MIMO vs SISO: Key Differences Explained

This article compares MIMO (Multiple Input Multiple Output) and SISO (Single Input Single Output) techniques, highlighting the key differences between them. These techniques are primarily distinguished by the number of antennas employed at the transmitter and receiver ends.

SISO has been a fundamental part of wireless communication since its inception. The MIMO concept, however, is a relatively recent addition designed to enhance wireless systems. Various MIMO algorithms have been developed with two primary goals: to increase coverage and to boost data rates.

What are SISO and MIMO?

• SISO (Single Input Single Output): Employs a single antenna at both the transmitter and the receiver.
• MIMO (Multiple Input Multiple Output): Utilizes multiple antennas at both the transmitter and the receiver.

Image: Illustrates a 2x2 MIMO configuration.

In a SISO system, a single antenna is responsible for both transmitting and receiving signals. Conversely, MIMO systems use multiple antennas for simultaneous transmission and reception. The figure above depicts a typical 2x2 MIMO setup.

Advantages of MIMO over SISO

MIMO systems generally achieve a better Bit Error Rate (BER) compared to SISO systems at the same Signal-to-Noise Ratio (SNR). This improvement is primarily due to a technique called Space-Time Block Coding (STBC).

• Coverage Enhancement: STBC allows for increased coverage.
• Higher Data Rates: MIMO systems can deliver significantly higher data rates because they transmit multiple data symbols simultaneously using multiple antennas. This technique is known as Spatial Multiplexing (SM).

Furthermore, MIMO systems incorporating both Spatial Multiplexing and beamforming can optimize both coverage and data rate performance in wireless systems.

Applications

• SISO: Commonly found in radio, satellite communication, GSM, and CDMA systems.
• MIMO: Used in advanced wireless technologies such as Mobile WiMAX (802.16e), WLAN (802.11n, 802.11ac, 802.11ad), and 3GPP LTE, among others.