Abstract:
A system and method for invoking one or more features of a wireless device when a signal strength of a channel approaches or drops below an RSSI threshold of the channel is disclosed. An embodiment of the invention includes the steps of (1) obtaining the RSSI threshold for the channel; (2) monitoring the signal strength during an operation mode of the wireless device; and (3) invoking the feature when the signal strength approaches a predetermined limit of the RSSI threshold. In an implementation on a cordless telephone, the feature can include playing a warning, switching to a different channel, or returning a telephone line to an idle state.

Description:
BACKGROUND  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to wireless devices and, more particularly, to a system and method for using received signal strength indication (RSSI) to invoke one or more features of a wireless device.  
           [0003]    2. Background of the Invention  
           [0004]    Cordless telephones have many limitations. One of these limitations relates to problems associated with a handset being out of the range of communication with its base station. As a user communicates with another party using a handset while walking away from the base station, at some point the handset will be out of range and fail to perform. At this time, even though the handset has ceased operation, the base station continues to engage the telephone line. This results in a waste of telecommunications resources and the user might even pay for valuable air time that he does not use. Accordingly, there is a need for a cordless telephone that can intelligently detect the handset being out of range and return the telephone line to an idle state when the handset is out of range.  
         SUMMARY OF THE INVENTION  
         [0005]    The invention provides a system and method that utilizes RSSI to invoke one or more features of a wireless device. One embodiment of the invention provides a method that saves an RSSI threshold associated with a channel of the wireless device; monitors a signal strength on the channel during an operation mode of the wireless device; and invokes a feature of the wireless device when the signal strength on the channel is within a predetermined limit of the RSSI threshold. A typical RSSI threshold can be about −100 dBm. Preferably, the predetermined limit is between about 100 percent and about 110 percent of the RSSI threshold. Preferably, the predetermined limit is about 105 percent of the RSSI threshold. The feature can involve one or more of playing a warning and changing to a different channel. The operation mode can involve a communications session using a telephone line associated with the wireless device, and the feature can include dropping the telephone line when the signal strength is below the RSSI threshold. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is a schematic diagram showing a cordless telephone in accordance with an embodiment of the invention.  
         [0007]    [0007]FIGS. 2 and 3 are collectively a flowchart showing an exemplary process of the invention.  
         [0008]    [0008]FIG. 4 is a flowchart showing an exemplary process involved in using a cordless telephone of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0009]    [0009]FIG. 1 is a schematic diagram showing a cordless telephone in accordance with an embodiment of the invention. Cordless telephone  100  includes base station  110 , handset  120 , and microprocessor  130 . Microprocessor  130  resides within base station  110 . An algorithm of the invention is preferably implemented on microprocessor  130 . Although the preferred embodiment of the invention is implemented in a cordless telephone, the invention can be implemented in other wireless devices, including wireless telephones.  
         [0010]    Base station  110  includes antenna  112  and cradle  114 . Handset  120  includes antenna  122 . Base station  110  is in an idle state when handset  120  is not being used. When handset  120  is away from cradle  114  and is being used by a user to make or receive a telephone call via telephone line  140  that is connected to PSTN  150 , handset  120  communicates with base station  110  via RF signals. The RF signals are exchanged between handset  120  and base station  110  via antenna  122  and antenna  112 .  
         [0011]    RSSI (Received Signal Strength Indication) is an important aspect of cordless telephone design. A common unit for RSSI is dBm. RSSI is a signal output that is proportional with the RF input power. As a result, this signal output can be used to measure the RF signal strength on a specific channel and indicate the usage on that channel.  
         [0012]    RSSI is typically higher when handset  120  is closer to base station  110 . For example, in the absent of other environmental factors (e.g., signal interfering devices, physical obstructions, etc.) RSSI is directly proportional to the distance between handset  120  and base station  110 . For example, the RSSI detected by base station  110  decreases as handset  120  moves away from base station  110 . In other words, the RSSI at x×3 is lower than that at x=2, and the RSSI at x=2 is lower than that at x=1. At some point, for example, when handset  120  is at x=4 or farther away from base station  110 , RSSI becomes so low that an effective communication between handset  120  and base station  110  can be not established. At x=4 and beyond, handset  120  is considered to be out of range.  
         [0013]    Many features of cordless telephone  100  can be implemented using the RSSI information. Conventionally, each cordless telephone is associated with an RSSI threshold, which can be quite difficult to determine. Traditionally, the RSSI threshold is preset at the factory. The factory preset RSSI threshold is frequently less than optimal for the cordless telephone when used by a user at home. The present invention provides a method that determines a reliable RSSI threshold. For the purpose of describing the invention depicted in FIG. 1, the RSSI threshold for cordless telephone  100  at the current channel is the RSSI measured at x=4.  
         [0014]    [0014]FIGS. 2 and 3 are collectively a flowchart showing an exemplary process of the invention. For clarity, references are made to FIG. 1. In the preferred embodiment, microprocessor  130  is configured to perform one or more steps described below.  
         [0015]    In step  202 , base station  110  returns to an idle state. Base station  110  can return to the idle state in one of several ways. For example, base station  110  is in the idle state after cordless telephone  100  finishes a startup initiation, when telephone line  140  is not being used to communicate, and where there is an unanswered call. It is not necessary to remove handset  120  from cradle  114 .  
         [0016]    In step  204 , a measurement period for the RSSI threshold detection on a current channel is started. A typical cordless telephone is associated with 30 channels one of which is used at a time for communication between the handset and the base station. The measurement period can be, for example, about 20 milliseconds. The measurement period is used to monitor (1) the background RF signal strength; and (2) the valid data signal from handset  120  on the current channel.  
         [0017]    In step  206 , the RF signal strength on the current channel is measured. Measurement of RF signal strength is generally known and is, therefore, not further described herein.  
         [0018]    In step  208 , it is determined whether any valid data pattern from handset  120  is detected. If so, the process goes to step  216  (shown in FIG. 3). Otherwise, the process goes to step  210 .  
         [0019]    In step  210 , if no valid data pattern from handset  120  was detected in step  208 , the measured signal strength of the current channel is saved as the RSSI threshold for the current channel. Preferably, the RSSI threshold for the current channel is stored in a memory accessible to microprocessor  130 .  
         [0020]    In step  212 , if the measurement period set in step  204  has not expired, the process returns to step  206 . Otherwise, the process goes to step  214 .  
         [0021]    In step  214 , another channel is selected and the process repeats steps  204  through  214  for each available channel. For example, this process can be repeated 30 times if cordless telephone  100  has 30 channels.  
         [0022]    In step  216  (FIG. 3), if valid data pattern from handset  120  was detected in step  208 , the measurement period set in step  204  is extended. The extension can include, for example, two 50-millisecond periods totaling 100 milliseconds. Therefore, the new measurement period in step  216  can be about 120 milliseconds long.  
         [0023]    In step  218 , base station  110  receives the data packet from handset  120 .  
         [0024]    In step  220 , if handset  120  enters into an operation mode, i.e., to answer an incoming call or to initiate an outgoing call, the process goes to step  224 . Otherwise, the process goes to step  222 .  
         [0025]    In step  222 , it is determined whether the extended measurement period has expired. If so, the process goes to step  214  (FIG. 2) for measurement on another channel. Otherwise, the process repeats steps  218  through  222  until the extended measurement period has expired.  
         [0026]    In step  224 , if handset  120  is used, e.g., to answer or initiate a call, a communications session between handset  120  and base station  110  is established to enable a voice link with another party on telephone line  140 . The voice link uses the most recently saved RSSI threshold for the current channel.  
         [0027]    In step  226 , the voice link is maintained.  
         [0028]    In step  228 , it is determined whether the call has ended. If so, the process returns to step  202  (FIG. 3). Otherwise, the process repeats steps  226  and  228 .  
         [0029]    Accordingly, the invention is configured to define different RSSI thresholds on different channels. For a cordless telephone that has 30 channels, as many as 30 different RSSI thresholds can be saved. By implementing a process of the invention, such as that illustrated in FIGS. 2 and 3, the best RSSI threshold that takes into consideration the environmental information can be saved for each channel. This process is superior to setting the RSSI threshold at the factory.  
         [0030]    The present invention provides other advantages. For example, the invention saves the production time of the cordless telephone by neglect the tuning of the RSSI threshold at the factory. In turn, a saving in production time can result in a saving in production cost. In addition, due to its measurement of RSSI threshold at the location when the cordless telephone is used, the invention provides RSSI information that is more reliable, which results in increased performance of the cordless telephone.  
         [0031]    The RSSI threshold measured and saved in accordance with the present invention can be used in many ways. For example, the RSSI threshold can be used to invoke one or more features of cordless telephone  100 .  
         [0032]    For example, the RSSI threshold measured for each channel can be used for out of range detection for the channel in use. Referring to FIG. 1, for example, as handset  120  moves away from base station  110  to a location between x=3 and x=4, a warning can be played by handset  120  to alert the user that it is approaching the out of range limit. The warning can be an audible tone and/or a visible indication produced by handset  120 . Further, when handset  120  moves away from base station  110  to a location where x is greater than 4, microprocessor  130  can immediately return telephone line  140  to an idle state, resulting in a saving in telecommunications resources.  
         [0033]    [0033]FIG. 4 is a flowchart showing an exemplary process involved in using a cordless telephone of the invention. For clarity, cordless telephone  100  shown in FIG. 1 is referenced herein.  
         [0034]    In step  402 , an RSSI threshold is obtained for a current channel of cordless telephone  100 . Preferably, an RSSI threshold is obtained for each channel of cordless telephone  100 . For example, if cordless telephone  100  has 30 channels, an RSSI threshold is obtained for each of the 30 channels. As a result, there are a total of 30 RSSI thresholds. Depending on factors associated with each channels, two or more of these RSSI thresholds may be identical. The RSSI thresholds can be obtained in accordance with the exemplary process shown in FIGS. 2-3.  
         [0035]    In step  404 , during an operation mode of handset  120  (e.g., handset  120  is being used during a telephone call on telephone line  140 ), a signal strength of the current channel (the channel being used) is monitored. Preferably, the signal strength of the current channel is compared with the RSSI threshold of the current channel.  
         [0036]    In step  406 , if the signal strength measured in step  404  is within a predetermined limit of the RSSI threshold, the process goes to step  408 , otherwise, the process returns to step  404 . The predetermined limit can be, for example, between about 100 percent and 110 percent of the RSSI threshold. In other words, if the RSSI threshold is −100 dBm, then the predetermined limit would be between −100 dBm and −110 dBm. Preferably, the predetermined limit is about 105 percent of the RSSI threshold (i.e., the limit is −105 dBm if the RSSI threshold is −100 dBm).  
         [0037]    In step  408 , a first feature of cordless telephone  100  is invoked. The first feature can be one of several possibilities. The first feature can include playing a warning at handset  120 . The warning can be either an audible tone or a visible clue, or both. The first feature can also include switching to a different channel having a lower RSSI threshold. The first feature can also be dropping the telephone call altogether.  
         [0038]    In step  410 , if the signal strength of the current channel is outside the predetermined limit of the RSSI threshold of the current channel, the process returns to step  404 . Otherwise, the process goes to step  412 . For example, the process can return to step  404  when the user of handset  120  walks closer to base station  110  resulting in an increase in the signal strength (e.g., greater than −110 dBm). Alternatively, the process can return to step  404  when a channel having a higher RSSI threshold is used.  
         [0039]    In step  412 , the signal strength of the current channel continues to be measured and compared against the RSSI threshold.  
         [0040]    In step  414 , if handset  120  has gone out of range, e.g., the measured signal strength has dropped below the RSSI threshold (i.e., lower than −100 dBm), the process goes to step  416 . Otherwise, the process repeats step  412 .  
         [0041]    In step  416 , a second feature is invoked. The first feature can be one of several possibilities. The second feature can include switching to a different channel having a lower RSSI threshold. The second feature can also be dropping the telephone line altogether.  
         [0042]    In another embodiment in which only one feature is to be invoked, the process can go from step  402  directly to step  412 . For example, the invention can be implemented on a cordless telephone that has an external charger for the handset to save valuable resources. During a conventional usage, if a user wants to hang up a telephone call, the user can either press a button, e.g., the “Phone Off” key or put the handset on the external charger. If the RF environment is not desirable, i.e., due to a long range between the handset and the base station, or if there is an interference emitted by other electronic equipment, the base station cannot receive any signal from the handset and the base station continues to engage in the call. Under those circumstances, the user would not know that the base station is still engaged in the call, resulting in a waste of telecommunications resources. One function of this invention is to prevent or reduce the wasted call time.  
         [0043]    The foregoing disclosure of the preferred embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many variations and modifications of the embodiments described herein will be apparent to one of ordinary skill in the art in light of the above disclosure. The scope of the invention is to be defined only by the claims appended hereto, and by their equivalents.  
         [0044]    Further, in describing representative embodiments of the present invention, the specification may have presented the method and/or process of the present invention as a particular sequence of steps. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. As one of ordinary skill in the art would appreciate, other sequences of steps may be possible. Therefore, the particular order of the steps set forth in the specification should not be construed as limitations on the claims. In addition, the claims directed to the method and/or process of the present invention should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the sequences may be varied and still remain within the spirit and scope of the present invention.