Standard IEEE 802.15.4 define two different operation modes : beacon-enabled networks and non-beacon networks. in this paper, the authors propose a priority based scheduling mechanism to implement the beacon-enabled devices. The authors focus on the design and implementation part, as well as performance evaluation in areal case, not in the simulation result.
Superframe Structure :
an IEEE 802.15.4 network which adopts superframe architecture is called a beacon-enabled network, otherwise, it is a non-beacon network. In a beacon-enabled network, beacons are transmitted periodically as the synchronization signals. Superframe period is the period between two successive beacons. it is controlled by Superframe Order(SO) and Beacon Order(BO). SO determine Superframe Duration(SD) , BO determines the Beacon Interval (BI).
SO and BO must be integer with valid range from 0 to 14, and the SO must be smaller than or equal to BO. The value of constant aBaseSuperframeDuration is 960 (symbols).
from this paper, We can find explanation more detail about The superframe structure and relationship between CAP,CFP,SD, BI packet format of a beacon frame and data transfer model.
There are several important things when designing an IEEE 802.15.4 beacon-enabled network device :
– Because of the precision timing requirement, it must be very responsive at any time.
– The integrity of our MAC layer with other possible upper protocol layers must be handled with care.
– Traditional embedded systems use an infinite polling loop in the main thread for handling various input events. The author use MOS (Mini Operating System) design to prevent the MAC processing from being blocked by other processes.
The RX mechanism :
RX mechanism is the end device’s responsibility to receive and parse the periodical beacon frame.
The TX mechanism :
this mechanism is implemented only in the coordinators since only coordinators can transmit beacons.
System Implementation :
The author use CC2420 DBK from chipson. they evaluate the influence of SO on packet transmissions and the influence of preamble on active periods.
With SO between 0 and 14, it can be shown that when SO is less than 3, they can hardly transmit any packets, but after that, the number of transmitting packets increases dramatically.
Design and Implementation of IEEE 802.15.4 Beacon-enabled Network Devices
Li-Chun Ko et all. Institute for Information Industry, ROC.
Note : This resume is created for self-learning only. Author and Publisher hold copyrights
Strive for independence February 11 2008,
High Speed Network Lab