Communication Technologies

Critical Requirements

Range (>200-400m).
Delays (<10msec).
Time for communication when in range (<10-20msec).
Bandwidth (>10Mbsec.... → as much as possible).

ITS-G5 (DSRC, IEEE 802.11p)

Developed for vehicle-to-vehicle communication (it also supports vehicle-to-infrastructure communication)
Based on IEEE 802.11a with PHY and MAC extensions (based on CSMA/CA: Carrier Sense Multiple Access/Collision Avoidance).
Adapted for latency-critical V2X communications in the 5.9 GHz band.
Frequency: 5.9GHz.
Range: LoS can go up to 1 km.
- Prone to obstructions: buildings, trees, cars.
Delay: < 10msec.
Time for communication when in range (10- 20msec).
Rate up to 27Mb/sec in the largest mode (usual is 12Mb/sec).

Challenges

Vehicle safety communication applications rely heavily on a periodic broadcast of basic safety messages (BSM) which contain the positions, velocities, and other information about the vehicles.

These messages with the PHY layer overheads typically measure around 300 bytes with the full security certificate header and are expected to be transmitted up to once every 100 ms. The periodicity is chosen to meet the latency and accuracy requirements of vehicle safety applications.

Channel congestion in dense vehicular environments (packet collisions).

Lack of handshake/ACK in delivering broadcast frames.

No QoS support.

The next generation of the specification, namely 802.11bd, has just been released.

C-V2X (LTE-based 3GPP Rel 14)

Based on 3GPP Rel 14.
Frequency: 5.9GHz.
Range: LoS can go up to 1 km.
- Prone to obstructions: buildings, trees, cars.
Delay: < 20msec.
Time for communication when in range (~100msec?).
Rate up to 150Mb/sec in the largest mode.
Cellular-V2X defines a new air interface called PC5 for V2V, and V2I communication.
V2N is still over the legacy LTE Uu air interface and provides over-the-top cloud services.

C-V2X defines two Complementary Transmission Modes:

Direct safety communication independent of the cellular network.
1. Low latency Vehicle-to-Vehicle (V2V), Vehicle-to-Infrastructure (V2I), and Vehicle-to-Person (V2P) operating in ITS bands (e.g., 5.9 GHz).
Network communications for complementary services.
1. Vehicle-to-Network (V2N) operates in the mobile operator's licensed spectrum.

Direct communications (V2V) via PC5 interface.

Building upon LTE Direct device-to-device design with enhancements for high speeds / high Doppler, high density, improved synchronization, and low latency.
- Proximal direct communications (100s of meters).
- Operates both in and out of coverage.
- Latency-sensitive use cases, e.g., V2V safety.

Network communications (V2N) via Uu interface.

Using LTE to broadcast messages from a V2X server to vehicles and beyond. Vehicles can send messages to the server via unicast.
- Wide area networks communications.
- Leverages existing LTE networks.
- More latency-tolerant use cases, e.g., V2N situational awareness.