Maybe not that much.
Maybe a lot.
It depends on the implementation.
802.11n defines a series of “High Throughput” options nearly all of which are optional.
You could almost take an 802.11g card, write 802.11n on the box and sell it.
Even if you did bother to implement these options, you were allowed to do a crappy job and if you detected even one 802.11g device in the area operating on or near your channel, even if it was not part of your network then you were required to turn most of the options off to avoid interfering with the old equipment.
The best thing in 802.11n was the ability to operate at 5 GHz.
If two devices implemented that then they could be sure of not encountering any 802.11g devices which only operated at 2.4GHz so they wouldn’t have to disable other optional things.
Also, the 5 GHz band happens to be much wider so more systems can avoid interfering with each other simply by choosing different channels.
One option for 802.11n was to use a 40 MHz bandwidth, up from 20 MHz in 802.11g.
That may sound faster but in practice it is often slower.
The reason is that bandwidth is not the same as data rate.
In theory you could achieve any data rate with any bandwidth as long as you use enough power.
But the FCC rules say that you have the same maximum total amount of power you can transmit whether you’re using 20, 40, 80 or a 160 MHz of bandwidth (the last two being added with 802.11 ac).
802.11n says, you have to implement the possibility of using 40 MHz bandwidth if you also have more than one antenna.
But you can just have one antenna and in that case, you don’t have to offer 40 MHz or anything else that doesn’t amount to software changes.
And, of course, stupid little cheap USB dongles only have 1 antenna and mostly didn’t change their hardware at all.
With each new standard there’s more aggressive Modulation and Coding Schemes.
This means that for the given power and bandwidth you can try to send more symbols at the same time.
Think of a computer that represents 0 as -1V and 1 as +1V.
You could use the same average power and define 0,1,2 and 3, as -1.5, -0.5, +0.5 and 1.5V.
But it would be harder to accurately transmit and detect all of those levels and if there was some noise disturbing the signal then no amount of accuracy in your transmitter and receiver would allow you to do it and you’d have to drop back to the older, slower scheme.
This is what happens in practice with Wifi.
You may get 1Gbps if your router and laptop are on the same table, but good luck if you are in the next room.
Each new standard gives you the option to use more antennas.
Again, with the limits on power.
If you have four antennas then each can transmit 1/4 the power a box with 1 antenna is allowed to transmit on it’s one antenna.
You can do some very clever things to direct the beam with 4 antennas or to send different signals on them and this can help your range or throughput.
Again, in theory.
It’s tricky in practice.
Each new standard lets you reduce your overhead by sending larger runs of data before asking for acknowledgement from the other side and by wasting less time on each bit.
You’re probably getting tired of hearing this, but if there’s interference, this tactic just makes things worse.
Now you have to wait longer and waste more bits when your transmission is interrupted which it’s more likely to be because it takes longer.
And the shorter times between bits means that a previous symbol still bouncing around the room may clobber your current symbol.
Having said all that, technology does get better and in general a newer box will have more range and throughput than an older one.
The maximum data rates set by the standards are theoretical and increasingly optimistic.
The quality of the implementation on both ends must be very high to even approach purported speeds.
And you must be lucky enough to operate in a low-noise environment even still.
I’m using the best equipment available, expertly tweaked and getting about 70 Mbps to a router two rooms away behind two walls.
Do your own testing.
If you can beat me, have a cookie.
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