Akinori Taira

System configuration for multiband MC-CDM systems

This paper studies efficient structure of multiband mobile communication system which can support both high data rate services and wide coverage. First, we show design criterion of appropriate bandwidths in multiple frequencies. Second, we show a realistic scenario of smooth migration from singleband system to multiband system, considering investment risk and frequency license problem. Third, we study multiband MC-CDM system for downlink, that is a multiband system combined with MC-CDM system. The presented multiband MC-CDM system includes efficient structures of pilot signals, two dimensional spreading, and simplified receiver.

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.

On the Design of a Point-to-Multipoint Gigabit WLAN System on 60 GHz Millimeter Wave

Increasing demand on the broadband wireless communication over Gigabits has focused renewed attention on 60 GHz millimeter wave. We developed a novel Point-to-Multipoint (P2MP) Gigabit WLAN System on 60 GHz millimeter wave. The proposed system employed wide angle beams antenna overcomes the usability of the conventional system, covers larger areas. Maximum transmission rate was designed to be 1.2 Gigabit/sec. Orthogonal frequency division multiplex (OFDM) using 1024 points FFT, and convolutional code were implemented with PHY layer of the WLAN equipments. Superframe for multiple beams and frame aggregation for high throughput were designed for MAC layer. All control channels for downlink such as broadcast, frame control and access feedback were aggregated to reduce overhead in addition to aggregation of data frame. Maximum improvement of throughput due to control channel aggregation was evaluated to be 200 % compared with individual transmission. Evaluated throughput using proposed frame aggregation was confirmed to be more than 852 Mbit/sec in the case of aggregation size of 16 × 1500byte.

Non-coherent ToA estimation for UWB multipath channels using max-eigenvalue detection

Due to the fine delay resolution in ultra-wideband (UWB) wireless propagation channels, a large number of multipath components (MPC) can be resolved; and the first arriving MPC might not be the strongest one. This makes time-of-arrival (ToA) estimation, which essentially depends on determining the arrival time of the first MPC, highly challenging. In this paper, we consider non-coherent ToA estimation given a number of measurement trials, at moderate sampling rate and in the absence of knowledge of pulse shape. The proposed ToA estimation is based on detecting the presence of a signal in a moving time delay window, by using the largest eigenvalue of the sample covariance matrix of the signal in the window as the test statistic. We show that energy detection can be viewed as a special case of the eigenvalue detection. Max-eigenvalue detection (MED) generally has superior performance, due to the following reasons: 1) MED collects less noise, namely only the noise contained in the signal space, and 2) if multiple channel taps fall into the time window, the MED detector can collect energy from all of them. Simulation results confirm that MED outperforms the energy detection in IEEE 802.15.3a and 802.15.4a channels. Finally, the selection of the threshold of the MED is studied both by simulations and by random matrix theory.

Performance Evaluation of Nonlinear Precoding Based on 44 GHz Band Experiments for 5G Ultra High Capacity Massive MIMO

For 5G massive MU-MIMO (Multi-User Multiple-Input and Multiple-Output) systems in high frequency bands, a favorable scenario is a line-of-sight (LOS) environment where the direct paths dominate the spatial channels. In the LOS environment, spatial correlation between user equipments (UEs) tend to be high and its capacity decreases, especially in the case where we have densely distributed UEs. The authors have already proposed a nonlinear precoding scheme incorporating block multi- diagonalization (NL-BMD) for highly correlated channel and demonstrated its effectiveness by computer simulation. In this paper, the authors present indoor propagation measurement results using a channel sounding system with 44 GHz active phased array antenna in the condition that UEs are sparsely and closely distributed. In addition, this paper shows the spectral efficiency of NL-BMD based on the measurement results compared with the conventional precoding schemes.

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.

A Mode S decoding scheme using equalization for multilateration systems

Multilateration (MLAT) systems, which receive and decode the signals such as SSR (Secondary Surveillance Rader) Mode S reply or extended squitter in airport surface, have problems in decoding performance due to not only asynchronous interference from other aircraft, but also multipath caused by reflection from buildings and other surroundings. This paper proposes a Mode S receiver with equalization. This scheme estimates both direct wave and reflected waves by use of the received signal of preamble duration, and performs the equalization with the estimated impulse response. The evaluation results show that the scheme gives better performance than conventional decoding method for the received signal under strong multipath environment.