MIMO (Multiple Input Multiple Output) is an antenna technology in LTE. It uses multiple antenna elements at the transmitter and the receiver to improve signal quality and bit rates. MIMO employs spatial multiplexing, diversity and beamforming techniques to improve link quality and data rates. MIMO implementation is complex in mobile networks, because it poses additional hardware requirements both on the transmitter and the receiver sides.

MIMO in LTE networks is primarily used due to spatial multiplexing that improves data rates by using multiple antenna elements that are physically separated in space on a transmitter or receiver.

LTE networks basically use MIMO configurations of 4×4 in the downlink and 2×2 in the uplink as per 3GPP Release 8. While LTE Advanced and LTE Advanced Pro enhancements uses 8×8 MIMO configuration in the downlink and 4×4 in the uplink which can be seen in the given figure.

Fig:MIMO configurations for LTE, LTE Advanced and LTE Advanced Pro

MIMO enhances the transmission layers by deploying multiple antennas both for transmission and reception in both LTE and LTE advanced networks.

LTE networks as part of 3GPP Release 8 employs 4 x 4 MIMO configuration for the downlink transmission (network to the phone) and 2 x 2 for the uplink transmission (phone to the network). This configuration means that four antennas can be used at the cellular base station to transmit the signal and four antennas at the receiver.

The fig shown below is a simplified network diagram that shows a 2 x 2 MIMO for downlink and 2 x 2 for uplink.

2 x 2 MIMO uplink and downlink: The communication between mobile phone to the base station is done by using two antennas at the transmitter (e.g. phone’s transmitter) and the receiver (base station receiver)

Because of LTE Advanced in Release 10, the MIMO configuration went up to 8 x 8 for the downlink and 4 x 4 for the uplink. LTE Advanced Pro networks in Release 13 maintained the same MIMO configuration as LTE Advanced.

Thus MIMO is an antenna technology which employs multiple antennas at the transmitter and receiver ends to improve the signal quality and bit rates for LTE networks. It creates multiple paths for the transmission and reception of the radio signal. MIMO also achieves signal and bit rate enhancements through spatial multiplexing, antenna diversity and beamforming.