Abstract:
A system for effecting communication between first and second radio transceivers, comprises a communicator for effecting communication between the first and second radio transceivers over a first channel; a determiner for determining the distance between the transceivers, and for determining if the distance falls below a predetermined threshold; and a channel charger responsive to a positive determination, for effecting direct mode communication between the transceivers over a second channel.

Description:
FIELD OF THE INVENTION 
   This invention relates to a method of communicating between first and second radio transceivers. This invention relates also to a system, and to a radio transceiver. 
   BACKGROUND OF THE INVENTION 
   Various radio channel types exist today for use by portable radio transceivers, global system mobiles (GSM) speech channels, general packet radio service (GPRS), Bluetooth and wireless local area network (WLAN) being examples of such channel types. Furthermore, the universal mobile telephone system (UMTS) allows the transfer of audio-visual information in both directions between portable radio transceivers. The term now adapted for portable radio transceivers of the UMTS standard is mobile station (MS), and this term is used hereafter to describe a mobile radio transceiver capable of communicating in any system. 
   With many MSs being equipped to communicate with two or more different channel types, it has become common for a user of an MS to have to decide which type of communication channel to use, which can constitute an inconvenience. 
   SUMMARY OF THE INVENTION 
   According to a first aspect of the invention, there is provided a method of communicating, the method comprising: effecting communication between first and second radio transceivers via a telecommunications network over a first channel; determining the distance between the first and second radio transceivers; determining whether the distance between the two transceivers meets a predetermined threshold; and in response to a determination that the threshold is met, effecting direct mode communication between the first and second radio transceivers over a second channel. 
   The invention also includes a radio transceiver, comprising: a communicator for communicating with a remote radio transceiver via a telecommunications network over a first channel; a determiner for determining the distance between the transceiver and the remote transceiver, and for determining whether the distance meets a predetermined threshold; and a channel charger, responsible to a determination that the threshold is met, for effecting direct mode communication between the transceiver and the remote transceiver over a second channel. 
   The second channel may have a greater bandwidth than the first channel and the first and second channels may be of different channel types. The method may include, prior to the effecting direct mode communication step, estimating the quality of the second channel. The determining steps may be carried out at the first radio transceiver and the distance determination step may include determining the locations of the first and second radio transceivers. 
   The location determination may involve a satellite-based position system or may involve triangulating from plural fixed radio transceivers, preferably forming part of the telecommunications network. 
   The direct mode communication step may be effected only if a bandwidth or other service demand exceeds the capability of the first channel. 
   Moreover, the threshold can be dependent on, preferably equal to, the sum of the radio coverage of the first and second radio transceivers. 
   The invention also extends to a system for effecting communication between first and second radio transceivers, comprising: a communicator for effecting communication between the first and second radio transceivers over a first channel; a determiner for determining the distance between the transceivers, and for determining if the distance meets a predetermined threshold; and a channel charger responsive to a determination that the threshold is met, for effecting direct mode communication between the transceivers over a second channel. 
   The invention will now be described, by way of example only, with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic drawing of a mobile station according to one aspect of the invention; 
       FIG. 2  is a schematic diagram of a telecommunication system according to one aspect of the invention and including the mobile station of  FIG. 1 ; 
       FIG. 3  is a flow chart illustrating operation of the mobile station of  FIG. 1 ; and 
       FIG. 4  is a chart showing signalling effected according to one embodiment. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   Referring to  FIG. 1 , a first mobile station (MS)  10  comprises generally a housing  11 , an antenna  12 , which is connected to transmit and receive circuitry  13 , and a central processing unit (CPU)  14 . The CPU  14  is connected to the transmit and receive circuitry  13  in four parallel paths  15 - 18 , each path including a respective one of a Bluetooth module  19 , a UMTS speech channel module  20 , a WLAN module  21  and a UMTS audio-visual module  22 . A database  24  containing threshold information, also is connected to the CPU  14 . Each of the modules  19  to  22  is configured to allow the first MS  10  to communicate via radio over a different respective channel type. Moreover, each of the channel types has a different bit rate, which equates to bandwidth, namely around 1000 kb/s for UMTS speech, 1 Mb/s for Bluetooth, 10 Mb/s for UMTS A-V, and around 100 MB/s for WLAN. The first MS  10  optionally includes a global positioning system (GPS) receiver  23  which is arranged, in response to a request by the CPU  14 , to determine the location of the MS, and to provide location information to the CPU. A receiver operable with another positioning system (such as Glonass or the proposed Galileo) could be used in place of the GPS receiver  23 . 
   Operation of the MS  10  in a telecommunications system will now be described with reference to  FIG. 2 . 
   In  FIG. 2 , the MS  10  is shown communicating with a first base station (BS)  30  of a UMTS system  31 . Second to fourth BSs on  32 - 34  are shown, along with their respective areas of coverage (the boundaries of which are given by dotted-line circles). Second to fourth MSs  35 - 38 , are shown in communication with, various ones of the BSs  30 ,  32 - 34 . 
   In this example, the first MS  10  is connected for speech communication with the second MS  35  over a UMTS speech channel. To this end, the first MS  10  is connected to the BS  30  via a two-way UMTS speech channel, as is the second MS  35 . Alternatively, the second MS  35  could be connected via the second BS  32 , in which case data would pass between the second BS and the first BS  30  via the network  31 , since the second MS is within the area of coverage of both the first and second BSs. It is not important for the purpose of this embodiment which BS or BSs the first and second MSs  10 ,  35  are using for communication. 
   On determination that the bandwidth of the channel being used for communication between the first and second MSs  10 ,  35 , which in this example is a UMTS speech channel, is not sufficiently high to communicate, the first MS sets a ‘more bandwidth desired’ flag (not shown) to TRUE. Examples of situations in which this might occur are when video signals are being communicated, and it is determined that a higher quality of picture is required, or when it is desired to send other data, e.g. gaming data, along with normal speech call data. Another situation when this might occur is when the channel type (and hence the bandwidth) is selected by a user or the users on the basis of cost effectiveness, when a higher bandwidth channel would be desired; for example when a speech call is in progress when a videophone call would be preferred. Since direct mode communication does not involve the transmission of large amounts of data over a network, it may be much cheaper than network calls, or even without charge. As long as the ‘more bandwidth desired’ flag remains TRUE, the software operation given by the flowchart of  FIG. 3  is run on the first MS  10 . 
   Referring to  FIG. 3 , the operation begins in this instance at step  40 , which describes the connection status at this time. In this context, it will be appreciated that ‘global connection’ refers to connection via the base stations  30 ,  32 - 34  of the network  31 . At step  41 , the first MS  10  determines its location using its GPS receiver  23 , and receives information identifying the location of the second MS  35 . 
   At step  42 , the positions of the two MSs  10 ,  35  are compared, and the distance between them calculated. This distance is then compared to values stored in a table which relate to predetermined feasibility parameters. The operation of step  42  is performed relatively infrequently, so as to save resources, e.g. processing resources and to avoid the need for frequent sending of location and other subsidiary information over the network  31 . A decision is made at step  43  as to whether the connection is potentially feasible, and return is made to step  41  if a negative decision is made. Otherwise, the positions of the MSs  10 ,  35  are compared again at step  44 , and the distance between them compared to the maximum permissible distance in step  45 . A threshold, which is the maximum permissible distance, is set at a value equal to the sum of the radio coverage of the first and second MSs, which coverages are made available to the first MS  10  in any suitable manner. The threshold and the maximum permissible distances are stored in the database  24 . This calculation is made significantly more frequently than the calculation of step  42 . If the threshold is exceeded, a NO result returns the operation to step  41 . If the threshold is not exceeded, a YES result causes the operation to progress to step  46 . Here, direct mode communication is established between the first and second MSs  10 ,  35  in any suitable manner. The global communication may remain in place or it may be disconnected. By step  47 , local connection, or direct mode communication, is established and on. 
   At step  48 , the first MS  10  again determines its location using the GPS receiver, receives location information about the second MS  35 , and determines the distance therebetween. At step  49 , this distance is compared with the threshold used in step  45 , and a decision made as to whether the threshold is exceeded at step  50  with a NO result returning the operation to step  48 , and a YES result causing progression to step  51 . It will be appreciated that a YES result is obtained from step  50  only when the first and second MSs  10 ,  35  have moved apart so that their radio coverages no longer overlap. In this case, the operation takes the appropriate step, step  51 , of switching communication from local (direct mode) to global (i.e. via at least one BS  30 ). If the global connection was broken at step  41 , then step  50  involves establishing a global connection, in any convenient manner. 
   In a further embodiment (not shown), the switching of a global connection to a local connection is carried out only if an MS determines that a channel of sufficiently high quality can be established. This is achieved by the sending of data from the first MS via the first BS  30 , indicating the channel which is to be used, which information is then passed onto the second MS  35 . The first MS  10  then transmits some test data via the identified channel, and this data is received by the second MS  35 . The bit error rate (BER) of the received data is calculated in a conventional manner, and the BER transmitted to the first MS  10  either directly or using the global connection. The connection is switched from global to local at step  46  only if the first MS determines from the BER received from the second MS  35  that the propagation channel between the first and second MSs  10 ,  35  is of sufficiently high quality. Channel quality is determined continuously, along with the distance between the first and second MSs  10 ,  35 , for the purpose of determining whether a switch from local to global communication should be made. 
   Many variations of this are possible. For example, any other measure of channel quality may be made and used for the purpose of deciding whether to switch, examples being received signal strength and packet error rate. Also, a measure of the quality of the propagation channel from the second MS  35  to the first MS  10  may be made and this may be dependent on how much data is required to be transmitted across that channel. 
   The operation of the flowchart of  FIG. 3  does not need to be carried out by the first MS  10 . Although it is preferred that the operation is carried out by the MS which determines that a higher bandwidth channel of communication is desired, this operation may be carried out instead by another MS or by the BS  30  or some other part of the network  31 . Running the operation of the  FIG. 3  flowchart other than in the first MS allows it to be of simpler design. 
   Reference is now made to  FIG. 4 , which is a signalling chart having the first MS  10  on the left hand side (Terminal A), the second MS  35  on the right hand side (Terminal B), and the network  31  in the centre. 
   Referring to  FIG. 4 , connection established signals  60 ,  61  are passed from Terminal A to network  31  and from there, to terminal B respectively once a channel has been allocated respectively. Connected signals  62 ,  63  are sent from terminal B and from the network  31 , respectively, in response. Communication between the terminals A and B is then established over a first channel, as is indicated at  64 . The network  31  subsequently, and while the channel  64  is still open, transfers location information to terminal B and to terminal A with signals  65  and  66 . In the embodiment of  FIG. 3 , it is not necessary to send signals  65  and  66  because location information is not stored on the network  31 . In other embodiments (not shown) however, a location information network (which may or may not form part of the network  31 ) is used to calculate and to hold information about the locations of the MSs  10  and  35 , and this information is passed to one or both of the MSs before direct-mode communication can be established. Identification and location information, as well as any other required information, is then passed between the terminals by signals  67  to  70 . Afterwards, direct mode communication is established by the sending of a connection establishment signal  71  directly from terminal A to terminal B and by a communication signal  72  sent in reply. Direct mode communication is then established at  73 . 
   The location of the first and/or second MSs  10 ,  35  may be determined in any suitable manner, such as by triangulating signals from plural base stations of known locations as is known. The triangulation calculations may be carried out by the network  31  or by the relevant MS  10 ,  35 . 
   Location information for each MS may be stored by the network  31 , and be accessible by any station as and when required. Location information may be transmitted to an MS by SMS message, which is particularly convenient since SMS messages can be received without interruption of any ongoing speech call. 
   In an alternative embodiment (not shown), the second channel has a bandwidth equal to or less than the first channel.