Abstract:
Wireless communication device tuning an antenna matching circuit responsive to a receive signal quality indicator and, optionally, responsive to a failed access probe is provided. Systems and methods are provided that increase the antenna efficiency in either the transmit frequency or the receive frequency in an idle or access state as needed, based on fading conditions, non-ideal antenna efficiency balance, mobile station forward versus reverse link usage and system forward versus reverse link usage. The antenna efficiency may be changed incrementally or may be optimized completely for the transmit frequency or the receive frequency. The re-balancing is accomplished by tuning the antenna matching circuit. One way to tune the antenna matching circuit is to apply a voltage to a ferro-electric capacitor in the matching circuit, thereby changing the capacitance of the ferro-electric capacitor, thereby changing the impedance of the matching circuit.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates generally to wireless electronic communications and more particularly to antenna tuning systems and methods. 
   2. Background 
   In a communication system with different transmit and receive frequencies, mobile station antenna efficiency is a balance between optimization for the transmit frequency and optimization for the receive frequency. Under typical operating conditions, the typical antenna efficiency balance allows for the best use of the transmit and receive resources. However, commonly, conditions occur in which the typical antenna efficiency balance is not preferred. In such conditions, it can be said that the forward and reverse link are not balanced. 
   The forward link is the communication link for data (voice data or other data) travelling from a base station transmitter to a mobile station receiver. The reverse link is the communication link for data (voice data or other data) from the mobile station transmitter to the base station receiver. 
   A first example of a forward and reverse link imbalance is when fading conditions may reduce either the forward link or the reverse link reception. In a second example, the antenna efficiency balance between the transmit and receive frequencies may not be ideal, as a result of some slowly changing parameter or even as a result of a fixed parameter. For example, the antenna matching circuit, or some other hardware component, may have been manufactured or calibrated in a way that provides a non-ideal balance between the transmit and receive frequencies. Alternatively, the antenna efficiency balance may become non-ideal under certain temperature conditions, such as, for example, when high temperatures result from extended continuous use. 
   In a third example, the typical antenna efficiency balance may not be preferred because of the forward and reverse link loading of the communication system at a particular time. For example, the mobile station may be transmitting or receiving only for some time periods. As another example, the wireless communication system may be overloaded in the forward link relative to the reverse link at a particular time. The communication system might be overloaded in the forward link if, for example, data is being transmitted from a base station simultaneously to many users, but relatively few users are transmitting data to the base station. 
   SUMMARY OF THE INVENTION 
   Systems and methods are provided for improving an antenna efficiency balance of a mobile station in either the idle or access state. In one case, the antenna efficiency is shifted toward the receive frequency when a receive signal quality indicator, such as, for example, message error rate (MER) or receive signal strength indicator (RSSI) drops below a predetermined threshold. In another case, the antenna efficiency balance is shifted toward the transmit frequency when the receive signal quality indicator is above the threshold and a threshold number of access probes have failed to create a connection or when the receive signal quality indicator is below the threshold, a threshold number of access probes have failed to create a connection and the mobile station is transmitting at its maximum power. 
   Other aspects, advantages, and novel features of the invention will become apparent from the following Detailed Description, when considered in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the present inventions taught herein are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings, in which: 
       FIG. 1  is a block diagram illustrating a wireless communication device tuning an antenna match. 
       FIG. 2  is a plot illustrating a tunable antenna efficiency. 
       FIG. 3  is a flow chart illustrating a method for tuning an antenna efficiency responsive to a receive signal quality indicator. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a block diagram illustrating a wireless communication device tuning an antenna match responsive to a received signal quality indicator. Wireless communication device  100  may be a cellular telephone for communicating with a base station, such as, for example, a code division multiple access (CDMA) mobile station. However, wireless communication device  100  may be any wireless communication device that communicates in at least two frequency bands. 
   Wireless communication device  100  includes antenna  102  for radiating electromagnetic signals into the air and for receiving electromagnetic signals from the air. Only one antenna  102  is shown, though multiple antennas are possible. Antenna  102  is connected to tunable matching circuit  104 . Tunable matching circuit  104  may be a ferro-electric tunable matching circuit as described in any of co-pending U.S. patent application Ser. Nos. 10/899,218; 10/899,278; 10/899,285; each filed Jul. 26, 2004; and Ser. No. 10/806,763, filed Mar. 22, 2004, which are each hereby incorporated by reference. Alternatively, tunable antenna matching circuit may be tunable by means of a varactor diode, micro-electrical mechanical switches switching various reactive components in and out of matching circuit  104 , or by any other convenient means of tuning matching circuit  104 . 
   Matching circuit  104  is connected to duplexer  106 . Duplexer  106  duplexes transmit and receive signals. Alternatively, duplexer  106  could be a switch for duplexing transmit and receive signals. Duplexer  106  is connected to transmit path  107 , represented by power amplifier (PA)  108 . Duplexer  106  is also connected to receive path  109 , represented by low noise amplifier (LNA)  110 . Transmit path  107  and receive path  109  are connected to processor  115 . Processor  115  may be a Qualcomm™ mobile station modem (MSM), such as a commercially available Qualcomm™ 6000 series MSM, for CDMA communications. 
   Processor  115  includes controller  120 . Processor  115  demodulates the received signal on receive path  109 . Power control signals are included in the received signal. That is, a base station (not shown) transmits power control signals to mobile station  100 . User interface devices, such as speaker  154 , microphone  157 , display  160  and keypad  163  are also connected to processor  115 . 
   In one embodiment, the mobile station  100  communicates in an IS-2000 cellular communication system. See TIA/EIA IS-2000, New York, N.Y., USA. In an idle state, mobile station  100  monitors overhead messages and any page for mobile station  100 , on a paging channel. From the monitored messages, mobile station  100 , that is, processor  115 , can determine a message error rate. Also, mobile station  100  monitors RSSI of the forward link pilot channel. 
   Processor  115  includes controller  120 . Controller  120  may include one or more of main input/output table,  125 , optimum transmit (Tx) table  130 , optimum receive (Rx) table  135 , and transmit/receive (Tx/Rx) table  140 . Controller  120  uses tables  125 ,  130 ,  135  and  140  to control antenna matching circuit  104 . 
   Main input/output table  125 , e.g., Table 1, is intended for use in the traffic state, and is included here simply for completeness. Table 1, below, shows examples of transmit gain adjust (TGA) and received signal strength indicator (RSSI) inputs and corresponding antenna matching outputs. There are many other possibilities. Table 1 is shown merely as an example. Particularly, the values in Table 1 may be optimally determined by experiment, and other rows may be added to Table 1 as a result of experimental determinations. 
   
     
       
             
             
             
             
           
         
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
               TGA 
               RSSI (dBm) 
               Output 
             
             
                 
                 
             
           
           
             
                 
               &gt;=7 
               &gt;−80 
               Optimum Tx 
             
             
                 
               5 to 6 
               &gt;−85 
               Move 3 bins toward Tx 
             
             
                 
               4 
               &gt;−85 
               Move 2 bins toward Tx 
             
             
                 
               3 
               &gt;−85 
               Move 1 bin toward Tx 
             
             
                 
               −5 to −6 
               &lt;−85 
               Move 1 bin toward Rx 
             
             
                 
               &lt;=−7 
               &lt;−90 
               Optimum Rx 
             
             
                 
                 
             
           
        
       
     
   
   Controller  120  keeps track of the sum of all of the transmit gain adjust commands received from the base station. The TGA column of Table 1 shows values of the sum of all of the transmit gain adjust commands. If, for example, TGA is greater than or equal to seven and RSSI is greater than −80 dBm, then the mobile station sets its antenna matching circuit to the optimum Tx setting. The optimum Tx setting is based on the transmit channel being used and the temperature. The optimum transmit setting may be stored in a table like Table 2, below. 
   
     
       
             
             
             
           
             
             
             
           
         
             
               TABLE 2 
             
             
                 
             
             
                 
                 
               Matching Circuit Setting 
             
             
               Channel or Group 
               Temperature (° C) 
               (Volts) 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               1 
                &lt;0 
               0.0 
             
             
               1 
                0 to 35 
               0.12 
             
             
               1 
               35 to 60 
               0.26 
             
             
               1 
               &gt;60 
               0.52 
             
             
               2 
                &lt;0 
               0.38 
             
             
               2 
                0 to 35 
               0.50 
             
             
               2 
               35 to 60 
               0.64 
             
             
               2 
               &gt;60 
               0.80 
             
             
                 
             
           
        
       
     
   
   Table 2 is stored in a memory of the mobile station, and referred to whenever called by the output of Table 1. In Table 2, only two transmit channels are shown for illustration. In practice many more channels will be stored. Further, the channel designations shown in Table 2 may not be actual transmit channels. Instead, the channel designations may refer to groups of channels. For example, the lowest 24 channels may be designated as channel (or group) 1 in Table 2. The second group of 24 channels may be designated as channel (or group 2) in Table 2. Thus, the lowest 24 channels may have the same matching circuit setting, for any given temperature. 
   Thus, to continue the example above, if TGA is 7 and RSSI is greater than −80 dBm, controller  125  determines from Table 1 that optimum Tx setting should be used. Controller looks optimum Tx setting up in Table 2, based on the temperature and the current transmit channel or group of channels. If, for example, the current Tx channel is channel 1 and the current temperature is 30° C., then controller  125  determines, based on Table 2, that the matching circuit setting is 0.12 Volts. Actual values for the matching circuit settings in Tables 2 and 3 will be determined experimentally. 
   Processor  115  is connected to matching circuit  104  by control line  142 . Control line  142  supplies a control voltage to matching circuit  104 , such as, for example, 0.12 Volts in the above example. A separate voltage source (not shown) may be provided for supplying the control voltage to matching circuit  104 . Or, as shown, the control voltage is supplied by processor  115  directly, responsive to the output of Table 2, 3 or 4, as determined by controller  120 . 
   Controller  120  is shown internal to processor  115 . In practice, controller may be external or partially external to processor  115 . A separate controller may be provided. For example, a controller may be a separate integrated circuit or may include one or more discrete components. In that case, processor  115  would provide the power control bits or TGA to controller externally. Additionally, RSSI may be provided to controller externally, that is, directly from an RSSI detector (not shown) to controller or from processor to controller. 
   Processor  115  is connected to memory  144 . Tables 1-4 are shown internal to controller  120 , which is shown internal to processor  115 . Tables 1-4 may be stored in memory  144 . Tables 1-4 are shown internal to controller  120  for illustration, since controller uses Tables 1-4 to look up matching circuit settings. 
   Optimum receive matching circuit settings are stored in memory  144  in a table such as Table 3, below, and referred to whenever the output of Table 1 calls for optimum receive settings. 
   
     
       
             
             
             
           
             
             
             
           
         
             
               TABLE 3 
             
             
                 
             
             
                 
                 
               Matching Circuit Setting 
             
             
               Channel or Group 
               Temperature (° C) 
               (Volts) 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               1 
                &lt;0 
               2.0 
             
             
               1 
                0 to 35 
               2.12 
             
             
               1 
               35 to 60 
               2.26 
             
             
               1 
               &gt;60 
               2.52 
             
             
               2 
                &lt;0 
               2.38 
             
             
               2 
                0 to 35 
               2.50 
             
             
               2 
               35 to 60 
               2.64 
             
             
               2 
               &gt;60 
               2.80 
             
             
                 
             
           
        
       
     
   
   Table 3 is stored in a memory of the mobile station, and referred to whenever called by the output of Table 1. In Table 3, only two receive channels are shown for illustration. In practice many more channels will be stored. Further, the channel designations shown in Table 3 may not be actual receive channels. Instead, the channel designations may refer to groups of channels. For example, the lowest 24 channels may be designated as channel (or group) 1 in Table 3. The second group of 24 channels may be designated as channel (or group 2) in Table 3. Thus, the lowest 24 channels may have the same matching circuit setting, for any given temperature. 
   Another table, such as Table 4, stores matching circuit settings for moving stepwise toward better transmit matching or stepwise toward better receive matching. Stepwise movement is used when the output of Table 1 is something other than Optimize Tx or Optimize Rx. For example, according to Table 1, if TGA is 5 or 6 and RSSI is&gt;85 dBm, then the mobile station tunes the antenna matching circuit 3 steps in the transmit direction (e.g., lower frequency in U.S. CDMA, higher frequency in Japan CDMA). An example Table 4 is shown below. As is the case for Tables 1-3, experiment will give optimum values for Table 4. 
   
     
       
             
             
             
           
             
             
             
           
         
             
                 
               TABLE 4 
             
             
                 
                 
             
             
                 
                 
               Matching Circuit Setting 
             
             
                 
               Bin Number 
               (Volts) 
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
                 
               1 
               0.0 
             
             
                 
               2 
               0.13 
             
             
                 
               3 
               0.26 
             
             
                 
               4 
               0.38 
             
             
                 
               5 
               0.50 
             
             
                 
               6 
               0.62 
             
             
                 
               7 
               0.73 
             
             
                 
               8 
               0.83 
             
             
                 
                 
             
           
        
       
     
   
   Table 4 does not include temperature as a parameter. Temperature may be included, increasing the complexity and accuracy of Table 4. Further, only eight bins are shown in Table 4. In practice, many more bins are recommended. 
   The above description was primarily intended for traffic state operation. Idle and access state operation will now be described with respect to Tables 2-4. In the idles state, if the received signal quality indicator is worse than a predetermined threshold, such as one percent for MER or −85 dBm for RSSI, then controller  120  shifts the antenna efficiency toward the Rx frequency. The shift can be an incremental shift as determined by Table 4, or an RX optimum shift as determined by Table 3. 
   In the access state, if the received signal quality indicator is worse than the predetermined threshold, and less than a threshold number of access probes have been performed, then controller  120  shifts the antenna efficiency toward the Rx frequency. The threshold number of access probes may be three. The shift can be an incremental shift as determined by Table 4, or an Rx optimum shift as determined by Table 3. If the received signal quality indicator is worse than the threshold and the threshold number of access probes has been met, then it may be advantageous for controller  120  to shift the antenna efficiency toward the Tx frequency. However, another check is performed prior to shifting toward the Tx frequency. Controller checks whether the present transmit power is equal to the maximum transmit power. If mobile station  100  is presently transmitting at maximum power, then controller shifts the antenna efficiency toward the transmit frequency. Otherwise, controller  120  does not need to change the antenna efficiency. Mobile station  100  can wait until another access probe is performed. According to TIA/EIA IS-95 or IS-2000, each successive access probe in a series is sent at a greater power than the previous access probe. Thus, it may not be necessary to increase the antenna efficiency in the transmit frequency. 
   As described above, controller  120  determines a matching circuit setting for matching circuit  104 .  FIG. 2  is a plot illustrating a tunable antenna efficiency which can be tuned responsive to the determined matching circuit setting. Antenna efficiency  147  is plotted against frequency  150 . An example antenna efficiency  153  is shown as curve  153 . Antenna efficiency  153  can be tuned by tuning matching circuit  104 . As matching circuit  104  is tuned, curve  153  can be moved to higher or lower frequencies, as shown by arrows  156  and  159 . As described in the above referenced copending U.S. patent application Ser. Nos. 10/899,278 and 10/899,218, curve  153  may be tuned to provide maximum efficiency for the currently used transmit and receive channels. Further, curve  153  is tuned responsive to commands from controller  120 , based on Tables 2-4. 
   For example, if controller  120  calls for an optimum Tx setting, controller  120  retrieves the optimum Tx setting from Table 2, and tunes curve  153 , so that peak  162  is positioned at the frequency corresponding to the current Tx channel or group of channels and the current temperature. Advantageously, the antenna efficiency is improved in the current Tx channel when improved Tx efficiency is necessary. In such a case, the Rx antenna efficiency will be degraded, but this occurs at a time when Rx antenna efficiency is not needed. As described above, the optimum Tx matching circuit efficiency is selected only when the reverse link (transmission from the mobile station) is doing poorly and the forward link (reception a the mobile station) is doing well. The reverse link and the forward link are rebalanced at least to some extent. System resources are more optimally utilized. 
   As described above with respect to Table 3, if the reverse link is doing well and the forward link is doing poorly, an optimum Rx matching circuit setting will be selected from Table 3. Matching circuit  104  is tuned to move peak  162  of curve  153  to the frequency of the current Rx channel or group of channels. 
   As described above with respect to Table 4, if a shift in matching circuit setting is called for other than an optimum Tx or Rx setting, then a matching circuit setting will be selected from Table 4. Controller  120  keeps track of which bin the matching circuit setting is currently in. Then, when controller  120  calls for a shift based on Table 4, controller  120  looks up the new matching circuit setting in Table 4, based on the current bin, the number of bins to move and the direction (Tx or Rx). For example, if the current matching circuit setting is 0.13 Volts, that is, bin number 2, and Table 1 calls for a shift of 2 bins toward Rx (or Tx) then controller  120  will look up bin 4 (start at bin 2 and add 2 bins for the selected 2 bin shift) and find the matching circuit setting corresponding to bin 4, which in this case is 0.38 Volts. Controller  120  will tune matching circuit  104  by applying 0.38 Volts to matching circuit  104 , thereby moving curve  153  two bins toward the Rx frequencies. 
     FIG. 3  is a flow chart illustrating a method for tuning an antenna efficiency (such as curve  153  in  FIG. 2 ) responsive to a received signal quality indicator, such as RSSI and MER. The method starts in step  165 . In step  170 , the mobile station enters an idle or access state. In idle state the mobile station has registered with a base station but is not sending or receiving data (which may be voice data or other data) to or from the base station, except that the mobile station monitors overhead channels, such as a paging channel. In access state, the mobile station is attempted to establish a traffic channel with a base station. The mobile station sends access probes to the base station. After each access probe, the mobile station waits a predetermined time for a response from the base station. After the mobile station waits the predetermined time, if the mobile station has not received a response from the base station, the mobile station sends another access probe at a higher power level. 
   In decision step  180 , the mobile station determines whether a first received signal quality indicator, MER, is less than a threshold, such as one percent. If not, then the mobile station determines whether the number of access probes, shown as ACCPROBE in decision step  185 , is less than a threshold, such as three. In idle state, the number of access probes is zero, so the answer to decision step  185  is always yes in idle state. In access state, the number of access probes may be any integer value from zero to a maximum value, such as five. 
   If the number of access probes is below the threshold in step  185 , then the antenna efficiency is shifted toward Rx frequency, as shown in step  190 . Advantageously, the quality of the forward link is improved, thereby improving the efficiency of network resource use. If not, then the present power level is compared to the maximum power, in decision step  195 . If the present power level is equal to or greater than the maximum power, then the antenna efficiency is shifted toward the Tx frequency, in step  200 . Advantageously, this permits some connections to be made that would not otherwise be possible. For example, at the edge of coverage, a customer may be able to make a call that otherwise would not go through. But if the present power is less than the maximum power, the antenna efficiency does not need to be shifted. 
   Returning to the discussion of step  180 , if MER is less than one percent, then the next step is decision step  210 , in which it is determined whether the RSSI is less than −85 dBm. If not, then the next step is step  185 , which was discussed above. In other words, if either MER or RSSI is worse than a predetermined threshold, then the method continues at step  185 . 
   But if the RSSI is less than −85 dBm, then the next step is decision step  215 , in which it is determined whether the number of access probes is less than a predetermined threshold, such as three. Step  215  is similar to step  185 , except that at step  215 , it has been determined that the received signal quality indicators, MER and RSSI, are better than their respective predetermined thresholds. Thus, there is not need to either shift the antenna efficiency toward Rx frequencies or check whether the present power is equal to or greater than the maximum power. Instead, if the access probe number threshold has been met, the antenna efficiency is shifted toward the Tx frequencies, in step  200 . If not, then the method returns to step  180 . 
   The shifting of antenna efficiency of steps  190  and  200  can be accomplished by any convenient means, such as, for example, by employing a table like Table 4 for both of steps  190  and  200 , or a table like Table 2 for step  200  and a table like Table 3 for step  190 . Thus, the method described with respect to  FIG. 3  may be accomplished using Table 4 and without Tables 2-3. Alternatively, even Table 4 may be avoided if, for example, the matching circuit settings are all equally spaced. Then, the shift steps  190  and  200  may be accomplished without Table 4, merely by changing the matching circuit setting by a predetermined amount in either the Tx or the Rx direction. For example, responsive to steps  190 , 0.1 Volt may be added to the current matching circuit setting, while, responsive to step  200 , 0.1 Volt may be subtracted from the current matching circuit setting. 
   While MER and RSSI are shown in  FIG. 3 , any received signal quality indicator can be used. Further, the method may include only one received signal quality indicator, such as MER or RSSI, or another received signal quality indicator. For example, symbol error rate (SER) can be used. But if SER is used in a system such as TIAIEIA IS-95 or IS-2000, then the gain of the decoder will not be accounted for. 
   Further, while embodiments and implementations of the invention have been shown and described, it should be apparent that many more embodiments and implementations are within the scope of the invention. Accordingly, the invention is not to be restricted, except in light of the claims and their equivalents.