Rashid Rashidzadeh

Robust indoor positioning using differential wi-fi access points

Location positioning systems using wireless area local network (WLAN) infrastructure are considered cost effective and practical solutions for indoor location tracking and estimation. However, accuracy deterioration due to environmental factors and the need for manual offline calibration limit the application of these systems. In this paper, a new method based on differential operation access points is proposed to eliminate the adverse effects of environmental factors on location estimation. The proposed method is developed based on the operation of conventional differential amplifiers where noise and interference are eliminated through a differential operation. A pair of properly positioned access points is used as a differential node to eliminate the undesired effects of environmental factors. As a result the strength of received signals, which is used to determine the location of a user, remains relatively stable and supports accurate positioning. To estimate wave propagation in indoor environments, log-distance path loss model has been employed at the system level. Experimental results indicate that the proposed method can effectively reduce the location estimation error and provide accuracy improvement over existing methods.

An All-Digital Self-Calibration Method for a Vernier-Based Time-to-Digital Converter

This paper presents a new calibration method for a Vernier-based time-to-digital converter (TDC). In the proposed method, delay lines in the TDC are configured as on-chip ring oscillators for generating a sequence of time events. These time events are applied to the TDC in the calibration mode, and then, the probability distribution of output codes is determined. The variations of the quantization step and the actual transfer characteristic representing the TDC are estimated through statistical analysis of the output codes. The proposed method eliminates the need for accurate external sources typically used for TDC calibration. Simulation and experimental results using a field-programmable gate array platform indicate that the method can successfully be employed to calibrate high-resolution TDCs with reasonable accuracy.

A Delay Generation Technique for Narrow Time Interval Measurement

A new architecture for the on-chip measurement of short-time intervals is proposed in this paper. The measurement method is similar to a typical low-voltage measurement setup where the input signals are first amplified and then measured to relax the dynamic range of the succeeding analog-to-digital converter. In the proposed method, narrow time intervals are first amplified by a time amplifier (TAMP) and then measured by a time-to-digital converter. A delay-locked-loop (DLL) circuit is utilized to design a feedback time amplifier in which the gain is readily programmed by input data to any integer value within a range specified by the number of delay cells in the DLL. The TAMPs gain remains rather unchanged under process and temperature variations due to the inherent negative feedback of the DLL system. The circuit is implemented using complementary metal--oxide semiconductor (CMOS) 0.18- mum technology occupying less than 0.63 mm2 of the silicon area. The simulation results show that the proposed scheme can successfully be employed to measure time intervals in the range of a few tens of picoseconds with acceptable accuracy.

Wi-Fi based indoor location positioning employing random forest classifier

Location positioning in indoor environments is a major challenge. Various algorithms have been developed over years to address the problem of indoor positioning. One of the most cost effective choice for indoor positioning is based on received signal strength indicator (RSSI) using existing Wi-Fi networks in commercial and/or public areas. This solution is infrastructure-free and offers meter-range accuracy. In this paper, machine learning approaches including k-nearest neighbor (k-NN), a rules-based classifier (JRip), and random forest have been investigated to estimate the indoor location of a user or an object using RSSI based fingerprinting method. Experimental measurements were carried out using 1500 reference points with received RSSIs of 86 installed APs in the second floor of Centre for Engineering Innovation (CEI) building at the University of Windsor. The results indicate that the random forest classifier presents the best performance as compared to k-NN and JRip classifiers with positioning accuracy higher than 91%.

Test and Measurement of Analog and RF Cores in Mixed-Signal SoC Environment

This paper describes the test and measurement of high-frequency analog/RF cores in a mixed-signal system-on-chip (SoC) environment using an embedded tester core. A new test methodology has been developed in which high-frequency tests are performed on-chip, but the control and test results are transmitted over the lower bandwidth connectivity associated with the SoC I/O terminals. A low-frequency analog signal is used to modulate a high-frequency squarewave and the resulting waveform is applied to a high-frequency circuit-under-test (CUT) as a test stimulus. The CUTs response is sampled using a coherent subsampling technique and the captured samples are transmitted at low-speeds off-chip from the SoC. A coupled phase-locked-loop and delay- locked-loop structure is employed to generate test waveforms in the 2.7-GHz range and to support high-resolution sampling with a sampling resolution of less than 10 ps. Simulation results using a reference low noise amplifier as a CUT shows the effectiveness of the proposed test method. The tester core has been sent for fabrication in CMOS 0.18-mum technology with a target area of 1 mm2.

Improved particle filter based on WLAN RSSI fingerprinting and smart sensors for indoor localization

Received Signal Strength Indicator (RSSI) is affected significantly by multi-path fading, building structure and obstacles in indoor environments, which lead to similar fingerprints problem and noise. To improve the performance of traditional fingerprinting method, the measurements provided by inertial sensors can be leveraged. Particle filter (PF) method is a widely chosen algorithm for sensor fusion. However, the initialization and weighting process are problematic in indoor positioning systems. This paper proposes a new PF scheme which yield a smooth and stable localization experience. To differentiate similar fingerprints, a single-hidden layer feed-forward networks (SLFNs) is used to model the multiple probabilistic estimations and improve the performance of the PF. Meanwhile, a new initialization algorithm using Random Sample Consensus (RANSAC) is presented to reduce the convergence time. Experimental measurements were carried out to determine the performance of the proposed algorithm. The results indicate that the positioning error of proposed scheme falls to less than 1.2?m which is better than the error reported in comparable approaches.

Testing 3-D IC Through-Silicon-Vias (TSVs) by Direct Probing

Testing the integrity of interconnects realized by through silicon vias (TSVs) in 3-D integrated circuits (3-D IC) is considered a challenging task. TSVs are excessively small and fragile for current probe technology. In this paper, a new spring-type probe using microelectromechanical systems (MEMS) technology is presented. The implemented MEMS probe supports the required pitch for TSV direct probing and minimizes the undesired scrub marks on TSV surface. Simulation results indicate that the implemented MEMS probe can operate at the gigahertz frequency range without significant test signal degradation.

Low-power oscillator for passive radio frequency identification transponders

Passive radio frequency identification tags extract energy from incoming electromagnetic waves to power up their internal circuitry. Such a limited source of power demands efficient circuits to minimise the power consumption. In this work a new technique is proposed to design a low-power ring oscillator in which the voltage swing of internal nodes are constrained to lower the dynamic power consumption. The proposed power reduction technique can be employed for RFID tags operating over different frequency bands from low frequency (LF) to microwave. A low-power oscillator operating in the medium-frequency range (6–16 MHz) for applications such as electronic article surveillance and item management has been implemented in this work. Post-layout simulation results using STMicroelectronics CMOS 65 nm technology indicate that the proposed method can reduce the power consumption by more than 25%.

Low-Contact Resistance Probe Card Using MEMS Technology

Multichannel die probing increases test speed and lowers the overall cost of testing. A new high-density wafer probe card based on MEMS technology is presented in this paper. MEMS-based microtest-channels have been designed to establish high-speed low-resistance connectivity between the die-under-test and the tester at the wafer level. The proposed test scheme can be used to probe fine pitch pads and interconnects of a new generation of 3-D integrated circuits. The proposed MEMS probe, which is fabricated with two masks, supports \(10^{6}\) lifetime touchdowns. Measurement results using a prototype indicate that the proposed architecture can be used to conduct manufacturing tests up to 38.6 GHz with less than -1-dB insertion loss while maintaining 11.4-m\(\Omega \) contact resistance. The measured return loss of the probe at 39.6 GHz is -12.05 dB.

Contactless test access mechanism for TSV based 3D ICs

In this paper, three coupling techniques for contactless TSV probing have been presented and their advantages and disadvantages are discussed. A contactless, noninvasive TSV probing scheme based on the principle of capacitive coupling is designed and simulated. The implemented scheme supports the high-density and the tight-pitch requirements for TSV probing.