Also the supported LTE and LTE Advanced in Releases 8-11 Downlink CA performance Offered Load [Mbps] Figure 2.13 Carrier aggregation compared to Release 8 operation without aggregation bandwidths that can be used with carrier aggregation in connection with a specific band combination are specified in [4]. 2.3.2 Multiple Input Multiple Output Enhancements The MIMO operation was enhanced to make it more efficient when increasing the number of antennas. The following improvements were done: Introduction of Channel State Information Reference Signals (CSI-RS). The UE will mea- sure these from many antennas that are in use (configured) and with the CSI-RS, there is no need to continuously send from too many antennas if the conditions are not sufficient or there are no data to schedule for a UE with capability for more than 2 MIMO streams. The CSI-RS does not occur in every sub-frame, and since the rate of those is parameterized to be up to 80 ms, the impact on legacy devices is minimal. Demodulation Reference Signals (DM-RS), also known as User-Specific Reference Signals (URS). These end together with the actual data, which allows UE-specific transmitter operation when the pre-coder is applied to the DM-RS as well in addition to the actual data. With DM-RS/URS also beamforming operation is enabled. Enabling up to eight-stream MIMO operation in the downlink direction and respectively up to four antenna MIMO transmission in the uplink direction. These improvements enable efficient use of more than two transmit antennas as supported by the UEs in the field as of today. With the CSI-RS, an LTE-Advanced UE supporting four- stream MIMO can measure and provide feedback for the eNodeB for the rank selection and pre-coder to be used. Only when the transmission for the four-stream capably UE is done, the network then sends the DM-RS together with the data from all four transmit antennas. This is illustrated in Figure 2.14. 2.3.3 HetNet Enhanced Inter-cell Interference Coordination Part of the work for LTE Advanced in Releases 1