Spur mitigation techniques

Abstract

Spurs cause significant problems with signal detecting, amplifier gain adjustment, and signal decoding. Various techniques can be used to mitigate the effects of spurs on a received signal. Generally, these techniques work by either canceling or ignoring the spurs. For example, a pilot mask can be used to ignore pilot information in one or more sub-channels. A Viterbi mask can determine the weighting given to bits in a sub-channel based on spur and data rate information. Channel interpolation can compute a pseudo channel estimate for a sub-channel known to have a spur location can be computed by interpolating the channel estimates of adjacent good sub-channels. Filtering of the received signal using a low-pass filter, a growing box filter, or a low-pass filter with self-correlation can be used to cancel a spur.

1 . A method of improving receiver performance by avoiding bad pilots, the method comprising: 
 using a pilot mask in the receiver,    wherein the pilot mask includes a set of flags, the set of flags associated with certain sub-channels,    wherein each flag in the set of flags determines whether its associated sub-channel is usable for pilot tracking.    
     
     
         2 . The method of  claim 1 , wherein if a spur will coincide with a sub-channel, then the pilot mask will not allow that sub-channel to be used for pilot tracking.  
     
     
         3 . The method of  claim 1 , wherein if a spur affects a sub-channel, then the pilot mask will not allow that sub-channel to be used for pilot tracking.  
     
     
         4 . The method of  claim 1 , wherein the set of flags includes 52 flags associated with 52 sub-channels.  
     
     
         5 . The method of  claim 1 , wherein the pilot mask is usable for any data rate.  
     
     
         6 . A pilot mask for improving receiver performance by avoiding bad pilots, the pilot mask comprising: 
 a set of flags, the set of flags associated with certain sub-channels, wherein each flag in the set of flags determines whether its associated sub-channel is usable for pilot tracking.    
     
     
         7 . A method of providing an accurate channel estimate to a decoder, the method comprising: 
 determining whether each sub-channel is one of a good sub-channel and a bad sub-channel;    converting any good sub-channel including a spur to a bad sub-channel; and    providing information regarding good and bad sub-channels, including converted sub-channels, to the decoder.    
     
     
         8 . A method of improving signal decoding in a receiver, the method comprising: 
 determining whether each sub-channel is one of a good sub-channel and a bad sub-channel;    converting any good sub-channel including a spur to a bad sub-channel;    weighting bits of a signal in a good channel more than bits a bad sub-channel; and    providing the weighted information to a decoder.    
     
     
         9 . The method of  claim 8 , wherein a Viterbi mask implements the weighting and the decoder is a Viterbi decoder.  
     
     
         10 . The method of  claim 8 , wherein weighting includes adjusting based on data rate.  
     
     
         11 . The method of  claim 10 , wherein bits affected by a spur at a higher data rate have a different weighting than bits affected by a spur at a lower data rate.  
     
     
         12 . A decoding circuit in a receiver, the decoding circuit comprising: 
 a Viterbi decoder; and    a Viterbi mask in operative relation to the Viterbi decoder, the Viterbi mask providing a weighted channel estimate for each sub-channel based on spur information.    
     
     
         13 . The decoding circuit of  claim 12 , wherein the Viterbi mask provides the weighted channel estimate further based on at data rate information.  
     
     
         14 . A filter system for canceling a spur from a signal, the filter system comprising: 
 a first mixer coupled to receive the signal;    a low-pass filter coupled to an output of the first mixer;    a second mixer coupled to an output of the low-pass filter; and    an adder coupled to receive the signal and subtract an output of the second mixer.    
     
     
         15 . The filter system of  claim 14 , wherein first mixer performs a rotation of the signal that generates a spur estimate at DC, thereby allowing the low-pass filter to estimate a phase and an amplitude of the spur.  
     
     
         16 . The filter system of  claim 14 , wherein the low-pass filter is a growing box filter.  
     
     
         17 . The filter system of  claim 16 , wherein the growing box filter includes: 
 a first accumulator for providing a cumulative sum of a sample; and    a second accumulator for providing a total sum of all samples to a current symbol.    
     
     
         18 . A method for canceling a spur from a signal, the method comprising: 
 rotating the signal to generate a first rotated signal;    performing a filtering computation based on the first rotated signal to generate a filtered signal;    rotating the filtered signal to generate a second rotated signal; and    subtracting the second rotated signal from the signal.    
     
     
         19 . The method of  claim 18 , wherein performing the filtering computation includes: 
 setting a sample set size;    computing a cumulative sum for the sample set over time;    when the sample set size is reached, then adding the cumulative sum to a total sum and resetting the cumulative size to zero;    computing an estimated spur value by dividing the total sum by a total number of samples, wherein the estimated spur value is provided as the filtered signal; and    periodically increasing the sample set size over time.    
     
     
         20 . The method of  claim 19 , wherein if the cumulative sum is denoted by cs [n] and the total sum is denoted by ts [n], then adding the cumulative sum to the total sum and resetting the cumulative size to zero occurs when n is a power of 2.  
     
     
         21 . A method of improving a sub-channel estimate for a received signal, the method comprising: 
 determining sub-channel estimates for a plurality of sub-channels of the received signal; and    if a first sub-channel includes a spur, then ignoring the determined sub-channel estimate of the first sub-channel, computing an interpolated sub-channel estimate based on sub-channels adjacent the first sub-channel, and providing the interpolated sub-channel estimate as the sub-channel estimate for the first sub-channel.    
     
     
         22 . A method for canceling a spur from a signal, the method comprising: 
 rotating the signal to generate a first rotated signal;    performing a filtering computation based on the first rotated signal to generate a filtered signal;    rotating the filtered signal to generate a second rotated signal;    subtracting the second rotated signal from the signal to generate a modified signal; and    after subtracting, computing self-correlation of the modified signal.    
     
     
         23 . A method for canceling a spur from self-correlation of a signal, the method comprising: 
 rotating the signal to generate a first rotated signal;    performing a filtering computation based on the first rotated signal to generate a filtered signal;    rotating the filtered signal to generate a second rotated signal, which represents a spur effect;    computing self-correlation of the signal to generate a modified signal; and    subtracting the spur effect from the modified signal.    
     
     
         24 . A filter system for canceling a spur from a signal, the filter system comprising: 
 a first mixer coupled to receive the signal;    a low-pass filter coupled to an output of the first mixer;    a self-correlation block coupled to receive the signal;    a second mixer coupled to an output of the low-pass filter; and    spur removal means coupled to receive the signal, an output of the second mixer, and an output of the self-correlation block.