Adaptive Cancellation Technique Research Articles

A fast disturbance cancellation scheme for orthogonal frequency division multiplexing‐based passive radar exploiting reciprocal filter

AbstractThis paper proposes a simple non‐adaptive approach for the suppression of direct signal and clutter contributions in a passive radar system based on orthogonal frequency division multiplexing transmissions, exploiting the properties of a reciprocal filter (RF). The use of a RF allows to circumvent the limits posed by the waveform ambiguity function, producing a data‐independent time‐invariant response to a stationary point‐like target echo at the output of the range compression stage. This feature enables simple clutter cancellation strategies, based on the subtraction of delayed portions of the surveillance signal, according to the conventional moving target indication methodologies. The proposed processing scheme consists of a range compression stage based on a RF, followed by a Single Canceller. Its performance is investigated against a simulated and an experimental data set, for the case of a digital video broadcasting‐terrestial‐based passive radar scenario, and it is compared to an alternative scheme based on a conventional matched filter and adaptive cancellation techniques. The proposed approach is shown to yield a perfect cancellation of the clutter returns from a stationary scene under ideal conditions. Moreover, it proves to be robust to real‐world conditions, despite its considerably limited computational load compared to adaptive clutter cancellation techniques.

Adaptive Blind CSO Cancellation Technique for RoF Systems Implemented by Using DMLs

We report on the adaptive cancellation technique of the dispersion-induced composite second-order (CSO) distortions for use in radio-over-fiber (RoF) systems implemented by using directly modulated lasers (DMLs). The proposed technique utilizes the magnitude of the CSO distortions measured at outside the signal’s bandwidth as a cost function of the steepest descent algorithm. As a result, this technique can blindly cancel out the CSO distortions without the necessity of measuring any device and fiber parameters used in the RoF system. The effectiveness of the proposed technique is confirmed in the RoF link implemented by using a 1.55- $\mu \text{m}$ DML and is capable of transporting 24 100-MHz filtered-orthogonal-frequency-division-multiplexing signals in 64 quadrature amplitude modulation format.

State-Space Adaptive Nonlinear Self-Interference Cancellation for Full-Duplex Communication

Full-duplex transmission comprises the ability to transmit and receive at the same time on the same frequency band. It allows for more efficient utilization of spectral resources, but raises the challenge of strong self-interference (SI). Cancellation of SI is generally implemented as a multi-stage approach. This work proposes a novel adaptive SI cancellation algorithm in the digital domain and a comprehensive analysis of state-of-the-art adaptive cancellation techniques. Inspired by recent progress in acoustic echo control, we introduce a composite state-space model of the nonlinear SI channel in cascade structure. We derive a SI cancellation algorithm that decouples the identification of linear and nonlinear elements of the composite state. They are estimated separately and consecutively in each adaptation cycle by a Kalman filter in DFT domain. We show that this adaptation can be supported by a-priori signal orthogonalization and decoding of the signal-of-interest (SoI). In our simulation results, we analyze the performance by evaluating residual interference, system identification accuracy and communication rate. Based on the results, we provide recommendations for system design. In case of input orthogonalization, our Kalman filter solution in cascade structure delivers best performance with low computational complexity. In this configuration, the performance lines up with that of the monolithic (parallel) Kalman filter or the recursive-least squares (RLS) algorithms. We show that the Kalman-based algorithm is superior over the RLS under time-variant conditions if the SoI is decoded and in this way the covariance information required by the Kalman filter can be provided to it.

RFI mitigation of GNSS signals for radio astronomy: problems and current techniques

Mitigation of man-made radio frequency interference (RFI) is a problem of increasing importance for radio astronomy. Indeed, numerous terrestrial and satellite services of all kinds create lots of electromagnetic signals in a large part of the radio spectrum that are likely to disturb radio astronomical observations. Moreover, the advent of large, highly sensitive radio telescopes such as SKA, LOFAR, etc., will permit the observation of extremely faint and distant radio sources which exhibit large amounts of red shift, hence overlapping with unprotected bands in the radio spectrum. Among various possible causes of RFI, GNSSs have specific characteristics which can be handled appropriately to design efficient mitigation techniques. GNSS signals are generally well documented and the ephemerides of satellites are well known. Therefore, various partially or fully informed methods can be used, which exploit knowledge of the characteristics of the modulations. Adaptive cancellation techniques can also be used that use auxiliary observations coming from additional antennas. Besides, knowing the spatial direction of the disturbing source, spatial filtering and related techniques that can be implemented in antenna arrays are likely to mitigate RFI with minimum knowledge of the GNSS. After recalling some radio astronomy basics, the paper presents a few examples of RFI caused by satellite systems on radio-astronomical observations. Then, we give a brief overview of state-of-the-art RFI mitigation techniques for radio astronomy and we present in some details the principles and results pertaining to some methods that seem particularly appropriate to mitigate RFI arising from GNSS signals. The importance of cooperation between GNSS designers and astronomers is finally pointed out.

Very loud speech over simulated environmental noise tends to have a spectral peak in the F1 region

In some professions, workplace noise appears to be a hazard to the voice, if not to hearing. Several studies have shown that teachers and sports instructors, for example, are more prone to voice problems than average, prompting research on loud voice. Since on-location recordings are in many ways impractical, the running speech of 23 untrained speaker subjects (12 female, 11 male) was instead recorded in several types of loud noise that was presented over high-quality loudspeakers. Using adaptive cancellation techniques, the noise was then removed from the recordings, thus exposing the strained voices for analysis. The experiment produced a large body of data, only one aspect of which is reported here. In most subjects, the vowel spectrum as a function of voice SPL showed the expected behavior for low to moderate efforts, but developed a very pronounced peak in the F1 region at the highest efforts. This peak can be ascribed to the concerted action of several acoustic mechanisms, including source waveform asymmetry, F1 approximating one of the lower partials, and increased formant Q values due to a longer closed phase. [Work supported by the Swedish Council for Working Life and Social Research, Contract No. 2001-0341.]

Simultaneous transmission and reception system by adaptive cancelling

Airborne and shipborne radar, communication, and related radio wave systems with simultaneous transmission and reception system (STR) have limited spatial interval between the transmitting and the receiving antenna. Thus, suppression of self-interference due to the strong transmitted signal is an important problem. We have made an engineering model of STR with an adaptive cancellation technique, and evaluated three kinds of interference: CW, pulse, wideband signals. © 1998 Scripta Technica, Electr Eng Jpn, 123(1): 1–7, 1998

アダプティブキャンセラ方式による同時送受信技術の実験的検討

Airborne and shipborne radar, communication, and related radio wave systems with simultaneous transmission and reception system (STR) have limited spatial interval between the transmitting and the receiving antenna. Thus, suppression of self-interference due to the strong transmitted signal is an important problem. We have made an engineering model of STR with an adaptive cancellation technique, and evaluated three kinds of interference: CW, pulse, wideband signals. © 1998 Scripta Technica, Electr Eng Jpn, 123(1): 1–7, 1998

Improvement of pyrometric sensing in rapid thermal processing via adaptive cancellation of lamplight interference

Rapid thermal processing (RTP) is an emerging and promising technology in semiconductor manufacturing that provides numerous advantages over traditional batch processing. A central problem in RTP technology is the precise control of wafer temperature. However, the inability to accurately measure wafer temperatures during processing has thus far proved a major obstacle to the effectiveness of temperature control strategies. Pyrometry, the most commonly encountered temperature-sensing technique used in RTP, suffers from large bias due to uncertainty in the emissivity of silicon wafers. Texas Instruments has recently proposed an innovative technique that overcomes the problem of emissivity uncetainty. However, the new technique suffers from interference of lamplight that is the heating source in RTP. This paper proposes a system-theoretic approach to greatly mitigate the lamplight interference. An on-line adaptive cancellation technique is adopted to estimate time-varying gains. Experimental results of the proposed method are described.

Reduction of noise and distortion in amplifiers using adaptive cancellation

Application of adaptive cancellation techniques to feed-forward networks for amplifier linearization is discussed. Results of a test showing over 25 dB reduction in third order intermodulation products are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Adaptive cancellation technique in processing myoelectric activity of respiratory muscles.

Spectral analysis of myoelectric activity of the chest muscles is a promising diagnostic tool for respiratory diseases. Reduction of the corrupting cardiac activity from the recorded myoelectric activity of the chest muscles is essential because of the spectral overlap of both the signals. The adaptive noise cancellation technique was used to reduce the interfering cardiac activity from the recorded myoelectric activity. The adaptive noise canceller implemented in a transversal structure was found to successfully reduce the corrupting cardiac activity. This paper describes the cancellation of the corrupting cardiac activity from the recorded myoelectric activity using adaptive noise cancellation technique and the characteristic features of spectra of EMG signals.

An adaptive offset cancellation technique for adaptive filters

Offset may be introduced in the adaptation process in certain implementations of adaptive filters. The adaptive filters. The adaptive filter still converges with the offset, however, to nonoptimal tap weights with excess mean square error. Here, an offset cancellation technique, also adaptive, is proposed. A set of new taps is introduced to counteract the offset. The convergence of this adaptive cancellation technique is demonstrated analytically and by using computer simulation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Adaptive method for cancellation of respiratory artefact in electrogastric measurements.

Electrogastric measurements are useful for medical research and in clinical diagnosis. The measurements, however, contain very heavy respiratory artefact. Existing conventional frequency-domain filters cannot be used because of the possible overlap of the frequencies of the gastric signals and respiratory artefact. In the paper, the methods of measuring cutaneous and intraluminal gastric signals and reference respiratory signals are described. An adaptive cancellation technique is developed, which is simple and easy to implement for online processing. It is proved by experiments to be very efficient, i.e. the respiratory artefact can be completely cancelled, while the gastric signal component is not affected. Other possible applications in biomedical signal analysis are also discussed.