Aidin Razavi

Characterizing Polarization-MIMO Antennas in Random-LOS Propagation Channels

In the 5G system, we foresee the use of LOS-dominated mm-wave radio links to moving users being subject to slow fading resulting from the users’ random locations and orientations. We refer to this as a random-LOS channel. MIMO processing algorithms will be used in 5G to improve performance in slow fading, similar to how they are used in Rayleigh fading. To this end, we study the probability of detection in the random-LOS channel when there are dual-polarized antennas on both sides of the link. We introduce two polarization deficiencies: the polarization non-orthogonality and the amplitude imbalance between the ports of a two-port antenna. The MIMO efficiency is evaluated as a function of these deficiencies. In the analysis, we consider the MRC algorithm for one bitstream, and the ZF and SVD algorithms for two bitstreams. We also present two analytical formulas for the MIMO efficiency that can be used to determine performance. We use the formulas on two ideally orthogonal dipoles, and show by means of coverage plots how much the 1- and 2-bitstream performances degrade due to the polarization deficiencies in off-boresight directions.

Maximum Aperture Power Transmission in Lossy Homogeneous Matters

We apply array signal processing techniques to the transmitting aperture field modes in order to determine the optimal field distribution that maximizes the power transmission through lossy media between a transmitting and an ideally receiving antenna aperture. The optimal aperture distribution is then used as a reference field for developing curves applicable to the design of many near-field systems, such as for the detection of foreign objects in lossy matters (e.g., food contamination detectors), wireless charging of batteries of human body implanted devices, and for in-body communication systems.

Optimal aperture distribution for near-field detection of foreign objects in lossy media

We determine the optimal source aperture field distribution to maximize the power transfer through a lossy medium from the transmitter aperture to a receiver aperture located in the near-field region. The optimal distribution is determined by applying array signal processing techniques to aperture field modes. By designing the system to be sensitive to the presence of foreign objects in a homogenous matter, the synthesized optimal aperture distribution increases the detection probability of foreign objects in various near-field applications, such as those that can detect potentially hazardous contaminations in food.

Probability of Detection Functions of Polarization-MIMO Systems in Random-LOS

We derive the probability of detection functions of 1- and 2-bitstreams for polarization multiple-input multiple-output antenna systems in random line-of-sight propagation conditions. The derivations are produced assuming that the angle-of-arrival of the field impinging at the receive antenna is fixed. Hence, randomness is only due to the direction of polarization of the incident field relative to the polarization of the far-field of the receiver antenna. Also, a general analytical orthogonalization transformation matrix has been derived for far-field functions of arbitrary dual-polarized antennas and used in the probability of detection derivations. Analytical results are obtained for the maximum ratio combining receiver diversity and the zero-forcing multiplexing receiver algorithms. These results provide a practical prediction tool of the impact of antennas on system performance due to polarization deficiencies of analytical, measured or simulated radiation field patterns of dual polarized antennas. This is illustrated by the provided numerical examples.