# A Cooperative Communication Protocol for QoS Provisioning in IEEE 802.11p/Wave Vehicular Networks
## 2 WAVE Protocols and Model  
The WAVE PHY layer is defined in the IEEE 802.11p standard [1]. IEEE 802.11p is a modified version of the IEEE 802.11a/g standard which is a conventional wireless LAN standard. Unlike the existing wireless LAN standard, it uses the frequency of 5.850-5.925 GHz instead of industrial, scientific, and medical (ISM) band and uses 10 MHz bandwidth as one basic channel. This is to reduce the influence of frequency selective fading which occurs in high speed moving road environment by reducing channel bandwidth. While the IEEE 802.11a/g standard has to perform an authentication procedure before establishing the connection between a wireless terminal and an access point (AP), the WAVE standard does not require the authentication procedure. Therefore, a vehicle to which the WAVE standard is applied can communicate immediately if only the channel setting between the vehicles or the RSU coincides with the other.  
The IEEE 802.11p standard may have security issues due to the lack of authentication procedures in existing wireless Internet standards for fast communication setup. The IEEE 1609 standard is further defined to address this problem. Currently, the IEEE 802.11p standard defines the PHY layer and MAC layer. The MAC layer and the upper layers are defined in the IEEE 1609 standard, and it is divided into four detailed definitions. The IEEE 1609.12 standard specifies allocations of WAVE identifiers defined in the IEEE 1609 series of standards. The IEEE 1609.2 standard provides security services for the WAVE networking stack and for applications that are intended to run over the stack. The IEEE 1609.3 standard specifies the functions associated with the LLC, network, and transport layers of the OSI model and calls them WAVE networking services. The IEEE 1609.4 standard provides enhancements to the IEEE 802.11p MAC to support multi-channel operations.  
The IEEE 1609.4 standard divides the wireless channel into a CCH and an SCH and allocates different frequency channels to each interval. Figure 1 shows the channel structure of the WAVE standard.  
The WAVE standard uses one CCH and six SCHs. The CCH is dedicated to system control messages, and the SCH is used to exchange service data packets. The CCH interval and the SCH interval are fixed as 50 ms, respectively. The OBU receives WAVE control packets in the CCH interval and transmits or receives service data frames. The channel access in the CCH interval and the SCH interval uses the IEEE 802.11e enhanced distributed channel access (EDCA) mechanism. The WBSS, which is configured to communicate using WAVE standard, consists of a provider that starts WBSS and a user that subscribes to WBSS. The provider periodically broadcasts a WAVE service announcement (WSA) message, which is a beacon frame containing network parameters such as WBSS identifiers required to join WBSS, service channels to be used by WBSS, and timing information for synchronization. When the user receives the WSA message, it can subscribe to the WBSS by switching the channel to the service channel used by the WBSS at the next SCH interval. The CCHInterval indicates the length of the CCH interval. During this interval, the management message for the service advertisement and the data message of the high priority application are transmitted. The SCHInterval indicates the length of the SCH interval, and a general data service message is transmitted during this interval.