Does repeating a data transmission constitute spreading?

  • #1
Tybalt
5
1
TL;DR Summary
This is a question about defining spread spectrum. It seems that spreading should involve more than just repeating data symbols.
Generally, spread spectrum is defined as using more spectrum (or bandwidth) than is needed to transmit a signal. But according to this definition, even TCP-IP would be a spreading scheme because it retransmits packets upon receiving a NACK. In OFDM, if you interleave data across the subcarriers instead of using a contiguous block of subcarriers, you increase the spectrum occupancy, but the total bandwidth (= number of subcarriers x subcarrier bandwidth) is the same. Some people call this spreading. Interleaving involves inserting zeros between data symbols that are operated upon by the IFFT, so this frequency-domain interleaving causes repetition in the time domain, i.e., the output of the IFFT repeats Z times, where Z is the number of zeros you insert between the data symbols.
 
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  • #3
Thanks. This is helpful.
 

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