ub-frames would be fully empty. When a UE is connected to small cell, while macro cell is stronger, it is very beneficial if the UE is able to cancel the interference from the macro cell transmission during the ABSs. As the source of interference is known and also it can be identified what reference signals are transmitted (by decoding the PCI), then the UE does not need to try blindly detecting the interfering symbols but it can take advantage of the knowledge. Cancelling the interference from any random cell would be clearly more demanding. LTE and LTE Advanced in Releases 8-11 = Almost blank sub-frame (ABS) = Sub-frame with normal transmission Sub-frame (1 ms) Macro Small Small cell can serve also such Small cell can reuse same UEs that receiver stronger frequency as macro when UE is closer to small cell macro cell signal. Macro RSRP not exceeding the small cell RSRP + offset Figure 2.15 Use of almost blank sub-frame and offset parameter for range extension The offset that can be used had limits as well, since the interference level from the macro cell will after some point in time start to limit the UE receiver performance, thus a UE cannot have tens of decibels stronger macro cell signal and still maintain good reception of the small cell on the same frequency. The higher the offset, the more users are served by the small cells instead of the macro cell. The study captured in Reference 5 concluded that going above 14 dB offset already started to reduce the system performance, while one also has to consider how much macro cell sub-frames are designated as ABS, since that will also reduce the data rate of those users not able to connect to the small cells, with further performance analysis presented in Chapter 7. With the Release 12 dual connectivity, as described in Chapter 4, there is of course no such dependency as macro and small cells operate on different frequencies. 2.3.4 Coordinated Multipoint Transmission As part of Release 11 work, the support was introduced for the operation of Coordinated Multipoin