Buffer Control by Delay Limitation for WBAN based Healthcare Monitoring Network Environment

Transcription

1 Buffer Control by Delay Limitation for WBAN based Healthcare Monitoring Network Environment Rae Hyun Kim, Jeong Gon Kim 1 1 Dept. of Electronic Engineering, Korea Polytechnic University Siheung-si, Gyeonggi-do, KOREA hjkl525@kpu.ac.kr, jgkim@kpu.ac.kr Abstract. Recently, the application of WBSN (Wireless Body Sensor Networks) has been gradually expanding due to the advanced wireless 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 monitor by mobile tools nearby. The MAC protocol proposed in this paper is in form of TDMA based technique in CSMA/CA environment. The proposed scheme applies the maximum delay restriction to each type of data packets in order to deal with the delayed packets time very effectively. Simulation results show that the proposed scheme attains the smaller packet delay for the audio transmission which has most delay sensitive characteristic and also reduce the packet loss for the audio and video packet transmission compared with the random allocation for delayed packets. Keywords: WBAN, WBSN, Time-Slot, CSMA/CA, TDMA, Buffer, Packet 1 Introduction Figure 1. WBSN Environment Figure 1 shows the concept of WBSN environment. WBSN 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 1 : Corresponding Author 97

2 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 which is used when a number of node are transmitted at the same time, triggers extremely high consumption of energy through high frequency of idle listening and packet collision. Therefore, many researches announced the advantages of TDMA (Time Division Multiple Access) method to support low electricity consumption and the reduction in packet delay for data transmission [5] [6]. If the packets of nodes failed to be scheduled in his time slots, they move to the buffer memory to get a next available time slot for packet transmission, however, if they finally fail to transmit the data within his delay requirement, they are treated as the packet loss or failure since it is not effective as an available data packets, we compared the random scheme and the proposed MAC protocol in the initial data transmission and buffer data processing together with same delay restriction. The structure of this paper is as the following. In section 2, the system model will be explained. In section 3, proposed MAC protocol will be discussed in detail. In section 4, the performance of MAC protocols will be examined, and its features will be analyzed. Finally, in section 5, the conclusion and future research topics will be presented. 2 System Model Table 1. WBAN requirement The delay requirements proposed in this paper comply with the functional requirements of IEEE WBAN standard recommendation as shown in above Table 1 with highlighted box shape. 3 Buffer Control with Delay Restriction In this paper, the occurrence rate of each node data is assumed as different rate by considering general WBSN environment based on WBAN requirements. The delay requirements from WBAN standard are applied in the initial data transfer environment and buffer packet transfer environment, the total transmission delay consider the delay of the packet that has been transmitted in the buffer. Also, the packets that failed to send within the delay requirement of WBAN are treated as the packet loss. The proposed MAC protocol is referred to as the DPL (Decreasing of the Packet-Loss) - MAC protocol. Figure 2 shows the packet transmission processing of the buffer and also shows the principle of calculating the sum of the total delay of packet. 98

3 The proposed scheme calculates the actual packet delay of the system by referencing whether the packet transmission is successful in the buffer packet processing environment. In the initial data transmission, the proposed scheme determines that whether the data that each sink node is successfully transmitted to the coordinator. In addition, if it occurs the empty period which all the nodes do not transmit data for channel allocation, the data packets in buffer memory are transmitted by predetermined transfer principle. Processing in the red square of Fig. 2 describes the summing process of packet delay including the packet processing in the buffer. For example, when the delay of the buffer data of EMG packet reaches 250 ms, which is the maximum allowable transmission delay of the EMG packets, we can change the priority temporarily and the corresponding node is guaranteed to transmit with first priority at that time. In other words, if one packet has the last opportunity to satisfy his maximum delay requirement, it can be transmitted with the first priority than other packets are not close to the maximum delay requirement. The delay in the buffer is summed to the total data transmission delay for the finally successfully transmitted data packets. After this processing, coordinator determines whether the packet-loss of the remaining node occurs or not. If the there is no packet-loss of the remaining nodes at this time, the buffer delay of the remaining nodes is increased by onetime slot. Finally, by returning to the initial data transmission environment, it repeats the process above mentioned. If the packet-loss of the in the buffer does occur, coordinator increases the number of packet loss, and the buffer delay for this loosed packet is subtracted from the sum of total delay of packet transmission. Figure 2. Initial data transmission & Buffer data processing on the Proposed Scheme 4 Simulation Results In this paper, the WBSN network environment was configured in a Star-Topology and the length of 1 Time-Slot was defined as 10 ms. Each cycle was composed of 100 Time-Slots, and the average collected from 100 cycles was calculated. In this paper, we assumed the same full amount of data in the same period. Also, the simulation environment is composed of both medical data and non- 99

4 medical data. We only considered data transmission delay of the WBAN requirement except for the priority of each node. The occurrence rate of each data was defined as same rate (Audio 33%, Video 33%, EMG 33%). The functional assessment was executed under assumption that the total data will occupy 100% of the whole Time-Slot randomly. Table 2 describes the average packet delay performance for two schemes when the offered sum traffic is 100 % compared with available time slots as expected, the proposed scheme attains the smaller packet delay for the audio transmission which has smallest delay requirements in WBAN for real time transmission while EMG and video packets achieves the larger packet delay compared with random scheme even if they still also satisfy the WBAN delay requirements. Figure 4 describes the rate of packet-loss performance for two schemes when the offered sum traffic is 100 % compared with available time-slots, respectively. It is observed that the proposed scheme performs the reduction of the packet loss for the audio and video packet transmission compared with the random allocation for delayed packets while the packet loss rate is slightly increases for the EMG packets. Two figures explain that the proposed scheme can be effective for supporting the real time service as audio packet transmission and maintain the packet loss rate in a reasonable level of operation for mixed packet transmission with different characteristics in WBAN based healthcare monitoring network environment. Figure 3. Average Packet Delay for Random Scheme and the Proposed Scheme Figure 4. Packet-Loss Rate for Random Scheme and the Proposed Scheme 5 Conclusions In this paper, we examined the performances of MAC protocol in WBAN based sensor networks. We proposed the buffer control with delay restriction in order to minimize the packet delay and packet loss rate for supporting the QoS and real time service transmission. We considered the actual delay of the buffer packet, hence, the proposed scheme calculated the actual packet delay of the system by referencing whether the packet in the buffer is successfully transmitted or not. Performance comparison was made to packet delay and packet loss rate for random scheme and the proposed scheme with delay reduced buffer control. From simulation results, the proposed scheme improved the QoS of the overall system by minimizing the packet delay for audio packet transmission and also significantly reducing the the packet loss rate for EMG and video packet transmission in WBAN based healthcare monitoring network environment. 100

5 References 1. J.S. Choi, J.G. Kim: An Improved MAC Protocol for WBAN through proposed frame structure, International Journal of Smart Home(IJSH), Vol.8 No.2 (2014) 2. J.S. Kim, J.H. Lee and K.W. Rim: Energy Efficient Key Management Protocol in Wireless Sensor Networks, IJSIA Vol.4, No.2, Page No. 1-12, April (2010) 3. 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 (2006) 4. LAN-MAN Standards Committee of the IEEE Computer Society: Wireless LAN Medium Access Control(MAC) and Physical Layer(PHY) Specification, IEEE, New York, NY (1997) 5. Gopalan, SA 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 (2010) 6. Kwon H and Lee S: Energy-efficient multi-hop transmission in Body Area Networks, IEEE PIMRC, Tokyo, pp (2009) 7. 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 (2014) 101