Everything you always wanted to know about 5G – But were afraid to ask

How many antennas do you need with 5G?

The starting point of the 5G design was performance requirements defined by the ITU-R.
Essentially, this is about:

• Higher data rates
• Larger number of IOT devices
• Short latencies and reliable communication

Higher data rates are achieved through wider channels, higher modulation order and, above all, multi-antenna technology (MIMO).
In contrast, IOT devices with extremely low data rates send only a few words per month over years. Here the transmit and receive path is reduced to the minimum and this is a common transmit and receive antenna (SISO).

3GPP Standard

The technical standard TS 138 306 from ETSI based on the 3GPP recommendation TS38.306 Release 15 ff, defines the capabilities of the 5G device. The TS38.101 standard defines the band combinations and the interaction with LTE, especially important for non-standalone operation. The properties of the 5G base station (gNB) are not defined in a single document.

• TS138.306
  4.2.7.6: maxNumberMIMO-LayersPDSCH Defines the maximum number of spatial multiplexing layer(s) supported by the UE for DL reception. For single CC standalone NR, it is mandatory with capability signaling to support at least 4 MIMO layers in the bands where 4Rx is specified as mandatory for the given UE and at least 2 MIMO layers in FR2.
  4.2.7.10 maxLayersMIMO-Indication Indicates whether the UE supports the network configuration of maxMIMO-Layersas specified in TS 38.331 [9].

• TS138.521-1
  7.2 Diversity characteristics
  The UE is required to be equipped with a minimum of two Rx antenna ports in all operating bands except for the bands n7, n38, n41, n77, n78, n79 where the UE is required to be equipped with a minimum of four Rx antenna ports. This requirement applies when the band is used as a standalone band or as part of a band combination.
  7.3.2.3 Note 1: Four Rx antenna ports shall be the baseline for this operating band except for two Rx vehicular UE.

In consultation with representatives of 5GAA and 3GPP, it was announced that the footnote for vehicular UE was created by the request of the car manufacturers.

Network operator's view

The mobile network operator can select his infrastructure manufacturer and also configure his network. The device reports its properties and the network determines which of them are used.
For frequency bands below 6 GHz (FR1), manufacturers offer configurations with 8x8, 32x32 and 64x64 MIMO. At higher frequencies, 256x256 are also offered. In the Multi-User MIMO variant, the entire cell capacity is not allocated to a single user. Regardless of the application, the balance between the end device and the base station should not be too extreme, because one bad element affects the overall performance.

End devices' view

While a variety of options are available on the network side, the device must support a maximum number of these. The Smartphone manufacturers Apple and Samsung have a significant influence on what functionalities are offered. On the modem side, there is a quasi-monopoly, as only Qualcomm's chipset is currently available. This means that it is only feasible, if it will be supported by this chipset.

The requirements for a 5G modem are much more complex than LTE-A. This is not only due to the additional radio technology (RAT), but also due to the additional frequency bands. Modern 5G modems support more than twice as many tapes. This makes the analog part (RFFE) very complex. In order to simplify filters and combiners and to keep losses low, different frequency groups are placed on different antenna ports. One also tries to keep FDD and TDD separate. As a result, 3 of the antenna ports are already occupied with output stages. Only one of the modem manufacturers in our investigation supports UL-MIMO.

The configuration options of the end device depend on the command set. After all modems are based on a Qualcomm chipset, the differences are small. As a rule, there is no way to switch from 4x4 MIMO to 2x2 MIMO or SISO.

There are also other aspects to consider. Compliance with guided and radiated emissions and intermodulation products is only guaranteed if all connections are properly connected. Otherwise, the modem loses its approval.

If a device is noticed by its performance data, it would be automatically sorted out from the mobile network, radio resource management and scheduler intervene at the various levels.

Summary

The standard requires 4 RX (reception) antennas for 5G bands with 3.5 GHz (TDD) as well as n7 2.6 GHz (FDD), n38 2.6 GHz (TDD) and n41 2.5 GHz (TDD).
Thus, the 4 RX antennas are mandatory for the 5G core bands. The modems require 3 transmitting antennas for the frequencies of the European network operators. Consequently, the NetModule 5G routers only support configurations where all 4 antenna plugs are occupied.