He means "twenty faculty", ie. 
.
n! happens to be the number of permutations of n distinct
objects, and this is my guess where he got that from; however,
(00000000001111111111) doesn't contain 20 distinct objects, e.g.
swapping the first two 0s doesn't change the vector.
This is nice "morning sports":
we've got twenty "places" where we can put in our ten 1s; the rest would be filled with 0s.
Hence, we've got to choose distinct 10-element subsets (places we
put a 1) from a 20-element tuple (index set). From 20 choose 10:
So you've got 184,756 twenty-bit sequences with as many 1s as 0s.
Best regards,
Marcus
On 16.07.2016 06:32, Henry Barton
wrote:
I know of Gold codes. I was curious as to whether there was an easier way to mass-produce spreading codes, but I guess not.
BTW, Johannes, what did you mean by “20!”
Good start point might be Gold code or Hadaramd code.
Dne 15.7.2016 v 09:24 Johannes Demel napsal(a):
> 20!
>
> On 15.07.2016 04:54, Henry Barton wrote:
>> I’m designing a CDMA system with a spreading factor of 20. I recently
>> wrote an app to go through all the binary permutations up to 2^20 and
>> report which ones have an equal number of 0’s and 1’s, or at least
>> differ by only one. It came up with so many “hits” that I have to wonder
>> if they're really orthogonal. Does anyone know offhand how many good
>> spreading codes I can realistically expect from 1048576 possible entries?
>>
>>
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