Low-complexity ACPR-enhancing digital RF MIMO transmitter

A multiple-antenna transmission system, comprising:

• a pre-processing element configured to generate a first digital control signal and a second digital control signal from a digital baseband signal;
• a plurality of phase delay elements configured to introduce separate phase delays into a local oscillator (LO) signal to generate a plurality of modified LO signals;
• a plurality of transmission branches respectively configured to receive one of the plurality of modified LO signals, to modulate phases of the one of the plurality of modified LO signals based on the first and second digital control signals, to generate first and second digital signals corresponding to the modulated phases, and to combine the first and second digital signals to form radio frequency pulse width modulated (RF-PWM) signals;
• and
• an antenna array comprising a plurality of antennas coupled to the plurality of transmission branches and configured to transmit one of the RF-PWM signals.

A method of transmitting a wireless signal, comprising:

• generating a first digital control signal and a second digital control signal from a digital baseband signal;
• introducing a first phase shift into a local oscillator (LO) signal based on the first digital control signal and generating a first digital signal corresponding to the first phase shift;
• introducing a second phase shift into the LO signal based on the second digital control signal and generating a second digital signal corresponding to the second phase shift;
• combining the first and second digital signals to generate a radio frequency pulse width modulated (RF-PWM) signal;
• introducing separate phase delays into the LO signal to generate a plurality of modified LO signals;
• modulating phases of the plurality of modified LO signals based on the first digital control signal and the second digital control signal to generate separate first and second digital signals for each of the modified LO signals;
• combining the separate first and second digital signals to generate a plurality of RF-PWM signals;
• and
• transmitting the plurality of RF-PWM signals by separate antennas of an antenna array.