Intelligent antennas (also known as adaptive antennas, multiple antennas and, recently, MIMO) are antennas with intelligent signal processing algorithms that are used to identify the spatial signal, such as the direction of arrival (DOA) of the signal, And use it to calculate beam forming Vectors, to track and locate the antenna beam at the mobile / destination. Smart antennas should not be confused with reconfigurable antennas, which have similar capabilities but are single-element antennas and not antennas.
Intelligent antenna techniques are used mainly in acoustic signal processing, tracking and scanning radar, radio astronomy and radio telescopes, and especially in cellular systems such as W-CDMA, UMTS and LTE. Smart antennas have two main functions: the estimation of DOA and Beamforming. The intelligent antenna system estimates the direction of arrival of the signal, using techniques such as MUSIC (Multiple Signal Classification), estimation of signal parameters through ESRIT algorithms, Matrix Pencil method or one of its derivatives. They involve finding a spatial spectrum of the antenna / sensor array, and calculating the DOA of the peaks of this spectrum. These calculations are computationally intensive.
Matrix Pencil is very efficient in the case of systems in real time, and under correlated sources. In conventional wireless communications, a single antenna is used at the source, and another single antenna is used at the destination. This is called SISO (single input, single output). These systems are vulnerable to problems caused by multipath effects. When an electromagnetic field (electromagnetic field) encounters obstructions such as hills, canyons, buildings and utility cables, wave fronts are dispersed, and therefore take many paths to reach the destination. Late arrival of scattered parts of the signal causes problems such as fading, cut (cliff effect) and intermittent reception (picket fencing). In a digital communications system such as the Internet, it can cause a reduction in data speed and an increase in the number of errors. The use of intelligent antennas can reduce or eliminate the problem caused by the propagation of multipath waves.
Smart antennas are divided into three main categories: SIMO (single input, multiple output), MISO (multiple input, single output) and MIMO (multiple input, multiple output). In SIMO technology, an antenna is used at the source, and two or more antennas are used at the destination. In MISO technology, two or more antennas are used at the source, and an antenna is used at the destination. In MIMO technology, multiple antennas are used both at the source and at the destination. MIMO has attracted attention more recently, as it can not only eliminate the adverse effects of multipath propagation, but in some cases can make it an advantage.
