Yasushi Takatori

No-Guard-Interval Coherent Optical OFDM for 100-Gb/s Long-Haul WDM Transmission

This paper describes coherent optical orthogonal frequency division multiplexing (CO-OFDM) techniques for the long-haul transmission of 100-Gb/s-class channels. First, we discuss the configurations of the transmitter and receiver that implement the optical multiplexing/demultiplexing techniques for high-speed CO-OFDM transmission. Next, we review the no-guard-interval (No-GI) CO-OFDM transmission scheme which utilizes optical multiplexing for OFDM signal generation and the intradyne receiver configuration with digital signal processing (DSP). We examine the transmission characteristics of the proposed scheme, and show that No-GI CO-OFDM offers compact signal spectra and superior performance with regard to tolerance against optical amplifier noise and polarization-mode dispersion (PMD). We then introduce long-haul high-capacity transmission experiments employing No-GI CO-OFDM; 13.4 Tb/s (134 times 111 Gb/s) transmission is successfully demonstrated over 3600 km of ITU-T G.652 single-mode fiber without using optical dispersion compensation.

Coherent Optical Single Carrier Transmission Using Overlap Frequency Domain Equalization for Long-Haul Optical Systems

In this paper, we present coherent optical single carrier transmission (COSC) using overlap frequency domain equalization (OFDE) for the chromatic dispersion (CD) compensation. Residual inter-symbol interference is suppressed by time domain equalization with small tap size. In single polarization transmission, 25-Gb/s COSC transmission with OFDE is demonstrated over 800 km to 4320 km of single-mode fiber (SMF) without optical dispersion compensation. The measured results show that the proposed configuration improves the transmission performance by setting adequate overlapped size of FFT windows and that it is suitable for long-haul optical communication systems.

High data-rate transmission with eigenbeam-space division multiplexing (E-SDM) in a MIMO channel

When channel state information is known at a transmitter in multiple-input multiple-output systems, the optimum capacity is given by eigenmode channel division with water-pouring power control. In this eigenbeam-space division multiplexing (E-SDM), bit assignment to substreams based on the capacity is not optimum due to the fact that the number of assigned bits is expressed by a discrete quantity. In the paper, a method to assign both bit and transmit power to each substream based on the criterion minimizing total bit error rate (BER) is developed, and the BER performance is numerically analyzed in comparison to spatial division multiplexing (SDM). The simulation results assuming 5-transmit and 2-receive antennas show that the E-SDM provides about 10 dB gain compared to the conventional SDM at average BER of 10/sup -3/.

Automatic calibration method using transmitting signals of an adaptive array for TDD systems

Adaptive arrays are especially effective in reducing cochannel interference and increasing channel capacity in time-division duplex (TDD) mobile communication systems because, ideally, the optimum pattern formed in the receiving mode can be applied to the transmitting pattern. However, since the radiation pattern of the adaptive array is generally formed on a baseband, the amplitude and phase errors must be calibrated between the branches of the array due to individual differences in the radio frequency (RF) devices of the receivers and transmitters. Moreover, since these errors change over time due to temperature variations, real-time calibration is required. This correspondence proposes an automatic calibration method using transmitting signals (ACT) for adaptive base station antennas that is suitable for TDD communication systems, i.e., it enables real-time calibration. The effectiveness of the proposed calibration method is demonstrated using an experimental adaptive array testbed.

13.5-Tb/s (135 × 111-Gb/s/ch) no-guard-interval coherent OFDM transmission over 6,248 km using SNR maximized second-order DRA in the extended L-band

By employing 111Gb/s no-guard-interval coherent OFDM and SNR maximized second-order distributed Raman amplification in the extended L-band, we demonstrate the record capacity-distance product of 84.3Petabit/s.km (13.5Tb/s × 6,248km), and also 1Tb/s transmission over 9,612km.

13.4-Tb/s (134 × 111-Gb/s/ch) no-guard-interval coherent OFDM transmission over 3,600 km of SMF with 19-ps average PMD

We demonstrate the record capacity-distance product of 48.2 Petabit/s.km by using 111-Gb/s no-guard-interval coherent OFDM with 2-b/s/Hz spectral efficiency.

Spatial Opportunity for Cognitive Radio Systems with Heterogeneous Path Loss Conditions

In this paper, the possibility for a short-range cognitive radio (secondary communication system) to be located within the service area of the primary system is discussed. Although the secondary system interferes with the primary system, there can be certain locations in the service area of the primary system where the cognitive radio can reuse the frequency of the primary system without disturbing it or being disturbed by the primary system. We say that in those locations there is a spatial opportunity for communication in the secondary system. The primary and secondary systems have different features and usage scenarios, which result in different deployment conditions. This gives rise to differences between the path loss for a link in the primary system and the path loss for the interference from the primary to secondary systems. This paper investigates the impact of the heterogeneous path loss conditions on the spatial opportunity for the secondary system. Our approach can be applied as a general way to investigate the coexistence among multiple systems. We clarify that the change of the path loss coefficient due to the different antenna heights of the primary and secondary systems can largely affect the spatial opportunity for frequency reuse by the cognitive radios.

Coherent optical transmission with frequency-domain equalization

We demonstrated 25-Gb/s (21.7-Gb/s after coding) single-carrier (SC) transmission with QPSK format over 240 km of SMF (4080 ps/nm) by employing frequency-domain equalization (FDE).

Proposal of compact MIMO terminal antenna employing Yagi-Uda array with common director elements

In this paper, a compact MIMO terminal antenna employing Yagi-Uda arrays with common director elements is proposed. The Yagi-Uda array provides a high gain in the horizontal direction even when the array is arranged horizontally. The size of the proposed antenna is fairly small because the director elements are shared between two Yagi-Uda arrays that face each other and the length of the array is approximately half of two individual Yagi-Uda arrays.

Wide-range and fast-tracking frequency offset estimator for optical coherent receivers

A blind spectrum-based frequency offset estimator with fast tracking time is presented. A receiver using the proposed estimator to eliminate the frequency ambiguity of the mth power algorithm can achieve precise estimation over a wide frequency range.