José Luis Valenzuela

Experimental Study of Bluetooth, ZigBee and IEEE 802.15.4 Technologies on Board High-Speed Trains

This paper studies the feasibility of using low-power wireless technologies such as Bluetooth, IEEE 802.15.4 and ZigBee in high-speed railway scenarios that involve bidirectional ground-to-train communication. The presented results have been obtained through experimental tests conducted at the Madrid-Barcelona high-speed rail line. A multiplatform communication system has been installed in a high-speed train, circulating at velocities up to 300 km/h, whereas autonomous devices have been disseminated along of the railway path to communicate with the onboard devices. The conclusions drawn from this work will be used as guidelines for the future implementation of autonomous communication platforms for high-speed rail connectivity.

Analytical and Experimental Performance Evaluation of BLE Neighbor Discovery Process Including Non-Idealities of Real Chipsets

The purpose of this paper is to evaluate from a real perspective the performance of Bluetooth Low Energy (BLE) as a technology that enables fast and reliable discovery of a large number of users/devices in a short period of time. The BLE standard specifies a wide range of configurable parameter values that determine the discovery process and need to be set according to the particular application requirements. Many previous works have been addressed to investigate the discovery process through analytical and simulation models, according to the ideal specification of the standard. However, measurements show that additional scanning gaps appear in the scanning process, which reduce the discovery capabilities. These gaps have been identified in all of the analyzed devices and respond to both regular patterns and variable events associated with the decoding process. We have demonstrated that these non-idealities, which are not taken into account in other studies, have a severe impact on the discovery process performance. Extensive performance evaluation for a varying number of devices and feasible parameter combinations has been done by comparing simulations and experimental measurements. This work also includes a simple mathematical model that closely matches both the standard implementation and the different chipset peculiarities for any possible parameter value specified in the standard and for any number of simultaneous advertising devices under scanner coverage.

Performance of a Token Bucket traffic shaper on a real IEEE 802.11 test-bed

The scientific and industrial community spends many efforts trying to provide quality of service to IEEE 802.11 wireless LANs. However, experimentation is quite difficult nowadays using real equipment available in the market. This situation remains the same until the approval of a standard. This paper proposes an alternative that can be implemented on a real environment as it does not modify at all the 802.11 MAC layer. This solution basically inserts a traffic shaper between the IP and MAC layer. QoS mechanisms are based on traffic handling mechanisms and bandwidth management mechanisms. The aim of the experiments is to evaluate the performance after applying a token bucket filter on a real test-bed of up to 11 mobile stations

The help4mood wearable sensor network for inconspicuous activity measurement

The Help4Mood EU FP7 project (H4M) [1] proposes to significantly advance the state-of-the-art in computerized support for people with Major Depression by monitoring mood, physical activity and voice characteristics while promoting activities in reaction to examined inputs. Employing actigraphy can provide supplementary data about patients with depression. Nonetheless, its use is not standardized and there is a lack of public analyses about treated patients with depression using this technique, which is the objective of the project. The purpose of the Personal Monitoring System (PMS) used in H4M is to compile objective data about the changes and trends of activity patterns during long periods of time. This would comprise daily activity, rest time and, if possible, sleep quality. The PMS uses inconspicuous methods but keeping the cost associated with sensor installation at the patient¿s home to a minimum. This work focuses on the Wireless Sensor Network (WSN) enhancements introduced after real testbeds and considering User Quality of Experience (QoE), mainly oriented to reduce energy consumption and required data transmission and consequently improving the autonomy and range of the sensors.

Multipolling and OFDMA reservation protocol for IEEE 802.11 networks

This paper presents an efficient multipolling scheme that improves the IEEE 802.11 MAC protocol — efficiency and does not suffer from the hidden terminal problem or inefficient channel usage problems. To design an efficient polling scheme, the access point (AP) needs to obtain information about the current transmission status and channel state for each station. In this new scheme, we propose the use of multipolling frames in the downlink and Orthogonal Frequency Division Multiple Access (OFDMA) for the uplink reservation frames in order to reduce signaling overhead.

Modeling Collision and Connection Statistics in Bluetooth Networks

Bluetooth is a digital data transmission standard in the 2.4-GHz ISM band that uses short-range wireless links between devices. As this band is free and it is used for other several wireless technologies such as IEEE 802.11b, Bluetooth uses a frequency hopping method to minimize interferences. The main goals of this paper are to provide a statistical characterization to describe the packet collision rate for multiple piconets in close proximity and to investigate the connection establishment procedure when different paging modes are used in order to measure and model the connection establishment time in operating conditions. These models are an important analysis tool to develop traffic analysis simulations

Link recovery in IEEE 802.11 WLAN using WDS

This work presents a new application scenario for the wireless distribution system (WDS) defined in the IEEE 802.11 standard. The WDS is here used to ensure connectivity of stations associated with an access point (AP) that at a certain moment loses its connection (wired or wireless) with the network. We study the performance of using the combination of 802.1D and WDS to recover connectivity through alternative links when one fails and analyze the convenience of using such a solution for highly mutable scenes where link changes are required often. The paper also proposes a solution as an extension to current deployed solutions in the form of signaling packets that enhance the performance of the system.

Proposal and Evaluation of BLE Discovery Process Based on New Features of Bluetooth 5.0

The device discovery process is one of the most crucial aspects in real deployments of sensor networks. Recently, several works have analyzed the topic of Bluetooth Low Energy (BLE) device discovery through analytical or simulation models limited to version 4.x. Non-connectable and non-scannable undirected advertising has been shown to be a reliable alternative for discovering a high number of devices in a relatively short time period. However, new features of Bluetooth 5.0 allow us to define a variant on the device discovery process, based on BLE scannable undirected advertising events, which results in higher discovering capacities and also lower power consumption. In order to characterize this new device discovery process, we experimentally model the real device behavior of BLE scannable undirected advertising events. Non-detection packet probability, discovery probability, and discovery latency for a varying number of devices and parameters are compared by simulations and experimental measurements. We demonstrate that our proposal outperforms previous works, diminishing the discovery time and increasing the potential user device density. A mathematical model is also developed in order to easily obtain a measure of the potential capacity in high density scenarios.

An experimental study of multi-radio platform coexistence in the 5 GHz band for railway applications

This paper studies the practical challenges that arise due to the coexistence of two wireless technologies, both operating in the license-exempt 5 GHz band. In particular, WiFi and WiMAX equipment have been used in the experiments. The mutual interference caused by the two technologies operating in different but narrowly separated frequency channels has a negative impact on the performance of both systems. Further challenges are introduced when the two systems are in close physical proximity of each other or, in a more extreme scenario, share the same antenna as could be required in railway applications. This paper investigates these issues through a series of experimental tests based on a multi-radio platform testbed. The conclusions drawn from this study will be used as a base for the implementation of a multi-radio platform to provide communications between train and land in both directions in the context of the Spanish high-speed railway system.

Bluetooth low energy sensor networks for railway applications

This paper analyzes the viability of Bluetooth Low Energy (BLE) as the enabling technology in railway scenarios to allow sensor data transmission from ground to train. This proposal is based on using the broadcasting capabilities introduced by the Bluetooth specifications since v4.0. The last version, v5.0, extends the range the speed and the broadcast capacity. However, due to its recent publication it is hard to find real devices with it implemented in the market. The proposed schema has been validated by means of experimental measurements using v4.2.