eeworldonline.com | designworldonline.com 6 • 2019 DESIGN WORLD — EE NETWORK 195G NEW RADIO
Shielded box or environmental noise camberDUTOTA probe
antennaeChannel
emulatorBase station
network emulator3GPP Standards identify a minimum level of performance for
user equipment (UE) terminals and base stations (gNB). These
requirements are defined in the RAN4 and RAN5 technical
specifications (TS). RAN4 defines minimum requirements for base
stations and UEs. It also specifies test cases and test methods for
base station conformance tests. RAN5 defines the UE conformance
test specifications and test methods.
5G NR products can operate in two frequency ranges- frequency range 1 (FR1: 410 MHz to 7.125 GHz) or frequency
range 2 (FR2: 24.25 to 52.6 GHz), or both FR1 and FR2. Testing in
FR1 below 3.5 GHz is firmly established with well understood test
methods and associated uncertainties.
Given that FR1 below 7 GHz operates under the same
characteristics, tests in FR1 will resemble that of LTE with most
conformance tests employing a cable connected to the device;
antenna characteristics and multiple input multiple output (MIMO)
performance will be completed over-the-air (OTA).
FR2 at millimeter-wave (mmWave) frequencies adds a
completely new twist on testing because all measurements in FR2
will be tested OTA.
Third-party test labs perform conformance tests to determine
if a UE is compliant. These tests are expensive, so most companies
conduct their own pre-conformance tests before engaging an
independent lab. Currently, these tests are still in development and
will be defined over the next year for different use cases.
5G NR introduces many new features that make testing more
complex. Higher-frequency operation, wider channel bandwidths,
flexible waveform structure, and the rising number of test cases that
must be validated all complicate test design. For the most part,
the testing of designs under 6 GHz in FR1 resembles that of LTE.
In FR1, the key challenges lie in testing designs operating between
3.5 GHz and 7.125 GHz that use wider bandwidths and massive
MIMO, and designs operating in FR2 because they require OTA
test methods. OTA introduces many challenges that UE and base
station designers haven’t seen and has big implications for the test
environment.
User Equipment Test Challenges: 5G NR must accommodate
many different usage scenarios from high throughput to low packet
size, to low latencies with high reliability. The 5G NR physical layer
was given the flexibility to support such a wide variety of use cases,
changing the way signals are created and operate. In addition,
there are seven different system architecture options and dual
connectivity with 4G LTE. Testing must cover the many different use
cases. Furthermore, testing involves signaling and full end-to-end
performance with real-world impairments like excessive path loss,
multi-path fading, and delay spread. Wringing out these functions
requires an OTA test solution that can emulate base station
protocols and channel conditions.
The drastically higher number of test cases that must
be validated for conformance and device acceptance testing
dramatically lengthens test times. To minimize the risk of parallel
development, ensure you are testing to the latest specifications and
getting regular 5G NR test software updates to help meet evolving
5G NR requirements.
Base Station Test Challenges: The active nature of 5G beam
steering and beamforming requires validation in an OTA setting.
Key aspects such as antenna gain, side lobe, and null depth for the
full range of 5G frequencies and bandwidths can severely impact
system performance. In particular, 3D antenna beam measurements
introduce many complexities into the test.
While path loss and signal impairments were not a big issue at
3.5 GHz and below, such phenomena are problematic at mmWave
frequencies. Therefore, test solutions for mmWave frequencies must
accommodate higher frequencies with wider channel bandwidths
and also address higher path loss at mmWave frequencies. To that
end, a test solution must have adequate signal-to-noise ratio (SNR)
to accurately detect and demodulate 5G signals.
When testing transmitters, high SNR in the test analyzer is
critical for accurate error vector magnitude (EVM) and adjacent
channel leakage ratio (ACLR) measurements, and achieving higher
SNR becomes even more of a challenge for those testing at
mmWave frequencies. The use of signal generators with higher
output power per EVM and ACLR becomes important for testing
receivers. In addition, it is also critical that a system-level calibration
correct for system-level phase and magnitude shifts over the
bandwidth of the measurement.A typical (simplified) OTA test
setup with a network emulator
and channel emulator. How OTA tests take placeKeysight — Test and Measurement HB 06-19.indd 19 6/7/19 1:10 PM