At MWC2019, Qualcomm showed videos of interesting scenarios for using an outdoor 5G mmWave network, both outside the office and, in some cases, indoors. Let's consider them in more detail.
The photo above shows the Qualcomm campus in San Diego, California, showing three buildings and 5G and LTE base stations. 5G coverage in the 28 GHz band (millimeter wave band) is provided by three small 5G NR cells - one is installed on the roof of the building, the other on the wall of the building, the third is in the yard on a pipe rack. There is also an LTE macro cell providing campus coverage.
The 5G network is of the NSA type, that is, it relies on the core and other resources of the LTE network. This improves the reliability of the connection, because in cases where the user device is outside the coverage of the 5G network in the millimeter frequency range, the connection is not interrupted, but switches to LTE mode (fallback) and then returns to 5G mode when it becomes possible again.
To demonstrate the operation of this network, a test subscriber device based on a Qualcomm X50 5G modem is used, which supports both sub6 and millimeter-wave frequencies. The device has 3 millimeter-wave antenna modules, two of which are installed on the left and right ends of the terminal, and the third is on the upper end.
This design of the terminal and network ensures high reliability of the connection even in cases where the beam from the 5G base station antenna is blocked by the subscriber's hand, body, or other obstacles. The connection quality practically does not depend on the orientation of the terminal in space - the use of three spatially separated antenna modules forms a near-spherical terminal antenna pattern.
This is what gNB looks like - a small 5G cell with a flat 256-element digital active antenna for the millimeter wave. The network demonstrates high downlink spectral efficiency of both the base station and the terminal - on average tending to 4 bit / s per 1 Hz for the base station and about 0.5 bit / s per 1 Hz for the terminal.
The diagram shows that communication with the terminal provides active beam number 6, while the station is ready to switch to communication with the terminal along beam 1 if the parameters of beam 6 deteriorate, for example, due to its overlap with some obstacle. The base station constantly compares the quality of communication on the active beam and on other beams, choosing the best candidate from the possible ones.
And this is what the situation looks like on the side of the terminal.
It can be seen that antenna module 2 is now active, because it currently provides the best communication parameters. But if something changes, for example, the subscriber moves the terminal or fingers so that it closes module 2 from the gNB beam, the one of the modules that can provide work with the 5G base station in the new device orientation “configuration” is immediately activated.
The elongated “ellipses” are the beam patterns of the terminal radiation pattern.
This ensures mobility, coverage and reliable connectivity.
Connectivity is provided both in the "line of sight" mode of the antennas of the base station and the terminal, and in the conditions of re-reflected signals.
Scenario 1: Line of sight
Please note that another antenna module is currently working in the device.
And here is what should happen when switching to a re-reflected beam.
We see a different number of the active beam, the connection is provided by another antenna module. (Data simulated).
Scenario 2. Working on reflection
The ability to work with re-reflected beams significantly expands the formed 5G coverage area in the millimeter range.
At the same time, the LTE network provides the role of a reliable foundation, always ready to pick up the subscriber's service at the moments when he leaves the 5G coverage area or give the subscriber to the 5G network in a situation where this becomes possible.
On the left is a subscriber entering the building. Its service is provided by gNB 5G. On the right is a subscriber located in the building, which is currently being handled by the LTE network.
The conditions have changed. A person approaching the building is still served by the 5G cell, and a person leaving the building, after opening the front door that weakened the 5G signal, was intercepted by the 5G network and is now served by it.
And now the person on the left, who entered the building and blocked the beam from the 5G base to his terminal with his body, has been switched to service with the LTE network, while the person who left the building is now “guided” by the beam from the 5G base.
In some cases, an outdoor 5G mmWave network may also be available indoors. It will also support multi-reflections from buildings when the environmental conditions between the antennas change.
It can be seen that the signal was originally received from the base station along the “direct beam”.
Then, the interlocutor approached and blocked the beam, but the 5G connection was not interrupted by switching to a beam reflected from the surface of a neighboring office building.
This is how the 5G network operates in the millimeter frequency range. Note that the experiment does not show that 5G terminal tracking can be transferred from one 5G base station to another (mobile handover). Probably, this regime was not tested in this experiment.
Source: habr.com