Patent Publication Number: US-2010110896-A1

Title: Method of improving discontinuous reception functionality and related communication device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/111,731, filed on Nov. 6, 2008 and entitled “Method of determining the start timing of DRX”, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and related communications device for improving discontinuous reception (DRX) functionality in a wireless communications system, and more particularly, to a method and related communications device for improving a start mechanism of an on duration timer of the DRX functionality. 
     2. Description of the Prior Art 
     Long Term Evolution wireless communications system (LTE system), an advanced high-speed wireless communications system established upon the 3G mobile telecommunications system, supports only packet-switched transmission, and tends to implement both Medium Access Control (MAC) layer and Radio Link Control (RLC) layer in one single communication site, such as in Node B alone rather than in Node B and RNC (Radio Network Controller) respectively, so that the system structure becomes simple. 
     In the LTE system, prior art discloses a Discontinuous Reception (DRX) functionality applied to the MAC layer for allowing a user equipment (UE) to enter a standby mode during certain periods of time and stop monitoring a Physical Downlink Control Channel (PDCCH), so as to reduce power consumption of the UE. 
     According to related specification, when the DRX functionality is configured, whenever a new DRX cycle begins, an on duration timer is started and the UE is awaked to monitor the PDCCH. Wherein, the DRX cycle comprises a long DRX cycle and a short DRX cycle. 
     When the UE enters a short DRX cycle or a long DRX cycle, the UE starts the on duration timer so as to monitor the PDCCH. The start mechanism of the on duration timer controls DRX to monitor PDCCH according to the following equations: 
       [(SFN×10)+SubFN] mod (Short DRX Cycle)=DRX Start Offset; and  Equation A 
       [(SFN×10)+SubFN] mod (Long DRX Cycle)=DRX Start Offset;  Equation B 
     where SFN indicates a system frame number, SubFN indicates a subframe number, mod indicates modulo operation, Short DRX Cycle and Long DRX Cycle indicate a short and a long DRX cycle parameters respectively, which specify the length of the short and long DRX cycle, and DRX Start Offset indicates a DRX start offset parameter, which specifies the initial time of DRX cycle. 
     Please note that [(SFN×10)+SubFN] in equation A and B represents which TTI (transmission time interval) the UE starts the on duration timer on. Detailed operation to obtain the TTI is well known by those skilled in the art, and is not narrated herein. 
     In short, the UE controls the timing to start the on duration timer base on the equations A and B. When the UE enters the short DRX cycle or the long DRX cycle, the corresponding equation A or B is executed. While the corresponding equation A or B is conformed, the on duration timer is started so that the UE can monitor the PDCCH. Whereas, according to the above equations A and B, a failure when using the short DRX cycle may occur due to the same DRX Start Offset for the short DRX cycle and the long DRX cycle, and hence results in problem that the UE fails to start the on duration timer to monitor the PDCCH. 
     In the prior art, DRX start offset parameter is set based on the long DRX cycle. In ordinary DRX functionality activated situation, the duration of the long DRX cycle is longer than the duration of the short DRX cycle, i.e. Long DRX Cycle&gt;Short DRX Cycle, which infers that DRX Start Offset would possibly be larger than Short DRX Cycle. Therefore, while the UE is in the short DRX cycle case, if DRX Start Offset&gt;=Short DRX Cycle, the problem that the UE fails to start the on duration timer to monitor the PDCCH. 
     An example is illustrated as follows besed on assumptions of DRX Start Offset=60, Long DRX Cycle=80, and Short DRX Cycle=40. When the UE enters the long DRX cycle and starts the on duration timer at a TTI=x, i.e. [(SFN×10)+SubFN]=x, it can be shown that x mod  80 =60 according to the above equation B. Therefore, the UE starts the on duration timer to monitor the PDCCH at TTIs=60, 140, 220, 300, . . . . By contrast, when the UE enters the short DRX cycle and starts the on duration timer at TTI=x, it can be shown that x mod  40 =60 according to the above equation A, which is illogical in mathematics calculation. It will cause an error in the UE system and result in problem that the UE fails to start the on duration timer to monitor the PDCCH in the short DRX cycle case. 
     In addition, prior art has provided a solution that when the UE enters the short DRX cycle, the UE gives a new DRX start offset parameter to be used in the above equation A situation. However, this solution leads to additional parameters or signalings. 
     SUMMARY OF THE INVENTION 
     It is therefore an objective of the present invention to provide a method and related apparatus of improving discontinuous reception (DRX) functionality for a user equipment (UE) of a wireless communication system. 
     The present invention discloses a method of improving DRX functionality for a UE of a wireless communication system comprising entering a DRX cycle; executing a first equation according to a system frame number, a subframe number, and a DRX cycle parameter, for generating a first result; executing a second equation according to a DRX start offset parameter and the DRX cycle parameter, for generating a second result; and starting an on duration timer for monitoring a Physical Downlink Control Channel when the first result is equivalent to the second result. 
     The present invention further discloses a communication device in a UE of a wireless communication system for improving DRX functionality, comprising a control circuit for realizing functions of the communication device; a processor installed in the control circuit for executing a program to control the control circuit; and a memory installed in the control circuit coupled to the processor for storing the program; wherein the program comprises entering a DRX cycle; executing a first equation according to a system frame number, a subframe number, and a DRX cycle parameter, for generating a first result; executing a second equation according to a DRX start offset parameter and the DRX cycle parameter, for generating a second result; and starting an on duration timer for monitoring a Physical Downlink Control Channel when the first result is equivalent to the second result. 
     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 
         FIG. 1  is a schematic diagram of a wireless communications system. 
         FIG. 2  is a functional block diagram of a communications device. 
         FIG. 3  is a schematic diagram of a program shown in  FIG. 2 . 
         FIG. 4  is a flowchart of a process according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 1 , which is a schematic diagram of a wireless communications system  10 . The wireless communications system  10  is preferred to be a Long Term Evolution (LTE) communications system, and is briefly formed with a network terminal and a plurality of user equipments (UEs). In  FIG. 1 , the network terminal and the UEs are simply utilized for illustrating the structure of the wireless communications system  10 . Practically, the network terminal may include a plurality of evolved base stations (eNBs), an evolved UMTS radio access network (EUTRAN) and so on according to actual demands, and the UEs can be apparatuses such as mobile phones, computer systems, etc. 
     Please refer to  FIG. 2 , which is a functional block diagram of a communications device  100 . The communications device  100  can be utilized for realizing the UE in  FIG. 2 . For the sake of brevity,  FIG. 2  only shows an input device  102 , an output device  104 , a control circuit  106 , a central processing unit (CPU) (or processor)  108 , a memory  110 , a program  112 , and a transceiver  114  of the communications device  100 . In the communications device  100 , the control circuit  106  executes the program  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 inputted 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, deliver received signals to the control circuit  106 , and output 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 . 
     Please continue to refer to  FIG. 3 .  FIG. 3  is a schematic diagram of the program  112  shown in  FIG. 2 . The program  112  includes an application layer  200 , a Layer  3   202 , and a Layer  2   206 , and is coupled to a Layer  1   218 . A MAC unit  222  located in the layer  2   206  is able to perform a plurality of HARQ processes to receive packages, and support a discontinuous Reception (DRX) functionality. The present invention provides an embodiment of a DRX functionality improving program  220  in the program  112 , which improves a start mechanism of an on duration timer of the DRX functionality, to avoid the problem that a system error occurs when the MAC unit  222  executes the DRX functionality according to a Radio Resource Control (RRC) command. 
     Please refer to  FIG. 4 .  FIG. 4  is a flowchart of a process  40  according to an embodiment of the present invention. The process  40  is used for improving DRX functionality for a UE of the wireless communication system  10  in  FIG. 1 , and can be compiled into the DRX functionality improving program  220 . The process  40  includes the following steps: 
     Step  400 : Start. 
     Step  402 : Enter a DRX cycle. 
     Step  404 : Execute a first equation according to a system frame number, a subframe number, and a DRX cycle parameter, for generating a first result. 
     Step  406 : Execute a second equation according to a DRX start offset parameter and the DRX cycle parameter, for generating a second result. 
     Step  408 : Start an on duration timer for monitoring a Physical Downlink Control Channel (PDCCH) when the first result is equivalent to the second result. 
     Step  410 : End. 
     According to the process  40 , when the UE enters the DRX cycle, the UE executes a first equation according to a system frame number, a subframe number, and a DRX cycle parameter, for generating a first result, and execute a second equation according to a DRX start offset parameter and the DRX cycle parameter, for generating a second result. When the first result is equivalent to the second result, the UE starts an on duration timer for monitoring a Physical Downlink Control Channel. 
     In short, whether to start the on duration timer is based on the equivalence of the first result and the second result. If the first result is equivalent to the second result, the on duration timer will be started. 
     Preferably, the first equation is R 1 =[(SFN×10)+SubFN] mod (DRX Cycle), wherein R 1  indicates the first result, SFN indicates the system frame number, mod indicates modulo operation, SubFN indicates the subframe number, and DRX Cycle indicates the DRX cycle parameter. Whereby the second equation is R 2 =(DRX Start Offset) mod (DRX Cycle), wherein R 2  indicates the second result, DRX Cycle indicates the DRX cycle parameter, mod indicates modulo operation, and DRX Start Offset indicates the DRX start offset parameter. 
     According to the embodiment of the present invention, if the first result and the second result generated respectively by the above first equation and the second equation are identical, the UE starts the on duration timer so as to monitor the PDCCH. Please note that the DRX cycle may be the long DRX cycle or the short DRX cycle, and correspondingly, DRX Cycle parameter may corresponds to Long DRX Cycle or Short DRX Cycle. 
     The embodiment of the present invention can be applied to both the long DRX cycle case and the short DRX cycle case for avoiding the problem that the UE fails to start the on duration timer to monitor the PDCCH in specific situation of the short DRX cycle case. An example is illustrated as follows based on assumptions of DRX Start Offset=60, Long DRX Cycle=80, and Short DRX Cycle=40. When the UE enters the long DRX cycle and starts the on duration timer at a TTI=y, i.e. [(SFN×10)+SubFN]=y, it can be shown that R 1 =y mod  80  according to the first equation and R 2 =60 according to the second equation. According to the embodiment of the present invention, the UE starts the on duration timer to monitor the PDCCH at the time the first result R 1  equals the second result R 2 , that is, in the long DRX case, the UE starts the on duration timer to monitor the PDCCH at TTIs=60, 140, 220, 300, . . . . Similarly, when the UE enters the short DRX cycle, it can be shown that y mod  40 =20 according to the first result and the second result derived from the first equation and the second equation respectively. As a result, in the short DRX case, the UE starts the on duration timer to monitor the PDCCH at TTIs=20, 60, 100 . . . 
     In the prior art, when the UE enters the short DRX cycle, if the value of the DRX start offset parameter is larger than the value of the short DRX cycle parameter, the UE cannot start the on duration timer. Compared to that, in the embodiment of the present invention, when the UE enters the short DRX cycle, even if the value of the DRX start offset parameter is larger than the value of the short DRX cycle parameter, through the process  40 , the on duration timer can still be started so that the UE is able to monitor the PDCCH. Meanwhile, the first equation and the second equation do not include additional parameters, thereof, the UE using the embodiment of the present invention does not require creating additional parameter or signaling. 
     In conclusion, the embodiment of the present invention provides a start mechanism of an on duration timer of the DRX functionality, and the problem that the UE fails to start the on duration timer to monitor the PDCCH in the short DRX cycle case is therefore avioded. 
     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.