A study on MAC protocol for urgent data transmission in Wireless Bio Signal Monitoring Environment

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1 , pp A study on MAC protocol for urgent data transmission in Wireless Bio Signal Monitoring Environment Rae Hyeon Kim, Pyung Soo Kim, Jeong Gon Kim 1 Department of Electronic Engineering, Korea Polytechnic University Si Heung City, Kyunggi Do, , KOREA hjkl525@naver.com, {pskim, jgkim}@kpu.ac.kr Abstract. Recently, the application range of WBSN has been gradually expanding due to the advanced wireless telecommunication techniques and the activated ubiquitous environment. WBSN is a network environment in which various types of bio-signals created directly or indirectly in and out of the body are measured and processed for transmission to monitoring or mobile tools nearby. The MAC protocol proposed in this paper is in form of TDMA based technique in CSMA/CA environment. We apply the priorities of bio-signal data with each different characteristic and the minimum delayed transmission time for each data. We also consider the preferential transmission of urgent data to reduce the delay and the packet loss of them in typical mixed transmission of urgent data and other types of data. Keywords: WBSN, DTD-MAC, MED-MAC, CSMA/CA, TDMA, GTS 1 Introduction WBSN (Wireless Body Sensor Network) environment is an applied network that was advanced from WBAN environment [1], that allows communication within body based on WSN (Wireless Sensor Network) [2]. It is an environment where the condition of patient is monitored in real-time by collecting bio-signal data from the tools or node transplanted inside the body or on the outside of the body. In the near future, WBSN is expected to replace the existing wired environments of medical surveillance or monitoring [3]. CSMA/CA (Carrier Sensed Multiple Access/Collision Avoidance) [4], a widely known MAC protocol used when numbers of node are transmitted in such sensor network environment, triggers extremely high consumption of energy of application system through high frequency of idle listening and packet collision. Therefore, there had already been many researches that announced the advantages of TDMA (Time Division Multiple Access) method regarding electricity consumption and reduction in delayed transmission of nodes or devices [5] [6]. Meanwhile, there are general and urgent types of data among the data transmitted by 1 : Corresponding Author ISSN: ASTL Copyright 2015 SERSC

2 each node, and the urgent data should especially be processed quickly without any delay. IEEE MAC Protocol [7] is a hybrid method that applies both competition-oriented method, that is universally applied for data processing in WBAN and WBSN environment, and schedule-oriented method. However, the GTS allocation method of IEEE MAC Protocol applies FIFS (First In First Service) queueing method where the channels are allocated by the order that packets arrive, that causes inevitable delay in transmission, making it inadequate for transmission of urgent data [8]. In this paper, the MAC protocol that guarantees fast process of urgent data through variable structures of super-frame and the fixed transmission of general data according to the relative occurrence rate of urgent and general data is proposed to minimize the rate of transmission delay and packet loss that inevitably occurs when urgent and general data, which randomly occur in such WBSN environment, are processed by he same method. The structure of this paper is as the following. In section 2, the existing methods of DTD (Decrease of Transmission Delay)-MAC Protocol [9] that reduces transmission delay and packet loss regarding data process in WBSN environment will be discussed. In section 3, the MAC protocol proposed in this paper will be examined, and then in section 4, the features of MAC protocol will be analyzed. Finally, in section 5, the conclusion and the future research topics will be proposed. 2 Related Research DTD-MAC Protocol that is considered as the existing method in this paper forms the structure as in Figure 1. Fig 1. Conventional DTD-MAC Super-frame Each node attempts to transmit the data for channel allocation and when it reaches the maximum transmission delay of 250 ms, it is allocated with channel before other nodes regardless of the priority decided by the coordinator. The maximum transmission delay is applied by the standards stated in requirements of WBAN application on Table 1. In addition, the original priority of each node is referred as standards in the section where none of the node transmits the data for channel allocation but a temporary change in priority ranking occurs when the buffer data of each node reaches 250ms, the maximum transmission delay, and the delayed node is guaranteed with transmission prior to others. On the other hand, the packets of node that failed to transmit the data from the same moment are added up to the transmission delay or damage. DTD-MAC protocol 94 Copyright 2015 SERSC

3 Table 1. Requirements of WBAN Application has principle of transmitting data within 250ms, the maximum transmission delay from its occurrence. However, DTD-MAC protocol only considered the environment where there is no urgent data that possibilities for lack of flexible response in processing of urgent data exist. 3 The proposed MAC Protocol Figure 2 shows the structure of proposed MED-MAC Protocol Super-Frame. Fig 2. MED (Measurement of Emergency Data)-MAC Super-frame MAC protocol procured the flexibility in processing urgent data by adding UP (Urgent Period) Frame to the original Super-Frame of DTD-MAC. The proposed MAC protocol adopts the variable Super-Frame structure where the structure changes according to the relative occurrence rate of urgent and general data. Therefore, UP Frame will allow flexible variation of Frame lengths according to the amount of Emergency Data Node measured at PET. The major topic to be considered will be to seek for a solution to yield the optimized transmission function by controlling the adaptable processing method according to the occurrence rate of urgent data through the two suggested methods. Copyright 2015 SERSC 95

4 3.1 Prioritized transmission method for urgent data In an environment with high occurrence rate of urgent data, all types of urgent data are guaranteed with priority in channel allocation and transmission before the nodes of all other general data in situations where urgent and general data compete for channel allocation. Therefore, prior transmission is guaranteed for urgent data through fast processing of urgent data, which improves the requirement of QOS and real time processing of urgent data transmission. In contrast, the standard of transmission within 250 ms is applied for general data. Hence, it is expected that the increase of the delay and the packet loss in the general data transmission. 3.2 Transmission method to reduce delay of urgent data In situation where urgent and general data of each node compete for channel allocation, each urgent data is classified according to the priority standards (ECG > EEG > EMG) and the urgent data should be transmitted within 100 ms, which is the maximum transmission delay for real time transmission. If the urgent data is not transmitted within minimum transmission delay time, it results in transmission delay and packet loss. Even though the general data yields time slot to the urgent data in competition for channel allocation, it should be transmitted within 250 ms by principle. If it fails, data flows into the buffer and are kept in standby condition and the transmission delay in buffer is also added up to the total transmission delay in the final delay calculation. When the general data had reached the maximum transmission delay of 250 ms, it has the priority of transmission over the urgent data if none of urgent data does not reach the maximum transmission delay in that channel allocation. When urgent data competes with another urgent data for channel allocation, the existing priority ranking is applied for classification and allocation. If one of the urgent data of node that reached the maximum transmission delay, the priority is changed to the urgent data with maximum transmission delay if other urgent data with higher priority had not reached to them. If two or more different nodes attempts to compete for channel allocation, the existing priority criterion should be applied until all nodes reached the maximum transmission delay in current cycle. However, the urgent data of node that exceeded the maximum transmission delay are added up to the packet loss and the transmission delay even though it is not finally given the time slot for channel allocation. 4 Performance Comparison In this paper, WBSN network environment was composed of Star-Topology, and the length of 1 Time-Slot was defined as 50ms. Each cycle was composed of 100 Time- Slot, and the average collected from 100 cycles was calculated. The priority of general data was ECG > EEG > EMG, and the occurrence rate of EEG, ECG and EMG are determined from the definition of Table I. The maximum transmission delay of each node was decided to be 250ms from the occurrence moment of transmission delay. When the transmission was not succeeded within 250ms, it is added up to the 96 Copyright 2015 SERSC

5 total transmission delay and packet loss. The occurrence rate of urgent data was defined as 10 % for competition with general data. The assessment for function was executed under assumption that the general and urgent data will occupy 60% of current traffic environment of data. Also, the maximum transmission delay was defined as 100 ms for the urgent data, the transmitting of urgent data always prior to the general data and the competitive condition with general data is applied for the criterion which is evaluated with the original DTD-MAC protocol. We assume that the condition of 10% of urgent and 90% of general data. Figure 4 and Figure 5 presents the values of average transmission delay of general data and urgent data, respectively. Fig 4. Average Data Transmission Delay of General Data (E.D : 10%, G.D : 90%) Fig 5. Average Data Transmission Delay of Emergency Data (E.D : 10%, G.D : 90%) Here, MED-MAC (1) is the transmission method of prioritized allocation, suggested in 3.1, and MED-MAC (2) shows the result of transmission method of reducing delay, suggested in 3.2. From the two images, the transmission delay of MED-MAC (1) is smaller in both, showing no huge difference in general data, but there many reductions in delay of urgent data, which proves its effectiveness in quick processing of urgent data. Copyright 2015 SERSC 97

6 5 Conclusion In this paper, MAC protocol with objective of quick processing of urgent data and reduction in the transmission delay in urgent data under WBSN environment was suggested and assessed. DTD-MAC protocol that was taken for precedent research under WBSN environment did not have the standards related to processing of urgent data that the urgent data were processed with the same standards of transmission delay for general data, resulting inevitable increase in transmission delay and inadequate environment for urgent data, which requires real-time processing. The two MAC protocols proposed in this paper provides method where the urgent data are given with absolute priority depending on the amount of urgent and general data and another method that guarantees the consistent transmission function of general data by restricting the maximum transmission delay of urgent data to 100ms. As a result of functionality assessment, the prioritized transmission method was very effective when the rate of urgent data was low, through the experiment. References 1. Jun Sung Choi, Jeong Gon Kim, An Improved MAC Protocol for WBAN through modified frame structure, International Journal of Smart Home(IJSH), Vol.8 No.2 [2014]. 2. Jin Su Kim, Jung Hyun Lee and Kee Wook Rim, Energy Efficient Key Management Protocol in Wireless Sensor Networks, IJSIA Vol.4, No.2, Page No. 1-12, April Morchon, O.G, Baldus H, Sanchez, D.S, 3-5, Resource Efficient Security for Medical Body Sensor Networks, Wearable and Implantable Body Sensor Networks, BSN International Workshop, 4pp, April LAN-MAN Standards Committee of the IEEE Computer Society. Wireless LAN Medium Access Control(MAC) and Physical Layer(PHY) Specification. IEEE, New York, NY Gopalan SA and Park J, Energy Efficient MAC Protocols for Wireless Body Area Network : Survey, International Congress on Ultra Modern-Telecommunications and Control Systems and Workshops, pp , Oct Kwon H and Lee S, Energy-efficient multi-hop transmission in Body Area Networks, IEEE PIMRC, Tokyo, pp , IEEE Standard-2003, Part 15.4 : Wireless Medium Access Control(MAC) and Physical Layer(PHY) Specifications for Low-Rate Wireless Personal Area Network(LR- WPANs), Hyeop Geon Lee, Kyoung hwa Lee, Yong tae Shin, A Priority Based MAC Protocol for Emergency Data Transmission in Wireless Body Area Networks., Telecommunication Journal of the institute of electronics engineers of korea, Vol.49 No.4[2012] 9. Rae Hyeon Kim, Jeong Gon Kim, Delay Reduced MAC Protocol for Bio Signal Monitoring in the WBSN Environment, th International Workshop Series, Advanced Science and Technology Letters, Vol. 94(Networking and Communication 2015), pp Cavallarari R, Flavia Martelli, Ramona Rosini, Chiara Buratti, Roberto Verdone, A Survey on Wireless Body Area Networks: Technologies and Design Challenges, IEEE Communications Surveys & Tutorials, Vol. 16, No3, Third Quarter Copyright 2015 SERSC