In multicarrier communications, reporting of downlink (DL) control information on the uplink (UL) is typically done for one DL carrier at a time. Therefore, existing multicarrier communication systems are lacking techniques for reporting control information on the UL for multiple concurrent DL carriers.
An example multicarrier wireless communications system is the Third Generation Partnership Project (3GPP) long term evolution (LTE) system that has been introduced into 3GPP Release 8 (R8). The LTE DL transmission scheme is based on an Orthogonal Frequency Division Multiple Access (OFDMA) air interface. According to OFDMA, a wireless transmit/receive unit (WTRU) may be allocated by the evolved Node B (eNB) to receive its data anywhere across the whole LTE transmission bandwidth. For the LTE uplink (UL) direction, single-carrier (SC) transmission is used based on discrete Fourier transform-spread-OFDMA (DFT-S-OFDMA), or equivalently, single carrier frequency division multiple access (SC-FDMA). A WTRU in the UL may transmit only on a limited, yet contiguous set of assigned sub-carriers in an FDMA arrangement. FIG. 1 illustrates the mapping of a transport block 102 to an LTE carrier 110, for UL or DL transmission. Layer 1 (L1) 106 receives information from the hybrid automatic repeat request (HARQ) entity 104 and the scheduler 108, and uses it to assign a transport block 102 to an LTE carrier 110. As shown in FIG. 1, an UL or DL LTE carrier 110, or simply a carrier 110, is made up of multiple sub-carriers 112. An eNB may receive a composite UL signal across the entire transmission bandwidth from one or more WTRUs at the same time, where each WTRU transmits on a subset of the available transmission bandwidth or sub-carriers.
LTE-Advanced (LTE-A) is being developed by the 3GPP standardization body in order to further improve achievable throughput and coverage of LTE-based radio access systems, and to meet the International Mobile Telecommunications (IMT) Advanced requirements of 1 Gbps and 500 Mbps in the DL and UL directions, respectively. Among the improvements proposed for LTE-A are carrier aggregation and support of flexible bandwidth arrangements. LTE-A proposes to allow DL and UL transmission bandwidths to exceed the 20 MHz limit in R8 LTE, for example, permitting 40 MHz or 100 MHz bandwidths. In this case, a carrier may occupy the entire frequency block.
LTE-A proposes to allow for more flexible usage of the available paired spectrum, and is not limited to operate in symmetrical and paired FDD mode, as in R8 LTE. LTE-A proposes to allow asymmetric configurations where, for example, a DL bandwidth of 10 MHz may be paired with an UL bandwidth of 5 MHz. In addition, LTE-A proposes composite aggregate transmission bandwidths, which may be backwards compatible with LTE. By way of example, the DL may include a first 20 MHz carrier plus a second 10 MHz carrier, which is paired with an UL 20 MHz carrier.
Carriers transmitted concurrently in the same UL or DL direction are referred to as component carriers. The composite aggregate transmission bandwidths of the component carriers may not necessarily be contiguous in the frequency domain. For example, the first 10 MHz component carrier may be spaced by 22.5 MHz in the DL band from the second 5 MHz DL component carrier. Alternatively, contiguous aggregate transmission bandwidths may be used. By way of example, a first DL component carrier of 15 MHz may be aggregated with another 15 MHz DL component carrier and paired with an UL carrier of 20 MHz. FIG. 2 shows a discontinuous spectrum aggregation with component carriers 205, and FIG. 3 shows a continuous spectrum aggregation with component carriers 305.
FIG. 4 illustrates a reserved time-frequency location for the transmission of the physical uplink control channel (PUCCH) according to LTE R8. PUCCH is used for transmitting control data on the uplink. FIG. 4 shows one subframe made up of two timeslots 402, where NRBUL denotes the number of resource blocks (RBs) available for uplink transmission and nPRB is the RB index. RBs on the edges of the frequency spectrum may be used for PUCCH transmission, and RBs on the opposite edges may be used in the two time slots to improve the diversity. By way of example, a WTRU may use the RBs indicated by m=1 for PUCCH transmission. The control data carried by PUCCH may include, but is not limited to, acknowledge/negative acknowledge (ACK/NACK) information for the DL transmission, scheduling requests (SRs), channel quality indicator (CQI) information to enable scheduling for DL transmission, rank indicator (RI) information, and precoding matrix indicator (PMI) information to enable MIMO operation. Herein, the term CQI is generalized to also include PMI and RI. According to LTE R8, PUCCH used for CQI reporting and PUCCH used for scheduling requests (SRs) are configured to be periodic, such that each PUCCH reports information for only one downlink carrier.
The PUCCH configuration in LTE R8 is designed for one component carrier. Therefore, it is desirable to develop new configurations for PUCCH for LTE-A with carrier aggregation, where more than one component carrier may be transmitted at a time in the DL, while supporting CQI (including PMI and RI) reporting for multiple downlink carriers, and efficient SR reporting with low impact from discontinuous reception (DRX) cycles on multiple carriers. More generally, it is desirable to develop techniques for simultaneous reporting of information for multiple concurrent DL carriers in multicarrier communications systems.
A multicarrier system employing carrier aggregation, such as LTE-A, may include anchor and non-anchor component carriers. This may reduce the overhead because system information, synchronization and paging information for a cell may be transmitted on anchor carrier(s) only. The anchor carrier(s) may enable synchronization, camping and access in a heterogeneous network environment where interference coordination may be provided for at least one detectable or accessible anchor carrier.
Multiple carriers may exist in the DL and UL for carrier aggregation. However, the carrier quality may change and/or the amount of DL or UL traffic may change in a dynamic or semi-persistent way. Thus, it would be desirable to provide flexible and efficient DL and UL component carrier assignment and switching to provide improved utilization and transmission quality for multiple carrier systems employing carrier aggregation, such as LTE-A.