Handoff control method and communication system in a multiple frequency environment
First Claim
1. A method of operating a communication system comprising:
- controlling calls within a second cell controlled by a second base station using a second frequency group; and
controlling calls within a first cell with a first base station, wherein the second base station is adjacent to the first base station, wherein the first base station determines a virtual cell boundary within the first cell, wherein the first base station establishes calls within the virtual cell boundary using a first frequency group and calls outside the virtual cell boundary using the second frequency group, and wherein when a call using a frequency in the first frequency group moves to the second base station, the first base station controls a hard handoff procedure to a frequency in the second frequency group based on the virtual cell.
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Accused Products
Abstract
A handoff control method and communication system is provided that uses a virtual cell boundary in a multiple frequency environment. The handoff control method includes forming a virtual cell boundary using a frequency coexisting between a terminal base station on a boundary area of multiple frequency environment and an adjacent base station. Pre-determining a likelihood of handoff possibilities is then based on distance or round trip delay between the virtual cell boundary when establishing calls in the terminal base station to thereby assign different frequencies to the calls. When a call assigned as a frequency group having small handoff possibilities transitions to an object base station, a handoff time point is determined as the call approaches the virtual cell during movement to the object base station to control a hard handoff processing procedure between frequencies. Thus, the frequencies are assigned using information already in CDMA protocol messaging to accurately determine which and when established calls are to be handed-off to adjacent base stations. Accordingly, the percentage of successful handoffs is improved.
101 Citations
26 Claims
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1. A method of operating a communication system comprising:
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controlling calls within a second cell controlled by a second base station using a second frequency group; and controlling calls within a first cell with a first base station, wherein the second base station is adjacent to the first base station, wherein the first base station determines a virtual cell boundary within the first cell, wherein the first base station establishes calls within the virtual cell boundary using a first frequency group and calls outside the virtual cell boundary using the second frequency group, and wherein when a call using a frequency in the first frequency group moves to the second base station, the first base station controls a hard handoff procedure to a frequency in the second frequency group based on the virtual cell. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A communication system comprising:
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a first base station that control calls within a first cell using a first frequency group; and a terminal base station that controls calls within a second cell that is adjacent the first cell, wherein the terminal base station determines a virtual cell boundary within the second cell, wherein the terminal base station establishes calls within the virtual cell boundary using a second frequency group and calls outside the virtual cell boundary using the first frequency group, and wherein when a call using a frequency in the second frequency group moves to the first base station, the terminal base station controls a hard handoff processing procedure to a frequency in the first frequency group based on the virtual cell. - View Dependent Claims (19)
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20. A method of operating a communication system comprising:
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assigning a call to one of the first group and a second group of frequencies based on distance between an originating mobile station and a first base station; forming a virtual cell boundary based on the distance, wherein the first frequency group has an associated first probability of handoff and the second frequency group has a second associated probability of handoff, and wherein the first probability is less than the second probability; and determining a hard handoff time point based on the virtual cell boundary when the call assigned to the first frequency group is moved to a second adjacent base station to control a hard handoff processing procedure between the first group and the second group of frequencies, wherein the hard handoff processing procedure comprises a hard handoff by the first base station from the first frequency group to the second frequency group and then a soft handoff from the first base station to the second base station using a frequency of the second frequency group.
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21. A method of operating a communication system comprising:
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assigning a call to one of the first group and a second group of frequencies based on distance between an originating mobile station and a first base station; forming a virtual cell boundary based on the distance, wherein the first frequency group has an associated first probability of handoff and the second frequency group has a second associated probability of handoff, and wherein the first probability is less than the second probability; and determining a hard handoff time point based on the virtual cell boundary when the call assigned to the first frequency group is moved to a second adjacent base station to control a hard handoff processing procedure between the first group and the second group of frequencies, wherein the determining step comprises the steps of, reporting at a predetermined interval a call round trip delay value between the mobile station and the base station to a control station, and driving a timer of the predetermined period if the call round trip delay value approximates the virtual cell boundary value, wherein the driving a timer step includes repeatedly measuring the call round trip delay value during the operation interval of the timer to accumulate a total value and a number of measuring times to determine a mean round trip delay value when the operation interval of the time is complete to process the hard handoff between frequencies.
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22. A method of operating a communication system comprising:
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assigning a call to one of the first group and a second group of frequencies based on distance between an originating mobile station and a first base station; and forming a virtual cell boundary based on the distance, wherein the first frequency group has an associated first probability of handoff and the second frequency group has a second associated probability of handoff, and wherein the first probability is less than the second probability, wherein the forming step comprises the steps of, selecting a first call in the first base station within the second frequency group and generating a pilot strength measurement message when a corresponding mobile station moves to the second base station, comparing and analyzing the pilot strength measurement message and determining whether a second base station pilot signal is greater than a first prescribed value and whether a second base station object cell strength is greater than a serving pilot signal strength, if the comparing step is satisfied, processing a hard handoff by frame offset variation to establish a corresponding call in the second base station, accumulating a round trip delay value of the corresponding call if the hard handoff is processed and incrementing a counter, releasing the first call, obtaining a virtual cell boundary value by repeating the hard handoff process until the counter reaches a prescribed value, and calculating the virtual cell boundary value and the round trip delay value for use as a first base station parameter. - View Dependent Claims (23)
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24. A method of operating a communication system comprising:
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assigning a call to one of the first group and a second group of frequencies based on distance between an originating mobile station and a first base station; and forming a virtual cell boundary based on the distance, wherein the first frequency group has an associated first probability of handoff and the second frequency group has a second associated probability of handoff, wherein the first probability is less than the second probability, and wherein the assigning step comprises the steps of, receiving an originating call establishing message for the first base station, comparing a round trip delay value of the originated call with the virtual cell boundary to assign a frequency resource, and processing a hard handoff between frequencies within cells or soft handoff between base stations in accordance with the compared result of the round trip delay value of call and the virtual cell. - View Dependent Claims (25, 26)
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Specification