Given the limited spectrum resources, planning of the future wireless networks such as fifth generation and beyond to be deployed in very congested and complex electromagnetic environments requires techniques for efficient co-channel external and internal (self-) interference cancelation. Benefited from electromagnetic concepts, signal processing techniques, or combination of both, the first part of this research reports on workable solutions for 1) the mitigation of self-interference issue in wireless transceivers for enabling full-duplex communication and 2) the cancelation of external interference caused by the other users, multipath effects, or jammers.
To develop the antenna system for enabling self-interference cancelation, in the first step, a compact, single-port slot antenna is designed which provides a minimum gain of 11 dB and an aperture efficiency of 65% over 40% fractional bandwidth. Next, the antenna is evolved to a common-aperture two-port antenna system with a very high level of isolation between channels over a wide bandwidth yet maintaining consistent radiation characteristics. A low-loss air-dielectric microstrip feed is designed which can be integrated with the other parts of the antenna and is amenable to 3D printing technology. The proposed decoupling method can potentially provide nearly 90 dB of channels isolation over 44% fractional bandwidth. For the fabricated antenna, a minimum isolation of 55 dB and a minimum gain of 10 dB is measured over the entire band.
To manage external interference, novel array signal segregation algorithms have been developed to spatially retrieve the desired signals in the presence of strong interfering signals. Using a uniform circular array, the algorithms are formulated to account for mutual coupling among array elements. A frequency domain Array Signal Segregation using an Iterative Approach (ASSIA) is presented to estimate the directions of arrival, magnitudes and phases of the signals’ spectral components. A statistical analysis in a complex environment with Rayleigh fading characteristics shows that ASSIA radio with a 12-element circular array can improve the signal to jammer ratio from -20 dB to at least +2 dB in more than 70% of occasions. In conjunction with ASSIA, a super-resolution signal detection algorithm based on a novel Closely spaced Nulls Synthesis Method (CNSM) is then developed which, for the first time, demonstrates capability of an antenna array in resolving direction of arrival of closely spaced correlated signals in the absence of a priori knowledge of the number of the incident signals. It is demonstrated that the proposed ASSIA-CNSM is superior to the other super-resolution Directions of Arrivals (DoA) estimation techniques such as Maximum Likelihood method. To improve the performance of the proposed algorithms, an efficient feed-forward technique is presented to mitigate the mutual coupling effects in multiple antenna systems.
Subsurface communication is another challenging task mainly due to the very lossy ground formations. In smart directional drilling, for instance, the existing telemetry methods do not meet the required data-rate for real time monitoring and controlling purposes. The second part of this work reports on a robust, cost-effective and high data-rate communication technique for enabling long-distance communication in drilling process. The concept of using the drilling tools as a Single Conductor Transmission Line (SCTL) is introduced and a very compact SCTL transducer that fits inside the borehole is designed at low HF band. The transducer provides 2% fractional bandwidth and can be used to enable data transmission at a data rate of 60 kbps.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/149873/1/smamjadi_1.pd
