Patent ID: 8064911

Claim:
A vertical handoff method of a mobile station that can access a first network having relatively wide service coverage and a second network having relatively narrow service coverage in an area where service coverages of heterogeneous networks are overlapped, the vertical handoff method comprising: (a) determining a serving network of the mobile station; (b) when the serving network is the first network, deciding whether or not to perform first vertical handoff by using a prediction result of a transition pattern of a received signal strength (RSS) received from the second network when the received signal strength is greater than a first threshold value; and (c) when the serving network is the second network, deciding whether or not to perform second vertical handoff by using the prediction result of the transition pattern of the received signal strength received from the second network when the received signal strength is less than a second threshold value, wherein the first threshold value is greater than the second threshold value, and the prediction result of the transition pattern of the received signal strength comprises calculating linear square lines of the received signal strengths by using a least squares method, wherein when a slope of the linear square line has a positive (+) sign, predicting moving of the mobile station into the second network by the transition pattern, and wherein when a slope of the linear square line has a negative (−) sign, predicting moving of the mobile station out of the second network by the transition pattern, wherein the transition pattern is calculated using the formula { σ = ∑ i = 1 n ⁢ s i ⁢ ∑ i = 1 n ⁢ t i 2 - ∑ i = 1 n ⁢ t i ⁢ ∑ i = 1 n ⁢ t i ⁢ s i n ⁢ ∑ i = 1 n ⁢ t i 2 - ( ∑ i = 1 n ⁢ t ) 2 θ = n ⁢ ∑ i = 1 n ⁢ t i ⁢ s i - ∑ i = 1 n ⁢ t i ⁢ ∑ i = 1 n ⁢ s i n ⁢ ∑ i = 1 n ⁢ t i 2 - ( ∑ i = 1 n ⁢ t ) 2 where n denotes a total number of received signal strength detections for an accurate vertical handoff decision, and is based on an experimental result, t i denotes a predetermined time (i.e., X-axis) taken until termination of the detection of the received signal strength for the vertical handoff decision, Si denotes a received signal strength of a least squares line S, and corresponds to the Y-axis, σ denotes a crossing region of the least squares line S and the Y-axis, and θ denotes a slope of the least squares line S.