Patent ID: 7170944

Claim:
A method for assessing presence of a multipath signal, the method comprising: (1) receiving a digital signal frame, of length at least L 1 +L 2 , expressed in temporal units Δt(sym) of length of a symbol, that includes a distinguishing reference symbol (RS) sequence RS(t;m 1 ) of length L 1 and a data sequence of length L 2 , where m 1 is an index value for the RS sequence corresponding to the received frame; (2) identifying the index value m 1 from the RS sequence; (3) setting an integer k=1, setting an initial background level estimate n 0 =0, providing an initial signal s(t;k=1;rec)=s(t;rec), and providing a first Fourier transform Φ(f;ref/m 1 )=FT{RS(t;m 1 )}, corresponding to a selected interrogation segment (IS) portion for the received frame, where f is a frequency variable, the IS portion is of length L 1 +D and includes the RS sequence for the frame, and D is a selected positive number; (4) providing a second Fourier transform Φ(f;k;rec)=FT{s(t;k;rec)}, corresponding to the IS of the signal s(t;k;rec); (5) computing an inverse Fourier transform σ(t;m 1 ;k)=FT −1 {Φ(f;k;rec)/Φ(f;ref/m 1 )} of the ratio of the first and second Fourier transforms; (6) estimating whether the received frame includes at least one multipath signal from an examination of σ(t;m 1 ;k); (7) when the received frame is estimated to contain at least one multipath signal: (8) estimating an average value <n k > for a background level for the inverse Fourier transform σ(t;m 1 ;k); (9) determining whether an average background level measure B k of the average background level <n k > satisfies B k ≦ε(thr), where ε(thr) is a first selected positive value; (10) when B k does not satisfy B k ≦ε(thr): (11) computing a filtered channel function σ(t;m 1 ;k;fil) that is equal to σ(t;m 1 ;k) if |σ(t;m 1 ;k)| >σ(thr), and is equal to 0 if |σ(t;m 1 ;k)| <σ(thr), where σ(thr) is a second selected positive value; (12) computing a convolved filtered channel function Cσ(t;m 1 ;k;fil) of the filtered channel function σ(t;m 1 ;k;fil) with RS (t;m 1 ); (13) computing a modified received signal s ( t;k;rec/ 1)= s ( t;k;rec )( t≦t 1 )= Cσ ( t;m 1 ; k;fil )( t>t 1 ), where t 1 is a selected value of t, determined in part by the length D and identifying s(t;k;rec/1) with a processed signal s(t;k+1;rec); (14) incrementing k(k→k+1) and returning to step (4); and (15) when B k satisfies B k ≦ε(thr), using a present version s(t;k;rec) of the received frame, with k=K 1 =present value of the index k, to determine presence of, and to characterize, at least one multipath signal present in the received frame.