System and method for I/Q imbalance compensation

A method of transmitting comprising:

• generating I/Q imbalance compensation pilot symbols located in time and frequency;
• generating a set of pilot symbols for channel estimation located in time and frequency;
• transmitting an orthogonal frequency division multiplexing (OFDM) signal containing the I/Q imbalance compensation pilot symbols and the pilot symbols for channel estimation;
• wherein the I/Q imbalance compensation pilot symbols are for use by a receiver to perform I/Q imbalance compensation to produce a corrected signal;
• and
• the pilot symbols for channel estimation are for use by the receiver to perform channel estimation based on the corrected signal;
• the method further comprising the steps of:
• generating a transmit signal, including a first plurality of data symbols;
• and a first I/Q imbalance compensation pilot symbol, at a first transmit time, wherein the first I/Q imbalance compensation pilot symbol is represented by a first pilot carrier, having a first predetermined value, and a second pilot carrier, having a different, second predetermined value, located at a first predetermined sample frequency and a second predetermined sample frequency, respectively, in a bandwidth of a communication channel;
• and
• the transmit signal also including a second I/Q imbalance compensation pilot symbol, wherein the second I/Q imbalance compensation pilot symbol is represented by a third pilot carrier, having a third predetermined value, and a fourth pilot carrier, having it fourth predetermined value, located at a third predetermined sample frequency and a fourth predetermined sample frequency, respectively, in the bandwidth of the communication channel, the first and third predetermined sample frequency being sufficiently close such that channel conditions and I/Q imbalance are similar for both the first and third predetermined sample frequencies, and second and fourth predetermined sample frequency being sufficiently close such that channel conditions and I/Q imbalance exist are similar for both the second and fourth predetermined sample frequencies;
• wherein the first, second, third and fourth pilot carriers are selected so that I/Q imbalance compensation is de-coupled from channel estimation by said receiver receiving the transmit signal;
• wherein the first and second carriers are symmetrically located about a direct current (DC) frequency in the bandwidth of the communication channel, and the third and fourth carriers are symmetrically located about the DC frequency.

A method for receiving comprising:

• processing a received orthogonal frequency division multiplexing (OFDM) signal to determine an I/Q imbalance estimate;
• performing I/Q imbalance compensation on the received signal to produce a corrected signal;
• performing channel estimation on the corrected signal using pilot symbols for channel estimation;
• the method further comprising:
• receiving a first receive signal, including a first I/Q imbalance compensation pilot symbol, at a first receive time, wherein the first I/Q imbalance compensation pilot symbol is represented by a first pilot carrier, having a first predetermined value, and a second pilot carrier, having a different, second predetermined value, located at a first predetermined sample frequency and a second predetermined sample frequency, respectively, in a bandwidth of a communication channel;
• determining a first value of the first pilot carrier, located at the first predetermined sample frequency, responsive to receiving the first receive signal;
• determining a second value of the second pilot carrier, located at the second predetermined sample frequency, responsive to receiving the first receive signal;
• receiving a second receive signal, including a second I/Q imbalance compensation pilot symbol, at a second receive time that is different from the first receive time, wherein the second I/Q imbalance compensation pilot symbol is represented by the first pilot carrier, having a third predetermined value, and the second pilot carrier, having a fourth predetermined value, located at the first predetermined sample frequency and the second predetermined sample frequency, respectively, in the bandwidth of the communication channel;
• determining a third value of the first pilot carrier, located at the first predetermined sample frequency, responsive to receiving the second receive signal;
• determining a fourth value of the second pilot carrier, located at the second predetermined sample frequency, responsive to receiving the second receive signal;
• generating a respective I/Q imbalance estimate from the first, second, third and fourth values for each of the first and second predetermined sample frequencies.

An apparatus comprising:

• a signal generator adapted to generate I/Q imbalance compensation pilot symbols located in time and frequency and to generate a set of pilot symbols for channel estimation located in time and frequency,
• wherein the I/Q imbalance compensation pilot symbols are for use by a receiver to perform I/Q imbalance compensation to produce a corrected signal, and the pilot symbols for channel estimation are for use by the receiver to perform channel estimation based on the corrected signal;
• a transmitter adapted to transmit an orthogonal frequency division multiplexing (OFDM) signal containing the I/Q imbalance compensation pilot symbols and the pilot symbols for channel estimation, wherein the signal generator is adapted to generate a first transmit signal, including a first plurality of data symbols and a first I/Q imbalance compensation pilot symbol, at a first transmit time, wherein the first I/Q imbalance compensation pilot symbol is represented by a first pilot carrier, having a first predetermined value, and a second pilot carrier, having a different, second predetermined value, located at a first predetermined sample frequency and a second predetermined sample frequency, respectively, in a bandwidth of a communication channel;
• and
• generate a second transmit signal, including a second plurality of data symbols and a second I/Q imbalance compensation pilot symbol, at a different, second transmit time, wherein the second I/Q imbalance compensation pilot symbol is represented by the first pilot carrier, having a third predetermined value, and the second pilot carrier, having a fourth predetermined value, located at the first predetermined sample frequency and the second predetermined sample frequency, respectively, in the bandwidth of the communication channel;
• wherein the first pilot carrier and the second pilot carrier are selected so that I/Q imbalance compensation is decoupled from channel estimation by said receiver receiving the first and second transmit signals;
• wherein the first predetermined sample frequency and the second predetermined sample frequency correspond to a predetermined positive frequency and a predetermined negative frequency, respectively;
• and
• the predetermined positive frequency and the predetermined negative frequency are symmetrical about a direct current (DC) frequency in the bandwidth of the communication channel.

An apparats comprising:

• a signal generator adapted to generate I/Q imbalance compensation pilot symbols located in time and frequency and to generate a set of pilot symbols for channel estimation located in time and frequency,
• wherein the I/Q imbalance compensation pilot symbols are for use by a receiver to perform I/Q imbalance compensation to produce a corrected signal, and the pilot symbols for channel estimation are for use by the receiver to perform channel estimation based on the corrected signal;
• a transmitter adapted to transmit an orthogonal frequency multiplexing (OFDM) signal containing the I/Q imbalance compensation pilot symbols and the pilot symbols for channel estimation,
• wherein the signal generator is adapted to generate a transmit signal, including a first plurality of data symbols and a first I/Q imbalance compensation pilot symbol, at a first transmit time, wherein the first I/Q imbalance compensation pilot symbol is represented by a first pilot carrier, having a first predetermined value, and a second pilot carrier, having a different, second predetermined value, located at a first predetermined sample frequency and a second predetermined sample frequency, respectively, in a bandwidth of a communication channel;
• and
• the transmit signal also including a second I/Q imbalance compensation pilot symbol, wherein the second I/Q imbalance compensation pilot symbol is represented by a third pilot carrier, having a third predetermined value, and a fourth pilot carrier, having a fourth predetermined value, located at a third predetermined sample frequency and a fourth predetermined sample frequency, respectively, in the bandwidth of the communication channel, the first and third predetermined sample frequency being sufficiently close such that similar channel conditions and IQ imbalance are similar for both the first and third predetermined sample frequencies, and second and fourth predetermined sample frequency being sufficiently close such similar channel conditions and IQ imbalance are similar for both the second and fourth predetermined sample frequencies;
• wherein the first, second, third and fourth pilot carriers are selected so that I/Q imbalance compensation is de-coupled from channel estimation by said receiver receiving the transmit signal;
• wherein the first and second carriers are symmetrically located about a direct current (DC) frequency in the bandwidth of the communication channel, and the third and fourth carriers are symmetrically located about the DC frequency.

A receiving apparatus comprising:

• I/Q imbalance estimator adapted to process a received signal to determine an I/Q imbalance estimate substantially decoupled from channel estimates;
• an I/Q imbalance compensator to perform I/Q imbalance compensation on the received signal to produce a corrected signal;
• and
• a channel estimator to perform channel estimation on the corrected signal using pilot symbols for channel estimation,
• wherein the I/O imbalance compensator is adapted to perform I/Q imbalance compensation of the received signal using said I/O imbalance estimate to generate the corrected signal;
• the receiving apparatus further comprising:
• receive circuitry adapted to receive a first receive signal, including a first I/Q imbalance compensation pilot symbol, at a first receive time, wherein the first I/Q imbalance compensation pilot symbol is represented by a first pilot carrier, having a first predetermined value, and a second pilot carrier, having a different, second predetermined value, located at a first predetermined sample frequency and a second predetermined sample frequency, respectively, in a bandwidth of a communication channel;
• wherein the I/Q imbalance estimator determines a first value of the first pilot carrier, located at the first predetermined sample frequency, responsive to receiving the first receive signal, and determines a second value of the second pilot carrier, located at the second predetermined sample frequency, responsive to receiving the first receive signal;
• the receive circuitry being further adapted to receive a second receive signal, including a second I/Q imbalance compensation pilot symbol, at a second receive time that is different from the first transmit time, wherein the second I/Q imbalance compensation pilot symbol is represented by the first pilot carrier, having a third predetermined value, and the second pilot carrier, having a fourth predetermined value, located at the first predetermined sample frequency and the second predetermined sample frequency, respectively, in the bandwidth of the communication channel;
• the I/Q imbalance estimator being further adapted to determine a third value of the first pilot carrier, located at the first predetermined sample frequency, responsive to receiving the second receive signal, and to determine a fourth value of the second pilot carrier, located at the second predetermined sample frequency, responsive to receiving the second receive signal, and to generate a respective I/Q imbalance estimate from the first, second, third and four values for of each of the first and second predetermined sample frequencies.