MIMO Basics: Types and Test & Measurement

This page describes MIMO basics, MIMO types, and MIMO test and measurement solution providers. MIMO stands for Multiple Input Multiple Output.

Let’s clarify what “input” and “output” refer to.

The following figure shows an example with two transmit (Tx) antennas and two receive (Rx) antennas. Tx refers to antennas in the transmitting device, and Rx refers to antennas in the receiving device, located at some distance from the transmitter. The area between the transmitting and receiving devices is the channel, represented by arrows.

Here, “input” refers to the signal going into the channel, and “output” refers to the signal coming out of the channel. Hence, Input and Output are defined with respect to the channel.

Source: wikimedia commons

SIMO means single input and multiple output. MISO means multiple input and single output.

You’re likely already familiar with systems without multiple antennas, which are referred to as SISO, i.e., Single Input Single Output. Understanding this terminology is crucial for understanding MIMO.

If a device is labeled ‘2x3 MIMO’, it signifies that two antennas are used for transmission and three are used for reception.

Types of MIMO

There are two main types of MIMO:

• Spatial Multiplexing (SM): Different data streams are transmitted from the transmitting antennas, effectively doubling the data rate for a 2-transmitter antenna system.

• Space-Time Block Coding (STBC): A copy of the data transmitted from two antennas at time instant T1 is transmitted again at time instant T2. This isn’t an exact copy, but rather a manipulated version. This helps in recovering the transmitted symbols after passing through a multipath channel. While STBC doesn’t increase the data rate, it extends coverage or range.

Systems often require both good coverage and high data rates. In such cases, beamforming is frequently used in conjunction with MIMO spatial multiplexing. Beamforming multiplies the transmit signal with a vector or matrix to amplify the transmitting vector in a specific direction.

MIMO in Modern Technologies

MIMO is now implemented in many next-generation and current technologies, including Mobile WiMAX (802.16e), LTE (3GPP standard), 802.16m, 802.20, 802.11n, 802.11ac, etc.

Advantages and Disadvantages of MIMO

Advantages:

• Increased coverage with appropriate MIMO techniques (e.g., STBC).
• Increased data rate with Spatial Multiplexing.

Disadvantages:

• For mobile handsets, the complexity increases to accommodate multiple antennas in a limited space.

MIMO Test and Measurement Solution Providers

Here’s a list of companies providing MIMO device test equipment:

• Agilent Technologies
• Rohde and Schwarz
• Keithley Instruments Inc.
• National Instruments
• Anritsu corporation

MIMO MATLAB Code

• MIMO STBC
• 2T1R
• 2T2R