Wireless communication systems are widely used to provide voice and data services for multiple users using a variety of access terminals such as cellular telephones, laptop computers and various multimedia devices. Such communications systems can encompass local area networks, such as IEEE 801.11 networks, cellular telephone and/or mobile broadband networks. The communication system can use one or more multiple access techniques, such as Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier Frequency Division Multiple Access (SC-FDMA) and others. Mobile broadband networks can conform to a number of standards such as the main 2nd-Generation (2G) technology Global System for Mobile Communications (GSM), the main 3rd-Generation (3G) technology Universal Mobile Telecommunications System (UMTS) and the main 4th-Generation (4G) technology Long Term Evolution (LTE).
In an LTE based wireless communications system, the communications system's capacity may be significantly improved when a transmitter such as a base station in a downlink channel has full or partial knowledge of a channel over which it will be transmitting. Information related to the channel may be referred to as channel state information (CSI). CSI may be obtained by the transmitter over a reverse feedback channel. A receiver such as a mobile station of transmissions made by the transmitter may transmit CSI back to the transmitter over the reverse feedback channel. The receiver may estimate the channel, generate the CSI, and feed the CSI back to the transmitter.
In a 4G LTE system, a reverse feedback channel referred to as a physical uplink control channel (PUCCH) is used to allow receivers to transmit (feedback) channel information to the transmitter serving the receivers. As an example, up to 13 information bits (information prior to encoding) may be transmitted in a single PUCCH packet. Actual PUCCH packet payload is 20 coded bits.
In LTE and earlier compliant communications systems, there may be several types of channel state information including Rank Indicator (RI), Precoding Matrix Indicator (PMI) and Channel Quality Indicator (CQI). CQI can be further divided into two categories, namely wideband CQI (W-CQI) and narrowband CQI (N-CQI). RI is an indication of a number of spatial layers that can be supported by a communications channel. The RI may be fedback infrequently. PMI and W-CQI are indications of channel quality or a codebook quantized version of the channel quality for a wideband channel. The wideband PMI/CQI may be fedback frequently. Moreover, N-CQI is an indication of channel quality for a narrowband channel. The N-CQI may be fedback frequently.
In LTE and earlier compliant communications systems, there may be at least three reports from a mobile station to a base station. Channel state information such as RI, PMI and CQI is allocated into different reports and sent back to the base station through the PUCCH. For example, based upon channel state information, a mobile station may select a matrix indicator in a codebook. Furthermore, through the PUCCH, the mobile station may send the matrix indicator to a base station in a particular report. Based upon the matrix indicator, the base station may perform multi-user multiple input multiple and multiple output (MU MIMO) beamforming.