Exploratory Advanced Research Program

FHWA White Paper On Mobile Ad Hoc Networks

Introduction

Advanced, next-generation communications technologies offer the potential to greatly improve safety, system efficiency, and mobility on our Nation’s roadways. However, significant adoption of mobile applications is likely to quickly exceed the design and capacity of existing wireless communications networks, limiting the potential mobility and safety benefits of these applications.

Mobile ad hoc networks (MANETs) are one of the potential solutions to this problem. A MANET is “a self-configuring network of mobile routers connected by wireless links with no access point.”⁽¹⁾ While research on general-purpose MANETs—networks that have no infrastructure or specific intended application—is abundant,⁽²⁾ potential applications of MANETs to the national transportation system have not advanced beyond small-scale research activities, such as traffic management for road segments in downtown areas⁽³⁾ and intelligent traffic signal scheduling algorithms.⁽⁴⁾ To explore further research and application of MANETs, FHWA’s Exploratory Advanced Research (EAR) Program, which focuses on longer-term, higher-risk research with a high payoff potential, commissioned the production of a white paper on the state of the practice of MANETs. The focus of the paper is on the potential application of MANET concepts to surface transportation and the potential Government role in facilitating the development and application of MANETs in the transportation sector.

Technology Overview

MANETs are fluid, movable wireless networks that can form independently on an as-needed basis. The network is defined by mobile nodes (smart devices, vehicles with data-sharing capability, etc.) that receive and transmit data, and which require no fixed or dedicated infrastructure. This network paradigm lends itself well to fast moving, complex, and dynamic applications (e.g., Transportation Systems Management and Operations). Nodes can transition into and out of the network through physical movements or through devices turning on or off. The network can then reconfigure itself to accommodate these changes. Further, each node may also act as a conduit, sending and receiving information that may not directly concern its own operation.

The nodes in a MANET can communicate through a combination of existing wireless technologies—Bluetooth [IEEE802.15.1], Wireless Personal Area Network (WPAN),^[1] Wi-Fi [IEEE 802.11],^[2] 5.9 GHz Dedicated Short Range Communication (DSRC), Wireless Local Area Network,⁽²⁾ Ultra-Wide Band (UWB), Worldwide Interoperability for Microwave Access, or ZigBee—a 802.15.4 standard low-power wireless network technology used for creating personal area networks [IEEE 802.15.4].⁽⁵⁾ This use of multiple wireless protocols could allow nodes of different types (and manufacturers) to communicate seamlessly within a MANET and without any network infrastructure. When all participating nodes operate on the same frequency, use the same wireless technology, and use the same networking protocols, however, it is more likely that critical communications will be interoperable and conveyed with very low end-to-end latency.

Benefits

A MANET can serve many needs that traditional physical infrastructure-dependent networks cannot. For example, MANETs can provide cellular network offloading. Network offloading can be crucial in situations where the number of users on a network approaches or exceeds the network capacity, causing delays and other interruptions in service. MANETs are capable of temporarily diverting traffic from traditional network infrastructure to reestablish service for, or increase the number of, users within a typical area of coverage. In a similar light, MANETs are able to expand the coverage of a given network to regions beyond what an infrastructure-dependent network usually covers. MANETs can also provide communication and information dissemination capabilities in areas that temporarily or permanently lack an efficient communication infrastructure. Some examples where this might be the case are post-natural disasters areas, rural areas, areas with few economic resources, or areas with high degrees of inaccessibility, such as tunnels. Another potential benefit of MANETs is proximity-based applications. Several potential use-cases or applications of MANETs utilize the co-location of nodes to identify opportunities and provide services such as parking availability, which can result in environmental and social benefits.⁽⁶⁾ Example MANET applications are described in detail in Appendix B.

^[1] WPAN is a very short-range network that consists of low power and low complexity wirelessly connected devices that operate in a personal operating space, which is usually within a radius of 10 meters or less. For more information, see: http://www.ieee802.org/15/pub/WPAN-FAQ.html. Accessed 4-7-17.

^[2] IEEE 802.11 is a standard for wireless technology as determined by the IEEE Standards Association. 802.11 builds on the 802 standard but incorporates Wireless LAN Medium Access Control and Physical Layer (PHY) Specifications. For more information see: http://standards.ieee.org/about/get/802/802.11.html. Accessed 6-9-17.