Patent ID: 8130851

Claim:
A method for encoding an OFDM signal comprising the steps of: pairing two adjacent subcarriers of an OFDM signal as a group, changing a modulated symbol set of the OFDM signal to a modified set for coding the OFDM signal, and providing a modified baseband OFDM signal with an increased frequency separation between the subcarriers and reducing the total number of subcarriers being used for transmission over each OFDM symbol interval wherein the modified baseband OFDM signal comprises a pair of symbols being jointly mapped to a pair of sub-carriers and the pair of symbols {X m , X m2 } is chosen from the following set {X m , X m2 }ε{(0, λ 1 ), (0, λ 2 ), . . . , (0, λ M ), (λ 1 , 0), (λ 2 , 0), . . . , (λ M , 0)}; where m(1, . . . N/2) is the total number of groups; and the step of changing comprises modifying the set of symbols {λ 1 , λ 2 , . . . , λ M } according to a modulated OFDM signal to a set of modified symbols {0, λ 1 , λ 2 , . . . , λ M } for a mapped OFDM signal; and the modified OFDM signal comprises only one of two sub-carriers in each pair being used for transmission over each OFDM symbol interval at all times thereby increasing frequency separation between sub-carriers compared to a conventional OFDM system.