In multi-carrier optical transmission systems, availability of a transponder decreases in accordance with the increase in the number of optical modules comprising the transponder. In this paper, we clarify promising schemes to improve availability by comprehensively comparing them. We first clarify the condition under which availability problems become apparent by analyzing the basic trend in availability. Then, we compare the improvement in availability and difficulty in transmission system development. As a result, we showed that the Pool scheme, where the small amount of shared backup optical modules are implemented to avoid transponder failure, is promising since it effectively increases availability with a small amount of additional optical modules and has enough feasibility.

In this paper, in order to improve the reliability of Ethernet communication, the effect of pulse disturbances on the communication quality of 100BASE-TX was evaluated experimentally. A relationship between the threshold level of Ethernet and disturbances affecting communication quality was revealed when the amplitude and width of the pulse disturbance were changed. A disturbance in which the pulse width was the same as 1 bit time of the signal degraded the communication quality the most. These findings should help in the effort to apply Ethernet to automotive area network.

We numerically evaluate Bit Error Rate (BER) performance of four- and eight-dimensional modulation formats with Bit-Interleaved Coded Modulation Iterative Detection (BICM-ID) compared with Gray mapped and natural binary mapped two-dimensional formats for high-speed optical communication systems. The BICM-ID, which is composed of a demodulator and a decoder, effectively improves power efficiency of the multi-dimensional formats taking into account receiver sensitivity and transmission capacity per symbol. Further, we quantitatively verify that the BER performances significantly depend on a priori/extrinsic mutual information exchange between a demodulator and a decoder, which is illustrated by Extrinsic Information Transfer (EXIT) chart.

This paper presents omega-shaped resonant elements constructing a reflectarray for a carpet cloak. The dimension of a unit cell in the x and the y directions are d_x = d_y = 10.0 [mm] and the thickness of dielectric substrate with permittivity ϵ_r = 1.67 is h = 5.0 [mm]. We use 12 kinds of elements at the design frequency 10 GHz. To verify usefulness of the proposed elements, a carpet cloak constructed by them is designed and fabricated for experimental consideration. The scatterer has a triangular shape, and the horizontal width and the height are 240 [mm] and 35 [mm], respectively. The effectiveness is verified thorough evaluation of the calculated and the measured radiation patterns.

In this letter, we propose a novel peak-to-average power ratio (PAPR) reduction scheme based on orthogonal pilot sequence (OPS) for orthogonal frequency division multiplexing (OFDM) systems. We change the pilot symbols’ phases iteratively according to a set of orthogonal sequences, and use the phases of the pilot subcarriers as the phase factors for data subcarrier groups. The proposed scheme can achieve up to three times more PAPR reduction compared to the conventional schemes without sacrificing side information (SI)-free transmission.

We propose a highly sensitive method that can safely measure the Raman gain coefficient spectrum by detecting the spontaneous Raman scattering emitted from the transmission fiber pumped by a single-polarization laser-diode light source in distributed Raman amplification systems. With the proposed method, we have successfully obtained an accurate Raman gain coefficient spectrum with a significantly low pump power of ∼0.35 mW at a small Raman gain of 0.01 dB.

In this paper, we provide a theoretical error analysis of a satellite ephemeris calibration for the dual-satellite TDOA/FDOA geolocation method. First, the error covariance matrix for the ephemeris calibration is derived. Then, the result is incorporated into the error covariance matrix for geolocation. The derived equation is numerically evaluated to provide an intensive error analysis in time and spatial coordinates. Further, Monte Carlo simulation results are provided, and it is shown that the theoretical results coincide with the Monte Carlo simulation results.

In this paper, we investigate the almost periodic frequency arrangement (APFA) asynchronous system for super-multi-access radio systems, and APFA configuration procedure on a frequency domain multiplex scheme by using almost periodic function (APF). We report on the relationship between the total number of prime numbers, the number of sub-carriers, and the normalized frequency standard deviation for a system with up to one million users. By using computer simulations, we show the multi-carrier modulation and asynchronous demodulation based on APFA, in which ICI interference by nonlinear elements is improved compared with the orthogonal frequency-division multiplexing (OFDM).