Ph.D Thesis


Ph.D StudentGinzberg Nimrod
SubjectTransmitter Architectures for Capacity Enhancement in 5G
Wireless Communications Systems
DepartmentDepartment of Electrical and Computer Engineering
Supervisor ASSOCIATE PROF. Emmanuel Cohen
Full Thesis textFull thesis text - English Version


Abstract

Capacity enhancement requirements in next-generation 5G wireless systems have motivated extensive research of circuit-level solutions for enabling simultaneous transmission and reception (STAR) in in-band full-duplex (IBFD) radios, in which the transmitter and the receiver operation at the same time in the same frequency band. For the operation of IBFD systems, it is required to suppress the strong transmitter self-interference at the receiver input to avoid the compression and desensitization of the receive path while imposing minimal degradation to the system’s energy efficiency and noise figure of the receive path.

To address these challenges, we have investigated the quadrature balanced power amplifiers (QBPA) topology as a transmitter building block in an IBFD transceiver, which allows for architectural and built-in transmit-receive (TX-RX) isolation in the order of 10−20 dB along with a dedicated pre-PA self-interference cancellation (SIC) signal injection technique that reused the gain of the TX channel. This SIC port can be used to inject a digitally synthesized cancellation signal that is neither limited in bandwidth nor sensitive to the frequency-selectivity of the leakage path.

This thesis presents several realizations of such a QBPA using analog Class-AB power amplifiers (PAs) and digital switched-capacitor RF digital-to-analog converters (DAC) in the 2.4 and 5 GHz Wi-Fi bands, fabricated in TSMC’s 180 nm and 65 nm standard bulk CMOS processes. In the RF domain, we demonstrate 50−70 dB of TX-RX isolation along with correct TX error vector magnitude (EVM) values with system efficiency similar to half-duplex (HD) TX mode. By evolving from analog to digital QBPA implementation, we reached the RX noise figure of around 5 dB in IBFD mode at 10 dB power backoff from maximum TX output power. Successful establishment of deep self-interference cancellation (SIC) in IBFD systems may also pave the way to advanced spectrum management that leverages STAR across the fragmented spectrum in frequency division duplex (FDD) wireless networks and also be exploited for carrier aggregation (CA) operation within the same hardware, enabling wider transmission bandwidths utilizing multiple concurrent channels across the available radio spectrum.

Two FDD examples are shown, one using the QBPA technique and the other by an active diplexer design based on quadrature balanced N-path mixers. Another two works on CA are included. In the first, a wideband linearization technique employing two-dimensional digital predistortion (2D-DPD) and out-of-band spurious content cancellation in the 5 GHz band is proposed. In the second, both in-band and out-of-band linearity requirements are satisfied by employing post-PA combining of low output impedance switched-capacitor power amplifies around the carrier frequency of 2.5 GHz.