Power loading in MU-MIMO

#Multiple-user multiple-input multiple-output (MU-MIMO) systems can transmit and receive signals to/from multiple users at a single antenna array at the same time. In a MU-MIMO system, multiple signals are sent in parallel and are kept separate from one another not by modulation or coding techniques, but by transmitting (or receiving) each signal in a different (e.g., orthogonal) direction. The process of transmitting (or receiving) a signal in a specific direction using an antenna array is known as beamforming. By selecting a beam for each signal that will produce limited interference with other parallel beams, multiple signals can be transmitted or received at the same time. Beams are often calculated to be orthogonal to one another in order to minimize the interference between the beams.

#FIG. 1 illustrates an example of a wireless communication system in accordance with embodiments.

#FIG. 2 illustrates an example of a mobile station for communicating in the wireless communication system of FIG. 1 in accordance with embodiments.

#FIG. 3 illustrates an example of an access point for communicating in the wireless communication system of FIG. 1 in accordance with embodiments.

#The following description and the drawings sufficiently illustrate specific embodiments to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Portions and features of some embodiments may be included in, or substituted for, those of other embodiments. Embodiments set forth in the claims encompass all available equivalents of those claims.

#In conventional systems, the lengths of a given mobile station's data stream can vary due to dynamic traffic conditions and the amount of data in the buffer. The transmission length of a given frame varies accordingly and is determined by the longest data stream. To align the terminations of the different data streams, padding bits are added to shorter data streams until all data streams have the same length. Transmission of padding bits, however, wastes transmission power since power is used transmitting bits with no information, and also increases the packet error probability. Additionally, the transmission of extra (padding) bits can add to interference caused to other data streams and co-channel networks.

#In accordance with embodiments, power loading of different data streams may be used to align terminations of the data streams with minimal padding. For example, modulation and coding scheme (MCS) adjustments can be made to some or all of the data streams to get the data streams to the same length. Power loading can then be used to compensate for the changes in MCS. In particular, for data streams that are shortened by making the MCS less robust, the transmission power for the data stream can be increased to compensate for the less robust MCS. The overall power can be maintained by reducing the power level and making the MCS more robust for shorter data streams.