Frequency-domain Channel Sounding Research Articles

Performance Evaluation of Massive MIMO With Beamforming and Nonorthogonal Multiple Access Based on Practical Channel Measurements

This letter presents a comprehensive performance analysis of a massive multiple-input-multiple-output (MIMO) system using nonorthogonal multiple access (NOMA) in both indoor and outdoor environments, based on practical channel measurements. The latter are performed using frequency-domain channel sounding experiments conducted at 3.5 GHz with 18 MHz bandwidth. Multiuser beamforming and NOMA clustering are used in the massive MIMO system. The system performance is evaluated in terms of sum-rate capacity for two precoding schemes-zero-forcing (ZF) and maximum ratio transmission (MRT). Two interbeam power allocation (PA) schemes are investigated-equal PA and water filling. Fractional transmit PA is used to perform intracluster PA between paired users. This study allows the identification of practical scenarios that are propitious to NOMA with beamforming. Results show that NOMA is particularly interesting with MRT, compared to ZF, especially when combined with water filling. However, ZF generally outperforms MRT for all system configurations.

Improved Communications in Underground Mines Using Reconfigurable Antennas

Fixed performing antennas are ineffective in providing optimum performance in a changing multipath environment, such as underground mines where channel conditions quickly change as the antenna is moved. Hence, we investigated the performance of a pattern reconfigurable antenna (RA) in improving the wireless communications link in a hard rock underground mine. An RA and a dipole were characterized and compared in line-of-sight (LOS) and nonline-of-sight (NLOS) propagation scenarios. As a proof of concept, experiments were performed at the University of Queensland Experimental Mine using a 1 GHz frequency band centered at 2.45 GHz. Analysis of complex channel impulses captured through the frequency-domain channel sounding is presented. Also, the results show that reconfigurability in the rich multipath environment achieves a 20% and 34% improvement in path loss and delay spread, respectively, compared to a fixed-beam antenna in NLOS propagation. Furthermore, more than 34% improvement in coherence bandwidth is observed in LOS and NLOS. Therefore, reliable high-data-rate communication is achievable in underground mines by the effective management of multipath effects using the RA.

Polarization Properties of Specular and Dense Multipath Components in a Large Industrial Hall

This paper presents a comprehensive analysis of the polarization characteristics of specular and dense multipath components (SMC and DMC) in a large industrial hall based on frequency-domain channel sounding experiments at 1.3 GHz with 22-MHz bandwidth. Twenty-nine positions were measured under line-of-sight (LOS) and obstructed LOS (OLOS) scenarios. The RiMAX maximum-likelihood estimator is used to extract the full-polarimetric SMC and DMC from the measurement data by taking into account the polarimetric radiating patterns of the dual-polarized antennas. Cross-polar discrimination (XPD) and copolar ratio (CPR) values are presented from the measured and de-embedded channels, as well as the polarimetric delay and angular spread distributions. Strong de-embedded SMC depolarization is obtained for the horizontal polarization in OLOS scenarios. Additionally, DMC depolarization is observed to be weaker than previously reported for indoor environments but constant across LOS/OLOS, polarization, and distance. The results also show that the copolar (cross-polar) DMC power to total channel power ratio is equal to 15% (40%) for LOS and 40% (60%) for OLOS and that this ratio does not correlate significantly with transmitter-receiver distance. Finally, the validity of the room electromagnetics theory was confirmed for transmitter-receiver distances larger than 15 m with no significant difference between polarized subchannels.

A Wideband Frequency-Domain Channel-Sounding System and Delay-Spread Measurements at the License-Free 57- to 64-GHz Band

A channel-sounding impulse-response identification system using the swept-frequency method is presented for the 57- to 64-GHz band. The swept-frequency channel sounder offers high time and frequency resolution of 1 ns and 625 kHz, respectively. The high dynamic range (70 dB) and the constant power output enable the nonlinearities of the channel-sounding system to be overcome within the coverage range, which is on the order of a picocell. This paper also reports the measurements and the analysis of wideband propagation data for various indoor radio channels at the 57- to 64-GHz band. The propagation characteristics are assessed for six different propagation environments. The results of the measurements for four environments are compared when horn antennas are employed at both terminal stations, and also when a horn and an omnidirectional antenna are used at the Tx and Rx terminals, respectively. Examining the statistical distributions of the multipath dispersion, the 90th percentile is about the same for both antenna configurations. For all environments under investigation, it was observed that the static delay spread values at the 90th percentile were below 62 ns.

The industrial indoor channel: Statistical analysis of the power delay profile

In this letter, measurements of the industrial power delay profile are presented. Measurements are performed through frequency-domain channel sounding in the range from 800 MHz to 4 GHz and by using the virtual antenna array method. Received power as a function of delay clearly exhibits clustering and is for this reason fitted to the well-known Saleh–Valenzuela model. With this, new statistical modifications to the rates of power decay in the Saleh–Valenzuela model are presented. It is found that the model's parameters do not seem to differ significantly between LOS and NLOS. Small-scale fading is Rayleigh distributed except for the first arriving delay tap, for which a Nakagami- m distribution provides a better fit.

Measurement and Modeling of an Ultra-Wide Bandwidth Indoor Channel

This paper describes the results of frequency-domain channel sounding in residential environments. It consists of detailed characterization of complex frequency responses of ultra-wideband (UWB) signals having a nominal center frequency of 5 GHz. A path loss model as well as a second-order autoregressive model is proposed for frequency response generation of the UWB indoor channel. Probability distributions of the model parameters for different locations are presented. Also, time-domain results such as root mean square delay spread and percent of captured power are presented.