In IEEE 802.15.4 (zigbee), how to divide bits efficiently, for example: I have 2000bits in one frame, i want to transmit this bits by dividing, for an efficient communication, (for eg: 1:4 ratio, 2000/4=500bits), but i want to know whether any technique or methods is exist to do it in efficient way.
Good question,
What is the optimum length of the useful data frame?
Looking on the relation between bit error rate (BER), packet error rate (PER) and frame length (N) PER=1-(1-BER)^N we can see that PER has an exponential increase by frame length (N). It is usually checked the integrity of whole frame and the erroneous frame is discarded, so we can draw the conclusion that the low frame length is the best choice.
But, every layer from OSI stack adds some packing bits that lead to spectral efficiency decrease. Looking on the UWB PPDU encoding process (Figure 84/802.15.4) it is obvious that the most of the PHY frame is used for frame packing (Reed-Solomon encoding, Convolutional encoding, Spreading, SHR Preamble) so the conclusion is that the high PSDU length is the best choice. (But, we do not forget that RS and convolutional encoding and spreading increase the SNR of the frame).
If you are going to work inside standards you do not have to take care of frame fragmentation. The 802.15.4 standard specifies 127 bytes as the PSDU length (PHY service data unit). The MAC layer checks frame integrity, over whole MAC frame including PSDU by FCS and discard erroneous frames. So: You can send to 802.15.4 MAC layer maximum 127 PSDU bytes. (Unfortunately a part of this bytes are used for the data fragmentation). The ZigBee standard stipulates the data fragmentation on application layer (more exactly in the APS), that specifications it is not very clear for me. The 6LoPan protocol specifies Maximum Transmission Unit (MTU) at 1280 bytes and RFC4944 specifies data fragmentation in order to send it to 802.15.4 MAC layer.
PHY Packet Fields
Preamble (32 bits) – synchronization
Start of Packet Delimiter (8 bits)
PHY Header (8 bits) – PSDU length
PSDU (0 to 1016 bits) – Data field
For details
http://www.cs.berkeley.edu/~prabal/teaching/cs294-11-f05/slides/day21.pdf
For Sukhwinder Singh Sran,
Did you read 802.15.4 standard? Where you did find1016 bits Data field?
@loan Domuta, Reference
http://www.cs.berkeley.edu/~prabal/teaching/cs294-11-f05/slides/day21.pdf
@Sukhwinder, 127 bytes x 8 bits = 1016 bits; the standard specifies bytes, and I have not done before this calculation.
Thank you for valuable answers but still i didn't get perfect answer, l'm looking for formula's...like, for example (eg:- 2000bits/4 frame =500bit's)... this example shows that, by dividing a 2000 bits into 4 frame, this may be a efficient way to split a total packet. i just said for example, can you please tell me i this way...
Ioan Domuta - Thank you i understand but do we have any exciting protocol to this method (to Splitting Frame).
https://www.google.si/patents/US7096274
https://pdfs.semanticscholar.org/ea91/2a561137854aea9cdee72e8ac286f4a38096.pdf
http://www.iis.sinica.edu.tw/JISE/2007/200705_14.pdf
http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=665076&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D665076
http://www.wi-fiplanet.com/tutorials/article.php/1468331/Improving-WLAN-Performance-with-Fragmentation.htm
etc.
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