A Novel Mitigation Scheme for JTIDS Impulsive Interference on LDACS System Based on Sensing and Symbol Retransmission

Future digital air/ground communication systems (LDACS) will operate on L-Band where the coexistence with existing legacy systems shall be guaranteed. This paper proposes a scheme to detect and mitigate the JTIDS impulsive interference on LDACS-1 system. The novel idea advised here is the transmission of two copies of the symbols received with interference that are suitably combined at the receiver after a blanking operation of the corrupted samples. In particular two alternatives are presented that differ for the retransmission policy: in the full combining scheme all the symbols are transmitted twice, in the partial combining scheme only the symbols where interference has been detected are retransmitted. These methods permit to efficiently remove the interference without affecting the useful information and exploiting profitably diversity gain against noise introduced by the soft combining approach. The numerical results provided in the paper highlight a good behaviour of the proposed methods and significant advantages in comparison with the traditional blanking method either in terms of Bit Error Rate and Throughput

Optimized threshold calculation for blanking nonlinearity at OFDM receivers based on impulsive noise estimation

Impulsive noise (IN) degrades the performance of OFDM-based communication systems. Performance degradation is usually measured in terms of signal-to-noise ratio (SNR) and symbol-error rate (SER). To improve the performance of the system of OFDM receivers, one of the effective methods is to use blanking nonlinearity. In this method, the samples whose magnitudes exceed a certain fixed threshold are considered to be IN-affected and are therefore blanked. A fixed threshold does not always determine the IN-affected samples truly for all probabilities of IN occurrence. This paper proposes an optimized threshold-calculation method for blanking nonlinearity which is based on distribution characteristics of the received signal, i.e., mean, median, and peak. The proposed method can calculate an optimized threshold for all probabilities of impulsive noise occurrence. Simulation results show over 2.2-dB gain in SNR and lower SER by using the proposed method as compared to fixed threshold

Observation of strong correlation between quasimonoenergetic electron beam generation by laser wakefield and laser guiding inside a preplasma cavity

We use a one-shot measurement technique to study effects of laser prepulses on the electron laser wakefield acceleration driven by relativistically intense laser pulses (lambda=790 nm, 11 TW, 37 fs) in dense helium gas jets. A quasimonoenergetic electron bunch with an energy peak similar to 11.5 MeV [Delta E/E similar to 10% (FWHM)] and with a narrow-cone angle (0.04 pi mm mrad) of ejection is detected at a plasma density of 8x10(19) cm(-3). A strong correlation between the generation of monoenergetic electrons and optical guiding of the pulse in a thin channel produced by picosecond laser prepulses is observed. This generation mechanism is well corroborated by two-dimensional particle-in-cell simulations

On the design of experiments to study extreme field limits

We propose experiments on the collision of high intensity electromagnetic pulses with electron bunches and on the collision of multiple electromagnetic pulses for studying extreme field limits in the nonlinear interaction of electromagnetic waves. The effects of nonlinear QED will be revealed in these laser plasma experiments. © 2012 American Institute of Physics