Convergence: The potential of hybrid narrowband and broadband networks


Digital Mobile Radio (DMR) networks have been around for years. This does not mean the technology is outdated or should be replaced in favor of mass consumer technologies such as UMTS 3G and 4G Long Term Evolution (LTE) cellular systems - far from it.

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Each technology has its advantages and disadvantages. Essentially DMR is best for voice applications, including group and emergency calls and voice quality, and 4G LTE for fast data services. If the two are interconnected to form a converged network, then end users can enjoy the best of both worlds.

A major advantage of private DMR networks is that they can be designed with exactly the coverage and capacity the customer requires. 4G LTE systems operated by carriers are ‘best effort’ in that coverage and capacity is dictated by commercial considerations.

Modern digital IP-based DMR networks can not only provide utilities, airports, ports, hospitals, logistics companies and many other industries with a resilient voice network, but they can also be used to transmit low bandwidth data, such as supervisory control and data acquisition (SCADA) as well.

For higher data rate applications, businesses can use a carrier’s 4G LTE commercial network. However, if the carrier has inadequate coverage in, for example, a power station in a remote location, then the utility could boost local coverage by installing a private 4G LTE base station, plus LTE core.

This has become possible in recent years, and Hytera’s integrated LTE-DMR products will be available in North America in early 2018.

By converging the two types of radio network, a device can transmit vital low bandwidth machine-to-machine (M2M) or Internet of Things (IoT) data over its IP-based DMR network. For example, the utility could use the network to automate parts of its power distribution system to enable real-time adjustments to changing loads, production rates, as well as technical supervision.

Gaining access to the world of fast broadband data is a major plus, as end users can send and receive images and video in the field and interrogate databases, which improves efficiency and productivity. Video can also be streamed automatically from remote or sensitive sites in the case of unauthorized entry or detection of faults.

Voice will continue to remain important, however. Voice applications in DMR systems have evolved to provide a wide range of functionality not found in cellular networks. Due to the one-to-one calling protocols in cellular networks, the one-to-many and direct one-to-one mode (bypassing the network) communication features in DMR systems are missing in LTE. It should be noted, however, that these kinds of DMR features are currently being written into the LTE standard.

Continuing with our utility example, a DMR system provides a resilient voice network to direct its field staff. The DMR system ensures that the user organization does not have to rely on the limitations of cell phone networks, especially in emergency situations. It also enables managers and other staff who do not have a radio to communicate with radio-equipped team members via their mobile devices.

Why an LTE-only solution for mission critical communications might not be advisable just yet

The standards body that governs LTE is the 3GPP (3rd Generation Partnership Project) organization. 3GPP is working on introducing mission critical features into the LTE by standards specification. Not all DMR features have been specified yet at the same depth for LTE, but mission critical push-to-talk (MCPTT) voice features are among the more advanced specifications.

Other features such as Proximity Services (ProSe) or Direct Mode Operation, IOPS (Isolated Operation), and Data Services, such as video PTT and group video broadcasting, are still under development. While some vendors are providing proprietary ways to support these features, Hytera’s approach is to support open standards.

Mission critical LTE is at a very immature stage of development. Conservative adopters of new technologies, driven by return on investment, may wish to wait until the industry development cycle matures.

A key point is that interoperability between vendor solutions at the service level is not guaranteed yet by any open process similar to the Digital Mobile Radio Association’s process used for DMR products. Customers wishing to purchase products from multiple vendors will want to be sure they can all work together.

Lack of spectrum for any kind of private LTE users is another major issue. Very few countries have allocated spectrum for private users yet. Even if they have or plan to do so, not all private users will be granted access to the spectrum.

Some countries may not allocate any LTE spectrum for private use, which means private users must turn to the licensed spectrum holders – usually commercial mobile operators – a solution that may not suit all customers.

Another consideration is the cost of deployment associated with an LTE-only mission critical network. Whereas DMR networks are typically deployed using lower bands (VHF and UHF), allocated bands for private LTE are higher (700MHz, 800MHz, 1.4GHz, 2.3/2.6 GHz), so the number of sites/towers, OPEX costs, etc., are generally more expensive for LTE networks.

Thus, a model with 100% coverage in DMR with bubbles of LTE coverage where required seems to make the most sense, especially for large deployments.

Converged communication networks enable businesses to benefit from both technologies – retaining the field-proven resilient voice technology of DMR, while accessing new fast LTE broadband technology, which is becoming a necessity in an increasingly data-driven world.