Methods and systems for transmission mode selection in a multi channel communication system

Abstract

Techniques to select a suitable transmission mode for a data transmission in a multi channel communication system with multiple spatial channels having varying SNRs are presented in this disclosure. For certain embodiments, a closed-loop technique may be applied, in which back-off factors used to calculate an effective SNR value fed back to a transmitter are adjusted. An open-loop rate control scheme is also presented in which a transmitter may select a data rate and number of streams based on whether transmitted packets are received in error at a receiver.

We claim: 
     
         1 . A method of selecting transmission modes in multi-channel communications system, comprising:
 calculating a signal to noise ratio (SNR) metric based on SNR values for a plurality of spatial streams;   calculating an effective SNR metric as a function of, at least, the SNR metric and one or more back-off parameters;   monitoring packets errors;   adjusting one or more of the back-off parameters based on the monitored packet errors;   selecting a data rate based on the effective SNR metric; and   generating rate feedback based on the selected data rate.   
     
     
         2 . The method of  claim 1 , wherein selecting a data rate based on the effective SNR metric comprises: selecting, from a lookup table, a highest data rate with a required SNR that is less than or equal to the effective SNR metric. 
     
     
         3 . The method of  claim 1 , wherein calculating a signal to noise ratio (SNR) metric based on SNR values for a plurality of spatial streams comprises: calculating an average SNR value and standard deviation for the plurality of streams. 
     
     
         4 . The method of  claim 3 , wherein calculating the effective SNR comprises:
 multiplying the standard deviation by a first one of the back-off parameters to obtain a product; and subtracting the product from, and adding a second back-off parameter to, the average SNR value to obtain an adjusted SNR value.   
     
     
         5 . The method of  claim 4 , wherein calculating the effective SNR further comprises:
 using a third back-off parameter as an exponent applied to the adjusted SNR value; and adding a fourth back-off parameter to the value generated by applying the third back-off parameter as an exponent to the adjusted SNR value.   
     
     
         6 . The method of  claim 3 , wherein calculating an average signal to noise ratio (SNR) value comprises calculating an average SNR value for multiple subcarriers of one or more of the spatial streams. 
     
     
         7 . The method of  claim 3 , wherein calculating an average signal to noise ratio (SNR) value comprises calculating an average SNR value for multiple subcarriers of one or more of the spatial streams. 
     
     
         8 . The method of  claim 1 , wherein one or more of the back-off parameters vary based on the number of spatial streams. 
     
     
         9 . The method of  claim 1 , wherein adjusting one or more of the back-off parameters based on the monitored packet errors comprises:
 adjusting at least one of the first back-off parameter in a manner that reduces the calculated effective SNR if N packet errors are observed, wherein N is a positive integer; and   adjusting at least one of the first back-off parameter in a manner that increases the calculated effective SNR if M consecutive packets are observed without errors, wherein M is a positive integer.   
     
     
         10 . The method of  claim 1 , further comprising: setting the back-off parameters to initial values. 
     
     
         11 . An apparatus for selecting transmission modes in multi-channel communications system, comprising:
 logic for calculating a signal to noise ratio (SNR) metric based on SNR values for a plurality of spatial streams;   logic for calculating an effective SNR metric as a function of, at least, the SNR metric and one or more back-off parameters;   logic for monitoring packets errors;   logic for adjusting one or more of the back-off parameters based on the monitored packet errors;   logic for selecting a data rate based on the effective SNR metric; and   logic for generating rate feedback based on the selected data rate.   
     
     
         12 . The apparatus of  claim 11 , wherein the logic for selecting a data rate based on the effective SNR metric is configured to: select, from a lookup table, a highest data rate with a required SNR that is less than or equal to the effective SNR metric. 
     
     
         13 . The apparatus of  claim 11 , wherein the logic for calculating a signal to noise ratio (SNR) metric based on SNR values for a plurality of spatial streams is configured to: calculate an average SNR value and standard deviation for the plurality of streams. 
     
     
         14 . The apparatus of  claim 13 , wherein the logic for calculating the effective SNR is configured to: multiply the standard deviation by a first one of the back-off parameters to obtain a product; and subtract the product from, and adding a second back-off parameter to, the average SNR value to obtain an adjusted SNR value. 
     
     
         15 . The apparatus of  claim 14 , wherein the logic for calculating the effective SNR is further configured to: use a third back-off parameter as an exponent applied to the adjusted SNR value; and add a fourth back-off parameter to the value generated by applying the third back-off parameter as an exponent to the adjusted SNR value. 
     
     
         16 . The apparatus of  claim 13 , wherein the logic for calculating an average signal to noise ratio (SNR) value is configured to calculate an average SNR value for multiple subcarriers of one or more of the spatial streams. 
     
     
         17 . The apparatus of  claim 13 , wherein the logic for calculating an average signal to noise ratio (SNR) value is configured to calculate an average SNR value for multiple subcarriers of one or more of the spatial streams. 
     
     
         18 . The apparatus of  claim 11 , wherein one or more of the back-off parameters vary based on the number of spatial streams. 
     
     
         19 . The apparatus of  claim 11 , wherein the logic for adjusting one or more of the back-off parameters based on the monitored packet errors is configured to:
 adjust at least one of the first back-off parameter in a manner that reduces the calculated effective SNR if N packet errors are observed, wherein N is a positive integer; and   adjust at least one of the first back-off parameter in a manner that increases the calculated effective SNR if M consecutive packets are observed without errors, wherein M is a positive integer.   
     
     
         20 . A computer-program product for selecting transmission modes in multi-channel communications system, comprising a computer readable medium having instructions stored thereon, the instructions being executable by one or more processors and the instructions comprising:
 instructions for calculating a signal to noise ratio (SNR) metric based on SNR values for a plurality of spatial streams;   instructions for calculating an effective SNR metric as a function of, at least, the SNR metric and one or more back-off parameters;   instructions for monitoring packets errors;   instructions for adjusting one or more of the back-off parameters based on the monitored packet errors;   instructions for selecting a data rate based on the effective SNR metric; and   instructions for generating rate feedback based on the selected data rate.