Beyond digital interference cancellation

Beyond digital interference cancellation

Venkateswaran, V.

Van der Veen, A.J. (promotor)

Electrical Engineering, Mathematics and Computer Science

Circuits and Systems

2010-09-20

One of the major drawbacks towards the realization of MIMO and multi-sensor wireless communication systems is that multiple antennas at the receiver each have their own separate radio frequency (RF) front ends and analog to digital converter (ADC) units, leading to increased circuit size and power consumption. Improvements in RF and ADC technology happen at a much slower pace when compared to digital circuits, so that this problem is likely to be more critical in future. In a dense multi-user wireless communication setup, these multiple RF front ends and ADCs spend most of their power in processing signals from interfering users. The purpose of this research is to look at alternative mobile receiver architectures, from the joint perspective of a digital signal processing engineer as well as that of an RF designer. We start by specifying the need for a communion of RF and DSP techniques. We propose that advanced signal processing algorithms can be used in combination with existing circuit configurations, such as integrated phased arrays and multi-channel feedback ADCs, to perform analog interference cancellation. Interference cancellation allows for a reduced number of receiver chains and low resolution ADCs, hence reduced circuit size and power consumption. In summary, the research addresses the following questions: - Can we potentially reduce the cost and power dissipation of MIMO transceivers, by optimization across the RF-baseband borderline? - Can we design a flexible baseband platform that is tailored to low power circuits, demonstrating a potential for low cost in a dense multi-user setup? One approach to cancel interference in RF and to reduce the number of receiver chains in antenna array systems is to design RF phase shift combiners. An alternative is to integrate existing ADCs with a feedback beamformer (this setup is especially compatible with Sigma-Delta ADCs) to identify and cancel the interferer. Interference cancellation in the RF and in the mixed signal components of the receiver allows ADC units to represent the desired user more effectively for a fixed precision. For both the above mentioned architectures, we consider the hardware limitations and propose closed form solutions minimizing the overall mean squared distortion between the transmitted signals and its received estimate, and illustrate significant power savings in the receiver. In both the cases we also specify approximate solutions, when the closed form solutions are not feasible. Given such architectures, we propose techniques to estimate the changes in state of the wireless channel. Finally, we also specify that these approaches have the capacity to cancel the intermodulation products arising from the non-linearity of the RF components. On a higher level, it is imperative for the DSP engineer to abandon looking at ADCs and RF components as "black boxes" within a sensing/ communications system. For example, viewing a digitally assisted Sigma-Delta ADC as an equalizer or viewing multi-antenna RF circuits as integrated phased arrays to cancel interference may result in highly efficient joint solutions for mapping radio waves into the digital domain. Clearly, such hybrid architectures will result in DSP techniques driving the wireless revolution rather than being an afterthought for coping with the imperfections.

interference cancellation
beamforming
signal processing
wireless communications
ADCs
RF phase shifters

http://resolver.tudelft.nl/uuid:ba0cd4c2-388a-4cc8-9b76-bed680378e22

Institutional Repository

doctoral thesis

(c) 2010 Venkateswaran, V.