Next-generation public safety communications will more than likely pair narrowband LMR networks for voice with broadband LTE networks for high-speed data.
One of the hottest topics in the Land Mobile Radio (LMR) industry today is the use of private Long Term Evolution (LTE) high-speed wireless communications. Although a plethora of information can be found about LTE and how it will affect the LMR industry, many questions remain unanswered. A common question is, “Does the emergence of LTE mark the beginning of the end for traditional LMR standards such as P25 and TETRA?” Although this is a difficult question to answer, most experts believe the answer is “no.” However, many believe that a profound transformation is on the horizon, and everyone in the LMR community needs to understand what the changes may be.
Every LMR industry segment will be affected in some way, but exactly how much LTE will affect an individual or organization will depend on what their roles are. For instance, frontline users, such as firefighters and police officers on the streets, will probably not care about LTE all that much. They are primarily concerned that whatever equipment they are given works reliably every time. It doesn’t matter if the underlying technology is LTE, P25, TETRA or analog. They just need a communications system that will be there when their safety is on the line.
Focus on Standards
LTE is well established in the consumer market, but enhancements to the standard to specifically address the needs of public safety and other critical communications are required. The 3rd Generation Partnership Project (3GPP) is in charge of the LTE standards and has been working hard during the past several years to incorporate the necessary changes to the LTE standards to address the needs of the public safety community.
Why the Demand for LTE?
The driving factor for adopting LTE in the LMR industry is the increased need for broadband data applications. For instance, many police departments are outfitting their officers with video cameras both for their safety and to document encounters in case questions or lawsuits arise from an incident. Most of these devices can only record events and cannot stream video in real time. There is an urgent need for real-time situational awareness, and an LTE-enabled recording device can relay the live video stream back to a command center where commanders can maintain real-time tactical situational awareness.
LTE technology enables extremely high-speed data communications that are not possible with current LMR technologies. LTE was designed to deliver high-bandwidth mobile data that allows mobile devices to stream video or transfer large amounts of data quickly. The enhanced data services of LTE are the main driving forces that make LTE attractive for public safety.
Public safety professionals need reliable communications to aid them in their lifesaving missions. Until recently, narrowband analog and digital LMR systems sufficed for most of their needs; however, many tasks today require broadband services (for instance, when these first responders need to access data-intensive applications, search databases or share videos). Modern smartphones on cellular networks are much more powerful communications devices than the typical LMR systems used by the public safety community. There is a clear need for rugged, easy-to-use devices designed to meet public safety requirements, as well as provide advanced features and services that enhance their agility on the job.
All of the leading LMR equipment manufacturers, including Motorola, Harris, Tait, Kenwood and Hytera, have already embraced LTE. Many of these manufacturers have either released or are about to release combined LTE/LMR solutions. With the rise in hybrid LTE/LMR devices, operators and maintainers will require test equipment to test both LTE and LMR equipment.
Role of FirstNet
On Feb. 22, 2012, the U.S. Congress created the First Responder Network Authority (FirstNet) with the passage of the Middle Class Tax Relief and Job Creation Act. The legislation allocated 20 megahertz of bandwidth in the 700-MHz band and $7 billion to support the construction of a nationwide broadband public safety network. The law mandates FirstNet to build, operate and maintain the first high-speed, nationwide wireless broadband network dedicated to public safety. The legislation also specifies that the network must be an interoperable platform used for emergency and daily public safety communications.
The three most influential public safety organizations in the United States, the Association of Public-Safety Communications Officials (APCO) International, the National Emergency Number Association (NENA), and the National Public Safety Telecommunications Council (NPSTC), have all endorsed LTE as the technological standard for the FirstNet national broadband network for first responders.
Around the World
LTE adoption is not limited to the United States. It is being adopted throughout the world as the technology of choice for nationwide broadband public safety networks. In the United Kingdom, the Emergency Services Mobile Communication Programme (ESMCP) will use LTE as its next-generation communications system for the three emergency services (fire and rescue, police and ambulance) and other public safety users. South Korea has deployed a dedicated nationwide public safety LTE network called SafeNet. Several other countries are expected to adopt nationwide LTE public safety networks.
LTE networks currently deliver extremely fast data, but current voice services do not have all the features required for mission-critical communications. As LTE technology evolves, it will include mission-critical voice communications. For the past several years, 3GPP has been working with LMR industry groups, such as APCO (with P25), the European Telecommunications Standards Institute (ETSI) (with TETRA), the TETRA and Critical Communications Association (TCCA) and the U.S. National Institute of Standards and Technology (NIST), to ensure broad representation on adding necessary features to support mission critical applications for the public safety community. Releases 121,2, 133,4and 145of the 3GPP LTE specification add significant features for true mission-critical functionality.
Release 12 is one of the most comprehensive standards that 3GPP has ever released, with a significant portion (about 70 percent) of its new features directly enhancing mission-critical applications in one way or another. Two main features have been added to address public safety applications: proximity services (ProSe) and group call system enablers. In addition, many new security features have been added to protect the system from unauthorized users, eavesdropping, denial of service attacks and other security risks.
ProSe allows mobiles to identify other mobiles in physical proximity and enables optimized direct device-to-device (D2D) calls (one-to-one). Direct D2D calls allow first responders to communicate with each other even when the network is down or where no network exists. Direct communication means mobiles can connect without transiting via the network, which saves valuable network resources. The 3GPP definition of proximity services also includes some features that are exclusively for public safety applications. The “user equipment to network relay” feature allows one mobile to act as a relay for another and provides access to network services outside the normal network coverage area. Another feature, “user equipment to user equipment relay,” allows one mobile to act as a relay point between two others and allows communication to take place without going via the network, even if the communicating mobiles are out of range for direct communication.
Other important features required for public safety and critical communications are mission-critical push-to-talk (MCPTT), mission-critical video (MCVideo) and mission-critical data (MCData), which were all finalized in Release 14.
Work on Release 15, including interoperability with legacy LMR technologies and continued additions to MCPTT, MCVideo and MCData, is underway, and the release is scheduled to be completed by the end of 2018.
LTE Replacement of LMR
The major LMR vendors are shifting their focus to LTE, but does that mean the end of innovation and support for LMR technologies? The consensus of industry experts is “no.” LMR will not be replaced by LTE any time soon, and all the venders will continue to innovate and support LMR technologies for the foreseeable future. Many factors favor LMR staying relevant for quite a long time; however, it is likely that LTE will augment instead of replace LMR for at least a decade or more.
Cost and Spectrum
The number one factor for LMR staying relevant is cost. Many LMR operators have just made the investment to convert from analog to digital systems, such as P25, TETRA and DMR (even though P25 and TETRA have been around for more than 20 years), while others are still running analog systems. This will remain the same for system owners considering LTE. The more likely scenario will have system owners augmenting existing LMR voice systems with LTE for data services. In fact, in the initial rollout of the FirstNet network, LTE is considered to be a complementary enabler to public safety systems that will sit on top of existing LMR voice systems. In addition to the cost of new equipment and infrastructure, LTE requires much more bandwidth than narrowband LMR systems and the need for sufficient spectrum is a barrier for scalable deployments around the world.
Other important factors are the technical challenges installers, maintainers and operators will face. One of the reasons LTE was selected as the technology of choice for broadband communications for the public safety sector is because it is the same technology that has been rolled out by commercial operators, so it should be well understood and easy to install, use and maintain. However, keep in mind that LTE systems for critical communications have special features and requirements that the commercial networks do not have to worry about. The primary concern is that it needs to be much more reliable, because lives are at stake. It also has to operate in conjunction with existing LMR networks that often occupy the same frequency bands. This can present challenging interference issues for system designers, installers and maintainers.
Other technical challenges include RF coverage and other system considerations. LMR handsets typically transmit with 3 to 5 watts of power, whereas, an LTE handset may only be capable of transmitting with about 1 watt. This translates directly into longer range for LMR systems. So, for an LTE network to provide the same coverage area as an LMR network, operators will need to install many more sites spaced closer together, thus resulting in higher equipment and maintenance costs. Because of infrastructure costs, a broadband network at 700 MHz will not be able to replace LMR in many locations across the United States because of RF propagation properties, and matching LTE to LMR coverage and reliability is just too cost-prohibitive.
Need for Second Network
In areas with existing LTE infrastructure, one may question why there is a need to build a second private network when the community already has an LTE network in place. The fundamental reason is that commercial LTE networks are not built to mission-critical standards of reliability. Another important consideration is that when a major incident occurs, many civilians get on the network and take up valuable network resources, leaving no bandwidth for the public safety professionals. In a worst-case scenario, the public may overwhelm the network, and all communications will be lost. This has happened many times in large disasters. There is no way to give preemptive priority to public safety traffic, so a dedicated private network for public safety is necessary.
Many questions and concerns about LTE must be addressed before it is accepted by the end users. LMR systems are a known quantity, and reliable voice communication is the number one requirement for any public safety system. The first question is reliability. Another basic question is how well will LTE be able to handle voice and data? These questions can only be answered with empirical evidence, once actual systems are in operation.
AT&T won the right to build out the FirstNet infrastructure, and all 50 states have opted in. However, it is highly likely that it will be many years, pe a decade or more, before the transition to LTE is made, and it may never fully replace LMR. It may just converge into a new hybrid LTE/LMR technology.
FirstNet public safety LTE in the United States will occupy two 10-megahertz-wide blocks of spectrum from 758 MHz to 768 MHz and its duplex spectrum offset +30 MHz away at 788 MHz to 798 MHz. These frequency bands lie adjacent to public safety narrowband spectrum for LMR at 769 MHz to 775 MHz and its duplex pair +30 MHz away at 799 MHz to 805 MHz. A recent study conducted by the U.S. Department of Homeland Security (DHS) suggests that LMR and LTE systems operating at the frequency bands above can coexist with proper engineering design practices and careful frequency planning.6Interference issues may still be of concern because the guard bands between the LTE and LMR spectra are only 1 megahertz wide. Some portions of the 700-MHz FirstNet bands may be heavily affected by passive intermodulation (PIM) interference generated by existing LTE cellular downlinks used by major wireless carriers. This means that all carriers operating those networks will need to ensure high-quality installations with special care taken to reduce or prevent PIM signal levels from degrading overall network performance.
LMR and LTE are quite different technologies and require different tools for testing and maintenance. Compared with LMR, LTE is a much more complex technology with its variable channel bandwidths and use of both multiple-input multiple-output (MIMO) communications and orthogonal frequency-division multiple access (OFDMA) modulation to support high data rates. LTE is definitely going to be used in the public safety and critical communications world. As previously mentioned, it is more than likely that LTE and LMR systems will coexist for some time. Supporting two separate networks can become challenging both in terms of personnel requirements and test equipment requirements. Both LTE and LMR systems have to contend with problems such as multipath and fading that degrade signal quality. Handheld test equipment that can deal with both the complexity of testing LTE networks and mapping bit error rate (BER) as well as the modulation fidelity of LMR networks is critical to providing technicians and engineers that install and maintain public safety communications systems with the confidence that these networks will work as expected. Such measurements often require a number of different tools, all of which must be carried into the field. Maintainers now have to train their crews to be proficient in two highly different technologies or employ two separate crews — one dedicated to LTE and one to LMR.
Next-generation public safety communications will more than likely pair narrowband LMR networks for voice with broadband LTE networks for high-speed data. Ensuring these networks are properly installed and maintained is critical to ensuring mission-critical public safety communications to keep the public safe. An instrument that can address this problem is Anritsu’s LMR Master S412E, the industry’s first and only battery-powered LMR field analyzer capable of testing both broadband LTE and narrowband LMR systems. It combines many of the tools needed to install, maintain and certify LTE and LMR systems into a single instrument with a single user interface. Multi-function analyzers such as the LMR Master S412E can significantly reduce the number of different tools technicians and engineers need to verify operation of wireless network infrastructure and to diagnose problems in the field.
1. 3GPP, “Understanding 3GPP Release 12: Standards for HSPA+ and LTE Enhancements,” Executive Summary, February 2015.
2. 3GPP, “Overview of 3GPP Release 12,” September 2015.
3. Flore, Dino; “Evolution of LTE in Release 13,” 3GPP article, February 2015.
4. 3GPP, “Release 13 Analytical View,” September 2015.
5. 3GPP, “Mission Critical Services in 3GPP,” June 2017.
6. Department of Homeland Security, “A Case Study of Interference Between Public Safety Long Term Evolution (LTE) And Public Safety 700 MHz Land Mobile Radio,” White Paper DHS-WP-PSC-13-06, March 2013.
Wayne Wong is the product manager for the LMR Master product at Anritsu. He has held various roles from senior hardware design engineer to field applications engineer during his 20 years in the test and measurement industry. Visit www.anritsu.com.