Communications: directive radio wave systems and devices (e.g. – Radar transponder system
Patent
1991-08-28
1993-09-14
Hellner, Mark
Communications: directive radio wave systems and devices (e.g.,
Radar transponder system
342 43, 342 51, G01S 1374
Patent
active
052453464
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a mobile communication system and, more particularly, to interrogation transponder system capable of high-speed communication at reduced power dissipation.
BACKGROUND ART
A mobile communication system for delivering communications between a transmitter (interrogator) stationarily mounted in a certain fixed place (hereinunder referred to as "on the fixed side") and a simple receiver (transponder) called tag which is mounted on a mobile object (hereinunder referred to as "on the mobile side") has attracted attention. Such a mobile communication system is used for, for example, identifying an object or a person in a communication zone noncontactingly from an identification signal reflected by the transponder with respect to an interrogation signal emitted from the interrogator to the transponder carried by said object or person.
In most of such mobile communication systems, batteries are used as a power source of the transponder due to its simplicity and light weight, and one of the problems to be solved is to prolong the life time of the battery by reducing the power dissipation.
To solve this problem, a power is only supplied to a circuit 64 which is necessary for the reception of an interrogation signal and at the point where the interrogation signal is received, a switching circuit 600 is actuated so as to feed a remaining signal processing means 65, thereby reducing the constant power dissipation, as shown in FIG. 8 (e.g., Japanese Patent Laid-Open No. 201177/1986. Hereinunder, this communication system is referred to as the former communication system).
As shown in FIG. 9, there is another mobile communication system for identifying data by using a compact transponder 70 having a simple structure which receives an unmodulated signal from an interrogator 75 and reflects a response signal imparted with identification data to the interrogator 75 (e.g., Japanese Patent Laid-Open No. 79476/1982. Hereinunder, this communication system is referred to as the latter communication system). However, in the latter communication system shown in FIG. 9 having the above-described structure, only the identification data which is set in advance can be read out. In addition, in order to make the transponder 70 compact and sufficed with a simple circuit structure, a code generator 74 and a low-frequency signal generator 73 for generating the data must also have a simple structure, so that the identification data are limited to several hundred bits (several ten bytes) at most and storage and control of a large amount of information such as several thousand bytes is very difficult. It is necessary for the interrogator 75 to store and control all the induced information based on the identification data read out, and in a system having an increased number of transponders 70 and a plurality of interrogators 75, there are problems to be solved for practical use such as an enlarged and complicated system due to the increase in memories and the necessity for networking. The former communication system has been aimed at only identifying the transponder and reading data from the transponder. In recent years, however, the application of the communication system to a wider field necessitates emitting from the interrogator to the transponder various command signals for commanding the delivery of necessary data or writing various data signals from the interrogator in the memory of the transponder.
In this case, it is necessary to increase the data transmission speed i.e., the rate of transmission of data, in order to communicate necessary command or data signals within a short time in which the transponder passes the communication zone with the interrogator. For this purpose, it is necessary to set the frequency band of the receiver of the transponder at a frequency so high as to sufficiently cover the data transmission speed, which inevitably increases the electric power dissipation of the receiver to which the power is constantly supplied.
To state this in detail, the former commun
REFERENCES:
patent: 4242661 (1980-12-01), Henoch et al.
patent: 4641374 (1987-02-01), Oyama
patent: 4926182 (1990-05-01), Ohta et al.
patent: 4980689 (1990-12-01), Kawakami
Harata Yoshihisa
Isikawa Souichi
Kozuka Kazuhiro
Nishimura Yoshihiro
Ohta Norikazu
Hellner Mark
Kabushiki Kaisha Toyota Chuo Kenyusho
Toyota Jidosha & Kabushiki Kaisha
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