Patent Publication Number: US-2005117552-A1

Title: Device and method for performing page scan on a communication channel

Description:
BACKGROUND OF THE INVENTION  
      The present invention relates to performing page scan on a physical channel by listening to it.  
      The recent development in mobile communications has significantly increased the versatility of subscriber terminals. A subscriber terminal has constantly been evolving from a mobile phone towards an intelligent device, providing the subscriber with a variety of services.  
      The developments in local communication options, especially in those utilizing low power radio frequency communications, have lead to an increasing choice of different peripherals or accessories being wirelessly connectable to the subscriber terminals. A remarkable market share of such local communication options has been obtained by Bluetooth devices. An example of such a peripheral or accessory is a wireless headset. In order to be able to communicate with the subscriber terminal, the headset has to have a connection with the subscriber terminal.  
      One way to establish a connection between a peripheral or accessory and the subscriber terminal is that the subscriber terminal is slave and the accessory or peripheral is master. Using the wireless headset as an example, the details for the establishment of a Bluetooth connection can be found in the Bluetooth standard; e.g., in Bluetooth specification 1.2. In the standard there is defined how the slave has to perform a page scan on a physical channel by listening to it, and how it should respond to the page detected.  
      As noted in the referred version of the specification, in choosing the manner in which the page scan is performed, a trade-off between current consumption and fast connection set-up has to be performed.  
      It has turned to be particularly problematic in a subscriber terminal to use the fast connection set-up, because of the larger current consumption which has always been a problem in a mobile device getting its operating power from a rechargeable battery. However, using the slow connection set-up would in some cases be particularly annoying to the user. In some cases, the slow connection set-up might even lead to missing another connection, if the accessory or peripheral is used on a first communication channel to command the subscriber terminal to accept a connection on a second communication channel.  
      A rather good introduction to the technical background of connection set-up related page and page scan procedures in Bluetooth ad-hoc wireless networks can be found in published US patent application 2003/0012173 A1.  
     SUMMARY OF THE INVENTION  
      The present invention is therefore directed toward improving a device and method for performing page scan on a first communication channel by listening to it.  
      By selecting a shorter interval between two page scans when a connection on the second communication channel is being initiated, and a longer interval between two page scans after the connection on the second communication channel has been initiated, the average time for a connection set-up on a first communication channel can be shortened, in cases when a connection on the second communication channel is being initiated. This may result in enabling a faster connection set-up and consuming less current.  
      By doing this, current consumption outside the initiation of a connection on the second communication channel can be reduced from the magnitude it would have if the shorter intervals were also used in these instances.  
      An example of such initiating of a connection on the second communication channel is an incoming call from the cellular network. A possible use case is establishing a connection between a wireless headset and a subscriber terminal.  
      Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Invention and the Figures.  
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       FIG. 1  shows a block diagram of a subscriber terminal wirelessly connectable to an accessory or a peripheral via a first connection channel CH 1  and to a cellular network via a second communication channel CH 2 .  
       FIG. 2  is a flow diagram showing an example of including the changing of a timer used in performing page scan. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIG. 1  shows a block diagram of a subscriber terminal  100  wirelessly connectable to an accessory or a peripheral  111  via a first connection channel CH 1  and to a cellular network  121  via a second communication channel CH 2 .  
      The subscriber terminal  100  is wirelessly connectable to a peripheral or an accessory  111 , such as a wireless headset. Therefore, the subscriber terminal  100  includes communication parts  101  for communication with the peripheral or accessory  111  over a first communication channel CH 1 . Preferably, the first connection channel CH 1  is a local communication channel, such as a Bluetooth communication channel. In the Bluetooth communication channel, the communications are performed using a low-power radio frequency transmitter-receivers. In the following description it is assumed that the communication channel CH 1  is a Bluetooth communication channel.  
      Further, the subscriber terminal  100  includes communication parts  102  for communication with the cellular network  121  over a second communication channel CH 2 . In particular, the subscriber terminal  100  can be in connection with an element  123 , such as a gateway or a switching center  123  in the cellular network  121  via a base station  122 . The communication between the cellular network  121  and the subscriber terminal  100  takes place over a second communication channel CH 2 . The second communication channel CH 2  may be as defined in any one of the relevant standards; in particular for GSM, GPRS, or UMTS. Typically, communications on the communication channel CH 2  is performed in the microwave frequency range.  
      The subscriber terminal further includes a central unit  103  and memory  104 . According to a first embodiment of the present invention, in the central unit there are defined the first timer  151  and the second timer  152 . The first and second timers  151 ,  152  are intended for defining intervals between two page scans. The first timer  151  defines a first interval T GAP  ( 108 ), whereas the second timer  152  defines a second interval T GAP  ( 106 ).  
      For a Bluetooth device, the most advantageous value for the second interval T GAP  ( 106 ) is approximately 100 ms, and for the first interval T GAP  ( 108 ) approximately 2.56 seconds. These values have been specified in BLUETOOTH SPECIFICATION, Version 1.2 [vol 3] as timer values for Interlaced scans. Of course, other suitable values for the first and second intervals T GAP  ( 108 ), T GAP  ( 106 ) can be used as well.  
       FIG. 2  is a flow diagram showing an example including the changing of a timer used in performing page scan.  
      In step J 11 , it is tested by the central unit  103  whether or not there is an incoming call. Because the central unit  103  controls communication parts  102  for communication with the cellular network  121  over the second communication channel CH 2 , it can detect when the cellular network  121  is paging the subscriber terminal  100 .  
      If there is an incoming call, then in step J 13  it is checked whether the using of communication parts  101  for communication with the peripheral or accessory  111  over a first communication channel CH 1  is enabled. If it is not enabled, the control is returned to step J 11 .  
      In step J 15  it is checked whether an entry  161  showing that an accessory or peripheral  111  is present has been previously defined. Preferably, this entry  161  is stored in the memory  104 . If the entry  161  has not been defined, the control is returned to step J 11 .  
      In step J 17 , the fast connection setup is enabled. In other words, the second timer  152  for defining a second interval T GAP  ( 106 ) between two page scans is selected to be used in the communication parts  101  for communication with the peripheral or accessory  111  over the first communication channel CH 1 .  
      In step J 19  it is checked whether the incoming call has been accepted or a hands-free connection established. In a positive case, in step J 23  the fast connection setup is disabled. In other words, in step J 23  the first timer  151  for defining a first interval T GAP  ( 108 ) between two page scans is selected to be used in the communication parts  101  for communication with the peripheral or accessory  111  over the first communication channel CH 1 . After step J 23 , the control is returned to step J 11 .  
      In the opposite case, that is if the incoming call has not been accepted nor a hands-free connection established, in step J 21  it is checked whether the incoming call is still ringing. If the incoming call is not ringing anymore, the control is passed to step J 23  where the fast connection setup is disabled. If the incoming call is still ringing, the control is passed back to step J 19 .  
      In order to ensure that the user of the peripheral or accessory  111  only gets connected to the right subscriber terminal  100  and not to another subscriber terminal in the area, the entry  161  may identify the peripheral or accessory  111  that correspond to the subscriber terminal  100 . Further, in the peripheral or accessory  111 , there may be a similar entry identifying the right subscriber terminal  100  corresponding to the peripheral or accessory  111 . In this manner, the peripheral or accessory  111  can be in a standby mode having a very low power consumption. In such a mode, the peripheral or accessory  111  is powered on but has no Bluetooth connection.  
      In the example of a wireless headset, when the subscriber terminal  100  is paging the user (i.e., ringing), the user can hear the ringing tone and pick up the headset and then push the accept call button. At that time, the headset tries to establish the connection and to accept the call.  
      Using the faster connection set-up, a connection on the first communication channel CH 1  can be performed approximately about 65% faster than using a normal connection set-up.  
      The skilled person appreciates that the present invention is not limited by the examples of using a GSM or UMTS subscriber terminal for receiving a call. Indeed, although the present invention has been described with reference to specific embodiments, those of skill in the art will recognize that changes may be made thereto without departing from the spirit and scope of the present invention as set forth in the hereafter appended claims.