Delta-Sigma Based Signal Processing Techniques for Broadband Radio Applications
Date
2019-01-22
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The growing network coverage and the sharp increase in the number of devices in the wireless network have generated a great demand for browsing and accessing data, high-definition video, and streaming services without experiencing delays or interruptions. This is made possible by the high-speed connection and minimal latency achieved by efficient and reliable wireless network infrastructures. These networks are continuously evolving to serve huge numbers of users and satisfy the growing demand for data, while providing a good signal quality and maintaining a low power consumption. New techniques and designs of wireless devices are currently being developed to respond to the emerging applications requiring low power consumption, higher bandwidth, and minimum latency. This work focuses on enhancing the wireless transmitter performance by using the Delta-Sigma Modulation (DSM) technique. In fact, DSM-based transmitters have shown a relatively strong performance in terms of linearity and power efficiency. However, limitations on speed could degrade the overall performance and bandwidth. Research efforts have been focusing on DSMs as a promising solution to further enhance the overall efficiency of wireless devices. By proposing robust hardware implementation methods and preserving the linearity of the transmitter, the DSM topologies can match other existing transmitter topologies in terms of power efficiency while offering more flexibility when aiming at the design of Software Defined Radio (SDR) based transmitters. First, a general study on DSM basics and different DSM topologies is conducted. The study covers different types of DSMs classified by their transfer function, order and type: low-pass, high-pass, and band-pass. Different DSM-based transmitter topologies are presented, namely, the Cartesian, Polar, Envelope and the Complex Delta-Sigma Modulator (CxDSM) topologies. Also, the concept of using a multi-level DSM quantization has been investigated. Second, the impact of the undesired delays occurring during the hardware implementation is investigated. A post-compensation block is needed to cancel the effect of these delays and recover the correct DSM transfer function. Additionally, an implementation of an all-digital DSM-based transmitter for Software Defined Radio (SDR) applications was developed. The SDR transmitter is reconfigurable and has a lower latency compared to previous architectures. Furthermore, to improve the performance of DSMs and find a substitute for the COordinate Rotation DIgital Computer (CORDIC) based multi-level CxDSM, a multi-level complex quantizer implementation method on Digital Signal Processors (DSP) is proposed. The latter uses a look-up table (LUT) to generate quantized output samples. This method was proven to be robust and achieved a minimum latency. Third, an implementation of a multi-level DSM-based wireless transmitter is developed to preserve the power efficiency of the Switch Mode Power Amplifiers (SMPAs). For this purpose, a dual-branch three-level DSM was implemented and validated on a digital signal processing platform. Finally, a digital Intermediate-Frequency (IF) High-Pass DSM (HPDSM)-based transmitter is implemented and validated. By integrating a complex quantizer in the HPDSM-based topology, the performance is significantly improved. This topology maintains a low oversampling ratio, saves the processing resources while enhancing the quality of the output signal.
Description
Keywords
Broadband transmitters, Complex Delta-Sigma modulation, Delta-Sigma modulator delay compensation, Hardware implementation, Transmitter design
Citation
Ben Arfi, A. (2019). Delta-Sigma based signal processing techniques for broadband radio applications (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.