System and method for a communication protocol for wireless sensor systems including systems with high priority asynchronous message and low priority synchronous message Number:7,426,190 from the United States Patent and Trademark Office (PTO) owispatent A method for initializing a wireless network is provided which includes discovering at least one node of the wireless network that is within hearing range of a base station of the wireless network, authenticating the at least one discovered node, assigning a node identifier to the at least one discovered node, and selecting a network frequency, at least one backup frequency, and a locally unique network identifier.<H communication, asynchronous, System, and, meth, 7426190.html, Patent, pto, 7426190

Title: System and method for a communication protocol for wireless sensor systems including systems with high priority asynchronous message and low priority synchronous message

Abstract: A method for initializing a wireless network is provided which includes discovering at least one node of the wireless network that is within hearing range of a base station of the wireless network, authenticating the at least one discovered node, assigning a node identifier to the at least one discovered node, and selecting a network frequency, at least one backup frequency, and a locally unique network identifier.

Patent Number: 7,426,190 Issued on 09/16/2008 to Manjeshwar, et al.

Inventors: Manjeshwar; Arati (Chandler, AZ), Venkatraman; Lakshmi (Mountain View, CA), Srinivasan; Bhaskar (Menlo Park, CA), Pandey; Anshul (San Ramon, CA), Berube; Jim (Farmington, NY)
Assignee: Robert Bosch GmbH (Stuttgart, DE)

Appl. No.: 11/240,436

Filed: September 30, 2005

Current U.S. Class: 370/254 ; 455/435.1

Current International Class: H04L 12/28 (20060101)

Field of Search: 370/254,328 455/435.1

References Cited [Referenced By]

U.S. Patent Documents


5862142	January 1999	Takiyasu et al.
2002/0011921	January 2002	Amtmann
2002/0181417	December 2002	Malhotra et al.
2004/0137927	July 2004	Mun
2004/0151137	August 2004	McFarland et al.
2004/0223466	November 2004	Schrader et al.
2005/0195760	September 2005	Lee et al.
2007/0258508	November 2007	Werb et al.

Foreign Patent Documents


1 107 512	Jun., 2001	EP
2 375 014	Oct., 2002	GB
WO 2004/088934	Oct., 2004	WO

Other References

International Search Report, Jan. 28, 2008, International Patent Application EP06020092. cited by other.

Primary Examiner: Harper; Vincent P.
Assistant Examiner: Holliday; Jaime M
Attorney, Agent or Firm: Kenyon & Kenyon LLP

Claims

What is claimed is:

1. A method for initializing a wireless network, comprising: discovering at least one node of the wireless network that is within hearing range of a base station of the wireless network; authenticating the at least one discovered node; assigning a node identifier to the at least one discovered node; and selecting a network frequency, at least one backup frequency, and a locally unique network identifier; wherein the step of assigning the node identifier to the at least one discovered node further includes: broadcasting a first cycle start message to the at least one node, the first cycle start message including a cycle number, a message type, and a total number of time slots in a cycle, the message type including one of broadcast and unicast; performing a RF wakeup by the at least one node to receive the broadcasted first cycle start message and sleeping until an allocated time slot; sending a node identifier message to the at least one node during the allocated time slot, the node identifier message include a device identifier; performing a RF wakeup by the at least one node during the allocated time slot to receive the node identifier message and sending an acknowledgement to the base station if the device identifier of the node identifier message matches a device identifier of the at least one node; sending a subsequent cycle start message to the at least one node, which includes a list of nodes that failed to acknowledge the node identifier message, sending the node identifier message to the at least one node during the allocated time slot if the at least one node failed to acknowledge the node identifier message, and performing a RF wakeup by the at least one node if the at least one node is included in the list; and repeating the above step for a predefined number of cycles.

2. The method of claim 1, wherein the step of discovering the at least one node of the wireless network includes: transmitting a wakeup signal to the at least one node; performing a RF wakeup by the at least one node to receive the wake up signal; and transmitting a device identifier of the at least one node to the base station.

3. The method of claim 2, wherein the device identifier transmitted to the base station is transmitted in a random time slot using a Carrier Sense Multiple Access (CSMA) protocol exchange.

4. The method of claim 1, wherein only those nodes whose slot identifier is present in a cycle start message wakeup for receipt of the node identifier message.

5. The method of claim 1, wherein the step of selecting the network frequency, at least one backup frequency, and the locally unique network identifier, includes collecting information regarding at least one of quality and network usage.

6. The method of claim 5, further comprising: performing an ambient received signal strength indication (RSSI) reading for at least one frequency.

7. The method of claim 5, further comprising: performing a signal-to-noise (SNR) reading for the at least one frequency.

8. The method of claim 5, further comprising: collecting information regarding which frequencies and network identifiers are being used by an adjacent installation.

9. The method of claim 8, wherein the information is collected using a network poll approach.

10. The method of claim 9, further comprising: sending a poll packet message to at least one node of the adjacent installation; and receiving a response message from the at least one node of the adjacent installation, the response message including at least one of a network identifier of the adjacent installation and a frequency used by the adjacent network installation.

11. The method of claim 10, wherein the poll packet is sent by the at least one node of the wireless network.

12. The method of claim 10, wherein the poll packet is sent during a back channel time slot.

13. A method for configuring a network, comprising: discovering at least one node of the network that is within communication range of a central station of the network; authenticating the at least one discovered node; assigning a node identifier to the at least one discovered node; collecting information regarding a quality of at least one transmission path between the central station and the at least one node; collecting information regarding which communication paths and network identifiers are used by an overlapping network; and selecting a preferred transmission path, at least one backup transmission, and a locally unique network identifier, based on the collected information; wherein the step of assigning the node identifier to the at least one discovered node includes: broadcasting a first cycle start message to the at least one node, the first cycle start message including a cycle number, a message type, and a total number of time slots in a cycle, the message type including one of broadcast and unicast; performing a RF wakeup by the at least one node to receive the broadcasted first cycle start message and sleeping until an allocated time slot; sending a node identifier message to the at least one node during the allocated time slot, the node identifier message include a device identifier; performing a RF wakeup by the at least one node during the allocated time slot to receive the node identifier message and sending an acknowledgement to the base station if the device identifier of the node identifier message matches a device identifier of the at least one node; sending a subsequent cycle start message to the at least one node, which includes a list of nodes that failed to acknowledge the node identifier message, sending the node identifier message to the at least one node during the allocated time slot if the at least one node failed to acknowledge the node identifier message, and performing a RF wakeup by the at least one node if the at least one node is included in the list; and repeating the above step for a predefined number of cycles.

14. The method of claim 13, wherein the information regarding which communication paths and network identifiers are used by an overlapping network is collected using a network poll approach.

15. The method of claim 14, further comprising: sending a poll packet message to at least one node of the overlapping network; and receiving a response message from the at least one node of the overlapping installation, the response message including at least one of a network identifier of the adjacent installation and a communication path used by the overlapping network.

16. A method for initializing a wireless communications network, comprising: transmitting a wakeup signal to at least one node of the wireless network that is within hearing range of a base station of the wireless network; performing a RF wakeup by the at least one node to receive the wake up signal; transmitting a device identifier of the at least one node to the base station; authenticating the at least one discovered node; broadcasting a first cycle start message to the at least one node, the first cycle start message including a cycle number, a message type, and a total number of time slots in a cycle, the message type including one of broadcast and unicast; performing a RF wakeup by the at least one node to receive the broadcasted first cycle start message and sleeping until an allocated time slot; sending a node identifier message to the at least one node during the allocated time slot, the node identifier message include a device identifier; performing a RF wakeup by the at least one node during the allocated time slot to receive the node identifier message and sending an acknowledgement to the base station if the device identifier of the node identifier message matches a device identifier of the at least one node; sending a subsequent cycle start message to the at least one node, which includes a list of nodes that failed to acknowledge the node identifier message, sending the node identifier message to the at least one node during the allocated time slot if the at least one node failed to acknowledge the node identifier message, and performing a RF wakeup by the at least one node if the at least one node is included in the list; repeating the above step for a predefined number of cycles; collecting information regarding a quality of at least one frequency; collecting information regarding which frequencies and network identifiers are being used by an adjacent installation; and selecting a network frequency, at least one backup frequency, and a locally unique network identifier, based on the collected information.

17. The method of claim 16, further comprising: sending a poll packet message to at least one node of the adjacent installation; and receiving a response message from the at least one node of the adjacent installation, the response message including at least one of a network identifier of the adjacent installation and a frequency used by the adjacent network installation.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent applications entitled "Method and System for Time Synchronization in Communication Networks" (Ser. No. 11/241,298), "Method and System for Providing Acknowledged Broadcast and Multicast Communication" (Ser. No. 11/240,401), "Method and System for Providing an Energy Efficient Exchange of Information in Wireless Networks" (Ser. No. 11/239,837), "Method and System for Providing Interference Avoidance and Network Coexistence in Wireless Systems" (Ser. No. 11/240,545), "Method and System for Reliable Data Transmission in Wireless Networks" (Ser. No. 11/239,839), "Method and System for Providing a Modified Time Division Multiple Access (TDMA) for Reduced Delay" (Ser. No. 11/241,639), "Method and System for Providing Reliable Communication with Redundancy for Energy Constrained Wireless Systems" (Ser. No. 11/241,300), "System and Method for a Communication Protocol for Wireless Sensor Systems Including Systems with High Priority Asynchronous Message and Low Priority Synchronous Message" (Ser. No. 11/241,296), "Method and System to Reconfigure a Network to Improve Network Lifetime Using Most Reliable Communication Links" (Ser. No. 11/240,434). The disclosure of each of the foregoing related applications is hereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to an exemplary system and method for a communication protocol for wireless sensor systems.

SUMMARY OF THE INVENTION

The present invention relates to an exemplary system and method for a communication protocol for wireless networks, including, for example, wireless sensor networks. The exemplary communication protocol may be used, for example, to initialize, configure, operate, maintain, reconfigure, and/or shutdown the wireless network, and may comply with governmental regulatory requirements, including, for example, US and European regulatory requirements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary method to initialize and configure a wireless sensor system that includes a hub, a base station and several network nodes.

FIG. 2A shows an exemplary method for initialization a wireless sensor system.

FIGS. 2B and 2C show an exemplary method for selecting a network identifier.

FIG. 3 shows an exemplary method to discover nodes in a wireless communications system, in which the base station discovers the sensor nodes and learns their device identifiers, and each node is assigned a temporary slot identifier.

FIG. 4 shows an exemplary basic flow for the discovery of nodes and how an interaction may occur between the hub, base station and a network installer.

FIG. 5A shows an exemplary method to discover nodes in a wireless communication network system.

FIG. 5B shows exemplary time intervals for the transmission of a Device Identifier message, for use with the exemplary discovery method of FIG. 5A.

FIG. 6 shows an exemplary node identifier distribution time slot structure.

FIG. 7 shows an exemplary method for distributing node identifiers, which may be performed at the base station.

FIG. 8 shows an exemplary method for performing a node identifier distribution at the node.

FIG. 9A shows an exemplary scenario in which a base station of an initializing network is within the radio range of the base station of an adjacent installation.

FIG. 9B shows an exemplary scenario in which the base station of the initializing network can hear certain nodes of the adjacent installation, but cannot hear the base station of the adjacent installation.

FIG. 9C shows an exemplary scenario in which the nodes of the initializing network can hear the base station of the adjacent installation.

FIG. 9D shows that the nodes of the initializing network hear the nodes of adjacent installation but do not hear the base station of the adjacent installation.

FIG. 10 shows an exemplary method for selecting and verifying the network identifier and frequencies of an initializing network, under the exemplary scenarios shown in FIGS. 9A through 9D.

FIG. 11 shows an exemplary method to perform ambient Received Signal Strength Indication (RSSI) reading.

FIG. 12 shows an exemplary method to perform RSSI data collection.

FIG. 13 shows an exemplary method to perform network identifier and frequency selection using a network poll approach.

FIG. 14 shows an exemplary time slot allocation for consecutive wakeup intervals.

FIG. 15 shows a time line for an exemplary network identifier poll sequence.

FIG. 16A shows an exemplary time slot structure for a protocol designed to meet US regulatory requirements.

FIG. 16B shows an exemplary time slot structure for a protocol designed to meet European regulatory requirements.

FIG. 17 shows an exemplary mobile node/back channel time slot structure

FIG. 18 shows exemplary network parameters for US compliant systems.

FIG. 19 shows exemplary network parameters for European compliant systems.

FIG. 20 shows exemplary supervision intervals for US and Europe compliant systems.

FIG. 21 shows an exemplary supervision mechanism overview.

FIG. 22 shows an exemplary slot allocation and frequency usage for US and European compliant systems.

FIG. 23A shows an exemplary alarm time slot structure for US compliant systems.

FIG. 23B shows an exemplary alarm time slot structure for European compliant systems.

FIG. 23C shows an exemplary method for alarm transmission for US compliant systems.

FIG. 24 shows an exemplary table for determining a range of random numbers, which are used to select a time slot to transmit alarms in order to minimize collisions.

FIG. 25A shows an exemplary back channel packet structure for multicast and unicast packets.

FIG. 25B shows an exemplary back channel packet structure for unicast list packets.

FIG. 26 shows exemplary back channel packet structure values.

FIG. 27 illustrates exemplary behavior at the base station for multicast packets for US compliant systems.

FIG. 28 illustrates exemplary behavior of the base station for unicast list packet for US compliant systems.

FIG. 29 illustrates an exemplary alternative use of the network and backup frequencies during retransmissions.

FIG. 30 shows exemplary values for the number and type of mobile nodes in a system.

FIG. 31A show an exemplary mobile node slot structure for US compliant systems.

FIG. 31B shows an exemplary mobile node slot structure for European compliant systems.

FIG. 32 shows an exemplary time slot structure for packet transmission at a key fob type mobile node.

FIG. 33 shows an exemplary key fob transmission pattern.

FIG. 34 shows an exemplary transmission of a message by a key fob for European compliant systems.

FIG. 35 shows an exemplary format of a synchronous message from the base station to the keypad.

FIG. 36 shows an exemplary network to synchronize sensor transceivers.

FIG. 37 shows an exemplary method to collect information from sensor transceivers.

FIG. 38 shows an exemplary message sequence diagram for hub replacement and power down.

FIG. 39 shows a timeline for an exemplary sequence for hub replacement.

FIG. 40A shows an exemplary alarm time slot structure for US compliant systems.

FIG. 40B shows an exemplary alarm time slot structure for European compliant systems.

FIGS. 41A and 41B show two exemplary sampling sequences performed by the sensor nodes.

FIG. 42 shows an exemplary truth table for continuous interference protection prescribing the action to be taken on every pass based on the status of a jamming detection flag and a reported flag.

FIG. 43 shows an exemplary jamming history field for cumulative interference protection.

FIG. 44 shows an exemplary wireless system, which includes a plurality of sensor devices, a key fob, two hubs, a control panel, and wireless keypad.

FIG. 45 shows an exemplary implementation of the two hubs of the exemplary wireless system of FIG. 44.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary method to initialize and configure a wireless sensor system that includes a hub, a base station and sensor nodes. In step S101, discovery of the sensor nodes in the system is performed. That is, all the sensor nodes that are within hearing range of the base station are discovered. In step S102, authentication of the nodes and assignment of node identifiers is performed. That is, nodes are authenticated by the installer (e.g., remote program or human), and all nodes that are approved and certified to belong to the system, are assigned unique node identifiers. In this regard, the node identifier may be used, for example, to address the nodes during network operation. In step S103, a network frequency, backup frequencies, and a network identifier, which is at least locally unique among adjacent networks, are selected. To manually select the frequency of an already installed network, the system may repeat step S103 so that selection of network frequency may occur on request from an operator.

FIGS. 2A, 2B and 2C show an exemplary method for initialization a wireless sensor system, including exemplary methods for discovering all nodes and selecting a network identifier.

In step S201, an installer starts initialization of the system. In step S202, the base (BS) station chooses a random n-bit base station identifier. In step S203, the hub sends a "Start Discovery" message to the base station. In step S204, base station discovers the nodes and passes the information to the hub. In step S205, the base station sends a "Discovery Process Complete" message to the hub. In step S206, the hub presents the discovered nodes to the installer. In step S207, if all the nodes are not discovered, the installer issues discovery again and the hub repeats step S203 to S207. In step S208, the hub sends a "Start Node Id Distribution" message. In steps S209, the base station distributes the node identifiers to the nodes. In step S210, the base station sends a "Node Id Distribution Complete" message to the hub. In step S211, the hub sends a "Start NW-Id Selection" message to base station. In step S212, the base station and nodes collect the ambient RSSI reading on all frequencies.

In Europe, when the base station and nodes listen on the backup frequencies, they may also keep track of number of networks on each of the backup frequency number. They may also keep a bit-mask of the network identifier received in both the frequencies. In step S213, the base station collects ambient RSSI data (for EU Complaint Systems back frequency count and network identifiers may also be collected) from all the nodes and sends it to the hub. The base station and nodes also read the Signal to Noise Ratio (SNR) at the default frequency during this process. In step S214, based on the data collected by the node and the base station, the hub selects a network frequency and sends a "Start Network Poll" message to the base station. In step S215, the base station performs a network poll at the selected frequency and sends the network identifiers found in this frequency to the hub. In step S216, the base station sends a "NW Poll Complete" message to the hub. If there are adjacent networks using this frequency, the hub may repeat steps S214 to S216 again. (For US compliant systems, the hub may send a "Start Network Id Verification" message to the base station. The base station and nodes verify if any of the adjacent networks are using the selected network identifier and frequency and send the data back to the base station. The base station also sends a completion message at the end of phase).

In step S217, based on the data collected, the hub selects a network frequency and backup frequencies for the network. In step S218, the hub sends a "SNR Verification" message to the base station for the selected frequency. In step S219, the base station and nodes collect the signal to noise ratio (SNR) on the selected frequency and send the data to the hub via the base station. In step S220, the base station sends a "SNR Verification Complete" message to the hub. In step S221, if the signal to noise ratio (SNR) is acceptable, the hub selects the final network identifier and backup frequency for the network. If the signal to noise ratio (SNR) is not acceptable, the hub repeats the network identifier selection process (from steps S214 or S217) In step S222, the hub sends a "Network Id Distribution" message to the base station. In step S223, the base station distributes the network parameters to all the nodes. In step S224, the base station sends the "NW-ID Distribution Complete" message to the hub. In step S225, the base station and nodes switch to the network frequency and network operation after a fixed interval. In steps S226, the hub performs recovery operation for those nodes which failed the network identifier distribution.

Discovery of Nodes in the System (Collection of Device IDs)

FIG. 3 shows an exemplary method to discover nodes in a wireless communications system, in which the base station discovers the sensor nodes and learns their device identifiers, and each node is assigned a temporary slot identifier. More specifically, in step S301, all the nodes that are within the hearing range of the base station are discovered, including, for example, nodes that are not part of the system being installed. In step S302, the device identifier of all the nodes is learned and passed to the hub. In step S303, slot identifiers are assigned to all the nodes, so that communication during node identifier distribution is time slotted and packet transmission from one node does not adversely affect other nodes. In steps S304, all the nodes are informed of the chosen base station identifier so that nodes may distinguish packets from other systems that may also be performing initialization. (Note: All communications in next step of initialization (node identifier distribution) occur in a time slotted fashion so that there is no collision of packets. Each node communicates with the base station in its respective time slot that is determined by the slot identifier).

FIG. 4 shows an exemplary basic flow for the discovery of nodes and how an interaction may occur between the hub, base station and installer. In step S401, the installer starts the initialization of the system. In step S402, the base station chooses a n-bit random identifier, which acts as temporary network identifier for the system. This identifier is called the base station identifier, which is a n-bit identifier because the permanent network identifier is also the same number of bits. The base station identifier distinguishes packets of one base station from another during initialization. Since more than one network may be installed and initialized at the same time, the base station identifier may be useful to distinguish them. Alternatively, the device identifier (e.g., six bytes) of the base station may be included, but to do so may increase the number of bytes transmitted. In particular, with each packet transmission in the system the six-byte base station device identifier would need to be sent. But since it is a random choice, two installations may pick same base station identifier. To handle this, additional randomness is added by using cyclic reducing checking (CRC).

In step S403, the hub sends a "Start Discovery" message to the base station, which indicates the number of nodes that the installer is installing. (This number makes this step scalable to number of nodes being installed). If the operator cannot provide this number, then the maximum number of nodes the panel can handled is passed. In step S404, the base station runs a discovery process and discovers the nodes it can. During the discovery process, it sends the device identifier of the discovered nodes to the hub. Further details of the discovery process are described below. In step S405, on completion of the discovery process, the base station sends a completion message to the hub. In step S406, the installer now checks if all the nodes that were installed have been discovered or not. If all the nodes have been discovered, the installer moves onto the next step, i.e., node identifier distribution. If some of the nodes are installed but not discovered, the installer reruns the discovery process with a reduced number of nodes. In this regard, the hub should pass the number of nodes which are yet undiscovered to the base station.

FIG. 5A shows an exemplary method to discover nodes in a wireless communication network system, and FIG. 5B shows exemplary time intervals for transmitting a Device Identifier message. In step S501, initially all nodes of the network perform RF wakeup with a RF wakeup interval of 200 milliseconds. The nodes are not yet synchronized to the network. In RF wakeup, nodes are in the sleep state and wake up periodically to sample the frequency. If a node senses a high signal, it continues to listen. The received bytes are checked for preamble bytes because wakeup tones include preamble bytes. If the bytes received are preamble bytes, the node waits for valid packets. If the node does not receive valid packets within a specified time period, or if the bytes received are not the preamble bytes, they go back to sleep. If the node does not sense a high signal when it wakes up and samples the frequency, it also goes back to sleep. The periodicity may be predefined and determined by the "RF wakeup interval". Initially, the RF wakeup interval is 200 milliseconds, that is, the nodes wakeup every 200 milliseconds to sample the frequency.

In step S502, the base station sends a wakeup tone for 210 milliseconds (a little more than the RF wakeup interval). In step S503, following the tone the base station transmits the "Start" message that includes the base station identifier, base station time (two bytes of hardware timer, so that the cyclic redundancy check cyclic redundancy check (CRC) is different even if the base station identifier matches), expected number of nodes in the network, device type to discover and cyclic redundancy check (CRC) for the packet. The device type is set to "0.times.00" if it is desired to discover all type of devices. In this regard, the expected number of nodes may be greater than the number given by the hub by a fixed number, to account for uninstalled nodes from adjacent installations. In step S504, the time at which the base station sends the start symbol of the start message and the time at which the node receives the start symbol of the "start" message is used as reference for synchronization of events between the base station and nodes. In step S505, the nodes, for which the device type matches the one the base station is trying to discover, send their device identifiers to the base station. Since multiple nodes may send device identifier packets, there may be a high chance of collisions.

In step S506, to minimize the number of collisions, each node selects a random slot within a specific interval "T1" to transmit the device identifier packet. The interval "T1" is divided into number of time slots based on the number of nodes. As described in step S503, the number of nodes in the network is based on the value received in the "start message". In step S507, the time slot to transmit is determined by selecting a random number "R" whose depends on "N", where "N" is the number of nodes in the network. In step S508, the node transmits the device identifier packet to the base station after performing a carrier sense multiple access (CSMA) protocol exchange. This packet also has one byte of cyclic redundancy check (CRC) of the time packet to ensure that any other base station that is also performing initialization does not mistake it to be a packet meant for it. Although the base station chooses a random base station identifier, this may also handle situations where the base stations from two adjacent installations chooses the same base station identifiers. The cyclic redundancy check ( CRC) for the two base stations should be different if number of nodes or the time at which they send start message is different. In step S509, if the carrier sense multiple access (CSMA) protocol exchange fails at the node, the node again chooses a random time slot in the interval T1 and sends a device identifier packet. In steps S510, the base station acknowledges the receipt of the device identifier packet. This is an "immediate-ack", that is, the base station sends the acknowledgement immediately without performing carrier sense multiple access (CSMA) protocol exchange. In step S511, the acknowledgement includes of a temporary slot identifier that is unique for every node. The slot identifier determines the time slot when the node and the base station should communicate hereafter until the node is assigned a permanent node identifier. In step S512, if the nodes do not receive an acknowledgement the node sleeps until the end of the time interval T1.

In step S513, after the end of T1, the nodes that did not receive an acknowledgement earlier wakeup and repeat steps S505 to S512 but with a new time interval "T2". The interval T2 is fixed to be smaller than T1 because only the subset of nodes that did not receive an acknowledgement should attempt to receive again. This process is again repeated for the nodes that did not receive an acknowledgement during their try in interval T2 by repeating steps S506 to S511 in interval "T3". In step 514, the entire cycle from step S501 is repeated (e.g., twice more) to ensure that the base station has discovered all nodes in its range. The sending of tone, start message etc. are repeated so that if a node did not detect the earlier tone it gets another opportunity. The time intervals T1, T2 and T3 for subsequent cycles should be smaller and based on number of nodes found in previous cycle. In step S515, after completion of initial discovery, the base station sends a "Device Id Collection Complete" message to the hub. During the device identifier collection phase, the base station passes each device identifier to the hub, which in turn passes it to the panel. The user verifies each device identifier and identifies those that belong to the network.

Node ID Distribution

During node identifier distribution, the base station provides a permanent node identifier to every node that belongs to the network. All nodes that do not belong to the network are sent a message indicating that they are not part of the network. Whether a node belongs to the network or not is determined by the installer at the panel or by the remote-programmer.

FIG. 6 shows an exemplary node identifier distribution time slot structure. The node identifier distribution starts with a "Start Node Id Distribution Message" from the hub. First, the base station sends the cycle start message to the nodes. Thereafter, the base station sends the node identifier to each node in predefined time slots based on a slot identifier that was assigned to the node during device identifier collection phase. The slot structure and message sequence in a time slot is shown in FIG. 6.

FIG. 7 shows an exemplary method for node identifier distribution, which may be performed as the base station. In step S701, the hub sends a "Start Node Id Distribution Message" to the base station. The message is of a `Broadcast` type, directing that node identifier distribution be performed for all nodes. In step S702, the base station sends the node identifier request for the first time slot to the hub. In step S703, the base station broadcasts the cycle start message to the nodes. The cycle start message includes the message type (e.g., broadcast or multicast), cycle number, and the total number of time slots. In step S704, the cycle start message in the first cycle is always a broadcast type and it indicates that all nodes should wake up in their assigned time slot for a node identifier message from the base station. In step S705, the cycle start message is sent using a carrier sense multiple access (CSMA) protocol exchange. If the carrier sense multiple access (CSMA) protocol exchange fails for `N` retries (in the same cycle), the base station sends the message without performing a carrier sense multiple access (CSMA) protocol exchange in the next attempt. In step S706, the base station waits until the slot start time to start node identifier distribution. In step S707, the base station receives the node identifier message from the hub for the first slot (note: request sent in step S702). The message includes the device identifier and node identifier for the selected time slot. If the time slot corresponds to an unapproved node the node identifier is set to zero in the message. If the time slot is invalid, the device identifier and node identifier is also set to zero in the message. It is expected that the node identifier message from the hub should be available at the base station at the beginning of the time slot. In step S708, the base station sends a node identifier request to the hub in the next time slot. In step S709, the base station sends the node identifier message to the node and waits for an immediate acknowledgement from the node. In step S710, when the base station receives the acknowledgement, it is forwarded it to the hub.

In step S711, the base station selects the next time slot and repeats the steps from S708 to S710 until it is finished with all of the time slots. In step S712, base station then sends a "Node Id Distribution Complete" message to the hub indicating that this is node identifier distribution "End of Cycle". In step S713, when the hub receives the completion message with "End of Cycle" flag, it checks the acknowledgement status for all slots and then sends the "Start Node Id Distribution" message to the base station with a message type based on the number of nodes that failed to provide an acknowledgement in previous cycle(s). In this regard, if the number of nodes that failed to provide an acknowledgement is less than 10, the hub sends a "unicast" list with the list of failed slot identifiers. Otherwise, if the number of nodes that failed to provide an acknowledgement is greater than 10, the hub sends the message type as "multicast". If all the nodes were successful, the hub sends the message type as unicast list with the number of slots failed `zero`. In step S714, if the start message from the hub is a broadcast type, the base station repeats the same procedure as explained above for each time slot. But, in this instance, there may be many time slots that have already acknowledged successfully in previous cycle(s). For those time slots that were successful, the hub will not send node identifier and device identifier values set to zero in the message in response to the base station request and there will not be any node identifier distribution to nodes for these time slots. In step S715, if the start message from the hub is a multicast type, the base station sends the start message to nodes as unicast list type with the list of slot identifiers in the message. The base station repeats the node identifier distribution steps for the failed time slots. Here the communication slot for a failed node is the position of its slot identifier in the start message. In step S716, if the start message from the hub is unicast list with no slot identifiers, it indicates that all the nodes were successful in previous cycles. The base station sends the start message to the nodes as unicast list with number of slots `zero`. In step S717, the base station repeats the above steps until all nodes acknowledged, or a total of five cycles for node identifier distribution. After that the base station sends a "Node ID Distribution Complete" message with end of phase flag, indicating end of the node identifier distribution phase. In step S718, the base station uses the carrier sense multiple access (CSMA) protocol for the node identifier message in the first three cycles and no carrier sense multiple access (CSMA) protocol is used in the last two cycles.

FIG. 8 shows an exemplary method for node distribution which is performed at the node. In step S801, the nodes perform a RF wakeup and sample the channel every 200 milliseconds to detect a node identifier start message. In step S802, when the node receives the start message, if the message is broadcast type or multicast type with its slot identifier present in the message, the node sleeps until its assigned time slot and wakes up expecting a node identifier message from the base station. If the message type is multicast and the node's slot identifier is present in the message, the communication time slot for the node is the position of its slot identifier in the message. In step S803, when the node receives the node identifier message, it compares its device identifier with the device identifier received in the message. If they match, the node accepts the node identifier and sends an immediate acknowledgement to the base station. The node sleeps until the end of the current cycle and then performs a RF wakeup, waiting for a node identifier start message. In step S804, if the device identifier received in the node identifier message is different, the node rejects the message and no acknowledgment is sent to the base station. The node sleeps until the end of the current cycle and then performs an RF wakeup, waiting for a node identifier start message. In step S805, if the device identifier matches and the node identifier indicates that the node is unapproved, the node immediately returns back to the device identifier collection phase. In step S806, if the node receives a multicast start message and if the node's slot identifier is not present in the message, this indicates that the base station received the acknowledgement from this node in a previous cycle. The node then goes to the next phase, which is RSSI collection.

At the end of five cycles, all nodes that did not receive a node identifier message from the base station return back to RF wakeup and wait for a device identifier collection start message. These nodes will fail the subsequent steps of initialization and the hub will send a configure node by device identifier command after network identifier distribution.

Network ID and Frequency Selection

During network identifier and frequency selection, the nodes and the base station collect frequency quality(s) and network usage, including usage by other wireless sensor network installations. This information is used to select a frequency(s) and a unique network identifier, with respect to other wireless sensor network installations, that is most suitable for all the nodes in the network. The procedure may differ for US and Europe compliant systems since backup frequency allotment is different. To choose a suitable frequency, which is not used by adjacent wireless sensor network installations, the base station may need to know which frequencies and network identifiers are being used by adjacent installations.

FIGS. 9A to 9D show example scenarios for overlapping installations. In the Figures, BS1 is the base station of the network that is being initialized and BS2 is the base station of the adjacent network. More specifically, FIG. 9A shows the base station BS1 of the initializing network is within the radio range of the base station BS2 of the adjacent installation. FIG. 9B shows that the base station BS1 of the initializing network can hear certain nodes of the adjacent installation, but cannot hear the base station BS2 of the adjacent installation. FIG. 9C shows that the nodes of the initializing network can hear the base station BS2 of the adjacent installation. FIG. 9D shows that the nodes of the initializing network hear the nodes of adjacent installation but do not hear the base station BS2 of the adjacent installation. (In this instance, adjacent installations with only nodes hearing one another may not adversely impact the working of the two networks as they may transmit very infrequently and node packets may be distinguished from base station packets).

To handle the aforementioned scenarios and learn the network identifier and frequencies, the following steps may be performed as shown in FIG. 10.

In step S1001, an ambient Received Signal Strength Indication (RSSI) reading is performed. In step S1002, listening on backup frequencies is performed (e.g., in Europe only). In step S1003, RSSI data collection is performed. In step S1004, network identifier and frequency selection is performed. In step S1005, network identifier poll is performed. In step S1006, network frequency verification is performed (e.g., in US only). In step S1007, signal to noise (SNR) verification is performed. In step S1008, network identifier distribution is performed. Details of these steps are provided below.

Ambient RSSI Reading

During ambient RSSI reading, the base station and the nodes sample all available frequencies to collect the average noise level in each frequency. Noise level is measured in terms of Received Signal Strength Indication (RSSI) when there is no packet transmission from wireless sensor network systems. A lower noise level (lower RSSI) implies a better channel.

FIG. 11 shows an exemplary method to perform ambient Received Signal Strength Indication (RSSI) reading. The nodes and base station sample each of the frequencies (e.g., around 100 samples/frequency) to collect the noise levels. When a sample is taken, it is taken on all the frequencies before taking the next sample. The nodes sample all the frequencies except the default frequency. The mobile network frequency is also sampled by nodes so that the user has a understanding of how the channel is around the network. So that if there are problems with mobile network, it may use this information. For example, there may be seven frequencies per channel in Europe and seventeen frequencies per channel in United States. The base station samples default frequency also (eight frequencies in Europe and eighteen frequencies in the United States). The nodes sample these frequencies immediately after completing node identifier distribution. Nodes do not sample on the default frequency since the base station may send packet on the default frequency during this time. The base station starts sampling when it receives the "Start Network Id Selection" command from the hub. The data collected by the node may be sent to the base station at a later time, such as, for example, during RSSI data collection from the nodes.

Listening on Backup Frequency (for EU only)

In Europe in addition to collecting a noise level, the base station and the nodes also collect the network identifiers of all parallel wireless sensor network installations within hearing range so that the network which is being installed may choose a locally unique network identifier. The network elements, including both the nodes and the base station, listen to the backup frequencies for two minutes each since each wireless sensor network installation transmits a time beacon in the backup frequencies, which contains the network identifier. The network can hear all the nodes that have a scenario similar to what is shown in FIG. 9A, in which the base station BS1 of the initializing network is within the radio range of the base station BS2 of an adjacent installation, and the scenario shown in FIG. 9C, in which the nodes of the initializing network hear the base station BS2 of adjacent installation. The scenario shown in FIG. 9B, in which the base station BS1 of the initializing network hears only the nodes of adjacent installations, is not handled by listening on backup frequency. Instead, this scenario is taken care by during a network identifier poll. The collected information may be sent to the base station in subsequent steps.

In the United States, since we do not have a certain set of frequencies assigned for backup, and since the number of backup frequencies to sniff (e.g., 16) is high, it may not be useful to listen for a network identifier at this stage. Instead it may be performed in the verification of the network frequency phase.

RSSI Data Collection from Nodes

During RSSI data collection, the base station receives the ambient RSSI data collected by the nodes. For Europe, this message also includes the data collected during listening on the backup frequency, which includes of the backup frequency count (i.e., the number networks using this frequency as backup) and the network identifiers observed. In addition, the base station and nodes measure the RSSI during this message exchange (which is at the default frequency) both at the node and the base station.

FIG. 12 shows an exemplary method to perform RSSI data collection. In step S1201, the base station broadcasts a message to the nodes to request the RSSI data. In step S1202, all the nodes measure the RSSI value with which the broadcasted message is received at the node. In step S1203, the nodes send the ambient RSSI data and the default frequency RSSI measured in step S1302 above, in its assigned time slot. For Europe, the data sent includes the data collected during backup frequency listening. In step S1204, when the base station receives the RSSI data from a node, it measures the RSSI value with which this message is received at the base station. In step S1205, the base station sends all these data (e.g., the ambient RSSI data, default frequency RSSI measured at the node and base station) for each node to the hub. In step S1205, the above steps are repeated three times in case there are failures. In step S1206, at the end of this phase, the base station sends data collected at the base station to the hub.

NW ID and Frequency Selection

The hub selects frequencies for network operation and backup (e.g., backup frequencies may be used only for retries) based on the frequency quality, the signal to noise ration (SNR) and the network usage. In particular, the hub chooses a frequency from a set of frequencies that has an ambient RSSI value below a certain threshold. Additional rules may include, for example:

Rule 1: Minimum number of networks should use the selected frequency.

Rule 2: If the network usage is same for more than one frequency, then the frequency that has the less number of networks using it as a backup frequency is chosen. This rule may only be applied, for example, in U.S. compliant systems.

Rule 3: If the parameters for selection are the same (in case of Europe parameter 1), then the frequency with smaller RSSI value is chosen.

Rule 4: if the number of frequencies for which RSSI below threshold is zero, then all the frequencies are inoperable. The frequency is still chosen based on the three rules above, but the chosen frequency may not lead to an efficient network operation.

Once the network frequency is chosen, the base station chooses the backup frequency. For US compliant systems, three backup frequencies are chosen from the list of sixteen frequencies using the same criteria as for network frequency selection. The network frequency and three backup frequencies should be distinct. For Europe compliant systems, one backup frequency is chosen out of two backup frequencies based on (i) the number of networks using a frequency as a backup frequency, and (ii) the RSSI value.

After network frequency and backup frequency selection, the hub selects a network identifier based on the selected frequency and unused network identifier in that frequency. The system may support, for example, network identifiers in the range 1-127 and the corresponding network frequency may be found by (NW-ID % 16) for US and (NW-ID % 4) for Europe. The network identifier is selected randomly from the unused network identifiers in the selected frequency.

Network ID Poll by BS

The network identifier is polled by the base station of the initialize network, whereby the base station hears the nodes of the adjacent installation but does not hear the base station of the adjacent network. In this instance, listening on a backup frequency or a selected network frequency may not help in obtaining information about the adjacent network since the base station is not in the listening range of the adjacent base station and therefore will not receive the time beacon transmissions from the adjacent base station. So, the procedure followed here is to send a poll packet to the nodes of the adjacent installation and get the details.

FIG. 13 shows an exemplary method to perform network identifier and frequency selection using a network poll approach. In step S1301, based on the data collected in the previous phases, the hub selects a frequency that is suitable for network operation and sends a "Start NW Poll" message with the chosen frequency to the base station. In step S1302, on receiving this message, the base station switches to the frequency received from the hub and sends out a network identifier poll packet. In step S1303, the base station precedes this poll packet with a tone of one second duration to wakeup all the nodes of the adjacent installation using the same network frequency. A tone of one second duration is sent because the nodes of the operational network perform a RF wakeup once every one second. In step S1304, all the nodes of adjacent installation, including the base station of the adjacent installation that can hear this poll packet respond with their network identifier and backup frequency used, at their convenience in default frequency (within a fixed period). The base station forwards this information to the hub. In step S1305, the base station repeats the above procedure a predefined number of times "N", spaced by a predefined time, allowing enough time to receive responses. This is performed to ensure that the responses are not lost due to collision or losses in the frequency.

In step S1306, at the end, the base station sends a "NW Poll Complete" message to the hub. In step S1307, if the hub discovers that this particular frequency is being used by another wireless sensor network installation for network operation, it may choose another network frequency and send the network poll again to the base station to repeat the above steps in the newly selected frequency. Since it is assumed to have a maximum of only three wireless sensor network installations in the hearing range of any installation it should be feasible to allot a unique frequency for network operation (both in US and Europe). However, if more than four installations are provided at the same location or the noise level in some frequencies is not suitable for network operation, the same frequency may have to be assigned to more than one installations. In such a scenario, a different network identifier may be assigned to distinguish packets. Having more than one installation operating in the same network frequency may not efficient. In step S1308, these steps may be repeated for each number of network frequency in the system, which should be a total of four frequencies for Europe and a total of sixteen frequencies for US. In step S1309, based on the result of the network identifier poll and the data collected in previous phases, the hub selects a frequency, which is unique with respect to adjacent installations.

The transmission of poll packets may pose a potential security risk since these packets may not have a mechanism to prevent replay attacks. To reduce the affect of this attack, any node or base station responds to only 3*N network identifier poll packets in only one supervision period.

Network ID Poll by Node

To handle network identifier poll at the nodes, if a new network is initialized when there is an adjacent network and only the nodes of the adjacent installation are in the hearing range of the new base station BS1 as shown in FIG. 9B, then the base station BS1 of the initializing network should listen for at least as long as the supervision interval of the adjacent installation to better guarantee that it can hear the supervision acknowledgement of at least one node. Since the base station BS1 of the initializing network does not know the supervision interval of the adjacent system it should listen for the maximum possible supervision interval, which may be, for example, twenty four hours.

This implies the initialization of the network may take longer than twenty four hours, which may not be acceptable. To reduce the time needed for initialization, the base station BS1 of the initializing network sends a poll requesting information such as network identifier used etc. from the nodes of the adjacent network. To handle this feature the nodes of the adjacent installation should be able to respond to polls sent asynchronously and also handle high priority network operations.

Handling NW ID Poll at the Nodes

To handle the network identifier poll, the nodes are in the receive mode for the following activities. At all other times their transceiver is switched off to save power. In a first activity, the nodes wakeup periodically once every wakeup interval to check for any back channel (BC) commands from the base station. If the channel is free they go back to sleep immediately. In a second activity, the nodes wakeup in their supervision slot (if status not already given) and wait for their poll to send the status. If the channel is free they go back to sleep immediately except in the final retry slot (e.g., seventh slot). In a third activity, the nodes wakeup every two minutes to receive a time beacon to adjust their clocks and frequency. If the channel is free they go back to sleep immediately. In a fourth activity, if the nodes have an alarm to send, then in the alarm slot (in retries) it samples for a free channel before transmitting.

The nodes may receive the network identifier poll from the adjacent installation when listening for any of the above packets. The base station BS1 of the new installation transmits a tone long enough to cover the entire wakeup interval to guarantee that the nodes of the adjacent system will hear it at least when they expect to receive the back channel (BC) commands since nodes may not have their supervision slot or it is not time for time beacon etc. Since the nodes are guaranteed to receive the tone in the back channel slot, they ignore the tone if received in any other slot. The network identifier poll is handled only in the back channel slot.

To process the network identifier received at the nodes the nodes wakeup in the back channel time slot to sense for a high signal in the channel. A node expects a network identifier poll if all the following conditions are true: (a) if a high signal received, (b) a back channel packet is not received within the back channel start sequence timeout, and (c) less than nine network identifier polls were received in the current supervision interval (this reduces the effect of replay attack. Hence, an intruder cannot replay a network identifier poll to drain the batteries of the nodes). The nodes continues to receive with a "Network ID Poll Start Sequence Timeout" for the network identifier poll. In the meantime, other network operations may be handled. For example, if it is time for the nodes supervision slot (e.g., other than seventh slot), and the node was not successful in transmitting the supervision acknowledgement in the earlier six slots, it ignores the network identifier poll packet and does not send a response. If the node senses an alarm and it is time for the alarm slot, the network identifier poll is ignored and the node tries to transmit the alarm in network frequency (e.g., the base station may not hear the network identifier poll). If an acknowledgement is not received, it is transmitted in the backup frequency. If a time beacon is received when the node is waiting for the network identifier poll (started at back channel slot), both the packets (time beacon and network identifier poll) may be dropped. If it is time for the third time beacon and the node did not receive the other two time beacon, stop stack, go and receive the third time beacon in the backup frequency. If the network identifier poll is received within the timeout, the node picks a random number (range R), and transmits "NW ID Response" (after CSMA) in one of the back channel time slots (if back channel is not received in that time slot) in the network frequency (since it will not be used for any other communication. The default frequency may potentially wipe out async alarms). For example, if the node picks random number 5 and the back channel time slots are subdivided (big enough to fit a response packet+skew extra), then it would transmit a resp