# A Cooperative Communication Protocol for QoS Provisioning in IEEE 802.11p/Wave Vehicular Networks
## 4 Proposed Scheme
### Resource Allocation Scheme for Cooperative Communication  
Figure 5 shows the format of a proposed WAVE service advertisement (WSA) message. The RSU announces the type of service applications to OBUs using the Service Info field. Using the Channel Info field, the RSU also announces the number of the channel in which it provides the service. The WAVE Routing Advertisement element provides information about infrastructure internetwork connectivity, allowing receiving devices to be configured to participate on the advertised IPv6 network. The Coop Info Element includes a WAVE Element ID, Length, Index, Path Info, and Resource Info fields. The value of the WAVE Element ID is selected one of the reserved values so that the proposed Coop Info Element can be distinguished. The Length field indicates the length in octets of Index, Path Info, Resource Info fields. The index field contains the number of relay paths included in the Coop Info Element. Figure 6 shows the format of the proposed Path Info field. The Dest Addr field indicates the MAC address of the device requesting the cooperative communication and the Relay Addr field contains the MAC address of the OBU selected as the relay node. The Src Addr field is set to the MAC address of the RSU. The PMETSR field indicates the PMET between the RSU and the relay node, and the PMETRD field indicates the PMET between the relay node and the destination node. Figure 7 shows the format of the proposed Resource Info field. Figure 5: The format of the proposed WSA message. Figure 6: The format of the proposed Path Info field. The Channel Number field indicates the SCH channel selected by the RSU for relay communication. The Start of Time field indicates the beginning of the resource allocated for the relay, which specifies the universal coordinated time (UTC) second of GPS. The Beacon Length field is the interval to relay the WSA message to the destination node. The Upper Link Length field is the interval that the RSU has allocated to communicate with the relay node. The remaining allocated resources are the intervals allocated for the relay node and the destination node to communicate. The End of Time field indicates the end of the resource allocated for relay communication and specifies the UTC second. Figure 8 shows the timing diagram of the path construction and the resource allocation for the cooperative communication. The RSU that receives the Coop Relay message from the relay candidate nodes calculates the RDP using the information in the received message and selects the OBU with the lowest RDP as the relay node. The RSU allocates resources for the cooperative communication in the SCH Interval and broadcasts the WSA including the information on the relay path and the allocated resources. The relay node receiving the WSA message generates a Coop Response message using the information included in the WSA. Figure 9 shows the format of the proposed Coop Response message. Figure 8: The timing diagram of the path construction and the resource allocation for the cooperative communication. Figure 7: The format of the proposed Resource Info field. The relay node sets the Type field Response and sets the Path Info and Resource Info fields to the values of the Path Info and Resource Info fields contained in the received WSA. The relay node transmits the Coop Response message to the destination device. The OBU receiving the Coop Response message checks the relay node selected from the Path Info field and ascertains the SCH channel and the allocated resource to perform cooperative communication from the Resource Info field. The relay node forwards the received WSA message to the destination node. Devices on the relay path exchange data frames in the allocated Relay interval. Figure 10 shows an example of the proposed cooperative communication scheme. In Figure 10, the Dest Dev computes the PMET after receiving the BSM message from the neighboring OBU. It transmits a Coop Request message including the calculated PMET and the data rate supported by the link to the neighboring OBU.