Abstract

Conceived by the U.S. Military, mobile ad hoc networks, commonly known as mesh networks, provide end-to-end Internet Protocol (IP) communications for broadband voice, data, and video service combined with integrated geographical location logic designed to function in a mobile wireless environment. Unlike 802.11 wireless local area networks (WLANs) and point-to-multipoint digital cellular networks, mesh networks accommodate a more dynamic operational environment where their radio frequency (RF)-independent, self-forming, and self-healing properties meld the best of both worlds between WLAN and cellular systems. This paper examines the concept of mesh networks with a look at recent commercial and military development of what some consider a disruptive, next-generation wireless communications technology.

Introduction

Loosely speaking, mesh networks form a wireless Internet where any number of host computing nodes can route data point-to-point in an intricate web of decentralized IP links built upon many of the routing features first employed by earlier packet radio networks [4]. Borne from a heritage of 1960s and 1970s packet data radios designed to provide reliable communications for connectionless, non-real-time traffic, today’s mesh networks have evolved to provide multicast IP traffic with real-time requirements [1]. In essence, mesh networks extend the concept of packet data radio communications by using sophisticated digital modulation schemes, traffic routing algorithms, and multi-hop architectures that challenge the laws of physics by using minimal

transmission power to increase data throughput over greater distances. With mesh networks, any node within the network can send or receive messages and can relay messages for any one of its hundreds or thousands of neighboring nodes, thus providing a relay process where data packets travel through intermediate nodes toward their final destination. In addition, automatic rerouting provides redundant communication paths through the network should any given node fail [2].  This ability to reroute across other links not only provides increased reliability but extends the network’s reach and transmitting power as well. This resilient, self-healing nature of mesh networks stems from their distributed routing architecture where intelligent nodes make their own routing decisions, avoiding a single point of failure. Because mesh networks are self-forming, adding additional nodes involves a simple plug-and-play event [3]. And because mesh networks don’t rely on a single access point for data transmissions, users of this technology can extend their communication reach beyond a typical WLAN. Furthermore, mesh networks and their low power, multi-hopping ability allow simultaneous transmissions to reach nearby nodes with minimal interference [17].

Achieving this self-forming, self-healing utopia with minimal power and signal interference involves the implementation of sophisticated routing logic within the software and hardware to account for minimum latency, and maximum throughput, as well as provide for maximum security and reliability [7].

As with all radio frequency (RF) communication systems, mesh networks must contend with noise, signal fading, and interference; however, unlike other RF systems, mesh networks deal with noise, signal fading, and interference through an air interface protocol originally designed to provide reliable battlefield communications.  Known as quad division multiple access (QDMA), this air interface provides the driving force behind mesh network capabilities. Conceived by Military Commercial Technologies (MILCOM) and a communications division of ITT Industries, QDMA allows mesh networks to facilitate higher throughput without sacrificing  range – or extending transmission range without sacrificing throughput. QDMA supports low-power, high-speed broadband access in any sub-10 GHz frequency band, providing non-line-of-sight node linking to dramatically increase signal range without sacrificing throughput. Geared toward wide area mobile communications, QDMA compensates for wild fluctuations in signal strength with powerful error correction abilities and enhanced interference rejection that allows multi-megabit data rates – even from a mobile node traveling at 100 mph and beyond. And with shorter distances between network nodes, the resulting decrease in interference between clients provides for more efficient frequency reuse. Furthermore, QDMA offers highly accurate location capabilities independent of the satellite-based global positioning system (GPS) [2], [4], [5], [6].

Commercial Deployments

Since the inception of QDMA and the subsequent commercialized version of this technology, venture capital firms have invested more than $100 million since 2001 for continued design and development of mesh networks that could ultimately compete with IEEE’s 802.11b [3].  One firm, appropriately named MeshNetworks, has adopted the QDMA technology with direct sequence spread spectrum (DSSS) modulation in the 2.4 GHz industrial, scientific, and medical (ISM) band, providing 6 Mbps burst rates between two terminals. Backed by almost $40 million in venture funding from 3Com Ventures, Apax Partners, and others, MeshNetworks signed its first customer, Viasys Corporation, in November 2002. Eventually, MeshNetworks plans to offer their networking capability in the 5 GHz unlicensed national information infrastructure (UNII) band [8].  For now, MeshNetworks, headquartered in Maitland, Florida, is testing a 2.4 GHz prototype in a five-square-mile test network around its Orlando suburb with an FCC experimental license to build a 4000-node nationwide test network [6]. To maintain Internet connectivity, MeshNetworks relies on multi-hop routing between nodes mounted on buildings, light poles, vehicles, and end-user devices [17]. Aside from designing prototype routers, relays, and PDA-size client devices, MeshNetworks plans to offer a software overlay solution for 802.11b clients in existing networks, effectively extending the range and link robustness of existing Wi-Fi networks through mesh-style multi-hopping [6].  Furthermore, MeshNetworks recently announced a deal with auto-parts manufacturer Delphi to test the feasibility of mesh networks in a telematics environment [9].  MeshNetworks competitors include FHP Wireless, which recently announced its formal launch date in March of 2003, and Radiant Networks from Cambridge, U.K., which has deals in place with British Telecom, Mitsubishi, and Motorola [3].

Interestingly, each of these potential mesh network providers will face a similar network coverage dilemma, a sort of catch-22 where the ability to expand network coverage hinges on the deployment of new subscribers whose mobile nodes will act as router/repeaters for other nodes. In this scenario, requirements for expanded coverage dictate the need for more subscribers – but the service provider can’t solicit new subscribers until the coverage extends to the new subscribers’ area.  To resolve this, MeshNetworks and Radiant Networks supply ‘seed nodes’ mounted on telephone poles or streetlights for initial coverage and redundancy with the level of required seeding determined by specific business objectives [10], [12].