Protocols for Self-Organization of a Wireless Sensor Network K. Sohrabi, J. Gao, V. Ailawadhi, and G. J. Pottie IEEE Personal Comm., Oct Presented By: earl

Introduction Self-Organization Wireless Sensor Network --wireless sensing + data networking Group of sensors (nodes) linked by wireless medium to perform distributed sensing tasks. Example: surveillance, security, health monitoring systems, etc

Goals Operate under dynamic condition: startup, steady state, failure operate unattended Energy-efficiency

Wireless Sensor Node

Design Challenges Hardware: digital circuit design Wireless networking: modulation, channel access, robust & energy efficient protocols, routing, mobility etc. Applications: detection and data collection, data diffusion, notification

Main difference Conventional Wireless Networks High QoS (high throughput/low delay) & High bandwidth efficiency Sensor Network Length of network ’ s lifetime need to conserve energy Performance highly depends on energy efficiency of algorithms

Energy-Conserving Energy consumptions: Sensing Data processing Communications Communications is the major energy consumer Therefore, local processing is key

ORM concept O -Organization of nodes to access shared medium  network formation R -Routing in the network M -Mobility management

Protocols Self-Organization Medium Access Control for Sensor Networks (SMACS) Network startup and link layer Eavesdrop-And-Register (EAR) Algorithm Seamless interconnection of mobile nodes in the field of stationary wireless nodes (mobility management) Sequential Assignment Routing (SAR) Facilitates multi-hop routing Single Winner Election (SWE) and Multi-Winner Election (MWE) Facilitates local cooperative information processing

SMACS Protocol Used for network startup and link-layer organization Forms a flat topology

SMACS Protocol SMACS Operation Discover neighbors Assign a channel to a links between neighboring nodes  Channel (time slot) = pair of time intervals (transmission/reception pattern)  Each link operates on a different frequency (which is randomly chosen)  Only local knowledge  quick  energy saving Node turns on/off communication according to its timeslots a e b d c f g h i

SMACS Protocol Node topology

SMACS Protocol

Type1: invitation [to B 、 G] (node’s id and number of attached neighbors) Type2: response to Type1 [from B 、 G] (inviter and invitee’ addresses and invitee’s attached state)

SMACS Protocol Type3: response to Type2 to notify chosen node [to B] Inviter not attached : none Inviter, invitee, attached : inviter’s schedule and frame epoch Invitee not attached, inviter attached: proposed channel for the link, calculated by inviter

SMACS Protocol Type4: response to Type3 [from B] Invitee not attached, inviter not attached: channel determined by the invitee Invitee not attached, inviter attached: none Invitee attached, inviter not attached: channel determined by the invitee

EAR Protocol The Ear algorithm ’ s motivation Designed to provide continuous communication capability between mobile and stationary nodes Mobile nodes join stationary wireless nodes Mobile node is “eavesdropping” on control signals Both side keep a “registry” of neighbors’ information

EAR Protocol EAR algorithm Broadcast Invite (BI):  The stationary node invites other nodes to join Mobile Invite (MI):  The mobile responds to BI to request a connection Mobile Response (MR):  The stationary node accepts the MI response Mobile Disconnect (MD):  The mobile informs the stationary response is needed node of a disconnect; no BI triggers EAR BI:{SNR, node ID, Tx Power,…} If MI info. possible, assign slot in TDMA frame Connect and disconnect thresholds stationary node mobile node BI [MI/MD] MR

Mobile nodes have the onus to manage connections/disconnections with stationary nodes based on the received signal-to-noise (SNR) ratio Connection and disconnection thresholds determine connectivity: Connection Threshold (CT) : minimum level where connectivity is enabled (SNR > CT) Disconnection Threshold (DT) : maximum level of connectivity (SNR < DT) EAR Protocol

EAR is an adaptable protocol that allows stationary and mobile nodes to self-organize and establish connectivity Mobile Connectivity List: [ SNR > CT ] MI Message MR MessageBI Message MOBILE EAR Protocol

SAR Protocol Supports multi-hop routing Route must be robust to failure It takes into consideration the energy resource and QoS on each path

SAR for Multi-hop routing Failure Protection Creates multiple trees where the root of each tree is a one-hop neighbor from the sink sink Consider power,QoS Backup route

SWE & MWE Protocols Handle signaling and data transfer in local cooperative signal processing: Noncoherent Processing  SWE Coherent Processing  MWE Elect Central Node (CN) for sophisticated information processing Sufficient energy reserve, computational capability, high SNR

Noncoherent Cooperative Function No need for path optimality 3-Phase process: Phase I: Target detection, data collection, and preprocessing Phase II: Membership declaration Phase III: Central node election

CN Election 2 components SWE algorithm —handle signaling for candidate information “Elecmessage”  Each node can announce itself as a CN candidate  Compare information, keep record of 1 best candidate  Disseminate information throughout the network Spanning Tree (ST) algorithm —compute a min- hop ST rooted at the CN

Multi-Winner Election (SWE) Process

Coherent Cooperative Function Differ from noncoherent algorithm Explicit computation of minimum energy path: Path optimality for energy efficiency Limited number of sensor source nodes (SNs) MWE Select SNs Calculate minimum energy paths from sensor node to each SN Use SWE to select CN from minimum energy consumption

Single Winner Election (SWE) Process

Simulation Network of 45 randomly scattered nodes having a density of 0.04 nodes/m 2 1mW transmit power, T frame = 8.0s

Simulation

Conclusion Wireless Sensor Network Protocols Low mobility, enough BW, energy-constrained Self-Organization Medium Access Control for Sensor Networks (SMACS) Eavesdrop-And-Register (EAR) Algorithm Sequential Assignment Routing (SAR) Single Winner Election (SWE) and Multi-Winner Election (MWE) Future work Determine Min energy bound for network formation Higher mobility