This paper presents the design and implementation of the first in-band full duplex WiFi radios that can simultaneously transmit and receive on the same channel using standard WiFi 802.11ac PHYs and achieves close to the theoretical doubling of throughput in all practical deployment scenarios. Our design uses a single antenna for simultaneous TX/RX (i.e., the same resources as a standard half duplex system). We also propose novel analog and digital cancellation techniques that cancel the self interference to the receiver noise floor, and therefore ensure that there is no degradation to the received signal. We prototype our design by building our own analog circuit boards and integrating them with a fully WiFi-PHY compatible software radio implementation. We show experimentally that our design works robustly in noisy indoor environments, and provides close to the expected theoretical doubling of throughput in practice.

https://dl.acm.org/doi/pdf/10.1145/2486001.2486033

Full duplex radios

In one aspect there is provided a method. The method may include receiving a first analog radio frequency signal including a signal of interest and an interference signal caused by a second analog radio frequency signal transmitted in full duplex over a channel from which the first analog transmission is received; combining the first analog radio frequency signal and a portion of the second analog radio frequency signal to generate an output analog radio frequency signal characterized by at least a reduction or an elimination of the interference signal included in the output analog radio frequency signal; and providing the output analog radio frequency signal. Related apparatus, systems, methods, and articles are also described.

Single channel full duplex wireless communications

In this paper, we present a novel digital predistorter structure for joint mitigation of frequency-dependent power amplifier (PA) and in-phase and quadrature (I/Q) modulator impairments in direct-conversion radio transmitters. The predistorter is based on an extended parallel Hammerstein structure, yielding a predistorter that is fully linear in the parameters. In the parameter estimation stage, the indirect learning architecture is utilized. The proposed technique is the first technique in the literature to consider the joint estimation and mitigation of frequency-dependent PA and I/Q modulator impairments. Extensive simulation and measurement analysis is carried out to verify the operation and efficacy of the proposed predistortion structure. It is shown that the adjacent channel power ratio is increased by more than 20 dB in all experiments when using the proposed method, and that the performance of the reference techniques is clearly exceeded.

Joint Mitigation of Power Amplifier and I/Q Modulator Impairments in Broadband Direct-Conversion Transmitters

A wireless communication device includes, in part, an analog interference cancellation circuit and a controller. The analog cancellation circuit includes a multitude of delay paths each including a delay element and a variable attenuator. The controller dynamically varies the attenuation level of each of the variable attenuators in accordance with the frequency response characteristic of that attenuator to remove a portion of a self-interference signal present in a signal received by the device. The device measures the frequency response characteristic of the communication channel, used in determining the attenuation levels, via one or more preamble symbols. A second portion of the self-interference signal is removed by the device using a multitude of samples of a transmitted signal and a multitude of samples of a signal to be transmitted.

Self-interference cancellation

Power amplifiers in a communication system are inherently nonlinear. Digital predistorters can compensate these nonlinearity effects. In this paper, two memory polynomial predistorters including direct and indirect learning architectures are compared with each other. To the best of our knowledge, no similar comparisons have been published. Both of these architectures are special cases of the self-tuning control. We have modeled predistorters and analysed nonlinear effects of a power amplifier and their digital compensation by using Matlab?. Simulation results show that the memory polynomial model has convergence problems at large amplitudes and also problems of accuracy of representation. We observed that the results of the compensation depend also on the amplitude, not only on the frequency. The results of the linearisation show that the direct learning architecture achieves a better performance in almost all cases.

Comparison of direct learning and indirect learning predistortion architectures

For my family. iii ACKNOWLEDGEMENTS It is time to draw a period to my PhD endeavor. I feel extremely lucky to meet so many talented people during these years. I am grateful for their friendship, help, encouragement, and support. First, I would like to thank my advisor, Dr. G. Tong Zhou, for providing this opportunity for me to study at Georgia Tech. Her constant encouragement and valuable advices are essential for the completion of this thesis. I will be always inspired by the high standards she sets for herself and her sharp focus and deep devotion to whatever she works on.

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Lei Ding

Papers

Digital Predistortion of Power Amplifiers for WirelessApplications