Radar Wi-Fi Coexistence

Part 1: Link Simulations

Researcher: Hossein Safavi

An accurate error model is a pre-requisite for studying this coexistence scenario. Though SINR based abstractions are often useful, such models are highly inaccurate when interference is bursty and not well approximated by an additive white gaussian noise process. To that end, we have constructed an accurate Wi-Fi link simulator (signal sample level) incorporating the canonical transceiver stages including:

  1. Frequency selective channel
  2. Preamble finding/synchronization
  3. Channel estimation
  4. Interleaving, coding/decoding, variable MCS
  5. Receiver diversity

The receive chain is then injected with a programmable radar interference waveform (typically a chirp signal with bursts of a few microseconds). Errors tables are created as a function of where in the Wi-Fi frame the interference occurred (e.g. during preamble vs. payload). The figure below shows an example output from the link simulations for a specific MCS.



Part 2: Link to System Mapping

Researcher: Benjamin Cizdziel

Modifications to ns-3 include a model for a radar transmitter that incorporates rotation and pulse repetition intervals. The error tables previously created through link simulations are used at the Wi-Fi nodes so that the results obtained for throughput and packet drops are highly accurate. We then study the throughput of WLAN systems at various distances and observe their behavior at the network and protocol level (e.g. impact on back-off statistics, etc…). The results from this work have been published in part in a Master’s Thesis by Benjamin Cizdziel. Briefly, the impact of radar on Wi-Fi networks is studied as a function of the following parameters:

  1. Distance from radar to WLAN
  2. WLAN traffic load (number of stations)
  3. Pulse duration
  4. Pulse repetition interval
  5. Radar rotation speed