Testbed based throughput analysis in a Wireless Sensor Network

Abstract: Real-time multimedia applications require quality of service (QoS) provisioning in terms of bounds on delay and packet loss along with soft bandwidth guarantees. The shared nature of the wireless communication medium results in interference. Interference combined with the overheads, associated with a medium access control (MAC) protocol, and the implementation of a networking protocol stack limit the available bandwidth in IEEE 802.15.4-based networks and can result in congestion, even if the transmission rates of nodes are well below the maximum bandwidth supported by an underlying communication technology. Congestion degrades the performance of admitted real-time multimedia flow(s). Therefore, in this paper, we experimentally derive the IEEE 802.15.4 channel capacity using an unslotted CSMA-CA MAC protocol. We experimentally derive channel capacity for two cases, that is, when the CSMA-CA protocol is working without ACKs and when it is working with ACKs. Moreover, for both cases, we plot the relationship of offered data load with delay and packet loss rate. Simulation results demonstrate that the parameters that affect the choice of a CSMA-CA MAC layer protocol are end-to-end delay and packet loss requirements of a real-time multimedia flow, data load within the interference range of transmitters along the forwarding path, and length of the forwarding path.

Abstract: In the wireless sensor networks domain, one of the most used standards is IEEE 802.15.4. This standard has been made available on many low power operating systems such as TinyOS and Contiki OS. It is crucial for the implementation to be compliant with the specifications of the standard. In the case of Contiki OS, the provided version of the main medium access algorithm, unslotted Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA), presents many flaws. In this paper, we discuss the implementation of the provided CSMA/CA algorithm and we point out to the parts that do not respect the standard specifications. We also propose and implement a compliant version of this algorithm and show through simulation the correctness of the implementation.

Abstract: Although the ZigBee technology is massively deployed the performance question still remains unanswered. There is a lack of serious performance evaluations and thus this paper provides a comprehensive and unbiased study of the ZigBee PRO technology. An extensive real measurement was conducted to accomplish this task. We found out a big performance gap among ZigBee implementations even though they are compliant with the ZigBee standard. The presented results and analysis could be beneficial for many wireless sensor network developers.

Abstract: With an expeditious increase in the vehicle transport in the major cities, it has become more difficult to find the free parking space to park the vehicles. Constant rise in the number of vehicles on the roads has led to increase in the unwanted traffic, drivers frustration, delay in the transportation and increase in the noise and air pollution. Due to lack of proper knowledge of parking space, it has become unable to utilize most of the nearby parking space. This work proposes an innovative approach to guide the vehicle drivers to the parking space using Hierarchical Wireless Sensor Networks. A three sensors per parking slot based technique is used to distinguish the type of parked vehicles and to find the free parking slots in the parking area. Free, partially-occupied and occupied parking slot states information is stored at the Parking Server in the form of parking location and the parking area layout with parking slot states marking on it. Parking Server makes the parking information available to the vehicle drivers by the mean of web and mobile applications for guiding vehicles for parking. The results show that the parking detection with multiple passive sensor nodes per parking slot system is more energy efficient and vehicle parking detection is as accurate as the single active sensor per parking slot system in the existing parking designs.

Abstract: As there is a rising demand on energy efficiency the proper network stack is an essential for every wireless sensor network application. This paper gives a comprehensive view on performance comparison of $$\hbox {Atmel}^{\circledR }$$ Atmel ® Lightweight Mesh (LWM) and ZigBee Pro technology based on extensive real measurements. We focused mainly on application layer throughput, routing latency and self-healing capability. Although the LWM clearly outperforms ZigBee Pro in most aspects, the LWM has particular drawbacks. Particularly, the LWM provides smaller footprint and faster stack processing along with higher application throughput. The most notable throughput difference where the LWM outperforms the BitCloud was by as much as thirteen times.

Abstract: IEEE 802.11 MAC mainly relies on two techniques to combat interference: physical carrier sensing and RTS/CTS handshake (also known as "virtual carrier sensing"). Ideally, the RTS/CTS handshake can eliminate most interference. However, the effectiveness of RTS/CTS handshake is based on the assumption that hidden nodes are within transmission range of receivers. In this paper, we prove using analytic models that in ad hoc networks, such an assumption cannot hold due to the fact that power needed for interrupting a packet reception is much lower than that of delivering a packet successfully. Thus, the "virtual carrier sensing" implemented by RTS/CTS handshake cannot prevent all interference. Physical carrier sensing can complement this in some degree. However, since interference happens at receivers, while physical carrier sensing is detecting transmitters (the same problem causing the hidden terminal situation), physical carrier sensing cannot help much, unless a very large carrier sensing range is adopted, which is limited by the antenna sensitivity. We investigate how effective is the RTS/CTS handshake in terms of reducing interference. We show that in some situations, the interference range is much larger than transmission range, where RTS/CTS cannot function well. Then, a simple MAC layer scheme is proposed to solve this problem. Simulation results verify that our scheme can help IEEE 802.11 resolve most interference caused by large interference range.

Abstract: IEEE 802.11 MAC mainly relies on two techniques to combat interference: physical carrier sensing and RTS/CTS handshake (also known as “virtual carrier sensing”). Ideally, the RTS/CTS handshake can eliminate most interference. However, the effectiveness of RTS/CTS handshake is based on the assumption that hidden nodes are within transmission range of receivers. In this paper, we prove using analytic models that in ad hoc networks, such an assumption cannot hold due to the fact that power needed for interrupting a packet reception is much lower than that of delivering a packet successfully. Thus, the “virtual carrier sensing” implemented by RTS/CTS handshake cannot prevent all interference as we expect in theory. Physical carrier sensing can complement this in some degree. However, since interference happens at receivers, while physical carrier sensing is detecting transmitters (the same problem causing the hidden terminal situation), physical carrier sensing cannot help much, unless a very large carrier sensing range is adopted, which is limited by the antenna sensitivity. In this paper, we investigate how effective is the RTS/CTS handshake in terms of reducing interference. We show that in some situations, the interference range is much larger than transmission range, where RTS/CTS cannot function well. Two independent solutions are proposed in this paper. One is a simple enhancement to the IEEE 802.11 MAC protocol. The other is to utilize directional antennas. Simulation results verify that the proposed schemes indeed can help IEEE 802.11 resolve most interference caused by large interference range.

Abstract: Research in the wireless sensor network field has been plagued by difficulties in realistic simulations. These difficulties are often the result of non-realistic assumptions which need to be removed from the equation. Recent work in the field has identified realistic radio consumption models, signal strength estimation and that reception cost may be more than the transmission cost. In our work we combine these techniques into a single model for estimating radio power costs. We also investigate the effects of discrete power levels on transmission cost and show that transmission costs do not always increase as the transmission distance increases.

Abstract: Designing a multi-hop wireless network is a challenge mainly because of high bit error rates and the inherent broadcast nature of the medium creating interference. To improve the capacity, protocols based on spatial reuse of frequencies with multiple orthogonal channels have been introduced. This is particularly useful in complete wireless environments such as wireless mesh networks and wireless sensor networks (WSN). Based on initial testbed experiments on WSN testbeds, we show that there is a gap between reality and simulation models due to overheads in implementing these protocols. In order to support QoS guarantees in critical paths for such networks, we present a generic channel allocation scheme based on k-distance coloring problem, for multiple channel networks. The scheme is designed keeping in mind the real time deployment issues in wireless networks. We report the results from experiments conducted using a IEEE 802.15.4 based testbed consisting of Xbow MicaZ nodes and results obtained using the OMNET4 simulation environment.

Abstract: This paper presents an implementation based study of multi-channel medium access control protocols in hardware constrained wireless sensor network(WSN) nodes with 802.15.4 radio. In the network architecture presented, each sensor node has a single radio transceiver that can be tuned to any of the available sixteen non-overlapping channels. The simplest way to select data channel is to use a common channel signaling between the nodes. We have conducted experiments to verify whether control channel congestion can occur in case of 802.15.4 radios using MicaZ and TelosB motes. The throughput results show the per-node throughput does not decline as significantly with increasing number of senders, with the proposed multi-channel protocol.