In a 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) time division duplex (TDD) system, a wireless frame has a length of 10 ms, and contains 10 sub-frames. Each sub-frame has a length of 1 ms. A network side device may configure the sub-frame to transmit downlink data or uplink data. The LTE TDD system supports various uplink and downlink sub-frame configurations, as described in Table 1, where D represents a downlink sub-frame, S represents a special sub-frame, and U represents an uplink sub-frame. For example, a sub-frame configuration 0 is “DSUUUDSUUU”. The network side device notifies, through a broadcasted first system information block (SIB1) message, a user equipment of a to-be-used sub-frame configuration.
TABLE 1Sub-frame configurations supported by an LTE TDD systemSub-Downlink-frameUplinkConfig-Switch PointSub-frame IndexurationPeriodicity012345678905msDSUUUDSUUU15msDSUUDDSUUD25msDSUDDDSUDD310msDSUUUDDDDD410msDSUUDDDDDD510msDSUDDDDDDD65msDSUUUDSUUD
The LTE TDD system supports a physical-layer HARQ technology. A corresponding HARQ timing relationship and the maximum number of HARQ processes supported are defined for each sub-frame configuration in Table 1. Table 2 describes the maximum number of downlink HARQ processes MDL_HARQ and the maximum number of uplink HARQ processes MUL_HARQ supported in each LTE TDD sub-frame configuration, where a downlink HARQ process and an uplink HARQ process respectively refer to an HARQ process used for downlink data transmission and an HARQ process used for uplink data transmission. The HARQ process for uplink data transmission supports two modes, which are respectively called a normal HARQ mode and a sub-frame binding mode, and N/A represents that the sub-frame binding mode is not supported in a corresponding sub-frame configuration. In the normal HARQ mode, one transmission of an uplink data packet is performed only in one sub-frame; and in the sub-frame binding mode, one transmission of an uplink data packet is performed in more than one sub-frame, and different sub-frames transmit different redundancy versions of the uplink data packet respectively.
TABLE 2Number of HARQ processes in different sub-frame configurationsMaximum Number Maximum Number of Uplink of Downlink HARQ Processes MUL_HARQSub-frameHARQ Processes Normal HARQ Sub-frame BindingConfigurationMDL_HARQModeMode047317422102N/A393N/A4122N/A5151N/A6663
During development of communications technologies, introduction of more advanced new functional characteristics, such as aggregation of TDD carriers having different sub-frame configurations, aggregation of a frequency division duplex (FDD) carrier and a TDD carrier, and TDD sub-frame configuration dynamic reconfiguration, is under discussion. There are multiple sub-frame configurations at this time, and carrier aggregation in the prior art is implemented only for carriers having the same sub-frame configuration, and therefore, to better support the new functional characteristics, an HARQ timing relationship used during communication between a UE and a base station is probably not an HARQ timing relationship corresponding to a sub-frame configuration notified through the SIB1 on the carrier. Moreover, when the used HARQ timing relationship is not the HARQ timing relationship defined by the sub-frame configuration notified through the SIB1, the base station and the UE may have inconsistent understanding on the maximum number of HARQ processes supported, which causes an error in size division of a soft buffer, and further results in a communication error.