Abstract:
A property of a wireless signal over time is monitored while a processor is maintained in a first power state that utilizes less power than a second power state. While the processor remains in the first power state, a measure of the property is compared to a first threshold and to a second threshold. The processor can be transitioned from the first power state to the second power state if the measure crosses the first threshold and the second threshold, and otherwise the processor is maintained in the first power state.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of and claims priority to U.S. patent Ser. No. 09/874,674 entitled “Digital Processor Update Of Single Channel Strength Signal,” by Garribrant et al., filed on Jun. 4, 2001, now U.S. Pat. No. 6,952,571 which is incorporated herein by reference, which is a continuation-in-part of U.S. patent application Ser. No. 09/847,768, entitled “Direct Digital Signal Processor Control of Multi-Channel Scan for Re-Establishing Connections in a Wirelessly Networked Device,” by C. Skinner, J. Brown, and W. Wong, filed May 1, 2001, now U.S. Pat. No. 6,901,276, assigned to the assignee of the present invention and hereby incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to portable computer systems such as personal digital assistants or palmtop computer systems. More specifically, the present invention relates to portable computer systems that are configured with wireless (radio) communication functionality. 
     BACKGROUND OF THE INVENTION 
     As the continuing advances in technology have enabled the further miniaturization of the components required to build computer systems, new categories of computer systems have been created. One of the newer categories of computer systems developed has been the portable, hand held, or “palmtop” computer system, referred to as a personal digital assistant or PDA. Other examples of a palmtop computer system include electronic address books, electronic day planners, electronic schedulers and the like. 
     A palmtop computer system is a computer that is small enough to be held in the user&#39;s hand and as such is “palm-sized.” As a result, a palmtop is readily carried about in the user&#39;s briefcase, purse, and in some instances, in the user&#39;s pocket. By virtue of its size, the palmtop computer, being inherently lightweight, is therefore exceptionally portable and convenient. 
     Continuing miniaturization has provided for the development of additional functionality, which can be incorporated into some portable computer systems. One such additional functionality incorporated into some portable computer systems has been wireless (radio) capability. Some portable computer systems are equipped with radio transceivers (receiver/transmitter) that provide two way communication between a wireless communications network and the portable computer system. Further, in addition to the main processor, the portable computer system may also include a DSP (digital signal processor), adapted for processing of data to be transceived. The DSP performs some of the communication processes that would have been performed by the main processor. 
     Generally, most portable computer systems are powered by disposable or rechargeable batteries. Because the reduced size of the portable computer system, such that it is deemed “palm-sized,” predicates the volume of energy which may be stored within, smaller batteries are being utilized to comply with the diminutive size of the portable computer system. Further, the portable computer system&#39;s power consumption is a significant consideration in reducing the rate with which the batteries either need to be replaced or recharged. Accordingly, portable computer systems are enabled to be placed into a minimum or low power mode, such as a sleep mode or a deep sleep mode, while the system is not processing a specific function or particular operation. 
     Until recently, when communication occurred between the portable computer system and a wireless network, the portable computer system was aware of an expected transmission of data. For example, when data was being wirelessly transceived by the portable computer system, is was in response to a request by the portable computer system. Accordingly, the portable computer system was purposefully placed into a transceiving state when a transmission was anticipated or desired, but otherwise was not in a transceiving mode. 
     Because of the ever increasing complexity within the portable computer system, the portable computer system is frequently being implemented in applications that require continuous transceiving readiness, much like a cellular telephone. For example, when a cellular telephone is powered up, it is enabled to receive calls at any time. By the same token, a portable computer system is able to receive, or transmit, data or information nearly any time the transceiver is powered up, regardless of whether other components are in a sleep (low power consumption) mode. 
     It is desirable for the portable computer system (with a wireless transceiver) to remain “in coverage” when the transceiver is powered up, such that uninterrupted wireless communication is enabled. However, due to, in part, its portability, there may be instances when the signal strength may fluctuate such that the communicative link between the portable computer system and the wireless network is lost. Additionally, dependent upon the amount of signal strength fluctuation, the portable computer system may entirely lose the communication link, so as to be considered “out of coverage.” For example, the portable computer system has, while in one location, an established connection utilizing a particular broadcast channel of a network. Subsequent to or during relocation, the signal strength of that channel may fluctuate such that the communication signal may be lost. 
     Currently, during signal strength monitoring, the radio components are powered up for checking and then powered down afterward, or the radio components are powered up continuously, which has an adverse affect on the power supply of the portable computer system. Additionally, the main processor is commonly activated during this monitoring, which is also a substantial drain on the portable computer system&#39;s power supply. 
     SUMMARY OF THE INVENTION 
     Thus, a need exists for a method and system for providing periodic monitoring of the strength of a communication signal being transceived without undue depletion of the retained power supply within a portable computer system. An additional need exists for a method and system that fills the above listed need and which further provides for an allowable range of signal strength fluctuation before causing the main processor to acquire a new communication channel over which data may be received. The present invention provides a novel solution to these and other needs. These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment, which are illustrated in the various figures. 
     The present invention pertains to a method and system for providing periodic signal strength monitoring without unduly depleting the power supply within a portable computer system. In one embodiment, the wireless network is a Mobitex wireless communication system, but could use any well known wireless communication medium. The present invention can be implemented when the portable computer system is communicating with a wireless network and the strength of the transceiving signal is fluctuating, such that the fluctuation may have a detrimental effect on the communication link. 
     The present invention can also be implemented during those periods when the portable computer system is out of coverage, monitoring the signal strength and consistency of other broadcast network channels considered for acquiring a new signal. 
     In one embodiment of the present invention, the portable computer system has a main processor and a DSP (digital signal processor). The main processor sends a command to the DSP which includes the channel to scan, two fluctuation threshold levels, and a sleep time. The main processor is put into a low power (sleep) mode, thereby conserving retained power. The DSP is also placed into a low power (sleep) mode, also conserving retained power. In accordance with the current embodiment, the internal timer of the DSP periodically (as specified by the sleep time) awakens the DSP to monitor the RSSI (radio signal strength indication) for fluctuation during communication. If the DSP detects fluctuation that exceeds the threshold levels, the DSP will interrupt or awaken the main processor to act upon this data. If no threshold crossing fluctuations are detected, the DSP will return to the low power mode until the next specified time for monitoring the RSSI. 
     The present invention provides a method and system for periodic signal strength monitoring without unduly depleting the power supply within a portable computer system. The present invention further provides, in one embodiment, a method and system that achieves the above listed accomplishment and which provides for an allowable range of signal strength fluctuation without unnecessarily activating the main processor. The present invention further provides a method and system that achieves the above listed accomplishments and which does so while in a low-power (sleep) mode, thereby inherently saving battery power. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention: 
         FIG. 1  is a block diagram of an exemplary network environment including a portable computer system in accordance with one embodiment of the present invention. 
         FIG. 2A  is a top side perspective view of a portable computer system in accordance with one embodiment of the present invention. 
         FIG. 2B  is a bottom side perspective view of the portable computer system of  FIG. 2A . 
         FIG. 3A  is a top side perspective view of a portable computer system having a hinged front cover in accordance with one embodiment of the present invention. 
         FIG. 3B  is a bottom side perspective view of the portable computer system of  FIG. 3A . 
         FIG. 4  is a block diagram of an exemplary portable computer system upon which embodiments of the present invention may be practiced. 
         FIG. 5  is a flowchart showing steps in a process for periodic measuring of channel signal strength during an established wireless communication link between a portable computer system and a wireless network in accordance with one embodiment of the present invention. 
         FIG. 6  is a linear representation of threshold limits utilized by the present invention when implemented for RSSI monitoring, in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     A method and system for periodically measuring channel signal strength during an established wireless communication link between a portable computer system and a wireless network are described. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be obvious, however, to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid obscuring the present invention. 
     Notation and Nomenclature 
     Some portions of the detailed descriptions, which follow, are presented in terms of procedures, steps, logic blocks, processing, and other symbolic representations of operations on data bits that can be performed on computer memory. These descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. A procedure, computer executed step, logic block, process, etc., is here, and generally, conceived to be a self-consistent sequence of steps or instructions leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated in a computer system. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like. 
     It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout the present invention, discussions utilizing terms such as “determining” or “scanning” or “waking” or “initiating” or “sending” or “receiving” or “transceiving” or “triggering” or “displaying” or “updating” or “measuring” and the like, refer to the action and processes of a computer system or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system&#39;s registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. 
     The present invention is discussed primarily in the context of a portable computer system, such as a palmtop or personal digital assistant. However, it is appreciated that the present invention can be used with other types of devices that have the capability to access some type of central device or central site, including but not limited to palmtop computer systems. 
     Exemplary Network Environment 
       FIG. 1  is a block diagram of an exemplary network environment  50  including a portable computer system  100  in accordance with one embodiment of the present invention. Portable computer system  100  is also known as a palmtop or palm-sized computer system, a hand-held device, a personal digital assistant (PDA), or a personal information device (PID). In one embodiment, portable computer system  100  has the ability to transmit and receive data and information over a wireless communication interface (e.g., a radio interface). 
     In the present embodiment, base station  32  is both a transmitter and receiver base station, which can be implemented by coupling it into an existing public telephone network  34 . Implemented in this manner, base station  32  enables portable computer system  100  to communicate with a proxy server computer system  36 , which is coupled by wire to the existing public telephone network  34 . 
     Furthermore, proxy server computer system  36  is coupled to the Internet  52 , thereby enabling portable computer system  100  to communicate with the Internet  52 . Coupled with Internet  52  are multiple computer systems (e.g., servers) exemplified by computer system  38 . When communicating with a Web site over Internet  52 , protocols such as CTP (Compact Transport Protocol) and WAP (wireless access protocol) and markup languages such as CML (Compact Markup Language) and WML (wireless markup language) can be used by portable computer system  100  in the present embodiment. 
     It should be appreciated that within the present embodiment, one of the functions of proxy server  36  is to perform operations over the Internet  52  on behalf of portable computer system  100 . For example, proxy server  36  has a particular Internet address and acts as a proxy device for portable computer system  100  over the Internet  52 . 
     It should be further appreciated that other embodiments of a communications network, planned or envisioned, may be utilized in accordance with the present invention. For example, a wireless connection may be made from portable computer system  100  either directly to the Internet  52  or directly to computer system  38 . It is also appreciated that portable computer system  100  may be coupled to computer system networks other than the Internet  52 , such as an Intranet, local area network, or the like. 
     The data and information that are communicated between base station  32  and portable computer system  100  are the same type of information and data that can conventionally be transferred and received over a wireless communication interface. It should be appreciated that one embodiment of a wireless communication system in accordance with the present invention is the Mobitex wireless communication system. 
     Exemplary Palmtop Platform 
       FIG. 2A  is a perspective illustration of the top face  100   a  of one embodiment of portable computer system  100 . The top face  100   a  contains a display screen  105  surrounded by a bezel or cover. A removable stylus  80  is also shown. The display screen  105  is a touch screen able to register contact between the screen and the tip of the stylus  80 . The stylus  80  can be of any material to make contact with the screen  105 . The top face  100   a  also contains one or more dedicated and/or programmable buttons  75  for selecting information and causing the computer system to implement functions. The on/off button  95  is also shown. 
       FIG. 2A  also illustrates a handwriting recognition pad or “digitizer” containing two regions  106   a  and  106   b . Region  106   a  is for the drawing of alphabetic characters therein (and not for numeric characters) for automatic recognition, and region  106   b  is for the drawing of numeric characters therein (and not for alphabetic characters) for automatic recognition. The stylus  80  is used for stroking a character within one of the regions  106   a  and  106   b . The stroke information is then fed to an internal processor for automatic character recognition. Once characters are recognized, they are typically displayed on the screen  105  for verification and/or modification. 
     Still referring to  FIG. 2A , RSSI (radio signal strength indicator)  2001  is shown as disposed upon the upper right corner of display screen  105 , in one embodiment of the present invention. In another embodiment, RSSI  2001  may be disposed nearly anywhere upon portable computer system  100 , and not necessarily disposed within display screen  105 . In this example, RSSI  2001  is a visual indicator using discreet lights, for example, to indicate signal strength. In this example, the stronger the signal, the greater the number of lights that will be illuminated. In another embodiment, a single light may be implemented to indicate RSSI fluctuations, such that when the signal strength is acceptable, the light is illuminated. In yet another embodiment, there may be two differently colored lights, for example, a red and a green light, such that the green light would be illuminated to indicate acceptable signal strength fluctuation. Accordingly, a red light would be illuminated to indicate an unacceptable signal strength fluctuation. In another example, the lights may be nearly any other shape and or size. 
     It should further be appreciated that in another embodiment, RSSI  2001  may be an audible indicator, where, in one example, a sequence of beeps may indicate signal strength and in another example, the louder a tone, a greater signal strength is indicated and the quieter the tone, a weaker signal strength is indicated. In yet another embodiment, RSSI  2001  may be a motion activating device, such that the signal strength is indicated by the intensity of a vibration, such that an intense motion indicates a strong signal strength. 
       FIG. 2B  illustrates the bottom side  100   b  of one embodiment of the palmtop computer system that can be used in accordance with various embodiments of the present invention. Battery storage compartment door  90  is shown. In one embodiment, an internal antenna (not shown) may be present and coupled with communication circuit  135  of  FIG. 4 . A communication interface  180  and an infrared port  64  are also shown. In one embodiment, communication interface  180  is a serial port. In another embodiment, communication interface  180  can be a parallel port, a USB (universal serial bus), an IEEE 1394 connection, and the like. In one embodiment, infrared communication mechanism  64  is compliant with the IrDA (Infrared Data Association) standard and protocol. 
       FIG. 3A  is a perspective illustration of the top face  100   c  of one embodiment of portable computer system  100 . The top face  100   a  contains a display screen  105  surrounded by a bezel or cover. A removable stylus  80  (as shown in  FIG. 2A ) is present, although not shown because of the viewing angle. The display screen  105  is a touch screen able to register contact between the screen and the tip of the stylus  80 . The stylus  80  can be of any material to make contact with the screen  105 . The top face  100   c  also contains one or more dedicated and/or programmable buttons  75  for selecting information and causing the computer system to implement functions. 
     Still referring to  FIG. 3A , front cover  175  for providing protection against damage to display screen  105  is also shown. Front cover  175  is adapted to rotate about an axis, or hinge, as indicated by the arrow. Also shown is RSSI  2001  disposed upon the upper left corner of display screen  105 . In this embodiment, a series of rectangular indicating LEDs (light emitting diodes) are used to visually indicate signal strength. In this example, the weaker the signal, less lights are illuminated and the stronger the signal, more lights are illuminated. 
       FIG. 3B  illustrates the bottom side  100   d  of one embodiment of the palmtop computer system that can be used in accordance with various embodiments of the present invention. A stylus  80 , an extendible antenna  85 , and a battery storage compartment door  89  are shown. A communication interface  180  and an infrared port  64  are also shown. In one embodiment, communication interface  180  is a serial port. In another embodiment, communication interface  180  can be a parallel port, a USB (universal serial bus), an IEEE 1394 connection, and the like. In one embodiment, infrared communication mechanism  64  is compliant with the IrDA (Infrared Data Association) standard and protocol. 
     Still referring to  FIG. 3B , external auxiliary card slot  140  is shown. Card slot  140  is adapted to receive compact and/or flash memory cards, e.g., SDs (secure digital cards), or MMCs (multimedia cards), or memory sticks and the like. Front cover  175  is also shown and is adapted to rotate about the axis, or hinge, as indicated by the arrow. 
       FIG. 4  is a block diagram of one embodiment of a portable computer system  100  upon which embodiments of the present invention may be implemented. Portable computer system  100  is also often referred to as a PDA, a PID, a palmtop, or a hand-held computer system. 
     Portable computer system  100  includes an address/data bus  130  for communicating information, a central (main) processor  131  coupled with the bus  130  for processing information and instructions, a volatile memory  132  (e.g., random access memory, RAM) coupled with the bus  130  for storing information and instructions for the main processor  131 , and a non-volatile memory  133  (e.g., read only memory, ROM) coupled with the bus  130  for storing static information and instructions for the main processor  131 . Portable computer system  100  also includes an optional data storage device  134  (e.g., auxiliary card slot  140  of  FIG. 3B ) coupled with the bus  130  for storing information and instructions. Device  134  can be removable. Portable computer system  100  also contains a display device  105  coupled to the bus  130  for displaying information to the computer user. 
     In the present embodiment, portable computer system  100  includes a signal input/output device (transceiver)  144  providing it with the capability for wireless communication. The transceiver  144  provides a wireless radio frequency (RF) communication link between computer system  100  and other devices, using any of the various RF protocols and standards. In one embodiment, the Mobitex wireless communication specification is used. In another embodiment, the Bluetooth wireless communication specification is used. In still another embodiment, a wireless LAN (local area network) communication specification is used. It is appreciated that transceiver  144  may be integrated into portable computer system  100 , or that transceiver  144  may be a separate component coupled to portable computer system using, for example, serial port  180 . 
     It is appreciated that in another embodiment portable computer system  100  may also include a telephony chipset or the like providing it with the functionality of a cellular phone, in particular the capability to transmit and receive cellular communications. In one embodiment, the telephony chipset is compatible with the standards for GSM and GPRS (Global System for Mobile Communications and General Packet Radio Service, respectively). It is appreciated that other telephony protocols and standards may also be used with the present invention. 
     In the present embodiment, portable computer system  100  of  FIG. 4  includes communication circuitry  135  coupled to bus  130 . In one embodiment, communication circuitry  135  is a universal asynchronous receiver-transmitter (UART) module that provides the receiving and transmitting circuits required for serial communication for both the serial port  180  and the infrared port  64 . Communication circuitry  135  also includes DSP (digital signal processor)  136  for processing data to be transmitted or data that are received via transceiver  144 . 
     Also included in computer system  100  is an optional alphanumeric input device  106  that, in one implementation, is a handwriting recognition pad (“digitizer”). Alphanumeric input device  106  can communicate information and command selections to main processor  131  via bus  130 . In one implementation, alphanumeric input device  106  is a touch screen device. Alphanumeric input device  143  is capable of registering a position where a stylus element (not shown) makes contact. 
     Portable computer system  100  also includes an optional cursor control or directing device (on-screen cursor control  143 ) coupled to bus  130  for communicating user input information and command selections to main processor  131 . In one implementation, on-screen cursor control device  143  is a touch screen device incorporated with display device  105 . On-screen cursor control device  143  is capable of registering a position on display device  105  where a stylus element makes contact. The display device  105  utilized with portable computer system  100  may be a liquid crystal display (LCD) device, a cathode ray tube (CRT), a field emission display device (also called a flat panel CRT), or other display device suitable for generating graphic images and alphanumeric characters recognizable to the user. In the preferred embodiment, display device  105  is a flat panel display. 
     Portable computer system  100  also includes RSSI (radio signal strength indicator)  2001  which is coupled to communication bus  130  and is shown in  FIGS. 2A and 3A . RSSI  2001  is adapted to provide a visual indication of a particular broadcast network&#39;s channel signal strength during periods of transceiving. 
     DSP Monitoring of Fluctuation in Channel Signal Strength 
     The purpose of the signal strength fluctuation measurement is to provide to a user a quicker more rapid update of the current channel signal strength. It should be appreciated that the present invention is applicable when in coverage and when out of coverage. The somewhat limited power resources contained within portable computer system  100  ( FIG. 4 ) are conserved by utilizing a DSP (digital signal processor) to perform the signal strength fluctuation measurements instead of having main processor  131  ( FIG. 4 ) perform that task. Additionally, the transceiving notification (signal strength) is updatable at a more frequent rate than what the stack (running on main processor  131  of  FIG. 4 ) was able to provide without severe negative impacting of the retained power supply. 
       FIG. 5  is a flowchart of the steps in a process  500  for periodic measuring of signal strength fluctuation of a wireless connection between portable computer system  100  ( FIG. 4 ) and wireless network  50  ( FIG. 1 ) in accordance with one embodiment of the present invention. In the present embodiment, process  500  is implemented as computer-readable program instructions executed by portable computer system  100 . For the significant conservation of power, portions of process  500  are performed by DSP  136  of  FIG. 4  while main processor  131  ( FIG. 4 ) remains in a low power mode, as will be seen. 
     In step  510  of  FIG. 5  and with reference to  FIG. 4 , DSP  136  receives from main processor  131  instructions for controlling the periodic measuring of signal strength fluctuation of a wireless connection to be performed by DSP  136 . The instructions provide the duration of a periodic timed interval of low power entered into by DSP  136 , in one embodiment of the present invention. The instructions further provide a particular broadcast channel frequency for DSP  136  to measure. The frequency to be measured for fluctuation by DSP  136  equates to the frequency of the wireless connection. The instructions also provide an upper threshold and a lower threshold which define the range of acceptable fluctuation of the signal strength of the wireless connection. 
     Still referring to step  510 , the duration of a periodic timed interval provides a regulated sleep time for DSP  136 . When the sleep time is over, the DSP is awakened to perform the measuring of the signal strength fluctuation. 
     In step  520  of  FIG. 5 , with reference also to  FIG. 4 , once main processor  131  has sent the controlling instructions regarding periodic measuring to DSP  136 , main processor  131  is automatically placed into a low power mode (e.g., a sleep mode or a deep sleep mode). In accordance with the present invention, main processor  131  will remain in a low power mode through step  570  of process  500 . 
     In step  530  of  FIG. 5  and with reference also to  FIG. 4 , once DSP  136  has received the controlling instruction regarding periodic measuring of signal strength fluctuation, DSP  136  is automatically placed into a low power mode (e.g., a sleep mode or a deep sleep mode). 
     In step  540  of  FIG. 5 , still with reference to  FIG. 4 , subsequent to the expiration of the periodic timed interval of low power mode in which DSP  136  was placed, DSP  136  is awakened to measure signal strength fluctuation of a wireless connection. In one embodiment, the duration of the periodic timed interval can be twenty seconds. In another embodiment, the duration may be fifteen seconds. In yet another embodiment, the duration may be for thirty seconds. It should be appreciated that the duration of periodic timed interval of low power mode is adjustable, such that a wireless connection prone to large and frequent fluctuation may required more frequent measurement, and a wireless connection having relatively constant signal strength may require less frequent measuring of signal strength. 
     In step  550  of  FIG. 5 , once awakened, DSP  136  measures signal strength fluctuation of the wireless connection, in one embodiment. It should be appreciated that DSP  136  performs the measuring of the signal strength fluctuation while main processor  131  remains in a low power mode. 
     In step  560  of  FIG. 5 , subsequent to the measuring of fluctuation of signal strength, provided the measured signal strength fluctuation is within the range of acceptable fluctuation, as defined in step  510 , DSP  136  returns to a low power mode until the period timed interval of low power mode expires and DSP  136  is again awakened to perform the measuring of the signal strength fluctuation of the wireless connection. However, when an instance occurs when the measured signal strength fluctuation exceeds the range of acceptable fluctuation, DSP  136  is automatically triggered to awaken main processor  131 . 
     In step  570 , once main processor  131  has been awakened, caused by the fluctuation of signal strength exceeding the range of acceptable fluctuation, main processor  131  acts upon this data. In one embodiment, main processor  131  may switch to an alternate broadcast channel which is known to have minimal signal strength fluctuation. In another embodiment, main processor may be instructed to search for an acceptable broadcast channel with which it may continue the wireless connection previously obtained. 
       FIG. 6  is a linear representation of the upper and lower threshold values utilized during implementation of the of the present invention, in accordance with one embodiment of the present invention. The upper and lower thresholds provide a range of fluctuation so that main processor  131  ( FIG. 4 ) is not unnecessarily awakened. Because the signal strength is affected by noise in the system, the RSSI (radio signal strength indicator) value calculated by the DSP  136  will have some variance. If utilizing a single threshold level, when the signal strength is close to the threshold, the RSSI read by DSP  136  could fluctuate around the threshold level and cause the DSP  136  to unnecessarily awaken main processor  131 . To avoid this problem, main processor  131  sends two threshold levels to the DSP  136 . This allows for a range of threshold levels so as not to trigger the DSP to awaken main processor  131 . 
     Still referring to  FIG. 6 , upper threshold level UT  606  and lower threshold level LT  607  which define a range of acceptable fluctuations are shown.  FIG. 6  has three sections which are sections A, B, and C. Section A is to the left, section B is in the middle, and section C is to the right. Each section has two examples of signal strength fluctuations. 
     For example, assume that an RSSI of 6 dB (decibels) is measured. The main processor may, in this example, want to be informed when the signal strength drops below an RSSI level of 5.0. Accordingly, the main processor could send to the DSP thresholds that correspond to 4.5 and 5.0, which is shown in UT  606  and LT  607 , respectively. The DSP would not awaken the main processor until the RSSI went below 4.5 dB, represented by LT  607 . Conversely, if the initial RSSI were 3 dB, the DSP would not awaken the main processor until the RSSI rose above 5 dB, represented by UT  606 . RSSI values between 4.5 and 5 dB would not trigger the DSP to awaken the main processor. 
     Referring to section A of  FIG. 6 , in one example, fluctuation  620  is shown to have an initial RSSI level which is above UT  606 . During transceiving,  620  falls below UT  606  (5 dB) but remains above LT  607 . Accordingly, fluctuation  620  does not trigger the DSP to awaken the main processor. 
     In another example, fluctuation  622  is shown to have an initial RSSI level which is below UT  606  but above LT  607 . During transceiving,  622  drops lower but does not fall below LT  607 . Accordingly, fluctuation  622  does not trigger the DSP to awaken the main processor. 
     Referring to section B of  FIG. 6 , in one example, fluctuation  624  is shown to have an initial RSSI of 6 dB. During transceiving,  624  drops below UT  606  and also drops below LT  607 . Accordingly, fluctuation  624  does trigger the DSP to awaken the main processor. 
     In another example, fluctuation  626  is shown to have an initial RSSI level which is between UT  606  and LT  607 . During transceiving,  626  falls below LT  607 . Accordingly, fluctuation  626  triggers the DSP to awaken the main processor. 
     Referring to section C of  FIG. 6 , fluctuation  628  is shown to have an initial RSSI level of 3 dB which is below LT  607 . During transceiving  628  rises above LT  607  and continues above UT  606 . Accordingly, fluctuation  628  would cause the DSP to awaken the main processor. 
     In another example, fluctuation  630  is shown to have an initial RSSI level which is below LT  607 . During transceiving  630  rises above LT  607  but remains below UT  606 . Accordingly, fluctuation  630  would not cause a triggering of the DSP to awaken the main processor. 
     In summary, the present invention provides a method and system which conserves retained power within a portable computer system while periodically measuring signal strength fluctuations in a wireless connection between a portable computer system and a wireless network. In accordance with the present invention, the DSP awakens periodically from a low power mode to measure signal strength fluctuation while the main processor remains in a low power mode. If the measured signal strength fluctuation is within an acceptable range, the DSP returns to a low power mode until the next periodic measurement. Not until an unacceptable range of fluctuation is measured, is the main processor awakened. With the main processor remaining in a low power mode during signal strength measurements, battery life is extended thereby reducing the frequency with which the batteries need to be recharged or replaced. 
     The present invention has been described in the context of a portable computer system; however, the present invention may also be implemented in other devices having, for example, a main processor and a DSP (digital signal processor) that enables the main processor to be placed into a low power mode while the DSP performs certain functions on behalf of the main processor, including those not necessarily associated with measuring signal strength fluctuations. 
     The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.