In this letter a planar tapered-slot-fed annular slot antenna with band-notched characteristics is presented for ultra-wideband radios. By etching a narrowband resonance slit on the non-radiating part of the antenna, the proposed antenna is capable of not only reducing the interference at the WLAN bands but also of avoiding the spatial-dependent bandstop characteristics that have commonly occurred in previous works.

This paper studies power spectrum density (PSD) of multi-user aggregate time hopping (TH) ultra wideband (UWB) signal with asynchronous transmission and synchronous transmission. TH codes under consideration are deterministic periodic code and random integer code. Based on the PSD, the in-band interference power for TD SCDMA is investigated as function of UWB system parameters. Two UWB modulations, TH pulse position modulation (PPM) and TH BPSK, are considered for calculating the in-band interference power. The numerical results indicate that asynchronous transmission is an effective way to decrease the peak in-band interference caused by multi-user aggregate TH-PPM UWB signal. Although increasing the maximum of time hopping code elements can smooth the PSD of TH UWB signal, it is not a good idea for reducing the peak in-band interference for TD SCDMA. For the random integer TH code, while only TH UWB continuous spectral exists in TD SCDMA band or multi-user signals of TH UWB are transmitted asynchronously, the in-band interference for TD SCDMA is in proportion to the number of the UWB users. For TD SCDMA in which band discrete spectral line exists the in-band interference caused by TH UWB with synchronous transmission is in proportion to the square of the number of the UWB users.

Short-range propagation measurements were carried out using ultra wideband (UWB) and continuous wave (CW) signals on a rectangular aluminum conductive plate, simulating typical office desks, with and without a low vertical metal partition panels. The frequency of the UWB signal spanned from 3.1 to 10.6 GHz and that of the CW signal was 6.85 GHz. A vector network analyzer and two omnidirectional UWB antennas were used to obtain the frequency-domain response of the propagation paths. With the partition panel, the CW reception level showed approximately a 20-dB spatial variation, induced by the interference between the direct and the reflected waves, but the UWB reception level had no particular plunges. The additional losses were also measured when the 500-mm propagation path was blocked with a human arm, a coffee cup, and a copy paper pile and when the receiving antenna was covered with a human palm on the plate without the partition panel. The maximum additional propagation losses were found as follows: 10-12 dB by a human arm, 10 dB with a coffee cup, and 2 dB with a paper pile. Further additional loss caused by a palm covering the antenna was found to be 10 to 12 dB, mainly due to palm absorption.

In this paper we present a novel method for improving RAKE receiver reception in UWB systems. Due to the fact that practical pulses that can be produced for UWB-IR (Ultra Wideband-Impulse Radio) may occupy a longer time than the typical multipath resolution of the actual UWB channel, multiple channel components may arrive within this typical pulse width. Performance degradation may occur due to the resulting intrapulse (overlapping received pulses) interference. We here propose an adaptive, pilot aided RAKE receiver for UWB communications in the multipath environment. The proposed system estimates the actual received signal with intrapulse interference in each RAKE finger using projections onto a Hadamard-Hermite subspace. By exploiting the orthogonality of this subspace it is possible to decompose the received signal so as to better match the template waveform and reduce the effects of intrapulse interference. By using the projections onto this subspace, the dimension of the received signal is effectively increased allowing for adaptive correlator template outputs. RAKE receivers based on this proposal are designed which show significant performance improvement and require less fingers to achieve required performance than their conventional counterparts.

This paper proposes wavelet packets for use in ultra wideband communications. The pulse shapes that are generated are quasi orthogonal and have almost identical time duration. After normalization, an M-ary signaling set can be constructed allowing higher data rate. Finally, the performance of such a system when multipath propagation occurs is investigated by computer simulations. In order to combat multipath fading, a Rake receiver using coherent channel estimation is designed. This channel estimation is carried out using adaptive algorithms such as least-mean square (LMS), normalized least-mean square (NLMS), or recursive least square (RLS) algorithms which adapt the received signal given a reference signal.

In this paper, Pre-Rake scheme for pulse based Ultra Wideband impulse radio (UWB-IR) communications system is proposed considering a standardized UWB channel model from IEEE 802.15 SG3a, which is based on an extensive set of short-range indoor channel measurements. Two kinds of pulse waveforms are taken in account here, namely, Gaussian mono-pulse and newly designed Prolate Spheroidal Wave Functions (PSWF) pulses corresponding to FCC Spectrum Mask. The Pre-Rake scheme is shown to contribute to the low-power, cost-efficient UWB system designing as well as Rake combining gain. Instead of building a Rake receiver at the receiving side (e.g. portable unit), the transmitter (e.g. access point) can pre-combine the UWB signal before transmission in the forward link by estimating the channel impulse response from the reverse link. While the Pre-Raked signal is convolved with the estimated channel impulse response, the function of Rake combination at the receiver is automatically performed. Meanwhile, in order to defeat inter-pulse-interferences (IPI) caused by severe multipath fading conditions, adaptive guard-time scheme for consecutive pulses is proposed as well. Monte-Carlo simulations are carried out to compare the Pre-Rake with Rake results and show that Pre-Rake scheme is as good as Rake combining for both types of pulse waveforms. Then the mobile or portable unit with a conventional receiver can still achieve the diversity gain of Rake combination. Moreover, the effects of placing guard-time between pulses are also verified.

This paper presents a novel decoding strategy called combined iterative demapping/decoding (CIDD), for coded M-ary biorthogonal keying-based direct sequence ultra-wideband (MBOK DS-UWB) systems. A coded MBOK DS-UWB system consists of a convolutional encoder, an interleaver, and an MBOK DS-UWB pulse mapper. CIDD improves the error rate performance of MBOK DS-UWB systems by applying the turbo principle to the demapping and decoding processes at the receiver side. To develop the CIDD, a soft-in/soft-out MBOK demapping algorithm, based on the max-log-MAP algorithm, was derived. Simulation results showed that using CIDD siginificantly improved the error rate performance of both static and multipath fading channels. It was also shown that the computational complexity of CIDD is comparable to that of the Viterbi decoding used in [133,171]8 conventional convolutional coding.

Performance of selective Rake (SRake) receiver is evaluated for direct sequence ultra wideband (DS-UWB) communications considering an independent Rayleigh channel having exponentially decaying power delay profile (PDP). BEP performances are shown. The results obtained are compared with similar results in a channel having flat PDP. Assumption of a flat PDP is found to predict the optimum spreading bandwidth to be lower and sub-optimum operating performance beyond optimum spreading bandwidth to be severely worse than that is achievable in a channel having exponentially decaying PDP by employing an SRake receiver having fixed number of combined paths. Optimum spreading bandwidth for SRake in a channel having exponentially decaying PDP is shown to be much larger than the one in a channel having flat PDP; that is specifically a good-news for UWB communications. Effects of partial band interference are also investigated. Interference is found to be less effective in exponentially decaying PDP.