# symbol periods

Discussion in 'Wireless & RF Design' started by jlatshaw, Nov 24, 2014.

1. ### jlatshaw Thread Starter New Member

Jul 20, 2013
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0
Hi,
I was reading this article about Zigbee, and I noticed a lot of mentions about symbols and symbol periods. My question is, how do symbols relate to packets of information?

Also, do you know how many bits of information are typically sent over the course of a packet/ symbol?

Thanks,
James

2. ### Papabravo Expert

Feb 24, 2006
10,338
1,850
Good question. Boolean logic uses two symbols, referred to as HIGH and LOW, ON and OFF, or '1' and '0'. A binary, or two valued logic system is not the only one possible. In a three valued logic system you might use the symbols '0', '2', and '4' as the do in the 802.4 standard. The information content of a three values system is log to the base 2 of 3. To figure out what Zigbee is doing you will have to dig deeper.

3. ### jlatshaw Thread Starter New Member

Jul 20, 2013
28
0
So basically, one symbol is equal to one bit of information?

On the table on that article, I see that it says:
aBaseSlotDuration 60 symbol periods

Does this mean that a packet is 60 symbols long?

And is a packet the same as a super frame?

Thank you so much,
James

4. ### Papabravo Expert

Feb 24, 2006
10,338
1,850
Not necessarily. One symbol can encode multiple bits. One symbol equals one bit ONLY for a system with two unique symbols. If there a 64 uniques symbols the the information content is 6 bits per symbol. Get the idea?

5. ### jlatshaw Thread Starter New Member

Jul 20, 2013
28
0
Ok, yes that does make sense. Alright, so I think I might understand it now. Back to the table on that webpage, I see there's a mention of:
PHY acknowledgement frame length 11 octets
PHY beacon frame length 23--100 octets
PHY data frame length 15--133 octets

I believe that an octet is a group of 6 bits, so this would imply that the actual packet (or super frame) is 11+100+133 octets or 1.464 kb in length. Am I right about this?
And if this is all true, then I would just have 11+100+133=244 symbols per packet, right?

Thank you so much for your time,
James

6. ### jlatshaw Thread Starter New Member

Jul 20, 2013
28
0
Sorry, I just realized an octet is 8 bits. So instead of 1.464kb I meant 1.952 kb.