Femtocell channel assignment and power control for improved femtocell coverage and efficient cell search

Abstract

A method and a communication system including femtocells within a macrocell efficiently manage interference between the different femtocells, and between each femtocell and a macrocell. An efficient frequency assignment scheme for the femtocells minimizes interference between a femtocell and a macrocell and among different femtocells using a spectrum-sensing technique carried out by the femtocells. The frequency assignment scheme selects a suitable channel from a set of candidate channels and ensures that the femtocell has an acceptable coverage area even when it is close to the macrocell base station (BS). The frequency assignment scheme favors a co-channel implementation to take advantage of the hand-off and cell search characteristics of the co-channel implementation. In one embodiment, a joint power control and frequency band assignment technique is used, which partitions the coverage area of the macrocell into an inner region, a power control region, and an outer region.

1 . A method for selecting a frequency band for use in a femtocell located within a coverage area of a macrocell, comprising:
 partitioning the coverage area of the macrocell into an inner region and an outer region;   selecting for the femtocell a frequency band used in the macrocell, when the femtocell is located within the outer region, and   selecting for the femtocell a different frequency band than a frequency band used in the macrocell, when the femtocell is located within the inner region, wherein a mobile station switches between the macrocell and the femtocell after a cell-search step.   
     
     
         2 . A method as in  claim 1 , wherein the macrocell neighbors a plurality of other macrocells, and wherein the different frequency band selected for the femtocell is also different from any frequency band used in such other macrocells. 
     
     
         3 . A method as in  claim 1 , wherein the different frequency band is selected using a spectrum-sensing technique. 
     
     
         4 . A method as in  claim 3 , wherein the different frequency band is selected in a manner that reduces inter-femtocell interference. 
     
     
         5 . A method as in  claim 1 , wherein the different frequency band is selected so as to maintain a femtocell coverage area greater than a threshold value. 
     
     
         6 . A method as in  claim 1 , further comprising determining both a coverage area and a coverage region for the femtocell, and based on the determined coverage area and the determined coverage region, positioning a base station of the femtocell within the coverage region. 
     
     
         7 . A method as in  claim 6 , wherein the coverage region covers a predetermined premise. 
     
     
         8 . A method as in  claim 1 , wherein the selected frequency band is selected for a downlink, and wherein a frequency assignment for an uplink is based on interference from one or more mobile stations in the macrocell. 
     
     
         9 . A method as in  claim 1 , wherein a base station in the femtocell measures a signal quality in a received signal and reports the signal quality to a base station in the macrocell, and wherein the base station of the macrocell determines if the femtocell is within the inner region or the outer region. 
     
     
         10 . A method as in  claim 1 , wherein the partitioning further partitions the coverage area of the macrocell into a power control region. 
     
     
         11 . A communication system, comprising:
 a macrocell having a coverage area partitioned into an inner region and an outer region;   a first femtocell within the outer region, the first femtocell communicating using a frequency band used in the macrocell; and   a second femtocell within the inner region, the second femtocell communicating using a different frequency band than a frequency band used in the macrocell.   
     
     
         12 . A communication system as in  claim 11 , wherein the coverage area is partitioned using a distance from a base station of the macrocell. 
     
     
         13 . A communication system as in  claim 11 , further comprising a mobile station that switches between the macrocell and one of the femtocells after a cell-search step. 
     
     
         14 . A communication system as in  claim 11 , further comprising a mobile station that switches between the macrocell and one of the femtocells after a hand-off step. 
     
     
         15 . A communication system as in  claim 11 , further comprising a plurality of other macrocells neighboring the macrocell, and wherein the different frequency band selected for the femtocell is also different from any frequency band used in such other macrocells. 
     
     
         16 . A communication system as in  claim 11 , wherein the different frequency band is selected using a spectrum-sensing technique. 
     
     
         17 . A communication system as in  claim 16 , wherein the different frequency band is selected in a manner that reduces inter-femtocell interference. 
     
     
         18 . A communication system as in  claim 16 , wherein the different frequency band is selected so as to maintain a femtocell coverage area greater than a threshold value. 
     
     
         19 . A communication system as in  claim 16 , further comprising a base station of one of the femtocells that is placed at a position determined based on a coverage area and a coverage region determined for the femtocell of the base station. 
     
     
         20 . A communication system as in  claim 19 , wherein the coverage region covers a predetermined premise. 
     
     
         21 . A communication system as in  claim 11 , wherein the selected frequency band is selected for a downlink, and wherein a frequency assignment for an uplink is based on interference from one or more mobile stations in the macrocell. 
     
     
         22 . A communication system as in  claim 11 , wherein a base station in one of the femtocells measures a signal quality in a received signal and reports the signal quality to a base station in the macrocell, and wherein the base station of the macrocell determines if the femtocell is within the inner region or the outer region.