Power Combining Networks for MIMO Transmission

Stanford University, Stanford CA

Investigators

Abstract

This research studies the use of power combining in multi-antenna radios. Modern radio systems often use multiple transmit antennas and appropriate signal coding to improve throughput and reliability of wireless links. Ideally, each amplifier should be rated at the maximum total (or sum) power that can be transmitted from all antennas. Due to cost and efficiency considerations, the power rating is usually designed to be lower (typically the maximum total power divided by the number of antennas), and this can lead to significant performance loss. This research explores a solution using Power Combining Networks (PCN) that enable the output of an amplifier to be switched/combined into any antenna, thus moving power from a weaker to a stronger antenna, resulting in improved link performance. The maximum output power of a MIMO (Multiple Input, Multiple Output) antenna transmitter is limited due to bio-safety considerations. MIMO transmission performs best when each power amplifier is rated at the full system transmit power. If the amplifiers are fractionally rated due to cost and efficiency considerations, the worst case loss with M antennas can reach log M dB in the presence of channel imbalances. A PCN can reduce this loss significantly, trading the loss of array gain for a better channel coupling efficiency. Use of a PCN alters the effective MIMO channel and therefore can also change the optimum transmit coding. The goal of this research is to study fast algorithms for PCN selection, appropriate signal coding schemes and the best realizable performance.