A New MAC Protocol for Emergency Handling in Wireless Body Area Networks Sabita Nepal1, Amod Pudasaini1, Jae-young Pyun2, Suk-seung Hwang3, Chung Ghiu Lee3, and Seokjoo Shin1 1 Department of Computer Engineering Department of Information and Communication Engineering, 3 Department of Electronic Engineering, Chosun University, Gwangju, 501-759 Republic of Korea Email:
[email protected],
[email protected] (corresponding author) 2
not reported within the time it can be a critical situation. So, emergency handling for WBAN is an important issue.
Abstract— Wireless Body Area Network (WBAN) is a special purpose sensor application network which can be applied for applications relating to the health care. WBAN should support immediate and reliable data transmission for medical service during an emergency situation. Hence this paper proposes a new MAC superframe structure which can handle emergency data as well as a regular periodic data at the time of emergency. Simulation result shows low latency and increased throughput of the proposed superframe.
Traffics in human body can be classified as irregular emergency traffic which occur suddenly due to unexpected onset of a health condition and regular periodic traffic which continuously occur before and after irregular emergency traffic. The human body signals are correlated i.e. one event can trigger another series of events. When emergency happens these events should be reported urgently within the deadlines for immediate and accurate diagnosis. If one of these events fails to report within the delay margin, the outcomes may be life threatening or results in serious and lasting damage to organs. Thus, the emergency handling mechanism in a WBAN should provide guaranteed throughput and delay.
Keywords— WBAN, Emergency, IEEE 802.15.4, MAC
I. INTRODUCTION The advancements in information and communication technology and the necessity of large-scale communication infrastructures had triggered the birth of Wireless Sensor Network (WSN) paradigm [1]. Wireless Body Area Network (WBAN) is a special purpose sensor application network which has emerged as a key technology to provide real-time health monitoring of a patient and diagnose many life threatening diseases. It provides short range, low power and highly reliable wireless communication for use in close proximity to or inside body. In the health domain, the WBAN consists of a set of medical sensors implanted in or on the user’s body to monitor the state of his or her health and equipped with communication board/antenna to forward the information to a medical system to display, store and process the data to detect any medical anomaly. Today the medical WBAN is considered a key element to provide health care services anywhere, anytime and will play an important role to enhance the quality of life for elderly in the future. For designing a robust WBAN system, fundamental wireless networking issues must be addressed and resolved.
Due to the lack of a traffic prioritization mechanism in IEEE 802.15.4, the critical data does not get any prioritized access in the medium and hence emergency handling is not efficient in IEEE 802.15.4 MAC. Over the past decades, a number of MAC protocols have been researched and proposed based on IEEE 802.15.4, such that it can fulfill the requirements of WBAN. The references [3], [4] deal with the emergency handling for WBAN. B. Kim et al. [3] focus on the emergency handling scheme for WBAN. They proposed a superframe structure with Mixed Period (MP) and Extended Period (EP). In MP, the contention time slot (CTS) is inserted in front of Guaranteed Time Slot (GTS) for immediate transmission of emergency data, while EP consists of an extending request period, a re-allocated contention free period (CFP), and an additional contention access period (CAP). EP guarantees transmissions of failed slot in MP at reallocated CFP and handles the bursty traffic of CE at additional CAP. MP and EP can handle emergency data with low latency. In [4] C. Lee et al. have proposed an enhanced MAC protocol of IEEE 802.15.4 for health-monitoring application with an enhanced superframe structure containing polling period (PP) and an emergency slot (ES) for emergency handling. The ES is a quite short period where data transmission is described by success or fail. The superframe contains a long CFP followed by an inactive period. Therefore, an emergency occurring in the CFP incurs an unnecessary delay due to the lengthy inactive period. All the MACs stated above were able to address emergency data but have ignored the regular periodic medical data which are strongly correlated with an emergency event and are necessary for the proper diagnosis.
IEEE 802.15.4 (published in 2006) specifies the physical (PHY) and medium access control (MAC) layers for shortrange wireless communications. It is devised to support low power, low cost, and low bit rate networks. It provides a solution for low-rate low-power WPAN in the personal operating space (POS) of 10 meters, typically sensor network [2]. IEEE 802.15.4 standard is widely used for WBAN because of its features such as energy efficiency, scalability, and design flexibility. However, it is unable to meet all the stringent network requirements of BAN yet because IEEE 802.15.4 does not have any emergency handling or traffic differentiation mechanisms. If the emergency data or alarm or indications are
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In this paper, a new WBAN MAC protocol is proposed to minimize the delay associated with regular periodic traffic which occurs after reporting emergency events. The proposed protocol also tends to minimize the delay of reporting emergency events. It provides an Emergency Contention Period (ECP) to transmit emergency alarm and DTS allocation in inactive period to transmit regular periodic data when emergency happens in order to reduce delay.
NB follows the PCAP. But NB is broadcasted by NC only if any DTS request frame is requested to NC from PCAP, otherwise NB period is used as inactive period. NB contains the transmission schedules (i.e. allocated Dedicated Transmission Slots (DTS)) in the following DTP. All the SNs who have requested DTS request frame in PCAP should listen to NB to check whether their reporting in PCAP are acknowledged by NC and are allocated with DTS schedule.
The rest of this paper is organized as follows. Section II briefly describes the proposed superframe structure and in section III simulation results are discussed. Finally section IV concludes the paper.
DTP is a TDMA based access period which appears after NB. DTP is divided into a number of slots called as DTS. The length of a DTS slot is so determined to accommodate regular periodic data and an ACK message. DTP may therefore grow or shrink depending on the number of successful requests obtained in the PCAP. The maximum number of such DTSs allocated for an instance in a superframe is equal to M. Here we considered M=7 (which is also equal to number of slots in PCAP period).
II. PROPOSED SUPERFRAME STRUCTURE In the conventional beacon enabled IEEE 802.15.4 MAC, after CAP and CFP, Sensor Nodes (SNs) and Network Coordinator (NC) go to sleep mode in inactive period. In our proposed scheme, the inactive period is utilized for sending periodic medical data when emergency condition is noted. The modified frame format consists of Beacon, Emergency Contention Period (ECP), Advertisement Beacon (AB), Contention Free Period (CFP), Periodic Contention Access Period (PCAP), Notification Beacon (NB), Data Transmission Period (DTP), and Inactive Period as shown in Fig. 1.
III. SIMULATION RESULTS AND DISCUSSION To evaluate the proposed scheme, Castalia-3.2 [6] which is a network simulator specifically designed for sensor and body area networks based on OMNET++ platform [7] has been used. The simulation was carried out with star topology, with the single hop communication between the Network Coordinator (NC) and Sensor Nodes. The numbers of nodes are varied starting from 5 nodes and the packet length is fixed to 40 bytes. The traffic is generated using the Poisson distribution. The detailed simulation parameters and their values are summarized in table 1(some parameters are adopted from reference [5]). TABLE I.
Fig. 1. Modified Superframe Structure
The superframe starts with a Beacon Period, where beacon contains the information on the addressing fields, the superframe specification, the GTS fields, the pending address fields, and other Personal Area Network (PAN) related. ECP starts just after the beacon ends. In this period if any node has emergency alarm and needs to be reported, they contend for channel in ECP period and upon success they transmit their emergency alarm directly to the network coordinator. CSMA/CA is used to access the channel during ECP. The emergency alarm is very small in size, so for our proposed scheme we assume ECP as two time slots. Upon receiving an emergency indication from sensor nodes in ECP, NC broadcasts a ‘set’ flag through Advertisement Beacon (AB) to indicate the presence of emergency events to the sensor nodes. And if there is no emergency, a ‘reset’ flag is broadcasted through AB. CFP functions same as that of IEEE 802.15.4 standard. PCAP starts immediately after CFP ends. Only the SNs with regular periodic data are allowed to report and transmit in these periods. If SN nodes receive the ‘set’ flag through AB, then they send DTS request frame to NC in order to transmit regular periodic traffics after emergency, otherwise they send GTS request frame to NC in order to operate normally as IEEE 802.15.4. CSMA/CA is used in PCAP.
SIMULATION PARAMETERS
Parameters/Variables
Values
Data rate (Rdata) Simulation time Frequency band aBaseSuperframeDuration macBeaconOrder (BO) macSuperframeOrder (SO) Beacon Interval (BI) aNumSuperframeSlots UnitBackoff Period aMaxSIFSFrameSize Notification Beacon Beacon macMinBE macMaxBE macMaxCSMABackoffs macMaxFrameRetries CCA Advertisement Beacon Max. number of DTS
250 kbps 50 sec 2.4 GHz 960 symbols (15.36ms) 4 3 245.76 ms 16 20 symbol (0.32ms) 18 octets 40 bytes 40 bytes (1.28ms) 3 5 4 3 8 symbols 40 bytes 7
The simulated result of the proposed scheme is evaluated against the conventional IEEE 802.15.4. The proposed scheme is compared using the performance matrices; end-to-end delay and throughput.
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IV. CONCLUSION
A. End-to-End Delay Fig. 2. shows the graph of the number of nodes versus endto-end delay comparing the proposed and the conventional IEEE 802.15.4. In general, delay increases as the number of nodes increases for both schemes. But the proposed scheme has a lower delay than the conventional one.
A modified IEEE 802.15.4 superframe structure is proposed such that it can handle both the irregular emergency alarm as well as regular periodic medical data within the delay margin. Our modified superframe structure uses ECP period to handle the emergency events and opportunistically uses the inactive period for handling regular periodic data when an emergency event occurs. The performance showed through simulation results proves that our proposed scheme has lower delay and higher throughput than those of the conventional IEEE 802.15.4 scheme. ACKNOWLEDGMENT This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF2015R1D1A1A01059962). REFERENCES [1] [2]
Fig. 2. Regular periodic traffic end-to-end delay comparison of
proposed and conventional schemes in case of emergency events.
[3]
A. End-to-End Throughput
[4]
[5] [6] [7]
Fig. 3. Regular periodic traffic end-to-end throughput comparison of proposed and conventional schemes in case of emergency events.
Fig. 3 shows the graph of the number of nodes versus end-toend throughput comparing the proposed and the conventional IEEE 802.15.4. Here throughput increases as the number of nodes increases up to a certain point for both schemes. But the proposed scheme has a higher throughput than the conventional one. And after a certain point throughput of the conventional IEEE 802.15.4 tends to decrease while the proposed does not. This is due to the fact that the system could handle a certain number of nodes and increasing more nodes caused the system to have more collisions.
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C. S. Raghavendra, K. M. Sivalingam, and T. Znati, “Eds. Wireless Sensor Networks,” Kluwer Academic Pub, 2004 IEEE Std. 802.15.6-2012, Part 15.4: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for Low-Rate Wireless Personal Area Networks (WPANs), 2006 B.Kim, J. Cho, and D-Y. Kim, "An Emergency Handling Scheme for Superframe-Structured MAC Protocols in WBANs." IEICE transactions on communications, vol. 94, no. 9 , 2011 C. Lee, H.S. Lee and S. Choi, “An Enhanced MAC Protocol of IEEE 802.15. 4 for Wireless Body Area Networks,” in Proc. of 5th International Conference of Computer Sciences and Convergence Information Technology (ICCIT), December, 2010. C. Li, H.B. Li, and R. Kohno, "Performance evaluation of IEEE 802.15. 4 for wireless body area network (WBAN)," IEEE International Conference on Communications Workshops, pp. 1-5, 2009. Castalia: Wireless Sensor Network Simulator, Available at: https://castalia.forge.nicta.com.au /index .php/en /. OMNeT++: Simulation Environment, Available at: https://omnetpp.org/.
