High data rate wireless bridging

• US 8,374,105 B1
• Filed: 01/28/2008
• Issued: 02/12/2013
• Est. Priority Date: 12/31/2002
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Perahia, Eldad, Douglas, Bretton, Pignatelli, David
• Primary Examiner(s): FILE, ERIN M
• Application Number:
  US12/011,546
• Time in Patent Office: 1,842 Days
• Field of Search: 375/260
• US Class Current: 370/260
• CPC Class Codes: H04B 7/0413 MIMO systems
• CPC Class Codes: H04B 7/10 Polarisation diversity; Directional diversity
• CPC Class Codes: H04L 25/0202 Channel estimation
• CPC Class Codes: H04L 25/0226 sounding signals per se
• CPC Class Codes: H04L 27/2655 Synchronisation arrangements
• CPC Class Codes: H04L 5/0023 Time-frequency-space
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver

Abstract

A specialized preamble is provided to facilitate matrix channel estimation of a MIMO channel. In a particular implementation, a channel training preamble provided by the IEEE 802.11a standard is modified to facilitate MIMO channel estimation.

Claims

1. In a wireless communication system, a method for receiving a signal, said method comprising:

receiving a first OFDM signal via a first antenna element;

receiving a second OFDM signal via a second antenna element;

during a first channel training period, within each of a plurality of frequency subchannels, obtaining received signal measurements via said first antenna element and via said second antenna element;

during a second channel training period, within each of a plurality of frequency subchannels, obtaining received signal measurements via said first antenna element and via said second antenna element; and

measuring a MIMO channel response based on said measurements made during said first channel training period and said second channel training period;

wherein a first transmitting antenna element is quiet during a portion of said first and second channel training periods and a second transmitting antenna element is quiet during another portion of said first and second channel training periods.

2. The method of claim 1 wherein channel training information transmitted during said first channel training period and said second channel training period is defined by the IEEE 802.11a standard.

3. The method of claim 1 wherein said first antenna element represents a horizontal polarization of an antenna and said second antenna element represents a vertical polarization of said antenna.

15. The method of claim 1 further comprising synchronizing a first receiver chain coupled to said first antenna element to a signal received via said antenna element and passing synchronization information from said first receiver chain to a second receiver chain coupled to said second antenna element.

16. The method of claim 15 further comprising synchronizing components of said second receiver chain based on said synchronization information passed from said first receiver chain.

17. The method of claim 15 further comprising selecting said first receiver chain as synchronization master and said second receiver chain as synchronization slave based on start of a packet being detected first by said first receiver chain.

4. In a wireless communication system, a method for receiving a signal, said method comprising:

receiving a first OFDM signal via a first antenna element;

receiving a second OFDM signal, co-channel to said first OFDM signal, via a second antenna element;

during a channel training period, obtaining received signal measurements in a first set of subcarriers and a second set of subcarriers, said first set of subcarriers and said second set of subcarriers being non-overlapping; and

measuring a MIMO channel response based on said measurements made during said channel training period; and

wherein transmissions from different remote antenna elements are expected in said first set of subcarriers and said second set of subcarriers during said channel training period and the remote antenna elements alternate even and odd subcarriers.

5. The method of claim 4 wherein said first antenna element represents a horizontal polarization of an antenna and said second antenna element represents a vertical polarization of said antenna.

6. The method of claim 4 wherein said first set of subcarriers and said second set of subcarriers alternate in order of frequency.

7. In a wireless communication system, apparatus for receiving a signal, said apparatus comprising:

a first receiver block that receives a first OFDM signal via a first antenna element;

a second receiver block that receives a second OFDM signal via a second antenna element;

a channel estimation block that, within each of a plurality of frequency subchannels, during first and second channel training periods, obtains received signal measurements via said first and second receiver blocks, and that estimates a MIMO channel response based on said measurements;

wherein a first transmitting antenna element is quiet during a portion of said first and second channel training periods and a second transmitting antenna element is quiet during another portion of said first and second channel training periods.

8. The apparatus of claim 7 wherein channel training information transmitted during said first channel training period and said second channel training period is defined by the IEEE 802.11a standard.

9. The apparatus of claim 7 wherein said first antenna element represents a horizontal polarization of an antenna and said second antennal element represents a vertical polarization of said antenna.

20. The apparatus of claim 7 wherein after said first channel training period and during said second channel training period, said first OFDM signal is processed to recover data and wherein only if data is not recovered during said second channel training period, said first OFDM signal and said second OFDM signal are thereafter processed as a MIMO signal.

10. In a wireless communication system, apparatus for receiving a signal, said apparatus comprising:

a first receiver block that receives a first OFDM signal via a first antenna element;

a second receiver block that receives a second OFDM signal via a second antenna element; and

a channel estimation block that, during a channel training period, obtaining received signal measurements in a first set of subcarriers and a second set of subcarriers, said first set of subcarriers and said second set of subcarriers being non-overlapping and measures a MIMO channel response based on said measurements made during said channel training period; and

wherein transmissions from different remote antenna elements are expected in said first set of subcarriers and said second set of subcarriers during said channel training period and the remote antenna elements alternate even and odd subcarriers.

11. The apparatus of claim 10 wherein said first antenna element represents a horizontal polarization of an antenna and said second antenna element represents a vertical polarization of said antenna.

12. The apparatus of claim 10 wherein said first set of subcarriers and said second set of subcarriers alternate in order of frequency.

18. The apparatus of claim 10 further comprising a first synchronization element within a first receiver chain coupled to said first antenna element, said first synchronization element operable to synchronize to a signal received via said first antenna element, wherein synchronization information is passed from said first receiver chain to a second receiver chain coupled to said second antenna element.

19. The apparatus of claim 18 wherein components of said second receiver chain are synchronized based on said synchronization information passed from said first receiver chain.

13. In a wireless communication system, apparatus for receiving a signal, said apparatus comprising:

means for receiving a first OFDM signal via a first antenna element;

means for receiving a second OFDM signal via a second antenna element;

means for, during a first channel training period, within each of a plurality of frequency subchannels, obtaining received signal measurements via said first antenna element and via said second antenna element;

means for, during a second channel training period, within each of a plurality of frequency subchannels, obtaining received signal measurements via said first antenna element and via said second antenna element; and

means for measuring a MIMO channel response based on said measurements made during said first channel training period and said second channel training period;

wherein a first transmitting antenna element is quiet during a portion of said first and second channel training periods and a second transmitting antenna element is quiet during another portion of said first and second channel training periods.

14. In a wireless communication system, apparatus for receiving a signal, said apparatus comprising:

means for receiving a first OFDM signal via a first antenna element;

means for receiving a second OFDM signal, co-channel to said first OFDM signal, via a second antenna element;

means for, during a channel training period, obtaining received signal measurements in a first set of subcarriers and a second set of subcarriers, said first set of subcarriers and said second set of subcarriers being non-overlapping; and

means for measuring a MIMO channel response based on said measurements made during said channel training period; and

wherein transmissions from different remote antenna elements are expected in said first set of subcarriers and said second set of subcarriers during said channel training period and the remote antenna elements alternate even and odd subcarriers.