Several technologies drive 5G's potential for groundbreaking speeds. Understanding 5G requires an appreciation of each of these technologies.
While the capabilities of 5G wireless are numerous, it isn’t a single technology. Several technologies, working in concert, drive its potential for groundbreaking speeds, including the following advanced antenna technologies:
• Four-transmit four-receive (4T4R) antenna arrays
• Small-cell transmitters
• Multi-user multiple-input multiple-output (MU-MIMO) data transmission
Understanding 5G requires an appreciation of each of these technologies.
The 4T4R antenna concept in wireless technology is well established and is several evolutionary steps past the “whip” antennas often seen on automobiles in the 1980s. 4T4R relies on multiple antennas oriented orthogonally to each other, or at some distance, to provide decorrelation between signals carried by each antenna. 2G wireless transmission introduced the one-transmit, one-receive (1T1R) concept, which later led to two-transmit, two-receive (2T2R) antennas, and finally 4T4R antennas with 4G wireless.
Today, this multi-antenna technology is applied primarily to base stations and not generally to handsets. While 4T4R antennas are basic technology at this point (nearly a decade old), this concept still forms the backbone of our wireless infrastructure.
In the realm of wireless communications, data throughput is based on three factors: available spectrum, data efficiency, and communications density. 5G uses a broad range of the electromagnetic spectrum, and the way 5G communicates gets an efficiency boost of about 10% over 4G just for making the switch. While large, traditional base stations work well in suburban or rural areas to transmit over several miles, in urban areas, small-cell antenna packages can be employed to transmit low-power signals over a shorter range.
With antennas under 2 feet tall, and power output in the 40-W range, in contrast with a typical macro base station’s 5- to 8-foot/300-W specs, these units can be installed en masse without becoming a significant nuisance. The result is that handsets across a city can share a greatly increased number of base units, which have the additional advantage of being installed close to ground level—on light poles and other existing structures.
While each is individually less expensive than a macro base station, many more need to be installed for sufficient coverage. This presents the challenge that electrical power and data infrastructure must be connected and maintained for each one. While very useful in urban situations, small cells are not generally appropriate for widespread rural, or even suburban, deployment.
Beamforming and MU-MIMO
While 4T4R and small cells enable data capabilities that would have been incredible even a decade ago, beamforming and MU-MIMO technologies enable geographically wide-ranging 5G coverage.
Beamforming uses an array of antennas to send a signal in specific directions. The concept is also known as a phased-array antenna arrangement, whereby one or multiple signals are transmitted from each antenna in slightly different phases. While each antenna has a relatively broad pattern, waves from each antenna (spaced at least half a wavelength from each other) are timed to combine and form a single pattern with much higher directivity.
This isn’t entirely new in cellular technology. Sprint experimented with beamforming in the 4G era, and China attempted it with 3G, with limited success. With several more years to mature, this technology, along with MU-MIMO (discussed below) and fully integrated into 5G, appears to be the wave of the future—if I’m allowed an electromagnetic pun.
3G and most 4G beamforming antennas were limited to eight transceivers, providing a moderate increase in gain—perhaps a factor of 3. With 5G, we are seeing massive MIMO (M-MIMO) beamformers with 16, 32, or even 64 transceivers. These antennas typically integrate the radio and antenna into a single package, as it would be extremely inconvenient to run 64 jumper cables between an antenna and radio in the field. M-MIMO antennas can provide improvement in performance by a factor of 2 compared with beamformers with eight transceivers.
MIMO allows for information to be split up and transmitted on multiple antennas simultaneously. While the technology seems exotic, the benefits are simple to understand and calculate: Twice the number of antennas equals twice the theoretical data speed.
This is not just a base station technology, as both the handset and carrier equipment must be capable of MIMO transmission. This technology has had some time to mature, and equipment with varying levels of MIMO technology is available today. The iPhone 13, for example, features 4 × 4 MIMO, meaning that the handset has four transmit and receive antennas and can theoretically send and receive information 4× faster than a non-MIMO-equipped phone, provided the channel is sufficiently strong enough to support this.
MIMO + beamforming is where things get really interesting, allowing for MU-MIMO. In this scenario, a base station uses beamforming to simultaneously transmit data to two (or theoretically more) user equipment (UE) at the same time. This does not improve data speed for the individual UE, but it does increase the throughput of the entire cell, allowing more UEs to communicate in a limited area.
To utilize this technology, UEs must be a sufficient distance from each other (i.e., a sufficient angle between each other relative to the transmitter) to avoid interference. To determine the correct beam transmission, the base station sends out reference signals from a collection of candidate beams, and the UE replies as to which beam gives the highest channel quality. If the beams for two UEs are sufficiently separated to avoid interference, then the base station can combine the data for these UEs into the same resource blocks, implementing MU-MIMO.
Towers can switch between UEs in a fraction of a millisecond, multiplying the potential number of users (while dividing total throughput), meaning it can still be used if greater numbers of devices are in range.
Two distinct simultaneous UEs is a significant accomplishment today, but who knows how this technology will develop? In the future, cellphone towers may operate more like tight-beam communication devices of science fiction lore than the omnidirectional information spewers that have been the norm since the dawn of radio.
Multiple technologies, multiple antennas
A wide range of technologies work together to allow modern 5G data transmission. Never has such a disparate arrangement of wireless tech come together to form the wonderful communication technology that we have today. The pinnacle of this development may be the ability to point a radio wave in a certain direction and communicate simultaneously with multiple devices. However, the full promise of 5G couldn’t fully be realized without the support of small cells and 4T4R base stations.
This article was originally published on EE Times.
Martin Zimmerman is the CTO of North America for the Outdoor Wireless Networks business segment at CommScope.