For mobile communication systems with code division multiple access (CDMA), a new modulation scheme, π/2-shift BPSK, is proposed. The performance has been evaluated in terms of relative out-of-band power, bit-error rate (BER), and spectral efficiency. As the result, it is shown that the proposed scheme has an advantage over conventional BPSK, conventional QPSK, and π/4-shift QPSK under nonlinear amplification.

This paper proposes a differentially-coded-quadrature-phase-shift-keying (DQPSK) coherent demodulator using a new simultaneous carrier and bit-timing recovery scheme (SCBR). The new DQPSK SCBR (DSCBR) scheme works with a frequently used preamble, whose baseband signal alternates between two diagonal decision points, for example, a repeated bit-series of "1001." With the DSCBR scheme, the proposed demodulator achieves a significantly agile carrier and bit-timing recovery using an open-loop approach with a one-part preamble. To illustrate this, a preamble of 8 symbols is applicable with the Eb/No degradation from the theory over AWGN of 0.2 dB. It is also shown that the proposed demodulator achieves an improvement in the required Eb/No of more than 2 dB over differential detection over Ricean fading communication channels. The channels are modeled for wireless broadband communication systems with directional antennas or line of sight (LOS) paths. This paper concludes that the proposed demodulator is a strong candidate for receivers in wireles broadband communication systems.

This paper presents a new offset-quadrature-phase-shift-keying (OQPSK) coherent demodulation scheme for wireless asynchronous transfer mode (WATM) systems that premise the Ricean fading communication channels (e.g., typically with derectional antennas). The presented demodulator is basically advanced from a simultaneous carrier and bit-timing recovery (SCBR) scheme by newly employing a phase compensated filter and a reverse-modulation scheme for OQPSK. This advancement aims to enhance the carrier phase tracking performance against the phase fluctuation due to the fading and/or the phase rotation caused by the carrier frequency error of the oscillator. Design consideration and performance evaluation of the demodulator are extensively carried out under Ricean fading channels typical of the WATM systems as well as additive white Gaussian noise (AWGN) channels. The evaluation ressults show that the advanced SCBR (ASCBR) scheme achieves a bit-error-rate/cell-error-rate (BER/CER) performance close to ideal coherent detection with a considerably short preamble, e.g., 8 symbols. Specifically, compared with differential detection (evaluated for QPSK with the hard-wired clock), the new coherent demodulator achieves a significant required Eb/No improvement, which becomes larger as the fading condition degrades. This paper concludes that the ASCBR scheme is a strong candidate for the Ricean-fading-premise WATM systems.

Approximate maximum likelihood (ML) detection implemented by a reduced state Viterbi algorithm (VA), called the reduced state Viterbi coherent detection (RSVCD) algorithm in this paper, is described for the reception of uncoded M-ary PSK (MPSK) signals transmitted over additive white Gaussian noise (AWGN) channels. An M-state trellis, each state representing one of M signal constellation points, is used. The RSVCD algorithm performs parallel channel estimation based on the per-survivor processing principle (PSPP). Simple decision feedback CD (DFCD) is deduced as a special case of RSVCD. Unified BER expressions are derived for RSVCD, DFCD, and approximate ML detection implemented as an ML-state Viterbi algorithm (referred to as VACD) [6] as well as ideal CD and differential detection (DD). Computer simulation results are also presented and compared with theoretical results.

Current-voltage characteristics of triple-barrier resonant tunneling diodes are theoretically analyzed taking phase breaking into account. The peak current in predicted using conventional theories is much smaller, typically by a factor of 1/3000 for a coherent length of 100 nm, than that measured because the incoherent tunneling process is neglected. We take both the coherent and the incoherent tunneling processes into account in the analysis and show that the product of the peak current and the voltage width at half maximum of the peak current is almost constant even when the phase coherent length varies between 50 and 1000 nm. The peak current density increases by two orders of magnitude in the model developed here.

A piece of information on the polarization effects on the effective dielectric constant εeff of a medium whose dielectric circular cylinders are randomly distributed is obtained by analyzing εeff for both E-wave and H-wave incidences. Our numerical analysis shows clearly the difference of εeff between E-wave and H-wave incidences and also shows the difference of εeff between our method and the Foldy's approximation.

Direct sequence code division multiple access (DS-CDMA) is a promising candidate for 3rd generation mobile communications systems. We recently proposed a coherent multicode DS-CDMA (CM-CDMA) scheme that uses pilot symbol-aided coherent RAKE, interference power measurement based transmit power control, orthogonal multicode transmission, and concatenated channel coding. We have implemented a CM-CDMA test-bed for a series of laboratory and field tests using the 2 GHz band. This paper describes the test-bed system and experimental results are presented. It is confirmed that pilot symbol-aided coherent RAKE can reduce the required signal energy per bit-to-interference plus background noise spectrum density ratio (Eb/Io) by 2-3 dB from that achievable with differential detection. Also shown is that by using both RAKE combining and SIR-based power control the transmit power of mobile stations can be significantly reduced. Measurement results show that the required Eb/Io degrades only slightly when 24 code-channels (768 kbps) are used since orthogonal Gold sequences are used as short spreading codes.

This paper describes a CDMA cellular system based on adaptive interference cancellation (CDMA-AIC) with a large capacity. In the CDMA-AIC, each base station employs a single-user type adaptive interference canceller (AIC), which consists of a fractionally chip-spaced code-orthogonalizing filter (COF) and a coherent detector. The AIC adaptively removes power-dominant multiple-access interferences (MAIs) in the cellular system, regardless of whether they are intra-cell interferences or inter-cell interferences, without any information about them, such as spreading codes, signal received timings and channel parameters. Evaluation under the multiple-cell environment demonstrates that the reverse link capacity of the CDMA-AIC with QPSK modulation is 3.6 times as large as the capacity of the CDMA without MAI cancellation. Further, the capacity is less sensitive to transmission power control errors than that of the conventional CDMA systems.

This paper discusses the performance of non-coherent reception for M-ary spread-spectrum (M-ary/SS) signals in the presence of carrier frequency offset. In general, the M-ary/SS scheme is expected to be of higher spectral efficiency than the conventional DS/SS schemes, but its performance may be degraded by the carrier frequency offset. We, therefore, analyze the effect of carrier frequency offset on the performance of the non-coherent M-ary/SS system with orthogonal modulation using a set of sequences generated by the Hadamard matrix. As a result of the analysis, it has been found that the carrier frequency offset may cause a great deal of degradation in the performance, and that its effect has a distinctive property which is due to the characteristic of Hadamard matrix, at the same time. Making use of this property, we propose two schemes that can mitigate the effect of carrier frequency offset: one is based on choise of the code sequences, the other is on the error correcting code. The effectiveness of the schemes is evaluated in the terms of symbol-error-rates through analysis and computer simulation.

This paper proposes a multiple optical wideband frequency modulation system and clarifies its phase noise insensitivity. In this system, an optical carrier is phase-modulated by a conventional FM signal to generate many sidebands in optical frequency band. The n-th order sideband component yields also FM signal with frequency deviation of n times the one of original FM signal. Therefore, by selecting the high order optical sideband, the wideband optical FM signal can be obtained. Moreover, if some sidebands are simultaneously extracted and multiplied at the receiver, a wideband FM signal with larger frequency deviation and no laser phase noise can be obtained, and FM threshold extension can be realized.

In coherent optical space communication systems, the phase noise generated from high power laser diodes and the polarization axis mismatch between transmitter and receiver are the serious problem. In this paper, a novel coherent optical space communication system, called optical polarization azimuth modulation (POLAM)/heterodyne detection system is newly proposed, and its system performance is theoretically investigated. It is clarified that the POLAM system can perfectly remove the laser phase noise, is actually insensitive to the polarization axis mismatch, and can provide the remarkable performance improvement compared to a conventional optical frequency modulation system.

The sensitivity degradation due to unmatched quantum efficiencies is theoretically investigated for coherent optical POLSK heterodyne, homodyne and balanced receivers with shot noise, thermal noise and LO intensity noise. This analysis is based on the exact expressions of the probability density function (PDF) of the noise process to calculate the bit-error-rate (BER) considering LO intensity noise and unmatched quantum efficiencies. We derive the optimum LO power to minimize the power penalty for POLSK receivers. The theoretical results clarify the relation between the unmatched quantum efficiencies and sensitivity degradation due to the LO intensity noise. Based on this analysis, it is found that the balanced receiver is preferable for the design of POLSK receivers.

This paper proposes a new burst coherent demodulator that improves transmission quality of microcellular TDMA/TDD systems for personal communications and has configuration suitable for low power consumption with LSIC-implementation. To achieve the better transmission quality, the proposed demodulator employs coherent detection with a unique carrier recovery scheme that can operate without any preamble for carrier recovery. In addition, the demodulator uses a clock recovery scheme with clock phase estimation using twice differentiation, which eliminates hangup and attains fast clock acquisition at 2 samples/symbol. Experimental results clarify the superiority of the proposed coherent demodulator for microcellular TDMA/TDD systems. The proposed coherent demodulator reduces the irreducible frame error rate by 40%, and achieves 4dB improvement at the frame error rate of 10% compared with differential detection under the Rayleigh fading (fD/fs=810-5, τrms/Ts=510-2) typical of personal communication environments.

This paper proposes Coherent-HYBrid Direct-Sequence Fast-Frequency-Hopping (CHYB-DS-FFH) CDMA with Adaptive Interference Cancelling (AIC) for cellular mobile communications. The features of CHYB-DS-FFH are symbol-by-symbol frequency diversity and low chip-rate DS multiplexing both of which are based on a coherent FFH modulation and demodulation scheme. The combination of coherent FFH, space diversity, and AIC is very effective for reducing the performance degradation due to interference. Computer simulations demonstrate BER performance of a 2 hop 500-kHz-interval frequency hopping system using () a linear canceller or () a nonlinear canceller. Both systems employ the two branch space diversity reception of 10kb/s QPSK with FFH over a 1MHz system bandwidth. In quasi-static channels, the average BER performance is 10-2 with average Eb/N0 less than 8dB. In dynamic fading channels under full interference conditions, CHYB-DS-FFH with the linear adaptive interference canceller realizes a BER of 10-2 at the average Eb/N0 of 15dB with maximum Doppler frequency fD of 5Hz, whereas CHYB-DS-FFH with the non-linear adaptive interference canceller achieves the same BER at the average Eb/N0 of 15dB with fD, equal to 30Hz.

The effective dielectric constant εeff of discrete random medium composed of many dielectric spheres has been analyzed by EFA (Effective Field Approximation), QCA (Quasicrystalline Approximation) and QCA-CP (Quasicrystalline Approximation and Coherent Potential) in the case where the optical path length is very large in the medium. These methods lead to a reasonable K for non-large dielectric constants of spheres, while their methods yield an unphysical dependence of εeff on large dielectric constants of spheres: that is, the εeff does not become large for increasing the dielectric constant. In this paper, we remove the unphysical dependence and present new results for εeff of our method, comparing with the results for εeff of EFA, QCA and QCA-CP.

We report on Brillouin optical-fiber time domain reflectometry (BOTDR) for distributed temperature or strain measurement along a single-mode optical fiber. BOTDR uses Brillouin scattering in optical fibers, whose Brillouin frequency shift increases in proportion to temperature or strain induced in the fiber. This method requires access to only one end of a fiber, as with conventional optical time domain reflectometry (OTDR) which uses Rayleigh scattering in optical fibers. In BOTDR, a coherent optical detection method is used as a backscattered light detection technique. This technique can achieve both high sensitivity and high frequency resolution and easily separate a weak Brillouin line from a strong Rayleigh scattering peak and Fresnel reflected light. Experimental results show the potential for measuring temperature and strain distribution with respective accuracies of 3 or 0.006%, and a spatial resolution of 100m in an 11.57km long fiber.

An intermediate-frequency-combining (IF-combining) polarization diversity using frequency conversion is proposed. The proposed diversity requires no phase controller as opposed to the conventional IF-combining diversity. It has been theoretically clarified that this diversity has polarization insensitive bit-error-rate (BER) characteristics. The effectiveness has been confirmed by experiments in which the sensitivity dependence on the polarization is suppressed to within 0.8dB and a stable 101km fiber transmission at 600Mbit/s is achieved.

We propose the coherent subcarrier multiplexed (SCM) system with distributing local oscillator (LO) in local loop. The proposed system can realize multichannel transmission with one optical carrier by using the SCM technique and has no need to have LO at each station. Therefore the proposed system becomes cost-effective. The proposed SCM system uses bandpass filter to select a specific channel. We analyze CNR of the system with frequency-shift keying (FSK) in a multioctave configuration. First, the general expression of CNR is derived and is shown for the following parameters such as the number of channels, the position of station on the loop, and the number of stations on the loop. Second, optimal phase modulation (PM) index is derived, and the optimal CNR, minimum required power of lasers, and maximum number of stations that the proposed system can serve are shown by using it. Moreover CNR of the proposed system is compared with that of the system having LO at each station in local loop. It is shown that the proposed system can obtain good performance at the expense of slight increase of the output power of only two lasers at the central station. Therefore the proposed system is cost-effective and practical.

We propose Polarization-Shift-Keying (POLSK) homodyne system using phase-diversity receivers and theoretically analyze its bit-error-rate (BER) performance. Since the proposed system uses polarization modulation and homodyne detection, it can cancel the phase noise and is attractive at a high bit-rate transmission. It is found that the receiver sensitivity of the proposed POLSK homodyne system is the same as that of POLSK heterodyne system and is much better than that of DPSK phase-diversity homodyne systems at high signal-to-noise ratio (SNR). We also cosider theoreically the effect of the fluctuation of state of polarization (SOP) on the BER performance of POLSK homodyne system.

We propose Polarization-Shift-Keying (POLSK) homodyne system using phase-diversity receivers and theoretically analyze its bit-error-rate (BER) performance. Since the proposed system uses polarization modulation and homodyne detection, it can cancel the phase noise and is attractive at a high bit-rate transmission. It is found that the receiver sensitivity of the proposed POLSK homodyne system is the same as that of POLSK heterodyne system and is much better than that of DPSK phase-diversity homodyne systems at high signal-to-noise ratio (SNR). We also cosider theoretically the effect of the fluctuation of state of polarization (SOP) on the BER performance of POLSK homodyne system.