Adaptive UWB pulse design method for multiple narrowband interference suppression

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.

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.

To solve the coexistence of ultra wideband (UWB) system with other existed narrowband systems operating within the UWB bandwidth, we propose an adaptive non-linear chirp UWB waveform based on the atan function in this paper. With the utilization of cognitive radio (CR) technology and the good time-frequency relationship of the chirp function, the flexible multiple narrowband interferences (NBIs) suppression can be achieved. Simulation results demonstrate the superior multiple NBIs suppression ability of the proposed scheme in direct sequence bipolar pulse amplitude modulation (DS-BPAM) UWB system, which is also compared with the linear chirp pulse based UWB system.

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.

Ultra wideband (UWB) is a promising technology in delivering high data rate for short range wireless communication systems. Because of their large bandwidth, UWB signals may encounter some problems especially with high sampling rate requirements. Moreover, coherence existence with other narrowband systems is a major concern which needs to be addressed through proper mechanisms. The problem becomes so complex if multiple users exist. Since narrowband interference (NBI) signals have sparse representation in the discrete cosine transform (DCT) domain, they can be estimated and suppressed using Compressive Sensing (CS). CS also has the ability to reduce the high sampling rate requirements. For training based NBI mitigation with CS, three groups of pilot symbols are used to estimate the NBI signal subspace, the UWB signal subspace, and to provide information about the channel. In this paper, the distribution of pilot symbols among the three groups is investigated in the presence of strong NBI. The investigation is based on the bit error rate performance and throughput. The influence of each pilot symbols group is studied. The performance is also evaluated in the presence of multiuser interference in addition to the NBI. Simulation results show that the size of the third group of pilot symbols which is used to estimate the channel is the most dominant one.

This paper discusses ultra wideband (UWB) system performance in additive white Gaussian noise (AWGN) channel in the presence of partial band interference, whose special case is tone interference. In UWB case, most of the interference can be seen as partial band interference due to the extremely large inherent bandwidth of the desired signal. The given redefined formulas are verified with the corresponding simulation results. Study has focused on direct sequence (DS) based UWB system that uses binary pulse amplitude modulation (HPAM) as a data modulation scheme. DS-UWB is selected due to its better performance when related to the corresponding time hopping system in the interfered environment. Interference is assumed to be band limited and Gaussian distributed, and the presented analysis allows freely spacing and arbitrary bandwidth for the interfering signal. It has been proved that the general bit-error-rate (BER) formulas for wideband systems can be applied also to UWB with some modifications to calculate the upper bound for the UWB performance. The given approaches are very simple and can benefit the real system parameters for the desired link.

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.

In order to mitigate the mutual interference between ultra-wideband (UWB) impulse radio and other existing wireless systems, a novel adaptive interference-avoiding UWB pulse, in the context of the appealing cognitive radio, is presented based on the radial basis function neural networks. Theoretical and implementation architecture for UWB pulse generator is addressed. Transmission performance in the presence of narrowband interference including tone interference is comprehensively analyzed. The presented generator can adaptively change the spectrum shape of UWB signals according to the authorized users’ working states, and hence the mutual interference between UWB and other systems sharing the frequency bands can efficiently be avoided. The critical performance indication parameters, such as the SNR, SIR, and BER of UWB communication links, are also derived. Performance evaluations and comparisons between the proposed scheme and other pulse optimization methods have been provided based on the extensive numerical simulations. It is demonstrated that the presented pulse can indeed achieve much superior performance in terms of either single-link BER or anti-jamming capability.

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.

In this paper, we provide performance analysis for direct-sequence multiple-access ultra-wideband (UWB) systems operating in multipath environments when the effect of overlap between received pulses is included. Pulse overlap occurs when the pulse width is larger than the fine delay resolution of the UWB channel and is particularly important to consider in multidimensional pulse modulations. A closed-form bit error rate expression is derived and compared with simulations that employ UWB signals complying with the FCC UWB indoor emission mask and the channel model recommended by IEEE 802.15.3a. The detailed theoretical analysis and simulations reveal that channel-induced pulse overlap has a significant impact on UWB system performance. The results also show that compared with binary modulations, multidimensional biorthogonal pulse keying can improve power efficiency for multiple-access UWB systems under multipath fading, thereby providing an advantage for power-limited UWB communications.

The impact of electromagnetic noises from a PC on the bit error rate (BER) performance of a multiband orthogonal frequency division multiplexing (MB-OFDM) ultra wideband (UWB) communication system equipped on the PC is analyzed. The results of numerical simulation indicate that the PC noise consisting of the harmonic components of the PC clock causes considerable bit error rate (BER) degradation in the UWB system particularly those systems operated in high data-rate communication modes. It is also found that the frequency modulation of a PC clock signal, the so-called spread spectrum clocking (SSC), has no effect on mitigating BER degradation, although SSC techniques are commonly used in PCs for reducing the power spectral density of radiated noise. An interference mitigation scheme using Viterbi decoding with channel state information (CSI) is proposed on the basis of a novel receiver structure in which a reference PC clock signal is fed into the UWB receiver by the PC in order to accurately estimate the instantaneous frequency of interfering clock harmonics.

This paper applies transmit antenna selection algorithms to spatial-temporal combining-based spatial multiplexing (SM) ultra-wideband (UWB) systems. The employed criterion is based on the largest minimum output signal-to-noise ratio of the multiplexed streams. It is shown via simulations that the bit error rate (BER) performance of the SM UWB systems based on the two-dimensional Rake receiver is significantly improved by antenna diversity through transmit antenna selection on a log-normal multipath fading channel. When the transmit antenna diversity through antenna selection is exploited in the SM UWB systems, the BER performance of the spatial-temporal combining-based zero-forcing (ZF) receiver is also compared with that of the ZF detector followed by the Rake receiver.

Ultra wideband (UWB) systems can cause potential interference to other narrowband systems sharing the same band, such as WiMax and Wi-Fi. Detect and avoid (DAA) mechanisms were suggested as a cognitive radio-based solution to reduce interference by adaptively reducing the transmitted power at the overlapping bands. Applying this mechanism may result in degrading the performance of UWB transmissions. In this paper, we suggest a minor modification to the DAA mechanism to mitigate this effect while preserving data rate, and thus providing UWB with more reliability. Simulation results show significant improvement in performance over various interference scenarios and data rates.

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.