Giovanni Gamba

Experimental Characterization of Wireless Sensor Networks for Industrial Applications

The effects of interference in the setup of wireless sensor networks (WSNs) represent a critical issue, and as such, it needs to be carefully addressed. To this aim, helpful information can be achieved through measurements to be carried out in advance on suitable prototypes and testbeds. In this paper, the measurement of industrial WSN performance is dealt with. In particular, a suitable testbed enlisting IEEE 802.15.4 wireless sensor nodes is presented along with the results of some experiments carried out even in the presence of interference. The purpose is to show how to evaluate some specific parameters of a WSN employed for industrial applications to obtain useful information for its setup optimization in the presence of interference. The analysis will show that from the measurement of these parameters (number of failed pollings, polling round-trip time, experimental cycle time, and alarm latency), interference effects can effectively be recognized, and the network setup can be optimized.

Retransmission Strategies for Cyclic Polling Over Wireless Channels in the Presence of Interference

In this paper, we consider retransmission strategies for centralized cyclic polling-based systems over wireless channels subject to external interference. The considered strategies differ in the time when retransmissions for one particular node are carried out, and in the number of retransmissions that can be carried out for one node. We show experimentally and by simulation that two related strategies introduced in this paper, called the queueing-based strategies, significantly outperform the traditional strategy (in which all admissible trials towards one node are carried out subsequently) in terms of the average number of nodes that cannot be successfully served in a cycle. These performance gains are achieved without increasing the average total transmission effort.

Is CSMA/CA really efficient against interference in a wireless control system? An experimental answer

The deployment of a wireless control system must cope with a number of effects usually negligible in a wired scenario. To this aim, an experimental analysis on suitable prototypes and testbeds can readably offer a valid and rapid method to forecast the behavior of a real network. In this paper, performance measurement of industrial wireless sensor network in the presence of various type of interference is provided. In particular a Bluetooth, WiFi and Zigbee disturbing network impairs a suitable testbed employing IEEE 802.15.4 wireless sensor nodes. The purpose is to optimize the effectiveness of the medium access control mechanism through the choice of a proper mode of use. The analysis will show that from the measurement of certain parameters (number of failed pollings, experimental cycle-time, and alarm latency) interference effects can be effectively recognized and the network setup optimized.

Performance indicators for wireless industrial communication networks

The recent improvements of the wireless networks performance offer a valuable opportunity also in the context of industrial communication systems. However, these systems are often subjected to such tight reliability requirements as well as timing constraints that wireless communications, especially in an interfered scenario, can hardly comply with. A thorough performance assessment is hence needed both at the design stage and during the typical operating life. In such a direction it is important to define some performance indicators that can monitor the main parameters of industrial communication systems employing wireless networks. In this paper a set of performance indicators for polling-based industrial communication is introduced. Then, two case studies of industrial communication systems that make use of two different wireless networks (namely the IEEE 802.11 WLAN and the IEEE 802.15.4 WPAN) are presented and the relevant performance indicators are experimentally measured. The purpose is to show how the performance indicators may provide useful insights in the behavior of the systems as well as how they may be positively influenced by a careful selection of some key parameters.

Assessment of Out-of-Channel Interference Effects on IEEE 802.15.4 Wireless Sensor Networks

The impact of out-of-channel interference on IEEE 802.15.4 wireless sensor networks (WSNs) performance is here dealt with. In particular, the effect on networks based on the carrier sense multiple access with collision avoidance (CSMA/CA) protocol is investigated. To this aim, a theoretical analysis of the problem is outlined, and results from both simulations and experiments are provided. Measurements are performed both at physical layer, through parameters like in-channel power, and at network layer, through packet error ratio estimates. The purpose is to provide from simulations and experiments a set of helpful information and hints to be used for an efficient measurement and troubleshoot of interference problems caused on IEEE 802.15.4 WSNs by out-of-band signals.

Investigating wireless networks coexistence issues through an interference aware simulator

In the modern wireless applications of factory automation, interference phenomena among near operating wireless networks can be the cause of severe performance degradation. To avoid this possibility and prevent deleterious system failures, simulations may offer a real and reliable solution. In this paper a new simulator is presented, allowing cross-layer analysis of interference phenomena arising among IEEE 802.15.4 wireless sensor networks (WSNs) and IEEE 802.11 wireless local area networks. The purpose is to provide an accurate tool able to forecast possible interference effects on a WSN and by which optimize the setup of some suitable network parameters such as the position of wireless nodes.

Modeling the Performance of CSMA-CA Based Wireless Networks Versus Interference Level

Wireless communication networks based on non-scheduled random medium access methods, such as carrier sense multiple access with collision avoidance (CSMA/CA), can be affected by in- channel interference at two different levels: at physical (PHY) layer, in terms of data packet collisions, and at medium access control (MAC) layer, in terms of channel occupation. The separate knowledge of such interference effects may represent an essential information to be used in a design or setup stage of CSMA/CA-based wireless networks. To this aim, a simple yet effective two-layer model is proposed in the paper. The model allows to clearly distinguish the effect of both interference contributions and to forecast the network performance in terms of packet error ratio, in the presence of interference. An example of how to use the model, and results from experiments, validating the model, are both reported. The experiments have been conducted through a suitable testbed enlisting a IEEE 802.15.4-compliant wireless sensor network.

Experimental analysis of UHF RFID impairments and performance

Radio frequency identification (RFID) is a modern wireless communication technology used for identification purposes. By now, experimental results showing the actual performances reachable by a UHF RFID system, are still missing, together with the problems that can be encountered in practice and the corresponding solutions. In this paper, the performance of an UHF RFID system in real-world conditions are experimentally assessed to experimentally investigate the reliability of UHF RFID systems typical environmental conditions; and to deduce helpful and practical hints in order to efficiently assess and enhance performances of an UHF RFID system.

Theoretical and experimental evaluation of polling times for wireless industrial networks using commercially available components

In the last years, several wireless standards have been profitably tested for possible application in factory communication systems, showing encouraging results even in time-critical applications. However, the achieved performance are clearly related to the specific applications considered and, more important, to the specific wireless components employed. In this paper, we consider the wireless extension of a very popular Real-Time Ethernet network, Ethernet Power-link, and we propose a practical implementation of it based on commercially available IEEE 802.11 Access Points. We first provide a theoretical analysis of the expected polling times and then we compare the obtained results with the outcomes of some experimental sessions carried out on a prototype installation, in order to characterize the behavior of the employed devices.

Effects of RSSI impairments on IEEE 802.15.4 wireless devices performance susceptibility to interference

The effects of interference on IEEE 802.15.4 devices performance are here dealt with, with special regard to the role played by the signal strength indication (RSSI) meter embedded in each device. In particular, attention is paid to some typical RSSI meter impairments, and on their effect on the device susceptibility to external interference. To the purpose, measurements are conducted on a purposely developed testbed enlisting a real IEEE 802.15.4 device. The aim of the work is to gain from experiments helpful notes for network designers showing how RSSI impairments may influence the performance of a IEEE 802.15.4 wireless sensor network in the presence of interference. In the experiments, single tone signals and additive white Gaussian noise are used as interferers.