Dr. Irfan S. Al-Anbagi and Prof. Hussein T. Mouftah

Transcription

1 Dr. Irfan S. Al-Anbagi and Prof. Hussein T. Mouftah School of Electrical Engineering and Computer Science University of Ottawa

2 Cyber Physical Systems (CPSs) integrate communication and information technology functions to control the physical elements of a system. A smart grid is the use of communications, sensors, computational ability and control to improve the overall functionality, performance and cost of the electric power system. A non smart system becomes smart by communicating, sensing, and exercising control. 2 of 30

3 Monitoring and controlling smart grid assets in a timely and reliable manner is essential for successful smart grid operation. Wireless Sensor Networks (WSNs) are expected to be widely utilized in a broad range of smart grid applications due to their numerous advantages. The use of WSNs in smart grid applications has brought forward a new challenge in fulfilling the Quality of Service (QoS). Providing QoS support is a challenging issue due to Limited resources of sensor nodes. Unreliable wireless links. Harsh operation environments. A typical WSN-based substation monitoring in the smart grid 3 of 30

4 WSNs used in smart grid monitoring applications need to meet the tight QoS requirements of smart grid monitoring applications. If the platform does not directly meet these requirements, protocols and algorithms are needed to manage the hardware and to provide the required functionality. The IEEE MAC protocol is not designed to provide priority or data differentiation to delay critical packets. Therefore, the issue of providing QoS to sensor nodes utilizing the IEEE MAC protocol without impacting other metrics in the network becomes a real challenge. 4 of 30

5 5 of 30

6 6 of 30

7 Certain WSN applications require; Accurate estimation of specific WSN parameters such as the end-to-end delay, the reliability and the power consumption. The estimation of these parameters calls for an accurate and lightweight WSN model suitable for the low processing capabilities of the sensor nodes. 7 of 30

8 Many studies propose different analytical models that investigate the network parameters. Some models become too complex and unsuitable for use in WSNs. Others use certain approximations, which lead to inaccuracies in the model itself. 8 of 30

9 We develop a model for the Carrier Sense Multiple Access with Collision Avoidance (CSMA-CA) mechanism used in the IEEE MAC protocol. Realistic and Stable Markov-based (RSM) model [1]. The model considers Actual traffic generation probabilities The impact of a finite MAC-level buffer on: oend-to-end delay oreliability opower consumption We carry out performance analysis under different traffic and network conditions in: Star Topology Cluster-tree Topology We test the accuracy of our model by performing simulations. [1] Irfan Al-Anbagi, Melike Erol-Kantarci and Hussein T. Mouftah, A Reliable IEEE Model for Cyber Physical Power Grid Monitoring Systems", IEEE Transactions on Emerging Topics in Computing, vol. PP, no. 99, pp. 1-1, 2013, DOI /TETC of 30

10 o WSN operates in the beacon-enabled mode of the IEEE protocol o MAC-level acknowledgement (ACK) is used o The WSN is of a one-hop star topology and or multi-hop cluster-tree topology o Packets arrive at the MAC layer with a probability of σ. o Node buffer is FIFO with no flow priority. 10 of 30

11 [2] P. Park, P. Di Marco, P. Soldati, C. Fischione, K.H. Johansson, A Generalized Markov Chain Model for Effective Analysis of Slotted IEEE in the Proc. of Mobile Adhoc and Sensor Systems, MASS '09, pp , 17 November 2009, Macau, China. 11 of 30

12 BO stage at time (t) state of the BO counter at time (t) state of the retransmission counter at time (t) 12 of 30

13 (1) probability of being in a BO state the packet transmission state and packet collision state probability of initiating CCA2 probability of being in the idle state when no packets are available 13 of 30

14 14 of 30

15 15 of 30

16 16 of 30

17 17 of 30

18 In a smart grid environment, the use of WSNs with cluster-tree topologies solve the limited coverage and multipath fading and interferences problems. WSNs with cluster-tree topologies suffer from bottleneck problem at intermediate level nodes that forward the data. We propose an Adaptive RSM (ARSM) [3] scheme to solve the latency problems in cluster-tree topologies. [3] Irfan Al-Anbagi, Melike Erol-Kantarci and Hussein T. Mouftah, An Adaptive QoS Scheme for WSN-based Smart Grid Monitoring in the Proc. of the 3 rd IEEE International workshop on smart communication protocols and algorithms (SCPA'13), IEEE International Conference on Communications, (ICC 2013) Workshops, pp , Budapest, Hungary, June of 30

19 The cause of excessive delay in cluster-tree topologies An upper level Cluster Head (CH) cannot fit the incoming packets in one SF. In ARSM the application layer marks packets that require QoS provisioning with a flag. The MAC sub-layer estimates the reliability (R) Using RSM model MAC sub-layer estimates the number of full Superframes (SF) (δ) a packet is expected to wait in the CH before it is forwarded to an upper level CH. 19 of 30

20 The value of δ depends on the level of the CH The value of δ is given by The occupancy of a CH k 1 buffer (B k ) the maximum number of data k packets that can be transmitted from a CH in a single SF duration The MAC layer estimates δ If δ is more than zero, Then the MAC sub-layer inserts a flag in its frame to request its CH to double its Guaranteed Time Slot (GTS) 20 of 30

21 To increase the probability of a node in transmitting the high priority data, ARSM implements the Delay Responsive Cross-layer (DRX) scheme [4] (with short Clear Channel Assessment CCA duration) In ARSM, a node also implements linear backoff period (LDRX) [5] instead of the exponential backoff period defined in the IEEE standard [4] Irfan Al-Anbagi, Melike Erol-Kantarci and Hussein T. Mouftah, Priority and Delay Aware Medium Access for Wireless Sensor Networks in the Smart Grid", IEEE Systems Journal, vol. PP, no. 99, pp. 1-11, 2013, doi={ /jsyst }, ISSN={ }. [5] Irfan Al-Anbagi, Melike Erol-Kantarci and Hussein T. Mouftah, A delay Mitigation Scheme for WSN-based Smart Grid Substation Monitoring," in the Proc. of the IEEE International Wireless Communications and Mobile Computing Conference, (IWCMC 2013), pp , Sardinia, Italy, July of 30

22 A flow chart of the ARSM scheme 22 of 30

23 We implement the model with MATLAB. We simulate the network using the QualNet network simulator In both the simulation and the analytical model results, we used Poisson traffic arrival We assume that all of the end nodes and CHs operate in the 2.4 GHz band with a bit rate of 250 Kbps We assume that there are 20 end devices in each cluster and that there are 9 clusters We run each simulation for 300 seconds, repeat each simulation 10 times and give the averaged results 23 of 30

24 With higher MAC buffers the nodes tend to buffer the arriving packets before transmitting them, and hence decrease the gradient of the delay with λ. The end-to-end delay in a cluster-tree topology. 24 of 30

25 The end-to-end reliability in a cluster-tree topology. As the MAC buffer increases the total endto-end reliability increases. This is attributed to the buffers that reduce the contention, which leads to fewer collisions. 25 of 30

26 The total power consumed in a cluster-tree topology. The power consumption is calculated by adding the total power consumed to transmit the data packets from an end node to the sink. The power consumption is therefore dependent on the number of relays between the end node and the sink. 26 of 30

27 Per-cluster throughput in a cluster-tree topology. For a cluster of 10 nodes, it is seen that the throughput is highest when the buffer is equal to 512B. Only a small number of nodes contending to access the medium, and therefore, using such buffer size is sufficient for a favorable throughput. 27 of 30

28 The proposed cluster-tree topology for the ARSM scheme. The end-to-end delay for a three-hop WSN. The total power consumed. The reliability. 28 of 30

29 RSM model considered actual traffic generation rates. RSM incorporated the effect of a finite MAC-level buffer on the performance of the WSN. ARSM was presented for cluster-tree WSNs in smart grid applications. ARSM could adaptively reduce the end-to-end delay for high data rate delay-critical events Without affecting other network parameters such as reliability and power consumption. The ARSM scheme solves the latency problem by Allocating longer GTS based on requests made from end devices after estimating the network conditions. 29 of 30

30 30 of 30