Abstract:
Apparatus and methods for controlling sleep mode in a wireless device are disclosed. The sleep mode is controlled using low power detection of RF beacon signals of known frequencies to reduce power consumption of the wireless device during sleep modes. Detection is achieved by using passive or low power elements in a receive chain that filters received signals allowing beacon signals of particular frequencies to pass, which are accumulated with passive or low power circuit elements requiring no external power source. The accumulated energy is compared to a threshold to determine the presence of the beacon with sleep circuitry. When the beacon is detected, the full RF receiver is triggered to wake up. Use of low power elements and passive elements, affords a beneficial increase in power savings for the wireless device, which is particularly helpful in wireless access points or relay stations that have an alternative power sourcing such as battery or solar power.

Description:
CLAIM OF PRIORITY UNDER 35 U.S.C. §119 
       [0001]    The present Application for Patent claims priority to Provisional Application No. 61/096,718 entitled “IDLE MODE OPERATION FOR ACCESS POINTS AND RELAYS” filed Sep. 12, 2008, and assigned to the assignee hereof and hereby expressly incorporated by reference herein. 
       REFERENCE TO CO-PENDING APPLICATIONS FOR PATENT  
       [0002]    The present Application for Patent is related to the following co-pending U.S. patent applications: 
         [0003]    “Apparatus and Methods for Controlling Idle Mode Operation in a Wireless Device” by Gorokhov et al., having Attorney Docket No. 081817, filed concurrently herewith, assigned to the assignee hereof, and expressly incorporated by reference herein 
     
    
     BACKGROUND 
       [0004]    1. Field 
         [0005]    The present disclosure relates generally to apparatus and methods for controlling an access point (AP) sleep mode, and more specifically to controlling the AP sleep or idle mode through the use of low power detection of RF signals of known frequencies in order to reduce power consumption for control of idle or sleep modes in an AP or Relay station (RS). 
         [0006]    2. Background 
         [0007]    New wireless communication deployment models are currently emerging where coverage and high capacity is enabled via dense networks of low-cost nodes. These nodes may be either wired access points (APs) or wireless relay stations (RS). Cost efficiency of such deployments is achieved not only due to low device cost but, more importantly, due to reduction in the costs of site acquisition, rental and maintenance. In this context, enabling cordless or non-wired RSs with an alternative source of power, such as through using a solar power source, has been proved efficient in some deployment scenarios. Alternatively, deploying an AP without an alternative power supply which is otherwise required to ensure robustness to power outages also yields a substantial reduction in the deployment cost. In both cases, the ability of an AP or RS to substantially reduce its power consumption during inactivity or idle periods is desirable. 
         [0008]    It is noted that for access terminals (ATs) such as handsets or other portable devices, various forms of power save operations are well known in wireless standards to improve battery life of user equipment or access terminal (AT). In wireless cellular systems, for example, typical forms of AT power save operation are “idle mode” and various forms of active “sleep mode.” Further, the concept of power efficient operation for network node type devices is also known, such as in the case of network nodes in IEEE Std. 802.11 that are enabled to provide power efficient forwarding in a mesh Wi-Fi network or micro cellular environment. The application of operations such as idle or sleep modes to APs or RSs (and even ATs) in a mesh or microcell network would be desirable to reduce power consumption during inactivity periods. Notwithstanding, sensing of RF network activity used to trigger awakening of sleeping devices in a network typically utilizes active devices in the receive chain to sense the RF signals (e.g., RF receiver blocks, amplifiers, Automatic Gain Control (AGC), etc). Although the hardware of such receive chains can be configured to operate at lower power, the power consumption of such devices can still be significant. Accordingly, it would be desirable to provide a further reduction in power consumption of components used to detect network activity to conserve power resources, as well as reduce costs of the AP or RS equipment. 
       SUMMARY 
       [0009]    According to an aspect, an apparatus for controlling a sleep mode in a wireless device is disclosed. The apparatus includes at least one bandpass filtering unit comprising at least one of passive and low power elements and configured to allow at least one beacon signal of one or more frequencies to pass. The apparatus further includes at least one accumulator unit configured to store energy from signals passed by the bandpass filtering unit, the accumulator unit comprising at least one of passive and low power elements. A comparator operable in a low power portion of the wireless device is configured to compare the level of stored energy in the accumulator to a predetermined threshold. Finally, the apparatus includes a sleep controller operable in the low power portion of the wireless device and configured to issue a wakeup trigger signal to other circuitry in the wireless device when the level of stored energy in the accumulator exceeds the predetermined threshold. 
         [0010]    In another aspect, a method for controlling a sleep mode in a wireless device is disclosed. The method includes bandpass filtering wireless signals to derive at least one RF narrowband beacon signal using at least one of passive and low power filter elements. Next, the method includes accumulating energy of the at least one RF narrowband beacon signal using at least one of passive and low power elements, and comparing the accumulated energy with a predetermined threshold. The presence of the at least one RF narrowband beacon signal is then determined when the accumulated energy is greater than the predetermined threshold; and signaling wakeup of wireless device circuitry based on determination of the presence of the at least one RF narrowband beacon signal. 
         [0011]    In still one further aspect, an apparatus for controlling a sleep mode in a wireless device is disclosed. The apparatus includes means for bandpass filtering wireless signals to derive at least one RF narrowband beacon signal using passive or low power filter elements, and means for accumulating energy of the at least one RF narrowband beacon signal also using one or more passive or low power elements. Furthermore, the apparatus includes means for comparing the accumulated energy with a predetermined threshold, and means for determining the presence of the at least one RF narrowband beacon signal when the accumulated energy is greater than the predetermined threshold; and means for signaling wakeup of wireless device circuitry based on determination of the presence of the at least one RF narrowband beacon signal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a diagram of an exemplary wireless network in which the disclosed apparatus and methods may be utilized. 
           [0013]      FIG. 2  is a block diagram of an exemplary apparatus for use in a wireless device to sense a particular wireless signal from another network device in order to control the idle or sleep mode of the wireless device. 
           [0014]      FIG. 3  is a block diagram of an alternative arrangement of the apparatus of  FIG. 2  where multiple sensing receive chains are utilized to simultaneously detect multiple signals of different frequencies. 
           [0015]      FIG. 4  is a block diagram of another exemplary apparatus for use in a wireless device to sense a particular wireless signal from another network device in order to control the idle or sleep mode of the wireless device. 
           [0016]      FIG. 5  is a flow diagram of a method for sensing a particular wireless signal from another network device in order to control the idle or sleep mode of the wireless device. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The present disclosure describes apparatus and methods for controlling an access point (AP) idle mode by using low power detection of RF signals of known frequencies in order to reduce power consumption in idle or sleep modes in a wireless device, such as an AP or Relay station (RS), as well as an AT. In an aspect, a low power RF receive chain may be implemented using one or more passive elements that do not require a power source for reception and accumulation of signal energy of a particular tone or frequency (e.g., a narrowband signal). According to one example, the particular signal may be a beacon signal having a pre-specified frequency and transmitted by an AT to indicate its presence within a network. The presence of the particular signal, such as a beacon signal, may then be detected during an idle or sleep mode when signal energy is accumulated such that a threshold is exceeded, which in turn may be used to initiate wake up of the full RF receiver and modem in the wireless device. By utilizing passive elements rather than powered active elements for even a portion of signal detection during idle mode, a power savings is realized. 
         [0018]    The techniques described herein may be used for various wireless communication networks including cellular networks with microcells or 3G micro-networks. The networks may be configured as Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, Single-Carrier FDMA (SC-FDMA) networks, etc. The terms “networks” and “systems” are often used interchangeably. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includes Wideband-CDMA (W-CDMA) and Low Chip Rate (LCR). cdma2000 covers IS-2000, IS-95 and IS-856 standards. A TDMA network may implement a radio technology such as Global System for Mobile Communications (GSM). An OFDMA network may implement a radio technology such as Evolved UTRA (E-UTRA), IEEE 802.11, IEEE 802.16 (WiMax), IEEE 802.20, Flash-OFDM , etc. UTRA, E-UTRA, and GSM are part of Universal Mobile Telecommunication System (UMTS). Long Term Evolution (LTE) is an upcoming release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS and LTE are described in documents from an organization named “3rd Generation Partnership Project” (3GPP). cdma2000 is described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). The techniques described herein may also be applied in future technologies such as International Mobile Telecommunications-Advanced (IMT Advanced), better known as 4G, or any other technology present or future that may employ mesh networks, microcell or micro networks, femtocell networks, picocell networks, peer-to-peer, or other similar schemes. 
         [0019]    Although the terminology used herein to describe the disclosed methods and apparatus refers to access points (APs) and relay stations (RSs), these terms are understood to include base station, NodeB, evolved Node B (eNodeB or eNB)), repeaters, or equivalent devices. Further, the term access terminal (AT) as used herein is understood to encompass devices described by terms such as User Equipment (UE), mobile device, terminal, wireless communication device, Subscriber Station (SS), or other equivalent terminology. 
         [0020]      FIG.1  illustrates one example of a network architecture in which the present apparatus and methods may be utilized. The network  100  may be a mesh type network, microcell or micro network, femtocell network, picocell network, Wi-Fi, or a heterogeneous network of a combination of different types of nodes or APs. Network  100  may include an AP  102  that provides network service for ATs, such as AT  104 . Additionally, AP  102  is shown connected to a wired network  106  (and may also be wired to a normal source of power). 
         [0021]    AP  102  is further illustrated wirelessly networked with another AP  108 , which may be not wired to a normal source of power. AP  108  provides network service to an AT  110 . As an example of peer-to-peer communication, AT  110  is shown in communication with another AT  112 . In an aspect, the presently disclosed apparatus and methods could be implemented in an AT, such as AT  110 , in detecting a beacon from another AT, such as AT  112 . 
         [0022]      FIG. 1  also illustrates a relay station RS  114 , which is in communication with AP  108 . RS  114  may effect relaying or repeating of wireless communications from one AP (e.g., AP  108 ) to one or more other APs, such as AP  116 . AP  116  provides network service to one or more ATs, such as AT  118 . 
         [0023]    It is noted that the APs illustrated in  FIG. 1  may be configured to broadcast one or more beacons or other similar identifying signals at known one or more predetermined frequencies or tones. In turn, when an AP detects the beacon, communication between the AP and AT may initiate to allow network access to the AT, for example. If the AP utilizes a sleep or idle mode where power consumption is reduced during idle periods or periodically, the AP will need to turn on at least a portion of the RF receive chain to detect the presence of AT beacon signals. If the RF receive chain is utilizing active components, the power usage will be higher than passive components, for example. Accordingly, the present apparatus and methods utilize one or more passive elements requiring no power source other than the energy of the received beacon(s). 
         [0024]    It is noted that the transmission of beacon signals is not limited to ATs, but could also be transmitted by APs or RSs, especially for mobile APs and RSs that need to registered or discovered when placed. Also, ATs may employ beacon detection, such as in the case of peer-to-peer communications as illustrated by ATs  110  and  112  in  FIG. 1 . 
         [0025]      FIG. 2  is a block diagram of an exemplary apparatus  200  for use in a wireless device to sense a particular wireless signal (i.e., the beacon(s)) from another network device in order to control the idle or sleep mode of the wireless device. As mentioned above, the wireless device may be an AP, RS or and AT. 
         [0026]    A detection portion of apparatus  200  can be fully or at least partially implemented by passive elements that detect a particular energy level of the signal at a particular narrowband frequency response. Thus, in an aspect a narrowband or bandpass filter of the signal will pass through energy to a means to accumulate the energy. If the energy accumulated reaches a threshold amount, this indicates the likelihood that the particular signal of interest is present. Accordingly, the example of  FIG. 2  illustrates a passive circuitry portion  202  consisting of solely passive circuit elements, which are used to filter and accumulate energy of those signals of a particular frequency passing through the filtering. 
         [0027]    Circuitry portion  202  is connected to an antenna to receive RF signals present in the vicinity. The narrowband response or bandpass filtering can be implemented, in one example, by a bandpass filter unit  206 . In an aspect, unit  206  may be implemented with a passive resonator circuit  206 . Resonator  206  allows energy of signals at a particular narrowband frequency to pass, while blocking energy from signals of other frequencies. In the illustrated example, the resonator  206  may consist of simply a parallel arrangement of a capacitor (C 1 ) and inductor (L 1 ) having values set to cause resonance in the C 1  and L 1  elements at a desired frequency. It is noted that more complex arrangements, such as an LC series resonant circuit, or a combination of LC series and parallel elements, are also contemplated dependent on desired additional features such as noise filtering. 
         [0028]    The passive circuitry  202  may also include a rectifier  208  to convert the alternating, zero-mean signal passed through by resonator  206  into a rectified, non-zero mean signal. In the example of  FIG. 2 , rectifier  208  could be implemented as simply as a half-wave rectifier using a diode D 1 , but more complex arrangements, such as full wave rectification or a gate controlled diode are contemplated. 
         [0029]    The rectified signal is passed to an integrator or accumulator  210  that is configured to accumulate the signal over a predefined time. The integrator  210  may be implemented by a capacitor C 2  having a predetermined value to effect a suitable charging constant. Other known devices for accumulating charge or energy known to those skilled in the art may also be used in lieu of capacitor C 2 . Integrator  210  may also include a switch Si that serves to discharge capacitor C 2 , either in the event that a predetermined threshold charge has been accumulated or to discharge partial charge on the capacitor when the predefined time has lapsed. 
         [0030]    If the integrator is implemented with a capacitor to accumulate charge, as shown in the example of  FIG. 2 , a DC or non-zero mean current is needed to cause charging of the capacitor C 2 . Thus, if other types of charge accumulation devices are used, it could be conceivable other circuit elements are needed. Thus, for purposes of this application, the combination of rectifier  208  and integrator  210  may be collectively considered an “accumulator” and other arrangements for effecting charge accumulation besides the rectifier  208  and integrator  210  are contemplated. 
         [0031]    The voltage on capacitor C 2  is input to low power active circuitry  212  for comparison with a predetermined threshold. It is noted that circuitry  212  may be low power circuitry used in an AP, RS, or AT to perform necessary monitoring, clocking, and other functions that need to occur during a sleep mode of the wireless device. Circuitry  212  includes a threshold comparator  214  to compare the voltage output from integrator  210  to a predetermined threshold (x). If the level is above the threshold, the comparator output state  216  changes (e.g., from a “0” to “1” state), which indicates that the beacon or desired signal is present. In certain situations, the beacon signal(s) could penetrate to multiple APs. Accordingly, there is a potential that more than one AP would detect the beacon and subsequently be woken up and even transmit a preamble (i.e., a signal enabling discovery of the AP) to the AT, thus leading to some loss in sleep time and unnecessary power consumption. Such false detections may be mitigated by proper adjustment of the predetermined threshold of comparator  214  such that only the closest AP(s) wakes up. 
         [0032]    The output state  216  is input to circuitry or an algorithm run on a processor configured for sleep mode management (represented by cloud to indicate a sleep-mode manager or “sleep controller”  218  that can be hardware, firmware, software, or a combination thereof). The sleep controller  218  is configured to recognize a particular output state (e.g., “1”) from the comparator  214  as detection of the beacon signal. In response, sleep controller  218  may, in turn, issue a wakeup trigger  222  to initiate full wakeup of normal operation active circuitry  224 . Circuitry  224 , which operates at higher power for RF signal reception and signal processing, is normally put to sleep either periodically or responsive to the lack of network activity to save power. 
         [0033]    The sleep controller  218  may also be configured to issue a reset signal  220  to reset the integrator  210  either after detection of the beacon signal or after the predefined time period. In the particular example illustrated in  FIG. 2 , the signal  220  operates a reset device, such as a switch  51  that is closed momentarily to discharge capacitor C 2 . It is noted that for the example in  FIG. 2 , the reset device may be implemented by any number of known switching devices such as a transistor, a thyristor, solid state relay, or any other suitable switching device. It will be appreciated that lower power switching devices are more beneficial in terms of power savings. 
         [0034]    The beacon signals detected by circuitry  202  and  212  may be a predetermined singular frequency. Alternatively, multiple predetermined tones or frequencies may be used effect beacon in a network. In such case, the passive circuitry  202  may need to detect multiple narrowband beacon signals. Accordingly,  FIG. 2  illustrates an alternative example where the resonator  202  may be variable to “tune” to various different frequencies. As one example, capacitor C 1  may be a variable device to vary the resonant frequency of the C 1 , L 1  combination. It is noted that capacitor C 1  may be a mechanically variable capacitor, or low power devices such as a MEMS capacitor or a digital capacitor. It is also contemplated (although not shown) that L 1  could be a variable digital inductor. 
         [0035]    In still another alternative,  FIG. 3  illustrates a modification  300  of apparatus  200  where multiple passive receive chain circuits ( 3021  through  302 N) may be utilized for an N number of beacons each having a different tone (note: elements unchanged from apparatus  200  use the same reference numbers as  FIG. 2 ). Each receive chain  302  is tuned to a distinct frequency corresponding to the respective tone of the beacons. The outputs  304  of the receive chains  302  may then be input to a multiplexer  306  or similar device in to low power active circuitry  308  to select between the inputs from receive chains to compare with the threshold by comparator  214 . It is also contemplated that rather than a multiplexer, multiple comparators could be used (not shown), each comparator coupled to a respective one of the receive chains  302 . 
         [0036]      FIG. 4  illustrates another apparatus  400  that may be used in a wireless device, such as an AP, to detect one or more beacon signals of particular tones. Apparatus  400  includes a means  402  for bandpass filtering wireless signals derived from an antenna to derive one or more RF narrowband beacon signals using one or more of passive or low power elements. In an aspect, the low power elements may be passive circuitry consisting of different arrangements of capacitive and inductive elements, such as in the example of resonator  206  in  FIG. 2 . Means  402  may also be implemented with a combination of lower power elements such as passive elements (e.g., capacitors and inductors) and active elements (which may also be low power elements such as MEMs capacitors and digital capacitors and inductors). 
         [0037]    Apparatus  400  is further illustrated with a bus  404  for coupling the different means or modules and represent means for communication of signals, voltages, currents, etc. Means  402  may pass the RF signals of the particular narrowband tones or frequencies via bus  404  to a means for  406  for accumulating energy of the one or more bandpass filtered narrowband signals using one or more passive or low power elements. Means  406  may, in one aspect, be implemented with a rectifier (e.g.,  208 ) and an integrator (e.g.,  210 ) comprising a capacitor (e.g., C 2  in  FIG. 2 ). Other suitable equivalent means for accumulating charge may also be utilized instead of a capacitor. 
         [0038]    The energy level of means  406  is then sensed by a means  408  for comparing the energy accumulated with a predefined threshold (e.g., the voltage accumulated is compared to a voltage threshold). Means  408  may implemented in one example by comparator  214 . Furthermore, means  408  may be implemented within low power or sleep circuitry portion of a wireless device, such as circuitry  212  in  FIG. 2 . 
         [0039]    The output of means  408  may be communicated to a means  410  for determining the presence of the one or more RF narrowband beacon signals based on the comparison between the energy accumulated and the predefined threshold. In an example, if the state of the output of means  408  changes (e.g., from a “0” to a “1”), which indicates that the threshold is exceeded, then means  410  will make a determination that at least one particular narrowband beacon signal is present. As an example, means  410  may be implemented as the sleep controller  218  shown in  FIG. 2 . Additionally, in an aspect, means  410  may be implemented within a low power or sleep circuitry portion of a wireless device, such as circuitry  212  in  FIG. 2 . Means  410  may also implement a timer to keep track of a predefined time period in which sensing occurs and effect sending a reset to the accumulation means  406  (which may include a means for reset, such as a switch (e.g., S 1 )) either after the time period has elapsed or after detection of a beacon. 
         [0040]    When means  410  makes a determination of the presence of the at least one narrowband RF beacon signal, a means  412  for signaling wakeup of wireless device circuitry make issue a wakeup signal to other circuitry (e.g., normal operation circuitry  224 ). 
         [0041]    It is noted that means  410  and  412  may be implemented by software, hardware, firmware, or any combination thereof. Software implementation may be effected through a processor (illustrated by block  414 ) executing stored code or instructions stored in a memory (e.g., memory  416 ). 
         [0042]      FIG. 5  illustrates an exemplary method  500  for control of a sleep mode in a wireless device that utilizes low power or passive components in its execution. As shown in block  502 , method  500  includes bandpass filtering received wireless signals to derive one or more RF narrowband beacon signals using one or more passive or low power elements. As discussed before, bandpass filtering may be performed by low power elements such as a resonator having all passive elements (capacitors and inductors), which require no power except the RF signals, or low power digital capacitors, digital inductors, or MEMs capacitors, which still provide elements utilizing less or low power than normal RF receive chain elements. 
         [0043]    The method further includes a process in block  504  where energy of the one or more bandpass filtered narrowband signals derived from the filtering processes of block  504  is accumulated using one or more passive or low power elements. As an example, the energy may be accumulated with an integrator comprising passive elements; namely a rectifier (e.g., diode D 1 ) to provide a non-zero mean signal from the narrowband beacon signal(s) and a capacitor (e.g., C 2 ) that accumulates the charge from the rectified signal(s). 
         [0044]    As the energy is accumulated in the process of block  506 , a comparison of the voltage or energy level in the integrator to a predetermined threshold is continuously performed (or, alternatively, performed periodically) as indicated by decision block  508  illustrating the check of a condition whether the accumulated energy is greater than predetermined threshold x. If the threshold has been exceeded, this means that a beacon is detected and flow proceeds from block  508  to signal wakeup of wireless device circuitry (e.g.,  224 ) based on determination of the presence of the one or more RF narrowband beacon signals  508   
         [0045]    If the condition of block  506  is not yet met, flow proceeds to decision block  510  where a check is made whether a predefined time period has been exceeded. If not, the flow is shown proceeding to a block  511  for incrementing the time and looping back to block  510 . Although not shown, it would be evident to one skilled in the art that a time increment count is reset when the predefined time has been reached. It is also noted that the processes blocks  502  and block  504  are continually performed since the passive circuit elements simply respond to certain RF frequencies received, and the charge accumulated would be reset upon either a detection of a beacon or exceeding the predefined time, whichever comes first. This is illustrated by flow from either block  510  or  508  to block  512  where the accumulation is reset (e.g., S 1  is operated discharging capacitor C 1  assuming the example of  FIG. 2 ). 
         [0046]    It is noted that for the alternative arrangements illustrated in  FIGS. 2 and 3  where different frequencies for beacons of multiple or different tones, one skilled in the art will appreciate that method  500  may be modified to account for the detection of multiple tones. For example, the processes of blocks  502 ,  504 , and  506  may be repeated for each method  500  may be executed for each receive chain  302  in the example of  FIG. 3  and block  506  may further include cycling through each receive chain  302  with multiplexer  304  and detection made when one or more of the receive chains  302  yields a voltage exceeding the predetermined threshold. Similarly, in the case of a variable capacitor to tune the resonator  206 , the process of blocks  502 ,  504 ,  506  may account for each “tuning” of resonator and signal detection when one or more of the different tunings results in an accumulator level exceed the predetermined threshold. 
         [0047]    It is understood that the specific order or hierarchy of steps in the processes disclosed is merely an example of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged while remaining within the scope of the present disclosure. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented. 
         [0048]    Those of skill in the art will understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof 
         [0049]    Those of skill will further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the examples disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention. 
         [0050]    The various illustrative logical blocks, modules, and circuits described in connection with the examples disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
         [0051]    The steps of a method or algorithm described in connection with the examples disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal 
         [0052]    In one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. In one example herein, the comparator  214  and sleep manager  218  may be implemented with code stored on a computer readable medium. 
         [0053]    It is noted that in the above discussion, the word “element” is intended to refer to circuitry components, such as a capacitors or inductors as merely two examples. The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any example described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other examples. 
         [0054]    The previous description of the disclosed examples is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these examples will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other examples without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the examples shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.