1. Field
The present invention relates generally to data communication, and more specifically to a novel and improved method and apparatus for utilizing (full or partial) channel state information to provide improved performance for a wireless communication system.
2. Background
Wireless communication systems are widely deployed to provide various types of communication such as voice, data, and so on. These systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), orthogonal frequency division modulation (OFDM), or some other modulation techniques. OFDM systems can provide high performance for some channel environments.
In a terrestrial communication system (e.g., a cellular system, a broadcast system, a multi-channel multi-point distribution system (MMDS), and others), an RF modulated signal from a transmitter unit may reach a receiver unit via a number of transmission paths. The characteristics of the transmission paths typically vary over time due to a number of factors such as fading and multipath.
To provide diversity against deleterious path effects and improve performance, multiple transmit and receive antennas may be used. If the transmission paths between the transmit and receive antennas are linearly independent (i.e., a transmission on one path is not formed as a linear combination of the transmissions on other paths), which is generally true to some extent, then the likelihood of correctly receiving a transmitted signal increases as the number of antennas increases. Generally, diversity increases and performance improves as the number of transmit and receive antennas increases.
A multiple-input multiple-output (MIMO) communication system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel may be decomposed into NC independent channels, with NC≦min {NT, NR}. Each of the NC independent channels is also referred to as a spatial subchannel of the MIMO channel and corresponds to a dimension. The MIMO system can provide improved performance if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
There is therefore a need in the art for techniques to utilize channel state information (CSI) to take advantage of the additional dimensionalities created by a MIMO system to provide improved system performance.