Comparison of L-DACS and FBMC performance in over-water air-ground channels

The demand for air transportation is continuously growing. Likewise, unmanned aircraft systems (UAS) are proliferating at a tremendous pace. Both current and future air-to-ground (AG) communications systems will be deployed in the L-band (960-1164 MHz), and possibly in other bands. Aiming toward modernization, Eurocontrol recently defined two L-Band Digital Aeronautical Communication Systems (L-DACS). Primary goals of LDACS are high data rate transmission and high reliability. There are two L-DACS technology candidates, LDACS1 and LDACS2. The LDACS1 scheme employs a fairly broadband (0.5 MHz) transmission using Orthogonal Frequency-Division Multiplexing (OFDM) together with adaptive coding and modulation. The LDACS2 scheme follows a more traditional approach which is based on GSM (Global System for Mobile Communications), i.e., on second generation cellular mobile radio technology. In this paper, we investigate and compare the physical layer characteristics of L-DACS1 and L-DACS2 and then via simulations we illustrate the performance of these two communication systems in an air-to-ground channel. The air-to-ground channel we employ is one based upon a recent extensive measurement campaign. Results for error probability vs. signal to noise ratio are the focus. We also propose a new filterbank multicarrier (FBMC) based air-ground communication air interface which is consistent with previous requirements of L-DACS. We compare the FBMC performance with that of the LDACS schemes and show that FBMC has higher spectral efficiency via better time-frequency localized prototype subcarrier filters. This enables use of some guard subcarriers as data carrying subcarriers, increasing throughput. The BER results of our FBMC based L-DACS system are equivalent to those of L-DACS1 and better than those of L-DACS2. The simulation results also show the sensitivity of L-DACS2 systems to channel phase shifts and show the necessity of channel equalization for L-DACS2 receivers.