MERLIN: A synergetic Integration of MAC and Routing for Distributed Sensor Networks A.G.Ruzzelli, M.J.O’Grady, R.Tynan, G.M.P.O’Hare. Adaptive Information Cluster project (AIC) Smart Media Institute (SMI) Department of Computer Science University College Dublin Ireland.

MERLIN: MAC and Routing Integration for WSNs by SAND project Summary Overview of WNSs and protocols Phase1: MERLIN design –Motivation and objectives –Fundamental concept –MAC details –Routing details Phase2: Simulation and results –Scheduling performance –Comparison against SMAC+ESR Conclusion

MERLIN: MAC and Routing Integration for WSNs by SAND project Overview of Wireless Sensor Networks Large number of tiny sensors (nodes) distributed in an area network; Sensor nodes: –have sensing devices attached; –are self-organizing; –are usually battery operated and of low cost hence power limited  multi-hop communication to save energy;

MERLIN: MAC and Routing Integration for WSNs by SAND project WSNs issues: Nodes must be cheap  Limited memory capabilities  Limited processing capabilities  Limited power capabilities  Maybe not very reliable Limited energy  Power consumption High node number  Scalability issues High dynamic condition  Reactivity and Self-organization Always on radio  node depletion in few days (e.g. Mobile phone) MAC issues Simultaneous msg to same device  Packet Collision Channel access delay Control packet overhead Multihop routing issues Route maintenance Overhead E-to-E latency Global addressing issue Only useful messages to deliver  In-network processing

MERLIN: MAC and Routing Integration for WSNs by SAND project Wireless sensor network architecture An example: Antenna Sensing devices Application Data aggregation Routing MAC Physical Sensing coverage Cross layer interaction Localization The most suitable network architecture for WSNs is still an open issue Each layer has its own task Any layer try to achieve the task using the smallest amount of energy possible Researchers are evaluating how to use the cross layer interaction at best

MERLIN: MAC and Routing Integration for WSNs by SAND project Mechanisms applied in Wireless Sensor Networks MACs: The CSMA/CA approach (Carrier sense multiple access with collision avoidance) A potential transmitter listen to the channel for a random time in a CW to sense any ongoing transmission in progress Channel assumed free  Transmit the packet with procedeure RTS/CTS/Data/ACK Channel busy  Transmission postponed then node switches off the radio Adv Flexible Dis High latency and idle listening node1 node2 node3 TX RTS CTS Contention Listen Preamble+Data ACK Sleep The TDMA approach (Time division multiple access) Time is divided into slots that are (in some way) assigned to neighbouring nodes ADV: collision free and energy efficient DIS: Low flexibility Random Time Tx Rx

MERLIN: MAC and Routing Integration for WSNs by SAND project Due to low duty cycle of WSNs, separate MAC and Routing layers cause an extremely high latency –(e.g. SMAC and DSR  tens of seconds delay for packets of nodes in hop 10 or more) Layer modularisation requires higher memory capability  Layer integration is beneficial Nodes are cheap and not reliable –failure, interference, depletion, mobility  Addressing a single node can result in high error probability Motivation for MERLIN

MERLIN: MAC and Routing Integration for WSNs by SAND project Objectives of MERLIN MAC+Routing integration features into a simple architecture; No usage of handshake mechanisms; No specific node addressing; Reduce latency while ensuring a very low energy consumption Controlled packet duplication to address sensor failure and bad channel condition;

MERLIN: MAC and Routing Integration for WSNs by SAND project What is the main IDEA behind the MERLIN protocol? Gateway Node Why Time Zones? Nodes with the same color are in the same time zone Nodes within the same subset belong to the same gateway Nodes within the same zone wake up and go into sleep simultaneously (European EYES project, NL)

MERLIN: MAC and Routing Integration for WSNs by SAND project Division of the network in timezones SYNC packets from the gateway are forwarded to further nodes. Every node sets its zone and forward the packet to more distant nodes.

MERLIN: MAC and Routing Integration for WSNs by SAND project 4-Zone V-scheduling table Nodes in the same timezone contend the slot for local broadcast only once each 4 frametimes

MERLIN: MAC and Routing Integration for WSNs by SAND project Data traffic Downstream multicast: Packets are transmitted to higher zones Local broadcast: Packets reach all neighbours. No forwarding is performed Upstream multicast: Packets are forwarded to smaller zones

MERLIN: MAC and Routing Integration for WSNs by SAND project Transmission Mechanism (I) The minimum wakeup concept through CCA Alternation of long period of inactivity to tiny period of channel assessment; The Clear Channel Assessment CCA is the shortest time period needed for nodes to sense any activity on the channel (~2.5msec in BMAC) Much shorter CCA period than time required for a control packet (e.g. 35msec for 5byte transmission with Tr1001) duty cycle reduced to less than 1% Ts Sleep period CCA Time

MERLIN: MAC and Routing Integration for WSNs by SAND project 2 questions: How can a Tx know when the Rx is awake? If not addressing a specific node (in multicast and broadcast), how can correct/incorrect receptions be notified?

MERLIN: MAC and Routing Integration for WSNs by SAND project Burst tone can help Properties –Are signal impulse  Do not contain any coded information –Are robusts  Several simultaneous burst can still be as one –They are shorter that a normal ACK Utilization Broadcast: Bursts identify reception errorsMulticast: Bursts identify correct receptions

MERLIN: MAC and Routing Integration for WSNs by SAND project Transmission Mechanism (II) Tx1 Tx2 Tx1

MERLIN: MAC and Routing Integration for WSNs by SAND project Disadvantages 1) MERLIN does not address a specific receiving node  multiple copy of the same msg sent can be generated   increase overhead! 2) Some collision due to the Hidden Terminal Problem (HTP) Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 A B Zone 3 A B ?

MERLIN: MAC and Routing Integration for WSNs by SAND project Routing characteristics (I) 3 small buffers of upstram, downstream and local broadcast are provided Packets organised in multiple msgs of the same data traffic type; Packets contain a msg-ID index of included msgs; Nodes, which lose the contention, keep on listening to the beginning of the transmitted packet then go into sleep; Nodes discard from their buffer the msgs already fowarded. Pro : Reduce overhead in transmission! Con : Small increase of node activity; Increase complexity. Channel contention messages Msg-index Discard msgs already forwarded from their queue P a c k e t Listen to the packet index Controlled multipath

MERLIN: MAC and Routing Integration for WSNs by SAND project Routing characteristics (II) Timezone maintenance Timezone update are sent periodically; Failed reception of timezone update from zone N-1 node to zone N node triggers a upstream multicast of Timezone Update request (TUR) –N-1 node/s reply  Connection reestablished N-1 failed  local broadcast TUR –At least one reply  change of zoen to N+1 N failed  downstream broadcast TUR TUR

MERLIN: MAC and Routing Integration for WSNs by SAND project Phase 2: Simulation and Comparison with two existing protocol architecture: SMAC (mac)+ ESR (routing)

MERLIN: MAC and Routing Integration for WSNs by SAND project Simulation and result Nodes with the same colors are in the same zone (same hop Count Number). Number slot /frame = 4 Contention period = 30ms DataRate = bits/sec DataSize = 16+8 Bytes (data + 3 bytes preamble + starting code) ParametersValues Energy Transmitting21 mW Energy Receiving14.4 mW Energy stand-by15 µW Switch time Tx/Rx518 µs Switch time Rx/Tx12 µs Switch stanby/Rx518 µs Switch stand-by/Tx15 µs Eyes node

MERLIN: MAC and Routing Integration for WSNs by SAND project V-scheduling Frametime (sec) Network Lifetime (days) V-Scheduling 1 Gateway 100 Nodes rand. Distributed. 800*500 area network Min signal strength(12 m) 50 msg/min sent by 5 rand. nodes Static network V scheduling Network lifetime. The network is considered to fail when 30% of nodes are depleted. Lifetime calculated for a linear depletion of 2 AA batteries. The network lifetime depends linearly on the frame length;

MERLIN: MAC and Routing Integration for WSNs by SAND project V scheduling setup time V scheduling can be setup in less than 10 seconds up to 250 nodes/100m^2 of network density.

MERLIN: MAC and Routing Integration for WSNs by SAND project End-to-end packet delay V-scheduling The controlled multiple path mechanism may cause a lower delay for nodes farther from the gateway; An increase of latency at the intersection of data traffic flows due to periodical stop of nodes activity that go into sleep. V-scheduling delay obtained for 2sec frametime length Frametime length should be based upon application requirements.

MERLIN: MAC and Routing Integration for WSNs by SAND project The SMAC protocol SMAC divides time in two periods: active time and sleeping time; Active period = SYNC period for node sync update, Request To Send (RTS), Clear to Send (CTS). Communication establishing: – neighboring nodes synchronize to the start of the active period then local broadcast of SYNC packets. Data message exchanges follow the RTS/CTS/DATA/ACK; –  nodes switch between different states periodically. RTS CTS Data Transmitter Receiver time ACK

SMAC Coordinated Sleeping sleep listen t1 t2 Timing relationship of packet Tx/Rx

MERLIN: MAC and Routing Integration for WSNs by SAND project Scenario and Setup Scenario 5 nodes two-hops 70 nodes Random multihop Metrics: Energy consumption per RX packet Network lifetime E-to-E latency Total packet overhead % sleeping time Parameters: Duty cycle (acting on CW and frametime size Low traffic conditions (12 packet/min) High traffic conditions (60 packet/min) Sources Forwarder Destinations

MERLIN: MAC and Routing Integration for WSNs by SAND project Low traffic 2-hops scenario

MERLIN: MAC and Routing Integration for WSNs by SAND project High traffic 2-hops scenario

MERLIN: MAC and Routing Integration for WSNs by SAND project Multihop scenario: Lifetime Note: These graphs have little relevance if not related to the EtoE latency

MERLIN: MAC and Routing Integration for WSNs by SAND project Multihop scenario: Latency/energy

MERLIN: MAC and Routing Integration for WSNs by SAND project Total packet overhead The MAC routing integrated nature MERLIN results in a smaller packet overhead than SMAC+ ESR.

MERLIN: MAC and Routing Integration for WSNs by SAND project Conclusion Description and simulated results of MERLIN have been presented; MERLIN is suitable for large scale sensor networks with energy consumption as main goal; MERLIN is suitable for communication to a from the gateway The multicast mechanism with burst ACK showed large improvement on the communication reliability The integrated nature, the absence of handshake mechanisms help reducing the EtoE packet delay EtoE delay can be traded-off for an longer network lifetime Results showed lifetime being extended by a factor of 2.5 of MERLIN with respect to SMAC

MERLIN: MAC and Routing Integration for WSNs by SAND project Thank you for your kind attention