Overview of interference situation and mitigation techniques for LDACS1

LDACS1 is the broadband candidate technology for the future L-band digital aeronautical communications system. As unused spectrum is very scarce in the L-band, LDACS1 pursues the approach to make use of the gaps between adjacent channels used by the distance measuring equipment to meet the capacity requirements of a new aeronautical data link. This is a challenging approach as the power of DME signals is well above the LDACS1 received power in many scenarios. In addition, further legacy system, operating in the L-band might affect LDACS1. In this paper, we will characterize the different sources of interference and derive scenarios for their influence onto LDACS1. We will also distinguish between the situations in the forward, i.e. at an airborne receiver, and in the reverse link, corresponding to a ground station receiver. Next we will have a look onto detecting interference pulses which is a challenging task for LDACS1, as it uses orthogonal frequency division multiplexing modulation, which leads to remarkable fluctuations of the useful signal power itself. The efficiency of the proposed interference detection will be confirmed by realistic simulations. Based on the investigated detection capabilities, we will finally assess, by means of bit-error rate simulations, how the different types of interference influence the LDACS1 performance if a basic interference mitigation algorithm is applied.