Carlos F. Lopez

Measurements and Analysis of Large-Scale Fading Characteristics in Curved Subway Tunnels at 920 MHz, 2400 MHz, and 5705 MHz

Wave propagation characteristics in curved tunnels are of importance for designing reliable communications in subway systems. This paper presents the extensive propagation measurements conducted in two typical types of subway tunnels - traditional arched “Type I” tunnel and modern arched “Type II” tunnel - with 300- and 500-m radii of curvature with different configurations - horizontal and vertical polarizations at 920, 2400, and 5705 MHz, respectively. Based on the measurements, statistical metrics of propagation loss and shadow fading (path-loss exponent, shadow fading distribution, autocorrelation, and crosscorrelation) in all the measurement cases are extracted. Then, the large-scale fading characteristics in the curved subway tunnels are compared with the cases of road and railway tunnels, the other main rail traffic scenarios, and some “typical” scenarios to give a comprehensive insight into the propagation in various scenarios where the intelligent transportation systems are deployed. Moreover, for each of the large-scale fading parameters, extensive analysis and discussions are made to reflect the physical laws behind the observations. The quantitative results and findings are useful to realize intelligent transportation systems in the subway system.

Measurement and Analysis of Extra Propagation Loss of Tunnel Curve

Wave propagation experiences extra loss in curved tunnels, which is highly desired for network planning. Extensive narrow-band propagation measurements are made in two types of Madrid subway tunnels (different cross sections and curvatures) with various configurations (different frequencies and polarizations). A ray tracer validated by the straight and curved parts of the measuring tunnels is employed to simulate the reference received signal power by assuming the curved tunnel to be straight. By subtracting the measured received power in the curved tunnels from the simulated reference power, the extra loss resulting from the tunnel curve is extracted. Finally, this paper presents the figures and tables quantitatively reflecting the correlations between the extra loss and radius of curvature, frequency, polarization, and cross section, respectively. The results are valuable for statistical modeling and the involvement of the extra loss in the design and network planning of communication systems in subway tunnels.

3D non-stationary wideband circular tunnel channel models for high-speed train wireless communication systems

This paper proposes three-dimensional (3D) non-stationary wideband circular geometry-based stochastic models (GBSMs) for high-speed train (HST) tunnel scenarios. Considering single-bounced (SB) and multiple-bounced (MB) components from the tunnel’s internal surfaces, a theoretical channel model is first established. Then, the corresponding simulation model is developed using the method of equal volume (MEV) to calculate discrete angular parameters. Based on the proposed 3D GBSMs, important time-variant statistical properties are investigated, such as the temporal autocorrelation function (ACF), spatial cross-correlation function (CCF), and space-Doppler (SD) power spectrum density (PSD). Results indicate that all statistical properties of the simulation model, verified by simulation results, can match well those of the theoretical model. The statistical properties of the proposed 3D GBSMs are further validated by relevant measurement data, demonstrating the flexibility and utility of our proposed tunnel GBSMs.

Poster: Excess propagation loss for train-to-x communications in curved subway tunnels

Wave propagation experiences the excess loss in curved tunnels, which is highly desired to involve in the network planning for train-to-x communications. Extensive propagation measurements are conducted in a curved subway tunnel. By subtracting the measured received power in the curved tunnel from the simulated reference power in the equivalent straight tunnel, the excess loss resulting from the tunnel curve is obtained. Finally, tables and figures are provided to quantitatively reveal how the radius of curvature and frequency influence the excess loss in subway tunnels.

Frequency-dependent modulation and coding rates for LTE link adaptation in static conditions

OFDM wireless cellular systems rely on link adaptation in order to match the Modulation and Coding Scheme (MCS) of the transmission blocks with the dynamic channel conditions experienced at the receive side. For simplicity, Long-Term Evolution (LTE) systems consider a single MCS format per codeword, which is optimized according to the average frequency response over the users allocated bandwidth. When the channel coherence bandwidth is smaller than the user bandwidth, the constituent codeblocks experience significantly different channel responses, thus rendering link adaptation less effective. This paper proposes a frequency-dependent link adaptation mechanism whereby codeblocks are independently assigned different MCS values that can be fine-tuned to the frequency characteristics of the channel. Post-detection SINR values at the receive side are exploited (instead of CQI values), along with horizontal mapping of resources with two variants: direct mapping and diversity mapping. A suitable in-band signaling scheme for the codeblock sizes and modulations is also described. Link-level simulations show moderate increases in median throughput, but significant improvements in instantaneous throughput, for a broad range of SINR conditions. The proposed scheme can be particularly beneficial when very large signal bandwidths are used as foreseen in future 5G cellular systems.

Performance comparison of six massive MIMO channel models

This paper compares the spatial cross-correlation functions (CCFs) and normalized channel capacities of four recently proposed massive multiple-input multiple-output (MIMO) channel models. Three of them are geometry-based stochastic models (GBSMs) and one is Kronecker-based stochastic model with birth death process on the array axis (KBSM-BD-AA). In addition, the impact of the elevation angles in the three dimensional (3-D) twin-cluster model and the 3-D unified GBSM on the resulting channel capacities, as well as the impact of polarization antennas in the 3-D unified GBSM on channel capacities, is investigated. Simulation results show that elevation angles can cause large impact on channel capacities and polarization antennas can halve the dimension of an antenna array at the cost of channel capacity loss.

A novel 2D non-stationary wideband massive MIMO channel model

In this paper, a novel two-dimensional (2D) non-stationary wideband geometry-based stochastic model (GBSM) for massive multiple-input multiple-output (MIMO) communication systems is proposed. Key characteristics of massive MIMO channels such as near field effects and cluster evolution along the array are addressed in this model. Near field effects are modeled by a second-order approximation to spherical wavefronts, i.e., parabolic wavefronts, leading to linear drifts of the angles of multipath components (MPCs) and non-stationarity along the array. Cluster evolution along the array involving cluster (dis)appearance and smooth average power variations is considered. Cluster (dis)appearance is modeled by a two-state Markov process and smooth average power variations are modeled by a spatial lognormal process. Statistical properties of the channel model such as time autocorrelation function (ACF), spatial cross-correlation function (CCF), and cluster average power and Rician factor variations over the array are derived. Finally, simulation results are presented and analyzed, demonstrating that parabolic wavefronts and cluster soft evolution are good candidates to model important massive MIMO channel characteristics.

Smart Product Management in Retail Environment Based on Dynamic Pricing and Location Services

Product management and pricing are complex tasks that in many occasions they can be a barrier to offer customers an improved shopping experience. Automatizing this process can help the trade business making easier dynamic services in a retail environment. In this paper, a system of autonomous management is proposed based on current requirements of retail environment. This system is able to acquire different information and integrate dynamic pricing updates based on previous set rules. The authors carried out a basic implementation of the proposed system creating a prototype. This prototype has being used for studying the scalability possibilities the system offers and also test out the compatibility between different subsystems. The requirements of this system have been drawn from proposals made by some Spanish Supermarket managers during execution of the project SMARKET, a project funded by the Ministry of Economy and Competitiveness of Spain.