Long Term Evolution (Advanced) - LTE(-A)
Multiple antenna transmission

Multiple antenna transmission represents techniques using more than one transmitting and/or receiving antennas for communication. This approach enables to achieve higher bit rates due to creation of several parallel channels. Multiple antennas can also introduce diversity gain against fading effects if antennas are deployed relatively far from each other as the channel characteristics are not correlated in this case. Multiple antennas can be deployed either only on one side (receiver or transceiver) or on both sides. The former case is denoted as SIMO (Single Input/Multiple Output) or MISO (Multiple Input / Single Output) for multiple receiving antennas and multiple transmitting antennas respectively. The later situation with multiple antennas on both sides is known as MIMO (Multiple Input / Multiple Output). Note that in UMTS, only two antennas on both sides are assumed. In LTE and LTE-A, up to four and eight antennas can be deployed on one side for MIMO respectively. An assignment of modulated data (symbols) to individual antennas is performed by an antenna mapping block. As the transmissions are deployed at the same time/frequency resources, the parallel transmissions introduce interference. Therefore advanced signal processing must be applied in the similar way like for beamforming. Consequently, each stream from an antenna is multiplied by complex weights to change phase of the signal.