Advantages of CDMA and spread spectrum techniques over FDMA andTDMA in cellular mobile radio applications

A unified theoretical method for the calculation of the radio capacity of multiple-access schemes such as FDMA (frequency-division multiple access), TDMA (time-division multiple access), CDMA (code-division multiple access) and SSMA (spread-spectrum multiple access) in noncellular and cellular mobile radio systems is presented for AWGN (additive white Gaussian noise) channels. The theoretical equivalence of all the considered multiple-access schemes is found. In a fading multipath environment, which is typical for mobile radio applications, there are significant differences between these multiple-access schemes. These differences are discussed in an illustrative manner revealing several advantages of CDMA and SSMA over FDMA and TDMA. Novel transmission and reception schemes called coherent multiple transmission and coherent multiple reception are briefly presented     

Error floor of MSK modulation in a mobile-radio channel with twoindependently fading paths

We investigate the error probability bit error rate (BER) of minimum shift keying (MSK) modulation with differential detection in a two-path fading channel without noise (error floor). We develop a new method for the computation of the BER: we show that errors occur if the phasors of the instantaneous impulse response fall into certain regions of the complex plane; then we average over the statistics of the phasors to arrive at the mean BER. With this method, we derive analytical expressions for the BER for arbitrary amplitude statistics of the paths. For the special case of two Rayleigh-fading paths with small delay, we find that the BER is proportional to the square of the mean delay spread (normalized to the bit length) if we sample between the two pulses. This proves the qualitative behavior of previous estimates, but our results allow also a more exact quantitative formulation. The quadratic dependence of the BER on the delay spread breaks down if we have one Rayleigh-fading and one Rician-fading path. We find that the bit combinations 1-11 and -11-1 do not lead to errors in the two-path model. However, additional Monte Carlo simulations show that these bit combinations do lead to errors in a three-path model     

Design, manufacture and evaluation of a scalable high-performanceneural system

The authors describe a scalable neural system, HyperNet, based on a probabilistic RAM-based architecture and using a custom VLSI IC. A system using five HyperNet VLSI ICs and capable of realising up to 10240 neurons has been designed, manufactured and demonstrated to have the potential to learn more than three orders of magnitude faster than simulations on current workstations     

Photonic packet switches: architectures and experimentalimplementations

Photonic packet switches offer high speed, data rate and format transparency, and flexibility required by future computer communications and cell-based telecommunications networks. In this paper, we review experimental progress in state-of-the-art photonic packet switches with an emphasis on all-optical guided-wave systems. The term all-optical implies that the data portion of a packet remains in optical format from the source to the destination. While the data remain all-optical, both optical and optoelectronic techniques have been used to process packet routing functions based on extremely simple routing protocols. An overview of the design issues for all-optical photonic packet switching is given and contrasted with electronic packet switch implementations. Low-level functions that have been experimentally implemented include routing, contention resolution, synchronization, and header regeneration. System level demonstrations, including centralized photonic switching and distributed all-optical multihop networks, will be reviewed     

Calculation of shift of avalanche transit time phase delay due tooptically injected carriers in indium phosphide avalanche diodes

A computer method for the calculation of the phase shift due to optically injected carriers in an InP avalanche transit time diode has been suggested using the numerically simulated negative resistance profiles in the depletion layer of the diode. The results show that the phase shift due to hole injection is larger than that due to electron injection which explains the pronounced effect of photogenerated hole leakage current in modulating the microwave properties of InP diodes     

Optimal discrimination and classification of neuronal actionpotential waveforms from multiunit, multichannel recordings usingsoftware-based linear filters

Describes advanced protocols for the discrimination and classification of neuronal spike waveforms within multichannel electrophysiological recordings. The programs are capable of detecting and classifying the spikes from multiple, simultaneously active neurons, even in situations where there is a high degree of spike waveform superposition on the recording channels. The protocols are based on the derivation of an optimal linear filter for each individual neuron. Each filter is tuned to selectively respond to the spike waveform generated by the corresponding neuron, and to attenuate noise and the spike waveforms from all other neurons. The protocol is essentially an extension of earlier work (S. Andreassen et al., 1979; W.M. Roberts and D.K. Hartline, 1975; R.B. Stein et al., 1979). However, the protocols extend the power and utility of the original implementations in two significant respects. First, a general single-pass automatic template estimation algorithm was derived and implemented. Second, the filters were implemented within a software environment providing a greatly enhanced functional organization and user interface. The utility of the analysis approach was demonstrated on samples of multiunit electrophysiological recordings from the cricket abdominal nerve cord     

Transition From Perturbed to Coupled-Cavity Behavior With Asymmetric Spectral Emission in Ridge Lasers Emitting at 1.55 μm

We have investigated a series of ridge waveguide lasers with deeply etched slots in the ridges. The slots do not penetrate the active region, but are deep enough to strongly perturb the longitudinal modes. By the addition of slots, a transition between perturbed-mode and coupled-cavity behavior is crossed. With a group of four or more slots, the below-threshold amplified spontaneous emission spectrum from each end of the laser has different periods and the facet-facet oscillations are suppressed indicating that the different sections have become quasi-independent. A model using a distributed emitter in the cavity reproduces this behavior. Above threshold, the single contact coupled cavity lasers are single mode with greater than 30-dB sidemode suppression ratio over a wide range of currents     

On the existence and the stability of solutions for higher-order semilinear Dirichlet problems

We investigate the existence and stability of solutions for higher-order two-point boundary value problems in case the differential operator is not necessarily positive definite, i.e. with superlinear nonlinearities. We write an abstract realization of the Dirichlet problem and provide abstract existence and stability results which are further applied to concrete problems.