Underlay Spectrum Sharing with L-Band Distance Measuring Equipment for Aeronautical Communications

The monitoring of an aircraft during its flight phases is crucial to the performance of air-to-ground (A/G) communication designed for air traffic management (ATM) purposes. Due to the everyday increasing air traffic, A/G communications have been transferred from the congested very high frequency band to occupy the guard bands between adjacent distance measurement equipment (DME) channels within the L-Band. However, the inlayed channels, called L-Band digital aeronautical communications (LDACS) channels, experience severe interference with the coexisting DME channels. The previous work depends on both DME interference detection and mitigation techniques. In this paper, a DME interference mitigation technique is proposed to improve the performance of the LDACS type I (LDACSI) system without requiring the detection process. The proposed technique depends on the underlay spectrum sharing for LDACSI signal. The underlay spectrum sharing concept is performed using spread spectrum technique. The spread spectrum technique is applied based on the idea of multiplexing the in-phase and the quadrature components of LDACSI signal by two Walsh orthogonal spreading codes in which they are transmitted over the quadrature branch. The resulting combined baseband signal is transmitted only over the quadrature branch then RF is up-converted to form the band pass signal in the presence of the DME interfering signal. Therefore, the spread LDACSI signal is friendly coexist on the top of DME interference signal. Moreover, the simulation results shows that the proposed underlay spectrum sharing for LDACSI system provides lower bit error rate and less complexity compared to the previous work.