Mohamed El-Hadidy

3D hybrid EM ray-tracing deterministic UWB channel model, simulations and measurements

Aim of this contribution is to validate our deterministic UWB channel model which integrates the real characteristics of the UWB antennas in the whole effective channel. Our analysis relies on a UWB ray tracing approach since this reflects the dependence on the angle of arrival (AoA) and angle of departure (AoD) of any multipath. In the meanwhile, EM-Simulation tool has been used to compute the transfer functions of the real antennas used. Office environment was considered in both the simulation and measurements with Line of Sight (LoS) and NLoS scenarios. A comprehensive comparison between the deterministic channel model and the real measurements from IMST shows a good agreement between them regarding to the Channel Impulse Response (CIR), Power Delay Profile (PDP) and Delay Spread (DS). This can offer the UWB system designers an efficient and reliable tool to examine their systems performance on a real world simulations.

Antenna Selection for Reliable MIMO-OFDM Interference Alignment Systems: Measurement-Based Evaluation

Interference alignment (IA) is a promising transmission technology enabling, essentially, the maximum achievable degrees of freedom (DOF) in K-user multiple-input-multiple-output (MIMO) interference channels. The ideal DOF of IA systems have been obtained using independent MIMO channels, which is, usually rarely observed in reality, particularly in indoor environments. Therefore, the data sum rate and symbol error-rate of IA are dramatically degraded in real-world scenarios since the correlation between MIMO channels decreases the signal-to-noise ratio (SNR) of the received signal after alignment. For this reason, an acceptable sum rate of IA in real MIMO-orthogonal frequency-division multiplexing (MIMO-OFDM) interference channels was obtained in the literature by modifying the distance between network nodes and the separation between the antennas within each node to minimize the spatial correlation. In this paper, we propose to apply transmit antenna selection to MIMO-OFDM IA systems either through bulk or per-subcarrier selection, aiming at improving the sum-rate and/or error-rate performance under real-world channel circumstances, while keeping the minimum spatial antenna separation of 0.5 wavelengths within each node. Two selection criteria are considered: maximum sum rate (Max-SR) and minimum error rate (Min-ER). To avoid subcarrier imbalance across the antennas of each user, which is caused by per-subcarrier selection, a constrained per-subcarrier antenna selection is operated. Furthermore, a suboptimal antenna selection algorithm is proposed to reduce the computational complexity of the optimal algorithm. An experimental validation of MIMO-OFDM IA with antenna selection in an indoor wireless network scenario is presented. The experimental results are compared with deterministic channels that are synthesized using hybrid electromagnetic (EM) ray-tracing models. Our performance evaluation shows that the practical feasibility of MIMO-OFDM IA systems is significantly increased by antenna selection in real-world scenarios.

UWB Reflectarray Antenna for chipless RFID applications

The main limitation of any chipless Radio Frequency Identification (RFID) system is the very short reading range. In this paper, we propose an Ultra Wideband (UWB) Reflectarray Antenna (RA) system with 2.2 GHz bandwidth centered at 6 GHz for the reader of chipless RFID applications. The proposed reader antenna system enhances reader sensitivity, reduces multipath effects, helps in tag localization and a lot of novel capabilities that cannot be provided by the conventional antenna systems. The cell used in the design is the double circular ring where the antenna panel consists of 100 elements (10×10). Simulations show that the proposed antenna system reaches fractional bandwidth (FBW) 37% covering all the feeder bandwidth. This achieved ultra wide bandwidth (UWB) satisfies the requirements of the frequency signature based chipless RFID systems.

Novel notch modulation algorithm for enhancing the chipless RFID tags coding capacity

The main objective of this contribution is to introduce a novel technique for increasing the coding capacity of the Frequency Coded (FC) chipless RFID system. The proposed scheme encodes 4 bits per single resonator exploiting the notch bandwidth and its corresponding frequency position. Hence, 72-bits could be achieved from 2 to 5 GHz preserving the operating frequency bandwidth. Furthermore, a Smart Singular Value Decomposition (SSVD) technique is utilized to estimate the notch bandwidth and ensure low probability of error. Consequently, high encoding efficiency and accurate detection could be achieved with simplified reader design. Likewise, a novel 4 × 5 cm2 tag is designed to fit the requirements of the devised coding technique. Different tag configurations are manufactured and validated with measurements using Software Defined Radio (SDR) platform. The introduced coding methodology is conclusively validated using Electromagnetic (EM) simulations and real world testbed measurements.

Impact of Ultra Wide-Band Antennas on Communications in a Spatial Cannel

Aim of this contribution is to study the impact of typical ultra-wideband (UWB) antennas for communications over a spatial wireless channel. In order to adequately consider the directivity properties of real antennas, out analysis is suitably based on a ray tracing UWB channel model since this reflects the dependence on the angle of arrival (AoA) and angle of departure (AoD) of any multipath. A mathematical framework is given which also allows an optimization of such an UWB multiple input multiple output (MIMO) system using different types of transmitting and receiving antennas on behalf of idealistic omnidirectional ones. Beside the angle dependence, the antenna transfer functions are without doubt frequency dependent on such a large UWB bandwidth, so that they will be evaluated with suitable analog design specialized tools for the fast and accurate three-dimensional electromagnetic simulation of high frequency circuits. Simulation results allowing concrete guidelines on the antenna influence are provided in the last section of this paper

Novel Pseudo-Noise coded chipless RFID system for clutter removal and tag detection

In this contribution a novel Frequency Coded (FC) chipless RFID system is introduced to significantly enhance the tag detection. The proposed system exploits the properties of Pseudo Noise (PN) random sequence, as a transmitted signal, to accurately estimate the Channel Impulse Response (CIR). Consequently, the undesired environmental clutter is filtered by a Selective-RAKE receiver. Hence, the tag is accurately identified in a heavily dense multipath environment using neither reference tags for calibration nor the non-practical no-tag deduction process. A real world simulation, based on ray-tracing tool is performed for to verify the system performance. Furthermore, the system testbed is realized on Software Defined Radio (SDR) platforms, where the tag detection is achieved with minimum latency and optimal precision.

Antenna selection for Interference Alignment based on subspace Canonical Correlation

The main objective of this contribution is to develop a novel antenna selection algorithm for Interference Alignment (IA) in multi-user communication systems. Successive IA requires high degree of independency among the channels, which could hardly exist in real-world environments. Therefore, the Bit Error Rate (BER) performance of the IA system suffers from a dramatic degradation, especially in indoor environments. Applying the developed antenna selection algorithm can effectively increase the channels diversity and improve the BER performance. This selection algorithm based on selecting the maximum Canonical Correlation (CC) between the desired signal subspace and the interference-free subspace in order to maximize the average received Signal-to-Noise Ratio (SNR) of the system. The influence of the CC on sum-rate would be presented mathematically. Simulation results show a significant improvement of the BER system performance based on the CC antenna selection algorithm compared with the maximum sum-rate selection algorithm.

Influence of the real UWB antennas on the AoA estimation based on the TDoA localization technique

Main contribution of this paper is to present the influence of the real ultra-wideband directional antennas on the Angle of Arrival estimation. Furthermore, is to mitigate this undesired impact of the ultra-wideband antennas to improve the overall system performance and enhance the Angle of Arrival estimation accuracy. In the first step we analyze the estimation error due to the antenna induced delay if Vivaldi antennas are used as receiving antennas within two different scenarios. In the second step we present the corrected AoA estimation after mitigation of the error resulting from the antenna induced delay. The Angle of Arrival estimations with error mitigation and without error mitigation are compared. Real measurements are used in the experiments.

A novel co/cross-polarizing chipless RFID tags for high coding capacity and robust detection

The aim of this work is to introduce a novel tag design enhancing the coding efficiency for the Frequency Coded (FC) chipless RFID system. The proposed approach relies on exploiting the backscattered co/cross-polarized signals from a tag excited with a linear-polarized wave. Consequently, the tag signature is encoded into Notch/Peak (N/P) format in two orthogonal planes. Furthermore, the introduced tag design exhibits narrow resonance bandwidth ensuring best utilization of the operating frequency range and sufficient coding capacity with compact tag size. Hence, 80-bit coding capacity is reached employing physical amplitude On Off-N/P (OO-N/P) modulation and N/P-Position (N/P-P) modulation principles. The presence or absence of a resonator resembles the OO-N/P modulation while the shift in the frequency position imitates the (N/P-P) modulation. In addition, the depolarization property increases the probability of tag detection in a real-world heavily dense multi-path environment. An asymmetry crossed dipole structure is employed to facilitate coding in both divergent polarities separately. The manufactured tags are verified in indoor real-world environment to proof the robustness of the introduced tag design and encoding algorithm. In the full paper, various parameters such as reading range, tag miniaturization and angular stability will be investigated.

Artificial diversity for UWB MB-OFDM Interference Alignment based on real-world channel models and antenna selection techniques

Main objective of this contribution is to apply Interference Alignment (IA) algorithms in real-world indoor environments for UWB MIMO MB-OFDM communication systems. In indoor environments, the required orthogonality between multi-users channels, which is necessary for proper IA, could be hardly reached. The spatial diversity among the users/nodes is mostly insufficient to obtain a robust performance for IA algorithms. In this work, a practical artificial channel diversity technique is applied through antenna selection to choose the best scenario providing the maximum orthogonality and consequentially the best overall system performance. Our analysis considers deterministic UWB MIMO channel model based on EM Ray-tracing in a real-world multi-user indoor environment. Simulation results present a significant enhancement in the overall system performance. Furthermore, the impact of the directional properties and the orientations of the antennas on the system are investigated.