Interference cancellation in respiratory sounds via amultiresolution joint time-delay and signal-estimation scheme

This paper is concerned with the problem of cancellation of heart sounds from the acquired respiratory sounds using a new joint time-delay and signal-estimation (JTDSE) procedure. Multiresolution discrete wavelet transform (DWT) is first applied to decompose the signals into several subbands. To accurately separate the heart sounds from the acquired respiratory sounds, time-delay estimation (TDE) is performed iteratively in each subband using two adaptation mechanisms that minimize the sum of squared errors between these signals. The time delay is updated using a nonlinear adaptation, namely the Levenberg-Marquardt (LM) algorithm, while the function of the other adaptive system-which uses the block fast transversal filter (BFTF)-is to minimize the mean squared error between the outputs of the delay estimator and the adaptive filter. The proposed methodology possesses a number of key benefits such as the incorporation of multiple complementary information at different subbands, robustness in presence of noise, and accuracy in TDE. The scheme is applied to several cases of simulated and actual respiratory sounds under different conditions and the results are compared with those of the standard adaptive filtering. The results showed the promise of the scheme for the TDE and subsequent interference cancellation     

Analysis of a simple successive interference cancellation scheme ina DS/CDMA system

Compensating for near/far effects is critical for satisfactory performance of DS/CDMA systems. So far, practical systems have used power control to overcome fading and near/far effects. Another approach, which has a fundamental potential in not only eliminating near/far effects but also in substantially raising the capacity, is multiuser detection and interference cancellation. Various optimal and suboptimal schemes have been investigated. Most of these schemes, however, get too complex even for relatively simple systems and rely on good channel estimates. For interference cancellation, estimation of channel parameters (viz. received amplitude and phase) is important. We analyze a simple successive interference cancellation scheme for coherent BPSK modulation, where the parameter estimation is done using the output of a linear correlator. We then extend the analysis for a noncoherent modulation scheme, namely M-ary orthogonal modulation. For the noncoherent case, the needed information on both the amplitude and phase is obtained from the correlator output. The performance of the IC scheme along with multipath diversity combining is studied     

Interference cancellation with an array processing MLSE receiver

the capacity and transmission quality in cellular systems can be improved by using receivers that mitigate cochannel interference and multipath propagation. In this paper, a class of multichannel maximum likelihood sequence estimation (MLSE) receivers is developed for this purpose. Interference mitigation is accomplished via adaptive antenna arrays, while multipath propagation is combated via MLSE. Practical considerations are included, such as fixed front-end filtering, sampling, and estimation of parameters from received samples. Maximal ratio combining, conventional array processing and metric combining (MC) are shown to be special cases of the proposed receivers. Performance is evaluated for π/4-shift DQPSK, using the parameters and transmission format of the time-division multiple-access (TDMA)-based IS-136 (D-AMPS) digital cellular standard. Semi-analytical performance predictions are developed which confirm simulation trends. The results show that these receivers can operate at significantly lower carrier-to-interferer (C/I) levels than conventional MC receivers     

INTERFERENCE CANCELLATION FOR MOBILE DISPERSIVE CHANNELS

A robust interference canceller for Multi-Carrier Code Division Multiple Access (MC-CDMA) using Orthogonal Frequency Division Multiplexing (OFDM) in Rayleigh fading is proposed. This interference canceller is robust in the sense that it cancels Inter-Carriers Interference (ICI) and is suitable for use in dispersive channels. To come up the effects of the slgnal dispersion, Doppler shifts and delay spreads on the performance of MC-CDMA systems over mobile fading channels, this interference canceller exploits the merit of the orthogonal signaling and pilot signals to evaluate the channel parameters. This interface canceller is well suited to work in iterative turbo interference cancellation.     

Interference cancellation for a multicellular CDMA environment

This paper considers the performance of adaptive interference cancellation applied to a CDMA microcellular environment, by employing a circular cell geometry and a closed form expression for the Bit Error Rate of a CDMA system with interference cancellation to analyze the effect of out-of-cell interference. Results are presented which indicate that out-of-cell interference will severely limit the benefits of interference cancellation in a multicellular system. Attempts to cancel all out-of-cell interference will further degrade performance. However, the use of selective interference cancellation in which only the strongest out-of-cell interferers are cancelled may result in significant performance enhancement. These results agree closely with those obtained using a hexagonal geometry.Portions of this paper have been presented at the PIMRC'95 conference in Toronto, Canada.     

LMS-LMF adaptive scheme for echo cancellation

The authors present a novel algorithm for echo cancellation. The algorithm consists of simultaneously applying the LMS algorithm to the near-end section of the echo canceller, and a controlled mixed LMS-LMF algorithm to the far-end section. This combination results in a substantial improvement in performance of the proposed scheme over the LMS and the LMF algorithms     

Interference avoidance and cancellation in automotive OFDM radar networks

With increasing use of millimeter-wave radars in driving safety applications, interference between vehicles becomes a significant issue. Moreover, oscillator imperfections and relative velocity effects induce inter-carrier interference (ICI) owing to frequency offset, leading to degradation of target detection. In this paper, time-frequency resources are divided into several orthogonal logical channels according to the time-frequency division (TFD) scheme. We propose a two-stage interference mitigation method. First, an interference avoidance technique is designed for each piece of radar equipment (RE) to select logical channels with the least ICI. Then, each RE reconstructs and cancels interference according to estimated parameters based on the proposed interference cancellation technique. Computer simulations reveal that the proposed interference avoidance technique can approximately achieve the performance of ground truth, especially when the number of interferers is small. In addition, noise enhancement effects can be effectively mitigated through the proposed cancellation technique.

     

Analysis of ICI cancellation scheme in OFDM systems with phase noise

Phase noise in orthogonal frequency division multiplexing (OFDM) systems destroys the orthogonality of the subcarriers and inter-carrier interference (ICI) is caused. In this paper, the ICI self-cancellation scheme is adopted to combat the ICI caused by phase noise in OFDM systems. Moreover, the error coefficients are defined and the theoretical expressions of carrier to interference ratio (C/I) with and without the ICI self-cancellation scheme are separately derived. From the simulation results, it is verified that the ICI self-cancellation scheme obviously decreases the amount of the ICI caused by phase noise and the improvement of C/I could reach 10 dB when the normalized 3 dB bandwidth of phase noise is 0.4. However, the convolutional coding OFDM (COFDM) system could supply more performance gain at the expense of increasing decoder complexity compared to OFDM system with the ICI self-cancellation scheme in the frequency-selective channel.     

Interference cancellation for cellular systems: a contemporary overview

Cellular networks today are interference-limited and only becomes increasingly so in the future due to the many users that need to share the spectrum to achieve high-rate multimedia communication. Despite the enormous amount of academic and industrial research in the past 20 years on interference-aware receivers and the large performance improvements promised by these multi-user techniques, today's receivers still generally treat interference as background noise. In this article, we enumerate the reasons for this widespread scepticism, and discuss how current and future trends increases the need for and viability of multi-user receivers for both the uplink, where many asynchronous users are simultaneously detected, and the downlink, where users are scheduled and largely orthogonalized; but the mobile handset still needs to cope with a few dominant interfering base stations. New results for interference cancelling receivers that use conventional front-ends are shown to alleviate many of the shortcomings of prior techniques, particularly for the challenging uplink. This article gives an overview of key recent research breakthroughs on interference cancellation and highlights system-level considerations for future multi-user receivers.     

Interference cancellation schemes for MIMO MC-CDM in fading channels

A novel interference cancellation (IC) scheme for MIMO MC-CDM systems is proposed. It is shown that the existing IC schemes are suboptimum and their performance can be improved by utilising some special properties of the residual interference after interference cancellation.     

An inter-lighting interference cancellation scheme for MISO-VLC systems

In this paper, we propose an inter-lighting interference cancellation (ILIC) scheme to reduce the interference between adjacent light-emitting diodes (LEDs) and enhance the transmission capacity of multiple-input–single-output (MISO)-visible light communication (VLC) systems. In indoor environments, multiple LEDs have normally been used as lighting sources, allowing the design of MISO-VLC systems. To enhance the transmission capacity, different data should be simultaneously transmitted from each LED; however, that can lead to interference between adjacent LEDs. In that case, relatively low-received power signals are subjected to large interference because wireless optical systems generally use intensity modulation and direct detection. Thus, only the signal with the highest received power can be detected, while the other received signals cannot be detected. To solve this problem, we propose the ILIC scheme for MISO-VLC systems. The proposed scheme preferentially detects the highest received power signal, and this signal is referred as interference signal by an interference component generator. Then, relatively low-received power signal can be detected by cancelling the interference signal from the total received signals. Therefore, the performance of the proposed scheme can improve the total average bit error rate and throughput of a MISO-VLC system.     

Effective interference cancellation scheme based on smart antennas

An effective interference cancellation scheme based on a new multipath model is introduced. A CM (constant modulus) equalisation approach based on an adaptive array with a spatial prefilter is derived. It has been proven by numerical simulation that this method achieves a better performance, even under serious multipath conditions     

一种基于串行干扰抵消的OFDM UWB多址方案

研究了高峰值传输速率时UWB系统的多址性能,对一种干扰抑制的OFDM传输方案进行了调整,提出了一种基于串行干扰抵消的两用户OFDM UWB多址方案.仿真结果显示所提出的方案可适度改善无纠错编码的OFDM UWB系统的误符号性能.     

A new evolving-update-based feedback cancellation scheme for hearing aids

This paper proposes an efficient adaptive feedback canceller (AFC) for hearing aid, which provides satisfactory performance both in sparse and in dispersive conditions as well as can adapt according to the variations in the sparseness level of the feedback path for coloured signal as input. This is achieved by incorporating the measure of sparseness intensity and the variable step size to the memory-improved proportionate affine projection algorithm (MIPAPA), and hence, an improved MIPAPA (IMIPAPA) is proposed. Further, in order to reduce the computations incurred by the AFC, an evolving-update IMIPAPA (E-IMIPAPA) is introduced, employing an intermittent update of taps of the adaptive filter by simultaneously adjusting the update interval. The proposed E-IMIPAPA is applied to the two-microphone-based AFC. The results of simulation-based experiments show the effectiveness of the proposed algorithm as compared to the existing methods for feedback cancellation in hearing aid in terms of misalignment and added stable gain. The proposed AFC model is further extended to the multiple-microphone and single-speaker set-up.     

Echo cancellation scheme for high speed digital subscriber lines

The authors discuss the implementation of a computationally efficient two stage echo cancellation system for high speed data transmission. In addition to a substantial reduction in hardware complexity, the two stage echo canceller offers the advantage of a speedier convergence compared to the conventional FIR filter     

Interference cancellation in GPS receiver using noise subspace tracking algorithm

In this paper, we address the problem of interference cancellation in global positioning system (GPS) receiver using a two-step approach: subspace projection technique and maximum signal-to-noise ratio (MSNR) beamforming. The interference signals can be effectively suppressed by projecting the received signal on the noise subspace. Here noise subspace tracking algorithm is employed to estimate the noise subspace directly. We then apply a beamformer to maximize the signal-to-noise ratio of the interference-free signal. Simulation results show that our approach can effectively eliminate the strong interference and enhance the performance of the GPS receiver.     

OFDM盲载波间干扰抑制与同步算法研究

针对载波频偏引起的子载波间干扰问题,提出一种基于独立分量分析的OFDM载波频率同步算法。本算法直接实现载波频率同步,可以避免基于导频机制的频偏估计和由频偏估计误差带来的频谱效率降低与性能损失。首先建立含频偏OFDM独立分量分析模型,然后从最大似然原则得到分离的代价函数,结合自然梯度优化得到OFDM源信号实现载波频率同步。理论分析表明,提出的算法不仅具有基于最大似然的频偏补偿性能而且提高了系统的输出信噪比。最后,仿真分析证明了算法的有效性。      

A bandwidth‐efficient cooperative relaying scheme with hard interference cancellation and iterative decoding

This paper considers a coded cooperative relaying scheme in which all successfully decoded signals from multiple sources are simultaneously forwarded by a multi‐antenna relay to a common multi‐antenna destination to increase bandwidth efficiency. Iterative decoding with hard interference cancellation is used at destination to recover user information. By using orthogonal transmission from sources to avoid their mutual interference, the multi‐antenna relay offers receive space diversity that greatly enhances the decoding performance at the relay. This makes the source‐relay transmission more robust, less sensitive to the source‐relay link SNR, and hence increases the contribution of the relay in cooperative transmission. Simulation results show that the proposed scheme significantly outperforms direct transmission under the same transmit power and bandwidth efficiency. Copyright © 2009 John Wiley & Sons, Ltd.     

Interference cancellation enhancement through generalized widely linear equalization in QAM systems

In this paper, we introduce a generalized widely linear (WL) equalizer for quadrature amplitude modulation (QAM) systems with single/multiple antennas. In our proposed implementation, the WL receiver first separates the in-phase (I) and quadrature (Q) parts of the complex-valued baseband received signal and jointly filters the two branches for signal detection. Infinite length WL minimum mean-square error (WL-MMSE) linear, and WL decision-feedback-equalizer (WL-DFE) settings are derived and performance is analyzed in co-channel interference limited channels. It is shown that, in frequency selective Rayleigh fading channels, the interference cancellation (IC) gain depends mainly on the rank (r) of the interference correlation matrix (ICM) which is defined as the covariance of the vector-valued signal which consists of the real and imaginary parts of the noise-plus-interference signal collected at multiple antenna branches. Assuming that the DFE feedback path is error free, we show that a WL QAM receiver with N antennas exhibits full IC capability (that is complete interference removal) when the ICM is rank deficient i.e., when: r ≪ 2N. This condition implies that a WL-DFE receiver can reject any combination of M1 pulse-amplitude-modulation (PAM) and M2 QAM interferers satisfying the constraint: M1 + 2M2 ≪ 2N. Simulation results show that, in the presence of PAM-type interference, the gain of WL-DFE is reduced by decision feedback errors while the IC benefit of WL-MMSE is limited by the noise enhancement problem. Nevertheless, the proposed receivers are shown to be useful in cellular systems that employ a combination of PAM and QAM schemes.     

Successive relaying secure transmission scheme based on inter-relay interference cancellation

A secure scheme based on inter-relay interference cancellation was proposed to solve untrusted relay eavesdropping problem in successive relaying systems.First inter-relay interference between trusted relay and untrusted relay was exploited as artificial noise to degrade untrusted relay’s eavesdropping condition,then interference iterative cancellation was adapted to improve signal quality at legitimate user by making use of correlation between signals in time domain.Based on this,a quick power allocation algorithm aiming to minimize untrusted relay’s sum rate was proposed.Analysis and simulation results show that the proposed scheme suppress untrusted relay’s eavesdropping without loss of communication efficiency,a promotion of at least 2 bit·s^-1·Hz^-1in secrecy rate can be observed.