Abstract:
The present invention takes the advantage of the wireless local area network (WLAN) resources in hotspots for voice and data connections and enables seamless handover between wireless wide area network (WWAN) and WLAN and vice versa, thus achieving cost savings for the end users and WWAN resources savings for the wireless operators. According to one embodiment of the invention, a mobile terminal having WWAN and WLAN interfaces establishes a WWAN call with a called mobile terminal via a WWAN. If a WLAN is present, the mobile terminal sends a handover request together with its network address to the called mobile terminal, using a short message service (SMS) technique or a watermarking technique, for initiating a WLAN call with the called mobile terminal via a WLAN. After the WLAN call is established with the called mobile terminal, the mobile terminal releases the WWAN call.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to methods and circuits for seamlessly roaming between a first wireless communication network and a second wireless communication network. 
       BACKGROUND OF THE INVENTION 
       [0002]      FIG. 1  illustrates typical service areas in which mobile terminals such as mobile phones are used. In these areas, the WWAN service area (e.g., GSM, GPRS, CDMA, 3G) may or may not overlap with a WLAN service area (as shown in  FIG. 1 ). In the case where there is an overlap between the WWAN and WLAN service areas, both the WWAN and WLAN services are available. These overlapping areas are also referred to as hotspots, which include airports, hotels, office buildings and home environment. 
         [0003]    In hotspots (e.g., airports and hotels), people normally use mobile terminals for making voice calls and using low-speed data services via the WWAN and for using high-speed data services via the WLAN through access points (APs). In situations in which two mobile terminals in the same hotspot or in different hotspots run by the same service provider are trying to communicate with each other, they still need to use the WWAN service to make voice calls. This is not cost effective even though a low cost alternative communication network, i.e., the WLAN, is available to both parties. 
         [0004]    US Patent application with the Pub. No. 2002/0085516 A1 discloses system and method for automatic and seamless vertical roaming (SVR) between a wireless local area network (WLAN) and a wireless wide area network (WWAN) while maintaining an active voice or data communication. However, US 2002/0085516 A1 only focuses on network infrastructure, and no structure and method for terminals are provided to achieve such roaming. 
       SUMMARY OF THE INVENTION 
       [0005]    Therefore, the object of the invention is to provide methods and circuits with effective cost for seamlessly roaming between a first wireless communication network and a second wireless communication network in areas in which both services are available. 
         [0006]    To achieve this object, a first aspect of the invention provides a method performed by a calling mobile terminal having at least dual radio interfaces respectively for a first wireless communication network and a second wireless communication network. The method comprises the steps of detecting presence of the first and second wireless communication networks and sending a handover request to a called mobile terminal for initiating a second communication via the second wireless communication network, if the second wireless communication network is present. When a response from the called mobile terminal indicates an acceptance of the handover request, a step of establishing the second connection with the called mobile terminal via the second wireless communication network is performed. Due to roaming to the second wireless communication network, which could have a cheaper billing system, the method has the advantage that end users can save communication cost and operator of the first wireless communication network can save network resource. 
         [0007]    In an embodiment in accordance with the invention, the method performed by the calling mobile terminal may reestablish a connection with the called mobile terminal via the first wireless communication network for maintaining communication, when the calling mobile terminal is moving away from the second wireless communication network. Such a method has the advantage that a continuous communication is ensured and a seamless handover is achieved. 
         [0008]    In another embodiment in accordance with the invention, the method performed by the calling mobile terminal may perform the step of sending the handover request according to the preferred radio interface based on the user profile in the calling mobile terminal. Such a method has the advantage that the user of the calling mobile terminal has more flexible choices for the handover, because the user may set the calling mobile terminal to handover automatically or manually. 
         [0009]    In another embodiment in accordance with the invention, the method performed by the calling mobile terminal may send the extra information via the voice channel. Since the extra information is sent via a conventional channel, such a method has the advantage that no additional channel resource is required. 
         [0010]    In another embodiment in accordance with the invention, the method performed by the calling mobile terminal may send the extra information together with the input voice. Since the extra information may be sent via the voice channel at any time during communication, such a method has the advantage that the extra information may be sent immediately regardless whether the user is talking or not. 
         [0011]    In another embodiment in accordance with the invention, the method performed by the calling mobile terminal may multiplex the extra information in DTMF-like signal form with input voice and output the combined signals. Since DTMF is a kind of watermarking technology, such a method has the advantage that in the combined signals, the extra information in DTMF-like signal form cannot be imitated by the input voice. 
         [0012]    A second aspect of the invention provides a method performed by a called mobile terminal having at least dual radio interfaces respectively for a first wireless communication network and a second wireless communication network. The method comprises the steps of detecting whether the second wireless communication network is present, if receiving extra information including a handover request from the calling mobile terminal for initiating a second connection via the second wireless communication network sending a response to the calling mobile terminal with an acceptance of the handover request if the second wireless communication network is present and 
         [0013]    accepting the second connection with the calling mobile terminal. Correspondingly, this method also provides cheaper communication and network resource saving. 
         [0014]    In another embodiment in accordance with the invention, the method performed by the called mobile terminal may reestablish a connection with the called mobile terminal via the first wireless communication network for maintaining communication, when the called mobile terminal is moving away from the second wireless communication network. Correspondingly, such a method also has the advantage that a continuous communication is ensured and a seamless handover is achieved. 
         [0015]    In another embodiment in accordance with the invention, the method performed by the called mobile terminal may perform the step of sending a response with an acceptance of the handover request according to the preferred radio interface of the called mobile terminal. Correspondingly, such a method also has the advantage that the user of the called mobile terminal has more flexible choices for the handover. 
         [0016]    In another embodiment in accordance with the invention, the method performed by the called mobile terminal may comprise the step of demultiplexing DTMF-like signal from the combined signals and demodulating the extra information from the DTMF-like signal. The extra information can be decoded to original extras information, so such a method has the advantage that the extra information may be received in the voice channel together with the voice signal. 
         [0017]    Other aspects of the invention provide a circuit including a plurality of means for performing the method performed by the calling mobile terminal, a circuit including a plurality of means for performing the method performed by the called mobile terminal, a computer program product for handover of the calling mobile terminal, and a computer program product for handover of the called mobile terminal, 
         [0018]    Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0019]    The invention is explained in further detail, and by way of example, with reference to the accompanying drawings wherein: 
           [0020]      FIG. 1  illustrates typical service areas in which mobile terminals are used; 
           [0021]      FIG. 2  shows a basic architecture of a mobile terminal with dual radio interfaces; 
           [0022]      FIG. 3  illustrates a method for seamlessly roaming between a WWAN and a WLAN; 
           [0023]      FIG. 4  shows a circuit for adding extra information as analog signals in a calling mobile terminal, in accordance with one embodiment of the invention; 
           [0024]      FIG. 5  shows a circuit for demodulating the extra information added as analog signals in a called mobile terminal, in accordance with one embodiment of the invention; 
           [0025]      FIG. 6  shows a circuit for adding the extra information as digital signals in a calling mobile terminal, in accordance with one embodiment of the invention; 
           [0026]      FIG. 7  shows a circuit for extracting the extra information inserted as digital signals in a called mobile terminal, in accordance with one embodiment of the invention; 
           [0027]      FIG. 8  shows a circuit for adding extra information as analog signals in a calling mobile terminal, in accordance with another embodiment of the invention; 
           [0028]      FIG. 9  shows a circuit for demodulating the extra information added as analog signals in a called mobile terminal, in accordance with another embodiment of the invention; 
           [0029]      FIG. 10  shows a circuit for adding the extra information as digital signals in a calling mobile terminal, in accordance with another embodiment of the invention; and 
           [0030]      FIG. 11  shows a circuit for extracting the extra information inserted as digital signals in a called mobile terminal, in accordance with another embodiment of the invention. 
       
    
    
       [0031]    Throughout the drawings, the same reference numerals indicate similar or corresponding features or functions. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]      FIG. 2  shows a basic architecture of a mobile terminal  10  with dual radio interfaces—WWAN and WLAN interfaces—for use in the invention. When a user tries to make a call with mobile terminal  10 , a user agent, which is responsible for profile management, service mediation, etc., will first make a WWAN call. After the call is set up, the user agent will determine which radio interface to use based on the user profile and the available radio interfaces. The user profile contains information about the radio interface preferences, handover permission during an active connection, etc. For example, if the user prefers a connection via the WLAN interface, the user agent will, after setting up the WWAN call, try to connect both parties via a WLAN. After the WLAN call (e.g., a voice or video call) is successfully set up, the WWAN call will be released without the user&#39;s direct involvement. 
         [0033]      FIG. 3  illustrates a method  20  for seamlessly roaming between a WWAN and a WLAN, according to one embodiment of the invention. When a party enters into a hotspot, the user agent of this party&#39;s mobile terminal will detect the types of wireless services available. When the party tries to make a call, the user agent of this calling party&#39;s mobile terminal will make a call via a WWAN in a conventional way, using the MSISDN (Mobile Station International ISDN Number) of a called mobile terminal (steps S 22  and S 26 ). After the WWAN call is properly set up, the user agent of the calling mobile terminal will decide which radio interface to use based on the user profile of the calling party. If a WLAN is preferred, and the WLAN interface is available, the user agent will send extra information including a handover request together with information about the IP address, user profile, etc. of the calling mobile terminal to the called mobile terminal for handing over the call to the WLAN (step S 32 ). The extra information is transferred using the short message service (SMS) or the watermarking technology. The watermarking technology allows the extra information to be hidden within the voice, as will be described later. 
         [0034]    Upon receiving the handover request, the user agent of the called mobile terminal will decide whether to accept the request, based on its own user profile and the available radio interface of the called mobile terminal. If the called mobile terminal agrees to hand over the call to the WLAN, its user agent will send similar extra information including a handover accept response together with information about the IP address, user profile, etc. of the called mobile terminal to the calling mobile terminal, using the SMS or the watermarking technology (step S 36 ). The calling mobile terminal will then initiate a call (e.g., a voice or video call) via a WLAN, using the received IP address of the called mobile terminal (steps S 42  and S 46 ). When the WLAN call has been successfully set up, the WWAN call may be released (steps S 52  and S 56 ). After the WLAN call is completed, it will also be released (steps S 62  and S 66 ). 
         [0035]    In the above, during an active WLAN call, one of the parties may leave a WLAN service area. In such case, the user agent of this party&#39;s mobile terminal will recognize a change in the radio signals. If the calling party is leaving the area, the user agent of the calling mobile terminal will try to initiate a new WWAN call to the called mobile terminal. On the other hand, if the called party is leaving the area, the user agent of the called mobile terminal will send a handover request via the WLAN to the calling mobile terminal to initiate a new WWAN call. This new WWAN call will be automatically accepted by the called mobile terminal. After the new WWAN call is successfully set up, the WLAN call will be immediately released by both parties. Optionally, the called mobile terminal may also initiate the new WWAN call to the calling mobile terminal when the called party is leaving the area. 
         [0036]    In the above, the handovers from a WWAN to a WLAN and vice versa are transparent to both users, so that the talk between them is not affected. Also, the parties may communicate with each other via two WLAN networks, within each of which one party is present, that are connected via Internet. 
         [0037]    The watermarking technology as used in the invention will now be described. By using this technology, the extra information (i.e., the handover request, IP address, user profile, etc.) is exchanged along with the voice in one channel, e.g., the voice channel between two mobile terminals. Such exchanges will not affect the normal voice conversation, since during a typical telephone conversation, 50% of the time is used for listening and 10% of the time is used for pausing between words and sentences. Therefore, there are sufficient resources for exchanging the extra information, without requiring modifications to the existing network infrastructure. The extra information may be added by the user agent in a mobile terminal as either analog signals or digital signals. 
         [0038]      FIG. 4  shows a circuit  50  for adding the extra information (i.e., the handover request, IP address, user&#39;s profile, etc.) in the voice channel of a calling mobile terminal, in accordance with one embodiment of the invention. Circuit  50  includes a silence control circuit  54 , a modulation circuit  56 , and a time division multiplexer  62 . The user agent of the calling mobile terminal provides the extra information in the form of a digital sequence to modulation circuit  56  for modulation into analog signals. When silence control circuit  54  detects a silence period in the input voice, it sends a control signal to modulation circuit  56 . Upon receiving the control signal, modulation circuit  56  outputs the extra information in an analog form to multiplexer  62 . Multiplexer  62  time multiplexes the voice input with the extra information and sends a combined output to an ADC for transmitting to a called mobile terminal in a voice channel. 
         [0039]    The extra information can be modulated as some patterns of frequencies in the voice band (0˜4000 Hz). For example, the Dual Tone Multi Frequency (DTMF) technique may be used to transfer 16 digits (0˜9, A˜F). Frequencies that last certain time durations (e.g., 5 ms) stand for a symbol. As an example, the combined frequencies of 1336 Hz and 770 Hz stand for 6, and the combined frequencies of 1477 Hz and 852 Hz stand for 8. If a party wants to transmit “68”, the frequencies to be added into the voice will be |1336 Hz+700 Hz| simultaneously for 5 ms and |1477 Hz+852 Hz| simultaneously for 5 ms. 
         [0040]      FIG. 5  shows a circuit  70  for demodulating the extra information received by a called mobile terminal in the voice channel, in accordance with one embodiment of the invention. Frequency detection circuit  70  includes a frequency detection circuit  72  and a demodulation circuit  76 . Frequency detection circuit  72  receives combined analog signals from a digital-to-analog converter (DAC), including both the voice and the extra information. Circuit  72  recognizes the frequencies used for representing symbols, and outputs the recognized frequencies to demodulation circuit  76  for decoding the pre-defined frequency patterns to extract the extra information. For example, if the frequency patterns |1336 Hz+700 Hz| and |1477 Hz+852 Hz| described above are recognized by frequency detection circuit  72  and output to demodulation circuit  76 , demodulation circuit  76  will decode the frequency patterns and output a digital sequence of “68”. 
         [0041]    To reduce decoding errors, the maximum time duration for the same frequency pattern is defined. For example, the same frequency that lasts longer than 50 ms is not allowed. If a calling mobile terminal sends more than 10 identical digits within a time duration over 50 ms (i.e., 10×5 ms), a disturbance frequency pattern (e.g., 11888 Hz+888 Hz|) will be added after the 10th digit. The called mobile terminal can locate the disturbance frequency pattern after the 10 identical digits. For instance, when the calling mobile terminal sends a digital sequence of 999,999,999,999 to the called mobile terminal, it will be sent as 9,999,999,999, x99, where x represents a disturbance frequency pattern. At the called mobile terminal, the received sequence 9,999,999,999, x99 will be restored to 999,999,999,999. 
         [0042]      FIG. 6  shows a circuit  80  for adding the extra information as digital signals in a calling mobile terminal in accordance with one embodiment of the invention. Circuit  80  includes a silence control circuit  82  and a watermarking circuit  83 . Silence control circuit  82  detects silent periods in the input voice and upon detecting a silent period, provides a control signal to watermarking circuit  83 . Watermarking circuit  83  receives the extra information, including the IP address, user profile, etc. from the user agent and upon receiving the control signal, outputs the extra information to a time multiplexer  84 . Watermarking circuit  83  may be implemented with a latch circuit. An ADC  86  converts the input voice into digital signals and provides the digital signals to a coding circuit  88  for coding to comply with a specific communication standard (e.g., GSM). The output from coding circuit  88  and the extra information from watermarking circuit  83  will be time multiplexed by multiplexer  84  to provide a combined output for baseband processing. In this way, the extra information is inserted in the silent periods of the input voice. 
         [0043]      FIG. 7  shows a watermarking detection circuit  90  for extracting the extra information inserted as digital signals, in a called mobile terminal in accordance with one embodiment of the invention. Watermarking detection circuit  90  detects a pair of pre-defined digital sequences (described below in detail) from the input voice to recover the extra information. The voice will be allowed to pass through watermarking detection circuit  90  and will be output to a decoding circuit  96 , which decodes the voice in accordance with a specific communication standard. A digital-to-analog (DAC)  98  converts the decoded voice into analog signals and provides them to an output device. 
         [0044]    In  FIGS. 6 and 7 , a pre-defined digital sequence is used for marking the start point and end point of the extra information. For example, a digital sequence 1010101010101010 may be used for marking the start and end of the extra information. All the extra information must be enclosed within a pair of two such sequences. If the extra information or the input voice contains the same sequence pattern as the start or the end sequence, then this sequence pattern must be transformed. For example, if the extra information contains 1010101010101010, this sequence will be changed to 101010101010101110, with “11” being inserted in between the last two bits. 
         [0045]    In addition, since DTMF signal cannot be imitated by human voice, with the watermarking technology, the extra information can be mixed with voice and exchanged in the voice channel in spite of whether there is a silence or not. 
         [0046]      FIG. 8  shows a circuit  100  for adding the extra information as analog signals in a calling mobile terminal, in accordance with another embodiment of the invention. The circuit  100  includes a watermarking modulation circuit  104  and a multiplexer  102 . The user agent of the calling mobile terminal provides the extra information in the form of a digital sequence to the watermarking modulation circuit  104  for modulation into DTMF-like analog signals. The watermarking modulation circuit  104  outputs the extra information in DTMF-like analog form to the multiplexer  102 . When the user is speaking, the multiplexer  102  multiplexes the input voice with the extra information and sends a combined output to the ADC for transmitting to a called mobile terminal in the voice channel. When the user isn&#39;t speaking, the multiplexer  102  only sends the extra information to the ADC. 
         [0047]      FIG. 9  shows a circuit  110  for demodulating the extra information added as analog signals in a called mobile terminal, in accordance with another embodiment of the invention. The circuit  110  includes a signal detection circuit  112 , a signal filtering circuit  114  and a watermarking demodulation circuit  116 . The signal detection circuit  112  receives the voice or combined analog signal from the DAC, including both the voice and the extra information in DTMF-like analog form. If the signal from the DAC is only the voice, the signal detection circuit  112  will disable the signal filtering circuit  114  and the voice will pass through the signal filtering circuit  114  without any modification. If the signal from the DAC is the combined analog signal, the signal detection circuit  112  will demultiplex separate DTMF-like analog signal from the combined analog signal, then feed the DTMF-like analog signal to the watermarking demodulation circuit  116 . The watermarking demodulation circuit  116  will demodulate the extra information from the DTMF-like analog signal and then output the extra information in digital form. At the same time, the signal detection circuit  112  will enable the signal filtering circuit  114  and feed the combined analog signal to the signal filtering circuit  114 , then the signal filtering circuit  114  will filter the DTMF-like analog signal from the combined analog signal, and output the voice signal. 
         [0048]      FIG. 10  shows a circuit  120  for adding the extra information as digital signals in a calling mobile terminal in accordance with another embodiment of the invention. The circuit  120  includes an ADC  124 , a time multiplexer  122  and a digital watermarking modulation circuit  126 . The digital watermarking modulation circuit  126  receives the extra information and outputs the extra information in DTMF-like digital signal form to the time multiplexer  122 . The ADC  124  converts the input voice into digital signals. The voice digital signal from the ADC  124  and the DTMF-like digital signal from the digital watermarking modulation circuit  126  will be time multiplexed by the multiplexer  122  to provide a combined output for subsequent processing. When the user isn&#39;t speaking, the multiplexer  122  only outputs the extra information. 
         [0049]      FIG. 11  shows a circuit  130  for extracting the extra information inserted as digital signals, in a called mobile terminal in accordance with another embodiment of the invention. The circuit  130  includes a digital signal detection circuit  132 , a digital signal filtering circuit  134 , a digital watermarking demodulation circuit  136  and a DAC  138 . The digital signal detection circuit  132  receives the voice digital signal or combined digital signal, including both the voice digital signal and the extra information in DTMF-like digital form. If there is only the voice digital signal, the digital signal detection circuit  132  will disable the digital signal filtering circuit  134  and the voice digital signal will pass through the digital signal filtering circuit  134  without any modification. If there is the combined digital signal, the digital signal detection circuit  132  will demultiplex separate DTMF-like digital signal from the combined digital signal, then feed the DTMF-like digital signal to the digital watermarking demodulation circuit  136 . The digital watermarking demodulation circuit  136  will decode the extra information from the DTMF-like digital signal and then output the extra information in digital form. At the same time, the digital signal detection circuit  132  will enable the digital signal filtering circuit  134  and feed the combined digital signal to the signal filtering circuit  134 , then the signal filtering circuit  134  will filter the DTMF-like analog signal from the combined digital signal, and output the voice digital signal. The DAC  138  converts the voice digital signal into analog signal and outputs the voice to a subsequent device. 
         [0050]    In the above, the invention has been illustrated in conjunction with a WWAN and WLAN. However, the invention may be used for roaming between any two wireless communication networks. 
         [0051]    The present invention may be embodied as methods, communication devices, communication systems, and/or computer program products. Accordingly, the present invention may be embodied in hardware and/or in software (including firmware, resident software, micro-code, etc.). Furthermore, the present invention may take the form of a computer program product on a computer-usable or computer-readable storage medium having computer-usable or computer-readable program code embodied in the medium for use by or in connection with an instruction execution system. In the context of this document, a computer-usable or computer-readable medium may be any medium that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. 
         [0052]    While the invention has been described in conjunction with specific embodiments, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit and scope of the appended claims.