This paper describes the architecture and implementations of an automatic digital tuning circuit for a complex bandpass filter (BPF) in a low-power and low-cost transceiver for applications such as personal authentication and wireless sensor network systems. The architectural design analysis demonstrates that an active RC filter in a low-IF architecture can be at least 47.7% smaller in area than a conventional gm-C filter; in addition, it features a simple implementation of an associated tuning circuit. The principle of simultaneous tuning of both the center frequency and bandwidth through calibration of a capacitor array is illustrated as based on an analysis of filter characteristics, and a scalable automatic digital tuning circuit with simple analog blocks and control logic having only 835 gates is introduced. The developed capacitor tuning technique can achieve a tuning error of less than 3.5% and lower a peaking in the passband filter characteristics. An experimental complex BPF using 0.18 µm CMOS technology can successfully reduce the tuning error from an initial value of -20% to less than 2.5% after tuning. The filter block dimensions are 1.22 mm1.01 mm; and in measurement results of the developed complex BPF with the automatic digital tuning circuit, current consumption is 705 µA and the image rejection ratio is 40.3 dB. Complete evaluation of the BPF indicates that this technique can be applied to low-power, low-cost transceivers.

This Paper presents the design of a wideband variable gain amplifier (VGA) using 0.18 µm standard CMOS technology. The proposed VGA realizes wideband flat gain using wideband flat negative capacitance. It achieves a 3 dB gain bandwidth of 1 GHz with a maximum gain of 23 dB. Also, it shows P1 dB of -33 to -6 dBm over the gain range of -28 to 23 dB. The overall current consumption is 5.5 mA under a 1.5 V supply.

Bessel beams are a family of diffraction-free beams. They have many unique properties and prospective applications. Much attention has been focused to this subject in optics. Recently, the studies of such beams at mm- and submm- wavebands have been carried out in our group. The investigation results, including their theories, generation, propagation and potential applications, are presented in this paper.

A coordinate plane representation of the resource requirements of digital modulation methods is presented, and an overall resource efficiency measure is proposed. This measure can be used for the comparison of digital modulation methods and the evaluation of an emerging modulation technique. Several typical digital modulation methods are compared based on this measure to show its validity.

This paper proposes a blind image-band interference canceller that enables heterodyne receivers with only a single receiver chain to demodulate signals in any frequency band. In this paper, such a receiver is called "multimode/multiband heterodyne receiver." If multimode/multiband receivers are desired to receive signals with carrier frequency ranging from several MHz to GHz, then, such receivers are not allowed to have a narrow band RF-BPF (Radio Frequency Band Pass Filter) at the RF front end. However, although heterodyne receivers have been applied to wireless systems due to their high performance, it is known that without an RF-BPF heterodyne receivers suffer from severe image-band interference. Therefore, a blind image-band interference canceller is proposed in this paper to mitigate the image-band interference. Moreover, a novel algorithm based on the CM (Constant Modulus) criterion is proposed to carry out the cancellation. Performance of the blind image-band interference canceller is theoretically analyzed and the performance of the proposed canceller is verified by computer simulation. As a result, it is shown that the blind image-band interference canceller achieves superior performance even in the presence of strong image-band interference, for example, CIR=-40 dB. In summary, the proposed canceller makes it possible for the receiver with the single receiver chain to achieve multimode/multiband communications with high quality.

This paper proposes an ultra-wideband double-directional spatio-temporal channel sounding technique using transformation between frequency- and time-domain (FD and TD) signals. Virtual antenna arrays, composed of omnidirectional antennas and scanners, are used for transmission and reception in the FD. After Fourier transforming the received FD signals to TD ones, time of arrival (TOA) is estimated using a peak search over the TD signals, and then angle of arrivals (AOA) and angle of departure (AOD) are estimated using a weighted angle histogram with a multiple signal classification (MUSIC) algorithm applied to the FD signals, inverse-Fourier transformed from the TD signals divided into subregions. Indoor channel sounding results validated that an appropriate weighting reduced a spurious level in the angle histogram by a factor of 0.1 to 0.2 in comparison with that of non-weighting. The proposed technique successfully resolved dominant multipath components, including a direct path, a single reflection, and a single diffraction, in line-of-sight (LOS) and non-LOS environments. Joint TOA and AOA/AOD spectra were also derived from the sounding signals. The spectra illustrated the dominant multipath components (agreed with the prediction by ray tracing) as clusters.

The Ethernet passive optical network (EPON), which is one of the PON technologies for realizing FTTx (Fiber-To-The-Curb/Home/Office), is a low-cost and high-speed solution to the bottleneck problem that occurs between a backbone network and end users. The EPON is compatible with existing customer devices that are equipped with an Ethernet card. To effectively control frame transmission from optical network units (ONUs) to an optical line termination (OLT), the EPON can use a multi-point control protocol (MPCP) with control functions in addition to the media access control (MAC) protocol function. In this paper, we propose a two-phase cycle dynamic bandwidth allocation (TCDBA) algorithm to increase the channel utilization on the uplink by allowing frame transmissions during computation periods, and combine the TCDBA algorithm with the queue management schemes performed within each ONU, in order to effectively support differentiated services. Additionally, we perform simulations to validate the effectiveness of the proposed algorithm. The results show that the proposed TCDBA algorithm improves the maximum throughput, average transmission delay, and average volume of frames discarded, compared with the existing algorithms. Furthermore, the proposed TCDBA algorithm is able to support differentiated quality of services (QoS).

This paper describes the characteristic of negative group delay (NGD) circuits for various configurations including first-order, distributed, and second-order RC circuit configurations. This study includes locus, magnitude, and phase characteristics of the NGD circuits. The simplest NGD circuit is available using first-order RC or RL configuration. As an example of distributed circuit configuration, it is verified that losses in a distributed line causes NGD characteristic at higher cut-off band of a coupled four-line bandpass filter. Also, novel wideband NGD circuits using second-order RC configuration, instead of conventional RLC configuration, are proposed. Adding a parallel resistor to a parallel-T filter enables NGD characteristic to it. Also, a Wien-Robinson bridge is modified to have NGD characteristic by controlling the voltage division ratio. They are fabricated on MMIC substrate, and their NGD characteristics are verified with measured results. They have larger insertion loss than multi-stage RLC NGD circuits, however they can realize second-order NGD characteristic without practical implementation of inductors.

This paper presents the dual-band bandpass filters (BPFs) design composed of λ/2 and symmetrically/asymmetrically paired λ/4 stepped impedance resonators (SIRs) for the WLAN applications. The filters cover both the operating frequencies of 2.45 and 5.2 GHz. The dual-coupling mechanism is used in the filter design to provide alternative routes for signals of selected frequencies. A prototype filter is composed of λ/2 and symmetrical λ/4 SIRs. The enhanced wide-stopband filter is then developed from the filter with the symmetrical λ/4 SIRs replaced by the asymmetrical ones. The asymmetrical λ/4 SIRs have their higher resonances frequencies isolated from the adjacent I/O SIRs and extend the enhanced filter an upper stopband limit beyond ten time the fundamental frequency. Also, the filter might possess a cross-coupling structure which introduces transmission zeros by the passband edges to improve the signal selectivity. The tapped-line feed is adopted in this circuit to create additional attenuation poles for improving the stopband rejection levels. Experiments are conducted to verify the circuit performance.

This paper proposes a hybrid multiband (MB) ultra wideband (UWB) system with direct sequence (DS) spreading. The theoretical error analysis for the DS-MB-UWB multiple access system with Rake receiver in the presence of multipath and narrowband interference is developed. The developed theoretical framework models the multiple access interference (MAI), multipath interference (MI) and narrowband interference for the designed UWB system. It is shown that the system error performance corresponding to the combining effects of these interference can be accurately modeled and calculated. Monte Carlo simulation results are provided to validate the accuracy of the model. Additionally, it is found that narrowband interference can be mitigated effectively in the multiband UWB system by suppressing the particular UWB sub-band co-existing with the interfering narrowband signal. A typical improvement of 5 dB can be achieved with 75% sub-band power suppression. On the other hand, suppression of UWB sub-band is also found to decrease frequency diversity, thus facilitating the increase of MAI. In this paper, the developed model is utilized to determine the parameters that optimize the UWB system performance by minimizing the effective interference.

Dual-band chip antennas usually have a narrow bandwidth in the first resonance frequency band due to an inter-coupling capacitance. In order to analyze the effect of the inter-coupling capacitance, an equivalent circuit of an antenna with a branch radiator is considered in this paper. Based on the equivalent circuit model, it is found that the inter-coupling capacitance reduces impedance bandwidth. This paper proposes a gap feeding method to alleviate the effect of the inter-coupling capacitance and explains it using an equivalent circuit.

A fully integrated CMOS wideband Low Noise Amplifier (LNA) operating over 2.3-7 GHz is designed and fabricated using a 0.18 µm CMOS process. The proposed structure is a common source-common source (CS-CS) cascode amplifier with a coupling capacitor. It realizes both low voltage drop at load resistor (Rload) and high gain over 2.3-7 GHz with simultaneous noise and input matching and low power consumption. This paper presents the proposed design technique of a wideband LNA, and verifies its performance by simulation and measurement. This wideband LNA achieves an average gain (S21) of 16.5 (dB), an input return loss (S11) less than -8 dB, a noise figure (NF) of 3.4-6.7 dB, and a third order input interception point (IIP3) of -7.5-3 dBm at 2.3-7 GHz with power consumption of 10.8 mW under 1.8 V VDD.

A hidden Markov model (HMM)-based parameter estimation scheme is proposed for wideband speech recovery. In each Markov state, the estimation efficiency is improved using a new mapping function derived from the weighted least squares of vector deviations. The experimental results reveal that the performance of the proposed scheme is superior to that combining the HMM and Gaussian mixture model (GMM).

We present a numerical analysis of the optimal number of active mobile users for minimizing average data delivery delay in intelligent people-centric urban sensing, in which context-aware mobile devices act as sensor-data carriers and sensor nodes act as data accumulators within CDMA cellular networks. In the analysis, we compute the optimal number of mobile users for different environmental conditions and then investigate the minimum average data delivery delay for this optimal number of mobile users.

A compact (13.38.05.6 mm) 40 Gbit/s 1.55-µm electroabsorption (EA) modulator monolithically integrated distributed feedback (DFB) laser diode (EML) [1] module integrated with a driver IC has been developed. Its compactness was realized by employing a broadband feed-through and a bias tee which were accurately designed by 3-dimensional (3D) electromagnetic simulation. It was confirmed that the simulation results of the frequency response and the actual measurement results are corresponding well. Clear eye opening of the 40 Gbit/s optical output waveform of the fabricated EML module was observed. Degradation was not observed even when the 40 Gbit/s electrical signal was launched into the module via the flexible printed circuit (FPC).

In this paper, a novel method of partially placing electromagnetic band-gap (EBG) unit cells on both the power and ground planes in multi-layer PCBs and packages is proposed; it can not only sufficiently eliminate simultaneous switching noise (SSN), but also prevent severe degradation of signal quality in high-speed systems with imperfect reference planes resulting from the perforated structures of uni-planar EBG unit cells. On the assumption that the noise sources and noise-sensitive devices exist only in specific areas, the proposed method partially arranges the EBG unit cells on both the power and ground planes, but only around the critical areas. The SSN suppression performance of the proposed structure is verified by a simulation and measurements.

The performance of ultra-wideband (UWB) multiple input multiple output (MIMO) receiver based on the RAKE maximal ratio combiner (MRC) followed by a zero forcing (ZF) detector is analytically examined. For a UWB MIMO system with NT transmit antennas, NR receive antennas, and L resolvable multipath components, the proposed MIMO detection scheme is shown to have the diversity order of LNR-NT+1 and its analytical error rate expression is presented in a log-normal fading channel. We also compare the analytical BERs with the simulated results.

This paper describes a design method of cosine-modulated filter banks (CMFB's) for an efficient coding of images. Whereas the CMFB has advantages of low design and implementation cost, subband filters of the CMFB do not have linear phase property. This prevents from employing a symmetric extension in transformation process, and leads to a degradation of the image compression performance. However, a recently proposed smooth extension alleviates the problem with CMFB's. As a result, well-designed CMFB's can be expected to be good candidates for a transform block in image compression applications. In this paper, we present a novel design approach of regular CMFB's. After introducing a regularity constraint on lattice parameters of a prototype filter in paraunitary (PU) CMFB's, we also derive a regularity condition for perfect reconstruction (PR) CMFB's. Finally, we design regular 8-channel PUCMFB and PRCMFB by an unconstrained optimization of residual lattice parameters, and several simulation results for test images are compared with various transforms for evaluating the proposed image coder based on the CMFB's with one degree of regularity. In addition, we show a computational complexity of the designed CMFB's.

Synchronization poses a major challenge in ultra wideband (UWB) systems due to low signal duty cycles in UWB. This study develops an effective synchronization scheme for frame-differential IR-UWB receivers to improve the synchronization speed. The proposed parallel search mechanism reduces the search region of the symbol boundaries to only a single frame duration. Moreover, only one delay element is needed in each branch, since a shared looped delay-line (SLD) is also proposed to lower the implementation complexity of the parallel search mechanism. Simulations and performance analysis show that the proposed scheme achieves a lower mean square error and a higher probability of detection than other alternatives.

This letter proposes a high-performance single-sided horn-shaped tapered bowtie antenna which is compact and covers more than the whole UWB frequency band. This design implements a bowtie radiating element and tapered strip-line feeder element on a single-sided dielectric substrate, which offers a measured return loss of less than -10 dB over the whole UWB frequency band of 3.0-10.8 GHz. The measured radiation pattern is bi-directional with consistent gain over the above frequency band. This compact-size design shows much enhanced performance, compared to the previously reported antenna, which is useful for UWB radar and communication applications.