RF interference suppression for VDSL system

Recently, a novel transmission technique was proposed for delay-spread channels that guarantees a low peak-to-average power ratio while also having low computational complexity. In this paper, we extend the technique to systems where the symbol length or number of parallel channels is large, such as in very high speed digital subscriber line (VDSL) or multiple-input multiple-output (MIMO) systems respectively. While operational complexity is low, the computational cost of initialisation in a VDSL or MIMO channel appears, at first sight, to be prohibitive. We show that initialisation can be carried out efficiently. Having so enabled the technique, we present simulation results in a MIMO-VDSL environment which demonstrate its superiority in comparison to other popular techniques such as V-DMT and DMMT when clipping in the transmit power amplifier is a dominant consideration

Impulse noise is a potential impairment of very-high speed digital subscriber line (VDSL) services. VDSL systems are protected from impulse noise using a combination of Reed-Solomon coding and interleaving. Since there are two competing proposals for VDSL, the first one based on the use of QAM line code and the second one using DMT modulation, it is interesting to compare their performance in terms of immunity to impulse noise. The paper presents a comparison of the behavior of QAM-VDSL and DMT-VDSL in the presence of impulse noise in real configurations. The required interleaving delay to correct all the generated errors for both systems is investigated. It is shown that when no notches are used in the radio-amateur bands, QAM and DMT systems require similar delays in order to achieve the same level of protection against impulse noise. However, when notches are implemented, DMT-VDSL achieves higher rates than QAM-VDSL. Therefore, larger error-correcting code redundancy can be used, which results in lower end-to-end delays for DMT-VDSL systems.

This paper presents a study of the effects of bridged taps on very high-speed digital subscriber line (VDSL) transmission systems. It is shown that the short bridged taps; which affect VDSL signals, are much more damaging than the longer bridged taps, which affect other xDSL signals, such as high-rate digital subscriber line (HDSL) and asymmetric digital subscriber line (ADSL). Specifically, short bridged taps introduce a lot of linear distortion in the loop's transfer function. In addition, they also tend to introduce more overall propagation loss than longer bridged taps. The peak-power-to-average-power ratio (PAR) of the signal increases for the loop with short bridged taps, and thus more AID bits are needed in the implementation of a digital VDSL transceiver as compared to the loop with long bridged taps. The performance of various equalizer structures is discussed in the presence of a severe channel distortion caused by the bridged tap.

Measurements of both the Soil Moisture and Ocean Salinity (SMOS) and Aquarius L-band microwave radiometers show a significant presence of radio frequency interference (RFI), although they operate in a protected frequency band where transmission is prohibited. RFI detection and mitigation remain a challenging problem for both missions, especially for low or moderate (i.e., on the order of 10 K or less) amplitude contributions. An algorithm for low-level source detection and mitigation is already included in Aquarius data sets, and both Aquarius and SMOS have distinct attributes that can potentially enable further improvements in detection and mitigation of these sources to some degree. The combination of SMOS and Aquarius data sets may enable further future improvements as well. Initial efforts toward this goal are reported in this paper. Similarities and differences in RFI effects on SMOS and Aquarius are examined, with a particular focus on instrument properties that cause differences in received RFI power in SMOS and Aquarius observations of a specific source. A study is also performed of SMOS observations for regions reported by Aquarius to contain “low-level” RFI. It is shown that the detection of these sources in the SMOS data set is challenging and that the dependence of the SMOS third and fourth Stokes parameters on incidence angle makes the polarimetric features of SMOS difficult to utilize for low-level source detection. However, an angular fitting procedure suggested previously in the literature can, in some cases, detect such sources in horizontal and vertical polarizations.

The paper investigates the power control problem in a frequency-selective interference channel. A centralized power control algorithm is developed with the objective of maximizing the achievable rate region given an average power constraint for each user. The proposed algorithm is based on the multi-user discrete bit-loading algorithm that considers the power allocation over frequency and users simultaneously. Simulation results for very high-speed digital subscriber line (VDSL) systems show that the proposed algorithm achieves a larger rate region than that achieved by a power control algorithm based on iterative waterfilling.

Multi-input multi-output (MIMO) receivers have generally been designed and their communication performance analyzed under the assumption of additive Gaussian noise. Wireless transceivers, however, may also be affected by radio frequency interference (RFI) that is well modeled using non-Gaussian impulsive statistics. In this paper, we derive bounds on the communication performance for a two transmit, two receive antenna MIMO system in the presence of RFI. Our contributions include derivation of (1) channel capacity in the presence of RFI, (2) probability of symbol error for uncoded transmissions, and (3) Chernoff bound on the pairwise error probability and cutoff rate as a measure of the throughput performance for coded transmissions. Comparison with the communication performance bounds for receivers designed assuming additive Gaussian noise demonstrates degradation in communication performance in the presence of RFI.

Activity recognition is an important component of many pervasive computing applications. Device-free activity recognition has the advantage that it does not have the privacy concern of using cameras and the subjects do not have to carry a device on them. Recently, it has been shown that channel state information (CSI) can be used for activity recognition in a device-free setting. With the proliferation of wireless devices, it is important to understand how radio frequency interference (RFI) can impact on pervasive computing applications. In this paper, we investigate the impact of RFI on device-free CSI-based location-oriented activity recognition. We conduct experiments in environments without and with RFI. We present data to show that RFI can have a significant impact on the CSI vectors. In the absence of RFI, different activities give rise to different CSI vectors that can be differentiated visually. However, in the presence of RFI, the CSI vectors become much noisier and activity recognition also becomes harder. Our extensive experiments shows that the performance of state-of-the-art classification methods may degrade significantly with RFI. We then propose a number of counter measures to mitigate the impact of RFI and improve the location-oriented activity recognition performance. Our evaluation shows the proposed method can improve up to 10% true detection rate in the presence of RFI. We also study the impact of bandwidth on activity recognition performance. We show that with a channel bandwidth of 20 MHz (which is used by WiFi), it is possible to achieve a good activity recognition accuracy when RFI is present.

The problem of multiuser detection for upstream very-high-speed digital subscriber line (VDSL) transmission, where far-end crosstalk (FEXT) signals at the input of a VDSL receiver are viewed as interferers that share the same channel as the remote user signal, is addressed. Knowledge of the FEXT impulse responses at the central office, as well as upstream transmission based on multicarrier modulation by all remote users, are assumed. The joint application of upstream power back-off with a reduced-complexity decision-feedback (DFE) multiuser detector, where only the most significant crosstalk interferers are suppressed, is considered, and the coefficients of the minimum mean-square error structure are determined. Then a novel optimum power back-off algorithm is introduced, and its performance in terms of achievable rates evaluated. Finally, numerical results that illustrate the impact of power back-off on achievable performance of a VDSL system with multiuser detection are presented.

A microwave radiometer specifically designed to detect and mitigate many types of Radio Frequency Interference (RFI) is described. The L-band RFI Detection and Mitigation Testbed (DetMit Testbed) will not be optimized for radiometric observation as much as it is optimized for flexibility in the presence of RFI. While the DetMit Testbed will be a fully functional polarimetric L-band radiometer, the ultimate application of this instrument is not so much brightness measurements as it will be validation of RFI mitigation strategies for employment in future L-band (and other frequency) radiometers. The design approaches for the L-band RFI Detection and Mitigation Testbed are expected to apply to C- band and X-band, and presumably also to other frequencies of interest that experience RFI.

This document defines a portion of the Management Information Base (MIB) module for use with network management protocols in the Internet community.In particular, it describes objects used for managing the Line Code Specific parameters of Very High Speed Digital Subscriber Line (VDSL) interfaces using Single Carrier Modulation (SCM) Line Coding.It is an optional extension to the VDSL-LINE-MIB, RFC 3728, which handles line code independent objects.

The Aquarius/SAC-D mission operated between August 2011 and June 2015 with the main goal of providing global estimates of sea surface salinity (SSS). It comprised both active and passive microwave sensors operating at L-band to observe the same surface area almost simultaneously. Measurements from both instruments underwent subsequent filtering to mitigate the effect of Radio Frequency Interference (RFI). However, RFI cannot always be detected, especially when the level of interfering signals is comparable to that of the natural surface emission. A study was performed here to assess the amount of missed detection in certain ocean region where low-level interference is a problem. The approach is to estimate the statistics of RFI starting from the acquired antenna temperature samples. The statistics are then used to simulate RFI and study its detection by the RFI filter. The results of this simulation are compared with the RFI actually detected in the acquired samples to provide an estimate of the level of missed detection.

STARFIRE: An algorithm for estimating radio frequency interference in orbits around Earth

This article proposes a new precorrelation interference detection technique based on the nonnegative matrix factorization (NMF) for global navigation satellite system (GNSS) signals. The proposed technique uses the NMF to extract the time and frequency properties of the received signal from its spectrogram. The estimated spectral shape is then compared with the spectrogram’s time slices by means of a similarity function to detect the presence of radio frequency interference (RFI). In the presence of RFI, the NMF estimated spectral shape tends to be well-defined, resulting in high similarity levels. In contrast, in the absence of RFI, the received signal is solely comprised of noise and GNSS signals resulting in a noise like spectral shape estimate, leading to considerably reduced similarity levels. The proposal exploits these different similarity levels to detect the presence of interference. Simulation results indicate that the proposed technique yields increased detection capability with low false alarm rate even in low jammer-to-noise ratio environments for both narrow and wideband interference sources without requiring fine tuning of parameters for specific RFI types. In addition, the proposal has reduced computational complexity, when compared with an existing statistical-based detector.

Assessment of the occurrence of radio frequency interference with AMSR-E observations over India

Radio observations of cosmic ray air showers can characterize cosmic ray mass composition, via precise Xmax measurements, at the energies of the likely shift from Galactic to extragalactic sources. Advantages over other methods include lower cost instrumentation and the ability to observe in a range of weather conditions. However, detecting cosmic rays via their radio emission alone amid radio frequency interference (RFI), without reference to an alternate particle detector, is a significant challenge. The Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA) cosmic ray detection system uses a multistage RFI rejection process including FPGA and CPU processing to address this challenge and operate in the presence of RFI. The OVRO-LWA is a multi-use array of 352 dual-polarization dipole antennas operating at ~30—80 MHz. The array recently completed a major upgrade, including the addition of the cosmic ray detection system, which operates simultaneously with the other radio astronomy observing modes. Detections of cosmic ray candidates began in 2024. The dense antenna spacing of the OVRO-LWA offers the opportunity for testing and developing new Xmax reconstruction techniques, such as interferometric reconstruction. This presentation will describe the cosmic ray detection system, present the sample of cosmic ray candidates, and discuss plans for the future.