Channel reuse with cognitive low interference signals

• US 8,805,427 B2
• Filed: 11/14/2008
• Issued: 08/12/2014
• Est. Priority Date: 11/14/2008
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Hassan, Amer A., de Vries, Pierre
• Primary Examiner(s): Pan, Yuwen
• Assistant Examiner(s): Wang, Fanghwa
• Application Number:
  US12/271,454
• Publication Number:
  US 20100124940A1
• Time in Patent Office: 2,097 Days
• US Class Current: 455/509
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 27/0006 Assessment of spectral gaps suitable for allocating digitally modulated signals, e.g. for carrier allocation in cognitive radio for spectrum sharing between different networks H04W16/14
• CPC Class Codes: H04W 16/14 Spectrum sharing arrangements between different networks
• CPC Class Codes: H04W 88/06 adapted for operation in multiple networks or having at least two operational modes, e.g. multi-mode terminals

Abstract

A computing system in which devices communicate wirelessly as secondary users in a band assigned to primary users. The computers communicate using new signals developed to reduce disruption to primary users of the band. The new signals may be produced by sensing, or otherwise determining, signals used by primary users and developing signals using a modulation scheme or other signal parameters that provides little disruption to primary users. These techniques make available to users unused and/or underused portions of the radio spectrum, such as whitespaces between television channels. The new signals may be generated by software defined radios within the computing devices or by switching between modulation schemes supported by conventional wireless network interface card.

Claims

1. A method of operating a communication device to communicate as a secondary user in a portion of a frequency spectrum that may be used by a primary user to transmit a primary signal to convey data to one or more primary recipients, the method comprising:

in response to receiving an indication of the primary signal, enabling communication with another device operating as a secondary user by;

based on the indication of the primary signal, obtaining first indicators of respective individual primary modulation symbols of a primary modulation scheme of the primary signal,

accessing second indicators of respective individual candidate modulation symbols in a pool of candidate modulation symbols,

using the indicators of the primary and candidate modulation symbols to compute correlation values, with the primary modulation scheme, of respective subsets of the second indicators, and identifying a minimal one of the correlation values, wherein a correlation value for a given subset is computed by computing pairwise values of correlations for respective symbol pairs, any given symbol pair including a primary modulation symbol and a candidate modulation symbol in the given subset,

constructing a secondary modulation scheme based on the modulation symbols in the given subset determined to have a minimal correlation value, the secondary modulation scheme being constructed for modulating a secondary signal for communication with the other communication device in a channel at least partly within the portion of the frequency spectrum,

wherein the secondary modulation scheme is used to modulate the secondary signal to communicate with the other communication device.

2. The method of claim 1, wherein the candidate modulation symbols in the pool of candidate modulation symbols are selected from at least two of a plurality of modulation schemes.

3. The method of claim 2, further comprising:

producing the secondary signal by encoding the data according to the derived secondary modulation scheme; and

transmitting the secondary signal comprising the encoded data.

4. The method of claim 2, further comprising constructing the secondary modulation scheme such that the secondary signal will be substantially disregarded during decoding by one or more primary recipients of the at least one primary signal.

5. The method of claim 1, further comprising detecting the primary signal based on information on the communication device regarding properties of respective primary signals.

6. The method of claim 1, further comprising detecting the primary signal by detecting use of a second channel adjacent to the portion of frequency spectrum.

17. A method according to claim 1, wherein the minimal one of the correlation values is identified by comparing the correlation values to a threshold value and selecting the minimal one of the correlation values responsive to determining that the minimal one of the correlation values satisfies the threshold value.

7. An apparatus comprising:

a radio comprising a modulator, the modulator configurable to transmit in a channel of spectrum in accordance with a configurable modulation scheme;

a controller for the radio, the controller adapted to, when the apparatus is operating;

sense the presence of a primary signal in the channel, the primary signal being transmitted by a primary device of a user of a portion of the spectrum;

responsive to sensing the primary signal, determine a primary modulation scheme for the primary signal, the primary modulation scheme comprising primary modulation symbols;

use the primary modulation symbols to derive or select a secondary modulation scheme having secondary modulation symbols determined according to the primary modulation symbols to have a minimal correlation with the primary modulation symbols, wherein the determination of minimal correlation is made by computing individual correlations of respective pairs of modulation symbols, each pair including a primary modulation symbol and a secondary modulation symbol, wherein the determination is made such that a secondary signal carrying data encoded with the secondary modulation scheme is received by primary devices communicating via the primary signal; and

configure the radio to communicate secondary signals with the selected secondary modulation scheme, the communicating the secondary signals comprising exchanging data with another apparatus, the secondary signals carrying the data exchanged between the apparatus and the other apparatus.

8. The apparatus of claim 7, wherein selecting or deriving the secondary modulation scheme comprises:

selecting secondary modulation symbols for the secondary modulation scheme according to respective individual correlations of the selected secondary modulation symbols.

9. The apparatus of claim 7, further comprising:

selecting a secondary code sequence by which to transmit data in the secondary signal, the secondary code sequence having a correlation, determined to be minimal according to the individual correlations, to a primary code sequence of the primary modulation scheme used to transmit data in the primary signal.

10. The apparatus of claim 7, wherein the radio is adapted to communicate according to at least a first predesigned signal and a second predesigned signal, and wherein configuring the radio to communicate a secondary signal with the secondary modulation scheme comprises configuring the radio to transmit a first symbol of the secondary signal according to the first predesigned signal and a second symbol of the secondary signal according to the second predesigned signal.

11. The apparatus of claim 7, wherein sensing the primary signal comprises sensing in a second channel adjacent to the channel.

12. The apparatus of claim 7, wherein the primary signal comprises a television signal being broadcast over a second channel adjacent to the channel, and the channel is whitespace between the second channel and a third channel.

13. An apparatus having encoded thereon computer-executable instructions that, when executed by a computer, cause the computer to carry out a method of operating a radio, the radio being adapted to be configured to operate in accordance with a plurality of encoding schemes, the plurality of encoding schemes comprising a first encoding scheme and a second encoding scheme, each encoding scheme corresponding to a respective constellation mapping a respective plurality of encoding scheme symbols to respective signal parameters, the method comprising:

defining a derived encoding scheme for a secondary signal, the derived encoding scheme comprising symbols individually selected from a pool of candidate symbols for encoding data during data communication between devices, wherein the symbols of the derived encoding scheme are selected from the pool of candidate symbols by evaluating correlations of features of the candidate symbols in different subsets of the candidate symbols with features of primary symbols to select a subset of the candidate symbols such that features of the symbols in the derived encoding scheme are determined to have a collective minima of correlation with features of the primary symbols, the derived encoding scheme including a symbol from the first encoding scheme and including a symbol from the second encoding scheme; and

exchanging data with a device by transmitting the data encoded with the derived encoding scheme by changing the configuration of the radio to operate in accordance with the at least two of the plurality of encoding schemes as the information is being communicated.

14. An apparatus of claim 13, wherein deriving the derived encoding scheme comprises:

defining the derived encoding scheme such that the secondary signal transmitted in accordance with the derived encoding scheme will be substantially disregarded by a receipt procedure of a destination of primary signals such that the secondary signal does not substantially disrupt the receipt procedure.

15. An apparatus of claim 13, the method further comprising changing the configuration of the radio to transmit a first symbol from the first encoding scheme and changing the configuration of the radio to transmit a second symbol from the second encoding scheme.

16. An apparatus of claim 15, wherein each of the first and second symbols comprises a phase-power pair defining a phase angle and a power with which a signal corresponding to the symbol will be generated.