • For given source power and receiver sensitivity, we calculate the range Rmax based on the FSO propagation model (atmospheric and geometric attenuation): • Depending on transmitter source power P, divergence angle θ, and visibility V, optimal number of transceivers n that should be placed on the 2-d circular FSO node can differ. Since coverage of a single transceiver C is dependent on P, θ, V and n; for given node and transceiver sizes the optimization problem can be written as: Rensselaer Polytechnic Institute, Troy, NY

9. FSO Node Design Recommendations • The source power P and the visibility V have little or no effect on the optimality of n; rather, the geometric shape of the FSO node and the divergence angle plays the major role. • FSO nodes allows adaptive tuning of the source power based on the actual visibility. Rensselaer Polytechnic Institute, Troy, NY

10. FSO Node Design Recommendations Rensselaer Polytechnic Institute, Troy, NY

11. Summary • Modeled communication coverage and range for FSO MANET node designs. • two-dimensional modeling • FSO node designs: • allow very dense packaging, • and can scale to very long communication ranges as well as large coverage. • Future work includes issues like: • optimal transceiver packaging patterns for desired coverage in three-dimensions, • and application-specific designs of such node designs. Rensselaer Polytechnic Institute, Troy, NY

12. Thank you !! Rensselaer Polytechnic Institute, Troy, NY