Digital Beamforming: Advantages and Disadvantages

This page covers the basics of Digital Beamforming, including its advantages and disadvantages.

The purpose of beamforming is to improve coverage by providing amplitude/phase variation using an antenna array. There are three main types of beamforming based on different architectures:

• Analog beamforming
• Digital beamforming
• Hybrid beamforming

What is Digital Beamforming?

In digital beamforming, amplitude/phase variation (i.e., wk) is applied to the digital signal after ADC/DDC conversion at the transmit end. At the receiver, received signals are first passed through ADC converters and digital down converters before being summed.

In this architecture, operations such as precoding, multiplexing, signal weighting, and phase shifting occur in the digital domain, which has many benefits. It’s particularly useful in frequency-selective beamforming applications.

Figure 1: Digital beamforming block diagram

Mathematical Equations

s(t) = x(t) + j*y(t)

Where:

• s(t) -> complex baseband signal
• x(t) -> i(t) i.e. real part (I)
• y(t) -> -q(t) i.e. imaginary part (Q)
• j = SQRT(-1)

Complex weights are applied to baseband signals (s(t)) in digital beamforming. Unlike analog beamforming, digital beamforming supports multiple RF chains proportional to the number of antenna elements in use.

Benefits or Advantages of Digital Beamforming

Here are the benefits and advantages of Digital Beamforming:

• Simplified Architecture: Each antenna has a dedicated RF chain. Silicon processes can fabricate the entire RF chain based on system requirements.
• Flexibility: The number of beams from the antenna is variable, depending on the number of elements in the beam. Beams are steerable, and algorithms can synthesize a drive signal to maximize beam characteristics.
• High Number of Beams: Digital beamforming can provide a high number of beams.
• Dynamic Beam Changes: The number of beams can be changed dynamically without hardware modifications.
• Full Array Gain: Each beam benefits from the full array gain.
• Wide Usage: It is widely used in sub-6 GHz bands due to its performance and capabilities.

Drawbacks or Disadvantages of Digital Beamforming

The following are the drawbacks and disadvantages of Digital Beamforming:

• Increased Digital Chip Content: This architecture increases digital chip content, leading to higher cost and power consumption. It consumes the highest DC power.
• I/Q Signal Routing Complexity: Offers complex I/Q signal routing.
• LO Signal Routing Complexity: Presents complex LO signal routing.
• High Hardware Complexity: Requires a full RF chain per element or column in the array, resulting in high hardware complexity.
• Hardware Limitations at High Frequencies: Hardware may not fit within the lattice at high frequencies, limiting 2D scan capabilities for planar arrays.