This article appeared in Microwaves & RF and has been published here with permission.
When studying 5G NR operation, it’s not immediately obvious that 5G meets all of the objectives of the 3GPP standard by using advanced antenna technology. Antennas are often overlooked and treated with indifference. After all, antennas are just that nuisance metal thing that you have to put on a radio to make it work. In the case of 5G, antennas play a major role in achieving the expected features and performance.
The primary objectives of 5G NR are:
- eMBB: Enhanced mobile broadband (eMBB) means more subscriber capacity and higher data rates. Increase subscriber capacity by at least a factor of 1,000 over LTE and boost downlink (DL) data rate to 10 Gb/s with a minimum of 100 Mb/s for every subscriber.
- mMTC: Massive machine-type communications (mMTC) effectively means the Internet of Things (IoT). The 5G standard meets the needs of low power consumption, low cost, and low data rate generally associated with IoT to wirelessly connect millions of different things to the internet.
- uRLLC: Ultra-reliable low-latency communications (uRLLC). Latency is the time delay between an initiating action and the time the action occurs. In many wireless systems, this delay is harmful or otherwise a knock-out factor.
Factory automation with robots, advanced driver-assistance systems (ADAS) that improves safety in new vehicles, and, ultimately, self-driving cars or trucks all rely on low latency. The new 5G standard claims a latency of 1 ms or less, which should satisfy these needs.
New 5G systems are proving that these objectives can be met, especially eMBB, by using multiple antenna methods:
MIMO
The first antenna technology that leads to the highly desirable features of 5G is multiple-input, multiple-output (MIMO). MIMO uses multiple antennas plus their transceivers. The serial data to be transmitted is divided into multiple data streams, each of which modulates an individual carrier. All such signals are then transmitted simultaneously over the same bandwidth.
Because the antennas for each channel are adequately spaced, each signal will travel a slightly different path. This ensures that fading and other problems are greatly minimized, thereby improving link reliability and leading to fewer dropped calls and texts.
MIMO systems define the number of antennas and paths. For example, there may be four transmitting antennas and four receive antennas expressed as 4 × 4 or 4T4R. A variety of MIMO configurations can be built; 5G can define up to 8T8R.
In addition to improving link reliability, the multiple streams can boost data rate by a factor of N, where N is the number of transmit antennas. Data rates to several gigabits per second are possible. Add to that the wider channels of 40, 80, and 160 MHz plus carrier aggregation and modulation up to 64QAM and the data rate can soar.
Beamforming
The other antenna technology that makes 5G work is agile beamforming. This is the process of using special antennas to produce very narrow beams that can be rotated to point in a desired direction. This technology is more likely to be used in the millimeter-wave (mmWave) bands.
The highly focused beams indicate that the signal has been concentrated or focused, which means the effective radiated power has been boosted. Stronger narrow beams will travel farther and sometimes penetrate buildings and other obstacles more effectively. And the ability to position beams over a wide angle makes it possible to minimize or null out strong interfering signals.
The technology that provides this capability is phased arrays. Phased arrays are panels of many small antenna elements, each with its one TX and RX plus gain control and phase variation. By adjusting the amplitude and phase out of each antenna, the signals from each antenna are summed so that they add or subtract (interfere), allowing for the generation of multiple beam sizes that can be pointed in a desired direction.
Phased arrays have been used for years in the military for radar. Some are as big as a building, with others mounted on the front of a ship or in the nose of a plane. They were and are expensive. Now you can buy a phased array on a chip. Phased arrays boost signal power, thereby extending the transmission range and helping the signals go deeper into buildings.
Oh yes, the phased arrays can be used as MIMO antennas. This makes it possible to implement multi-user MIMO, a variant of plain-old MIMO that lets one antenna be partitioned into smaller antennas, each group dedicated to one of the many users accessing the cell site.
Smartphone Antennas
We don’t think about antennas when we’re buying or using a smartphone. Yet they’re more important than you think. The typical smartphone has maybe a half-dozen antennas. At least two are for the lower and upper cellular frequencies. But with 5G, MIMO must be added. To do so would require two each for the upper and lower bands. One popular combination is 4 × 2 (or 4T2R).
That means many, if not most, new 5G phones will have four antennas for the cellular bands. These antennas will likely have some automatic antenna-tuning capability.
Also in the mix are one or two antennas for Wi-Fi and Bluetooth. Since both wireless technologies operate at 2.4 GHz, it’s possible to share an antenna. Then there’s a GPS receiver antenna. If you know a little about antennas, you probably know that each individual antenna should be spaced as far away as possible from the others to avoid interaction. That’s tough to do in a small handset. Thankfully, the operating frequencies are high and the wavelength and antennas short.
One more thing. If we’re talking about a 5G mmWave phone, you will need another antenna. With 5G on the lower cellular bands, the regular smartphone antennas will work. But if you have a mmWave version of 5G, you’ll have a small phased array inside the handset
I almost forgot the NFC antenna. The near-field communications radio operates on 13.56 MHz. Its antenna is usually a small coil. It too eats up lots of space inside the phone. NFC use is increasing, and it could see future new applications now that the standard has implemented two-way data exchanges.
So, it really is all about the antennas these days. Can’t do without them.
