Receiver Initiated Network Allocation Vector Clearing Method in WLANs

802.11 DCF defines a virtual carrier sense mechanism, via RTS/CTS handshaking, to reserve wireless channel. All the nodes overhearing either RTS or CTS set their network allocation vector (NAV) respectively, and defer the channel access for the expected time to finish the packet sequence transmission. The problems arise when RTS or CTS is not successfully received by the addressed node, which causes the channel waste resulted from unnecessary NAV setting. We specify them as RTS-induced and CTS-induced unnecessary NAV setting problems depending on the type of the packet where NAV is set from. Some literatures resolve the problem by channel sensing, though, they are focusing on RTS-induced problems, and infeasible in CTS-induced case due to the unavailability of transmission status at those nodes surrounding the destination. Besides, taking into consideration the path loss, multipath fading, movement, etc., the packet error rate of CTS becomes severe in wireless propagation environment. Therefore, it is necessary to resolve the CTS-induced problem as well. To this end we propose the receiver initiated NAV clearing (RINC) method to enhance the system performance. The method aims to notify surrounding nodes the transmission status via a clear packet initiated from the receiver. It eliminates the wasted inhibition period in case of broken sequence without interfering with ongoing transmissions. This paper first describes the unnecessary NAV setting problems and further illustrates the MAC operation of the proposed idea. After that, the performance in terms of throughput, average delay, etc. is evaluated by simulation. It is observed that the proposed method enhanced the throughput by utilizing the channel in a more efficient way