A communications system comprising: a plurality of base stations (110, 120) configured to respectively transmit reference signal groups (111, 121) that include a reference signal that is allocated a common channel resource allocated to a reference signal in another reference signal group among the reference signal groups; and a channel estimating apparatus comprising: a receiver configured to receive reference signal groups (111, 121) that are respectively transmitted from the base stations (110, 120) and wherein the channel estimating apparatus further comprises:: a first estimating unit that, based on a reference signal that is in a first reference signal group among the reference signal groups received by the receiver and that is allocated a unique channel resource not allocated to a reference signal in another reference signal group, is configured to reduce noise by applying a filtering operation from a reference signal that is in the first reference signal group and allocated the common channel resource, which is also allocated to a reference signal in a second reference signal group among the reference signal groups; and a second estimating unit that is configured to subtract the reference signal with reduced noise obtained from the first estimating unit from said reference signal in the second reference signal group. a plurality of base stations (110, 120) configured to respectively transmit reference signal groups (111, 121) that include a reference signal that is allocated a common channel resource allocated to a reference signal in another reference signal group among the reference signal groups; and a channel estimating apparatus comprising: a receiver configured to receive reference signal groups (111, 121) that are respectively transmitted from the base stations (110, 120) and wherein the channel estimating apparatus further comprises:: a first estimating unit that, based on a reference signal that is in a first reference signal group among the reference signal groups received by the receiver and that is allocated a unique channel resource not allocated to a reference signal in another reference signal group, is configured to reduce noise by applying a filtering operation from a reference signal that is in the first reference signal group and allocated the common channel resource, which is also allocated to a reference signal in a second reference signal group among the reference signal groups; and a second estimating unit that is configured to subtract the reference signal with reduced noise obtained from the first estimating unit from said reference signal in the second reference signal group. a receiver configured to receive reference signal groups (111, 121) that are respectively transmitted from the base stations (110, 120) and wherein the channel estimating apparatus further comprises:: a first estimating unit that, based on a reference signal that is in a first reference signal group among the reference signal groups received by the receiver and that is allocated a unique channel resource not allocated to a reference signal in another reference signal group, is configured to reduce noise by applying a filtering operation from a reference signal that is in the first reference signal group and allocated the common channel resource, which is also allocated to a reference signal in a second reference signal group among the reference signal groups; and a second estimating unit that is configured to subtract the reference signal with reduced noise obtained from the first estimating unit from said reference signal in the second reference signal group. a first estimating unit that, based on a reference signal that is in a first reference signal group among the reference signal groups received by the receiver and that is allocated a unique channel resource not allocated to a reference signal in another reference signal group, is configured to reduce noise by applying a filtering operation from a reference signal that is in the first reference signal group and allocated the common channel resource, which is also allocated to a reference signal in a second reference signal group among the reference signal groups; and a second estimating unit that is configured to subtract the reference signal with reduced noise obtained from the first estimating unit from said reference signal in the second reference signal group.