# WISCANet: A Rapid Development Platform for Beyond 5G and 6G Radio System Prototyping
## 4 Over-the-Air Demonstrations
### 60 GHz Communications System  
To support higher frequency ranges, WISCANet deployments may be augmented by either mixing directly from baseband or superheterodyning inside the equipped RFFEs. In our specific deployment (pictured in Figure 2), we have executed over-the-air applications as high as 71 GHz. To support 6G research, we plan to extend support into the THz band; unfortunately, commercial THz SDRs are not widely available, so we implemented a superheterodyning approach similar to the technique discussed in [31].  
Using the Sivers EVK in combination with USRP N210's with LFRX and LFTX daughterboards, we implemented a simple mmWave communications system leveraging the adaptive waveform development kit. Operating at 60 GHz adds several challenges that are often be ignored at lower frequencies; for lower sampling rates, the carrier frequency offset (CFO) can become an appreciable fraction of the bandwidth, thus applications require some form of robust CFO correction. To address this issue, we added a robust CFO estimation and correction technique based on [79]. We add an underlying tone to the transmitted waveform as a fiducial for the CFO estimator. After the CFO correction is complete, a simple DC-blocking IIR filter is constructed and applied to remove the tone. With these two additions, the WDK performs comparably to the sub-6 GHz implementations at the new 60.48 GHz carrier frequency. These challenges were easy to identify and resolve thanks to the flexible debugging nature of WISCANet, and easy to address because of the ease of adapting code that is running on-the-air.  
We adapted the \"ping-pong\" communications demonstration and adaptive waveform toolbox to demonstrate flexible waveform implementation on NR Frequency Range 2 (FR2) systems. This showcases WISCANet's frequency flexibility and support for increasing frequency ranges. In Figures 15-19, we plot a snapshot of the power spectral densities and received symbols. The carrier frequency for the experiment is the WiGig Channel 2 at 60.48 GHz. We used a 10 MHz sampling rate and oversampled the BPSK waveform by 5 to achieve an occupied bandwidth of about 2 MHz. This allows plenty of flexibility in correcting CFO and reduced the risk of aliasing. Between Figures 17 and 18, we observe some residual carrier frequency offset in the symbols, which reduces the effectiveness of the applied MMSE equalizer. A more accurate and computationally-expensive fine frequency estimation algorithm could help reduce these residual effects.  
Figure 14: Block diagram of the dynamic spectral access configuration. Three users labeled “others” operate in different spectral allocations with arbitrary timing. The two users engaged in the ping-pong application constantly measure the spectrum, identify opportunities, and use these openings to communicate. The goal of this demonstration is to highlight how WISCANet and the pre-built ping-pong application enable rapid implementation and validation of novel PHY and MAC layer techniques over-the-air.  
Figure 16: Snapshot of the over-the-air, received power spectral density in the WiGig Channel 2 band at 60.48 GHz after matched filtering and CFO correction.  
Figure 15: Snapshot of the over-the-air, received power spectral density in the WiGig Channel 2 band at 60.48 GHz.  
Figure 17: Received training symbols after CFO correction.  
Figure 18: Received message symbols after CFO correction.