On the capacity of binary and Gaussian channels withrun-length-limited inputs

Bounds on the capacity of binary symmetric channels and additive Gaussian channels with run-length-limited two-level (binary, bipolar) inputs are presented, and their tightness is demonstrated for some cases. Stationary input sequences, which do not degrade capacity, are considered when deriving the bounds. Lower bounds on the magnetic recording density for a simple continuous-time recording model incorporating a minimal intertransition constraint are evaluated for soft and hard decisions. A superiority of about 1.5 dB in signal-to-noise ratio is observed for the soft-decision scheme     

Advances in multibeam communications satellite antennas

The evolution of satellite antennas over the past quarter of a century is presented. Five major areas of advances in communications satellite antenna technology are reviewed: single offset reflectors with feed arrays, shaped reflector systems, active phased arrays, phased-array-fed dual reflector systems, and lightweight feed elements. Examples are given of existing systems and of the ongoing development of new technologies     

High-current snapback characteristics of MOSFETs

The high-current snapback characteristics of MOSFETs with different channel lengths and widths, gate oxide thicknesses, and substrate dopings were studied to determine their effectiveness in electrostatic discharge stress protection. Filamentary conduction was not observed for currents up to 7 mA/μm of channel width for a pulsewidth of 500 ns. MOSFETs with shorter channel lengths require lower voltages to sustain the same current, independent of gate oxide thickness. Increasing the substrate doping does not necessarily reduce the high current voltage. These trends can be explained using a simple lateral n-p-n bipolar transistor snapback model     

300 ps switching of spontaneous emission by quantum confined fieldeffect in a light emitting triode

A high-speed switching, as fast as 300 ps, of spontaneous emission is achieved in the recently developed quantum-confined field-effect light emitting triode. As a result of the combination of the field control of radiative life time with modulation of carrier-generation rate, the light intensity modulation does not rely on changes in carrier population at all but on the field control of the radiative life time in the quantum well structure of the device. Elaborated is the allowance for the deviation of the modulation depth of injection current from an optimum value in the modulation scheme     

The current distribution and AC resistance of a microstripstructure

The AC resistance of the strip in a microstrip structure is compared with that of an isolated strip for better understanding of the conductor loss mechanism. An analysis is presented of the AC resistance in a microstrip structure for any metallization thickness by deriving the current distribution over the strip cross section. The analysis uses the separation of variables technique and the Green's function method. It shows that the skin current of the strip is concentrated toward the ground plane in a microstrip structure. In the extreme case, the AC resistance of the strip can be twice as high as the AC resistance of the same isolated strip. The imperfect ground plane also adds to the total conductor loss of a microstrip line. For a wide strip over a lossy ground plane at high frequency, the ground plane surface current distribution is concentrated directly under the strip, and the ground plane AC resistance can be as large as the strip AC resistance. Therefore, the total AC resistance at the microstrip line can be four times as high as that of an isolated strip conductor     

An algorithm for near-optimal placement of sensor elements

An important question in array design is that of where to place the elements of a sparse array for optimal performance in terms of its ability to detect and resolve a greater number of sources than conventionally possible. In particular, it has been shown that when sensor elements are arranged in the minimum redundancy fashion, by performing an augmentation technique on the covariances obtained from the array outputs, an M element array can be made to estimate the directions of arrival of as many as M(M-1)/2 uncorrelated sources unambiguously. Constructive procedures are developed to evaluate integer locations for an array of given sensors that span a prescribed distance, such that any missing integer is expressible as the difference of two sensor locations. New upper bounds for the ratio of the square of the minimum number of elements to the spanning distance are also established     

Nearly dispersion-penalty-free transmission using blue-shifted1.55-μm distributed feedback lasers

Nearly dispersion-penalty-free transmission over 40 km of nondispersion-shifted single-mode fiber was demonstrated using blue-shifted 1.55-μm distributed feedback lasers. This good system performance is attributed to the narrow and blue-shifted modulated optical spectrum which is in turn associated with the soft turn-on light-current characteristics. Transmission experiments using lasers with hard turn-on light-current characteristics give rise to broad modulated spectra and higher dispersion penalties     

External-cavity semiconductor laser with focusing grating mirror

A novel external-cavity semiconductor laser with a focusing grating mirror (FGM), which enables a single-mode oscillation at a specified wavelength, is proposed. The optical properties of the FGM, which is a computer-generated holographic grating with chirp and bend structure, are numerically analyzed. An optimally designed FGM for realizing laser oscillation at a specific wavelength of 1.30 μm is fabricated by using a computer-controlled electron-beam writing system. The fabricated FGM with grating area of 1×1 mm² is combined as an external feedback mirror with an InGaAsP-InP semiconductor laser of 1.3 μm wavelength range, and the lasing characteristics are experimentally measured. Stable and single-mode oscillations with spectral line width less than 10 MHz are observed     

Binary orthogonal signaling over the Gaussian channel with unknownphase/fading: new results and interpretations

The problem of binary orthogonal signaling over a Gaussian noise channel with unknown phase/fading is considered. By viewing the problem in a rotated coordinate system, the orthogonal signal structure is considered as the combination of an antipodal signal set and a pilot tone for channel measurement. For data detection the optimum matched-filter envelope-detector is shown to be identical to a novel detector-estimator receiver in which the detector performs partially coherent detection, using an absolute coherent reference generated by the estimator from the channel measurement provided by the pilot-tone component of the orthogonal signal structure. This detector-estimator interpretation shows that it is incorrect to refer to the optimum receiver as a noncoherent receiver. It also leads to the development of new approaches for analyzing the error probability of the receiver. An exponential Chernoff upper bound is obtained for the Rician channel     

Double-active-layer index-guided InGaAsP-InP laser diode

A buried crescent InGaAsP-InP laser with two active layers was fabricated to study the temperature behavior of the double-carrier-confinement structure. An anomalously high characteristic temperature T₀ was measured, and optical switching behavior was observed. A mode analysis and numerical calculation using a rate equation approach explained qualitatively very well the experimental results. It was revealed that both the Auger recombination in this special double-active-layer configuration and the temperature-dependent leakage current, which leads to uniform carrier distribution in both active regions, are essential to increase T₀