Beacon frame is one of the management frames in IEEE 802.15.4 based WSNs and contains all the information about the network.

A coordinator in a PAN can optionally bound its channel time using a SuperFrame structure which is bound by beacon frames and can have an active portion and an inactive portion. The coordinator enters a low-power (sleep) mode during the inactive portion.


The structure of this SuperFrame is described by the values of macBeaconOrder and macSuperframeOrder. The MAC PIB attribute macBeaconOrder, describes the interval at which the coordinator shall transmit its beacon frames. The value of macBeaconOrder, BO, and the beacon interval, BI, are related as follows:


For 0 ≤ BO ≤ 14, BI = aBaseSuperframeDuration * 2BO symbols.


If BO = 15, the coordinator shall not transmit beacon frames except when requested to do so, such as on receipt of a beacon request command. The value of macSuperframeOrder, SO shall be ignored if BO = 15.

An example of a SuperFrame structure is shown in following Figure.


                                                                                                        Fig: An example of the Super Frame structure

Theoretical Analysis:

From the above SuperFrame structure,

If SuperFrame Order (SO) is same as Beacon Order (BO) then there will be no inactive period and the entire SuperFrame can be used for packet transmissions.

If BO=10, SO=9 half of the SuperFrame is inactive and so only half of SuperFrame duration is available for packet transmission. If BO=10, SO=8 then (3/4)th of the SuperFrame is inactive and so nodes have only (1/4)th of the SuperFrame time for transmitting packets and so we expect throughput to approximately drop by half of the throughput obtained when SO=9.


Percentage of inactive and active periods in SuperFrame for different SuperFrame Orders is given below:


Beacon Order (BO)
SuperFrame Order (SO)
Active part ofSuperFrame(%)
Inactive part of SuperFrame (%)
Throughput estimated (%)
10
10
100
0
> 200% of T
10
9
50
50
Say T = 20.18
(Got from simulation)
10
8
25
75
50 % T
10
7
12.5
87.5
25 % T
10
6
6.25
93.75
12.5 % of T
10
5
3.125
96.875
6.25 % of T
10
4
1.5625
98.4375
3.12% of T
10
3
0.78125
99.21875
1.56 % of T


You can expect throughput to vary in the active part of the SuperFrame as sensors can transmit a packet only in the active portion.