Method and apparatus for estimating carrier frequency offset and fading rate using autoregressive channel modeling

1. A method for use by a receiver ( 23 ) of a wireless communication system in providing information for use in adapting to changing characteristics of a communication channel ( 22 ) over which the receiver ( 23 ) receives a signal at a carrier frequency, the receiver ( 23 ) having a local oscillator oscillating at a local frequency initially tuned to a frequency suitable for receiving the carrier frequency, the method characterized by:

a step ( 23 b - 1 b 23 b - 2 b ), responsive to received signal samples extracted from the received signal and corresponding to transmitted symbols, of providing estimates of autoregressive parameters representing the changing communication channel ( 22 ) based on a predetermined parametric model of how as a result of stochastic processes the communication channel ( 22 ) changes over time; and

a step ( 23 b - 1 c 23 b - 2 c ), responsive to the estimated values of the autoregressive parameters, of providing an estimate of the channel impulse response and an estimate of a frequency offset of at least one multipath signal.

2. The method of claim 1 , wherein the estimates of autoregressive parameters are expectation maximization estimates.

3. The method of claim 1 , wherein in the step ( 23 b - 1 c 23 b - 2 c ) of providing an estimate of the channel impulse response and an estimate of a frequency offset of at least one multipath signal, an estimate of power spectral density is also provided.

4. The method of claim 1 , wherein in the step ( 23 b - 1 c 23 b - 2 c ) of providing an estimate of the channel impulse response and an estimate of a frequency offset of at least one multipath signal, an estimate of fading rate is also provided.

5. The method of claim 1 , wherein in the step ( 23 b - 1 c 23 b - 2 c ) of providing an estimate of the channel impulse response and an estimate of a frequency offset of at least one multipath signal, the receiver ( 23 ) uses the estimate of the channel impulse response to provide a value for at least either the offset or a fading rate for at least one multipath signal.

6. The method of claim 1 , wherein the predetermined parametric model is an autoregressive model providing linear equations describing the change over time of the communication channel ( 22 ), wherein at least one of the equations including a deterministic model matrix is used in determining a next state of the communication channel from a previous state based only on deterministic processes, and wherein the method is further characterized by obtaining at least either the offset or a fading rate from the deterministic model matrix.

7. The method of claim 6 , wherein the autoregressive model is a first-order frequency-flat autoregressive channel model having a single-component deterministic model matrix, and the fading rate and offset are given respectively by:

f

a

′

⁢

T

^

.

=

1

2

⁢

π

⁢

arccos

⁡

(

4

⁢



a

^



-

1

-



a

^



2

2

⁢



a

^



)

Ω

^

=

1

2

⁢

π

⁢

arg

⁡

(

a

^

)

,

in which â is the value of the single component of the deterministic model matrix.

8. The method of claim 6 , wherein the autoregressive model is a lightly damped second-order autoregressive channel model having a two-component deterministic model matrix, and the fading rate and offset are given respectively by:

f

d

⁢

T

^

=

1

2

⁢

π

⁢

arccos

⁡

(

a

^

1

2

⁢

(

a

^

2

)

)

Ω

^

=

1

2

⁢

π

⁢

(

arg

⁡

(

p2

)

+

(

arg

⁡

(

p1

)

+

arg

⁡

(

p2

)

)

/

2

)

in which:

p1

=

-

a

^

1

+

a

^

1

2

-

4

⁢

a

^

2

2

,

⁢

and

p2

=

-

a

^

1

+

a

^

1

2

-

4

⁢

a

^

2

2

,

and â 1 and â 2 are respectively the values of the first and second components of the deterministic model matrix.

9. The method of claim 1 , wherein the autoregressive parameters are determined using an iterative expectation-maximization method.

10. The method of claim 1 , wherein the autoregressive parameters are determined using a recursive gradient based method.

11. A receiver ( 23 ) of a wireless communication system comprising means for providing information for use in adapting to changing characteristics of a communication channel ( 22 ) over which the receiver ( 23 ) receives a signal at a carrier frequency, the receiver ( 23 ) having a local oscillator oscillating at a local frequency initially tuned to a frequency suitable for receiving the carrier frequency, the receiver ( 23 ) characterized by:

means ( 23 b - 1 b 23 b - 2 b ), responsive to received signal samples extracted from the received signal and corresponding to transmitted symbols, for providing estimates of autoregressive parameters representing the changing communication channel ( 22 ) based on a predetermined parametric model of how as a result of stochastic processes the communication channel ( 22 ) changes over time; and

means ( 23 b - 1 c 23 b - 2 c ), responsive to the estimated values of the autoregressive parameters, for providing an estimate of the channel impulse response and an estimate of a frequency offset of at least one multipath signal.

12. A telecommunication system, including a base transceiver station and a user equipment, both of which include a receiver ( 23 ), characterized in that both receivers ( 23 ) are as recited in claim 11 and so provide information of use in adjusting to changing parameters of the communication channel ( 22 ).

13. A telecommunication system, including a base transceiver station and a user equipment, both of which include a receiver ( 23 ), characterized in that both receivers ( 23 ) are as recited in claim 11 and so provide information of use in adjusting to changing parameters of the communication channel ( 22 ), and further comprising means ( 23 b - 1 c 23 b - 2 c ) for providing an estimate of fading rate, and wherein both the base transceiver station and the user equipment also include a transmitter (21) responsive to the information of use in adjusting to changing parameters of the communication channel ( 22 ).