System and method for measuring signal to noise values in an adaptive wireless communication system

• US 20030165157A1
• Filed: 07/26/2002
• Published: 09/04/2003
• Est. Priority Date: 07/27/2001
• Status: Active Grant

• Current Assignee: Zarbana Digital Fund LLC (Intellectual Ventures LLC)
• Original Assignee: Harington Valve LLC (Intellectual Ventures LLC)
• Inventors: Gazelle, David, Stanwood, Kenneth, Pollmann, Stephen
• Granted Patent: US 7,577,100 B2
• Time in Patent Office: Days
• US Class Current: 370/465
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/20 using signal quality detector

Abstract

The system and method optimizes a SNR calculation for a signal received during a downlink burst even in the absence of a node'"'"'s preferred modulation. This system and method are used in communication systems that include a multi-modulation modem. An adaptation factor is selected whereby its use during portions of the downlink burst, which were not modulated using the preferred modulation, provides the SNR. The selected adaptation factor is used by an equalizer to perform channel inversion to the signal. The system and method can be used in, for example, an FDD or TDD communication system. Such communication systems can be, for example, symmetric, asymmetric, and/or adaptive in their operation.

Claims

1. A wireless communication system capable of determining a signal to noise ratio (“

SNR”

) for a multi-modulation downlink burst, the system comprising;

a base station configured to modulate a signal for transmission as a downlink burst to nodes using multiple modulation techniques;

a node, comprising a modem configured to measure a first SNR during a first portion of the downlink burst and measure a second SNR during a second portion of the downlink burst, the first portion being modulated using a preferred modulation technique and the second portion being modulated using a more robust modulation technique than the preferred modulation technique;

a processor configured to receive the first and second SNRs and determine if the preferred modulation technique should be changed; and

an equalizer module in communication with the processor and configured to perform channel inversion on the second portion of the downlink burst utilizing an adaptation factor that is optimized for use with the preferred modulation technique.

2. The system of claim 1, the node further comprising a decoder module configured to demodulate the second portion of the downlink burst.

3. The system of claim 2, the node further comprising a detector and synchronization module configured to identify a beginning of the downlink burst and synchronize the downlink burst to the equalizer module and the decoder module.

4. The method of claim 1, wherein the multiple modulation techniques are selected from the group consisting of quadrature amplitude modulation (“

QAM”

)-16, quadrature phase shift keying (“

QPSK”

) modulation, and QAM-64.

5. The system of claim 1, wherein the second portion is transmitted earlier in the downlink burst than the first portion.

6. The system of claim 1, wherein the processor is located at the base station to receive the first and second SNRs from the node.

7. The system of claim 1, wherein the processor is located at the node.

8. A method for determining a signal to noise ratio (“

SNR”

) for a multi-modulation burst modem which uses multiple modulation techniques for transmitting downlinks from a base station to a node, the node having a preferred modulation technique, the method comprising;

determining an adaptation factor for each modulation technique;

selecting a first preferred adaptation factor for use by a node, the first preferred adaptation factor being optimized for a first preferred modulation technique of the node;

receiving a first portion of a first downlink burst, the first portion being modulated using a first modulation technique;

determining a first SNR for the first portion using the first preferred adaptation factor;

if the node receives its preferred modulation technique in a second portion of the first downlink burst,

then determining a second SNR for the second portion using the first preferred adaptation factor,

comparing the first and the second SNRs to one or more threshold values,

selecting a second preferred modulation technique based on the comparison,

selecting a second preferred adaptation factor that is associated with the second preferred modulation technique; and

if the node does not receive its preferred modulation technique in the second portion of the first downlink burst,

then comparing the first SNR to the one or more threshold values,

selecting the second preferred modulation technique based on the comparison,

selecting the second preferred adaptation factor that is associated with the second preferred modulation technique.

9. The method of claim 8, further comprising:

receiving a request for the base station to use the second preferred modulation technique; and

transmitting a second downlink burst to the node using the second preferred modulation technique.

10. The method of claim 8, wherein the one or more threshold values are associated with adjacent modulation techniques of the preferred modulation technique.

11. The method of claim 10, wherein the one or more threshold values comprise an upper threshold value that exceeds an analytical upper SNR threshold associated with the preferred modulation technique.

12. The method of claim 11, wherein the one or more threshold values comprise a lower threshold value that is below an analytical lower SNR threshold associated with the preferred modulation technique.

13. A method for changing a node'"'"'s preferred modulation technique, the preferred modulation technique having an optimized preferred adaptation factor, the node being configured to receive data from a base station that uses a multi-modulation burst modem to transmit a downlink burst, the method comprising:

receiving a first portion of a downlink burst, the first portion being modulated using a modulation technique that is more robust than a preferred modulation technique;

determining a first SNR for the first portion using a preferred adaptation factor that is optimized for the preferred modulation technique;

receiving a second portion of the downlink burst, the second portion being modulated using the preferred modulation technique;

determining a second SNR for the second portion using the preferred adaptation factor;

comparing the first and the second SNRs to one or more threshold values; and

selecting a new preferred modulation technique based on the comparison.

14. The method of claim 13, wherein the first SNR determined for the first portion is within a first range, and the second SNR determined for the second portion is within a second range, the second range having a higher fidelity than the first range.

15. The method of claim 13, wherein the preferred modulation technique is quadrature amplitude modulation-16.

16. The method of claim 15, wherein the more robust modulation technique is quadrature phase shift keying.

17. The method of claim 13, wherein the one or more threshold values comprise an upper threshold value and a lower threshold value, both associated with the preferred modulation technique.

22. The method of claim 13, further comprising:

determining a third SNR for a third portion of the downlink burst using the preferred adaptation factor that is optimized for the preferred modulation technique;

comparing the third SNR to the one or more threshold values; and

selecting the new preferred modulation technique based on the comparison.

18. The method of 16, wherein the one or more threshold values comprise a lower threshold value associated with the quadrature amplitude modulation-16.

19. The method of 18, wherein the one or more threshold values comprise an upper threshold value associated with the quadrature amplitude modulation-16.

20. The method of claim 19, wherein the upper threshold value exceeds an analytical upper SNR threshold associated with the quadrature amplitude modulation-16.

21. The method of claim 20, wherein an analytical lower SNR threshold associated with the quadrature amplitude modulation-16 exceeds the lower threshold value.