Multilayered arrangement for load sharing in a cellular communication system

• US 5,633,915 A
• Filed: 05/16/1995
• Issued: 05/27/1997
• Est. Priority Date: 05/16/1995
• Status: Expired due to Fees

• Current Assignee: Southern Methodist University
• Original Assignee: Southern Methodist University
• Inventors: Yang, Cheng, Matula, David W.
• Primary Examiner(s): CUMMING, WILLIAM D
• Application Number:
  US08/442,336
• Time in Patent Office: 742 Days
• Field of Search: 379/58, 379/60
• US Class Current: 455/443
• CPC Class Codes: H04W 16/06 Hybrid resource partitioning, e.g. channel borrowing
• CPC Class Codes: H04W 16/32 Hierarchical cell structures
• CPC Class Codes: H04W 28/0861 between base stations
• CPC Class Codes: H04W 72/0453 Resources in frequency domain, e.g. a carrier in FDMA
• CPC Class Codes: H04W 72/21 in the uplink direction of a wireless link, i.e. towards the network

Abstract

A multiple-layered cellular communication system particularly adapted to mobile phones and LAN type communication is provided with an overlaid arrangement of cell transceivers. By having this overlay, multiple service providers can provide a cooperative method of load sharing. The usage of the frequency spectrum can be improved and an advanced hand-off arrangement can be used to prevent or reduce the possibility of blocked calls due to cell saturation.

Claims

1. A cellular communication system for communicating with mobile phones comprising:

a plurality of base stations, for communicating with said mobile phones, each of said base stations coupled to a plurality of transceivers, each of said plurality of transceivers defining a cell in which the transceiver selectively provides frequency channel assignments to said mobile phones within said cell, the cells being arranged in a cellular pattern, said transceivers covering a geographic service area and being partitioned such that respective cells form plural cellular layers of communication, each of the plural cellular layers substantially covering all of said geographic service area;

substantially all of the cells of each of the plural cellular layers overlapping a plurality of cells in each other cellular layer such that at least first and second transceivers from different cellular layers of the plural cellular layers selectively provide a frequency channel assignment to a requesting mobile phone requesting a frequency channel assignment within the geographic service area; and

a means to select between said at least first and second transceivers from the different cellular layers based on load balancing between said at least first and second transceivers such that a selected one of said at least first and second transceivers and a corresponding base station of said plurality of base stations provide said frequency channel assignment for said requesting mobile phone.

2. A system as in claim 1, wherein the number of cellular layers is at least three.

3. A system as in claim 1, wherein the service provided by each cellular layer is from a different service provider.

4. A system as in claim 1, wherein said plural cellular layers are arranged such that corresponding cells of a first cellular layer are offset geographically from corresponding cells of a second cellular layer by substantially one cell radius.

5. A system as in claim 1, wherein said means to select includes means for obtaining said frequency channel assignment for said requesting mobile phone by causing the selected transceiver to hand-off another mobile phone that is currently assigned said frequency channel assignment to another frequency channel assignment provided by a third transceiver defining a respective cell in one of the plural cellular layers, said requesting mobile phone being outside the cell of said third transceiver.

6. A method of assigning a frequency channel to a requesting mobile phone requesting a frequency channel assignment in a cellular communication system that includes a plurality of base stations, each base station coupled to a plurality of transceivers, the cellular communication system including first and second transceivers, each transceiver defining a respective cell in which the transceiver selectively provides frequency channel assignments to requesting mobile phones within said cell, such cells being arranged in an overlapping cellular pattern covering a geographic service area, said overlapping cellular pattern being arranged such that each cell overlaps a plurality of other cells, thereby defining a plurality of respective overlap regions such that, within a given overlap region, a requesting mobile phone is able to receive a frequency channel assignment from any transceiver defining a respective cell covering said given overlap region, the method comprising the steps of:

assigning to a first requesting mobile phone a first frequency channel assignment from said first transceiver, said first requesting mobile phone being within an overlap region defined by said first and second transceivers;

receiving at said first transceiver a request for a new frequency channel assignment from a second requesting mobile phone that is within the cell of said first transceiver but is not within said overlap region defined by said first and second transceivers; and

responsive to receiving the request from said second requesting mobile phone, the method further comprising the sub-steps of;

handing-off said first requesting mobile phone to a second frequency channel assignment from said second transceiver;

releasing said first frequency channel assignment; and

reassigning said first frequency channel assignment to said second requesting mobile phone.

7. A method of assigning a frequency channel to a requesting mobile phone requesting a frequency channel assignment in a cellular communication system that includes a plurality of base stations, each base station coupled to a plurality of transceivers, each transceiver defining a respective cell, the cellular communication system including first, second and third transceivers defining respective first, second and third cells, each of the first, second and third transceivers selectively providing frequency channel assignments to requesting mobile phones within the respective first, second and third cells, the first, second and third cells being arranged in an overlapping cellular pattern covering a geographic service area, said overlapping cellular pattern being arranged such that each cell overlaps a plurality of other cells, thereby defining a plurality of respective overlap regions such that, within a given overlap region, a requesting mobile phone is able to receive a frequency channel assignment from a transceiver for any cell covering such overlap region, the method comprising the steps of:

assigning to a first requesting mobile phone a first frequency channel assignment from said first transceiver, said first requesting mobile phone being within a first overlap region defined by an overlap of the first cell defined by said first transceiver and the second cell defined by said second transceiver;

assigning to a second requesting mobile phone a second frequency channel assignment from said second transceiver, said second requesting mobile phone being within a second overlap region defined by an overlap of the second cell defined by said second transceiver and the third cell defined by said third transceiver;

receiving at said first transceiver a request for a new frequency channel assignment from said third requesting mobile phone that is within the first cell but is not within either of said second and third cells; and

responsive to receiving the request from said third requesting mobile phone, the method further comprising the sub-steps of;

handing-off said second requesting mobile phone to a third frequency channel assignment from said third transceiver,

releasing said second frequency channel assignment;

handing-off said first requesting mobile phone to said second frequency channel assignment from said second transceiver;

releasing said first frequency channel assignment; and

reassigning said first frequency channel assignment to said third requesting mobile phone.

8. A method as in claim 7, further comprising the step of determining for all assigned mobile phones, after the step of receiving and responsive to said request from said third requesting mobile phone, a hand-off chain comprising said third requesting phone, said first transceiver, said first requesting mobile phone, said second transceiver, said second requesting mobile phone and said third transceiver by a breadth first search in a graph, said graph comprising the plurality of transceivers and all assigned mobile phones and, for each transceiver of the plurality of transceivers, a line between each of the requesting mobile phones and each of the transceivers defining a cell covering each of the requesting mobile phones.

9. A method of determining a hand-off chain from a mobile phone to a transceiver having an available frequency channel in a cellular communication system, the cellular communication system coupled to a plurality of base stations, each base station including a plurality of transceivers, each transceiver defining a respective cell in which the transceiver selectively provides frequency channel assignments to requesting mobile phones within said cell, such cells being arranged in an overlapping cellular pattern covering a geographic service area, said overlapping cellular pattern being arranged such that each cell overlaps a plurality of other cells, thereby defining a plurality of respective overlap regions such that said mobile phone within a given overlap region selectively receives a frequency channel assignment from any transceiver defining a respective cell covering said given overlap region, the method comprising the steps of:

a) generating first and second sets which are empty;

b) unmarking all transceivers and all mobile phones;

c) placing all transceivers defining cells covering the mobile phone in the first set and marking all the transceivers placed in the first set;

d) placing, for unmarked mobile phones that have been assigned frequency channel assignments from the transceivers placed in the first set, the unmarked mobile phones in the second set and marking the unmarked mobile phones;

e) emptying the first set;

f) placing, for unmarked transceivers covering one of the mobile phones in the second set, the unmarked transceivers in the first set and marking the unmarked transceivers;

g) emptying the second set;

h) determining if the first set is empty;

i) determining if any of the transceivers in the first set have an available frequency channel for assignment if step h) indicates that the first set is not empty;

j) repeating steps d) through i) if step i) determines that no transceiver in the first set has an available frequency channel for assignment; and

k) generating a hand-off chain by backtracking from a marked transceiver having an available frequency channel assignment in the first set to the mobile phone.