Time Compression Multiplexing for Loop Transmission of Speech Signals

This paper considers the use of time compression multiplexing (TCM) for telephone loop communications. The analysis treats TCM transmission degradations in general, and applies the results to telephone speech transmission. To gain an understanding of the nature of TCM degradations, transmission through a linear, time invariant network and demultiplexing is considered. The channel signals are then assumed to be wide-sense stationary random processes, and expressions for the spectral properties of the TCM distortion and interchannel crosstalk are determined. To accurately evaluate the performance of a TCM system, a practical and economical equalizer is proposed. It is designed to meet speech transmission requirements for the telephone loop plant. A worst case application is chosen to evaluate the system performance. The evaluation of the TCM transmission performance utilizes both the random signal model and a computer simulation using digitized speech. The random signal analysis shows that the spectra of the distortion and crosstalk are significant for human speech. Results of the digitized speech simulation demonstrate that the subjective effect of the signal distortion is not severe, but the crosstalk is somewhat intelligible and more severe than expected.     

Bandwidth efficient transmultiplexers. II. Subband complements andperformance aspects

For pt.I see ibid., vol.40, no.1, p.70-84 (1992). The performance issues related to the quadrature amplitude modulation (QAM) and vestigial sideband (VSB) transmultiplexers synthesized previously are examined. An analysis of the limitations of the configured systems regarding intersymbol interference and crosstalk suppression arising from the use of practical filters is made. A new design technique for an finite impulse response (FIR) low-pass prototype that takes the practical degradations into account is formulated. The procedure involves the unconstrained optimization of an error function. A performance evaluation reveals that for four of the five systems, the new method is superior to a minimax approach in that lower intersymbol interference and crosstalk distortions are achieved with a fewer number of filter taps. For the other transmultiplexer, the advantage of the optimized design over the minimax design is in the added flexibility of taking crosstalk into account, thereby diminishing the crosstalk distortion. The five transmultiplexers can be converted into new subband systems. The authors show how the optimized design approach formulated for the transmultiplexers over to the new subband systems     

Crosstalk Loss Requirements for PCM Transmission

We present in this paper a unified approach to the crosstalk interference problem arising in PCM transmission on paired cables. For bipolar signaling, and three types of commonly used channel shaping, viz., cosine, raised cosine, and Gaussian, we present the minimum average near-end crosstalk (NEXT) and far-end crosstalk (FEXT) loss requirements at any transmission rate as a function of repeater spacing and number of interfering pairs so as to meet a desired error rate objective. This will aid in indicating if new cables need to be developed for a proposed rate of transmission or, for a given cable, the error margin available for degradations other than crosstalk can be readily determined. Extension to other coding schemes is indicated, and crosstalk compatibility is examined for mixedTsystems, such asT1,T1C, andT2. Graphical results are presented to readily aid in system design of anyTcarrier with repeater spacings up to 70 dB.     

New gain compression factor determination by harmonic analysis insemiconductor lasers

Measurements, on CATV DFB strained QW lasers, of first-order, second-order optical modulation depth (OMD) and, for the first time, of DC component decrease with modulation Δ_DC are fitted within a nonlinear model giving a precise determination of gain compression factor ϵ. This direct determination method at intermediate modulation frequencies is simpler and gives higher precision of ϵ than existing measurement methods such as relaxation resonance peak characteristics or emission wavelength shift     

Guaranteeing the BER in transparent optical networks using OOKsignaling

A network consisting of transparent optical nodes (TONs) can provide high speed end-to-end communication paths with very low bit-error rates (BERs). However, owing to component crosstalk and other degradations at TONs, the BER of a particular communication path traversing several TONs can be degraded by a few orders of magnitude even in the absence of component failure. Monitoring the quality-of-service (QoS) of a communication path has typically relied on sporadic BER testing and operation monitoring by the nodes using probe signals. Intermittent BER testing cannot provide continuous monitoring of the network QoS. On the other hand, the use of probe signals is not sensitive enough to detect the BER degradation. This work investigates a novel approach of monitoring service degradation at individual nodes using a wrap-around device which taps and compares signals from the input and the output at each TON along the lightpath. We propose a modification using hard limiters at TON inputs and derive the BER value that this modified method can guarantee in the presence of signal degradation due to coherent crosstalk at TONs     

A three-terminal band-trap-band tunneling model for drainengineering and substrate bias effect on GIDL in MOSFET

A new three-terminal partial band-trap-band tunneling (BTB) model is proposed to predict the drain engineering effect and substrate bias effect on gate-induced-drain-leakage (GIDL) characteristics for virgin devices free from electric stress. The lateral field ϵ_L and the ratio of lateral field w.r.t. total field ϵ(ϵ_L /ϵ) are two key factors responsible for the tunneling barrier lowering and the enhancement of GIDL. The principle to suppress GIDL are two-fold: the first one is to eliminate process induced intrinsic interface states and the second one is to minimize ϵ_L and ϵ_L/ϵ by using drain engineering or changing bias conditions such as applying forward substrate biases     

Postdetection selection diversity reception with correlated,unequal average power Rayleigh fading signals for π/4-shift QDPSKmobile radio

The diversity gain degradations due to fading correlation and unequal average power are investigated for practical, two-branch postdetection selection diversity reception. The average bit error rate (BER) of π/4-shift QDPSK is theoretically analyzed taking into account additive white Gaussian noise (AWGN), cochannel interference, and multipath channel delay spread; exact diversity gain degradations are calculated. Simple and useful approximate expressions for the gain degradations are also presented     

Leaky-wave propagation and radiation for a narrow-beammultiple-layer dielectric structure

Previous work has demonstrated that very narrow beam radiation patterns can be obtained from a simple source embedded within multiple dielectric layers of appropriate thicknesses above a ground plane. The configuration consists of dielectric layers having permittivities ϵ₁ and ϵ₂ stacked in an alternating arrangement, with ϵ₂>ϵ₁. This narrow-beam effect can be attributed to weakly attenuated leaky waves that exist on the structure. Simple asymptotic formulas for the propagation and attenuation constants are derived. The formulas show how the beamwidth varies with the number of layers and the material constants. The exact radiation pattern is compared with the leaky-wave pattern for a specific case to demonstrate the role of the leaky waves in determining the total pattern     

Asymptotic bounds on optimal noisy channel quantization via randomcoding

Asymptotically optimal zero-delay vector quantization in the presence of channel noise is studied using random coding techniques. First, an upper bound is derived for the average rth-power distortion of channel optimized k-dimensional vector quantization at transmission rate R on a binary symmetric channel with bit error probability ϵ. The upper bound asymptotically equals 2/sup -rRg(ϵ,k,r/). where k/(k +r) [1 - log₂(l +2√(ϵ(1-ϵ))] ⩽g(ϵ,k,r)⩽1) for all ϵ⩾0, lim_ϵ→0 g(ϵ,k,r)=1, and lim_k→∞g(ϵ,k,r)=1. Numerical computations of g(ϵ,k,r) are also given. This result is analogous to Zador's (1982) asymptotic distortion rate of 2^-rR for quantization on noiseless channels. Next, using a random coding argument on nonredundant index assignments, a useful upper bound is derived in terms of point density functions, on the minimum mean squared error of high resolution, regular, vector quantizers in the presence of channel noise. The formula provides an accurate approximation to the distortion of a noisy channel quantizer whose codebook is arbitrarily ordered. Finally, it is shown that the minimum mean squared distortion of a regular, noisy channel VQ with a randomized nonredundant index assignment, is, in probability, asymptotically bounded away from zero     

Effect of the nonlinear gain in the visibility of a semiconductorlaser with incoherent feedback in the coherence collapsed regime

We study the influence of the gain saturation parameter ϵ on the visibility of a semiconductor laser subject to optical feedback in the coherence collapsed state. The experimental measurements are compared with the results obtained integrating the Lang and Kobayashi equations and a good agreement is found varying the amount of feedback and using different values of ϵ. The analysis reveals that there is a best value of ϵ that fits the experimental measurements and that, for this value of ϵ, the values of γ found are in the expected relation with the attenuation used experimentally     

Dielectric constant measurements of finite-size sheet at microwavefrequencies by pseudo-Brewster's angle method

Dielectric constant (ϵ_r) measurements for finite-size dielectric sheets (DS's) at centimeter wavelengths are presented using the method-of-measuring pseudo-Brewster's angle. This method is applied to measure ϵ_r of sheets of Plexiglas and window glass. In the experiment, two horn antennas are used to transmit and receive p-polarized waves. A dielectric sheet is located between the two antennas and rotated 180°, which produces two peaks in the transmittance curves. For a more accurate measurement of Brewster's angle, an optical spectrometer with 1-min accuracy is also used. By this method, ϵ_r of Plexiglas and window glass are obtained to be 2.55±0.13 and 5.35±0.1, respectively. This method measures |ϵ_r|, but the measurement is easy and nondestructive for DS's. Finally, an accurate method of error calculation is used to calculate the error in the measured values of ϵ_r     

Sensitivity limitation of a superconducting quantum interferometersensor-based gravity gradiometer

Differential displacement due to a gravitational force gradient, acting on two superconducting test masses which are elastically suspended from the instrument frame, is sensed by a superconducting quantum interference device (SQUID), coupled to the masses by a current flowing in the sensing circuits. The SQUID transducer absorbs energy from the masses, and, hence, it reacts with a random force (fluctuation-dissipation principle). This force increases if the coupling current grows. Additionally, the transducer outputs an amplification noise that is independent of the coupling. This output noise is equivalent to a force, applied to the masses, which decreases with stronger coupling, Hence, the strength of the total equivalent gravity gradient noise has a minimum with respect to the coupling. The minimum is found to be about 1.5ϵ_Aω₀ ²/(ml²), where ϵ_A means the equivalent energy sensitivity, in the white noise limit, of the SQUID junctions; ω₀ is the natural frequency of the mass suspension; m is the test mass, and l is the base length,     

Compositional design of Pb(Zr, Ti)O3 for highly reliableferroelectric memories

We have investigated Pb(Zr,Ti)O₃ (PZT) film composition suitable for highly reliable ferroelectric RAM (FeRAM) application. To obtain a wide operational margin for 2T/2C (two transistors and two capacitors) FeRAMs, the PZT film capacitor is needed to have a low coercive voltage (V_c) and a high dielectric constant on the polarization switching (ϵ_S) and a low dielectric constant on the nonswitching (ϵ_N), or essentially a large ϵ_S/ϵ_N ratio. Concerning the B-site composition in the perovskite structure, it is found that lowering the Zr/Ti ratio from 47/53 to Ti-richer ones increases the ratio of ϵ_S/ϵ_N as a positive effect on the wide operational margin, but increased V_c as a negative effect. Taking the balance of these factors into consideration, it is concluded that an optimum composition, such as Zr/Ti=30/70, provides the maximum operational margin. The A-site composition, on the other hand, affects the long-term reliability of a PZT capacitor. The endurance to the fatigue and imprint are enhanced by reduction of the Pb-excess and dope of La in the A-site. A La-doped PZT (Zr/Ti =30/70) capacitor is successfully integrated to the 8 kbit FeRAM macro with double-layer Al wiring to confirm the feasibility of this capacitor     

A matrix-algebraic approach to successive interference cancellationin CDMA

In this paper, we describe linear successive interference cancellation (SIC) based on matrix-algebra. We show that linear SIC schemes (single stage and multistage) correspond to linear matrix filtering that can be performed directly on the received chip-matched filtered signal vector without explicitly performing the interference cancellation. This leads to an analytical expression for calculating the resulting bit-error rate which is of particular use for short code systems. Convergence issues are discussed, and the concept of ϵ-convergence is introduced to determine the number of stages required for practical convergence for both short and long codes     

Experimental comparison of the effect of discrete and distributedpath inband crosstalk on system performance: application to predictingsystem performance penalties

The system performance degradations of inband crosstalk produced by distributed Rayleigh scattering and a single discrete time delayed path have been measured in the same system. Rayleigh scatter crosstalk degrades performance more than equal amounts of discrete crosstalk. By parameterizing the system bit error rate (BER) and received power, we have separated the optical and electrical noise contributions to the BER based on their intensity and crosstalk scaling. We observed behavior consistent with earlier models, but found an unexpected increase in the total optical noise. This excess noise had a very regular linear scaling with crosstalk power. Because of its well defined crosstalk and intensity scaling, this easily measured noise term can be used as a correction to established models to more accurately estimate system performance at high optical powers and low crosstalk levels     

Crosstalk and interference penalty in all-optical networks usingstatic wavelength routers

The crosstalk and interference penalty in an all-optical network using static wavelength routers is analyzed in this paper. A worst case methodology is used to derive the upper bound of the penalty. We show that the penalty strongly depends on the linewidth of the laser source. Up to -20 dB in crosstalk can be tolerated in a moderate-size network (≈10⁵ nodes), with the ratio of the laser linewidth to the electrical bandwidth less than or equal to unity. Larger linewidth has the advantage of reducing the power penalty incurred by phase-to-amplitude noise conversion. However, the number of wavelength channels will he reduced as well. The maximum tolerable component crosstalk for a network with arbitrary size is reduced to -30 dB     

Crosstalk interference in FSK coherent optical systems

In this work, the impairment due to crosstalk interference in a FSK coherent optical system is investigated. The crosstalk can arise from both co-channel interference due to the dual-filter receiver structure, and inter-channel interference due to the frequency division multiplexing technique in multichannel systems. Here, we perform the analysis of a multichannel system, taking into account simultaneously the two contributions to interference. An approximation of the crosstalk contributions seems necessary in order to carry out the analysis. The joint moment characterization of the filtered phase noise and of the interference is suitable to get accurate results     

Efficient erasure correcting codes

We introduce a simple erasure recovery algorithm for codes derived from cascades of sparse bipartite graphs and analyze the algorithm by analyzing a corresponding discrete-time random process. As a result, we obtain a simple criterion involving the fractions of nodes of different degrees on both sides of the graph which is necessary and sufficient for the decoding process to finish successfully with high probability. By carefully designing these graphs we can construct for any given rate R and any given real number ϵ a family of linear codes of rate R which can be encoded in time proportional to ln(1/ϵ) times their block length n. Furthermore, a codeword can be recovered with high probability from a portion of its entries of length (1+ϵ)Rn or more. The recovery algorithm also runs in time proportional to n ln(1/ϵ). Our algorithms have been implemented and work well in practice; various implementation issues are discussed     

Analysis of dispersion and series gap discontinuity in shieldedsuspended striplines with substrate mounting grooves

Dispersion and series gap discontinuity of shielded suspended striplines (SSLs) on Duroid substrate (ϵ_r=2.22) are analyzed using the finite-difference time-domain method (FD-TD). Numerical accuracy of better than 0.15% is achieved when the FD-TD is used to calculate the effective dielectric constant (ϵ_reff ) of an air-filled rectangular coaxial transmission line. Data obtained for the frequency-dependent ϵ_reff of uniform SSLs and both scattering and equivalent circuit parameters of various series gap discontinuities are presented. In general, the presence of sidewall mounting grooves causes a nearly frequency-independent small reduction in ϵ_reff. On the other hand, proximity effects of the housing are found to be more important. For the gap discontinuity, coupling across the gap is stronger for wider strips and/or narrower gap width. Irregular transmission behavior is also found when the strip is wide enough to interact strongly with the sidewalls