Exceptional Points of Degeneracy Directly Induced by Space-Time Modulation of a Single Transmission Line

We demonstrate how exceptional points of degeneracy (EPDs) are induced in a single transmission line (TL) directly by applying periodic space-time modulation to the per-unit-length distributed capacitance. In such space-time modulated (STM)-TL, two eigenmodes coalesce into a single degenerate one, in their eigenvalues (wavenumbers) and eigenvectors (voltage-current states) when the system approaches the EPD condition. The EPD condition is achieved by tuning a parameter in the space-time modulation, such as spatial or temporal modulation frequency, or the modulation depth. We unequivocally demonstrate the occurrence of the EPD by showing that the bifurcation of the wavenumber around the EPD is described by the Puiseux fractional power series expansion. We show that the first order expansion is sufficient to approximate well the dispersion diagram, and how this "exceptional" sensitivity of an STM-TL to tiny changes of any TL or modulation parameter enables a possible application as a highly sensitive TL sensor when operating at an EPD

Enabling wireless in-band full-duplex

This paper presents a baseband model and an enhanced implementation of the wireless full duplex analog method introduced by [1].Unlike usual methods based on hardware and software self- interference cancelation, the proposed design relies on FSK modulation. The principle is when the transmitter of a local end is sending data by modulating the carrier with the appropriate frequency deviation, its own receiver is checking if the remote transmitter is using the opposite deviation. Instead of architectures often used by both non-coherent and coherent receivers that require one filter (matched filter for coherent detection) for each frequency deviation, our design uses one mixer and one single integrator-decimator filter. We test our design using Universal Software Radio Peripheral as radio frequency front end and computer that implements the signal processing methods under free and open source software. We validate our solution experimentally and we show that in-band full duplex is feasible and synthesizable for wireless communications

Novel High Isolation Antennas for Simultaneous Transmit and Receive (STAR) Applications

Radio frequency (RF) spectrum congestion is a major challenge for the growing need of wireless bandwidth. Notably, in 2015, the Federal Communications Commission (FCC) auctioned just 65 MHz (a bandwidth smaller than that used for WiFi) for more than $40 billion, indicating the high value of the microwave spectrum. Current radios use one-half of their bandwidth resource for transmission, and the other half for reception. Therefore, by enabling radios to transmit and receive across their entire bandwidth allocation, spectral efficiency is doubled. Concurrently, data rates for wireless links also double. This technology leads to a new class of radios and RF frontends. Current full-duplex techniques resort to either time- or frequency-division duplexing (TDD and FDD respectively) to partition the transmit and receive functions across time and frequency, respectively, to avoid self-interference. But these approaches do not translate to spectral efficiency. Simultaneous transmit and receive (STAR) radios must isolate the transmitter from the receiver to avoid self-interference (SI). This SI prevents reception and must therefore be cancelled. Self-interference may be cancelled with one or more stages involving the antenna, RF or analog circuits, or digital filters. With this in mind, the antenna stage is the most critical to reduce the SI level and avoid circuit saturation and total system failure. This dissertation presents techniques for achieving STAR radios. The initial sections of the dissertation provide the general approach of stage to stage cancellation to achieve as much as 100 dB isolation between the receiver and transmitter. The subsequent chapters focus on different antennas to achieve strong transmit/receive isolation. As much as 35 dB isolation is shown using a new spiral antenna array with operation across a 2:1 bandwidth. Also, a new antenna feed is presented showing 42 dB isolation across a 250 MHz bandwidth. Reflections in the presence of a dynamic environment are also considered

High-Performance Multi-Antenna Wireless for 5G and Beyond

Over the next decade, multi-antenna radios, including phased array and multiple-input-multiple-output (MIMO) radios, are expected to play an essential role in the next-generation of wireless networks. Phased arrays can reject spatial interferences and provide coherent beamforming gain, and MIMO technology promises to significantly enhance the system performance in the coverage, capacity, and user data rate through the beamforming or diversity/capacity gain which can substantially increase the range in wireless links, that are challenged from the transmitter (TX) power handling, receiver (RX) noise perspectives and a multi-path environment. Furthermore, the multi-user MIMO (MU-MIMO) can simultaneously serve multiple users which is vital for femtocell base stations and access points (AP). Full-duplex (FD) wireless, namely simultaneous transmission and reception at the same frequency, is an emerging technology that has gained attention due to its potential to double the data throughput, as well as provide other benefits in the higher layers such as better spectral efficiency, reducing network and feedback signaling delays, and resolving hidden-node problems to avoid collisions. However, several challenges remain in the quest for the high-performance integrated FD radios. Transmitter power handling remains an open problem, particularly in FD radios that integrate a shared antenna interface. Secondly, FD operation must be achieved across antenna VSWR variations and a changing EM environment. Finally, FD must be extended to multi-antenna radios, including phased array and multi-input multi-output (MIMO) radios, as over the next decade, they are expected to play an essential role in the next generation of wireless networks. Multi-antenna FD operation, however, is challenged not only by the self-interference (SI) from each TX to its own RX but also cross-talk SI (CT-SI) between antennas. In this dissertation, first, a full-duplex phased array circulator-RX (circ.-RX) is proposed that achieves self-interference cancellation (SIC) through repurposing beamforming degrees of freedom (DoF) on TX and RX. Then, an FD MIMO circ.-RX is proposed that achieves SI and CT-SI cancellation (CT-SIC) through passive RF and shared-delay baseband (BB) canceller that addresses challenges associated with FD MIMO operation. Wireless radios at millimeter-wave (mm-wave) frequencies enable the high-speed link for portable devices due to the wide-band spectrum available. Large-scale arrays are required to compensate for high path loss to form an mm-wave link. Mm-wave MIMO systems with digitization enable virtual arrays for radar, digital beamforming (DBF) for high mobility scenarios and spatial multiplexing. To preserve MIMO information, the received signal from each element in MIMO RX should be transported to ADC/DSP IC for DBF, and vice versa on the TX side. A large-scale array can be formed by tiling multiple mm-wave IC front-ends, and thus, a single-wire interface is desired between DSP IC and mm-wave ICs to reduce board routing complexity. Per-element digitization poses the challenge of handling high data-rate I/O in large-scale tiled MIMO mm-wave arrays. SERializer – DESerializer (SERDES) is traditionally being used as a high-speed link in computing systems and networks. However, SERDES results in a large area and power consumption. In this dissertation, a 60~GHz 4-element MIMO TX with a single-wire interface is presented that de-multiplexes the baseband signal of all elements and LO reference that are frequency-domain multiplexed on a single-wire coax cable