Hiroshi Nishimoto

Fast optical channel recovery in field demonstration of 100-Gbit/s Ethernet over OTN using real-time DSP

A field trial of 100-Gbit/s Ethernet over an optical transport network (OTN) is conducted using a real-time digital coherent signal processor. Error free operation with the Q-margin of 3.2 dB is confirmed at a 100 Gbit/s Ethernet analyzer by concatenating a low-density parity-check code with a OTN framer forward error correction, after 80-ch WDM transmission through 6 spans x 70 km of dispersion shifted fiber without inline-dispersion compensation. Also, the recovery time of 12 msec is observed in an optical route switching experiment, which is achieved through fast chromatic dispersion estimation functionality.

Channel characteristics and performance of MIMO E-SDM systems in an indoor time-varying fading environment

Multiple-input multiple-output (MIMO) systems employ advanced signal processing techniques. However, the performance is affected by propagation environments and antenna characteristics. The main contributions of the paper are to investigate Doppler spectrum based on measured data in a typical meeting room and to evaluate the performance of MIMO systems based on an eigenbeam-space division multiplexing (E-SDM) technique in an indoor time-varying fading environment, which has various distributions of scatterers, line-of-sight wave existence, and mutual coupling effect among antennas. We confirm that due to the mutual coupling among antennas, patterns of antenna elements are changed and different from an omnidirectional one of a single antenna. Results based on the measured channel data in our measurement campaigns show that received power, channel autocorrelation, and Doppler spectrum are dependent not only on the direction of terminal motion but also on the antenna configuration. Even in the obstructed-line-of-sight environment, observed Doppler spectrum is quite different from the theoretical U-shaped Jakes one. In addition, it has been also shown that a channel change during the time interval between the transmit weight matrix determination and the actual data transmission can degrade the performance of MIMO E-SDM systems.

Block lower multi-diagonalization for multiuser MIMO downlink

For multiuser-MIMO (MU-MIMO) downlink, the authors propose a novel precoding concept of block lower multi-diagonalization. Extending the conventional block diagonalization method, the proposed precoder for the desired user is computed to incorporate a predetermined number of interfering users. Consequently, the concept enables us to ensure extra degrees of freedom at the transmit array even after null steering in a linear MU-MIMO strategy, and also to reduce computational load at transmit precanceling in a nonlinear MU-MIMO strategy. From an implementational viewpoint, we here examine two approaches: block bi-diagonalization, allowing one interfering user, and block lower tri-diagonalization, allowing up to two interfering users. In the paper, prior to a study on practical management schemes for residual interference, we reveal the significant potential of the proposed concept through the discussion and numerical evaluation using sum-rate capacity.

Nonlinear block multi-diagonalization precoding for high SHF wide-band massive MIMO in 5G

In the paper, we propose a novel transmit precoding named “nonlinear block multi-diagonalization (NL-BMD) precoding,” composed of block multi-diagonalization and adjacent inter-user interference pre-cancellation, for multiuser MIMO downlink toward 5G. It is revealed through computer simulations that, the proposed NL-BMD precoding yields up to 77% performance improvement in average sum-rate throughput and enables large-capacity transmission regardless of the user configuration, compared with the conventional block diagonalization precoding.

3GPP standardization activities in relay based 5G high speed train scenarios for the SHF band

Activities related to the 3GPP high speed train (HST) scenario in the super high frequency (SHF) band are described in this paper. Communication between an onboard relay station and remote radio head placed along the railway is considered in the scenario. The content of the paper focuses on motivations for considering the scenario in 3GPP, descriptions of the HST channel model, proposed new radio (NR) technologies and evaluation results. The design elements considered in the evaluation include frame format, numerology, synchronization mechanism, reference signal design and waveform.

Static sequence wrapped DFT-s-OFDM for high-speed train scenarios in high-SHF bands

A discrete Fourier transform (DFT)-spread-orthogonal frequency division multiplexing (OFDM) waveform without cyclic prefix (CP) is described in this paper to suppress out-of-band (OoB) emission. To maintain phase continuity, a static sequence is inserted prior to DFT. Performance of the waveform in the high speed train scenario adopted in 3GPP is evaluated with simulation. The waveform is modified to suppress out-of-band emission when pilot symbols are multiplexed with data in DFT-spread-OFDM. Out-of-band suppression performance of the proposed hybrid DFT-s-OFDM waveform is also evaluated with simulations.