Codebook with nested structure

#The present invention relates to the field of wireless communications, particularly wireless, high-rate communications using multiple-antenna systems.

#The hostility of the wireless fading environment and channel variation makes the design of high rate communication systems very challenging. To this end, multiple-antenna systems have been shown to be effective in fading environments by providing significant performance improvements and achievable data rates in comparison to single antenna systems. Wireless communication systems employing multiple antennas both at the transmitter and the receiver demonstrate tremendous potential to meet the spectral efficiency requirements for next generation wireless applications.

#Moreover, multiple transmit and receive antennas have become an integral part of the standards of many wireless systems such as cellular systems and wireless LANs. In particular, the recent development of UMTS Terrestrial Radio Access Network (UTRAN) and Evolved-UTRA has raised the need for multiple antenna systems to reach higher user data rates and better quality of service, thereby resulting in an improved overall throughput and better coverage. A number of proposals have discussed and concluded the need for multiple antenna systems to achieve the target spectral efficiency, throughput, and reliability of EUTRA. While these proposals have considered different modes of operation applicable to different scenarios, a basic common factor among them, however, is a feedback strategy to control the transmission rate and possibly a variation in transmission strategy.

#FIG. 1 is a schematic block diagram of a wireless multiple-antenna MIMO communications system with quantized feedback of channel state information.

#FIG. 2 is a block diagram of an exemplary embodiment of a transmitter in accordance with the present invention.

#FIG. 3 is a block diagram of an exemplary embodiment of a receiver in accordance with the present invention.

#An exemplary multiple-antenna communication system 100 with quantized feedback is schematically shown in FIG. 1. A transmitter 110, such as at a base station (“NodeB”), transmits from m transmitting antennas 111.1-111.m over a fading channel 130 to n receiving antennas 121.1-121.n coupled to a receiver 120, such as at user equipment (UE). The system 100 may be, for example, an orthogonal frequency-division multiplexing (OFDM) system, in which each of a plurality of orthogonal sub-carriers is modulated with a conventional modulation scheme, such as quadrature amplitude modulation (QAM), quadrature phase shift keying (QPSK), or the like.

#The system 100 also incorporates an exemplary multi-rank beamforming (MRBF) scheme with precoding in accordance with the present invention. The transmitter 110 controls the transmitting antenna outputs in accordance with a set of precoding parameters, or a precoding matrix, which is selected based on an estimate of the channel 130 made at the receiver 120.

#At receiver 120, a channel estimator 125 provides an estimate of the channel 130 to the receiver 120. One or more parameters determined as a function of the channel estimate are also provided from the receiver 120 to the transmitter 110 via a feedback channel. In an exemplary embodiment, such fed-back parameters may include a channel quality indicator (CQI) and the index of a recommended precoding matrix that the transmitter 110 should use based on the channel conditions. The determination of this information and its use by the transmitter are described in greater detail below.