Multicarrier receiver and method for carrier frequency offset correction and channel estimation for receipt of simultaneous transmissions over a multi-user uplink

• US 20070004337A1
• Filed: 06/29/2005
• Published: 01/04/2007
• Est. Priority Date: 06/29/2005
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Intel Corporation
• Inventors: Sondur, Lakshmipathi, Biswas, Ashim, Lawrence, Sean, Sahib, Anees
• Granted Patent: US 7,480,497 B2
• Time in Patent Office: Days
• US Class Current: 455/63.100
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/0228 with direct estimation from sounding signals
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2695 with channel estimation, e.g. determination of delay spread, derivative or peak tracking channel estimation H04L25/0202

Abstract

Multicarrier receivers and methods for carrier frequency offset correction and channel estimation for receipt of simultaneous transmissions over a multi-user uplink are generally described herein. Other embodiments may be described and claimed.

Claims

1. A multicarrier receiver comprising:

a plurality of receive-signal paths to receive training signals concurrently transmitted from a plurality of transmitting stations; and

signal processor to generate channel estimates and carrier frequency offset estimates for each of the transmitting stations from the received training signals and to perform an iterative decoding process using previously generated channel estimates and previously generated carrier frequency offset estimates to cancel intercarrier interference from the received training signals induced by carrier frequency offsets.

2. The receiver of claim 1 wherein the training signals are frequency interleaved among a plurality of subcarriers of a multicarrier communication channel,

wherein the training signals transmitted by each of the transmitting stations are substantially orthogonal to each other, and

wherein the training signals are followed by non-orthogonal data signals transmitted concurrently by each of the transmitting stations on the same frequency subcarriers of the multicarrier communication channel.

3. The receiver of claim 2 wherein the signal processor generates separate data streams for each transmitting station using a final channel estimate and a final carrier frequency offset for each transmitting station, and

wherein the separate data streams for each transmitting station are generated from the non-orthogonal data signals.

4. The receiver of claim 1, wherein each receive-signal path is associated with a receive antenna and wherein a number of the receive antennas is greater than or equal to a number of the transmitting stations, the signal processor to take advantage of antenna diversity to distinguish between signals from the transmitting stations.

5. The receiver of claim 1 wherein for each of the transmitting stations, the signal processor regenerates the channel estimates and carrier frequency offset estimate for said each transmitting station using the previously generated channel estimates and the previously generated carrier frequency offset estimates for reprocessing samples of the received signals.

6. The receiver of claim 5 wherein as part of the regeneration of the carrier frequency offset and channel estimates for each transmitting station, the iterative decoding process is performed by the signal processor for each transmitting station, wherein the signal processor is adapted to:

shift the received signal by a current carrier frequency offset estimate for a current transmitting station;

remove portions of the received signal due to transmitting stations other than the current transmitting station;

calculate the intercarrier interference for the current transmitting station using the current channel estimate and the current carrier frequency offset estimate for the current transmitting station;

subtract the intercarrier interference from the received signal to generate a final processed signal; and

regenerate the channel estimates and the carrier frequency offset estimate for the current transmitting station from the final processed signal.

7. The receiver of claim 6 wherein the signal processor repeats the iterative process a predetermined number of times based on a spacing between the carrier frequency offset estimates to generate a final channel estimate and a final carrier frequency offset estimate for each transmitting station, and

wherein the final channel estimate and the final carrier frequency offset estimate are used by the signal processor to generate separate data streams associated with each transmitting station.

8. The receiver of claim 6 wherein, after the signal processor shifts the received signal by the current carrier frequency offset estimate, the signal processor multiplies the received signal by the current carrier frequency offset estimate for the current transmitting station,

wherein as part of the iterative process, the signal processor performs a discrete Fourier transform after the received signal is multiplied by the current carrier frequency offset estimate to generate a set of frequency-domain samples, and

wherein additional intercarrier interference is cancelled from the set of frequency-domain samples for each iteration.

9. The receiver of claim 6 wherein after the signal processor selectively removes portions of the received signal due to transmitting stations other than the current transmitting station, the signal processor performs a band-pass filtering operation on the received signals to at least in part remove tones of the received training signals except those tones known to be transmitted by the current transmitting station.

10. The receiver of claim 9 wherein the training signals transmitted by the transmitting stations comprise frequency-interleaved orthogonal subcarriers which unique to each transmitting station, and

wherein the signal processor selectively filters out portions of the received training signal that were not transmitted by the current transmitting station.

11. The receiver of claim 1 wherein the iterative decoding process performed by the signal processor uses long-training signals transmitted by the transmitting stations,

wherein the transmitting stations transmit short-training signals prior to transmitting the long-training signals, and

wherein the signal processor initially generates a coarse carrier frequency offset estimate for each of the transmitting stations based on the received short-training signals, the coarse carrier frequency offset estimates being used as initial carrier frequency offset estimates for the iterative decoding process.

12. The receiver of claim 3 wherein the training signals and the data signals transmitted by the transmitting stations comprise one of either orthogonal frequency division multiplexed signals or orthogonal frequency division multiple access signals, and

wherein the receiver transmits a downlink frame for receipt by the plurality of transmitting station to instruct the transmitting stations which frequency interleaved subcarriers to use for transmitting the training signals and which subcarriers of the multicarrier communication channel to use for transmitting the data signals.

13. A method comprising:

receiving training signals from a plurality of transmitting stations through a plurality of receive-signal paths; and

generating channel estimates and carrier frequency offset estimates for each of the transmitting stations from the received training signals by performing an iterative decoding process using previously generated channel estimates and previously generated carrier frequency offset estimates to cancel intercarrier interference from the received training signals induced by carrier frequency offsets.

14. The method of claim 13 wherein the training signals are frequency interleaved among a plurality of subcarriers of a multicarrier communication channel,

wherein the training signals transmitted by each of the transmitting stations are substantially orthogonal to each other, and

wherein the training signals are followed by non-orthogonal data signals transmitted concurrently by each of the transmitting stations on the same frequency subcarriers of the multicarrier communication channel.

15. The method of claim 14 further comprising generating separate data streams for each transmitting station using a final channel estimate and a final carrier frequency offset for each transmitting station, and

wherein the separate data streams for each transmitting station are generated from the non-orthogonal data signals.

16. The method of claim 13 wherein each receive-signal path is associated with a receive antenna, and

wherein a number of the receive antennas is greater than or equal to a number of the transmitting stations.

17. The method of claim 13 wherein for each of the transmitting stations, the method comprises iteratively regenerating the channel estimate and carrier frequency offset estimate for said each transmitting station using the previously generated channel estimates and the previously generated carrier frequency offset estimates for samples of the received signals.

18. The method of claim 17 wherein the iteratively regenerating comprises:

shifting the received signal by a current carrier frequency offset estimate for a current transmitting station;

removing portions of the received signal due to transmitting stations other than the current transmitting station;

calculating intercarrier interference for the current transmitting station using the current channel estimate and the current carrier frequency offset estimate for the current transmitting station;

subtracting the intercarrier interference from the received signal to generate a final processed signal; and

regenerating the channel estimates and the carrier frequency offset estimate for the current transmitting station from the final processed signal.

19. The method of claim 18 further comprising repeating the iteratively regenerating a predetermined number of times based on a spacing between the carrier frequency offset estimates to generate a final channel estimate and a final carrier frequency offset estimate for each transmitting station;

and

using the final channel estimate and the final carrier frequency offset estimate to generate separate data streams associated with each transmitting station.

20. The method of claim 18 further comprising performing a discrete Fourier transform after the received signal is multiplied by the current carrier frequency offset estimate to generate a set of frequency-domain samples, wherein additional intercarrier interference is cancelled from the set of frequency-domain samples for each iteration.

21. The method of claim 18 further comprising performing a band-pass filtering operation on the received signals to at least in part remove tones of the received training signals except those tones known to be transmitted by the current transmitting station.

22. The method of claim 21 wherein the training signals transmitted by the transmitting stations comprise frequency-interleaved orthogonal subcarriers which are unique to each transmitting station, and

wherein portions of the received training signal that were not transmitted by the current transmitting station are selectively filtered out.

23. The method of claim 13 wherein the iterative decoding uses long-training signals transmitted by the transmitting stations,

wherein the transmitting stations transmit short-training signals prior to transmitting the long-training signals, and

wherein the method further comprises initially generating a coarse carrier frequency offset estimate for each of the transmitting stations based on the received short-training signals, the coarse carrier frequency offset estimates being used as initial carrier frequency offset estimates for the iterative decoding process.

24. The method of claim 15 wherein the training signals and the data signals transmitted by the transmitting stations comprise one of either orthogonal frequency division multiplexed signals or orthogonal frequency division multiple access signals, and

wherein the method further comprises transmitting a downlink frame for receipt by the plurality of transmitting station to instruct the transmitting stations which frequency interleaved subcarriers to use for transmitting the training signals and which subcarriers of the multicarrier communication channel to use for transmitting the data signals.

25. A receiver system comprising:

a plurality of omnidirectional receive antennas; and

a multicarrier receiver comprising a plurality of receive-signal paths to receive training signals concurrently transmitted from a plurality of transmitting stations, and a signal processor to generate channel estimates and carrier frequency offset estimates for each of the transmitting stations from the received training signals,

wherein each receive-signal path is associated with one of the receive antennas, and

wherein the signal processor performs an iterative decoding process using previously generated channel estimates and previously generated carrier frequency offset estimates to cancel intercarrier interference from the received training signals induced by carrier frequency offsets.

26. The system of claim 25 wherein the training signals are frequency interleaved among a plurality of subcarriers of a multicarrier communication channel,

wherein the training signals transmitted by each of the transmitting stations are substantially orthogonal to each other, and

wherein the training signals are followed by non-orthogonal data signals transmitted concurrently by each of the transmitting stations on the same frequency subcarriers of the multicarrier communication channel.

27. The system of claim 26 wherein for each of the transmitting stations, the signal processor to regenerate the channel estimates and carrier frequency offset estimate for said each transmitting station using the previously generated channel estimates and the previously generated carrier frequency offset estimates for reprocessing samples of the received signals,

wherein as part of the regeneration of the carrier frequency offset and channel estimates for each transmitting station, the iterative decoding process is performed by the signal processor for each transmitting station, and

wherein the signal processor is adapted to:

shift the received signal by a current carrier frequency offset estimate for a current transmitting station;

remove portions of the received signal due to transmitting stations other than the current transmitting station;

calculate the intercarrier interference for the current transmitting station using the current channel estimate and the current carrier frequency offset estimate for the current transmitting station;

subtract the intercarrier interference from the received signal to generate a final processed signal; and

regenerate the channel estimates and the carrier frequency offset estimate for the current transmitting station from the final processed signal.

28. A machine-accessible medium that provides instructions, which when accessed, cause a machine to perform operations comprising:

processing training signals from a plurality of transmitting stations through a plurality of receive antennas; and

generating channel estimates and carrier frequency offset estimates for each of the transmitting stations from the received training signals by performing an iterative decoding process using previously generated channel estimates and previously generated carrier frequency offset estimates to cancel intercarrier interference from the received training signals induced by carrier frequency offsets.

29. The machine-accessible medium of claim 28 wherein the training signals are frequency interleaved among a plurality of subcarriers of a multicarrier communication channel,

wherein the training signals transmitted by each of the transmitting stations are substantially orthogonal to each other, and

wherein the training signals are followed by non-orthogonal data signals transmitted concurrently by each of the transmitting stations on the same frequency subcarriers of the multicarrier communication channel.

30. The machine-accessible medium of claim 28 wherein the instructions, when further accessed cause the machine to perform operations comprising iteratively regenerating the channel estimate and carrier frequency offset estimate for said each transmitting station using the previously generated channel estimates and the previously generated carrier frequency offset estimates for samples of the received signals, wherein iteratively regenerating comprises:

shifting the received signal by a current carrier frequency offset estimate for a current transmitting station;

removing portions of the received signal due to transmitting stations other than the current transmitting station;

calculating intercarrier interference for the current transmitting station using the current channel estimate and the current carrier frequency offset estimate for the current transmitting station;

subtracting the intercarrier interference from the received signal to generate a final processed signal; and

regenerating the channel estimates and the carrier frequency offset estimate for the current transmitting station from the final processed signal.