IEEE 1609.4:2006 pdf free download – IEEE Trial-Use Standard for Wireless Access in Vehicular Environments(WAVE) – Multi-channel Operation
4.General description
WAVE devices shall be able to accommodate an architecture that supports a CCH and multiple SCHs. TheCCH is used to transmit wSMs and announce WAVE services;the SCHs are used for applicationinteractions/transmissions. The specific designations of these channels and the specification of the PHY aredefined in IEEE Std 802.11 , as amended by IEEE P802.11p.
In a WAVE system, there are two types of devices: roadside units (RSUs) and onboard units (OBUs).AnRSU is a WAVE device that operates at a fixed position (usually along the road transport network) thatsupports communication and data exchange with OBUs.An OBU is a mobile or portable WAVE device thatsupports information exchange with RSUs and other OBUs.Upon startup, a device monitors the CCH (seeIEEE P1609.3) until a WAVE service advertisement (WSA) is received that announces a service thatutilizes an SCH,or the device chooses to utilize the SCH based on WAVE announcement frames ittransmits.WAVE devices must also monitor the CCH for additional safety or private service advertisementsduring specific intervals known as control channel intervals (CCH intervals).If suspension of transactionsin progress on an SCH is necessary when CCH monitoring is required, the data exchange may be resumedwhen CCH monitoring is no longer required (i.e., when the device can return to the SCH). This may occur,for example, in a single channel device that can perform exchanges on only one RF channel at a time, and inthis case,it is recommended that a means be implemented to support buffering data packets whilemonitoring the CCH until the device can return to the SCH to complete transactions in progress.
To accommodate devices that want exchange data on SCHs, but can not monitor the CCH while doing so,synchronization is necessary. Synchronization is the procedure by which a device adopts the time referenceof another source of time. In addition to being synchronized to each other, such devices must also knowwhen it is permissible to cease monitoring the CCH, and for this purpose,CCH and SCH intervals areuniquely defined with respect to an absolute external time reference,Coordinated Universal Time (UTC).uTC is commonly provided by Global Positioning Systems(GPS); however，the time base accuracyrequirements for WAVE devices are sufficiently lenient that management frames containing UTC timeestimates from other devices can be used as well. Once synchronized, single-channel devices can ensurethey meet the requirement to be monitoring the CCH during specified CCH intervals. It is important to note that synchronization is not required to make data exchanges on SCHs. While synchronization is optional,internal time base generation is required for security purposes (see IEEE Std 1609.2).
4.1 Reference model
The basic reference model relevant to this standard is shown in Figure 1.A WAVE system supports both IPand non-IP based applications. Non-IP based applications are supported through the WAVE short messageprotocol (WSMP) defined in IEEE P1609.3.
This standard presents the architectural view, emphasizing the multi-channel coordination of the system.The channel coordination is an enhancement to the IEEE 802.11 MAC and interacts with the IEEE 802.2logical link control(LLC) and IEEE P802.11p PHY. The WAVE management entity (WME) andcorresponding network services are specified in IEEE P1609.3.