Multitone signal generation for a new Fourier-domain DAC-based transmitter

Bayram, Erkan; Negra, Renato (Thesis advisor); Heinen, Stefan (Thesis advisor)

Aachen : RWTH Aachen University (2020, 2021)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020


The tremendous increase in data consumption in the previous decades is driven by the high demand on increasing download and upload speed for various applications. Thus, broadband communication technologies are required in order to follow the increment in data traffic for coming years. In last 10 years new communication technologies have been presented to increase data transmission. However, they are not enough to meet expectations of the coming years. Therefore, 5th Generation mobile network has been presented as a next phase of the mobile communication standards to satisfy the growing demands on bandwidth beyond the current 4th Generation communication technology. However, these future standards bring a huge challenging on the existing hardware. Therefore, state-of-the-art transmitters are pushed to their limits in order to achieve such a high transmit data rate while keeping low energy consumption. Since the available spectrum is rather limited and expensive, any violation of spectral masking has to be avoided during the signal transmission. Therefore, the oversampling has to be realised for aliasing reduction. This operation increases the sampling rate of digital and mixed-signal blocks to multiple times of the transmitted bandwidth which is quite challenging for a bandwidth in the gigahertz-range. The goal of this work is to enable realisation of multiband and multistandard high speed transmitter based on disruptive data converter concept which is the Fourier domain-DAC (FD-DAC) transmitter (Tx) by implementing the frequency generation subsystem. The designed FD-DAC Tx pushes away all the stringent barriers regarding the sampling rate, power consumption and feasibility issue for high modulation bandwidth and allows covering different communication standards and worldwide frequency bands with only one highly reconfigurable transmitter. Since a revolutionary approach is introduced, it also brings a huge design challenges regarding the implementation of the frequency synthesizer which requires multiple of equidistantly spaced tones for data conversion. Thus, several frequency generators have to be integrated into a single chip to generate 16 tones with a equidistant space of 125MHz. Additionally, all of these signals have to be synchronised with respect to the baseband data. The presented work focuses on the implementation of the frequency synthesiser subsystem and the complete integration of the Txs. The designed synthesiser block meets the performance requirements of the transmitter and achieves 35 dBc of SFDR in the operating frequency range from 3GHz to 4.875GHz, −105 dBc/Hz of phase noise performance at 1 MHz offset frequency is recorded. Thus, the presented FD-DAC Txs provide 2GHz of modulation bandwidth and data rate up to 8 Gbps while digital signal processing and digital-to-analogue converter operating at 250MHz. Thus, each subsystem operates at two orders of magnitude slower compared to state-of-the-art inphase/quadrature (I/Q) transmitters. EVM values of 7.28% and 11.8% with QPSK are measured for 1GHz and 2GHz modulation bandwidths, respectively. Furthermore, the presented work exhibits an excellent spectral shaping which can fulfill the spectral mask requirements for multiple communication standards. The modulation bandwidth and its centre frequency can also be changed which allows the FD-DAC Tx operating as a multimode and multistandard transmitter. The developed concept enables new consumer experience in applications such as wireless virtual reality, 5G and beyond wireless communications such as 6G, and extremely low latency high data rate use cases. Furthermore, it is also going to pave the way for the next generation of data communication infrastructure, both wired and wireless. Therefore, it will have a huge impact on the capacity of data transmission.