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Bench Talk for Design Engineers

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Bench Talk for Design Engineers | The Official Blog of Mouser Electronics


P2P Centimeter Accuracy Position and Tracking with UWB JJ DeLisle

UWB Compared to Other Wireless Data & Location Sensing Technologies

(Source: Сake78 (3D & photo) - stock.adobe.com)

UWB has recently (2019) received yet another facelift. This time it comes with significantly enhanced distance/ranging/location sensing technology and enhanced communications. It is now in a league to compete with other everyday wireless communication and sensing technologies. How does it compare?

UWB Primer

Ultra-wideband (UWB) is based on the IEEE 802.15.4a and 802.15.4z and is specifically designed for micro-location services and secure communications. The underlying operation of UWB is very different than most other wireless communication and sensing technologies. UWB relies on wideband but short-in-time pulses (~2 nanoseconds) with highly sharp rise and fall times. UWB encodes data within the pulses, using two consecutive impulse radio (IR) signals per UWB symbol.

UWB uses binary phase-shift keying (BPSK) and/or burst position modulation (BPM). Each UWB communication is timestamped, and this use of time-hopping code makes for very accurate position sensing and interference immunity from other UWB signals. The use of timestamping also enables Time-of-flight (TOF) calculations between two UWB devices and allows for point-to-point (P2P) Two-Way Ranging (TWR) between two UWB radios. Additional synchronized "anchors" in an environment can enable real-time navigation through the environment using Time Difference of Arrival (TDoA) or Reverse TDoA (RTDoA).

The FCC definition for UWB is that the communications must operate with an absolute bandwidth greater than 500MHz. The UWB central frequency maximum power density is above 2.5GHz or has a fractional bandwidth over 0.2 with a center frequency lower than 2.5GHz. This prevents interference with ISM-band technologies at 2.5GHz, such as Wi-Fi® and BLUETOOTH®.

From Figure 1, it is clear that the UWB carrier frequencies and bandwidths typically range from ~3.5GHz to ~9.5GHz around the world. Some UWB channels allow for bandwidth as high as 1354.97MHz at 9484.8MHz carrier frequency. That is an enormous bandwidth for communication technology but given that UWB uses a time-pulse method of communication, the throughput for UWB is capped at 27Mbps.

Figure 1: UWB Channels and their use in different global regions. (Source: Qorvo)

UWB Versus the Wireless World

UWB was built with an entirely different approach to communications and position sensing. Essentially, the standard seems to be a makeshift way of enabling communication out of a position sensing standard—similar to radar—that has various key advantages due to this approach (Figure 2).

Figure 2: Comparing UWB to Bluetooth, Wi-Fi, RFID, and GPS. (Source: Qorvo)

Namely, UWB has a much faster throughput than GPS (none), Bluetooth, Zigbee, RFID, and other non-proprietary wireless communication standards. Functionally, Wi-Fi and 4G/5G cellular telecommunications are the only standards that exceed UWB in raw throughput. However, neither Wi-Fi nor 4G/5G offers an accurate position sensing feature (several meters maximum accuracy). RFID is the next closest competitor to UWB in "on-paper" absolute position accuracy, but RFID has a minimum sensing range of under a meter maximum. Even high-end user GPS accuracy (several centimeters) is less accurate P2P position sensing than UWB. However, in long-term and stationary GPS tracking, GPS accuracy can reach measurements to the millimeter level. In this case, high-accuracy GPS is strictly only accessible in uncluttered environments with minimal interference, as the reference comes from satellite constellations in orbit.

Reliability and interference immunity are other areas where UWB shines. GPS is very sensitive to obstructions and interference, as the relatively narrow-band GPS signal is feeble when it reaches a user device. On the other hand, RFID is relatively robust as it uses a close-range resonant mechanism that is rather robust. Wi-Fi, Bluetooth, and Zigbee are sensitive to interference and multi-path but somewhat immune to obstructions. The extremely wideband operation and timing method of UWB enables powerful immunity to interference in general but also multi-path. Obstructions that can prevent RF signal penetration will obstruct UWB and other wireless communication/sensing technologies.

GPS tracking range is virtually global if counting for other position-sensing satellite constellations. RFID has a very limited range, at most several meters. Wi-Fi is typically limited to roughly 100m for 5m accuracy and a maximum of 150m range. In contrast, Bluetooth can reach approximately 2m accuracy at approximately 25m, with a maximum of 100 meters. UWB features a maximum range of 250 meters with anchors while maintaining P2P centimeter accuracy.

Both Wi-Fi and Bluetooth require a few seconds to acquire XYZ position for position sensing. RFID is typically able to read position within one second. GPS typically position times are around 100ms. The UWB protocol can achieve full XYZ position sensing in less than 1ms, which allows for high-speed tracking between peers or within an environment with anchors.

Most wireless protocols have some form of highly power-efficient operation mode to enable long-term battery operation. For GPS, the only consideration is the terminal's battery life. Still, these are generally less efficient than other wireless standards due to the high-gain, low-noise amplifiers needed to sense GPS signals. Both Wi-Fi and Bluetooth low-energy modes require over 10nJ/bit for RX and TX. UWB requires less than 10nJ/bit RX/TX, a substantial efficiency gain over Bluetooth and Wi-Fi. RFID sensors are typically passive on the tag side but require power on the terminal side, usually utility powered.

UWB anchors and modules designed to be integrated into user equipment and handhelds are relatively inexpensive, similar to Bluetooth modules. These modules are generally much less expensive than Wi-Fi and GPS modules. RFID modules have a wide range of relative costs depending on how the tags are deployed and may be relatively cheap for basic disposable units or more expensive for more sophisticated units.

Security is a complex area to compare UWB, as this protocol iteration is relatively new, and there haven't been significant efforts to breach UWB security methods. Time will tell how UWB compares to other wireless protocols that have been around for some time and whose security vulnerabilities are well known. Similarly, practical scalability of deployed UWB systems hasn't been widely tested the way it has for Bluetooth, Wi-Fi, Zigbee, etc. However, on paper, UWB does boast the potential for 10s of thousands of tags to be deployed in a dense environment, which far exceeds the practical limits of Bluetooth, Wi-Fi, and Zigbee.

Conclusion

It is unlikely that UWB will be a replacement for Bluetooth, Wi-Fi, Zigbee, GPS, or RFID technologies, which is acceptable, as that doesn't seem to be the goal with the technology. UWB appears to be specifically designed to target applications that require more precise position sensing with much lower latency and greater reliability. In this way, UWB seems more to compete with some of the features of Ultra-reliable low latency communications (URLLC) use cases for 5G. However, 5G doesn't include position tracking/sensing (possibly around 1 meter or less with millimeter-wave technology) on the same order of magnitude as UWB. What UWB does is enable highly accurate P2P position and tracking applications that benefit from a reasonable throughput technology at short and relatively long ranges, which is unique and a potential enabler of a wide variety of applications.



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Principal of Information Exchange Services: Jean-Jacques DeLisle
Jean-Jacques (JJ) DeLisle attended the Rochester Institute of Technology, where he graduated with a BS and MS degree in Electrical Engineering. While studying, JJ pursued RF/microwave research, wrote for the university magazine, and was a member of the first improvisational comedy troupe @ RIT. Before completing his degree, JJ contracted as an IC layout and automated test design engineer for Synaptics Inc. After 6 years of original research—developing and characterizing intra-coaxial antennas and wireless sensor technology—JJ left RIT with several submitted technical papers and a US patent.

Further pursuing his career, JJ moved with his wife, Aalyia, to New York City. Here, he took on work as the Technical Engineering Editor for Microwaves & RF magazine. At the magazine, JJ learned how to merge his skills and passion for RF engineering and technical writing.

In the next phase of JJ’s career, he moved on to start his company, RFEMX, seeing a significant need in the industry for technically competent writers and objective industry experts. Progressing with that aim, JJ expanded his companies scope and vision and started Information Exchange Services (IXS).


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