Frequency-modulated Interference Research Articles

Theoretical Analysis of AM and FM Interference Robustness of Integrating DDR Receiver for Human Body Communication.

Prolific growth of miniaturized devices has led to widespread use of wearable devices and physiological sensors. The state-of-art technique for connecting these devices and sensors is through wireless radio waves. However, wireless body area wireless body area network (WBAN) suffers from limited security (wireless signals from energy-constrained sensors can be snooped by nearby attackers), poor energy-efficiency (up conversion and down conversion), and self-interference. Human body communication (HBC), which uses human body as a conducting medium, has emerged as a new alternative physical layer for WBAN, as it can enable communication with better energy efficiency and enhanced security. Broadband (BB) HBC uses the human body channel as a broadband communication medium and can enable higher energy efficiency compared to narrowband HBC. However, due to the antenna effect of human body, ambient interferences get picked up from the environment, proving to be one of the primary bottlenecks for BB-HBC systems. In this paper, we analyze the performance of an integrating dual data rate (I-DDR) receiver, which enables interference robust BB-HBC, under continuous wave (CW), amplitude modulated (AM), and frequency modulated (FM) interferences. Theoretical derivations along with simulations provide key insights into the behavior of I-DDR receiver under different interference scenarios, highlighting the efficacy (>22dB improvement in SIR tolerance for both FM and AM) of the technique. Finally, measurements are carried out by applying the I-DDR principle on signals transmitted through the human body and captured on an oscilloscope. Measurements from an I-DDR receiver fabricated in TSMC 65nm technology shows <10-4 BER in presence of CW, AM, and FM interference with -21dB SIR further demonstrating the efficacy of the I-DDR method in interference rejection.

GPS Antijam via Subspace Projection: A Performance Analysis for FM Interference in the C/A Code

Zhao, L., Amin, M. G., and Lindsey, A. R., GPS Antijam via Subspace Projection: A Performance Analysis for FM Interference in the C/A Code, Digital Signal Processing 12 (2002) 175–192 This paper is concerned with frequency modulated (FM) interference cancelation in GPS receivers. FM signals are instantaneously narrowband and have clear time–frequency signatures that are distinct from the GPS C/A spreading codes. Interference cancelation is performed by first constructing the interference subspace and then projecting the data onto the orthogonal subspace. Interference subspace estimation can be provided by the time–frequency distribution (TFD) or any other instantaneous frequency (IF) estimator. The GPS receiver signal-to-interference and noise ratio in the presence of IF or phase estimation errors is derived. The errors are assumed Gaussian and independent. From both analysis and simulations, it is shown that phase estimation errors can substantially impede interference rejection in GPS using subspace projection techniques.

Across-channel Masking of Changes in Modulation Depth for Amplitude- and Frequency-modulated Signals

This study examines a form of masking that can take place when the signal and masker are widely separated in frequency and cannot be explained in terms of the traditional concept of the auditory filter or critical band. We refer to this as across-channel masking. The task of the subject was to detect an increment in modulation depth of a 1000-Hz sinusoidal carrier. The carrier could either be sinusoidally amplitude modulated or sinusoidally frequency modulated at a 10-Hz rate. Modulation increment thresholds of this "target" signal were measured for the target alone, and in the presence of two interfering sounds with carrier frequencies of 230 and 3300 Hz. When the interfering sounds were unmodulated, they had no effect on modulation increment thresholds. When the interfering sounds were either amplitude or frequency modulated, thresholds increased. Amplitude modulation (AM) increment thresholds were affected by both amplitude-modulated and frequency-modulated interference. Similarly, frequency modulation (FM) increment thresholds were affected by both amplitude-modulated and frequency-modulated interference. For both types of signal, the interference was tuned for modulation rate; across-channel masking was greatest when the interfering sounds were modulated at rates close to 10 Hz, and declined for higher or lower rates. However, the tuning was rather broad. When the target and interfering sounds were modulated at the same rate, there was no effect of the relative phase of the modulators. Two possible explanations for the results are discussed. One is based on the idea that carriers that are modulated in a similar way tend to be perceptually "grouped". The other is based on the idea that there are "channels" in the auditory system tuned for AM and FM rate. Neither explanation appears completely satisfactory.

Estimating noise intensity against a background of frequency-modulated interference

Estimating noise intensity against a background of frequency-modulated interference