, pp.282-286 http://dx.doi.org/10.14257/astl.2015.116.57 Improved MAC protocol for urgent data transmission in wireless healthcare monitoring sensor networks Rae Hyeon Kim, Jeong Gon Kim 1 Department of Electronic Engineering, Korea Polytechnic University Si Heung City, Kyunggi Do, 429-793, KOREA hjkl525@naver.com, jgkim@kpu.ac.kr Abstract. The applications of wireless body sensor networks (WBSNs) have been increasing due to the advanced wireless telecommunication techniques and activated ubiquitous environment. The WBSN is a network environment in which various types of bio-signals generated directly or indirectly inside and outside the body are measured and processed for transmission to monitor the condition of the patient. We propose two types of adaptive MAC protocols to deal with emergency data separately in the system. The first proposed protocol reduces the delay by prioritizing emergency data over other general data by sending them first. The second proposed protocol applies the maximum delay requirement to emergency data to reduce the packet loss of general and emergency data. Keywords: WBSN, DTD-MAC, MED MAC, CSMA/CA, TDMA, MED-MAC 1 Introduction A wireless body sensor network (WBSN) environment is an applied network that was advanced from a WBAN environment [1], that allows communication within a body based on wireless sensor networks (WSNs)[2]. It is an environment where the condition of a patient is monitored in real time by collecting bio-signal data from the tools or node transplanted inside or outside the body. In near future, the WBSN is expected to replace the existing wired environments of medical surveillance or monitoring [3]. Carrier sensed multiple access/collision avoidance (CSMA/CA) [4] is a widely known MAC protocol, and is used when a numbers of nodes are transmitted in such a sensor network environment, and triggers extremely high consumption of energy of application systems through high frequency of idle listening and packet collision. Therefore, there had already been many researches that studied the advantages of the time division multiple access (TDMA) method considering electricity consumption and reduction in delayed transmission of nodes or devices [5] [6]. Meanwhile, general and urgent data are the two types of data transmitted by each node, and the urgent data should especially be processed quickly without any delay. The IEEE 802.15.4 MAC protocol [7] is a hybrid method that applies both the 1 : Corresponding Author ISSN: 2287-1233 ASTL Copyright 2015 SERSC
competition-oriented method, which is universally applied for data processing in the WBAN and WBSN environments, and schedule-oriented method. However, the GTS allocation method of the IEEE 802.15.4 MAC protocol applies the first in first service (FIFS) queuing method where the channels are allocated in the order the packets arrive, that causes inevitable delay in transmission, making it inadequate for transmission of urgent data [8]. In this paper, we propose a MAC protocol to reduce the average delay and packet loss rate when the ratio of emergency data over general data is varied. The structure of this paper is as the following. In section 2, the existing method of the decrease of transmission delay (DTD)-MAC protocol [9] will be discussed. In section 3, proposed MAC protocol will be discussed in detail. In section 4, the MAC protocols proposed in this paper will be examined, and its features will be analyzed. Finally, in section 5, the conclusion and future research topics will be proposed. 2 Related Researches Fig 1. Conventional DTD-MAC super-frame Each node attempts to transmit data for channel allocation and when it reaches the maximum transmission delay of 250 ms, it is allocated a channel before other nodes regardless of the priority decided by the coordinator. In addition, the original priority of each node is standard in the section where none of the nodes transmit data for channel allocation, but a temporary change in priority ranking occurs when the buffer data of each node reaches 250 ms, and the delayed node is guaranteed with transmission prior to others. However, the DTD-MAC protocol only considered the environment where there is no urgent data, which leads to a lack of flexible response in processing the existing urgent data. 3 The proposed MAC Protocol Fig 2. MED-MAC super-frame Copyright 2015 SERSC 283
Figure 2 shows the structure of the proposed MED-MAC protocol super-frame. The MAC protocol obtained the flexibility in processing urgent data by adding the urgent period (UP) frame to the original super-frame of the DTD-MAC protocol. The main topic to be considered will be to obtain 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. 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. However, the delay requirement of maximum 250 ms is still applied for general data. Hence, it is expected that there is an increase of packet loss in general data transmission. 3.2 Transmission Method to Reduce Delay of Urgent Data In situations 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, the maximum transmission delay for real time transmission. If the urgent data is not transmitted within 100 ms, it results in transmission delay and packet loss. Even though general data acquires time slots as compared to urgent data while competing for channel allocation, it should be transmitted within 250 ms by WBAN delay requirement. If it fails, data flows into the buffer and are kept in standby condition, and the transmission delay in the 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 reach the maximum transmission delay in that channel allocation. If one of the urgent data of the node reaches the maximum transmission delay, the priority is changed to the urgent data with maximum transmission delay if the other urgent data with higher priority had not reached them. If two or more different nodes attempts to compete for channel allocation, the existing priority criterion should be applied until all nodes reach the maximum transmission delay in the current cycle. However, the urgent data of the node that exceeded the maximum transmission delay are added up to the packet loss and total delay even though it is not finally assigned as the time slot for channel allocation. The proposed scheme considers the first priority to the maximum delay requirement regardless of the type of data and priority criterion of the WBAN standard. It provides the real-time transmission of data with lower priority as much as possible. Hence, we can expect that this scheme can be applied to the target system, and the important factor is the prevention of increased delay and packet loss. 284 Copyright 2015 SERSC
4 Performance Comparisons In this paper, the length of one time-slot was defined as 50 ms. Each cycle was composed of 100 time slots, 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 similar in this paper. The maximum transmission delay of each node was assumed as 250 ms from the occurrence moment of transmission delay. When the transmission was not succeeded within 250 ms, it is added up to the total transmission delay and packet loss. The assessment for function was executed under assumption that the general and urgent data will occupy 240% of the current traffic environment of data. In addition, the maximum transmission delay was defined as 100 ms for the urgent data, the transmission of urgent data is always prior to the general data, and other competitive conditions with general data are applied for the criterion, which is evaluated with the original DTD-MAC protocol. We evaluate the average time delay and the amount of packet loss when the ratio of emergency data has a value of 10%, 20%, 30%, and 50% over the total data traffic. Table 1. Average data transmission delay (total data traffic: 240%). Table 2. Packet loss (total data traffic: 240%). Here, MED-MAC (1) is the transmission method of both prioritized allocation and reducing the average time delay, and MED-MAC (2) shows the result of transmission method by reducing the amount of packet loss. From the two tables, the transmission delay of MED-MAC (1) attains the smallest value of average time delay in all the variation cases of general and emergency data. Particularly, it also shows that much reduction of delay of the urgent data, and hence, this implies its effectiveness in prior Copyright 2015 SERSC 285
processing of the urgent data. From Table 2, the packet loss for MED-MAC (2) is decreased compared with DTD-MAC and MED-MAC (1) when the ratio of emergency data exceeds 20% of the total data traffic. It indicates that MED-MAC (2) can be applied to the target system, in which the packet loss needs to be restricted or minimized even if they have a lower priority data packet. 5 Conclusions In this paper, two types of MAC protocol for the reduction of time delay and packet loss of urgent data in the WBSN environment were suggested and evaluated. The DTD-MAC protocol that was considered for previous research in the WBSN environment does not have any standard related to processing of urgent data. Namely, it may result in an inevitable increase in transmission delay and a lot of packet loss for urgent data, which requires real-time processing. The first proposed MAC protocol provides a method where the urgent data are given absolute priority depending on the amount of urgent and general data, and the second proposed MAC protocol guarantees the consistent transmission function of general data by restricting the maximum transmission delay of urgent data to 100 ms. References 1. Choi, J.S., Kim, J.G.: An Improved MAC Protocol for WBAN through modified frame structure. Int. j. smart home. 8 (2) (2014) 2. Kim, J.S., Lee, J.H., Rim, K.W.: Energy Efficient Key Management Protocol in Wireless Sensor Networks. International Journal of Security and Its Applications 4 (2), pp. 1--12 (2010) 3. Morchon, O.G., Baldus, H., Sanchez, D.S.: Resource Efficient Security for Medical Body Sensor Networks, Wearable and Implantable Body Sensor Networks. In: Wearable and Implantable Body Sensor Networks, 2006. International Workshop on, pp. 4-pp. IEEE 4. LAN-MAN Standards Committee of the IEEE Computer Society.: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specification. IEEE. New York (1997) 5. Gopalan, S.A., Park, J.: Energy Efficient MAC Protocols for Wireless Body Area Network: Survey. In: Ultra Modern-Telecommunications and Control Systems and Workshops (ICUMT), 2010 International Congress on, pp.739--744 (2010). 6. Kwon, H., Lee S.: Energy-efficient multi-hop transmission in Body Area Networks. In: IEEE 20th International Symposium on Personal, Indoor and Mobile Radio Communications, pp. 2141--2146, Tokyo (2009). 7. IEEE 802.15.4 Standard-2003.: Part 15.4: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for Low-Rate Wireless Personal Area Network (LR- WPANs). IEEE Computer Society (2003) 8 Lee, H.G., Lee, K.H., Shin, Y.T.: 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 (4) (2012) 9. Kim, R.H., Kim, J.G.: Delay Reduced MAC Protocol for Bio Signal Monitoring in the WBSN Environment. 6th International Workshop Series, Advanced Science and Technology Letters, vol. 94 (Networking and Communication 2015), pp.42--46 (2015) 286 Copyright 2015 SERSC