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OPINION / Flexible modernization of government wireless communication system

By Dr. Jeffrey Harris


Wireless communication systems, like anything else, need updating from time to time.  But, unlike a house that can be remodeled by having a wall painted here or a carpet replaced there, land mobile radio (LMR) systems were not designed to have individual pieces updated.

The computing revolution has standardized the interconnection between networked elements in the form of the Internet Protocol, which is most commonly known as IP. Unfortunately, even though it is possible to treat a radio network as just another communications network with radio endpoints, there tends to be resistance towards this open standards-based approach.

Fortunately, a technology called Network Level Interoperability realized by network level gateways has been created to facilitate flexible modernization and enhanced interoperability. When an agency can add services to their legacy system instead of installing a completely new system, their investment in the legacy system is preserved and a risk-reduced pathway to a new technology and additional capacity is formed.

Network Level Interoperability

The idea behind Network Level Interoperability is that disparate systems are connected together at the network level using private IP networks that employ standard protocols. Protocol conversions between the two systems occur at wire speed. This differs from the typical form of interoperability which uses radio level gateways, such as the ACU-1000 from Raytheon, MOTOBRIDGE from Motorola, Interoperability and Communications System (IPICS) from Cisco, and the like. Radio gateways are simply a high-tech method of swapping radios between agencies.

Network Level Interoperability is a technology that facilitates a high level of integration between any two communication systems using standards-based protocols, and can adapt to the proprietary interfaces of most LMR systems. This technology works for LMR from different vendors, different technology LMR systems, private or public communication systems, cellular or push-to-talk, and so on. It facilitates taking many heterogeneous communication systems, systems of disparate type, and making them function as one homogeneous communication system -- one large system with different types of endpoints.

Network Level Interoperability has several advantages over radio gateway interoperability. First and foremost, Network Level Interoperability is scalable. Unlike radio gateway interoperability, where each dialog mapped between two systems required a “proxy” or “donor” radio, with its associated cabling, Network Level Interoperability can carry a varying number of dialogs over a single physical IP connection. Avoiding connecting the two systems with an over-the-air interface also avoids other RF problems such as interference, and the need to have the two systems physically co-located within the same RF footprint.

The scalability of Network Level Gateways gives this technology tremendous cost advantages over radio gateway technology. Consider interoperating 10 channels or talk-groups between two LMR systems using radio gateways. Each system would need a radio gateway hosting 10 proxy radios, for a total of 20 proxy radios. Depending on the LMR system, these proxy radios can easily cost approximately $5,000 each, for a total cost of $100,000 in proxy radios, not counting the cost of the radio gateways themselves. Network Level Gateways on the other hand are implemented with software running on a generic server-style computer, costing about what one proxy radio costs.

The other advantage of Network Level Interoperability over radio gateway interoperability is that radio gateway interoperability is only able to pass voice between the two systems, whereas Network Level Interoperability can pass any form of digital data. Traditional tadio gateways are only able to share the bottom most rung of the ladder, namely analog voice, whereas Network Level Interoperability is able to share the entire value stack.

For example, digital data that can be passed between the two systems include voice, caller ID information, textual messages, telemetry information such as biological or environmental sensors, data from applications, images and motion video.

The following scenarios summarize how to use Network Level Gateways to augment an existing legacy LMR system:

Add coverage. In this instance, additional coverage is added to an existing LMR system. We start by deploying the new LMR equipment in the uncovered areas, and then use a Network Level Interoperability Gateway to seamlessly interoperate the new equipment with the existing infrastructure, so that they appear to the users as a single system.

Add capacity. In this instance, we are increasing capacity of a legacy conventional LMR system by replacing high traffic areas with trunked LMR radios. The Network Level Gateway interworks the trunked equipment with the conventional equipment to provide seamless functionality across the entire system. In this way, you replace only the equipment in high utilization areas and you do not have to replace the entire system.

Add new features and capability. In this instance, we want to deploy a new capability such as broadband as an overlay in certain areas. The new capability could be any of a myriad of communications capabilities, including broadband, satellite, connections to the public telephone network, inclusion of IP telephones, commercial PTT such as Nextel, or many others. Here, we deploy the new capability at the desired locations to support the coverage needed. We use a Network Level Interoperability gateway to map talk-groups or chat-rooms from the broadband system to channels in the legacy conventional system, thereby interworking the LMR and broadband systems into a unified system.


Upgrading an LMR system is difficult because LMR systems were not designed to be upgraded on a component-by-component basis. General Dynamics has invested significant R&D to create a technology and product called CrossComm that facilitates Network Level Interoperability between heterogeneous communication systems.

Augmenting an existing LMR system allows an agency to preserve the investment in the legacy system while mitigating the risk associated with adopting new products or technology. Doing so helps agencies preserve the investment in their legacy system, provides service over and above the legacy system, and provides a risk-reduced path to new technology. It allows an agency to tailor the roll-out of the new capability to meet their fiscal constraints.

As government departments, components and agencies begin to modernize their legacy tactical radio communications systems, consideration should be given to using Network Level Gateways as a way to maximize operational and fiscal flexibility. Most importantly, Network Level Gateways allow the government to incrementally modernize legacy communication systems while continuing to leverage the sunken investment in those legacy systems.

Dr. Jeffrey Harris is a chief technologist at General Dynamics. He can be reached at: [email protected]


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