EP0607562A1 - Radio alarm system with asynchronous transmission of messages on time channels of differing periods - Google Patents

Abstract

Radio alarm systems are known which have a multiplicity of communication channels (traffic channels) for the transmission of messages between glass break detector, opening detector, and the like and a microprocessor-controlled central unit. The individual communication channels are in this case formed according to the time-division multiplex system or by using the frequency-division multiplex system. So that the possibility of direct manipulation from outside is reliably prevented and the interference immunity is increased, the communication channels are formed, in the direction of transmission from the detectors (sensors) to the central unit, by different cycle durations, characteristic for the individual detectors, of message repetition. Preferably, the difference between the different cycle durations is larger than, equal to the duration of transmission for a message. <IMAGE>

Description

The invention relates to a radio alarm system according to the preamble of patent claim 1.

• a) Das Erkennen eines Einbruchsvorgangs erfolgt mit automatischen Detektoren (Meldern), die je nach Anwendungszweck nach verschiedenen Prinzipien arbeiten,
• b) die Auswertung der Meldungen geschieht in einer Zentraleinheit, abhängig von unterschiedlichen Zustandsbedingungen,
• c) die Alarmierung erfolgt entweder durch Weiterleitung des Alarms, etwa zu einer Polizeidienststelle oder in Form eines örtlichen Alarms durch Aktivieren von Alarmgebern wie Sirenen, Alarm-Blitzleuchten oder dgl..

The Security- (Sicherheit-) Electronic has developed into a valuable aid to immediately report fire, robbery, theft, burglary, robbery and kidnapping. The various components of an alarm system essentially have to perform the following tasks: detection, evaluation, alarming.

• a) The detection of a break-in process takes place with automatic detectors (detectors), which work according to different principles depending on the application,
• b) the evaluation of the messages takes place in a central unit, depending on different status conditions,
• c) the alarm is given either by forwarding the alarm, for example to a police station, or in the form of a local alarm by activating alarm devices such as sirens, alarm flashing lights or the like.

Modern alarm systems usually consist of a central unit (including power supply), switching devices for arming / disarming, automatic intrusion detectors, manually operated hold-up alarms, transmission devices and / or local alarm devices and a network.

Depending on the object to be protected and the effort involved, the detectors used range from simple bolt or magnetic contacts to ultrasonic detectors of various types. Regardless of their mode of action, one can divide the detectors into three groups: detectors for outdoor surveillance, detectors for outer skin surveillance and detectors for indoor and property surveillance.

In conventional alarm systems, the automatic intrusion detectors are connected to the control center in series via so-called alarm lines and work according to the closed-circuit principle. A certain quiescent current flows through all detectors. If the current is interrupted by the triggering of a detector, an alarm message is issued. The alarm is also triggered if the detection line is destroyed or short-circuited at any point.

Various components, such as switching devices, local alarm devices, etc. are additionally protected via a so-called sabotage line, i.e. an alarm is triggered if these components are opened or damaged.

Conventional wired alarm systems thus meet the high requirements of the association of property insurers with regard to interference immunity. The advantages of using optical fibers are: high immunity to electromagnetic waves, high transmission capacity and galvanic isolation of the transmitter and receiver. However, it is disadvantageous that there is a great deal of effort involved in laying the line network, particularly if this is done subsequently.

From DE-OS 40 35 070 a radio alarm system is known, which offers adequate protection against interference by blocking the radio links and against manipulation from outside. The known radio alarm system consists of a central unit with a receiver unit for receiving radio signals from detectors in the form of data telegrams. The receiver units are designed so that only data telegrams from detectors belonging to the radio alarm system are processed in order to trigger an alarm or a function. In particular, in order to prevent manipulation from the outside with a radio transmitter of the same system, each detector of the radio alarm system sends out at least two radio signals of different carrier frequencies, which are coded the same or different (in the sense of an identifier). Accordingly, the central unit with its receiver unit receives at least two different radio signals from each detector and checks the affiliation of the detectors emitting the radio signals by checking the validity of the coding (identifier).

In addition, it is proposed in the radio alarm system known from DE-OS 40 35 070 that the radio signals emitted by the individual detectors are subjected to a field strength check in an evaluation unit, which further increases the interference immunity can be. In order to meet the VdS guidelines, the message channels are formed using the frequency division multiplex method in this radio alarm system.

Furthermore, a radio transmission method for an alarm system is known from EP-A1-0 293 627, in which the same radio frequency is used to transmit information between a central unit and the components of the alarm system. The individual message channels are formed using a time division multiplex method. These message channels are cyclical, i.e. queried sequentially in time in the central unit whether a message is transmitted via the respective time channel. In order to avoid useless and time-consuming polling cycles, a polling cycle is only carried out in the radio transmission method according to EP-A1-0 293 627 if it has been found in a previous, much shorter total poll, in which all components are polled at the same time, that Information has arisen for at least one component (eg a detector).

Finally, a radio alarm system is known from EP-A1-0 316 853, in which additional impulses, so-called pseudo impulses, are transmitted to protect against sabotage. The timely arrival of the additional pulses is recognized in the central unit and evaluated accordingly.

In principle, three basic methods are known for the transmission of messages via a transmission medium (e.g. line, radio link) used jointly by a large number of devices, namely the time division multiplex method, the frequency division multiplex method and the code multiplex method.

In the time-division multiplex method, the entire bandwidth of a single radio channel is available to each device, which, however, may only be used by the device for short periods of time. The characters or character strings of different devices are interleaved and are transmitted at a correspondingly higher bit rate in the single radio channel, the time channel (message channel) assigned to each device being repeated periodically with the frame period.

In the frequency division multiplex method, the total bandwidth available for message transmission is divided into narrow frequency bands, each of which corresponds to a message transmission channel. Such a narrow frequency band is available to each device for the duration of the radio transmission. In practice, frequency-division multiplex or time-division multiplex methods are used in radio alarm systems for message transmission, but applications of the code multiplex method are not known.

Applications of the code division multiplex method are known in car telephone systems (see also EP-A2-0 241 954 or EP-A2-0 211 460). In the case of code multiplexing, the various messages carried over the common transmission medium (e.g. radio link) are modulated onto a carrier by basic modulation and the resulting narrow-band signal compared to the channel bandwidth is converted to the channel bandwidth by multiplex modulation with the aid of a code word characterizing the receiver spectrally spread. A code generator is arranged in the transmitting devices of the radio stations, which generates a code identifying the transmitting device.

The invention has for its object to make the formation of message channels in a radio alarm system in such a way that the possibility of direct manipulation from the outside is reliably prevented and nevertheless an inexpensive implementation for the devices connected to the central unit is achieved.

This object is achieved in a radio alarm system with the features of claim 1.

The radio alarm system according to the invention has the advantage that no effort is required for time slot synchronization, as is essential for a TDMA system (Time Division Multiple Access). Only this makes it possible to design the predominantly numerical connections between detectors and central unit as unidirectional routes.

Furthermore, it is ensured in the radio alarm system according to the invention that, even in the event of a superimposition of several messages, the currently selected transmitter is reliably received.

The cost-effective implementation results from the fact that only one transmitter is required in the detectors. The high receiver effort arises only in the (few) central unit (s); there at least the power supply is not a problem.

According to the invention, the messages have to be repeated at sufficiently small time intervals since they are listened to asynchronously by the receiver. The association of property insurers is currently stipulating a data telegram exchange every 10 seconds. If one assumes that there are no disturbances during the majority of the time and thus the average time between two data telegrams is about 25 seconds, the energy consumption can be reduced by the Reduce security queries by a factor of 2.5 without having to accept any restrictions in the operational safety of the alarm system.

The design of the radio alarm system according to claim 2 has the advantage that a blockage of the radio channel with high probability is a sabotage and not a "natural" event (e.g. co-users of the frequency band). According to the invention, the detectors and the radio link detectors to the central unit are monitored by cyclical messages.

Transmission pauses could possibly be made in the case of routine reports if the interference field strength of the radio channel is monitored by the central unit. A transmission block between two pauses must be longer than the longest observation time T _k .

The embodiment according to claim 3 has proven to be particularly advantageous for increasing the transmission security if each data telegram comprises successive blocks with code words of the same length. If a signal is received outside of the given code words or time intervals, this is a first indication of sabotage.

The embodiment of the radio alarm system according to claim 4 requires a small Circuit effort without having to accept restrictions in the operational safety of the alarm system.

Fig. 1

das Blockschaltbild einer bevorzugten Ausführungsform und

Fig. 2

einen zeitlichen Verlauf am Beispiel einer Überlagerung von Sendebursts.

The radio alarm system according to the invention is described and explained in more detail below with reference to an embodiment shown in the drawing. It shows:

Fig. 1

the block diagram of a preferred embodiment and

Fig. 2

a time course using the example of an overlay of transmission bursts.

The block diagram of Fig. 1 shows a radio alarm system with asynchronous transmission of messages via time channels of different periods. In particular, in the radio alarm system according to the invention, a multiplicity of message channels for transmitting messages in the form of data telegrams between detectors M 1... Mn, in particular glass break detectors, infrared detectors, capacitive detectors, structure-borne sound detectors, opening detectors, microwave detectors, ultrasound detectors etc., between switching devices S, in particular block lock, time-controlled switching devices and electronic switching devices, and between control units ST, in particular automatic dialing devices for alarm devices, in particular sirens and flash lamps or the like. and a microprocessor-controlled central unit ZE are formed. In the transmission direction from the detectors M to the central unit ZE, the formation of the message channels takes place through different period duration of the message repetition T _{Mi which is} characteristic of the individual detectors M. At least one radio channel is available for the transmission of the data telegrams.

As can be clearly seen in FIG. 2, the time difference between the individual period durations T _{Mi is} greater than / equal to the transmission duration T _{T of} the longest data telegram. Each data telegram comprises successive blocks with code words of the same length to identify the respective detector M and to transmit the actual information.

In a preferred embodiment of the radio alarm system according to the invention, L = 200 message channels are formed. The radio alarm system is operated in a frequency range of two to three GHz. With a transmission power of approx. 10 mW, the range (radio link) is approx. 30 m in the building and approx. 100 m in the free field. In normal operation, ie when there is no interference field strength (for example from other devices in the Working microwave range) is detected, a data telegram exchange is initiated, for example every 20 - 30 seconds. In interference mode, ie when an interference field strength is detected, the data telegram is exchanged, for example, every 4 - 5 seconds, as is proposed in an unpublished application with the official file number P 42 39 702.2. The system delay T _s from the response of a detector M to the triggering of the alarm (as well as for sabotage detection) is 10 s. With a net data volume of 32 bits (4 bytes per telegram) and a number of 2²⁴ (16 million) different encodings, less than one false alarm can be expected in 100 years. This high level of transmission security more than fulfills the demands placed on operational security by the association of property insurers.

In the embodiment shown in FIG. 1, the central unit ZE has a memory SP connected to the microprocessor MP, in which the required system query time T _K and / or different periods of the repetition of the message are stored. An adjustable divider T connected to a clock source TQ is arranged in the detector M, the division ratio of which can be remotely controlled or manually adjusted according to the assigned period T _Mi.

Further central units, sirens, telephone dialing devices etc. are connected to the central unit ZE via bidirectional radio transmission channels; i.e. these transmissions are additionally secured by returning an acknowledgment.

The connection sequence in the radio alarm system according to the invention with asynchronous transmission of messages via time channels of different period duration T _Mi is described in more detail below with reference to FIG. 2.

• 1) Die Differenz der Periodendauern T_Mi zwischen zwei Sendern ist mindestens wie die Sendedauer T_T eines Telegramms, d.h.
  
  ${\text{T}}_{\text{T}}{\text{< T}}_{\text{Mi}}{\text{- T}}_{\text{Mj}}\text{mit i, j aus (1..200) und i >< j}$
  
  
  
  
• 2) T_T « T_Mi
  oder genauer:
  keine der Periodendauern T_Mi ist ein ganzzahliges Vielfaches einer anderen, d.h.
  
  ${\text{T}}_{\text{M min}}{\text{> 1/2 T}}_{\text{M max}}{\text{+ 1/4 T}}_{\text{T}}$
  

Wie Fig. 2 deutlich zeigt, tritt bei Beobachtung von drei Sendebursts mindestens einmal keine Überlagerung auf.Each detector M sends the data telegrams asynchronously with a repetition period T _Mi (i = detector number) via the same radio transmission channel (the PN sequence is uniform for the system) and provides the message telegram with a distinctive detector number (approximately 16 million different identifications). Asynchronous transmission can overlap telegrams and make them unusable. According to the invention, each transmitter repeats the telegrams with its own period T _Mi. The following must apply to the T _Mi :

• 1) The difference in period T _Mi between two transmitters is at least like the transmission time T _{T of} a telegram, ie
  
  ${\text{T}}_{\text{T}}{\text{<T}}_{\text{Wed}}{\text{- T}}_{\text{Mj}}\text{with i, j from (1..200) and i><j}$
  
  
  
  
• 2) T _T «T _Mi
  or more precisely:
  none of the period T _Mi is an integer multiple of another, ie
  
  ${\text{T}}_{\text{M min}}{\text{> 1/2 T}}_{\text{M max}}{\text{+ 1/4 T}}_{\text{T}}$
  

As FIG. 2 clearly shows, when three transmission bursts are observed, there is no overlap at least once.

Since this consideration applies to two arbitrarily selectable transmission bursts out of n possible, this is also shown for the superimposition of transmission bursts of different period duration T _M.

The receiver, ie the central unit (or the switching device, control elements), observes the radio transmission channel during the period T _K and evaluates all of them incoming telegrams according to their sender number. After T _K has expired, at least one undisturbed telegram must have arrived from each transmitter.

$\text{i = 1 .. 200}$

${\text{T}}_{\text{T}}\text{= 1 ms}$

${\text{T}}_{\text{M200}}{\text{= max {T}}_{\text{Mi}}\text{}}$

folgt

${\text{T}}_{\text{M200}}{\text{= (T}}_{\text{K}}{\text{- T}}_{\text{T}}\text{)2 = 4999.5 ms}$

${\text{T}}_{\text{M1}}\text{= 4799.5 ms}$

D.h. das Tastverhältnis S_T der Sendebursts beträgt hier ca. 1 : 5000, was eine erhebliche Energieeinsparung im Melder bedeutet.For the system configuration or system parameters described above, for example:
out:

${\text{T}}_{\text{K}}\text{= 10 s}$

$\text{i = 1 .. 200}$

${\text{T}}_{\text{T}}\text{= 1 ms}$

${\text{T}}_{\text{M200}}{\text{= max {T}}_{\text{Wed}}\text{}}$

follows

${\text{T}}_{\text{M200}}{\text{= (T}}_{\text{K}}{\text{- T}}_{\text{T}}\text{) 2 = 4999.5 ms}$

${\text{T}}_{\text{M1}}\text{= 4799.5 ms}$

This means that the pulse duty factor S _{T of} the transmission bursts is approximately 1: 5000, which means considerable energy savings in the detector.

In addition, the mutual interference of the individual detectors is already taken into account in this method, i.e. these are not "co-users" of the same frequency band.

Claims (4)

Radio alarm system with a large number of message channels for the transmission of messages in the form of data telegrams between detectors, (M1 ... Mn) in particular glass break detectors, infrared detectors, capacitive detectors, structure-borne sound detectors, opening detectors, microwave detectors, ultrasound detectors, etc., between switching devices (S), in particular a block lock , time-controlled switching devices and electronic switching devices, and between control units (ST), in particular automatic dialing devices for alarm devices, in particular sirens and flash lamps or the like and a microprocessor-controlled central unit (ZE),
characterized in that in the direction of transmission from the detectors (M) to the central unit (ZE) the formation of the message channels by different, for the individual detector (M) characteristic period of the repetition of the message (T _Mi ) and that at least one radio channel is available for the transmission of the data telegrams. Radio alarm system according to claim 1,
characterized in that the time difference between the individual period durations (T _Mi ) is greater than / equal to the transmission duration (T _T ) of the longest data telegram. Radio alarm system according to claim 1,
characterized in that each data message comprises successive blocks with code words of the same length for identifying the respective detector and for transmitting the actual information. Radio alarm system according to one or more of claims 1 to 3,
characterized in that the central unit (ZE) one with the Microprocessor (MP) connected memory (SP), in which the required system polling time (T _K ) is stored and that in the detector (M) an adjustable divider (T) connected to a clock source (TQ) is arranged, the division ratio of which corresponds to the assigned one Period duration (T _Mi ) is remotely controlled or manually adjustable.

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