Variable loop gain in double loop power control systems

Abstract

An apparatus and method for using a variable loop gain in a double-loop power control system to control the power of a forward link signal sent by a gateway to a user terminal to compensate for fading in a wireless communications system. In one embodiment the invention includes the steps of detecting fast fading in the forward link signal and informing the gateway of the fast fading; and at the gateway, reducing the loop gain of the power control loop when fast fading is indicated. In another embodiment, the invention includes the steps of, at the gateway, detecting fast fading in a reverse link signal received from the user terminal and reducing the loop gain of the power control loop when fast fading is indicated.

What is claimed is:  
     
         1 . An apparatus comprising: 
 means coupled to a first station for measuring a signal-to-noise ratio of a signal transmitted by a second station;    means for adjusting a transmitted signal power of said signal as a function of a loop gain, said signal-to-noise ratio, and a signal-to-noise ratio threshold;    means coupled to said first station for measuring a signal quality of the received signal;    means for adjusting said signal-to-noise ratio threshold as a function of said signal quality and a signal quality threshold;    means coupled to said first station for measuring a fading rate of said signal; and    means for adjusting said loop gain as a function of said fading rate and a fading rate threshold.    
     
     
         2 . The apparatus of  claim 1 , wherein said signal quality and said signal quality threshold are based on detection of error events.  
     
     
         3 . The apparatus of  claim 2 , wherein said error events are selected from the group comprising error rate, bit error rate, and frame error rate.  
     
     
         4 . The apparatus of  claim 1 , further comprising: 
 means for determining that said fading rate is above said fading rate threshold when multiple excursions of said signal-to-noise ratio below said signal-to-noise ratio threshold occur between successive adjustments of said transmitted signal power.    
     
     
         5 . The apparatus of  claim 1 , further comprising: 
 means for accumulating a plurality of said signal-to-noise ratio measurements to produce a time series; and a high-pass filter that filters said time series to produce said fading rate.    
     
     
         6 . An apparatus comprising: 
 means coupled to a first station for measuring a signal-to-noise ratio of a signal transmitted by a second station;    means for adjusting a transmitted signal power of said signal as a function of a loop gain, said signal-to-noise ratio, and a signal-to-noise ratio threshold;    means coupled to said first station for measuring a signal quality of the received signal;    means for adjusting said signal-to-noise ratio threshold as a function of said signal quality and a signal quality threshold;    means coupled to said second station for measuring a fading rate of a further signal transmitted by said first station; and    means for adjusting said loop gain as a function of said fading rate and a fading rate threshold.    
     
     
         7 . The apparatus of  claim 6 , wherein said signal quality and said signal quality threshold are based on detection of error events.  
     
     
         8 . The apparatus of  claim 7 , wherein said error events are selected from the group comprising error rate, bit error rate, and frame error rate.  
     
     
         9 . The apparatus of  claim 6 , wherein said means for measuring a fading rate comprises means for measuring a further signal-to-noise ratio of said further signal.  
     
     
         10 . The apparatus of  claim 9 , further comprising means for determining that said fading rate is above said fading rate threshold when multiple excursions of said further signal-to-noise ratio below a further signal-to-noise ratio threshold occur between successive adjustments of said transmitted signal power.  
     
     
         11 . The apparatus of  claim 6 , wherein said means for measuring a fading rate comprises: 
 means for accumulating a plurality of said further signal-to-noise ratio measurements to produce a time series; and    a high-pass filter that filters said time series to produce said fading rate.    
     
     
         12 . A method comprising the steps of: 
 measuring, at a first station, a signal-to-noise ratio of a signal transmitted by a second station;    adjusting a transmitted signal power of said signal as a function of a loop gain, said signal-to-noise ratio, and a signal-to-noise ratio threshold;    measuring, at said first station, a signal quality of the received signal;    adjusting said signal-to-noise ratio threshold as a function of said signal quality and a signal quality threshold;    measuring, at said first station, a fading rate of said signal; and    adjusting said loop gain as a function of said fading rate and a fading rate threshold.    
     
     
         13 . The method of  claim 12 , wherein said signal quality and said signal quality threshold are based on detection of error events.  
     
     
         14 . The method of  claim 13 , wherein said error events are selected from the group comprising error rate, bit error rate, and frame error rate.  
     
     
         15 . The method of  claim 12 , further comprising the step of determining that said fading rate is above said fading rate threshold when multiple excursions of said signal-to-noise ratio below said signal-to-noise ratio threshold occur between successive adjustments of said transmitted signal power.  
     
     
         16 . The method of  claim 12 , further comprising the steps of: 
 accumulating a plurality of said signal-to-noise ratio measurements to produce a time series; and    high-pass filter in said time series to produce said fading rate.    
     
     
         17 . A method comprising the steps of: 
 measuring, at a first station, a signal-to-noise ratio of a signal transmitted by a second station;    adjusting a transmitted signal power of said signal as a function of a loop gain, said signal-to-noise ratio, and a signal-to-noise ratio threshold;    measuring, at said first station, a signal quality of the received signal;    adjusting said signal-to-noise ratio threshold as a function of said signal quality and a signal quality threshold;    measuring, at said second station, a fading rate of a further signal transmitted by said first station; and    adjusting said loop gain as a function of said fading rate and a fading rate threshold.    
     
     
         18 . The method of  claim 17 , wherein said signal quality and said signal quality threshold are based on detection of error events.  
     
     
         19 . The method of  claim 18 , wherein said error events are selected from the group comprising error rate, bit error rate, and frame error rate.  
     
     
         20 . The method of  claim 17 , wherein said step of measuring a fading rate comprises measuring a further signal-to-noise ratio of said further signal.  
     
     
         21 . The method of  claim 20 , further comprising the step of determining that said fading rate is above said fading rate threshold when multiple excursions of said further signal-to-noise ratio below a further signal-to-noise ratio threshold occur between successive adjustments of said transmitted signal power.  
     
     
         22 . The method of  claim 17 , wherein said step of measuring a fading rate comprises the steps of: 
 accumulating a plurality of said further signal-to-noise ratio measurements to produce a time series; and    high-pass filter in said time series to produce said fading rate.