Channel estimation for OFDM communication systems including IEEE 802.11A and extended rate systems

A method of channel estimation for a receiver of a multiple input, multiple output (MIMO) communication system wherein signals are transmitted using orthogonal frequency division multiplexing (OFDM) over a plurality of OFDM subcarriers, the method comprising:

• receiving, at each of a plurality of receive antennas, training signals from a plurality of transmit antennas, wherein the signal from each transmit antenna includes a different subset of the plurality of OFDM subcarriers;
• transforming the received training signals at each receive antenna to a plurality of impulse coefficients for that receive antenna, each impulse coefficient corresponding to a different one of the OFDM subcarriers;
• for each of the receive antennas, computing a channel impulse response for one of the transmit antennas using the impulse coefficients for the subset of the OFDM subcarriers transmitted by the one of the transmit antennas;
• and
• adaptively truncating the time domain channel impulse response estimate to improve the signal-to-noise ratio of the channel estimates.

A method of tracking channel variations during receipt of a packet using one or more receive antennas, comprising:

• determining an initial channel estimate from training data included in the packet;
• identifying a received symbol in the packet, wherein the received symbol corresponds to an input symbol value that is not part of a training sequence;
• estimating the input symbol value using the received symbol value and the initial channel estimate;
• deriving a per-symbol channel estimate from the received symbol value and the estimated input symbol value;
• and
• updating the initial channel estimate using the per-symbol channel estimate.

A method for determining channel estimates at a receiver for a wireless communication system using orthogonal frequency division multiplexing (OFDM) over a plurality of OFDM subcarriers, the method comprising:

• receiving training signals from one or more receive antennas;
• computing an estimated channel response from the received training signals by reference to a training sequence;
• and
• adaptively truncating the estimated channel response in the frequency domain to improve a signal-to-noise ratio of the channel estimates.

A method of channel estimation for a receiver of a multiple input, multiple output (MIMO) communication system wherein signals are transmitted using orthogonal frequency division multiplexing (OFDM) over a plurality of OFDM subcarriers, the method comprising:

• receiving, at each of a plurality of receive antennas, training signals from a plurality of transmit antennas, wherein the training signals comprise both an IEEE 802.11a standard preamble and a MIMO preamble;
• transforming the received training signals at each receive antenna to a plurality of impulse coefficients for that receive antenna, wherein the plurality of impulse coefficients depend, at least in part, on the received MIMO preamble;
• and
• for each of the receive antennas, computing a channel impulse response for one of the transmit antennas using the impulse coefficients, wherein computing a channel impulse response includes adaptively truncating the channel impulse response in the frequency domain.

A method for determining channel estimates at a receiver for a wireless communication system using orthogonal frequency division multiplexing (OFDM) over a plurality of OFDM subcarriers, the method comprising:

• receiving training signals from one or more receive antennas;
• computing an estimated channel impulse response from the received training signals by reference to a training sequence, wherein the training sequence for each transmit antenna is such that the training symbols sent from any two of the plurality of transmit antennas differ only in a cyclic shift and the receiver is configured to receive such signals;
• and
• adaptively truncating the estimated channel impulse response in the frequency domain.