A Primer on Beamforming and Massive MIMO in 5G Technology
By Marco Contento
June 5, 2020
By Marco Contento
June 5, 2020
The first wave of ultralow latency, high-speed 5G has already arrived. Standalone (SA) 5G networks were successfully tested in Asia and Europe last year. U.S. carriers are finally catching up with SA testing while deploying non-standalone (NSA) 5G in cities all over the country. Still, we are in the earliest stages of the technology. Current radio configurations remain fragmented, and much of the infrastructure needed to support technologies like beamforming and massive multiple-input and multiple-output (MIMO) arrays is under construction. These technologies will play critical roles in creating stable 5G networks connecting millions of mobile and IoT devices.
5G networks will carve paths through new territory for mobile: the previously unusable frequencies at the high end of the RF spectrum (FR2). Since earlier wireless standards are unable to operate in these higher bands, this solves the problem of overcrowding at the middle and lower frequencies (FR1). Using millimeter wave (mmWave) and thousands of miniature base stations called small cells, 5G will operate at frequencies up to 300 GHz compared to bands below 6 GHz used by current mobile standards.
5G requires an entirely new network structure that will enable more targeted use of bandwidth; however, it will require new technologies to compensate for the propagation loss at higher frequencies and the massive number of new users and devices 5G is expected to connect. Two of those technologies, beamforming and massive MIMO, help direct and amplify signals, reducing interference and possible traffic jams. Analog, digital and hybrid beamforming can be thought of as traffic-signaling systems conducting wireless signals in the right direction.
Cellular signals, especially those carried by millimeter waves, can be blocked by objects easily and weaken over longer distances. Beamforming addresses the problem by shaping signals and turning them into concentrated beams that are aimed only directly at the receiver or bounced off walls and other obstacles like a billiard ball. Rather than sending signals in several directions at once, which increases signal loss, beamforming applies relative amplitude and phase shifts to antenna elements to cancel out interference and create streamlined signal paths.
Beamforming applies processing to signals at the transmission end. In analog beamforming, those signals are summed up and receive analog-to-digital conversion (ADC) at the receiving end. In digital beamforming, amplitude and phase variation are reversed at reception by ADC and digital down (DDC) converters. Beamforming transceivers are integrated into massive MIMO arrays at both the device as well as the cell-site ends.
Massive MIMO can be thought of as a kind of traffic routing system that multiplies the number of available network connections by a factor of 20 or more. Since higher-band signals can use smaller antennas, many mmWave antenna elements can fit into a fingernail-sized pad on the device side. 4G base stations have around a dozen antenna ports, whereas 5G ones have around a hundred for antennas directing cell signals. Beamforming separates those signals and keeps them from interfering with each other.
Smaller base stations with more ports mean that many more transceivers can take the place of a single transceiver on a typical cell tower. One array can have up to 64 transmitters and 64 receivers (hence the word “massive”). Among many other processes, techniques like maximum ratio filtering can maximize the signal-to-noise ratio to amplify signals in dense urban areas. As ambitious as this technology is, massive MIMO arrays are already being deployed. For example, as part of its “bridge to 5G” strategy, Sprint doubled its network capacity with massive MIMO small cell technology in Atlanta in 2019.
Massive MIMO arrays can be used to increase LTE speeds and improve latency even before 5G becomes widely available. However, massive MIMO and beamforming technologies will eventually work together to achieve 5G’s promised scale of IoT connectivity speeds in double-digit gigabits per second and almost instant data delivery with less than a millisecond of delay.
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