University of Nevada, Reno

Performance Analysis of Voice Transfer Using Multi-Transceiver OpticalCommunication Structures

Abdullah Sevincer, Hasan T. Karaoglu, and Murat Yuksel

asev@cse.unr.edu, karaoglu@cse.unr.edu, yuksem@cse.unr.edu

Project Website: http://www.cse.unr.edu/~yuksem/fso-manet.htm

IEEE ICSOS 2011, Santa Monica, CA

Outline

• Motivation• Literature Survey• Previous work & LOS Algorithm• Prototype Implementation• Experiments & Results• Conclusion & Future Work

Motivation• RF spectrum is highly saturated – need alternative mediums for

MANETs– Free-Space-Optical communication may serve as an alternative

complementary medium to RF• Spectrum characteristics

– 100+ GHz bandwidth – Low power per bit– License free

• Directional communication– Spatial reuse– Low probability of intercept– Full-duplex transceivers

• Device characteristics– Smaller form factor – dense packaging is possible– More durable

– Issues to be solved (among others):• LOS – availability, and detection when available• Mobility or sway – LOS maintenance

4

Motivation: FSO-MANETs

Free-Space-Optical (FSO)

Communications

Mobile Ad-Hoc Networking

• High bandwidth• Low power• Dense spatial reuse• License-free band of operation

• Mobile communication• Auto-configuration

Free-Space-OpticalAd Hoc Networks

• Spatial reuse and angular diversity in nodes• Low power and secure• Electronic auto-alignment• Optical auto-configuration (switching, routing)

Project Website: http://www.cse.unr.edu/~yuksem/fso-manet.htm

Motivation: FSO-MANETs

• Our approach and focus to achieve the vision of FSO-MANETs– Low altitude and shorter ranges• LOS becomes the major issue not the visibility• Obstacles are common than the visibility problems

– Cheaper devices (LEDs) with redundancy• Packaging and managing many transceivers per node• Electronic steering becomes possible if packaging

provides angular diversity• No need for mechanical steering

Motivation• Electronic steering over multi-transceiver FSO nodes

– By using multiple transceivers per node and automatically detecting neighbor nodes that are in LOS each other, we showed how to maintain the LOS alignment on FSO nodes. [IEEE ICC’10]

• Question: “Can we use such multi-transceiver structures for streaming-style applications which may require little or no disconnection?”

3-D optical antenna design.

FSO Literature

• High altitudes and longer ranges– FSO communications with a focus on coding and

modulation techniques– Attaining longer transmission ranges, hardware

design issues, and solutions against mobility– Focus on long distance (up to 7 kms) point-to-

point applications with employing high-speed laser or VCSEL hardware.

• Our focus: Low altitudes and shorter ranges

FSO Literature

• Multiple elements/transceivers in FSO communication in interconnects which communicate over very short distances.

• The main issues: – interference (or cross-talk) between adjacent

transceivers due to finite divergence of the light beam

–Misalignment due to vibration.

FSO Literature

• FSO transmitters are highly directional:– comes with a cost of LOS alignment problem– Requires smart mechanisms to manage LOS

among transceivers during an ongoing transmission.– Mechanical systems: (High maintenance and

expensive, not fast enough to recover disruptions, multi-point-to-multi-point communication are not considered).

• Our focus: Electronic steering with a redundancy of transceiver devices

Previous Work & LOS Detection Algorithm

• Instead of mechanical steering, we implemented

“electronic steering” over spherical optical antennas.• LOS detection and alignment establishment protocol

via fast handshakes among transceivers of neighboring nodes. – Quick and automatic hand-off of data flows among

different transceivers– Omni-directional propagation and spatial reuse at the

same time– Assigning logical data streams to appropriate physical

transceivers/channels

Prototype Implementation• Improved prototype with faster transceivers• Voice file transfers to evaluate performance of our LOS

detection and alignment establishment protocol over streaming-style application traffic.

• Mean Opinion Score (MOS) to evaluate voice transfer.

MOS Rating Perceived Quality

4-5 Excellent Toll Quality

3-4 Good Cell Phone Quality

<3 Fair Unacceptable

<2 Bad Unintelligible

Prototype-Hardware

• Controller Board:– PIC32 Ethernet Starter Kit– Expansion board

• FSO Transceivers

Prototype-SetupNODE-B

NODE-C

NODE-A

TR-B

TR-C

TR1-A

TR2-A

Wireless Link

Wireless Link

Prototype-Experiments

• Transceiver Performance Test:– Half Duplex Line– Portable Document File (PDF): 3637 bytes– File Transfer at varying distances

NODE-BNODE-A

TR-BWireless Link

Prototype-Setup-ExperimentsNODE-B

NODE-C

NODE-A

TR-B

TR-C

TR1-A

TR2-A

Wireless Link

Wireless Link

Prototype-Experiments

• Simultaneous File Transfer– Image Transfer from Node-A to both Node-B and

Node-C– Half Duplex and Full Duplex Line– Image File Length: 7572 bytes

• Voice File Transfer– 6 different voice file transfer for MOS evaluation– Voice File Transfer at varying distances

ResultsTransceiver Performance Test

Half Duplex

Image File Transfer

Full Duplex

MOS Performance: 6 FilesMOS Performance: varying distance

Good MOS Values!

Unacceptable Quality

Conclusion & Future Work

• Prototype: FSO system: multiple data streams • Simultaneous voice file transfers with minimal

disruptions and overheads• Multimedia service with off-the-shelf

components: Multi-transceiver & directionality• Future Work:

• Improvement on the quality of voice transfer• Improve the prototype: faster transceivers• Link-and physical layer buffering mechanisms: reduce

misalignment effects

Questions?

AcknowledgmentsThis work was supported by the U.S. National Science Foundation under awards 0721452 and 0721612 and DARPA under contract W31P4Q-08-C-

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