Toru Takamichi

Experimental verification of minimum overlap size design in a FDE-based chromatic dispersion compensation circuit with a 50Gb/s PM-QPSK signal

We propose a simple design method of minimum overlap data size for overlap-FDE based CD compensation. We confirmed its validity using a real-time DSP circuit and 50.7Gbps PM-QPSK signal for up to 56,200ps/nm.

Development and evaluation of a digital signal processing for single polarization QPSK modulation format

Single polarization high-speed optical transmission is important for bidirectional free-space optical communication system in order to have enough isolation up-link and down-link by signal discrimination using orthogonal polarization states. At recent advance in digital coherent technology, polarization re-combining in combination with polarization diversity receiver is widely used to suppress performance degradation when polarization states of signal and local oscillator are misaligned by system vibration or shocks. However, in order to implement the re-combining function in digital signal processing, appropriate algorithm is required for realizing the system stability. In this paper, we demonstrate a new algorithm implementation for single polarization receiver with maximal-ratio-combining (MRC) technique. First we exhibited the problem for state-of-the-art polarization re-combining in instability due to singularity condition at 45-degree-azimuth elliptic polarization. In order to overcome this problem, we proposed a newly MRC algorithm added splitting ratio dependent phase correction coefficients and achieved stable re-combining at 45-degreeazimuth elliptic polarization signal. And we successfully demonstrated the stable receiving for 50-Gb/s single polarization QPSK signal with all polarization states by our digital coherent receiver platforms added the newly MRC algorithm, compared with previous-proposed MRC algorithm.

Expansion of system dynamic chromatic-dispersioncompensation range by optimal FIR filter adaptation

A novel method for FIR filter control optimization is proposed to expand the chromatic dispersion compensation range in electrical digital signal processing systems in transmitters and receivers. A reduction of the number of coefficients of FIR filter by 40% is observed, which allowed to reduce the instability occurred by mis-configuration during the filter control.

Comparison of three policing algorithms for ABR conformance

A closed loop rate based feedback control to support ABR service has been defined. In this approach the network at periodic intervals informs all transmitting sources the maximum rate at which the sources are allowed to transmit. For the scheme to be successful in that the network utilization is high and fairness is ensured for all competing users, it is imperative that all sources conform to the maximum rate at which they are allowed to transmit. To ensure the goals of ABR service are satisfied, especially in public networks, it is essential to police sources and penalize violating sources when deemed necessary. In this paper we investigate the effect of misbehaving or violating users on the network performance and the effectiveness of policing such sources.