Patent ID: 8805427

Claim:
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.