The cellular antenna technologies have evolved considerably since the introduction of 4G LTE networks that employ the MIMO (Multiple Input Multiple Output) antenna systems. The latest generation of mobile networks, 5G NR, also uses the MIMO technology.
MIMO is a modern antenna technology that employs multiple antennas at the transmitter and the receiver in 4G and 5G networks to improve data rates and signal quality. Massive MIMO is a type of MIMO in 5G that uses more than eight (8) antennas to offer MIMO benefits to multiple simultaneous users.
While the key reason for using MIMO in 4G LTE networks is spatial multiplexing, beamforming is another crucial benefit of MIMO that is especially important in 5G networks that use Massive MIMO systems.
Spatial multiplexing uses a number of physically separated antennas to transmit and receive data in multiple streams where each stream carries unique data to improve network capacity. Beamforming directs the mobile signal to individual users to extend network coverage and minimise interference.
MIMO uses multiple antennas to transmit and receive the signal
MIMO is an antenna technology used in HSPA, 4G LTE and 5G NR networks, and it employs multiple antennas at the transmitter and the receiver. Multiple antennas allow MIMO to take advantage of spatial multiplexing, antenna diversity, and beamforming to offer higher data rates and extended coverage.
MIMO or Multiple Input Multiple Output has been an essential part of mobile communications for many years. The MIMO technology was first introduced in the 3G UMTS (Universal Mobile Telecommunication System) networks as part of the HSPA (High-Speed Packet Access) evolution.
However, MIMO gained more popularity when 4G LTE (Long Term Evolution) networks were launched. The latest generation of mobile networks, 5G New Radio (NR), also employs the MIMO technology. MIMO has been part of the 4G LTE radio networks since the first LTE launch in 2009 based on 3GPP Release 8.
The basic scheme of MIMO relies on multiple antenna elements at the transmitter and the receiver. The transmitter and receiver antennas consist of various smaller antennas called the antenna elements. The MIMO configuration needs to be defined separately for the uplink and downlink communication.
Downlink is the communication from the cellular base station to the mobile phone, and it helps with the downloads. Uplink is the communication from the mobile device to the base station, and it helps with the uploads. The original LTE networks use a MIMO configuration of 4 x 4 in the downlink and 2 x 2 in the uplink.
So, for example, if you download something on your cell phone when connected to the LTE network (as per 3GPP release 8), the base station can use multiple antennas (up to four) to transmit the data. Likewise, your phone can use multiple antennas (up to four) at the receiving end to receive the data sent by the base station.
If you upload something when connected to the LTE network (3GPP Release 8), your phone’s transmitter can use up to two antenna elements to send the data, and the base station can use up to two antenna elements to receive what you send.
LTE Advanced and LTE-Advanced Pro networks use MIMO configurations of 8 x 8 in the downlink and 4 x 4 in the uplink. For MIMO to work correctly, both the base station and the user device must be compatible with the latest MIMO configurations.
LTE user devices such as phones, dongles, MiFi routers, smartwatches etc., exist in many categories. Each new category includes a list of devices that support higher technical specifications than the earlier device categories. It means that not every LTE phone is the same, and if you use a phone of an older category, it may not support the full MIMO capabilities.
Spatial multiplexing enables higher data rates in MIMO
Spatial multiplexing is the primary reason for using the MIMO technology in 4G LTE networks because it allows MIMO to offer higher data rates. In addition to spatial multiplexing, MIMO also benefits from spatial diversity and beamforming, which improve the signal quality and the network range.
Spatial multiplexing is also referred to as Space Division Multiplexing (SDM), and it is one of the critical building blocks for MIMO in 4G LTE and 5G NR networks. Spatial multiplexing uses various antennas separated physically in space by their angular direction.
The spatially separated antennas in MIMO can send and receive multiple data streams in parallel through the same block of frequency and time resources.
Each data stream in spatial multiplexing acts as a separate individual channel which allows the overall data payload to be communicated in smaller chunks to increase the available network capacity. When the individual data streams arrive at the receiver, they are combined to create the output data, which results in improved data rates for the mobile user.
The original LTE networks had a MIMO configuration of 4 x 4 in the downlink (network to the phone) and 2 x 2 in the uplink (phone to the network). A configuration of 4 x 4 means four layers of communication can take place between the network and the phone as long as the phone’s receiver has four antennas.
LTE Advanced and LTE Advanced Pro networks have a MIMO configuration of 8 x 8 in the downlink which means eight layers of communication can occur between the network and the phone.
Massive MIMO in 5G uses a large number of antenna elements
5G NR networks employ an enhanced version of MIMO called Massive MIMO, which has a large number of antennas at the transmitter and the receiver.
As per the 3GPP specifications, this number can be any number that is higher than eight (8) because the “regular” MIMO in LTE Advanced Pro uses a maximum configuration of 8 x 8. Massive MIMO in 5G, therefore, employs a much higher antenna configuration than MIMO in 4G LTE networks.
With Massive MIMO, the antenna configuration involves tens or even hundreds of antenna elements in a single antenna. For example, it is already possible today to have a Massive MIMO system with a configuration of 64 x 64 in the downlink.
Another critical aspect of Massive MIMO in 5G is the multi-user capability which allows it to support multiple simultaneous cell phone users. 4G LTE networks primarily use MIMO for spatial multiplexing to improve the data rates, but Massive MIMO focuses mainly on increased network capacity.
The capacity increase in Massive MIMO antennas is due to the use of a large number of antennas and multi-user support. Thus, Massive MIMO in 5G improves the data rates while increasing the network capacity to support multiple simultaneous phone users.
Beamforming creates directivity in MIMO systems
Beamforming is an advanced antenna technology enabled by the MIMO antenna systems. In conventional base stations that do not employ MIMO technology, the radio signals transmitted by the base station antennas propagate in all directions throughout the cell radius.
Beamforming was introduced in 5G in its first release as per 3GPP Release 15 as part of the Massive MIMO specifications. Beamforming introduces directivity, which allows the cellular base stations to target the transmission of the signal in specific directions. It enables the base station antennas to send the signal in the form of narrower beams which can be directed toward one or multiple user devices.
In 5G Massive MIMO antenna systems, beamforming is considered three-dimensional (3G), which means that the beams created by the antennas can be horizontal and vertical. The 3D beamforming improves the data rates for all users irrespective of their location horizontally or vertically. An example of horizontal and vertical beams through 3D beamforming is a user within a high-rise building.
Beamforming extends the range of the radio signal by shaping the transmission such that the desired beam gets most of the transmission power to become longer whilst suppressing the other beams in the non-desired direction. Look at the simplified diagram below to visualise this concept.
Beamforming improves capacity by allowing the same radio network resources to be used for multiple devices within a cell area. When separate beams are sent towards individual devices, the chances of interference are minimised, and the capacity is well utilised.
As a result, beamforming provides spectral efficiency and adds more capacity to the existing base stations. It improves both the network coverage as well as the network capacity. The radio link performance can be enhanced to extend the network coverage.
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.