Adaptive equalizer with a dual-mode active taps mask generator and a pilot reference signal amplitude control unit

Abstract

An adaptive equalizer including an equalizer filter and a tap coefficients generator used to process a sample data stream derived from a plurality of received signals is disclosed. The tap coefficients generator includes an equalizer tap update unit, a vector norm square estimator, an active taps mask generator, a switch and a pilot amplitude reference unit used to minimize the dynamic range of the equalizer filter. A dynamic mask vector is used to mask active taps generated by the equalizer tap update unit when an unmasked signal output by the equalizer filter is selected by the switch to generate an error signal fed to the equalizer tap update unit. A fixed mask vector is used to mask active taps generated by the equalizer tap update unit when a masked signal output by the equalizer filter is used to generate the error signal.

1 . A method for adaptive equalization comprising:
 generating an unmasked equalizer signal from an input data stream using equalizer filter tap coefficients;   generating a masked equalizer signal from the input data stream using masked equalizer filter tap coefficients, wherein the masked equalizer filter tap coefficients are generated by masking the equalizer filter tap coefficients with an active taps mask;   selecting one of the masked equalizer signal and the unmasked equalizer signal;   generating an error signal based on the selected one of the masked equalizer signal or the unmasked equalizer signal;   updating the equalizer filter tap coefficients based on the error signal; and   generating the active taps mask for masking the equalizer filter tap coefficients.   
     
     
         2 . The method of  claim 1 , wherein a dynamic mask vector is used as the active taps mask on a condition that the unmasked equalizer signal is selected to generate the error signal, and a static mask vector is used as the active taps mask on a condition that the masked equalizer signal is selected to generate the error signal. 
     
     
         3 . The method of  claim 2  wherein the active taps mask is generated by comparing the equalizer filter tap coefficients with a threshold. 
     
     
         4 . The method of  claim 3  wherein the threshold is generated based on at least one of average of the equalizer filter tap coefficients, step size, Doppler spread, and a signal-to-noise ratio (SNR). 
     
     
         5 . The method of  claim 3  wherein an element of the active taps mask is set to 1 on a condition that an absolute value of a corresponding equalizer filter tap coefficient is above an upper threshold and set to 0 on a condition that the absolute value of the corresponding equalizer filter tap coefficient is below a lower threshold. 
     
     
         6 . The method of  claim 1  further comprising:
 generating a reference signal; and 
 comparing the reference signal with the selected one of the masked equalizer signal and the unmasked equalizer signal to generate the error signal. 
 
     
     
         7 . The method of  claim 6  wherein the reference signal is generated by scaling a pilot channel signal with a pilot amplitude reference signal. 
     
     
         8 . The method of  claim 7  further comprising:
 generating a first vector norm square of an equalizer tapped delay line (TDL) signal; 
 generating a second vector norm square of the equalizer filter tap coefficients; 
 multiplying the first vector norm square and the second vector norm square to generate an equalizer output power signal; and 
 dividing a power target by the equalizer output power signal to generate a quotient result measurement signal, wherein the pilot amplitude reference signal is generated based on the quotient result measurement signal. 
 
     
     
         9 . The method of  claim 7  further comprising:
 generating an equalizer output power signal from the masked equalizer signal; and 
 dividing a power target by the equalizer output power signal to generate a quotient result measurement signal, wherein the pilot amplitude reference signal is based on the quotient result measurement signal. 
 
     
     
         10 . An apparatus for adaptive equalization comprising:
 an equalizer filter configured to generate an unmasked equalizer signal from an input data stream using equalizer filter tap coefficients and generate a masked equalizer signal from the input data stream using masked equalizer filter tap coefficients, wherein the masked equalizer filter tap coefficients are generated by masking the equalizer filter tap coefficients with an active taps mask;   a switch configured to select one of the masked equalizer signal and the unmasked equalizer signal;   an error signal generation unit configured to generate an error signal based on the selected one of the masked equalizer signal or the unmasked equalizer signal;   an equalizer tap update unit configured to update the equalizer filter tap coefficients based on the error signal; and   an active taps mask generator configured to generate the active taps mask for masking the equalizer filter tap coefficients.   
     
     
         11 . The apparatus of  claim 10  wherein a dynamic mask vector is used as the active taps mask on a condition that the unmasked equalizer signal is selected to generate the error signal, and a fixed mask vector is used as the active taps mask on a condition that the masked equalizer signal is selected to generate the error signal. 
     
     
         12 . The apparatus of  claim 11  wherein the active taps mask is generated by comparing the equalizer filter tap coefficients with a threshold. 
     
     
         13 . The apparatus of  claim 12  wherein the threshold is generated based on at least one of average of the equalizer filter tap coefficients, step size, Doppler spread, and a signal-to-noise ratio (SNR). 
     
     
         14 . The apparatus of  claim 12  wherein an element of the active taps mask is set to 1 on a condition that an absolute value of a corresponding equalizer filter tap coefficient is above an upper threshold and set to 0 on a condition that the absolute value of the corresponding equalizer filter tap coefficient is below a lower threshold. 
     
     
         15 . The apparatus of  claim 10  further comprising:
 a reference signal generation unit configured to generate a reference signal, and compare the reference signal with the selected one of the masked equalizer signal and the unmasked equalizer signal to generate the error signal. 
 
     
     
         16 . The apparatus of  claim 15  wherein the reference signal is generated by scaling a pilot channel signal with a pilot amplitude reference signal. 
     
     
         17 . The apparatus of  claim 16  wherein the reference signal generation unit comprises:
 a vector norm square unit configured to generate a first vector norm square of an equalizer tapped delay line (TDL) signal, 
 a multiplier configured to multiply the first vector norm square and a second vector norm square of the equalizer filter tap coefficients to generate an equalizer output power signal; and 
 a divider configured to divide a power target by the equalizer output power signal to generate a quotient result measurement signal, wherein the pilot amplitude reference signal is generated based on the quotient result measurement signal. 
 
     
     
         18 . The apparatus of  claim 16  wherein the reference signal generation unit comprises:
 a power measurement unit configured to generate an equalizer output power signal from the masked equalizer signal; and 
 a divider configured to divide a power target by the equalizer output power signal to generate a quotient result measurement signal, wherein the pilot amplitude reference signal is based on the quotient result measurement signal.