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Researchers of USC Viterbi School of Engineering, Segura, Niranjayan, Hashemi and Andreas Molisch, have experimentally demonstrated the first wireless network synchronized with nanosecond accuracy. They have developed a prototype, consisting of four nodes that synchronize to each other with an accuracy of approximately three nanoseconds. They also introduced a scalable protocol, which they call the “Blink” algorithm that extends the same accuracy to hundreds or even thousands of wireless devices.
There are a variety of applications that require very high timing synchronization accuracy, coordinated jamming of enemy military receivers, distributed beam forming, fine grain localization, tracking, and navigation, require timing synchronization with nanosecond precision or even better.
Hashemi said. “Even though GPS is widely used and is considered very precise, it does not easily provide this level of accuracy and cannot be used in many indoor settings.”
There are also many military and civilian scenarios, where differential GPS signals may not be available. Maintaining such accurate timing synchronization in large wireless networks is challenging; because, the timer in each node is derived from an independent oscillator that is affected by random drifts and jitter.
To maintain nanosecond-level timing synchronization in a network (1) timing deviation between pairs of nodes must be measured accurately with nanosecond precision, and (2) fast correction algorithms must be applied across the entire network. Ultra-Wide Band (UWB) signals are used to precisely extract the timing information between the nodes due to their accurate distance measurement capability as well as superior resiliency to multi-path effects. UWB systems have been used previously to demonstrate high-precision timing synchronization between two nodes
They have also developed timing protocol called “Blink” that enables network timing synchronization without requiring an external broadcast signal from a coordinator. The blink algorithm uses a consensus approach such that timing information propagates through the network, while timing errors are averaged, and exploits the path diversity present in the network. Simulations demonstrate excellent scalability, such that the obtained timing precision in large (hundreds of nodes) networks is only
Inside the physical network, a virtual network called Timing Virtual Network (TVN) is defined. The TVN consist of nodes, links and the fast re-sync algorithm that maintains the timing in the network. All nodes (slaves and masters) learn the propagation delays (pseudo-ranges) from their neighbors and record the values.
The master initializes the blink cycles transmitting a timing signal; in this implementation, a length 31 m-sequence is used for the timing signal. Slave nodes receive this sequence, perform correlation and peak detection to extract the timing information, use the result to correct their internal timers, and transmit the same sequence according to their tier associations. The nodes then use a consensus algorithm where each neighbor node can be weighted with a different factor to provide a timing correction value. The blinking cycles continue indefinitely. Reference signals from the master “pull” the timing in the network to agree with the master timing.
Added Molisch: “Our group’s “Blink” protocol will allow for wireless transmission over longer distances with less energy and stands to improve the overall efficiency of wireless networks.”
While this work has several applications for the military, it also has practical use for other situations in which increased precision is necessary, such as communication among a group of driverless cars to share location information. Other possible applications include helping a person with limited sight navigate an indoor physical space or providing a map for robots employed in the home or in industrial settings.
The research was supported primarily by the Office of Naval Research and the Ming Hsieh Institute at USC Viterbi.
