【Introduction】It is clear that vehicle communication is an important enabler to achieve higher levels of autonomous driving. However, automakers have long been studying whether the radio access technology required for analysis should be based on cellular technology (also known as C-V2X) or direct access technology (known as DSRC). In this article, we will show that future autonomous driving scenarios require the coordinated or combined use of both technologies. Advanced multi-wireless standard equipment requires the integration of individual modules that employ different technologies. Therefore, in the absence of a standard interface for wireless interconnection, it is very difficult to realize such a cooperative system. We use a recently released single-chip solution to implement a dual-band, dual wireless standard in-vehicle communication system. With a single chip, signals can be transmitted and received simultaneously in multiple frequency bands. Although this device is not certified for automotive applications, the technology used can support automakers by providing product differentiation and enhanced control to improve service quality.
This article will focus on the development of vehicular communication (V2X) devices. The V2X application scenarios will be outlined and two radio access technologies that can be used to perform V2X communication will be introduced. Through a brief introduction to V2X, we will understand that wireless access to V2X communications controlled by cellular networks (also known as cellular V2X or C-V2X) can complement other wireless access alternative technologies in unlicensed frequency bands and dedicated spectrum. , such as Dedicated Short-Range Communications (DSRC) or IEEE 802.11p. To do this, the requirements of the use case need to be combined with the need to take advantage of multiple access technologies. When it comes to implementing multi-standard V2X devices, multiple modules and their own separate software/firmware are currently available. However, this limits the potential of the collaboration/coordination function of the access technology. These limitations can be found in the “Introducing a Single RF IC (ADRV9026) for Future V2X Systems” section. The ADRV9026 is a radio frequency transceiver (TRx) in the ADI RadioVerse® portfolio covering the sub-6 GHz frequency range. This multi-channel, multi-band transceiver technology enables multi-band V2X communication devices.
Vehicle-to-Everything (V2X) Communication
The automotive industry is rapidly innovating to achieve full automation in all possible driving scenarios, operating conditions and situations. Wireless connectivity has proven to be one of the foundational technologies for enabling not only full automation but also low-level automation. In particular, safety-critical applications for autonomous vehicles will rely heavily on wireless connectivity. Performing safe operations with extremely high (99.999%) reliability will be critical in situations where other entities share driving spaces or traffic systems. These entities may include other vehicles, people, transportation systems on the road, or traffic management networks. Therefore, in order to exchange information, cooperate and coordinate with other entities in the system, each vehicle must be equipped with wireless connectivity.
Figure 1. Entity, infrastructure and V2X communication system interfaces
To this end, European governing bodies such as ETSI have already laid the groundwork for automotive intelligent transport systems (ITS). Similar systems have been developed around the world, including the US and Asia Pacific. ITS defines and specifies communication nodes, architectures, protocols and messages for various applications and use cases. Additionally, new infrastructure is required to enhance DSRC-based applications in unlicensed or dedicated frequency bands. With the implementation of smart highway and smart city initiatives, many regions are actively deploying related infrastructure. For C-V2X, existing cellular infrastructure can be used. Figure 1 shows the interface through which an ITS vehicle communicates with other vehicles or other entities in the transportation system. The various interfaces are described below:
● V2V (Vehicle-to-Vehicle) communication: Originally it was only used for broadcast messages, but now vehicles can also perform unicast or multicast messages. Such an interface can be used to transmit any information directly from one vehicle to another within communication range, for example, during emergency braking.
● V2P (Vehicle-to-Person) communication: Using this interface, vehicles and road users can communicate via smartphones equipped with V2X applications. For example, vulnerable road users can be alerted to approaching vehicles.
● V2N/V2I (Vehicle-to-Network or Vehicle-to-Infrastructure) communication: This interface can be used to transmit any information that contributes to intelligent transportation.
Wireless Access Technology for V2X
Figure 2 shows the layered architecture of the entire ITS. The top application layer contains use case definitions such as emergency braking warning, collision avoidance at intersection and traffic light cycle 1. Other layers provide information and communication support services such as location/location information, reminder messages and notifications. Finally, these protocol messages are transmitted in space by using wireless technology.
Figure 2. ITS in the form of communication layers
The United States has established DSRC to support vehicle communications, and Europe has established IEEE 802.11p-based wireless access for the same purpose. However, these wireless technologies were developed based on the IEEE 802.11x Wi-Fi standard for proprietary communications2. It is therefore limited in range and faces similar congestion and quality of service (QoS) issues as other Wi-Fi-based systems. In addition, significant capital investment is required to deploy roadside infrastructure to ensure the coverage of traffic management servers. On the other hand, enabling wireless access through public land mobile radios (also known as cellular communication systems) can address coverage and QoS issues. The cellular network already covers most roads, and we also offer planned access controlled by the network, ensuring quality of service by avoiding congestion or dropped calls.
V2X services are already available in the 4th Generation Long Term Evolution (4G LTE) cellular system standard3. However, the primary goal of 4G LTE is the basic security use case. The 5th generation (5G) targets more safety-critical and high-reliability use cases. Cellular V2X (C-V2X) refers to V2X services delivered over a mobile network, be it 4G LTE or 5G. The overall picture of in-vehicle communication systems allows us to use multiple technologies and standards not only in different regions, but also in different frequency bands. The overall picture is more complicated when we consider the different frequency bands that apply to different regions and different standards.
Cellular V2X (C-V2X)
Providing 100% cellular coverage is a very difficult challenge for mobile network operators. On the other hand, for connected and autonomous vehicles, radio coverage holes are worse than street holes. Therefore, C-V2X provides enhanced features to make it work without network coverage. Figure 3a shows a scenario where vehicles communicate with network coverage. For vehicles to communicate, two options are available:
Option 1: Using the classic Uu interface (the 3GPP-defined name for the radio link between the end user equipment and the radio base station), a cellular network is used between the two V2X communication nodes.
Option 2: Use a new interface called PC5 that provides direct communication between V2X nodes. This is also known as sidechain (SL) communication.
Figure 3b shows a scenario without network coverage. However, communication between V2X nodes is still possible when using the PC5 interface. In scenarios with network coverage, the network may use the allocated cellular frequency band. The next section describes what frequency bands are used when there is no network coverage.
Figure 3. The use of cellular frequency resources for V2X communication with or without cellular coverage
Table 1. Uu-PC5 bands used for concurrent V2X operation in 4G LTE and 5G NR
V2X spectrum allocation
Europe has allocated a dedicated spectrum with a bandwidth of 70 MHz in the 5.9 GHz band for vehicle communications4. A global distribution of deployments is currently underway. In addition, coordination work is underway to enable the use of ITS-G5 and C-V2X in this frequency band. In a C-V2X environment, the service may already use multiple cellular bands by using a combination of PC5 and Uu interfaces. The cellular standard is working on V2X dual-band concurrent operation. In accordance with 3GPP specifications 5, 6, we have created Table 1 to summarize examples of frequency band combinations used for concurrent operation of V2X services using 4G LTE and 5G New Radio (5G NR) interface cellular radio access technologies, respectively. The highlighted row is only for 5G NR.
Dual Band and Dual RAT V2X Systems
With multiple radio access technologies (RATs) available and capable of communicating in multiple frequency bands, automotive OEMs must decide which to use. In the US, the FCC tends (at the time of writing) to use DSRC-based wireless access7,8, and the Asia Pacific region tends to develop and deploy C-V2X9. Europe remains neutral on radio access technologies10. In this regard, several research results have been published to illustrate the advantages of ITS-G5/DSRC over C-V2X. Similar studies also believe that C-V2X has advantages over ITS-G5. As a result, partners in the automotive and telecom industries are working to develop a solution that enables V2X services to take advantage of the advantages that radio access technologies offer in both licensed and unlicensed spectrum11.
Figure 4 is a modified version of Figure 2, we add a new sublayer between the radio access layer and the packet access layer to show the access layer in detail. We call this Wireless Access Management (WAM). This sublayer is used to ensure optimized V2X services are provided from the network to the radio layer. It can select different radio access technologies by coordinating diversity or cooperating for higher throughput based on use case (latency requirements, QoS, etc.), traffic (congestion) and link (radio quality) conditions. For example, if congestion is detected in the ITS-G5 wireless interface, the same message is sent over the PC5 using C-V2X. This will provide diversity differentiation gain and ensure reliability. In the use case of vehicles exchanging high-density map data, the Uu interface can be used in combination with PC5 or ITS-G5 for high throughput requirements.
IEEE papers 12, 13 use analytical and simulation methods to detail and explore the advantages of similar concepts (shown in Figure 4). As previously described using Table 1, within the framework of C-V2X, cellular systems standardization bodies are already exploring concurrent operation in the 4G LTE Uu and 5G NR Uu bands via PC5 and ITS-G5 technologies in the 5.9 GHz band. Therefore, based on the band concurrent operation and concepts introduced earlier, we can say that the standardization bodies and related industrial research communities have laid the groundwork for dual-band, and even dual-RAT, V2X systems. Now, the automotive industry should look for the best hardware setup to take advantage of the dual-band and dual-RAT V2X concept.
Figure 4. Enables collaboration and coordination among multiple radio technologies at the ITS access layer
Introduces a single RF IC (ADRV9026) for future V2X systems
Today’s wireless devices are equipped with multiple wireless technology standards, each requiring the use of its own unique modules or hardware. In most cases, these modules provide solutions from the RF layer to the application layer. Implementing such dual-band V2X systems and providing mechanisms for collaboration and cooperation in this architecture is not easy because the manufacturers or suppliers of such modules do not provide free access to the middle layer, and implement across multiple standards Collaboration or collaboration requires this permission. Achieving these configurations through the available wireless modules requires the use of external standardized interfaces.
Therefore, we need to support designs that implement such systems. Radio transmitter and receiver designs using Software Defined Radio (SDR) give us complete freedom to access and process digital data at any stage. The ADI RadioVerse product family includes many wideband radio transceivers that convert RF to bits and bits to bits. The conversion of this signal to and from the RF band and baseband is based on a zero intermediate frequency (ZIF) architecture. Fundamentally, it requires less power than conversion based on direct RF sampling because all circuits operate over a narrower bandwidth. In addition, because ZIF relaxes the filtering requirements on the transmitter and receiver, it makes the RF front-end simpler and less expensive.
The ADRV9026 is an extension to the dual-band SDR products in the RadioVerse product family. This is a single chip fully integrated RF IC. It has 4 transmit and 4 receive channels that can be independently programmed and controlled to transmit and receive any carrier frequency between 75 MHz and 6 GHz. The receive bandwidth can be up to 200 MHz, while the transmitter combined bandwidth can be up to 450 MHz. In addition, an on-chip observation path (up to 450 MHz bandwidth per channel) is provided to support linearization correction of power amplifiers in high power transmission scenarios. Figure 5 shows a functional block diagram of the entire transceiver.
Figure 5. Functional block diagram of the 4-channel transmitter and 4-channel receiver ADRV9026 RF IC from ADI. 14
Figure 6. ADRV9026 can transmit and receive in multiple frequency bands simultaneously
Using an advanced local oscillator architecture, the ADRV9026 can transmit and receive in multiple sub-6 GHz frequency bands simultaneously. Figure 6 shows an example of simultaneous transmission and reception in different frequency bands or with different radio access technologies using a single RF IC, the ADRV9026. In this example, we only select three sets of band combinations. It is important to highlight that the ADRV9026 can operate in any frequency band between 75 MHz and 6 GHz. Because there are 4 independent RF channels in the ADRV9026, we can even implement 2 × 2 MIMO functionality with each independent frequency band or technology. When using the ADRV9026, we gain several advantages.
● Any frequency band in C-V2X can be flexibly selected without additional certification cost.
● Combining multiple RATs requires higher synchronization performance. This synchronization is easier to achieve with the ADRV9026 because both bands are controlled by a single RF IC. In the “Dual-Band and Dual-RAT V2X Systems” section, we discussed the concept of a dual-band V2X system and how a single RF IC can be used to achieve this. In the future, we will provide more details on the architecture and design of such dual-band V2X devices.
● By using the ADRV9026, RF-to-bit conversion can be performed very close to the antenna. This avoids RF signal losses in coaxial cables, which are quite high in the 5.9 GHz V2X band.
● As for RF performance, ADRV9026 can meet the wireless base station requirements. Existing wireless modules are based on ASICs developed for end-user equipment. Therefore, the ADRV9026 provides higher RF performance and therefore lower latency, higher reliability and higher QoS. All of these metrics provide higher data rates and wireless throughput, resulting in a better driving experience, as well as increased safety.
● High data rates and low latency enable drivers or autonomous driving systems to react faster, providing greater support for safety-related use cases. For example, in high-traffic scenarios where license-exempt/dedicated radio resources are about to reach congestion limits, cooperative/coordinated systems (as described in “Dual-band and dual-RAT V2X systems”) can be compared to standalone or single-access systems Provides higher reliability and better safety standards.
Therefore, a collaborative/coordinated configuration with cognitive intelligence and support for a single RF IC is required to meet the requirements of V2X use cases. Analog Devices offers technology to achieve this in a single device such as the ADRV9026.
In this article, we present the current state of the art in V2X communication, a key enabler of autonomous vehicles. In this area, two wireless technologies can be used together to meet the key requirements of V2X services. The two technologies, C-V2X and DSRC/ITS-G5, operate in licensed and license-exempt frequency bands. There are different options for implementing a coordinated/collaborative V2X system. Analog Devices provides technology that supports dual-band and dual-band wireless standards with higher RF performance, lower latency, higher data rates and higher reliability. We have discussed how this RF IC can be used to design a V2X communication device that provides wireless access to two V2X technologies simultaneously on two different radio frequency bands.
1 ETSI TS 102 894-1 V1.1.1 (2013-08): Intelligent Transportation Systems (ITS); User and Application Requirements; Part 1: Device Layer Structure, Functional Requirements and Specifications. ETSI, August 2013.
2 Khadige Abboud, Hassan Aboubakr Omar, Weihua Zhuang. “DSRC and Cellular Network Technology Interworking for V2X Communications: A Survey.” IEEE Transactions on Vehicular Technology, Volume 65, Issue 12, December 2016.
3 3GPP TS 36.300 V15.7.0 (2019-09): 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overview; Phase 2 (Release 15).
4 ETSI EN 302 571 V2.1.1 (2017-02) Intelligent Transportation System (ITS);
Radiocommunication equipment operating in the frequency band 5 855 MHz to 5 925 MHz; tuning criteria covering the essential requirements of Article 3.2 of Directive 2014/53/EU. ETSI, February 2017.
5 3GPP TR 36.786 V14.0.0 (2017-03) LTE-based Vehicle-to-Everything (V2X) Services; User Equipment (UE) Radio Transmission and Reception.
6 3GPP TR 38.886 V0.5.0 (2020-02) NR-based V2X services; User Equipment (UE) radio transmission and reception.
7 Fact Sheet – Use of the 5.850-5.925 GHz Band: Regulatory Proposal Notice – ET Dossier No. 19-138. Federal Communications Commission. November 2019.
8 Dedicated Short-Range Communications (DSRC) Services: Regulations (47 CFR, Parts 90 and 95). Federal Communications Commission. April 2019.
9 ITS spectrum usage in Asia Pacific. 5G Automotive Association.
10 Position paper: Europe’s leadership in connected and autonomous driving depends on technology-neutral, innovation-oriented policies. 5G Automotive Association. November 2018.
11 5G solutions for future connected mobility. 5G NetMobil.
12 Richard Jacob, Norman Franchi, Gerhard Fettweis. “Hybrid V2X Communications: Multi-RAT Enabling Connected Autonomous Driving.” 2018 IEEE 29th International Annual Conference on Personal, Indoor and Mobile Radio Communications (PIMRC), September 2018.
13 Richard Jacob, Waqar Anwar, Gerhard Fettweis, Joshwa Pohlmann. “Using Multi-RAT Diversity in Vehicle Private Networks to Improve the Reliability of Collaborative Autonomous Driving Applications.” 2019 IEEE 90th Automotive Technology Conference (VTC2019-Fall), September 2019.
14 ADRV9026 Data Sheet. Analog Devices, January 2021
About the Author
Danish Aziz is a field applications engineer and subject matter expert for RF products and systems at Analog Devices. As part of the technical sales team, he is actively involved in driving growth in the EMEA region and providing technical support to customers. The main focus is on wireless connectivity applications in the automotive, industrial, defense and cellular sectors. He is the representative of Analog Devices in the 5G Automotive Association (5GAA). Before joining Analog Devices in 2017, he worked as an R&D engineer at Bell Labs in Germany; contributed to the standardization of 3G, 4G and 5G systems; represented Bell Labs in several flagship research projects funded in Europe and Germany . He has authored or co-authored more than 25 technical papers on wireless communications, which have been published on the IEEE platform, which is viewable by international peers; holds more than 20 active and published international patents. Danish holds a PhD and MS in Electrical Engineering from the University of Stuttgart and a BS in Electrical Engineering from NED University in Karachi, Pakistan. Contact: email@example.com.
Chris Böhm holds a degree in Telecommunications from the Higher Institute of Professional Studies in Regensburg, Germany, and a master’s degree from the University of Limerick, Ireland. He joined ADI in 1995 and has worked as a digital design engineer for various ASIC products, including video decoders, optical transport reference designs for data transmission, and (most recently) RF systems for the upcoming 5G standard. He is currently responsible for digital signal processing and algorithm development for radio transmissions below 6 GHz. Contact: firstname.lastname@example.org.
Fionn Hurley is Marketing Manager for the Automotive Cockpit Electronics business unit at Analog Devices in Limerick, Ireland. He joined Analog Devices in 2007. Previously worked as an RF design engineer. He is a graduate of the University of Cork (UCC) in Ireland with a BA in Electrical and Electronic Engineering. Contact: email@example.com.
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