("SU-MIMO") for higher data rates (more users per cell) in a given bandwidth Figure 3.30 Multi-antennas transmission techniques. Reproduced with permission from Dahlman et al. C IEEE [24] with network MIMO to improve overall efficiency. One of the challenges with downlink MIMO im- plementations is the latency for exchange of information between base stations. In the current Release 8 of the LTE standard, the minimum X2 interface latency for exchange of information between base stations is 20 ms, whereas radio bearers are typically assigned on a 1 ms subframe basis, making real time processing of interference cancellation data from adjacent base stations unfeasible [25]. 3.9.4 Interference Coordination and Cancellation The basic concept behind interference cancellation (IC) is to regenerate the interfering signals and subsequently subtract them from the desired signal. Traditionally, it involves the cancellation of undesired pilot signals (reference signals) and implementation in the base station receivers in order to avoid terminal complexities. During the last few years, there is also a focus to cancel the inference from data (traffic) signals which is more complex than simple pilot IC. In a typical radio environment, SINR (signal-to-interference-plus-noise ratio) values go from very positive +20 dB) to very negative (up to - 15 dB). Thus, to robustly deploy an LTE OFDM system one will have to mitigate the inevitable negative SINR coverage regions that will exist. IC techniques can be used to cancel both intra-cell and inter-cell interference. For effective cancellation of inter- cell interference, inter-cell communication is essential. Inter-cell interference coordination (ICIC) is in essence a scheduling strategy used to limit the inter-cell interference. LTE offers the capability to provide a flexible dynamic inter-base station approach to interference coordination through the use of inter-base station signaling capabilities, including the use of uplink reactive overload indicators (OIs) and proactive high in