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Eric Hsu
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RF + Microwave
IEEE 802.15.4 HRP UWB Ranging Process and Measurements
2021-07-28 | 8 min read
A variety of wireless communications standards provide indoor positioning systems, such as Wi-Fi, Bluetooth®, RFID, and HRP UWB. They are using different positioning methods for indoor ranging, including received signal strength indication (RSSI), angle of arrival (AoA), angle of departure (AoD), remote coupling, and time of flight (ToF), also called the time of arrival. Table 1 shows key attributes and techniques for each wireless standard.
Wireless systems
Wi-Fi
Bluetooth
RFID
HRP UWB
Standard
IEEE 802.11az
Bluetooth 4.0 / 5.1
EPC / ISO
IEEE 802.15.4/4z
Technique
RSSI
AoA or AoD
Remote coupling
AoA or ToF
Frequency
2.4, 5, 7 GHz
2.4 GHz
12.5 kHz to 5.8 GHz
Sub-GHz; 3.1 to 4.8 GHz; 6 to 10.6 GHz
Modulation
OFDM
GFSK
ASK, 2-FSK, OOK
BPM and BPSK
Range
< 150 meters
< 75 meters
< 1 meter
< 100 meters
Accuracy
<15 meters
< 1 meter (BT 5.1); < 8 meters (BT 4.0)
Presence detection only
< 30 cm
Power consumption
Medium
Low
Passive powered
Low / medium
Among these standards, the HRP UWB offers fine-ranging and security capabilities and has been adopted by major mobile phone makers. It enables new applications such as real-time spatial context to mobile devices, advanced ranging, location-based services, and seamless and secure point-to-point (peer-to-peer) services.
The IEEE 802.15.4-2020 standard has updated the physical layer (PHY) and medium access control (MAC) sublayers of the technology for high precision, secure-ranging applications. The HRP UWB ranging system is based on ToF and AoA measurements to provide reliable and robust ranging timestamps to accurately measure the distance and direction between devices.
Two-Way Ranging
The measurements for ranging are using a data frame acknowledge frame sequence. The HRP UWB uses the ToF measurements for single-sided two-way ranging (SS-TWR). Figure 1 shows the SS-TWR scheme. The ranging marker (RMARKER) is the location of the first chip after the start of the frame delimiter and is a timestamp used for calculating ToF. Device A sends a frame to Device B and receives a reply from Device B. Device B needs to communicate its reply time Treply to Device A. Then, Device A can calculate the estimated time of flight Tprop by the following formula:
Tprop = (Tround - Treply) / 2
The distance or range between devices is based on estimating the propagation time (Tprop).
Similarly, the double-sided two-way ranging (DS-TWR) requires Device B to initiate the same process. Figure 2 illustrates the DS-TWR procedure. It improves accuracy when clock synchronization between the two devices is not available. Both devices measure the time between packets. With all four times measured the propagation time can be estimated by the equation below.
Tprop = (Tround1 * Tround2 - Treply1 * Treply2) / (Tround1 + Tround2 - Treply1 - Treply2)
Figure 3 illustrates the test setups for ToF measurements and the test procedures for DS-TWR as follows.
Angle of Arrival (AOA)
AoA is related to the position of the target node. Each angle translates into a time difference between the arrival of the signals to array antennas. For example, Figure 4 shows that the simplest antenna array is the uniform linear array.
The time delay between the arrival of the signals to the consecutive antenna is given by
t = d * sinø / c
where t is the time delay, d is the distance between antennas, ø is AoA, and c is the speed of light.
Figure 5 shows using a high-precision delay line to simulate propagation delay for one of the test channels to validate the AoA for an HRP UWB device.
Please be aware that chipset makers may use different ranging algorithms and measurement setups to calibrate and validate both ToF and AoA.
Enable Accurate Ranging Measurements
The accurate position is one of the key features of the HRP UWB technology. UWB uses up to 500 MHz channel bandwidth with a pulse period of about 2 ns that enables centimeter-ranging accuracy. However, it also increases test challenges to generate and analyze the wide bandwidth signals. . Keysight offers a flexible suite of signal generation tools that reduce the time you spend on signal simulation and powerful analysis tools to understand the structure and quality of the transmitted HRP UWB signal as shown in Table 2. To learn more about IEEE 802.15.4 HRP UWB tests, download the white paper: An Overview of IEEE 802.15.4 HRP UWB Test Requirements.
Signal analyzer
Signal generator
Vector transceiver1
Model
N9042B UXA
N9040B UXA
N9032B UXA
N9030B PXA
M9384B VXG
M9415A VXT
Frequency (GHz)
26.5, 44, 50
13.6, 26.5, 44, 50
13.6, 26.5
13.6, 26.5, 44, 50
14, 20, 31.8, 44
12
RF bandwidth (GHz)
1, 1.5, 2, 4
0.51, 1
1, 1.5, 2
0.51
0.5, 1, 2
0.8, 1.2
Software
PathWave vector signal analysis for IoT modulation analysis (89601BHTC)
PathWave signal generation for IoT waveform signal creation (N7610C)
1 Vector transceiver integrates a vector signal generator and a vector signal analyzer in a three-slot PXIe module.
Further Reading
Related Content
White Paper
An overview of the technology and test requirements for IEEE 802.15.4 HRP UWB
Related Products
M9415A VXT PXI Vector Transceiver
M9384B VXG Microwave Signal Generator
Technical Overview
802.15.4 HRP UWB Analysis with PathWave Vector Signal Analysis
N7610C Signal Studio for IoT
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