METHOD AND SYSTEM FOR POWER EFFICIENT DYNAMIC WIRELESS

COMMUNICATIONS

FIELD OF THE INVENTION

[0001] The present application relates to a method and system for wireless communication and in particular to the establishment of a dynamic network for transponders, sensors or other similar electronic components.

BACKGROUND

[0002] Tags, such as, radio frequency identification tags are used in a variety of industries and for a variety of purposes. For example, these tags can be used in transportation industries to monitor temperature, shock, vibrations, etc. of goods being transported. They can also be used for product management, inventory control, home automation and a variety of other applications which would be known to those skilled in the art.

[0003] In present systems, a tag needs to communicate with a reader. Readers therefore need to be strategically placed in order to ensure that they receive the maximum coverage required by the network. Further, the range of the network is determined by the communication capabilities of the tags. A tag that needs to transmit farther needs to use more battery resources in order to increase the signal strength of the transmitted signal. This can be undesirable for many tags in the industry since these tags are remote and therefore require battery power to operate. Further, power limits exist based on radio standards such as those set by the European Telecommunications Standards Institute (ETSI) and the Federal Communications Commission (FCC). Also, increasing power can eventually result in increasing the cost of the equipment and especially in that of the battery which is one of the costliest components of the transponder. Even with power increases, inevitably tags may fall outside of the range of detection of the reader.

[0004] Other problems with creating networks where tags communicate only with a reader are that the tags will intermittently be moved and therefore may fall outside the

range of a reader. Also, the tag may be moved behind an obstacle such as a pillar or other structure that is either fixed or temporary, and this may prevent the tag from communicating with the reader.

[0005] While several solutions exist that provide communication between readers and tags via communication bridges to attain more distant tags, increased consumption of energy is typically required. Bridging utilized to reach remote equipment requires a source of continuous uninterrupted energy.

SUMMARY

[0006] The present method and system overcome the deficiencies of the prior art by providing for a power efficient dynamic architecture that is created based on the presence of tags within range of the reader and of other tags. Tags may be used as communication bridges. The present method and system provides for reduced battery consumption by placing tags in a slotted communications mode once they are established in the network. Furthermore, tags can become masters to other tags; thereby creating a communications bridge to tags that may have been out of range of the reader initially.

[0007] Specifically, in the present method and system, the reader establishes communications with tags within range of the reader. The reader can then query these tags to see if any other tags are detected and intelligence either at the reader or at the tag level can determine that the tag can and/or should become a master tag to further slave tags. A communications protocol for establishing and varying the network is described in more detail below.

[0008] The present application therefore provides a method for power efficient dynamic wireless communications in a system having a reader and a plurality of tags, each of said plurality of tags having at least a transmitter adapted to transmit data, a receiver adapted to receive data, a power supply, a processor and memory, the method comprising the steps of: detecting, at the reader, one or more of said plurality of tags and assigning said each said detected one or more of plurality of tags to be a slave tag; monitoring, at each

slave tag, receipt of a paging signal from one or more of said plurality of tags; connecting said one or more of said plurality of tags from which a paging signal was received in said monitoring step, said connecting step including: converting the slave tag receiving the paging signal to a master tag; and assigning each said one or more of said plurality of tags from which a paging signal was received in said monitoring step to be a slave tag; and recursively performing said monitoring and connecting step at each said slave tags and each said master tags.

[0009] The present application further provides a system for power efficient dynamic wireless communications comprising: a reader; and a plurality of tags, each tag in said plurality of tags having: a transmitter adapted to transmit data; a receiver adapted to receive data; a power supply; a processor; and memory wherein said reader is adapted to detect and establish communications with one or more of said plurality of tags, said one or more tags becoming slave tags, and wherein said slave tags are further adapted to detect and establish communications with one or more of said plurality of tags that is not already a slave tag, the slave tag becoming a master tag and the detected one or more of said plurality of tags becoming slave tags.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present application will be better understood with reference to the drawings in which:

Figure 1 is a block diagram showing an exemplary network having a number of tags associated with a reader;

Figure 2 is a block diagram illustrating the tags and reader of Figure 1 in which connections have been made;

Figure 3 is a block diagram illustrating the system of Figure 1 in which the tags had been assigned states;

Figure 4 is a block diagram illustrating the system of Figure 3 in which initial connections had been made;

Figure 5 is a block diagram illustrating the system of Figure 4 in which secondary connections are in the process of being established;

Figure 6 is a block diagram illustrating the system of Figure 5 in which the secondary connections are now established;

Figure 7 is a block diagram illustrating the system of Figure 6 in which further connections are considered;

Figure 8 is a block diagram illustrating the system of Figure 6 in which further connections are established;

Figure 9 is a block diagram illustrating the system of Figure 8 in which further connections are considered;

Figure 10 is a block diagram illustrating the system of Figure 9 in which further connections are established;

Figure 11 is a communications flow diagram between a tag, a second tag and a reader;

DETAILED DESCRIPTION OF THE DRAWINGS

[0011] The present application is illustrated with reference to radio frequency identification tags. However, the term "tag" will be used in this application to refer to radio frequency identification transponders, other electronic components such as wireless sensors, wireless data recorders, etc. or other devices that could communicate in accordance with the present system and method. The present application is not meant to be limiting to any specific type of tag, and any tag with a minimum of a receiver, transmitter, memory and processing capabilities could be used in association with the present system.

[0012] Reference is now made to Figure 1. Figure 1 illustrates an exemplary system with a reader 110 and eleven tags, labeled as tags 120, 122, 124, 126, 128, 130, 132, 134, 136, 138 and 140. These tags will be collectively referred to as tags 115. The exemplary system with eleven tags is not meant to be limiting and other systems with more or less tags are possible. Further, other systems with more readers than one are also possible, as described below.

[0013] Reader 110 is a device capable of communicating and receiving information from tags 115. In a preferred embodiment, reader 110 is in a fixed location and is connected to a power supply. Examples include an inventory system in which reader 110 is affixed within a warehouse and connected to a building power supply. Another example is in a transportation system in which the reader is connected within a transport truck and connected to the truck's power supply. The present system and method is not meant to be limiting to any specific type of reader or any specific power source, however, and one skilled in the art will appreciate that various readers could be used, including those operated with batteries.

[0014] As indicated above, tags 115 at minimum include a receiver, transmitter, memory and processor. Further, tags 115 include a power source, which in most cases will be a battery. Tags 115 can be affixed to various items being tracked or within various locations. Examples include being affixed to inventory such as pallets being transported, affixed to medical equipment, within the inside of a trailer of a transport truck or within the hold of a ship. Other examples of where the tags could be used would be evident to those skilled in the art.

[0015] In the embodiment of Figure 1, reader 110 includes a range 150 that it can read information from tags within. Range 150 is typically created by the signal strength generated by tags 115. Signal strength is directly correlated to battery life. Therefore, in systems where battery life of tags is important, the signal strength will be lower when transmitting.

[0016] As illustrated in Figure 1, tags 128, 130, 134, 136, 138 and 140 are outside of the zone 150 that reader 110 is capable of receiving signals within.

[0017] Further, an obstacle 155 is in the way between tag 132 and reader 110. This may prevent reader 110 from detecting tag 132.

[0018] Reference is now made to Figure 2. Figure 2 illustrates one exemplary way of connecting the network to communicate with reader 110. In the example of Figure 2, tags 120, 122, 124 and 126 communicate directly with reader 110. Further, tag 120 becomes a master for communication with a slave tag 140. Similarly, tag 126 becomes a master for communication with slave tag 132 and with tag 128. Tag 128 communicates with tag 130 and therefore is also a master. Further, tag 130 is a master since it communicates with tags 134, 136 and 138, which are all slave tags.

[0019] As illustrated in Figure 2, tag 132 can communicate with reader 110 regardless of the obstacle being in the way by becoming a slave tag to tag 126. In accordance with the example of Figure 2, tags 120, 126, 128 and 130 become bridges for communication with a reader 110.

[0020] The method of establishing this network is discussed below. Further, the dynamic relationship of the tags to the reader and to other tags is also discussed.

[0021] While the prior art discusses several methods and systems for communicating between a reader and tags that uses tags as communication bridges, the prior art solutions require significant battery resources on the communication tags for the bridging. Further discussed below is an energy efficient dynamic bi-directional communications protocol. This is accomplished by creating a slotted communications mode in which the duration of data transmission and reception is very limited.

[0022] As discussed in the example above and with reference to the following figures, a tag can be in one of three states. These are: not connected: a tag that does not yet belong to a network is considered to be not connected; slave: a tag that has no tags reporting to it. A slave tag can communicate with a reader directly or with a master tag master: a tag that also has other tags reporting to it. A master tag can communicate with a reader or with other master tags.

[0023] Reference is now made to Figure 3. Figure 3 shows that all tags are not connected initially. In this scenario, all tags are sending a periodic message indicating that they exist.

[0024] Referring to Figure 4, reader 110 detects tags 120, 122, 124 and 126 and connects with these tags and places these tags in slave mode.

[0025] As will be appreciate by those skilled in the art, intelligence in the present network can exist either on the reader 110 or on tags 115. The present application is not meant to be limiting to placing the intelligence on either of these two, and in the examples below, the intelligence being in the reader is only meant for illustrative purposes.

[0026] As illustrated in Figure 4, reader 110 detects tags 120 to 126, and places them in slave mode. Tags 120 to 126 then are able to see if they can detect any tags on their own. Tags 120 and 122 detect tag 140 and tag 126 detects tags 128 and 132.

[0027] Again, depending on where the intelligence is, the tag detection can be reported to reader 110 which can then direct tags to become masters to the detected tags.

[0028] In the example of Figures 5 and 6, both tags 120 and 122 detected tag 140. A determination can be made by reader 110 to indicate which of tags 120 and 122 will become the master. This determination can be based on a variety of criteria and in a preferred embodiment is based on the received signal strength at the receiving tag.

[0029] Therefore, for example, in Figures 5 and 6, tag 120 detected tag 140 with a greater signal strength than that detected by tag 122, and therefore reader 110 indicates to tag 120 that it should become the master to tag 140. As illustrated in Figure 6, tag 140 thus becomes the slave to tag 120.

[0030] Similarly, tag 126 detected both tags 128 and 132. Since only tag 126 detected these tags, tag 126 becomes the master to tags 128 and 132.

[0031] The tags can then periodically check to see whether other tags are located within the network.

[0032] Reference is now made to Figure 7. Figure 7 shows that tag 128 detects tag 130 and in one embodiment reports this back to reader 110. Reader 110 can then instruct tag 128 to connect with tag 130 creating a master and slave relationship between these two tags. This is illustrated in Figure 8.

[0033] The tags in the network continue to scan for further tags and tag 130 in the example of Figure 9 detects tags 134, 136 and 138 and reports this back to reader 110 in one embodiment.

[0034] In Figure 10, tag 130 is illustrated as becoming the master to tags 134, 136 and 138.

[0035] The examples of Figures 3 to 10 show the dynamic creation of a network. The creation of the network is based on tags becoming communication bridges, therefore eliminating the limitations of the detection zone 150 for reader 110 and the problems with obstacles 155 between tags 115 and reader 110.

[0036] In order to effectively eliminate the possibility of collisions between multiple tags transmitting at the same time, and further to save battery resources, in a preferred embodiment of the present application tags are synchronized and are permitted to operate in a slotted mode. By this means, the tags are assigned a slot within which they are permitted to transmit and further a slot in which they can expect to receive data. The goal of this synchronization is to create temporary windows for communication and to leave inactive tags outside of these windows. As will be appreciated by those skilled in the art, the duration and period of these temporary windows is a system parameter that can be set

according to the needs of the network. A shorter period between communications from a tag or longer frames within the communication window will drain battery life of the tags more quickly. However, it may be required depending on the application. The parameter can be set according to a desired balance of the amount of data, reaction time and capacity of batteries available.

[0037] In accordance with the present system and method, global synchronization exists. In other words, each tag within the network is assigned a unique communication frame, thereby ensuring that collisions during regular communication do not occur.

[0038] As will be explained in more detail with reference to Figure 11 below, a reader that detects tags assigns these tags to become slaves and allocates to them a period of transmission as well as a precise temporary window in which to transmit.

[0039] As a reader assumes responsibility for tags, it synchronizes them by assigning temporary windows to the tags. In a preferred embodiment, the temporary window is a coupled window consisting of an up-link transmission from the tag to the reader or to a tag closer to the reader. The second part of the temporary window is an acknowledgement of delivery or an order to the tag.

[0040] The temporary windows are assigned so that the totalities of the coupled temporary windows are as short as possible. Master tags also synchronize their slave tags in a way that is identical to the way a reader synchronizes tags. The intelligence of this can come either from the reader which can assign the slave tags with time slots, or from the master tags if they are given a period of time within which to assign windows. Thus, master tags need to communicate with all of their slave tags as well as communicate with their master tag or the reader. Further, slave tags only have one temporary window to communicate with the reader or the master tag and the duration of this activity is very short, resulting in better battery life.

[0041] The position of temporary windows can be optimized in such a way that slave tags can transmit sequentially to their master. Thus, tags 134, 136 and 138 from Figure 2 could have sequential windows when communicating with their master tag 130. In other words, in one example, tag 134 communicates to tag 130 during its time slot up-link portion, and listens for an acknowledgement from tag 130 during the down-link portion of the communication slot. Once this ends, tag 136 can start communicating with tag 130. In this way, tag 130 receives, in short sequential order, communications from all of its slave tags.

[0042] Further, optimization can exist to ensure that tag 130 transmits to master tag 128 soon after it has received all of the data from tags 134, 136 and 138, and tag 128 can then transmit immediately or very soon after to tag 126, which is then optimized to send data to reader 110 shortly thereafter. In this way, data from tags 134, 136 and 138 will arrive at the reader very quickly.

[0043] As will be appreciated by those skilled in the art, a command then transmitted from reader 110 to, for example tag 134, will only be propagated in the next communications cycle.

[0044] Also, data speed can be altered based on the protocol used. Thus data speed could be faster from the reader to the tags if the inverse to the above is used. Also, doubling the query could result in fast data in both directions.

[0045] In the preferred embodiment of the present system and method, all tags listen for a long duration to detect the presence of non-connected tags. This can, for example, be one second in one embodiment. If master or slave tags detect tags that are not connected, they transmit this information to the reader, and the reader consequently re-defines a new architecture and distributes orders for the not connected tags to be connected to the network. As indicated above, this can be based on received signal strength if the not connected tag is detected by multiple tags.

[0046] The duration of the listening period of master and slave tags is preferably greater than or equal to the transmission period of tags that are in the not connected mode, and can be determined by network and battery requirements.

[0047] Depending on the tags that are being used, various frequencies can be assigned to the tags. At certain frequencies, multiple channels are also available to tags, and it is envisioned that the use of multiple channels can be beneficially used by the present method and system. For example, if a 2.4 gigahertz frequency band is used by a WiFi or Bluetooth network, 16 channels are available.

[0048] In one embodiment of the present application, tags that are not connected can use a first channel to transmit. Tags that are connected can use a different channel to transmit.

[0049] Further, in an alternative example, each master tag can have its own channel. Thus, in the examples of Figure 3, no tags are connected and therefore all the tags transmit on channel 1 that they are not connected. In Figure 4 reader 110 detects tags 120, 122, 124 and 126 and when connecting these tags and placing them into slave mode, it tells these tags to transmit on channel 2.

[0050] As will be appreciated by those skilled in the art, tags 120, 122, 124 and 126 will still need to have a listening period in channel 1 to detect additional not connected tags.

[0051] Thus tag 126 detects tags 132 and 128 on channel 1 and relays this information to reader 110 in channel 2 during its allocated time slot. In the response time slot of the present or the next time cycle, reader 110 can tell tag 126 to become a master and to connect tags 132 and 128 as slaves. Further, reader 110 can tell tag 126 to perform communications between it and its slaves on channel 3.

[0052] Tag 128 then scans channel 1 to see if it can receive information from any non- connected tags and it receives information from tag 130. This information is relayed on

channel 3 to tag 126 and on channel 2 to reader 110. Reader 110 can then tell tag 128 to become a master to tag 130 and tag 130 to become a slave. Further, it can tell tag 128 to communicate with tag 130 on channel 4.

[0053] The above can then be implemented until all of the channels are used up. As will be appreciated, reader 110 can use various algorithms to allocate channels to tags in various parts of the network in order to try to minimize the possibility of interference and possible collisions.

[0054] In a further embodiment, multiple readers can be used. These readers could be interconnected directly or through tags to create an outside communication link. For example, in the case of tags used for the monitoring of shipping, if several trailers are individually equipped with a reader and several tags, and these trailers are parked in a storage yard, networks could be created between the tags and readers. Each one of the trailers can create a communication link. For example, fixed equipment in the field could be used as a communication relay to computers, the Internet or other network resources.

[0055] In one embodiment with multiple readers, it is desirable to slightly offset the transmission/reception period in relation to other readers. In this way, if two readers are placed adjacent to each other or close to each other and thus the tags are transmitting to the reader, the collision of two signals that are close to each other in one time cycle will not occur in a subsequent time cycle and thus each tag will eventually be able to communicate with its reader.

[0056] Reference is now made to Figure 11. Figure 11 shows the example of one reader having two tags. The tags are labeled 126 and 128 and are configured initially as seen in Figure 3. Tag 126 sends a signal indicating that it is not connected with the purpose that another tag or a reader will hear this signal. The signal is labeled signal 1110 in Figure 11.

[0057] Reader 110 hears signal 1110 from tag 126 and sends an acknowledgement 1112 back. Acknowledgement 1112 includes a number of parameters for tag 126. These can include an order for tag 126 to go into slave mode, an order to change channels for communication, along with synchronization parameters for the time slot in which tag 126 should communicate.

[0058] Tag 126 then sets the parameters for the cycle time within which to communicate and at the next cycle frame window sends a frame of information. This frame includes any data that the tag should send. This could include the temperature of the tag's environment, vibrations detected, the position of the tag or any other purpose for which the tag exists. This is sent in signal 1114.

[0059] Reader 110 acknowledges signal 1114 with signal 1116. Further, signal 1116 can include a command to go to channel 1 and listen for unconnected tags.

[0060] When tag 126 goes into a listening mode it detects a "here I am" message 1120 from tag 128. In the next cycle for communications for tag 126, tag 126 sends its cycle communication data along with the fact that it has detected tag 128 in message 1122.

[0061] Reader 110 acknowledges message 1122 in message 1124, and sends information to connect to tag 128. This could include telling the tag 126 to go into a master mode and tag 128 to go into a slave mode, the communications channels that should be used for communications, and the synchronization parameters for tag 128.

[0062] This information is then sent from tag 126 to tag 128 in message 1128. Thereafter, communication between tags 126 and 128 is allocated to fall within a window.

[0063] Tag 128 in message 1130 sends its cycle communication to tag 126 and tag 126 acknowledges this in message 1132. Further, tag 126 then sends its cycle communication to reader 110 in message 1134. Message 1134 includes information for tag 126 along

with the cycle communication from tag 128, along with any other information that tag 128 may have.

[0064] This cycle communication 134 is acknowledged from reader 110 in an acknowledgement message 1136.

[0065] In this way, the network is established, each tag is given a slot within which to communicate and new tags can be detected, channels assigned, tags assigned either slave or master mode, etc.

[0066] The frame size in one embodiment of the present application includes enough bytes for multiple tags. Thus the situation of tag 126 from Figure 2 having to send information about tags 128, 132, 130, 134, 136 and 138 in a cycle slot will be accommodated. For example, each frame can have 250 bytes which is enough for 16 tags in one embodiment. If a master has more than 16 tags as slave tags, additional slots can be allocated to that tag for communications to ensure that the tag has enough bandwidth to communicate all the information about the slaves that are connected to it. In a preferred embodiment, the additional slot is consecutive to the originally assigned slot.

[0067] A slave in the present application will therefore be asleep for most of its life, thereby saving battery time. With a 250 byte slot, the transmission time can be fairly short (in the order of milliseconds). If the information is required every thirty minutes from a tag, the cycle time can be set to, for example, 15 minutes. Thus the tag is asleep for almost the entire 15 minutes with the exception of a brief time period to wake up and transmit information in a time slot and then listen in a fixed time slot.

[0068] The tag will also need to be awake to monitor whether other tags that are not connected can be heard by that tag. This, however, can be still set to a fairly short time period. For example, one second every minute is dedicated to listening to see if other tags are not connected. This parameter can be set based on battery life considerations and the reliability of connection requirements of the network. The example of Figure 11 is

not meant to be limiting but merely shows exemplary communications that could exist between a reader and various tags.

[0069] The world of RPID and wireless communications in general is not entirely reliable. Wireless communication is affected by real conditions and the environment in which the transmissions take place. To maximize reliability, the most frequently used method is to raise the power of the equipment in order to increase the read range. There is always a power limit that is dependant on radio standards. Additionally, equipment which may be near a metal obstacle, for example, would probably have its normal transmission range decreased. This may result in an inability to communicate with a distant reader even if power is increased.

[0070] The present method and system, rather than moving towards the above mentioned expensive solution that requires more power, provides for the implementation of a dynamic network that allows low emission power while still permitting communication despite an obstruction being in the way and for communication with tags that are out of the range of the reader itself.

[0071] If, in the above system, a tag is removed, it will be detected by the reader to not be communicating any more. Furthermore, some tags themselves will not receive any acknowledgements and will realize that they are no longer connected and go back into a not connected mode. The network will then dynamically reconfigure itself based on the above, by having the unconnected tags send "here I am" messages and having connected tags or the reader detect the "here I am" messages and re-establishing the network. Thus, the present network is also robust and allows for the possibility of tags moving, obstacles being placed between the reader and the tag, tag failures in part of the network or other conditions which may cause tags to become disconnected.

[0072] The above-described embodiments are meant to be illustrative of preferred embodiments and are not intended to limit the scope of the present application. Also, various modifications, which would be readily apparent to one skilled in the art, are

intended to be within the scope of the present application. The only limitations to the scope of the present application are set forth in the following claims.