Method and arrangement for fast frequency searching in broadband mobile radio receivers

1. A method for searching for the carrier frequency f of a mobile radio transmitter in a mobile radio receiver, having the following steps:

a) measuring two or more values e(k) of a variable which is characteristic of the spectral reception power at various discrete test frequencies f k , with the test frequencies f k differing by multiples of a step width frequency Δ and with f k being less than f k+1 for all measured values e(k) and e(k+1);

b) searching for the maximum e(k max ) of the values e(k), with e(k max ) being associated with a specific test frequency f kmax ; and

c) determining of an estimated value f′, which is characteristic of the sought carrier frequency f, from knowledge of the values of at least one value pair e(k 1 ) and e(k 2 ) where k 1 <k max <k 2 , and of the specific test frequency f kmax .

2. The method according to claim 1 , wherein the determination of the estimated value f′ in step c) includes the following step:

determining an error variable S from knowledge of the values of the at least one value pair e(k 1 ) and e(k 2 ), where S represents a measure of the discrepancy between the respective values of the at least one value pair e(k 1 ) and e(k 2 ).

3. The method according to claim 2 , wherein k 1 =k max −1 and k 2 =k max +1.

4. The method according to claim 3 , wherein the error variable S is obtained using the following equation:

S

=

e

⁡

(

k

max

+

1

)

e

⁡

(

k

max

-

1

)

-

e

⁡

(

k

max

-

1

)

e

⁡

(

k

max

+

1

)

.

5. The method according to claim 2 , wherein the method for determination of the estimated value f′ of the carrier frequency in step c) uses an analytical equation, which the error variable S links either to the two variables of the estimated value f′ of the carrier frequency and the test frequency f kmax , or to the frequency mistuning f v , formed as the difference between f′ and f kmax .

6. The method according to claim 5 , wherein the analytical equation includes the following variables:

one or more variables for characterization of the form of the transmission spectrum and/or of the received spectrum, in particular the bandwidth of the transmission and/or received spectrum and/or the bandwidth of the transmission and/or reception filter.

7. The method according to claim 6 , wherein the estimated value f′ of the carrier frequency in step c) is obtained as follows:

f

′

=

f

k

⁢

⁢

max

+

B

-

Δ

S

⁢

(

4

+

S

2

-

2

)

,

where B indicates the bandwidth of the transmission and received spectrum.

8. The method according to claim 1 , wherein during the determination of the estimated value f′ of the carrier frequency in step c), either the measured values e(k) are corrected directly by the broadband white noise floor of the received spectrum or, correction terms which correspond to the broadband white noise floor are used in the calculation in step c).

9. The method according to claim 1 , wherein a radio signal strength indicator (RSSI) measurement is carried out in step a).

10. The method according to claim 1 , wherein an additional step d) is carried out after step c) which comprises:

a correlative frequency fine tuning process on the basis of a comparison of a synchronization sequence, which is contained in the received signal, and the synchronization sequence which is known in the receiver, taking into account the estimated value f′ of the carrier frequency as determined in step c).

11. The method according to claim 10 , wherein step d) is carried out as follows:

producing differently frequency-shifted signals s i based on the received signal, which are shifted with respect to the received signal by the estimated value f′ of the carrier frequency and multiples of a step width frequency Δ′, where Δ′<Δ;

determining two or more values of a variable c(i) which is characteristic of the correlation between the synchronization sequence which is contained in the respective signal s i and the synchronization sequence which is known in the receiver; and

determining a new estimated value f″, which is characteristic of the carrier frequency f, by evaluation of the values c(i).

12. A circuit arrangement for searching for the carrier frequency f of a mobile radio transmitter in a mobile radio receiver, comprising

a) a measurement device for measurement of two or more values e(k) of a variable which is characteristic of the spectral transmission power at different discrete test frequencies f k , with the test frequencies differing by multiples of a step width frequency Δ,

b) an evaluation device which determines the maximum e(k max ) of the values e(k), where e(k max ) is associated with a specific test frequency f kmax , and

c) a computation means which determines the estimated value f′ of the carrier frequency f from knowledge of the values of the at least one value pair e(k 1 ) and e(k 2 ) and of the test frequency f kmax , where k 1 <k max <k 2 .

13. The circuit arrangement according to claim 12 , wherein k 1 =k max −1 and k 2 =k max +1.

14. The circuit arrangement according to claim 12 , wherein the circuit arrangement further comprises:

d) a correlator for comparison of a synchronization sequence which is contained in the received signal and of the synchronization sequence which is known in the receiver,

e) a frequency shifting means for spectral shifting of the received signal, and

f) a second evaluation device, which compares the output variable from the correlator at different frequency shifts for frequency fine tuning.

15. The circuit arrangement according to claim 14 , wherein

the frequency shifting means produces differently frequency-shifted signals s i based on the received signal, which are shifted with respect to the received signal by the estimated value f′ of the carrier frequency and multiples of a step width frequency Δ′, where Δ′<Δ;

the correlator determines two or more values of a variable c(i) which is characteristic of the correlation between the synchronization sequence which is contained in the respective signal s i and the synchronization sequence which is known in the receiver; and

the second evaluation device determines a new estimated value f″, which is characteristic of the carrier frequency f, by evaluation of the values c(i).

16. The circuit arrangement according to claim 12 , wherein the measurement device carries out an radio signal strength indicator (RSSI) measurement.

17. The circuit arrangement according to claim 12 , wherein the circuit arrangement is used in a UMTS receiver.

18. A circuit arrangement for searching for the carrier frequency f of a mobile radio transmitter in a mobile radio receiver, comprising

a) a measurement device for measurement of two or more values e(k) of a variable which is characteristic of the spectral transmission power at different discrete test frequencies f k , with the test frequencies differing by multiples of a step width frequency Δ,

b) an evaluator which determines the maximum e(k max ) of the values e(k), where e(k max ) is associated with a specific test frequency f kmax , and

c) a processor which determines the estimated value f′ of the carrier frequency f from knowledge of the values of the at least one value pair e(k 1 ) and e(k 2 ) and of the test frequency f kmax , where k 1 <k max <k 2.

19. The circuit arrangement according to claim 18 , wherein k 1 =k max −1 and k 2 =k max +1.

20. The circuit arrangement according to claim 18 , wherein the circuit arrangement further comprises:

d) a correlator for comparison of a synchronization sequence which is contained in the received signal and of the synchronization sequence which is known in the receiver,

e) a frequency shifter for spectral shifting of the received signal, and

f) a second evaluator, which compares the output variable from the correlator at different frequency shifts for frequency fine tuning.