SMACK: a SMart ACKnowledgment scheme for broadcast messages in wireless networks

Network protocol designers, both at the physical and network level, have long considered interference and simultaneous transmission in wireless protocols as a problem to be avoided. This, coupled with a tendency to emulate wired network protocols in the wireless domain, has led to artificial limitations in wireless networks. In this paper, we argue that wireless protocols can exploit si-multaneous transmission to reduce the cost of reliable multicast by orders of magnitude. With an appropriate application inter-face, simultaneous transmission can also greatly speed up common group communication primitives, such as anycast, broadcast, leader election and others. The proposed method precisely fits into the domain of directly reachable nodes where many group communication mechanisms are commonly used in routing protocols and other physical-layer mechanisms. We demonstrate how simultaneous transmission can be used to implement a reliable broadcast for an infrastructure and peer-to-peer network using a prototype reconfigurable hard-ware. We also validate the notion of using simple spectrum sensing techniques to distinguish multiple transmissions. We then describe how the mechanism can be extended to solve group communication problems and the challenges inherent to build innovative protocols which are faster and reliable at the same time