antenna larger and increases the antenna gain. The spacing of the antenna elements depends on the frequency: the physical size of the antenna is larger at lower frequencies. The number of antenna elements defines the antenna gain and antenna size. The size is also heavily dependent on the frequency. The antenna becomes smaller at high bands. The number of TRXs can be equal to or lower than the number of antenna elements, and it defines the capacity gain. The number of MIMO streams can be equal to or lower than the number of TRXs. The number of MIMO streams defines the peak data rate capability, and it is mainly dependent on the baseband processing capability. When the number of antenna elements is larger than the number of TRXs, the addi- tional elements are typically added as more rows. A typical MIMO antenna could have 192 antenna elements, 64 transmitters, and support up to 16 MIMO streams. There are three rows per TRX in this antenna. 192 antenna 64 TRXs elements Number of XXXXXXXX Number of antenna transmitters define the elements defines the number of antenna gain, which simultaneous beams controls coverage. that can be created. More antenna elements More transmitters give more coverage give more capacity But more antenna But more transmitters TRX63 XXXXXXXX elements increase the also increase power size of the antenna consumption and cost TRX64 Figure 3.6 Massive MIMO principles with more transmitters and more antenna elements. 3.4 Flexible Physical Layer and Protocols Figure 3.7 Common channel beamforming in 5G with beam sweeping. sweeping There are a number of reasons why beamforming can yield more gains in 5G than in Beamforming is supported for 5G common channels with beam sweeping; see Figure 3.7. Beam sweeping refers to the operation where the synchronization signal and broadcast channel are transmitted in different beams in the time domain. Common channel beamforming is not supported in LTE. User-specific reference signals in 5G support user-specific beamforming. LTE must use cell-specific reference