1090 ES receiving capacity improvement using ADS-B ground receivers with signals discrimination capability

A typical ADS-B (Automatic Dependent Surveillance – Broadcast) ground receiver is equipped with an omnidirectional antenna to receives the messages transmitted by the ADS-B equipped aircraft. The aircraft transmit unsolicited ADS-B messages periodically, on the 1090 MHz downlink channel. There are other ATC systems using the same frequency (Secondary Surveillance Radar SSR, Traffic Information System – Broadcast TIS-B), then, considering that the ADS-B receiving stations use omnidirectional antenna or in some cases a six sector antenna, the probability of interference grows with the air traffic increase. Therefore there is a risk of data loss due to “garbled” ADS-B OUT 1090 ES messages in the receiving station, with a reduction of the valid data rate. In this paper an ADS-B ground receiver with signals discrimination capability is proposed. Such device is able to detect and solve signals overlapping events. This feature is useful to improve the 1090 extended squitters receiving capacity for a ground receiver station. The proposed receiver is composed by the antenna system, an analog-digital front-end and a pre-processing unit followed by a RTCA-DO 260 compliant 1090 MHz decoder. The pre-processing unit implements the signal discrimination and separation procedures. These procedures are based on processing algorithms studied and developed by Tor Vergata University RadarLab. This unit differs depending if the antenna is single element or an array, for which case the underlying algorithm has better performances. The algorithms are introduced, and their analyses allow to evaluate the resulting channel capacity as a function of the environmental messages density.