Link adaptation algorithm for packet based radio system

Abstract

A method is disclosed for operating a channel coder, as is a channel coder that operates in accordance with the method. The method includes steps of (a) maintaining a first count (N_Number) of transmitted packets and a second count (K_Number) of packets that are erroneously decoded at a receiver; (b) periodically performing a plurality of statistical tests using current values of the first and second counts; and (c) based on a result of the statistical tests, controlling the channel coder to either maintain a current channel coding technique or to switch to another channel coding technique. The step of controlling includes a further step of resetting the first count and the second count.

What is claimed is:  
     
         1 . A method for operating a channel coder, comprising steps of: 
 maintaining a first count (N_Number) of transmitted packets and a second count (K_Number) of packets that are erroneously decoded at a receiver;    periodically performing a plurality of statistical tests using current values of the first and second counts; and    based on a result of said statistical tests, controlling said channel coder to either maintain a current channel coding technique or to switch to another channel coding technique.    
     
     
         2 . A method as in  claim 1 , wherein said step of controlling is comprised of a further step of resetting said first count and said second count.  
     
     
         3 . A method as in  claim 1 , wherein the step of periodically performing a plurality of statistical tests is comprised of steps: 
 at a crossing point where a first channel coding algorithm (CS- 1 ) and a second channel coding algorithm (CS- 2 ) provide a same net bit rate, assuming as a first hypothesis that a packet error rate (PER) is greater than a PER of CS- 1 , P1, if CS- 1  is currently being used, or assuming as the first hypothesis that the PER is less than a PER of CS- 2 , P2, if CS- 2  is currently being used;    assuming as reference case that N_Number of packets have been transmitted with a constant PER equal to either P1 or P2, depending on the currently used channel coding algorithm CS- 1  or CS- 2 ;    determining a first probability (P-value) using said first count and said second count and the constant PER P1 or P2, depending on the currently used channel coding algorithm CS- 1  or CS- 2 ;    comparing P-value to a risk level (RL) for determining whether the first hypothesis can be rejected; and    only if the first hypothesis is rejected, changing to the other channel coding algorithm and resetting N_Number and K_Number;    assuming as a second hypothesis that PER is less than the PER of CS- 1 , P1, if CS- 1  is currently being used, or assuming as the second hypothesis that PER is greater than the PER of CS- 2 , P2, if CS- 2  is currently being used;    assuming the same reference case that N_Number of packets have been transmitted with a constant PER equal to either P1 or P2, depending on the currently used channel coding algorithm CS- 1  or CS- 2 ;    determining a second probability (P-value) using said first count and said second count and the constant PER P1 or P2, depending on the currently used channel coding algorithm CS- 1  or CS- 2 ;    comparing P-value to RL for determining whether the second hypothesis can be rejected; and    only if the second hypothesis is rejected, resetting N_Number and K_Number without changing to the other channel coding algorithm.    
     
     
         4 . A method as in  claim 1 , wherein the step of periodically performing a plurality of statistical tests comprises steps of: 
 accessing at least one look-up table using the current values of the first and second counts to retrieve a probability value (P-value); and    comparing the retrieved P-value to a threshold to determine whether an assumed hypothesis should be accepted or rejected.    
     
     
         5 . A method for operating a channel coder to operate with a first channel coding algorithm (CS- 1 ) or a second channel coding algorithm (CS- 2 ), comprising steps of: 
 maintaining a first count (N_Number) of transmitted packets and a second count (K_Number) of packets that are erroneously decoded at a receiver;    periodically performing a plurality of statistical tests in accordance with the steps of, if a current channel coding is CS- 1 :    determining if a change should be made to CS- 2  by assuming as a hypothesis that: PER>P1;    assuming as a reference case that N_Number of packets have been transmitted with a constant PER value of P1;    determining a probability (P-value) in accordance with:              P        -        value     =       ∑     i   =   0       K                 …                 Number                         (           N                 …                 Number             i         )              P1   i          (     1   -   P1     )           N                 …                 Number     -   i                             if P-value is less than a risk level (RL), rejecting the hypothesis with (1-RL) confidence;    if the hypothesis is rejected, changing to CS- 2 , and resetting N_Number and K_Number, else if the hypothesis is accepted, continuing to average channel readings; and then    confirming CS- 1  by    assuming as a hypothesis that: PER<P1;    assuming the same reference case;    determining the probability (P-value) in accordance with:              P        -        value     =       ∑     i   =     K                 …                 Number         N                 …                 Number                         (           N                 …                 Number             i         )              P1   i          (     1   -   P1     )           N                 …                 Number     -   i                             if P-value is less than RL, rejecting the hypothesis with (1-RL) confidence;    if the hypothesis is rejected, resetting N_Number and K_Number, else if the hypothesis is accepted, continuing to average channel readings;    else if the current channel coding is CS- 2 :    determining if a change should be made to CS- 1  by assuming as a hypothesis that: PER<P2;    assuming the same reference case;    determining the probability (P-value) in accordance with:              P        -        value     =       ∑     i   =     K                 …                 Number         N                 …                 Number                         (           N                 …                 Number             i         )              P2   i          (     1   -   P2     )           N                 …                 Number     -   i                             if P-value is less than RL, rejecting the hypothesis with (1-RL) confidence;    if the hypothesis is rejected, changing to CS- 1 , and resetting N_Number and K_Number, else if the hypothesis is accepted, continuing to average channel readings; and then    confirming CS- 2  by    assuming as a hypothesis that: PER>P2;    assuming the same reference case;    determining the probability (P-value) in accordance with:              P        -        value     =       ∑     i   =   0       K                 …                 Number                         (           N                 …                 Number             i         )              P2   i          (     1   -   P2     )           N                 …                 Number     -   i                             if P-value is less than RL, rejecting the hypothesis with (1-RL) confidence;    if the hypothesis is rejected, resetting N_Number and K_Number, else if the hypothesis is accepted, continuing to average channel readings.    
     
     
         6 . A method as in  claim 5 , wherein the steps of determining the P-value comprise an initial step of pre-computing P-values for a range of values of N_Number and K_Number and P1 and P2 values; storing the pre-computed values in at least one look-up table; and accessing the look-up table with current values of N_Number and K_Number to retrieve a corresponding P-value.  
     
     
         7 . A method for operating a channel coder, comprising steps of: 
 while operating with a first channel coding technique, updating a first count (N_Number) of transmitted packets and a second count (K_Number) of packets that are erroneously decoded at a receiver; and    periodically performing a plurality of statistical tests using current values of the first and second counts, wherein the step of periodically performing the plurality of statistical tests is comprised of sub-steps of,    determining if a first hypothesis is rejected, and if yes, switching to a second channel coding technique, and resetting the first and second counts, before continuing the step of averaging; while if the first hypothesis is accepted,    determining if a second hypothesis is rejected, and if yes, resetting the first and second counts, before continuing the step of averaging; while if the second hypothesis is also accepted,    continuing the step of averaging without first resetting the first and second counts.