A low voltage 3-5 GHz CMOS ultra-wideband low noise amplifier is presented in this paper. A second order bandpass input impedance matching technique is used to achieve the broadband input matching. A folded cascode structure is employed to reduce the supply voltage and power consumption. A source follower acts as the buffer stage for broadband output impedance matching. The supply voltage is only 0.7 V. The operation frequency is 3-5 GHz. The maximum power gain is 13.2 dB. The noise figure is 3-4.2 dB. The power consumption of the core circuit is only 6.3 mW.

This paper presents an ultra-wideband (UWB) bandpass filter using a combination of broadside-coupled structure and lumped-capacitor-loaded shunt stub resonator. The broadside-coupled microstrip-to-coplanar waveguide structure provides an ultra-wide bandpass filtering operation and keeps a good stopband at lower frequencies from DC at the same time. The lumped-capacitor-loaded shunt stub resonator creates two transmission zeros (attenuation poles which can be located at the outsides of the two bandedges of the UWB bandpass filter to improve the out-band performance by selecting a suitable combination of the length of the shunt stubs and the capacitance of the loaded chip capacitors. The filter was designed based on electromagnetic simulation for broadside-coupled structure, microwave circuit simulation and experiments for determining the transmission zeros. The filter was fabricated on a one-layer dielectric substrate. The measured results demonstrated that the developed UWB bandpass filter has good performance: low insertion loss about 0.46 dB and low group delay about 0.26 ns at the center of the passband and very flat over the whole passband, and less than -10 dB reflection over the passband. The implemented transmission zeros, particularly at the low frequency end, dramatically improved the out-band performance, leading the filter satisfy the FCC's spectrum mask not only for indoor but also for outdoor applications. These poles improved also the skirt performance at both bandedges of the filter. A lowpass filter has been also introduced and integrated with the proposed bandpass filter to have a further improvement of the out-band performance at the high frequency end. The filters integrated with lowpass section exhibit excellent filter performance: almost satisfying the FCC's spectrum mask from DC to 18 GHz. The developed UWB bandpass filter has a compact size of 4 cm1.5 cm, or 4.8 cm1.5 cm with lowpass section implemented.

We propose the "Two-Step Search scheme with Linear search based Second step (TSS-LS)" by improving the conventional "Two-Step Search scheme with Bit reversal search based Second step (TSS-BS)" for reliable as well as rapid acquisition of Ultra Wide Band (UWB) signals in multipath channels. The proposed TSS-LS utilizes two different thresholds and search windows to achieve fast acquisition. Furthermore, unlike the TSS-BS in which the bit reversal algorithm is applied in both steps, the linear search is adopted for the second step in the proposed TSS-LS to correctly find the starting point in the range of effective delay spread of the multipath channels, and to obtain reliable bit error rate performance of the UWB systems.

The transmit power of Ultra Wideband (UWB) is limited in short range communications to avoid the interference with existing narrow-band communication systems. Since this limits UWB communication range, this paper proposes a novel relay scheme that uses shared frequency repeaters for impulse UWB signal relay to improve system range. After considering possible problems with the repeater, in particular the coupling interference between the input and output and relay-delay, a switching control method is proposed that offers short relay-delay and suppresses the coupling interference at the repeaters. With respect to the proposed relay scheme, Pulse-Position-Modulation (PPM) UWB-based signal relay is evaluated by analyzing its BER performance using the point-to-point transmission link model.

Target shape estimation with UWB pulse radars is a promising imaging technique for household robots. We have already proposed a fast imaging algorithm, SEABED, that is based on a reversible transform BST (Boundary Scattering Transform) between the received signals and the target shape. However, the target image obtained by SEABED deteriorates in a noisy environment because it utilizes a derivative of received data. In this paper, we propose a robust imaging method with an envelope of circles. We clarify by numerical simulation that the proposed method can realize a level of robust and fast imaging that cannot be achieved by the original SEABED.

UWB pulse radars enable us to measure a target location with high range-resolution, and so are applicable for measurement systems for robots and automobile. We have already proposed a robust and fast imaging algorithm with an envelope of circles, which is suitable for these applications. In this method, we determine time delays from received signals with the matched filter for a transmitted waveform. However, scattered waveforms are different from transmitted one depending on the target shape. Therefore, the resolution of the target edges deteriorates due to these waveform distortions. In this paper, a high-resolution imaging algorithm for convex targets is proposed by iteration of the shape and waveform estimation. We show application examples with numerical simulations and experiments, and confirm its capability to detect edges of an object.

Ultra-wideband impulse-radio systems have the ability to resolve multiple paths of the transmit radio and to mitigate the fading. Rake reception is capable of combining these paths, thereby improving the signal-to-noise ratio. In LOS channel, however, the improvement may be comparatively small for the cost of increasing receiver system complexity. This is because the LOS path should be dominant for the total energy in all paths. In this paper the distribution of the energy captured by Rake receiver is first presented for 160 measured LOS channel cases and then discussed. Rake reception with reflector is next suggested in order to effectively increase the signal energy without increasing the complexity, that is, increased number of Rake fingers. The use of reflector is also suggested for non-LOS channel and experimentally discussed where the Rake gain is compared with conventional Rake without reflector. The measurement results show the usefulness.

This paper investigates a design and performance of 4-parallel MB-OFDM UWB receiver. The performance of the proposed MB-OFDM UWB receiver using a 4-parallel synchronization structure is degraded by 0.25 dB compared with that of a receiver using a 1-parallel synchronization structure in the maximum frequency/sampling clock offset tolerance in an AWGN channel. Considering other impairments, including imperfect synchronization algorithms, the effect of quantization error by the 4-parallel synchronization structure is negligible in a multi-path channel environment as well as in an AWGN channel, as identified in simulation results.

This paper surveys and introduces propagation studies and models that are expected to contribute to the development of broadband wireless systems. The survey focused on theory-based propagation models, experimental measurement data useful for modeling, and transmission characteristic evaluations using propagation models. The survey did not attempt to cover all papers in the research fields, but rather took key papers for various relevant subjects and described them in some detail. The basic characteristics of multipath propagation are summarized from the viewpoints of narrow-band (NB), wide-band (WB), and ultra wide-band (UWB). Recent studies on spatio-temporal propagation models and the relationship between models and systems are introduced. To clarify the relationship between OFDM, which is a representative of wideband data transmission schemes, and wave propagation factors, problems due to large delay spread and large Doppler spread are highlighted. Finally, studies on UWB propagation measurement and propagation models are introduced.

Ultra-wideband pulse radars are promising candidates for 3-dimensional environment measurements by autonomous robots. Estimating 3-dimensional target shapes by scanning with an omni-directional antenna is an ill-posed inverse problem. Conventional algorithms such as the synthetic aperture method or parametric algorithms have a problem in terms of their calculation times. We have clarified the existence of a reversible transform between received data and target shapes for 3-dimensional systems. Calculation times are remarkably reduced by applying this transform because it directly estimates target shapes without iterations. We propose a new algorithm based on the transform and present an application example using numerical simulations. We confirm that the proposed algorithm has sufficient accuracy and a short calculation time.

In this paper the coexistence issue between the DS-UWB systems and Wi-Max/IEEE-802.16 based Fixed Broadband Wireless Access (FBWA) systems has been investigated. The aim is to evaluate the impact that the interference resulting from a realistic UWB hot spot scenario may have on the performance of a FBWA receiver. A mathematical model is developed through which the interference power produced by the UWB hot spot can be calculated. The benchmarks against which the UWB interference is assessed are also developed using the specifications of Wi-Max/IEEE-802.16 systems. Several simulations have been done to both validate the analytical results and calculate the UWB interference. In doing so, the effects of parameters like victim receiver bandwidth, carrier frequency, activity factor, the number of users and the distance from victim receiver in a realistic hot spot scenario have been studied.

The UWB (ultra-wideband) pulse radar is a promising candidate as an environment measurement method for rescue robots. Radar imaging to locate a nearby target is known as an ill-posed inverse problem, on which various studies have been done. However, conventional algorithms require long computational time, which makes it difficult to apply them to real-time operations of robots. We have proposed a fast radar imaging algorithm, the SEABED algorithm, for UWB pulse radars. This algorithm is based on a reversible transform, BST (Boundary Scattering Transform), between the target shape and the observed data. This transform enables us to estimate target shapes quickly and accurately in a noiseless environment. However, in a noisy environment the image estimated by the SEABED algorithm is degraded because BST utilizes differential operations. We have also proposed an image stabilization method, which utilizes the upper bound of the smoothness of received data. This method can be applied only to convex objects, not to concave ones. In this paper, we propose a fractional BST, which is obtained by expanding the conventional BST, and an image stabilization method by using the fractional BST. We show that the estimated image can be stabilized regardless of the shape of target.

In this paper, we apply iterative detection to typical time hopping (TH) pulse position modulation (PPM) ultra wideband (UWB) spread spectrum systems. Unlike a typical TH-PPM UWB which employs repetition code, the proposed system uses self-encoded code which is updated by user information itself. To take advantage of self-encoded spread spectrum, we apply iterative detection to the TH-PPM UWB system. Simulations are conducted to investigate the bit error rate (BER) performance of the proposed system in additive white gaussian noise (AWGN) channels as well as in fading and multipath channels. We observe a significant BER performance improvement over conventional TH-PPM UWB systems.

An InGaP/GaAs HBT MMIC amplifier with an active balun has been developed for ultra-wideband radio systems (UWB). The MMIC was designed to drive a self-complementary antenna with a balanced mode, where an input impedance is 60π ohms. The MMIC consists of a common mode negative feed back ultra-wideband amplifier circuit, an active balun circuit, and a high impedance drive circuit. The developed amplifier provides a 3-dB gain roll-off bandwidth from 2.4 GHz to 10.8 GHz with a 14.1-dB linear power gain, and a linear power output up to 3 dBm. The developed amplifier with the active balun provides a 3-dB gain roll-off bandwidth from 2.3 GHz to 8.6 GHz with a 21.3-dB power gain in a balanced mode, and a linear power output up to 0.6 dBm. The measured total group delay is less than 32 psec. Output signals at the balanced output terminals of the MMIC were kept inverted with a steep pulse shape for an impulse input signal of 57-psec pulse width.

A novel UWB system for a new indoor short distance radio-communication is examined. Various types of UWB systems have been proposed in the literature. Particularly direct sequence (DS) systems and time hopping (TH) systems are attractive due to low power consumption and a simple transceiver construction. In this paper, we consider to apply modulated and modified Hermite pulses (MMHP) for both DS-UWB and TH-UWB systems. Furthermore, MMHP are extended to a novel pulse set referred as limited bandwidth MMHP set in order to reduce various interferences. It is composed of pseudo-orthogonal pulses that have both good auto-correlation characteristics in all orders and low cross-correlation characteristics between different orders. The proposed pulse set also have some specific notches, which can be used to reduce narrow-band interference (NBI). Additionally, we propose a novel pulse shape hopping that employs the proposed MMHP set. Multi-user interference (MUI) and inter-symbol interference (ISI) can be reduced by such a pulse shape hopping scheme for the DS or TH UWB signal format. Simulation results show significant performance improvements by using the proposed UWB system.

This paper investigates the impact of chip duty factor (DF) in DS-UWB system with Rake receiver over AWGN and UWB indoor multipath environment corresponding to system parameters such as spreading bandwidth and chip length. Manipulating DF in DS-UWB system offers several advantages over multipath channel and thus, capable of improving system performance for better quality of communication. Although employing lower DF generally improves performance, in some exceptional cases on the other hand, degradation can be observed despite decreasing DF. Therefore, the objective of this paper is to clarify the relationship between DF and DS-UWB system performance. We discovered that with constant processing gain and spreading bandwidth, performance improvement can be observed at DF lower than 0.17. Additionally, with spreading bandwidth as tradeoff parameter, significant performance improvement can only be observed below DF of 0.85.

An enhanced Ultra Wideband (UWB) signaling scheme that employs PSWF (Prolate Spheroidal Wave Functions)-based orthogonal chip pulses and ternary complementary code sets is proposed for Direct-Sequence (DS) UWB systems. Every information bit of each user is modulated and transmitted over a set of parallel sequences of PSWF-based orthogonal chip pulses and are further assigned to a ternary complementary code set with additional zero padding if necessary. Moreover, the ternary complementary code sets are generated to be mutually orthogonal and assigned to any pair of multiple users. Hence, the mitigation of multipath interference as well as multiple user interference (MUI) can be expected. Furthermore, the ternary code length can be greatly shortened by taking advantage of pulse and code orthogonality. Thus, the proposed transmission scheme is especially suitable for high data rate DS-UWB systems that offer very high flexibility.

In this paper, an Ultra-Wideband (UWB) double-directional channel sounding measurement and spatio-temporal analysis of UWB propagation based on the clusterization approach were reported. After separating the propagation paths and diffuse components both on the transmitter (Tx) antenna and receiver (Rx) antenna positions, the propagation paths both on Tx and Rx positions were observed for clusters separately, while coupling the clusters between Tx and Rx position based on similar time of arrivals, and ray tracing by utilizing high temporal and spatial resolution, respectively. The relation between direction of departure and direction of arrival will then be investigated. For cluster properties, parameters of model characteristics are discussed and compared to other earlier works.

This paper presents an overview of research, development, standardization and regulation activities on ultra wideband (UWB) technologies in National Institute of Information and Communications Technology (NICT). NICT started a project on UWB technologies since 2002, and organized UWB consortium in cooperation with more than 20 companies and 7 universities in Japan. Up to now, we have been conducting numerous UWB R&D including the following main works: i) key technology development such as MMIC chips, antennas and other devices, ii) measurement and channel modeling for UWB signal propagation, iii) standardization in international activities of IEEE 802.15, ITU-R TG1/8 as well as in a national regulatory committee of Ministry of Internal Affair and Communications (MIC). The UWB systems we have studied occupy frequency bands range from microwave band (3-5 GHz) to quasi-millimeter wave band (24-29 GHz). Various prototype UWB systems including multi-functional terminals have been developed. The output of NICT has been succeeded by industrial parties with with national and international standardization and regulation.

Currently, multiband orthogonal frequency division multiplexing (MB-OFDM) is considered to be one of the modulation schemes of UWB and is being actively investigated. It is necessary to provide low-cost receivers for consumers to receive wide support for the MB-OFDM system. Such receivers can be achieved by utilizing direct-conversion architecture. Direct-conversion architecture suffers from IQ imbalance. IQ imbalance causes intercarrier interference (ICI) in the demodulated signals. In this paper, a new scheme of IQ imbalance compensation using transmit diversity is proposed. This scheme enables the system to achieve frequency diversity and simultaneously compensates for the influence of IQ imbalance. It is shown that the performance of the proposed scheme is better than that of the conventional IQ imbalance compensation scheme.