The creation of a beam using the constructive interference between the signals transmitted by each antenna element is known as beamforming.
Using the MIMO technique we can construct a phased array antenna with which based on the antenna spacing and phase signal we can control the shape and direction of a signal.
Watch the following video to understand more about altering the beam direction by changing the phase of each antenna.
Advantages of Beamforming:
- The higher frequency waves like mmwave experience greater air-interference attenuation. So, by using beamforming we can increase the antenna gain which reduces the loss in both uplink and downlink and improves the throughput.
- Using beamforming we can generate the narrow beams to the desired direction which will reduce the inter-cell interference when compared with wide beams in all directions.
- With beamforming, we can achieve MU-MIMO, where eNB can serve two different UE’s in two different directions at the same time by forming two beams. To do this both users should be spatially separated. The same PRB’s can be allocated to different users at the same time as they are being served with different beams in different directions which improves the bandwidth efficiency.
Beamforming needs the antenna array with multiple antenna elements. We can arrange the antenna elements in multiple ways. Following are some examples.
- The following array contains 8 antenna connectors with 2 cross-polar antennas in each row. This refers to {4, 1, 2} antenna array where 4 = columns, 1=rows & 2 = antenna polarisations. With this type of array, we can generate a beam from left to right i.e. the azimuth of the beam can be controlled.
2. The following array contains 12 antenna connectors. This type of pattern can produce the beam in all directions (Left, right, up, down).
Why the antenna array size is small in 5G?
Antenna elements are designed using a half-wave dipole. Each antenna element size is half a wavelength. In 5G, we use mmwaves. The wavelength of mmWave is very small when compared to 4G.
At 3GHz the wavelength is almost 10 cms. Whereas in 30GHz the antenna size reduces to 9mm. So antenna array panel can be designed with more compact size & this, in turn, unlock the possibility to place antenna arrays in the UE.
As told, at transmitter the beamforming depends upon the constructive interference between the signals transmitted by each antenna element. So, by altering the phase of a signal generated by each antenna we can steer the beam towards a particular direction which is known as beam steering.
With the following figure, you can visualize how changing the phase of each antenna alters the direction of the beam.
If the no of antenna elements increases at the transmitter side, then the signal gain will also increase which results in more directional and narrow beams.
Fig 85 shows the antenna gain pattern when using 4 antennas & Fig 86 shows the antenna gain pattern when using 8 antennas. Doubling the antennas halves the bandwidth usage and also increases the signal gain. To serve all the UE’s in all the directions, we have to form multiple directional beams.
