The dipole-dipole interaction among excitons is shown to give rise to an intrinsic nonlinearity, which yields a localized mode in a forbidden band, providing a coherent state for quantum computation. Employing this mode, a quantum XOR (exclusive OR) gate is proposed. A block structure of quantum dot arrays is also proposed, to implement quantum circuits comprising the quantum XOR gates for computation.

A comparison among the possible nonlinear photonic interactions for scalable nanometer networks and quantum gates as well as for coherence retention in solids is made theoretically, and then numerical plottings are given, on the basis of the dipole length estimated from our µ-PL (microphotoluminescence) spectra of GaAs/AlGaAs coupled quantum dots (QDs) having a pair of 0.3 meV splittings. Furthermore, prospective device concepts based on these nonlinear multipolar interactions are given.

We evaluated the transmission performance, including received power and transmission throughput characteristics, in 4×4 single-user multiple-input multiple-output (SU-MIMO) transmission for synchronous time division duplex (TDD) and downlink data channels in comparison with single-input single-output (SISO) transmission in an environment where a local 5G wireless base station was installed on the roof of a research building at our university. Accordingly, for the received power characteristics, the difference between the simulation value, which was based on the ray tracing method, and the experimental value at 32 points in the area was within a maximum difference of approximately 10 dB, and sufficient compliance was obtained. Regarding the transmission throughput versus received power characteristics, after showing a simulation method for evaluating throughput characteristics in MIMO, we compared the results with experimental results. The cumulative distribution function (CDF) of the transmission throughput shows that, at a CDF of 50%, in SISO transmission, the simulated value is approximately 115Mbps, and the experimental value is 105Mbps, within a difference of approximately 10Mbps. By contrast, in MIMO transmission, the simulation value is 380Mbps, and the experimental value is approximately 420Mbps, which is a difference of approximately 40Mbps. It was shown that the received power and transmission throughput characteristics can be predicted with sufficient accuracy by obtaining the delay profile and the system model at each reception point using the both ray tracing and MIMO simulation methods in actual environments.

A novel optoelectronic mesoscopic neural device is proposed. This device operates in a neural manner, involving the electron interference and the laser threshold characteristics. The optical output is a 2–dimensional image, and can also be colored, if the light emitting elements are fabricated to form the picture elements in 3–colors, i.e. R, G, and B. The electron waveguiding in the proposed device is analyzed, on the basis of the analogy between the Schrödinger's equation and the Maxwell's wave equation. The nonlinear neural connection is achieved, as a result of the superposition an the interferences among electron waves transported through different waveguides. The sizes of the critical elements of this device are estimated to be within the reach of the present day technology. This device exceeds the conventional VLSI neurochips by many orders of magnitude, in the number of neurons per unit area, as well as in the speed of operation.

The ATM Wireless Access (AWA) System allows portable terminals such as notebook PCs to provide up to 10Mbits/s to each user. AWA will be one of the last hops of the fiber system; it seamlessly provides wireless terminals with most of the services available in the fiber system. A prototype is developed to confirm system realization and the technical feasibility of the radio transmission rate of 80 Mbit/s, the highest yet reported in wireless access systems, by employing ATM technology to support multimedia communication with different communication quality requirements. The prototype uses TDMA as the multiple access method. This paper proposes the system concept and technical issues of the AWA system. The design and performance of the AWA prototype are clarified. It is confirmed that the target performance of the prototype can be achieved and technical issues are feasible.

This paper describes the design and performance of a new adaptive IF equalizer for correcting amplitude and group delay dispersion due to selective fading in a 200 Mb/s, 16 QAM digital radio system. This equalizer contains only a simple variable-resonance circuit automatically controlled by a microcomputer. This adaptive equalizer can reduce both amplitude and delay dispersions due to minimum phase fading and amplitude dispersion due to non-minimum phase fading. In field trial tests (over-water, 52.6 km span), outage time for 16 QAM signals was significantly reduced by about 80% during severe fading periods by about 97.5% during two fading months using this equalizer. Additionally, the in-band amplitude dispersion probability was reduced by about 99%.

This paper describes a new control algorithm for a transversal filter in a cross polarization interference canceller (XPIC) for digital microwave radio systems. The proposed new algorithm includes the shift bit select (SBS) method whose abjustment function of optimal correlation provides complete adaptability to the severe propagation condition changes. High speed control response under fading, as well as stability under steady state, can be achieved. Moreover, by combining the SBS method with the maximum level error method, wide acquisition range and short acquisition time can be realized. An analysis of convergence properties of the XPIC is presented, and using a 256 QAM signal, the availability with the SBS method experimentally confirms the superiority over conventional algorithm.

A mobility management scheme that reduces signaling traffic load and connection setup time is a pivotal issue in designing future personal communication service (PCS) networks to satisfy Quality of Services requirements and use network resources efficiently. Particularly, required is scalable mobility management, to meet the explosive growth in number of users for the current second-generation wireless communication systems, and to materialize PCS concepts such as terminal, personal, and service mobility. Many mobility management schemes have been proposed for the reduction of signaling traffic. However, these schemes have not been sufficiently compared using a unified performance measure that is free of assumptions as to mobility model or database architecture. In this paper, we categorize the various mobility management schemes for advanced PCSs in distributed environments into four types and clarify the appropriate domain for each type. To do this, we settled on the number of signals at connection setup and location registration as a unified performance measure, since this value closely relates to connection setup time and network efficiency. We found two kinds of schemes with replicating and caching functions of user information that are extremely effective for reducing signaling load and hence connection setup time. These schemes are appropriate when the probability that a user is in his/her home area is relatively small or the connection setup rate is relatively high compared to the location registration rate. These are the most likely situations in the advanced PCS for global environments.

The dipole-dipole interaction in the quantum mechanical treatment of the matter-radiation dynamics, is shown to give rise to split energy levels reminiscent of the nonlinear coupled spectral features as well as a self-sustained coherent modes. Wiener's theory of nonlinear random processes is applied to the second harmonic generation (SHG), leading also to coupled spectral pulling and dipping features, due to the dual noise sources in the fundamental and the harmonic polarizations. Furthermore, the nonlinear spectral features are suggested to be applied to implement quantum (qubit) gates for computation.

A novel method to enhance the practical security of interferometric quantum cryptography is proposed, giving the protocol and detailed constructions including a controlled spontaneous photon emitter, a superradiance amplifier, beam splitters, phase shifters, and a pair of Mach-Zehnder interferometers. The intrinsic uncertainty due to the random phase selection out of three, leads to the detection of eavesdropping. The physical uncertainty of the controlled spontaneous emission of coherent photons also adds temporal equivocation to confuse eavesdroppers.