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This paper demonstrates a power efficient design of high-speed Digital-to-Analog Converters (DACs) for wideband communication systems. For Wireless personal area network applications with a 250 MHz signal bandwidth, a 6 bit DAC capable of two times the Nyquist rate sampling is implemented in a current steering segmented 2 + 4 architecture optimized for power efficiency. Along with a proposed master-slave deglitch circuit, several circuit techniques are investigated to improve dynamic performances such as linearity. Implemented in a 0.18 um CMOS process, our DAC achieved a superior conversion performance over the state-of-the-arts, exhibiting integral nonlinearity of less than 0.27 LSB and differential nonlinearity of less than 0.15 LSB. Measured spurious free dynamic range for 251 MHz output signal is 40.92 dB, with total power consumption at 1 GS/s of 6mW, yielding a figure-of-merits of 78.3 pJ/(conversion step*W). [ABSTRACT FROM AUTHOR]

In this paper, an ultra-wideband internal antenna for use in mobile applications is proposed. The proposed antenna has symmetrical bi-arm structures printed on the top and bottom of the substrate, and it occupies a compact area of 10 mm × 10 mm × 1 mm. The designed antenna has an impedance bandwidth from 3 GHz to 12 GHz and near omnidirectional radiation patterns over the frequency band of interest. The group delay between two antennas fabricated using the proposed design is less than 0.8 ns, and the maximum gain variation is about 3.16 dB. [ABSTRACT FROM AUTHOR]

A variable fractional delay (VFD) filter is presented that constitutes an efficient alternative to the usual Farrow structure. The filter is constructed by multiplying the signal to interpolate by a window with proper truncation properties, and then applying the Sampling Theorem. The resulting interpolator involves less arithmetic operations than the existing variants of the Farrow structure. Besides, if its coefficients are flumerically optimized, its performance is close to that of the FIR equi-ripple filter. The final part of the correspondence includes a description of the VFD filter implementation corresponding to this interpolator. [ABSTRACT FROM AUTHOR]

Fast sampling is desirable to describe signal transmission through wide-bandwidth systems. The delta-operator provides an ideal discrete-time modeling description for such fast-sampled systems. However, the estimation of delta-domain model parameters is usually biased by directly applying the delta-transformations to a sampled signal corrupted by additive measurement noise. This problem is solved here by expectation-maximization, where the delta-transformations of the true signal are estimated and then used to obtain the model parameters. The method is demonstrated on a numerical example to improve on the accuracy of using a shift operator approach when the sample rate is fast. [ABSTRACT FROM AUTHOR]

Block digital filtering has been suggested to reduce the computational complexity and to increase the parallelism of computation in digital filtering systems. In this letter, a fast algorithm for optimal design of block digital filters (BDFs) is developed. This algorithm, based on circulant, Toeplitz and shift cyclic matrices, not only reduces the computational complexity of the design process but also decreases the memory requirements. [ABSTRACT FROM AUTHOR]

A symmetrical four-port microstrip coupler has been proposed for crossover application. Models have also been developed to provide insight into the performance of such a coupler, which is based on the double-ring design. Laboratory tests have confirmed that the measured isolation and return loss of the prototype coupler exceed 20 dB over a bandwidth of 20% (from 0.92 to 1.12 GHz). [ABSTRACT FROM AUTHOR]

In this paper, a new power divider concept, which provides high flexibility of transmission line characteristic impedance and port impedance, is proposed. This power divider is implemented on a parallel-strip line, which is a balanced transmission line. By implementing the advantages and uniqueness of the parallel-strip line, the divider outperforms the conventional divider in terms of isolation bandwidths. A swap structure of the two lines of the parallel-strip line is employed in this design, which is critical for the isolation enhancements. A lumped-circuit model of the parallel-strip swap including all parasitic effects has been analyzed. An equal power divider with center frequency of 2 GHz was designed to demonstrate the idea. The experimental results show that the equal power divider has 96.5% - 19-dB impedance bandwidth with more than 25-dB isolation and less than 0.7-dB insertion loss. In order to generalize the concept with an arbitrary power ratio, we also realize unequal power dividers with the same isolation characteristics. The impedance bandwidth of the proposed power divider will increase with the dividing ratio, which is opposite to the conventional Wilkinson power divider. Unequal dividers with dividing ratios of 1 :2 and 1 : 12 are designed and measured. Additionally, a frequency independent 180° power divider has been realized with less than 2° phase errors. [ABSTRACT FROM AUTHOR]

We propose a new class of methods for VLIW code compression using variable-sized branch blocks with self-generating tables. Code compression traditionally works on fixed-sized blocks with its efficiency limited by their small size. A branch block, a series of instructions between two consecutive possible branch targets, provides larger blocks for code compression. We compare three methods for compressing branch blocks: table-based, Lempel-Ziv-Welch (LZW)-based and selective code compression. Our approaches are fully adaptive and generate the coding table on-the-fly during compression and decompression. When encountering a branch target, the coding table is cleared to ensure correctness. Decompression requires a simple table lookup and updates the coding table when necessary. When decoding sequentially, the table-based method produces 4 bytes per iteration while the LZW-based methods provide 8 bytes peak and 1.82 bytes average decompression bandwidth. Compared to Huffman's 1 byte and variable-to-fixed (V2F)'s 13-bit peak performance, our methods have higher decoding bandwidth and a comparable compression ratio. Parallel decompression could also be applied to our methods, which is more suitable for VLIW architectures. [ABSTRACT FROM AUTHOR]

Video multicast is a challenging problem due to heterogeneous and best-effort nature of the Internet. In this paper, we present a novel video multicast framework that exploits the potential of object scalability offered by MPEG-4. Specifically, we introduce the concept of object transmission proxy (OTP), which filters incoming streams using object-based bandwidth adaptation to meet dynamic network conditions. Multiple OPTs can form an overlay network that interconnects diverse multicast islands with semi uniform demands within each single island. We concur with the wisdom that an application best knows the utility of its data. Hence, the bandwidth adaptation algorithm for the OTPs adaptively allocates bandwidth among video objects according to their respective utilities and then performs application-level filtering based on an effective stream classification and packetization scheme. Extensive simulation results demonstrate that our framework has substantial performance improvement over conventional bandwidth adaptation schemes. It is particularly suitable for object-based video multicasting where the objects are of different importance. [ABSTRACT FROM AUTHOR]

We design novel space-time multipath (STM) coded multi-antenna transmissions over frequency-selective Rayleigh fading channels. We develop STM coded systems that guarantee the maximum possible space-multipath diversity, along with large coding gains, and high bandwidth efficiency for any number of transmit-receive antennas. By incorporating subchannel grouping, we also enable desirable tradeoffs between performance and complexity. Our designs rely on digital phase sweeping or block circular delay operations and apply to both single- and multi-carrier systems. Their merits are confirmed by corroborating simulations and comparisons with existing approaches. [ABSTRACT FROM AUTHOR]

In order to realize beam forming with an identical radiation characteristic over a wide bandwidth, this paper describes a method of design for two-dimensional FIR fan filters with wedge-shaped transition regions. In order to provide excellent amplitude approximations in a wide range from low to high frequencies with different transition range widths, a method based on the two-dimensional Fourier series approximation is used. The approximate amplitude characteristic of the target fan filter for which the widths of the passband and the transition band are specified in proportion to the frequency from the origin is greatly degraded at low frequencies near the origin. To reduce this degradation, the target amplitude characteristic at low frequencies of the fan filter is replaced with a rectangular cross-sectional shape. The width of the rectangular amplitude characteristic is set such that the amplitude of the designed result takes the specified value on the center line. Design examples are given for an axially symmetric fan filter and a diagonally symmetric fan filter. Further, the characteristics of the beam formers using these filters are derived and the effectiveness of the method is demonstrated. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 85(7): 38–49, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.1106 [ABSTRACT FROM AUTHOR]

A new scheme, based on Bragg gratings written in highly birefringent fibre that allows both increasing the channel density and relaxing the filter bandwidth requirements in future radio-over-fibre wavelength interleaved distribution networks, is presented and tested. [ABSTRACT FROM AUTHOR]