The dual stage optical splitter configuration is often utilized in PON systems to effectively accommodate widely-dispersed users. This paper introduces a more effective user accommodation approach that places bidirectional optical amplifiers in some branches of the optical splitter inside the central office (CO); it allows a single optical line terminal (OLT) to achieve the coexistence of normal- and extended-distance areas. To ease the issue of amplified spontaneous emission (ASE) noise, which is inherent in this system configuration, we propose to use a semiconductor optical amplifier (SOA)-based burst-mode optical amplifier with a fast automatic level control (ALC) circuit for upstream amplification.

View full abstract

The bit-error-rate performance of M-ary direct-sequence code-division multiple-access (DS-CDMA) systems with square-law combination in multipath Nakagami-Rice fading channels is analyzed. The signal is modulated by using the M orthogonal signals to enhance the spectral efficiency. Rake combining for square-law detection is applied to improve the performance in the multipath channel. The bit-error-rate probability is derived in closed-form under the assumption that each user is assigned a random signature code. The bit-error-rate performance is evaluated in terms of the number of users and rake fingers.

View full abstract

We propose a novel technique that can generate an optical return to zero quadrature amplitude modulation (RZ-QAM) signal without using a pulse carver. This technique permits electronic pre-compensation of the chromatic dispersion (CD) because the envelope of the optical waveform is not restricted by pulse carver performance. We successfully generate polarization multiplexed RZ-64 QAM signals (72Gbit/s) with and without electronic CD pre-compensation. By utilizing 50% CD pre-compensation, the Q-factor is improved by 0.4dB after 240km (+4900ps/nm) transmission.

View full abstract

This paper reports an experiment result of the design and implementation of a link-load ranking (LLR) scheme for open shortest path first traffic engineering (OSPF-TE) networks where routing control is centrally performed by a network controller. The network controller needs to know the maximum link load in the network to enhance routing performance by minimizing the maximum link load. The LLR scheme reduces the number of advertisements in the network. Only the necessary information is advertised. All action cases of entire link load are confirmed using a link load changing scenario in the experiment. Results show that our design and implementation performs as the idea of the LLR scheme.

View full abstract

This paper clarifies the frequency dependency of channel capacity improvement in near-field MIMO system with metal wire. And the proper location for the metal wire is found related with the corresponding wavelength of each specific frequency. The maximum channel capacity improvement is found best in the range of frequency from 10GHz to 20GHz. When the frequency is very large, the effect of the metal wire is negligible. As antenna distance increases, the channel capacity improvement decreases.

View full abstract

This paper discusses multipath interference (MPI) of passive optical networks (PON) using hybrid-Raman amplifiers, which are previously proposed. In access networks, there are many splice points, which may cause MPI. Generally, the degradation due to MPI is enhanced by an optical amplification. To evaluate the degradation, we made bit error rate (BER) experiments using artificially causing MPI in Raman amplification. Obtained data are compared with calculated ones and they show in good agreement. Then, we evaluate required reflection coefficients of splices using two models.

View full abstract

This letter presents a subcarrier multiplexing with spread spectrum (SCM-SS) scheme for optical multiple-input multiple-output (MIMO) transmission over multimode fibers. Optical MIMO is dedicated to increasing link capacity by exploiting the space domain, which provides a new dimension in addition to conventional time division multiplexing (TDM) and wavelength division multiplexing (WDM). SCM-SS scheme is a promising way that avoids resolving channels in optical domain, and multiple channels are recovered by off-line MIMO signal processing. Up to 2000m transmissions of 100Mbps per channel 2×4 MIMO over graded index multimode fiber link with direct detection have been experimentally demonstrated. Advantageous performance in the presence of intermodal coupling is shown.

View full abstract

This paper presents a numerical technique for determining the phase center of an antenna on the basis of the distance dependence of the gain, which is measured using the Friis transmission equation. The proposed gain-fitting technique is based on the numerical simulation of the two-antenna method using the method of moments with higher-order basis functions. The phase center of a standard-gain horn antenna is determined using the proposed method, and the results show the effectiveness of this approximation technique.

View full abstract

This paper proposes antenna arrangements which realize a unitary matrix for 4×4 multiple-input multiple-output (MIMO) system in line-of-sight (LOS) environment. It is shown that the channel matrix is unitary matrix by properly adjusting the element spacing and the high channel capacity is obtained by the proposed antenna arrangements with directional antennas even if the multipath signals in indoor scenario are considered.

View full abstract