Data Fragmentation Scheme in IEEE 802.15.4 Wireless Sensor Networks

Data Fragmentation Scheme in IEEE 802.15.4 Wireless Sensor Networks

Reference :

Data Fragmentation Scheme in IEEE 802.15.4. Wireless Sensor Networks.
Jongwon Yoon, Hyogon Kim and Jeong-Gil Ko
Korean University.

The IEEE 802.15.4 Medium Access Control (MAC) protocol is designed for low data rate, short distance and low power
communication applications such as Wireless Sensor Networks (WSN).
In the standard 802.15.4 MAC, if the remaining number of backoff periods in the current superframe are not enough to
complete data transmission procedure, the sensor nodes hold the transmission untuil the next superframe.
When two or more sensor nodes hold data transmission and restart the transmission procesure simultaneously in the
next superframe, it cause a collision of data packets and waste of the channel utilization.


In this paper, the authors propose a data fragmentation scheme to increase channel utilization and avoid inevitable collision.
WSN are ideal for applications such as security systems, emvironmental monitoring, industrial automation,etc.
The IEEE 802.15.4 MAC standard wastes the number of backoff periods at the end of a superframe. This is because typical data frame is too large to be transmitted during the small number of remaining backoff periods. This causes inevitable collision and waste of channel utilization. The authors propose to fragment large data frames into smaller frames to transmit in small number of backoff periods that are not being used.

IEEE 802.15.4 MAC :
https://alkautsarpens.wordpress.com/2008/01/28/superframe-structure-2/
The IEEE 802.15.4 WSNs consist of sensor device nodes and a controlling coordinator. THe coordinator manages all
device nodes and handles the superframe structure. The superframe is bounded by the transmission of a beacon frames
and have active and inactive portions.

The active portion consists of a contention access period (CAP), where the sensor nodes aqually access the channel
using contention, and a optional contention free period (CFP). The length of superframe is controlled by the value of beacon order (BO) and the length of CAP is represented by superframe order (SO). The values of BO and SO are determined by the coordinator.

Channel detection in 802.15.4 is based on CSMA-CA procedure. The CSMA-CA algorithm is used before the transmission of data or MAC command frames transmitted within the CAP. The backoff in processed within CSMA-CA. The initial value is given as macMinBE and the system randomly selects a backoff time from a number between [0::2^BE – 1]. After the random backoff, the remaining CSMA-CA can be undertaken and the data transmission can be performed until the end of the CAP.
fig2_datafragmen.jpg

Inevitable Collision :
in some cases two or more sensor nodes proceed CCA procedure simultaneouly at the start of a new superframe, due to
the shortage of the remaining backoff periods in the CAP from the previous superframe. These nodes perform CCA in the same time, therefor all nodes detected the channel is idle. This causes the nodes to transmit data at the same time, leading to an evitable collision.

Waste Channel Utilization :
When the remaining number of backoff periods in the CAP are not enough to proceed CCA and the transmission of data
frames, the channel remains idle because the sensor nodes wait for the next superframe.

Data Fragmentation Scheme :
The fragmentation scheme divides the data to fit into the remaining number of backoff periods in the CAP of a superframe.By fitting the data into the remaing number of backoff periods in the CAP, the authors can avoid the inevitable collision.
fig3_datafragalgorithm.jpg

Simulation Experiment :
The authors evaluate the performance of data fragmentation scheme compared to the legacy of IEEE 802.15.4. The
authors present the simulation results for the collision probability and aggregate throughput under the two different aMaxBE values (5 and 7).

Reference :
Data Fragmentation Scheme in IEEE 802.15.4. Wireless Sensor Networks.
Jongwon Yoon, Hyogon Kim and Jeong-Gil Ko
Korean University.

Note : This resume is created for self-learning only. Author and Publisher hold copyrights

[Paper Predator Mode ON]

February 03 2008,
Taipei City
High Speed Network Lab

Udin Harun

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