VERTICAL HANDOVER METHOD FOR OVERLAY COMMUNICATION SYSTEM

• US 20080085712A1
• Filed: 09/27/2007
• Published: 04/10/2008
• Est. Priority Date: 10/10/2006
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: HAN, Jung
• Granted Patent: US 8,023,948 B2
• Time in Patent Office: Days
• US Class Current: 455/440
• CPC Class Codes: H04W 36/04 Reselecting a cell layer in multi-layered cells

Abstract

A vertical handover method in a heterogeneous overlay network communication system is provided. A vertical handover method for an overlay communication system including a plurality of base stations each serving at least one communication network technology to a mobile terminal includes determining whether a mobile terminal is located in a measurement region with reference to a vertical handover map in relation to a serving base station; detecting reachable base stations by activating all network interfaces when the mobile terminal locates in a measurement region; selecting one of the reachable base stations as a handover target base station; determining if the mobile terminal is located in a handover region with reference to the vertical handover map; and performing a handover if the mobile terminal is located in a handover region.

Claims

1. A vertical handover method for an overlay communication system including a plurality of base stations each providing at least one communication network technology to a mobile terminal, comprising:

determining if a mobile terminal is located in a measurement region with reference to a vertical handover map in relation to a serving base station;

detecting reachable base stations by activating all network interfaces when the mobile terminal is located in a measurement region;

selecting one of the reachable base stations as a handover target base station;

determining if the mobile terminal is located in a handover region with reference to the vertical handover map; and

performing a handover if the mobile terminal is located in a handover region.

2. The vertical handover method of claim 1, wherein determining if a mobile terminal is located in a measurement region comprises:

determining if {[D≧

D_advMT] or [L≧

L_advMT]} is satisfied, where D is a distance between the serving base station and the mobile terminal, L is a traffic load of the serving base station, D_advMT is a handover determination distance of the vertical handover map, and L_advMT is a handover determination traffic load of the vertical handover map.

3. The vertical handover method of claim 2, wherein D is calculated by

$\mathrm{distance}$

( D ) = [ RSS drop RSS ⁡

( N , w l ) ] 1 4 , 0 ≤

D ≤

1 ,

where RSS_drop is a minimum received signal strength (RSS) for maintaining a connection to the serving base station, RSS(N,w_I) is an average RSS, N is a number of samples, and w_I is a weight of I_th sample.

4. The vertical handover method of claim 2, wherein L is calculated by

$\mathrm{network}$

 

⁢

load ⁡

( L ) = RTT ⁡

( N , w l ) RTT drop , 0 ≤

L ≤

1 ,

where RTT_drop is a maximum round trip time for maintaining a connection to the serving base station, RTT(N,w_I) is an average RTT, N is a number of samples, and w_I is a weight of I_th sample.

5. The vertical handover method of claim 1, wherein detecting reachable base stations comprises determining if there is a base station satisfying {└

D_n<

D<sub>n—

MT</sub>┘ and

└

L_n<

L<sub>n—

MT</sub>┘

}, where D_n is a distance between the mobile terminal and n_th base station, L_n is a traffic load of n_th base station, D<sub>n—

MT</sub> is a reachable threshold distance, and L<sub>n—

MT</sub> is a reachable threshold traffic load of the n_th base station.

6. The vertical handover method of claim 5, wherein detecting reachable base station further comprises registering the reachable base station to a handover candidate base station list.

7. The vertical handover method of claim 1, wherein the handover target base station is selected by min{(D_l+L_l), . . . , (D_m+L_m)}, where D_m is a distance between the mobile terminal and m_th candidate base station, and Lm is a traffic load of m_th candidate base station.

9. A vertical handover method for an overlay communication system including a plurality of base stations each providing at least one communication network technology to a mobile terminal, comprising:

periodically measuring a received signal strength and a round trip time to a serving base station;

calculating an average distance between a serving base station and the mobile terminal and an average traffic load of the serving base station using the measured received signal strength and round trip time;

periodically comparing the average distance and the average traffic load to corresponding threshold values of a vertical handover map;

determining if the average distance and the average traffic load are greater than or equal to a measurement threshold distance and a measurement threshold traffic load, respectively;

detecting handover candidate base stations by activating all network interfaces if the average distance is greater than or equal to a measurement threshold distance or the average traffic load is greater than or equal to a measurement threshold traffic load;

selecting a candidate base station having an optimal condition as a handover target base station among the candidate base stations; and

performing a handover to the target base station if the average distance and the average traffic load exceeds a handover threshold distance or a handover threshold traffic load, respectively.

10. The vertical handover method of claim 9, wherein the vertical handover map is constructed in the form of a graph indexing the threshold values.

11. The vertical handover method of claim 9, wherein the vertical handover map is provided with a non-handover region, a measurement region, and a handover region that are defined by threshold distances between the mobile terminal and the network and threshold traffic loads.

12. A vertical handover method for an overlay communication system including a plurality of base stations each providing at least one communication network technology to a mobile terminal, comprising:

calculating a distance between the mobile terminal and a serving base station and a traffic load of the serving base station;

detecting handover candidate base stations if the distance is greater than a first threshold distance or the traffic load is greater than a first threshold traffic load;

generating a candidate base station list including the handover candidate base stations;

selecting a target base station from the candidate base station list if the distance is greater than a second threshold distance or the traffic load is greater than a second threshold traffic load; and

performing a handover to the target base station.

13. The vertical handover method of claim 12, wherein the second threshold distance is greater than the first threshold distance and the second threshold traffic load is greater than the first threshold traffic load

14. The vertical handover method of claim 12, wherein calculating a distance and a traffic load comprises:

measuring received signal strengths from the serving base station and round trip times of packets to the serving base station during a predetermined period of time;

averaging the received signal strengths and traffic loads; and

obtaining the distance and the traffic load based on the average received signal strength and the average round trip time.

15. The vertical handover method of claim 14, wherein generating a candidate base station list comprises:

determining if the distance is greater than or equal to a first threshold distance or the traffic load is greater than or equal to a first threshold traffic load;

activating all network interfaces if the distance is greater than or equal to a first threshold distance or the traffic load is greater than or equal to a first threshold traffic load;

determining, for each neighbor base station, whether a distance between the mobile terminal and the neighbor base station and a traffic load calculate on the basis of the received signal strength and the round trip time to each network interface, are less than a first threshold distance and a first threshold traffic load;

if the distance between the mobile terminal and the neighbor base station and the traffic load of the neighbor base station are less than the first threshold distance and traffic load, registering the neighbor base station to the candidate base station list.

16. The vertical handover method of claim 15, wherein performing a handover comprises:

determining if the distance is greater than or equal to the second threshold distance or the traffic load is greater than the second threshold traffic load; and

performing the handover to the target base station if the whether the distance is greater than or equal to the second threshold distance or the traffic load is greater than the second threshold traffic load.

17. A vertical handover method for an overlay communication system including a plurality of base stations each providing at least one communication network technology to a mobile terminal, comprising;

constructing a handover map in the form of a graph in which the X axis denotes a distance between the mobile terminal and a serving base station;

estimating a current distance between the mobile terminal and the serving base station and a traffic load of the serving base station;

projecting a coordinate consisting of the current distance and the traffic load to the handover map; and

performing a handover-related operation on the basis of a region of the handover map at which the coordinate is positioned.

18. The vertical handover method of claim 17, wherein the vertical handover map includes a non-handover region in which a communication channel with the serving base station is stable, a measurement region in which base station detection is performed, and a handover region in which a handover is executed, the regions being defined by the distance and traffic load in relation to the serving base station.

19. The vertical handover method of claim 17, wherein estimating a current distance and a traffic load comprises:

periodically measuring received signal strengths from the serving base station and traffic loads of the serving base station during a predetermined duration;

averaging the received signal strengths and the traffic loads; and

calculating the current distance and the traffic load based on the average signal strength and the average traffic load.

20. The vertical handover method of claim 17, wherein performing a handover-related operation comprises:

determining if the mobile terminal is located in a measurement region of the handover map;

obtaining a coordinate of a current position in handover maps of respective neighbor base stations by activating all network interfaces;

determining if a handover map exists in which the coordinate belongs to the non-handover region; and

registering the neighbor base stations of having the handover map in which the coordinate belongs to the non-handover region to a handover candidate list.

21. The vertical handover method of claim 20, wherein performing a handover-related operation further comprises:

determining if the coordinate if located in a handover region of the handover map;

selecting a handover target base station from the handover candidate list; and

executing a handover to the handover target base station.

22. The vertical handover method of claim 21, wherein selecting a handover target base station comprises:

comparing the distances of the handover candidate base stations with each other; and

choosing the candidate base station having the shortest distance as the handover target base station.

23. The vertical handover method of claim 22, wherein selecting a handover target base station further comprises:

determining if there are at least two candidate stations having the shortest distance; and

if there are at least two candidate stations having the least distance, choosing the candidate station having the least traffic load among the candidate stations having the shortest distance as the handover target base station.

24. The vertical handover method of claim 21, wherein selecting a handover target base station comprises:

comparing the traffic loads of the handover candidate base stations with each other; and

choosing the candidate base station having the smallest traffic load as the handover target base station.

25. The vertical handover method of claim 24, wherein selecting a handover target base station further comprises:

determining if there are at least two candidate stations having the smallest traffic load; and

if there are at least two candidate stations having the smallest traffic load, choosing the candidate station having the smallest distance among the candidate stations having the smallest traffic load as the handover target base station.