Andrew Charles Mallory Austin

Modeling the Effects of Nearby Buildings on Inter-Floor Radio-Wave Propagation

Two buildings (A and B) have been modeled and analyzed with a 2D TEz implementation of the finite-difference time-domain (FDTD) algorithm in order to identify and characterize the mechanisms allowing signals to propagate between floors, specifically reflection and scattering from nearby buildings. Results have been extended to 2.5D by assuming isotropic spreading in the third dimension. In both scenarios considered, reflections from surrounding buildings are found to increase the average received power on adjacent floors-up to 9.7 dB and 32 dB for buildings A and B respectively. Measurements of the impulse response in Building A, made with a sliding correlator channel sounder, show a number of long-delay pulses, which can be attributed to specific reflection paths. Based on these findings, a simple two-component propagation model to predict the sector-average signal strengths is proposed and validated against measurements of the received power. The direct component is modeled as free space with a 22 dB/floor attenuation factor, and the reflected component is modeled as free space with reflection/transmission coefficients of 0.5. The RMS prediction error for this model is 3.2 dB.

Modeling Propagation in Multifloor Buildings Using the FDTD Method

A three-dimensional parallel implementation of the finite-difference time-domain (FDTD) method has been used to identify and isolate the dominant propagation mechanisms in a multistorey building at 1.0 GHz. A novel method to visualize energy flow by computing streamlines of the Poynting vector has been developed and used to determine the dominant propagation mechanisms within the building. It is found that the propagation mechanisms depend on the level of internal clutter modeled. Including metallic and lossy dielectric clutter in the environment increases attenuation on some propagation paths, thereby altering the dominant mechanisms observed. This causes increases in the sector-averaged path loss and changes the distance-dependency exponents across a floor from 2.2 to 2.7. The clutter also reduces Rician K-factors across the floor. Directly comparing sector-averaged path loss from the FDTD simulations with experimental measurements shows an RMS error of 14.4 dB when clutter is ignored. However, this is reduced to 10.5 dB when the clutter is included, suggesting that the effects of clutter should not be neglected when modeling propagation indoors.

Modelling inter-floor radio-wave propagation in office buildings

A 2D model of an office building has been analysed at 1.0 GHz using the FDTD method. Results indicate inter-floor radio-wave propagation is supported by two distinct mechanisms: direct penetration and floor-edge diffraction. The power of the direct component decreases linearly by 10-15 dB/floor penetrated, whereas the diffracted component is significantly smaller and asymptotes toward a constant value. The presence of floor-edge diffraction is a noteworthy finding, as it provides a physical basis for previously reported, but hitherto, unexplained, results.

Modelling interference for indoor wireless systems using the FDTD method

A 2D TMz implementation of the Finite-Difference Time-Domain algorithm is used to model radio-wave propagation from multiple transmitter locations in an eight storey building. From the steady-state field data, the Signal-to-Interference Ratio (SIR) is calculated for down-link scenarios. One transmitter is located on each floor and two base-station configurations are examined: aligned and staggered. Vertically-aligned transmitters are found to have better SIR performance - 9% of the sectors in the aligned configuration and 23% in the staggered configuration have SIRs less than 5 dB. The central services core significantly reduces the SIR, however this effect can be alleiviated by including another set of vertically-aligned transmitters.

Sliding Window Spectrum Sensing for Full-Duplex Cognitive Radios with Low Access-Latency

In a cognitive radio system the failure of secondary user (SU) transceivers to promptly vacate the channel can introduce significant access-latency for primary or high-priority users (PU). In conventional cognitive radio systems, the backoff latency is exacerbated by frame structures that only allow sensing at periodic intervals. Concurrent transmission and sensing using self-interference suppression has been suggested to improve the performance of cognitive radio systems, allowing decisions to be taken at multiple points within the frame. In this paper, we extend this approach by proposing a sliding-window full-duplex model allowing decisions to be taken on a sample-by-sample basis. We also derive the access-latency for both the existing and the proposed schemes. Our results show that the access-latency of the sliding scheme is decreased by a factor of 2.6 compared to the existing slotted full-duplex scheme and by a factor of approximately 16 compared to a half-duplex cognitive radio system. Moreover, the proposed scheme is significantly more resilient to the destructive effects of residual self-interference compared to previous approaches.

Digital predistortion of power amplifier non-linearities for full-duplex transceivers

Non-linearities introduced by the power amplifier stage can significantly reduce the performance of self-interference cancellation in full-duplex transceivers. Accordingly, we propose a full-duplex system architecture that predistorts the digital baseband transmit signal to account for the non-linear memory effects of the power amplifier. Implementation results for a 5 MHz OFDM signal (operating with 20 dBm average transmit power) on a full-duplex testbed show that a further 13 dB suppression can be obtained, compared to the case when no predistortion is applied. The power levels of out-of-band emissions are also significantly reduced.

Wireless Channel Characterization in Burning Buildings Over 100–1000 MHz

A 3-D implementation of the finite-difference time-domain (FDTD) method is used to model 100-1000-MHz radio wave propagation in a generalized office building. Fire within this building is modeled as a cold plasma medium. The presence of fire is found to decrease the sector-averaged received power by up to 10 dB. The FDTD results also showing propagation through fire can introduce rotation in linearly polarized signals, increasing the power of cross-polarized components. Uncertainties in the plasma properties are modeled using nonintrusive polynomial chaos, and can introduce up to ±8 dB variation in the sector-averaged power.

Efficient Field Reconstruction Using Compressive Sensing

Compressive sensing is used to reconstruct the time-harmonic electric field created by multipath fading from a limited number of measurement points over a planar region. The multipath fading signal is shown to be the superposition of multiple plane wave components and thus has a sparse representation in the spatial-frequency domain. The discrete Fourier basis used as the dictionary for orthogonal matching pursuit is oversampled to ensure sufficient resolution in the spatial-frequency domain. Experimental results at 10 GHz using an arbitrary plane wave expansion show that the signal-to-error ratio of the compressive sensing reconstruction is approximately 16 dB when randomly selecting only 7.5% of the total points.

Spatial Multiplexing of QPSK Signals With a Single Radio: Antenna Design and Over-the-Air Experiments

This paper describes the implementation and performance analysis of the first fully operational beam-space multiple-input multiple-output (MIMO) antenna for the spatial multiplexing of two QPSK streams. The antenna is composed of a planar three-port radiator with two varactor diodes terminating the passive ports. Pattern reconfiguration is used to encode the MIMO information onto orthogonal virtual basis patterns in the far field. A measurement campaign was conducted to compare the performance of the beam-space MIMO system with a conventional 2 × 2 MIMO system under realistic propagation conditions. Propagation measurements were conducted for both systems and the mutual information and symbol error rates were estimated from Monte-Carlo simulations over the measured channel matrices. The results show the beam-space MIMO system and the conventional MIMO system exhibit similar finite-constellation capacity and error performance in nonline-of-sight scenarios when there is sufficient scattering in the channel. In comparison, in line-of-sight channels, the capacity performance is observed to depend on the relative polarization of the receiving antennas.

Demo: Concurrent Spectrum Sensing and Transmission for Cognitive Radio using Self-Interference Cancellation

A demonstration of a cognitive radio network that supports concurrent spectrum sensing and transmission is presented. To detect primary users while transmitting, the secondary user node must suppress the self-interference signals. The system is implemented on a National Instruments Universal Software Radio Peripheral (USRP) platform. The demonstration will show that continuous spectrum sensing avoids the overhead for dedicated sensing periods and can detect the primary user within at most 10~ms from the start of transmission.