1. Field of the Invention
The present invention relates to alarm handling in wireless security or fire alarm systems, and, more particularly, to alarm handling in IEEE 802.11-based wireless security or fire alarm systems.
2. Description of the Related Art
Generally proprietary technologies or ZigBee/IEEE802.15.4 based technologies are used for wireless security systems, such as intrusion detection, fire, and alarm systems. However, IEEE802.11 based wireless security/fire alarm systems are not known in the prior art.
In typical wireless security/fire systems, the length of the network lifetime is critical. Because changing the battery of the sensor unit/station is very inconvenient for the customer, such networks are designed to have long battery lifetimes of multiple years. On the other hand, it would be desirable for such delay sensitive systems that stations in a network be able to receive or transmit network packets at any time. Thus, it is not desired to allow a sensor/station to stay in a power saving mode all the time because the sensor/station would not be able to receive or transmit any network packets while in the power saving mode.
Another problem of the prior art is that the channel from the sensor unit/station to the access point/hub may have such bad quality that alarm messages from the sensor/station cannot reach the destined access point/hub.
What is neither disclosed nor suggested by the prior art is a IEEE802.11 based wireless security/fire alarm system in which the above-described and other limitations of the prior art may be improved upon.
The present invention may provide a method referred to as a “wake-up-overhear-relay method” that can increase the reliability of alarm handling in IEEE802.11-based wireless security or fire alarm systems. The method of the invention may enable intrusion detection/fire sensors/stations to relay their messages reliably, even if the communication link between the sensor/station and the hub/central unit/access point (AP) has poor quality, as long as the sensor/station is operational.
In order to save energy and thereby lengthen the network lifetime, sensors/stations may be in the sleep mode for most of the time. During the sleep mode, the receiver of a sensor/station is off and thus the sensor/station cannot receive any message from other sensors/stations or from the central unit. Therefore, in order to receive user-issued messages from the central unit, a sensor/station needs to wake up and listen to the channels regularly.
The present invention provides a scheme for IEEE802.11-based wireless security/fire systems in which sensors/stations wake-up regularly and can overhear messages from their neighboring sensors/stations. Thus, the overhearing sensors/stations may relay alarm messages to the access unit/hub from those neighboring sensors/stations that have poor channel qualities and that may be unable to independently transmit alarm messages that may be received by the access unit/hub. When it results in better performance, a sensor/station may transmit packets via a relay instead of transmitting the packets directly to the destination.
The present invention provides a method that can increase the reliability of alarm handling in security or fire alarm systems. The communication protocols of the system of the present invention may be based on the IEEE802.11 standard.
The invention comprises, in one form thereof, a method of wirelessly transmitting alarm signals, including wirelessly transmitting an alarm signal from a transmitting station. It is determined whether an acknowledgement signal wirelessly transmitted from an access point in response to the access point receiving the alarm signal has been received by the transmitting station. A relaying station is woken up and kept awake during a plurality of periodic time intervals for overhearing transmissions from the transmitting station. If it is determined that an acknowledgement signal from the access point has not been received by the transmitting station, then the alarm signal is wirelessly re-transmitting from the transmitting station during at least one of the time intervals in which the relaying station is awake. The alarm signal is received at the relaying station. The alarm signal is transmitted from the relaying station to the access point.
The invention comprises, in another form thereof, a method of wirelessly transmitting alarm signals, including wirelessly transmitting an alarm signal from a transmitting station. It is determined whether a first acknowledgement signal wirelessly transmitted from an access point in response to the access point receiving the alarm signal has been received by the transmitting station. A relaying station is maintained in an awake state during a plurality of periodic time intervals. If it is determined that a first acknowledgement signal from the access point has not been received by the transmitting station, then the alarm signal is wirelessly re-transmitted from the transmitting station during at least one of the time intervals in which the relaying station is awake. The alarm signal is received at the relaying station. The alarm signal is transmitted from the relaying station to the access point. It is determined whether a second acknowledgement signal transmitted from the access point in response to the access point receiving the alarm signal has been received by the relaying station. If it is determined that a second acknowledgement signal from the access point has not been received by the relaying station, then the alarm signal is re-transmitted from the relaying station.
The invention comprises, in yet another form thereof, a wireless network for a security system. The network includes an access point that wirelessly receives an alarm signal and wirelessly transmits an acknowledgement signal in response to receiving the alarm signal. A relaying station includes a security sensor. The relaying station periodically listens for the alarm signal, and relays the alarm signal overheard during the periodic listening, with the alarm signal being relayed to the access point. A transmitting station senses a security breach and wirelessly transmits at least one alarm signal in response to sensing the security breach. The transmitting station re-transmits the alarm signal during the periodic listening by the relaying station if an acknowledgement signal is not received from the access point. The transmitting station enters a sleep mode after receiving an acknowledgement signal.
An advantage of the present invention is that it accommodates schemes in which sensors/stations are in the power saving mode some or most of the time, and in which each sensor/station turns its transceiver on only under two conditions: 1) When the sensor/station wants to transmit to, or receive network packets from, the AP; and 2) When the sensor/station needs to relay overheard messages from other sensors/stations. Condition 2) necessitates that at certain periods the sensor/station needs to stay awake longer to overhear messages from other stations/sensors.
Another advantage of the present invention is that it enables sensors/stations to overhear network packets transmitted from other sensor/stations. Thus, the overhearing sensor/station may be able to relay the overheard network packets to the desired destination, which enables reliable operation with a possibility of reduced energy consumption, when the signal between a station/sensor and AP is weak.
Yet another advantage of the present invention is that it does not require dedicated relay stations in the network, but rather may enable all sensor/stations to relay packets for other sensor/stations.
Still another advantage of the present invention is that a station may transmit packets via both a relay and the direct path in order to increase the rate of successful transmissions, and to thereby increase the reliability of the network.
The above mentioned and other features and objects of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. Although the exemplification set out herein illustrates embodiments of the invention, in several forms, the embodiments disclosed below are not intended to be exhaustive or to be construed as limiting the scope of the invention to the precise forms disclosed.
Referring now to the drawings, and particularly to
In order to have long network lifetimes, all stations 16 may be in the sleep mode for most of the time to thereby save energy. During the sleep mode, the receiver of a station 16 may be off and that station 16 may not be able to receive any message from other stations 16 or from central unit 12. Therefore, in order to receive user-issued messages from central unit 12, a station 16 may need to wake up and listen to the channel periodically, e.g., at regular intervals.
In the IEEE 802.11 standard, a station can stay in a type of sleep mode referred to as a “Power Save (PS) mode” to save energy. If a station in the PS mode, it turns on its radio only when necessary. Hence it cannot receive any packet during the sleep mode. If the AP has packets to send but the destination station is in sleep mode, then the AP may first buffer the packets in its memory. The AP broadcasts beacon signals periodically, and when there are packets buffered, the AP sends Traffic Indication Map (TIM) messages in the beacons. If the destination station happens to wake up and receive that beacon, the destination station then later sends a PS-Poll to the AP and requests the AP to send the buffered packets to the station.
According to the present invention, it may be assumed that all stations 16 (also referred to as “nodes”) can talk to an Access Point (AP) 14 directly when the station's transmitter is on and the channel condition is good. It may be further assumed that a station 16 might be able to “overhear” another station's transmissions if those two stations are in communication range.
The invention includes several novel features. First, stations 16 are generally in sleep mode. After stations 16 wake up and receive the beacon signal of AP 14, stations 16 stay in wake-up mode for a while to overhear their neighboring stations' transmissions if any. Second, a station 16 can use neighboring stations 16 to relay its messages to AP 14 while the neighboring stations wake up. Third, the overhearing relay method can increase network reliability.
With regard to alarm handling, alarm messages may be rarely generated, but once an alarm message is generated, it may be desirable to deliver the message to a central unit 12 as soon as possible. Therefore, the low latency and high reliability may be two important requirements for alarm handling.
If a station 16 generates an alarm, the station 16 can send the alarm based on the 802.11 standard (CSMA/CA). The station 16 may stop sending the alarm after station 16 receives an acknowledgment from the central unit 12 indicating that the alarm is received successfully (or the maximum number of retries of sending the alarm has been reached).
With regard to a wake-up-overhear-relay method of the present invention, in an 802.11 network, a station can overhear its neighbors' transmissions. Based on that, a wake-up-overhear-relay method of the invention may increase the reliability of alarm transmissions.
With reference to network 10 (
Station 216a may be referred to herein as a “transmitting station”, and station 216b may be referred to herein as a “relaying station.” However, it is to be understood that where these two terms are used herein, the terms may describe only the tasks being performed by the stations in a particular situation, and should not be construed as describing any limitations on the stations' structure or functionality. That is, a “transmitting station” and a “relaying station” may be substantially identical both physically and functionally. In another situation, a “relaying station” may sense a security breach and originate and transmit an alarm signal. Further, a “transmitting station” may relay to an access point an alarm signal received from a “relaying station.”
In one embodiment of a network of the invention, in order to have a longer network lifetime, the stations are required to stay in the power saving mode when there is no transmission taking place. However, in order to apply overhearing, a station may be required to stay awake and remain listening to channels for a longer period of time. As illustrated in
As can be seen from
The performance of the simple example network 210 (
PBCA=(1−PBC)*(PCANPBC*PCAN−1+PBC2*PCAN−2+ . . . +PBCN−1*PCA1)+PBCN.
Therefore, the probability that an alarm fails to be transmitted from station B to station C to AP or from station B to AP is given by
Pf=PBCN+1*PBCA.
Let N=3, and PBC=PCA=0.3. The performance of the case where only station B tries to transmit the alarm messages (probability of success=1−PBCN+1) may be compared to the case where station C can overhear the alarms from station B and relay it (probability of success=1−Pf). The result is plotted in
On the other hand, the maximum delay (Dmax;
Dmax=Toverhearing*N+tmax
where Toverhearing is the overhearing period of a station (in the example of
Toverhearing=EO/PO,
where EO is the energy used for overhearing, and PO is defined as the overhearing power.
Given EO=19.5 uJ, N=3, and tmax
Given PBA=PBC=PCA=Pe and tmax
The overhearing relay method may be especially useful when the link between a station and the AP is broken temporarily. In this case, a transmitting station can use other stations as a relay and pass the transmitting station's alarm messages on to the AP within desired time limits and parameters.
There may be two ways in which the performance of the overhearing relay method may be further improved. First, more than one station may be used to relay the alarm messages from each transmitting station. This may increase the reliability of the system but may decrease the lifetime. Second, the stations may be partitioned into different groups using the method described in “Wakeup Scheduling in Wireless Sensor Networks,” by A. Keshavarzian, H. Lee, L. Venkatraman, D. Lai, K. Chintalapudi, and B. Srinivasan, Proc. Of the ACM International Symposium on Mobile Ad Hoc Networking and Computing, Florence, Italy, May 2006, and in European Patent Publication 1780951, entitled “Node Control Using Crossed Ladder Pattern in Wireless Sensor Networks,” by A. Keshavarzian, L. Venkatraman and H. Lee, 2007, each of which is hereby incorporated by reference herein in their entireties. Each station group created by this method may perform overhearing alternatively, or on an alternating basis. In this embodiment, each group of stations may spend less power on overhearing but the delay may not be increased.
The invention includes several novel features. First, stations may normally be in power saving mode. After relaying stations wake up and receive beacon signals from the access point, the relaying stations stay in wake-up mode for an extended period in order to overhear transmissions, if any, from their neighboring stations. Second, a transmitting station can use neighboring stations to relay the transmitting station's messages to the access point while the neighboring stations are awake. Third, the overhearing relay method can increase network reliability by increasing the rate of successful reception of the transmitting station's message by the access point.
One embodiment of a method 1000 of the present invention for wirelessly transmitting alarm signals is illustrated in
In a next step 1004, an alarm signal is wirelessly transmitted from a transmitting station. That is, transmitting station 216a may include a security sensor such as a smoke sensor or an infrared motion detector, for example. Upon the security sensor detecting a security breach, such as the presence of smoke or of motion, station 216a may wirelessly transmit an alarm signal, as indicated at 424, which is intended to be received by access point 214 and passed on by access point 214 to a central controller, such as central unit 12. The central controller may then evaluate whether the alarm signal is indicative of an actual security breach, and, if so, may notify via land-based telephone lines an appropriate responding authority, such as a fire department or police station, for example.
Next, in step 1006, it is determined whether the transmitting station has received a first acknowledgement signal that has been wirelessly transmitted from the access point in response to the access point receiving the alarm signal. For example, after access point 214 has received the wireless alarm signal from transmitting station 216a, access point 214 may respond by wirelessly transmitting an acknowledgement signal in order to thereby notify transmitting station 216a that the alarm signal has been received by access point 214. If, however, access point 214 does not receive the alarm signal, which may be due to a poor quality communication link 218a between station 216a and access point 214, for example, then transmitting station 216a will not receive the acknowledgement signal. If transmitting station 216a has received the acknowledgement signal from access point 214, then transmitting station 216a may go back into the sleep mode. If, however, transmitting station 216a has not received the acknowledgement signal from access point 214, then operation proceeds to step 1008.
In step 1008, the relaying station is woken up and kept awake during a plurality of periodic time intervals for overhearing transmissions from the transmitting station. For example, as best shown in
In a next step 1010, the alarm signal is wirelessly re-transmitted from the transmitting station during at least one of the time intervals in which the relaying station is awake. That is, transmitting station 216a may wirelessly re-transmit an alarm signal as indicated at 426 during time intervals 428 in which station 216b is awake.
Next, in step 1012, the alarm signal is received at the relaying station. For example, the final or right-most arrow 426 in
In a next step 1014, the alarm signal is transmitted from the relaying station to the access point. That is, as indicated by arrows 430 in
Next, in step 1016, it is determined whether the relaying station has received a second acknowledgement signal that has been wirelessly transmitted from the access point in response to the access point receiving the alarm signal. For example, after access point 214 has received the wireless alarm signal from relaying station 216b, access point 214 may respond by wirelessly transmitting an acknowledgement signal in order to thereby notify relaying station 216b that the alarm signal has been received by access point 214. If, however, access point 214 does not receive the alarm signal, which may be due to a poor quality communication link 218b between station 216b and access point 214, for example, then relaying station 216b will not receive the acknowledgement signal. If relaying station 216b has received the acknowledgement signal from access point 214, then relaying station 216b may go back into the sleep mode. If, however, relaying station 216b has not received the acknowledgement signal from access point 214, then operation proceeds to step 1018.
In the final step 1018, the alarm signal is re-transmitted from the relaying station. That is, relaying station 216b may re-transmit the alarm signal as indicated by the second or right-most arrow 430 in
While this invention has been described as having an exemplary design, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles.
Number | Name | Date | Kind |
---|---|---|---|
3839707 | Woodward et al. | Oct 1974 | A |
4023139 | Samburg | May 1977 | A |
4060803 | Ashworth, Jr. | Nov 1977 | A |
4091384 | Green, Jr. | May 1978 | A |
4560978 | Lemelson | Dec 1985 | A |
4785284 | Kimura | Nov 1988 | A |
4864519 | Appleby et al. | Sep 1989 | A |
5528219 | Frohlich et al. | Jun 1996 | A |
5638046 | Malinowski | Jun 1997 | A |
5892441 | Woolley et al. | Apr 1999 | A |
5977913 | Christ | Nov 1999 | A |
6166644 | Stroda | Dec 2000 | A |
6317039 | Thomason | Nov 2001 | B1 |
6624750 | Marman et al. | Sep 2003 | B1 |
7242294 | Warrior et al. | Jul 2007 | B2 |
7274907 | Perotti et al. | Sep 2007 | B1 |
7304976 | Mao et al. | Dec 2007 | B2 |
7330457 | Panwar et al. | Feb 2008 | B2 |
7383019 | Thorsted et al. | Jun 2008 | B1 |
7738413 | Varaiya et al. | Jun 2010 | B2 |
7761049 | Zeng et al. | Jul 2010 | B2 |
7813326 | Kelm et al. | Oct 2010 | B1 |
7843867 | Gopalakrishnan et al. | Nov 2010 | B2 |
20040140925 | Kim | Jul 2004 | A1 |
20040190476 | Bansal et al. | Sep 2004 | A1 |
20040224713 | Schreyer et al. | Nov 2004 | A1 |
20050242943 | Matsumoto et al. | Nov 2005 | A1 |
20060090079 | Oh et al. | Apr 2006 | A1 |
20060176169 | Doolin et al. | Aug 2006 | A1 |
20060176863 | Robinson et al. | Aug 2006 | A1 |
20070060157 | Gopalakrishnan et al. | Mar 2007 | A1 |
20070152813 | Mathur et al. | Jul 2007 | A1 |
20070198850 | Martin et al. | Aug 2007 | A1 |
20080122655 | Sedelius Horberg et al. | May 2008 | A1 |
20080137585 | Loyola et al. | Jun 2008 | A1 |
20080181101 | Oh et al. | Jul 2008 | A1 |
20100008286 | Abedi | Jan 2010 | A1 |
20100067422 | Kadous et al. | Mar 2010 | A1 |
20100182916 | Drewes et al. | Jul 2010 | A1 |
Number | Date | Country |
---|---|---|
1176567 | Jan 2002 | EP |
1244081 | Sep 2002 | EP |
1 780 951 | May 2007 | EP |
1780951 | May 2007 | EP |
2 081 313 | Jul 2009 | EP |
2081313 | Jul 2009 | EP |
WO 2009006092 | Jan 2009 | WO |
Entry |
---|
Keshavarzian, Abtin; Lee, Huang; Venkatraman, Lakshmi: “Wakeup Scheduling in Wireless Sensor Networks”; Proc. of the ACM International Symposium on Mobile Ad Hoc Network and Computing; May 22-25, 2006; Florence, Italy; Copyright 2006 ACM 1-59593-368-9/06/0005; 12 pages. |
Lu, Mei-Hsuan; Steenkiste, Peter; Chen, Tsuhan; “Design, Implementation and Evaluation of an Efficient Opportunistic Retransmission Protocol”; MobiCom; Sep. 20-25, 2009; Beijing, China; Copyright 2009 ACM 978-1-60558-702-8/09/09, 12 pages. |
Keshavarzian, Abtin; Lee, Huang; Venkatraman, Lakshmi; “Wakeup Scheduling in Wireless Sensor Networks”; MobiHoc, May 22-25, 2006; Florence, Italy; Copyright 2006 ACM 1-59593-368-9/06/0005; 12 pages. |
Number | Date | Country | |
---|---|---|---|
20120038475 A1 | Feb 2012 | US |