1. doc.: IEEE 15-04-0618-00-004b Submission Nov. 2004 S. W. Park, J. Y. Kim, and S. S. Choi, ETRISlide 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.

2. doc.: IEEE 15-04-0618-00-004b Submission Nov. 2004 S. W. Park, J. Y. Kim, and S. S. Choi, ETRISlide 2 MAC Improvements in IEEE 802.15.4 Sung-Woo Park, Jae-Young Kim, and Sang-Sung Choi ETRI

3. doc.: IEEE 15-04-0618-00-004b Submission Nov. 2004 S. W. Park, J. Y. Kim, and S. S. Choi, ETRISlide 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 are expected –The proposed solution in comment #1 cannot deal with packet transmissions with no ACK requested

4. doc.: IEEE 15-04-0618-00-004b Submission Nov. 2004 S. W. Park, J. Y. Kim, and S. S. Choi, ETRISlide 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

5. doc.: IEEE 15-04-0618-00-004b Submission Nov. 2004 S. W. Park, J. Y. Kim, and S. S. Choi, ETRISlide 5 Usage Example 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 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 PAN coordinator Device

6. doc.: IEEE 15-04-0618-00-004b Submission Nov. 2004 S. W. Park, J. Y. Kim, and S. S. Choi, ETRISlide 6 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 TR5 TR9TR8 TR1 TR2 TR3 TR4 TR6 TR12 TR11 TR10 TR7 TR14 TR13 TR15 PAN Coordinator

7. doc.: IEEE 15-04-0618-00-004b Submission Nov. 2004 S. W. Park, J. Y. Kim, and S. S. Choi, ETRISlide 7 Simulations (2) 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 Case 1: without hidden terminalsCase 2: with hidden terminals