Pulse or digital communications – Systems using alternating or pulsating current
Reexamination Certificate
1997-12-26
2001-03-27
Luther, William (Department: 2664)
Pulse or digital communications
Systems using alternating or pulsating current
C375S312000, C375S344000, C375S376000
Reexamination Certificate
active
06208694
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to communications devices and protocols such as those used in wireless alarm systems having multiple sensors in communication with one or more receiver control units; and in particular to such alarm systems where the transmitting element of the system is designed to transmit messages at different power levels.
Most radio frequency (RF) wireless security systems available today, such as those manufactured by Alarm Manufacturing Device Co. (ADEMCO) 165 Eileen Way, Syosset, N.Y. 11791, employ a multiplicity of transmitters in communication with a central receiver control unit. The information transmitted typically describes the state of various transducers or sensors associated with each transmitter, such as smoke, motion, breaking glass, shock and vibration detectors; door, window and floor mat switches; etc. These transmitters are designed to be inexpensive to manufacture and generally are capable of transmission only rather than reception only or transmission and reception, which would add significant cost to the design. In order to meet certain regulatory agency requirements, the transmitters must periodically transmit supervisory messages to the central receiver control unit in order to identify potential problems with the communication link from any transmitter in the alarm system as soon as possible. The supervisory message (as well as a normal alarm message) comprises a unique embedded identification code, which serves to identify to the central receiver control unit the source of the particular supervisory message (or alarm message). Typically, when a supervisory message is properly received and detected by the central receiver control unit, the identification code is made available to the remainder of the system for further processing.
For Safety of Life applications, where an alarm condition may signify a health or security emergency, the RF wireless system must also comply with more stringent regulations, such as Underwriters Laboratories regulation UL864. This regulation requires that supervisory messages be transmitted at a reduced power level below that of the alarm message (i.e. normal, non-supervisory signals) by a minimum of 3 dB. Equivalent means may be utilized as long as the transmission of alarm messages comprises an effective power margin over that of the periodic transmission of supervisory messages sent by each transmitter in the alarm system.
Therefore, it would be advantageous if the alarm system would transmit supervisory messages at a power level below that of alarm messages, thereby ensuring that the transmission of alarm messages would have an effective margin over that of the periodic transmission of the supervisory message from each transmitter in the alarm system. Such a feature would be most beneficial if it could be applied without substantial modification to existing receivers already in commercial use.
Additional considerations may be found to hinder the implementation of such a concept such as overall cost, and various system parameters comprising message formats and protocols and repetition of messages. The ideal implementation would be transparent to such parameters that could very well differ from country to country or even among different manufacturers.
Therefore, it would be advantageous if the alarm system would provide a cost effective means for reducing the transmitted signal power of supervisory messages and also transmit alarm messages at full power, which is independent of such parameters as message format, repetition of messages, etc. Such a system would likely require differentiation between supervisory and alarm message in the transmitter prior to transmission.
SUMMARY OF THE INVENTION
In accordance with these and other objects, the present invention utilizes a method for periodically self-testing a communications path in wireless alarm systems, which comprises timing a supervisory period to provide a delay between transmissions of supervisory messages, generating a supervisory message, generating a transmission power control signal comprising one of at least two states upon termination of the supervisory period, and transmitting the supervisory message at a reduced power level as indicated by the state of the transmission power control signal. The present invention also utilizes the steps of generating an alarm status message in response to receipt of an alarm status signal from an alarm sensor, generating the transmission power control signal in response to receipt of the alarm status signal from the alarm sensor, and transmitting the alarm status message at a normal power level as indicated by the state of the transmission power control signal.
The present invention is embodied by an apparatus for periodically self-testing a communications path in wireless alarm systems, which comprises supervisory period timing means for timing a duration of a supervisory period existing between transmissions of supervisory messages, means for outputting a supervisory period termination signal upon termination of the supervisory period, message generation means for generating the supervisory message and a transmission power control signal, the transmission power control signal comprising one of at least two states, and transmission means for transmitting the supervisory message at a predetermined reduced power level in response to a first state of the transmission power control signal.
The present invention is also characterized as being embodied in an alarm sensor transmitter for use in a wireless alarm system, which comprises a supervisory period timer which times a duration of a supervisory period existing between transmissions of supervisory messages and outputs a supervisory period termination signal upon termination of the supervisory period, a message generator which generates the supervisory message and a transmission power control signal in response to the supervisory period termination signal, the transmission power control signal comprising at least two states, the message generator generating an alarm status message and the transmission power control signal in response to receipt of an alarm status signal from an alarm sensor, a radio frequency transmitter which transmits the supervisory message at a predetermined reduced power level in response to the state of the transmission power control signal and transmits the alarm status message at a predetermined normal power level in response to the state of the transmission power control signal, the radio frequency transmitter modulating the transmission signal with the generated supervisory message and the alarm status message and outputting the modulated transmission signal, an oscillator which outputs a data clock signal for synchronizing the message generator and a phase detection clock signal for synchronizing the radio frequency transmitter, the data clock signal and the phase detection clock signal being substantially in phase with each other, and a phase lock loop circuit which substantially maintains correlation between a phase of the transmission signal and a phase of the phase detection clock signal.
Thus, the present invention is also embodied in a data communications method and system comprising a plurality of remote devices, each comprising means for transmitting supervisory messages and non-supervisory messages at different power levels, and a receiver providing means for receiving such messages.
The present invention is based on the premise that system reliability and integrity are improved if supervisory messages are transmitted at lower power relative to the power of alarm transmissions. This invention provides a unique method of accomplishing the stated objectives without increasing receiver cost or complexity and without increasing on-air time to provide unique supervisory message formats.
The first requirement of the transmitter is that it should have the ability to generate a certain logic level during the time period when a supervisory message is being generated. This logic level may then be used to cont
Barkume Anthony R.
Luther William
Pittway Corp.
Traurig LLP Greenberg
LandOfFree
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