Antenna diversity and MIMO (Multiple Input Multiple Output) are two technology concepts frequently used in mobile communications. Antenna diversity is a more fundamental concept, whereas MIMO is an antenna technology that benefits from antenna diversity.
Antenna diversity is a technique in mobile networks that improves the radio link reliability through multiple antennas at the transmitter OR receiver; MIMO is an antenna technology in 4G and 5G that employs multiple antennas at the transmitter AND receiver for spatial diversity and multiplexing.
Difference between MIMO and Diversity
Diversity, antenna diversity or spatial diversity is a fundamental concept that has been used in mobile communications for years. It involves using multiple antennas primarily at the receiver of a base station (cell tower) so that mobile signals coming from different directions get a better chance to be picked up by the receiver. MIMO or Multiple Input Multiple Output is an antenna technology that is an application of antenna diversity. MIMO was introduced in mobile networks as part of 3GPP Release 7, which introduced HSPA Evolution (HSPA+) in 3G UMTS networks. MIMO employs multiple antennas at the transmitter and the receiver to benefit from spatial diversity and spatial multiplexing to improve radio link quality and data rates.
Antenna diversity improves the quality of the radio signal
Mobile networks use antenna diversity to minimise the impact of multipath signal fading that occurs due to the nature of radio signal propagation. The radio network improves the chances of receiving the signals from cell phones by using multiple antennas at the base station’s receiver.
Antenna diversity or spatial diversity is a technique used by radio (RF) antennas in mobile networks and other wireless systems. Diversity employs multiple antennas either at the transmitter or the receiver. The antennas are physically separated in space with the intention to overcome the negative impact of multipath fading. Antenna diversity has historically been used in cellular networks at the radio base station, where multiple antennas are deployed to receive the signals coming from the mobile phones successfully.
The concept of antenna diversity is based on the principle of multipath fading that a radio signal experiences as it travels through the air. In the air interface, a radio signal can take several routes to reach the receiving antennas depending on the obstructions in the way.
For example, if you are sitting in an office building trying to make a phone call through your mobile phone, your phone will communicate with the nearest possible cellular base station. However, your mobile signal may take various routes to travel from your phone’s transmitter to the base station’s receiver due to the thick walls, glass windows, reflecting surfaces and many other obstructions. By the time the signal arrives at the receiver, it may have experienced fading due to multipath losses. Therefore, mobile operators use multiple receiving antennas at the base station to improve the likelihood of successfully receiving the signal.
The primary idea of antenna diversity is to provide each receiving antenna with a replica of the signal. At the receiving end, the signal is reconstructed by combining the output of each of the antennas. Due to the spatial separation of the antennas, the signal is more likely to be received without too much overall fading. Typically, diversity is either applied at the transmitter end or the receiver end, which means we can have multiple antennas at the transmitter or the receiver.
MIMO improves signal quality and throughput (data rates)
MIMO is used in 3G UMTS, 4G LTE and 5G NR networks to improve the radio signal quality and data rates. MIMO achieves this goal by employing multiple antennas at the transmitter and the receiver to take advantage of antenna diversity, spatial multiplexing and beamforming.
MIMO or Multiple Input Multiple Output is an antenna technology that uses multiple antenna elements at the transmitter and receiver to improve radio signal quality and data rates. Unlike the conventional antenna diversity, MIMO uses multiple antennas at both the transmitter and the receiver, which enables diversity at both ends.
In MIMO, the transmitter antenna has multiple antenna elements, e.g. 2, 4, 8 or more, which transmit multiple signal data streams to the receiver. The receiver antenna also has a number of antenna elements to receive the data streams. The configuration of the MIMO system is defined by the number of antenna elements at the transmitter and receiver. For example, 4G LTE-Advanced networks have a configuration of 8×8 for the downlink, which means eight antenna elements at the transmitter and another eight at the receiver side when sending the signal from the base station to the mobile phone. LTE-Advanced networks use a lower configuration for the uplink with four antenna elements at the transmitter and four at the receiver (4×4) when sending the signal from the mobile phone back to the base station.
Antenna diversity is only one of the building blocks of MIMO systems where MIMO benefits from spatial diversity at both the transmitter and the receiver sides. 4G LTE and 5G NR networks employ MIMO technology due to the spatial multiplexing capability.
Unlike antenna diversity, spatial multiplexing can improve the overall network capacity and possible data rates for the customer. Spatial multiplexing is based on the concept of Space Division Multiple Access or SDMA. With spatial multiplexing, the multiple antenna elements that are part of one transmitter antenna send numerous data streams, each carrying bits and pieces of the overall data (e.g. a WhatsApp message) aimed toward the target user device (e.g. a 4G phone). The receiver antenna elements of the user device pick up the various data streams to put the overall data back together as a single data stream. This way, the mobile network can utilise the available radio network resources (i.e. frequency and timeslots) more efficiently by transmitting multiple data streams in parallel to improve the data rates for mobile phones users. Another benefit of MIMO is that it enables beamforming, which directs the signal and points the antenna beams towards the target user device to improve the range of the signal.
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.