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

1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [MAC Improvements in IEEE 802.15.4] Date Submitted: [11 November 2004] Source: [Sung-Woo Park, Jae-Young Kim, Sang-Sung Choi] Company [ETRI] Address [161 Gajeong-Dong, Yuseong-Gu, Taejon, 305-350, Korea] Voice:[+82 42 860-4921], FAX: [+82 42 860-5218], E-Mail:[{swp64160, jyk, sschoi}@etri.re.kr] Re: [Response to the call for proposal of IEEE 802.15.4b] Abstract: [This document proposes improvements to the IEEE 802.15.4 MAC.] Purpose: [This document is submitted for consideration for revisions to the 802.15.4 specification.] 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. S. W. Park, J. Y. Kim, and S. S. Choi, ETRI

2. MAC Improvements in IEEE 802.15.4 Sung-Woo Park, Jae-Young Kim, and Sang-Sung Choi ETRI S. W. Park, J. Y. Kim, and S. S. Choi, ETRI

3. Problem Statement • The rate of packet collision can be severely affected by the variety of network conditions such as • Hidden terminals • Duty cycle • Packet size • Traffic pattern/load • Network topology etc. • The current backoff procedure in CSMA-CA does not satisfactorily consider the adverse effects of packet collisions • aMaxBE & aMaxFrameRetries are fixed • Only default values are specified for macMinBE & macMaxCSMABackoffs • By adjusting the backoff parameters dynamically to the changing network situations, performance improvements at the MAC sublayer areexpected • The proposed solution in comment #1 cannot deal with packet transmissions with no ACK requested S. W. Park, J. Y. Kim, and S. S. Choi, ETRI

4. Suggested Solution • Allow each device to change macMinBE at every beacon interval based on the collision status obtained from the PAN coordinator • Define one unused bit in the superframe specification field of a BEACON frame as the “collision” bit to indicate the occurrence of packet collision • The PAN coordinator determines whether packet collisions occur excessively and, if so, reports to the devices via the collision bit • Upon receiving the BEACON frame, devices may increment or decrement macMinBE over the predefined range depending on the collision status S. W. Park, J. Y. Kim, and S. S. Choi, ETRI

5. Usage Example PAN coordinator Step 1: measure the collision ratio CR = no. of collision pkts / no. of received pkts Step 2: if CR exceeds TH_COL set the collision bit to one else set the collision bit to zero Step 3: send out the BEACON frame Device Step 1: check the collision bit in a BEACON frame Step 2: if “1” appears consecutively more than TH_INC times increment macMinBE by one else if “0” appears consecutively more than TH_DEC times decrement macMinBE by one else do nothing S. W. Park, J. Y. Kim, and S. S. Choi, ETRI

6. TR1 TR2 TR15 TR3 TR14 TR4 TR13 TR5 TR12 PAN Coordinator TR11 TR6 TR10 TR7 TR9 TR8 Simulations (1) • Data rate: 250 kbps • Topology • Star with PAN coordinator+15 terminals • Transmission range • Case 1: no hidden terminals exist • Case 2: hidden terminals exist maximally • Duty cycle: 1/128 (<1%) • SO: 0~7/BO: 7~14 • Traffic source • Type: CBR • Packet size: 50 bytes • Generation rate • Case 1: 50 bps/terminal • Case 2: 30 bps/terminal • Backoff parameters • Fixed BE • aMaxBE: 5, 7, 9, 11 • macMinBE = aMaxBE – 2 • Adaptive BE • TH_COL = 0.05 • TH_INC = TH_DEC = 2 • aMinBE=3/aMaxBE=11 S. W. Park, J. Y. Kim, and S. S. Choi, ETRI

7. Simulations (2) Case 1: without hidden terminals Case 2: with hidden terminals • We observe that the CSMA-CA algorithm with the adaptive BE shows constantly better performance than any others with the fixed BE over the wide range of superframe order S. W. Park, J. Y. Kim, and S. S. Choi, ETRI