Monday, December 11, 2017

ASN.1 in C-V2X Communications

Cellular Vehicle to Everything (C-V2X) communications, designed to improve road safety, achieve more efficient traffic flow, reduce environmental impacts, and provide new useful services to travelers, uses several ASN.1 based control plane signalling protocols - RRC, M2, and M3.
3GPP defines four types of C-V2X communications - vehicle to vehicle (V2V), vehicle to pedestrians (V2P), vehicle to roadside infrastructure (V2I), and vehicle to network (V2N).
V2V and V2P communications are based on broadcast capabilities between vehicles or between vehicles and pedestrians, and are designed  to avoid accidents by providing information about the location, velocity, and direction of vehicles.
V2I communication occurs between vehicles and roadside units (RSU) which may act as repeaters to extend the range of V2X messages. V2I also includes communication between vehicles and traffic control devices such as signs, markers, barricades, and signal devices which are used to inform, guide, and control traffic.
V2N communication, over 4G/5G networks, occurs between vehicles and servers (e.g. traffic operation servers) in order to provide a complete view of road events.
There are two modes of operation for C-V2X - direct communication, and network communication.  ASN.1 protocols are used in both of these modes of operation.
Direct communication mode uses the LTE PC5 interface based on  3GPP Proximity Services (ProSe). This mode is used for V2V, V2P, and V2I communications. ProSe supports three coverage scenarios, in-coverage, out-of-coverage, and partial coverage. In the in-coverage scenario, the network controls the resources used in ProSe communications. In the out-of-coverage mode, vehicles use pre-configured resources for sidelink communication with nearby vehicles. However, in the scenario of partial coverage, the vehicle out-of-coverage uses the preconfigured values, while the vehicle in-coverage gets its resources from the network.

The OSS ASN.1 Tools, development toolkits for ASN.1 based applications, can be used to develop C-V2X solutions.  A sample program included with the OSS ASN.1 Tools demonstrates how to implement C-V2X signaling using the partial coverage scenario. The sample demonstrates how an in-coverage vehicle, acting as synchronization reference for the transmitting (out-of-coverage) vehicle, receives SystemInformationBlockType21 (part of BCH-DL-SCH-Message) from the eNB, configures its sidelink, and transmits MasterInformationBlock-SL (part of SBCCH-SL-BCH-Message) message to the transmitting vehicle, which in turn modifies the received MasterInformationBlock-SL message and re-transmits it for C-V2X sidelink communication and discovery for other out-of-coverage vehicles. Using Sidelink discovery vehicles repeatedly broadcast short and fixed-size MasterInformationBlock-SL (SBCCH-SL-BCH-Message) messages that can be detected by nearby vehicles, so they can synchronize with each other to establish wireless connectivity.  The control plane messages in this exchange are based on ASN.1 RRC.
The other mode, mainly used for V2N communication, utilizes the LTE Uu air interface between UEs (vehicles) and eNBs. As an example of V2N mode, a vehicle sends a message via an eNB to an application server which, using Evolved Multimedia Broadcast Multicast Services (eMBMS) - a point-to-multipoint LTE interface for efficient delivery of broadcast and multicast service - in turn broadcasts the message to all nearby vehicles.. The control plane messages in this exchange are based on ASN.1 RRC, M2, and M3 protocols.

The OSS ASN.1 Tools are packaged with sample programs for 3GPP protocols such as RRC, M2, M3, and various other protocols.  These samples can be found under the “samples/standards” directory. To learn more about the ASN.1 Tools, please visit or contact us at

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