A method to be performed by a user equipment, UE for operating in a 3GPP Long Term Evolution, LTE, network, the method comprising: receiving configuration information for a plurality of serving cells to indicate respective time division duplexing, TDD, uplink-downlink, UL-DL, configurations for individual serving cells of the plurality of serving cells, wherein at least two of the serving cells have different TDD UL-DL configurations; receiving a downlink assignment index, DAI; determining a value for W DAI UL based on the DAI from a look-up table, wherein the look-up table is DAI MSB, LSB w DAI UL 0,0 1 0, 1 2 1,0 3 1,1 4 determining, for a first serving cell of a plurality of serving cells, a number of subframes of the bundling window of the first serving cell; and selecting a minimum value of two terms, wherein a first term of the two terms is the determined number of subframes of the bundling window of the first serving cell, and wherein a second term of the two terms is a function of the W DAI UL and U, wherein the function includes a sum of W DAI UL and four multiplied by a value determined by dividing the difference of U and W DAI UL by four, where U is a maximum value of U c among all configured serving cells, and where U c is the total number of subframes with received physical downlink shared channels, PDSCH, and physical downlink control channels, PDCCHs, indicating downlink semi-persistent scheduling, SPS, release in the bundling window of the c th serving cell; wherein the selected minimum value of the two terms is a number of subframes for which the UE needs to feedback hybrid automatic repeat request - acknowledgement, HARQ-ACK, bits for the first serving cell. receiving configuration information for a plurality of serving cells to indicate respective time division duplexing, TDD, uplink-downlink, UL-DL, configurations for individual serving cells of the plurality of serving cells, wherein at least two of the serving cells have different TDD UL-DL configurations; receiving a downlink assignment index, DAI; determining a value for W DAI UL based on the DAI from a look-up table, wherein the look-up table is DAI MSB, LSB w DAI UL 0,0 1 0, 1 2 1,0 3 1,1 4 determining, for a first serving cell of a plurality of serving cells, a number of subframes of the bundling window of the first serving cell; and selecting a minimum value of two terms, wherein a first term of the two terms is the determined number of subframes of the bundling window of the first serving cell, and wherein a second term of the two terms is a function of the W DAI UL and U, wherein the function includes a sum of W DAI UL and four multiplied by a value determined by dividing the difference of U and W DAI UL by four, where U is a maximum value of U c among all configured serving cells, and where U c is the total number of subframes with received physical downlink shared channels, PDSCH, and physical downlink control channels, PDCCHs, indicating downlink semi-persistent scheduling, SPS, release in the bundling window of the c th serving cell; wherein the selected minimum value of the two terms is a number of subframes for which the UE needs to feedback hybrid automatic repeat request - acknowledgement, HARQ-ACK, bits for the first serving cell.