Abstract:
A mobile communication device with a processor is provided. The processor determines whether an Inter-Radio Access Technology (IRAT) procedure is ongoing when receiving a request for a Mobile Originated (MO) call, starts a first guard timer in response to the IRAT procedure being ongoing, and performs an Access Domain Selection (ADS) for making the MO call in response to the IRAT procedure being completed and the first guard timer not expiring.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application claims priority of U.S. Provisional Application No. 61/979,114, filed on Apr. 14, 2014, the entirety of which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention generally relates to handling a request for a Mobile Originated (MO) call, and more particularly, to apparatuses and methods for Access Domain Selection (ADS) during an ongoing IRAT (Inter-Radio Access Technology) procedure when the request for an MO call is received. 
     Description of the Related Art 
     With growing demand for ubiquitous computing and networking, various Radio Access Technologies (RATs) have been developed, such as the Global System for Mobile communications (GSM) technology, General Packet Radio Service (GPRS) technology, Enhanced Data rates for Global Evolution (EDGE) technology, Wideband Code Division Multiple Access (WCDMA) technology, High Speed Packet Access (HSPA) technology, Long Term Evolution (LTE) technology, Time-Division LTE (TD-LTE) technology, LTE-Advanced (LTE-A) technology, and others. 
     Generally, a mobile phone only supports one RAT with one subscriber identity card for providing users with the flexibility of mobile communications at all times via the supported RAT using the single subscriber identity card. However, due to the complexity of various network deployments, so-called multimode mobile phones have been developed, which generally support two or more RATs and select one of the RATs for obtaining mobile services. 
     Since multimode mobile phones support multiple RATs, the Access Domain Selection (ADS) becomes an important issue for such mobile phones, especially when receiving a request for making a Mobile Originated (MO) call, such as a voice call or video call. For example, in second-generation (2G) networks (e.g., GSM/GPRS/EDGE networks) or third-generation (3G) networks (e.g., WCDMA networks), voice calls can only be made through the Circuit-Switched (CS) domain. In HSPA or LTE-based networks, voice or video calls can only be made through the IP Multimedia Subsystem (IMS) domain. That is, a multimode mobile phone is required to decide in which access domain the MO call should be made depending on the currently used RAT. 
     However, when an IRAT procedure is ongoing (i.e., when the multimode mobile phone is switching from one RAT to another, e.g., moving from an LTE network to a GSM network), the ADS may not be able to decide a proper access domain for the MO call due to the currently used RAT being indeterminate. As a result, the probability of the MO call being rejected by the network may increase if an improper access domain is selected. 
     BRIEF SUMMARY OF THE INVENTION 
     In order to solve the aforementioned problem, the invention proposes to defer the ADS when an IRAT procedure is ongoing, thereby enabling the ADS to decide a proper access domain and increasing the successful rate of making the MO call. 
     In one aspect of the invention, a mobile communication device comprising a processor is provided. The processor is configured to determine whether an IRAT procedure is ongoing when receiving a request for an MO call, start a first guard timer in response to the IRAT procedure being ongoing, and perform an ADS for making the MO call in response to the IRAT procedure being completed and the first guard timer not expiring. 
     In another aspect of the invention, a method for ADS during an IRAT procedure, executed by a mobile communication device, is provided. The method comprises the steps of: determining whether an IRAT procedure is ongoing when receiving a request for an MO call; starting a first guard timer in response to the IRAT procedure being ongoing; and performing an ADS for making the MO call in response to the IRAT procedure being completed and the first guard timer not expiring. 
     Other aspects and features of the present invention will become apparent to those with ordinarily skill in the art upon review of the following descriptions of specific embodiments of the mobile communication devices and the methods for ADS during an IRAT procedure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is a block diagram illustrating a wireless communications environment according to an embodiment of the invention; 
         FIG. 2  is a block diagram illustrating the mobile communication device  110  according to an embodiment of the invention; 
         FIGS. 3A and 3B  show a flow chart illustrating the method for ADS during an IRAT procedure according to an embodiment of the invention; and 
         FIGS. 4A and 4B  show a flow chart illustrating the method for ADS during an IRAT procedure according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. It should be understood that the embodiments may be realized in software, hardware, firmware, or any combination thereof. Note that the 3rd Generation Partnership Project (3GPP) specifications described herein are used to teach the spirit of the invention, and the invention is not limited thereto. 
       FIG. 1  is a block diagram illustrating a wireless communications environment according to an embodiment of the invention. The wireless communications environment  100  comprises a mobile communication device  110 , and service networks  120  and  130 . The service network  120  is an LTE-based network, such as an LTE, TD-LTE, or LTE-A network, while the service network  130  is a legacy network, such as a 2G network (e.g., a GSM, GPRS, or EDGE network) or a 3G network (e.g., a WCDMA network). For example, the service network  120  may be an LTE network while the service network  130  may be a GSM/GPRS/EDGE network. An LTE network may comprise an access network and a core network, wherein the access network may be an Evolved-Universal Terrestrial Radio Access Network (E-UTRAN) which includes at least an evolved NB (eNB), and the core network may be an Evolved Packet Core (EPC) which includes a Home Subscriber Server (HSS), Mobility Management Entity (MME), Serving Gateway (S-GW), Packet Data Network Gateway (PDN-GW or P-GW). A GSM/GPRS/EDGE network may comprise an access network and a core network, wherein the access network may be a Base Station Subsystem (BSS) which includes at least a Base Transceiver Station (BTS) and a Base Station Controller (BSC), and the core network may be a GPRS core which includes a Home Location Register (HLR), at least one Serving GPRS Support Node (SGSN), at least one Gateway GPRS Support Node (GGSN). Alternatively, if the service network  130  is a WCDMA network, it may comprise an access network and a core network, wherein the access network may be a UTRAN which includes at least a Node B and a Radio Network Controller (RNC), and the core network may be a GPRS core. 
     The mobile communication device  110  may selectively communicate with the service network  120  or  130  for obtaining mobile services, including CS and/or PS services. The CS services may include voice call services, and Short Message Service (SMS), etc., and the PS services may include Video-over-LTE (ViLTE) services, Voice-over-LTE (VoLTE) services, and data services, such as e-mail transmission, web browsing, file upload/download, instant messaging, streaming video, or others. That is, the mobile communication device  110  is a multimode mobile phone which supports multiple RATs including the RATs utilized by the service networks  120  and  130 . In another embodiment, the mobile communication device  110  may be used as an external data card for a computer host, notebook, or panel PC to access Internet resources. 
       FIG. 2  is a block diagram illustrating the mobile communication device  110  according to an embodiment of the invention. The mobile communication device  110  comprises a Radio Frequency (RF) device  10 , a Baseband chip  20 , a display device  30 , an input device  40 , and a storage device  50 , wherein the RF device  10 , the display device  30 , the input device  40 , and the storage device  50  are coupled to the Baseband chip  20 . The Baseband chip  20  comprises a processor  21 , such as a general-purpose processor, a Micro Control Unit (MCU), a Digital Signal Processor (DSP), or the like, for controlling the RF device  10 , sending a series of frame data (e.g. representing text messages, graphics, images or others) to the display device  30 , receiving signals from the input device  40 , and storing and retrieving data to and from the storage device  50 . Most importantly, the processor  21  coordinates the above mentioned operations of the RF device  10 , the display device  30 , the input device  40 , and the storage device  50  for performing the method for ADS during an IRAT procedure in the invention. 
     Additionally, the Baseband chip  20  may also contain other hardware components to perform baseband signal processing, including Analog-to-Digital Conversion (ADC)/Digital-to-Analog Conversion (DAC), gain adjusting, modulation/demodulation, encoding/decoding, and so on. The RF device  10  may receive RF wireless signals via the antenna, convert the received RF wireless signals to baseband signals, which are processed by the Baseband chip  20 , or receive baseband signals from the Baseband chip  20  and convert the received baseband signals to RF wireless signals, which are later transmitted via the antenna. The RF device  10  may also contain multiple hardware devices to perform radio frequency conversion. For example, the RF device  10  may comprise a mixer to multiply the baseband signals with a carrier oscillated in the radio frequency of the supported RATs, wherein the radio frequency may be 900 MHz, 1800 MHz or 1900 MHz utilized in GSM/GPRS/EDGE technology, or may be 900 MHz, 1900 MHz or 2100 MHz utilized in WCDMA technology, or may be 900 MHz, 2100 MHz, or 2.6 GHz utilized in LTE/LTE-A/TD-LTE technology, or others, depending on the RAT in use. 
     The display device  30  may be a Liquid Crystal Display (LCD), Light-Emitting Diode (LED) display, or Electronic Paper Display (EPD), etc., for providing a display function. Alternatively, the display device  30  may further comprise one or more touch sensors disposed thereon or thereunder for sensing touches, contacts, or approximations of objects, such as fingers or styluses. 
     The input device  40  may comprise one or more buttons, a keyboard, a mouse, a touch pad, a video camera, a microphone, and/or a speaker, etc., serving as the Man-Machine Interface (MMI) for interaction with users. 
     The storage device  50  may be a memory, such as a FLASH memory or a Non-volatile Random Access Memory (NVRAM), or a magnetic storage device, such as a hard disk or a magnetic tape, or an optical disc, or any combination thereof for storing communication data for the Baseband chip  20 , instructions and/or program codes of applications, and/or user data. 
       FIGS. 3A and 3B  show a flow chart illustrating the method for ADS during an IRAT procedure according to an embodiment of the invention. In this embodiment, the method is applied to the mobile communication device  110  which supports the LTE technology and the 2G or 3G technology, and specifically executed by a processor of the mobile communication device  110 . To begin, the mobile communication device  110  receives a request for an MO call (step S 301 ). The MO call may be requested by the upper layer (e.g., the Non-Access Stratum (NAS) layer or the Application layer) of the communication protocol in use. Next, the mobile communication device  110  determines whether an IRAT procedure is ongoing (step S 302 ), and if so, starts a guard timer T 1  (step S 303 ). 
     Subsequent to step S 303 , the mobile communication device  110  determines whether the IRAT procedure is completed before the guard timer T 1  expires (step S 304 ), and if not, rejects the request for the MO call (step S 305 ), and the method ends. In one embodiment, the mobile communication device  110  may reject the request for the MO call by sending an indication with a failure cause (e.g., “Service Not Available”) to the upper layer. 
     Subsequent to step S 304 , if the IRAT procedure is completed before the guard timer T 1  expires, the mobile communication device  110  stops the guard timer T 1  (step S 306 ), and then starts another guard timer T 2  (step S 307 ) and performs the ADS (step S 308 ). Specifically, the ADS may take the following factors into account for deciding an access domain for making the MO call: 1) the state of the mobile communication device  110  in the CS domain (e.g., the state information may indicate “Detached” or “Attached”); 2) the state of the mobile communication device  110  in the IMS domain (e.g., the state information may indicate “Registered” or “Unregistered”); 3) the access domain used by an existing session/call for the same service; 4) user preferences and any available operator policy (e.g., the IMS domain for VoLTE is preferred); 5) the “IMS voice over PS session supported indication” as defined in the 3GPP Technical Specifications (TS) 23.030 and 23.401; 6) whether the mobile communication device  110  is expected to behave in a “Voice centric” or “Data centric” way; 7) whether the mobile communication device  110  supports the IMS PS voice service; 8) indications provided by the service network  120  or  130  via the Evolved Packet System/International Mobile Subscriber Identity (EPS/IMSI) ATTACH or TRACKING AREA UPDATE message (e.g., “SMS-only” indication or “CSFB Not Preferred” indication as defined in the 3GPP TS 23.272). 
     After that, it is determined whether the decision of the ADS is the CS domain, the IMS domain, or others (step S 309 ). If the decision of the ADS is the CS domain, the mobile communication device  110  makes the MO call through the CS domain of the service network  130  (step S 310 ). In one embodiment, if the mobile communication device  110  is currently camped on or connected with the service network  120  and the decision of the ADS is the CS domain, it is first required to perform a Circuit Switched Fallback (CSFB) procedure to switch from the service network  120  to the service network  130  before step S 310 . 
     If the decision of the ADS is the IMS domain, the mobile communication device  110  makes the MO call through the IMS domain of the service network  120  (step S 311 ). If the decision of the ADS is not the CS domain and not the IMS domain, the mobile communication device  110  performs other actions (step S 312 ), e.g., performs Public Land Mobile Network (PLMN) search. 
     Subsequent to steps S 310  and S 311 , it is determined whether the MO call is made successfully (step S 313 ), and if so, the mobile communication device  110  stops the guard timer T 2  (step S 314 ) and the method ends. Otherwise, if the MO call fails, it is determined whether the guard timer T 2  has expired (step S 315 ). If the guard timer T 2  has expired, the method ends. If the guard timer T 2  has not expired, the method goes to step S 308  to repeat the ADS. 
       FIGS. 4A and 4B  show a flow chart illustrating the method for ADS during an IRAT procedure according to another embodiment of the invention. Similar to the embodiment of  FIGS. 3A and 3B , the method is applied to the mobile communication device  110 , and specifically executed by a processor of the mobile communication device  110 . To begin, the mobile communication device  110  receives a request for an MO call (step S 401 ). The MO call may be requested by the upper layer (e.g., the NAS layer or the Application layer) of the communication protocol in use. Next, the mobile communication device  110  determines whether an IRAT procedure is ongoing (step S 402 ), and if so, starts a guard timer T (step S 403 ). 
     Subsequent to step S 403 , the mobile communication device  110  determines whether the IRAT procedure is completed before the guard timer T expires (step S 404 ), and if not, rejects the request for the MO call (step S 405 ), and the method ends. In one embodiment, the mobile communication device  110  may reject the request for the MO call by sending an indication with a failure cause (e.g., “Service Not Available”) to the upper layer. 
     Subsequent to step S 404 , if the IRAT procedure is completed before the guard timer T expires, the mobile communication device  110  performs the ADS (step S 406 ). The ADS is similar to that in the embodiment of  FIGS. 3A and 3B , and the detailed description is not repeated herein for brevity. 
     After that, it is determined whether the decision of the ADS is the CS domain, the IMS domain, or others (step S 407 ). If the decision of the ADS is the CS domain, the mobile communication device  110  makes the MO call through the CS domain of the service network  130  (step S 408 ). If the decision of the ADS is the IMS domain, the mobile communication device  110  makes the MO call through the IMS domain of the service network  120  (step S 409 ). If the decision of the ADS is not the CS domain and not the IMS domain, the mobile communication device  110  performs other actions (step S 410 ). 
     Subsequent to steps S 408  and S 409 , it is determined whether the MO call is made successfully (step S 411 ), and if so, the mobile communication device  110  stops the guard timer T (step S 412 ) and the method ends. Otherwise, if the MO call fails, it is determined whether the guard timer T has not expired (step S 413 ). If the guard timer T has not expired, the method goes to step S 406  to repeat the ADS. If the guard timer T has expired, the method ends. 
     Please note that, unlike the embodiment of  FIGS. 3A and 3B  using two separate guard timers T 1  and T 2  for guarding the IRAT procedure and the ADS, respectively, the embodiment of  FIGS. 4A and 4B  only uses one guard timer T for guarding both the IRAT procedure and the ADS. 
     In another embodiment, if another RAT change is required after the MO call is made successfully through the IMS domain of the service network  120 , the mobile communication device  110  may perform the Single Radio Voice Call Continuity (SRVCC) procedure to continue the MO call through the CS domain of the service network  130 . Alternatively, if another RAT change is required during the making of the MO call through the IMS domain of the service network  120 , the MO call may fail. 
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. Those who are skilled in this technology can still make various alterations and modifications without departing from the scope and spirit of this invention. For example, the method of  FIGS. 3A, 3B, 4A, and 4B  may be implemented in program code stored in a machine-readable storage medium, such as a magnetic tape, semiconductor, magnetic disk, optical disc (e.g., CD-ROM, DVD-ROM, etc.), or others, which is loaded and executed by the processor of the mobile communication device. Therefore, the scope of the present invention shall be defined and protected by the following claims and their equivalents.