signals received at multiple anten- point, the achievable data rates start to saturate and any nas will also increase the signal-to-interference ratio further increase in the number of transmit or receive after the antenna combining. antennas, although leading to a correspondingly The use of beam-forming by means of multiple improved signal-to-noise ratio at the receiver, will only transmit antennas will focus the transmit power provide a marginal increase in the achievable data rates. in the direction of the target receiver, leading to This saturation in achievable data rates can be avoided reduced interference to other radio links and thus though, by the use of multiple antennas at both the improving the overall signal-to-interference ratio in transmitter and the receiver, enabling what can be the system. referred to as spatial multiplexing, often also referred to as MIMO (Multiple-Input Multiple-Output). One important difference between interference and An alternative to increasing the received signal power noise is that interference, in contrast to noise, typically is to reduce the noise power, or more exactly the noise has a certain structure which makes it, at least to some power density, at the receiver. This can, at least to some extent, predictable and thus possible to further suppress extent, be achieved by more advanced receiver RF or even remove completely. As an example, a dominant design, allowing for a reduced receiver noise figure. interfering signal may arrive from a certain direction in which case the corresponding interference can be further suppressed, or even completely removed, by means of 4.3.1.2 Higher data rates in interference- spatial processing using multiple antennas at the receiver. limited scenarios Also any differences in the spectrum properties between the target signal and an interfering signal can be used to The discussion above assumed communication over suppress the interferer and thus reduce the overall a radio link only impaired by noise. However, in actual interference leve