The autonomous vehicle market receives its fair share of hype for its potentially huge market size, but it might be small GPS antennas and receivers that push the market closer to reality. In the autonomous industry, precision location—down to the centimeter level—is everything. Reaction time and safety issues are critical; the vehicle’s absolute location must be known at all times, which requires more sophisticated technology than what the market has seen thus far.

Reliable, secure connectivity has been one hurdle to overcome, and the industry is moving closer to that with today’s existing LTE (Long Term Evolution) networks and oncoming 5G (fifth generation) networks, plus extra availability of GNSS (Global Navigation Satellite System) satellites with higher gain signals. But it’s the emerging technology advances in GNSS receivers and high-quality antenna systems that will enable centimeter-level positioning and, in turn, the autonomous revolution.

Current location solutions use the GPS (Global Positioning System) L1 band in the 1500-1600 MHz range. However, if you’ve ever heard the words “recalculating” as you’re trying to navigate on highways or city streets, you know that standard locations capabilities aren’t precise enough for autonomous vehicles. These errors are caused by ever-changing signal delays in the atmosphere. By listening to signals from the same satellite systems (such as the Galileo, GLONASS, and BeiDou) at more than one frequency (commonly referred to as L1, L2, and L5 GPS frequencies), these errors can be removed. With the combination of a multi-constellation and -frequency receiver, and high-performance, low-profile antennas that are able to cover multiple bands, location can be accurately reached within a few centimeters.

How we got here

When GPS was developed by the U.S. military in the 1970s, a lot of thought was put into understanding how to get very good location accuracy of the receiver. One of the keys to achieving best performance was understanding the effects of ionospheric delay and refraction effects. From empirical testing came a model, and from that model came a solution for removing the effects and resulting error from the computation of a GPS receiver’s location. That solution was to send a GPS signal on two separate frequencies.

When the system was built, all its transmissions were encoded such that only U.S. military equipment could decode them. Since 1983, the GPS L1 signal has been sent un-encoded, allowing civilian use of the GPS system. It’s interesting to note that encryption of the whole GPS system can be turned on again at any time by order of the U.S. president.

Dan Michael, Director of Automotive, Taoglas, wrote this article for AVT

The L1 GPS signal is sent on a center frequency of 1575.42 MHz. The original L2 signal, however, which is sent at 1227.6 MHz, was historically always encrypted. Because of the original encryption on L2, civilian GPS receivers have only listened to the single L1 transmission. That limitation of only being able to use L1 is why civilian GPS receiver accuracy is generally limited to an RMS value of around 3 m. There are multiple modulated signals on each of these frequencies that a GPS receiver can receive. As the GPS system has been modernized, additional signals have been added to the existing frequencies for civilian use, as well as a third transmission called L5 at 1176.45 MHz. 

These additional civilian signals on L2 and L5 set the stage for civilian GPS receivers able to achieve similar accuracies to military GPS receivers. However, dual-band GPS receivers from the beginning of their availability have been expensive, limiting their application to things that can clearly justify the additional cost.

Economies of scale

Autonomous vehicles, with their complex, integrated systems of a variety of sensors, will change all that.

Production vehicles will include sonar, radar, LiDAR, infrared and visible light machine vision, and—of course—dual-band GPS. The mass-production scale of vehicles in general, autonomous or not, is driving the cost of dual-band GPS receivers down dramatically. Major commercial GPS receiver manufacturers will be deploying new lines of dual-band GPS receivers within the next year or so.

While dual-band receivers will likely still sell at a significant price premium to L1-only units, they will still be orders of magnitude cheaper than they have been historically. This, in turn, enables new business models that rely on centimeter-level absolute position accuracy far beyond autonomous vehicles.

The trucking industry will likely adopt autonomous vehicles first. In the near future, we’ll see such trucks, specially marked or even lighted, rolling along at about 45 mph (72 km/h) or so on our major highways. (Trucks only go faster than that because drivers can only drive for a specific period of time.) This relatively low speed saves a lot of fuel (or energy, if they’re electric) and, if you’re not paying a driver by the hour or worried they’ll fall asleep, slower speeds extend range, save money, and generally make good business sense.

Diesel-powered trucks will house larger fuel tanks specifically to extend point-to-point range. However, there will be situations where even such a truck would need to refuel, and out of that, we’ll likely see a new kind of gas station as well. Envision automated fueling islands where the truck parks in a specific spot and indicates it needs fueling. Of course, initially a human will likely need to come out and fill that tank, but eventually this will be replaced by an automated fueling system where the truck has an industry-standard fueling interface. Perhaps that interface supports both electric and chemical fueling.

And what about that truck driver? For the highway, there will likely not be a driver. Where the driver will come into play is getting that truck from the industrial park warehouse, through town, and out to the highway. But that’s where they get out and head back to the warehouse. The truck drives off into the horizon by itself. Hours later, that truck gets to its exit, where it stops and calls for a driver, who drives that truck to its final destination. Driving a heavy truck through tight, highly populated areas will continue to be best addressed by a human. But now that human sleeps in their own bed after work instead of in a cab at a truck stop.

While dual-band receivers and antennas will help drive precision accuracy that will benefit several industries such as manufacturing, construction, agriculture, and others, it’s the autonomous vehicle industry that will drive the costs down and push the technology forward for everyone.

For more info on Taoglas, visit http://www.taoglas.com/product-category/automotive-antennas/.