Patent ID: 7907909

Claim:
A radio device comprising: a receiver unit operable in an orthogonal frequency division multiplexing (OFDM) system to receive a modulated signal that comprises multiple groups of consecutive sub-carriers or tones in one of a partially used sub-channel (PUSC) tile and an adaptive modulation and coding (AMC) slot; a group delay (GD) estimator operable in frequency domain and configured to estimate a particular group delay associated with a particular frequency bandwidth or a number of consecutive tones, a GD compensator operable in the frequency domain and configured to perform phase rotation to correct the particular group delay individually on tones of an OFDM symbol of the modulated signal in response to phase shifts resulted from the group delay to generate a GD compensated modulated signal; wherein for the PUSC tile the phase rotation ø k for each of the tones of the OFDM symbol within the tile is defined according to ø 1 =θ; ø 2 =ø 1 −2πτ 2 Δf=θ− 2 π{tilde over (λ)}Δf; ø 3 =ø 2 −2πτ 2 Δf=θ− 6 π{tilde over (λ)}Δf; and ø 4 =ø 3 −2πτ 3 Δf=θ− 12 π{tilde over (λ)}Δf where k is a tone index that takes a value from 1 to 4; θ is the phase rotation ø 1 of a first tone of the PUSC tile; Δf is a tone spacing that depends on an OFDM signal bandwidth and a Fast Fourier Transform (FFT) size; and {tilde over (λ)} is an averaged group delay compensation (GDC) coefficient defined as λ ~ = 1 T ⁢ ∑ t = 1 T ⁢ ⁢ λ t where T is a total number of PUSC tiles having a same physical frequency; and λ t is an estimated group delay value for the PUSC tile t, which is calculated based on the received pilot subcarrier signals according to λ t = 1 2 ⁢ ( ϕ 1 , 1 - ϕ 1 , 4 12 ⁢ ⁢ πΔ ⁢ ⁢ f + ϕ 3 , 1 - ϕ 3 , 4 12 ⁢ ⁢ πΔ ⁢ ⁢ f ) where ø m,k represents a phase shift of a demodulated pilot subcarrier signal on tone k and OFDM symbol m within the PUSC tile t; and an equalizer operable in the frequency domain and configured to receive the GD compensated modulated signal from the GD compensator.