1. Field of the Invention
The present invention relates to a method used in a wireless communication system and related communication device, and more particularly, to a method of uplink control information transmission in a wireless communication system.
2. Description of the Prior Art
A long term evolution-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of the eNB, and includes subjects, such as bandwidth extension, coordinated multipoint transmission/reception (CoMP), UL multiple-input multiple-output (MIMO), etc.
For bandwidth extension, a carrier aggregation (CA) is introduced to the LTE-A system by which two or more component carriers are aggregated to achieve a wider-band transmission. Accordingly, the LTE-A system can support a wider bandwidth up to 100 MHz by aggregating a maximum number of 5 component carriers, where bandwidth of each component carrier is 20 MHz and is backward compatible with 3GPP Rel-8. An LTE-A specification supports CA for both continuous and non-continuous component carriers with each component carrier limited to a maximum of 110 resource blocks. The CA increases a bandwidth flexibility by aggregating the non-continuous component carriers. In addition, in carrier aggregation, the UE only has one RRC connection with the network. At RRC connection establishment/re-establishment/handover, one serving cell provides the NAS mobility information, and at RRC connection re-establishment/handover, one serving cell provides the security input. This cell is referred to as a primary cell (PCell). In the downlink, the component carrier corresponding to the PCell is the downlink primary component carrier (DL PCC) while in the uplink it is the uplink primary component carrier (UL PCC). In addition, cells other than the PCell are named secondary cell (SCell).
Further, for Rel-11, carrier aggregation is supported by both formats of LTE-A system, namely the Frequency Division Duplex (FDD) and Time Division Duplex (TDD) variants. The aggregated component carriers operated on TDD system may have different UL-DL configurations. The supported UL-DL configurations are listed in FIG. 1. As can be seen, 7 UL-DL configurations are supported in LTE TDD systems. In FIG. 1, the UL-DL configuration #0 implies that subframes ‘0’ and ‘5’ are DL subframes, subframes ‘1’ and ‘6’ are special subframes, and subframes ‘2’, ‘3’, ‘4’, ‘7’, ‘8’, ‘9’ are UL subframes.
Uplink control information includes an acknowledgement/negative acknowledgement (ACK/NACK) feedback, a channel quality indicator (CQI) report, a precoding matrix indicator (PMI) report, a rank indicator (RI) report, a precoding type indicator (PTI), channel state information (CSI), and scheduling request (SR), etc. In LTE system, a UE transmits the uplink control information to the eNB on a physical uplink control channel (PUCCH). However, the applicant notices a problem associated to the uplink control information transmission. In Rel-10, UE is configured with more than one serving cell (i.e. one PCell and one or more SCells), but PUCCH is transmitted only on the PCell. On the other hand, in Rel-11, each serving cell may have different UL-DL configurations. Hence, the conflicting situation may happen when PCell is downlink and one of the SCell is uplink on the same subframe. In detail, please refer to FIG. 2, which is a schematic diagram of uplink control information transmission on cells with different UL-DL configurations. In FIG. 2, a UE is configured with a Cell 1 as PCell and a Cell 2 as SCell. In addition, the Cell 1 is configured with UL-DL configuration #1 and the Cell 3 is configured with UL-DL configuration #0 as shown in FIG. 1. The UE receives PDSCH transmissions in DL subframe ‘0’ on Cell 1 and in DL subframe ‘0’ on Cell 3. In this situation, the UE shall reply ACK/NACK in subframe ‘4’ for the PDSCH transmission in DL subframe ‘0’ on SCell. Conventionally, the UE transmits PUCCH only on the PCell (namely Cell 1). However, as shown in FIG. 2, the subframe ‘4’ on Cell 1 is a DL subframe. Thus, no PUCCH resource in subframe ‘4’ on PCell is for the UE to feedback ACK/NACK. In this situation, the UE cannot transmit PUCCH for the UCI (e.g. ACK/NACK, CQI, PMI, RI and/or CSI) on the PCell. Without clear specification, the UE does not know how to deal with this situation.