Abstract:
A mobile communication device having a Semi-Persistent Scheduling (SPS) Cell Radio Network Temporary Identifier (C-RNTI) is provided. In the mobile communication device, a wireless module performs wireless transmission and reception to and from a cellular station, and a controller module performs operations for communication controls. The operations include: determining whether SPS has been enabled for downlink (DL), and instructing the wireless module to monitor a Physical Downlink Control Channel (PDCCH) for a DL assignment reception from the cellular station for a Transmission Time Interval (TTI), in response to the mobile communication device having the SPS C-RNTI and SPS having been enabled for DL.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This Application claims priority of U.S. Provisional Application No. 61/707,173, filed on Sep. 28, 2012, and the entirety of which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention generally relates to Physical Downlink Control Channel (PDCCH) monitoring, and more particularly, to PDCCH monitoring for a downlink assignment reception and an uplink grant reception when the User Equipment (UE) has a Semi-Persistent Scheduling (SPS) Cell Radio Network Temporary Identifier (C-RNTI). 
     2. Description of the Related Art 
     With growing demand for ubiquitous computing and networking, various wireless technologies have been developed, such as the Wireless Local Area Network (WLAN) technologies, including the Wireless Fidelity (WiFi) technology, Bluetooth technology, and the ZigBee technology, etc., as well as cellular technologies including 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, Code Division Multiple Access 2000 (CDMA2000) technology, Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) technology, Worldwide Interoperability for Microwave Access (WiMAX) technology, Long Term Evolution (LTE) technology, Time-Division LTE (TD-LTE) technology, and LTE-Advanced technology, etc. 
     Taking the LTE technology as an example, a feature called Semi-Persistent Scheduling (SPS) has been proposed to reduce control channel overhead for applications that require persistent radio resource allocations such as Voice over Internet Protocol (VoIP). For the LTE technology, both downlink (DL) and uplink (UL) are fully scheduled since the DL and UL traffic channels are dynamically shared channels. This means that the PDCCH must provide access grant information to indicate which user device(s) should decode the Physical Downlink Shared Channel (PDSCH) in each subframe and to indicate which user device(s) is(are) allowed to transmit on the Physical Uplink Shared Channel (PUSCH) in each subframe. Without SPS, every DL or UL Physical Resource Block (PRB) allocation must be granted via an access grant message on the PDCCH. This is sufficient for most bursty best-effort types of applications which generally have large packet sizes and thus typically only a few users must be scheduled in each subframe. However, for applications that require persistent allocations of small packets (e.g. VoIP), the access grant control channel overhead can be greatly reduced with SPS. 
     BRIEF SUMMARY OF THE INVENTION 
     In a first aspect of the invention, a mobile communication device having an SPS C-RNTI is provided. The mobile communication device comprises a wireless module and a controller module. The wireless module performs wireless transmission and reception to and from a cellular station. The controller module performs operations for communication controls, wherein the operations comprise: determining whether SPS has been enabled for DL, and instructing the wireless module to monitor a PDCCH for a DL assignment reception from the cellular station for a Transmission Time Interval (TTI), in response to the mobile communication device having the SPS C-RNTI and SPS having been enabled for DL. 
     In a second aspect of the invention, a method for monitoring a PDCCH by a mobile communication device having an SPS C-RNTI configured by a cellular station is provided. The method comprises the steps of: determining whether SPS has been enabled for DL; and monitoring the PDCCH for a DL assignment reception from the cellular station for a TTI, in response to the mobile communication device having the SPS C-RNTI and SPS having been enabled for DL. 
     In a third aspect of the invention, a mobile communication device having an SPS C-RNTI is provided. The mobile communication device comprises a wireless module and a controller module. The wireless module performs wireless transmission and reception to and from a cellular station. The controller module performs operations for communication controls, wherein the operations comprise: determining whether SPS has been enabled for UL, and instructing the wireless module to monitor a PDCCH for an UL grant reception from the cellular station for a TTI, in response to the mobile communication device having the SPS C-RNTI and SPS having been enabled for UL. 
     In a fourth aspect of the invention, a method for monitoring a PDCCH by a mobile communication device having an SPS C-RNTI configured by a cellular station is provided. The method comprises the steps of: determining whether SPS has been enabled for UL; and monitoring the PDCCH for an UL grant reception from the cellular station for a TTI, in response to the mobile communication device having the SPS C-RNTI and SPS having been enabled for UL. 
     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 monitoring the PDCCH. 
    
    
     
       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 mobile communication environment according to an embodiment of the invention; 
         FIG. 2  is a block diagram illustrating the mobile communication device  10  according to an embodiment of the invention; 
         FIG. 3  is a flow chart illustrating the method for monitoring the PDCCH according to an embodiment of the invention; and 
         FIG. 4  is a flow chart illustrating the method for monitoring the PDCCH 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. 
     It is noted that, according to the 3rd Generation Partnership Project (3GPP) Technical Specification (TS) 36.321 v10.0.0, a UE having a Semi-Persistent Scheduling Cell Radio Network Temporary Identifier (referred to herein as SPS C-RNTI for brevity) should always monitor the PDCCH for a DL assignment reception for a TTI. However, there may be a situation where the cellular station configures SPS with the UE for UL only. Similarly, according to the 3GGP TS 36.321 v10.0.0, a UE having an SPS C-RNTI should always monitor the PDCCH for an UL grant reception for a TTI. However, there may be a situation where the cellular station configures SPS with the UE for DL only. As a result, the PDCCH monitoring for the non-configured UL or DL may cause unnecessary power consumption. 
     In order to solve the aforementioned problems, the invention proposes solutions for a UE to avoid unnecessary PDCCH monitoring when it is configured with an SPS C-RNTI. 
       FIG. 1  is a block diagram illustrating a mobile communication environment according to an embodiment of the invention. In the mobile communication environment, the mobile communication device  10  wirelessly communicates with the service network  20  via an air interface. The mobile communication device  10  may be a smart phone, a panel Personal Computer (PC), a laptop computer, or any computing device supporting at least the wireless technology utilized by the service network  20 . The service network  20  comprises a cellular access network  210  and a core network  220 , wherein the cellular access network  210  is responsible for processing radio signals, terminating radio protocols, and connecting the mobile communication device  10  with the core network  220 . The cellular access network  210  may comprise one or more cellular stations, such as base stations, Node-Bs, or evolved Node-B (eNB), depending on the wireless technology in use. The core network  220  is responsible for performing mobility management and network-side authentication. Although not shown, the core network  220  may further enable interfacing with external networks, such as the Public Switched Telephone Network (PSTN), which is called the Circuit Switched (CS) domain functionality, and/or interfacing with the Internet Protocol (IP) based Network, such as the Internet, which is called the Packet Switched (PS) domain functionality. 
     In one embodiment, the service network  20  may be an LTE network, the cellular access network  210  may be an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) which comprises at least one eNB, and the core network  220  may be an Evolved Packet Core (EPC) which includes a Home Subscriber Server (HSS), Mobility Management Entity (MME), Serving Gateway (S-GW), and Packet Data Network Gateway (PDN-GW or P-GW). Please note that, in another embodiment, a different wireless technology, such as the LTE-Advanced technology or any future evolution of the LTE technology family, may be utilized by the service network  20  and the mobile communication device  10 , and the invention is not limited thereto. 
       FIG. 2  is a block diagram illustrating the mobile communication device  10  according to an embodiment of the invention. The mobile communication device  10  comprises a wireless module  110  and a controller module  120 . The wireless module  110  is responsible for performing the functionality of wireless transmission and reception to and from the service network  20 . The controller module  120  is responsible for controlling the operations of the wireless module  110  for communication controls with the service network  20 , and other functional components (not shown), such as a display unit and/or keypad serving as the Man-Machine Interface (MMI), a storage unit storing the program codes of applications or communication protocols, or others. Also, the controller module  120  controls the wireless module  110  for performing the method for monitoring the PDCCH when the mobile communication device  10  has an SPS C-RNTI. 
     To further clarify, the wireless module  110  may be a Radio Frequency (RF) unit (not shown), and the controller module  120  may be a general-purpose processor or a Micro Control Unit (MCU) of a baseband unit (not shown) (which may be called a baseband processor). The baseband unit may contain multiple hardware devices 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 unit may receive RF wireless signals, convert the received RF wireless signals to baseband signals, which are processed by the baseband unit, or receive baseband signals from the baseband unit and convert the received baseband signals to RF wireless signals, which are later transmitted. The RF unit may also contain multiple hardware devices to perform radio frequency conversion. For example, the RF unit may comprise a mixer to multiply the baseband signals with a carrier oscillated in the radio frequency of the mobile communication system, wherein the radio frequency may be 900 MHz, 2100 MHz, or 2.6 GHz utilized in LTE technology, or others depending on the wireless technology in use. 
     Similar to the mobile communication device  10 , each cellular station in the cellular access network  210  may comprise a wireless module (not shown) and a controller module (not shown), wherein the wireless module is configured to perform the functionality of wireless transceiving for the service network  20  and the controller module is configured to control the operation of the wireless module. 
       FIG. 3  is a flow chart illustrating the method for monitoring the PDCCH according to an embodiment of the invention. In this embodiment, the method for monitoring the PDCCH is applied to a mobile communication device having an SPS C-RNTI configured by a cellular station. To begin, the mobile communication device determines whether SPS has been enabled for DL (step S 310 ), and then monitors the PDCCH for a DL assignment reception from the cellular station for a TTI, in response to the mobile communication device having the SPS C-RNTI and SPS having been enabled for DL (step S 320 ). In one embodiment, the monitoring of the PDCCH for the DL assignment reception from the cellular station may be performed for each serving cell, including Primary Cell (PCell) and Secondary Cell(s) (SCell(s)). In another embodiment, the monitoring of the PDCCH for the DL assignment reception from the cellular station may be performed for PCell only. Unlike the conventional UE, the mobile communication device of the invention checks to see if SPS has been enabled for DL before monitoring the PDCCH for a DL assignment reception, and only performs the PDCCH monitoring when SPS has been enabled for DL. That is, the mobile communication device does not monitor the PDCCH for the DL assignment reception from the cellular station for each TTI and each serving cell, in response to the mobile communication device having the SPS C-RNTI and SPS not having been enabled for DL. Thus, the mobile communication device of the invention advantageously avoids unnecessary PDCCH monitoring for a DL assignment reception when SPS has not been enabled for DL. 
     In one embodiment, the SPS for DL is enabled by the Radio Resource Control (RRC) layer of the communication protocol for the LTE technology, and steps S 310  and S 320  may be performed in compliance with the Media Access Control (MAC) layer of the communication protocol for the LTE technology. 
       FIG. 4  is a flow chart illustrating the method for monitoring the PDCCH according to another embodiment of the invention. In this embodiment, the method for monitoring the PDCCH is applied to a mobile communication device having an SPS C-RNTI configured by a cellular station. To begin, the mobile communication device determines whether SPS has been enabled for UL (step S 410 ), and then monitors the PDCCH for a UL grant reception from the cellular station for a TTI, in response to the mobile communication device having the SPS C-RNTI and SPS having been enabled for UL (step S 420 ). In one embodiment, the monitoring of the PDCCH for the UL grant reception from the cellular station may be performed for each serving cell, including Primary Cell (PCell) and Secondary Cell(s) (SCell(s)). In another embodiment, the monitoring of the PDCCH for the UL grant reception from the cellular station may be performed for PCell only. Unlike the conventional UE, the mobile communication device of the invention checks to see if SPS has been enabled for UL before monitoring the PDCCH for an UL grant reception, and only performs the PDCCH monitoring when SPS has been enabled for UL. That is, the mobile communication device does not monitor the PDCCH for the UL grant reception from the cellular station for each TTI and each serving cell, in response to the mobile communication device having the SPS C-RNTI and SPS not having been enabled for UL. Thus, the mobile communication device of the invention advantageously avoids unnecessary PDCCH monitoring for an UL grant reception when SPS has not been enabled for UL. 
     In one embodiment, the SPS for UL is enabled by the RRC layer of the communication protocol for the LTE technology, and steps S 410  and S 420  may be performed in compliance with the MAC layer of the communication protocol for the LTE technology. 
     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. Therefore, the scope of the invention shall be defined and protected by the following claims and their equivalents.