Adaptive non-linear chirp UWB waveform design for multiple narrowband interferences suppression

To improve the performance of the ultra-wideband (UWB) system against multiple interferences existed in wireless personal area network (WPAN), such as narrowband interference (NBI), multiple-access interference (MAI), and multipath interference (MI), we present an orthogonal complementary code (OCC)-based UWB system with modified chirp waveforms. Considering the time–frequency characteristics of the chirp functions and the principle of NBI suppression, we first propose the modified linear and nonlinear chirp function-based flexible UWB pulses to suppress the multiple NBIs. Furthermore, with the implementation of OCC spread modulation, the modified chirp waveform-based UWB system is presented to effectively alleviate the influence of the MAI and MI. Simulation results and analysis validate the efficiency of the modified chirp pulse-based OCC-UWB system in the suppression of NBIs, MAI, and MI.

Narrow-band interference (NBI) from the coexisting narrow-band services affects the performance of ultra wideband (UWB) systems considerably due to the high power of these narrow-band signals with respect to the UWB signals. Specifically, IEEE 802.11a systems which operate around 5 GHz and overlap the band of UWB signals may interfere with UWB systems significantly. In this paper, we suggest a novel NBI suppression technique based on singular value decomposition (SVD) algorithm in time hopping UWB (TH-UWB) systems. SVD is used to approximate the interference which then is subtracted from the received signals. The algorithm precision and closed-form bit error rate (BER) expression are derived in the wireless multipath channel. Comparing with the conventional suppression methods such as a notch filter and a RAKE receiver, the proposed method is simple and robust and especially suitable for UWB systems.

Adaptive pulses in ultra wideband (UWB) wireless communication system are applied by forming notches at some frequencies as a way to suppress its interference to the existing narrowband systems. This paper proposes a novel method in designing adaptive pulses by using the Cognitive Radio technology and Parks-McClellan algorithm. Cases of arbitrary narrowband interferences are studied. The simulation results show that the power spectrum density of the proposed pulses not only meets the constraints of the FCC indoor mask but also avoid the narrowband interferences. The comparison of bit error rate performance is presented by using the proposed pulses and the fifth-order derivative Gaussian pulse to the time hopping UWB system in the additive white Gaussian noise channel. With low computational complexity, the proposed pulses have lower bit error rate and hence improve whole UWB system performance.

We propose a direct-sequence pulse-amplitude modulation (DS-PAM) ultra-wideband (UWB) system which employs a non-linear chirp waveform instead of the conventional Gaussian monocycle in this paper.In the approved frequency for UWB, there exist myriad narrowband interferers.Specifically, we focus on the mutual interference between UWB systems and 802.11aWLAN.This paper offers a method to suppress this inband narrowband interference by introducing a kind of non-linear chirp waveform.Using the proposed non-linear chirp waveform, the effects of one or more narrowband interference sources with different frequencies can be suppressed.System performance of UWB systems in the narrowband interference environment can be improved.Computer simulations with additive white Gaussian noise successfully demonstrate an increase in performance with the proposed system as compared to traditional linear chirp systems.

In order to alleviate the narrowband interference (NBI) to ultra wideband (UWB) systems, we propose two non‐linear UWB chirp waveforms based on the arctrigonometric and archyperbolic function in this paper. The proposed UWB pulses can obtain good performance in NBI suppression. Both of the two chirp pulses require only the time domain processing because of the inherent relationship between the frequency domain and the time domain. Theoretical analysis and simulation results show that the direct sequence pulse binary amplitude modulation (DS‐BPAM) UWB systems with the proposed chirp waveforms can achieve excellent NBI suppression performance and outperform the linear chirp waveform based UWB system significantly. Copyright © 2010 John Wiley & Sons, Ltd.

Time-hopping ultra wideband (TH-UWB) and direct-sequence ultra wideband (DS-UWB) systems are among the standards proposed for UWB communications scenarios. A general unified mathematical approach has been proposed for calculating the bit error rate (BER) for both TH-UWB and DS-UWB systems in the presence of multiple-user interference and a strong narrow-band interference in a multi-path scenario. Unlike many other mathematical models that provide upper or lower bounds for BER, this model calculates the exact values for BER in given scenarios. A partial rake receiver has been chosen as the receiving terminal. The modified Saleh-Valenzuela channel model has been used in this analysis. The model can asses the effect of any given narrow-band interfering systems. For the purpose of simulation, the narrow-band interfering system used is a Wi-Max transceiver based on IEEE 802.16-2004 standard. The validity of the model has been checked by comparing the mathematical results with numerical values achieved trough simulation. It is important to notice that this method can simultaneously be applied to both TH-UWB and DS-UWB.

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

The research work in this dissertation addresses reduced complexity equalization technique for multipath channels with large delay spread. This has been one of the key challenges for high data rate impulse radio based Ultra-Wideband (UWB) communication systems using low cost receiver design. Our research focus is on developing efficient and effective tap selection techniques for non-uniformly spaced Minimum Mean Squared Error (MMSE) equalization and applying it to UWB systems to achieve high performance with reduced receiver complexity. In this dissertation, a new class of tap selection techniques based on Order Recursive Least Squares (ORLS) and Matching Pursuit (MP) algorithms is proposed for UWB multipath channel equalization in the presence of Inter Symbol Interference (ISI) and unknown co-channel interference. The proposed tap selection techniques are directly implemented based on training symbol sequence under Least Squares (LS) criterion without the need for explicit channel estimation. In addition, Diagonal Loading (DL) technique is incorporated into the tap selection and MMSE equalization processes to insure system robustness given limited number of training symbols in the case of practical implementation. The proposed tap selection based equalizer is shown to outperform the conventional uniformly spaced linear equalizer and is with reduced computational complexity. The LS based technique proposed for equalizer tap selection is then extended to receive antenna selection for high data rate UWB systems with multiple receive antenna elements to achieve improved performance in the presence of Narrow Band Interference (NBI). Based on the LS criterion, antenna selection techniques for Multiple Input Multiple Output (MIMO) systems are also explored in our research work. Novel transmit and receive antenna selection techniques are proposed for MIMO spatial multiplexing systems with linear receivers under LS criterion. Unlike conventional approaches, xii

For precise synchronization of ultra wide band (UWB) signals in wireless channels, narrow band interference (NBI) suppression is a challenging issue. This is more relevant for real time channels which are non-linear in nature and are coexisted by narrow band wireless systems. An interference suppression scheme coupled to an energy detection based synchronization approach designed using second-order complex adaptive notch filter (ANF) is reported in this paper. This ANF uses a gradient descent algorithm for tracking the filter coefficients. The use of the same exploits the correlation difference property of signals received and suppresses NBIs in UWB signals. Consequently, it significantly reduces the computational complexity compared to the existing adaptive filters and requires lower power for an efficient hardware implementation. The data rate of UWB is usually high, so a combined pipelined-parallelism (CPP) approach is proposed which effectively simplifies the hardware design unlike direct and cascade forms. Detailed analysis suggest that the proposed scheme provides better performance in terms of power, speed, convergence and stability. Moreover, this scheme when used in conjunction with energy detection receivers significantly improves the interference tolerance margin, thereby raising the performance levels of synchronization with energy detection approach in non-coherent energy detection receivers.

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this work, the performance of a DS-CDMA ultra-wideband (UWB) system with multiple antennas at the receiver, in the presence of multiple users and narrow-band interference (NBI), is evaluated. A spatio-temporal UWB receiver is proposed which first forms an estimate of the channel in the presence of multi-access interference and NBI, and then uses this estimate to optimally combine the multipath components such that the output signal-to-interference-plus-noise-ratio is maximized. The performance of this system, through an analytically-derived expression for the probability of error, is investigated. In particular, a closed-form expression for the probability of error is established when the temporal correlation between the NBI during the channel-estimation phase and the data-detection phase is negligible. The effects of both quality of channel estimates and antenna correlation on the system performance are analyzed. </para>

Ultra wideband (UWB) is a reliable candidate for supporting a physical layer in Body Area Networks (BAN) and because of their wideband, UWB systems can have their performance degraded due to the interference from narrowband transmission. Methods must be developed to protect UWB systems that are exposed to this negative impact of the narrowband interference (NBI). Most proposed solutions have been developed for coherent and transmitted-reference receivers but a very few of these principles are eligible with the noncoherent energy detector (ED) receiver. The work presented thereafter aims at proposing a novel method to identify and mitigate the narrowband interference in ultra wideband transmissions. We use an efficient algorithm with a modified but still simple energy detector, and the performance of the method is evaluated by means of computer simulations.

Ultra-Wideband (UWB) systems are considered excellent candidates for future-generation short-range, high-throughput wireless communications. Today, UWB transmit strategies include equally-spaced pulse positioning, time-hopping, and direct-sequence spreading. In this work, we begin by comparing the BER performance of all three UWB architectures in multi-path fading channels. We then propose a multi-carrier pulse waveform (named the Carrier Interferometry (CI) waveform) for UWB systems: When employing the Cl waveform at the transmitter, UWB receivers utilize a frequency-domain processing to exploit available frequency diversity gains (improving both performances and throughput). We compare the BER performance of equally-spaced pulse positioning, time-hopping, and direct sequence spreading UWB systems using traditional time-domain and the proposed frequency-domain processing. Simulation results suggest that frequency-domain processing in UWB systems leads to very significant gains in performance and/or throughput relative to time-domain processing.

This paper proposes a novel method of using chaotic binary sequence in pulse amplitude modulation based ultrawideband (UWB) system to suppress interference and hence to improve the Bit Error Rate (BER) performance in the presence of narrowband interference (NBI). It is one of the very important considerations in the UWB systems as the spectrum of UWB overlays with the existing narrowband wireless systems. In the proposed method, the chaotic binary sequence is used across the frames within one symbol duration. The performance of the proposed scheme is analyzed using the channel models proposed by IEEE 802.15.3a working group for short range, high data rate wireless communications. The simulation results show that the proposed system has better BER performance compared to the existing systems, in the presence of NBI. In addition to the suppression of NBI, the proposed scheme has an added level of security due to the chaotic spreading.

Ultra wide band (UWB) is an extremely promising wireless technology for researchers and industrials. One of the most interesting is its high data rate and fading robustness due to selective frequency fading. However, beside such advantages, UWB system performance is highly affected by existing narrowband interference (NBI), undesired UWB signals and tone/multi-tone noises. For this reason, research about NBI cancellation is still a challenge to improve the system performance vs. receiver complexity, power consumption, linearity, etc. In this work, the two major receiver sections, i.e., analog (radiofrequency or RF) and digital (digital signal processing or DSP), were considered and new techniques proposed to reduce circuit complexity and power consumption, while improving signal parameters. In the RF section, different multiband UWB low-noise amplifier key design parameters were investigated like circuit configuration, input matching and desired/undesired frequency band filtering, highlighting the most suitable filtering package for efficient UWB NBI cancellation. In the DSP section, due to pulse transmitter signals, different issues like modulation type and level, pulse variety, shape and color noise/tone noise assumptions, were addressed for efficient NBI cancelation. A comparison was performed in terms of bit-error rate, signal-to-interference ratio, signal-to-noise ratio, and channel capacity to highlight the most suitable parameters for efficient DSP design. The optimum number of filters that allows the filter bandwidth to be reduced by following the required low sampling rate and thus improving the system bit error rate was also investigated.

A dual-mode tunable Q-enhanced active filter is proposed and designed. The filter is capable of processing both 5 GHz narrowband (NB) and ultra wideband (UWB) services by switching mode dynamically. The design uses the mainstream 0.18 mum CMOS technology. In the UWB mode, the filter behaves as an LNA, however, when the NB interference is detected, the filter notches the NB frequency and provides gain for the UWB signals. Under this operation, the filter has an input matching of 10 dB, again of at least 5.6 dB, a narrowband rejection of 9.8 dB for a BW of 100 MHz and a 1 dB compression point of -15.1 dB. The filter performs better if it operates as a sole UWB LNA. In the NB mode, the filter is used for bandpass channel selection. It exhibits an input matching of 20.5 dB, a gain of 23 dB at 100 MHz BW, a noise figure of 7.1 dB and a 1 dB compression point of -26.8 dB. The circuit consumes less than 27 mW of power at 1.8 V supply. The design allows the same receiver front-end to provide both services while reducing system complexity and cost