Sunday, 14 October 2018
Massive MIMO Beamforming - from Keysight
Terms beamforming and mMIMO are sometimes used interchangeably. One way to put it is that beamforming is used in mMIMO, or beamforming is a subset of mMIMO. In general, beamforming uses multiple antennas to control the direction of a wave-front by appropriately weighting the magnitude and phase of individual antenna signals in an array of multiple antennas. That is, the same signal is sent from multiple antennas that have sufficient space between them (at least ½ wavelength). In any given location, the receiver will thus receive multiple copies of the same signal. Depending on the location of the receiver, the signals may be in opposite phases, destructively averaging each other out, or constructively sum up if the different copies are in the same phase, or anything in between. Beamforming is further divided to subcategories as explained as below...
As can be seen from Figure 3, the different SSBs (beams) of a cell are transmitted at different times. Therefore, there is no intra-cell interference among the SSB beams, and at least the scanning receivers should be able to detect also extremely weak SSB beams, even in presence of a dominant, strong beam from the same cell. As an example, let’s imagine a place of poor dominance in an LTE network, where a scanner or a test UE detects reference signals from 6 different cells. If it were a 5G network, the device could see, for example, six beams of each sox cells, in total 36 reference signals. Provided of course that the scanner or test UE is fast enough to catch all these signals. The performance of the UEs as well as scanners is yet to be seen both in the spec sheets and in practice.
Of course, it must be kept in mind that 5G can operate without beamforming, in which case there would be one SSB beam covering the whole cell area, and all the coverage testing methodology would default back to same as in LTE as SSB beam equals to cell in that case.