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Figure 3 shows the resulting multi-emitter test spectrum, which was measured with the RF signal analyzer. The multiemitter 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. 

Check For Co-Existence Between LTE And Radar, Fig. 3

The RF signal analyzer is used to measure the spectrum and EVM performance to evaluate the co-existence between the LTE source and radar emitter. Figure 4 shows the spectrum and demodulation results of the first scenario. The RF signal analyzer is used to zoom into the portion of the multi-emitter spectral environment which contains the LTE and radar emitters. The 89600 VSA software is applied to the RF signal analyzer to demodulate the LTE emitter. The 89600 VSA demodulation measurement shows the constellation (upper left), spectrum (lower left), EVM versus subcarrier (upper right), and EVM error summary (lower right).

Check For Co-Existence Between LTE And Radar, Fig. 4

The radar signal has some impact on the LTE signal in this scenario. The EVM is approximately 1.3% in the presence of the radar interferer, and the EVM versus subcarrier measurement shows performance degradation resulting from the radar interferer.

The LTE signal is set for a 5-MHz configuration, but can easily be varied for the many configurations supported by LTE, ranging from 1.4 to 20 MHz. The radar signal is configured for a linear-frequency-modulated (LFM) chirp with a user-specified pulse width, pulse repetition interval, and LFM chirp bandwidth. The settings can easily be modified by the user. Different modulation on pulse settings can also be configured (e.g., Barker coded).

For the second scenario, the radar signal was moved closer to the LTE signal (Fig. 5). The multi-emitter simulation was rerun to create the new test signal. The EVM demodulation results in Fig. 5 show that the radar signal has a more significant impact on the LTE signal in this scenario, relative to the first scenario. The EVM has degraded to approximately 14.1%, as a result of more spectral overlap with the radar spectrum. The EVM versus subcarrier measurement also shows additional performance degradation resulting from the radar interferer, relative to the first scenario.

Check For Co-Existence Between LTE And Radar, Fig. 5

The second case study examines the coexistence of an S-band radar system with an LTE wireless communications system by performing a simulation of LTE bit-error-rate (BER) performance as affected by interference from S-band radar signals. BER and throughput can be key metrics for receiver sensitivity, both with and without interferers present. The second case study employs the simulation schematic shown in Fig. 6 to evaluate the impact of an S-band radar interferer on simulated LTE downlink coded BER as the interferer’s center frequency is swept.

Check For Co-Existence Between LTE And Radar, Fig. 6

The schematic consists of an LTE downlink signal source on the upper left. This simulation signal source is hierarchical, so pushing down into it would reveal the physical layer coding applied to the signal, such as code-block segmenting, Turbo encoding, rate matching etc. This is not shown, however, in the top level schematic. Below the LTE downlink signal source is an LFM radar signal source. The center frequency of the LFM radar signal source will be swept for the LTE BER simulation. The LTE signal and radar signal are combined by a signal combiner element to resample and combine the two signals. The combined signal is then fed into the LTE receiver for the coded BER simulation measurement. The LTE receiver performs the physical layer decoding—code-block de-segmenting, Turbo decoding, rate dematching, and so forth—to recover the data bits so that coded BER and data throughput can be measured in simulation.

Figure 7 shows the LTE coded BER results as a function of the radar interferer’s center frequency, which was swept in the simulation. The LTE coded BER performance is significantly impacted as the radar interferer’s center frequency is swept across the LTE downlink frequency, increasing from a 0 % BER to approximately a 24 % BER. The LTE configuration, radar interferer configuration, and power levels can be varied to evaluate potential coexistence issues. An RF transmitter design and a receiver design with modeled design impairments could have also been evaluated as part of this simulation.

Check For Co-Existence Between LTE And Radar, Fig. 7

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