FSO-MANETs: Free-Space-Optical Mobile Ad-hoc Networks


Problem Statement and Motivation - People - Prototype - Publications - Deliverables - Funding


Problem Statement and Motivation

Mobile ad-hoc communication is starting to find real-world applications beyond its military origins, in areas such as vehicular communications and delay tolerant networking. As the RF spectrum is getting saturated by recent advances in wireless communications, enabling optical spectrum in wireless communications is the needed revolution for ultra-high-speed mobile ad-hoc networks (MANETs) of the future. This project explores the potential for free-space-optics (FSO) in the context of very-high-speed mobile ad-hoc and opportunistic networking.


This project introduces basic building blocks for MANETs using FSO and prototypes multi-hop high-capacity FSO building blocks and protocols operating under high mobility. 3-d spherical structures covered with inexpensive FSO transceivers (e.g., VCSEL and photo-detector pair) solve issues relevant to mobility and line-of-sight (LOS) management via availability of several transceivers per node. Such structures facilitate electronic LOS tracking (i.e., “electronic steering”) methods instead of traditional mechanical steering techniques. The project also investigates reliability protocols as management of logical datastreams through multi-interface FSO structures pose a major challenge. By abstracting FSO directionality and LOS characteristics, the project explores issues relating to routing and localization, and develops layer 3 protocols and FSO-MANET demonstration in a lab setting. Results of this research can revolutionize the MANET technologies by enabling optical spectrum. FSO has been used at high-altitude communications, and this project enables FSO communications at lower-altitudes and in ad-hoc settings. This research will provide a new application for solid-state lighting technology due to potential integration of illumination and communication functions.





We have recently published results of our proof-of-concept prototype on the concept of “electronic steering” on a multi-transceiver node. The aim of the prototype is to illustrate that it is possible to seamlessly switch (i.e. steer) an ongoing data flow from one FSO transceiver to another without giving a significant disturbance to the ongoing data flow. We first designed a transceiver (shown in Figure 1) composed of two infrared LEDs and a photo-detector (PD). Each transceiver has a serial port interface through which it is possible to modulate the LEDs and read the signal received at the PD. We placed the PD at the rear of the transceiver board to reduce the amount of optical feedback from LEDs.


Figure 1: Front and rear views of our FSO transceiver with two LEDs and one PD. The transceiver diameter is 25mm.


We, then, combined multiple of such transceivers on a circular structure (shown in Figure 2) and connected them to a breadboard microcontroller. We programmed the microcontroller so that a line-of-sight (LOS) alignment protocol is applied to detect availability of alignments on the transceivers and if so use those alignments to transmit data. The LOS alignment protocol probes availability alignments by periodically sending search frames from transceivers and uses three-way handshakes to assure bi-directional alignments with neighbor nodes.


Description: three-txc-antenna

Figure 2: A 3-transceiver circular node structure.


The microcontroller also interfaces with a laptop via serial port. The laptop sends and receives data (e.g., an image or voice) via its serial port without knowing the fact that a multi-transceiver FSO structure is being used to send or receive the data. We assembled three such combinations of laptop, 3-transceivers and microcontroller and tested the possibility of seamless switching of data transmissions from one FSO transceiver to another while the node structures move with respect to each other. The experimental setup is shown in Figure 3. The three laptops establish two simultaneous separate data transmission (e.g. from A to C and C to B) and during these transmissions we move the nodes with respect to each other and observe that the electronic steering hands off the ongoing transmission to a new transceiver that is aligned with the neighbors. We plan to migrate our prototype to Ethernet ports of the laptops and attain higher transmission rates with better quality FSO transmitters and PDs. The end goal of our prototyping efforts to realize an FSO-MANET utilizing several of such multi-transceiver nodes performing simultaneous data transfers among each other. Further details and results of our prototype are available in our papers below.


Figure 3: Three laptops communicating via the multi-transceiver FSO node structures.


As shown in Figure 4, we envision a spherical multi-transceiver optical antenna that will include many more transceivers and apply advanced learning and algorithmic methods to guide LOS alignment across its transceivers. With dense packaging of hundreds of transceivers on these node structures it will be possible to establish several simultaneous ongoing data transmissions with each neighbor separately. Further, by using the directionality of the FSO signals it will also be possible to detect angle-of-arrival and use it for relative localization, a concept that we explored with simulation-based experiments in our papers.


Description: :docs:omnidirectional-fso-antenna.pdf

Figure 4: “Soccer ball” 3-D optical antenna.







This project is supported by National Science Foundation awards 0721452 and 0721612.


Problem Statement and Motivation - People - Prototype - Publications - Deliverables - Funding


Last updated on November 18, 2011