What is LTE, and why is it right for a public safety network?

A National Public Safety Broadband Network has been in the works for several years now. Spectrum has been set aside for it in the 700 MHz band and the First Responder Network Authority (FirstNet) has been established in the Commerce Department’s National Telecommunications and Information Administration to hold the spectrum license and oversee deployment of the network.

Funds for development and implementation have been appropriated and testbeds have been established, but the details of the network have not been worked out. The consensus of the public safety community, however, is that it should be based on the emerging Long Term Evolution standard for advanced cellular communications.

One of the primary reasons for choosing LTE is that the technology is being widely adopted by commercial carriers, which means that although a public safety network itself is likely to be segregated from public networks it would be able to use interoperable off-the-shelf technology.

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LTE standards are being developed by the 3rd Generation Partnership Project, a consortium of six telecommunications standards organizations that has released multiple iterations of specifications. It is called a Fourth Generation wireless service, but as now used the 4G label is more of a marketing term than a technical term. Current implementations of LTE do not meet International Telecommunications Union technical requirements for Fourth Generation wireless communications. But the LTE Advanced standard, finalized by 3GPP in 2011, is recognized by the ITU as True 4G.

Work on LTE began in 2004 and the first commercial offerings were introduced in Sweden in 2009 for data service. North American commercial cellular service began in 2011, and LTE now is being rolled out or is in development by most major carriers. The ability to operate on 4G or LTE networks is a selling point for advanced smart phones, such as Apple’s new iPhone 5.

Services based on the LTE Advanced standard are expected to begin in 2013.

LTE operates in a range of radio frequencies, including the 700 MHz band, so it will work in the D Block in that band that has been set aside by the Federal Communications Commission for a public safety network.

The first wave of commercial LTE service is based on Release 8 of the standard, which was finalized in 2008. It is built on TCP/IP and provides a packet-based alternative to circuit-switched GSM networks. It provides peak downlink rates of about 300 megabits/sec and uplink rates of 75 megabits/sec and incorporates quality of service provisions to minimize latency. This makes it possible to manage handoffs more effectively, which allows efficient use by fast-moving mobile devices.

It supports both frequency and time division duplex communications, as well as half-duplex FDD (with only one-direction in operation at a time), which enables the use of push-to-talk features that can be used by police to access traditional land mobile radio systems. One cell operating with a 5 MHz slice of spectrum can support up to 200 data clients. Voice traffic can be carried either as a packet-switched data stream in a native LTE system, or as circuit-switched traffic over a legacy voice network used by the same handset.

The ability to combine off-the-shelf equipment with high speeds for voice, video and data that can be operated on a segregated network and that will continue to evolve functionally has made LTE a practical choice for a nationwide public safety system.


About the Author

William Jackson is a Maryland-based freelance writer.


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