Akihiro Kajiwara

Line-of-sight indoor radio communication using circular polarized waves

This paper presents an anti-multipath fading scheme employing a circular polarized wave for line-of-sight (LOS) indoor radio communications. The circular polarized wave transmission/reception significantly mitigates the multipath fading caused by reflections from walls, ceiling, and floor since the energies of single-bounce reflected waves do not appear at the receiver, thereby resulting in significant amplitude fade and delay spread reduction. The received signal intensity variations and delay spread are investigated numerically using a 14-path propagation model and the usefulness is confirmed by comparing with a linear polarized wave transmission/reception under a same LOS condition. >

Non-invasive respiration monitoring sensor using UWB-IR

Ultra-wideband impulse-radio (UWB-IR) has lately attracted considerable attention as remote medical sensor, since the effective range is in the order of a few meters and it is not affected by clothes or blankets as well. It is therefore expected to detect the respiratory movement of human body such as patient, which is unique as compared with conventional sensors. It is also friendly to the environment including the human body due to the very low electromagnetic energy emission. However, high speed A/D device should be required to detect the small respiratory displacement using a ranging based approach. This paper suggests a remote respiration sensing scheme using the UWB-IR. It also makes possible to design the simultaneous sensing of multiple persons in hospital beds, for example. In this paper the measurements were conducted for various scenarios and the feasibility is discussed.

Effects of polarization, antenna directivity, and room size on delay spread in LOS indoor radio channel

This paper presents results of experiment and computer simulation based on a three-dimensional (3-D) ray-tracing method for various directional polarized antennas, where the effects of polarization, antenna directivity, and room size on delay spread (measured at 94 GHz) are investigated in the line-of-sight (LOS) indoor channel. These results indicate that the delay spread can be reduced significantly by the directional circularly polarized antenna. It is also found that the delay spread increases almost proportionally with the square root of the room floor area.

Human Body Detection using UWB-IR Indoor Channel

Delay profile of an indoor ultra-wideband impulse-radio (UWB-IR) channel should change for the movement of a human body. This paper suggests a human body sensor using the UWB-IR in order to protect a house, not a room, because the radio with high range resolution can penetrate into the walls and the reflected paths from human body and the like should be able to be discriminated in time domain. The usefulness is experimentally investigated under a scenario which a human intrudes into a typical house with four rooms and walks around. It is found from the results that the intruder should be recognized everywhere he stands in the house.

Mobile satellite CDMA system robust to Doppler shift

This paper suggests a dual-channel PSK demodulator for LEO satellite DS/CDMA communications, whose performance is absolutely invariant to time-variant Doppler offset of a carrier and local oscillator instability. The demodulator does not require any preamble (pilot signal) for carrier recovery, differential encoder/decoder, and carrier recovery circuit such as PLL and Costas loop, thereby resulting in high transmission efficiency and system complexity reduction. In a CDMA channel with the demodulator, the transmitted CDMA signal is composed of two orthogonal linear polarized components, which are spread by different spreading codes, and only one of which is modulated by the data stream. At the receiver, one of the two components despread by the corresponding matched-filter is utilized as a pilot reference carrier for the demodulation. Thereby, the Doppler offset is completely eliminated from the received signal since both these components exhibit the same Doppler and local oscillator instability. >

Performance Evaluation of Vehicular Ultra-Wideband Radio Channels

Ultra-wideband impulse-radio (UWB-IR) channel with omni-directional antenna was experimentally investigated inside a vehicle body with passengers where the interference power out-radiated from the vehicle is also discussed. From the result, the RMS delay spread and average delay, which are considerably degraded as compared with the use of directional antenna, are likely to decrease in proportion with the number of passengers in either channel of line-of-sight (LOS) and non-LOS. Also remarkable difference was not seen for the channel bandwidth. And the interference power is found to depend on the antenna height as well as antenna directivity. For example, the attenuations at 3 m away are approximately 80 dB and 60 dB for the antenna height of 0.8 m (below the window) and 1 m (above the window) respectively.

Ultra-Wideband Impulse-Radio Propagation for In-Vehicle Wireless Link

In-vehicle ultra-wideband impulse-radio propagation characteristics are investigated experimentally for two types of vehicle, sedan and one-box, and the effects of in-vehicle antenna locations and passengers on propagation characteristics are discussed where four frequency spans of 1, 3, 5 and 7 GHz are considered. From the measurement results, these delay spreads are 1~5 and 4~8 nsec respectively and the effect of passengers are found to be relatively small.

Elderly-care motion sensor using UWB-IR

Requirement for monitoring the state of the elderly in care facilities is increasing year by year and the increase in accidents involving them becomes great concern. In this paper, an ultra-wideband impulse-radio (UWB-IR) monitoring sensor is suggested which focuses on the bed status most critical to the elderly that need the assistance immediately. Employing our developed state detection algorithm based on ranging and motion estimation, the state can be detected that includes sleeping in a bed, sitting up in bed, falling down, wandering in room, going in and out at the door. The measurements were conducted in care facilities and the detection performance about the above mentioned state is investigated where various scenarios are considered. The measurement result shows that the detection rate is more than 95%.

Empirical study of stepped-FM UWB microwave sensor

This paper presents an ultra wideband (UWB) microwave sensor using a stepped-FM scheme. Impulse-radio UWB sensor requires high speed A/D in order to synchronize and detect the nanosecond pulse echo. Also it may be difficult to use the bandwidth wider than 500MHz without causing interference with other wireless systems. Our suggested scheme which does not require any high speed A/D devices can coexist with other wireless systems since spectrum holes (non-activated within a portion of the radio spectrum) are easy to be designed over specific bandwidth. In this paper, the measurements were conducted using the experimental device and the above mentioned characteristic is investigated.

Elderly-care monitoring sensor using stepped-FM UWB scheme

Elderly-care support is a very important issue in many developed countries because of the arrival of increasingly aging society. The increase in accidents involving the elderly becomes great concern and the requirement for monitoring their activity and state is especially increasing in care facilities. We have therefore developed a wireless monitoring sensor where a stepped-FM based ultra-wideband (UWB) scheme is employed to coexist with other existing wireless systems. This is because some interference mitigation device is required to be implemented by the UWB regulation. Our developed sensor system can take any optional spectrum hole (non-activated within a portion of the wide radio spectrum) for the UWB transmission. This paper presents the measurement results conducted in a care/nursing home.