1. What Is Ultra-wideband (UWB)?
UWB is the abbreviation for Ultra-wideband. UWB wireless communication is wireless communication that uses the ultra-wideband frequency bandwidth. Its main feature is that it enables high-precision positioning. UWB wireless communication has spread to consumer equipment in recent years. For example, UWB wireless communication is being equipped to smartphones to prevent loss and for other purposes and is being equipped to smart keys of luxury cars. It is expected that UWB wireless communication will spread to many fields in the future.
We explain here the features, history, uses and other elements of this UWB wireless communication.
2. Features of UWB Wireless Communication
IEEE802.15.4z is given as a representative standard of USB wireless communication. There is a method which uses impulse radio using pulse signals with a short duration in this. Its main features are listed below.
- High-precision ranging and positioning
- High security
- Low interference with other communications
- Low power consumption
We explain here how UWB wireless communication exhibits these features.
As shown in Fig. 1, pulses with a duration of about 2 ns (nanoseconds; 10-9 seconds) are sent as data in UWB wireless communication. These short-duration pulses have the property of high resolution with respect to ranging and positioning.
On the other hand, a small pulse duration in the time domain means that the power spectrum in the frequency domain occupies a wideband. (We will explain the time domain and the frequency domain in communications on another page.)
Fig. 2 qualitatively shows the transmission power (power spectrum density) of UWB wireless communication in that frequency domain. We can see, for example, that UWB wireless communication is overwhelmingly wide if we compare it with the frequency bandwidth used by conventional communication like 2G mobile phones or Wi-Fi and 3G mobile phones.
Moreover, in addition to being lower than other communication methods, the peak value of the transmission power in UWB wireless communication is set lower than the noise level regulation value for digital equipment that emits radio waves - radiated electromagnetic noise regulation value established by the U.S. Federal Communication Commission (FCC)*1 of −41.3 dBm/MHz*2 (75 nW/MHz).
In this way, UWB wireless communication is noted as having the feature of low interference with respect to other communications from its communication characteristics of a wide frequency band used and a transmission power level lower than the noise level. Moreover, as the communication itself is not known by third parties, it has high security. Furthermore, communication with low power consumption is possible.
*1: The U.S. Federal Communication Commission (FCC) is a government agency which is involved in managing and regulating all communications, whether wireless or wired, in the United States.
*2: dBm/MHz refers to the power level per 1 MHz frequency width (power spectrum density). dBm is the unit when power is converted to a common logarithm. The numerical range handled is extremely wide in communication systems. As it is inconvenient to handle it directly, it is customary to use a logarithmic expression to reduce the range.
3. History and Regulations of UWB Technology
Research on UWB technology was advanced primarily for military radar in the U.S. from the 1960s. It was a communication technology classified as a military secret until around 1994. The FCC in the U.S. began to consider the civilian use of UWB from around 1998. It approved that in 2002. Since then, research such as on chipsets for UWB has been advanced.
It has only been since 2019 that UWB has become widely recognized by society. The trigger for that was the emergence of smartphones equipped with UWB modules. As a result, UWB has been approved by various countries where it was not used in the civilian sector in the past.
UWB technology has progressed in this way. If we focus on the frequency bandwidth regulations in particular, the frequency bandwidth of UWB wireless allocated by the FCC is 7.5 GHz from 3.1 GHz to 10.6 GHz. On the other hand, the bandwidth allocated by countries and regions including the EU, Eurasia, East Asia and Oceania differs slightly from that. It is regulated so that it can mainly be used indoors and outdoors in the bandwidth of around 6.0 GHz to 9.0 GHz.
Nevertheless, at present, most UWB modules observe the specifications of channel number 9 (central frequency: 7,987.2 MHz / frequency bandwidth: 499.2 MHz), which specifies preferential use for UWB in the IEEE802.15.4a short-range wireless standardization standard adopted in 2007 by the U.S. Institute of Electrical and Electronic Engineers (IEEE)*3.
*3: The U.S. Institute of Electrical and Electronic Engineers (IEEE) is the world's largest academic research organization in the electrical field. It is also a standardization organization in the same field.
4. Uses of UWB Wireless Communication
We introduce here the main uses of UWB wireless communication in consumer and industrial use as well as uses expected in the future.
4.1. UWB Wireless Communication Equipment and Services for Consumers
Attaching UWB tags to belongings prevents them from being lost. For instance, let's say you attach UWB tags to bags, wallets, keys, and other such items. You can then locate the items by positioning the location of the UWB tags precisely in the order of centimeters using a smartphone equipped with a UWB module. Moreover, although the batteries of UWB tags are button batteries, it is said that they last for about a year because of their low power consumption.
UWB modules have increasingly being equipped to consumer equipment like tablets, smartwatches, and smart speakers in addition to smartphones since 2019. It is expected this will grow into a large market with the emergence of various products and services that have adopted UWB wireless communication in the future.
Secure Building and Room Entry and Exit
It is possible to build a hands-free and secure building and room entry and exit system by using smartphones and other devices equipped with UWB modules.
You can safely unlock residences such as condominiums that until now used PINs, physical keys, IC cards, and other mechanisms and offices and factories where confidential information is handled while your smartphone or other device is still in your pocket or bag without taking out a key or IC card by taking advantage of the high-precision ranging and high security features of UWB. In this way, there are expectations for the spread of applications that will realize smooth building and room entry and exit.
Hands-free Payment and Fee Billing
It is possible to build a hands-free and secure payment system for supermarkets, convenience stores, and restaurants and other commercial facilities by using smartphones and other devices equipped with a UWB module. It is also possible to build billing fee systems for station gates, entertainment and recreational facilities, accommodation facilities, parking, and other such facilities.
There are expectations for the practical use and spread of applications that will realize hands-free smooth payment and fee billing without the need to take out your wallet, IC card, smartphone, or similar by taking advantage of the high-precision ranging and high security features of UWB.
4.2. UWB Wireless Communication Equipment and Applications for Automobiles
Automobile smart keys are an application of UWB wireless that takes advantage of its high-precision ranging and positioning. For example, it is possible to set up operating functions such as one that can unlock a vehicle after determining the owner is within about 1 m of it and can then start the engine when the owner is within a few dozen centimeters of it by employing wireless communication using UWB near that automobile.
Moreover, UWB wireless is confidential communication with extremely low transmission power. This means that it enhances security. For instance, it can prevent a theft technique called a "relay attack" in which a third party unlocks a vehicle by relaying the radio waves being continually output by conventional wireless keys.
Making In-vehicle Networks Wireless
It is said that wire harnesses (in-vehicle components consisting of electric wires and connection terminals) used as in-vehicle networks such as the Controller Area Network (CAN) reach a total length of 10 km and a total weight of 50 kg depending on the vehicle model nowadays when automobiles are being made compatible with IoT by equipping them with a wide range of sensors, radars, AI systems, and other technologies and then linking those elements together. It is said that UWB wireless, which has low interference with other communications, is effective in making in-vehicle networks wireless in a situation where there is parallel evolution as connected cars.
4.3. UWB Wireless Communication Equipment and Systems for Industry
Real-time Positioning Systems in Factories, Warehouses and Other Facilities
It is possible to build a real-time location system (RTLS) using multiple UWB anchors and UWB tags*4. This is a system that grasps in high precision and real time the location of components, packages, and other items placed in sites such as factories and logistics facilities.
*4: It is possible with positioning using UWB wireless communication for multiple anchors to receive signals emitted from tags and to then process that information to accurately understand the location of that tag (refer to the column). UWB anchors for industry are usually operated in conjunction with positioning engines, application servers, and other systems.
5. Murata Manufacturing's UWB Modules
Murata Manufacturing (hereinafter, "Murata") has a lineup of small and low power consumption UWB modules that we have configured with our highly reliable filters, clocks, antennas, and other peripheral components by adopting NXP or Qorvo UWB chipsets.
5.1. NXP-based UWB Modules
Main uses: General IoT devices containing battery-powered devices.
We have adopted the NXP Trimension™ SR150 UWB chipset for these modules. They are small modules composed of a conformal shield in addition to a resin mold. They support 2D AoA and 3D AoA with three-antenna specifications.
Main uses: UWB tags/trackers that operate with the low power consumption of coin batteries and general IoT equipment.
These modules are combo modules for which we have adopted the NXP Trimension™ SR040 UWB chipset and the NXP QN9090 Bluetooth® LE + MCU chipset. They are equipped all-in-one with onboard antennas and peripheral components.
5.2. Qorvo-based UWB Modules
Main uses: IoT devices and applications which operate on small batteries.
These modules are UWB modules with an ultra-small, high-quality, and low power consumption design for which we have adopted the Qorvo QM33120 chipset. They are equipped with a Bluetooth® LE chipset for UWB wake-up (sleep cancellation) and firmware updates, our accelerometer, UWB and MCU reference clock, among other components.
Column: Method of Position Measurement in UWB
It is typical to combine ranging with Time of Flight (ToF) and angle measurement with Angle of Arrival (AoA) between terminals such as smartphones equipped with a UWB function or UWB anchors for industry and UWB tags as the methods of positioning using UWB wireless communication. We explain each method below.
Ranging with Time of Flight (ToF)
Ranging with Time of Flight (ToF) using UWB wireless communication is a mechanism to calculate the distance to a target object by measuring the time from the transmission to the reception of a message (signal). Specifically, a UWB transmitter emits short pulse signals, and a receiver then receives those signals. The time required from the transmission to reception of those signals is called the ToF.
UWB ranging using ToF technology makes it possible to calculate distance from the speed of the electromagnetic waves (speed of light) and the time required. Specifically, the distance is obtained using the product of the time required and the speed of light. The ultra-wideband characteristics of UWB make it possible to use short pulse signals. Therefore, it is possible to obtain high time resolution and measurement precision. As a result, we can expect the acquisition of high-precision measurement results in sensing and positioning applications. Accordingly, it is used in various fields.
There are two main techniques to UWB ranging technology: Single-Sided Two-Way Ranging (SS-TWR) and Double-Sided Two-Way Ranging (DS-TWR). These techniques adopt differing approaches to distance measurement with the round trip of signals.
SS-TWR (Single-Sided Two-Way Ranging):
SS-TWR is a method to measure the round-trip time with just one device. In this technique, device A transmits signals to device B and device B then receives those signals before sending reply signals back to device A. Device A measures the time required from transmission to reception of the signals to calculate the round-trip time. This method enables measurement with only device A. Nevertheless, clock synchronization of both devices is required.
DS-TWR (Double-Sided Two-Way Ranging):
DS-TWR is a method to measure the round-trip time with both devices and to then share the results. In this technique, device A transmits signals to device B and device B then receives those signals before sending reply signals back to device A. Device A and device B measure the time required from the transmission to reception of those signals, respectively. They then calculate the round-trip time using those results. Clock synchronization is not required in this method. That means even simpler and higher precision measurement is possible.
Angle Measurement with Angle of Arrival (AoA)
AoA is a method to calculate the angle of the direction in which device B is placed as seen from device A. As shown in Fig. 4, angle measurement with AoA in UWB wireless is a mechanism in which radio waves emitted from device B are received in the multiple antennas of device A to calculate the angle from the phase contrast of the radio waves received. As a result, it is possible to perform planar positioning with angle measurement (2D AoA) using two antennas and three-dimensional positioning with angle measurement (3D AoA) using three antennas.