Abstract:
The present disclosure provides a method for making mobility measurements in a cellular telephone network that includes assessing the quality of the downlink signal from an active cell during multiple discontinuous operation time periods. If the quality metric exceeds a threshold, the method calls for performing a mobility measurement on the downlink signal during a first time interval. If the quality metric is less than the threshold, the method calls for performing the mobility measurement on both the downlink signal from the identified cells and a downlink signal from a previously un-identified cell during a second time interval that is greater than the first time interval.

Description:
INCORPORATION BY REFERENCE 
     This application is a continuation of U.S. application Ser. No. 12/175,265, filed on Jul. 17, 2008, which claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 60/950,462, filed on Jul. 18, 2007. The disclosures of the applications referenced above are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     Release 7 of the third generation partnership program (3GPP) TR 25.903 V7.0.0 (2007-03) technical report defines a capability for packet data users called Continuously Packet Connected or Continuous Packet Connectivity (CPC). A mobile user equipment (UE), such as a cell phone, that has both a CPC capability and a low data rate requirement may selectively switch off some UE circuits to save battery power. For example, a UE that transfers voice over internet protocol (VoIP) data packets to and from a cellular base station (BS) or cell of a cellular network can switch on the radio frequency (RF) front end and other selected circuits, process voice data packets, then switch off the RF front end and other selected circuits. 
     A UE that switches receiver and transmitter circuits on and off as needed uses the discontinuous reception (DRX) and discontinuous transmission (DTX) features of CPC. The DRX and DTX features can save battery power and extend the connect or talk time of the UE. For example, a UE that receives a 2 ms data packet in a transmission time interval (TTI) every 20 ms can use the DRX feature to reduce the average power to the RF and selected circuits by 90%. 
     The DRX feature can interact with mobility measurements that determine which cells the UE can or might communicate with. The mobility measurements are performed by the UE and can include: 1) identifying cells, 2) measuring and reporting the identified cells to the cellular network, and 3) receiving a command from the network to add a newly identified cell to the set of active cells. Active cells are BSs that can transfer packets to or receive packets from the UE. One of the active cells may be designated as the serving cell. 
     Mobility measurements are reported to the network in accordance with cellular telephony standards, such as the 3GPP TS 25.133-7.8.0 technical specification. For example, section 8.1.2.2.2 (“UE CPICH measurement capability”) of TS 25.133-7.8.0 specifies the rate at which cells should be measured and how fast a newly identified cell should be reported to the network. Specifically, TS 25.133-7.8.0 requires 1) identifying a newly detectable cell within 800 ms and 2) reporting eight identified cells every 200 ms. In general, the process of identifying a new cell is longer and more power-consuming than measuring an already-identified cell, whereas a mobility measurement on a previously identified cell may consume very little UE power in comparison. 
     One proposed modification to TR 25.903 V7.0.0 (2007-03) calls for making the mobility measurement interval proportional to the percentage of a DRX cycle that the UE receiver is active. For example, a UE that has a 10% activity factor may take 8 seconds to detect a new cell, rather than 800 ms. Such proposed modifications may reduce the mobility of a UE that uses CPC, especially for small activity factors, and may lead to a larger probability of dropped calls. For example, if the time that a UE uses to identify a new cell increases, then there is an increased probability that the cell will become obsolete or unsuitable for data packet transfer due to motion of the UE, the signal propagation condition change, and the like. 
     SUMMARY 
     The present disclosure provides a method for making mobility measurements in a cellular telephone network that includes assessing the quality of the downlink signal from an active cell during multiple discontinuous operation time periods. If the quality metric exceeds a threshold, the method calls for performing a mobility measurement on the downlink signal during a first time interval. In this case, the mobility measurement may be performed on the signals from some or all currently identified cells without attempting to identify new cells. However, if the quality metric is less than the threshold, the method calls for identifying additional cells and performing mobility measurements on both the previously identified and the additionally identified cells. The additional cell identification can be performed during a second time interval that is greater than the first time interval. As a result, the time allotted to identify additional cells can increase when signal reception quality falls below a quality metric as opposed to when the reception quality exceeds the quality metric. In the latter case, measurements may be performed for previously identified cells without searching for additional cells. In other words, a cell identification portion of a mobility measurement may be performed more often, i.e. using a larger portion of a DRX cycle, when the link quality is poor as compared to when the link quality is adequate. 
     The present disclosure provides for a mobile user equipment (UE) in a cellular network. The mobile UE can include a transceiver that can operate in a continuous packet connectivity (CPC) mode, receive an RF signal from an active cell of the cellular network, demodulate a data packet signal from received signal, and synchronize the mobile UE to a discontinuous reception (DRX) cycle. The mobile UE can also include a quality metric assessor that can measure the quality of the RF signal, a mobility measurement unit (MMU) that, during a mobility measurement interval, can identify and measure the quality and identify new cells as needed, and a controller that can adjust the mobility measurement interval based on the quality. The controller can adjust the mobility measurement interval, that is to say, the time between mobility measurements taken at a given measurement frequency, to increase the time allotted to perform mobility measurements when the reception quality is less than a first threshold and the MMU can identify the set of active cells during the shortest time interval. The controller can adjust the mobility measurement interval to reduce the time allotted to perform mobility measurements the when the reception quality exceeds the threshold. 
     The present disclosure provides for a cellular network that can include UEs operating in CPC mode. The UEs in CPC mode can include mobility measurement intervals that are adjusted according to reception quality. The parameters of the mobility measurements can be provided to the UEs by the cellular network cells through communications protocol layers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will refer to the accompanying figures, wherein like numerals represent like elements, and wherein: 
         FIG. 1  shows an example program flowchart for adaptive mobility measurement; 
         FIG. 2  shows an example reception cycle; 
         FIG. 3  shows an example functional dependence of a normalized activity factor on reception quality; and 
         FIG. 4  shows an adaptive mobility measurement device. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG. 1  shows an example program flowchart  100  of a method for adapting mobility measurements to the downlink reception quality for mobile user equipment (UE) in continuous packet connectivity (CPC) mode in a cellular network. The program flowchart  100  may begin at program step S 110  and may then proceed to program step S 115  in which the UE can obtain CPC parameters. For example, the UE can receive discontinuous reception (DRX) and discontinuous transmission (DTX) cycle durations, thresholds, mobility measurement thresholds, measurement schedules, and the like. The CPC parameters can be sent from the network to the UE through communications protocol layers. The CPC parameters can be used in subsequent program steps to adjust or adapt the UE resources that detect and identify new cells. For example, the CPC parameters may determine whether a mobility measurement should occur during or after a data packet demodulation interval, set an upper or lower bound on the portion of a DRX cycle over which the UE can perform mobility measurements, and the like. 
     Program flow can proceed from program step S 115  to program step S 120  in which the UE can wait for a CPC activity time interval, such as an active portion of a DRX cycle during which the UE can receive a data packet on a downlink radio frequency (RF) signal from the BS. For example, the UE can wait for a voice packet, which may be sent once every 20 ms. 
     From program step S 120 , the program can proceed to program step S 122  in which the program can determine the reception quality of the downlink RF signal from the serving cell. For example, the program can extract the reception quality of the RF signal of the serving cell based on 1) a Common Pilot Channel (CPICH) Ec/Io level, where Ec/Io is the received energy per pseudo-noise chip for the CPICH divided by the total received energy at the UE antenna, 2) a channel quality indication (CQI), or 3) other reception quality metrics. In step S 122 , the program may filter the extracted reception quality to reduce the variability of the reception quality supplied to subsequent program steps. For example, program step S 122  may lowpass filter, median filter, or otherwise reduce statistical dispersion in the extracted reception quality and produce a filtered reception quality. 
     From program step S 122 , program flow can proceed to program step S 125  in which the UE can compare the reception quality to a first threshold. The first threshold may be downloaded from a network cell or may be set to a default value, such as by a controller element in the UE. The first threshold can correspond to a maximum reception quality or normalized quality metric. For example, the first threshold can correspond to a normalized reception quality or quality metric of 75%, as described with respect to  FIG. 3 . The first threshold can correspond to a “very good” reception quality of the serving cell compared with a reception quality for which the data packet from the serving cell might include an error. If the reception quality is greater than the first threshold, program flow can proceed to program step S 130 . Otherwise, program flow can proceed to program step S 135 . 
     In program step S 130 , the UE can perform mobility measurements on currently or presently identified cells only. In other words, the UE can take mobility measurements for cells that have been previously recognized as active by the UE, for example. The process of performing mobility measurements on currently or presently identified cells can consume less time and power than mobility measurements on other cells. 
     In an embodiment, program step S 130  may use the smallest adaptive mobility measurement time to identified cells and skip the identification of new cells. For example, in step S 130 , the program may direct the UE to measure the mobility of identified cells for 20% of a DRX cycle. The program step S 130  can save the UE power by minimizing the mobility measurement time for identified cells and not attempting to identify additional cells. From program step S 130 , program flow can proceed back to program step S 120 . 
     If the reception quality of the serving cell in program step S 125  is not greater than the first threshold, the program flow can proceed to program step S 135 , in which the program can compare the reception quality with a second threshold. The second threshold can be less than the first threshold. For example, the second threshold can correspond to a normalized reception quality or quality metric of 40%, as described with respect to  FIG. 3 . The second threshold can correspond to an “acceptable” reception quality of the serving cell. If the reception quality exceeds the second threshold, program flow can proceed to program step S 140 , otherwise program flow can proceed to program step S 145 . 
     When program flow arrives at program step S 140 , then, during a first time period, the program can attempt to identify additional or previously un-identified cells. From program step S 140 , the program flow can proceed to program step S 142  in which the program can measure previously identified and the additionally identified cells. It may be noted that the mobility measurement can consume little UE power and time once cells have been identified. The additional cells may be cells that have not been previously identified or cells that were not identified for a long period of time. This time period can be set by a parameter of the network or may be UE implementation dependent. 
     In step S 140 , the program can perform mobility measurements of the additional cells at a rate that is a fraction of the full mobility measurement rate or speed by allotting a lesser portion of the DRX cycle to the mobility measurement. For example, in program step S 140 , the program can measure mobility at 50% of full speed. From program step S 140 , the program can proceed to program step S 142 . 
     In program step S 142 , the program can measure the mobility of previously identified and additionally identified cells. For example, the program may measure all identified cells during an interval of approximately 10 ms within a 20 ms VoIP period. From program step S 142 , program flow can proceed back to program step S 120 . 
     When program flow arrives at program step S 145 , the UE can attempt to identify additional cells during a second time period greater than the first time period. For example, in an embodiment at step S 145 , the UE can decide not to shut off the UE reception circuitry at all, even though DRX is enabled, and perform mobility measurements continuously. From program step S 145 , program flow can proceed to program step S 142 . With respect to program step S 145 , it may be noted that, although the power consumption may increase when identifying new cells at full speed, the full speed mobility measurements may offer the best possible mobility during “poor” reception conditions. 
     The example program flowchart  100  may be understood to enable the UE to perform mobility measurements as a function of channel conditions. The channel conditions may be characterized or quantified by reception quality. The functional dependence of the adaptive mobility measurement interval on reception quality may be a discrete or step function characterized by thresholds or may be continuous function as discussed, for example, with respect to  FIG. 3 . With either a discrete or a continuous function, the UE may perform mobility measurements at a higher rate when conditions worsen, such as near a cell edge where reception quality drops. 
       FIG. 2  shows an example VoIP reception cycle  200  that can include a Rx data demodulation interval  210 , an adaptive mobility measurement interval  220 , and a Rx OFF interval  230 . In the example shown, a reception cycle  200  can be a 20 ms interval corresponding to a period of a voice over internet protocol (VoIP) packet transfer. 
     The Rx data demodulation interval  210  can correspond to a data packet transfer between the BS and a mobile UE. The data packet may be carried on a downlink RF signal that the UE demodulates. For example, the Rx data demodulation interval  210  can correspond to a 2 ms interval within a 20 ms VoIP period. 
     The adaptive mobility measurement interval  220  can include an interval during which a CPICH common pilot channel or an SCH synchronization channel is analyzed. For example, adaptive mobility measurement interval  220  can correspond to an interval during which a UE performs mobility measurements by 1) identifying cells, and 2) measuring the identified cells. The duration of the adaptive mobility measurement interval  220  relative to the reception cycle  200 , can be described as a normalized activity factor, as described with respect to  FIG. 3 . It may be noted that the adaptive mobility measurement interval  220  can include or subsume the Rx data demodulation interval  210  since, when reception is performed, mobility measurements can be performed in parallel at the cost of very little extra UE power. The duration of the measurement interval  220  can be adaptive based on reception quality and the VoIP reception cycle  200  can be constant. The receiver may be powered off during the portion of the VoIP reception cycle  200  other than the mobility measurement interval  220 , such as during the Rx OFF interval  230 . 
     The Rx OFF interval  230  can include an interval during which the RF front end and selected circuits can be de-powered or shut off. For example, a UE that uses DRX can de-power RF preamplifiers, amplifiers, down-conversion filters, automatic gain control (AGC) circuits, analog to digital (A/D) data converters or samplers, and the like during the Rx OFF interval  230 . 
       FIG. 3  shows an example functional dependence  300  of the adaptive mobility measurement interval, such as the adaptive mobility measurement interval  220  shown with respect to  FIG. 2 , on reception quality. The measurement interval may be described as a normalized activity factor  320 . For example, the normalized activity factor  320  may equal the mobility measurement interval scaled by a DRX cycle, such as a 20 ms period for VoIP. 
     The functional dependence  300  can include a first threshold  330 , a second threshold  340 , a super-threshold region  350 , sub-threshold regions  360  and  370 , and a relation  380 . The first and second thresholds  330  and  340  may be the edges of step functions, as described with respect to  FIG. 1 , the vertices of piecewise linear functions, inflection points in smoothly varying functions, and the like. 
     The super-threshold region  350  can indicate the proportion of time a UE can take to measure previously identified cells. For example, the super-threshold region  350  can correspond to a 3 ms mobility measurement interval out of a 20 ms DRX cycle, for a normalized activity factor  320  of 15%. 
     In the sub-threshold region  360 , the normalized activity factor  320  can increase, relative to super-threshold region  350 . The sub-threshold region  360  can correspond to a step increase, relative to super-threshold region  350 , in the normalized activity factor  320 . The relation  380  can correspond to a linear change in the normalized activity factor  320  as a function of the normalized reception quality metric  310 . 
     The second threshold  340  can indicate the value of a normalized reception quality metric  310  below which the normalized activity factor  320  can be at a maximum or larger than the normalized activity factor  320  in the super-threshold region  350 . In other words, the mobility measurement may be performed at full speed or at an increased speed, respectively. For example, when the normalized reception quality is less than the second threshold  340 , the normalized activity factor  320  may be 100%, i.e. mobility measurements can be performed continuously. 
       FIG. 4  shows an adaptive mobility measurement device  400  that can include a radio frequency (RF) front end  410 , a CPC synchronizer  420 , a quality metric assessor  430 , a mobility measurement unit (MMU)  440 , and a controller  450 . In an embodiment, the RF front end  410  and the CPC synchronizer  420  can be subsumed into a CPC capable transceiver. In an embodiment, the MMU  440  can include a cell identifier functionality  442  and a measurement functionality  444 . The RF front end  410  can couple to the CPC synchronizer  420 , which can couple to the quality metric assessor  430 , which can couple to the mobility measurement unit  440 . The controller  450  can couple a threshold to the MMU  440 , and can couple command and control signals to the MMU  440 , the quality metric assessor  430 , the CPC synchronizer  420 , and the RF front end  410 . 
     The RF front end  410  can transmit and receive an RF signal to or from a BS. For example, the RF signals can be a wideband code division multiple access (WCDMA) signal, using a discontinuous reception cycle, DRX. The RF front end  410  can receive, downconvert, filter, demodulate the RF signal, and the like. 
     The RF front end  410  can send the demodulated RF signal to the CPC synchronizer  420 , which can synchronize bits, bytes, blocks, and the like to standardize time intervals, such as time slots in a 3GPP standard signal structure. For example, the CPC synchronizer  420  can synchronize internal clocks, such as timers, phase-locked loops, and the like to assign demodulated and decoded data to appropriate standardized time slots. In particular, the CPC synchronizer  420  can cause the mobile UE  400  to wait for a CPC activity time or activity interval, such as a data packet transfer interval within a DRX cycle. Once synchronized to the CPC activity time, the CPC synchronizer  420  may send a synchronization flag to the quality metric assessor  430 . 
     The quality metric assessor  430  may extract a reception quality metric from the demodulated RF signal. For example, the quality metric assessor  430  may process a portion of the demodulated RF signal to examine a continuous CPICH common pilot channel signal and extract a reception quality metric, such as Ec/Io. The quality metric assessor  430  may, in addition to or instead of using the CPICH, assess a signal quality based on a signal-to-noise ratio (SNR), a signal-to-interference ratio (SIR), a statistical analysis of the demodulated and decoded data packet, and the like. For example, the quality metric assessor  430  can examine statistical moments of the downconverted signal, analyze the mean and variance of the downconverted signal, determine coherence and correlation functions of the data, and the like. The quality metric assessor  430  may select an individual quality metric or may combine multiple quality metrics, such as a CPICH Ec/Io metric and SIR. The quality metric assessor  430  may transfer the reception quality metric to the MMU  440 . 
     The MMU  440  can include a cell identification functionality  442  and a measurement functionality  444  and can determine an adaptive mobility measurement interval based on a predetermined functional dependence on reception quality. For example, the MMU  440  may use a first and a second threshold as described with respect to  FIG. 1  or a discrete or continuous functional dependence as shown with respect to  FIG. 3 . In the example of a discrete functional dependence, the MMU  440  can compare the reception quality to a first threshold, access a list of identified cells and perform mobility measurements on only the identified cells when the reception quality exceeds the first threshold. The MMU  440  may attempt to identify additional cells and perform mobility measurements on the additionally identified cells as well when the reception quality metric is below the first threshold. 
     The controller  450  may receive CPC parameters from the network through the RF front end  410 , supply or distribute the CPC parameters to the CPC synchronizer  420 , the quality metric assessor  430 , and the MMU  440 . For example, the controller  450  may obtain DRX parameters that determine the power-saving behavior of the mobile UE  400 , a threshold or a set of thresholds, the speeds at which mobility measurements may be made, and the like. In other words, the controller  450  may assign a mobility measurement rate or a mobility measurement interval, such as the normalized activity factor  320  discussed with respect to  FIG. 3 . 
     The controller  450  can supply one or more thresholds or a functional dependency to the MMU  440  and can control the behavior of MMU  440  dynamically or in a predetermined fashion. In other words, the controller  450  may adjust the parameters of the functional dependence or may use a single functional dependence. For example, the controller  450  may supply the MMU  440  with a startup set of thresholds when the mobile UE  400  is initially powered on, and may switch to another set of thresholds thereafter. 
     When the quality metric is above a first threshold, the controller  450  may configure the MMU  440  to limit mobility measurements to identified cells. When the quality metric is below the first threshold, the controller  450  may configure the mobile UE  400  such that the MMU  440  searches for previously un-identified cells at either a higher frequency or for a longer duration. For example, the controller  450  may configure the MMU  440  to increase a second time interval during which the mobile UE  400  can search for new cells. 
     It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also, various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art, and are also intended to be encompassed by the following claims.