Riichi Kudo

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.

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.

Non-data-aided wide-range frequency offset estimator for QAM optical coherent receivers

We propose and experimentally demonstrate a novel blind frequency offset estimator for coherent quadrature amplitude modulation (QAM) receivers. Its frequency offset estimation range is more than three times the conventional estimation range.

A channel state information feedback method for massive MIMO-OFDM

Combining multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) with a massive number of transmit antennas (massive MIMO-OFDM) is an attractive way of increasing the spectrum efficiency or reducing the transmission energy per bit. The effectiveness of Massive MIMO-OFDM is strongly affected by the channel state information (CSI) estimation method used. The overheads of training frame transmission and CSI feedback decrease multiple access channel (MAC) efficiency and increase the CSI estimation cost at a user station (STA). This paper proposes a CSI estimation scheme that reduces the training frame length by using a novel pilot design and a novel unitary matrix feedback method. The proposed pilot design and unitary matrix feedback enable the access point (AP) to estimate the CSI of the signal space of all transmit antennas using a small number of training frames. Simulations in an IEEE 802.11n channel verify the attractive transmission performance of the proposed methods.

Performance Evaluation of 8×8 Multi-User MIMO-OFDM Testbed in an Actual Indoor Environment

Multiple input multiple output (MIMO) systems have attracted much attention as they can provide increased channel capacity within a limited frequency band. In some important applications, such as wireless LAN and cellular systems, MIMO systems will likely operate in environments for which a single base station should simultaneously communicate with many users. Such applications require development of multiuser(MU)-MIMO techniques. The prior work on MU-MIMO systems have resulted in derivation of the ideal channel capacity as well as various proposed schemes for transmission control and scheduling. In order to incorporate MU-MIMO technologies into commercial systems, extensive evaluations are needed, since the amount of system parameters in MU-MIMO is much larger as compared to the Signleuser(SU)-MIMO. Due to such a volume of system parameters, the performance of MU-MIMO in actual systems is still not well understood. This paper describes MU-MIMO testbed which can deal with 8times8 MIMO-OFDM transmission based on the IEEE 802.11a signal format. We have conducted experiments in an actual indoor environment in order to evaluate the frequency utilization for downlink scheme implemented in the MU-MIMO testbed. Finally, we discuss the effectiveness of MU-MIMO for SU-MIMO when the number of receiving antennas is changed

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).

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.

Two-stage overlap frequency domain equalization for long-haul optical systems

We propose two-stage overlap frequency domain equalization (OFDE) to compensate chromatic dispersion and polarization mode dispersion in practical long-haul optical systems. This paper evaluates the performance of 25-Gb/s coherent optical single-carrier transmission using two-stage OFDE.

Spatial Domain Resource Sharing for Overlapping Cells in Indoor Environment

As microcell wireless systems become more widespread, intercell interference among the access points will increase due to the limited frequency resource. In the overlapping cell scenario, radio resources should be shared by multiple cells. Although time and frequency resource sharing has been described in many papers, there is no detailed report on dynamic spatial resource sharing among multiple cells for microcell wireless systems. Thus, we present the effectiveness of spatial resource sharing among two access points. We introduce two scenarios based on the zero forcing method; one is the primary-secondary AP scenario and the other is the cooperative AP scenario. To evaluate the transmission performance of spatial resource sharing, channel matrices are measured in an indoor environment. The simulation results using the measured channel matrices show the potential of spatial resource sharing.