In-building LTE coverage research

Researchers have found that to achieve reliable coverage, transmissions from cell towers needed to be supplemented.

As part of its mission to improve communications for public safety, the First Responder Network Authority (FirstNet), an independent entity within the US Commerce Department’s National Telecommunications and Information Administration (NTIA), identified improved in-building communications as a critical need for first responders and a required component of the nationwide public safety broadband network it’s been tasked with deploying.

Providing reliable coverage indoors is a long-standing challenge. The Institute for Telecommunication Sciences (ITS), NTIA’s research laboratory in Boulder, Colorado, has been researching in-building communications for many years, independently and as part of its Public Safety Communications Research (PSCR) partnership with Commerce’s National Institute of Standards and Technology.

ITS has released a new report that describes the results of experiments conducted to investigate both the in-building coverage characteristics of future public safety mobile networks and ways to improve performance in such environments.

This research not only can be used to help first responders better communicate during emergencies, but it also may help spur innovation in commercial wireless networks also interested in enhancing indoor coverage.

The research, sponsored by the US Department of Homeland Security, involved a team of researchers led by ITS and the University of Colorado at Boulder that developed experimental techniques to characterise and improve in-building communications with and without supplemental radio transmitters.

The team targeted the LTE technology envisioned by FirstNet operating in public safety frequency bands.

These diagrams illustrate the results of measurements of signal strength along one walk route. On the left are the results of when signals are being transmitted only by the cell tower located two kilometres from the test site. On the right are the results of when transmissions are supplemented by in-building systems. The benefits of supplemental cells are easily seen by comparing the colours between the left and right diagrams, with red showing poor coverage and blue showing good coverage.

Using a backpack-mounted measurement system, ITS researchers collected two independent LTE data streams while walking through multiple levels of two buildings — modelling the path that a first responder might take in response to an incident.

The researchers found that to achieve reliable coverage, transmissions from the cell tower needed to be supplemented.

Three different methods to improve in-building coverage were tested: a portable base station commonly referred to as a cell on wheels (COW), a small cell using standalone antennas that bring the network closer to the user and a small cell using a distributed antenna system.

The researchers were able to improve cell coverage with the help of these supplemental systems. However, even with better coverage, data transfers were still slow in some cases due to the challenge of coordinating all the systems.

The report provides preliminary data that can be used to begin effective planning of in-building public safety LTE communications. It also identifies additional research needed to reliably predict in-building coverage and points to the need to enhance coordination of all aspects of a network.

Reproduced courtesy of NIST