Abstract:
In order to prevent a preferred frequency providing Multimedia Broadcast Multicast Service, called MBMS hereinafter, services, from getting congestion, the present invention provides a method of selecting an operating frequency for a user equipment, called UE hereinafter, in a wireless communications system. The method includes switching the operating frequency from a first frequency to a second frequency when the UE activates to receive a MBMS service of a service group; and switching the operating frequency from the second frequency to the first frequency when the UE determines not to receive any MBMS services provided on the second frequency.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/844,387, filed on Sep. 14, 2006 and entitled “Method And Apparatus for Stopping Reception of the Mobile TV Services in a Wireless Communications System”, the contents of which are incorporated herein by reference. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a method of selecting an operating frequency in a wireless communications system and related communications device, and more particularly to a method of selecting an operating frequency related to multimedia broadcast multicast service, called MBMS, services for a UE in a wireless communications system and related communications device. 
         [0004]    2. Description of the Prior Art 
         [0005]    The third generation (3G) mobile telecommunications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. To enhance multimedia functions in the 3G mobile telecommunications system, a protocol specification developed by the 3rd Generation Partnership Project (3GPP) provides Multimedia Broadcast Multicast Service (MBMS). MBMS is a point-to-multipoint bearer service and is established on an existing network architecture of the Universal Mobile Telecommunications System (UMTS), utilizing Internet Protocol (IP) packets as a medium. Thus, MBMS allows a single source entity to transmit data to multiple user equipments (UEs) simultaneously. 
         [0006]    According to the protocol specification developed by the 3GPP, MBMS offers two delivery modes: MBMS Broadcast delivery mode and MBMS Multicast delivery mode. When interested in a specific MBMS service, the UE needs to order the MBMS service from a Broadcast Multicast Service Center (BM-SC) by establishing a service agreement including specific service provision phases. These two delivery modes have different service provision phases. The service provision phase of MBMS Broadcast delivery mode includes Service announcement, Session Start, MBMS notification, Data Transfer and Session Stop. The service provision phase of MBMS Multicast delivery mode includes Subscription, Service announcement, Joining, Session Start, MBMS notification, Data Transfer, Session Stop and Leaving. For realizing customized services, Joining and Leaving sessions utilized in MBMS Multicast delivery mode enable the BM-SC to execute authorization and payment recording for the UEs at the Joining session. The service provision phases mentioned above are well known in the art, and will not be described in detail. 
         [0007]    From the standpoint of the radio resource control (RRC), all logical data communication exchange channels, be they for providing data transmission exchange to the UE or for providing RRC layer control signal transmission exchange, are defined in the context of a Radio Bearer (RB). In the UE end, the RB comprises one unidirectional, or a pair of, uplink/downlink logic data transmission exchange channels. In the network end, the RB comprises one unidirectional, or a pair of, uplink/downlink logic data transmission exchange channels. For example, a UMTS Terrestrial Radio Access Network (UTRAN) transmits MBMS configuration to the UE by establishing RBs and the UE stops receiving MBMS service by releasing the RBs. According to the RRC protocol specification provide by the 3GPP, an RRC state of the UE can be a disconnection mode or an RRC connection mode. The disconnection mode includes Idle mode, and the RRC connection mode includes CELL_PCH, URA_PCH, CELL_FACH and CELL_DCH states. 
         [0008]    The MBMS services include two types: Broadcast and Multicast types. Generally, the Broadcast type services are free so that the UE does not need to perform the Joining session before receiving them. For Broadcast type services, the UTRAN always adopts the broadcast transmission mode using point-to-multipoint (p-t-m) RBs to transmit service data and configuration. On the other hand, for the Multicast type services, the UTRAN determines whether to utilize the broadcast or multicast transmission mode based on the service charge policy. In the multicast transmission mode, the UE needs to perform the Joining session, whereas in the broadcast transmission mode, the UE doest not need to. In addition, the UTRAN performs a counting procedure to obtain the number of the UEs interested in receiving MBMS services and thereby determines to use point-to-point (p-t-p) or p-t-m RBs. In the following, a transmission via the p-t-p RBs is regarded as a p-t-p transfer mode, and a transmission via the p-t-m RBs is regarded as a p-t-m transfer mode. 
         [0009]    The UTRAN generally includes two or more carrier frequencies for providing a variety of services for UEs, and the UEs are appropriately distributed on these carrier frequencies. The UTRAN may provide MBMS services only on one of the carrier frequencies to avoid same MBMS data stream being transmitted on the different frequency layers. Furthermore, the UTRAN may transmit an MBMS MODIFIED SERVICES INFORMATION message to notify the UE of transition to a cell of the preferred frequency layer for the concerned MBMS services. After the frequency transition, the UE will store the previous frequency which the UE operates at. 
         [0010]    At the Session Stop of an MBMS service, the UTRAN transmits an MBMS required UE action Information Element (IE) included in the MBMS MODIFIED SERVICES INFORMATION message to the UE in Idle mode, CELL_PCH state, URA PCH state or CELL_FACH state under the p-t-m transfer mode. By setting the MBMS required UE action IE to ‘Release PTM RB’, the UTRAN can notify the UE of the Session Stop, and thereby the UE releases corresponding p-t-m RBs to stop receiving the MBMS service. In addition, if the MBMS MODIFIED SERVICES INFORMATION message also includes an MBMS dispersion indicator IE, the UE will return to the cell of the stored previous frequency if the UE does not decide to receive another MBMS services on the current frequency. Thus, a notification of the Session Stop transmitted by the UTRAN can direct the UE to transit out of the preferred frequency layer. 
         [0011]    Additionally, the UTRAN periodically transmits an MBMS GENERAL INFORMATION message to notify the UE of the current use condition of the preferred frequency layer. For example, if the MBMS GENERAL INFORMATION message includes an MBMS PL Service Restriction Information IE, the UTRAN will not provide any non-MBMS Services (e.g. a mobile-terminated call service). This also indicates that the preferred frequency layer is congested. On the contrary, if the MBMS GENERAL INFORMATION message does not include the MBMS PL Service Restriction Information IE, there are still free radio resources available on the preferred frequency layer where the UTRAN can also provide the non-MBMS Services. 
         [0012]    To enhance the MBMS for mobile TV delivery, the 3GPP introduces a concept of MBMS Selected Services, which are a subset of MBMS activated services of the Broadcast type, for which the UE applies RRC procedures to inform the UTRAN which MBMS services have been selected by upper layers in the UE. An MBMS_ACTIVATED_SERVICES variable, related to the MBMS activated services, stores information about the MBMS Multicast services the UE has joined, as well as the MBMS Broadcast services the UE is interested in receiving. The stored information may include Activated service list, Service type, etc. According to the prior art, the MBMS Selected Services, especially the Mobile TV services, are assumed to be available all the time. Hence, there will be no Session Stop notification from the UTRAN and the reception of the MBMS Selected Services will be stopped by the UE. Moreover, according to the RRC specification of 3GPP, if the reception of any MBMS services is stopped by the UE in the p-t-m transfer mode, the UE in Idle mode, CELL_PCH state, URA PCH state or CELL_FACH state only releases related p-t-m RBs without considering returning to the previous frequency layer which the UE operates at. As a result, all the UEs receiving the MBMS Selected Services will stay on the preferred frequency layer after stopping the service reception. 
         [0013]    Besides the UEs receiving the MBMS Selected Services, the new UEs, which are not on the preferred frequency layer and decide to receive the MBMS services, will enter the preferred frequency layer. Therefore, the preferred frequency layer is liable to get congested due to increase of the UE number. If the preferred frequency layer is congested, the UE staying on this layer will not be able to receive any new non-MBMS services, such as the mobile-terminated call service. 
       SUMMARY OF THE INVENTION 
       [0014]    Therefore, the present invention provides a method of selecting an operating frequency for a UE in a wireless communications system and related communications device that can prevent a frequency layer, which provides MBMS services, from getting congested. 
         [0015]    The present invention discloses a method of selecting an operating frequency for a UE in a wireless communications system. The method includes switching the operating frequency from a first frequency to a second frequency when activating to receive an MBMS service of a service group and switching the operating frequency from the second frequency to the first frequency when determining not to receive any MBMS services provided on the second frequency. 
         [0016]    The present invention discloses a communications device of a wireless communications system utilized for accurately selecting an operating frequency to prevent a frequency used for provision of MBMS services from getting congested. The communications device includes a control circuit, a central processing unit and a memory. The control circuit is used for realizing functions of the communications device. The central processing unit is installed in the control circuit and used for executing a program code to operate the control circuit. The memory is coupled to the central processing unit and used for storing the program code. The program code includes switching the operating frequency from a first frequency to a second frequency when activating to receive an MBMS service of a service group and switching the operating frequency from the second frequency to the first frequency when determining not to receive any MBMS services provided on the second frequency. 
         [0017]    The present invention further discloses a method of selecting an operating frequency for a UE in a wireless communications system. The method includes switching the operating frequency from a first frequency to a second frequency when activating to receive an MBMS service of a service group and switching the operating frequency from the second frequency to the first frequency when any MBMS services provided on the second frequency are determined not to be received and a service state corresponding to the second frequency is determined to be congested. 
         [0018]    The present invention further discloses a communications device of a wireless communications system utilized for accurately selecting an operating frequency to prevent a frequency used for provision of MBMS services from getting congested or to prevent from missing opportunities of receiving non-MBMS services. The communications device includes a control circuit, a central processing unit and a memory. The control circuit is used for realizing functions of the communications device. The central processing unit is installed in the control circuit and used for executing a program code to operate the control circuit. The memory is coupled to the central processing unit and used for storing the program code. The program code includes switching the operating frequency from a first frequency to a second frequency when activating to receive an MBMS service of a service group and switching the operating frequency from the second frequency to the first frequency when any MBMS services provided on the second frequency are determined not to be received and a service state corresponding to the second frequency is determined to be congested. 
         [0019]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a functional block diagram of a communications device. 
           [0021]      FIG. 2  is a diagram of the program code shown in  FIG. 1 . 
           [0022]      FIG. 3  is a flowchart diagram of a process according to an embodiment of the present invention. 
           [0023]      FIG. 4  is a flowchart diagram of a process according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Please refer to  FIG. 1 , which is a functional block diagram of a communications device  100 . For the sake of brevity,  FIG. 1  only shows an input device  102 , an output device  104 , a control circuit  106 , a central processing unit (CPU)  108 , a memory  110 , a program code  112 , and a transceiver  114  of the communications device  100 . 
         [0025]    In the communications device  100 , the control circuit  106  executes the program code  112  in the memory  110  through the CPU  108 , thereby controlling an operation of the communications device  100 . The communications device  100  can receive signals input by a user through the input device  102 , such as a keyboard, and can output images and sounds through the output device  104 , such as a monitor or speakers. The transceiver  114  is used to receive and transmit wireless signals, delivering received signals to the control circuit  106 , and outputting signals generated by the control circuit  106  wirelessly. From a perspective of a communications protocol framework, the transceiver  114  can be seen as a portion of Layer  1 , and the control circuit  106  can be utilized to realize functions of Layer  2  and Layer  3 . Preferably, the communications device  100  is utilized in a third generation (3G) mobile communications system. 
         [0026]    Please continue to refer to  FIG. 2 .  FIG. 2  is a diagram of the program code  112  shown in  FIG. 1 . The program code  112  includes an application layer  200 , a Layer  3   202 , and a Layer  2   206 , and is coupled to a Layer  1   218 . The Layer  3   202  includes a radio resource control (RRC) entity  222 , which is used for controlling the Layer  1   218  and the Layer  2   206  and performing peer-to-peer RRC communication with other communications devices, such as a base station or a Node-B. In addition, the RRC entity  222  can change an RRC state of the communications device  100 , switching between an Idle mode, CELL_PCH, URA_PCH, CELL_FACH or CELL_DCH state. 
         [0027]    The UTRAN can generate RRC messages and IEs to include MBMS configuration and then transmit them with p-t-m RBs to the communications device  100 . In Idle mode, CELL_PCH state, URA PCH state or CELL_FACH state, the RRC entity  222  release the p-t-m RBs to stop receiving an MBMS service as the application layer  200  deactivates the MBMS service. In this situation, the embodiment of the present invention provides an operating frequency selecting program code  220  to improve utilization condition of a preferred frequency layer where MBMS services is provided. Please refer to  FIG. 3 , which illustrates a schematic diagram of a process  30  according to an embodiment of the present invention. The process  30  is utilized for selecting an operating frequency for a UE in a wireless communications system, and can be compiled into the operating frequency selecting program code  220 . The process  30  includes the following steps:
       Step  300 : Start.   Step  302 : Switch the operating frequency from a first frequency to a second frequency when activating to receive an MBMS service of a service group.   Step  304 : Switch the operating frequency from the second frequency to the first frequency when determining not to receive any MBMS services provided on the second frequency.   Step  306 : End.       
 
         [0032]    According to the process  30 , the embodiment of the present invention uses the second frequency to provide the service group for the UE. The second frequency is regarded as the preferred frequency layer. The UE operates at the first frequency before activating to receive the MBMS service. The service group includes at least one MBMS service and each MBMS service is Broadcast type or Multicast type. Preferably, the MBMS service belongs to the above-mentioned MBMS Selected Services, such as the Mobile TV service. In the process  30 , the UE may simultaneously receive more than one MBMS service of the service group. 
         [0033]    As the MBMS service is activated, the UE switches the operating frequency from the first frequency to the second frequency and stores the first frequency. When the MBMS service is stopped by the UE, the UE releases corresponding p-t-m RBs. Furthermore, the UE switches the operating frequency from the second frequency to the first frequency when determining not to receive any MBMS services on the second frequency. As a result, the UE will not use the radio resources related to the second frequency any more, and the radio resources can be allocated for other UEs. Therefore, the process  30  can properly control the UE number of the second frequency to prevent the second frequency from getting congested. 
         [0034]    Please refer to  FIG. 4 , which illustrates a schematic diagram of a process  40  according to an embodiment of the present invention. The process  40  is utilized for selecting an operating frequency for a UE in a wireless communications system, and can be compiled into the operating frequency selecting program code  220 . The process  40  includes the following steps:
       Step  400 : Start.   Step  402 : Switch the operating frequency from a first frequency to a second frequency when activating to receive an MBMS service of a service group.   Step  404 : Switch the operating frequency from the second frequency to the first frequency when any MBMS services provided on the second frequency are determined not to be received and a service state corresponding to the second frequency is determined to be congested.   Step  406 : End.       
 
         [0039]    According to the process  40 , the embodiment of the present invention uses the second frequency to provide the service group for the UE. The second frequency is regarded as the preferred frequency layer. The UE operates at the first frequency before activating to receive the MBMS service. The service group includes at least one MBMS service and each MBMS service is Broadcast type or Multicast type. Preferably, the MBMS service belongs to the above-mentioned MBMS Selected Services, such as the Mobile TV service. In the process  40 , the UE may simultaneously receive more than one MBMS service of the service group. During operating at the second frequency, the UE periodically receives an MBMS GENERAL INFORMATION message to know the current utilization condition of the second frequency. If the MBMS GENERAL INFORMATION message includes an MBMS PL Service Restriction Information IE, the UE determines that the service state corresponding to the second frequency is congested. Meanwhile, no new non-MBMS services will be provided on the second frequency. On the contrary, if the MBMS PL Service Restriction Information IE is not included, the new non-MBMS services, such as the mobile-terminated call service, can be provided for the UE on the second frequency. 
         [0040]    According the above, the UE switches the operating frequency from the first frequency to the second frequency as the MBMS service is activated and further stores the first frequency. When the MBMS service is stopped by the UE, the UE releases corresponding p-t-m RBs. Furthermore, the UE switches the operating frequency from the second frequency to the first frequency when the UE determines not to receive any MBMS services on the second frequency and also determines that the service state corresponding to the second frequency is congested. Thus, the process  40  can mitigate radio resource utilization of the second frequency. Moreover, in the congested state of the second frequency, the process  40  can move the UE out of the second frequency to prevent the UE from missing opportunities to receive non-MBMS services. 
         [0041]    In conclusion, according to the prior art, the UE in Idle mode, CELL_PCH state, URA PCH state or CELL_FACH state only releases p-t-m RBs each time when the reception of the MBMS services is stopped by the UE. In this situation, no frequency transition is considered. Compared to the prior art, the embodiments of the present invention provide two alternatives. One is that the UE moves out of the preferred frequency layer when determining not to receive any MBMS services on the preferred frequency layer. The other is that the UE moves out of the preferred frequency layer when the UE determines not to receive any MBMS services on the preferred frequency layer and also determines that the service state of the preferred frequency layer is congested. Therefore, the embodiment of the present invention can prevent the preferred frequency layer from getting congested or prevent the UE from missing opportunities to receive non-MBMS services. 
         [0042]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.