Frequency synchronization in wireless communication systems

1. A method of wireless communication over a communication link that comprises a plurality of sub-carriers, comprising:

providing, from a mobile unit to a base station, a pilot signal on a random access channel of the communication link, wherein the pilot signal comprises a sounding reference signal comprising at least one reference symbol; and

modifying, at the mobile unit, at least one frequency of at least one uplink sub-carrier in response to a signal transmitted to the mobile unit by the base station, the signal indicating a modification of said at least one frequency, the modification being determined by the base station based on a value of a frequency of the pilot signal measured at the base station, wherein the modification of said at least one frequency is determined by down-modulating the received frequency at an expected subcarrier frequency and estimating a frequency offset between the expected subcarrier frequency and said at least one frequency using autocorrelation properties of the at least one reference symbol in an equivalent complex baseband representation of the down-modulated signal.

2. The method of claim 1 , wherein providing the pilot signal comprises providing a non-synchronized signal on the random access channel prior to initialization of dedicated communication channels between the mobile unit and the base station.

3. The method of claim 2 , wherein modifying said at least one frequency comprises modifying said at least one frequency based upon a signal indicating a modification of said at least one frequency, the modification being determined based upon a measured value of the frequency of the non-synchronized signal provided on at least one of the random access channel and the dedicated channel.

4. The method of claim 1 , wherein modifying said at least one frequency comprises changing said at least one frequency of said at least one uplink sub-carrier by a percentage of said at least one frequency, the percentage being determined by a difference between the measured value of the frequency of the pilot signal and an expected value of the frequency of the pilot signal.

5. The method of claim 4 , wherein changing said at least one frequency by the percentage of said at least one frequency comprises changing said at least one frequency by a percentage of said at least one frequency that is within a selected range of frequency offsets.

6. The method of claim 4 , wherein modifying said at least one frequency comprises modifying said at least one frequency at one or more predetermined intervals or when a frequency error exceeds a predefined value.

7. The method of claim 1 , comprising providing at least one uplink signal using said at least one uplink sub-carrier having the modified frequency.

8. The method of claim 1 , comprising providing, from the mobile unit to the base station, at least one non-synchronized signal on at least one dedicated channel of the communication link and modifying, at the mobile unit, at least one frequency of at least one uplink sub-carrier in response to a signal transmitted to the mobile unit by the base station, the signal indicating a modification of said at least one frequency, the modification being determined by the base station based on a value of frequency of at least one non-synchronized signal measured at the base station.

9. A method of wireless communication over a communication link that comprises a plurality of sub-carriers, comprising:

receiving, from a mobile unit at a base station, a pilot signal on a random access channel of the communication link, wherein the pilot signal comprises a sounding reference signal comprising at least one reference symbol;

measuring, at the base station, a value of a frequency of the pilot signal; and

providing, from the base station to the mobile unit, a signal indicating a modification of at least one frequency of at least one uplink sub-carrier of the communication link, the modification being determined by the base station based on the measured value of the frequency of the pilot signal and by down-modulating the received frequency at an expected subcarrier frequency and estimating a frequency offset between the expected subcarrier frequency and said at least one frequency using autocorrelation properties of the at least one reference symbol in an equivalent complex baseband representation of the down-modulated signal.

10. The method of claim 9 , wherein receiving the pilot signal comprises receiving a non-synchronized signal on the random access channel prior to initialization of dedicated communication channels between the mobile unit and the base station.

11. The method of claim 9 , wherein determining the modification of said at least one frequency comprises determining a frequency error indicating a difference between a measured value of a frequency of the non-synchronized signal and an expected value of the frequency of the non-synchronized signal.

12. The method of claim 11 , wherein determining the modification of said at least one frequency comprises determining a modification of said at least one frequency that corresponds to a percentage of said at least one frequency, the percentage being determined by a difference between the measured value of the frequency of the pilot signal and an expected value of the frequency of the pilot signal.

13. The method of claim 12 , wherein determining the modification of said at least one frequency comprises determining a modification of said at least one frequency that corresponds to a percentage of said at least one frequency, the percentage being within a selected range of frequency offsets.

14. The method of claim 9 , comprising receiving at least one uplink signal transmitted by the mobile unit using said at least one uplink sub-carrier having the modified frequency.

15. The method of claim 9 , comprising determining the modification of said at least one frequency at one or more predetermined intervals or when a frequency error exceeds a predefined value.

16. The method of claim 9 , wherein providing the signal indicating the modification of said at least one frequency comprises providing the signal on a random access channel prior to initialization of dedicated communication channels between the mobile unit and the base station.