Ehsan Tabatabaei Yazdi

Study of target tracking and handover in Mobile Wireless Sensor Network

Mobile Wireless Sensor Networks (MWSN) are becoming increasingly common these days and are hugely used in different applications like remotely monitoring health of patients, wild life tracking, localization and target tracking. In all these applications, mobile sensor nodes associate and communicate with different fixed coordinators. Reliable data transmission, maintaining an acceptable level of resiliency, providing seamless handover, effective target tracking and low energy consumption are few of the key requirements of effective communication in MWSNs. Out of these, the work done in this paper focuses on target tracking and the tangible need to have a seamless as well as fast handover in MWSNs. A few studies have been conducted to evaluate the performance of the IEEE 802.15.4 Media Access Control (MAC) layer in MWSNs. Moreover, the paper proposes three different target tracking schemes as part of the handover activity of sensor nodes to demonstrate the feasibility of experiencing seamless handover procedure. The schemes are properly validated through simulation studies.

Study of resource utilization in IEEE 802.15.4 Wireless Body Sensor Network, Part II: Greedy Channel Utilization

The channel scarcity phenomenon has recently introduced new challenges in the field of Wireless Body Sensor Networks (WBSNs). Within a WBSN, nodes communication is restricted throughout their defined active period. As the number of WBSNs increases, the overlapping active periods are elevated due to inefficient utilization of the spectrum. This consequently results in higher packet loss ratio and eventually performance degradation of the WBSNs entirely. To overcome the aforementioned issue, in this paper, we have proposed a new scheme called “Greedy Channel Utilization” (GCU) scheme in which coordinators compete for slot reservation and attempt to utilize the channel voraciously by pushing other contestants in to sleep mode. To evaluate the performance of our proposed scheme, we compared it with the bare IEEE 802.15.4 Std. in terms of channel utilization percentage, packet loss ratio, sensors orphan time and energy consumption of sensors and coordinator. Eventually, this study concludes the outperformance of GCU scheme over the blind scheme.

On channel adaptation in IEEE 802.15.4 mobile body sensor networks: What can be Gained?

One of the main problems affecting reliable transmission in wireless body sensor networks based on IEEE 802.15.4 is interference caused by sharing the unlicensed 2.4 GHz ISM band with other technologies such as Wifi. One possible approach to deal with this problem is to allow a body sensor network to change its operating frequency in response to changes in the observed interference. We assess the potential performance gains of different frequency channel adaptation schemes, both idealistic and realistic ones, in a scenario where a human carrier of a body sensor network walks through an area with scattered Wifi interferers, for example in densely populated urban areas. Our results show that substantial gains in delivery rate can be achieved by frequency adaptation. Furthermore, relatively simple “realistic” schemes are able to achieve the performance of an “ideal” adaptation scheme.

Coupling power and frequency adaptation for interference mitigation in IEEE 802.15.4-based mobile body sensor networks

One of the main problems affecting reliable transmission in wireless body sensor networks based on IEEE 802.15.4 is interference caused by sharing the unlicensed 2.4 GHz ISM band with other technologies such as Wifi. One possible approach to deal with this problem is to allow a body sensor network to change its operating frequency and its transmit power in response to changes in the observed interference. In this paper we consider the effect of the variation of transmit power in the presence and absence of frequency adaptation.

Adaptive channel utilisation in IEEE 802.15.4 wireless body sensor networks: Continuous hopping approach

IEEE 802.15.4 is arguably considered as a well designed standard protocol to address the need for low-rate, low-power and low-cost Wireless Body Sensor Networks (WBSNs). Within a WBSN, Nodes communication occurs during their confined active periods. The increase in number of active WBSNs would consequently result in the elevation of the overlapping ratio between the active periods of neighbouring WBSNs. In this paper, we address the interference caused by neighbouring WBSNs and its devastating consequences. Frequency hopping could be considered as a possible approach to alleviate the WBSNs performance degradation due to such interference. Our proposed “Continuous-Choice” scheme is compared with previously introduced “Initial-Choice” and “Blind-Choice” schemes in terms of channel utilisation, success rate, Satisfaction rate and energy consumption (both sensors and coordinator). Eventually, it is concluded that Continuous-Choice outperforms both Initial-Choice and Blind-Choice schemes in terms of above-mentioned performance measures.

Shortening orphan time in IEEE 802.15.4: What can be gained?

The duration time spent by end devices in orphan state in beacon-enabled IEEE 802.15.4 networks has a direct relationship with their energy consumption. The latency experienced for performing a coordinator discovery process and a successful association is related to such factors as beacon interval length, channel interference, message signaling, etc. To mitigate the overall energy consumption of the end devices in Wireless Body Sensor Networks (WBSNs), different coordinator discovery schemes are proposed in this study. The main focus of this paper is to improve the overall energy consumption and success rate of end devices. However, the performance evaluation results reveal that the proposed passive coordinator discovery schemes have insignificant statistical difference in the overall success rate and energy consumption of the WBSN.

Investigations on passive discovery schemes for IEEE 802.15.4 based Body Sensor Networks

In this paper, we investigate passive discovery of IEEE 802.15.4-based Body Sensor Networks (BSNs). BSNs are wearable networks that monitor the vital functions of the body while the person can roam around freely. One challenging task that BSNs has to perform is the discovery of certain coordinator nodes, for example gateways towards data processing and storage services. We are presenting a cooperative passive discovery scheme (the rumour-based scheme) for the beacon-enabled mode that is based on a simple class of listening strategies called sweep strategy. We consider a simple scenario of unbounded targeted discovery where a specific mobile BSN is searching for a specific destination network. We evaluate the performance of our scheme in terms of the average discovery time using simulations. The results show that our strategy can significantly reduce the time required to discover the target network.

Adaptive channel utilisation in IEEE 802.15.4 Wireless Body Sensor Networks: Adaptive Phase-Shifting Approach

Research communities have recently focused on the issues related with the internal interference in homogeneous IEEE 802.15.4 Wireless Body Sensor Networks (WBSNs). Frequency-hopping strategies seem to be an effective way to reduce the destructive impact of internal interference on WBSN performance. However, this strategy has its limitations. In this paper, a new strategy called “phase-adjustment” is considered in which occupants of the same channel are capable to communicate with each other by re-arranging their phases in such a way that they become equidistantly spread over time. The new proposed scheme is called Adaptive Phase-shifting Approach and utilises both phase-adjustment and frequency-hopping strategies. The performance of the new scheme is compared with previously introduced initial-, continuous- and blind-choice schemes, by considering satisfaction rate, carrying capacity and energy consumption. The results indicate that the Adaptive Phase-shifting scheme outperforms other considered schemes in terms of the above-mentioned performance measures.

Coupling power and frequency adaptation for interference mitigation in IEEE 802.15.4-based mobile body sensor networks: Part II

One of the crucial issues with IEEE 802.15.4-based wireless body sensor networks operating in the unlicensed 2.4 GHz band is to maintain reliable transmission while being subjected to external interference (i.e. WiFi). One approach to mitigate this problem is to enable body sensor networks to adaptively change their current frequency channel and to change the transmit-power in response to the observed interference variations. In previous work we have considered these two mechanisms separately for high interference scenarios. In this paper we have considered the impact of varying data rates, interferer densities and traffic intensities on the performance measures for low to medium interference scenarios. Furthermore, we present a new scheme that joints transmit-power with frequency adaptation. The schemes are evaluated and presented for different scenarios.