The present invention discloses an effective apparatus and method to measure the received signal quality for digital communication systems by measuring error vector measurement (EVM) with embedded EVM measurement block in receivers. The distinction of the present invention is that the EVMSIG and the EVMDATA are measured in the receiver for the SIGNAL fields and DATA fields, respectively. EVMSIG is a good indicator for one spatial stream and EVMDATA is a good indicator for current multiple streams. The receiver determines the optimum number of spatial data streams for feedback to the transmitter based on the combinations of EVMSIG and EVMDATA with or without other algorithms such as analysis on periodically requested sounding packet. The receiver also determines the optimum modulation and coding schemes for feedback based on the EVM measurements.