Methods and apparatus for multiple-antenna communication of wireless signals with embedded synchronization/pilot sequences

• US 8,379,752 B2
• Filed: 03/17/2010
• Issued: 02/19/2013
• Est. Priority Date: 03/19/2008
• Status: Active Grant

• Current Assignee: General Dynamics Mission Systems Inc. (General Dynamics Corporation)
• Original Assignee: General Dynamics C4 Systems Incorporated (General Dynamics Corporation)
• Inventors: Kleider, John E., Hamilton, Benjamin Russell
• Primary Examiner(s): PATEL, DHAVAL V
• Application Number:
  US12/725,985
• Publication Number:
  US 20100172427A1
• Time in Patent Office: 1,070 Days
• Field of Search: 375/260, 375/262, 375/267, 375/295, 375/316, 375/340, 375/343, 375/346, 375/347, 370/203, 370/204, 370/205, 370/208, 370/209, 370/210, 370/328, 370/329, 370/338, 370/339
• US Class Current: 375/267
• CPC Class Codes: H04B 7/0669 using different channel coding between antennas space-time coding H04L1/0618
• CPC Class Codes: H04L 2027/0024 at the receiver end
• CPC Class Codes: H04L 25/0232 by interpolation between sounding signals
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/262 Reduction thereof by selection of pilot symbols
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2675 Pilot or known symbols

Abstract

Embodiments include methods for determining synchronization/pilot sequences (SPS) to be utilized in conjunction with transmissions by antennas of a multiple-antenna transmitter. The SPS include pilot signals that are positioned at subcarriers that are orthogonal in frequency with subcarriers at which pilot signals of other antennas are positioned. The pilot signals may be unevenly spaced across the in-band subcarriers. The multiple-antenna transmit system generates a plurality of wireless signals, each of which may include an SPS having synchronization information in a first plurality of in-band subcarriers and the pilot signals in a second plurality of in-band subcarriers. The wireless signals are simultaneously radiated over a wireless communication channel using a different antenna. A receiver receives channel-affected versions of the wireless signals, and produces a corrected signal by applying corrections to the received signal based on estimated channel perturbations within the received signal.

Claims

1. A method for generating synchronization and pilot sequences for multiple antennas of a multiple-antenna transmit system in which signals are communicated across a frequency range that includes one or more sets of consecutive null subcarriers and a set of in-band subcarriers that is adjacent to the one or more sets of consecutive null subcarriers, the method comprising the steps of:

determining, for a first antenna of the multiple antennas, a set of first pilot subcarriers for a plurality of pilot signals, wherein the first pilot subcarriers are positioned at subcarriers that are orthogonal in frequency with subcarriers at which pilot signals of other antennas of the multiple antennas are positioned, and the first pilot subcarriers are unevenly spaced across the in-band subcarriers;

specifying a first frequency domain power profile for a first set of synchronization and pilot sequences to be utilized in conjunction with the first antenna, wherein the first frequency domain power profile has non-zero power for the first pilot subcarriers; and

generating the first set of the synchronization and pilot sequences using the first frequency domain power profile.

2. The method of claim 1, wherein the first frequency domain power profile is further specified to have zero power at subcarriers corresponding to the pilot signals of the other antennas.

3. The method of claim 1, wherein generating the first set of synchronization and pilot sequences comprises:

generating a candidate synchronization and pilot sequence using the first frequency domain power profile and initial conditions;

repeating the generating step a first number of iterations using different initial conditions for each iteration to generate a plurality of candidate synchronization and pilot sequences;

performing a plurality of correlations among the candidate synchronization and pilot sequences to generate a plurality of correlation values;

determining a plurality of permutations of the candidate synchronization and pilot sequences, wherein each permutation of the plurality of permutations includes a different set of candidate synchronization and pilot sequences, and wherein each permutation includes a number of candidate synchronization and pilot sequences; and

identifying a selected permutation from the plurality of permutations, wherein the selected permutation corresponds to the set of synchronization and pilot sequences being generated.

4. The method of claim 1, wherein subcarrier indices for the first pilot subcarriers are determined using a third order or higher order polynomial parameterization of pilot subcarriers.

5. The method of claim 4, wherein the polynomial parameterization is a cubic polynomial parameterization.

6. The method of claim 4, wherein the polynomial parameterization is a fifth order polynomial parameterization.

7. The method of claim 1, wherein the multiple antennas are co-located, and the first pilot subcarriers are in adjacent subcarrier positions with respect to pilot subcarriers of at least one other one of the multiple antennas.

8. The method of claim 1, wherein the multiple antennas are distributed, and the first pilot subcarriers are located in subcarrier positions that are offset with respect to subcarrier positions of all other ones of the multiple antennas by at least two subcarrier positions.

9. The method of claim 1, further comprising:

determining an unavailable portion of the in-band subcarriers,

wherein determining the set of first pilot subcarriers comprises determining the set so that it excludes subcarriers within the unavailable portion, and

wherein the first frequency domain power profile is further specified to have zero power at subcarriers corresponding to the unavailable portion.

10. A method for wirelessly communicating signals across a frequency range that includes one or more sets of consecutive null subcarriers and a set of in-band subcarriers that is adjacent to the one or more sets of consecutive null subcarriers, the method comprising the steps of:

generating a plurality of wireless signal for transmission, wherein each of the plurality of wireless signals includes a synchronization and pilot sequence having synchronization information in a first plurality of in-band subcarriers and a plurality of pilot signals in a second plurality of in-band subcarriers, wherein the second plurality of in-band subcarriers are unevenly spaced across the in-band subcarriers for at least one of the plurality of wireless signals, and pilot signals of each of the plurality of wireless signals are positioned at subcarriers that are orthogonal in frequency with subcarriers at which pilot signals of all other ones of the plurality of wireless signals are positioned; and

simultaneously radiating each of the wireless signals over a wireless communication channel using a different one of a plurality of antennas.

11. The method of claim 10, wherein the plurality of antennas are co-located, and generating the plurality of wireless signals includes positioning pilot signals of each of the plurality of wireless signals in adjacent subcarrier positions with respect to pilot signals of at least one other one of the plurality of wireless signals.

12. The method of claim 10, wherein the plurality of antennas are distributed, and generating the plurality of wireless signals includes positioning pilot signals of each of the plurality of wireless signals in subcarrier positions that are offset with respect to subcarrier positions of all other ones of the plurality of wireless signals by at least two subcarrier positions.

13. The method of claim 10, wherein generating the plurality of wireless signals includes allocating substantially equal power to pilot signals positioned at corresponding but offset subcarrier positions in each of the plurality of wireless signals.

14. The method of claim 10, wherein generating the plurality of wireless signals includes allocating unequal power levels to at least two pilot signals of each plurality of pilot signals.

15. The method of claim 10, wherein generating the plurality of wireless signals includes determining subcarrier indices for the plurality of pilot signals using a third order or higher order polynomial parameterization of pilot subcarriers.

16. The method of claim 15, wherein the polynomial parameterization is a cubic polynomial parameterization.

17. The method of claim 15, wherein the polynomial parameterization is a fifth order polynomial parameterization.

18. The method of claim 15, wherein generating a wireless signal of the plurality of wireless signals comprises:

selecting a set of multiple synchronization pilot sequences that includes the synchronization and pilot sequence and one or more additional synchronization and pilot sequences;

combining a plurality of phase shifted input data signals with the multiple synchronization and pilot sequences to produce a plurality of combined signals;

performing frequency domain-to-time domain transformations of the combined signals to produce a plurality of candidate signals;

determining peak-to-average ratios for at least some of the plurality of candidate signals;

identifying a selected signal from the plurality of candidate signals based on the peak-to-average ratios; and

further processing the selected signal to generate the wireless signal.

19. The method of claim 10, further comprising:

determining an unavailable portion of the in-band subcarriers, wherein each of the plurality of wireless signals has zero power at in-band subcarriers within the unavailable portion.

20. A method comprising the steps of:

receiving a received signal from a wireless communication channel, wherein the received signal represents channel-affected versions of a plurality of wireless signals that were transmitted by a multiple-antenna transmitter, and wherein each of the wireless signals includes a synchronization and pilot sequence with synchronization information and a plurality of pilot signals represented within a plurality of pilot subcarriers, wherein the plurality of pilot signals for at least one of the plurality of wireless signals are unevenly spaced with respect to adjacent pilots, and pilot signals of each of the plurality of wireless signals are orthogonal in frequency with pilot signals of all other ones of the plurality of wireless signals;

producing a corrected signal by applying corrections to the received signal based on estimated channel perturbations within the received signal, which estimated channel perturbations are determined based on the plurality of pilot signals; and

producing an output data symbol from the corrected signal.

21. The method of claim 20, wherein the wireless signals that were transmitted by the transmitter represent signals selected by the transmitter from a plurality of candidate signals, and the received signal includes a combination of a phase shifted input data signal with a synchronization and pilot sequence, and wherein the method further comprises:

determining an estimate of a selective mapping (SLM) index, which identifies the synchronization and pilot sequence from a plurality of synchronization and pilot sequences; and

wherein producing the corrected signal is performed by applying the corrections to the received signal based the estimated channel perturbations within the received signal, wherein the estimated channel perturbations are determined based on the estimate of the SLM index and the plurality of pilot signals.

22. The method of claim 21, wherein the SLM index also identifies the associated transmit antenna from which the SLM index was applied.

23. The method of claim 20, further comprising:

performing a plurality of correlations of the received signal with a plurality of candidate synchronization and pilot sequences to produce a plurality of correlation outputs, wherein a length of each of the correlations approximately equals a number of the pilot signals within each of the wireless signals; and

determining, based on the plurality of correlation outputs, a synchronization and pilot sequence that was embedded in the received signal at the multiple-antenna transmitter.

24. The method of claim 20, further comprising:

estimating a carrier frequency offset (CFO) and a sampling frequency offset (SFO) of the received signal using a weighted estimator that adjusts estimator weights according to a signal-to-noise ratio (SNR) of the received signal, wherein first portions of the received signal having a relatively high SNR are weighted higher during the process of estimating, and second portions of the received signal having a relatively low SNR are weighted lower during the process of estimating.

25. A system comprising:

one or more signal generators configured to generate a plurality of wireless signals for transmission, wherein each of the plurality of wireless signals includes a synchronization and pilot sequence with synchronization information and a plurality of pilot signals, and the pilot signals within each of the plurality of wireless signals are represented in a plurality of in-band subcarriers that are unevenly spaced across the in-band subcarriers, and pilot signals of each of the plurality of wireless signals are orthogonal in frequency with pilot signals of all other ones of the plurality of wireless signals; and

a plurality of antennas, operably coupled with the one or more signal generators, and configured simultaneously to radiate each of the wireless signals over a wireless communication channel.

26. The system of claim 25, wherein the plurality of antennas include a plurality of co-located antennas.

27. The system of claim 25, wherein the plurality of antennas include a plurality of distributed antennas.

28. The system of claim 25, wherein the transmitter is a wireless communication device selected from the group consisting of a cellular telephone, a radio, an unmanned autonomous vehicle, a one-way pager, a two-way pager, a personal data assistant, a computer, a base station, a wireless transmitter, and a wireless transceiver.

29. The system of claim 25, further comprising:

a receiver adapted to receive a received signal from the wireless communication channel, wherein the received signal represents a channel-affected version of the wireless signals that were radiated by the plurality of antennas, to produce a corrected signal by applying corrections to the received signal based on estimated channel perturbations within the received signal, which estimated channel perturbations are determined based on the plurality of pilot signals, and to produce an output data symbol from the corrected signal.

30. The system of claim 25, wherein each of the plurality of wireless signals has zero power at in-band subcarriers within the unavailable portion that are determined to be unavailable to the system.

31. The system of claim 25, wherein the system is a multi-carrier communication system selected from the group consisting of a multi-carrier based, ultra-wideband system, an orthogonal frequency division multiplexing (OFDM) system, an orthogonal frequency division multiple access (OFDMA) system, a multi-carrier code division multiple access (MC-CDMA) system, a wideband code division multiple access (W-CDMA) system, a wireless local area network (WLAN), a digital video broadcast (DVB) system, a digital audio broadcast (DAB) system, a broadband radio access network (BRAN), a WiMAX (Worldwide Interoperability for Microwave Access) system, a Wireless Regional Area Network (WRAN) system, a multiple-input multiple output (MIMO) system, and a multiple-input single-output (MISO) system.