Future generations of cellular networks are expected to provide high data rates, up to several gigabytes per second while at the same time being energy efficient. One possible way to achieve such high data rates and/or to lower the energy consumption in cellular networks is to deploy a reconfigurable antenna system (RAS) or reconfigurable antenna systems. A RAS is an antenna system whose radiation characteristics can be changed by the network after deployment and adapted to, e.g., current traffic needs.
The most common antenna parameter that can be remotely controlled has been the antenna tilt. More possibilities to modify the antenna lobe shapes, far beyond the one-dimensional tilt, will be introduced, and this opens up for new possibilities to improve network performance. For example, an antenna system can be reconfigured to better serve a traffic hotspot by, e.g., increasing the antenna gain toward the hotspot location.
To efficiently use a RAS it has to be automatically controlled, for example by using a self-organizing network (SON) algorithm. A RAS controlled by SON algorithms is called RAS-SON. It is important to distinguish a RAS from UE-specific beamforming. A RAS is used to shape the cell-specific beam patterns for cell-specific reference signals (CRSs) and control signals, and is typically changed quite slowly, accommodating for changes in the infrastructure or user behaviors, for example on a weekly basis. The UE-specific beamforming is used to shape the beams for UE-specific signals and is typically changed very quickly, for example on a millisecond basis.
When steering the radiation pattern for reconfigurable antennas, there are typically some directions where it is un-desirable to transmit energy; for example at the horizon or at buildings with indoor systems. Tilting antennas towards the horizon in an urban scenario may lead to reduced performance in the network, for example due to a large amount of interference that will be generated towards other cells.
However, many algorithms that tune reconfigurable antennas, such as for example certain SON algorithms, do not consider any directions as undesired options. This may lead to unnecessarily slow adaption and to temporarily worse performance during the adaptation process, as these sub-optimal antenna settings are tried by the automatic algorithm.
Generally, it is desirable to obtain a reconfigurable and/or electrically controllable antenna arrangement where undesired radiation directions are automatically handled in an efficient, reliable and uncomplicated manner.
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