Cooperative Buffering for Wireless Sensor Networks

1. Cooperative Buffering for Wireless Sensor Networks Yu Takada Masaki Bandai Takashi Watanabe Graduate School of Informatics, Shizuoka University November 25, 2008

2. 1 Background (1/2) • Wireless sensor networks (WSNs) • Many tiny sensor nodes • Each nodes sends their data to sink • Resource restriction of a sensor node • Processor, Transreceiver, Buffer size, etc. • Battery-powered →Saving energy of each sensor nodes • Advanced monitoring using images or sound • Cheap CMOS sensor, Small Camera • Microphone node sink ・camera（lens radius is about 1mm） ・several million pixel

3. 1 Background (2/2) • The examples of advanced WSNs • surveillance video camera system • habitat monitoring • The characteristics of data on our research • Conventional model • air temperature, degree of humidity, vibration → small • Our model • large size • burst data generation • no immediacy • Ex) DTN: Delay Tolerant Networks • Large data transmission • multi-hop transmission may not suitable for large data Goal: Large data transmission with low power consumption in Wireless Sensor Networks

4. Cooperative Buffering with Mobile Sinks • using neighbor node’s buffer • multiple nodes buffer the data cooperatively until the sink’s arrival→node’s power saving, large data buffering 2 Wireless sensor networks with large amount of delay-tolerant data • each nodes buffer their data • the size of a node’s buffer is limited → overflow • Related Works（wireless sensor networks with mobile sinks） • Data Mules [R. Shah, S. Roy, S. Jain, W. Brunette., IEEE Workshop on Sensor Network Protocols and Applications (SNPA), 2003]

5. 3.1 CB (Cooperative Buffering) • buffer the data with 1-hop neighbor nodes • the source node still have data・・・ • buffer the data with 2-hop neighbor nodes • sink collects their data node generates large amount of data （define as source node） sink data each node’s data transmission to the sink is 1hop

6. 3.2 Details of CB (1/2) <buffer division> • Saving region for data relay • Data relay regardless of the amount of buffering data <neighbor table> • node ID (node_ID) • hop count from a source node（HC: Hop Count） • remaining buffer level (RBL) • Total RBL of leaf node（L_RBL: Leaf RBL） If RBL = 0, then data relay start RBL (Remaining Buffer Level) buffer relay buffered data node’s buffer

7. 7 8 6 5 1 2 s 3 4 3.2 Details of CB (2/2) <selecting method of cooperative node> • ns→n3: DATA 1 ～ 50 • n3→ns: L_RBL = 20 • ns→n2: DATA 51 ～ 90 • n2 → ns : L_RBL = 0 • ns →n1: DATA 91 ～ 120 • n1 → ns : L_RBL = 60 • ns → n1 →n6: DATA 121 ～ 160 • ns → n1 →n5: DATA 161 ～ 180 • ns → n3 →n4: DATA 181 ～ 200 RBL: remaining buffer level L_RBL: total RBL of leaf node 40 20 40 30 50 20 assumption: data buffer region = 100

8. Problem S2 sends the data to distant node, needs more power 3.3 Multi-source CB (1/2) • Multiple neighbor source nodes • S2 starts data relay after S1 have finished CB The RBL of s1 , s2,n1 ,n2 ,n3 =0 n5 n2 n6 s2 s1 n3 source node n1 buffered node n4 vacant node

9. multiple buffer region 　→ acceptance of multi requests s2 3.3 Multi-source CB (2/2) • Solution • Dividing the buffer region into m buffer The division number of buffer regionm = 2 buffersource 2 buffersource 1 s1 n5 n2 transfer s2 s1 n3 The number of cooperative node increases as m increases n1 settings of m is very important n4

10. The relational expression of analyze the relation of C, D and 4.1 Evaluation 1 • Total power consumption： • Source node cooperate within h-hop neighbors • transmission power consumption • source node → cooperative nodes • cooperative nodes → mobile sink • receive power consumption of each nodes formulation

11. 4.2 Result 1 （the number of neighbor nodes: N = 5,transmission power consumption: Pt=12, receive power consumption: Pr=1.8） ※mote based C=1 h = 5 h = 4 h = 3 C=2 h = 2 h = 1 • total power consumption decreases as C increases • If C is big, the number of cooperative nodes decreases • According to D gets large, more power is required • source node needs to buffer data with far outer nodes C=5 D

12. 5.1 Evaluation 2 (1/2) • Computer Simulation • Performance metric：total power consumption • Simulation Parameters • MAC protocol：CSMA/CA 2way • Transmission rate： zigbee • Power consumption： mote • Data generation： CBR • Generation interval： 1(s)

13. 5.1 Evaluation 2 (2/2) • Simulation Environment • # of nodes: 36 • node’s transmission range：16m • topology: random node mobile sink • source node runs CBaccording to the amount of data • mobile sink arrives at the source nodeafter it has finished CB • cooperative nodes and the source nodesend data to a mobile sink directly • node’s buffer size： 512kB※mote • buffer region: 128 and 256 of 512kB

14. 128kB 256kB 5.2 Result 2 • CB’s power consumption lower than Multi-hop • CB can decrease message relays • The bigger buffer region leads to low power consumption • node has bigger buffer region can buffer more data

15. 6 Summary and Future Work • Summary • CB (Cooperative Buffering) with mobile sink • Performance evaluation • CB outperforms conventional Multi-hop data transmission in terms of the total power consumption • Bigger buffer region leads to lower power consumption • Future Work • CB in Sparse WSNs • Setting of the number of division of buffer region (m)

16. Thank you very much for your attention!!Yu Takada