Existing flooding algorithms have demonstrated their effectiveness in achieving communication efficiency and reliability in wireless sensor networks. However, further performance improvement has been hampered by the assumption of link independence, a design premise imposing the need for costly acknowledgements (ACKs) from every receiver. In this paper, we present Collective Flooding (CF), which exploits the link correlation to achieve flooding reliability using the concept of collective ACKs. CF requires only 1-hop information from a sender, making the design highly distributed and scalable with low complexity. We evaluate CF extensively in realworld settings, using three different types of testbeds: a single hop network with 20 MICAz nodes, a multihop network with 37 nodes, and a linear outdoor network with 48 nodes along a 326-meter-long bridge. System evaluation and extensive simulation show that CF achieves the same reliability as the state-of-the art solutions, while reducing the...