CLACK: Cross-layer ACK-Aided Opportunistic Transmission in Wireless Networks

Wi-Fi has gained tremendous attention from the research community, yielding successful technological advancements. However, the data throughput efficiency (the ratio of application throughput to the maximum achievable physical data rate) degrades rapidly as the PHY data rate increases when using the current 802.11 medium access control (MAC) protocol. To address this MAC inefficiency, many protocols have been introduced and standardized. This paper describes and examines these state-of-the-art enhancements to MAC efficiency for the 802.11 standard, and proposes a CLACK (Cross-Layer ACK) method that tackles this issue in totally different manner to those previous schemes. The main idea is simple: When a receiver sends an ACK, it transmits the data using the ACK transmission opportunity, and avoids channel contention necessary for data transmissions. The receiver’s short signature is piggybacked in the PHY instead of the MAC to acknowledge the packet reception. We have implemented CLACK using USRP toolkits and GNU Software Define Radio. Our implementation demonstrates the feasibility of our key techniques for both PHY and MAC design. Further, we use detailed simulation to evaluate CLACK in general wireless environments under different traffic loads and varying channel conditions. Our results show that CLACK gains up to 52 % in terms of throughput, when compared to the basic 802.11 scheme, and up to 18 % when compared to existing advanced 802.11e/n schemes.