Moulay El Azhari

Characterization of an Off-Body Channel at 2.45 GHz in an Underground Mine Environment

Underground mines are challenging environments for off-body wireless communication, since the signal propagation is majorly affected by small scale and large scale fading. The use of multiple antennas at the transmitter and the receiver sides is a known technique to combat fading and enhance capacity. In this paper, the channel parameters of a 2 × 2 Multiple-Input Multiple- Output (MIMO) off-body system are investigated in an underground gold mine and compared to the Single-Input Single-Output (SISO) system parameters. Measurement campaigns were conducted using monopole antennas at a center frequency of 2.45 GHz for both Line Of Sight (LOS) and None Line of Sight (NLOS) scenarios. The measured frequency responses are converted into impulse responses through an Inverse Fourier Transform (IFT). The results show that for a constant transmitted power, the path loss exponents at NLOS are smaller than their counterpart values at LOS. The channel capacity values decrease as the propagation distance increases and when the link is obstructed at NLOS. The RMS delay spread is generally increasing with distance for both LOS and NLOS situations. When a fixed Signal-to-Noise Ratio (SNR) is assumed, MIMO topologies improved the SISO capacity by roughly 8 bps/Hz. The channel characterization results demonstrate that the MIMO configurations provided a remarkable improvement in terms of capacity, coherence bandwidth, and time delay spread compared to the SISO topologies.

Characterization of a NLOS Off-Body Channel at 2.45 GHz Using Patch Antenna Inside a Mine

In underground environments, the safety of the miners depends on the quality of the used communication systems. Currently, wireless underground communications suffer from small-scale and large-scale fading, compromising the propagation quality and limiting the achieved bit rate. In this paper, the performance of a patch antenna set in off-body channels under None Line of Sight (NLOS) conditions is evaluatedat a frequency of 2.45 GHz. Measurement campaigns were performed in a gold mine in order to determine the channel parameters for NLOS configurations and compare them with previously published Line Of Sight (LOS) results. Hence, the channel parameters were determined from the measured frequency responses. The off-body channel is characterized in terms of the impulse response, path loss, RMS delay spread, coherence bandwidth, and channel capacity.

Multipath effect on off-body channel parametters of a MIMO system using patch antennas inside a mine

The use of multiple antennas at the transmitter and receiver is known to improve the channel capacity. In this paper, experimental results of the Rician K-factor and time dispersion parameters are obtained and discussed from measurements conducted at an underground mine gallery using patch antennas. It is found that the multipath richness as expressed by the k-factor results-is highly correlated to the time dispersion results and to the capacity values assuming a fixed SNR. Hence, multipath richness is an important factor to increase capacity.

Path loss effect on off-body channel capacity of a MIMO system using patch antennas inside a mine

The effect of path loss on the channel capacity of a MIMO off-body system using patch antennas is considered in this paper. Experimental results of the channel capacity at a constant transmitted power, and path loss are derived from measurements conducted at an underground gold mine. Results show that path loss is highly correlated to the channel capacity at a constant transmitted power.

CHANNEL CHARACTERIZATION OF CIRCULARLY POLARIZED ANTENNA MIMO SYSTEM IN AN UNDERGROUND MINE

In this paper, a channel characterization of an RF link using circularly polarized antennas inside a mine is performed. The association of circular polarization with multiple-input-multiple-output (MIMO) radio technologies represents a powerful tool to improve the performance of an underground RF channel. The statistical parameters of the channel are derived from in-mine measurements at the 2.4 GHz band for both co-polarization (CP) and cross-polarization (XP) scenarios. Results show a remarkable improvement through the use of MIMO combined with circular polarization compared to the regular patch MIMO antenna system, in terms of channel capacity and path loss. This improvement increases significantly at the XP scenarios, reaching up to 18 bps/Hz for channel capacity and up to 21 dB for path loss. The RMS delay spread for a circularly polarized setup is generally higher than the linearly polarized MIMO patch setup due to surface roughness of the gallery. In the linear polarization case, a signal degradation of more than 15 dB at the XP case is observed compared to the CP scenario. This signal loss that is due to depolarization is somewhat mitigated by the surface roughness. Due to its superior and stable performance, MIMO combined with circular polarization is better suited than a regular MIMO patch system for in-mine uses especially in the applications where the transmitter may change direction with respect to the receiver.

Performance Evaluation of a MIMO-on-Body System in a Mine Environment

In this contribution, the On-body propagation measurements at 40 m underground mine gallery and their statistical analysis are presented. Monopole antennas were installed on the body in order to form three on-body channels, namely belt-chest, belt-wrist and belt-head. The channel parameters of a 2 × 2 Multiple-Input Multiple-Output (MIMO) On-body system are evaluated and compared to the single-input single-output (SISO) system parameters. It was shown that the RMS delay spread and capacity values of the MIMO channels are higher than those of the SISO channels. The average value of the Ricean K-factor shows little difference between the MIMO and SISO beltchest measurements. The calculated capacity values for a constant signal to noise ratio (SNR) and those calculated at a constant transmitted power demonstrate that the propagation performance is significantly improved by using the MIMO compared to the conventional SISO scheme. Hence, MIMO technology is a suitable candidate for On-body underground communications.

Off-body performance of patch antenna in underground mine

This paper presents the performance of a patch antenna in an off-body channel within a mine gallery. A measurement campaign was performed in a gold mine in order to characterize the off-body channel by determining the channel parameters. Measurements were performed in the frequency domain using the Vector Network Analyzer (VNA). Hence, the channel parameters were determined from the measured frequency responses, namely, the channel impulse response, path loss, RMS delay spread, coherence bandwidth, and capacity.

Characterization of an on-body quasi-static channel in underground mine environment

In this paper, the on-body performance of three quasi-static channels was evaluated, when the human body undergoes certain typical movements. The main contribution of this work is the analysis of the impact of body movements on the performance of the on-body system in a mine environment. The quasi-static channels parameters were determined and compared to those of a corresponding static channel.