July 31, 2015
Nearly everyone is familiar with the need to step outside a building to complete a wireless call. Modern building materials, such as aluminum, steel and even specially-coated window glass, significantly reduce or even block wireless signals. While it might be inconvenient for your average mobile device user, it could become a matter of life or death for an emergency first responder. Police officers and firefighters cannot stop what they are doing to leave a building in order to communicate during a time of crisis. Providing reliable coverage indoors is a long-standing challenge; ITS has been researching in-building communications for many years, independently and as part of its Public Safety Communications Research (PSCR) program. As reported in a Department of Commerce blog posting, NTIA Technical Report TR-15-518: In-Building LTE Testing at the University of Colorado, released July 31, 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. Using a backpack mounted measurement system, researchers from ITS and the University of Colorado collected two independent LTE data streams while walking through multiple levels of two buildings—modeling 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 cell on wheels (COW), a small cell using standalone antennas, and a small cell using a distributed antenna system. Supplemental systems did improve cell coverage, but data transfers were still slow in some cases. Results showed that peak performance requires both adequate coverage and optimization of the network to ensure the smooth transfer of data or calls among transmitters. This 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.