Early versions had a fairly fatal flaw. They responded to bad reception (reception but failure of checksum etc due to interference) by 'downshifting' e.g. reducing their transmission rate from 10Mbit to lower rates.
This seems rational, but in practice it usually shifted all the way to the minimum (1Mbps!) and got no relief. In fact, packets were 10 to 100 times 'longer' in airtime, congesting the channel so nobody got anything through.
Why did they get no relief? Because frequently the noise was bursty e.g. microwave oven pulse or auto spark plug noise. Going slower meant larger (longer to transmit) packets, which provided a 'bigger target' for the noise to poke a hole in.
A more useful response was to try the fastest rate, a smaller packet which got hit with fewer 'darts' impacting any particular packet.
bri3d•1h ago
This is a very good text and regarded as one of the greats for a reason, but it glosses over a lot of lower concepts (like OFDM, which if I recall occupies only a single short chapter) and focuses very heavily on MIMO. Proakis and Salehi ("Digital Communications") and Goldsmith ("Wireless Communications") cover some of the "lower level" concepts like OFDM pretty well in depth from a theory standpoint. Goldsmith is a particularly good middle ground book. A highly underrated book is also Andreas Schwarzinger's "Digital Signal Processing in Modern Communication Systems", which covers how modems for these systems are actually implemented in real life and is quite approachable from an engineering standpoint.
JoeAltmaier•1h ago
Early versions had a fairly fatal flaw. They responded to bad reception (reception but failure of checksum etc due to interference) by 'downshifting' e.g. reducing their transmission rate from 10Mbit to lower rates.
This seems rational, but in practice it usually shifted all the way to the minimum (1Mbps!) and got no relief. In fact, packets were 10 to 100 times 'longer' in airtime, congesting the channel so nobody got anything through.
Why did they get no relief? Because frequently the noise was bursty e.g. microwave oven pulse or auto spark plug noise. Going slower meant larger (longer to transmit) packets, which provided a 'bigger target' for the noise to poke a hole in.
A more useful response was to try the fastest rate, a smaller packet which got hit with fewer 'darts' impacting any particular packet.