Performance Evaluation of IEEE 802 15 4 MAC

Performance Evaluation of IEEE 802. 15. 4 MAC for Low Rate Low Power Wireless networks Gang Lu Bhaskar Krishnamachari Cauligi S. Raghavendra Department of Electrical Engineering-Systems April 9, 2004 http: //ceng. usc. edu/~anrg/ 1

Outline • Overview of IEEE 802. 15. 4 TM/Zig. Bee. TM • Physical Layer • MAC Layer – – Super frame Structure CSMA and polling GTS in CFP Synchronization • Simulation April 9, 2004 2

Introduction to LR-WPAN • Low-Rate Low-Power Wireless Networks – – – Wireless sensor networks Industrial Control and Monitoring Environmental and Health Monitoring Home Automation, Entertainment and Toys Security, Location and Asset Tracking Emergency and Disaster Response • IEEE 802. 15. 4 – A new MAC for LR-WPAN – IEEE 802. 11: an “overkill technology” – Bluetooth: high data rate for multimedia applications, small size network, high power consumption April 9, 2004 3

Features of IEEE 802. 15. 4 • 16 channels in the 2450 MHz band, 10 channels in the 915 MHz band, and 1 channel in the 868 MHz band • Over-the-air data rates of 250 kb/s, 40 kb/s, and 20 kb/s • Star or peer-to-peer operation • Allocated 16 bit short or 64 bit extended addresses • Allocation of guaranteed time slots (GTSs) • Carrier sense multiple access with collision avoidance (CSMA-CA) channel access • Fully acknowledged protocol for transfer reliability • Low power consumption • Energy detection (ED) • Link quality indication (LQI) April 9, 2004 4

Network Topologies IEEE 802. 11 only describes the MAC and PHY layer. Upper layers are designed by Zig. Bee which has not be released. April 9, 2004 From ``Home Networking with IEEE 802. 15. 4: A Developing Standard for Low-Rate Wireless Personal Area Networks", Ed Callaway, Paul Gorday and Lance Hester, IEEE Communications Magazine Aug. 2002 5

PHY: Channel Structure From ``Home Networking with IEEE 802. 15. 4: A Developing Standard for Low-Rate Wireless Personal Area Networks", Ed Callaway, Paul Gorday and Lance Hester, IEEE April 9, 2004 Communications Magazine Aug. 2002 6

PHY Features Power feature of CC 2420 Rx Tx April 9, 2004 19. 7 m. A P=-25 d. Bm 8. 5 m. A P=-15 d. Bm 9. 9 m. A P=-10 d. Bm 11 m. A P=-5 d. Bm 14 m. A P=0 d. Bm 17, 4 m. A • • • Both PHYs are based on DSSS 2. 4 GHz PHY provides 250 kbps 868/915 MHz PHY provides 20 kbps and 40 kbps respectively Sensitivity: -85 d. Bm for 2. 4 GHz and -92 d. Bm for 868/915 MHz Range: 10 -20 m From ``Home Networking with IEEE 802. 15. 4: A Developing Standard for Low-Rate Wireless Personal Area Networks", Ed Callaway, Paul Gorday and Lance Hester, IEEE Communications Magazine Aug. 2002 7

MAC: Super frame • Beacon Mode: – – – • PAN coordinator broadcasts a beacon which tells the superframe structure CAP: Contention Access Period CFP: Contention Free Period GTS: Guaranteed Time Slot Turn off radio in inactive period to save energy Beaconless mode – Just CSMA-CA April 9, 2004 8

Collision Access Period • Transaction – either the coordinator needs to indicate in its beacon when messages are pending for devices – or the devices themselves need to poll the coordinator to determine whether they have any messages pending. • CSMA-CA – Power consumption during the backoff period – IEEE 802. 15. 4 provides a “Battery Life Extension” (BLE) mode which limited the backoff exponent to 0 -2. – Reduced the idle listening period April 9, 2004 9

GTS in CFP • A device can request dedicated bandwidth to achieve low latency • Used only for communication between PAN coordinator and devices • PAN coordinator maintain and assign the GTS slots used by devices • A device enables its radio at a time prior to the start of the GTS and transmit during GTS without CSMA-CA April 9, 2004 10

Synchronization • PAN coordinator transmits beacon frames periodically to announce the superframe structure • A device need to know the superframe before any data transmission • Synchronization methods: – Tracking • Enable its radio periodically to receive the beacon – Non-tracking • Enable its radio when necessary and search for the next beacon April 9, 2004 11

Simulation • Only evaluate the beacon mode on star topology • Radio parameters in table 1 • 7 X 7 grid with 49 node • 4 m distance between adjacent node • CBR traffic with 50% randomization April 9, 2004 12

CSMA-CA April 9, 2004 13

Duty Cycle-Energy April 9, 2004 14

GTS in CFP April 9, 2004 15

Synchronization Tracking April 9, 2004 Non-tracking Tracking: Enable radio periodically to receive the beacon Non-tracking: Enable radio when necessary and search for the next beacon 16

Synchronization Crossover curve April 9, 2004 Analysis & Simulation result 17

Conclusion • An overview of IEEE 802. 15. 4 • Evaluation of MAC – CSMA-CA in CAP – Energy Latency Tradeoff of Duty Cycle – Energy Latency Tradeoff of GTS in CFP – Tradeoff between tracking and non-tracking synchronization • Plan to make NS-2 model available online April 9, 2004 18