Method and system for estimating movement speed of mobile unit

1. A method for estimating a movement speed of a mobile unit in a mobile radio communication system, comprising:

(A) receiving a signal corresponding to a mobile unit transmitting signal;

(B) generating a first signal by using a first filter unit to filter said signal, said first filter unit having a first cut-off frequency;

(C) obtaining a first speed by estimating said movement speed based on said first signal;

(D) generating a second signal by using a second filter unit to filter said signal, said second filter unit having a second cut-off frequency, said second cut-off frequency being lower than said first cut-off frequency;

(E) obtaining a second speed by estimating said movement speed based on said second signal;

(F) selecting one of said first speed and said second speed to be said movement speed; and

(G) selecting said second speed as said movement speed if said first speed is slower than a predetermined speed.

2. The method of claim 1 , wherein said first cut-off frequency is 375 Hz, and said second cut-off frequency is 250 Hz.

3. The method of claim 2 , wherein said predetermined speed is 120 km/hour.

4. The method of claim 1 , wherein said first cut-off frequency is 250 Hz, and said second cut-off frequency is 125 Hz.

5. The method of claim 4 , wherein said predetermined speed is 60 km/hour.

6. The method of claim 1 , wherein said first cut-off frequency is 125 Hz, and said second cut-off frequency is 62.5 Hz.

7. The method of claim 6 , wherein said predetermined speed is 30 km/hour.

8. The method of claim 1 , wherein step (C) further comprises:

obtaining a first Doppler frequency according to the first signal; and

obtaining said first speed according to the first Doppler frequency.

9. The method of claim 1 , wherein step (E) further comprising:

obtaining a second Doppler frequency according to the second signal; and

obtaining said second speed according to the second Doppler frequency.

10. A system for estimating a movement speed of a mobile unit, comprising:

a receiving unit for receiving a signal corresponding to a transmitting signal of said mobile unit;

a first filter unit for filtering said signal to generate a first signal, said first filter unit having a first cut-off frequency, said first filter unit corresponding to a first speed zone;

a second filter unit for filtering said signal to generate a second signal, said second filter unit having a second cut-off frequency, said second filter unit corresponding to a second speed zone, a predetermined speed being located between a lower edge of the first of the first speed zone and a higher edge of the second speed zone;

an estimated unit for obtaining a first speed by estimating said movement speed based on said first signal, and obtaining a second speed by estimating said movement speed based on said second signal; and

a selecting unit for selecting said second speed as said movement speed if said first speed is slower than said predetermined speed.

11. The system of claim 9 , wherein said first cut-off frequency is 375 Hz, and said second cut-off frequency is 250 Hz.

12. The system of claim 11 , wherein said predetermined speed is 120 km/hour.

13. The system of claim 9 , wherein said first cut-off frequency is 250 Hz, and said second cut-off frequency is 125 Hz.

14. The system of claim 13 , wherein said predetermined speed is 60 km/hour.

15. The system of claim 9 , wherein said first cut-off frequency is 125 Hz, and said second cut-off frequency is 62.5 Hz.

16. The system of claim 15 , wherein said predetermined speed is 30 km/hour.