MIMO decision feedback equalization from an H/sup /spl infin// perspective

We approach the multiple input multiple output (MIMO) decision feedback equalization (DFE) problem in digital communications from an H/sup /spl infin// estimation point of view. Using the standard (and simplifying) assumption that all previous decisions are correct, we obtain an explicit parameterization of all H/sup /spl infin// optimal DFEs. In particular, we show that, under the above assumption, minimum mean square error (MMSE) DFEs are H/sup /spl infin// optimal. The H/sup /spl infin// approach also suggests a method for dealing with errors in previous decisions.     

MIMO linear equalization with an H/sup /spl infin// criterion

In this paper, we study the problem of linearly equalizing the multiple-input multiple-output (MIMO) communications channels from an H/sup /spl infin// point of view. H/sup /spl infin// estimation theory has been recently introduced as a method for designing filters that have acceptable performance in the face of model uncertainty and lack of statistical information on the exogenous signals. In this paper, we obtain a closed-form solution to the square MIMO linear H/sup /spl infin// equalization problem and parameterize all possible H/sup /spl infin//-optimal equalizers. In particular, we show that, for minimum phase channels, a scaled version of the zero-forcing equalizer is H/sup /spl infin//-optimal. The results also indicate an interesting dichotomy between minimum phase and nonminimum phase channels: for minimum phase channels the best causal equalizer performs as well as the best noncausal equalizer, whereas for nonminimum phase channels, causal equalizers cannot reduce the estimation error bounds from their a priori values. Our analysis also suggests certain remedies in the nonminimum phase case, namely, allowing for finite delay, oversampling, or using multiple sensors. For example, we show that H/sup /spl infin// equalization of nonminimum phase channels requires a time delay of at least l units, where l is the number of nonminimum phase zeros of the channel.     

Asymptotic properties on codeword lengths of an optimal FV code for general sources

This correspondence is concerned with asymptotic properties on the codeword length of a fixed-to-variable length code (FV code) for a general source {X/sup n/}/sub n=1//sup /spl infin// with a finite or countably infinite alphabet. Suppose that for each n /spl ges/ 1 X/sup n/ is encoded to a binary codeword /spl phi//sub n/(X/sup n/) of length l(/spl phi//sub n/(X/sup n/)). Letting /spl epsiv//sub n/ denote the decoding error probability, we consider the following two criteria on FV codes: i) /spl epsiv//sub n/ = 0 for all n /spl ges/ 1 and ii) lim sup/sub n/spl rarr//spl infin///spl epsiv//sub n/ /spl les/ /spl epsiv/ for an arbitrarily given /spl epsiv/ /spl isin/ [0,1). Under criterion i), we show that, if X/sup n/ is encoded by an arbitrary prefix-free FV code asymptotically achieving the entropy, 1/nl(/spl phi//sub n/(X/sup n/)) - 1/nlog/sub 2/ 1/PX/sup n/(X/sup n/) /spl rarr/ 0 in probability as n /spl rarr/ /spl infin/ under a certain condition, where P/sub X//sup n/ denotes the probability distribution of X/sup n/. Under criterion ii), we first determine the minimum rate achieved by FV codes. Next, we show that 1/nl(/spl phi//sub n/(X/sup n/)) of an arbitrary FV code achieving the minimum rate in a certain sense has a property similar to the lossless case.     

Lossless and near-lossless source coding for multiple access networks

A multiple access source code (MASC) is a source code designed for the following network configuration: a pair of correlated information sequences {X/sub i/}/sub i=1//sup /spl infin// and {Y/sub i/}/sub i=1//sup /spl infin// is drawn independent and identically distributed (i.i.d.) according to joint probability mass function (p.m.f.) p(x,y); the encoder for each source operates without knowledge of the other source; the decoder jointly decodes the encoded bit streams from both sources. The work of Slepian and Wolf describes all rates achievable by MASCs of infinite coding dimension (n/spl rarr//spl infin/) and asymptotically negligible error probabilities (P/sub e//sup (n)//spl rarr/0). In this paper, we consider the properties of optimal instantaneous MASCs with finite coding dimension (n相似文献   

Finite horizon H/sub /spl infin// fixed-lag smoothing for time-varying continuous systems

In this paper, we aim to solve the long-standing H/sub /spl infin// fixed-lag smoothing problem for time-varying continuous systems. By applying a novel innovation analysis approach in an indefinite linear space, a sufficient and necessary condition for the existence of an H/sub /spl infin// fixed-lag smoother is derived. The H/sub /spl infin// smoother is calculated by performing the linear matrix differential equation and the integral equation.     

35-dB gain Tm-doped ZBLYAN fiber amplifier operating at 1.65 /spl mu/m

We demonstrate the first high gain rare-earth-doped fiber amplifier operating at 1.65 /spl mu/m. It consists of ZBLYAN fiber with a Tm/sup 3+/-doped core and Tb/sup 3+/-doped cladding, pumped by 1.22 /spl mu/m laser diodes. It is possible to achieve efficient amplification with Tm/sup 3+/ ions if their amplified spontaneous emission (ASE) in the 1.75 to 2.0 /spl mu/m wavelength region is suppressed by doping Tb/sup 3+/ ions in the cladding. A two-stage-type fiber amplifier is constructed and a signal gain of 35 dB is achieved for a pump power of 140 mW. A gain over 25 dB is realized in the 1.65 /spl mu/m to 1.67 /spl mu/m wavelength region.     

H/sub /spl infin// filtering for multiple-time-delay measurements

The aim of this paper is to study the H/sub /spl infin// filtering problem for linear continuous-time systems with both current and multiple-time-delay measurements. The key technique applied for deriving the filter is the reorganized innovation analysis approach in Krein space. A necessary and sufficient condition for the existence of an H/sub /spl infin// filter is derived, and the solution to the H/sub /spl infin// filter is given in terms of solutions of Riccati and matrix differential equations. An example is finally presented to show the effectiveness of the proposed approach.     

A quasi-invariant single-parameter criterion for linear two-port unconditional stability

This letter presents a novel unconditional stability criterion for linear two-port networks. The criterion involves a new symmetrical single-parameter defined as. It is shown that K/sub t/>1 if and only if a two-port network is unconditionally stable. Moreover, K/sub t/ is invariant under arbitrary lossless termination and reactive matching at either port when unconditional stability exists. Such invariant property is retained so long as |/spl Delta/|/spl les/1, which occurs more frequently than |/spl Delta/|>1 for most devices. The parameter can also be aptly related to the maximum available gain of an unconditionally stable device.     

An H/sub /spl infin// optimization and its fast algorithm for time-variant system identification

In some estimation or identification techniques, a forgetting factor /spl rho/ has been used to improve the tracking performance for time-varying systems. However, the value of /spl rho/ has been typically determined empirically, without any evidence of optimality. In our previous work, this open problem is solved using the framework of H/sub /spl infin// optimization. The resultant H/sub /spl infin// filter enables the forgetting factor /spl rho/ to be optimized through a process noise that is determined by the filter Riccati equation. This paper seeks to further explain the previously derived H/sub /spl infin// filter, giving an H/sub /spl infin// interpretation of its tracking capability. Additionally, a fast algorithm of the H/sub /spl infin// filter, called the fast H/sub /spl infin// filter, is presented when the observation matrix has a shifting property. Finally, the effectiveness of the derived fast algorithm is illustrated for time-variant system identification using several computer simulations. Here, the fast H/sub /spl infin// filter is shown to outperform the well known least-mean-square algorithm and the fast Kalman filter in convergence rate.     

Experimental implementation of spatial H/sub /spl infin// control on a piezoelectric-laminate beam

This paper is aimed to develop a feedback controller that suppresses vibration of flexible structures. The controller is designed to minimize the spatial H/sub /spl infin// norm of the closed-loop system. This technique guarantees average reduction of vibration throughout the entire structure. A feedthrough term is incorporated into the truncated flexible-structure model to compensate for the neglected dynamics in the finite-dimensional model. Adding the feedthrough term reduces the uncertainty associated with the truncated model, which is instrumental in ensuring the robustness of the closed-loop system. The controller is applied to a simply-supported piezoelectric-laminate beam and is validated experimentally to show the effectiveness of the proposed controller in suppressing structural vibration. It is shown that the spatial H/sub /spl infin//. control has an advantage over the pointwise H/sub /spl infin// control in minimizing the vibration of the entire structure. This spatial H/sub /spl infin// control methodology can also be applied to more general structural vibration suppression problems.     

Electrical characteristics and reliability of UV transparent Si/sub 3/N/sub 4/ metal-insulator-metal (MIM) capacitors

In this paper, we discuss the electrical characteristics and reliability of UV transparent Si/sub 3/N/sub 4/ metal-insulator-metal (MIM) capacitors. We examine film thicknesses in the range of 55 to 25 nm with capacitance densities from 1.2 ff//spl mu/m/sup 2/ to 2.8 ff//spl mu/m/sup 2/, respectively, for single MIM capacitors. A new approach for projecting the dielectric reliability of these films extends the limits of maximum operating voltage. Accounting for temperature acceleration and area scaling, the projected lifetimes can be met for a wide range of operating conditions.     

Robust H/sub /spl infin// filtering for stochastic time-delay systems with missing measurements

In this paper, the robust H/sub /spl infin// filtering problem is studied for stochastic uncertain discrete time-delay systems with missing measurements. The missing measurements are described by a binary switching sequence satisfying a conditional probability distribution. We aim to design filters such that, for all possible missing observations and all admissible parameter uncertainties, the filtering error system is exponentially mean-square stable, and the prescribed H/sub /spl infin// performance constraint is met. In terms of certain linear matrix inequalities (LMIs), sufficient conditions for the solvability of the addressed problem are obtained. When these LMIs are feasible, an explicit expression of a desired robust H/sub /spl infin// filter is also given. An optimization problem is subsequently formulated by optimizing the H/sub /spl infin// filtering performances. Finally, a numerical example is provided to demonstrate the effectiveness and applicability of the proposed design approach.     

High-power broadly tunable Ho/sup 3+/-doped silica fibre laser

Tuning of the 2.1 /spl mu/m Ho/sup 3+/-doped silica fibre laser is demonstrated for the first time. The /sup 5/I/sub 7//spl rarr//sup 5/I/sub 8/ transition provides tuning over 144 nm, from 2019 to 2163 nm, and a maximum pump-limited output power of 1.58 W at 2100 nm was produced.     

Efficient tunable laser operation of Tm:KGd(WO/sub 4/)/sub 2/ in the continuous-wave regime at room temperature

Tm:KGd(WO/sub 4/)/sub 2/ is studied as a three-level laser on the /sup 3/F/sub 4/ /spl rarr/ /sup 3/H/sub 6/ transition and a tunable source in the 2-/spl mu/m spectral range, operating at room temperature. An overall tunability extending from 1790 to 2042 nm is achieved with maximum output powers of 400 mW for an absorbed pump power of 1 W. Various doping levels, pump wavelengths and polarization configurations are compared and the advantages of the monoclinic double tungstates over other Tm-hosts are outlined.     

1.49-/spl mu/m-band gain-shifted thulium-doped fiber amplifier for WDM transmission systems

This paper describes in detail the amplification characteristics of gain-shifted thulium-doped fiber amplifiers (GS-TDFAs) operating in the 1480to 1510-nm wavelength region (1.49-/spl mu/m S-band) for use in wavelength-division-multiplexing (WDM) systems. Gain shifting of a TDFA, which normally has a gain band at 1.47 /spl mu/m (S/sup +/-band), is achieved by two types of dual-wavelength pumping: (1) 1.05 and 1.56 /spl mu/m or (2) 1.4 and 1.56 /spl mu/m. The main pump source at 1.05 or 1.4 /spl mu/m creates population inversion between /sup 3/F/sub 4/ (upper laser level) and /sup 3/H/sub 4/ (lower laser level), while the auxiliary pump source at 1.56 /spl mu/m reduces the average fractional inversion down to approximately 0.4, which is a desired level for gain shifting. We show experimentally that the former provides a low internal noise figure (<4 dB) due to high fractional inversion at the input end of a thulium fiber, while the latter provides a very high optical efficiency but a higher internal noise figure (/spl sim/5 dB) due to the lower fractional inversion at the input end. These characteristics were verified by numerical simulation based on a comprehensive rate equation modeling. We demonstrated a 1.4- and 1.56-/spl mu/m laser-diode-pumped GS-TDFA with an optical efficiency of 29.3% and high output power of +21.5 dBm. Gain flatness and tilt control were also investigated. These results strongly confirm the feasibility of using GS-TDFAs in practical ultralarge-capacity WDM networks.     

Robust and precision motion control system of linear-motor direct drive for high-speed X-Y table positioning mechanism

In this paper, design and implementation of an H/sub /spl infin//-based precision motion control system is presented for a high-speed linear-motor direct-drive X-Y table positioning mechanism in semiconductor wire-bonding applications. The system works with a cascaded robust feedback control, which has an inner loop velocity controller and an outer loop position controller, and an autotuning feedforward compensator. The design aim is to achieve high and consistent tracking performance even in the presence of considerable resonance uncertainties and external disturbances. Toward this aim the velocity controller is designed using H/sub /spl infin// optimization technique, based on reduced-order modeling that considers three significant resonance modes and neglects all other resonance modes having an insignificant amplitude and/or too high frequency. These neglected modes and variations of the three resonance modes from machine to machine (due to manufacturing tolerance) and/or with different operating conditions are taken care of by appropriate additive uncertainty representation in the design phase. The resulting system is validated and implemented with a profile motion of a maximum acceleration of 5.2 g (1g=9.81 m/s/sup 2/) on mass-produced wire bonding machines.     

Improved bounded-real-lemma representation and H/sub /spl infin// control of systems with polytopic uncertainties

This brief concerns the problem of the bounded-real-lemma (BRL) representation and H/sub /spl infin// control of linear systems with real convex polytopic uncertainties. In order to use a parameter-dependent Lyapunov function for a system with polytopic uncertainties, the derivative term for the state, which is in the derivative of the Lyapunov function, is reserved; and free weighting matrices are used to express the relationship between the terms of the system equation. This yields a new linear-matrix-inequality approach to BRL representation. In addition, this method is extended to the design of a state-feedback controller that solves the H/sub /spl infin// control problem. Numerical examples demonstrate that the proposed method is effective and is an improvement over previous ones.     

4H-SiC power bipolar junction transistor with a very low specific ON-resistance of 2.9 m/spl Omega//spl middot/cm/sup 2/

This letter reports a newly achieved best result on the specific ON-resistance (R/sub SP/spl I.bar/ON/) of power 4H-SiC bipolar junction transistors (BJTs). A 4H-SiC BJT based on a 12-/spl mu/m drift layer shows a record-low specific-ON resistance of only 2.9 m/spl Omega//spl middot/cm/sup 2/, with an open-base collector-to-emitter blocking voltage (V/sub ceo/) of 757 V, and a current gain of 18.8. The active area of this 4H-SiC BJT is 0.61 mm/sup 2/, and it has a fully interdigitated design. This high-performance 4H-SiC BJT conducts up to 5.24 A at a forward voltage drop of V/sub CE/=2.5 V, corresponding to a low R/sub SP-ON/ of 2.9 m/spl Omega//spl middot/cm/sup 2/ up to J/sub c/=859 A/cm/sup 2/. This is the lowest specific ON-resistance ever reported for high-power 4H-SiC BJTs.     

H/sup /spl infin// repetitive control of DC-AC converters in microgrids

This paper proposes a voltage controller design method for DC-AC converters supplying power to a microgrid, which is also connected to the power grid. This converter is meant to operate in conjunction with a small power generating unit. The design of the output voltage controller is based on H/sup /spl infin// and repetitive control techniques. This leads to a very low harmonic distortion of the output voltage, even in the presence of nonlinear loads and/or grid distortions. The output voltage controller contains an infinite-dimensional internal model, which enables it to reject all periodic disturbances which have the same period as the grid voltage, and whose highest frequency components are up to approximately 1.5 kHz.     

Compression mappings on primitive sequences over Z/(p/sup e/)

Let Z/(p/sup e/) be the integer residue ring with odd prime p/spl ges/5 and integer e/spl ges/2. For a sequence a_ over Z/(p/sup e/), there is a unique p-adic expansion a_=a_/sub 0/+a_/spl middot/p+...+a_/sub e-1//spl middot/p/sup e-1/, where each a_/sub i/ is a sequence over {0,1,...,p-1}, and can be regarded as a sequence over the finite field GF(p) naturally. Let f(x) be a primitive polynomial over Z/(p/sup e/), and G'(f(x),p/sup e/) the set of all primitive sequences generated by f(x) over Z/(p/sup e/). Set /spl phi//sub e-1/ (x/sub 0/,...,x/sub e-1/) = x/sub e-1//sup k/ + /spl eta//sub e-2,1/(x/sub 0/, x/sub 1/,...,x/sub e-2/) /spl psi//sub e-1/(x/sub 0/,...,x/sub e-1/) = x/sub e-1//sup k/ + /spl eta//sub e-2,2/(x/sub 0/,x/sub 1/,...,x/sub e-2/) where /spl eta//sub e-2,1/ and /spl eta//sub e-2,2/ are arbitrary functions of e-1 variables over GF(p) and 2/spl les/k/spl les/p-1. Then the compression mapping /spl phi//sub e-1/:{G'(f(x),p/sup e/) /spl rarr/ GF(p)/sup /spl infin// a_ /spl rarr/ /spl phi//sub e-1/(a_/sub 0/,...,a_/sub e-1/) is injective, that is, a_ = b_ if and only if /spl phi//sub e-1/(a_/sub 0/,...,a_/sub e-1/) = /spl phi//sub e-1/(b_/sub 0/,...,b_/sub e-1/) for a_,b_ /spl isin/ G'(f(x),p/sup e/). Furthermore, if f(x) is a strongly primitive polynomial over Z/(p/sup e/), then /spl phi//sub e-1/(a_/sub 0/,...,a_/sub e-1/) = /spl psi//sub e-1/(b_/sub 0/,...,b_/sub e-1/) if and only if a_ = b_ and /spl phi//sub e-1/(x/sub 0/,...,x/sub e-1/) = /spl psi//sub e-1/(x/sub 0/,...,x/sub e-1/) for a_,b_ /spl isin/ G'(f(x),p/sup e/).