Aerospace & Defense Technology - October 2022 - 26

RF & Microwave Technology
Quad-channel VXG signal generator
Device
under test
Fading
Channel
simulator
Channel
simulator
Channel
simulator
UE
Tx 2
Tx 1
Channel
simulator
Channel
simulator
Channel
simulator
Channel
simulator
Channel
simulator
HARQ feedback
Figure 2. Test setup for 5G NR base station performance tests using a quad-channel signal generator.
IEEE 802.11
standard
Maximum signal
bandwidth
802.11be (Wi-Fi 7) 320 MHz
802.11ax (Wi-Fi 6) 160 MHz
Table 2. IEEE 802.11 standard.
Modulation scheme Number of spatial
streams
OFDM, up to
4,096 QAM
OFDM, up to
1,024 QAM
Up to 16
Up to 8
Σ
Σ
Σ
Σ
AWGN
AWGN
AWGN
AWGN
Rx 1
Rx 2
Rx 3
Rx 4
AWGN
munications. In addition to creating
more system noise, wider bandwidths
at higher frequency bands introduce
other design and test challenges such
as path loss, frequency responses, and
phase noise.
gNB
Higher-Order Modulation Schemes
Higher-order modulation schemes
achieve faster data rates without increasing
signal bandwidth and require closer
symbols that are more sensitive to
noise. Devices require better modulation
quality as the modulation density
increases. Table 1 shows the error vector
magnitude (EVM) requirements for 5G
NR base stations defined in 3GPP release
16 technical specification 38.141. Under
consideration is the adoption of 1,024
QAM for 3GPP, which requires tighter
design and test margins.
Both wider signal bandwidths and
higher-order modulation schemes
increase throughput. However, more
bandwidth may not mean more system
capacity. You must consider the signalto-noise
ratio (SNR) in the communication
system. Proper SNR is critical to
maintaining communication links.
Wider bandwidths introduce more
noise into the system, and higher-order
modulation schemes are more susceptible
to noise. You will need to transmit a
high-power signal without distortion
and reduce system noise to sustain the
communication links. To test your
designs, an accurate characterization of
each component and subsystem is
required, as shown in Figure 1.
Figure 3. A multichannel test solution with a Keysight M9484C VXG four-channel vector signal generator
and a four-port oscilloscope.
26
mobilityengineeringtech.com
Multi-Antenna Techniques
Most wireless systems, whether in
commercial applications or aerospace
and defense, use multiple antenna techniques
at the receiver, transmitter, or
both to improve overall system performance.
These techniques include spatial
diversity, spatial multiplexing, and
beamforming. Engineers use multi-antenna
techniques to achieve diversity,
multiplexing, or antenna gains.
Through these gains, wireless systems
can increase a receiver's data throughput
and SNR.
For example, 5G NR uses eight spatial
streams for FR1 to improve spectral efficiency
without increasing signal bandAerospace
& Defense Technology, October 2022

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Aerospace & Defense Technology - October 2022

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