Per stream rate control (psrc) for improving sysem efficiency in ofdm-mimo communication systems

Abstract

A method and apparatus for separating a user-data stream into a plurality of sub-streams. The apparatus determines channel conditions for each of a plurality of sub-carriers. Next, a plurality of sub-carriers are modulated and encoded with the sub-stream data according to the selected modulation schemes and coding rates. The modulated sub-carriers are each allocated to one or more transmit antennas for transmission. The adaptive modulation and coding function, the sub-carrier allocation function, and the power control function are jointly controlled to optimize throughput, signal quality, and system efficiency.

1 . A wireless communications method comprising:
 separating a user data stream into a plurality of data sub-streams;   determining channel conditions for each of a plurality of sub-carriers;   selecting a modulation scheme and coding rate for each sub-carrier;   modulating the sub carriers with the plurality of data sub-streams according to the selected modulation scheme and coding rate;   allocating each modulated sub-carrier to a transmit antenna; and   transmitting the data sub-streams.   
   
   
       2 . The method of  claim 1  wherein each sub-carrier has a separate transmission power. 
   
   
       3 . The method of  claim 2  wherein the separate transmission power of each sub-carrier is selectively adjusted prior to transmission. 
   
   
       4 . The method of  claim 1  wherein determining channel conditions is based on feedback information provided by a receiver. 
   
   
       5 . The method of  claim 1  wherein determining channel conditions is based on measuring predetermined quality metrics of received signals. 
   
   
       6 . The method of  claim 1  wherein selecting a modulation scheme utilizes an adaptive modulation and coding technique based on channel conditions. 
   
   
       7 . The method of  claim 1  wherein modulating the sub-carriers with the data sub-streams includes mapping a sub-stream to multiple sub-carriers. 
   
   
       8 . The method of  claim 1  wherein allocating each modulated sub-carrier to a transmit antenna is based on increasing the sub-carrier transmit quality. 
   
   
       9 . The method of  claim 1  wherein allocating each modulated sub carrier to a transmit antenna is based on a transmission quality and a throughput level. 
   
   
       10 . The method of  claim 1  further comprising:
 monitoring the modulation and coding rate, the sub carrier allocation, and power adjustment functions.   
   
   
       11 . A transmitter comprising:
 a separation processor configured to separate a user data stream into a plurality of data sub-streams;   a channel analyzer configured to determine channel conditions for each of a plurality of sub-carriers;   a selector configured to select a modulation scheme and coding rate for each sub-carrier;   a modulator configured to modulate the sub carriers with the plurality of data sub-streams according to the selected modulation scheme and coding rate; and   an allocation processor configured to assign each modulated sub-carrier to an antenna for transmission.   
   
   
       12 . The transmitter of  claim 11 , further comprising:
 a power controller configured to adjust a transmit power of each of the modulated sub-carriers.   
   
   
       13 . The transmitter of  claim 8 , further comprising:
 a diversity processor configured to map sub-stream data to multiple sub-carriers based on channel condition information.   
   
   
       14 . The transmitter of  claim 11 , wherein the channel analyzer is further configured to measure quality metrics of received signals to determine current channel conditions. 
   
   
       15 . The transmitter of  claim 11 , wherein the channel analyzer is further configured to analyze feed back information to determine current channel conditions. 
   
   
       16 . The transmitter of  claim 12 , further comprising a controller configured to control the selector, the allocation processor, and the power controller.