8T8R vs 64T64R: Understanding Massive MIMO Antennas

This article compares conventional 8T8R antennas with 64T64R massive MIMO antennas, highlighting the key differences between these two types of Massive MIMO antenna configurations.

What is Massive MIMO?

Massive MIMO (mMIMO) is a system that employs a large number of antenna elements in the form of an active antenna array. This array transmits multiple data streams in a specific direction, significantly boosting system capacity, data throughput, and coverage. The core principle behind Massive MIMO is beamforming, which focuses energy towards the intended user, minimizing interference from other users.

Massive MIMO systems are categorized into two main types, based on the number of users served by the Base Station (eNB):

• SU-MIMO (Single-User MIMO): All the streams from the antenna array are directed towards a single user.
• MU-MIMO (Multi-User MIMO): Multiple streams are directed to multiple users simultaneously, allowing the antenna system to provide radiated energy to more than one user at a time. Massive MIMO primarily uses MU-MIMO, combining multiple radio transceiver units with antenna elements on a single active unit.

Conventional 8T8R Antenna

• Each column utilizes 8 antenna elements to create a vertically fixed direction pattern.
• The eight columns, each connected to a single transceiver for signal transmission, are designed for horizontal beamforming only.
• “8T8R” signifies 8 transmit and 8 receive antenna elements, resulting in a total of 16 antenna elements.

64T64R Massive MIMO Antenna

• “64T64R” represents 64 transmit and 64 receive antenna elements, for a total of 128 antenna elements (arranged as Row x Column x polarization = 8 x 8 x 2).
• Supports a maximum of 16 layers (Lm).
• Equipped with 64 RF Transceiver units, each mapped to two antenna elements. These elements use different polarizations to transmit unique data streams. The polarizations are at 90 degrees to each other (cross polarization).
• All 128 antenna elements create an antenna pattern, with the array design enabling both vertical and horizontal beamforming.
• The vertical dimension, with per antenna element adjustments, allows for more layers and finer adjustments, transforming a column of antennas into a true antenna array.
• Massive MIMO can operate with both Frequency Division Duplex (FDD) and Time Division Duplex (TDD). TDD uses the same frequency for downlink (DL) and uplink (UL), while FDD uses different frequencies. TDD is often preferred due to channel reciprocity. With FDD, the feedback overhead increases with the number of antenna elements.