Akihiro Okazaki

Likelihood Estimation for Reduced-Complexity ML Detectors in a MIMO Spatial-Multiplexing System

This paper proposes a likelihood estimation method for reduced-complexity maximum-likelihood (ML) detectors in a multiple-input multiple-output (MIMO) spatial-multiplexing (SM) system. Reduced-complexity ML detectors, e. g., Sphere Decoder (SD) and QR decomposition (QRD)-M algorithm, are very promising as MIMO detectors because they can estimate the ML or a quasi-ML symbol with very low computational complexity. However, they may lose likelihood information about signal vectors having the opposite bit to the hard decision and bit error rate performance of the reduced-complexity ML detectors are inferior to that of the ML detector when soft-decision decoding is employed. This paper proposes a simple estimation method of the lost likelihood information suitable for the reduced-complexity ML detectors. The proposed likelihood estimation method is applicable to any reduced-complexity ML detectors and produces accurate soft-decision bits. Computer simulation confirms that the proposed method provides excellent decoding performance, keeping the advantage of low computational cost of the reduced-complexity ML detectors.

Likelihood Estimation for Reduced-Complexity ML Detectors in a MIMO System

This paper proposes a likelihood estimation method for reduced-complexity maximum-likelihood (ML) detectors in a multiple-input multiple-output (MIMO) system. Reduced-complexity ML detectors, e.g., sphere decoder (SD) and QR decomposition (QRD)-M algorithm, are very promising candidates as a MIMO detector because they can estimate the ML or quasi-ML symbol with very low computational complexity. However, they may lose likelihood information about signal vectors having the opposite bit to hard decisions. Therefore, bit error rate performances of the reduced-complexity ML detectors are inferior to that of the ML detector when soft-decision decoding is employed. This paper proposes a simple estimation method of the lost likelihood information suitable for the reduced-complexity ML detectors. Computer simulation confirms that the proposed method provides excellent decoding performance, keeping the advantage of computational cost of the reduced-complexity ML detectors.

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.

Static sequence assisted out-of-band power suppression for DFT-s-OFDM

A novel static sequence assisted discrete Fourier transform (DFT)-spread-orthogonal frequency division multiplexing (OFDM) waveform is proposed to suppress out-of-band (OoB) emission. In the proposed scheme, a deterministic sequence, which functions as cyclic prefix (CP), is used to suppress OoB emission. A measure of continuity is proposed to determine the location of the static sequence to maximize the amount of OoB suppression. Perturbation is added to the static sequence to further improve phase continuity at block transitions. It is shown that the spectra of the proposed static sequence assisted waveforms are more compact that those of the conventional waveforms. A frequency offset estimation method using the static sequence is described and its performance is evaluated by simulations.

R&D activities for 5G in IEICE technical committee on radio communication systems

As the demand for higher transmission rates and spectral efficiency is steadily increasing, the research and development of novel mobile communication systems has gained momentum. This paper focuses on providing a comprehensive survey of research and development activities on fifth generation mobile communication systems reported in IEICE technical committee on radio communication systems. We try to survey a vast area of wireless communication systems and the developments that led to future 5G systems.

Peak power reduction techniques for multi-channel SC-OFDM

SC-OFDM (single carrier orthogonal frequency division multiplexing) has received considerable attention in recent years due to its low peak power and robust performance against multipath fading channels. There are emerging demands in a variety of wireless communication systems to transmit multiple SC-OFDM signals in different channels to improve bandwidth efficiency. However, the peak power of such multi channel SCOFDM (MCH-SC-OFDM) signals increases as more signals are multiplexed. In this paper, we present two techniques which can lower the peak power of MCH-SC-OFDM signals by applying phase rotation to SC-OFDM signals in the frequency domain. It is shown through simulation results that the proposed techniques do not introduce any penalties on error performance of the receivers.

Channel estimation technique for OFDM systems spread by chirp sequences

A frequency domain equalization for multipath fading is widely used for OFDM systems and accurate channel estimation is required. In conventional OFDM systems, pilot symbols are inserted periodically in time and frequency domain by a transmitter for channel estimation. Channel estimation error is quite large, especially in frequency-selective fading channel, because the estimates are interpolated with the restricted pilot subcarriers. The channel estimation error can be decreased by assigning pilot symbols to all subcarriers in specified OFDM blocks. In that case, however, no data symbols can be transmitted in OFDM blocks where pilot symbols are transmitted. In this paper we propose a new channel estimation scheme in which OFDM signal is transmitted after spread by chirp sequences, and channel estimation of all subcarriers is achieved with only one pilot symbol without interpolation. Simulation results show that the MSE performance of channel estimation and the BER performance can be significantly improved by the proposed scheme.

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.