ped for each radio channel. As the process number is shown in the DCI control information, the number of open HARQ processes is not fixed and depends on transmission needs. Radio Interface Procedures For the FDD mode, the number of open HARQ processes is less than or equal to 8. The eight HARQ processes are only open if the eNB entity allocates resources to the mobile every millisecond. The PUCCH or PUSCH physical channel transports the ACK or NACK indicator with a shift of 4 milliseconds after the transmission of the transport block in the PDSCH physical channel. Under a HARQ process, if a transport block is acknowledged, a new transport block can be transmitted. If a transport block is not acknowledged, the RV1 redundancy version is transmitted. In the two cases, the moment used by the HARQ process is not imposed by timing as is the case for the uplink. For the TDD mode, the HARQ process number, by the HARQ entity depends on the configuration of the time frame (Table 4.9). Configuration of the time frame Number of sub-frames downlink HARQ process number Table 4.9. HARQ process number in the TDD mode data transfer for the downlink Table 4.10 shows the number of ACK/NACK bits to be transmitted, through the HARQ entity in the PUCCH physical channel, depending on the configuration of the time frame, for transmission mode 1. The indicated values are doubled in the case of transmission mode 2. Configuration of the time frame Number of sub-frames for the PUCCH physical channel Number of ACK / NACK bits Number of bits through sub-frame Table 4.10. Number of ACK / NACK bits to be transmitted in the PUCCH physical channel for the TDD mode and the transmission mode 1 142 VoLTE and ViLTE In certain cases, the capacity of the PUCCH physical channel is insufficient for recovering all the ACK / NACK information: format la has a capacity of one bit; format 1b has a capacity of 2 or 4 bits. Two methods are defined to reduce the number of bits: coupling carried out from a logical AND of various ACK / NACK information: - the NACK