“Beamforming is a mature technology used in cellular communications and other applications. Beamforming was originally developed based on various analog signal chain technologies and processes. Generally speaking, beamforming combines antenna array elements to steer the signal at a controlled angle so that a particular receiver can receive the maximum signal.
Beamforming is a mature technology used in cellular communications and other applications. Beamforming was originally developed based on various analog signal chain technologies and processes. Generally speaking, beamforming combines antenna array elements to steer the signal at a controlled angle so that a particular receiver can receive the maximum signal.
Analog beamforming can improve the spatial selectivity and efficiency of the transmitter and receiver. However, it is still limited by the next-generation beamforming technology based on digital technology to enhance analog processing. Digital beamforming or hybrid digital/analog beamforming can overcome the limitations of analog beamforming, including:
The antenna element is fed by a single data stream, which limits the data rate;
Not very flexible;
The number of available beams is fixed in the hardware;
Since a different signal is optimized for each antenna in the digital domain, digital beamforming can overcome these limitations and provide greater flexibility. Through digital beam forming, different powers and phases can be allocated to different antennas and different frequency bands. In addition, digital beamforming supports spatial multiplexing, so that different frequency bands (subcarriers) have different directivity. Frequency domain beamforming includes the ability to support different beams of different subcarriers, but the realization of frequency domain beamforming requires digital beamforming.
In the case of time-domain beamforming, the same beam is applied to the entire frequency carrier. Time-domain beamforming is usually implemented using analog beamforming techniques, although it can also be implemented using digital beamforming. However, there are some technical limitations that hinder the full adoption of digital beamforming.
Today, two important issues for full millimeter wave digital beamforming are the cost and power requirements of the baseband processor. In order to reduce these concerns, low-resolution converters must be used to achieve full millimeter wave digital beamforming to keep the front-end power consumption at a manageable level. Therefore, the spatial multiplexing gain expected from the all-digital approach can only be achieved at the cost of unacceptable signal degradation.
To make matters worse, today’s communication protocols are designed based on the assumption of using analog or hybrid beamforming. This limits the ability to take full advantage of the potential advantages of digital beamforming. In the future, the specifications of control and data channel protocols may be modified to enable all-digital beamforming to deliver the required low-latency communications and high-quality services (QoS).
Aiming at the problems and limitations of all-digital beamforming or all-analog beamforming, a promising solution was born—hybrid beamforming. Hybrid beamforming uses a combination of baseband digital processing and radio frequency domain analog processing. Several hybrid beamforming solutions are under development, using different system partitioning methods between the digital domain and the analog domain and within the domain. In order to seek the best combination of digital baseband processing and analog RF signal chain processing.
In the RF domain, a tangible hybrid beamforming structure combining digital baseband processing and analog phase shifters
Among the many possible hybrid beamforming systems, two examples are the fully connected system and the sub-connected system. In a fully connected structure, each radio frequency chain is connected to all antennas. The transmission signal of each digital transceiver passes through a dedicated radio frequency path (with mixer, power amplifier, phase shifter, etc.). It is superimposed before connecting to the antenna. This method has higher performance, but at the same time it also brings higher complexity and energy consumption. Each transceiver using this method achieves full beamforming and is expected to be used in base stations and similar fixed installations.
Another method called sub-connected beamforming architecture is more suitable for mobile phones and other applications, such as cars. In sub-connected beamforming, each radio frequency signal chain is connected to only a subset of the available antennas. This makes the sub-connection architecture simpler and more energy-efficient, but its spectrum efficiency is lower, and it is not suitable for large-scale installations where spectrum efficiency is important.
At present, in order to supplement the existing simulation and hybrid methods, researchers are still developing new technologies for beamforming and millimeter wave transmission. For example, holographic beamforming can also shape the radio pattern of an antenna under software control. You can think of this as a software-defined antenna. The recently developed Electronic scanning antenna technology, called metamaterial surface antenna technology, is based on the concept of diffractive metamaterials and uses highly birefringent liquid crystals to achieve electronic scanning.
In addition to metamaterial antennas and holographic beamforming, there are also people who are interested in developing metamaterials to make smart, digitally controlled reflective surfaces for 5G and future 6G networks. However, using smart reflective surfaces to control the wireless propagation environment is a big challenge. To this end, researchers will develop a two-dimensional metamaterial array of intelligent reflective surfaces, which can be controlled by the interaction with electromagnetic waves, for example, by adjusting the changes in surface impedance. In 6G, these surfaces can direct wireless signals from the transmitter to the receiver. The final idea is to describe the behavior of the smart reflective surface based on wireless signal data, and develop a control algorithm to configure the reflective surface to help wireless communication.
The digital beamforming and related technologies of 5G communication are developing rapidly. These technologies and related technologies such as intelligently controlled reflective surfaces are expected to become important elements in the design of future 5G installations.