# A Cooperative Communication Protocol for QoS Provisioning in IEEE 802.11p/Wave Vehicular Networks
## 4 Proposed Scheme  
### Relay Node Selection  
In this paper, we assume that the received signal amplitude in the vehicular networks follows the Rayleigh PDF. The Rayleigh distribution is frequently used to model multi-path fading with no direct line-of-sight (LOS) path. In vehicular networks, as the separation between source and destination devices increases, the LOS component may be lost, and the PDF of the received signal amplitude follows the Rayleigh distribution [43; 44; 45]. In ITS applications using a WAVE system, all WAVE devices periodically broadcast basic safety message (BSM) messages. BSM messages are messages defined in SAE ]2735 to increase the safety of the vehicle in operation and frequently broadcast from all vehicles [46]. Each vehicle and RSU receives the BSM messages and determines whether it is related to the safety service. Table 2 shows the information in the BSM message. As shown in Table 1, the BSM message includes a time (GPS time), a position of the vehicle (3D position), a position accuracy, a moving speed of the vehicle, a heading of the vehicle, the steering wheel angle of the vehicle, the acceleration of the vehicle, the break status of the vehicle, and the vehicle size. All OBUs can know the location, speed, and direction of nearby vehicles by using the received BSM message. The proposed scheme selects the relay node considering the information of the BSM message and the link status of the device requesting cooperative communication. The existing cooperative communication schemes have selected the relay node considering the data rate on the wireless link [47; 48]. However, in the VANET environment, since the moving speed of the vehicle is fast, the mobility of the vehicle greatly affects the network performance such as the packet delivery success rate. Therefore, in this paper, we calculate the path maintenance expectation time (PMET) \begin{table}
\begin{tabular}{l l c} \hline \hline \multicolumn{1}{c}{**Type**} & \multicolumn{1}{c}{**Description**} & \multicolumn{1}{c}{**Size (byte)**} \\ \hline DSRCmsgID & Data elements used in each message to define the Message type & \(1\) \\ \hline \multirow{2}{*}{MsgCount} & It can check the flow of consecutive messages having the same & \\  & DSRCmsgID received from the same message sender. & \(1\) \\ \hline \multirow{2}{*}{TemporaryID} & Represents a 4-byte temporary device identifier. When used in a mobile & \\  & OBU device, this value is periodically changed to ensure anonymity. & 4 \\ \hline Descond & Represents two bytes of time information. & 2 \\ \hline Latitude & Represents the geographic latitude of an object. & 4 \\ \hline Longitude & Represents the geographic longitude of an object. & 4 \\ \hline Elevation & Represents an altitude measured by the WGS84 coordinate system. & 2 \\ \hline \multirow{2}{*}{PositionAccuracy} & Various quality parameters used to model the positioning accuracy for & 4 \\  & each given axis. & \\ \hline TransmissionAndSpeed & Represents the speed of the vehicle. & 2 \\ \hline Heading & The current direction value is expressed in units of 0.0125 degrees. & 2 \\ \hline SteeringWheelAngle & Represents the current steering angle of the steering wheel. & 1 \\ \hline AccelerationSet4 Way & It consists of three orthogonal directions of acceleration and yaw rate. & 7 \\ \hline \multirow{2}{*}{BrakeSystemStatus} & Represents a data element that records various control states related to & 2 \\  & braking of the vehicle. & \\ \hline VehicleSize & Represents the length and width of the vehicle. & 3 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Basic safety message (BSM) information. that uses the speed and location information of the vehicle and propose the relay node selection scheme using the calculated PMET. The OBU that does not receive the WSA can receive the BSM message from the neighboring OBUs in the CCH interval. After receiving the BSM, it calculates the PMET between the neighboring OBU and itself, the equation for the PMET is as follows.