CRC Over WLAN Layer 2 Header
Original Publication Date: 2002-Jul-02
Included in the Prior Art Database: 2002-Jul-02
The Air Interface of WLAN systems is capable of very high throughputs. Current 802.11a systems can operate at 54 Mbps at close range. However, the throughput of the system drops quickly as the distance increases. 802.11a drops to 6 Mbps as a raw throughput rate, and 802.11b can operate as low as 1 Mbps. Since there is limited bandwidth, there needs to be mechanisms to make the air interface more efficient. Further, in current WLAN systems, a CRC is calculated over the entire packet and placed at the end of the Layer 2 message. Figure 1 shows the MAC frame structure, with the CRC. The CRC encompasses both the L2 header (from Frame Control to QoS Control, inclusive) and the L2 payload. However, it is not always important that all of the payload bits be correct. If the payload delivery is of an unconfirmed type, there is no need to retry the packet if there is an error in the payload. Retrying packets of type unconfirmed adds to making the WLAN air interface even more inefficient.