Multiple-input and multiple-output systems, or MIMO systems, rely on the use of multiple antennas on both the transmitter-side as well as the receiver-side. MIMO technology is increasingly being adopted for numerous wireless communication applications since such technology tends to increase data throughput and link range without requiring additional transmit power over non-MIMO configurations. In particular, MIMO systems tend to have higher spectral efficiency, as well as improved link reliability by reducing fading effects.
With reference to FIG. 1, in a typical MIMO communication system 100, the transmitter-side 110 is comprised of multiple individual transmitters (TX1-TXn), each having its own antenna and related signal-transmission circuitry (as is generally known in the art). The receiver-side 120 is comprised of multiple receivers (RX1-RXn) each also having its own antenna and related signal-receiving circuitry (as is generally known in the art). The MIMO communication system 100 is based on the concept of sending multiple communication streams using the multiple transmit antennas on the transmitter-side 110. These communication streams pass through a channel matrix 130, which is comprised of multiple communications paths extending between the various transmit antennas on the transmitter-side 110 and corresponding receive antennas on the receiver-side 120. The MIMO communication system 100 also includes a return channel 140, which is used to provide feedback to the transmitter-side. Such examples of feedback include: authentication, reception quality and coordinating a frequency jump to a new channel.
Each of the transmitters (TX1-TXn) typically has its own power amplifier (PA) and variable gain amplifier (VGA), while each receiver (RX1-RXn) will have its own VGA. It is not uncommon for one channel to perform better than another, or a certain group of channels to perform better than another group of channels. Ideally, all of the transmitters (TX1-TXn) should be very closely matched in output characteristics. In fact, transmitter channels exceeding certain output tolerances may not satisfy the manufacturer's quality control requirements. As such, what is needed is a method for improving the output characteristics of MIMO transmitters so as to improve system performance and/or reduce manufacturing-related costs.