Road debris are considered as a major safety hazard for vehicles. For example, the debris causes over 100 injury accidents every year in Japan, thereby demand to detect road debris has increased. In bad weather environment such as rain and fog, however, it is difficult to detect the debris from a distance using the imaging sensor. 79GHz- band radar may offer high-detection performance with high range- resolution and all-weather capability compared with imaging sensor. This paper presents road debris detection using 79GHz-band radar. We conducted measurement for road debris and road clutter in 79GHz-band and discussed the feasibility on road. Please note that there is no report regarding to the road debris by millimeter-wave radar as far as the authors know.

Radar echo contains unwanted echoes called as clutter, which make it difficult to detect vehicle or obstacle. Especially short-range/wide-angle vehicle radar at 24 GHz suffers from heavy clutter unlike long-range radar at 77 GHz. It is therefore expect to improve the detection performance by suppressing the clutter using a pulse integration and CFAR (Constant False Alarm Rate). However the radar echo should include multiple vehicle targets as well as the clutter, thereby it is not easy to improve the performance. In this paper the target discrimination technique, let say, power delay profile matching scheme is proposed and the usefulness is investigated by conducting the measurement at 24 GHz where the clutter suppression scheme is also considered. As a result, a vehicle target is found to be recognized from multiple vehicles. We have also investigated the effect of bandwidth on the target discrimination capability.

High range-resolution radar using ultra wideband radio attracts considerable attention as a short range automotive radar. Radar echo from a target often contains unwanted echoes called as clutter, which make it difficult to detect the target. In order to suppress the clutter, therefore, it is important to investigate the clutter distribution and to develop the clutter model. In this paper, traffic road clutter is measured and characterized for various bandwidths from 10 MHz to 5 GHz. It is also quantitatively compared with the model of log-normal, Weibull and log-Weibull.

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 systems have the ability to resolve multiple paths of the transmit radio and to mitigate the fading. Rake reception is capable of combining these paths, thereby improving the signal-to-noise ratio. In LOS channel, however, the improvement may be comparatively small for the cost of increasing receiver system complexity. This is because the LOS path should be dominant for the total energy in all paths. In this paper the distribution of the energy captured by Rake receiver is first presented for 160 measured LOS channel cases and then discussed. Rake reception with reflector is next suggested in order to effectively increase the signal energy without increasing the complexity, that is, increased number of Rake fingers. The use of reflector is also suggested for non-LOS channel and experimentally discussed where the Rake gain is compared with conventional Rake without reflector. The measurement results show the usefulness.

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.

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.

This paper investigates an obstructed radio channel by foliage for LMDS (local multipoint distribution services) where a relative evaluation of attenuation characteristics of foliage at 29.5 and 5 GHz is performed. Results show that the attenuation in dB should be treated statistically as Rician distribution. It is also found that swaying foliage in wind causes a significant channel fading at 29.5 GHz, ranging over 10 dB, while the fading depth at 5 GHz is approximately 2 dB.

This paper proposes an anti-shadowing scheme employing site diversity combined with orthogonal frequency division multiplexing (OFDM) modulation for 60 GHz wireless LAN. In the proposed system which we name overlapped-spot diversity, multiple access points (APs) sufficiently separated on a ceiling cover a same terminal so that it can receive more than one direct LOS paths even under shadowing situation. By using OFDM modulation, multiple APs within a single cell can transmit identical information using an identical frequency band while a terminal can simply add up all the arrived signals from those APs without any specific combining technique. Our computer simulation results by means of ray-tracing showed the system with multiple APs achieves better robustness to shadowing compared to that with single AP in terms of average bit error rate and outage probability.

In an ad-hoc radio network of cluster architecture the connections between two adjacent clustering heads are significantly affected by shadowing since a high spot antenna can not be usually expected for each head. The use of a backup node is suggested to support the connection failure of clustering head in shadowing channel and its performance is investigated using computer simulations. The simulation result shows that its use brings the less average delay and high arrival rate to destination node.

Circular polarization diversity with reflector is suggested under indoor environments and its performance is investigated using a three-dimensional ray-tracing simulation in conjunction with a geometric-optics based facet approximation. The simulation result shows that the use of a reflector improves the outage probability of the indoor channel by 1.5/spl sim/3 dB as compared with a circular polarization diversity without reflector.

The paper presents the effects of directional antennas, cell size, diversity reception, log-normal shadowing, and path loss exponent on the reverse-link operated CDMA capacity. The simulation results show that a CDMA system with the directional antennas associated with smaller cell architecture suppresses the outside cell co-channel interference, resulting in significant capacity improvement. It is also found that two-branch antenna diversity reception at the base can improve the capacity by 2.2-2.3 times and the shadowing with a standard deviation of 10 dB decreases the capacity by 10-15% in comparison with that for 2 dB standard deviation.

This paper presents an anti-multipath fading scheme employing a circular polarization wave for line-of-sight (LOS) indoor radio communications. The circular polarization wave transmission 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.

The paper describes the effects of directional base station and terminal antennas, cell size, diversity reception, log-normal shadowing, and path loss exponent on the reverse-link capacity of a millimeter-wave indoor radio communication using a DS/CDMA scheme.>

In the paper, the authors suggest an asynchronous microcellular CDMA system with a matrix-based multiuser interference canceler for the reverse link, in which multiuser interference is completely removed on a symbol-by-symbol basis. The linear interference cancellation scheme, whose matrix order is equal to the number of active users, does not require knowledge of their received power levels, thereby resulting in high capacity and near/far resistance. In the paper, the influence of surrounding cell interference on a given base station receiver for various propagation path loss models is also analyzed and then the system performance is investigated theoretically. Provided the normalized capacity is defined by a required SNR (=E/sub b//N/sub 0/) of 7 dB at the binary DPSK detector, the CDMA system can provide capacity per cell of 46/spl sim/54%.>