  To meet an ever-increasing demand of the spectrum for communication between
aircraft and ground terminals, orthogonal frequency division multiplexing
(OFDM) based L-band (960-1164MHz) Digital Aeronautical Communication System
(LDACS) has been recently proposed as an alternative to existing narrowband
systems. However, OFDM based LDACS needs additional control signaling for time
and frequency alignment and the use of cyclic prefix and high out-of-band
emission limits the spectrum utilization efficiency to less than 50%. In this
paper, a new waveform has been proposed which offers better spectrum
utilization than OFDM without compromising on computational complexity and
interference to legacy users in L-band. It also allows transceivers to
dynamically adapt the transmission bandwidth to meet the desired quality of
service. Since the proposed waveform employs a reconfigurable multiband linear
phase filter, it is referred to as reconfigurable filtered OFDM (Ref-OFDM).
Simulation results and extensive analysis show that the proposed Ref-OFDM
offers around 40 dB better out-of-band emission than OFDM which in turn leads
to significant increase in the transmission bandwidth for a given BER and
interference constraints. The computational complexity of Ref-OFDM is slightly
higher than that of OFDM but it is significantly less than other waveforms
making Ref-OFDM an attractive waveform for next generation air-to-ground
communications. An end to end hardware prototyping of LDACS-DME coexistence is
also presented in this report.
