Jon W. Wallace

LOS and NLOS millimeter-wave MIMO measurements at 24 GHz in a hallway environment

Indoor 4×4 MIMO measurements in a hallway environment at 24 GHz for both LOS and non-LOS (NLOS) conditions are presented. Initial characterizations of the measured channels include receive power, delay spread, and wideband channel capacity.

Secure Array Synthesis

A new array synthesis problem, whose objective is to maximize secure information shared with a legitimate recipient in the presence of a passive eavesdropper, is posed for line-of-sight (LOS) wireless transmission. By casting the problem into the form of a semidefinite program, it is found that the problem is convex and that optimal solutions can be efficiently found irrespective of the array topology. Representative results for a uniform linear array (ULA) and uniform circular array (UCA) are presented to demonstrate the utility of the method. Furthermore, it is shown that the radiated power of the optimal solution can be naturally decomposed into a signal pattern and noise pattern, providing an intuitive description of the optimal solutions and allowing comparison with standard array synthesis techniques.

UAV attitude estimation using antenna arrays

This paper presents a new algorithm for estimating all three Euler angles that specify the relative attitude between two unmanned aerial vehicles based on multiple-input multiple-output (MIMO) radio transmissions. The algorithm uses direction-of-arrival estimates as well as estimates of the multi-polarized MIMO channel response to construct the coordinate frames describing the UAV attitudes. These coordinate frames then allow specification of the rotations required to align one UAV with the other. Simulations reveal that estimation errors are relatively small even for low signal-to-noise ratio.

A comparison of 24 GHz and 2.55 GHz MIMO measurements in two indoor scenarios

MIMO measurements at 24 GHz and 2.55 GHz are compared for two buildings consisting of classrooms and offices on two college campuses. The results indicate that mutual information for 4×4 MIMO with 15 dB SNR is very similar, suggesting similar multipath structure for the two different bands. Path loss is approximately 30 dB higher at 24 GHz, mainly due to the reduced receive aperture at the higher frequency. These results suggest that 24 GHz may be a suitable replacement for near and medium range indoor wireless applications currently using the 2.4 GHz ISM band.

Efficient optimization method for a reconfigurable OTA chamber

A reconfigurable over-the-air chamber (ROTAC) allows the synthesis of arbitrary propagation environments inside a reverberation chamber for wireless device testing by controlling the reflection of waves along the chamber walls with reconfigurable elements. This work proposes an efficient two-step algorithm for realizing desired channels by first optimizing a linearized ROTAC model and then using gradient ascent optimization to refine the reconfigurable reflector states. Representative results demonstrate the effectiveness of the proposed method for power angular spectrum synthesis.

A Comparison of Indoor MIMO Measurements and Ray-Tracing at 24 and 2.55 GHz

Colocated

Studying the interaction of UAS and human pilots using the X-Plane flight simulator

4\times 4

Physical-Layer Key Generation and Reconciliation

multiple-input multiple-output measurements at 2.55 and 24 GHz are presented for two university buildings consisting of classrooms and offices. Link gain in hallways and connected laboratories looks similar at the two frequencies when the effect of lower effective receive antenna aperture with increasing frequency is removed. Non-line-of-sight (NLOS) propagation through a wall or around hallway corners exhibits approximately 5–20 dB (11 dB on average) greater loss beyond the 20 dB aperture loss at 24 GHz compared to that at 2.55 GHz. Fixed directional antennas increase path loss (PL) by an average of 13 dB when misaligned. Capacity for normalized signal-to-noise ratio is very similar in the two bands and is close to that for the optimal independent identically distributed case, indicating sufficient multipath for spatial multiplexing at 24 GHz. A ray-tracing study suggests that material loss must increase from 2.55 to 24 GHz to correctly predict the higher PL at 24 GHz in severely obstructed scenarios, indicating a need for future material characterization in high microwave bands. The results suggest that 24 GHz is a viable option to replace medium-range (10–30 m) NLOS wireless services currently operating at 2.4 GHz.

Reconfigurable OTA chamber for MIMO wireless device testing

A system of networked computer components is described allowing realistic simulation and performance assessment of see-and-avoid algorithms for unmanned aircraft systems (UAS). Due to its realistic physics engine and relatively open architecture, the X-Plane flight simulator is adopted to simulate computer-generated traffic or an aircraft controlled by a human pilot. Using the UDP interface in X-Plane, real-time collision avoidance algorithms are then implemented, where the simulated unmanned aerial vehicle (UAV) controller reads aircraft positions from X-Plane and updates control inputs to the UAV using sequential quadratic programming (SQP) to avoid collisions in real time. The basic concept is illustrated through an example flight involving a single aircraft in an airport pattern and a UAV flying through the same airspace. A second experiment is performed where a human pilot intentionally flies across the path of the UAV.

Secure Array Synthesis in Multipath Channels

Physical layer security is a technique that makes use of the physical communication channel or medium to provide additional robustness to eavesdroppers and attackers. Key establishment exploiting a multiple-input multiple-output (MIMO) reciprocal wireless channel is proposed and its performance investigated, indicating that secure keys can be rapidly generated between two nodes, even in the presence of close eavesdroppers. The use of reconfigurable antennas is investigated and experimentally proven as a key establishment solution for static channels with limited multipath. Additionally, different options are discussed to handle key-differences due to non-correlated noise together with quantization, either by simply introducing guard intervals or by joint source coding with LDPC codes.