Patent Grant
6844808
The present invention relates to public and industrial warning systems employing multiple remote warning units and more particularly to a method and apparatus for detecting false activation of the remote warning units.
Outdoor warning sirens are the modern equivalent of what used to be known as civil defense sirens. Outdoor warning sirens are high power voice and siren systems used to notify the public of a potential safety hazard related to severe weather, darn failure, nuclear plant is emergency, chemical plant emergencies or hazardous material spills and the like. A typical outdoor warning system includes a number of warning units dispersed over a geographical area. Each of the warning units includes a high power siren and/or voice warning capability, a power supply with battery backup, a connection to the municipal power grid and a communication interface to link the remote warning units to a centralized base station. The communications link between the remote warning units and the base station typically comprises a one-way or two-way radio frequency (RF) link. In a one-way RF link system, the remote warning units are activated or deactivated by a command transmitted from the base station. Activation and deactivation of warning units operate similarly in a two-way RF link system with the additional feature that the remote warning units can communicate with the base station to relay information regarding status of the warning unit. Status reports may include an alert notifying the base station of some fault in the remote unit, such as failure of the backup power supply.
In a warning siren system, RF communications between the base station and the warning units are typically carried out in either of a dual-tone multi format (DTMF) or frequency shift keying (FSK), although other communications formats are possible.
The base station is typically located in an emergency management center where information and personnel are gathered to evaluate developing threats to public safety. Public safety personnel activate the outdoor warning system from the base station. An activation signal from the base station causes each of the remote warning units to emit a pre-determined tone and/or voice warning alerting the public to the hazard. Different tones and/or voice warnings may be assigned to each hazard and the warning units may store several warning patterns. Thus, there may be several activation commands, depending on the warning siren system configuration.
The term “base station” as used herein refers to that portion of an outdoor warning siren system used to interact with remotely located warning units. The emergency management center is typically equipped with a base radio and antenna. The outdoor warning siren system “base station” therefore typically includes an interface and audio frequency transceiver which allow the siren system to use the existing radio equipment. The “base station” may be a PC-based system or a stand alone unit. Either configuration includes a user-interface permitting emergency personnel to activate and monitor the warning siren system.
A concern raised about such public warning systems is the possibility of a system breach enabling an unauthorized party to generate a false alarm. Such a false activation might be carried out by monitoring the frequency used for communications between the base station and the warning units, recording a coded activation command when transmitted from the base station and replaying the activation command on the correct frequency. This means of false activation is available regardless of whether the activation is coded in the DTMF or FSK format.
One approach to preventing this type of system breach is to provide the base unit and warning units with synchronized clocks and to encode a time along with all system radio communications. The warning units are then programmed to reject or ignore activation command including a time stamp that does not match (or come very close to matching) the time on its clock. This approach increases the maintenance burden by requiring the clocks to be maintained in synchronicity. A particularly severe side effect of this approach is that if the proper maintenance is not performed, the clocks will be out of time and reject even a legitimate warning activation.
Time stamps and other complex data encryption algorithms often require additional, expensive hardware. The additional equipment and complexity may also result in increased maintenance expense.
There is a need in the art for a method and apparatus for detection of a system breach in an outdoor warning siren system. The method and apparatus are preferably capable of distinguishing a valid transmission from an unauthorized transmission.
The method and apparatus for detection of system breaches in outdoor warning siren systems comprises apparatus and steps for validating encoded RF transmissions used for communications between a base station and remotely located warning units. An aspect of the invention relates to the detection and validation of all command signals that could activate the warning units of an outdoor warning siren system. The invention may be as simple as the addition of computer-implemented steps to the operating software of the base station equipment, although changes to the outdoor warning siren system may be necessary.
A typical outdoor warning siren system has one or more base stations capable of transmitting encoded RF command signals to activate one or more remotely located warning units. In an exemplary embodiment of the present invention, each of the base stations is programmed to monitor the system communication radio frequency (RF). A system with a two-way RF link between the base station and the warning units will necessarily monitor the system communication RF. In a system with a one-way RF link, implementation of the exemplary embodiment of the invention may require the addition of system communication RF monitoring capability. It should be noted that the outdoor warning siren system monitoring function for a particular base station is suspended when that base station is transmitting on the system communication RF.
The present invention may be implemented by adding a security device to the existing base station equipment. The security device is a stand alone unit interfaced with the base station radio and equipped to accept inputs from emergency personnel as well as provide outputs indicating siren system status to emergency personnel. The security device may replicate the base radio interface and audio frequency protocol transceiver to provide the necessary monitoring and transmission capability. In this manner, a siren system using a one-way RF link is upgraded by interfacing the security device with the base station radio and existing alarm activation transceiver.
In an outdoor warning siren system with multiple base stations capable of transmitting an activation command, part of the coded activation command identifies the base station generating the command. An aspect of the invention relates to each base station being provided with a validation procedure. The validation procedure relies on two simple facts. The monitoring function is suspended on a transmitting base station for the brief period of transmission, e.g., a base station does not transmit and monitor at the same time; and a legitimate activation command must be generated by one of the base stations in the outdoor warning siren system. Thus, a legitimate command signal cannot be detected by a base station generating the command signal.
The validation procedure comprises computer-implemented steps of:
Upon detection of an invalid activation command, the outdoor warning siren system may be configured to automatically transmit a command turning off the warning units. The outdoor warning siren system may also be configured to alert relevant personnel to the detection of a system breach. The emergency personnel are then able to deal with the situation accordingly.
An object of the present invention is to provide a new and improved method and apparatus for ensuring the integrity of RF communications in outdoor warning siren systems that is compatible with existing equipment.
Another object of the present invention is to provide a new and improved method and apparatus for ensuring the integrity of RF communications in outdoor warning siren systems that is efficient and reliable.
A further object of the present invention is to provide a new and improved method and apparatus for ensuring the integrity of outdoor warning siren systems that is effective regardless of the format used to encode RF command signals from a base station to the warning units.
An exemplary outdoor warning siren system illustrative of several aspects of the present invention is shown in
One or more base stations 20 provide emergency personnel with the capability to activate the remotely located warning units 30 by transmission of command signals.
It will be understood that control circuitry of the security device 20a is preferably implemented using a programmable microcontroller 40. Alternatively, the security device 20a user interface 44, data system 42 and microcontroller 40 may be emulated by software installed on a personal computer (not shown) and interfaced with a radio system 22. Whatever the physical form of the security device 20a, it will be understood that the security device is programmable and includes memory for storage of, for example, validation program steps and steps permitting activation of the radio system 22 to transmit a clear command.
The method and apparatus of the present invention may be built into the base station 20 or may be implemented as an add-on security device 20a as shown in FIG. 5. The security device 20a “learns” the base station ID of the base station to which it is attached and uses it in the validation steps as described below. This “plug and play” ease of installation allows the security device to be easily added to existing outdoor warning siren systems without disrupting the system or requiring extensive training of personnel using the system.
New or existing outdoor warning siren systems may be configured as a one-way or two-way system. In a one-way outdoor warning siren system, the remotely located warning units 30 do not have the capability to transmit signals back to the base station equipment. In a two-way outdoor warning siren system 10 as shown in
In the representative outdoor warning siren system 10, command signals from the base station 20 to the warning units 30 have a particular format, for example, a ten-digit DTMF string. Returning signals from the warning units 30 to the base station 20 have a different format, for example, a fourteen- to eighteen-digit DTMF string.
An aspect of the invention relates to monitoring the system communication RF and computer implemented steps that validate detected command signals. A security device 20a in accordance with the present invention includes the monitoring capability even if the existing base station 20 to which it is added does not. In an outdoor warning siren system configured for two way communications, the security device may be implemented without changes to the existing hardware.
In accordance with a further aspect of the present invention, each transmission from a base station 20 includes an encoded portion associating the transmission with the base station that generated it. Each base station 20 or security device 20a is programmed to monitor the system communication RF. Upon detection of a command signal, the base station 20 or security device 20a decodes the signal to determine the originating base station ID. If the detected command signal indicates that the detecting base station was the originating base station, the signal is determined to be invalid and indicative of a system breach. If the detected signal contains the base station ID of another of the base stations; the detecting base station ignores the command signal.
A further aspect of the present invention relates to how an outdoor warning siren system improved according to the present invention reacts to detection of an invalid command signal. The base station 20 or security device 20a may be configured to automatically transmit a command signal turning off any warning units activated by the invalid control signal. This option is indicated at steps 100 (Yes), 102 (Yes) and 104 of FIG. 2. Another option is to alert authorized personnel to the system breach so that they may deal with the situation as they see fit. This option is indicated at steps 100 (Yes), 102 (No) and 106. Step 106 corresponds to sending notice to relevant personnel that a system breach has occurred. This may include visual and/or audio alarm indications at the base station. In either case, the invention provides a reliable means for detecting invalid command signals in an outdoor warning siren system.
Data System
The data system 42 is comprised of the EEPRom Data Storage 54 and PC Port Interface 56 functional blocks. The data system 42 provides a means by which an end-user can enter, store, view or change system configuration data.
Configuration data includes system area code, station ID and counter measure scenario, (a counter measure scenario could be audio/visual contact closures and/or automatic sending of a cancel command to siren or system). On power-up the microcontroller 40 loads configuration data into RAM from EEProm 54 at step 110 of FIG. 2. The operating program of the security device 20a, including the main routine of FIG. 2 and the Validate String sub-routine of
The microcontroller 40 has reserved commands for updating data stored in EEPRom Data Storage 54. When these commands are received, the microcontroller 40 will update the corresponding data field or fields.
Depending on the microcontroller used, the EEPRom Data Storage 54 may be external or internal to the microcontroller. Also, the EEPRom Data Storage 54 is interfaced to the microcontroller 40 serially and that protocol is either I2C or polled, depending on the microcontroller used.
The PC Port Interface 56 connects the microcontroller 40 to a PC's serial or USB port. Through the PC Port Interface, commands and data are exchanged-between the microcontroller 40 and a PC (not illustrated).
User Interface
The user interface 44 is comprised of the Audio/Visual Closures and. Breach Acknowledge functional blocks. The user interface 44 is provides contact closures, if configured as part of a counter measure scenario, when a system breach is detected. The term “contact closures” is used to describe the activation of electronic or electromechanical relays to provide control to user-selected devices that may include audio and/or visual signaling devices. An authorized person may disable (open or de-activate) the audio/visual closures by using the breach acknowledge functionality also provided by the user interface. The breach acknowledge is a control input (contact closure) to the security device 20a.
If the microcontroller 40 detects a system breach and if contact closures are configured as a counter measure, contact closures will move from the “Normally Open” to “Normally Closed” state. Likely external equipment connected to the audio/visual closures might be a flashing light or audible alarm device. Activation of these or similar warning devices signals an operator that a system breach has occurred. A breach acknowledgment from an authorized person will revert the contact closures back to the “Normally Open” state.
Radio System
The radio system 22 includes Audio Frequency Protocol (AFP) Transceiver 50 and Base Radio Interface 52 functional blocks. This provides an electrical interface between the security device microcontroller 40 and the signal handling portions (transmitter/antennae) of the radio system 22. Functionality for encoding and decoding either the FSK or DTMF audio frequency protocol signals is provided by this system. It will be understood that the security device radio system may duplicate some functions in the existing equipment.
The Audio Frequency Protocol Transceiver 50 monitors all radio and/or landline communications within the outdoor warning siren system 10. Typically DTMF and/or FSK are the audio frequency protocols (AFPs) being monitored. As each character, as defined by the protocol in use, is detected an interrupt is issued to the microcontroller 40 informing it of the character's presence.
Should the microcontroller 40 require a transmission, the Audio Frequency Protocol Transceiver 50 will convert digital characters from the microcontroller 40 into a format that corresponds to the protocol in use. Several characters together form a string.
The Base Radio Interface 52 provides electrical isolation and signal conditioning between the system's base radio 22 and the microcontroller 40. To accommodate a variety of radios, configuration options may be provided.
Microcontroller
The microcontroller 40 acts as the “brain” of the base station 20. The microcontroller 40 interacts with the functional components of the base station 20 through an operating program uploaded from memory on system power up. System variables such as area code and base station ID are retrieved from Eeprom. The microcontroller:
The microcontroller 40 is programmed to extract the area code and station ID information from any received AFP string. It will then validate that information against system variables retrieved from EEPRom as shown in
The software algorithms for the PC Port Interface 56 and Audio Frequency Protocol Transceiver 50 are interrupt driven. The Base Radio Interface 52 and Breach Acknowledge algorithms are polling routines. Sub-routines related to Audio/Visual closures and EEPRom Data Storage 54 are active only when necessary.
The two primary software algorithms relevant to the method disclosed herein are:
The main routine is always running and manages polling and general services.
Power Bus
The Power Buss 48 brings power into the base station and distributes power to the several components. Power from the Power Bus may be distributed to an external signal encoder.
While a preferred embodiment of the foregoing invention has been set forth for purposes of illustration, the foregoing should not be deemed a limitation of the invention herein. Accordingly, various modifications, adaptations and alternatives may occur to one skilled in the art without departing from the spirit and the scope of the present invention.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4229734 | Schultz | Oct 1980 | A |
| 5282250 | Dent et al. | Jan 1994 | A |
| 5875395 | Holmes | Feb 1999 | A |
| Number | Date | Country | |
|---|---|---|---|
| 20040212490 A1 | Oct 2004 | US |
