Ed Driscoll


USS CLUELESS TRANSMITTING INSTRUCTIONS TO UNKNOWN ENEMY IN SECRET CODE: What else to make of a post that includes paragraphs such as:

So there’s users Alice and Betty and Charlie. Alice’s Walsh code is 11110000. Betty’s is 11001100. Charlie’s is 10101010. 11110000 xor 11110000 is all zeros, a match. But 11110000 xor 11001100 is 00111100, and 11110000 xor 10101010 is 01011010. In each case, half ones and half zeros. (The pattern of 1’s and 0’s doesn’t matter, as you’ll see. What’s important is how many of each there are.)

Alice’s receiver runs an accumulator, and it adds for each match (each 0) and subtracts for each non-match (each 1). This requires us to differentiate between chips and bits. A chip is part of a bit. The cell system sends chips at a rate of 1.2288 MHz, but it takes a lot of chips to transmit one bit. Each chip contains a little piece of the information about each bit (hence the name). Right now in most CDMA systems the bit rate per phone is only 9600 per second in voice calls; the rest run 14400 per second. So there are a huge number of chips per bit.

And I’m sure the model playing Lara Croft that’s posted further down on the same page has some secret microfilm hidden on her somewhere