Method using differentially encoded feedback information in precoded MIMO-OFDM systems

A method of transmitting from a transmitter to a receiver over a wireless multiple-input-multiple-output channel comprising a series of frequency intervals, the method comprising:

• based on one or more performance criteria evaluated in relation to a previously received transmission from the transmitter, selecting at the receiver a first precoding matrix out of a predetermined set of precoding matrices for transmitting from the transmitter to the receiver on a first of said frequency intervals;
• and for each successive frequency interval in the series:
• determining, from said predetermined set of precoding matrices, a subset of precoding matrices;
• based on one or more performance criteria evaluated in relation to the previously received transmission, selecting at the receiver a respective precoding matrix from said predetermined set for transmission from the transmitter to the receiver on said successive frequency interval;
• and
• feeding back an index of that respective precoding matrix from the receiver to the transmitter using a differential encoding scheme whereby the respective index is indicated relative to said subset of most-probable precoding matrices;
• wherein said subset for each successive time interval is a subset of most probable precoding matrices having a conditional probability of being selected for transmission from the transmitter to the receiver, the conditional probability being computed by accumulating data on previous observed transitions in the selected precoding matrix and being used to determine the subset.

A method of transmitting from a transmitter to a receiver over a wireless multiple-input-multiple-output channel comprising a series of frequency intervals, the method comprising:

• based on one or more performance criteria evaluated in relation to a previously received transmission from the transmitter, selecting at the receiver a first precoding matrix out of a predetermined set of precoding matrices for transmitting from the transmitter to the receiver on a first of said frequency intervals;
• and
• for each successive frequency interval in the series:
• determining from said predetermined set of precoding matrices a preferred subset of precoding matrices;
• based on one or more performance criteria evaluated in relation to the previously received transmission, selecting at the receiver a respective precoding matrix from said predetermined set for transmitting from the transmitter to the receiver on said successive frequency interval;
• and
• feeding back an index of that respective precoding matrix from the receiver to the transmitter using a differential encoding scheme whereby the respective index is indicated relative to said preferred subset;
• wherein the method further comprises transmitting an indication of at least one of the preferred subsets from the receiver to the transmitter.

A method of transmitting from a transmitter to a receiver over a wireless multiple-input-multiple-output channel comprising a series of frequency intervals, the method comprising:

• based on one or more performance criteria evaluated in relation to a previously received transmission from the transmitter, selecting at the receiver a first precoding matrix out of a predetermined set of precoding matrices for transmitting from the transmitter to the receiver on a first of said frequency intervals;
• and
• for each successive frequency interval in the series:
• determining from said predetermined set of precoding matrices a preferred subset of precoding matrices;
• based on one or more performance criteria evaluated in relation to the previously received transmission, selecting at the receiver a respective precoding matrix from said predetermined set for transmitting from the transmitter to the receiver on said successive frequency interval;
• and
• feeding back an index of that respective precoding matrix from the receiver to the transmitter using a differential encoding scheme whereby the respective index is indicated relative to said preferred subset;
• wherein the method further comprises transmitting the size of at least one of the preferred subsets from the receiver to the transmitter.

A method of transmitting a sequence of transmissions at respective time intervals from a transmitter to a receiver over a wireless multiple-input-multiple-output channel comprising one or more frequency intervals, the method comprising:

• based on one or more performance criteria evaluated in relation to a previously received transmission from the transmitter, selecting at the receiver a first precoding matrix out of a predetermined set of precoding matrices for transmitting from the transmitter to the receiver at a first of said time intervals;
• and
• for each successive time interval in the sequence:
• determining from said predetermined set of precoding matrices a preferred subset of precoding matrices based on a suitable metric computed with respect to the matrix determined for the previous time interval;
• based on one or more performance criteria evaluated in relation to the previously received transmission, selecting at the receiver a respective precoding matrix from said predetermined set for transmitting from the transmitter to the receiver on said successive time interval;
• feeding back an index of that respective precoding matrix from the receiver to the transmitter using a differential encoding scheme whereby the respective index is indicated relative to said preferred subset;
• and
• wherein the method further comprises resetting the differential encoding scheme upon detecting a condition;
• and one of:
• (a) said condition comprises the condition that the selected precoding matrix is not in the preferred subset;
• or
• (b) for each of said successive time intervals the method comprises:
• determining from said predetermined set, separately from the determination of said preferred subset, a subset of most-probable precoding matrices having some conditional probability of being selected for transmission from the transmitter to the receiver, the conditional probability being computed by accumulating data on previous observed transitions in the selected precoding matrix and being used to determine the subset, and said condition comprises the condition that the most-probable subset differs from the preferred subset by a predetermined amount.

A method of transmitting a sequence of transmissions at respective time intervals from a transmitter to a receiver over a wireless multiple-input-multiple-output channel comprising one or more frequency intervals, the method comprising:

• based on one or more performance criteria evaluated in relation to a previously received transmission from the transmitter, selecting at the receiver a first precoding matrix out of a predetermined set of precoding matrices for transmitting from the transmitter to the receiver at a first of said time intervals;
• and for each successive time interval in the sequence:
• determining, from said predetermined set of precoding matrices, a subset of precoding matrices;
• based on one or more performance criteria evaluated in relation to the previously received transmission in the sequence, selecting at the receiver a respective precoding matrix from said predetermined set for transmission from the transmitter to the receiver on said successive time interval;
• and
• feeding back an index of that respective precoding matrix from the receiver to the transmitter using a differential encoding scheme whereby the respective index is indicated relative to said subset of most-probable precoding matrices;
• wherein said subset for each successive time interval is a subset of most probable precoding matrices having a conditional probability of being selected for transmission from the transmitter to the receiver, the conditional probability being computed by accumulating data on previous observed transitions in the selected precoding matrix and being used to determine the subset.

A method of transmitting a sequence of transmissions at respective time intervals from a transmitter to a receiver over a wireless multiple-input-multiple-output channel comprising one or more frequency intervals, the method comprising:

• based on one or more performance criteria evaluated in relation to a previously received transmission from the transmitter, selecting at the receiver a first precoding matrix out of a predetermined set of precoding matrices for transmitting from the transmitter to the receiver at a first of said time intervals;
• and
• for each successive time interval in the sequence:
• determining from said predetermined set of precoding matrices a preferred subset of precoding matrices;
• based on one or more performance criteria evaluated in relation to the previously received transmission, selecting at the receiver a respective precoding matrix from said predetermined set for transmitting from the transmitter to the receiver on said successive time interval;
• and
• feeding back an index of that respective precoding matrix from the receiver to the transmitter using a differential encoding scheme whereby the respective index is indicated relative to said preferred subset;
• wherein the method further comprises transmitting an indication of at least one of the preferred subsets from the receiver to the transmitter.

A method of transmitting a sequence of transmissions at respective time intervals from a transmitter to a receiver over a wireless multiple-input-multiple-output channel comprising one or more frequency intervals, the method comprising:

• based on one or more performance criteria evaluated in relation to a previously received transmission from the transmitter, selecting at the receiver a first precoding matrix out of a predetermined set of precoding matrices for transmitting from the transmitter to the receiver at a first of said time intervals;
• and
• for each successive time interval in the sequence:
• determining from said predetermined set of precoding matrices a preferred subset of precoding matrices;
• based on one or more performance criteria evaluated in relation to the previously received transmission, selecting at the receiver a respective precoding matrix from said predetermined set for transmitting from the transmitter to the receiver on said successive time interval;
• and
• feeding back an index of that respective precoding matrix from the receiver to the transmitter using a differential encoding scheme whereby the respective index is indicated relative to said preferred subset;
• wherein the method further comprises transmitting the size of at least one of the preferred subsets from the receiver to the transmitter.