Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Wireless Mesh Personal Area Networks] Date Submitted: [28 February, 2007] Source: [Inhwan Lee (1), Sungrae Cho (2), Wonsuk Choi (2), Seongjae Kwon (2), Laihyuk Park (2), and Bong Soo, Kim (1))] Company [ETRI (1), School of Computer Science and Engineering, Chung-Ang University (2)] Address [221 Heukseok, Dongjak, Seoul 156-756, Republic of Korea] Voice:[+82-2-820-5766], FAX: [+82-2-820-5766], E-Mail:[ihlee@etri.re.kr] Re: [IEEE P802.15.5 WPAN MESH Networking Call for Additional Contributions dated on July, 2006 at IEEE P802.15-06-0333-04-0005] Abstract: [This document is a summary of the proposed Timer-based Reliable Broadcast (TRB) for WPAN mesh networks.] Purpose: [A response to the call for additional contributions.] Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15. <Inwhan Lee>, <ETRI>

Timer-based Reliable Broadcasting Scheme for LR-WPAN Mesh MAC Inhwan Lee (1), Sungrae Cho (2), Wonsuk Choi (2), Seongjae Kwon (2), Laihyuk Park (2), and Bongsoo Kim (1) (1) ETRI (2) Chung-Ang University <Inwhan Lee>, <ETRI>

Contents • Introduction • Motivation • Timer-based Reliable Broadcast (TRB) for LR-WPAN Mesh MAC • Scheme 1 • Scheme 2 • Performance Evaluation • Summary <Inwhan Lee>, <ETRI>

INTRODUCTION • Broadcast is necessary for disseminating data for various reasons, e.g., sensor network query dissemination, S/W updates at mesh nodes, hello messages conveying important routing info, etc. • Threat: Current spec. does not have an acknowledgement for broadcast data. • Reliability should be guaranteed in some or most cases in broadcasting. → Reliable Broadcast <Inwhan Lee>, <ETRI>

MOTIVATION (1/2) • Suppose that Transmitter broadcast a data frame and Receivers respond with their feedback (with ACK or NAK) for broadcast data, e.g., • The receiver nodes will contend to access the channel almost at the same time which will increase collision rate in the reverse direction of the broadcasting data. <Inwhan Lee>, <ETRI>

MOTIVATION (2/2) • The collision problem also causes the problems of Unnecessary Power Consumption • Solution: De-synchronize the acknowledgements (Randomization) • Timer-based Reliable Broadcast (TRB): Our solution uses a timer for acknowledgement at each receiver <Inwhan Lee>, <ETRI>

TRB Scheme 1 Scheme 2 <Inwhan Lee>, <ETRI>

Scheme 1 • Proposed in 15-06-0480-00-0005-timer-based-reliable-broadcast-wpan-mesh-networks.ppt • Idea: limit the number of feedbacks (ACK/NAK) from the receiver. • Only few of NAKs or ACKs are enough to let Tx do the appropriate behavior. <Inwhan Lee>, <ETRI>

Error NAK timer ACK timer Scheme 1 • Receiver Behavior (after receiving broadcast data) • When a node receives a broadcast data, it delays its acknowledgement by a random timer described below: • If the received data is erroneous, the node activates a NAK timer. • If the received data is OK, the node activates an ACK timer. • If NAK timer expires, the node unicastsits NAK back to the Tx • If ACK timer expires, the node broadcasts the data piggybacked by ACK to the Tx and its children. <Inwhan Lee>, <ETRI>

αD (NAK Period) (1-α)D (ACK Period) D Broadcast Data Received Scheme 1 • NAK timer is generated at random in range of [0, αD] while ACK timer is generated at random in range of [αD, D]. • Shorter timer for NAK causes early rebroadcast of the original data to fix errors. • Longer timer for ACK is for the case that all nodes successfully received the data. <Inwhan Lee>, <ETRI>

Broadcast Rebroadcast Scheme 1 • Receiver Behavior (after receiving rebroadcast data) • The receiver node cancels its timer (NAK or ACK). • This will reduce unnecessary feedbacks to the transmitter. • Based on the result of error detection/correction, the receiver uses NAK/ACK timer as in the previous slide. • This series of procedure will continue up to predefined number of times. • Overall behavior will look like as the following for an example: Tx ACK NAKs NAK Rx’s Many of receivers will suppress their timer <Inwhan Lee>, <ETRI>

Scheme 1 • Transmitter Behavior (when it has broadcast data): • If it has a data to send, it broadcasts the data and sets its timer D. • If timer D expires before receiving feedback (ACK/NAK), it retransmits the original data as above. • Once the transmitter receives a NAK, it rebroadcasts its data to fix the error, and sets its timer D. • When an ACK received, the transmitter transmits its next broadcast data if any, and sets its timer D. <Inwhan Lee>, <ETRI>

Scheme 1 • TxCount = 1 Level N-1 A B C D Level N Level N+1 E F G H I J K L Level N+2 <Inwhan Lee>, <ETRI>

Scheme 1 • TxCount = 2 Level N-1 A B C D Level N Level N+1 E F NAK G H I J K L Level N+2 <Inwhan Lee>, <ETRI>

Scheme 1 • TxCount = 4 Level N-1 A B C D Level N ACK Level N+1 E F G H I J K L Level N+2 <Inwhan Lee>, <ETRI>

Scheme 1 • TxCount = 5 Level N-1 A B C D Level N NAK Level N+1 E F G H I J K L Level N+2 <Inwhan Lee>, <ETRI>

Scheme 1 • TxCount = 7 Level N-1 A ACK B C D Level N Level N+1 E F G H I J K L Level N+2 <Inwhan Lee>, <ETRI>

Scheme 1 • TxCount = 8 Level N-1 A NAK B C D Level N Level N+1 E F G H I J K L Level N+2 <Inwhan Lee>, <ETRI>

Scheme 1 • TxCount = 11 Level N-1 A ACK B C D Level N Level N+1 E F G H I J K L Level N+2 <Inwhan Lee>, <ETRI>

Scheme 1 • TxCount = 12 Level N-1 A B C D Level N Level N+1 E F ACK G H I J K L Level N+2 <Inwhan Lee>, <ETRI>

Scheme 2 • Receiver Behavior • On successful receipt of broadcast data, each receiver acts as a transmitter by broadcasting the data using random timer DR. • The data consists of • Original data, • ACK, and • and Recipient Address of the ACK. • If the broadcast data’s ACK recipient address = receiver’s address, the receiver do nothing. • OW, receivers do nothing, i.e., NO NAK in this scheme!! <Inwhan Lee>, <ETRI>

Scheme 2 • Transmitter Behavior • Transmitter broadcasts data and waits for DT which. • Transmitter maintains a Bit Mapindicating whether it received an ACK from a particular one-hop neighbor derived from the connectivity matrix. • If the Bit Maps are all set (Tx received all ACKs) before DT expires, the transmitter broadcasts the next data. • If any of the Bit Maps are not set after DT expires, the transmitter rebroadcasts the data. <Inwhan Lee>, <ETRI>

Performance Evaluation(1) SimulationsSetup • Results • -- 10 nodes • -- 20 nodes • -- 30 nodes • -- 40 nodes • -- 50 nodes <Inwhan Lee>, <ETRI>

Performance Evaluation (2) Experimental setup • Simulation platform: NS2 + LR-WPAN • # of nodes: Variable • Neighbor distance:7 m ~ 11m • Tx range:12 m • PAN Coordinator (PC):bottom node (or any designated node) • Network startup: • PC starts at:0.0 • Any other node starts at:random time between 1.0 and 3.0 • Packet error rate : 10% <Inwhan Lee>, <ETRI>

Performance Evaluation (3) 10 nodes : Reliable Broadcasting Parent ID [18] 25 Node ID PAN Coordinator Node having associated and being leaf node Node having associated and being coordinator <Inwhan Lee>, <ETRI>

# of Transmissions per node Scheme 2 Scheme 1 <Inwhan Lee>, <ETRI>

Success Tx Ratio Scheme 2 Scheme 1 <Inwhan Lee>, <ETRI>

Summary • Scheme 1 • Better energy efficiency, but errors • Scheme 2 • No failure, but more energy consumption • We can choose either of them depending upon desirable level of reliability or energy efficiency • OR • One solution consisting of both capabilities and adapting its capability <Inwhan Lee>, <ETRI>

This work has been supported partially by HNRC of IITA. <Inwhan Lee>, <ETRI>

Thank You! <Inwhan Lee>, <ETRI>

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)