A method implemented in a base station used in a wireless communications system that supports flexible-time division duplex, flexible-TDD, uplink-downlink, UL-DL, configuration and third generation partnership project, 3GPP, long term evolution, LTE, technology, the method comprising: configuring a first type of user equipment, UE, with a first type of configuration, wherein the first type of configuration comprises a long term UL-DL TDD configuration; configuring a second type of UE with a second type of configuration, wherein the second type of configuration comprises a flexible-TDD configuration; and receiving from a user equipment a hybrid automatic repeat request-acknowledgement, HARQ-ACK, signal according to a DL association set, wherein the DL association set comprises: a first DL association set for a UL-DL TDD configuration used by the first type of UE; and a second DL association set for a reference UL-DL TDD configuration including a third DL association set for PUCCH resource mapping used by the second type of UE , and wherein the third DL association set comprises: a first subset indicating one or more subframes including at least one of a fixed DL subframe and a special subframe, and a second subset indicating one or more flexible subframes ; and performing physical uplink control channel, PUCCH, resource allocation according to the received DL association set, wherein, for subframes in the second subset, a PUCCH resource is allocated to first flexible subframes followed by PUCCH resource for second flexible subframes , the first flexible subframes have a larger possibility of being used as DL subframes than the second flexible subframes ; wherein none of the PUCCH resource for the first flexible subframes are allocated following the PUCCH resources for the second flexible subframes . configuring a first type of user equipment, UE, with a first type of configuration, wherein the first type of configuration comprises a long term UL-DL TDD configuration; configuring a second type of UE with a second type of configuration, wherein the second type of configuration comprises a flexible-TDD configuration; and receiving from a user equipment a hybrid automatic repeat request-acknowledgement, HARQ-ACK, signal according to a DL association set, wherein the DL association set comprises: a first DL association set for a UL-DL TDD configuration used by the first type of UE; and a second DL association set for a reference UL-DL TDD configuration including a third DL association set for PUCCH resource mapping used by the second type of UE , and a first DL association set for a UL-DL TDD configuration used by the first type of UE; and a second DL association set for a reference UL-DL TDD configuration including a third DL association set for PUCCH resource mapping used by the second type of UE , and wherein the third DL association set comprises: a first subset indicating one or more subframes including at least one of a fixed DL subframe and a special subframe, and a second subset indicating one or more flexible subframes ; and a first subset indicating one or more subframes including at least one of a fixed DL subframe and a special subframe, and a second subset indicating one or more flexible subframes ; and performing physical uplink control channel, PUCCH, resource allocation according to the received DL association set, wherein, for subframes in the second subset, a PUCCH resource is allocated to first flexible subframes followed by PUCCH resource for second flexible subframes , the first flexible subframes have a larger possibility of being used as DL subframes than the second flexible subframes ; wherein none of the PUCCH resource for the first flexible subframes are allocated following the PUCCH resources for the second flexible subframes . <EOS>