We show that if a signal (random or deterministic) is sampled nonuniformly (with Poisson or uniform distribution) and then low pass filtered, the output signal is equal to the input signal plus an additive white noise uncorrelated to the input signal. Hence, the power spectrum of random nonuniform samples and SNR is derived. Similar results can be derived for uniform sampling with some missing samples or with time jitter. We finally, show that the original signal can be recovered exactly (in the mean squared error sense) from random nonuniform samples by an iterative method provided that the average sampling rate is greater than the Nyquist rate.

A new fading reduction technique applicable to small shipborne antennas in the future maritime satellite communications is proposed. This technique has simple hardware construction and a good fading reduction effect. In this paper, the principle of the proposed fading reduction technique and the theoretical reduction effects of the technique are presented, comparing with those of the Polarization Shaping Method.

Friction coefficient between coated optical fibers and a loose-tube was evaluated theoretically and experimentally. Simple method was investigated for direct measurement of frictional force and the measured coefficient by the method has been found to represent frictional characteristics of a long stranded optical cable excellently.

A new waterproof optical fiber cable is proposed which used absorbent polymer yarn instead of the conventional jelly-compound as a filling material. This yarn limits the length of water penetration into cable less than 10 cm that is short enough to guarantee long-term reliability. And it is found that the cable has superior characteristics for dynamic bend-tension test.

1.55µm GaInAsP/InP BH lasers with multiple p-n current blocking layer were fabricated entirely by low-pressure OMVPE. The undercut portions were filled in a manner similar to mass transport process. The laser shows a threshold current of 48 mA at 300 K under CW operation.

The optical damage in proton-exchanged and Ti-indiffused LiNbO₃ optical waveguide are first quantitatively measured by photorefractive (photoinduced) grating method. The measured optical damage in the proton-exchanged waveguide is found to be 10^-4 times as small as that in Ti-indiffused waveguide.

The letter deals with theoretical analysis on Lamb waves propagating in a composite membrane of ZnO and SiO₂. Calculation was done for the lowest pseudo symmetric (S₀) and antisymmetric (A₀) modes. It was shown that, for example, when the thickness of each film is of the order of 0.1 wavelengths or less, S₀ mode has a large electromechanical coupling coefficient of about 6% and a velocity of more than 5,000 m/s. A₀ mode, as may be expected, has a quite small velocity of less than 1,500 m/s with an electromechanical coupling coefficient of about 3%. The result suggests that it may be possible to realise various monolithic acoustic wave devices based on Lamb waves propagating in the ZnO/SiO₂ composite membrane.

To utilize the common-key encryption foe the message protection in a communication network, it is desired to settle the problem of how to distribute the common keys. This paper discusses a sort of schemes (the direct schemes, we call) that smartly provide different keys in different communications. Such a property has not attained via the basic scheme for the public key distribution systems proposed by Diffie and Hellman. This paper shows that the recently introduced five direct schemes are classified into three sets (called sequences) of infinite schemes, and points out that there are some tight relations among the sequences. And it is clarified which is the best in the three sequences by a systematic evaluation of the complexities for the normal update and for the deliberate forgery of the shared common keys.

This paper describes experiments for evaluating the speech quality of packetized voice communications. The experimental conversations are performed through experimental packetized voice communications equipment, which provides packet transmission delays and packet losses. Three experimental results are apparent: packet losses degrade speech quality much more than packet transmission delays in PCM, packet delays affect speech quality more than packet losses in ADM, and inserting the last received codes for lost packets reduces the degradation of speech quality in PCM.

This paper describes a design method for a 446 Mb/s optical repeater with four kinds of monolithic integrated circuits. It is mainly concerned with the circuit division, optical receiver and timing amplifier design methods. Repeater circuit is divided based on maximum allowable gain and power consumption. Allowable gain determined by IC package crosstalk characteristics at 400 MHz transmission band is presented here. Allowable maximum power consumption of 1 W/chip is also determined. Effective amplification bandwidth adjustment methods for the optical receiver and the d.c. drift control (DCFB) system design method, specific in the d.c. coupled monolithic integrated optical receiver, are described. Finally, a useful design method for small-phase-shift timing amplifier is proposed. This is a circuit parameter optimizing method which monitors operating point dependence of small signal amplification bandwidth. The 446 Mbit/s submerged optical repeater has successfully been developed using these design methods.

Four sets of on-board experiments regarding the measurements of 1.5 GHz multipath fading on propagation paths with low elevation angles and evaluation of fading reduction effects using the polarization shaping method were carried out. This paper describes the outline of the experiments, results obtained, and the comparison with theoretical values of the model presented by the authors. Results indicate that fading depth hardly depends on the wave height when the wave height is higher than 1 m, and that the polarization shaping method is effective for both up-link and down-link fadings for sea conditions with a wave height of up to at least 3 m.

This paper presents a numerical analysis for the plane wave scattering by an infinite plane grating. First, the induced surface currents on conducting strips are expanded in Fourier series with a weighting function corresponding to field singularities near edges of the strips. Second, all the boundary conditions are satisfied in Fourier spectral domain, which leads to infinite sets of algebraic equations. Since the field singularities have been taken into account, the final numerical results show very rapid convergences for the near fields as well as for the far fields. From numerical comparison of the present method with other various methods, it is found that the present method provides us precise values as for transmitted powers. Numerical calculations are also made for distributions of the surface currents.

In the Morita and Higuti (M-H) attenuation prediction method, the spatial correlation function of specific attenuation for conditional time, ρ_Γ, is, approximated by ρ, the spatial correlation function of rainfall rate. The accuracy of this approximation is examined in this paper. An equation relating ρ_Γ to ρ is theoretically derived assuming a bi-lognormal distribution of rainfall rates at two points. Theoretical examination shows that the approximation ρ_Γ=ρ does not necessarily hold accurately in the frequency range 10 to 100 GHz, except for frequencies near 30 GHz. This is also confirmed experimentally by measurements from a rain gauge network. A modified M-H method in which attenuation is predicted using ρ_Γ is proposed, and an extensive numerical comparison between both methods is made. It is shown that the approximation ρ_Γ=ρ can limit the applicability of the M-H method in terms of rain climatic condition, frequency, and path length, and that the modified M-H method has the advantage of improved applicability, compared with the M-H method.

A new boundary integral formulation is presented in order to solve a general Laplace-Poisson's equation, which is one of the basic equations of semiconductor devices. As this formulation is based on Green's second identity or Gauss' divergence theorem, no conventional volume integral is needed, regardless of arbitrary distributions of space charge. The potentials and electric field intensities at interface nodes put between a Laplace and a Poisson domain are analytically calculated, because interface nodes are treated as same as internal points. It is effective and powerful to device analysis of such a junction-gate field effect transistor with interfaces movable according to operation bias conditions. On the basis of simple numerical experiments, the present method is applied to a simplified device models. It is shown that device analysis can be easily obtained for a more small discretized model. In consequence, numerical results also demonstrate the effectiveness of this approach.

The apparatus of a rotating linearly polarized light source was constructed using an Acoustooptic Tunable Filter (AOTF) employing a Tellurium dioxide (TeO₂) crystal. The characteristics of optical devices, such as birefringence of optical fiber, and film thickness and refractive index of optical thin-film, were measured using this apparatus. The advantages of this apparatus are its simple construction, and ability to use various laser beams.