Testing UWB’s New Features
By Adam SmithSeptember 20, 2021
Wireless technologies that enable new micro-location capabilities are expanding use-cases of applications, including those that demand a higher level of security. In the automotive industry, for example, there is a demand for a more secure authentication between the car and the key fob. This has created a perfectly-timed opportunity for ultra-wideband (UWB) technology to flex its unique advantages in localization, position detection and direction, compared to other technologies that make it a good fit for the increased security needed. UWB is ideal for applications that enable two devices to securely find each other and understand where they are relative to one another in space.
UWB uses a technique called time of flight (TOF) to enable its secure method of authentication. Unlike other technologies, which estimate the distance separating two devices by signal strength, TOF involves sending and receiving signals and calculating distance based on the time it takes for a complete send/receive cycle. It is relatively easy to hack signal-strength measurements, but time is nearly impossible to fake. This high level of security makes UWB relevant today.
The three primary use cases for UWB are:
Access control: Embedding UWB into a device such as a key fob allows tight access control, whether access to a secure building or car. A UWB-based system can estimate proximity within 10 centimeters. The access system can be set to allow access only when an authorized user is within a given distance and anyone not carrying the UWB device will be denied entry automatically.
Location-based services: The precise proximity detection enables location-based services such as navigation for indoor spaces and contextual content based on the user’s location. As you move from room to room, the system provides information relevant to each room. Think of a museum, or an office complex, where there is information readily available specific to a certain location within the facility.
Device-to-device communication: UWB allows devices to securely share information, and this can be combined with its localization capabilities to push relevant information from one device to another.
UWB Ranging: A Closer Look
UWB uses electronic pulses that are short in time and wide in frequency—hence the name ultra-wideband. Essentially, one UWB devices emits a signal, and a device that detects the signal sends back a response. This is called either single-sided ranging or single-sided two-way ranging. By measuring the time between sending the signal (called a ping) and receiving the reply (pong), the sending device can calculate the distance separating them with precision.
In some cases, the sending device will send another signal upon receiving the reply, which allows both devices to measure the time. This technique, called double-sided two-way ranging adds a second layer of security and accuracy to the positioning.
Crucial UWB Quality Tests
When evaluating UWB device performance, there are three areas where measurements are important.
Regulatory: UWB signals overlap licensed spectrum, so it is important to validate that the device is not running afoul of regulations established by the country’s spectrum governing bodies. While the absolute transmitter power and power spectrum mask are the main regulatory metrics, other factors in the device’s performance are indicative of whether or not the device will meet the power mask requirements. This includes transmitter calibration and testing pulse shape. The more power the device emits, the more energy will splatter out of the desired channel and potentially interfere with neighboring devices, or worse, violating licensed frequency bands. Mask refers to the device’s ability to prevent that signal bleed, due to either spurious or linearity of the transmitter, while the power output impacts the operating range of the end-device. Good calibration maximizes power while delivering valid spectral mask performance.
Interoperability: A key metric for UWB interoperability is frequency accuracy. Wireless devices use tuning capacitors to adjust the crystal that determines the broadcast frequency. If this tuning isn’t done properly, the result is carrier frequency offset (CFO), or frequency error. Put simply, this means the device isn’t exactly operating at the same frequency as the other devices. If the CFO is small, the device will be able to communicate, but ranging measurements will have error. If CFO is large, the badly tuned device might not communicate with others at all. Frequency calibration is a key part of ensuring device interoperability. Another tool is a measurement called the normalized mean square error (NMSE), which captures several different effects in the system and provides a summary measurement.
Time of flight: There are two schools of thought about calibrating TOF. One is to calibrate the system at the printed circuit board level and assume that the over-the-air performance with the antenna attached will be within a narrow tolerance range. The other approach is to test the assembled device and calibrate TOF using its actual over-the-air performance. Either approach is effective, but the key takeaway here is that there are many different components and sources of variation in the system. The goal is to minimize variation and achieve the positional accuracy that UWB can provide.
The Angle of Arrival: What it is and How it Works
UWB can work in two modes, triangulation and peer-to-peer. Triangulation requires a series of “anchor” devices placed in the environment that a UWB “tag” device can use to compare its relative position to the multiple anchors. Peer-to-peer operation allows two devices to communicate directly without the need for anchor devices in the environment. Peer-to-peer operation requires that the device can determine both distance and direction. Distance is achieved from TOF, direction is determined by Angle-of-Arrival (AoA). AoA requires that the device has at least two antennas. AoA determines the time (or phase) difference between the different antennas as they detect an incoming signal. This time (or phase) difference provides information that enables the device to calculate the angle from which the signal is coming.
The FiRa Consortium
The FiRa Consortium, founded in 2019, is an organization seeking to bring together industry and product experts and develop an ecosystem in which UWB products are interoperable and work seamlessly with each other. The membership has grown dramatically in the past year. The consortium will be launching a certification program that will ensure devices meet FiRa specifications for interoperability. The certification program will cover conformance test cases for both physical layer functions (PHY) and medium access control (MAC).
Certification means the device has been tested at an independent authorized testing lab (ATL) and found, after rigorous testing, to conform to FiRa specifications. That provides manufactures and users a high degree of confidence that the devices will be interoperable with other devices.
LitePoint’s UWB testing system includes both hardware and software that enables pre-programmed testing scripts to maximize the testing of a particular chip. LitePoint’s IQgig-UWB is a fully-integrated, FiRa-validated system, designed for UWB PHY layer testing. Turnkey test solutions for UWB chipset and device manufacturers are available, including a FiRa PHY Conformance automation solution. IQgig-UWB is ideal for lab or high-volume manufacturing environments, for UWB-enabled modules and end-products and for UWB-enabled automotive, mobile, asset tracking or healthcare devices.
IQfact+, developed in close collaboration with leading UWB chipset vendors, is a software-based turnkey calibration solution for chipset manufacturers. It supports all of the key wireless connectivity technologies, including UWB.
UWB technology offers powerful capabilities for a wide range of settings where access control, location-based services and device-to-device communications are important. However, actual performance achieved in the end- application depends on ensuring that the key RF parameters meet a high degree of accuracy. These key measurement parameters seek to ensure the devices meet regulatory guidelines and interoperability requirements as well as deliver a positive user experience. From a test point of view calibrating a UWB device’s frequency and transmitter power are crucial. Precise time-of-flight and angle-of-arrival measurements are needed to validate the centimeter-level accuracy that UWB devices can provide. LitePoint’s solutions provide that testing, helping to unlock UWB’s power.
To listen to my entire webinar on UWB testing, please go to the LitePoint webinar page.
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