Maria Calle

MAC Protocols Used by Wireless Sensor Networks and a General Method of Performance Evaluation

Many researchers employ IEEE802.15.4 as communication technology for wireless sensor networks (WSNs). However, medium access control (MAC) layer requirements for communications in wireless sensor networks (WSNs) vary because the network is usually optimized for specific applications. Thus, one particular standard will hardly be suitable for every possible application. Two general categories of MAC techniques exist: contention based and schedule based. This paper explains these two main approaches and includes examples of each one. The paper concludes with a unique performance analysis and comparison of benefits and limitations of each protocol with respect to WSNs.

MAC Protocols for GSP in Wireless Sensor Networks

The Gossip-based Sleep Protocol (GSP) is a routing protocol designed to save energy in Wireless Sensor Networks. This work presents two MAC protocols designed to complement the characteristics of GSP: MACGSP1 and MACGSP2 were evaluated in combination with GSP on square grids of 100, 400 and 900 simulated nodes. Both protocols show increased energy savings compared to GSP by itself. MACGSP1 provided the greatest energy savings, however MACGSP2 exhibited the best trade off between overhead, delay and packet reception probability. MACGSP2 reduces the duplicate packets generated by GSP, with no significant difference in end-to end delay and a reduced GSP packet reception probability of 10%.

The grey area in wireless communications: A multiplatform experimental study

Experimental studies in wireless sensor networks reveal a region with random packet loss and highly unreliable links. Some studies refer to the region as the Grey Area. This area may affect upper layer protocol performance. Unlike previous studies, our paper presents an experimental study of link performance using three different hardware platforms: one for Radio Frequency Identification (RFID) and two for Wireless Sensor Networks (WSNs). Therefore, our study considers short and long distance (up to 400 meters) behavior. The study measures Received Signal Strength Indicator (RSSI) values and Packet Reception Ratio (PRR). Preliminary results demonstrate that the Grey Area appears in all platforms and it occupies a maximum 28.6% of the radio range. However, one WSN platform (XbeePro900) presents the smaller proportional Grey Area. Moreover, our results support the hypothesis that Grey Area is mainly due to SNR decrease because of attenuation, and previously proposed explanations such as multipath and shadowing may be negligible. Additionally, we verified that better radio technologies experience a smaller grey area.

Testbed for evaluating Wireless Sensor Networks with non-line of sight links

The paper presents a testbed for Wireless Sensor Networks (WSN) located at Universidad del Norte in Barranquilla Colombia, created for testing different communication protocols in a real scenario with non-line of sight (NLOS) links and interference. The testbed uses XTend RF Modules at 900MHz, with 1 mW transmission power, and covers an area of 11,000 m2. Results show that the testbed has propagation characteristics difficult to reproduce in testbeds present in the literature. Experiments demonstrate testbed performance regarding path loss, average packet loss and number of duplicates. Despite poor performance of links in the network, percentage of successful packet reception in the sink node was 70%, using a controlled flooding protocol with 8 nodes. Testbed implemented is a real scenario for WSN applications where nodes are deployed randomly to cover a determined area. Given the radio employed, the testbed has the possibility of extending experiments to long range applications.

A novel multivariable algorithm for detecting and tracing metal mobile objects employing a simple RFID setup

Radio Frequency Identification (RFID) is a solution for automated inventory and object detection applications. However, if RFID tags are attached to metal objects, detection errors may occur due to Foucault currents and interferences caused by multiple simultaneous reflections. Errors may increase if metal objects are moving. The paper presents a novel algorithm using RFID low-level reader variables, such as RSSI (Received Signal Strength Indicator), phase angle, and Doppler shift, to detect and trace metal objects. The algorithm was designed to identify if a tag is static or moving and, in the latter case, to compute its speed and direction. The algorithm differs from previous approaches since it uses a simple setup with one commercial portal reader coupled with one single element antenna. Experiments employed one tag located on one metal moving object and 12 static interferer tags, in both outdoor and indoor locations. Results show that the algorithm identifies static tags with no errors. For moving tags, the algorithm shows a maximum 12% error. The algorithm correctly estimates direction and computes object speed. Test conditions emulate fork lift speeds when carrying objects in an industrial warehouse.

MACGSP6: A protocol for supporting internet of things applications with Non-Line-of-Sight links

Abstract Wireless Networks with random topologies include multipath and Non-Line-of-Sight (NLOS) links, especially in urban environments. As the Internet of Things emerges many links will be NLOS. However, network protocols are often only evaluated using Line-of-Sight radio channels. Previous simulations of the MACGSP6 (Medium Access Control for Gossip-based Sleep Protocol Version 6) protocol demonstrate packet reception rates exceed 90% for networks of more than 1000 nodes with Line-of-Sight conditions. This paper measures the performance of MACGSP6 using a prototype testbed where all links are NLOS. Results demonstrate that MACGSP6 achieved better Average Packet Loss, Average Duplicate Packets and energy consumption than a controlled flooding protocol. Additionally, MACGSP6 made all degraded paths from nodes to sink appear as one ideal hop to the application layer. Therefore, MACGSP6 is an energy and data efficient protocol for Internet of Things networks which include NLOS links.

Irrigation Measurement System for Dry Areas Based on WSN

Agriculture requires a certain amount of water and the land has a maximum liquid holding capacity that should not be exceeded. Water pressure provides the kinematic energy used on irrigation systems to spray the water on the field. The amount of water that the irrigation system can provide per hour should be carefully monitored to save water in dry areas. The paper presents a system with wireless nodes for water flow measurement in several pipes simultaneously. The system employs YF S201C flow sensors, connected to wireless nodes. Each node sends reports every second to a master node connected to a computer. The received data is presented in a web-based platform to see the current water flow on each of the three pipes. Results show sensor nodes exhibit a 4% average error, and 9% packet loss maximum. Both values are adequate for crop irrigation applications.

Algorithm for Detection of Unwanted Tag Reads in Passive UHF RFID Systems for Static Metallic Objects

Passive Ultra High Frequency Radio Identification (UHF RFID) systems used in metal objects exhibit challenges due to generation of Foucault currents and multiple reflections, creating reading problems and detection errors. One of these problems is unwanted RFID tag reads i.e., tags unintentionally detected by the reader. The paper presents one algorithm for reduction of such unwanted tag reads using normalized read rate and range of RFID tags. The algorithm was designed using extensive data from measurements of an actual RFID system with tags located over metal objects. Results show that the algorithm detects 96% of unwanted tag reads.

System for Estimation of Significant Height and Direction of Waves by using Radar Intensities

the paper explains the process for obtaining ocean variables using one band X radar located ashore. The system includes one algorithm for selecting a sea clutter area with required information to calculate sea variables such as direction, period and significant height of the waves. The research enhanced reported algorithms to extract those variables by including filtering stages. The system has 10% maximum error compared to an in situ sensor. The results motivate the usage of radar ashore for swell monitoring with direct application in coastal erosion studies

System for estimation of significant height and direction of waves by using radar intensities

The paper explains the process for obtaining ocean variables using a radar located ashore. The paper presents one algorithm for selecting a sea clutter area with required information to calculate sea variables. The reported algorithms to extract those variables have been enhanced by including filtering stages. The system has 10% maximum error compared to an in situ sensor. The results motivate the usage of radar ashore for swell monitoring with direct application in coastal erosion studies.