Abstract:
A method for controlling a wireless terminal operating in a hibernation cycle alternating between a wake mode and a hibernation mode includes communicating with a first wireless network during a first waking period having a first duration, and with a second wireless network during a second waking period following the first waking period. The second waking period is extended to a second duration, greater than the first duration, responsively to detecting that the second wireless network is different from the first wireless network. Network information relating to the second wireless network is received during the second waking period.

Description:
RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 60/708,649, filed on Aug. 15, 2005, and U.S. Provisional Application No. 60/748,731, filed on Dec. 8, 2005. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to wireless communication, and particularly to methods and systems for controlling the wake-up period of wireless terminals that use hibernation protocols. 
     BACKGROUND 
     In some wireless communication applications, mobile wireless terminals alternate between a hibernation mode and a wake mode. In one typical example, the hibernation mode is substantially longer than the wake mode. Accordingly, networks that support such devices are referred to as a low duty cycle (LDC) networks, and the mobile terminals that operate in such networks are referred to as LDC terminals. LDC terminals are small-size communication devices used in a variety of position tracking, tagging, telemetry and similar applications. LDC terminals operate such that each terminal wakes-up to receive and transmit data for only a small percentage of the time. This low duty cycle operation minimizes the utilization of the air interface and the energy consumption from the terminal&#39;s power source. 
     SUMMARY 
     In some applications, wireless terminals have the ability to move (roam) between different wireless networks. In particular, a wireless terminal operating in a hibernation cycle sometimes wakes-up, registers with the network and begins communicating with a wireless network other than the network it had communicated with in the previous wake-up period. 
     In some embodiments, registration with a network other than the network most recently used triggers transmission from the new network to the wireless terminal of additional network information that would not be transmitted in consecutive registration procedures within the same network. The addition of this information to the communication between the terminal and the network requires more time. In order to enable the terminal to receive this network information, it is sometimes desirable to extend the length of the wake-up period of the terminal. 
     Embodiments of the disclosed method and apparatus control wireless terminals roaming from one wireless network to another. In some embodiments, a control module in the terminal detects that the current network is different from the network to which the terminal communicated in the previous wake-up period. If it is determined that the network to which the terminal is communicating in the current wake mode is not the same network to which the terminal was communicating in the previous wake mode, the control module extends the length of the wake mode to ensure that all of the desired data can be communicated before the end of the wake mode. 
     In some embodiments, the terminal monitors overhead messages broadcast by the wireless network. The overhead messages typically comprise a network identification (NID) number and/or a server identification (SID) number. In these embodiments, the terminal compares the NID and/or SID numbers with previously stored values to determine whether or not the network has changed. 
     In some embodiments, the terminal may, during the extended wake-up period, receive network information regarding the new network it has joined, such as an address of an application server with which the terminal is to communicate. 
     A wireless terminal and a wireless communication system that implements these control methods are also disclosed. 
     There is, therefore, disclosed a method for controlling a wireless terminal operating in a hibernation cycle alternating between a wake mode and a hibernation mode, including: communicating with a first wireless network during a first waking period having a first duration; communicating with a second wireless network during a second waking period following the first waking period; extending the second waking period to a second duration greater than the first duration responsively to detecting that the second wireless network is different from the first wireless network; and receiving network information relating to the second wireless network during the second waking period. 
     In an embodiment, the wireless terminal includes a low duty-cycle (LDC) terminal in an LDC network, and communicating with the first and second wireless networks includes applying an LDC service. 
     In another embodiment, one of the first and second wireless networks includes a home network of the wireless terminal, and the other of the first and second networks includes a foreign network with respect to the wireless terminal. In an alternative embodiment, the first and second wireless networks include foreign networks with respect to the wireless terminal. 
     In yet another embodiment, communicating with the first and second wireless networks includes registering with the respective wireless network. 
     In still another embodiment, detecting that the second wireless network is different from the first wireless network includes receiving a first identification (ID) number from the first wireless network during the first waking period, receiving a second ID number from the second wireless network during the second waking period, and detecting that the first ID number is different from the second ID number. 
     In an embodiment, receiving the network information includes receiving a dedicated message including an address in the second wireless network with which the terminal is to communicate. 
     Also disclosed is a wireless terminal, including: a transmitter configured to transmit information to first and second wireless networks; a receiver configured to receive information from the first and second wireless networks; and a control module configured to control the transmitter and receiver in a hibernation cycle alternating between a wake mode and a hibernation mode so as to communicate with the first wireless network during a first waking period having a first duration, to communicate with the second wireless network during a second waking period following the first waking period, to extend the second waking period to a second duration greater than the first duration responsively to detecting that the second wireless network is different from the first wireless network, and to receive network information relating to the second wireless network during the second waking period. 
     The disclosed method and apparatus will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram that schematically illustrates a wireless communication system, in accordance with an embodiment of the disclosed method and apparatus; and 
         FIG. 2  is a flow chart that schematically illustrates a method for controlling a wake-up period of a wireless terminal, in accordance with an embodiment of the disclosed method and apparatus. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG. 1  is a block diagram that schematically illustrates a wireless low duty-cycle (LDC) communication system  20 , in accordance with an embodiment of the disclosed method and apparatus. The LDC system  20  may operate as part of a conventional wireless network comprising, for example, a cellular network, a personal communication system (PCS) or any other suitable public or private wireless network. Different embodiments of the LDC system  20  can be adapted to use any wireless standard, protocol or air interface used by the conventional wireless network, such as cdmaOne, CDMA2000, 1xEVDO, UMTS, GSM or any other suitable standard. As such, the LDC system  20  can be adapted to operate on any frequency band being used by a conventional wireless network. 
     In the embodiment of  FIG. 1 , the system  20  comprises two wireless networks  24 , denoted  24 A and  24 B. The two networks are interconnected by a wide-area network (WAN)  28 , such as the Internet. Each wireless network  24  communicates with wireless terminals  32 . In the present example, two terminals are denoted  32 A and  32 B. Communication is performed via wireless base stations  42 , denoted  42 A and  42 B, which serve as wireless access points to each network  24 . In some embodiments, each wireless network  24  covers a certain geographical area, which may or may not overlap with coverage areas of other wireless networks (not shown). 
     Downlink messages transmitted using radio signals transmitted from the base station  42  to the terminal  32  are received, downconverted, filtered, demodulated and otherwise processed by a receiver  44 . Uplink messages transmitted from the terminal  32  to the base station  42  are modulated, upconverted, filtered and amplified by a transmitter  46  to produce an uplink signal. The uplink signal is then transmitted to the base station  42 . 
     Some LDC applications (such as tracking applications for tracking people, pets and property) make use of the position of the LDC terminal. In some embodiments, the terminal  32  uses a position sensor, such as a global positioning system (GPS) receiver  48 , to determine the position of the terminal  32 . The terminal  32  transmits this information to the base station  42 . In some cases, the terminal  32  receives and/or transmits information after it leaves the service area of one wireless network  24 A and enters the service area of another network  24 B, as will be described below. 
     A control module  50  in the terminal  32  performs all control and management functions of the LDC terminal  32 . In accordance with one embodiment of the disclosed method and apparatus, the terminal  32  operates in half duplex mode. Accordingly, the terminal  32  cannot transmit and receive at the same time. Therefore, among other functions, the control module  50  causes the terminal  32  to alternate between transmit and receive modes. The control module  50  also causes the terminal  32  to alternate between a wake mode and a hibernation mode, in accordance with a hibernation cycle synchronized between the terminal  32  and a base station  42  to which the terminal  32  is communicating. It should be noted that both the transmit mode and receive mode occur during the wake mode. In accordance with one embodiment of the disclosed method and apparatus, transmitting or receiving do not occur during the hibernation mode. 
     Generally, when in hibernation mode, most of the terminal&#39;s hardware functions are shut down to conserve battery power. In some embodiments, some of the hardware itself may also be shut down during hibernation mode, leaving only the hardware necessary for time-keeping and for waking the terminal at the next wake-up period. The time between consecutive wake-up periods (i.e., duration of the hibernation mode) can typically take any value from several minutes (or less) to several weeks (or even longer), depending on the application. 
     In particular, the control module  50  adapts the duration during which the terminal  32  is awake (referred to as a “wake-up period”) in response to the roaming status of the terminal  32 . The method of adaptation is explained in detail below. The control module  50  may be implemented using hardware, such as digital circuitry implemented using discrete components or within an integrated circuit (IC). Alternatively, the control module  50  can be implemented using software running on a microprocessor or using a combination of hardware and software elements. 
     In the embodiment of  FIG. 1 , each wireless network  24 A and  24 B comprises an LDC server  34 . The LDC server  34  performs various management functions associated with terminals  32  used in the network  24 . An application server  35  (separate and unique from the LDC server  34 ) runs the specific LDC application. For example, the application server  35  may comprise a web-server that displays the position of terminals  32  on a map and/or provides users of the application with certain control functions over the terminals  32 . The application server  35  may be located either inside or outside of the wireless network  24 . Typically, the application server  35  is the source of downlink messages transmitted to the terminals  32  in the wireless network  24 , and is the destination of uplink messages transmitted from the terminals  32  to the wireless network  24 . 
     The communication of each wireless network  24  with its terminals  32  is managed by a mobile switching center (MSC)  36 . Each MSC performs all switching and routing functions of messages to and from terminals  32  in its wireless network. Typically, when a the terminal  32  joins one of the wireless networks  24 , it performs a registration procedure with the MSC of this network  24 . For each terminal  32 , one of the wireless networks  24  is defined as its home network, although the terminal  32  may generally register and communicate with any wireless network in the system  20 . A terminal communicating with a wireless network different from its home network (sometimes called a “foreign network”) is referred to as a “roaming” or “visiting” terminal. A terminal communicating with its home network is referred to as a “local” terminal. 
     In accordance with one embodiment, each wireless network  24  includes two databases, namely a home location register (HLR)  38  and a visitor location register (VLR)  40 . Each HLR  38  keeps information related to all terminals  32  for which the specific wireless network  24  is the home network. At any given time, some of these terminals  32  may be registered with the home network, some may be turned off and others may be roaming (i.e., registered with a foreign wireless network). Each VLR  40  keeps information related to the roaming terminals that are currently registered with its wireless network  24 . When a terminal  32  moves from one wireless network  24  to another, relevant routing information is sent to the HLR of the terminal&#39;s home network, so as to enable downlink messages to be routed to it. When a terminal  32  registers with a foreign network, the VLR  40  of the foreign network is updated with routing information with respect to the home network. 
     Although the exemplary configuration of  FIG. 1  shows two wireless networks  24 A and  24 B, the system  20  in general may comprise any number of wireless networks  24 . Additionally or alternatively, each wireless network  24  typically comprises a plurality of base stations  42  and may comprise more than one MSC  35 . 
     In a typical transaction in which a downlink message is sent to a destination terminal  32 A, an application server  35 A in the destination terminal&#39;s home network  24 A sends a message addressed to the terminal  32 A. The destination terminal  32 A may be registered with its home network  24 A or it may be roaming. In the case in which the destination terminal  32 A is not roaming, the application server  35 A provides the downlink message to the LDC server  34 A, which in turn sends it to the MSC  36 A within its wireless network  24 A. The MSC  36 A determines, by querying its HLR, the appropriate routing information, and routes the downlink message to the destination terminal  32 A. If, however, the destination terminal  32 A is roaming in the network  24 A, the routing path goes through the local MSC  36 B (assuming that network  24 B is the home of destination terminal  32 A), to the foreign MSC  36 A via WAN  28 , and from there to the destination terminal  32 A. 
     In a typical uplink transaction, a source terminal  32 A initiates an unsolicited uplink message addressed to its home network application server  35 A (assuming the source terminal  32 A is not roaming). If the source terminal  32 A is currently registered with its home network, the uplink message is routed via the local MSC  36 A and the LDC server  34 A to the application server  35 A. If, on the other hand, the source terminal  32 A is registered with a foreign network  24 A, the MSC  36 A of the foreign network  24 A receives the uplink message, queries its VLR  40 A for the appropriate routing information to the source terminal&#39;s home network  24 B, for example, and routes the uplink message from the foreign MSC  36 A via the WAN  28  to the MSC  36 B of the terminal&#39;s home network  24 B and from there, via the LDC server  34 B of the home network to the application server  35 B. 
     In general, when a terminal  32 A initiates communication with a wireless network  24 A, it first performs a registration procedure with this network  24 A. In some embodiments, the terminal  32 A periodically renews its registration with the wireless network  24 A, in accordance with a predetermined registration time-out. In such cases, when the terminal  32 A wakes-up from hibernation, it checks whether or not the registration time-out has expired. If expired, the terminal  32 A re-registers with the network  24 A and resets the time-out. Certain events, referred to as “implicit registrations,” are sometimes considered as registrations for the purpose of resetting the registration time-out. For example, if the terminal  32 A sets up a traffic channel with the wireless network  24 A, this event is counted as an implicit registration. Communicating via a common channel, such as using short message service (SMS) messages, is typically not considered a registration. In alternative embodiments, the terminal  32 A registers with the wireless network  24 A each time it wakes-up from hibernation. 
     In some embodiments, after the terminal  32 A wakes-up, it monitors overhead messages broadcasted by the wireless network  24 A it intends to communicate with. The overhead messages typically comprise a network identification (NID) number identifying the wireless network and/or a system identification (SID) number identifying the MSC  36 A. 
     When a terminal first wakes-up after moving from one wireless network  24 B to another network  24 A, the terminal  32 A decodes the NID and/or SID numbers from the overhead messages and compares them to previously-stored SID and/or NID values. If a change is detected in these parameters, the terminal  32 A realizes it moved to a new network  24 A and initiates a registration procedure with the new network  24 A. Registration with a new network  24 A typically disregards the status of the registration time-out described above. 
     In some embodiments, there is a hierarchy between NID and SID such that NID is a subset of SID. In these cases, the terminal  32 A concludes that it is in a new network  24 A when either the SID has changed (regardless of the NID value) or when both NID and SID have changed. 
     In some embodiments, in response to the registration procedure with the new network  24 A, application server  35 A sends the terminal  32 A network information regarding the LDC network  24 A it has joined. For example, in some embodiments the network information comprises a dedicated downlink message comprising a new address for sending uplink LDC messages, such as the address of the relevant application Server  35 A. Additionally or alternatively, the application server  35 A and/or LDC server  34 A may send any other network information to the terminal  32 A upon its registration with a new network  24 A. 
     Because additional network information is sent from the application server  35 A, the registration procedure with a newly-joined network  24 A typically involves the transfer of more data than is the case with consecutive registration procedures within the same network  24 B. For this reason, when the terminal  32 A wakes-up and registers with a new wireless network  24 A (i.e., a network  24 A different from the network  24 B it registered with in the previous wake-up period), the control module  50 A extends the length of the wake-up period of the terminal  32 A, to allow for the additional data to be transferred. 
     In typical applications, the nominal duration of the wake-up period is on the order of 10-30 ms. When joining a new network, it is desirable for the duration of the wake-up period to be typically doubled or tripled. 
       FIG. 2  is a flow chart that schematically illustrates a method for controlling the wake-up period of a terminal  32 , in accordance with an embodiment of the disclosed method and apparatus. The method begins with the terminal  32 A operating in a synchronized hibernation cycle, as described above. At the appropriate time, the control module  50 A wakes up the receiver  44 A, the transmitter  46 A and/or other components of the terminal  32 A, at a wake-up step  60 . 
     After waking up, the control module  50  checks whether the current wireless network  24 A with which the terminal  32 A intends to communicate is the same or different from the wireless network  24 B with which it communicated in the previous wake-up period. This occurs at a network change checking step  62 . In some embodiments, the terminal  32 A monitors the overhead messages broadcasted by the wireless network  24 A and decodes the SID and/or NID numbers from these overhead messages. The control module  50 A then compares the decoded SID and/or NID identification numbers with the identification number or numbers received in the previous wake-up period. A change in these numbers may indicate a change of network. Alternatively, any other suitable mechanism can be used by the terminal  32 A for this purpose. 
     If the control module  50 A concludes that the current wireless network  24 A is the same as in the network detected in the previous wake-up period, it continues the normal wake-up/hibernation cycle, at a normal hibernation step  70 . At hibernation step  70  and as part of the normal hibernation cycle, the terminal  32 A may renew its registration with the wireless network  24 A, as explained above. The control module  50 A wakes up the terminal  32 A at the next wake-up period and the method returns to wake-up step  60  above. 
     If, on the other hand, the control module  50 A concludes that the current wireless network  24 A is different from the network  24 B previously detected in the previous wake-up period, the terminal  32 A registers with the new network  24 A at a new registration step  64 . 
     In response to the registration with the new network  24 A, the application server  35 A sends a dedicated downlink message to the terminal  32 A, as described above. In order to allow for the additional data transfer required for receiving this message, the control module  50 A extends the length of the wake-up period, at an extension step  66 . 
     During the extended wake-up period, the receiver  44 A of the terminal  32 A receives downlink data sent to it from the base station  42 A, at a communication step  68 . In some embodiments, the downlink data comprises the dedicated downlink message carrying the additional network information regarding the new LDC network  24 A. In addition to receiving the downlink data, the terminal  32 A may perform any additional communication with the new network  24 A through the base station  42 A during the extended wake-up period. These additional communication functions typically depend on the specific functionality of the LDC service carried out by the system  20 , and are outside the scope of the present patent application. 
     Having completed the communication functions for the present wake-up period, the terminal  32 A returns to hibernation mode in accordance with the normal hibernation cycle, at a hibernation step  70 . The length of the wake-up period is reset to the default value assuming no network change. When the time comes for the terminal to wake up again, the method returns to wake-up step  60  above. 
     Although the methods and systems described herein relate mainly to controlling the wake-up period of LDC terminals, these methods and systems can also be used to control wake-up periods in other types of wireless terminals that operate in a hibernation cycle. Such terminals may include, for example, pagers, cellular telephones, telemetry transponders and radio-frequency identification (RFID) transponders. 
     It will thus be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.