Enhanced multiple SIM time tracking

A technique for time tracking helps a mobile communication device with multiple SIMs to more accurately maintain synchronization with a base station. By utilizing synchronization information from both SIMs, the technique is able to more frequently and more accurately adjust timing information for each SIM. As a result, the mobile communication device exhibits an increased ability to accurately synchronize without the need for a higher precision reference or increased power consumption.

2. TECHNICAL FIELD

This disclosure relates to communication devices with multiple Subscriber Identity Modules (SIMs). The disclosure also relates to enhanced time tracking in communication devices with multiple SIMs.

Rapid advances in electronics and communication technologies, driven by immense customer demand, have resulted in the widespread adoption of mobile communication devices. The extent of the proliferation of such devices is readily apparent in view of some estimates that put the number of wireless subscriber connections in use around the world at nearly 80% of the world's population. Furthermore, other estimates indicate that (as just three examples) the United States, Italy, and the UK have more mobile phones in use in each country than there are people living in those countries.

Relatively recently, cellular phone manufactures have introduced phone designs that include multiple SIM cards. Each SIM card facilitates a separate connection to the same network or different networks. As a result, the SIMs provide the owner of the phone with, for example, two different phone numbers handled by the same phone hardware. Accordingly, the multiple SIM approach alleviates to some degree the need to carry different physical phones, and improvements in multiple SIM communication devices will continue to make such devices attractive options for the consumer.

DETAILED DESCRIPTION

The discussion below makes reference to user equipment. User equipment may take many different forms and have many different functions. As one example, user equipment may be a cellular phone capable of making and receiving wireless phone calls. The user equipment may also be a smartphone that, in addition to making and receiving phone calls, runs general purpose applications. User equipment may be virtually any device that wirelessly connects to a network, including as additional examples a driver assistance module in a vehicle, an emergency transponder, a pager, a satellite television receiver, a networked stereo receiver, a computer system, music player, or virtually any other device. The discussion below addresses how to track symbol timing in user equipment that includes multiple (e.g., two) SIMs.

FIG. 1shows an example of user equipment100with multiple SIMs, in this example the SIM1102and the SIM2104. An electrical and physical interface106connects SIM1102to the rest of the user equipment hardware, for example, to the system bus110. Similarly, the electrical and physical interface108connects the SIM2to the system bus110.

The user equipment100includes a communication interface112, system logic114, and a user interface118. The system logic114may include any combination of hardware, software, firmware, or other logic. The system logic114may be implemented, for example, in a system on a chip (SoC), application specific integrated circuit (ASIC), or other circuitry. The system logic114is part of the implementation of any desired functionality in the user equipment. In that regard, the system logic114may include logic that facilitates, as examples, running applications, accepting user inputs, saving and retrieving application data, establishing, maintaining, and terminating cellular phone calls, wireless network connections, Bluetooth connections, or other connections, and displaying relevant information on the user interface118. The user interface118may include a graphical user interface, touch sensitive display, voice or facial recognition inputs, buttons, switches, and other user interface elements.

The communication interface112may include one or more transceivers. The transceivers may be wireless transceivers that include modulation/demodulation circuitry, amplifiers, analog to digital and digital to analog converters and/or other logic for transmitting and receiving through one or more antennas, or through a physical (e.g., wireline) medium. As one implementation example, the communication interface112and system logic114may include a BCM2091 EDGE/HSPA Multi-Mode, Multi-Band Cellular Transceiver and a BCM59056 advanced power management unit (PMU), controlled by a BCM28150 HSPA+ system-on-a-chip (SoC) baseband smartphone processer. These integrated circuits, as well as other hardware and software implementation options for the user equipment100, are available from Broadcom Corporation of Irvine Calif.

The transmitted and received signals may adhere to any of a diverse array of formats, protocols, modulations, frequency channels, bit rates, and encodings that presently or in the future support communications including paging notifications associated with SIMs. As one specific example, the communication interface112may support transmission and reception under the Universal Mobile Telecommunications System (UMTS). The techniques described below, however, are applicable to other communications technologies that include paging whether arising from the 3rd Generation Partnership Project (3GPP), GSM (R) Association, Long Term Evolution (LTE)™ efforts, or other partnerships or standards bodies.

In order for user equipment100to reliably transmit and receive data over a network, user equipment100may synchronize its internal timing with the timing of a base transceiver station (BTS) on the network. User equipment100may synchronize with the timing from a BTS of the network by aligning an internal time base140of the user equipment100with the timing information received from the BTS. In order to assist with synchronization, the BTS may periodically send timing information to the user equipment100so that the user equipment100can correct its internal time base140. In order to receive the timing information, the user equipment100may actively listen on the synchronization channel or may periodically listen on the paging channel.

The user equipment100may connect with a network in either active mode or idle mode. When user equipment100connects to a network in active mode, user equipment100is in frequent communication with the network and frequently receives timing information from the network. When the network connection is in idle mode, the user equipment100can remain in a reduced power “sleep” mode, “waking up” periodically to listen for synchronization information contained on the paging channel of the network. User equipment100may utilize multiple internal time bases, including, for example, an active mode time base142and an idle mode time base144. The active mode time base142may be more accurate than the idle mode time base144. The active mode time base142may be used while the user equipment is connected to a network in active mode and actively transmitting/receiving data. User equipment100may have an idle mode time base144that is used when user equipment100is connected to the network in idle mode and not actively transmitting/receiving data. User equipment100may use idle mode time base142to determine the particular time that user equipment100should wake up from sleep mode. Due to the fact that the active mode time base142may be more accurate and may consume additional power, the user equipment100may, while in sleep mode, power down the active mode time base142.

During periods when user equipment100is in sleep mode and does not receive timing information from the BTS, user equipment100may rely on its internal time base140. However, internal time base140may be inaccurate and may “drift” with respect to the timing of the BTS. The time drift may be due to phase error or frequency error with respect to the phase and/or frequency of the BTS. If user equipment100does not periodically wake up to listen for the synchronization information contained in the paging block from the network, the user equipment100may lose synchronization with the network. As a result, the user equipment100may not receive a paging indicator from the network and may miss a call, message, or data that the network has designated for the user equipment100.

When in idle mode, user equipment100may be scheduled to wake up at a specified interval to receive the synchronization information contained in the paging block from the network. The specified interval may be based on a background paging schedule (BPS). As one example of the background paging schedule, the network's discontinuous reception cycle (DRX) interval may be used as the background paging schedule. The BPS provides the length of time specified by the network during which the user equipment100remains asleep between periods of listening for the synchronization information contained in the paging block. The length of time for the BPS may vary, depending on the type of communication technology used (e.g., GSM, CDMA, UMTS, etc.) and the particular settings used by the particular service provider that operates the network. As one example for one network, the BPS may be 2 seconds, while for other networks, the BPS may be shorter or longer.

Synchronization information from the network may be contained in a paging block sent from the BTS to the user equipment100on the paging channel.FIG. 2shows an example of paging block202. Paging block202may contain bursts of data in the paging block. For example, the burst210is contained in the paging block202. Burst210includes data bits212and midamble220. The midamble is a known sequence of bits, such as a training sequence, that may be contained in each burst of paging block202. Midamble220can be used for synchronization because the midamble arrives at a known location within each burst. When the user equipment100identifies and locates the midamble, the user equipment100can identify the start position and/or stop position of the data burst.

FIG. 3shows an example of using midamble220to determine a timing error306. The user equipment100may use its internal time base140to predict the arrival of midamble220at predicted arrival time302. Once the user equipment100identifies midamble220, the user equipment100identifies the actual arrival time304of midamble220. The time difference between the predicted arrival time302and actual arrival time304results in the timing error306. User equipment100may use timing error306to compensate the internal time base140when predicting the arrival time of the next paging block.

In order to predict the arrival time of the next paging block, user equipment100may use a time tracking loop. The time tracking loop may correct for the drift in the internal time base140. The time tracking loop may apply a correction factor to account for the timing drift of the internal time base140. The correction factor may be updated each time user equipment100receives a paging block and determines timing error306from the burst.

Where a user equipment has multiple SIMs for connecting to multiple networks, the user equipment may require synchronization with multiple BTS's on multiple networks. Each network (e.g., network130or132) may supply its own timing information, and the BPS may have a different time period for each network. User equipment100may track the timing difference that may exist between the user equipment's internal time base140and the timing for each network. As a result, the user equipment100may apply a different correction factor for each network with which it is synchronized. As will be described in more detail below, user equipment100may use the timing information received from one network, either network, or both networks when tracking the timing correction factor for the user equipment100.

In some implementations, user equipment100may share radio frequency resources between multiple SIMs. As a result, both SIMs cannot simultaneously receive paging blocks from the network. Because both SIMs may not simultaneously receive paging blocks from the network, in situations, for example, where user equipment100is scheduled to receive a paging block from SIM1network130at the same time user equipment100is scheduled to be receive a paging block from SIM2network132, the paging blocks “collide.” When the paging blocks from multiple networks collide, user equipment100may choose whether to receive the paging block from SIM1network130, SIM2network132, or neither. As a result, one or both paging blocks may be ignored or lost. If user equipment100ignores or loses a paging block, user equipment may wait for the next scheduled paging block.

FIG. 4shows an example of “collisions” between paging blocks from multiple networks. Timing graph400shows a schedule of paging blocks from SIM1network130and SIM2network132that are designated for user equipment100. Paging blocks402,404, and406are scheduled by SIM1network130at BPS1time interval401. Paging blocks412,414,416are scheduled by SIM2network132at BPS2time interval411. Based on the schedule, paging block402and paging block412are scheduled to arrive at user equipment100in a partially overlapping manner, indicated by timing overlap420. Because paging block402and paging block412are scheduled to collide (i.e., overlap), user equipment100may choose to receive paging block402, paging block412, or neither. Similarly, paging block404and paging block416are scheduled to arrive at user equipment100at the same time, indicated by timing overlap432. Because paging block404and paging block416are scheduled to collide, user equipment100may choose to receive paging block404, paging block416, or neither. As a result of the collisions, user equipment100may lose opportunities to receive timing information from either SIM1network130or SIM2network132. When paging blocks collide and user equipment100waits for additional paging blocks, the internal time base may drift further out of synchronization with the network. As a result of lost paging blocks, user equipment100may not be able to update the timing correction factor as frequently as desired. Thus, the user equipment may lose synchronization between the user equipment100and network130or132. System logic114provides certain advantages.

In one implementation, the system logic114includes one or more processors116and a memory120. The memory120stores, for example, time tracking logic122that the processor116executes. The memory120may also store SIM1network timing information124, SIM2network timing information126, and time tracking parameters128. As will be described in more detail below, the time tracking logic122facilitates timing correction so that user equipment100can more accurately synchronize with each network, even when some paging blocks collide.

The time tracking logic122may independently track the drift of internal time base140for each network with which user equipment100is connected. The time tracking logic122may independently track the time base drift by having independent tracking loops for each network. For example, if user equipment100is connected in idle mode to SIM1network130, the time tracking logic122may use the timing error determined from paging blocks received from SIM1network130. Using the timing error from paging blocks received from SIM1network130, the time tracking logic122may apply an appropriate correction factor to the internal time base140. Similarly, if user equipment100is connected in idle mode to SIM2network132, the time tracking logic122may use the timing error determined from paging blocks received from SIM2network132. Using the timing error from paging blocks received from SIM2network132, the time tracking logic122may apply an appropriate correction factor to the internal time base140.

In another implementation, the time tracking logic124may track the drift of internal time base140by combining—into a single tracking loop—the timing error determined from paging blocks received from the multiple networks with which user equipment100may be connected. For example, if user equipment100is connected to SIM1network130and SIM2network132, the time tracking logic122may use the SIM1network paging blocks and SIM2network paging blocks in order to determine the appropriate time base compensation for synchronizing user equipment100with SIM1network130and SIM2network132. In particular, by combining the timing error determined from paging blocks received from multiple networks, the user equipment is able to take advantage of timing information received from both networks in order to more frequently update the timing compensation and more accurately synchronize the timing of the user equipment100to the timing of the network, even when some paging blocks collide and/or are lost.

The time tracking logic122may use certain time tracking parameters128in order to utilize timing error determined from paging blocks received from multiple networks for improved time tracking. The time tracking logic122may store the time tracking parameters128in memory120and update the time tracking parameters128as the processor116calculates and processes the timing information. For example, when user equipment100is in idle mode, each time a paging block is received from SIM1network130or SIM2network132, the time tracking logic122may update the time tracking parameters128.

In one implementation, example time tracking parameters128may include:

TABLE 1ParameterVariableTypeDescriptionα1constantGain of the first order phase locked loop.This constant may be used to stabilize theloop and may be set to a rational numberless than oneαdconstantGain of the “delta loop.” This constantmay be used to stabilize the loop and maybe set to a rational number less than onenindexAn index representing receipt of the currentpaging block; n + 1 is the next scheduledpaging blocki(n)inputNetwork Identification (e.g., SIM1 networkor SIM2 network) for the n-th paging blockê(n)inputThe measured timing error from the n-thpaging blockcinternal stateFirst order loop filter output, representingvariablethe timing adjustment due to phase errordinternal stateThe differential adjustment applied whenvariablethe next scheduled paging block is from adifferent networkδinternalTiming adjustment between the previousvariablepaging block and the current paging block

In one implementation, using the time tracking parameters128listed above, the time tracking logic122may implement the following algorithm:

FIG. 5shows an example timing graph500that includes a series of paging blocks from SIM1network130and SIM2network132that are scheduled for user equipment100. Because of radio frequency resource sharing, as described above, paging blocks412,414,416, and418, in this example, are lost due to collisions with paging blocks from SIM1network130. User equipment100may chose instead to receive paging blocks402,404, and406from SIM1network130. Following timing graph500from left to right and using one implementation of time tracking logic122, user equipment100receives paging block402. Using the midamble of the burst, user equipment100determines the timing error between the expected arrival of the midamble and the actual arrival of the midamble of the burst, labeled ê1. Time tracking logic122uses timing error ê1and gain factor α1to determine the loop filter output c1. Time tracking logic122updates the differential adjustment factor, d1, subtracting the currently calculated loop filter output c1from the prior differential adjustment factor, d. Note that time tracking logic122subtracts c1from d1because user equipment100is currently listening to the network with network identification one (i.e., SIM1network130). Time tracking logic122determines the timing adjustment, δ1, for the next scheduled paging block using the loop filter output c1. User equipment100may use timing adjustment, δ1, as the compensation factor to apply to internal time base140for predicting the expected arrival of the next paging block404. After user equipment100receives and processes paging block402, it may enter a sleep mode until the next paging block is scheduled to arrive. While in sleep mode, user equipment100may use its internal time base140along with timing adjustment, δ2, to predict the expected arrival of the next paging block404.

When user equipment100expects the next scheduled paging block404, user equipment wakes up from sleep mode to listen for paging block404. Again, using the midamble of the burst, user equipment100determines the timing error between the expected arrival of the midamble and the actual arrival of the midamble of the burst, labeled ê2. Time tracking logic122uses timing error ê2and gain factor α1to determine the loop filter output c2. Time tracking logic122updates the differential adjustment factor, d2, subtracting the currently calculated loop filter output c2from the prior differential adjustment factor, d1. Note that time tracking logic122subtracts c2from d1because user equipment100is currently listening to the network with network identification one (i.e., SIM1network130). Time tracking logic122determines the timing adjustment, δ2, for the next scheduled paging block using the loop filter output c2. User equipment100may use timing adjustment, δ2, as the compensation factor to apply to internal time base140for predicting the expected arrival of the next paging block406. After user equipment100receives and processes paging block404, it may enter a sleep mode until the next paging block is scheduled to arrive. While in sleep mode, user equipment100may use its internal time base140along with timing adjustment, δ2, to predict the expected arrival of the next paging block406.

When user equipment100expects the next scheduled paging block406, user equipment wakes up from sleep mode to listen for paging block406. Again, using the midamble of the burst, user equipment100determines the timing error between the expected arrival of the midamble and the actual arrival of the midamble of the burst, labeled ê3. Time tracking logic122uses timing error ê3and gain factor α1to determine the loop filter output c3. Time tracking logic122updates the differential adjustment factor, d3, subtracting the currently calculated loop filter output c3from the prior differential adjustment factor, d2. Note that time tracking logic122subtracts c3from d2because user equipment100is currently listening to the network with network identification one (i.e., SIM1network130). Because the timing adjustment, δ3, for the next scheduled paging block depends on whether the next scheduled paging block will be received on the same network or whether the paging block with be received from another network, the time tracking logic122may not determine the timing adjustment for the next paging block until user equipment100determines whether the next scheduled paging block will arrive from SIM1network130or SIM2network132.

FIG. 6shows another example of how the user equipment100may use a similar series of paging blocks. Timing graph600includes a series of paging blocks from SIM1network130and SIM2network132that are scheduled for user equipment100. Because of radio frequency resource sharing, as described above, paging blocks404,406, and412, in this example, are lost due to collisions between paging blocks from SIM1network130and SIM2network132. User equipment100may chose instead to receive paging blocks402,414,416, and418. Following timing graph600from left to right and using one implementation of time tracking logic122, user equipment100receives paging block402. Using the midamble of the burst, user equipment100determines the timing error between the expected arrival of the midamble and the actual arrival of the midamble of the burst, labeled ê1. Time tracking logic122uses timing error ê1and gain factor α1to determine the loop filter output c1. Time tracking logic122updates the differential adjustment factor, d1, subtracting the currently calculated loop filter output c1from the prior differential adjustment factor, d. Note that time tracking logic122subtracts c1from d because user equipment100is currently listening to the network with network identification one (i.e., SIM1network130). Time tracking logic122determines the timing adjustment, δ1, for the next scheduled paging block using the loop filter output c1and adds the differential adjustment factor d1. Note that time tracking logic122adds d1because the currently received paging block402is from SIM1network130while the next scheduled paging block414is from SIM2network132. User equipment100may use timing adjustment, δ1, as the compensation factor to apply to internal time base140for predicting the expected arrival of the next paging block414. After user equipment100receives and processes paging block402, it may enter a sleep mode until the next paging block is scheduled to arrive. While in sleep mode, user equipment100may use its internal time base140along with timing adjustment, δ1, to predict the expected arrival of the next paging block414.

When user equipment100expects the next scheduled paging block414, user equipment wakes up from sleep mode to listen for paging block414. Again, using the midamble of the burst, user equipment100determines the timing error between the expected arrival of the midamble and the actual arrival of the midamble of the burst, labeled ê2. Time tracking logic122uses timing error ê2and gain factor α1to determine the loop filter output c2. Time tracking logic122updates the differential adjustment factor, d2, adding the currently calculated loop filter output c2and the prior differential adjustment factor, d1. Note that time tracking logic122adds c2and d1because user equipment100is currently listening to the network with network identification two (i.e., SIM2network132). Time tracking logic122determines the timing adjustment, δ2, for the next scheduled paging block using the loop filter output c2. Note that time tracking logic122does not add or subtract d2because the currently received paging block414is from SIM2network132and the next scheduled paging block416is also from SIM2network132. User equipment100may use timing adjustment, δ2, as the compensation factor to apply to internal time base140for predicting the expected arrival of the next paging block416. After user equipment100receives and processes paging block414, it may enter a sleep mode until the next paging block is scheduled to arrive. While in sleep mode, user equipment100may use its internal time base140along with timing adjustment, δ2, to predict the expected arrival of the next paging block416.

When user equipment100expects the next scheduled paging block416, user equipment wakes up from sleep mode to listen for paging block416. Again, using the midamble of the burst, user equipment100determines the timing error between the expected arrival of the midamble and the actual arrival of the midamble of the burst, labeled ê3. Time tracking logic122uses timing error ê3and gain factor α1to determine the loop filter output c3. Time tracking logic122updates the differential adjustment factor, d3, adding the currently calculated loop filter output c3and the prior differential adjustment factor, d2. Note that time tracking logic122adds c3and d2because user equipment100is currently listening to network identification two (i.e., SIM2network132). User equipment100may use timing adjustment, δ3, as the compensation factor to apply to internal time base140for predicting the expected arrival of the next paging block418. After user equipment100receives and processes paging block416, it may enter a sleep mode until the next paging block is scheduled to arrive. While in sleep mode, user equipment100may use its internal time base140along with timing adjustment, δ3, to predict the expected arrival of the next paging block418.

When user equipment100expects the next scheduled paging block418, user equipment wakes up from sleep mode to listen for paging block418. Again, using the midamble of the burst, user equipment100determines the timing error between the expected arrival of the midamble and the actual arrival of the midamble of the burst, labeled ê4. Time tracking logic122uses timing error ê4and gain factor α1to determine the loop filter output c4. Time tracking logic122updates the differential adjustment factor, d4, adding the currently calculated loop filter output c4and the prior differential adjustment factor, d3. Note that time tracking logic122adds c4and d3because user equipment100is currently listening to the network with network identification two (i.e., SIM2network132). Because the timing adjustment, δ4, for the next scheduled paging block depends on whether the next scheduled paging block will be received on the same network or whether the paging block with be received from another network, the time tracking logic122may not determine the timing adjustment for the next paging block until user equipment100determines whether the next scheduled paging block will arrive from SIM1network130or SIM2network132.

FIG. 7shows another example of how the user equipment100may use a similar series of paging blocks. Timing graph700includes a series of paging blocks from SIM1network130and SIM2network132that are scheduled for user equipment100. Because of radio frequency resource sharing, as described above, paging blocks412,416, and418, in this example, are lost due to paging blocks collisions between paging blocks from SIM1network130and SIM2network132. User equipment100may chose instead to receive paging blocks402,414,404, and406. Following timing graph700from left to right and using one implementation of time tracking logic122, user equipment100receives paging block402. Using the midamble of the burst, user equipment100determines the timing error between the expected arrival of the midamble and the actual arrival of the midamble of the burst, labeled ê1. Time tracking logic122uses timing error ê1and gain factor α1to determine the loop filter output c1. Time tracking logic122updates the differential adjustment factor, d1, subtracting the currently calculated loop filter output c1from the prior differential adjustment factor, d. Note that time tracking logic122subtracts c1from d because user equipment100is currently listening to the network with network identification one (i.e., SIM1network130). Time tracking logic122determines the timing adjustment, δ1, for the next scheduled paging block414using the loop filter output c1and adds the differential adjustment factor d1. Note that time tracking logic122adds d1because the currently received paging block402is from SIM1network130while the next scheduled paging block414is from SIM2network132. User equipment100may use timing adjustment, δ1, as the compensation factor to apply to internal time base140for predicting the expected arrival of the next paging block414. After user equipment100receives and processes paging block402, it may enter a sleep mode until the next paging block is scheduled to arrive. While in sleep mode, user equipment100may use its internal time base140along with timing adjustment, δ1, to predict the expected arrival of the next paging block414.

When user equipment100expects the next scheduled paging block414, user equipment wakes up from sleep mode to listen for paging block414. Again, using the midamble of the burst, user equipment100determines the timing error between the expected arrival of the midamble and the actual arrival of the midamble of the burst, labeled ê2. Time tracking logic122uses timing error ê2and gain factor α1to determine the loop filter output c2. Time tracking logic122updates the differential adjustment factor, d2, adds the currently calculated loop filter output c2and the prior differential adjustment factor, d1. Note that time tracking logic122adds c2and d1because user equipment100is currently listening to the network with network identification two (i.e., SIM2network132). Time tracking logic122determines the timing adjustment, δ2, for the next scheduled paging block using the loop filter output c2and subtracts the differential adjustment factor d2. Note that time tracking logic122subtracts d2because the currently received paging block414is from SIM2network132while the next scheduled paging block404is from SIM1network130. User equipment100may use timing adjustment, δ2, as the compensation factor to apply to internal time base140for predicting the expected arrival of the next paging block404. After user equipment100receives and processes paging block414, it may enter a sleep mode until the next paging block is scheduled to arrive. While in sleep mode, user equipment100may use its internal time base140along with timing adjustment, δ2, to predict the expected arrival of the next paging block404.

When user equipment100expects the next scheduled paging block404, user equipment wakes up from sleep mode to listen for paging block404. Again, using the midamble of the burst, user equipment100determines the timing error between the expected arrival of the midamble and the actual arrival of the midamble of the burst, labeled ê3. Time tracking logic122uses timing error ê3and gain factor α1to determine the loop filter output c3. Time tracking logic122updates the differential adjustment factor, d3, subtracting the currently calculated loop filter output c3from the prior differential adjustment factor, d2. Note that time tracking logic122subtracts c3from d2because user equipment100is currently listening to the network with network identification one (i.e., SIM1network130). Time tracking logic122determines the timing adjustment, δ3, for the next scheduled paging block using the loop filter output c3. Note that time tracking logic122does not add or subtract d3because the currently received paging block404is from SIM1network130and the next scheduled paging block406is also from SIM1network130. User equipment100may use timing adjustment, δ3, as the compensation factor to apply to internal time base140for predicting the expected arrival of the next paging block406. After user equipment100receives and processes paging block404, it may enter a sleep mode until the next paging block is scheduled to arrive. While in sleep mode, user equipment100may use its internal time base140along with timing adjustment, δ3, to predict the expected arrival of the next paging block406.

When user equipment100expects the next scheduled paging block406, user equipment wakes up from sleep mode to listen for paging block406. Again, using the midamble of the burst, user equipment100determines the timing error between the expected arrival of the midamble and the actual arrival of the midamble of the burst, labeled ê4. Time tracking logic122uses timing error ê4and gain factor α1to determine the loop filter output c4. Time tracking logic122updates the differential adjustment factor, d4, subtracting the currently calculated loop filter output c4from the prior differential adjustment factor, d3. Note that time tracking logic122subtracts c4from d3because user equipment100is currently listening to the network with network identification one (i.e., SIM1network130). Because the timing adjustment, δ4, for the next scheduled paging block depends on whether the next scheduled paging block will be received on the same network or whether the paging block with be received from another network, the time tracking logic122may not determine the timing adjustment for the next paging block until user equipment100determines whether the next scheduled paging block will arrive from SIM1network130or SIM2network132.

As shown throughFIGS. 6-8, time tracking logic122may use paging blocks from either SIM1network130or SIM2network132to compensate for the phase timing error of the internal time base140, even if the paging blocks collide. In some implementations, the time tracking logic122may also compensate for the frequency timing error due to the frequency drift of the internal time base. The frequency timing error may be used in addition to the phase timing error to compensate the internal time base when user equipment100predicts the arrival of the next paging block.

In such an implementation, example time tracking parameters128may include:

TABLE 3ParameterVariableTypeDescriptionα1constantGain of the first order phase locked loop.This constant may be used to stabilize theloop and may be set to a rational numberless than oneαdconstantGain of the “delta loop.” This constantmay be used to stabilize the loop and maybe set to a rational number less than oneαpconstantGain of internal time base drift. Thisconstant may be used to stabilize theupdates to the internal time base driftand may be set to a rational number lessthan oneLconstantLength (in time) of the averaging windowused in estimating the internal time basedriftnindexAn index representing receipt of the currentpaging block; n + 1 is the next scheduledpaging blocki(n)inputNetwork Identification (e.g., SIM1 networkor SIM2 network) for the n-th paging blockê(n)inputThe measured timing error from the n-thpaging blockΔs(n)inputTime since last paging block was receivedcinternal stateFirst order loop filter outputvariabledinternal stateThe differential adjustment applied whenvariablethe next scheduled paging block is from adifferent network{circumflex over (p)}sinternal stateEstimated drift rate of the internal timevariablebase (in Hertz)δinternalTiming adjustment between the previousvariablepaging block and the current paging blockSΔ, ii = 1, 2internal stateCumulative counts of the internal timevariablebaseSδ, ii = 1, 2internal stateCumulative timing adjustmentsvariableqoutputTime base adjustment for the next pagingblock

Using the time tracking parameters128listed above, the time tracking logic122may implement the following algorithm:

In one implementation using the above parameters and algorithm, time tracking logic122, in addition to determining the time base adjustment due to phase timing error, time tracking logic122may include an adjustment due to the frequency drift of the internal time base. Time tracking logic122may estimate the time base adjustment due to the frequency drift of the internal time base by multiplying the estimated internal time base frequency drift, {circumflex over (p)}s, by the time elapsed since the last paging block was received, Δs(n). The internal time base frequency drift, {circumflex over (p)}s, may be estimated over a series of paging blocks using an averaging window, L. Time tracking logic122accumulates the actual time elapsed, SΔ, between reception of paging blocks and accumulates the accumulated phase timing error, Sδ. Each time the actual time elapsed, SΔ, exceeds the length of the averaging window, L, the time tracking logic122may update the estimated internal time base frequency drift, {circumflex over (p)}s. Time tracking logic122may update the estimated internal time base frequency drift, {circumflex over (p)}s, by the estimated frequency error, calculated by a gain constant, αp, multiplied by the accumulated phase timing error, Sδ, divided by the length of the averaging window, L. In addition, the time tracking logic122may accumulate the actual time elapsed between reception of paging blocks and accumulate the accumulated phase timing error for each SIM independently.

FIGS. 8-10are similar in aspects toFIGS. 5-7. As discussed above, the time tracking logic122may use paging blocks from either SIM1network130or SIM2network132to compensate for the phase timing error of the internal time base140, even if the paging blocks collide, and even if the paging blocks arrive from different SIM networks. For each reception of the paging block, time tracking logic122may calculate, ê, c, d, and δ in the same way as described above forFIGS. 5-7. However, rather than using δ as the compensation factor to apply to internal time base140for predicting the expected arrival of the next paging block, the time tracking logic122may use timing compensation q, as shown inFIGS. 8-10. Timing compensation q includes the compensation factor for the phase timing error and differential offset, δ, as described above, and an additional compensation factor for the timing error from the frequency drift Δs(n) {circumflex over (p)}sof the internal time base.

FIG. 11shows flow diagram1100and is one implementation of the time tracking logic122. User equipment100receives a paging block on SIM1network130or SIM2network132(1102) and processes the paging block to determine the timing error, ê(n), between the expected arrival of the paging block and the actual arrival of the paging block (1104). Next, time tracking logic122determines whether the current network is SIM1network130or SIM2network132(1106). If the current network is SIM1network130, timing differential, d, is updated by subtracting the loop output, c=α1ê(n), from the prior timing differential (1108). If the current network is SIM2network132, timing differential, d, is updated by adding the loop output, c=α1ê(n), and the prior timing differential (1110).

Next, the time tracking logic122determines which SIM network will receive the next paging block (1112). At block1114, if the next paging block is on the same network, the timing offset is determined using option1(1118). If the time tracking logic122uses option1, the timing offset is set to the phase timing error from the loop output, δ=c=α1ê(n), and does not account for the timing differential, d. On the other hand if, at block1116, the next paging block switches from SIM2to SIM1, then the timing offset is determined using option2(1120). If the time tracking logic122uses option2, the timing offset is set to the phase timing error from the loop output and subtracts the timing differential, d, between SIM2and SIM1. Thus, δ=c−αdd. On the other hand if, at block1116, the next paging block switches from SIM1to SIM2, then the timing offset is determined using option3(1122). If the time tracking logic122uses option3, the timing offset is set to the phase timing error from the loop output and adds the timing differential, d, between SIM1and SIM2. Thus, δ=c+αdd.

Next, the time tracking logic122determines the time base adjustment, q, which takes into account the phase timing error, the timing differential, and the frequency timing offset (1124). q=δ+Δs(n){circumflex over (p)}s. User equipment100may use q as the compensation factor for adjusting the internal time base140when predicting the timing of the next scheduled paging block. Next, time tracking logic122accumulates the actual time elapsed, SΔ, between reception of paging blocks and accumulates the accumulated phase timing error, Sδ(1126). At block1128, time tracking logic122determines whether the actual time elapsed, SΔ, exceeds the length of the averaging window, L. If the actual time elapsed, SΔ, exceeds the length of the averaging window, L, the time tracking logic122may update the estimated internal time base frequency drift, {circumflex over (p)}s(1130). In block1132, the time tracking logic122determines whether to continue listening for the next paging block.

The methods, devices, techniques, and logic described above may be implemented in many different ways in many different combinations of hardware, software or both hardware and software. For example, all or parts of the system may include circuitry in a controller, a microprocessor, or an application specific integrated circuit (ASIC), or may be implemented with discrete logic or components, or a combination of other types of analog or digital circuitry, combined on a single integrated circuit or distributed among multiple integrated circuits. All or part of the logic described above may be implemented as instructions for execution by a processor, controller, or other processing device and may be stored in a tangible or non-transitory machine-readable or computer-readable medium such as flash memory, random access memory (RAM) or read only memory (ROM), erasable programmable read only memory (EPROM) or other machine-readable medium such as a compact disc read only memory (CDROM), or magnetic or optical disk. Thus, a product, such as a computer program product, may include a storage medium and computer readable instructions stored on the medium, which when executed in an endpoint, computer system, or other device, cause the device to perform operations according to any of the description above.

The processing capability of the system may be distributed among multiple system components, such as among multiple processors and memories, optionally including multiple distributed processing systems. Parameters, databases, and other data structures may be separately stored and managed, may be incorporated into a single memory or database, may be logically and physically organized in many different ways, and may implemented in many ways, including data structures such as linked lists, hash tables, or implicit storage mechanisms. Programs may be parts (e.g., subroutines) of a single program, separate programs, distributed across several memories and processors, or implemented in many different ways, such as in a library, such as a shared library (e.g., a dynamic link library (DLL)). The DLL, for example, may store code that performs any of the system processing described above. While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.