In-band Interference Research Articles

Analysis and Rate Optimization of OFDM-Based Cognitive Radio Networks Under Power Amplifier Nonlinearity

The nonlinear behavior of power amplifier (PA) in orthogonal frequency-division multiplexing (OFDM)-based cognitive radio (CR) system introduces in-band and adjacent channel interferences. The power in the adjacent channels is an important issue in the CR because it can act as interference to primary users. In this paper, we derive a closed-form expression for the leakage power at adjacent channels when CR devices use OFDM modulation. Moreover, the PA nonlinearity creates in-band distortion that produces intercarrier interference and reduces the secondary system capacity. To control this effect, we derive the optimum power scaling factor for the input signal that maximizes the secondary user rate. The optimization process is executed by considering nonlinear effects on signal-to-interference-and-noise ratio under the constraints of the powers in the adjacent channels. The power in the adjacent channels should not exceed the interference temperature limit. The analytical results are verified by simulation studies.

An Ultra Low Energy FSK Receiver With In-Band Interference Robustness Exploiting a Three-Phase Chirped LO

An ultra-low-energy Binary Frequency Shift Keying (BFSK) receiver is proposed. It features improved in-band interference tolerance by chirping the transmission frequency. To reduce the receiver power consumption, a novel three-phase passive mixer along with a three stage digitally controlled ring oscillator is proposed, while still allowing quadrature detection. A mixer-first direct conversion receiver architecture moves the required gain to lowest frequency and lowest bandwidth to reduce power consumption. A low power flip-flop based BFSK demodulator is proposed that reduces the baseband power further. The receiver is designed and fabricated in a 65 nm complementary metal-oxide-semiconductor process. It consumes 219 μW from 1.2 V power supply, while having a sensitivity of -70 dBm for a bit error rate of 0.1% at 2.4 GHz. Except the off-chip 64 MHz clock generation, the total receiver requires 27 pJ/bit. Using a chirped clock spreading of 360 MHz and chirp repetition rate of 1 MHz, it can tolerate up to -8 dB signal to interference ratio for all interferer frequencies. This is 13.5 dB better than previously reported in literature and 12 dB better than ideal noncoherent BFSK receiver interference robustness.

Receiver Performances Considering Effects of Gain Control and Quantization in FDM-Based Narrowband Communication Systems

In wireless receivers, in order to prevent the saturation of a received signal in an analog-to-digital converter (ADC), an automatic gain control (AGC), which maintains the amplitude of an analog signal at an appropriate fixed level, is frequently employed. This paper discusses the effects of gain control and quantization in the AGC and ADC on the receiver performance in frequency division multiplexing-based narrowband communication systems. Each communication channel is very narrow in these systems, so the channels are packed without breaks, making it difficult to extract the desired signal using an analog bandpass filter. Therefore, other multiple communication signals are in-band interference signals in these systems. In comparison with a single interference signal, a peak amplitude of multiple interference signals is greater than the that of single interference signal given the same interference power. It is well known that signals having a large peak value cause the degradation of bit resolution due to the AGC and ADC processes. The purpose of this paper is to provide a theoretical and numerical analysis of the effects of gain control and quantization on the receiver performance in such an environment. The analysis results indicated that (i) in-band interference signals decreased the bit resolution of the desired signal amplitude because of these processes and (ii) the effects of these processes depend on the amplitude intensity and the number of in-band interference signals, given the same interference power.

Interference Rejection in UWB LNA using Front-End Triode MOSFET

In this study, an Ultra Wide Band Low Noise Amplifier (UWB LNA) with new input stage for interference rejection is presented. In this scheme, a common gate front end MOS device in triode mode is used to reject in-band and out-band interferences. Furthermore, advantage of weak inversion mode of MOS device is used. While this stage has no DC power consumption, it is possible to easily reject in band and out band interferences with 12.5 and 9.2 dB, respectively. In order to increase power gain of the circuit two stages are added as an amplifier to the circuit. Also, in order to improve the Noise Figure (NF) and bandwidth of the circuit, the advantages of thermal noise cancellation technique in the second stage and the series-peaking method in the output buffer are used. The circuit is design in 0.18 μm technology. Simulation results show peak gain of 17.6 dB in the low band (3.1-4.75 GHz) and 15.6 dB in the high band (6.1-10.6 GHz). Minimum NF in mentioned frequency band is 3 and 2.3 dB, respectively. Hence, this circuit rejects in band and out band interferences 15.6 and 11.5 dB, respectively, while UWB LNA consumes 16 mW DC power from 1.8 V. The s11 is less than -9.6 dB over entire bandwidth since worst value of IIP3 over entire bandwidth is -14 dBm which occurs at 10.6 GHz.

Resolution optimization with irregularly sampled Fourier data

Image acquisition systems such as synthetic aperture radar (SAR) and magnetic resonance imaging often measure irregularly spaced Fourier samples of the desired image. In this paper we show the relationship between sample locations, their associated backprojection weights, and image resolution as characterized by the resulting point spread function (PSF). Two new methods for computing data weights, based on different optimization criteria, are proposed. The first method, which solves a maximal-eigenvector problem, optimizes a PSF-derived resolution metric which is shown to be equivalent to the volume of the Cramer–Rao (positional) error ellipsoid in the uniform-weight case. The second approach utilizes as its performance metric the Frobenius error between the PSF operator and the ideal delta function, and is an extension of a previously reported algorithm. Our proposed extension appropriately regularizes the weight estimates in the presence of noisy data and eliminates the superfluous issue of image discretization in the choice of data weights. The Frobenius-error approach results in a Tikhonov-regularized inverse problem whose Tikhonov weights are dependent on the locations of the Fourier data as well as the noise variance. The two new methods are compared against several state-of-the-art weighting strategies for synthetic multistatic point-scatterer data, as well as an ‘interrupted SAR’ dataset representative of in-band interference commonly encountered in very high frequency radar applications.

Miniaturized UWB Filters Integrated With Tunable Notch Filters Using a Silicon-Based Integrated Passive Device Technology

This paper reports on the implementation of miniaturized ultra-wideband filters integrated with tunable notch filters using a silicon-based integrated passive device technology. An ultra-wideband bandpass filter is realized on a micromachined silicon substrate, showing an insertion loss of 1.1 dB, return loss of better than 15 dB, and attenuation of more than 30 dB at both lower and upper stop-bands, with a spurious-free response up to 40 GHz. The filter occupies only 2.9 mm 2.4 mm of die area. To address the in-band interference issues associated with ultra-wideband communication, very compact tunable notch filters are monolithically integrated with the bandpass filters. A two-pole tunable notch filter integrated with an ultra-wideband filter provides more than 20 dB rejection in the 5-6 GHz range to reject U-NII interferences, with a total footprint of 4.8 mm 2.9 mm. The power handling, linearity, and temperature stability of filters are characterized and presented in this paper.

Digital predistortion technique with in-band interference optimisation applied to DVB-T2

The efficient transmission and nonlinear modelling of orthogonal frequency division multiplexing (OFDM) signals are difficult to address owing to the special characteristics of this modulation scheme. Proposed is a digital predistortion technique suitable for the implementation in an OFDM transmitter to optimise the in-band interference caused by the nonlinear distortion generated in the amplification chain. The approach is experimentally validated by its application in one of the world's most advanced broadcasting systems, achieving an outstanding linearisation performance in the transmitter; specially for the in-band interference, a modulation error ratio (MER) of 42.1 dB is obtained.

Multiple narrowband interference suppression for UWB communication systems in Nakagami fading channels

This paper investigates the performance of ultra-wideband (UWB) communication systems in the presence of multiple in-band narrowband interference signals in a Nakagami-m frequency selective fading channel. The UWB systems have a restraint on their transmission power levels in order to control its interference to other in-band operating services; however UWB systems unavoidably suffer from the interference caused by the coexisting systems such as the IEEE802.11a signal, making it extremely difficult to maintain adequate signal-to-noise-and interference ratio (SNIR) levels. In order to mitigate the impact of such strong interference the paper proposes a suppression technique which introduces spectral nulls at the operating frequencies of the narrowband interference (NBI) signals. The bit error rate performance of the proposed scheme is derived in a Nakagami multi-path frequency selective fading channel and validated with simulation. The results show that with the use of such proposed technique the NBI impact can be effectively suppressed leading to an improvement to the bit error rate performance of the UWB communication systems. A comparison with a notch filter-based case is also presented where it will be shown that the proposed technique out performs a perfectly tuned notch filter.

An Ultra-Low Voltage, Low-Noise, High Linearity 900-MHz Receiver With Digitally Calibrated In-Band Feed-Forward Interferer Cancellation in 65-nm CMOS

We present an ultra-low voltage, highly linear, low noise integrated CMOS receiver operating from a 0.6-V supply. The receiver incorporates programmable, in-band feed-forward interferer cancellation at the baseband to obtain high linearity and low noise operation at ultra-low supply voltages. Being able to reject adjacent channel or far-out blockers, the digitally calibrated interferer cancellation improves the IIP3 and IIP2 by more than 13 dB and 8 dB respectively with very little impact on the receiver noise figure. As such, it breaks the trade-off between linearity and noise figure, making it possible to use a high-gain RF front-end to achieve low noise figure without affecting the linearity of the ultra-low voltage baseband circuits. The 0.6-V 900-MHz direct-conversion receiver prototype integrates a differential LNA, RF transconductors, linear quadrature current driven passive mixers, feed-forward interferer cancellation circuits, baseband variable gain transimpedance amplifiers and second-order channel-select filters. It has a nominal conversion gain of 56.4 dB, noise figure of 5 dB, IIP3 of -9.8 dBm and IIP2 of 21.4 dBm. The receiver operates reliably from 0.55-0.65 V, consumes 26.4 mW and occupies an active area of 1.7 mm2 in a 65-nm low-power CMOS process, of which the feed-forward interferer cancellation circuits consume 11.4 mW and occupies 0.43 mm2 .

Method for Assessing the Interference Impact on GNSS Receivers

The definition of new families of curves named interference error envelope (IEE) and interference running average (IRA) is presented. Such tools are able to assess the impact of RF interference on different GNSS receivers, taking into account the features of the in-band interference source. In fact the actual impact on the final performance is strictly related to the specific receiver architectures. Continuous wave (CW) and wide band (WB) interference signals are considered in order to assess by means of IEE and IRA the robustness of new modulations based on the multiplexed binary offset carrier (MBOC) scheme for several receiver configurations, by varying the discriminator spacing, type, and the front-end filter bandwidth. Interference robustness is evaluated and compared with those of the well-known binary phase shift keying (BPSK) and binary offset carrier BOC(1,1) modulations. Simulation and theoretical results are validated by means of laboratory tests, proving the reliability of IEE curves for interference impact assessment.

Spectrum Broadening Due to Phase Noise Interaction in Cognitive Radio Systems

Spectrum broadening due to the interaction of local oscillator (LO) phase noise with an adjacent channel signal is analyzed, and applied to the situation where a cognitive radio (CR) detector experiences in-band interference from a strong adjacent channel signal. Expressions for the resulting in-band interference and modified detection performance are presented.

Min-norm method for estimating delay and Doppler profiles from FMCW channel data with in-band interference

The min-norm (MN) method is shown to improve estimates of delay profile and Doppler spectrum from frequency modulated continuous-wave (FMCW) channel data corrupted with in-band interference. Results of MN estimates are examined by comparing with those obtained from FFT processing.

Investigation of the Performance of Multiband Orthogonal Frequency Division Multiplexing Ultrawideband Over Fiber Transmission Under the Presence of In-Band Interferers

Multiband (MB) orthogonal frequency division multiplexing (OFDM) ultrawideband (UWB) wireless, which provides high-data-rate access, must be distributed by use of optical fiber. UWB receivers are anticipated to operate under hostile interference environments. So the study of the coexistence of various communication standards with MB-OFDM UWB over fiber is an important issue. The performance of MB-OFDM UWB over fiber transmission system is investigated, considering the effect of in-band narrowband jammers such as WiMAX, MIMO WLAN, WLAN, and marine radar. Experiments were performed to show the effect of fiber transmission under various interferer power levels. It is found that in-band interferers can cause severe degradation in system performance if any interferer to the UWB peak power ratio is not held below a certain level. The results also show that MB-OFDM UWB over fiber transmission is more vulnerable to certain interferers such as WiMAX and radar signals than to the other in-band jammers.

On the cumulative distribution function of quadratic-form receivers over generalized fading channels with tone interference

In this paper, we develop a general and unified framework for estimating the Cumulative Distribution Function (CDF) of quadratic-form receivers. The expression of the CDF that we finally achieve takes on the form of a single integral with finite limits and integrand composed of elementary functions, which can be readily integrated using standard techniques. In particular, the specific contribution of this manuscript is twofold: i) we present a comprehensive framework for the analysis of multi-channel reception systems using either non-coherent or differentially-coherent detectors, diversity systems with practical (i.e., noisy) channel estimators, and Transmitted-Reference (TR) receiver architectures working in frequency-selective fading channels, and ii) we show that the framework can be efficiently used for performance assessment of wireless systems over generalized fading channels and, under mild assumptions, over generalized fading channels further impaired by in-band multi-tone interference.

In-band interference reduction in FMCW channel data using Prony modelling

He is shown that Prony modelling can be used to reduce the effect of in-band interference in frequency modulated continuous-wave (FMCW) channel data. Results of the modelling are examined by comparing average power delay profiles and Doppler spectra with those obtained from FFT processing.

Downlink co-channel interference cancellation in multihop relay networks

In this paper, we study the use of iterative multi-user detectors for co-channel interference suppression in wireless cellular systems. We investigate the benefits of using iterative interference cancellation in the mobile receiver in the downlink scenario of traditional single-hop wireless cellular networks as well as two-hop relay networks. To illustrate these benefits, as an example we consider a receiver with a single receive antenna that is capable of detecting and cancelling a single in-band interferer that uses the same coding and modulation scheme as the desired signal. Simulation results show significant improvements with iterative interference cancellation in terms of the average system throughput and outage probability. Because the interference canceller is so effective, more aggressive frequency reuse schemes can be now considered, such as using smaller cluster sizes, using 3-sectored cells where all sectors share the same frequency band, and using non-orthogonal channels for relaying.

Analysis on IR/TR-UWB Interference against Narrowband Systems

This paper presents the analysis of in-band interference caused by pulse-based ultra-wideband (UWB) systems. The analysis contains both plain Impulse Radio UWB (IR-UWB) and Transmitted Reference UWB (TR-UWB) systems as a source of interference. The supposed victim is a narrowband BPSK system with a band-pass filter. The effect of pulse-based UWB systems is analyzed in terms of bit error rate. The analysis is given in terms of the specific combinations of pulse repetition frequency and center frequency of the narrowband bandpass filter. In those situations, the UWB interference cannot be modeled as a Gaussian noise. It also manifests situations in which the victim is under the severest or the slightest interference from TR-UWB. According to its result, the analysis is validated via simulation.

Adaptive Narrowband Interference Suppression in Multiband OFDM Receivers

The analysis and optimization of a notch filter to combat in-band narrowband interference (NBI) for multiband orthogonal frequency division multiplexing (MB-OFDM)-based ultra-wideband (UWB) systems is presented. Unintentional radiation of electronic devices can reside in the UWB band and jam the communication. Erasing the interference with a programmable analog notch filter reduces the requirement for the analog-to-digital converter resolution in the presence of NBI. The order and approximation of the notch filter are determined, and the filter’s bandwidth is optimized to minimize the packet error rate. Simulation results indicate that the UWB system with suppression scheme can handle up to 14 dB more in-band interference power.

차세대 위성항법체계 갈릴레오 센서스테이션 유치 후보지 전파 수신환경 조사: I. KVN 탐라전파천문대 인근 부지에 대한 2006년 한국천문연구원 조사 결과

2007년에 Giove-A 실험위성의 항법메시지 송신 시험이 성공적으로 끝마침으로써, 차세대 위성 항법시스템인 갈릴레오 계획이 초기궤도 검증단계를 앞두고 있다. 한국천문연구원의 우주측지연구부와 전파천문연구부는 제주 탐라대학교 내 유치 후보지에 대한 갈릴레오 센서 스테이션 전파 수신환경 공동조사를 2006년 8월 3일부터 5일까지 실시했다. 전계강도 스펙트럼은 전 대역<TEX>$(800{\sim}2000MHz)$</TEX>과 내 대역(E5, E6, L1 밴드)에 대해서 24시간 주파수 영역 관측을 했다. 이 단계에서 관측된 강한 내 대역 간섭 신호에 대해서 시간영역 분석을 했다. As the next generation of global satellite navigation system, the Galileo project is about to witness an initial orbit validation stage as the successful test of navigation message transmission from Giove-A in 2007. The Space Geodesy division ana the Radio Astronomy division of the Korea Astronomy & Space Science Institute had collaborated on the field survey for the Galileo Sensor Station (GSS) RF environment of the proposed site near Jeju Tamla University from August 3rd to August 5th, 2006. The power spectrums were measured in full-band <TEX>$(800{\sim}2000MHz)$</TEX> and in-band (E5, E6 and L1 band) in frequency domain for 24 hours respectively. Finally, we performed a time domain analysis to characterize strong in-band interference source based on the result of the previous step.

An Analog Approach to Suppressing In-Band Narrow-Band Interference in UWB Receivers

Due to the huge bandwidth of ultra-wide-band (UWB) systems, in-band narrow-band interference (NBI) may hinder receiver performance. Sources of potential NBI that lie within the IEEE 802.15.3a UWB bandwidth are presented. To combat interference in multi-band orthogonal frequency-division multiplexing (MB-OFDM) UWB systems, an analog notch filter is designed to be included in the UWB receive chain. The filter's architecture is based on feedforward subtraction of the interference, and includes a least-mean-square (LMS) tuning scheme to match amplitudes of the two paths. An 8-bit discrete control is used to adjust the filter's center frequency across the UWB baseband. It was fabricated in TSMC's 0.18-mum process, and experimental results are provided