MIMO Multiple-input–multiple-output

Last updated on May 2, 2023

MIMO (Multiple-input–multiple-output) is a wireless communication technique that uses multiple antennas at both the transmitter and receiver ends to improve the data throughput, system capacity, and reliability of wireless communication systems. MIMO is one of the key technologies used in modern wireless communication systems such as Wi-Fi, 4G/LTE, 5G, and beyond.

In this article, we will explain what MIMO is, how it works, its advantages, and its applications in modern wireless communication systems.

Introduction to MIMO

MIMO is a wireless communication technique that uses multiple antennas at both the transmitter and receiver ends to improve the system capacity and reliability. MIMO was first introduced in the late 1990s, and since then, it has become a key technology in modern wireless communication systems.

In a MIMO system, multiple antennas are used to transmit and receive multiple data streams simultaneously over the same frequency band. This is achieved by exploiting the spatial diversity of the wireless channel, which refers to the fact that the wireless channel can support multiple parallel paths between the transmitter and receiver due to reflections, diffraction, and scattering.

By using multiple antennas at both ends, the MIMO system can increase the spatial diversity of the wireless channel, thereby improving the data throughput, system capacity, and reliability of wireless communication systems.

How MIMO works

MIMO works by exploiting the spatial diversity of the wireless channel, which refers to the fact that the wireless channel can support multiple parallel paths between the transmitter and receiver due to reflections, diffraction, and scattering.

In a MIMO system, multiple antennas are used to transmit and receive multiple data streams simultaneously over the same frequency band. This is achieved by using a technique called spatial multiplexing, which involves transmitting different data streams over different spatial channels using different antennas.

Spatial multiplexing is achieved by using a technique called singular value decomposition (SVD), which decomposes the wireless channel into a set of orthogonal spatial channels. Each of these channels corresponds to a different antenna, and can be used to transmit a different data stream.

At the transmitter end, the data streams are modulated and transmitted over the different spatial channels using the corresponding antennas. At the receiver end, the received signal is demodulated and decoded to extract the different data streams.

The receiver then combines the decoded data streams to reconstruct the original data. This is achieved by using a technique called maximum ratio combining (MRC), which combines the different received signals using the corresponding channel gains.

Advantages of MIMO

MIMO offers several advantages over traditional single-antenna communication systems. These advantages include:

Increased data throughput: MIMO can increase the data throughput of wireless communication systems by transmitting multiple data streams simultaneously over the same frequency band. This allows MIMO systems to achieve higher data rates than traditional single-antenna systems.
Improved system capacity: MIMO can improve the system capacity of wireless communication systems by exploiting the spatial diversity of the wireless channel. This allows MIMO systems to support more users and devices than traditional single-antenna systems.
Improved reliability: MIMO can improve the reliability of wireless communication systems by reducing the effects of fading and interference. This is achieved by using multiple antennas to exploit the spatial diversity of the wireless channel, which reduces the probability of a deep fade occurring on all the spatial channels simultaneously.
Improved coverage: MIMO can improve the coverage of wireless communication systems by reducing the effects of shadowing and multipath fading. This is achieved by using multiple antennas to exploit the spatial diversity of the wireless channel, which allows the MIMO system to use multiple paths to overcome the effects of obstacles and reflections.

Applications of MIMO

MIMO is used in a wide range of wireless communication systems, including:

Wi-Fi:

MIMO is a key technology in Wi-Fi systems, which use MIMO to achieve high data rates and improved coverage. Wi-Fi systems typically use 2x2 or 3x3 MIMO configurations, which use two or three antennas at both the transmitter and receiver ends.

4G/LTE:

MIMO is a key technology in 4G/LTE systems, which use MIMO to achieve high data rates and improved coverage. 4G/LTE systems typically use 2x2 or 4x4 MIMO configurations, which use two or four antennas at both the transmitter and receiver ends.

5G:

MIMO is a key technology in 5G systems, which use MIMO to achieve high data rates, improved coverage, and support for massive machine-type communications (mMTC) and ultra-reliable low-latency communications (URLLC). 5G systems use a variety of MIMO configurations, including 2x2, 4x4, 8x8, and even higher-order configurations.

Wireless LANs:

MIMO is also used in wireless LANs (WLANs) such as IEEE 802.11n/ac/ax systems, which use MIMO to achieve high data rates and improved coverage. WLANs typically use 2x2 or 4x4 MIMO configurations, which use two or four antennas at both the transmitter and receiver ends.

Cellular systems:

MIMO is also used in cellular systems such as CDMA2000, WCDMA, and TD-SCDMA systems, which use MIMO to achieve high data rates and improved coverage. Cellular systems typically use 2x2 or 4x4 MIMO configurations, which use two or four antennas at both the transmitter and receiver ends.

Conclusion

In conclusion, MIMO is a wireless communication technique that uses multiple antennas at both the transmitter and receiver ends to improve the data throughput, system capacity, and reliability of wireless communication systems. MIMO achieves this by exploiting the spatial diversity of the wireless channel, which allows MIMO systems to transmit and receive multiple data streams simultaneously over the same frequency band.

MIMO offers several advantages over traditional single-antenna communication systems, including increased data throughput, improved system capacity, improved reliability, and improved coverage. MIMO is used in a wide range of wireless communication systems, including Wi-Fi, 4G/LTE, 5G, WLANs, and cellular systems. As wireless communication systems continue to evolve, MIMO is expected to play an increasingly important role in enabling high-speed and reliable wireless communication.