Opher Yaron

Avoiding collisions between IEEE 802.11 and IEEE 802.15.4 through coexistence aware clear channel assessment

More and more devices are becoming wirelessly connected. Many of these devices are operating in crowded unlicensed bands, where different wireless technologies compete for the same spectrum. A typical example is the unlicensed ISM band at 2.4 GHz, which is used by IEEE 802.11bgn, IEEE 802.15.4, and IEEE 802.15.1, among others. Each of these technologies implements appropriate Media Access Control (MAC) mechanisms to avoid packet collisions and optimize Quality of Service. Although different technologies use similar MAC mechanisms, they are not always compatible. For example, all CSMA/CA-based technologies use Clear Channel Assessment (CCA) to detect when the channel is free; however, in each case it is specifically designed to improve detection reliability of the specific technology. Unfortunately, this approach decreases the detection probability of other technologies, increasing the amount of cross-technology collisions. In this article, we introduce the concept of coexistence aware CCA (CACCA), which enables a node operating in one technology to backoff for other coexisting technologies as well. As a proof of concept, we analyze the Packet Error Rate(PER) incurred by an IEEE 802.15.4 network in the presence of IEEE 802.11bg interference, and assess the PER reduction that is achieved by using CACCA.

Analysis and experimental verification of frequency-based interference avoidance mechanisms in IEEE 802.15.4

More and more wireless networks are deployed with overlapping coverage. Especially in the unlicensed bands, we see an increasing density of heterogeneous solutions, with very diverse technologies and application requirements. As a consequence, interference from heterogeneous sources-also called cross-technology interference-is a major problem causing an increase of packet error rate (PER) and decrease of quality of service (QoS), possibly leading to application failure. This issue is apparent, for example, when an IEEE 802.15.4 wireless sensor network coexists with an IEEE 802.11 wireless LAN, which is the focus of this work. One way to alleviate cross-technology interference is to avoid it in the frequency domain by selecting different channels. Different multichannel protocols suitable for frequency-domain interference avoidance have already been proposed in the literature. However, most of these protocols have only been investigated from the perspective of intratechnology interference. Within this work, we create an objective comparison of different candidate channel selection mechanisms based on a new multichannel protocol taxonomy using measurements in a real-life testbed. We assess different metrics for the most suitable mechanism using the same set of measurements as in the comparison study. Finally, we verify the operation of the best channel selection metric in a proof-of-concept implementation running on the testbed.

Techno-economical viability of cognitive solutions for a factory scenario

Recent advances in wireless communication theory and semiconductor technology brought wireless to virtually every aspect of our life, and this trend is expected to continue to increase in the future. Unfortunately, as the number of wireless applications grows, the same scarce spectrum is reused over and over again, resulting in increased interference, which jeopardizes the prospect of wireless meeting its high expectations. Dynamic Spectrum Access proposes to mitigate this problem by adapting the operational parameters of wireless networks to varying interference conditions. However, the involved increase in cost threatens to reduce the benefit of wireless in different environments. In this paper we examine the economic balance between the added cost and the increased usability brought about by DSA. We focus on a particular real-life scenario — the production floor of an industrial installation — where there is typically extensive utilization of the ISM band. IEEE 802.15.4 wireless sensors monitor production machinery, and IEEE 802.11 WLAN is used as the data backbone. We model the benefit achieved by adding RF sensing technology in terms of reliability and battery lifetime, and qualitatively assess the cost of interference and the potential gain of introducing sensing technology. Based on this techno-economic analysis, we conclude that if implemented correctly, spectrum sensing can bring business gains in real-life applications.

Real-time wide-band spectrum sensing for cognitive radio

Cognitive radio has received considerable amount of attention as a promising technique to provide dynamic spectrum allocation. Wide-band spectrum sensing is the corner stone for cognitive radio to be functional. Most existing commercial sensing solutions lack either the required flexibility or speed. Software-defined radio (SDR) on the other hand offers very high flexibility and therefore becomes a common platform for CR implementation. Among various SDR platforms, the universal software-defined radio peripheral (USRP) gained broad popularity. This paper presents a real-time wide-band-capable spectrum sensing solution based on USRP. The concept of energy detection and the methodology for wide-band sensing are explained. Finally, the performance of the proposed sensing solution is verified and compared with another popular commercial sensing solution, Airmagnet.

Various Detection Techniques and Platforms for Monitoring Interference Condition in a Wireless Testbed

Recently the constant growth of the wireless communication technology has caused a huge demand for experimental facilities. Hence many research institutes setup public accessible experimental facilities, known as testbeds. Compared to the facilities developed by individual researchers, a testbed typically offers more resources, more flexibilities. However, due to the fact that equipments are located remotely and experiments involve more complex scenarios, the required complexity for analysis is also higher. A deep insight on the underlying wireless environment of the testbed becomes necessary for comprehensive analysis.

Techno-economic evaluation of cognitive radio in a factory scenario

Wireless applications gradually enter every aspect of our life. Unfortunately, these applications must reuse the same scarce spectrum, resulting in increased interference and limited usability. Cognitive Radio proposes to mitigate this problem by adapting the operational parameters of wireless devices to varying interference conditions. However, it involves an increase in cost. In this paper we examine the economic balance between the added cost and the increased usability in one particular real-life scenario. We focus on the production floor of an industrial installation - where wireless sensors monitor production machinery, and a wireless LAN is used as the data backbone. We examine the effects of implementing dynamic spectrum access by means of ideal RF sensing, and model the benefit in terms of increased reliability and battery lifetime. We estimate the financial cost of interference and the potential gain, and conclude that cognitive radio can bring business gains in real-life applications.

FPGA-based wireless link emulator for wireless sensor network

Wireless sensor testbeds lack the flexibility for topology control and the accuracy for interference generation. Once the testbed is set up, the topology becomes fixed. Due to the nature of the wireless environment, experimenters often suffer from unpredictable background interference, while at the same time, find it hard to get accurate and repeatable interference sources.

Energy awareness in self-growing sensor networks

An ever increasing variety of applications are being addressed by wireless sensor networks, resulting in a continuous proliferation of their deployments, which are in many cases co-located. This development is mostly hindered by the operational complexity involved with management and maintenance of large numbers of small, battery powered wireless sensor devices. The paradigm of energy aware self-growing networks addresses these difficulties. It focuses on power saving which reduces the major maintenance complexity of replacing batteries, and on automatic cooperation between networks which reduces the management complexity. However, cross-network cooperation requires cross-network communication, which is not straightforward as they typically operate on different frequencies. Receiver Directed Transmission is a MAC layer protocol which can bridge this gap, while also minimizing interference and thus reducing the number of transmissions. In this work we study how Receiver Directed Transmission can be combined with Low Power Listening in order to take advantage of the reduced number of transmissions to improve power consumption. We then implement the selected approach on TinyOS and verify its operation experimentally.