US 6,389,040 B1 · Apparatus and method for generating a frequency offset estimate for communication systems having frequency selecting fading channels

Abstract

A frequency offset estimation is generated without explicitly generating a channel estimation for a frequency selective fading communication channel. This is realized by recognizing that, in the absence of additive noise, the channel output at a time n depends only on the last previous predetermined number, L, of data symbols, and that a “state” is a sequence of the last L symbols. Specifically, in a receiver, a received signal is mixed with a locally generated frequency corresponding to a frequency offset to generate a mixed signal. A calculation is made on the mixed signal in which channel outputs of the same state are combined and accumulated. Then, a summation is made over all possible states of the combined and accumulated channel outputs to yield a so-called metric calculation value for that mixed signal. The metric calculation is then repeated for a plurality of different locally generated frequencies corresponding on a one-to-one basis with a plurality of frequency offsets. The frequency offset corresponding to the largest metric calculation value is selected as the desired frequency offset estimate. In one embodiment of the invention, a representation of a frequency offset estimation value is obtained by employing an open loop arrangement. In another embodiment of the invention, a frequency offset estimation value is generated by employing an closed loop arrangement.

Claims39

Dependent claims

Apparatus for use in a receiver to generate a frequency offset estimate in response to a received signal comprising:

a plurality of oscillators for generating a plurality of frequency signals each having a its own respective frequency;
a plurality of mixing units, each mixing unit being supplied with said received signal and on a one-to-one basis with a corresponding one of said plurality of frequency signals for generating a mixed signal which is a version of said received signal multiplied by said corresponding one of said plurality of frequency signals;
a plurality of metric calculation units, each metric calculation unit being supplied with one of said mixed signals for generating a metric value at the frequency of said supplied mixed signal in accordance with prescribed criteria including obtaining a first sum ∑ n = 0 , n :
s ⁡ ( n ) = s N - 1 ⁢ r ⁡ ( n ) ⁢ ⅇ - j2π ⁢ ⁢ f 0 ⁢ n
and obtaining a second sum ∑ s = 0 2 L - 1 ⁢ [LeftBracketingBar] ∑ n = 0 , n :
s ⁡ ( n ) = s N - 1 ⁢ r ⁡ ( n ) ⁢ ⅇ - j2π ⁢ ⁢ f 0 ⁢ n [RightBracketingBar] ,
where r(n) is said received signal, s(n)is a state, L is a number of fast data symbols, N is a number of discrete frequencies, n is a time, e−j2πf0n is a discrete frequency and f0 is one of f1 through fN, said plurality of metric calculation units thereby generating a metric calculation over each of said plurality of frequencies;
and
an apparatus supplied with said plurality of metric calculations for selecting a metric calculation having a maximum magnitude, wherein the frequency over which said metric calculation having the maximum magnitude was made is the frequency offset estimate.

6 more elements

Apparatus for use in a receiver to generate a frequency offset estimate in response to a received signal comprising:

a plurality of oscillators for generating a plurality of discrete frequency signals each having a its own respective discrete frequency;
a plurality of mixing units, each mixing unit being supplied with said received signal and on a one-to-one basis with a corresponding one of said plurality of discrete frequency signals for generating a mixed signal which is a version of said received signal multiplied by said corresponding one of said plurality of discrete frequency signals;
a plurality of metric calculation units, each metric calculation unit being supplied with one of said mixed signals for generating a metric value at the discrete frequency of said supplied mixed signal in accordance with prescribed criteria, each of said metric calculations being made over said supplied mixed signal and wherein each of said metric calculation units includes a combiner for combining channel outputs of the same state and an accumulator for accumulating the combined outputs of the same state over all possible states, where a state s(n) at time n is defined as s(n)=[x(n),x(n−1), . . . , x(n−L+1)] and L is a number of past data symbols, said plurality of metric calculation units thereby generating a metric calculation over each of said plurality of discrete frequencies;
and
an apparatus supplied with said plurality of metric calculations for selecting a metric calculation having a maximum magnitude, wherein the frequency over which said metric calculation having the maximum magnitude was made is the frequency offset estimate.

2 more elements

Apparatus for use in a receiver to generate a frequency offset estimate in response to a received signal comprising:

means for generating a plurality of frequency signals each having its own respective frequency;
a plurality of means each for mixing said received signal and on a one-to-one basis with a corresponding one of said plurality of frequency signals for generating a mixed signal which is a version of said received signal multiplied by said corresponding one of said plurality of frequency signals;
a plurality of means each for making a metric calculation over one of said mixed signals in accordance with prescribed criteria including obtaining a first sum ∑ n = 0 , n :
s ⁡ ( n ) = s N - 1 ⁢ r ⁡ ( n ) ⁢ ⅇ - j2π ⁢ ⁢ f 0 ⁢ n
and obtaining a second sum ∑ s = 0 2 L - 1 ⁢ [LeftBracketingBar] ∑ n = 0 , n :
s ⁡ ( n ) = s N - 1 ⁢ r ⁡ ( n ) ⁢ ⅇ - j2π ⁢ ⁢ f 0 ⁢ n [RightBracketingBar] ,
where r(n) is said received signal, s(n)is a state, L is a number of fast data symbols, N is a number of discrete frequencies, n is a time, e−j2πf0n is a discrete frequency and f0 is one of f1 through fN each of said means for making a metric calculation generating a metric calculation over a corresponding one of said plurality of frequencies;
and
means supplied with said plurality of metric calculations for selecting a metric value calculation having a maximum magnitude, wherein the frequency over which said metric calculation having the maximum magnitude was made is the frequency offset estimate.

6 more elements

Apparatus for use in a receiver to generate a frequency offset estimate in response to a received signal comprising:

means for generating a plurality of discrete frequency signals each having its own respective discrete frequency;
a plurality of means each for mixing said received signal and on a one-to-one basis with a corresponding one of said plurality of discrete frequency signals for generating a mixed signal which is a version of said received signal multiplied by said corresponding one of said plurality of discrete frequency signals;
a plurality of means each for making a metric calculation over a supplied one of said mixed signals in accordance with prescribed criteria, each of said means for making a metric calculation generating a metric calculation over a corresponding one of said plurality of discrete frequencies, each of said plurality of means for making said metric calculation includes a means for combining channel outputs of the same state and means for accumulating the combined outputs of the same state over all possible states, where a state s(n) at time n is defined as s(n)=[x(n),x(n−1), . . . , x(n−L+1)] and L is a number of past data symbols;
and
means supplied with said plurality of metric calculations for selecting a metric value calculation having a maximum magnitude, wherein the frequency over which said metric calculation having the maximum magnitude was made is the frequency offset estimate.

2 more elements

A method for use in a receiver including to generate a frequency offset estimate in response to a received signal comprising the steps of:

generating a plurality of frequency signals each having its own respective frequency;
mixing said received signal with said plurality of frequency signals on a one-to-one basis for generating a plurality of mixed signals, each of said mixed signals being a version of said received signal multiplied by a corresponding one of said plurality of frequency signals;
making a plurality of metric calculations, each metric calculation being of one of said mixed signals for generating a metric value over the frequency of said supplied mixed signal in accordance with prescribed criteria including obtaining a first sum ∑ n = 0 , n :
s ⁡ ( n ) = s N - 1 ⁢ r ⁡ ( n ) ⁢ ⅇ - j2π ⁢ ⁢ f 0 ⁢ n
and obtaining a second sum ∑ s = 0 2 L - 1 ⁢ [LeftBracketingBar] ∑ n = 0 , n :
s ⁡ ( n ) = s N - 1 ⁢ r ⁡ ( n ) ⁢ ⅇ - j2π ⁢ ⁢ f 0 ⁢ n [RightBracketingBar] ,
where r(n) is said received signal, s(n)is a state, L is a number of fast data symbols, N is a number of discrete frequencies, n is a time, e−j2πf0n is a discrete frequency and f0 is one of f1 through fN wherein a metric calculation is generated over each of said plurality frequencies;
and
selecting a metric calculation having a maximum magnitude, wherein the frequency over which said metric calculation having the maximum magnitude was made is the desired frequency offset estimate.

6 more elements

A method for use in a receiver to generate a frequency offset estimate in response to a received signal comprising the steps of:

generating a plurality of frequency signals each having its own respective discrete frequency;
mixing said received signal with said plurality of discrete frequency signals on a one-to-one basis for generating a plurality of mixed signals, each of said mixed signals being a version of said received signal multiplied by a corresponding one of said plurality of discrete frequency signals;
making a plurality of metric calculations, each metric calculation being over a supplied one of said mixed signals for generating a metric value over the frequency of said supplied mixed signal in accordance with prescribed criteria, wherein a metric calculation is generated over each of said plurality of discrete frequencies, each of said metric calculations including combining channel outputs of the same state and accumulating the combined outputs of the same state over all possible states, where a state s(n) at time n is defined as s(n)=[x(n),x(n−1), . . . , x(n−L+1)] and L is a number of past data symbols;
and
selecting a metric calculation having a maximum magnitude, wherein the frequency over which said metric calculation having the maximum magnitude was made is the desired frequency offset estimate.

2 more elements

Apparatus for use in a receiver to generate a frequency offset estimate in response to a received signal comprising:

a controllable oscillator being responsive to an error signal for generating a discrete frequency signal having a predetermined discrete frequency e−j2πf0n, where n is a time;
a mixing unit being supplied with said received signal and said discrete frequency signal for generating a mixed signal which is a version of said received signal multiplied by said discrete frequency signal;
a metric calculation unit being supplied with said mixed signal for generating a first metric value at the discrete frequency of said supplied mixed signal plus an incremental frequency value and for generating a second metric value at the discrete frequency of said supplied mixed signal minus an incremental frequency value in accordance with prescribed criteria, said metric calculation unit including a combiner for combining channel outputs of the same state and an accumulator for accumulating the combined outputs of the same state over all possible states, where a state s(n) at time n is defined as s(n)=[x(n),x(n−1), . . . , x(n−L+1)] and L is a number of past data symbols;
an algebraic combiner for algebraically subtracting said second metric value from said first metric value to generate a difference signal;
and
a filter supplied with said difference signal for yielding said error signal.

3 more elements

Apparatus for use in a receiver to generate a frequency offset estimate in response to a received signal comprising:

controllable means being responsive to an error signal for generating a discrete frequency signal having a predetermined discrete frequency e−j2πf0n, where n is a time;
means being supplied with a received signal and said discrete frequency signal for generating a mixed signal which is a version of said received signal multiplied by said discrete frequency signal;
means being supplied with said mixed signal for generating a first metric value at the discrete frequency of said supplied mixed signal plus an incremental frequency value and for generating a second metric value at the discrete frequency of said supplied mixed signal minus an incremental frequency value in accordance with prescribed criteria, said means for generating said first and second metric values including means for combining channel outputs of the same state and means for accumulating the combined outputs of the same state over all possible states, where a state s(n) at time n is defined as s(n)=[x(n),x(n−1), . . . , x(n−L+1)] and L is a number of past data symbols;
means for algebraically subtracting said second metric value from said first metric value to generate a difference signal;
and
means for filtering said difference signal to yield said error signal.

3 more elements

A method for use in a receiver to generate a frequency offset estimate in response to a received signal comprising the steps of:

controllably generating a frequency signal having a predetermined frequency;
generating a mixed signal which is a version of said received signal multiplied by said frequency signal;
generating a first metric value at the frequency of said supplied mixed signal plus an incremental frequency value in accordance with prescribed criteria;
generating a second metric value at the frequency of said supplied mixed signal minus an incremental frequency value in accordance with prescribed criteria;
algebraically subtracting said second metric value from said first metric value to generate a difference signal;
and
filtering said difference signal to yield said error signal,
each of said steps of generating said first and second metric values includes combining channel outputs of the same state and a step of accumulating the combined outputs of the same state over all possible states, where a state s(n) at time n is defined as s(n)=[x(n),x(n−1), . . . , x(n−L+1)] and L is a number of past data symbols.

5 more elements

Dependencies are inferred from the claim text.

Apparatus and method for generating a frequency offset estimate for communication systems having frequency selecting fading channels

Life of this patent

Apparatus and method for generating a frequency offset estimate for communication systems having frequency selecting fading channels

Life of this patent

Abstract

Claims39