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.

People

• Murat Yuksel (University of Nevada - Reno), murat.yuksel@ucf.edu
• Mona Hella (Rensselaer Polytechnic Institute), hellam@ecse.rpi.edu
• Mehmet Bilgi (University of Nevada - Reno), mehmetbilgi@gmail.com
• Abdullah Sevincer (University of Nevada - Reno), asev@cse.unr.edu
• Behrooz Nakhkoob (Rensselaer Polytechnic Institute), nakhkb@rpi.edu
• Michelle Ramirez (University of Nevada - Reno), beemyladybug1@yahoo.com

Prototype

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.

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.

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

Publications

• M. Bilgi, A. Sevincer, M. Yuksel, and N. Pala, Optical Wireless Localization, to appear in Wireless Networks, ACM/Springer.
  Abstract: In this paper, we explore the possibility of using directionality of free-space-optical (a.k.a. optical wireless) communications for solving the 3-D localization problem in ad-hoc networking environments. Range-based localization methods either require a higher node density (i.e., at least three other localized neighbors must exist) than required for assuring connectedness or a high-accuracy power-intensive ranging device such as a sonar or laser range finder, which exceeds the form factor and power capabilities of a typical ad-hoc node. Our approach exploits the readily available directionality information provided by a physical layer using optical wireless and uses a limited number of GPS-enabled nodes, requiring a very low node density (2-connectedness, independent of the dimension of space) and no ranging technique. We investigate the extent and accuracy of localization with respect to varying node designs (e.g., increased number of transceivers with better directionality) and density of GPS-enabled and ordinary nodes as well as messaging overhead per re-localization. Although denser deployments are desirable for higher accuracy, our method still works well with sparse networks with little message overhead and small number of anchor nodes (as little as 2). We also present a proof-of-concept prototype of our FSO-based localization techniques and show the validity of our approach even with three transceivers per node.
• M. Bilgi and M. Yuksel, Capacity Scaling in Free-Space-Optical Mobile Ad Hoc Networks, to appear in Ad Hoc Networks, Elsevier Science.
  Abstract: Wireless networking has conventionally been realized via radio-frequency-based communication technologies. Free-Space-Optical (FSO) communication with an innovative multi-element node design leverages spatially diverse optical wireless links; making it a viable solution to the well-known diminishing per-node throughput problem in large-scale RF networks. Although it has the advantage of high-speed modulation, maintenance of line-of-sight between two FSO transceivers during a transmission is a challenge since FSO transmitters are highly directional. In this paper, we present our simulation efforts to make high-level assessments on throughput characteristics of FSO-MANETs while considering properties of FSO propagation and existence of multiple directional transceivers. We identify the intermittent connectivity problem that is caused by the relative mobility of nodes with multiple directional transceivers. We propose two cross-layer buffering schemes to remedy this problem and present their performance results. We conclude that sophisticated buffering mechanisms are required to properly buffer a packet during the misalignment period of two communicating nodes to avoid negative effects of this intermittency on the transport layer.
• A. Sevincer, H. T. Karaoglu, and M. Yuksel, Performance Analysis of Voice Transfer Using Multi-Transceiver Optical Communication Structures, Proceedings of IEEE International Conference on Space Optical Systems and Applications (ICSOS), pages 72-77, Santa Monica, CA, May 2011. (slides)
  Abstract: Free-space-optical (FSO) communication has recently attracted attention as a complementary alternative to radio frequency (RF) wireless networks. However, the directionality of FSO communication is prone to mobility, which requires maintenance of line-of-sight (LOS) alignment between FSO transceivers. 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. In this paper, we present a prototype implementation of such multi-transceiver electronically steered communication structures to measure the performance of a voice file transfer over such multi-transceiver systems. We show that by using multiple directional transceivers and LOS detection and establishment protocol, we can assign multiple logical data streams to appropriate physical transceivers and transfer different voice files simultaneously to multiple FSO nodes with tolerable disruptions and overhead.
• M. Bilgi, M. Yuksel, and N. Pala, 3-D Optical Wireless Localization, Proceedings of IEEE GLOBECOM Workshop on Optical Wireless Communications (OWC), pages 1087-1091, Miami, FL, December 2010. (slides)
  Abstract: In this paper, we explore the possibility of using directionality of free-space-optical (a.k.a. optical wireless) communications for solving the 3-D localization problem in ad-hoc networking environments. Range-based localization methods either require a higher node density (i.e., at least three other localized neighbors must exist) than required for assuring connectedness or a high-accuracy power-intensive ranging device such as a sonar or laser range finder, which exceeds the form factor and power capabilities of a typical ad-hoc node. Our approach exploits the readily available directionality information provided by a physical layer using optical wireless and uses a limited number of GPS-enabled nodes, requiring a very low node density (2-connectedness, independent of the dimension of space) and no ranging technique. We investigate the extent and accuracy of localization with respect to varying node designs (e.g., increased number of transceivers with better directionality) and density of GPS-enabled and ordinary nodes as well as messaging overhead per re-localization. We conclude that although denser deployments are desirable for higher accuracy, our method still works well with sparse networks with little message overhead and small number of anchor nodes (as little as 2).
• B. Nakhkoob and M. M. Hella, Power-Aware Design for High Data Rate Free Space Optical Receivers, Proceedings of IEEE International Conference on Microelectronics (ICM), pages 72-75, Cairo, Egypt, December 2010.
  Abstract: A design methodology for low power front-end receiver targeting CMOS imagers for free space optical FSO communications is presented. The differential front-end is formed of two transimpedance amplifiers integrated with a Spatially Modulated Light detector SML, a Cherry-Hopper amplifier, an equalizer and a buffer stage. The circuit is implemented in 130 nm CMOS technology and is intended for incorporation in a CMOS imager for Line Of Sight LOS tracking in mobile FSO links. The front-end circuit achieves a 4GHz bandwidth, 64 dBW transimpedance gain and occupies an active area of 109 × 136 (μm)². It consumes 17.7 mW in total, including the differential 50 W output buffer, of which only 0.65 mW is consumed in the regulated cascode TIA input stage. The average input referred current noise is 17 PA/ÖHz in 4 GHz bandwidth.
• M. Bilgi and M. Yuksel, Throughput Characteristics of Free-Space-Optical Mobile Ad-Hoc Networks, Proceedings of ACM International Conference on Modeling, Analysis and Simulation of Wireless and Mobile Systems (MSWiM), pages 170-177, Bodrum, Turkey, October 2010. (slides)
  Abstract: Wireless networking has conventionally been realized via radio-frequency-based communication technologies. Free-Space-Optical (FSO) communication with an innovative multi-element node design leverages spatially diverse optical wireless links; making it a viable solution to the well-known diminishing per-node throughput problem in large-scale RF networks. Although it has the advantage of high-speed modulation, maintenance of line-of-sight between two FSO transceivers during a transmission is a crucial problem since FSO transmitters are highly directional. In this paper, we present our simulation efforts to make high-level assessments on throughput characteristics of FSO-MANETs while considering properties of FSO propagation and existence of multiple directional transceivers.
• A. Sevincer, M. Bilgi, M. Yuksel, and N. Pala, Multi-Transceiver Free-Space-Optical Communication Structures (demo), ACM Annual International Conference on Mobile Computing and Networking (MobiCom), Chicago, IL, September 2010.
• A. Sevincer, M. Bilgi, M. Yuksel, and N. Pala, Multi-Transceiver Free-Space-Optical Communication Structures (poster/demo), ACM International Conference on Mobile Systems, Applications, and Services (MobiSys), San Francisco, CA, June 2010.
• M. Bilgi and M. Yuksel, Packet-Based Simulation for Optical Wireless Communication, Proceedings of IEEE Workshop on Local and Metropolitan Area Networks (LANMAN), pages 1-6, Long Branch, NJ, May 2010. (slides)
  Abstract: This paper presents packet-based simulation tools for free-space-optical (FSO) wireless communication. We implement the well-known propagation models for free-space-optical communication as a set of modules in NS-2. Our focus is on accurately simulating line-of-sight (LOS) requirement for two communicating antennas, the drop in the received power with respect to separation between antennas, and error behavior. In our simulation modules, we consider numerous factors affecting the performance of optical wireless communication such as visibility in the medium, divergence angles of transmitters, field of view of photo-detectors, and surface areas of transceiver devices.
• M. Bilgi and M. Yuksel, and N. Pala, 3-D for Optical Wireless Localization, (poster) IEEE Workshop on Local and Metropolitan Area Networks (LANMAN), Long Branch, NJ, May 2010.
• A. Sevincer, M. Bilgi, M. Yuksel, and N. Pala, Prototyping Multi-Transceiver Free-Space-Optical Communication Structures, Proceedings of IEEE International Conference on Communications (ICC), pages 1-5, Cape Town, South Africa, May 2010. (slides)
  Abstract: Wireless networking has conventionally been realized via radio frequency (RF) based communication technologies. However, the capacity of these networks are limited by the availability of the RF spectrum. Free-Space-Optical (FSO) communication has the potential to deliver wireless communication links at optical-level speeds. Although it has the advantage of high-speed modulation, maintenance of line-of-sight (LOS) between transceivers during an on-going transmission is an important issue since FSO transmitters are highly directional. In this paper, we present a prototype implementation of such multi-transceiver electronically-steered communication structures. Our prototype uses a simple LOS detection and establishment protocol and assigns logical data streams to appropriate physical links. We show that by using multiple directional transceivers we can maintain optical wireless links with minimal disruptions that are caused by relative mobility of communicating nodes.
• M. Bilgi and M. Yuksel, Multi-Transceiver Simulation Modules for Free-Space-Optical Mobile Ad Hoc Networks, Proceedings of SPIE Defense, Security, and Sensing, Volume 7705, pages 77050B, Orlando, FL, April 2010. (slides)
  Abstract: This paper presents realistic simulation modules to assess characteristics of multi-transceiver free-space-optical (FSO) mobile ad-hoc networks. We start with a physical propagation model for FSO communications in the context of mobile ad-hoc networks (MANETs). We specifically focus on the drop in power of the light beam and probability of error in the decoded signal due to a number of parameters (such as separation between transmitter and receiver and visibility in the propagation medium), comparing our results with well-known theoretical models. Then, we provide details on simulating multi-transceiver mobile wireless nodes in Network Simulator 2 (NS-2), realistic obstacles in the medium and communication between directional optical transceivers. We introduce new structures in the networking protocol stack at lower layers to deliver such functionality. At the end, we provide our findings resulted from detailed modeling and simulation of FSO-MANETs regarding effects of such directionality on higher layers in the networking stack.
• B. Nakhkoob, M. Bilgi, M. Yuksel, and M. Hella, Multi-Transceiver Optical Wireless Spherical Structures for MANETs, IEEE Journal on Selected Areas of Communications, pages 1612-1622, Volume 27, Number 9, December 2009.
  Abstract: Due to its high bandwidth spectrum, Free-Space-Optical (FSO) communication has the potential to bridge the capacity gap between backbone fiber links and mobile ad-hoc links, especially in the last-mile. Though FSO can solve the wireless capacity problem, it brings new challenges such as frequent disruption of wireless communication links (intermittent connectivity) and the line-of-sight (LOS) requirements. In this paper, we study a multi-transceiver spherical FSO structure as a basic building block for enabling optical spectrum in mobile ad-hoc networking. We outline optimal designs of such multi-transceiver subsystems such that coverage is maximized and crosstalk among neighboring transceivers is minimized. We propose a low-level packaging architecture capable of handling hundreds of transceivers on a single structure. We also present MANET transport performance over such multi-element mobile FSO structures in comparison to legacy RF-based MANETs.
• M. Yuksel, J. Akella, S. Kalyanaraman, and P. Dutta, Free-Space-Optical Mobile Ad-Hoc Networks: Auto-Configurable Building Blocks, ACM/Springer Wireless Networks, Volume 15, Number 3, pages 295-312, April 2009.
  Abstract: Existence of line of sight (LOS) and alignment between the communicating antennas is one of the key requirements for free-space-optical (FSO) communication. To ensure uninterrupted data flow, auto-aligning transmitter and receiver modules are necessary. We propose a new FSO node design that uses spherical surfaces covered with transmitter and receiver modules for maintaining optical links even when nodes are in relative motion. The spherical FSO node provides angular diversity in 3-dimensions, and hence provides an LOS at any orientation as long as there are no obstacles in between the communicating nodes. For proof-of-concept, we designed and tested an auto-configurable circuit, integrated with light sources and detectors placed on spherical surfaces. We demonstrated communication between a stationary and a mobile node using these initial prototypes of such FSO structures. We also performed the necessary theoretical analysis to demonstrate scalability of our FSO node designs to longer distances as well as feasibility of denser packaging of transceivers on such nodes.
• B. Cheng, M. Yuksel, and S. Kalyanaraman, Orthogonal Rendezvous Routing Protocol for Wireless Mesh Networks, IEEE/ACM Transactions on Networking, Volume 17, Number 2, pages 542-555, April 2009.
  Abstract: Routing in multi-hop wireless networks involves the indirection from a persistent name (or ID) to a locator. Concepts such as coordinate space embedding help reduce the number and dynamism complexity of bindings and state needed for this indirection. Routing protocols which do not use such concepts often tend to flood packets during route discovery or dissemination, and hence have limited scalability. In this paper, we introduce Orthogonal Rendezvous Routing Protocol (ORRP) for meshed wireless networks. ORRP is a lightweight-but-scalable routing protocol utilizing directional communications (such as directional antennas or free-space-optical transceivers) to relax information requirements such as coordinate space embedding and node localization. The ORRP source and ORRP destination send route discovery and route dissemination packets respectively in locally-chosen orthogonal directions. Connectivity happens when these paths intersect (i.e., rendezvous). We show that ORRP achieves connectivity with high probability even in sparse networks with voids. ORRP scales well without imposing DHT-like graph structures (e.g., trees, rings, torus etc.). The total state information required is O(N^3/2) for N-node networks, and the state is uniformly distributed. ORRP does not resort to flooding either in route discovery or dissemination. The price paid by ORRP is suboptimality in terms of path stretch compared to the shortest path; however we characterize the average penalty and find that it is not severe.
• B. Cheng, M. Yuksel, and S. Kalyanaraman, Using Directionality in Mobile Routing, (short paper) Proceedings of IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS), pages 371-376, Atlanta, GA, September 2008. (slides)
  Abstract: The increased usage of directional methods of communications has prompted research into leveraging directionality in every layer of the network stack. In this paper, we explore the use of directionality in layer 3 to facilitate routing in highly mobile environments. We introduce Mobile Orthogonal Rendezvous Routing Protocol (MORRP), a lightweight, but scalable routing protocol utilizing directional communications (such as directional antennas or free-space-optical transceivers) to relax information requirements such as coordinate space embedding, node localization, and mobility. This relaxation is done by introducing a novel concept called the directional routing table (DRT) which maps a set-of-IDs to each directional interface to provide probabilistic routing information based on interface direction. We show that MORRP achieves connectivity with high probability even in highly mobile environments while maintaining only probabilistic information about destinations. We also compare MORRP with various proactive, reactive, and position-based routing protocols using single omni-directional interfaces and 8 directional interfaces and show that MORRP gains over 10-14X additional goodput vs. traditional protocols and 15-20% additional goodput vs. traditional protocols using multiple interfaces.
• M. Bilgi and M. Yuksel, Multi-Element Free-Space-Optical Spherical Structures with Intermittent Connectivity Patterns, Proceedings of IEEE INFOCOM Student Workshop, Phoenix, AZ, April 2008. (slides)
  Abstract: Due to its high bandwidth spectrum, Free-Space-Optical (FSO) communication has the potential to bridge the capacity gap between backbone fiber links and mobile ad-hoc links, especially in the last-mile. Though FSO can solve the wireless capacity problem, it brings new challenges, like frequent disruption of physical link (intermittent connectivity) and the line of sight (LOS) requirements. In this paper, we study a spherical FSO structure as a basic building block and examine the effects of such FSO structures to upper layers, especially to TCP behavior for stationary and mobile nodes.
• B. Cheng, M. Yuksel, and S. Kalyanaraman, Rendezvous-based Directional Routing: A Performance Analysis, Proceedings of IEEE International Conference on Broadband Communications, Networks, and Systems (BROADNETS), pages 271-279, Raleigh, NC, September 2007. (invited paper) (slides)
  Abstract: Routing in wireless ad-hoc networks have had to grapple with the twin requirements of connectivity and scalability. Recently, [1] has attempted to mitigate this issue by using directional communication methods to find intersections between source-rendezvous and rendezvous-destination paths, providing effective routing in unstructured, flat networks. [1] showed that by “drawing” two lines orthogonal to each other at each node, it is possible to provide over 98% connectivity while maintaining only order O(N^(3/2)) states. It is interesting, however to investigate what happens when additional lines are “drawn” and how that affects connectivity, path length, state complexity, control packet overhead, and aggregate throughput. In this paper, we examine how transmitting along one, two, three, and four lines affects routing and provide both analytical bounds for connectivity as well as packetized simulations on how these methods stack up in a more realistic environment. We show that by sending packets out in more directions, increased connectivity and smaller average path length results only up to a point. The trade-off, however, is added state information maintained at each node. We also show that in mobile environments, adding additional lines increases the chances for successful packet delivery only marginally.

Deliverables

• Latest version of our FSO package for ns-2 is available from here.

Funding

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

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

Last updated on May 19, 2023