Pulse or digital communications – Systems using alternating or pulsating current – Plural channels for transmission of a single pulse train
Reexamination Certificate
2000-08-15
2004-06-01
Phu, Phoung (Department: 2631)
Pulse or digital communications
Systems using alternating or pulsating current
Plural channels for transmission of a single pulse train
C375S347000, C375S299000, C455S101000
Reexamination Certificate
active
06744823
ABSTRACT:
FIELD OF THE INVENTION
The present invention is generally related to a roadway communication system wherein a plurality of road antennas are disposed along a road in a manner to define cells on the road, thereby providing mobile communications between a stationary station and a mobile station.
BACKGROUND OF THE INVENTION
Demand for communications between the road administration and ground vehicles tends to grow even more in the future. Particularly, drivers on highways need frequent information exchanges between the stationary station and the mobile stations in order to drive under less load and to prevent accidents. A developed form of such a system is exemplified by an automatic driving system with extensive provision of various sensors and cameras on both the road and vehicle for close communications between the stationary station and vehicle (see, for example, Japanese Unexamined Patent Publication No.8-241495(1996).
The consideration of future expansion of the automatic driving system dictates the need to construct a driver support system (hereinafter referred to as “roadway communication system”) based on the communications with vehicles. Preparatory to the construction of such a system, communication areas (cells) must be provided over the roads.
It may be contemplated to lay leakage coaxial cables along the roads, which involves a large scale cable-laying work. Besides, the leakage coaxial cables need be embedded at a relatively great depth in the roads and hence, the wave energy presents a disadvantageously small range with respect to a transverse direction of the lane.
In contrast, as shown in
FIG. 28
, a system with road antennas
120
disposed at given space intervals along the road for communications permits one road antenna
120
to define a relatively broad cell
121
. In this case, the road antennas are each connected to a respective control station of the road administration via an optical fiber, coaxial cable or the like.
(A) In a case where the road antennas are disposed, a large vehicle approaching a small vehicle may sometimes cut in a line of sight of the small vehicle.
FIG. 29
illustrates a particular state where the small vehicle is in a wave blocking area of the large vehicle. The microwaves and millimeter waves at high frequencies have small diffraction angles and hence, are prone to be blocked. This results in a breakdown of roadway communications.
It is therefore, an object of the invention to provide a roadway communication system accomplishing seamless communications between the stationary station and the mobile station.
(B) The installation of the road antennas generally entails inter-carrier interference or inter-symbol interference associated with the occurrence of delayed multipath waves, causative factors of which are structures near the road or plural vehicles in the cell which reflect the waves. When the inter-symbol interference occurs, a bit error rate is not improved even if the waves are received at high reception levels. This leads to a so-called floor error.
In the mobile communication system based on a single carrier, a receiver is generally equipped with an equalizer having inverse characteristics of those of a transmission line thereby to eliminate the effect of the inter-symbol interference associated with the delayed multipath waves.
Unfortunately, the automobile travels through the cell at such high speeds that the radio frequency energy field presents too sharp fluctuations per unit time for the equalizer to cope with the calculations. Thus, it is impossible to transmit signals at less than a given transmission error rate. Additionally, a large-scale hardware is required for implementing the equalizer, which results in great power consumption.
On this account, the invention has an object to provide a roadway communication system capable of preventing the inter-carrier interference and inter-symbol interference for accomplishing stable communications between the stationary station and the mobile station.
DISCLOSURE OF THE INVENTION
(1) A roadway communication system according to the invention for achieving the above object has an arrangement wherein a plurality of road transmission antennas are disposed at different places along a road, each radiating the same cell with electromagnetic waves carried at the same frequency and containing the same content, and wherein a vehicle mounted device receiving the waves from the road transmission antennas performs antenna pattern diversity reception (Claim
1
).
According to the invention, the plural road transmission antennas radiate the waves based on signals modulated with data of the same content. In this case, the road transmission antennas each have a specific directivity (including non-directivity) and therefore, the waves from the road transmission antennas are incident on the vehicle along different directions. Accordingly, when an incoming wave in one direction of the vehicle is blocked by a large vehicle, the wave incident on the vehicle in another direction becomes relatively higher in reception level than the blocked wave. Hence, the vehicle reception antennas performing the diversity reception can provide communications between the road transmission antennas and the vehicle mounted device even when one of the waves is blocked.
Within the same cell, seamless communications are ensured between the stationary station and the vehicle because the radiation to the vehicle is provided in plural different directions. This permits every vehicle to receive road traffic information seamlessly and hence, the inventive roadway communication system is best-suited to the automatic driving system, as well.
The diversity reception may be performed based on the reception level of each directive wave received by the vehicle reception antenna (Claim
2
).
The reception level of a wave received by the vehicle reception antenna normally increases in value as the vehicle approaches a road transmission antenna radiating the wave. In a case where a wave to be received at the highest reception level is blocked by the large vehicle cutting in the transmission path thereof, for example, a reception level of another wave from a different road transmission antenna may become relatively higher than that of the former wave. In consideration of this event, an arrangement may be made such that the reception levels of the waves received by the vehicle reception antennas are directly detected and the directivity of wave to be received is switched. Thus are attained more preferable communications.
The diversity reception may be accomplished by either of the following operations: (a) an operation of switching or combining the signals which were received by the vehicle reception antennas and are to be decoded; and (b) an operation of switching or combining the codes which were received by the vehicle reception antennas and then decoded (Claim
3
).
The vehicle reception antennas may be an array antenna, whereas the vehicle mounted device may further comprise reception-signal detection means for detecting a reception level or phase of the wave received by each of the vehicle reception antennas, so that the diversity reception means may perform the diversity reception using information on the reception level or phase detected by the reception-signal detection means (Claim
4
).
This configuration assumes a case where the array antenna or adaptive array antenna is applied to the vehicle reception antennas. The phase control of the antenna provides a desired directivity.
If an optical fiber radio signal transmission system is used as a transmission system for supplying the signals to the transmission antennas (Claim
5
), no need exists for each road transmission antenna to have a signal transmission unit with a frequency converter. This results in a simplified configuration of the road transmission antenna.
Orthogonal Frequency Division Multiplex (OFDM) modulation technique in which a guard time is provided at each symbol may be used as a data modulation technique (Claim
6
). OFDM system resisting multipath effe
Araki Tadashi
Hirakata Noriyuki
Kamemura Akihiro
Kutsuki Kenji
Tanaka Keiji
McDermott & Will & Emery
Phu Phoung
Sumitomo Electric Industries Ltd.
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