The Low-Power High-Frequency Transceivers with a Received Signal Power Indicator Used in the Access Control System

Abstract

The article deals with relevant issues to implement automatic disarming through the radio channel of car alarm when approaching the car. Notes that the implementation of automatic (keyless) access in standard automotive systems, using wireless communication between the owner's transponder tag and the car's transponder at a frequency of 125 kHz and a set of active antennas, requires large costs and is therefore available only in business-class cars. To implement this function in the same form at the stage of installation of additional equipment is expensive and time-consuming. As an alternative, the proposal is to use the radio car alarm. A disarming process involves two devices, namely a RFID-tag, which the owner carries around, and an alarm unit. Both the tag and the alarm unit radio channel contain transceivers, i.e. devices capable of operating both as a transmitter and as a receiver. The paper justifies that it is expedient to place the transceiver of unit on the car windshield and use a passive label responding to the request signal from the transceiver of unit. Formulates requirements for transceiver characteristics and based on the analysis of publications proves the CC2400 (Texas Instruments) transceiver selection. Analyses the possible types of antennas the manufacturer offers for the CC2500 transceiver. Estimates their using efficiency in RFID-tags through manufacturing and testing a developed batch with PCB antennas of different type. A developed proprietary antenna design, as compared to the manufacturer’s antennas, has a polarization diagram close to circular. The paper shows its experimentally estimated effectiveness. An algorithm is analysed when the distance of automatic disarming is adjusted only through the power of the transmitter of the alarm transceiver. It is noted that the algorithm does not use information about the signal from the tag to the unit. It is experimentally justified that its use of the algorithm without feedback allows us to obtain a stable automatic disarming zone. A radio-exchange algorithm between the car alarm transceiver and the tag transceiver is proposed and justified using the power indicator of the signal received from the tag. The operation and effectiveness of the proposed algorithm are tested experimentally.