Understanding massive MIMO and what it means for 5G
What is massive MIMO?
Before going into “massive MIMO,” a potential enabler of 5G, it is important to understand the technology behind the traditional, smaller scale MIMO (multiple-input/multiple-output). MIMO deployment uses multiple antennas that are located at both the source (transmitter) and destination (receiver). Those antennas are linked in order to minimize error and increase efficiency of a network. This method’s ability to multiply the capacity of the antenna links has made it an essential element of wireless standards including 802.11n (Wi-FI), 802.11ac (Wi-Fi), HSPA+, WiMAX and LTE.
Massive MIMO, as you might guess, takes MIMO technology and scales it up to hundreds or even thousands of antennas and terminals. These antennas, attached to a base station, focus the transmission and reception of signal energy into small regions of space, providing new levels of efficiency and throughput. The more antennas that are used, the finer the spatial focusing can be.
The general idea of MIMO has been around for decades, but the deployment of base stations with multiple antennas is not very widespread. To reach “massive” heights, even 4X4 MIMO (4 transmit streams, 4 receiver streams) doesn’t qualify. The term massive MIMO is thought to have originated with Tom Marzetta of Bell Labs, and is often understood to denote at least 16 antennas on both the transmit and the receive end.
- Inexpensive, low power components
- Reduced latency
- Simplification of the media access control (MAC) layer
- Robustness to interference and intentional jamming
- Increasing data rate
- Increasing basic link signal to noise ratio
- Channel hardening
Challenges with massive MIMO
As you can imagine, deploying a system with hundreds or thousands of antennas and terminals isn’t exactly plug-and-play. This requires more advanced processing capability in the nodes. Also, each node must be able to determine the data transmitted from one antenna to that transmitted from another, otherwise network performance will be limited. This requires sophisticated channel estimation and sounding techniques, according to Cambium Networks.
Some other challenges, according to the Institute of Electrical and Electronics Engineers (IEEE), include:
- Making many low-cost low-precision components that work effectively together
- Acquisition and synchronization for newly joined terminals
- the exploitation of extra degrees of freedom provided by the excess of service antennas
- and finding new deployment scenarios
- reducing internal power consumption to achieve total energy efficiency reductions
What this means for 5G?
By 2020, Cisco forecasts that 5.5 billion people will own mobile phones. In the United Kingdom alone, tens of millions of these mobile users will each consume 20 GB of data per month and use more than 25 different smart devices in their daily routines. Factor in applications like 4K video, driverless vehicles, smart factories and broadband access expanding to the most rural places on Earth, and it’s no surprise that today’s wireless networks cannot handle the “hyperconnected future,” says National Instruments.
The next generation of wireless data networks, or 5G, must address not only future capacity constraints but also existing challenges—such as network reliability, coverage, energy efficiency and latency—with current communication systems. Massive MIMO, offers significant gains in wireless data rates and link reliability. It allows for data consumption from more users in a dense area without consuming any more radio spectrum or causing interference. This results in fewer dropped calls, a significant decrease in dead zones, and better quality data transmission, without spreading thin the increasingly scarce radio spectrum.
Three potential types for 5G
Massive MIMO is one of the most talked about technologies when it comes to creating the next generation of network standards. But there are some questions as to what implementation should be used for 5G. There are three different shapes of MIMO that need to be considered, each having their own pros and cons, according to Dr. Robert Heath, professor in the department of electrical and computer engineering at the University of Texas at Austin:
- Cooperative MIMO
- Cooperation will be used in some form, more powerful with better infrastructure, need to be mindful of overheads in system design
- Massive MIMO
- Some potential for system rates, need large base station arrays, can be used with cooperation
- mmWave MIMO
- Large potential for peak rates, more hardware challenges, requires more spectrum, more radical system design potential
NI, Bristol and Lund show off its capabilities
Representatives of standards-setting organizations emphasize expanding the amount of available data, some arguing a 1,000-fold increase in capacity is needed to reach the next generation standard. The University of Bristol and Lund University set out to test the feasibility of massive MIMO as a viable technology for bringing greater than 10-times capacity gains to future 5G networks. They worked with National Instruments for a massive MIMO prototyping platform with flexible software-defined radio hardware and open reconfigurable LabVIEW software.
The team implemented the world’s first live demonstration of a 128-antenna, real-time massive MIMO testbed. It was a success, setting two consecutive world records in spectral efficiency. They achieved over 79 b/s/Hz of spectral efficiency over a 20 MHz bandwidth, fully bidirectional, real-time, over-the-air link at 3.5 GHz with 12 simultaneous users. Shortly after, the team extended the system to achieve over 145 b/s/Hz of spectral efficiency by increasing the number of users to 22 sharing the same time-frequency resource.