Device-to-device communication in 5G, also known as sidelink, promises to bring new flexibility and functionality, but the potential range is expected to pale in comparison to the land-mobile radio (LMR) direct offering used. by public safety according to research by the National Institute of Standards and Technology (NIST).
Chunmei Liu, a researcher in the Wireless Networks Division of the Communications Technology Laboratory (CTL) at NIST, said the 5G New Radio (NR) sidelink is expected to support device-to-device communication at a maximum distance of 981.8. meters – just under 5/8th of a mile – in an “idealistic” outdoor scenario with line of sight, based on simulation research (graph above). More realistic scenarios in the study indicate a device-to-device range of 644.9 meters (705.3 yards) for a pedestrian and 582.0 meters (636.5 yards) for a user in a vehicle.
These projected baseline figures indicate that the 5G NR sidelink would provide comparable range to ProSe (proximity Services) functionality in LTE. ProSe has been largely abandoned as a technology, with Samsung developing the only commercially available ProSe device that supported a range of “maybe half a mile”, according to a Samsung official.
Liu noted that 5G NR sidelink offers several options that can be used to extend device-to-device range, such as increasing the number of transmissions to ensure the signal is received. This technique can increase range by as much as 70%, but it also results in increased latency and decreased data throughput to levels that can render many applications useless to a first responder, she said.
“Our preliminary results show that 5G sidelink has the potential to significantly increase range…and there are some key factors that influence range, such as deployment environment, device power class, numerology and HARQ configurations,” said Liu during a recorded presentation for the recent PSCR 2022 Broadband Stakeholders Meeting.
“Our results also show that greater reach comes at a cost, and careful design is required to balance range and other service requirements.”
Liu said one way to increase device-to-device communication range without sacrificing performance is to use high-power user equipment (HPUE), which can transmit a signal at 1.25 watts — more than six times the normal 0. .2 watts of a normal handheld mobile device. With HPUE operating on the 700MHz Band 14 spectrum licensed to the FirstNet Authority, the device-to-device range is increased by more than 50% resulting in the “idealistic” scenario with a reach of 1,554 .4 meters or almost a mile.
But even this HPUE range represents a significant decrease in range compared to the device-to-device communication supported by LMR devices, which can use 3 to 5 watts of power to transmit signals. In addition to the extra power, LMR often operates on spectrum which provides much better signal propagation, and an LMR device often has an external antenna, unlike the internal antennas found in most LTE handsets.
Meanwhile, the expected 5G sidelink range is significantly reduced in scenarios where the devices are not outdoors with a clear line of sight between them, according to the unique simulation study, Liu said.
“To our knowledge, our simulator is the first link-level 5G sidelink simulator developed,” said Liu. “We are in the process of documenting it and planning to release it for public use.”
In outdoor non-line-of-sight (NLOS) scenarios, the device-to-device range is expected to be 389.0 meters (425.4 yards) for pedestrians, while the same scenario has a device-to-device range of 354 yields ,1. meters (387.2 yards) for users in vehicles, according to the simulator study.
Indoors, the maximum projected range is 304.4 meters (332.9 yards), but this assumes a line-of-sight (LOS) scenario, Liu said. Barriers such as walls will reduce device-to-device performance indoors, but how much depends on a number of factors, including the materials used in the structure.
The most difficult scenario modeled by the simulator was device-to-device communication, with one user outside and the other inside. In this outdoor-to-indoor (O2I) scenario, the range is expected to be 139.0 meters (152.0 yards) between pedestrians and 126.6 meters (138.5 yards) between users in vehicles.
Many industry sources argue that such limitations in device-to-device communications over LTE or 5G are a major factor in major public safety agencies being reluctant to transition mission-critical voice communications from LMR to broadband wireless solutions. After all, first responders often have to communicate when commercial mobile services are not available, because the system is not working or because they operate outside the range of the terrestrial network.
With the availability of coverage expansion technologies such as HPUE and “bring the network with you” deployable solutions — from pelican case form factors to the Compact Rapid Deployable (CRD) asset that agencies can own — the question is how often first responders will require device-to-device communication in the future.
Another potential factor that could influence this discussion is the development of companies such as Lynk Global and AST SpaceMobile, which plan to provide connectivity from a LEO satellite-supported “LTE tower in space” directly to unmodified ones. smart devices outside a carrier’s terrestrial coverage footprint. Both companies expect to provide global service by 2025.