Reasonable avoidance: Supporting seamless communication and non-interference vehicle-to-everything design

Vehicle-to-everything (V2X) is an umbrella term for a class of vehicle technologies. It allows vehicles to communicate with their surroundings, such as bicycles, motorcycles, and other vehicles. To achieve this, information from sensors and other sources, both inside and outside the vehicle, is transmitted over low-latency, high-reliability links, which will ultimately pave the way for fully autonomous driving. See Figure 1.

One of the main selling points of V2X communication is safety. V2X communication technology has the potential to reduce the number of vehicle accidents, and thus the number of related injuries and deaths. A study by the National Highway Traffic Safety Administration (NHTSA) found that connected car technology has the potential to reduce crashes that do not cause harm to the driver by up to 80%. In fact, by 2024, auto industry bodies (NHTSA and the Society of Automotive Engineers) expect to require vehicles to provide certain V2X features to receive a full five-star safety rating. The technology will also greatly improve traffic management. Using data provided by roadside units (RSUs) and onboard units (OBUs), V2X technology can establish connections between cars and connect pedestrians, drivers and cyclists to traffic lights. Information about traffic patterns, lights and other vehicles can be transmitted to the car through the vehicle's infotainment system connected to Wi-Fi or cellular networks, or even through an app on the driver's phone, allowing the driver to adjust to a safer and more efficient driving mode. This can improve the environmental performance of the vehicle by reducing harmful carbon dioxide emissions and lowering fuel costs.

V2X consists of several components: see the sidebar “Vehicle communications acronyms and what they mean.” Given the numerous safety benefits and other benefits to consumer communications, enhancing V2X and bringing it to market is often a top priority for many automakers. However, to design a robust system solution, we first need to understand the complexity and technical challenges of V2X.

Cellular-V2X (C-V2X) technology presents challenges to vehicle engineering, such as wireless coexistence issues caused by multiple radios inside and outside the vehicle. New cars of the future will be equipped with a large number of radios to meet the development trend of safety, security and entertainment. These radios will bring coexistence issues. One obvious coexistence challenge is that both dedicated short-range communication (DSRC) and C-V2X (cellular operator licensed carrier) use the same 5.9 GHz frequency band for communication. In addition, the frequency bands of 4G LTE, 5G and Wi-Fi are closely connected with the 5.9 GHz frequency range.

As mentioned previously, connected cars involve many connectivity technologies. Each technology is unique and must not interfere with each other’s signal quality in order to communicate seamlessly. These technologies include:

• V2X for automotive safety (DSRC and C-V2X)

• 4G/5G cloud connectivity for in-vehicle OEM services such as remote diagnostics, over-the-air software updates, and remote operations

• In-car 4G/5G cloud connected entertainment

• Wi-Fi

• Bluetooth®

• Satellite Digital Audio Broadcasting Service (SDARS)

  
  

Let’s look at how filter technology solutions can help address V2X coexistence with Wi-Fi and cellular spectrum. Here are the three main challenges:

• V2X and 5 GHz Wi-Fi coexistence

• Wi-Fi 2.4 GHz coexistence with cellular bands 7, 40, and 41

• Electronic Toll Collection (ETC) and V2X Coexistence

As shown in Figure 2, the Wi-Fi 5 GHz Unlicensed National Information Infrastructure 3 (UNII 3) band overlaps the 5.9 GHz V2X band. To allow these two radios to operate without interfering with each other, a filter is required. The filter needs to have a very steep outer edge of the attenuation band near the 5.855 GHz region to ensure that the V2X and Wi-Fi UNII 3 signals do not cause communication interference. In addition, noise in the UNII 2C receive band can cause desensitization of the received signal. In this case, the multiple radios of the wireless device operate simultaneously, causing mutual interference, and the design challenge is desensitization. These signals may interfere with or even destroy the receiver's sensitivity to weak signals. For example, if the transmit signal is not properly isolated from the receiver, it may interfere with the receive path signal, resulting in desensitization. Therefore, an additional filter is required to reduce the noise in the 5 GHz receive signal.

Another coexistence issue in V2X is interference between cellular bands 7, 40, and 41 and the 2.4 GHz Wi-Fi band. As shown in Figure 3, Wi-Fi 2.4 GHz sits between and close to these TDD (B40 and B41) and FDD (B7) signals. When transmitting and receiving Wi-Fi 2.4 signals in the car, filters must be used to ensure that certain users on the cellular band can continue to communicate without interruption. Again, this is accomplished with BAW filter technology, both in discrete form and in highly integrated Qorvo modules.

In addition to the above coexistence challenges, there is also the issue of V2X interfering with Electronic Toll Collection (ETC) services. The operating frequency bands of ETC in China and Europe are too close to the V2X band. As shown in Figure 4, the European V2X band is only 40 MHz away from the European ETC band . Without a notch filter at the input of the V2X front-end module to allow ETC and V2X to coexist, the European V2X spectrum emission specification cannot be met.

The same problem exists for ETC applications in China. The downlink of the V2X band in China is only 65 MHz away from the ETC band. Notch filters must be used at the front-end input to reduce spectrum emissions for proper coexistence. In the future, the Chinese ETC band may be closer to the V2X band, as Chinese operators are facing capacity limitations that may be caused by bandwidth. Discussions on this topic are currently underway in China.

What is the best filter technology to address these V2X coexistence challenges? Qorvo has helped many companies address these types of applications with BAW filters, as described below.

To avoid interference in these situations, high-performance RF bandpass filters should have high-frequency capabilities. BAW is well suited for such high operating frequencies. BAW filters also provide a steep transition band to prevent signals from interfering with adjacent frequency bands, and the passband should have low insertion loss to maintain output power and coverage.

Filters used in automotive applications must be able to operate reliably in extreme temperature, humidity, and vibration conditions throughout the life of the vehicle, where quartz crystal filters will not cut it. Using BAW filters in these harsh conditions in automotive applications means engineers can now eliminate filter technologies that are larger and more difficult to implement.

Unique BAW filters have the required characteristics to provide all the functions required in the 5.9 GHz band. They provide the necessary steep transition bands with high quality factors (Q) up to 3000 and are much smaller than traditional ceramic or dielectric filters. BAW filters are well suited for advanced automotive RF applications due to their high selectivity and small size. These filters are typically used in applications above 1.5 GHz where high performance is required. In addition, this technology is generally capable of accommodating operating frequencies up to 7 GHz and beyond.

Qorvo offers BAW filter technology in both discrete and module form factors. Qorvo V2X Front-End Solution Kit Includes the first 47-band/Wi-Fi BAW coexistence filter that enables Wi-Fi coexistence with the V2X 5.9 GHz band. This helps establish a reliable connection between the vehicle and its surroundings. It also includes two integrated front-end modules (FEMs) supporting C-V2X and DSRC systems, a digital step attenuator, transmit/receive switches, and low-noise amplifiers. This front-end solution is chipset-independent and enables a stable V2X link with sufficient transmit linear power and excellent receive performance in a Wi-Fi environment where Wi-Fi and V2X coexist.

As we move forward, we will see more content on this topic as we rely on high-tech electronic innovations in road vehicles and advances in radio technology to help drive safely. If you are interested in getting the best understanding of V2X from a technical perspective, you can watch this video: How to resolve spectrum challenges associated with V2XA .

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