One Clock to Rule Them All: A Primitive for Distributed Wireless Protocols at the Physical Layer
Omid Abari, Hariharan Shankar Rahul, Dina Katabi · DSpace@MIT (Massachusetts Institute of Technology) · 2014
Implementing distributed wireless protocols at the physi-cal layer today is challenging because different nodes have different clocks, each of which has slightly different frequen-cies. This causes the nodes to have frequency offset relative to each other, as a result of which transmitted signals from these nodes do not combine in a predictable manner over time. Past work tackles this challenge and builds distributed PHY layer systems by attempting to address the effects of the frequency offset and compensating for it in the transmitted signals. In this paper, we address this challenge by address-ing the root cause- the different clocks with different fre-quencies on the different nodes. We present AirClock, a new wireless coordination primitive that enables multiple nodes to act as if they are driven by a single clock that they receive wirelessly over the air. AirClock presents a synchronized ab-straction to the physical layer, and hence enables direct im-plementation of diverse kinds of distributed PHY protocols. We illustrate AirClock’s versatility by using it to build three different systems: distributed MIMO, distributed rate adap-tation for wireless sensors, and pilotless OFDM, and show that they can provide significant performance benefits over today’s systems. 1.