V2V – LTE Technology for Vehicular Safety

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Safety is undoubtedly the most important concern for the auto industry the world over. That is one of the reasons there is such a focus on investing in autonomous vehicles. Autonomous vehicles eliminate human errors and limitations—slow reaction speed, blind spots, inattention—which are the primary reason for most accidents.

LTE (4G), which is the most widely-used technology for cellular communication around the world, has introduced some key improvements to the standard with the Release 14 specifications. These improvements will enable automotive manufacturers develop reliable communications between vehicles (V2V), and between vehicles and infrastructure (V2I), such as Road Side Units (RSU), mobile devices and pedestrians. Vehicle communications with other vehicles, infrastructure, mobile devices and pedestrians is typically referred to as vehicle to everything (V2X).

There are technologies in use today that are used to address vehicular safety today, but they are mainly line-of-sight (LoS) communications, which has its limitations. For example, LoS systems have trouble at blind intersections, avoiding disabled vehicles and obstacles in blind curves, and at night due to the limitations of today’s sensors and cameras.

LTE for V2V addresses some of these limitations. In the case of blind intersections and blind curves, LTE enables vehicles to communicate their geospatial coordinates to each other directly when in low-or no-connectivity range up to 100 meters. Also, the vehicles can communicate indirectly through an RSU or cellular tower when connected at a range of up to 500 meters. Both direct and indirect options help avoid collisions as the drivers are aware of each other by using broadcast short messages, which flash a warning on the vehicle’s dashboard, giving the driver time to react.

In its earlier Release 12, 3GPP described a method for proximity-based services—the direct communication between two LTE devices—also called device-to-device (D2D) communications. The concept behind this direct connection between any number of devices, without the need for cellular-network infrastructure in between, is a boon for V2X communication.

In the Release 14 extension to D2D, 3GPP came up with specific V2X communications methods, which enable communication either when the device and vehicle are connected to the cellular network (RRC_CONNECTED) or even when they are out of coverage and not connected at all (RRC_IDLE).

These communication types help in various V2X use cases. Apart from the non-LoS use cases, there are other important use cases that are highlighted in Figure 1.

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Figure 1: Examples of V2X safety applications
Source: Aricent

Figure 2 below captures the three types of V2X services.

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Figure 2
The left panel depicts V2V, which uses the LTE D2D interface named ‘sidelink’ (SL) also called as ‘PC5’ to establish direct V2V communications between many vehicles. The center panel depicts V2I, using Uu interface, which is used when Network speaks to a vehicle in coverage to reach other vehicles that are out of range of each. The right panel depicts V2X, which supports both PC5/SL and Uu, enabling communications using the LTE network’s cellular towers between vehicles within range of each other.

In the in-coverage scenario in Figure 2, the cellular network controls the radio/frequency resources used for V2V communication. It may assign specific resources to a transmitting VUE (V2V User Equipment) present in the vehicle, or may assign a pool of resources, which the VUE can select from. For the out-of-coverage case, such a control is not possible. The VUE uses resources that are preconfigured, either in the VUE or in the USIM (Universal Subscriber Identity Module) installed in the device. However, the term out-of-coverage must be interpreted carefully. It does not mean that there is no coverage at all. Rather, it means there is no coverage on the carrier frequency or band used for V2V direct communication, although the VUE might be in coverage on a different carrier frequency or band for cellular traffic.

Some of the advantages and disadvantages of the LTE-based V2V communication are mentioned below:

Advantages

  • Reliable communication due to 'dedicated frequency resources' and 'no time domain normal cellular transmission/interference.' Both solutions can be achieved only through a network-controlled architecture, which is reliable in LTE.
  • Longer range non-LoS communication both ways: direct V2V and indirect V2I communications.
  • Precise positioning of vehicles (in the 10’s of centimeters) based on geospacial co-ordinates and highly accurate identification and communication between them. This is enabled either by using 3GPP-based OTDOA or non-3GPP-based DGPS mechanisms.
  • Less Latency due to LTE’s 1ms frame structure and less RTT.
  • Test simulations prove that high reliability and precise positioning with less latency can be achieved for vehicles that are mobile at the relative speed of 280 Km/hr.
  • Strong evolution path towards 5G and vehicular IOT.
  • Enabler for autonomous vehicles, aka driverless cars.
  • Existing LTE network infrastructure can be re-used with few hardware and software upgrades.

Disadvantages

  • Potential for single-vehicle crashes, such as lose of control or leaving the road, cannot be controlled by V2V as there is no other vehicle or infrastructure to communicate with.
  • Areas with dense vehicle populations might be a concern in terms of providing broadcast resources for all of them, which could result in interference or cancellation of signals.
  • 3GPP’s initial V2V standard was based on Rel-14, which was officially released at the end of November 2016. An enhanced version is expected to be released in March 2017. Non-cellular technologies are way ahead in vehicular technology and existing customer base.

The Aricent Advantage

Aricent has developed its own 4G/LTE IPR stack and is well positioned to enhance its product portfolio for customers who already possess the software. In addition, Aricent can support any customer looking to integrate V2V into its platform by providing deep Rel-14 knowledge and technical expertise, as well as design support, and engineering and testing services. Aricent’s standard compliant—IEEE 802.11p Wave & ETSI—offering on the V2X software stack can be used as a standalone product or can be integrated with V2V LTE for more unique offerings.

References:

  • 3GPP TR 22.885 V14.0.0; Study on LTE support for Vehicle to Everything (V2X) services
  • 3GPP TR 36.785 V14.0.0; Vehicle to Vehicle (V2V) services based on LTE sidelink
  • 3GPP TR 36.885 V14.0.0; Study on LTE-based V2X Services

 

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