In this paper, we propose a cell-free distributed antenna system (DAS) architecture with adaptive resolution-(AR-) analog-to-digital converters (ADCs) in access points (APs). The proposed scheme adopts accurate models of the combined effects of clipping, quantization, and thermal noise in the ADC to analyze the quantization characteristics with different resolutions at different received signal-to-interference-and-noise ratios (SINRs). The proposed resolution bit selection criterion of the AR-ADC scheme is then applied. The AR-ADC scheme is to minimize the ADC resolution bits under allowable quantization distortion, and obtain the corresponding optimal clipping factor of the signal-to-interference-plus-quantization-and-noise ratio (SIQNR) for the desired received signal. The contributions of this paper are as follows; 1) the AR-ADC scheme provides a receiver architecture that realizes better energy efficiency (EE), 2) the spectral efficiency (SE) performance is improved by allocating more resolution bits to the APs closer to each UE with the proposed criterion. Numerical results demonstrate that the proposed AR-ADC scheme improves the EE more than tenfold as compared with the other schemes except the system with only 1-bit ADCs. Moreover, the proposed AR-ADC doubles the SE as compared with the system with only 1-bit ADCs.
NHK has been studying transmission technologies that contribute to increasing spectral efficiency and developing large capacity wireless transmissions. An effective technology is dual-polarized multiple-input multiple-output (MIMO), which uses both horizontal and vertical waves. We are currently developing an advanced Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) system to provide simultaneously a 4K8K broadcasting service for fixed reception and 2K service for mobile reception. The advanced ISDB-T adopts not only single-input single-output (SISO) but also MIMO for the expansion of the transmission capacity. However, a difference of radio propagation or that of a transmitter antenna's radiation pattern can easily cause an imbalance of received power between each polarization even if the transmitted power of each polarization is the same. A broadcasting network usually consists of multiple transmitter stations to cover target broadcasting areas across cities. In this case, a single frequency network (SFN) is considered for an efficient usage of frequency. The transmission performance in an SFN environment depends on the desired-to-undesired power ratio (DUR) of a main station and relay station because of the interference between received signals from them. In the case of MIMO-SFN, both power imbalance between each polarization and the DUR of each polarization need to be considered to analyze the transmission characteristics. In this paper, the transmission performance of dual-polarized MIMO in an SFN environment considering the imbalance of received power is evaluated by computer simulation, laboratory experiment, and field experiment. Furthermore, the distribution of the imbalance of received power is obtained by a large-scale field experiment.
We are currently developing the advanced Integrated Services Digital Broadcasting-Terrestrial (advanced ISDB-T) system for the next generation of digital terrestrial television broadcasting (DTTB). In advanced ISDB-T, subcarriers for auxiliary data transmissions are randomly placed in each segment, as is done in the Auxiliary Channel (AC) of ISDB-T. The transmission scheme using these subcarriers is named Low-Latency Channel (LLch). Since differential binary shift keying (DBPSK) is used for the subcarrier modulation scheme, LLch transmissions are expected to be robust. Furthermore, LLch data can be transmitted speedy because they do not have time interleaving and can be demodulated without a channel estimation by using the pilot signal. This paper reports a study of earthquake early warning (EEW) transmission for the next generation of DTTB with using LLch. Here, a new low-density parity-check (LDPC) code was designed in accordance with the EEW specification. The LDPC codewords are modulated with DBPSK and transmitted on the LLch subcarriers. The transmission performance of LLch was evaluated in a computer simulation. Furthermore, the feasibility of LLch transmission was verified in a laboratory experiment with a prototype modulator and demodulator.
Various techniques have been proposed for restoring JPEG compressed images degraded with inevitable artifacts. Convex optimization is often used for such techniques, where a prescribed function is minimized over the narrow quantization constraint set (NQCS) characterized by a scaling parameter. Although the scaling parameter significantly affects the restoration quality, the optimal determination of the scaling parameter is actually difficult because it is highly dependent on the target JPEG compressed image. To overcome this difficulty, we propose a novel NQCS-based artifact reduction framework requiring no explicit parameter optimization. In our framework, a set of candidate images is first obtained, whereupon the restored image is computed by applying simple statistical operations for the set. The advantages of our approach are demonstrated by comparing it with several existing approaches in terms of the theoretical error bounds and experimental restoration results.
We investigate the transmittance properties of a thermo-responsive smart window utilizing poly(N-isopropyl acrylamide) aqueous solution (PNIPAM) that exhibits a lower critical solution temperature (LCST)-type phase separation. The transmittance in the transparent state remained around 80 %, which is almost the same when the device is empty. In contrast, the transmittance in the opaque state for the device with Mn ∼40 K and Mn ∼10 K decreased 55 % to 10 % with increasing PNIPAM concentration. Moreover, with increasing PNIPAM concentration, the clouding point for the device decreased slightly because of emphasizing the cooperativity in hydration, even when the device thickness was as thin as 20 μm. Although the transmittance for the device in the opaque state is controllable using the PNIPAM concentration. There is however a trade-off between transmittance and its variation in the opaque state. We believe these results to be useful in developing thermo-responsive smart window products.