CAESAR: Carrier Sense-Based Ranging in Off-The-Shelf 802.11 Wireless LAN

8 Apr

Domenico Giustiniano, Senior Researcher and Lecturer, Communication Systems Group (CSG), ETH Zurich, Switzerland

External Presentation (IN Speaker)


802.11 wireless local area networks have been designed for wireless communication. The principle for 802.11 communication is that frames are acknowledged (ACKed) after a short and predefined MAC idle time. Despite the MAC idle time is designed to be constant, we find that it varies with i) the physical distance between stations, caused by the delay of wireless signal propagation, and ii) the time to detect the ACK at the local station, which varies with the signal strength of the incoming ACK. Exploiting this knowledge, we present CAESAR, CArriEr Sense-bAsed Ranging, that combines time-of-flight and signal-to-noise ratio measurements to calculate the distance between two stations. CAESAR measures the distance by estimating the MAC idle time in a data/ACK communication at a 44 MHz clock resolution and the ACK detection time on a per-frame basis. CAESAR is a software-based solution that is entirely implemented at the transmitter and it requires no 802.11 protocol modifications. We implement CAESAR on commodity hardware and conduct extensive experiments both in controlled network conditions and dynamic radio environments.  Our measurements confirm the accuracy of the solution and show the capability to track the distance to WLAN smartphones at pedestrian speeds.

The work above has been conducted at Disney Research and published at ACM Conext’11.

The last part of the talk will briefly present ongoing research activities conducted at ETHZ in the area of time-of-flight WLAN localization.

About Domenico Giustiniano:

Domenico Giustiniano is Senior Researcher and Lecturer in the Communication Systems Group (CSG) of ETH Zurich since April 2012. Before joining ETH, he was a Post-Doctoral Researcher at Disney Research Zurich and at Telefonica Research Barcelona. He holds a PhD in Telecommunication Engineering from the University of Rome Tor Vergata. He also worked as research assistant in other labs, such as the Hamilton Institute, Ireland; Intel Lab, CMU Pittsburgh, USA; University of Palermo, Italy; and the University of Ulm, Germany.

Personal site

This event will be conducted in English

Image: Flickr- By Dana Spiegel


  • Location: Sala de Juntas 3.3.B01 - Building Rey Pastor (Biblioteca), University Carlos III of Madrid, Avda. Universidad, 30, 28911 Leganés – Madrid

  • Time: 01:00 pm