NTT DOCOMO Gains a Go-to-Market Advantage in 5G with Flexible Channel Sounding

NTT DOCOMO Gains a Go-toMarket Advantage in 5G with Flexible Channel Sounding

In pursuit of 5G’s most extreme goals, developers are using a combination of millimeter-wave (mmWave) frequencies, ultra-wide bandwidths, and massive multiple-input/multiple-output (MIMO) methods. And while these add uncertainty to the design of transmitters and receivers, the biggest unknowns are in the resulting over-the-air (OTA) radio channels between 5G user equipment (UE) and base stations. To fully characterize the channel, it is necessary to create mathematical models of channel performance and then use those models to define new air interface standards for 5G. A technique called channel sounding is an effective way to understand the channel and thereby enable the data rates, spectrum flexibility and bandwidth needed for 5G. This was the challenge facing NTT DOCOMO, Japan’s largest mobile network operator. While its name is officially derived from the phrase “do communications over the mobile network,” it is also a contraction of the Japanese phrase “doko ni demo” which, in the spirit of wireless mobility, means “everywhere.” As one of the industry’s leading innovators, NTT DOCOMO is working to deploy its 5G mobile network in time for a major athletic event in the summer of 2020 in Tokyo. To define and optimize a network that fulfills on the promise of 5G—without being overdesigned—NTT DOCOMO needed an accurate, reliable and repeatable way to characterize channel propagation.

The Challenge: Modeling Multiple mmWave Use Cases

For NTT DOCOMO’s developers, the overarching driver is a 10-year plan aimed at creating an industry-leading communication platform. The major goals are to enable new subscriber services that include more bandwidth for human users, more capacity for machine-to-machine and Internet of Things (IoT) connectivity, and minimal latency for virtual reality (VR) and augmented reality (AR) applications (Figure 1). To accelerate the commercialization of this platform, NTT DOCOMO’s investigations focused on the 5G New Radio (NR) interface at 28 GHz for high-speed mobile scenarios and 67 GHz for fixedwireless applications. That research revealed two crucial challenges: capturing data over the mmWave channel, and calculating a mathematical model that could be used in the design of mobile network cells. To create the necessary models, signals must be captured within a 2x2 matrix of scenarios: urban and rural; fixed wireless and high-speed mobile (e.g., on a “bullet” train). Key measurements include frequency response, path loss, power-delay profile (PDP), Doppler shift, angle of arrival (AoA), and angle of departure (AoD). The various measurements present some daunting underlying challenges: generating and analyzing wideband mmWave MIMO signals; performing wideband system calibration; achieving precise transmit/receive timing; and managing data collection and storage. Captured data is used as inputs to the channel model, which includes the effects of obstructions such as the human body or foliage, attenuation caused by precipitation or humidity, and multipath and reflections caused by buildings and other structures. Signal-analysis software must be capable of extracting a model of the wireless channel at all frequencies of interest. The resulting model is then used in the design of the mobile network, helping developers determine the optimum location and number of cell sites.