Mobile communication switching across cell boundaries

• US 5,432,842 A
• Filed: 03/17/1992
• Issued: 07/11/1995
• Est. Priority Date: 03/19/1991
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Suzuki, Hideya, Nakasawa, Hideo, Kinoshita, Yasuaki, Kurosawa, Michiaki, Nakagoshi, Arata, Fujiwara, Yukinari
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): Bost, Dwayne D.
• Application Number:
  US07/852,810
• Time in Patent Office: 1,211 Days
• Field of Search: 379/59, 379/60, 455/33.1-33.4, 455/56.1, 342/357, 342/457
• US Class Current: 455/440
• CPC Class Codes: H04W 36/32 by location or mobility data, e.g. speed data
• CPC Class Codes: H04W 36/326 by proximity to another entity
• CPC Class Codes: H04W 52/0216 using a pre-established activity schedule, e.g. traffic indication frame
• CPC Class Codes: H04W 52/0219 where the power saving management affects multiple terminals
• CPC Class Codes: H04W 52/0245 according to signal strength
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

With respect to a mobile communication system, intelligence learns a cell boundary where the field strength of adjacent base stations becomes equal, by measuring field strength of communications, and from this data determined and stored over a period of time, the intelligence calculates the position and velocity vector of each mobile unit, from which a priority for hand-off can be determined. Hysteresis of the hand-off is determined with respect to hand-off boundaries located a fixed distance from the measured cell boundary, with hand-off preferably being soft hand-off within the narrow hand-off boundaries. Priority is particularly determined using fuzzy logic and calculation of the time estimated for the mobile unit to reach the cell boundary. Battery consumption of the mobile units is improved by prolonging the interval of checking the position of mobile units, when the mobile units are moving slowly or not moving at all. The determination of the cell boundary is updated continuously, to compensate for environment changes affecting field strength.

Claims

1. A mobile communication system, comprising:

a plurality of mobile units;

a plurality of base stations units;

means for providing two-way radio communication via radio channels between said the mobile units and said base station units;

said base station units being located to define a cell boundary of equal field strength of base station transmission radio communication between each two adjacent base station units;

means for determining and storing mobile unit position data with a reference representing field strength of radio communications from said base station units and each of said mobile units; and

means for initiating switching, in response to the positional data, a mobile unit from a radio channel of one of said adjacent base stations to a radio channel of the other of the adjacent base station units that belong to the cell boundary in response to determining that the mobile unit has crossed the cell boundary in the direction of said one to said other of the adjacent base station units and the field strength of the one of said adjacent base stations has thereafter decreased a fixed threshold amount that is sufficient to provide hysteresis in the switching with respect to the cell boundary.

2. The system of claim 1, wherein said means for storing uses the cell boundary as the reference.

3. The system of claim 2, wherein each of said base stations has means for measuring a line of equal field strength for the radio communication of the two adjacent base stations to the mobile units as the cell boundary.

4. The system of claim 1, wherein each of said base stations has means for measuring a line of equal field strength for the radio communication of the two adjacent base stations to the mobile units as the cell boundary.

5. The system of claim 1:

wherein each of said base stations include means for measuring and storing field strength data of the radio communication with the mobile units and updating the same continuously; and

each of said base stations include means for repeatedly determining the positional data of each mobile unit relative to the base stations in response to the updating of stored field strength data and with respect to the cell boundary.

6. The system of claim 5, including means for comparing the positional data of each of the mobile units over time for more than one of said base stations and thereby determining a velocity vector for each mobile unit.

7. A mobile communication system, comprising:

a plurality of mobile units;

a plurality of base stations units;

means for providing two-way radio communication via radio channels between said the mobile units and said base station units;

said base station units being located to define a cell boundary of equal field strength of base station transmission radio communication between each two adjacent base station units;

means for determining and storing mobile unit positional data with a reference representing field strength of radio communications from said base station units and each of said mobile units;

means for switching, in response to the positional data, a mobile unit from a radio channel of one of said adjacent base stations to a radio channel of the other of the adjacent base station units that belong to the cell boundary;

said means for determining and storing positional data continuously updating the positional data; and

fuzzy reasoning means for continuously updating the cell boundary between the adjacent base stations according to a membership function of an audio signal composite ratio obtainable from the positional data.

8. A mobile communication system, comprising:

a plurality of mobile units;

a plurality of base stations units;

means for providing two-way radio communication via radio channels between said the mobile units and said base station units;

said base station units being located to define a cell boundary of equal field strength of base station transmission radio communication between each two adjacent base station units;

means for determining and storing mobile unit positional data with a reference representing field strength of radio communications from said base station units and each of said mobile units;

means for switching, in response to the positional data, a mobile unit from a radio channel of one of said adjacent base stations to a radio channel of the other of the adjacent base station units that belong to the cell boundary;

said means for determining and storing continuously updating the positional data from field strengths of the two adjacent base stations; and

means, in response to the updated positional data, for repeatedly determining the cell boundary between two adjacent base stations where the respective field strengths are equal and storing the location of the cell boundary as an equistrength field cell boundary.

9. The system of claim 8, wherein said means for switching transferring a mobile unit from a channel of one of said adjacent base stations to a channel of the other of said adjacent base stations when the field strength of the radio communication of said one base station falls a substantial amount below the set reference value as received by the mobile unit, and similarly transferring a mobile unit from a channel of the other of said adjacent base stations to a channel of said one of the base stations when the field strength of the radio communication of said other base station falls a substantial amount below the set reference value as received by the mobile unit, with the substantial amount being sufficient to provide hysteresis in the transferring to overcome instability in the transferring.

10. The system of claim 8, wherein each of said base stations include means for measuring and storing field strength data of the radio communication with the mobile units and updating the same continuously.

11. A mobile communication system, comprising:

a plurality of mobile units;

a plurality of base stations units;

means for providing two-way radio communication via radio channels between said the mobile units and said base station units;

said base station units being located to define a cell boundary of equal field strength of base station transmission radio communication between each two adjacent base station units;

means for determining and storing mobile unit positional data with a reference representing field strength of radio communications from said base station units and each of said mobile units;

means for switching, in response to the positional data, a mobile unit from a radio channell of one of said adjacent base stations to a radio channell of the other of the adjacent base station units that belong to the cell boundary;

means for comparing the positional data of each of the mobile units over time for more than one of said base stations and thereby determining a velocity vector for each mobile unit;

means responsive to the positional data and the velocity vector of each of said mobile unbits and further responsive to the cell boundary for determining a mobile unit among the mobile units most urgently in need of switching from the channel of one base station to the channelof another adjacent base station and producing a corresponding urgency determination; and

said means for switching being responsive to the urgency determination.

12. A mobile communication system, comprising:

a plurality of mobile units;

a plurality of base stations units;

means for providing two-way radio communication via radio channels between said the mobile units and said base station units;

said base station units being located to define a cell boundary of equal field strength of base station transmission radio communication between each two adjacent base station units;

means for determining and storing mobile unit positional data with a reference representing field strength of radio communications from said base station units and each of said mobile units;

means for switching, in response to the positional data, a mobile unit from a radio channel of one of said adjacent base stations to a radio channel of the other of the adjacent base station units that belong to the cell boundary; and

fuzzy reasoning means responsive to the positional data for continuously determining the cell boundary between adjacent base stations.

13. A mobile communication system, comprising:

a plurality of mobile units;

a plurality of base station units;

means for providing two-way radio communication via radio channels between said mobile units and said base station units;

means for storing data defining a cell boundary between two adjacent base station units;

means for determining the position of each mobile unit relative to an adjacent cell boundary;

means for initiating switching one mobile unit from a radio channel of one of said adjacent base station units to a radio channel of the other of said adjacent base station units that belong to the cell boundary when the one mobile unit has crossed the cell boundary and moved toward the other of the adjacent base station units that belong to the cell boundary by a fixed threshold amount away from the cell boundary that is sufficient to provide hysteresis in the switching with respect to the cell boundary.

14. The mobile communication system according to claim 13, wherein said fixed threshold amount is a percentage of the filed strength of radio transmission.

15. The mobile communication system according to claim 13, wherein said fixed threshold amount is a fixed field strength amount of radio transmission.

16. The mobile communication system according to claim 13, wherein the cell boundary is an equal field strength line of radio communications between the two adjacent base station units.

17. The mobile communication system according to claim 13, wherein said cell boundary is fixed.

18. The mobile communication system according to claim 13, further including means for repeatedly gathering and storing updated information of field strength of radio transmission from said base station units to said mobile units relative to positions of said mobile units and repeatedly updating the position of the cell boundary in accordance with the updated information of field strength.

19. A mobile communication system, comprising:

a plurality of mobile units;

a plurality of base station units;

means for providing two-way radio communication via radio channels between said mobile units and said base station units;

means for storing data defining a cell boundary between each two adjacent base station units;

means for repeatedly determining updated positional data of each mobile unit relative to an adjacent cell boundary;

means for switching a mobile unit from a radio channel of one of said adjacent base station units to a radio channel of the other of said adjacent base station units that belong to the cell boundary in response to the cell boundary and the positional data; and

further including means for repeatedly gathering and storing updated information of field strength of radio communication between said base station units and said mobile units relative to positions of said mobile units and for repeatedly updating the stored cell boundary in accordance with the updated information of field strength.

20. A mobile communication system, comprising:

a plurality of mobile units;

a plurality of base station units;

means for providing two-way radio communication via radio channels between said mobile units and said base station units;

means for determining positional data of each mobile unit;

means for comparing positional data of each mobile unit at different times thereby determining and storing a velocity vector for each of said mobile units;

means for specifying at least one mobile unit needing urgent hand-off from among said mobile units on the basis of said velocity vectors;

means for normally switching each mobile unit from a radio channel of one of said base station units to a radio channel of another of said base station units on the basis of said positional data; and

means for priority switching said one mobile unit in priority over others of said mobile units from a radio channel of one of said base station units to a radio channel of another of said base station units in response to said means for specifying.

21. The mobile communication system of claim 20, wherein said means for normally switching performs soft hand-off type switching by switching each mobile unit having a received field strength of the one base station fall a fixed threshold value below a fixed field strength to the another of said base stations having a received field strength at least at the fixed field strength to provide hysteresis in the switching.

22. A mobile communication system, comprising:

a plurality of mobile units;

a plurality of base station units;

means for providing two-way radio communication via radio channels between said mobile units and said base station units;

means for repeatedly determining updated positional data of each mobile unit;

means for switching a mobile unit from a radio channel of one of said adjacent base station units to a radio channel of the other of said adjacent base station units in response to the positional data and in preference to other mobile units based upon a switching priority urgency value;

means for repeatedly comparing the updated positional data for each mobile unit over time to determine a velocity of movement of each of said mobile units; and

in response to the velocity of each of said mobile units, individually changing the switching priority urgency value and individually changing the frequency of updating the positional data for the corresponding mobile unit so that the switching occurs more quickly and the updating occurs more frequently for higher velocity mobile units.

23. The mobile communication system according to claim 22, wherein the velocity includes a velocity vector for each of said mobile units.

24. A mobile communication system, comprising:

a plurality of mobile units;

a plurality of base station units;

means for providing two-way radio communication via radio channels between said mobile units and said base station units;

means for storing data defining a cell boundary between each two adjacent base station units;

means for determining positional data of each mobile unit relative to an adjacent cell boundary;

means for switching a mobile unit from a radio channel of one of said adjacent base station units to a radio channel of the other of said adjacent base station units that belong to the cell boundary in response to an urgency value unique to each of said mobile units; and

means responsive to the positional data for determining the urgency value correlated to time for each mobile unit to reach a position for switching by said means for switching.