Suppression of Mutual Interference in OFDM Based Overlay Systems

A promising appraoch for overcoming spectrum scarcity are overlay systems that share a frequency band with already existing licensed systems by using the spectral gaps left by the licensed systems. Due to its spectral efficiency and flexibility orthogonal frequency-division multiplexing (OFDM) is an appropriate modulation technique for overlay systems. To enable a successful co-existence, techniques for suppressing mutual interferences between the overlay and the licensed system are proposed

Overview of legacy systems in L-band and its influence on the future aeronautical communication system LDACS1

L-band digital aeronautical communications system type 1 (LDACS1) is the broadband candidate technology for the future aeronautical communications system in the L-band. 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 (DME) 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 most cases. Moreover, additional legacy system operating in the L-band will interfere with LDACS1. Herein, we will first introduce LDACS1, focusing on the physical layer design. Next, the different systems operating in the L-band are briefly described, with a particular emphasis on their influence onto LDACS1. For comparison of the influence from the different systems, we will calculate an interference duty-cycle, specifying the fraction of time LDACS1 is exposed to interference from the different legacy systems

Radar Signal Processing for Interference Mitigation

It is necessary for radars to suppress interferences to near the noise level to achieve the best performance in target detection and measurements. In this dissertation work, innovative signal processing approaches are proposed to effectively mitigate two of the most common types of interferences: jammers and clutter. Two types of radar systems are considered for developing new signal processing algorithms: phased-array radar and multiple-input multiple-output (MIMO) radar. For phased-array radar, an innovative target-clutter feature-based recognition approach termed as Beam-Doppler Image Feature Recognition (BDIFR) is proposed to detect moving targets in inhomogeneous clutter. Moreover, a new ground moving target detection algorithm is proposed for airborne radar. The essence of this algorithm is to compensate for the ground clutter Doppler shift caused by the moving platform and then to cancel the Doppler-compensated clutter using MTI filters that are commonly used in ground-based radar systems. Without the need of clutter estimation, the new algorithms outperform the conventional Space-Time Adaptive Processing (STAP) algorithm in ground moving target detection in inhomogeneous clutter. For MIMO radar, a time-efficient reduced-dimensional clutter suppression algorithm termed as Reduced-dimension Space-time Adaptive Processing (RSTAP) is proposed to minimize the number of the training samples required for clutter estimation. To deal with highly heterogeneous clutter more effectively, we also proposed a robust deterministic STAP algorithm operating on snapshot-to-snapshot basis. For cancelling jammers in the radar mainlobe direction, an innovative jamming elimination approach is proposed based on coherent MIMO radar adaptive beamforming. When combined with mutual information (MI) based cognitive radar transmit waveform design, this new approach can be used to enable spectrum sharing effectively between radar and wireless communication systems. The proposed interference mitigation approaches are validated by carrying out simulations for typical radar operation scenarios. The advantages of the proposed interference mitigation methods over the existing signal processing techniques are demonstrated both analytically and empirically