1. Performance Evaluation of IEEE 802. 15
Performance Evaluation of IEEE MAC for Low Rate Low Power Wireless networks
Gang Lu
Bhaskar Krishnamachari
Cauligi S. Raghavendra
Department of Electrical Engineering-Systems
April 9, 2004

2. Outline Overview of IEEE 802.15.4TM/ZigBeeTM Physical Layer MAC Layer
Super frame Structure
CSMA and polling
GTS in CFP
Synchronization
Simulation
April 9, 2004

3. 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
A new MAC for LR-WPAN
IEEE : an “overkill technology”
Bluetooth: high data rate for multimedia applications, small size network, high power consumption
April 9, 2004

4. Features of IEEE
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

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

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

7. PHY Features Rx 19.7mA Tx Power feature of CC2420
Both PHYs are based on DSSS
2.4GHz PHY provides 250kbps
868/915 MHz PHY provides 20kbps and 40kbps respectively
Sensitivity: -85dBm for 2.4GHz and -92dBm for 868/915MHz
Range: 10-20m Rx
19.7mA Tx
P=-25dBm 8.5mA
P=-15dBm 9.9mA
P=-10dBm 11mA
P=-5dBm 14mA
P=0dBm 17,4mA
From ``Home Networking with IEEE : A Developing Standard for Low-Rate Wireless Personal Area Networks", Ed Callaway, Paul Gorday and Lance Hester, IEEE Communications Magazine Aug. 2002
April 9, 2004

8. MAC: Super frame Beacon Mode: Beaconless 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

9. 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 provides a “Battery Life Extension” (BLE) mode which limited the backoff exponent to 0-2.
Reduced the idle listening period
April 9, 2004

10. 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

11. 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

12. Simulation Only evaluate the beacon mode on star topology
Radio parameters in table 1
7X7 grid with 49 node
4m distance between adjacent node
CBR traffic with 50% randomization
April 9, 2004

13. CSMA-CA
April 9, 2004

14. Duty Cycle-Energy
April 9, 2004

15. GTS in CFP
April 9, 2004

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

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

18. 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