For the efficient and interference free transmission of high data rates antennas are needed, which steer themselves to the direction of arrival of the wanted signal and suppress interferers from other directions efficiently. For this purpose, array antennas are used. They consist of several elements which are fed by the same signal but with different amplitudes and phases. Apart from an increase of the antenna gain the deployment of array antennas leads to a significant improvement in flexibility when using algorithms to beamforming, since the antenna pattern can be adapted to the current scenario. Besides the shaping and direction of the main beam in real time it is possible to suppress incident spurious signals and multi-path components. Basically, the signals of the individual antenna elements must be weighted in amplitude and phase to form the desired beam pattern. With digital beamforming this weighting takes place during the processing of the data and makes the efficient employment of such algorithms possible.
Antenna pattern after applying the LCMV algorithm to suppress interferers and directing the main beam to the data signal
In the antenna working group, a variety of methods for beamforming and –steering is investigated and further developed. Two classes of algorithms can be distinguished. On the one hand there are deterministic, i.e. data-independent procedures. Here the weighting coefficients mentioned above are adjusted on the basis of additional information and desired characteristics of the diagram. This also comprises the classical procedures for antenna pattern synthesis.
In the second class, the statistical procedures, the real antenna signals are included into the computation of the weights by the algorithms. For this reason statistic procedures are limited to digital beamforming in the case of reception. The advantage lies in the fact that with the help of mathematical procedures information can be extracted from the received signals, which is used for the determination of an optimal antenna pattern according to certain criteria in the statistical sense. An example is the determination of the direction of arrival (DOA) of interfering signals and the subsequent minimization of noise by undisturbed reception of the information signal and simultaneous fading out of the detected interferers. The figure shows an antenna pattern where the principle of linear constrained minimum variance (LCMV) was used for this purpose.