Does repeating a data transmission constitute spreading?

  • Thread starter Thread starter Tybalt
  • Start date Start date
  • Tags Tags
    Data Transmission
AI Thread Summary
Repeating a data transmission can be seen as a form of spreading, as it utilizes more bandwidth than necessary for the signal. This is illustrated by TCP-IP's retransmission of packets upon receiving a NACK, which could be classified as a spreading scheme. In OFDM, interleaving data across subcarriers increases spectrum occupancy without changing total bandwidth, leading some to refer to this as spreading. Frequency-domain interleaving introduces repetition in the time domain, where the output of the IFFT can repeat based on the number of zeros inserted between data symbols. Understanding the distinction between spread spectrum techniques and data duplication in diversity schemes is crucial for clarity in this discussion.
Tybalt
Messages
5
Reaction score
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.
 
Engineering news on Phys.org
Thanks. This is helpful.
 

Thread 'Underwater piezoelectric sensor array receive sensitivity'

Hi all I have some confusion about piezoelectrical sensors combination. If i have three acoustic piezoelectrical sensors (with same receive sensitivity in dB ref V/1uPa) placed at specific distance, these sensors receive acoustic signal from a sound source placed at far field distance (Plane Wave) and from broadside. I receive output of these sensors through individual preamplifiers, add them through hardware like summer circuit adder or in software after digitization and in this way got an...
View full post »

Thread 'Following up on the recent thread about Earth Resistance measurements'

I have recently moved into a new (rather ancient) house and had a few trips of my Residual Current breaker. I dug out my old Socket tester which tell me the three pins are correct. But then the Red warning light tells me my socket(s) fail the loop test. I never had this before but my last house had an overhead supply with no Earth from the company. The tester said "get this checked" and the man said the (high but not ridiculous) earth resistance was acceptable. I stuck a new copper earth...
View full post »
Thread 'Electromagnet magnetic field issue'

Thread 'Electromagnet magnetic field issue'

Hi Guys We are a bunch a mechanical engineers trying to build a simple electromagnet. Our design is based on a very similar magnet. However, our version is about 10 times less magnetic and we are wondering why. Our coil has exactly same length, same number of layers and turns. What is possibly wrong? PIN and bracket are made of iron and are in electrical contact, exactly like the reference design. Any help will be appreciated. Thanks. edit: even same wire diameter and coil was wounded by a...
View full post »

Similar threads

MATLAB Is There a Missing 'rcpulse' Function in Your MATLAB Code?
Replies
1
Views
6K

Hot Threads

Recent Insights

Back
Top