Precoding with reduced feedback for coordinated multipoint transmission on the downlink

A method for determining transmission parameters in a mobile communications network using coordinated transmissions from multiple transmitter sites, the method comprising:

• estimating path loss between a mobile station and each of a plurality of geographically separated transmitter sites, each transmitter site having at least one transmitter antenna;
• selecting one of a plurality of pre-determined subsets of a pre-determined set of antenna precoding vectors, based on the estimated path losses;
• transmitting a group index to the mobile station, the group index identifying the selected subset of antenna precoding vectors;
• subsequently receiving a first vector index from the mobile station, the first vector index corresponding to a first antenna precoding vector in the selected subset;
• and
• transmitting first data to the mobile station, using the first antenna precoding vector applied to the transmitter antennas at the plurality of transmitter sites.

A method in a mobile station for determining transmission parameters in a mobile communications network using coordinated transmissions from multiple transmitter sites, the method comprising:

• receiving transmitter site information identifying a plurality of geographically separated transmitter sites, each transmitter site having at least one transmitter antenna;
• determining a group index, the group index identifying a selected one of a plurality of pre-determined subsets of a pre-determined set of antenna precoding vectors, wherein the determining step includes estimating path loss between the mobile station and each of the plurality of geographically separated transmitter sites, selecting one of a plurality of pre-determined subsets of a pre-determined set of antenna precoding vectors, based on the estimated path losses, and identifying the group index corresponding to the selected subset;
• transmitting the group index to the mobile communications network;
• evaluating channel conditions between the transmitter antennas and the mobile station;
• selecting a first antenna precoding vector from the selected subset, based on the channel conditions;
• and
• transmitting a first vector index to the mobile communications network, the first vector index identifying the first antenna precoding vector, given the selected subset.

A mobile station for use in a mobile communications network using coordinated transmissions from multiple transmitter sites, the mobile station comprising:

• one or more memory circuits storing a set of antenna precoding vectors, wherein each antenna precoding vector is indexed by a group index and by a vector index;
• a receiver circuit configured to receive transmitter site information identifying a plurality of geographically separated transmitter sites, each transmitter site having at least one transmitter antenna;
• a transmitter circuit;
• and
• one or more baseband processing circuits configured to determine a group index identifying a selected one of a plurality of pre-determined subsets of the set of antenna precoding vectors;
• evaluate channel conditions between the transmitter antennas and the mobile station;
• select a first antenna precoding vector from the selected subset of antenna precoding vectors, based on the channel conditions;
• and transmit a first vector index to the mobile communications network via the transmitter circuit, the first vector index identifying the first antenna precoding vector, given the selected subset;
• wherein the one or more baseband processing circuits are configured to determine the group index by:
• estimating path loss between the mobile station and each of the plurality of geographically separated transmitter sites;
• selecting one of a plurality of pre-determined subsets of a pre-determined set of antenna precoding vectors, based on the estimated path losses;
• and
• identifying the group index corresponding to the selected subset.