# On Analyzing Beamforming Implementation in O-RAN 5G
## 4 O-RAN Beamforming
### O-RAN Beamforming Methods  
The following are the methods proposed by O-RAN in order to achieve acceptable performance in beamforming:  
* **Beamforming indexing method (predefined-beam beamforming).** O-DU sends information about the beamforming type to the O-RU predicated on BeamID, and the O-RU stores this information in a table of beam indexes. This table contains beam weights, which could be frequency domain beam weights (digital beamforming), time-domain beam weights (analog beamforming), or both of them as hybrid beamforming; the BeamID is utilized as a pointer to a pre-defined beamforming weight vector. Therefore, BeamID is only a weight vector value exchanged between O-DU and O-RU to indicate which beam should be applied.
* **Real-time weights method (weight-based dynamic beamforming).** In this method, the O-DU sends the beamforming weights generated in real time to the O-RU to be associated with a specific user's data. A beam index can be assigned (and utilized in subsequent messages) if the beamforming weights are stable for a period of time. There are two implementation cases in this method: weight-based dynamic (digital and analog) beamforming and weight-based dynamic hybrid beamforming; in the first case, the beamforming weights can be updated in real time with the BeamID value associated with the weights. In the second case, two sub-cases are considered: (1) both the frequency-domain and time-domain weights may be updated in real-time, and (2) the frequency-domain weights may be updated in real-time, and the time-domain beams are fixed. Let us remark that frequency domain weights are applied to the frequency domain IQ data per section, and the time domain weights are applied to the time domain IQ data per OFDM symbol.
* **Beam attributes method (attribute-based dynamic beamforming).** The main drawback of the previous method is that it requires additional processing capability in the O-RU for adjusting transmission to the beam weights provided by the O-DU. Therefore, a modification to the previous method has been proposed so that we obtain the beam attributes method. The modification is that the O-RU is in charge of generating the beamforming weights using a set of beam attributes signaled by the O-DU and carried (to the O-RU) by the control plane. These attributes are (1) azimuth and elevation, (2) beam width (narrow, wide), (3) side lobe suppression, and (4) beam weights calculated by RU. The consequence of the generation of beam weights by the O-RU is that the hybrid beamforming is not allowed in the beam attributes method. The reason is that the weights generated by O-RU will be either frequency-domain or time-domain but not hybrid.
* **Channel information method (channel-information-based beamforming).** This method is based on digital beamforming. It is known that digital beamforming is a good solution for capacity and flexibility in the case of a high-traffic communication environment since it offers steerable beams. Each antenna has a dedicated RF signal and path and provides a high number of beams that can be transmuted dynamically with no change in the hardware. Thus, in this method, the O-RU generates beam weights based on the channel information from O-DU. The algorithms can synthesize a drive signal to obtain the maximum of any beam characteristics. However, implementing the precoding in RU will lead to inter-RU interferences in the O-RU. The zero-forcing algorithm (ZF) is one of the algorithms that can be implanted to overcome this interference issue in received signals.