1. A method for a serving base station to enable a mobile station existing in a serving cell area to perform a handover procedure in a broadband wireless communication system including the mobile station, the serving base station providing a service to the mobile station in the serving cell area, and at least one target base station adjacent to the serving base station, the method comprising the steps of: determining a handover when the serving base station needs to make the mobile station performed the handover procedure; notifying one of the target base stations to perform the handover procedure; and transmitting a handover message to the mobile station including forced handover information signifying that the serving base station commands the mobile station to be handed over to the notified target base station.

2. The method as claimed in Claim 1, wherein a predetermined field in the handover message includes one bit representing the forced handover information.

3. The method as claimed in Claim 2, wherein another value of the one bit represents a suggested handover information. When the one bit represents the suggested handover information, the handover message includes a list of the target base stations possible to perform the handover procedure and the mobile station is able to choose one target base station in the list.

4. The method as claimed in Claim 1, further comprising: receiving a handover indication message from the mobile station; and releasing a link with the mobile station.5. The method as claimed in Claim 4, wherein the handover indication message includes a handover indicator type field representing a normal handover.

5. The method as claimed in Claim 4, wherein the handover indication message includes a handover indicator type field representing a normal handover.

6. The method as claimed in Claim 1, wherein the step of notifying one of the target base stations comprise: transmitting a handover notification message to the target base stations; receiving a handover notification response message from the target base stations; and transmitting a handover confirm message to one of the target base stations.

7. A method for handover of a mobile station located in a serving cell area of a serving base station in a broadband wireless communication system including the mobile station, the serving base station, and at least one target base station having a target cell area adjacent to the serving cell area, the serving base station providing a service to the mobile station in the serving cell area, the method comprising the steps of: receiving a message including handover information from the serving base station; confirming by the mobile station the handover information in the message, and releasing link between the mobile station and the serving base station when the message is a forced handover indication message; and performing handover toward one handover- executable target base station included in the message.

8. The method as claimed in Claim 7, wherein a predetermined field in the handover message includes one bit representing forced handover indicating information.

9. The method as claimed in Claim 7, wherein, when the confirmed handover information is a proposed handover message, handover-executable target base stations included in the message are confirmed, one optimum base station is selected from handover-executable target base stations, and handover to the optimum base station is performed

10. A method for a mobile station to enable a mobile station existing in a serving cell area to perform a handover procedure in a broadband wireless communication system including the mobile station, a serving base station providing a service to the mobile station in the serving cell area, and one or more target base stations adjacent to the serving base station, the method comprising the steps of: transmitting a handover request message to the serving base station when it is detected that a handover is necessary; and transmitting a handover indication message including handover cancellation information to the serving base station when the mobile station decides to cancel the handover during a time period in which the mobile station performs the handover to one of the target base stations

11. The method as claimed in Claim 10, further comprising: receiving a scanning permission message for a carrier to interference and noise ratio (CINR) of the target base stations from the serving base station; and scanning the carrier to interference and noise ratio of the target base stations in response to the scanning permission message, and storing information on the carrier to interference and noise ratio of the target base stations according to a result of the scanning

12. The method as claimed in Claim 10, wherein a predetermined handover indicator type field located in the handover indication message includes the handover cancellation information represented by two bits

13. The method as claimed in Claim 10, wherein the mobile station determines to perform a handover procedure when a carrier to interference and noise ratio (CINR) of the serving base station is less than a first threshold value

14. The method as claimed in Claim 10, wherein the mobile station determines to perform a handover procedure when a carrier to interference and noise ratio (CINR) of the serving base station is less than a carrier to interference and noise ratio (CINR) of a selected one of the target base stations

15. The method as claimed in Claim 10, wherein the mobile station decides to cancel a handover procedure when a carrier to interference and noise ratio (CINR) of the serving base station is more than a second threshold value during the handover

16. The method as claimed in Claim 10, wherein the mobile station decides to cancel a handover procedure when a carrier to interference and noise ratio (CINR) of the serving base station is more than a carrier to interference and noise ratio (CINR) of a selected one of the target base stations during a performance of the handover

17. A method for performing handover by a serving base station in a broadband wireless communication system including a mobile station, the serving base station, and at least one target base station having a target cell area station adjacent to a serving cell area of the serving base station, the serving base station providing a service to the mobile station located in the serving cell area, the method comprising the steps of: progressing handover process between the serving base station and the target base station after receiving a handover request message from the mobile station; canceling the handover process when the serving base station has received a handover cancellation message including handover cancellation information from the mobile station while the handover process is in progress; and maintaining link between the mobile station and the serving base station after the serving base station cancels the handover process

18. The method as claimed in Claim 17, wherein the handover cancellation message is a message transmitted from the mobile station in order to stop the handover process before the mobile station receives a handover response message including a list of target base stations

19. The method as claimed in Claim 17, wherein the serving base station ends the handover process when the serving base station has received the handover cancellation message before transmitting a handover confirm message for the handover progress to the target base station.

20. The method as claimed in Claim 17, further comprising a step of transmitting the handover cancellation message from the serving base station to the target base station after transmitting a handover confirm message for the handover progress to the target base station, when the serving base station has received the handover cancellation message from the mobile station.

21. The method as claimed in Claim 20, wherein the handover cancellation message includes a predetermined handover indication type field of two bits.

22. A method for a mobile station to enable a mobile station existing in a serving cell area to perform a handover procedure in a broadband wireless communication system including the mobile station, a serving base station providing a service to the mobile station in the serving cell area, and one or more target base stations adjacent to the serving base station, the method comprising the steps of: transmitting a handover request message to the serving base station when it is detected that a handover is necessary; receiving a first handover response message from the serving base station; and transmitting a handover indication message including handover rejection information to the serving base station when the mobile station determines a rejection of the handover after receiving the handover response message.

23. The method as claimed in Claim 22, further comprising the steps of: receiving a scanning permission message for a carrier to interference and noise ratio of the target base stations from the serving base station; and scanning the carrier to interference and noise ratio of the target base stations in response to the scanning permission message, and storing information on the carrier to interference and noise ratio of the target base stations according to a result of the scanning.

24. The method as claimed in Claim 22, wherein the first handover response message includes information on the target base stations capable of providing a service to the mobile station from among the target base stations.

25. The method as claimed in Claim 22, wherein a predetermined handover indicator type field in the handover indication message includes the handover rejection information represented by two bits.

26. The method as claimed in Claim 22, wherein the mobile station determines to perform a handover procedure when a carrier to interference and noise ratio (CINR) of the serving base station is less than a first threshold value.

27. The method as claimed in Claim 22, wherein the mobile station determines to perform a handover procedure when a carrier to interference and noise ratio (CINR) of the serving base station is less than a carrier to interference and noise ratio (CINR) of a selected one of the target base stations.

28. The method as claimed in Claim 22, wherein the mobile station retransmits the handover request message after transmitting the handover indication message including the handover rejection information.

29. The method as claimed in Claim 22, further comprises: receiving a second handover response message includes a list of the target base stations according to a result of scanning a carrier to interference and noise ratio (CINR) of the target base stations from the serving base station after transmitting the handover indication message including the handover rejection information.

30. A method for performing handover by a serving base station in a broadband wireless communication system including a mobile station, the serving base station, and at least one target base station having a target cell area station adjacent to a serving cell area of the serving base station, the serving base station providing a service to the mobile station located in the serving cell area, the method comprising the steps of: progressing handover process between the serving base station and the target base station after receiving a handover request message from the mobile station; stopping the handover process when the serving base station has received a handover rejection message including handover rejection information from the mobile station while the handover process is in progress; and transmitting a list of the target base stations from the serving base station to the mobile station after the serving base station stops the handover process.

31. The method as claimed in Claim 30, further comprising a step of transmitting a handover response message from the serving base station to the mobile station, the handover response message including information about at least one base station from among the target base stations, which can provide service to the mobile station.

32. The method as claimed in Claim 30, wherein the handover rejection message is a message transmitted to the serving base station in order to stop the handover process after the mobile station receives the handover response message including the list of the target base stations.

33. The method as claimed in Claim 30, wherein the handover rejection message includes a predetermined handover indication type field of two bits.

34. The method as claimed in Claim 30, wherein the serving base station maintains link between the serving base station and the mobile station and transmits a message reporting stop of the handover process to the target base stations, when the serving base station has received the handover rejection message from the mobile station.

35. A method for a mobile station to enable a mobile station existing in a serving cell area to perform a handover procedure in a broadband wireless communication system including the mobile station, a serving base station providing a service to the mobile station in the serving cell area, and one or more target base stations adjacent to the serving base station, the method comprising the steps of: receiving a handover request message from the serving base station and performing the handover procedure; and transmitting a handover indication message including handover cancellation information to the serving base station when the mobile station decides to cancel the handover during a time period in which the mobile station performs the handover to one of the target base stations.

36. The method as claimed in Claim 35, wherein the mobile station decides to cancel a handover procedure when a carrier to interference and noise ratio (CINR) of the serving base station is more than a predetermined threshold value during the handover.

37. The method as claimed in Claim 35, wherein the mobile station decides to cancel a handover procedure when a carrier to interference and noise ratio (CINR) of the serving base station is more than a carrier to interference and noise ratio (CINR) of a selected one of the target base stations during a performance of the handover.

38. A method for performing handover by a serving base station in a broadband wireless communication system including a mobile station, the serving base station, and at least one target base station having a target cell area station adjacent to a serving cell area of the serving base station, the serving base station providing a service to the mobile station located in the serving cell area, the method comprising the steps of: transmitting a handover request message from the serving base station to the mobile station and progressing handover process between the serving base station and the target base station; canceling the handover process when the serving base station has received a handover cancellation message including handover cancellation information from the mobile station while the handover process is in progress; andmaintaining link between the mobile station and the serving base station after the serving base station cancels the handover process.

39. The method as claimed in Claim 38, wherein the serving base station ends the handover process when the serving base station has received the handover cancellation message before transmitting a handover confirm message for the handover progress to the target base station.

40. The method as claimed in Claim 38, further comprising a step of transmitting the handover cancellation message to the target base station when the serving base station has received the handover cancellation message after transmitting a handover confirm message for the handover progress to the target base station.

41. A method for a mobile station to enable the mobile station existing in a serving cell area to perform a handover procedure in a broadband wireless communication system including the mobile station, a serving base station providing a service to the mobile station in the serving cell area, and one or more target base stations adjacent to the serving base station, the method comprising the steps of: receiving a handover request message including a list of the target base stations from the serving base station ; and transmitting a handover indication message including handover rejection information to the serving base station when the mobile station determines a rejection of the handover after checking the list of the target base stations.

42. The method as claimed in Claim 41, further comprising the steps of: receiving a scanning permission message for a carrier to interference and noise ratio (CINR) of the target base stations from the serving base station; and scanning the carrier to interference and noise ratio (CINR) of the target base stations in response to the scanning permission message, and storing information on the carrier to interference and noise ratio (CINR) of the target base stations according to a result of the scanning.

43. The method as claimed in Claim 41, wherein the handover request message includes information on the list of the target base stations capable of providing a service to the mobile station from among the target base stations.

44. The method as claimed in Claim 41, further comprising the steps of: transmitting a handover request message to the serving base station after transmitting the handover indication message including the handover rejection information. receiving a handover response message includes an updated list of the target base stations according to a result of scanning a carrier to interference and noise ratio (CINR) of the target base stations from the serving base station after transmitting the handover request message.

45. A method for performing handover by a serving base station in a broadband wireless communication system including a mobile station, the serving base station, and at least one target base station having a target cell area station adjacent to a serving cell area of the serving base station, the serving base station providing a service to the mobile station located in the serving cell area, the method comprising the steps of: transmitting a handover request message from the serving base station to the mobile station and progressing handover process between the serving base station and the target base station, the handover request message including a list of the target base stations; stopping the handover process when the serving base station has received a handover rejection message including handover rejection information from the mobile station while the handover process is in progress; and transmitting a new list of the target base stations from the serving base station to the mobile station.

46. The method as claimed in Claim 45, wherein the serving base station maintains link between the serving base station and the mobile station and transmits a message reporting stop of the handover process to the target base stations for performing the handover process, when the serving base station has received the handover rejection message from the mobile station.']