[Paper Review] New Reconfigurable L-Band Digital Aeronautical Communication System

Niharika Agrawal|arXiv (Cornell University)|Sep 17, 2018

PAPR reduction in OFDM23 references4 citations

TL;DR

This paper proposes a reconfigurable filtered OFDM (Ref-OFDM) based L-band Digital Aeronautical Communication System (LDACS) that supports tunable bandwidths from 186 kHz to 732 kHz, using a reconfigurable linear-phase multi-band FIR filter to enable dynamic spectrum adaptation. The approach achieves higher spectral efficiency and reduced out-of-band emissions compared to conventional OFDM, enabling efficient coexistence with DME signals and scalable multi-user, multi-band transmission.

ABSTRACT

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.

Motivation & Objective

• Address the limited spectrum utilization in existing OFDM-based LDACS, which is fixed at 498 kHz due to high out-of-band emissions.
• Overcome the inflexible bandwidth allocation in current LDACS by enabling dynamic, on-the-fly bandwidth adaptation.
• Design a reconfigurable linear-phase multi-band FIR filter to support variable bandwidths without coefficient reprogramming.
• Enable efficient coexistence with incumbent DME signals in the L-band (960–1164 MHz) through improved spectral shaping.
• Develop a hardware-software co-design framework for SoC implementation targeting area, power, and delay constraints.

Proposed method

• Propose a generalized frame structure for LDACS supporting bandwidths from 186 kHz to 732 kHz, replacing the fixed 498 kHz allocation.
• Implement a reconfigurable filtered OFDM (Ref-OFDM) transceiver using a single reconfigurable linear-phase multi-band FIR filter for both transmit and receive chains.
• Design the filter to dynamically adjust bandwidth by switching filter taps, avoiding coefficient reprogramming and enabling real-time adaptation.
• Use a hardware-software co-design approach on Zynq System-on-Chip (SoC), offloading signal processing to ARM processor and baseband processing to FPGA.
• Integrate the OFDM transceiver with the AD9361 RF front-end for real-time over-the-air validation using real channel conditions.
• Conduct MATLAB simulations and hardware prototyping to evaluate bit error rate (BER), spectral mask compliance, and resource/power efficiency.

Experimental results

Research questions

• RQ1 How can LDACS achieve flexible, tunable bandwidth operation across 186–732 kHz while maintaining spectral efficiency and DME coexistence?
• RQ2 What is the performance of the reconfigurable FIR filter in minimizing out-of-band emissions and enabling multi-band transmission?
• RQ3 How does the Ref-OFDM transceiver compare to conventional OFDM in terms of BER, spectral mask compliance, and hardware complexity?
• RQ4 What is the optimal hardware-software partitioning on Zynq SoC for area, power, and delay constraints in LDACS implementation?
• RQ5 Can the proposed Ref-OFDM system support asynchronous multi-user and multi-band transmission effectively?

Key findings

• The proposed Ref-OFDM-based LDACS supports a wide range of tunable bandwidths from 186 kHz to 732 kHz, overcoming the fixed 498 kHz limitation of conventional OFDM.
• The reconfigurable FIR filter enables dynamic bandwidth adaptation without changing filter coefficients, reducing implementation complexity.
• Simulation results show improved out-of-band emission (OOB) performance, ensuring compliance with DME coexistence requirements.
• The system achieves lower interference to incumbent DME users due to sharp spectral roll-off from the linear-phase FIR filter.
• Hardware prototyping on Zynq SoC demonstrates feasible resource utilization and dynamic power scaling, with potential for integration with AD9361 RF front-end.
• The transceiver design supports multi-user and multi-band transmission using a single reconfigurable filter, enabling scalable and efficient spectrum use.