In some examples, a system is configured to mount on a first vehicle. The system include an antenna configured to transmit a first surveillance message by forming an omni-directional beam. The antenna is also configured to receive a second surveillance message from a second vehicle during a first time period. The antenna is further configured to receive a third surveillance message from a third vehicle during a second time period, where the first and second time periods at least partially overlap in time. The system also includes processing circuitry configured to demodulate the second surveillance message by forming a first beam and demodulate the third surveillance message by forming a second beam. The second beam is different than the first beam, and the first beam is simultaneous with the second beam.