In all the detail on DSSS and OFDM, I have missed which characterics of DSSS and OFDM make these distinct technologies. Nothing I've read appears to contrast the two.
As I understand it, both DSSS and OFDM are intended to send many bits in parallel. DSSS spreads data across a channel for redundancy, and the books say that bits are sent in parallel. OFDM divides a channel into "subcarriers" and likewise sends bits in parallel. This might suggest the main difference between the two, that DSSS somehow sends data in parallel on a single carrier, whereas OFDM accomplishes this with multiple carriers. Either way, both take up more bandwidth than 1 signal, so I don't get how they're much different.
What should a network engineer know, about how DSSS and OFDM are fundamentally different from each other?
Update: According to the current CWNA book, OFDM is not a spread spectrum technology.
Best Answer
From what I've gathered, the primary differentiation between DSSS and OFDM comes in a congested or constrained RF environment. Because DSSS is transmitting as many bits as possible all at once, it runs the risk of having some of the transmission disrupted in transit should the RF become less than ideal. In contrast, OFDM sacrifices a bit of performance to transmit the data in those multiple carrier "packets" that allow for reassembly or retransmission in the event of a failure.
If I use an extra-large semi truck to haul freight, it works well so long as the highway doesn't have any obstructions (like narrow lanes or short overpasses). If I break my freight up into a greater number of smaller trucks, I can ensure that some of the freight arrives even if conditions (like a traffic jam) prevent the entire shipment from arriving.