SYSTEM AND METHOD FOR I/Q IMBALANCE COMPENSATION

• US 20100220825A1
• Filed: 05/10/2010
• Published: 09/02/2010
• Est. Priority Date: 04/04/2002
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: DUBUC, CHRISTIAN, KIRKLAND, WILLIAM R., BOUDREAU, DANIEL
• Granted Patent: US 8,213,543 B2
• Time in Patent Office: Days
• US Class Current: 375/346
• CPC Class Codes: H04L 2027/0016 Stabilisation of local oscillators
• CPC Class Codes: H04L 25/0226 sounding signals per se
• CPC Class Codes: H04L 25/0228 with direct estimation from sounding signals
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/26134 Pilot insertion in the transmitter chain, e.g. pilot overlapping with data, insertion in time or frequency domain
• CPC Class Codes: H04L 27/2655 Synchronisation arrangements
• CPC Class Codes: H04L 27/364 Arrangements for overcoming imperfections in the modulator, e.g. quadrature error or unbalanced I and Q levels
• CPC Class Codes: H04L 27/3863 Compensation for quadrature error in the received signal
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver

Abstract

A transmitter (102) generates a first set of data symbols and a first pilot symbol (601) at a first time, and a second set of data symbols and a second pilot symbol (602) at a different, second time. The first (601) and second (602) pilot symbols are each represented by first (701) and second (702) pilot carriers, respectively, located at first (703) and second (704) predetermined sample frequencies, respectively, in a channel bandwidth. For the first pilot symbol (601), the first (701) and second (702) pilot carriers have first and second predetermined values, respectively. For the second pilot symbol (602), the first (701) and second (702) pilot carriers have third and fourth predetermined values, respectively. A receiver (104) measures the first, second, fourth and third predetermined values responsive to receiving the first (601) and second (602) pilot symbols to determine first, second, third and fourth estimates of channel distortion, respectively, for compensating and recovering the first and the second sets of data symbols.

Claims

1. A method for receiving comprising:

receiving a first receive signal, including a first pilot symbol, at a first receive time, wherein the first 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 pilot symbol, at a second receive time that is different from the first receive time, wherein the second pilot symbol is represented by a third pilot carrier, having a third predetermined value, and a fourth pilot carrier, having a fourth predetermined value, which is different than the third predetermined value, located at a third predetermined sample frequency and a fourth predetermined sample frequency, respectively, in the bandwidth of the communication channel;

determining a third value of the third pilot carrier, located at the third predetermined sample frequency, responsive to receiving the second receive signal;

determining a fourth value of the fourth pilot carrier, located at the fourth predetermined sample frequency, responsive to receiving the second receive signal;

generating a distortion estimate based on the first, second, third and fourth values for each of the first, second, third and fourth predetermined sample frequencies.

2. The method according to claim 1 further comprising:

receiving the first receive signal at the first receive time and receiving the second receive signal at the second receive time, wherein the first receive time and the second receive time are spaced apart in time.

3. The method according to claim 1, 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 third predetermined sample frequency and the fourth predetermined sample frequency correspond to a predetermined positive frequency and a predetermined negative frequency, respectively, the third predetermined sample frequency and the fourth predetermined sample frequency being different than the first predetermined sample frequency and the second predetermined sample frequency, respectively.

4. The method according to claim 3, wherein the respective predetermined positive frequencies and negative frequencies are symmetrical about a direct current (DC) frequency in the bandwidth of the communication channel and wherein the pilot carriers of the first pilot symbol are located at carrier locations +/−

k for multiple spaced k, where k is an integer value, and the pilot carriers of the second pilot symbol are located at carrier locations +/−

j for multiple spaced j, where k is an integer value.

5. The method according to claim 1 further comprising performing the method in an analogous manner for each of a plurality of receive paths in a multi-antenna receiver to generate a distortion estimate for each receive path.

6. A receiving apparatus comprising:

a distortion estimator configured to process a received signal to determine a distortion estimate;

a distortion compensator configured to perform distortion compensation on the received signal to produce a corrected signal; and

receive circuitry configured to receive a first receive signal, including a first pilot symbol, at a first receive time, wherein the first 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 distortion estimator is configured to;

determine a first value of the first pilot carrier, located at the first predetermined sample frequency, responsive to receiving the first receive signal; and

determine 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 configured to receive a second receive signal, including a second pilot symbol, at a second receive time that is different from the first receive time, wherein the second pilot symbol is represented by a third pilot carrier, having a third predetermined value, and a fourth pilot carrier, having a fourth predetermined value, which is different than the third predetermined value, located at a third predetermined sample frequency and a fourth predetermined sample frequency, respectively, in the bandwidth of the communication channel;

wherein the distortion estimator further;

determines a third value of the third pilot carrier, located at the third predetermined sample frequency, responsive to receiving the second receive signal;

determines a fourth value of the fourth pilot carrier, located at the fourth predetermined sample frequency, responsive to receiving the second receive signal; and

generates a respective distortion estimate based on the first, second, third and fourth values for each of the first, second, third and fourth predetermined sample frequencies.

7. The apparatus of claim 6 wherein the distortion compensator is configured to perform distortion compensation of the received signal using said distortion estimate to generate a corrected signal.

8. The apparatus of claim 6 comprising a plurality of receive antennas each having an associated receive path, and configured to generate a respective distortion estimate for each receive path.

9. The apparatus of claim 6 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 third predetermined sample frequency and the fourth predetermined sample frequency correspond to a predetermined positive frequency and a predetermined negative frequency, respectively, the third predetermined sample frequency and the fourth predetermined sample frequency being different than the first predetermined sample frequency and the second predetermined sample frequency, respectively.

10. The apparatus of claim 6 wherein the respective predetermined positive frequencies and negative frequencies are symmetrical about a direct current (DC) frequency in the bandwidth of the communication channel and wherein the pilot carriers of the first pilot symbol are located at carrier locations +/−

k for multiple spaced k, where k is an integer value, and the pilot carriers of the second pilot symbol are located at carrier locations +/−

j for multiple spaced j, where k is an integer value.

11. The apparatus of claim 6 wherein the distortion estimate is configured to generate a respective distortion estimate for each of a plurality of receive paths in a multi-antenna receiver.

12. A mobile terminal comprising:

at least one antenna;

a distortion estimator configured to process a received signal to determine a distortion estimate;

a distortion compensator configured to perform distortion compensation on the received signal to produce a corrected signal; and

receive circuitry configured to receive a first receive signal, including a first pilot symbol, at a first receive time, wherein the first 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 distortion estimator is configured to;

determine a first value of the first pilot carrier, located at the first predetermined sample frequency, responsive to receiving the first receive signal; and

determine 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 configured to receive a second receive signal, including a second pilot symbol, at a second receive time that is different from the first receive time, wherein the second pilot symbol is represented by a third pilot carrier, having a third predetermined value, and a fourth pilot carrier, having a fourth predetermined value, which is different than the third predetermined value, located at a third predetermined sample frequency and a fourth predetermined sample frequency, respectively, in the bandwidth of the communication channel;

wherein the distortion estimator further;

determines a third value of the third pilot carrier, located at the third predetermined sample frequency, responsive to receiving the second receive signal;

determines a fourth value of the fourth pilot carrier, located at the fourth predetermined sample frequency, responsive to receiving the second receive signal; and

generates a respective distortion estimate based on the first, second, third and fourth values for each of the first, second, third and fourth predetermined sample frequencies.

13. The mobile terminal of claim 12 wherein the distortion compensator is configured to perform distortion compensation of the received signal using said distortion estimate to generate a corrected signal.

14. The mobile terminal of claim 12 comprising a plurality of receive antennas each having an associated receive path, and configured to generate a respective distortion estimate for each receive path.

15. The mobile terminal of claim 12 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 third predetermined sample frequency and the fourth predetermined sample frequency correspond to a predetermined positive frequency and a predetermined negative frequency, respectively, the third predetermined sample frequency and the fourth predetermined sample frequency being different than the first predetermined sample frequency and the second predetermined sample frequency, respectively.

16. The mobile terminal of claim 12 wherein the respective predetermined positive frequencies and negative frequencies are symmetrical about a direct current (DC) frequency in the bandwidth of the communication channel and wherein the pilot carriers of the first pilot symbol are located at carrier locations +/−

k for multiple spaced k, where k is an integer value, and the pilot carriers of the second pilot symbol are located at carrier locations +/−

j for multiple spaced j, where k is an integer value.

17. The mobile terminal of claim 12 wherein the distortion estimate is configured to generate a respective distortion estimate for each of a plurality of receive paths in a multi-antenna receiver.