On the design of a modern broadband communications waveform for tactical air-to-ground links

Tactical air-to-ground channels present a number of challenges for physical (PHY) layer waveform design including: (i) airborne platform dynamics (i.e., Doppler, frequency offset, jerk, etc.), (ii) benign to severe ground-level multipath, and (iii) partial to full blockage of the line-of-sight (LOS) path. Legacy military waveforms are not sufficiently robust to operate effectively in these severe channels while providing the data rates required for modern tactical communications. This paper presents a waveform design incorporating flexible low-density parity-check (F-LDPC) forward error correction and a bandwidth efficient continuous phase modulation (CPM) that provides the required robustness and throughput for use in broadband tactical air-to-ground links. The proposed waveform employs per-survivor processing (PSP) and adaptive iterative detection (AID) in order to mitigate multipath and platform dynamics effects. It is demonstrated via simulation that the proposed waveform reliably delivers data rates of 1.3 Mbps over a single 1.2 MHz bandwidth channel and over 5 Mbps utilizing four 1.2 MHz carriers in both representative air-to-ground channels and other tactically relevant scenarios. Developed with the digital signal processing and RF front-end constraints of current software defined radio (SDR) platforms in mind, the proposed waveform is an excellent candidate for delivering robust, broadband connectivity in air-to-ground links.