GB2607914A

GB2607914A - Alarm system

Info

Publication number: GB2607914A
Application number: GB2108537.8A
Authority: GB
Inventors: Andrew Veal James
Original assignee: Pyronix Ltd
Current assignee: Pyronix Ltd
Priority date: 2021-06-15
Filing date: 2021-06-15
Publication date: 2022-12-21
Also published as: GB202108537D0

Abstract

Mitigating interference in a first alarm system 100 may include determining that there is a risk of interference with wireless communication within the first alarm system 100. In response thereto, one or more adjustments of a master clock time origin in the first alarm system 100 may be caused (see figure 5). The master clock time origin may be for use in timing of scheduled communications within the first alarm system 100. The determining may be based on a message received from an element 310 of a second alarm system 300 by an element 110 of the first alarm system 100, and may include an assessment, based on the received message, of a risk of interference with wireless communication within the first alarm system 100 due to the second alarm system 300. Each adjustment may be less than a synchronisation window of devices 130 in the first alarm system 100, and devices 130 in the first alarm system 100 may be to receive a transmission including information indicative of adjustment of the master clock time origin between each adjustment.

Description

ALARM SYSTEM

[0001] This application relates to alarm systems and elements for use in alarm systems. In particular, this application relates to alarm systems having devices or elements that communicate wirelessly.

BACKGROUND

[0002] Alarm systems may be wired, wireless or a combination thereof. Wireless alarm systems may be easier and less expensive to install than wired systems. However, wireless signaling may be less reliable than wired signaling, which may present challenges in maintaining performance of the alarm systems.

[0003] Wireless alarm systems may include battery powered elements (e.g. detectors or sensors that are not mains powered). Reducing power usage in these elements may extend battery life. Some approaches to increasing reliability of wireless communication (e.g. increasing transmission power or repeating transmissions) may increase power usage, and so be at odds with extending battery life of battery powered wireless elements.

BRIEF SUMMARY OF THE DISCLOSURE

[0004] In accordance with aspects of present invention there is provided an alarm system or a method, a control portion, computer program or a computer readable storage medium for use in an alarm system, as set out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which: Figure 1 illustrates an alarm system consistent with some examples.

Figure 2 illustrates signal timing according to some embodiments.

Figure 3 shows an example of a first alarm system and a second alarm system.

Figure 4 shows signal timing in an example system having a synchronization window and clock drift.

Figure 5 shows signal timing in an example system having a synchronization window and a clock origin adjustment.

Figure 6 illustrates a method 600 according to some examples.

Figure 7 shows a device suitable for use as a device of the alarm system.

Figure 8 shows an example of a device suitable for use as a control portion of the system.

DETAILED DESCRIPTION

[0006] Figure 1 illustrates an alarm system 100 consistent with some examples. The alarm system 100 may include a control element or control portion 110 and one or more devices 130.

The control portion 110 may be included in a single device. In some examples the functionality of the control portion 110 may be spread over two or more devices that cooperate to form the control portion 110. In such cases, the two or more devices may communicate over a wired or a wireless medium. In some examples, the control portion 110 may include a panel. The panel may include a key pad, display screen or other user interface elements. In some examples the alarm system 100 may include a panel that is not part of the control portion 110. The control portion 110 may be, or may include, a hub. The control portion 110 may be arranged to wirelessly communicate with the devices 130.

[0007] Devices 130 may be elements of the alarm system, such as detection devices, bell boxes, sounders, key pads, touch screens, RFID readers, etc. The devices 130 may receive signals from the control portion 110 and may send signals to the control portion 110. For example, the control portion 110 may send control signals to the devices 130.

[0008] Where the device 130 is a sensor or detector, the control signals may set an armed/unarmed status of the device 130. The device 130 may signal a detection or activation to the control portion 110. Where the device 130 is a sounder or bell box the control portion 110 may send a signal to cause an alarm to be sounded. Where the device 130 is a key pad the device 130 may send a signal to the control portion 110 indicative of an input to the key pad. Where the device 130 is an RFID reader the device 130 may send a signal to the control portion 110 indicative of information read from an RFID tag.

[0009] An element of the alarm system, such as the control portion, may be arranged to communicate with an external network 150, such as the Internet. This may be via a wired connection, a wireless connection or a combination of wired and wireless connections.

[0010] The device or devices forming the control portion may also perform other functions, such as sensing, sounding, key pad input, RFID reading, etc. [0011] The system may also include components that use wired communication. For example, where the system includes a hub and panel, the communication between the hub and panel could be wired instead of wireless. Similarly, the control portion 110 may have a wired communication path to some devices 130.

[0012] In some examples, elements of the alarm system 100 may be connected to mains power. For example, the control portion 110 may be mains powered in some examples. Some or all of the devices 130 may be battery powered. It is to be understood that mains powered elements may also be provided with a battery backup. Herein, unless otherwise stated, references to a mains powered element are intended to describe an element that is primarily mains powered but may be provided with an alternative power source, such as a backup battery. Similarly, references to a battery powered element are intended to describe an element that is primarily powered by a battery (or other energy storage device), typically without a connection to mains electricity. In some examples a device 130 may be solely powered by a battery.

[0013] A device 130 may transmit a message to the control portion 110 for use in re-synchronizing a clock of the device 130 with a clock of the control portion 110. For example, if there is a drift in synchronization between the clocks of the control portion 110 and the device 130 (e.g. such that a time difference between the clocks exceeds a threshold value), a message from the control portion 110 to the device 130 may instruct the device 130 to perform a clock adjustment. The device 130 may also, in the same or a different message, provide information to the control portion 110 about the status (e.g. the state and/or performance) of the device 130, allowing the control portion 110 to confirm that the device 130 is operating correctly. In some examples, the control portion 110 may acknowledge receipt of the message by sending an ACK message to the device 130. In some examples, a device 130 may retransmit the message until an ACK is received from the control portion 110 or until a threshold number of transmission attempts has been reached.

[0014] In some examples, wireless communication within the alarm system 100 may include communications that are to be transmitted and/or received with specific timing, for example where a transmission is to occur in an assigned time slot. Transmission timings (e.g. slots) may be managed and assigned by the control portion 110. These transmission timings may be assigned to devices 130 (or other elements of the alarm system 100). In some examples the transmission timings may be assigned in a pseudo random manner. In some examples, a pseudo random seed may be used to assign the transmission timings, the pseudo random seed may be based on, inter alia, a unique encryption key and a network identifier associated with the control portion 110. In some examples the transmission timing assignments may be periodic with a first period. In some examples the first period may be between 200 s and 400 s. In some examples the first period may be about 300 s.

[0015] Timing in the alarm system may be defined as an offset from a time origin of a master clock. In some examples the time origin may be set by the control portion 110 (e.g. where the master clock is included in the control portion 110) and communicated to the other elements 130 of the system 100 in messages transmitted by the control portion 110. The control portion may monitor devices 130 in the system 100 to check for correct message timing. The control portion 110 may monitor signals from elements of the system 100 and adjust the timing in real-time for elements that appear out of sync with their designated time slot. For example, in some examples the control portion 110 may indicate a modified clock to a particular device 130 or a particular group of devices 130. For example, the modified clock may be indicated to the particular device(s) instead of the actual master clock. The modified clock may be a time-shifted version of the master clock (e.g. having a modified clock origin that is time-shifted with respect to the master clock time origin). This may allow the control portion 110 to adjust a timing of a device 130 by a greater amount that would normally be permitted by an adjustment at the device 130 based on the master clock. This may be useful in moving, adjusting or recalibrafing synchronization of one or more devices 130. This can be used to for offset drift calibration (e.g. caused by expected variation within manufacturing tolerances, physical shock event, aging of timing elements, etc.). This can also be used to implement a decision at a control portion 110 to avoid a particular time slot or to align or group together a particular group of wireless devices 130.

[0016] In some examples a first alarm system may be located nearby a second alarm system.

Alarm systems may be considered to be nearby, or neighboring, if signals from one alarm system have non-negligible signal strength at devices of the other alarm system. The first and second alarm systems may be the same or similar (e.g. having the same or similar communication protocols). Distinct alarm systems (e.g. systems having different control portions 110) may have different time origins. For example, the time origins of different alarm systems may be essentially independent. Different alarm systems may have different and/or independent transmission timing assignments.

[0017] In some examples, when a control portion is powered-up a random delay (e.g. between 0 and 60 s) may be selected. The time origin may be set after a period of time corresponding to the random delay has elapsed. This may reduce the likelihood of nearby systems having time origins that are synchronized with each other if they are powered-up at the same time. Nearby systems may power-up at the same time if, for example, a power cut affects multiple alarm systems in a particular area. For example, a power cut affecting a block of flats having multiple separate installations of similar alarm systems may cause all of the alarm systems to restart at the same time when power is restored. If the time origin for all of the systems was set immediately on power-up, or at the same stage of a restart process, the alarm systems are likely to have coincident time origins, and so are more likely to cause interference for each other.

[0018] In some examples the control portion 110 may define periods for particular signaling purposes. For example, separate periods may be defined for (i) supervised slots (for supervision signaling between devices 130 and the control portion 110), 00 NACK messages, and (iii) broadcast messages and associated acknowledgements. The control portion 110 may define a repeating period that is subdivided between (i), (ii) and (iii), as shown schematically in Figure 2. The repeating period may have a periodicity between 1 s and 5 s, for example, a periodicity of around 2 s, as shown in Figure 2.

[0019] In some examples the broadcast period and NACK messaging period may be protected from in-sync and ad hoc messaging, such that elements of the alarm system 100 will only transmit during these periods in slots that they have been allocated.

[0020] Some examples may implement frequency-hopping spread spectrum (FHSS) for communication between elements of the alarm system 100. Synchronization of elements of the system 100 may be employed to maintain elements of the alarm system 100 on the same channel at the same time. In some examples the control portion 110 may repeatedly scan a plurality of channels (e.g. four channels). The channels may be scanned in a cyclic loop. Each of the channels may be scanned for a fixed time period. In some examples the fixed time period may be between 1 ms and 5 ms. For example, the fixed time period may be approximately 2.5 ms. In some examples the plurality of channels may include of a main FHSS channel, a previous FHSS channel and two re-sync channels. In some examples, the channel scanning may alternate between FHSS channels and re-synch channels. The main FHSS channel may change periodically, e.g. with a period of between 200 ms and 500 ms, e.g. a period of around 400 ms. The scanned previous FHSS channel may change with the same periodicity but with an offset, e.g. with a period of around 400 ms and an offset of around 200 ms from the change of the main channel (e.g. the offset may result in the previous FHSS channel changing 180° out of phase with the main FHSS channel). This arrangement may allow for a wide acceptance rate for devices 130 that drift in the time domain between synchronization re-sync events. When a device 130 loses synchronization, e.g. through clock drift or device reset, it will be unable to communicate on the correct (i.e. main) FHSS channel. The device 130 may diagnose a loss of synchronization, and in response the device 130 may begin using the re-sync channel(s) for all communication. In some examples the control portion 110 may scan the re-sync channels regularly. The control portion 110 may scan the re-sync channels with a short periodicity (or continuously, in some examples). Accordingly, in some examples, device 130 that has lost synchronization may message the control portion 110 on any re-sync channel at any time.

[0021] In response to receiving a message on the re-sync channel indicating that a device 130 has lost synchronization, the control portion 110 may communicate with the device 130 on the re-sync channel to restore synchronization for the device 130. The device 130 may then use the main FHSS channel. In some examples the re-sync channels may be located at or near opposite ends of available frequency band limits to reduce the likelihood of a single source of interference interfering with, or jamming, both re-sync channels. For example, the channels that are usable by the control portion 110 may be bounded by the re-sync channels [0022] In some examples, devices 130 may be configured to sleep, and to periodically wake and listen for messages from the control portion 110. Devices may wake from sleep and listen on the current (main) FHSS channel at a predetermined interval. In some examples, the interval may be between 1 s and 5 s, and may be an interval of around 2 s, for example).

[0023] When all devices are in-sync with the control portion 110, the control portion 110 may transmit a message at a time when all devices 130 are to be awake and listening, such that all of the devices 130 will be capable of receiving the same message at the same time. Where a message is intended for a single device 130 or a subset of devices the control portion 110 may transmit the message when at least the device 130 or subset of devices are scheduled to be awake.

[0024] To achieve the synchronization between devices 130 listening and the control portion transmitting, a synchronized broadcast slot may be used. In some examples broadcast messages may be between 10 ms and 100 ms in length, and may be around 50 ms in length, for example. In some examples, a preamble portion of the broadcast message may span approximately 50% of the device reception slot. The preamble may be repeated multiple times in the preamble portion. In some examples, a broadcast message may begin transmission before a designated device receive slot and may finish transmission after the designated device reception slot and the preamble and/or message may be repeated during this period. This may provide tolerance for drift in synchronization between the control portion 110 and the devices 130, the synchronization drift that can be tolerated may be referred to as a synchronization window. For example, the broadcast message may begin transmission approximately 20ms before the designated device receive slot and finish approximately 30ms after the designated device reception slot. In this arrangement, the size of the overlap between the transmit and receive slots provides approximately 20ms of device 130 to control portion 110 synchronization drift tolerance, depending on the size of the preamble portion of the broadcast and the preamble-detect bit length suitable for successful message reception at the receiver end of the link.

[0025] The control portion 110 may expect an acknowledgement to a broadcast message from one or more designated devices 130. The broadcast message may contain information indicating a device 130 or devices 130 that the broadcast is intended for. For example, the devices may each have a device ID by which the device may be indicated in the message from the control portion 110 (e.g. in a header of the transmission). The device ID may be unique to that device (such that no other device is produced with the same device ID) or may be unique to that device within the alarm system (such that the control portion 110 does not communicate with two devices having the same device ID). In some cases, the device ID maybe set at the point of manufacture, in other examples the device ID may be set when the device 130 is configured for use in the alarm system (e.g. when the device 130 is registered with the control portion 110). In some examples one or more devices may be assigned to a group and devices and the group may be designated by identifying the group (e.g. using a group ID). Matching devices 130 (e.g. devices designated by the message from the control portion 110) may be instructed to respond with an ACK message. ACK messages may take the form of a straight forward ACK, a single supervision message response that itself does not require an ACK (SNACK), or a Multi-SNACK (where several devices are to ACK the broadcast at the same time). The time domain mechanism may provide slots for all types of ACK immediately following the broadcast slot. Each device may be responsible for calculating the correct ACK slot in the time domain and transmitting the ACK in that slot. In some examples, ACK, SNACK and MSNACK slots may be tightly packed so as to use up only a small amount of time slot resources. In this case, timing may be relied on to be accurate (i.e. without drift between the device clock and control portion clocks) due to the small amount of time that may have passed between transmission to the received broadcast (which can use used by the devices 130 to correct any synchronization drift). Messages from the control portion 110 may target specific device types. For example, an arming broadcast for arming detectors may target only detectors, or a sounder broadcast for turning sounders on/off may target only sounders. In some examples, devices 130 of the same type may be associated with the same group to facilitate designating those devices 130 in a broadcast message. Similarly, a group may be defined to include devices 130 in a particular geographic location (e.g. to facilitate controlling devices in a particular location, for example, when the system is to be armed for a part of a building and unarmed for another part of the building the devices 130 in the part of the building to be armed may be assigned to the same group to allow those devices to be designated more efficiently). A payload of the broadcast message may contain a broadcast message type, device IDs (and/or group IDs) that the message is targeting and the feature or effect that the targeted device(s) 130 should implement (e.g. arm the device, turn the sounder on etc.) In some examples, bit masks may be used to identify target devices. For example, a single broadcast can turn on or off the same feature for different device IDs by using a bit mask to identify the device ID's.

[0026] Figure 3 shows an example of a first alarm system 100 and a second alarm system 300. The first alarm system 100 may be the same or similar to the system of Figure 1. The second alarm system 300 may also be similar, with a second control portion and second devices 330. The second control portion 310 may be connected to a second network 350. The first 110 and second 310 control portions may be connected to the same network (e.g. the Internet), such that the first 150 and second 350 networks are the same network. In this example, the first alarm system 100 and second alarm system 300 have overlapping control portions 110 and 310. Here, an overlapping control portion 110 is defined as a control portion that can 'hear another control portion, e.g. signals transmitted by the other control portion 310 arrive at the control portion 110 with a signal strength that is detectable by the control portion 110. In some examples, as the alarm systems 100, 300 are distinct, the first control portion 110 may be unable to decode at least some transmissions of the second control portion 310, and vice-versa (e.g. due to the use of different inbuilt security mechanisms that are not shared between the first 100 and second 300 systems).

[0027] In some examples, overlapping control portions 110, 310 may co-exist without problems, since the chance of overlapping and having the exact same time origin (or sufficiently close to be problematic) is unlikely. However, overlapping and in-sync systems are a possibility that may exist in the field. This possibility increases when different systems may be deployed densely, e.g. in a block of flats.

[0028] Overlapping control portions is an example of overlapping alarm systems, in which elements of one alarm system 100 may hear transmissions from another alarm system 300. For example, a device 130 of a first alarm system 100 may overlap with an element (e.g. device 330 or control portion 310) of a second alarm system 300, such that signals transmitted by the element 310, 330 of the second alarm system 300 arrive at the device 130 with a signal strength that is detectable by the device 130.

[0029] If two or more overlapping alarm systems are in synchronization with each other, regular communication errors may occur for systems that clash (i.e. systems with matching transmission timing, e.g. sync slots, and communication channels). This may result in excessive RE messaging and battery drain on devices that clash with neighbouring systems. For example, if a device 130 receives messages from a control portion 310 of a different system 300 (by being on the same RF channel slot at the same time), increased battery drain may occur for that device 130. It is to be noted that the device 130 may receive the message from control portion 310 of the other system 300, but that, in some examples, the device 130 may be unable to decode the message. Examples may provide a mechanism to detect this scenario and desynchronize the first 110 and second 310 control portions from each other. This allows the potential problems associated with synchronization between systems 100, 300 to be avoided or mitigated.

[0030] In some examples, the control portion 110 may transmit a Network Presence Message (NPM). The NPM may include information to identify the control portion 110 and/or the alarm system 100, e.g. an identification number for the control portion 110 or alarm system 100. The information to identify the control portion110 or alarm system 100 may be used in the alarm system 100 (e.g. by the control portion 110) only in NPMs. The identifier may be a random number, for example. The random number may be selected at manufacture of the control portion 110 or at power-up of the control portion 110, for example. Using an identifier in the NPMs that is not used elsewhere within the alarm system 100 (e.g. that is, is not used to identify the alarm system except for in NPMs) may provide increased security and robustness for the system 100, since knowledge by a potential attacker of the identifier in the NPM does not provide the potential attacker any additional information about the system 100.

[0031] Any control portion 110, 310 may be arranged to transmit an NPM. In some examples, NPMs have no source or destination address and no response to the NPM is required or expected. An NPM may include, for example, information describing radio resources to be used by the alarm system associated with the control portion. For example, the NPM may describe a master clock time origin, radio channels to be used by the alarm system, etc. In some examples an NPM may indicate a version number or capability of the control portion 110 that transmits the NPM. This may allow for more flexible development and future proofing of the system. In some examples, the control portion 110 may include in the NPM information about a channel arrangement used by the control portion 110. For example, a band allocation, a channel whitelist and/or a channel blacklist used by the control portion 110 may be included in the NPM transmitted by the control portion 110. This may help neighboring control portions 110, 310 to reduce mutual interference.

[0032] According to some examples, the control portion 110 may determine that there is a risk of interference within the alarm system 100. In some examples the control portion 110 may respond to the determination that there is a risk of interference by causing an adjustment of the time origin of the master clock. The master clock may be used in the timing of scheduled communications in the alarm system 100. In some examples the adjustment of the time origin may be implemented as a change of phase of periodic transmission periods defined in the system 100 (e.g. a change of phase of the periodic signaling periods described in relation to Figure 2). By adjusting the time origin, all associated synchronization and time domain timing for that system may also be shifted in time.

[0033] The determination that there is a risk of interference may be based on a message received from an element of a second alarm system 300 by an element of the alarm system 100. The determination may include an assessment of a risk of interference with wireless communication within the first alarm system due to the second alarm system. For example, the control portion 110 may be receive an NPM from a control portion 310 of the second alarm system 300. In some examples, other information may be used in concluding that there is a risk of interference in addition to or instead of an NPM. Detecting an NPM may assist in detecting overlapping of control portions 110, 310 of different alarm systems 100, 300.

[0034] In some examples, each adjustment may be less than a synchronization window of devices 130 in the first alarm system 100. The control portion 110 may transmit a preamble repeatedly in a period around the scheduled transmission time. This provides a synchronization window, during which a device that is out of synch with the control portion 110 may wake and still receive the message. Figure 4 shows an example of a synchronization window. In the example of Figure 4 the receiving device 130 and sending device (e.g. control portion) 110 clocks have drifted out of synchronization, such that device 130 is not expecting to receive a transmission at the scheduled transmission time (as measured by the clock of the control portion 110). In this example, the preamble of the message is repeatedly transmitted around the scheduled time (e.g. before and after the scheduled transmission) and the clock drift is less is less than the synchronization window. Accordingly, when the device 130 wakes at the time the transmission is expected by the device 130 (i.e. at the scheduled time according to the clock of the device 130), the control portion 110 may still be transmitting the message, such that the device 130 may still successfully receive the message.

[0035] In some examples, each adjustment may be equal to or less than 25% of the synchronization window (maximum in-sync window). In some examples the maximum in-sync window may be 25ms, and each adjustment may be approximately 6ms.

[0036] In some examples, a maximum of one adjustment may be carried out in each supervision period of the system. Where the supervision period is 300s and each adjustment is 6ms, the clock origin may be adjusted at a rate of 6ms every 300s.

[0037] In some examples the control portion may set a maximum number of adjustments for a given period. For example, the control portion 110 may set a maximum of 12 adjustments per 24 hour period, where each adjustment is within a synchronization window.

[0038] Devices in the first alarm system 100 may receive a transmission including information indicative of adjustment of the master clock time origin between each adjustment. For example, a device 130 in the first alarm system may receive a transmission from the control portion 110 that allows synchronization of the device clock with the clock of the control portion 110. Any such transmission may be referred to herein as a synchronizing transmission, synchronizing message, etc. An adjustment to the master clock time origin may be such that a next synchronizing transmission will be received within a synchronization window of the receiving device 130. This may allow the time origin to be shifted without (or with less risk of) losing synchronization between a control portion 110 and a device 130, such that the device 130 may adjust the time origin to match the adjusted time origin of the control portion 110 without a going through a resynchronization process. Where there are multiple devices 130 in the alarm system 100, an adjustment larger than the synchronization window of the devices may lead to all of the devices 130 in the system 100 losing synchronization and going through a resynchronization process. Thus, the adjustment may increase power usage for all devices 130 in the system 100.

Further, the resynchronization process could lead to a delay in a device 130 signaling an alarm, for example, since the alarm state would be signaled after the resynchronization was completed.

[0039] Figure 5 shows an example in which a control portion 110 adjusts a time origin (e.g. in response to a determination that there is a risk of interference). The next scheduled synchronizing transmission takes place in accordance with the adjusted clock (e.g. at a time differing from the original scheduled time by the clock adjustment). The device 130 does not expect to receive the transmission at the adjusted transmission time (scheduled time according to adjusted clock of the control portion 110). However, as the adjustment in the clock of the control portion 110 is less than the synchronization window the device 130 expects the transmission (based on the scheduled time according to the device's clock) at a time within the synchronization window. Accordingly, the message is transmitted when the device 130 is listening for the transmission (at the expected time according to the device's clock). Following receipt of the transmission the device 130 may adjust its clock based on the received transmission to synchronize the device clock 130 with the clock of the control portion 110 in the same manner as correcting for clock drift. Accordingly, the mechanism for correcting drift in the device clock may be used to propagate a clock adjustment at the control portion 110 to the device 130. For clarity, Figure 5 shows the adjustment of the device clock occurring after the end of the synchronization window. However, the adjustment of the device clock may occur at any time after the transmission has been received by the device 130.

[0040] In some examples an adjustment within the synchronization window of devices 130 in the system 100 may be too small to avoid the interference from the other system 300.

Accordingly, control portion 110 may determine that a plurality of adjustments is to be performed. Each of the adjustments may be within the synchronization window of devices 130, or less than the synchronization window of the devices, but the overall or cumulative adjustment may be larger than the synchronization window.

[0041] In some examples the control portion 110 may be arranged such that a determination to adjust the time origin may be made with a maximum frequency. For example, the control portion may be arranged such that a decision to adjust the time origin may be made at a rate of one full adjustment (i.e. a cumulative adjustment, which may consist of a plurality of adjustments within the synchronization window) per 24 hour period. The 24 hour period may be measured, for example as a fixed repeating interval (e.g. between midnight and midnight), a 24 hour period from the start of the previous adjustment, or a 24 hour period from the end of the previous adjustment.

[0042] In some examples, when a cumulative adjustment has been completed (e.g. when a planned cumulative adjustment has been carried as a plurality of adjustments within a synchronization window of the system) monitoring in the system (e.g. counters at the control portion 110 and/or device 130 indicative in interference) may be reset to determine whether there is interference at the adjusted time origin.

[0043] In some examples the control portion 110 may assess whether the interference from the second alarm system has reduced. For example, an assessment may be made after each adjustment or may be made after a set number of adjustments. In some examples where it is determined that there is no reduction in interference adjustment of the clock origin may be stopped and an alternative action may be taken, such as alerting a user.

[0044] In some examples the NPM may include a rolling code value that is updated in each subsequent NPM. This may mitigate a playback injection of the NPM message by an attacker. The control portion 110 that receives the NPM may check that the rolling code of the received NPM is unique and only accept NPM's with unique rolling code values. If an NPM is received with a duplicate rolling code the NPM may be treated as malicious, e.g. by discarding the NPM. In some examples, the control portion 110 may wait until at lest two NPM's have been received before determining whether the master clock time origin should be adjusted. If two or more NPM's have been received the control portion 110 may check for duplication of rolling code values to reduce susceptibility to a playback injection attack. Accordingly, in some examples a determination to adjust the master clock time origin may be based on the first network presence message and a second network presence message, both received from a second alarm system. The first and second network presence messages may include respective rolling code values. Determining whether to adjust the master clock time origin may include verifying the respective rolling code values of the first and second network presence messages (i.e. verifying that the rolling code values in the first and second network presence message are different/unique).

[0045] In some examples a minimum time interval may be defined and a time interval between consecutive NPM's may be at least the minimum time interval. This may avoid excessive bandwidth usage by NPM's. Further, in some examples, reception of a second or subsequent NPM at a control portion 110 from the same second alarm system 300 within a period corresponding to the minimum time interval may be treated as a hacking attempt. For example, the second or subsequent NPM's received within the minimum time interval from the first NPM may be ignored and/or may prompt an alert to a user. In some examples a first interval may be defined that is less than the minimum time interval. For example, the first interval may be half of the minimum time interval. In some examples, second or subsequent NPM's within a time period having a duration of the first interval may be treated as a hacking attempt. For example, the minimum time interval may be defined to be 24 hours and a control portion 110 receiving a first NPM and second NPM from a second system 300 may treat the second NPM as a hacking attempt if it is received within 12 hours of the first NPM.

[0046] In some examples, when the control portion 110 is powered-up a random delay may be selected and an NPM transmitted after the random delay has passed. In some examples the random delay may be between 0 and 60 s. Where multiple neighboring alarm systems are powered-up at essentially the same time (e.g. due to simultaneous restoration of power following a power cut) the use of a random delay reduces the likelihood of multiple systems transmitting NPM's simultaneously and interfering with each other.

[0047] In some examples, when it is decided by the control portion 110 that the time origin should be adjusted, the control portion 110 may determine whether to advance or delay the time origin. In some examples this determination may be made based on a comparison between synchronization count values of the control portion 110 (e.g. a first control portion 110) with synchronization count values of the other control portion 310 (e.g. a second control portion 310). The NPM transmitted by the other (second) control portion 310 may indicate the synchronization count values of that other control portion 310. A synchronization count value in an NPM transmitted by the other (second) control portion 310 may provide an indication of a timing (or phase) of a master clock of that (second) control portion 310. The synchronization count may indicate a time that has elapsed since a time origin, or a zero, of the master clock of the (second) control portion 310, for example. The master clock may repeat cyclically, being reset to a zero, or to a time origin, at specified intervals. In some examples, the synchronization count may increase by one every millisecond. A (first) control portion 110 that receives the NPM including the synchronization count value of another (second) control portion 310 may determine how close it is to being in-sync with the transmitting (i.e. second) control portion 310: if the synchronization counts of both control portions 110, 310 are the same (or within a set range of each other) the control portions 110, 310 may be considered to be in-synch. The synchronization count values may be used to create a temporary shared time origin for the clocks of the (first) control portion 110 and the other (second) control portion 310. When a time origin on the other control portion 310 is adjusted, the (first) control portion 110 may determine, based on NPMs received from the other control portion, that the time origin is moving and in which direction (forwards or backwards). An adjustment of the time origin of the (first) control portion 110 may be based on the determined change in the time origin of the other (second) control portion 310.

[0048] In some examples, in response to a determination by control portion 110 that there is a risk of interference and that the time origin is to be adjusted, the control portion 110 may transmit a message indicating that the time origin is to be adjusted. In some examples, this message may be decodable by elements of alarm systems 300 outside the alarm system 100 of the transmitting (first) control portion 110. This message may be received by a (second) control portion 310 of the other alarm system 300. The other (second) control portion 310 may take this information into account when determining whether it should adjust its time origin. For example, the other (second) control portion 310 may decide not to adjust its time origin or may adjust it's time origin in an opposite direction to the adjustment by (first) control portion 110.

[0049] The NPM message may contain an INTENTION field. This field may be used by the transmitting control portion to announce its intention to adjust its clock origin. In some examples, this this field will be set only if no other NPM message received by that control portion has the same field set. In some examples, a control portion receiving an NPM with this field set will not initiate its own clock origin adjustment (e.g. until the other control portion has completed its clock origin adjustment). In some examples the INTENTION field may indicate that the clock origin is to be adjusted (e.g. a "yes"/"no" indication). In some examples the INTENTION field may indicate whether the intention is to advance or delay the clock (shift the clock up or down).

In some example, the INTENTION field may be a simple 2-bit flag that instructs other control portions not to carry out a clock origin adjustment. In some examples the INTENTION field may allow other control portions 110 to adjust their own clock origins at the same time, for example by ensuring that the clock origins are adjusted in opposite directions.

[0050] In some examples, the control portion 110 may determine that a second alarm system 300 is causing interference, such that an adjustment of the clock origin is appropriate. The control portion 110 may receive a message from the second alarm system 300 indicating that the second alarm system 300 will adjust its clock origin. In response to this message, the control portion 110 may suppress an adjustment of its own clock origin. This may avoid unnecessary adjustment of the clock origin and may improve coordination of clock adjustments between alarm systems.

[0051] In some examples, control portion 110 may receive a message from a second alarm system 300 indicating that the second alarm system 300 will adjust its clock origin. In response to this message, the control portion 110 may adjust its clock origin based at least in part on the received message. For example, the control portion 110 may adjust its clock in an opposite direction to the adjustment in the second alarm system 300. This may improve coordination of clock adjustments between alarm systems.

[0052] In some examples, the determination that there is a risk of interference may be based on a synchronization count value derived from the NPM, indicative of how close synchronization is between the control portions 110.

[0053] In some examples, the determination that there is a risk of interference may be based on other information available to the control portion 110 (e.g. in addition to a message such as an NPM).

[0054] In some examples, a device 130 may implement listen before talk. Prior to transmitting on a channel device 130 may monitor the channel and transmit only if the channel is not in use.

The determination that there is a risk of interference may be based, in whole or in part, on an indication from a device 130 in the alarm system 100 of a number of listen before talk processes performed by the device 130 within a period of time. An excessive number of listen before talk attempts, i.e. where the device does not transmit due to a determination that the channel is in use, may indicate that another system is interfering with the alarm system 100. An adjustment in the signal timing of the system 100 (e.g. by adjusting or shifting the virtual time origin of the system) may reduce the interference. In some examples, the number of listen before talk attempts by a device 130 within a certain time period may be reported to the control portion 110 and it may be determined that the virtual time origin should be adjusted if the number of listen before talk attempts exceeds a threshold value. The listen before talk count may count the number of listen before talks that occur in a supervision period of the device 130 and may be reset at the start or end of each supervision period. Determination of interference based on a device's listen before talk count may assist in detecting overlap of the device 130 with an element 310, 330 of another alarm system 300.

[0055] In some examples, the determination may be based, in whole or in part, on an indication from a device 130 in the alarm system of a number of transmission retries performed by the device within a period of time. Device 130 may determine that a transmission from the device has been unsuccessful, for example based on a subsequent communication, or lack thereof, from the intended destination of the transmission. For example, receipt or non-receipt of an ACK/NACK communication. When it is determined that a transmission from the device 130 has not been received, the device 130 may repeat or retry the transmission. For example, the device may wait until a timing assigned to the device 130 and may then repeat the transmission. The device 130 may monitor the number of transmission retries. For example, the device 130 may increment a counter each time a transmission is repeated. The counter may reset after a set period (e.g. a supervision period). In some examples, retransmissions are logged and all retransmission attempts within a time window of a set duration may be counted. In some examples a ratio of transmissions to retransmissions (e.g. within a time window) may be calculated. The device 130 may report the number or ratio of retransmissions to the control portion 110. If the number or ratio of retransmissions is determined by the control portion 110 to indicate excessive interference, e.g. by exceeding a threshold, the control portion may determine that the virtual time origin should be adjusted. In some examples the device 130 may determine that the number of retransmissions is excessive and inform the control portion 110 of this determination. Determination of interference based on a device's retransmission count may assist in detecting overlap of the device 130 with an element 310, 330 of another alarm system 300.

[0056] In some examples, the determination may be based, in whole or in part, on an indication from a device in the alarm system of a number of false wake events performed by the device within a period of time. A false wake event may be due to reception at the device 130 of a message that is not intended for the device 130. For example, in some arrangements the device 130 should not communicate (transmit to or receive from) a neighboring alarm system 300. However, if an element of the neighboring alarm system 300 is transmitting at the same time and on the same channel as the device 130 is listening, the device 130 may begin to receive or decode the transmission, for example if the device 130 is able to decode a preamble of the transmission. This may lead to an increase in the time during which a receiver of the device 130 is active, leading to an increase in power usage and reduction in battery life of the device 130. Determination of interference based on a device's false wake count may assist in detecting overlap of the device 130 with an element 310, 330 of another alarm system 300.

[0057] In some examples, network presence messages may provide a more reliable indicator of overlapping systems than other measures of interference. Accordingly, a decision to adjust the clock origin may be based on the network presence messages in the first instance. If the network presence messages do not indicate overlapping systems, other indications of interference (e.g. listen before talk count, transmission retries, etc.) may be used to determine whether the clock origin should be adjusted. In some examples, the control portion 110 may decide to adjust the clock origin in response to interference within the system 100, even if the interference does not appear to be due to another alarm system 300, as the adjustment may reduce the interference.

[0058] The risk of interference between two alarm systems 100, 300 that are synchronized is greater when the alarm systems are similar or of the same type (e.g. as they may be more likely to remain in synch). For example, where they use the same or similar wireless communication protocols. In some examples, alarm systems 100, 300 systems that are similar may be produced by the same manufacturer. In some examples, alarm systems 100, 300 may be similar if an NPM transmitted by one of the alarm systems 100 may be received and decoded by the other alarm system 300, or where the other alarm system 300 is able to extract usable information from an NPM transmitted by the alarm system 100. For example, a receiving alarm system 100 may extract information to identify a transmitting alarm system 300.

[0059] Figure 6 illustrates a method 600 according to some examples. The method may be carried out by a control portion 110 of an alarm system 100, for example. The method 600 begins at 610. At 620 one or more messages are received from an element of another alarm system 300. The message may be a network presence message, for example. At 630 it is determined whether there is a risk of interference to wireless communication within the alarm system 100. The determining may be based on the received message, and may include an assessment of a risk of interference in the alarm system 100 due to the other alarm system 300.

[0060] In some examples, in response to a determination that there is a risk of interference, a master clock origin may be shifted or adjusted 640 in the alarm system 100.

[0061] In some examples, the adjustment may be smaller (i.e. within) a synchronization window of the alarm system. For example, devices 130 in the alarm system 100 may receive a transmission including information indicative of the adjustment of the master clock origin between each adjustment.

[0062] The master clock origin may be for use in timing of scheduled communications within the alarm system.

[0063] Figure 7 shows a device 700 suitable for use as a device 130 of the alarm system 100. The device 700 may include processing circuitry 710. The processing circuitry 710 may include a processor 720 and memory 730, for example. The device 700 may also include wireless communication circuitry 740 for receiving signals, such as messages from a control portion 110, and for transmitting signals, such as device status messages. The device 700 may also include alarm system components 750 to provide functionality in the alarm system 100, such as one or more of a sensor, a sounder, a light, a key pad, an RFID reader, etc. The components of the device 700 may communicate through a communication medium, such as a bus 760.

[0064] Figure 8 shows an example of a device 800 suitable for use as a control portion 110 of the system 100. The device 800 may include processing circuitry 810. The processing circuitry 810 may include a processor 820 and memory 830, for example. The device 800 may also include wireless communication circuitry 840 for receiving signals, such as supervision messages, and for transmitting signals, such as reverse supervision messages. The components of the device 800 may communicate through a communication medium, such as a bus 860.

[0065] In some examples the devices described herein, such as devices 110, 130, 700 or 800, may be controlled by a computer program. Similarly, the methods described herein, such as method 600 may be implemented by a computer program. A computer program may be embodied in software, firmware, etc. The computer program may be stored as computer readable instructions on a computer readable storage medium, such as a memory device 730, 830, optical storage device, etc. The medium may be a non-transitory storage medium.

[0066] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0067] Features, integers, characteristics, or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0068] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

CLAIMS1. A method for mitigating interference in a first alarm system, the method comprising: determining that there is a risk of interference with wireless communication within the first alarm system; in response to the determining, causing one or more adjustments of a master clock time origin in the first alarm system, the master clock time origin for use in timing of scheduled communications within the first alarm system, wherein: the determining is based on a message received from an element of a second alarm system by an element of the first alarm system, and includes an assessment, based on the received message, of a risk of interference with wireless communication within the first alarm system due to the second alarm system, each adjustment is less than a synchronisation window of devices in the first alarm system, and devices in the first alarm system are to receive a transmission including information indicative of adjustment of the master clock time origin between each adjustment.
2. The method of claim 1, wherein the determining is further based on one or more of: an indication from a first device in the first alarm system of a number of listen before talk processes performed by the first device within a first period of time, an indication from a second device in the first alarm system of a number of transmission retries performed by the second device within a second period of time, and an indication from a third device in the first alarm system of a number of false wake events performed by the third device within a third period of time, the false wake events due to reception of a message by the third device that is not intended for the third device.
3. The method of claim 1, wherein the message is a first network presence message and the determining is based on the first network presence message and a second network presence message from the second alarm system, the first and second network presence message including respective rolling code values, and the determining includes verifying the respective rolling code values of the first and second network presence messages.
4. The method of any one of claims 1 to 3, wherein a control portion of the first alarm system is to transmit a network presence message to indicate the existence of the first alarm system to other alarm systems, the network presence message including: information to identify the first alarm system, the information to identify the first alarm system used by the control device only in network presence messages, a rolling code value.
5. The method of claim 1, wherein a control portion of the first alarm system is to, on power up of the control portion: randomly select a delay period, and transmit, after waiting the selected delay period, a network presence message to indicate the existence of the first alarm system to other alarm systems.
6. The method of claim 4 or claim 5, further comprising transmitting subsequent network presence messages with at least a minimum time interval between consecutive network presence messages.
7. The method of any preceding claim, further comprising verifying whether the interference from the second alarm system has reduced after each adjustment.
8. The method of any preceding claim further comprising: in response to the determining, causing transmission of a message indicating that the adjustment of the master clock time origin of the first alarm system is to be carried out.
9. The method of any one of claims 1 to 7, further comprising: receiving a message from the second alarm system indicating that adjustment of a master clock time origin of the second alarm system is to be carried out, and in response suppressing an adjustment of the master clock time origin of the first alarm system.
10. The method of any one of claims 1 to 7, further comprising: receiving a message from the second alarm system indicating that adjustment of a master clock time origin of the second alarm system is to be carried out, wherein the one or more adjustments of the master clock time origin in the first alarm system is based at least in part on the received message indicating adjustment of the master clock of the second alarm system.
11. A control portion for use in a first alarm system, the control portion comprising: processing circuitry, wherein the processing circuitry is arranged to: determine that there is a risk of interference with wireless communication within the first alarm system; in response to the determining, cause one or more adjustments of a master clock time origin in the first alarm system, the master clock time origin for use in timing of scheduled communications within the first alarm system, wherein: the determining is to include concluding, based on a message received from an element of a second alarm system by an element of the first alarm system, that there is a risk of interference with wireless communication within the first alarm system due to the second alarm system, each adjustment is to be less than a synchronisation window of devices in the first alarm system, and between each adjustment, the devices in the first alarm system are to receive a transmission including information indicative of the adjustment of the master clock time origin.
12. The control portion of claim 11, wherein the determining is further based on one or more of: an indication from a first device in the first alarm system of a number of listen before talk processes performed by the first device within a first period of time, an indication from a second device in the first alarm system of a number of transmission retries performed by the second device within a second period of time, and an indication from a third device in the first alarm system of a number of false wake events performed by the third device within a third period of time, the false wake events due to reception of a message by the third device that is not intended for the third device.
13. The control portion of claim 11, wherein the message is a first network presence message and the determining is to be based on the first network presence message and a 25 second network presence message from the second alarm system, the first and second network presence message including respective rolling code values, and the determining is to include verifying the respective rolling code values of the first and second network presence messages.
14. The control portion of any one of claims 11 to 13, wherein a control portion of the first alarm system is to transmit a network presence message to indicate the existence of the first alarm system to other alarm systems, the network presence message including: information to identify the first alarm system, the information to identify the first alarm system to be used by the control portion only in network presence messages, a rolling code value.
15. The control portion of claim 11, wherein a control portion of the first alarm system is to, on power up of the control portion: randomly select a delay period, and transmit, after waiting the selected delay period, a network presence message to indicate the existence of the first alarm system to other alarm systems.
16. The control portion of claim 14 or claim 15, wherein the processing circuitry is further arranged to transmit subsequent network presence messages with at least a minimum time interval between consecutive network presence messages.
17. The control portion of any preceding claim, wherein the processing circuitry is further arranged to verify whether the interference from the second alarm system has reduced after each adjustment.
18. The control portion of any preceding claim, wherein the processing circuitry is further arranged to: in response to the determining, cause transmission of a message indicating that the adjustment of the master clock time origin of the first alarm system is to be carried out.
19. The control portion of any one of claims 11 to 17, wherein the processing circuitry is further arranged to: receive a message from the second alarm system indicating that adjustment of a master clock time origin of the second alarm system is to be carried out, and in response suppress an adjustment of the master clock time origin of the first alarm system.
20. The control portion of any one of claims 11 to 17, wherein the processing circuitry is further arranged to: receive a message from the second alarm system indicating that adjustment of a master clock time origin of the second alarm system is to be carried out, and wherein the one or more adjustments of the master clock time origin in the first alarm system is based at least in part on the received message indicating adjustment of the master clock of the second alarm system.
21. The control portion of any one of claims 11 to 20 wherein the control portion includes one or more of: a hub device; a panel device; a cloud-connected control device.
22. An alarm system comprising the control portion of any one of claims 11 to 21.
23. A computer program comprising instructions to cause a processing means to carry out the method of any one of claims 1 to 10.
24. A computer readable storage medium storing instructions that, when performed by a processing means, causes the processing means to carry out the method of any one of claims 1 toil.