1. A wireless communication system comprising: at least one user equipment (UE); and an evolved universal terrestrial radio access network (E-UTRAN) including a source cell/Node-B and a target cell/Node-B, wherein the source cell/Node-B sends a handover command message to the UE when the E- UTRAN determines it is time to perform a handover, and the UE adjusts uplink transmission timing when sending an initial transmission to the target cell/Node-B immediately after handover based on information included in the command handover message.

2. The system of claim 1 wherein the handover command message indicates that a UE autonomous tuning advance measurement is to be performed during handover.

3. The system of claim 2 wherein the handover command message further indicates a time difference between the source cell/Node-B and the target cell/Node-B.

4. The system of claim 2 wherein the handover command message further indicates that that the source cell/Node-B and the target cell/Node-B are synchronized.

5. The system of claim 1 wherein the handover command message indicates whether the UE should access the target cell/Node-B via at least one pre-allocated non-contention based radio resource in the target cell/Node-B.

6. The system of claim 1 wherein the handover command message indicates whether the UE should access the target cell/Node-B via a synchronous random access channel (RACH) with an applied timing advance value autonomously computed by the UE.

7. The system of claim 1 wherein the handover command message includes pre-allocated uplink non-contention based radio resource information.

8. The system of claim 7 wherein the handover command message indicates whether at least one pre-allocated uplink non-contention based radio resource will be used for a resource request or direct data transmissions to the target cell/Node-B.

9. The system of claim. 7 wherein the handover command message indicates an amount of pre-allocated uplink non-contention based radio resources and the life-span of the radio resources

10. The system of claim 1 wherein when the UE receives the handover command message, the UE performs one or more measurements to determine a difference in propagation delays between the source cell/Node-B and the target cell/Node-B

11. The system of claim 10 wherein the measurements are performed on beacon channel reference signals of the source cell/Node-B and the target cell/Node-B

12. The system of claim 11 wherein each beacon channel reference signal is comprised by a synchronization channel (SCH)

13. The system of claim 1 wherein the UE performs one or more measurements to determine a difference in a first significant path between the source cell/Node-B and the target cell/Node-B

14. The system of claim 1 wherein the UE autonomously computes a timing advance value to adjust the uplink transmission timing

15. The system of claim 1 wherein the UE uses pre-allocated non- contention based radio resources indicated by the information in the handover command message to adjust the uplink transmission timing

16. The system of claim 1 wherein radio resource control (RRC) signaling is used to send the handover command message

17. The system of claim 1 wherein the UE autonomously determines an amount of timing advance to adjust the uplink transmission timing based on reference signals of beacon channels associated with the source cell/Node-B and the target cell/Node-B

18. The system of claim 17 wherein the UE determines an initial difference in range between the UE and the source and target cells/Node-Bs

19. The system of claim 1 wherein the UE computes an initial timing advance value and sends a scheduling request message with the computed initial timing advance value through pre-allocated uplink non-contention based radio resources.

20. The system of claim 1 wherein the UE computes an initial timing advance value and sends a scheduling request message with the computed initial timing advance value through a synchronous random access channel (RACH) to the E-UTRAN.

21. The system of claim 20 wherein the E-UTRAN computes a refined time advance value that is more accurate than the initial timing advance value in response to receiving the scheduling request message, and the E-UTRAN signals the refined timing advance value and assignment of uplink radio resources to the UE via downlink signaling.

22. The system of claim 20 wherein the E-UTRAN sends the refined timing advance value and assignment of uplink radio resources to the UE via downlink signaling in a radio resource control (RRC) message, or via layer 1 (Liyiayer 2 (L2) signaling.

23. The system of claim 21 wherein the UE sends an initial transmission to the target cell/Node-B using the refined timing advance value and the assigned uplink radio resources.

24. The system of claim 1 wherein the system is a long term evolution (LTE) system.

25. A long term evolution (LTE) handover method which is implemented in a wireless communication system including at least one user equipment (UE) and an evolved universal terrestrial radio access network (E- UTRAN) including a source cell/evolved Node-B (eNB) and a target cell/eNB, the method comprising: the source cell/eNB sending a handover command message to the UE when the E-UTRAN determines it is time to perform a handover; and the UE adjusting uplink transmission timing when sending an initial transmission to the target cell/eNB immediately after handover based on information included in the command handover message.

26. The method of claim 25 wherein the handover command message indicates that a UE autonomous timing advance measurement is to be performed during handover.

27. The method of claim 26 wherein the handover command message further indicates a time difference between the source cell/eNB and the target cell/eNB.

28. The system of claim 26 wherein the handover command message further indicates that that the source cell/eNB and the target cell/eNB are synchronized.

29. The method of claim 25 wherein the handover command message indicates whether the UE should access the target cell/eNB via at least one pre-allocated non-contention based radio resource in the target cell/eNB.

30. The method of claim 25 wherein the handover command message indicates whether the UE should access the target cell/eNB via a synchronous random access channel (RACH) with an applied timing advance value autonomously computed by the UE.

31. The method of claim 25 wherein the handover command message includes pre-allocated uplink non-contention based radio resource information.

32. The method of claim 31 wherein the handover command message indicates whether at least one pre-allocated non-contention based uplink radio resource will be used for a resource request or direct data transmissions to the target cell/eNB.

33. The method of claim 31 wherein the handover command message indicates an amount of pre-allocated uplink non-contention based radio resources and the life-span of the radio resources.

34. The method of claim 25 further comprising: the UE receiving the handover command message; and the UE performing one or more measurements to determine a difference in propagation delays between the source cell/eNB and the target cell/eNB.

35. The method of claim 34 wherein the measurements are performed on beacon channel reference signals of the source cell/eNB and the target cell/eNB.

36. The method of claim 35 wherein each beacon channel reference signal is comprised by a synchronization channel (SCH).

37. The method of claim 25 further comprising: the UE performing one or more measurements to determine a difference in a first significant path between the source cell/eNB and the target cell/eNB.

38. The method of claim 25 wherein the UE autonomously computes a timing advance value to adjust the uplink transmission timing.

39. The method of claim 25 wherein the UE uses pre-allocated non- contention based radio resources indicated by the information in the handover command message to adjust the uplink transmission timing.

40. The method of claim 25 wherein radio resource control (RRC) signaling is used to send the handover command message.

41. The method of claim 25 further comprising: the UE autonomously determining an amount of timing advance to adjust the uplink transmission timing based on reference signals of beacon channels associated with the source cell/eNB and the target cell/eNB.

42. The method of claim 41 further comprising: the UE determining an initial difference in range between the UE and the source and target cells/eNBs.

43. The method of claim 25 further comprising: the UE computing an initial timing advance value; and the UE sending a scheduling request message with the computed initial timing advance value through pre-allocated uplink non-contention based radio resources.

44. The method of claim 25 further comprising: the UE computing an initial timing advance value; and the UE sending a scheduling request message with the computed initial timing advance value through a synchronous random access channel (RACH) to the E-UTRAN.

45. The method of claim 44 further comprising: the E-UTRAN receiving the scheduling request message; the E-UTRAN computing a refined time advance value that is more accurate than the initial timing advance value; and the E-UTRAN signaling the refined timing advance value and assignment of uplink radio resources to the UE via downlink signaling.

46. The method of claim 44 wherein the E-UTRAN sends the refined timing advance value and assignment of uplink radio resources to the UE via downlink signaling in a radio resource control (RRC) message, or via layer 1 (Liyiayer 2 (L2) signaling.

47. The method of claim 45 further comprising: the UE sending an initial transmission to the target cell/eNB using the refined timing advance value and the assigned uplink radio resources.

48. A long term evolution (LTE) handover method which is implemented in a wireless communication system including at least one wireless transmit/receive unit (WTRU) and an evolved universal terrestrial radio access network (E-UTRAN) including a source cell/evolved Node-B (eNB) and a target cell/eNB, the method comprising: the source cell/eNB sending a handover command message to the WTRU when the E-UTRAN determines it is time to perform a handover; the WTRU autonomously computing an initial timing advance value; the WTRU sending a scheduling request message with the computed first timing advance value through a synchronous random access channel (RACH) to the E-UTRAN; and the E-UTRAN computing a refined tune advance value that is more accurate than the initial timing advance value based on information in the scheduling request message.

49. The method of claim 48 further comprising: the E-UTRAN sending the refined timing advance value to the WTRU in a downlink signaling message; the E-UTRAN assigning uplink and/or downlink radio resources for use by the UE for subsequent data transmissions; and the WTRU sending an initial transmission to the target cell/eNB using the refined timing advance value and the assigned uplink and/or downlink radio resources.

50. A wireless communication system comprising: at least one wireless transmit/receive unit (WTRU); and an evolved universal terrestrial radio access network (E-UTRAN) including a source cell/evolved Node-B (eNB) and a target cell/eNB, wherein the source cell/eNB sends a handover command message to the WTRU when the E-UTRAN determines it is time to perform a handover, the WTRU autonomously computes an initial timing advance value, the WTRU sends a scheduling request message with the computed first timing advance value through a synchronous random access channel (RACH) to the E-UTRAN, and the E-UTRAN computes a refined time advance value that is more accurate than the initial timing advance value based on information in the scheduling request message.

51. The system of claim 50 wherein the E-UTRAN sends the refined timing advance value to the WTRU in a downlink signaling message, the E- UTRAN assigns uplink and/or downlink radio resources for use by the WTRU for subsequent data transmissions, and the WTRU sends an initial transmission to the target cell/eNB using the refined timing advance value and the assigned uplink and/or downlink radio resources.']