FD-MIMO in LTE and 5G: Explained

This page provides an overview of FD-MIMO (Full Dimensional Multiple Input Multiple Output) features used in LTE and 5G systems. It outlines the benefits and advantages of FD-MIMO, as well as some drawbacks and disadvantages.

What is FD-MIMO?

Introduction: FD-MIMO stands for Full Dimensional Multiple Input Multiple Output.

In FD-MIMO, signals are transmitted in virtual beam formats, powering receivers from all three dimensions. This is why it’s also known as 3D-MIMO. It’s supported in 3GPP specifications for LTE up to Release 14.

Image Courtesy : arxiv.org

As illustrated above, FD-MIMO utilizes a 2D array structure, accommodating a large number of antenna elements. These elements are packed in smaller form factors, a design consideration crucial for LTE/5G Base Stations (BS).

FD-MIMO employs both horizontal and vertical beamforming, enabling beams to be focused in three-dimensional space. This technology is implemented in both frequency bands below 6 GHz and millimeter wave (mmWave) bands.

Antenna arrays can be arranged in any rectangular format, with an 8x8 array commonly used in LTE. The same antenna array, potentially smaller in size, can be used in 5G NR systems.

With advancements in technology, the BBU (Baseband Unit) and RRU (Remote Radio Unit) are often installed separately. In this architecture, only analog RRUs are located at the cell site, reducing equipment and simplifying network installation. BBUs are installed indoors, often far from the outdoor cell site. The BBU and RRU communicate using CPRI/eCPRI interfaces.

FD-MIMO also supports higher-order MU-MIMO (Multi-User MIMO).

Benefits and Advantages of FD-MIMO

Here are the key benefits and advantages of FD-MIMO:

• Increased Spectrum Efficiency: FD-MIMO supports multiple users on the same bandwidth, leading to a more efficient use of the available spectrum.
• Reduced Interference: It minimizes interference at the receiver from overlapping transmissions, boosting signal strength.
• Improved Cellular Capacity: FD-MIMO significantly enhances cellular capacity, potentially by 3 to 5 times.
• Compact Antenna Arrays: Smaller antenna arrays can be utilized at cellular towers.
• Dynamic Beam Pattern Adaptation: The use of AAS (Active Antenna System) in FD-MIMO allows for dynamic beam pattern adaptation in three-dimensional space.
• Simplified Operation & Management: FD-MIMO offers streamlined and efficient operation and management of the system.
• Increased Throughput: FD-MIMO antenna arrays can increase average system throughput by 2 to 3 times compared to conventional antenna arrays.

Drawbacks and Disadvantages of FD-MIMO

Here are the drawbacks and disadvantages of FD-MIMO:

• Increased System Complexity: As the number of antenna elements increases, the system becomes more complex, requiring robust signal processing algorithms at the receiver.
• Higher Cost: FD-MIMO systems are generally more expensive compared to conventional MIMO systems.