# A Full-Duplex 60 GHz Transceiver with Digital Self-Interference Cancellation
## 4 System Measurement
### Full-Duplex Measurement  
Figure 12 shows the single-tone signal's power spectrum received together with the local SI at 0.8 m. The measured transmission power is \(-3\) dBm. The 450 MHz is the received signal from the antenna, and the 550 MHz is the SI from the local transmitter. Here, both transmitters are configured at the same condition with similar PA output power, and both the transmitter and receiver are operated on channel 2. The transmission loss here is 42 dB as calculated in (4), where the antenna gains for the transmitter \(\rm G_{tx}\) and receiver \(\rm G_{rx}\) are all 12 dBi. The received power achieves the maximum peak-to-peak output voltage \(\rm V_{pp}\) of the DVGA. The measured receiver chain gain \(\rm G_{rec}\) here is 26.08 dB as calculated in (5), where \(\rm P_{rec\_out}\) is the output power of the receiver chain and \(\rm P_{rec\_in}\) is the input power to the LNA. \[G_{rec}\left(\rm dB\right)=P_{rec\_out}\left(\rm dBm\right)-P_{rec\_in}\left( \rm dBm\right)=-19.08\,-\,\left(-3-42\right)=25.92\,\rm dB \tag{5}\]  
As plotted in Figure 12, the estimated isolation between the output of the PA and the input of the LNA is 54.2 dB based on the measured SI power level of \(-31.28\) dBm, as shown in (6); when the \(\rm P_{rec\_in\_SI}\) is the input SI power at the receive chain, \(\rm P_{PA\_out}\) is the output power from the PA. The \(\rm P_{rec\_in\_SI}\) is calculated based on the output power of the  
Figure 11: The measured EVM for the frequency division duplex operation. Figure 12: The received power versus the SI power at 0.8 m.  
receiver chain and the gain of the chain. The maximum isolation for the FD mode can be achieved at around 35 dB when setting the programmable amplifier (DVGA and IFA) to the minimal gain condition. However, the communication distance must be reduced to 0.45 m to compensate for gain drops. \[G_{iso}\left(\text{dB}\right)=P_{rec\_in\_SI}\left(\text{dBm}\right)-P_{PA\_out} \left(\text{dBm}\right)=\left(-31.28-25.92\right)-\left(-3\right)=-54.2\ \text{dB} \tag{6}\]  
For the modulated signal measurement, the RF isolation is around 30 dB, as a 5 dB gain is set at the receiver's DVGA to attain enough baseband signal amplitude. Figure 13 shows the time domain signal before and after DSIC processing. Two frame packages available with a 2 us gap between them are captured in Figure 13a. The SI signal is available all the time, and it can be observed easily during the 2 us package gap. The I and Q signals are captured by the oscilloscope in channels 1 and 2, as shown in Figure 13a. Figure 13b plots the received package data after the DSIC module. Here, the Rohde and Schwarz RTO 1044 oscilloscope captured data at 10 GSym/s, with 8 bits of valuable ADC output. The symbol rate of the test sequence is 1 GSym/s for both transmitters. The captured data are resampled at 4 GHz, and the out-band noise is removed before sending them to the DSIC. The dominant SI signal in the system comes from the 60 GHz domain before the LNA input. To measure the isolation between the transmitter and the receiver chain, the gain of the receiver's IFA is set to a minimum, and the DVGA gain is set to 5 dB. The output data from the DSIC are demodulated by a Keysight 89,600 VSA as shown in Figure 14. The reported EVM values for QPSK and 16-QAM are \(-17.05\) dB and \(-17.8\) dB, respectively. Here, the 16-QAM-based EVM is worse than the actual value, as 1/8 of the symbols are piloted and modulated by \(\pi/2\)-BPSK. It is not mapping correctly. Assuming all the pilot symbols have a similar vector error as the data symbols, the amended EVM for all symbols should be \(-18.7\) dB in 16-QAM. As the VSA software cannot decode the original package before the DSIC, we assume the EVM is the same as the received SINR, which is 12 dB, as shown in Figure 12. Hence, the MATLAB-based DSIC in this measurement achieved a 6.7 dB EVM improvement. The super-heterodyne architecture is the key contributor to canceling the image frequency.