1. New Ways to Use Radio Waves in the 6G Era

Currently, research and standardization activities are advancing worldwide toward Beyond 5G/6G. Within this context, there is a growing movement to utilize radio waves for purposes other than communication. One of these is a technology called "Integrated Sensing and Communication (ISAC)," which aims to merge communication and sensing.
The term "sensing" broadly refers to the collection of environmental and physical data, and within this field, we are focusing on technology that captures location information and human movement using radio waves.
There are two main methods for realizing this: one is the RADAR method that utilizes reflected waves, and the other is the CSI method that utilizes the reflection paths and variations of radio waves. Each method has its own characteristics, and we are conducting research to determine which technology is most effective for different use cases.

IMT-2030 (6G) Usage Scenarios announced by ITU-R in June 2023

2. Explanation of the Technology

2-1. RADAR Technology

RADAR is a technology that emits radio waves toward an object, measures and analyzes the reflected waves, and performs positioning of the target object.
Since radio waves travel through the air at the speed of light, the distance to the target object can be calculated by measuring the time from transmitting the radio waves to receiving the reflected waves.

The method varies based on the difference in the waveform of the transmitted radio waves, with "Pulse Radar" and "Frequency-Modulated Continuous-Wave (FMCW)" methods being well-known.

Pulse Radar Method

The pulse radar method measures the time it takes for the transmitted pulse to be reflected and received, allowing for distance measurement to the target object.
A characteristic of pulse radar technology is that the shorter the length of the pulse, the higher the measurement accuracy (resolution) becomes.　

Pulse Radar Method

FMCW Radar Method

The FMCW method uses radio waves (such as chirp signals) that change frequency over time. After receiving the reflected waves, the time from transmitting the radio waves to receiving them is calculated by performing correlation with the transmitted waveform, allowing for distance measurement to the target object.

A characteristic of the transmission signal is that the wider the frequency bandwidth, the higher the measurement accuracy (resolution) becomes. It is well-suited for compatibility with millimeter-wave communication, which can utilize a maximum bandwidth of 400MHz, and discussions on specification formulation are being conducted within 3GPP under Rel-19.

Waveform of Chirp Signal
(Left : Amplitude Changes with Time, Right : Frequency Changes with Time)

2-2. CSI Sensing Technology

CSI (Channel State Information) sensing is a technology that estimates the state of the space (referred to as a channel) through which radio waves propagate by measuring how the received waveform changes compared to the transmitted waveform. From the information about this channel, it is possible to calculate and estimate the changes that occur between the transmitter and receiver.

The radio waves used in everyday LTE, 5G, and WLAN (IEEE 802.11n, etc.) employ a modulation method called OFDM. The OFDM signal includes "pilot signals" that are transmitted at fixed frequencies and times. While the pilot signal propagates through the channel, the power (amplitude) and arrival time (phase) of the radio waves undergo changes. By interpreting these changes, it becomes possible to capture the variations that occurred in the channel.

Channel (Hn) state and changes can be determined by obtaining the variations in amplitude and phase of the pilot signal.

By utilizing multiple antennas, it becomes possible to gather more information during the process. Since the channel changes just by people moving in the space, it is possible to detect actions such as the presence or absence of people and activities like sitting, standing, and walking. Furthermore, research papers have been published that successfully developed AI models that can recreate human contours by combining this with camera imagery.

3. SoftBank's Approach

SoftBank's Research Institution of Advanced Technology began examining the integration of communication and sensing in 2021. In 2022, we conducted experiments aiming to use 5G base stations to acquire location information for vehicles and pedestrians moving throughout a city. In an outdoor experiment conducted in 2022, 5G modulation signals were transmitted from a base station installed at a height of approximately 8 meters. By receiving and analyzing the reflected waves from cars and people without 5G terminals, position estimation was successfully achieved with an accuracy of approximately 2 meters.

To address the various challenges identified in the experiments, we will continue to advance our research and development.

4. Futuristic Vision Enabled by the Fusion of Radio Wave Sensing and Communication

With the widespread adoption of AI, there are now numerous cameras prevalent throughout various aspects of everyday life. While there are many applications that analyze images captured by cameras using AI to utilize the results, privacy concerns due to camera surveillance have become an issue. As a result, some facilities have removed previously installed cameras to address these privacy concerns.

On the other hand, radio wave sensing has the advantage of protecting privacy. For applications where camera-level resolution is not necessary, radio wave sensing, which can gather information at a resolution that does not identify individuals, is considered suitable. This approach can address privacy concerns while still collecting useful data. Additionally, radio waves exhibit the ability to propagate around obstacles, enabling the capture of movements that are not within line of sight. This characteristic opens up possibilities for applications such as detecting intruders hiding in blind spots or detecting people trapped inside buildings.

However, introducing dedicated sensing equipment and maintaining infrastructure incurs costs.
At SoftBank, we aim to leverage our strengths as a telecommunications provider by enhancing our existing base stations with sensing capabilities, thereby promoting the widespread adoption of ISAC.