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Ultrawide-band impulse radio (UWB-IR) technology and multiple-input multiple-output (MIMO) systems have attracted interest regarding their use in next-generation high-speed radio communication. We have studied the use of MIMO ultrawide-band (MIMO-UWB) systems to enable higher-speed radio communication. We used frequency-domain equalization based on the minimum mean square error criterion (MMSE-FDE) to reduce intersymbol interference (ISI) and co-channel interference (CCI) in MIMO-UWB systems. Because UWB systems are expected to be used for short-range wireless communication, MIMO-UWB systems will usually operate in line-of-sight (LOS) environments and direct waves will be received at the receiver side. Direct waves have high power and cause high correlations between antennas in such environments. Thus, it is thought that direct waves will adversely affect the performance of spatial filtering and equalization techniques used to enhance signal detection. To examine the feasibility of MIMO-UWB systems, we conducted MIMO-UWB system propagation measurements in LOS environments. From the measurements, we found that the arrival time of direct waves from different transmitting antennas depends on the MIMO configuration. Because we can obtain high power from the direct waves, direct wave reception is critical for maximizing transmission performance. In this paper, we present our measurement results, and propose a way to improve performance using a method of transmit (Tx) and receive (Rx) timing control. We evaluate the bit error rate (BER) performance for this form of timing control using measured channel data.

MIMO (Multiple-Input Multiple-Output) technologies have attracted much interest for high-rate and high-capacity wireless communications. MIMO technologies under frequency-selective fading environments (wideband MIMO technologies) have also been studied. A wideband MIMO system is affected by ISI (Inter Symbol Interference) and CCI (Co-Channel Interference). Hence, we need a MIMO signal detection technique that simultaneously suppresses ISI and CCI. The OFDM system and SC-FDE (Single Carrier-Frequency Domain Equalization) techniques are often used for suppressing ISI. By employing these techniques with the ZF (Zero Forcing) or the MMSE (Minimum Mean Square Error) spatial filtering technique, we can cancel both ISI and CCI. To use ZF or MMSE, we need channel state information for calculating the receive weights. Although an LS (Least Square) channel estimation technique has been proposed for MIMO-OFDM systems, it needs a large estimation matrix at the receiver side to obtain sufficient estimation performance in heavy multipath environments. However, the use of a large matrix increases computational complexity and the circuit size. We use frequency domain channel estimation to solve these problems and propose an iterative method for achieving better estimation performance. In this paper, we assume the use of a MIMO-UWB system that employs a UWB-IR (Ultra-Wideband Impulse Radio) scheme with the FDE technique as the wideband wireless transmission scheme for heavy multipath environments, and we evaluate the iterative frequency domain channel estimation through computer simulations and computational complexity calculations.

Recently, hybrid vehicles (HVs) have become widespread. In the current HVs, a high-voltage (200 V) battery supplies power to the Power Control Unit (PCU) for driving a motor, generator and air conditioner compressor. It is expected that such kinds of power electronic devices will increase in number in the future. We previously proposed a power line communication (PLC) that uses a high-voltage power line. In this paper, we present the development of a high-voltage PLC system that can simultaneously control multiple power electronic devices in real time and demonstrate the system operation. First, in a system of a commercially available HV, the results of transmission characteristics and electromagnetic noise characteristics that are superimposed on the high-voltage power line are shown. Then the bit error rate (BER) performance under the above noise environment is clarified by computer simulations. Finally, we construct a prototype of the high-voltage PLC system and demonstrate that the system can simultaneously control the rotational speed of two motors.

The noise-related phenomenon, stochastic resonance (SR), may improve the performance of signal detection devices. In digital signal processing, the effect of SR depends on the observation time and sampling frequency. To apply it to digital signal processing, these two parameters must be determined. This paper investigates the observation time and sampling frequency for efficient SR in a digital system.

An inter-vehicle communication system is highly advantageous for driving safety support systems, such as collision avoidance systems at intersections. In an inter-vehicle communication system, a channel-tracking scheme is essential to achieve reliable wireless communication under the fast fading environment caused by surrounding vehicles. For coherent detection, decision feedback is a well-known channel-tracking scheme. In this scheme, replica signals are generated and channel estimation is performed by using the replica signals. However, because channel estimation performance depends on the signal-to-noise (SNR) at symbol time, decision feedback errors occur by the lower SNR caused by fast fading. The feedback errors degrade the transmission performance significantly. In an orthogonal frequency division multiplexing (OFDM) system, the time domain 0-padding scheme is a well-known channel estimation technique. Although better channel tracking performance is expected by applying the 0-padding scheme, the tracking performance is degraded when employing guard-bands in the OFDM system. In this paper, we propose an improved time domain 0-padding scheme for an STBC-OFDM system employing guard-bands based on the IEEE802.11p standard for inter-vehicle communication, and show the improved performance through computer simulations.

The UWB-IR (ultra wideband-impulse radio) technology and MIMO system have attracted interest for next generation high rate radio communications. The authors researched IMO-UWB systems using the FDE (frequency domain equalization) technique with the MMSE spatial filtering technique. The UWB system will be used in short range wireless transmissions. Then, we usually have line-of-sight (LOS) environments in the MIMO-UWB systems. The authors conducted propagation measurement and evaluated the transmission performance of MIMO-UWB systems in LOS environments. Then, the authors proposed a timing control scheme for performance improvement. SIC (successive interference canceller) and PIC (parallel interference canceller) are known as better signal separation techniques in MIMO systems. In these techniques, the authors obtain diversity gain subtracting the data detected by a spatial filtering technique from the received signal. Therefore, we can achieve better signal separation performance by the diversity gain. The authors found that the timing control scheme is also needed for the SIC and PIC techniques in LOS MIMO-UWB environments by bit error rate (BER) evaluation. In this paper, the authors show the signal separation performance applying the SIC and PIC techniques with the timing control scheme in LOS environments.