I. Field
The following description relates generally to wireless communications, and more particularly, but not limited to, using channel state information reference signals in a wireless communication system.
II. Relevant Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple terminals by sharing the available system resources (e.g., bandwidth and transmit power). Each terminal communicates with one or more base stations via transmissions on the forward and the reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out, multiple-in-single-out or a multiple-in-multiple-out (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min{NT, NR}. Each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
A wireless network may also include relays that can improve the coverage and capacity of the wireless network without the need for a potentially expensive wired backhaul link. A relay may be a “decode and forward” station that may receive a signal from an upstream station (e.g., a base station), process the received signal to recover data sent in the signal, generate a relay signal based on the recovered data, and transmit the relay signal to a downstream station (e.g., a user equipment (UE)). A relay may communicate with a base station on a backhaul link and may appear as a UE to the base station. The relay may also communicate with one or more UEs on an access link and may appear as a base station to the UE(s). The relay may be a half-duplex relay that cannot transmit and receive at the same time on the same frequency channel. Hence, the backhaul link and the access link may be time division multiplexed.
In addition, a base station, a relay device or a UE can transmit reference signals to maintain or improve performance of the wireless system. Reference signals are typically signals known a priori to a receiver. A receiving device may receive reference signals and based on the received reference signals may alter certain operational parameters or generate feedback to alter certain operational parameters of wireless communication. The receiving device may also measure or estimate certain operational parameters such as the channel transfer function and interference.