eeworldonline.com | designworldonline.com 6 • 2019 DESIGN WORLD — EE NETWORK 115G TESTING
have a much stronger foundation than was the case with LTE,
thankfully. Test companies have worked with customers to determine
likely 5G test processes and procedures. Additionally, leading test
equipment manufacturers have made accelerated contributions in
the development of 5G 3GPP specifications, not the case in early
stages of 4G.
The result is a consensus in the industry about the likely
specifications for the first phase of 5G New Radio (5G NR), also
known as 3GPP Rel-15. Based on all this data, guidelines have
been established to help test vendors introduce solutions that help
engineers develop accurate models, thereby expediting the design
process and controlling the cost-of-test.The key aspects engineers must address to successfully launch
5G include:Antenna and device design
Beamforming/millimeter wave (mmWave)
Price and timePresent-day LTE mobile terminals have several built-in antennas
which can be physically connected to test equipment; 5G terminals
could have a significantly higher variety of antennas. The 5G device
has LTE antennas as well as 5G antennas, and 5G antennas may
include an array of antenna elements. In 5G mmWave applications,
high-gain, steerable phased array antennas will be used to overcome
high propagation loss.
Adding to the complexity is that mmWave antenna arrays
are embedded in the chip of a 5G mobile device which makes
it impossible to test with a physical connection. Implementing a
measurement connector for each antenna would boost the mobile/
terminal size and contradict cost-reduction trends. And use of cable
would also increase signal loss. All these factors make it significantly
more challenging for engineers to verify antenna performance.
The testing of 5G antennas employs Over-the-Air (OTA)
measurements, including power and sensitivity. OTA and
interoperability testing ensure the mobile device performs according
to 3GPP 5G NR specifications by simulating 5G NR technologies
in a real-world environment across a broad set of use cases and
deployment scenarios. These tests take place in low-band spectrum
below 1 GHz, mid-band spectrum such as 2.5 GHz, 3.7 GHz to 4.
GHz, as well as the 28 GHz and 39 GHz mmWave bands.
To control test costs, engineers must decide which tests must
take place in an OTA chamber. Chipset/device manufacturers and
carriers all must agree on an acceptable margin of error for certain
performance parameters to eliminate the need for some OTA tests.
For example, there are a considerable number of protocol tests.
Because the verification of the protocol stack does not require RF
measurements, protocol testing may take place without a chamber.
The measurement of RF parameters in the mmWave range
requires simultaneous OTA antenna measurements. Signal analyzersA summary of the KPIs associated with 5G.Downlink peak data rate 20 GbpsUplink peak data rate 10 GbpsAverage data rates anywhere in the cell 100 GbpsDevices per km2 1 millionArea capacity 10 Mbps/mOver-the-air latency in user plane 1 ms roundtripOver-the-air latency in control plane 1 msmust be able to accurately test parameters that include Effective
Isotropic Radiated Power (EIRP), Total Radiated Power (TRP), and
Effective Isotropic Sensitivity (EIS).
Most OTA antenna measurements should take place either in
the far field or in a computationally simulated far field. The far-
field distance rises with frequency and drops with antenna size. For
example, at 28 GHz, the far field distance begins at 34.2 cm whereas
at 39 GHz it begins at 24.5 cm. Antennas must also be calibrated at
mmWave frequencies to ensure accurate directivity and beam width,
as well phase and gain.
Conventional OTA tests on mmWave designs can be costly.
Traditionally, they require two test chambers – the reverberation
chamber and the more-expensive anechoic chamber. Studies indicate
that better results on mmWave designs come from conducting far-
field measurements (FFM). That implies measurements taken 1.5 – 2
m away from devices supporting 28 GHz. Such testing will require a
significant additional investment, considering RF measurements at
LTE frequencies could take place in conducted mode.
A second testing method is to develop FFM conversions
or reflection parameters. Using this approach, engineers can
conduct near-field measurements (NFM) and use industry-accepted
algorithms to transform them to FFM.
An NFM application can employ compact mmWave measuring
instruments and the radiation pattern can be measured using a
simple radio anechoic box in a room. This approach eliminates the
high cost and long configuration time associated with measurements
in a large radio anechoic chamber.
OTA measurements are necessary for other reasons as well. With
4G UE, the transceiver and antenna are separately evaluated. In 5G
mmWave, the introduction of high frequency and massive MIMO
force the transceiver and antenna to be tightly integrated, making it
difficult to evaluate each separately.Anritsu — Test and Measurement HB 06-19.indd 11 6/7/19 12:04 PM