# A Full-Duplex 60 GHz Transceiver with Digital Self-Interference Cancellation
## 2 System Requirement
### FDD and FD Modes of Operation  
Unlike the traditional TDD mode, the transmission and reception happen simultaneously in the FDD and FD modes, which are supported in the proposed system. The FDD operation mode is achieved by adopting a wider bandwidth baseband DVGA, IFA, and LNA. The proposed transceiver supports an offset frequency operation up to 2.16 GHz, such that the carrier frequency difference between the two local oscillators is 2.16 GHz. In such a condition, the transmitter up-converts the signal to the specified RF frequency band, while the received signal down-converts it to a 2.16 GHz IF band. The DVGA design reported in [16] with a 0.3 dB gain step using a 6-bit digital gain control is employed here. The optimization for bandwidth extension in [16] achieves a 3 dB bandwidth of more than 4 GHz. To cover all possible FDD operation bands, which satisfy the 802.11 ad standard, the IFA requires a vast bandwidth of 6 GHz, centered from 12.096 GHz to 12.48 GHz, where the receiver works using channel 2 or channel 3, respectively, because the received IF signal may locate on either side of the IF LO with a 2.16 GHz carrier offset for those channels. For channels 1 and 4, the received IF signal will be located at certain bandwidths within the band mentioned above. The IFA design has a 3 dB bandwidth from 9.0 GHz to 15.5 GHz that completely covers the signal band. The SI signal in the FDD mode is important, as the SI is always located at zero carrier frequency. The low-frequency noise may degrade the system's performance by reducing the DVGA's operation range or even failing the system when the DVGA is saturated. However, a physical separation in the spectrum enables the FDD system to achieve a level of performance close to the HD system. The performance is not affected even with the strong SI leakage when the DVGA is ensured to work in the linear range.  
In the FD operation, the SI and the wanted signal overlap at the baseband. Recently, RF-related active cancellation [8; 17; 18], pure digital cancellation [19; 20], or a hybrid of both RF and digital cancellation [11] was introduced. The RF frontend-related cancellation approach achieves good performance, usually for a specified frequency range and limited bandwidth with a complex circuit design and area [8; 21]. In this work, RF isolation and digital cancellation are used due to the low design complexity and acceptable performance across the interested frequency band. Since the received signal power must be higher than \(-49.6\) dBm for MCS12 with an EVM better than \(-21\) dB, it is harder to achieve an SI signal power that is lower than the noise floor just by using RF frontend isolation [8]. The digital-based SI cancellation is involved in increasing the SINR and reducing the FD's performance degradation. The FD with a lower SINR loss can be assumed to be approximately double the spectral efficiency, whereas with a high SINR loss, the effective spectral efficiency might be even lower than the HD mode. An SINR loss of 3 dB illustrates the point at which the FD mode can still be expected to provide a capacity gain compared to the HD transceiver [22; 23]. Hence, the system's SI power should be lower than \(-67.6\) dBm to make the FD mode meaningful.