UWB: Enhancing Positioning, Safety and Security for Connected Vehicles
Ultra-wideband (UWB) is an RF wireless technology that could enhance advanced driver assistance systems (ADAS) and connected autonomous vehicle (CAV) sensor suites. The addition of UWB could increase the number of lives saved by avoiding deadly collisions and ensuring the trusted rollout of vehicle-to-everything (V2X) connections.
Technology advancements are changing our everyday lives and significantly impacting whole industries. This holds true for the automotive industry, which continues to adopt new technologies to enhance consumer experiences, safety and security. Among today’s biggest concerns are severe traffic collisions, an area where technology can be applied to save lives. Many efforts are underway to define, develop, standardize and implement the best technologies to improve road safety. Initially, manufacturers have used stand-alone ADAS technologies inside vehicles, such as radar and cameras. With these technologies, each manufacturer could implement its own system without the need for standardization.
The next big leap in safety will be for vehicles to share information, enabling them to cooperate with each other. This will require standardization to ensure connectivity of vehicles from different manufacturers. Efforts are underway to provide the basis for connected vehicles by standardizing V2X connectivity, including vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I) and vehicle-to-pedestrian (V2P) protocols. V2X standardization efforts open the way for the adoption of new technologies that enhance the ADAS and CAV sensor suites.
UWB is a low-cost RF technology that can be used to accurately measure the distance between two points. This leads to the perfect marriage: UWB + V2X. The adoption and standardization of UWB + V2X can add capabilities, including precise positioning, secure identification and ultra-low latencies at high update rates. This article will focus on a few critical life-saving applications of UWB + V2V and UWB + V2P. However, it is important to note that there are also many applications where UWB + V2I could greatly improve consumer convenience, such as automated valet parking and alignment with electric vehicle chargers.
IEEE 802.15.4z provides a specification for the standardization of UWB for secure ranging. The security aspects of the standard ensure distance measurements are accurate and not spoofed by external sources. UWB secure ranging works by measuring the time it takes for very narrow RF pulses to travel from a transmitter to a receiver. This “time of flight” is multiplied by the speed of light to obtain the distance. Narrow pulses enable the system to accurately understand multi-path interference and choose the first path, ensuring identification of the nearest object.
Many pulses are grouped together to form frames. Each secure ranging frame contains a scrambled time stamp, which is created using cryptographic techniques to ensure the reliability of the distance measurement. A single frame can be transmitted in less than 200 µs. Frames are sent back and forth between the transceivers of all nodes in a group, providing round-trip distance measurements between all nodes. For a simple one-sided, two-way ranging operation, round-trip measurements can be completed in under 1 ms, enabling an update rate of 1000/s.
UWB operates with a bandwidth greater than 500 MHz and, when coupled with the proper signal processing techniques, can provide distance measurements with an accuracy down to 10 cm. All these capabilities can be implemented on a single low-cost CMOS device. More background information and an overview of UWB technology can be found in the Qorvo publication Ultra-Wideband for Dummies.1
The automotive industry is beginning to envision its connected future, ushering in a new era of cooperative autonomous driving. This includes use cases such as group start from traffic lights, intersection crossing, vehicle platooning and merging between lanes. These use cases require knowing vehicles’ relative position to an accuracy better than 1 m and down to 10 cm in some cases. By sharing accurate positioning information, vehicles can work together to perform these functions more safely and with faster reaction times than a human, allowing them to operate with minimal or no human intervention.
One of the basic functions of V2V communications is the exchange of basic safety messages (BSM) in the U.S. or cooperative awareness messages (CAM) in Europe. These messages include information such as vehicle position, speed and heading. From this rough positional data, a vehicle’s autonomous navigation system (ANS) can determine which other vehicles are in the vicinity. Groups can then be formed for cooperative maneuvers.
In complex cooperative maneuvers of connected vehicles, maintaining proper separation is imperative to avoid fatal contact between vehicles. According to the 5G Automobile Association (5GAA), a global organization working on future connected mobility and intelligent transportation solutions, precise positioning is one of the critical problems to be solved. Keeping vehicles separated requires technology that can provide exact position measurements with fast update rates.
UWB can perform this function with accuracy down to 10 cm, which is one of the reasons the technology is growing globally. UWB can also save lives by preventing collisions between vehicles and vulnerable road users (VRUs) such as bicycles, motorcycles and pedestrians. UWB is rapidly proliferating in many consumer products and applications. Many of the leading cell phones include UWB, and the technology is being added to cars to enable phones to act as secure digital keys.
Wouldn’t it be great if UWB in vehicles and UWB in cell phones could be used together to save lives? If a vehicle could talk to a pedestrian’s cell phone (V2P) and use UWB to measure the distance between them, then vehicle-pedestrian collisions could be avoided. UWB can increase the security of communications by preventing malicious spoofing, which is a significant concern with CAVs. By verifying a vehicle’s ID and position, UWB can validate communications are with the intended vehicle instead of someone impersonating that vehicle for malicious purposes. Recent reports have demonstrated the impact of costly infrastructure blackmail exploits that have compromised many systems and led to loss of service. Can you imagine traveling down the highway in a CAV and receiving blackmail demands to pay or else the vehicle might be crashed?
UWB WITH LARGE OBJECTS
Most of the literature about UWB focuses on determining the distance to a small object. But when UWB is applied to large objects such as vehicles, knowing the distance to a single point somewhere on the vehicle is not adequate. In the case of moving vehicles, the measurements must be relative and continuous. Using multiple UWB sensors, each vehicle can continuously calculate the relative position of all four corners of another vehicle. Throughout the rest of this article, the term position will refer to relative position.
For a cooperative maneuver, the ANS could identify the appropriate vehicles and form a group using the V2V link. After a group has been formed, the ANS would identify, initialize and start continual measurements with the appropriate UWB sensors, again using the V2V link. Figure 1 shows how UWB sensors near the corners of two vehicles could form a crossbar arrangement. With two sensors located on each of the front, rear and side surfaces of each vehicle, the position and orientation of both vehicles could be determined. Each of the UWB links provides a unique, secure method of measuring the precise distance, as well as supporting data communications. Data communications can further enhance security by enabling the exchange of additional details.
SAFETY AT HIGH SPEED
During high speed maneuvers involving several vehicles, it is vital that the CAVs function without failure. One common example is platooning (see Figure 2), where several vehicles travel in tight formation, drafting each other to save fuel. Platooning will help the trucking industry increase safety while reducing fuel costs and emissions, as well as reducing congestion and delivering goods faster. It could also help maximize the range of electric vehicles with limited battery capacity.
UWB links enable platooning vehicles to accurately measure the distance between them and maintain proper separation and orientation. In a platoon, each vehicle follows another at a close distance. Reaction time is critical. If the platoon is traveling at 60 m/s (135 MPH) and the separation between the vehicles is 6 m (20 ft), vehicles in the platoon must react in less than 100 ms to avoid a collision if the lead vehicle suddenly applies its brakes. This can easily be achieved with UWB.
With four sensors in a many-to-many UWB architecture, a ranging round should be completed in well under 10 ms, with the exact timing dependent on implementation. A ranging round is the time it would take for the four sensors to measure the four distances shown in Figure 2. For a vehicle traveling at 60 m/s, a ranging round time of 10 ms means the vehicle would travel only 60 cm between messages, giving each vehicle adequate time to react safely to speed changes of the lead vehicle. Multiple UWB links enable the platooning vehicles to maintain the correct orientation to each other. This could enable each vehicle’s ANS to follow the lead vehicle around curves, staying in the same track as the lead vehicle.
Merging is another process where CAVs can benefit from UWB sensors. Examples of situations where vehicles need to merge include entering a highway from an on-ramp or joining the middle of a platoon. Figure 3 shows a situation where one vehicle needs to merge with two other connected vehicles. The ANS first establishes a connection using V2V, forms a group and communicates the need to merge. The system would then determine the UWB sensors needed for the operation, initialize those sensors and launch continuous UWB sensing (see Figure 3a).
The next step is for the two vehicles to form a gap for the merging vehicle to join. The merging vehicle would then move into the lane between the two other vehicles as shown in Figure 3b. The ANS determines the appropriate UWB sensors required to participate. After joining the platoon, the UWB sensors maintain continuous operation to regulate the distance and orientation of the vehicles.
UWB AND V2P
Another key potential life-saving application takes advantage of UWB coupled with V2P communications using a VRU’s smartphone or other UWB-enabled device. This works similarly to V2V: the ANS, coupled with V2P, can determine if a VRU is in the vicinity and then start the UWB distance measurement process. UWB tracks the exact position of the VRU and determines the possibility of a collision. As an example, vehicles stopped at an intersection, such as the three-way stop shown in Figure 4, could use UWB sensors to determine the distance to the VRUs and avoid a collision.
VALIDATING FOR IMPROVED SECURITY
UWB can also be used to mitigate risk for connected car threat scenarios. The Car Connectivity Consortium already includes UWB in its Digital Key 3.0 specification, which enables drivers to securely use their phones to open and start their cars. UWB increases security by measuring the distance between the owner and the vehicle. Ensuring the owner is in the proximity of the vehicle prevents “person in the middle” vehicle attacks where thieves intercept and relay distant signals from an owner’s phone to gain access.
With V2V communications, it is vital for safety that vehicles can trust the information received from other vehicles. Detecting misbehaving actors transmitting inaccurate information, whether unintentionally or maliciously, is an important security and safety concern. UWB can provide the required trust between vehicles by ensuring they know each other’s position, validating their identity and detecting misbehavior. This is especially important when the communication includes life-critical information. The analysis in Table 1 summarizes the most critical 5GAA cooperative driving use cases where inaccurate information could be deadly.
UWB sensors could be used to verify that the vehicle being communicated with over V2V is really in the position indicated. If the position does not correlate with the GPS coordinates transmitted in the BSM or CAM, then any transaction between the vehicles would be in doubt and appropriate precautions could be taken. Identification of misbehaving actors in the system and then revoking their certification will help ensure a trusted V2V system.
In one potential example of fatal spoofing (see Figure 5), a spoofing vehicle (SV) traveling behind a passing vehicle (PV) pretends to be in front of the vehicle by transmitting incorrect GPS coordinates, falsely indicating it is in front of the PV instead of behind it. If the PV requests “see through for passing” information, the SV could then transmit an image of a clear road. Based on this false information, the PV would start to pass and could collide head-on with an oncoming vehicle. This can be avoided if the PV is able to verify, using UWB, whether the SV is truly the vehicle in front.
UWB can also be used to accurately identify vehicles in other use cases. Following directly behind two vehicles closely tailgating each other, it could be difficult to know with which of the two your vehicle was communicating. UWB distance measurement could confirm communication with the appropriate vehicle. Another example: following two vehicles traveling side by side in adjacent lanes. If one vehicle is using real-time kinematics to adjust its GPS coordinates and the other vehicle is not, the two vehicles could be reporting the same location.
AUGMENTING THE CAV SENSOR SUITE
UWB provides an excellent augmentation to the existing CAV sensor suite. Its high frame rate provides much faster reaction times than any other system. The ability to provide communications in addition to sensing enables UWB to provide secure distance measurements and accurately identify other vehicles. Being an RF technology, it operates much better than optical systems in poor weather. UWB’s small size, low complexity and low cost make placing multiple sensors around a vehicle feasible.
UWB sensors offer the benefit of simplicity, which helps vehicles process and respond to information more quickly. The processing power required to implement UWB secure ranging is relatively small. To provide the same information about the relative distance and orientation of two vehicles without using UWB requires both radar and cameras. The camera would need to look at the scene, analyze the image, extract key features and determine orientation. The radar would measure the distance between the vehicles, with the accuracy dependent on the radar’s resolution and its short distance performance. The camera and radar data would then be merged using sensor fusion, which may require raw source data and an extensive library of 3D image processing algorithms to combine and then extract the information. The maximum frame rate of such a system could be more than 3x slower than UWB frame rates. The simplicity of a UWB based system also reduces the probability that an issue with the code could cause an accident.
Figure 6 compares CAV sensors. The introduction of UWB into the CAV suite provides a robust, faster, secure and accurate system with superior price for the performance.
Many of the techniques discussed in this article already exist. The 802.15.4z specification provides for a many-to-many UWB architecture, providing the basis for a secure multi-point ranging area network (RAN). V2V defines the ability for vehicles to form a group, which is the basis for selecting the vehicles to participate in the UWB many-to-many RAN. Once a group is formed, there is a need for specifications covering how the system using the V2V link can identify, select, initialize and operate a secure UWB RAN. For broad adoption, standards need to be developed to enable UWB devices on vehicles from different manufacturers to interoperate. Qorvo is leading an effort to have its patent-pending UWB + V2X concept adopted as a key part of the connected vehicle rollout.
UWB technology is a much simpler system than radar or cameras, requiring far fewer lines of code and less processing resources. With a low cost for implementation, centimeter accuracy and low latency, UWB provides a high performance to cost ratio, enabling manufacturers to implement a more robust CAV sensor suite.
Connected vehicles will introduce a new era of vehicle safety. The key to this will be the creation of a trustworthy communication environment between vehicles. UWB can provide the required trust between vehicles by ensuring they know each other’s position, validating their identities. This is especially important when communicating life-critical information. High speed cooperative maneuvers are some of the most critical CAV operations. UWB can provide the speed and accuracy needed to enable the ANS to avoid life threatening situations by reacting much faster than a human, even faster than existing radar and camera systems. Even at slow speeds, vehicle maneuvering can result in fatal accidents, especially when a VRU is involved. By using UWB to measure the distance to VRUs, the navigation system can help ensure that accidents can be avoided.
1. Qorvo, “Ultra-Wideband for Dummies,” www.qorvo.com/design-hub/ebooks/ultra-wideband-for-dummies.