Nazar T. Ali

Compact WLAN disc antennas

A novel conical beam patch antenna design, suitable for local area network applications, uses a central cylindrical connection from the disc to ground to achieve a large reduction in resonant size. Results on efficiency, bandwidth, and pattern are reported for several prototypes.

Performance evaluation of CIR based location fingerprinting

Location fingerprinting has received considerable attention as a practical solution to the indoor localization problem. Specifically Received Signal Strength (RSS) based fingerprinting has been studied extensively and some improvements in performance have been reported for certain pattern recognition algorithms. Recently channel impulse response (CIR) based fingerprinting received attention due to its potential for significant improvements in accuracy. The performance evaluation of CIR fingerprinting, however, has not been addressed adequately in literature. This paper presents the performance evaluation of CIR location fingerprinting in an indoor environment. A simulation framework has been developed using the Ray-Tracing software to emulate the indoor wireless channel. The CIR-based simulation results showed noticeable improvements in the location estimation compared to the RSS-based approach. The paper highlights new findings for some parameters that affect the performance of the CIR-based fingerprinting with respect to the system bandwidth and training point spacing.

A power and efficiency measurement technique for active patch antennas

In this paper, the power input to the radiating element of an active microstrip patch antenna is measured using a small sensing patch, which is weakly coupled to a radiating edge. Combined with an estimate of patch radiation efficiency, this also yields a measurement of total radiated power. The method has advantages of convenience, insensitivity to room reflections, and a weakly frequency-dependent calibration factor.

On the performance of DWT and WPT modulation for multicarrier systems

The discrete wavelet transform, DWT, is being considered for multicarrier modulation, and intensive investigations are underway on how this scheme can best be deployed. The performance of the DWT and wavelet packet transform (WPT) has been investigated and compared. There are more narrowband sub-channels in WPT than those that exist in DWT owing to the style of multiresolution adopted by the latter. However, it is found that DWT and WPT perform differently as multicarrier modulations over AWGN and multipath channels. This work helps to inform the selection of base-wavelet families when studying or designing a multicarrier system of this kind.

Real time evaluation of RF fingerprints in wireless LAN localization systems

RF location fingerprinting has received significant attention as a practical solution to the indoor localization problem due to its use of the available wireless infrastructure (WLANs) and the simplicity of measuring the Received Signal Strength (RSS) fingerprint. The improvement of RSS-based fingerprinting has been limited due to RSS being a weak fingerprint structure; where it has been reported in literature that using more complex pattern recognition algorithms provides diminishing gains. Recently channel-based RF fingerprints such as the channel impulse response (CIR), channel transfer function (CTF) and frequency coherence function (FCF) have been proposed to improve the accuracy at the physical layer. An empirical evaluation of the physical layer fingerprints does not exist in literature and there is a need to understand the advantages/limitations of these fingerprint structures/signatures. As a result in this paper we provide a comprehensive empirical performance evaluation of location fingerprinting with a focus on analytical comparison of the RSS, CIR, CTF and FCF -based fingerprints using the weighted k-nearest neighbor (kNN) pattern recognition technique. By conducting frequency domain channel measurements in the IEEE 802.11 band at the university campus we evaluate the accuracy of the fingerprints and their robustness to human induced motion perturbations to the channel. We also provide analysis on the impact of system parameters such as the number of access points and the number of nearest neighbors.

Optically controlled 2.4GHz MMIC amplifier

In this paper a 2.4GHz MMIC amplifier for mobile applications is used to demonstrate the significant control that can be achieved in the amplifiers performance using optical illumination. The results presented show a 15dB variation in the amplifiers S21 figure and a 6 to 10dB variation in the input and output return loss when the incident optical power is varied.

Linear and nonlinear crosstalk in MIMO OFDM transceivers

This paper studies the effect of nonlinear and linear crosstalk in a MIMO (multiple in, multiple out) transceiver. These effects are mainly due to the power amplifier (PA) nonlinear behaviour and mutual coupling of antennas in the MIMO transmitter. The effects of the crosstalk interference on the signal performance are studied based on the measured error vector magnitude (EVM) at the transmitting antennas. The simulation and measurement results show that PA nonlinearity and RF crosstalk need to be considered in the design process.

Optical performance of the silicon heterostructure switch

The optical performance of a logical optical detector, that has been developed from a thin-oxide MIS silicon switch, is considered in relation to its fabrication. The analysis accounts for quantum efficiency and absorption depth. Predicted and measured results, taking these into account, show a very good correspondence. Applications include bistable switching sensors, pyroelectric detection, and robotic control systems. Since only standard processing is required, the construction of the device can be directed toward a wide range of requirements. >

Classification of indoor environments based on spatial correlation of RF channel fingerprints

This paper presents a realistic indoor multipath environment classification based on practical RF measurements. The classification is based on correlation statistics that accounts for grid spacing and system bandwidth. The Channel Transfer Function (CTF) and Frequency Coherence Function (FCF) are obtained for each grid, then inter-correlated to obtain the spatial coherence spectrum which shows a unique pattern that distinguishes LOS open space and LOS cluttered.

Gyro-chirality effect of bianisotropic substrate on the operational of rectangular microstrip patch antenna

In this paper, the gyrotropic bi-anisotropy of the chiral medium in substrate constitutive parameters (ξc and ηc )o f a rectangular microstrip patch antenna is introduced in order to observe its effects on the complex resonant frequency, half-power bandwidth and input impedance. Numerical calculations and analysis based on the dominant mode are carried out to show that the latter is directly related to the former. This paper is based on the Moment Method as full-wave spectral domain approach using sinusoidal basis functions. Two new results, namely the appearance of the difference (ξc − ηc )a nd sum (ξc + ηc )o f the two magneto-electric elements are obtained in the electric transverse components and Green tensor expressions, respectively. These new results can be considered as a generalisation form of the previously published work.