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Keysight Technologies
A Flexible Testbed to Evaluate
Potential Co-Existence Issues
Between Radar and Wireless
Application Note
Photo courtesy US Department of Defense
Problem: Radar and wireless may interfere with each other
Today's radar and electronic warfare (EW) equipment operate in increasingly cluttered
RF and microwave spectral environments, with many potential interference issues.
Spectral environments may consist of many different types of emitters including
radar, wireless communications, wireless networking, and other potential interference
sources. Co-existence between radar and wireless systems has the potential to be a
significant issue.
Investigating potential interference issues between complex wireless signals such as
LTE (Long Term Evolution), WLAN (Wireless Local Area Network), WCDMA (Wide-
band Code Division Multiplexing Access), and radar can be useful to ensure successful
deployment. Testing these systems for co-existence prior to deployment may provide
discernible benefits in terms of helping to identify potential co-existence issues earlier
to reduce field testing time and potential re-work time. Finding and addressing
problems in a lab environment is typically much less costly than trying to correct
issues after deployment to the field.
Solution: A flexible R&D testbed combining
The last case study will examine how radar and LTE signals can co-
design simulation with a precision arbitrary exist, and what happens when radar signals interfere with LTE signals.
waveform generator
The flexibility and adaptability of this R&D test solution allows multiple
Recent advances in integrating the Keysight Technologies, Inc.
combinations of emitters to be tested for co-existence and evaluated
SystemVue electronic-system-level (ESL) design simulation with its
for performance degradation. One set of test hardware can be used to
M8190A precision wideband arbitrary waveform generator (AWG) has
test many combinations of potential interference scenarios, reducing
made possible a new approach to creating and analyzing multi-emitter
and quantifying system integration risks for new hardware deployment.
test signals using a commercial-off-the-shelf (COTS) approach. For
example, design simulation arbitrary resampling techniques enable
Evaluating the level of interference being imposed by one system
signals with different sampling rates (e.g., multiple radar, wireless
on another can be determined using metrics such as Error Vector
communications, and wireless networking signals) to be combined
Magnitude (EVM) and Bit Error Rate (BER) measurements. An RF
into a single waveform which is downloaded to a high precision
signal analyzer is used to measure the spectrum and EVM perfor-
Keysight M8190A COTS AWG to create the multi-emitter test signal
mance to evaluate potential degradation due to interference. BER and
(Figure 1).
throughput can be key metrics for receiver sensitivity, both with and
without interferers present.
As will be shown with three different case studies, it is possible to
combine Keysight's SystemVue design simulation with wideband
COTS test equipment to create and analyze wideband multi-emitter
test signals.
In the first case study, radar signals will be combined with LTE GSM
(Global System for Mobile communications), EDGE (Enhanced Data
rates for GSM Evolution), and WCDMA cellular signals, along with
WLAN signals, to create several multi-emitter test signals. This case
study will examine how radar and WCDMA signals can coexist.
The second case study will examine how radar and emerging 802.11ac
wireless networking signals can co-exist, and what happens when
radar signals interfere with 802.11ac WLAN signals.
Keysight SystemVue
Creates Emitters:
Figure 1. Creating multi-emitter signals.
3
Results, part 1: Coexistence of S-band radar
and WCDMA
The first case study involves creating a multi-emitter test signal
comprised of radar signals, LTE, EDGE, GSM, and WCDMA signals.
The signals will be created in simulation, and then downloaded to
the M8190A precision AWG to create the multi-emitter test signal on
the test bench. Wideband signal analysis will then be performed with
an ultra-wideband real-time oscilloscope with vector signal analysis
(VSA) software. Modulation-domain analysis, by means of EVM analy-
sis, will be performed with an RF signal analyzer with VSA software.
Figure 2 shows in schematic form some of the different wireless and
radar signals that can co-exist and that would need to be combined
to create a realistic interference signal for testing. Each signal type--
radar, GSM and EDGE, LTE, and WCDMA--has its own unique center
frequency, bandwidth, and sample rate appearing at the input to the
Signal Combiner model prior to being resampled, combined, and down-
loaded to the M8190A AWG for generation of interference signals.
Figure 2. Multi-emitter simulation for radar and WCDMA co-existence case study.
4
Figure 3 shows the COTS test setup used to create and analyze multi- The PXA RF signal analyzer is used to effectively zoom into each
emitter test-signal environments. The SystemVue design simulation of the wireless emitters and demodulate them with the 89600 VSA
software (upper left) is installed in the AXIe embedded controller. The software. Figure 5 shows the GSM, EDGE, LTE, and WCDMA emitters
M8190A AWG output is analyzed by an Keysight Infiniium 62-GHz being demodulated with the PXA RF signal analyzer and 89600 VSA
high-performance real-time oscilloscope with Keysight 89600 VSA software. The low residual EVMs demonstrate the signal fidelity of the
software (upper right) and an N9030 PXA RF signal analyzer with VSA precision AWG.
software (lower right). Wideband radar and multi-emitter spectral
analysis is performed with the Infiniium oscilloscope, while demodula-
tion (EVM) of the wireless emitters is accomplished by the PXA RF
signal analyzer and the 89600 VSA software (lower right).
Figure 5. Demodulation of wireless signals unencumbered by radar interferer.
The multiple-emitter environment shown in figure 4 contains two
WCDMA signals: one at 2.1 GHz (which is unencumbered by interfer-
ers within its 5-MHz channel bandwidth), and one at 3.4 GHz (which is
sitting within the S-band radar's bandwidth).
Figure 5 shows a measured EVM of approximately 0.85% for the
Figure 3. COTS test setup to create and analyzer multi-emitter test signals.
WCDMA signal at 2.1 GHz. However, Figure 6 shows that demodulat-
ing the WCDMA signal within the bandwidth of the S-band radar sig-
Figure 4's upper display shows the multi-emitter test signals as mea-
nificantly impacts the WCDMA EVM performance. EVM has degraded
sured by the oscilloscope and VSA software. The L-band radar emitter
to approximately 10%, while the radar signal is also impacted by the
is on the left, followed by the LTE, EDGE, GSM, and WCDMA emitters.
presence of the WCDMA emitter.
The S-band radar emitter is on the right, with a WCDMA emitter sit-
ting within the S-band radar's bandwidth.
Figure 6. Demodulation of WCDMA signal in the presence of the
Figure 4. Multi-emitter test signal. radar interferer.
5
Results, part 2: Coexistence of C-band radar The same COTS test setup used in the previous case study was also
used to create and analyze this test signal; however, in this case the
and 802.11ac VHT wireless LAN M8190A AWG was used to generate differential I/Q outputs which
The second case study uses the same COTS test setup to study were then fed to the wideband I/Q inputs ports of the E8267D vector
potential coexistence issues between radar systems and emerging PSG signal generator. This configuration is used because the 5.8 GHz
wireless networking signals. The test setup is reconfigured to examine carrier frequency for the 802.11ac WLAN signal exceeds the maximum
the interaction between a C-band radar emitter and an 802.11ac Very RF bandwidth of the AWG, so the PSG is used to modulate the
High Throughput (VHT) WLAN emitter to help determine potential M8190A AWG I/Q outputs on a 5.8 GHz carrier frequency. The PSG
co-existence issues. can be used for carrier frequencies to 44 GHz, however the external
wideband I/Q inputs of the vector PSG are limited to a 2 GHz modula-
To examine this, a design simulation schematic was created to com- tion bandwidth.
bine an 802.11ac WLAN 5.8-GHz emitter with a C-band radar signal
(Figure 7). The 802.11ac simulation signal source is configured for a The C-band radar signal was set to several different frequencies to
160-MHz bandwidth, while the radar signal source is configured for a effectively "walk-through" the WLAN OFDMA (Orthogonal Frequency-
200-MHz LFM chirp bandwidth. Division Multiple Access) emitter (centered at 5.8 GHz) so that
co-existence effects could be analyzed at different frequencies. Figure
8 shows one scenario where the radar emitter's center frequency
was set to 5.6 GHz, where it only slightly overlaps with the 5.8 GHz
802.11ac emitter. The EVM of the WLAN was measured at 3.1% for
this case.
Figure 7. Multi-emitter simulation for C-band radar and 802.11ac WLAN co-existence case study
Figure 8. Slight overlap between 802.11ac WLAN and C-band radar signal.
6
Figure 9 shows a more severe case for the offending radar emitter,
where its center frequency is set to 5.7 GHz, resulting in significant
overlap between the radar and the 802.11ac WLAN OFDMA emitter. In
this case, the radar emitter destructively impacts the 802.11ac WLAN
emitter's EVM. Because the 89600 VSA software cannot achieve
synchronization with the WLAN emitter due to the radar interferer, it is
unable to demodulate the waveform.
Figure 10. Multi-emitter spectrum with LTE and S-band radar signals.
The multi-emitter spectrum includes GSM, EDGE, and LTE emitters,
two S-band radar emitters, and two WCDMA emitters. The LTE emitter
and S-Band radar emitter are shown near the center of the measured
frequency spectrum.
The PXA RF signal analyzer is used to zoom into the portion of the
multi-emitter spectral environment which contains the LTE and
radar emitters, as shown in Figure 11. The 89600 VSA demodulation
Figure 9. Significant overlap between 802.11ac WLAN and C-band radar signal. measurement with the PXA RF signal analyzer shows the constellation
(upper left), spectrum (lower left), EVM vs. subcarrier (upper right),
and EVM error summary (lower right).
Results, part 3: Coexistence of S-band radar
and LTE
This final scenario focuses on an LTE downlink signal in the S fre-
quency band and an S-band radar signal. The S-band radar simulation
signal source is generated along with the LTE downlink, EDGE, GSM,
WCDMA signal source. An additional S-band radar signal source and
WCDMA signal source are also included.
A COTS test setup similar to the one shown in figure 2 is used to
generate the multi-emitter test spectrum shown in figure 10, which
was measured with the RF signal analyzer.
Figure 11. Scenario 1: LTE demodulation in the presence of S-band radar with
slight overlap.
7
The EVM is approximately 1.3% in the presence of the radar interferer, The EVM demodulation results in figure 12 show that the radar signal
and the EVM vs. subcarrier measurement shows performance degra- clearly has a more significant impact on the LTE signal in this scenario,
dation resulting from the radar interferer. relative to the first scenario. The EVM has degraded to approximately
14.1%, as a result of more spectral overlap with the radar spectrum.
To further illustrate the impact of the interference, the radar signal The EVM versus subcarrier measurement also shows additional
was moved closer to the LTE signal as shown in figure 12. The performance degradation resulting from the radar interferer, relative
multi-emitter simulation was re-run to generate the new test to the first scenario.
signal scenario.
A third scenario evaluates the BER degradation of an interference
signal. Figure 13 shows the simulation schematic used to evaluate
the impact of an S-Band radar interferer on a simulated LTE downlink
coded BER as the interferer's center frequency is swept.
Figure 12. Scenario 2: LTE demodulation in the presence of S-band radar with
significant overlap.
Figure 13. Simulation schematic to evaluate S-band radar interferer on coded BER.
8
The schematic consists of an LTE downlink signal source on the upper Conclusion
left. Below the LTE downlink signal source is an LFM radar signal
source. The center frequency of the LFM radar signal source will be Systems being designed to operate in today's crowded and complex
swept for the LTE BER simulation. The LTE signal and radar signal are spectral environments may require additional testing in the R&D
combined by a Signal Combiner element to re-sample and combine the lab environment to evaluate potential interference scenarios. Signal
two signals. The combined signal is then fed into the LTE receiver for generation flexibility is required to address the many types of signals
the coded BER simulation measurement. The LTE receiver performs which may need to be considered, including radar, wireless network-
the physical layer decoding recover the data bits so that coded BER ing, and wireless communication signals.
and data throughput can be measured in simulation.
Having the ability to perform pre-deployment co-existence R&D
Figure 14 shows the LTE coded BER results as a function of the radar testing can save schedule and rework costs by allowing issues to be
interferer's center frequency, which was swept in the simulation. addressed in the lab environment instead of in the field.
The LTE coded BER performance is significantly impacted as the
radar interferer's center frequency is swept across the LTE downlink Keysight provides a flexible R&D testbed solution allowing quantitative
frequency, increasing from 0% BER to approximately 24% BER. The performance evaluations of complex spectrum interference scenarios.
LTE configuration, radar interferer configuration, and power levels can Although this is not real-time capability, this cost effective and flexible
be varied to evaluate potential co-existence issues. An RF transmitter approach to generating test spectrums using COTS hardware and
design and a receiver design with modeled design impairments could software can allow development teams the ability to explore and
have also been evaluated as part of this simulation. investigate what-if scenarios in the R&D lab environment long before
potential co-existence issues may develop in the operational environment.
Figure 14. Simulation results for coded BER versus swept radar
interferer frequency.
9
10 | Keysight | A Flexible Testbed to Evaluate Potential Co-Existence Issues Between Radar and Wireless - Application Note
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