Hybrid Mesh Networks for Mission Critical Applications

Public Safety Network and First Responder Applications. Emergency response situations require guaranteed connectivity despite high mobility and where coverage from a infrastructure mesh backhaul is not assured. An Ad hoc mesh network coupled to the infrastructure mesh backhaul provides the best of both worlds. The infrastructure mesh shown above provides a high bandwidth and redundant backhaul connectivity between the high mobility units marked as E. Additionally, the E units are 2 radio mobile units where one radio connects to the backhaul and the other radio is part of an Independent BSS e.g. ad hoc mesh.

1-radio vs. multi-radio approaches While our control layer supports both one and multi-radio systems, One radio Ad hoc meshes are inferior to multi-radio infrastructure mesh networks in multihop situations. In the case of 1 radio ad hoc mesh networks, available bandwidth is reduced by 50% with each hop: bandwidth available at the 3rd hop is 1/8 of the available capacity.

However, while one-radio ad hoc mesh networks are unsuitable for multihop situations, they are useful in one-hop situations for quickly establishing peer-to-peer communications. In some cases, this may be the only means of communication when AP based connectivity is not available. For example, some nodes may not be in the coverage areas shown as shaded ovals and cannot be serviced by the 2-radio infrastructure mesh shown above. Conversely, 2-radio infrastructure meshes are ideal for multihop situations with no restrictions on the number of hops. They is also more reliable since the AP is intended to be stationary and therefore provides dependable service in its coverage area.

Mission critical applications must support both needs. Mission critical applications such as pubic safety, require high bandwidth - regardless of how many hops you are away, to be able to download maps or upload video. And they must also have assured connectivity at all times –every node must be able to reach all other nodes in the network.

One radio mobile ad hoc network connectivity combined with two radio backhaul support provides the best of both worlds; ubiquitous connectivity but with multiple levels of redundancy built in. Consider the situation depicted above. The ad hoc wireless link between E2 and E3 has been lost – typical of dynamic, uncertain or hostile environments. With no 2-radio backhaul, Nodes E1 and E2 are stranded. The backhaul link becomes their lifeline.

Two radio mobile backhauls are particularly relevant for emergency response systems where the team may be scattered over large areas. A fatal limitation of single radio mesh networks is that multiple routing paths must be maintained for assured connectivity in high mobility situations. Note that because the same mesh network is addressing both peer-to-peer connectivity and backhaul infrastructure needs within one framework. A lack of multiple routing paths can potentially kill both networking services.

Hybrid mesh networks approaches meet the mission critical requirements for homeland security, where other conventional mesh network approaches fail.

Assured Redundancy: Multiple routing paths may exist for segments of the network as shown for E9-E8-E7. However it is impractical to assume this for all segments of the network. Since all E nodes are intended to be highly mobile: their movement cannot be restricted to operate only within areas with coverage from another E unit. Emergency response staff will stray outside coverage areas provided by each other’s radios and/or noise may affect the effectiveness of the coverage being provided. For these reasons, a reliable communication infrastructure cannot rely on mobile units alone because

1- the string of pearls pattern (E4-E5-E6-E7) is not robust and
2- Redundant routing configurations (E7-E8-E9) cannot be assured.

The root of the problem lies in the fact that capabilities of one radio ad hoc mesh - while ideal for peer-to-peer connectivity - are being taxed to also provide a stable infrastructure mesh . A separate network - supported by 2-radio Portable Backhaul units (Marked P in the figure) - should address needs for a stable infrastructure backbone and a backup for broken links (e.g. E2, E3).

With plummeting costs of 802.11 radios, the best of both worlds is accomplished easily – provide 2 radios with each mobile unit. One radio is dedicated to the ad hoc mesh for peer-to-peer connectivity, while another connects to the backhaul to communicate with the world outside.

It also assures connectivity with all nodes of the network: E2 and E3 are now connected, through the backhauls, despite a break in the ad hoc network. With the mobile backhaul in place all 2-radio E units in the figure above are assured of robust connectivity with each other and with the world outside.

Multipurpose functionality at low cost. The 2-radio Portable backhaul and the 2 radio mobile units can use the same hardware. Based on the choice of radio, either unit may be used in another mode – all changes are software based and configurable.

This is an added bonus to have 2 radio systems for both peer-to-peer and infrastructure needs. In the event that the backhaul is compromised, one “E” unit may be configured on the fly to serve as a backhaul. By the same token, an unused backhaul may serve as a mobile unit. To simplify production issues, the 2-radio Portable backhaul and mobile units may be the same hardware - dynamically configured to operate differently. This also favors manufacturing economies of scale since the same hardware services both peer-to-peer and infrastructure requirements.

Studies conducted for the USAF indicate that when connectivity needs to be assured, hybrid mesh is more effective than other approaches. Demonstrations available on request.

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Hybrid Mesh Networks for Mission Critical Applications

Send mail to Robert Hoskins with questions or comments about this web site. Copyright © 2006 Broadband Wireless Exchange, Inc.

Send mail to Robert Hoskins with questions or comments about this web site.
Copyright © 2006 Broadband Wireless Exchange, Inc.