The Uncertain Outlook for ProSe
Monday, December 10, 2018 | Comments
As the industry begins to adopt Long Term Evolution (LTE) for its broadband data needs and many mission-critical features are standardized in the Third Generation Partnership Project (3GPP) process, one area where many questions remain is LTE device-to-device (D2D) communications.

While the feature, called proximity services (ProSe), was included in Release 13 in the 3GPP process, the feature is not available or on the horizon, more than three years after initial standards were set.

Comparatively, mission-critical push to talk (MCPTT) was finalized in Release 14 and has made great strides. In fact, the second MCPTT Plugtests event to test interoperability between products and technology was held in June. MCPTT was initially defined in Release 13 in 2016, while ProSe was initially defined in Release 12.

However, products with ProSe technology do not yet exist. The reasons for the feature’s slow deployment are many and varied. The most obvious challenge is that chipmakers are not offering ProSe technology in chipsets.

“There are no commercially available devices with ProSe features, and we don’t know of any chipmakers that offer chipsets with ProSe,” says a Motorola Solutions spokeswoman.

TCCA Chief Executive Tony Gray agrees. “For the meantime, there is no publicly announced availability of chipsets from any manufacturer incorporating ProSe, hence no market or competition,” he says.

Qualcomm, one of the wireless industry’s largest chipset makers, did not respond to questions by press time.

Dan Ericson, Harris senior scientist, says commercial chipset manufacturers are challenged to spend development time on ProSe when faced with much larger markets for capabilities such as vehicle to everything (V2X). That technology is designed to enhance vehicular safety and provide essential communications services with nearby vehicles and infrastructure that enable driver assistance services and eventually, fully autonomous vehicles. Market insiders predict V2X will be deployed in every vehicle, every cellphone and ubiquitously along roadways.

“The overall market for ProSe in public safety and other critical communications applications is limited and therefore not very appealing to chipset and UE (user equipment) manufacturers used to dealing in millions of units,” TCCA’s Gray says.

Industry consultant Mel Samples says even when chipsets do come to market, it will probably take two to three iterations before the ProSe feature and the device capabilities will be in sync so realistic tests, similar to the MCPTT Plugtests, can start being conducted.

More Limiting Factors
“I think it is rather myopic to strictly consider ProSe as a device feature without a serious discussion of all the surrounding factors, including but not limited to range, device battery life, latency and interoperability with LMR,” Samples says.

One of those surrounding factors is interference, although specifics will depend on ProSe’s potential future implementation. In the United States, no dedicated carrier has been allocated for ProSe public-safety operations; therefore, it must co-exist with network operations. Band 14 was initially proposed as a dedicated channel for public safety — network and ProSe operations — and is now simply one of many bands deployed by AT&T for U.S. First Responder Network Authority (FirstNet) network operations, Ericson says.

Samples says anticipating interference problems is difficult with so many unknowns but offered an example of potential ProSe interference. He described a situation where a number of direct-mode devices are in use while still within the coverage footprint of the macro network, a common occurrence in LMR.

“If a network-homed device were trying to operate in close proximity to these ProSe users, what might happen, especially if the direct-mode devices were operating at high power?” he says. “What if this incident takes place near a macro site? What if it is on the fringe, and what about other uncontrolled or unknown RF sources?”

Gray says ProSe would require using portions of the overall LTE spectrum available to the network operator — a concern to commercial operators. It has also been proposed that in practical use cases for ProSe where the LTE band is heavily loaded with network traffic or other ProSe communications, system self noise may be an additional limiting factor on D2D range.

However, Gray says the primary concern is around range for D2D communications using ProSe. A 2016 study by consultancy P3 found that comparing TETRA direct mode operation (DMO) with ProSe, using at least twice the frequency and one-quarter of the power, represents severe limitations for ProSe compared with TETRA or other LMR technologies’ DMO ranges. A range of no more than one-third that of DMO will be unacceptable to most users, Gray says.

Ericson says Bluetooth and Wi-Fi are well-established communications protocols that provide direct communications over moderate distances and offer a variety of data services including voice communications. ProSe may be able to support larger communications distances under certain conditions. Therefore, its primary advantage could be for applications in which longer-distance communications is important. At the same time, to provide ever-greater capacity for their cellular networks, carriers continue to deploy more base stations that decrease cell sizes.

“Therefore, at least commercially, ProSe would provide services that compete directly with established communications protocols while providing a communications distance advantage that continues to shrink as LTE base stations and Wi-Fi access points provide ever greater coverage,” Ericson says.

Other Players
Public-safety LTE network operators will grapple with how to offer public-safety users this critical feature. The U.K. Emergency Services Mobile Communications Programme (ESMCP) last year released an open early engagement for D2D communications for the Emergency Services Network (ESN) nationwide public-safety network.

An open early engagement means that a procurement idea is active and is in the early stage of development and judging interest from potential suppliers. The exercise aimed to further ESMCP’s understanding of the market options for D2D communications for the ESN. U.K. officials have not announced plans to roll out ProSe features to ESN users.

“LTE ProSe is one of the 3GPP mission-critical services that we’ve committed to making available to FirstNet users, but we cannot share more on our road map at this time,” says a spokeswoman for AT&T, which was awarded the contract for the FirstNet dedicated public-safety broadband network in the United States.

“We are committed to working with AT&T to test and implement MCPTT on FirstNet based on 3GPP standards to help meet the needs of public safety,” says a FirstNet spokeswoman in response to questions about its ProSe plans.

Several device suppliers say they will move forward with ProSe features in devices as opportunities arise. Harris received a grant from the U.S. Public Safety Innovation Accelerator Program (PSIAP) to research configurations and improvements to existing standards to ensure mission-critical performance objectives are achieved by its operations. Harris intends to ensure that broadband direct communications solutions for public safety are properly defined as standards that support the FirstNet objective of interoperability across vendors and systems, Ericson says.

“We are always evaluating new technologies and studying ways to bring them to market to help our customers,” says the Motorola spokeswoman. “Because our customers trust their safety to our products, we do this deliberately and thoughtfully. We recognize that direct-mode communication is a critical feature for our public-safety customers. We are studying multiple options for bringing this capability to broadband devices.”

In the end, the lack of a business model for the commercial entities involved is hindering development. “I do not see a value proposition that supports ProSe in its true LTE form in place of LMR technologies anytime in the next several years,” Samples says.

“TCCA’s view is that in the fullness of time, alternative strategies for device-to-device LTE communications will need to be developed that will adequately address ProSe’s range limitations and deliver against users’ needs,” Gray says. “These may or may not leverage ProSe in some form, or perhaps other 3GPP mission-critical features such as Isolated E-UTRAN operation for public safety (IOPS). However, for the meantime, TETRA and other LMR DMO capabilities will remain the best and most acceptable solution for critical device-to-device communications.”

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