Wireless radio transmission systems can be configured on the basis of transmitters and receivers capable of transmitting and receiving multiple carrier data signals. One example of a multiple carrier radio transmission system is Orthogonal Frequency Division Multiplexing (OFDM) in which an OFDM transmitter broadcasts information consisting of symbols containing a plurality of equally spaced carrier frequencies. The characteristics of the wireless communication channel typically vary over time due to changes in the transmission path. For demodulating OFDM modulated data in the presence of substantial time variations of the transmission channel, knowledge of the transmission channel frequency response is required. This necessitates that the receiver provides an appropriate channel estimate of the transmission channel.
In order to facilitate channel estimation, known cell-specific reference symbols (CRS), called pilots, can be inserted at specific locations in the time-frequency grid of the OFDM signal. In addition to cell-specific reference signals, other reference signals like positioning reference signals (PRS), user equipment (UE) specific reference signals, or Multicast Broadcast Single Frequency Network (MBSFN) reference signals can be transmitted. These different types of reference signals can be transmitted by different physical antennas or they can be transmitted, at least in part, by the same antennas. More specifically, the reference signals correspond to logical antennas ports and the number of logical antenna ports can be higher than the number of physical antennas so that one physical antenna may transmit two or more reference signals of different types.
USPTO Backgrounds
USPTO Backgrounds