Time Delay Estimation by Cross-covariance Maximization of Quadrature Sampled Narrowband Signals

A numerically efficient algorithm for estimating the time delay from observations of a stationary narrowband signal and its delayed version is investigated. Quadrature sampling, a variant of bunched sampling, is applied to estimate samples of the quadrature components of the cross-covariance function of the two signals. The baseband magnitude squared of this function can be maximized for time delay estimation. Because the time delay is unknown, the baseband cross-covariance function cannot be interpolated from the estimated samples. Numerical maximization of the samples' magnitude squared and quadratic interpolation, however, results in a reasonable time delay estimate.     

60 km色散补偿8×50 GHz光纤光栅梳状滤波器设计

设计了一种新颖的60km色散补偿8信道50GHz信道间隔的啁啾光纤Bragg光栅(CFBG)梳状滤波器。采用基于LP算法的IS光纤光栅设计技术,设计出CFBG的折射率调制函数和啁啾分布。根据设计得出的耦合系数分布,采用传输矩阵法分析所设计CFBG的反射谱、时延曲线和群时延抖动。结果表明,所设计的CFBG不仅满足了设计指标要求,性能优良,而且在已知的制作技术条件下可以实现。     

Performance Analysis of the ATM Adaptation Layer 2 (AAL2)

In this paper, we analyze the performance of AAL2 multiplexer for a continuous time Markovian arrival process. AAL2 CPS (Common Part Sublayer) packets are multiplexed in the AAL2 multiplexing queue and transmitted in the transmission queue. This tandem structure suggests that the statistics of AAL2 CPS requires at least 2 dimensional state space. Furthermore, from a network-level point of view, cell multiplexing and de-multiplexing procedures are repeated at each AAL2 switching node. That requires simple analysis model. To solve this problem, we reduce the state space by showing that the output process of multiplexing queue can be modeled with the Coxian distribution. We propose a single dimension analysis model of the CPS transmission queue. When AAL2 convey both real and non real time short packets, QoS management is a problem. This is because the QoS of real time as well as non-real time packets is measured using different metrics – delay and cell loss ratio respectively. Most previous work is concentrated around delay performance due to the real time applications getting the primary attention. From the direct comparison of delay and CLR performance, we show that delay constraint is the dominant parameter in QoS of AAL2.     

Efficient Design of High-Capacity Dense Wavelength-Division Multiplex Systems

An efficient design methodology for high-capacity dense wavelength-division multiplexed systems is presented. In contrast to complex and time-consuming numerical simulations, analytical equations and heuristicapproximations are used to model the system performance. They facilitate first-order performance estimates and the identification of limiting effects even for multi-Tb/s systems within a few seconds.Taking into account local and accumulated group velocity dispersion, impairments due to fibre nonlinearities are described as a function of the average optical input power per channel. In combination with thedegradation of the optical signal-to-noise ratio caused by optical amplifier noise the maximum transmission distance versus optical input power can bedetermined.The validity of the models is verified by means of numerical simulations and system experiments. The dependence on data rate, modulation format, fibre type and dispersion compensation scheme is determined. Practical examples illustrate the usefulness of our design approach.     

Optical circuits for equalizing group delay dispersion of opticalfibers

Optical circuits are synthesized for equalizing the group delay dispersion of single-mode fibers. The transfer function of the equalizing circuits are given by Chebyshev polynomials of the second kind. The various realization methods for the group delay equalizer are shown, including periodic structures using birefringent crystals, birefringent fibers, and Mach-Zehnder interferometric planar optical circuits. An optical equalizer employing TiO₂ birefringent crystals was fabricated and evaluated by using an optical network analyzer, which operates by making modulation-envelope phase and amplitude measurements while scanning the optical carrier frequency. The measured optical equalizer characteristics show excellent agreement with the simulation analysis. The effectiveness of the equalizer for substantial reduction of the dispersion penalty for a 10 Gb/s signal transmitted over 30 km of normal dispersion fiber was demonstrated. The periodicity of the equalizer results in periodic dispersion-free bands, and hence, the equalizer is suitable for use in future multichannel FDM systems     

Turbo Multiuser Detection for TD-CDMA

In this paper the novel detection scheme multi-step joint detection for TD-CDMA mobile radio systems is presented. Multi-step joint detection uses the turbo principle for iteratively improving data detection. Extrinsic information obtained by FEC-decoding in a previous step is used for a joint reduction of interference and improvement of asymptotic efficiency of the linear multiuser detector. Multi-step joint detection helps to overcome the problems of small asymptotic efficiencies present in linear multiuser detectors like the zero forcing equalizer in TD-CDMA mobile radio systems in the case of high system loads. Simultaneously complexity is much lower than that of optimum nonlinear multiuser detectors based on the Viterbi algorithm. As an alternative to simulations the performance of multi-step joint detection can be theoretically determined under certain not too restrictive assumptions. Both approximate and simulative performance results are presented in the paper. It is shown that in typical mobile radio systems the required SNR at the receiver input can be reduced by approximately 10 dB compared to linear multiuser detection. Thus, multi-step joint detection helps to increase the permissible number of mobile stations per cell or to decrease the required cluster size in TD-CDMA mobile radio systems and thus improves spectrum efficiency and capacity.     

DISPERSION COMPENSATION CFBG IN100km 10Gbit／s RECIRCULATING SYSTEMS

A 10Gbit/s recirculating system is configured with Chirped Fiber Bragg Grating (CFBG) for the dispersion compensation. For the first time, the transmission distance in the loop reaches 1000km with bit error rate of 10-9. The effect of the group delay ripple of the fiber grating is also investigated in the recirculating systems, and it is shown that the transmission distance is limited to 4 cycles (4×167.1km ) in the loop with the power penalty fluctuation below 1.0dB. Thus the group delay ripple should be reduced to allow for the wavelength drift of±5GHz. At the end of this letter, the principles are given for designing long haul recirculating systems with dispersion compensation CFBG.     

Plasmatron with Microwave Excitation of Nonequilibrium Plasma

Testing results of a microwave plasma generator (plasmatron) intended for excitation of a strongly nonequilibrium plasma arepresented. Nonequilibrium properties of the plasma are described in detail.The plasma flame is formed at an open end of a coaxial line under atmospheric pressure. Argon is used as plasma forming gas, and a 10 GHz CW magnetron with 10 W output power is used for plasma excitation.The efficiency of absorption of microwave power in the plasma is higher than90% with specific absorbing capacity of 0,4.4 kW/cm³     

A New State-space-based Algorithm to Assess the Stability of the Finite-difference Time-domain Method for 3D Finite Inhomogeneous Problems

The finite-difference time-domain (FDTD) method is an explicit time discretization scheme for Maxwell's equations. In this context it is well-known that explicit time discretization schemes have a stability induced time step restriction. In this paper, we recast the spatial discretization of Maxwell's equations, initially without time discretization, into a more convenient format, called the FDTD state-space system. This in turn allows us to derive a new algorithm in order to determine the stability limit of FDTD for lossy, inhomogeneous finite problems. It is shown that a crucial parameter is the spectral norm of the matrix resulting from the spatial discretization of the curl operator. In a rectangular simulation domain the time step upper bound can be calculated in closed form and results in a time step limit less stringent than the Courant condition. Finally, the validity of the technique is illustrated by means of some pertinent numerical examples.     

Statistical Evaluation of Adaptive Threshold Alignment for a Multi-Carrier CDMA Code Synchronization

This letter presents a statistical analysis of the decision threshold for a multi-carrier (MC) DS/CDMA acquisition system with a reference filter. The probabilities of detection and false alarm are derived, and the mean acquisition time is evaluated as a measure of the system performance. From the results, it is shown that in the performance analysis of the hybrid acquisition system with reference filtering, the statistical evaluation of the decision threshold seems more appropriate than the approximation of the decision threshold adopted in other schemes [7,8].     

Dispersion compensation of fiber Bragg gratings in 3100 km high speed optical fiber transmission system

By optimizing the fabrication process of the chirped optical fiber Bragg grating (CFBG), some key problems of CFBG are solved, such as fabrication repetition, temperature stability, group delay ripple (GDR), fluctuation of the reflection spectrum, polarization mode dispersion (PMD), interaction of cascaded CFBG, and so on. The CFBG we fabricated can attain a temperature coefficient less than 0.0005 nm/℃, and the smoothed GDR and the fluctuation of the reflection spectrum are smaller than 10ps and 0.5dB, respec-tively. The PMD of each CFBG is less than 1 ps and the dispersion of each grating is larger than -2600 ps/(nm·km). With dispersion compensated by the CFBGs we fabricated, a 13×10 Gbit/s 3100 km ultra long G.652 fiber transmission system is successfully imple-mented without electric regenerator. The bit error rate (BER) of the system is below 10-4 without forward error correction (FEC); when FEC is added, the BER is below 10-12. The power penalty of the carrier-suppressed return-to-zero (CSRZ) code transmission system is only 2.5 dB.     

Model Order Estimation for Joint Demodulation in DS-CDMA Systems

An iterative algorithm for estimating the number of relevant transmission paths characterized by the model order vector L in the uplink of a direct sequence code division multiple access (DS-CDMA) system is presented. Estimates of simplelower bounds on the probability of correct one-shot symbol estimates are formulated as a function of bit-error rate estimates of all users and maximized w.r.t. L. The joint demodulation for a given value Lis accomplished using a combination of a space-alternating generalized expectation-maximization (SAGE) algorithm for channel parameter estimation and a°multistage detector. Simulation results indicate that the modelorder is estimated correctly even in situations with considerably differentsignal power levels.     

Spectral Efficiency of Cellular Mobile Radio Systems with Different Traffic Loads

A lower bound on the Shannon capacity of the uplink channel of a narrowband cellular system is evaluated as a function of the reuse distance and the level of shadowing affecting the interfering signals assuming perfect channel state information (CSI) at the receiver. The effect of the first two tiers of interferers is determined, and compared with a simplified evaluation that takes into account only the first tier.Spectral efficiency is evaluated for different traffic loads, to assess the usefulness of traffic control. The performance improvementthat may be obtained by adopting the space diversity, to avoid deep fades in the received signal, is also evaluated. Our results show that traffic control may have a negative effect on the system performance.     

High Bit Rate OTDM-Transmission on Standard Fibre

In this paper we describe experimental and numerical studies on high bit rate, single span transmission system over a length of 160 km without amplifiers in the link (unrepeatered). From these studies we revealed that the tolerance of the residual dispersion is very restrictive. Proper dispersion management and PMD compensation techniques are important topics in these and future systems.     

A New and Exact Analysis of DS-CDMA Cellular Radio System Based on the Physical Interpretation of Nakagami Wideband Channel

In this paper we present the performance of two uplink/downlink DS-CDMA receivers in a Nakagami wideband channel. Two detection methods were considered; namely, coherent and differential detection RAKE receivers based on maximal ratio combining technique. We consider a new physical interpretation of the Nakagami channel and the instantaneous power of the multiple access interferers. In comparison with the previous researches in the literature, which are based on Gaussian approximation, this approach results in a more accurate solution for the problem. We analyzed and derived closed form formulae for probability of bit error for DS-CDMA cellular radio system in the Nakagami wideband channel. We presented a set of numerical results for coherent downlink receivers.     

Near Field Analysis of the Modal Scattering at Radiating Apertures

A rigorous method for the determination of the modal scattering at radiating apertures is presented. Near-field boundary conditions to be satisfied on the outer surface of the conducting structure containing the aperture (e.g. a horn antenna) are completely taken into account. The resulting scattering matrix of the radiating aperture can be integrated into any mode-matching technique as a termination for the cascaded structure commonly used to match the aperture to the exciting waveguide. The method is based on a multiple-multipole expansion of the electromagnetic field outside the radiating object in conjunction with a point-matching technique. Horn antennas with elliptical and circular apertures have been analyzed using the suggested method. Excellent agreement with measurement results has been achieved for both the radiation pattern and the aperture scattering parameters.     

Tunable Optical Delay Using Four-Wave Mixing in a 35-cm Highly Nonlinear Bismuth-Oxide Fiber and Group Velocity Dispersion

In this paper, an optically controlled tunable delay scheme has been proposed using four-wave mixing (FWM) wavelength conversion in a 35-cm highly nonlinear bismuth-oxide fiber (Bi-NLF) together with group velocity dispersion (GVD) in a chirped fiber Bragg grating (CFBG). The Bi-NLF offers a very large nonlinearity and gives rise to significant FWM over a short fiber segment. With the use of a CFBG, a delay range over 185 ps has been experimentally demonstrated. To investigate the performance of the tunable delay, we have applied the scheme for variable delays of 10-Gb/s amplitude-shift keying (ASK) and differential phase-shift keying (DPSK) data signals. The bit error rate (BER) measurements show a power penalty of less than 3.5 dB for both amplitude- and phase-modulated data formats. To further increase the delay time, the CFBG has been replaced by a dispersion compensated fiber (DCF) that provides a wider bandwidth of operation. A variable delay up to 840 ps has been obtained using dual-pump FWM that offers a conversion bandwidth of about 40 nm. The large conversion range helps to minimize GVD-induced pulse distortion as a shorter DCF can be used for a given delay. The Bi-NLF provides an enhanced stimulated Brillouin scattering (SBS) threshold, a reduced latency, and an increased compactness of the approach for practical applications.     

Electromagnetic Prospection via Homogeneous and Inhomogeneous Plane Waves: The Case of an Embedded Slab

This paper deals with the linear approximation of the inverse scattering problem for a dielectric slab embedded into a homogeneous half-space. After a proper normalization of the scattered field, the problem at hand is recognized to be related to a Fourier transform inversion with limited data. This permits to resort to the well-known results available in signal processing in order to discuss about the class ofthe retrievable unknowns and the resolution limits achievable by inversion. In particular, the role of both homogeneous and inhomogeneous incident plane waves in carrying out information about the profile under test is investigated and the role played by the dielectric permittivity of the host medium in determining the information content of the scattered field is pointed out.     

Low-Voltage Low-Power CMOS RF Four-Quadrant Multiplier

This paper describes a CMOS four-quadrant multiplier intended for use in the front-end receiver by utilizing the square-law characteristic of the MOS transistor in the saturation region. The circuit was simulated in standard 0.5 μm CMOS level 3 MOSIS (BSIM3 SPICE-based). The mixer has a third-order inter modulation (IM3) of 34.7 dBmV, a third-order intercept point (IP3) of -5.7 dBm, 1-dB compression (P-1dB) of -10.4 dBm and the power consumption is 1.18 mW from a single 1.5 V power supply. One of the features of the proposed design is using two MOS transistors limitation to reduce the supply voltage, which leads to reduce the power consumption.     

A New Algorithm for Optimum Multiuser Detection in Synchronous CDMA Systems

Optimum multiuser detection for Code Division Multiple Access (CDMA) systems requires the solution of an NP-hard combinatorial optimization problem. It is well known that the computational complexity of the optimum multiuser detector is exponential with the number of active users in the system. In order to reduce the complexity of the optimum multiuser detection, we propose a Reduced Complexity Maximum Likelihood (RCML) algorithm that includes a set of novel certain boundary rules and characteristics. We investigate the performance and complexity tradeoffs for the RCML algorithm by conducting a set of simulations; Maximum Likelihood (ML) detection as a reference for performance comparisons, and relaxation based Semidefinite Programming (SDPB) algorithm as a reference for complexity comparisons. We show that the RCML algorithm is a promising algorithm for its computational savings over relaxation based algorithms in lightly-to-moderately loaded CDMA systems, and for its optimality in highly loaded CDMA systems.