GB/T 31024.2-2014Cooperation of roadside to vehicle—Dedicated short range communications—Part 2: Specification of medium access control layer and physical layer (English PDF)

2.1 MAC protocol data unit; MPDU

A data unit that is exchanged between two equivalent MAC entities by using PHY layer service.

2.2 MAC management protocol data unit

A data unit that is exchanged between two equivalent MAC entities to implement the MAC management protocol.

2.3 MAC service data unit

The information that is delivered as a unit between MAC service access points (SAP).

5.1 Overview

MAC layer is used to manage and control the allocation and sharing of physical layer transmission resources between multiple users. See Figure 2 for the function composition.

5.2 Adaptation sublayer

MAC layer is divided into adaptation sublayer and MAC sublayer. The adaptation sublayer uses the services provided by MAC sublayer. The functions of the adaptation sublayer are as follows. […]

5.3 Medium access control sublayer

The basic functions of the MAC sublayer are divided into the management control plane and the data plane.

6.1 Common medium access control frame format

6.1.1 Overview of common medium access control frame format

See Figure 4 for the frame format of MAC protocol data unit (MPDU). Every MPDU can be divided into three parts.

6.1.2 Frame control field

6.1.2.1 Description of frame control field

The frame control field contains the following fields. protocol version, frame type, subtype, flow identification (FID), retransmission indication, and reservation.

6.1.2.2 Protocol version field

The protocol version field length is 2 bits. And the length and position remain the same in all revisions of this Part. The protocol version value in this Part is 0, all other values are reserved.

6.1.4 Sequence number field

The length of sequence number field is 12 bits. The value ranges from 0~4095.

It is used to indicate the sequence number of MSDU / MMPDU. All MSDUs / MMPDUs sent in an FID flow are assigned a sequence number.

6.1.5 Reservation

The reservation field is 3 bits. The default setting is 0.

6.2 Data frame

6.2.1 Overview of data frame

See Figure 6 for the frame format of data frame.

6.2.2 Reserved field

The length of this filed is 1 bit. The default setting is 0.

7.1 Adaptable sublayer

The function of the adaptable sublayer is to classify the IP layer data and use an FID to identify a service flow.

7.2 Medium access control sublayer

7.2.1 Address searching and connection

OBU and RSU both have a 48-bit globally-unique MAC address as identification.

This address is used for mutual acknowledgement and network packet forwarding during the network access phase.

7.2.2 Medium access control address

Both OBU and RSU use a globally-unique 48-bit MAC address as the identifier.

7.2.3 Broadcast on board unit identification

The BOBUID length is 12 bits. Value range is. 0x000 and 0x001.It is used to broadcast to all OBUs within the scope of this RSU.

7.3 Network access process of on board unit

7.3.1 Overview

The network access process refers to the process by which OBU discovers the network and establishes a connection with RSU. The network access includes the following steps.

7.9 Frame acknowledgement

This clause uses ACK frame or GroupACK frame for frame acknowledgement.

For management control frames, the unicast management control frames without corresponding response frames need to use ACK or GroupACK to conduct acknowledgement. Otherwise, it shall directly use the corresponding response frame for acknowledgement. See Table 25 for the corresponding response frames.

8.1 Description of medium access control layer of communication

mode without center node The communication mode without center node directly transmits message between vehicles.

8.2 Medium access

control layer frame structure of communication mode without center node

8.2.1 Overview

See Figure 54 for the frame format of MAC layer of the communication mode without center node. The MAC frame can be divided into three parts. The first part is the fixed-length MAC header. The second part is the data carried in the MAC frame.

8.2.3 Hop indication field

The hop count indication field contains 8 bits, as shown in Figure 56. The first four bits indicate the number of hops in the current frame. From 0000 to 1111, it indicates the 0th to the 15th hops. The last four bits indicate the maximum hop limit. From 0000 to 1111, it indicates that the maximum hop limit is the 0th to the 15th hops.

8.2.5 Serial number field

The serial number field is 8 bits long. The value range is 0~255, used to indicate the sequence number of MSDU / MMPDU.

8.2.6 Length indication field

The length indication field has 12 bits in total, used to indicate the length of the following data field.

8.2.7 Reserved field

The reserved filed is 8 bits. The default setting is 0.

8.2.8 Data field

The data field length is variable. The minimum data length is 0 byte. The maximum data length is 4095 bytes.

9.1.1 Frame structure

See Figure 57 for the frame structure of the physical layer.

9.1.3 Symbols of physical layer

See Table 30 for the definitions of relevant symbols of physical layer in this Part.

9.2 Transmitter block diagram and signal processing flow

9.2.1 Transmitter block diagram

See Figure 59 for RSU side transmitter block diagram.

9.2.3 Channel coding

9.2.3.1 Overview

The channel coding module performs FEC protection on the scrambled data bit sequence. This Part supports two types of forward error correction codes. convolutional coding and LDPC coding. […]