Patent Abstract:
A method and apparatus for managing power during discontinuous reception (DRX) mode are disclosed. A DRX mode is defined for a wireless transmit/receive unit (WTRU) for reducing power consumption of the WTRU. During the DRX mode, the WTRU enters into a sleep state and periodically wakes up for processing paging blocks for detecting a paging indication for the WTRU and a corresponding paging message. If the WTRU is paged the WTRU terminates the DRX mode. If the WTRU is not paged, the WTRU reenters the sleep state. For power management during the DRX mode, a synchronization update period is defined. The synchronization update period is a period for performing automatic frequency correction and/or frame time correction.

Full Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of U.S. Provisional Patent Application No. 60/717,997 filed Sep. 16, 2005, which is incorporated by reference as if fully set forth. 
     
    
     FIELD OF INVENTION  
       [0002]     The present invention is related to wireless communication systems. More particularly, the present invention is related to a method and apparatus for managing power during a discontinuous reception (DRX) mode.  
       BACKGROUND  
       [0003]     Reducing power consumption is one of the most important challenges when designing the wireless transmit/receive units (WTRUs). Increased bandwidth, higher data rates and multimedia user interfaces result in higher power demands for new WTRUs as compared to previous generations of WTRUs.  
         [0004]     The DRX mode is intended to identify periods of relative inactivity of the WTRU, which provides opportunities to conserve battery power by powering down various on-board components in the WTRU. The WTRU is informed of occasions when the WTRU must wake up to receive transport information.  
         [0005]     The WTRU radio resource control (RRC) has a connected mode and an idle mode. The connected mode includes an active connected mode and an inactive connected mode. In the connected mode, the WTRU RRC has four states: CELL_DCH, CELL_FACH, CELL_PCH, and URA_PCH. The CELL_DCH and the CELL_FACH states take place only in the active connected mode, and the CELL_PCH and the URA_PCH states take place only in the inactive connected mode. The DRX mode takes place in the inactive connected mode, (CELL_PCH, URA_PCH states), and in the idle mode.  
         [0006]     The basic difference between DRX in the idle mode and the connected mode is that, in the idle mode, it is the core network (CN) that controls the DRX cycle; whereas in the inactive connected mode, it is the universal mobile telecommunication system (UMTS) terrestrial radio access network (UTRAN) that controls the DRX cycle.  
         [0007]     During DRX mode, the WTRU must wake up on Paging Occasions (POs) as directed by the RRC, based on system information settings. A PO indicates the beginning of a paging block. The RRC is responsible for scheduling the time, the duration and on which channel the physical layer of the WTRU must listen to.  
       SUMMARY  
       [0008]     The present invention is related to a method and apparatus for managing power during DRX mode. During the DRX mode, the WTRU enters into a sleep state and periodically wakes up for processing paging blocks for detecting a paging indication for the WTRU and a corresponding paging message. If the WTRU is paged, the WTRU terminates the DRX mode. If the WTRU is not paged, the WTRU reenters the sleep state. For power management during the DRX mode in the WTRU, a synchronization update period is defined. The synchronization update period is a period for performing automatic frequency correction (AFC) and/or frame time correction (FTC). 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     A more detailed understanding of the invention may be had from the following description, given by way of example and to be understood in conjunction with the accompanying drawings wherein:  
         [0010]      FIG. 1  is a diagram of time slot level timing requirements for DRX mode in accordance with the present invention;  
         [0011]      FIG. 2  shows inputs and outputs for an AFC algorithm;  
         [0012]      FIG. 3  is a block diagram of a closed loop AFC;  
         [0013]      FIG. 4  shows inputs and outputs for FTC operation; and  
         [0014]      FIG. 5  is a block diagram showing relationship between an FTC unit and a timing manager in a WTRU. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]     Hereafter, the terminology “WTRU” includes but is not limited to a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, or any other type of device capable of operating in a wireless environment.  
         [0016]     The features of the present invention may be incorporated into an integrated circuit (IC) or be configured in a circuit comprising a multitude of interconnecting components.  
         [0017]     Hereinafter, the present invention will be explained with reference to UMTS time division duplex (TDD) systems. However, the present invention is applicable to any wireless communication systems including, but not limited to, UMTS frequency division duplex (FDD), TD-SCDMA, CDMA 2000, or the like.  
         [0018]     The present invention provides an efficient power management method for the physical layer of a WTRU. In accordance with the present invention, AFC and FTC are performed during DRX mode, and a sleep timer is preferably provided for synchronization during DRX mode. The WTRU updates its frame synchronization and timing synchronization periodically during DRX mode to be able to successfully read paging indicators (PIs) and perform cell reselection measurements. Periodic DRX activities for the physical layer include cell reselection and the related measurements, monitoring PIs and maintaining frame and timing synchronization.  
         [0019]     Five different physical layer states are defined as follows: an active connected state, an inactive connected state, a sleep state, a PI reading state, and a synchronization update state. During the active connected state, almost all components are powered on and normal operation for communication is performed. During the inactive connected state, some components are powered down. During the sleep state, most of the components are powered down and the WTRU neither reads the paging block nor updates the frame or timing synchronization. Functionality required during the sleep state is limited to monitoring clock, detection of user activity and interface with debug equipment, and activation of triggers to wake-up various on-board components in sequence. During the PI reading state, the WTRU wakes up from the sleep state to read the related PI via a paging indicator channel (PICH) in each paging block. If the WTRU detects that it is paged through the related PI in the PICH, the WTRU reads a paging channel (PCH) to access the paging message. Otherwise, the WTRU returns to the sleep state. During the synchronization update state, synchronization updating is performed, AFC and FTC are run and TCXO control voltage and frame synchronization are updated.  
         [0020]      FIG. 1  is a diagram of time slot level timing requirements for DRX mode in accordance with the present invention. A frame offset  102  is generated by the FTC for frame synchronization, which will be explained hereinafter. During DRX mode, the WTRU may be in the sleep state, in the PI reading state or in the synchronization update state. The WTRU enters the PI reading state sometime in the paging block  104  and enters the synchronization update state in the sync update block  106 . The WTRU is in the sleep state in the remaining blocks  108 .  
         [0021]     A DRX cycle length is the time difference between two POs for a specific WTRU. In UMTS TDD, one PO corresponds to one paging block. Therefore, the DRX cycle length is the time difference between two paging blocks  104 . A paging block  104  comprises a PICH block  112 , a gap period  114  and a PCH block  116 . The PICH block  112  comprises 2 or 4 frames of PIs. The gap period  114  comprises 2, 4, or 8 frames where physical resources can be used by other channels. The PCH block  116  comprises 2 to 16 frames of paging messages for one to eight paging groups. For the idle mode, the allowed DRX cycle lengths are 0.64, 1.28, 2.56 and 5.12 seconds. For the inactive connected mode, the allowed DRX cycle lengths are 0.08, 0.16, 0.32, 0.64, 1.28, 2.56 and 5.12 seconds.  
         [0022]     The synchronization update period is a period between two consecutive sync update blocks  106 . The synchronization update period is preferably set to 256 or 512 frames depending on the DRX cycle length. The sync update block  106  preferably, but not necessarily, comprises 21 frames. The first frame  122   1  is for TCXO settle time and every fifth frame  124   1 - 124   4  starting from the second frame is processed for AFC and FTC, which will be explained in detail hereinafter. The TCXO settle frames  122   2 - 122   5  are also provided before each frame  124   1 - 124   4  to be processed. During the intervening frames  126   1 - 126   4 , each of which is three frames, the WTRU is powered is down. Therefore, during the synchronization update block, the WTRU is periodically powered up and powered down for AFC and FTC. If the DRX cycle length is 16 frames, the sync update block  106  may overlap one paging block  104 , and if the DRX cycle length is 8 frames, the sync update block  106  may overlap two paging blocks  104 . In these cases, regular paging procedures and synchronization update activities are implemented in parallel.  
         [0023]     AFC operation will now be described. Since a specific implementation of AFC is not within the scope of the present invention, AFC operation will only be briefly described.  FIG. 2  shows inputs and outputs for an AFC unit  200  which implements an AFC algorithm. A received signal  202  (preferably 2× over-sampled), an odd/even frame indicator  204 , a cell parameter  206 , RF carrier frequency  208  and initial voltage controlled oscillator (VCO) digital-to-analog converter (DAC) control voltage  210  are input for the AFC unit  200  based upon a user defined value or a previously stored value. The AFC unit  200  outputs are a control voltage to the VCO  212 , an estimated frequency error  214  and a convergence indicator  216 . The operating frequency of the VCO is determined by the control voltage  212 . The convergence indicator  226  indicates that the AFC algorithm reaches a steady state.  
         [0024]      FIG. 3  is a block diagram of a closed loop AFC unit  300 . Received signals  302  are mixed with signals  308  generated by the VCO  306  by a multiplier  304  to be converted to baseband signals  310 . The baseband signals  310  are converted to a digital data  314  by an analog-to-digital converter (ADC)  312 . The digital data is processed by a raised root cosine (RRC) filter  316  and fed into a frequency estimation block  318 . A frequency error is computed by the frequency estimation block  318  and a cell search/FTC block  320  and the estimated frequency error  214  is sent to a loop filter that generates the correction voltage for the VCO  306 . This correction voltage is converted to a digital signal by a digital-to-analog converter (DAC)  324  and filtered by a low pass filter (LPF)  326  and drives the measured frequency error to zero in a steady state. Baseband transmit data  332  is converted to an analog data  335  by a DAC  334  and multiplied with a VCO output  309  by a multiplier  336  for transmission.  
         [0025]     During the active connected state, AFC is running as normal. Before entering into the DRX mode, the last value of the VCO DAC register is saved in memory. This value is used during the DRX mode until the next VCO value is available from synchronization update. During the sleep state and the inactive connected state, since there is no data reception, AFC is shut down when the processing from the previous active timeslots is completed. During the PI reading state, AFC is running and the P-CCPCH beacon is read during each frame in the paging block. During the synchronization update state, AFC runs using only one midamble per frequency update and with special timing as shown in  FIG. 1 . However, during the PI reading period, the number of midambles processed per frame depends on the frequency error, which is similar to the AFC operation during the active connected mode.  
         [0026]     There are two reasons for running AFC during the DRX mode. The first reason is the effect of WTRU motion on the acquired sampling period of the WTRU, which is controlled by the VCO  306 . If the speed of the WTRU changes during the sleep interval, the difference in speed of the WTRU before and during the sleep cycle will look like an extra drift rate change in the VCO  306 . As an example, assume that the WTRU is not moving before the DRX cycle. Afterwards, the WTRU goes into the DRX mode. Also assume that, when the WTRU goes into a synchronization update state during DRX mode, the speed of the WTRU becomes 120 km/h, which is the maximum speed from WG4 test cases. As a result, the difference in speed is Vd=120 km/h. This speed corresponds to Drift ppm =(vd/c)×1.0e6=0.11 ppm drift, where c is the speed of light. However, this drift is extremely unlikely since the maximum time difference between the beginning of a DRX cycle and the next synchronization update may be approximately five seconds. Since this number is not the driving requirement for the design, it can be kept as described hereinbefore. Additionally, a possibility of an extra drift rate change due to turning off the VCO during the DRX period requires a VCO control voltage update during DRX.  
         [0027]     To correct for this possible change in drift rate, the WTRU wakes up at the beginning of the sync update block and performs AFC and FTC. Since AFC needs to update the VCO control voltage, all the physical layer components preceding AFC should be working as well. This includes a root raised cosine (RRC) filter, an automatic gain control (AGC), and a gain scaler.  
         [0028]     At the beginning of the sleep period of a DRX cycle, the receiver and the TCXO are shut down. The radio must be powered up before every synchronization update. The TCXO and phase locked loop (PLL) joint power up time is around 5 msec. The synthesizer and other hardware components require much less time to power up. Therefore, the radio should preferably power-up at least 5 msec before the first frame necessary to process, (i.e., paging blocks and frames for AFC and FTC). This is a radio power-up time, (which is shown as “TCXO settle time” before each paging block and during the sync update block in  FIG. 1 ). The radio power-up time may be designated to a start of a given frame, (i.e., one frame earlier than the start of each paging block or first P-CCPCH beacon frame to be read).  
         [0029]     The synchronization update block preferably comprises 21 frames. The first frame (and every fifth frame thereafter) is for TCXO settling time as explained hereinbefore. A beacon, (i.e., P-CCPCH signal), is then acquired every fifth frame starting from the second frame of the synchronization update block. The midamble part of the first P-CCPCH timeslot is extracted and passed to the frequency estimation unit for new frequency error estimation. After reading the beacon, the power is shut down and then up again at the next TCXO settle time for reading the next beacon. This is repeated four times during the synchronization update state.  
         [0030]     Using beacons separated in time, instead of using four beacons from consecutive frames, increases robustness of frame synchronization under slow fading conditions. The midambles processed during the synchronization update state are summarized in Table 1. It should be noted that the specific numerical selections in the foregoing paragraphs and Table 1, (and throughout this document), are provided as an example, not as a limitation, and any other numbers may be used alternatively.  
                               TABLE 1                           synchro-                       nization       Radio wake       DRX cycle   update   P-CCPCH frame   up frame       length   period   numbers used   number   Next PO                   8, 16, 32, 64,   256   256N- 20   256N - 21   256N       128, 256       256N- 15               256N- 10               256N- 5       512   512   512N- 20   512N - 21   512N               512N- 15               512N- 10               512N- 5                  
 
         [0031]     The timing of these frames for AFC is also used for FTC. Since AFC has its own multipath search window, AFC can work without waiting for a frame synchronization update. Therefore, AFC and FTC may run at the same time. Since both AFC and FTC only use P-CCPCH midambles, it is computationally easier to run them at the same time. Therefore, AFC simply borrows this timing schedule from FTC.  
         [0032]     The synchronization update rate preferably depends on the DRX cycle length as summarized in Table 1. For DRX cycle lengths up to 256 frames, the synchronization update period is 256 frames and for the DRX cycle length of 512 frames, the synchronization update period is 512 frames.  
         [0033]     The midamble processing and frequency update for AFC during DRX mode is the same as in the connected mode, with the exception of the number of midambles used per frequency update. In the connected mode, the number of midambles per frequency update depends on the previous frequency error as described hereinbefore. In the synchronization update state, only one midamble per update is used, independent of the frequency error.  
         [0034]     During paging blocks, AFC runs only if it has not converged during the preceding sync update period, which will be described in detail hereinafter. In each PO, the WTRU wakes up from the sleeping state and checks for a PI. As soon as the WTRU decides that it is not being paged, it goes back to the sleep state by powering down the receiver and the TCXO. If the WTRU is being paged, the DRX operation is discontinued. If AFC convergence is declared by the convergence indicator at the start of a paging block following the sync update block, AFC does not run until the next sync update block. For paging blocks not succeeding a sync update block, AFC does not run at all.  
         [0035]     If AFC convergence is not declared at the end of the sync update block, AFC performs one frequency update from every P-CCPCH (every frame) during the upcoming paging block. This continues until either AFC has converged or the paging block is over, which ever happens earlier. The convergence is checked after each frequency update. After AFC convergence is declared, there is no need to run AFC further until the next sync update block. If the convergence is not declared by the end of the paging block following the sync update block, AFC continues to run in the upcoming sleep periods.  
         [0036]     AFC does not operate during DRX sleep periods, except for the case of non-convergence at the end of a paging block following a sync update block as described hereinbefore. If AFC has converged by the start of a sleep period, the receiver and the TCXO is shutdown. If AFC has not converged at the start of a sleep period, the TCXO remains ON and AFC operates as it does in the connected mode. If convergence is declared during the sleep period, the TCXO and the receiver are shut down for the remainder of the sleep period if the next wake-up time is at least a frame apart from convergence declaration time.  
         [0037]     FTC operation will be described hereinafter. Timing within the WTRU should be synchronous to the received signal frame boundaries. Frame synchronization of the WTRU is based on the location of the first significant path (FSP) in the delay spread of the multipath channel. Although the initial cell search performs the initial frame synchronization, there is still a need to maintain frame synchronization to compensate for WTRU motion, shadowing and possible error in the initial cell search. The FTC starts running after initial cell search is completed and AFC comes into a steady state.  
         [0038]      FIG. 4  shows inputs and outputs for an FTC operation and  FIG. 5  is a block diagram showing the relationship between an FTC unit  502  and a timing manager  506  in a WTRU. Since a specific implementation of FTC is not within the scope of the present invention, FTC operation will only be briefly described hereinafter. As shown in  FIG. 4 , broadcast channel (BCH) received signals  402 , (preferably 2× over-sampled), a system frame number (SFN) and an even/odd indicator  404 , a BCH transmit diversity indicator  406  and a cell ID  408  are inputs for an FTC unit  400  which implements an FTC algorithm. The FTC unit  400  generates a frame sync correction signal  410  as an output. Referring to  FIG. 5 , an FTC unit  502  finds the position of the FSP by performing correlations of the received BCH midamble(s) over different time lags. After accumulating processing results multiple times, the FTC unit  502  finds the most significant path (MSP) and verifies the validity of the MSP, (i.e., determines if a signal-to-noise ratio (SNR) of the outputs are strong enough to assume that a valid path has been identified). If the MSP value is above a threshold, MSP Valid is ON, otherwise MSP Valid is OFF. If MSP Valid is ON, the FTC unit  502  finds the FSP position by checking each accumulated results above the threshold.  
         [0039]     The FSP processing unit  504  receives the FSP location and MSP Valid signal form the FTC unit  502  and sends the Frame Sync Correction signal to the timing manager  506 . If MSP Valid is ON, Frame Sync Correction is computed as follows: 
 
Frame Sync Correction=FSP position−Frame Offset. 
 
 The constant Frame Offset is set to five chips currently. This is due to the assumption that the maximum delay spread considered is up to 47 chips from the WG4 test cases. For a channel estimate vector of length 57 chips, this leaves a room of 10 chips. Five chips in each direction are reserved for the purpose of possible drifts of frame sync in either direction. Therefore, the WTRU always sees the FSP in the channel estimator output without any frame synchronization correction up to five chips drift. Therefore, there is no update necessary for short DRX cycles. This prevents unnecessary wake ups of WTRUs and helps conserve battery power. If the magnitude of Frame Sync Correction is greater than S max , it is hard limited to ±S max . If MSP Valid is OFF, Frame Sync Correction is set to zero. 
 
         [0040]     During the active connected state, FTC is running. The FTC algorithm continuously adjusts the frame synchronization, (i.e., the frame beginning by controlling the timing manager). The last frame synchronization update in the active connected mode should be used during the DRX cycles until the next update in a synchronization update state. During the sleep state and the inactive connected state, since there is no data reception, FTC is shut down if all the processing from the preceding frames is completed. If all the processing from the preceding frame is not completed, FTC may run in the sleep state, which will be explained hereinafter. During the PI reading state, FTC may be running and P-CCPCH beacon may be read during each frame in the paging block. During the synchronization update state, FTC runs in a different way than in the active connected state.  
         [0041]     The FTC tracks frame synchronization under WTRU motion, TCXO drift due to a possible AFC bias and RTC drift. FTC corrects the shifts of the frame beginning in either direction. Since a frame beginning is referenced to an FSP, FTC searches and locates the FSP. Whenever FTC updates the FSP location, the FTC re-calculates the frame synchronization. The FTC is also scheduled during the synchronization update state, and the timing of the frame synchronization update and VCO control voltage update is exactly the same as shown in Table 1.  
         [0042]     At the beginning of the sleep period of a DRX cycle, the receiver and the TCXO are shut down. Every synchronization update block, the radio is powered up before the first frame to be read. During sync update blocks, FTC makes one frequency update. The WTRU preferably reads the midambles of four P-CCPCHs, each separated by five frames, as shown in  FIG. 1 . FTC makes a frame sync update after processing four midambles.  
         [0043]     At each PO, (i.e., during the PI reading state), the WTRU wakes up from the sleep state and checks the PI. As soon as the WTRU decides that it is not being paged, it goes back to the sleep state by powering down the receiver and the TCXO. If the WTRU is paged, the DRX operation is discontinued. If MSP Valid is declared by the FTC at the start of a paging block following the sync update block, there is no FTC operation during the paging block. If the MSP Valid is not declared by the FTC at the start of the paging block followed by the synchronization update block, the FTC continues to work during the paging block until it finds an FSP update with MSP Valid declared. During this extended time, FTC uses four consecutive frames instead of separated ones. FTC makes FSP detection from four consecutive frames until it finds one update with MSP Valid. This continues until the paging block is over.  
         [0044]     FTC does not operate during the sleep state, except for the case that MSP Valid is not declared at the end of a paging block. If MSP Valid is declared by the start of the sleep period, the receiver and the TCXO are shutdown. If MSP Valid is not declared at the start of the sleep period, the TCXO remains ON and FTC operates on four consecutive frames. If MSP Valid is declared during the sleep period, the TCXO and the receiver are shut down for the remainder of the sleep period if the next wake-up time has not yet occurred.  
         [0045]     Although the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the preferred embodiments or in various combinations with or without other features and elements of the present invention.

Technology Classification (CPC): 8