Mobile networks today use advanced antenna systems that make use of multi-antenna technologies. MIMO, SISO, SIMO and MISO are types of antenna systems where SISO is the most basic and MIMO is the most advanced form of the radio communication link between the transmitter and the receiver.
MIMO is an advanced antenna system that uses multiple antennas at the transmitter and the receiver; SISO uses one antenna at the transmitter and one at the receiver; SIMO uses multiple antennas at the receiver and one at the transmitter; MISO uses multiple antennas at the transmitter and one at the receiver.
MIMO, SISO, SIMO and MISO comparison
The key difference between MIMO, SISO, SIMO and MISO is the use of a different number of antennas at the transmitting and receiving ends. The reason behind the existence of these terminologies is the use of multi-antenna systems, which in mobile communications started in the 1990s.
The simplest way to enable radio communication is by using a SISO antenna technology that has one antenna to transmit and one to receive. The most complex but advanced form of radio communication uses MIMO antenna technology that employs multiple antennas to transmit and receive.
MISO and SIMO fall between SISO and MIMO, where MISO employs multiple transmitting antennas and a single receiving antenna, whereas SIMO uses a single transmitting antenna and multiple receiving antennas.
| Antenna system | Transmitter (Tx) | Receiver (Rx) |
|---|---|---|
| SISO (Single Input Single Output) | One antenna | One antenna |
| MISO (Multiple Input Single Output) | Multiple antennas (two or more) | One antenna |
| SIMO (Single Input Multiple Output) | One antenna | Multiple antennas (two or more) |
| MIMO (Multiple Input Multiple Output) | Multiple antennas (two or more) | Multiple antennas (two or more) |
Single Input Single Output – SISO
SISO stands for Single Input Single Output, and it is the simplest radio communication link between a transmitter and a receiver. SISO employs a single transmitting antenna (Single Input) and a single receiving antenna (Single Output).
When a radio signal travels through the air, it encounters many obstructions such as buildings, mountains, trees, poles, cables, reflecting surfaces, etc. Radio signals are electromagnetic waves, and they undergo a scattering effect when they face any obstacles. These obstructions negatively impact the signal strength, making it very weak by the time it arrives from the transmitter to the receiver.
The signal can take multiple routes between the transmitter and the receiver and experiences multipath fading. When multipath fading happens, the characteristics of the signal change leading to a drop in signal quality which introduces errors into the signal. One way to overcome this challenge is through diversity (spatial diversity) which requires multiple antennas at the transmitter or the receiver.
When used between a base station and a mobile phone, SISO antennas are not able to overcome the negative impact of signal fading because they cannot achieve transmit or receive diversity due to using only one antenna to transmit and one to receive. Even though SISO is simple to implement, the options for improving signal quality and reducing interference in SISO are limited.
Multiple Input Single Output – MISO
MISO or Multiple Input Single Output employs multiple transmitting antennas (Multiple Inputs) but only one receiving antenna (Single Output). The benefit of MISO is that it has the capability to address the negative impact of signal fading to improve radio link reliability.
MISO utilises transmit diversity where multiple copies of the same signal are sent toward the receiving antenna. The communication from the multiple transmitting antennas is encoded differently so that the receiving antenna can accurately decode the communication from different transmitting antennas.
MISO ensures better signal quality while consuming less power when used between a base station transmitter and a mobile phone receiver. It also benefits from the fact that all the power-intensive work of diversity and antenna redundancy is at the base station, which is connected to a dedicated power supply instead of a mobile phone that has a small battery.
Single Input Multiple Output – SIMO
SIMO or Single Input Multiple Output employs a single transmitting antenna (single input) and multiple receiving antennas (multiple outputs). The benefit of SIMO is that it allows a network to reduce the negative impact of signal fading by allowing the receiver to catch the same signal through multiple antennas.
When a radio signal leaves the transmitter, it experiences multipath fading because the different obstacles in its way, such as buildings, trees, and other signals, make it weaker. As a result, the radio signal splits into pieces where different pieces take multiple routes or paths to arrive at the receiver.
SIMO is based on the principle of receive diversity that exploits the multipath fading of a radio signal by introducing multiple antennas for multiple paths. The receiving antennas then use antenna diversity to combine the received signals to recreate the signal. SIMO improves the signal link quality while the channel capacity stays the same.
When used between a mobile phone and a radio base station (cell tower), SIMO allows the radio signals from a mobile phone to have a better chance of being received by the multiple receiving antennas of the base station. Diversity requires additional work, which in SIMO is carried out by the radio base station, which is connected to the main power supply.
Multiple Input Multiple Output – MIMO
MIMO or Multiple Input Multiple Output offers the best solution to improve the radio link quality while also improving the throughput (bit rates) for the end-user. MIMO is also referred to as multiple-transmit, multiple-receive (MTMR).
The focus of MIMO antenna technology is on network coverage and network capacity. MIMO is an antenna system that employs multiple antennas at the transmitter (Multiple Input) and multiple antennas at the receiver (Multiple Output).
MIMO improves the signal-to-noise ratio (SNR) of a communication system and employs spatial multiplexing, which consists of multiple spatially separated antennas to send and receive the signal in separate data streams.
In MIMO, the available transmission power is spread over multiple antenna arrays to achieve array gain, which improves spectral efficiency. In addition, diversity gain is achieved by implementing multiple antennas at the transmitter and the receiver to enhance the quality of the signal.
MIMO can efficiently utilise the available channel bandwidth to offer better radio link quality through diversity and higher data rates through spatial multiplexing. It also has beamforming which provides directivity to the signal making it easier to provide targetted coverage and bit rates to individual user devices.
Since multi-antenna technologies like MIMO require support from both the mobile network and the mobile phone, the uptake of the antenna technology for a given cellular technology is better when mobile phones support the required antenna configuration from the beginning.
The MIMO technology was first introduced in the mobile networks in the HSPA Evolution (HSPA+) enhancement as part of the 3G network evolution. However, the uptake of MIMO was more noticeable when 4G LTE (Long Term Evolution) networks were launched as they supported MIMO from the first LTE release (3GPP Release 8).
The latest generation of mobile networks, 5G NR (New Radio), employs an advanced form of MIMO called Massive MIMO. I have written dedicated posts on MIMO for 4G LTE networks and Massive MIMO for 5G NR networks.
Here are some helpful downloads
Thank you for reading this post. I hope it helped you in developing a better understanding of cellular networks. Sometimes, we need extra support, especially when preparing for a new job, studying a new topic, or buying a new phone. Whatever you are trying to do, here are some downloads that can help you:
Students & fresh graduates: If you are just starting, the complexity of the cellular industry can be a bit overwhelming. But don’t worry, I have created this FREE ebook so you can familiarise yourself with the basics like 3G, 4G etc. As a next step, check out the latest edition of the same ebook with more details on 4G & 5G networks with diagrams. You can then read Mobile Networks Made Easy, which explains the network nodes, e.g., BTS, MSC, GGSN etc.
Professionals: If you are an experienced professional but new to mobile communications, it may seem hard to compete with someone who has a decade of experience in the cellular industry. But not everyone who works in this industry is always up to date on the bigger picture and the challenges considering how quickly the industry evolves. The bigger picture comes from experience, which is why I’ve carefully put together a few slides to get you started in no time. So if you work in sales, marketing, product, project or any other area of business where you need a high-level view, Introduction to Mobile Communications can give you a quick start. Also, here are some templates to help you prepare your own slides on the product overview and product roadmap.
