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I am currently customizing a Lenovo Thinkpad.

Under the section "Integrated WiFi wireless LAN adapters" there are two options.

Default: ThinkPad 1x1 b/g/n
Upgraded: ThinkPad 2x2 a/b/g/n (+$10 AUD)

What does the 1x1 and 2x2 mean?

For reference, here is the link. 5th option from the bottom. Customize Lenovo Thinkpad

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3 Answers 3

up vote 22 down vote accepted

That's a no-brainer. Pay the +$10 AUD and get the 2x2 a/b/g/n. It can move data at up to twice the speed of the "1x1 b/g/n" solution, and it supports the much larger, less congested 5GHz frequency band, making it less likely to interfere with (or receive interference from) all the other uses of the 2.4GHz band.

1x1 and 2x2 refer to the number of transmit and receive radio chains built into the Wi-Fi card. 2x2 means it has two transmit and two receive radio chains, and usually implies that it supports 2 "spacial streams", which is a key way that 802.11n is faster than the previous generation of Wi-Fi technologies. 802.11n is the first standard in the 802.11 family to support MIMO (pronounced "MY-moh"), which stands for "Multiple Inputs, Multiple Outputs", which is basically a way of ganging together multiple radios to get faster data rates than you can get with a single radio on each end of the connection. Because it's possible to create a wireless card with 2 transmit and 2 receive radio chains but still not do real 2 spacial stream MIMO, some people in the industry now use the notation TxR:S, where T is the number of Transmit radio chains, R is the number of Receive radio chains, and S is the number of supported "spacial streams".

Because MIMO was the raison d'être for 802.11n, when the first N gear hit the market in 2007, it was all 2x2:2, which means it can support up to 300 megabit per second data rates when used with 40MHz-wide channels.

Unfortunately, within the last year or so, some companies have been being cheap, and, in my opinion, a bit deceptive, and selling 1x1:1 radios as 802.11n. Technically they do support a few of the slowest 802.11n-style modulation schemes, but since they only have a single transmit and receive radio, they aren't MIMO, and 802.11n without MIMO is like a BLT without bacon.

The maximum data rate a 1x1:1 radio can get is 150 megabits per second, and that's when using a 40MHz-wide channel (sometimes called simply a "wide channel", because before 802.11n, all standard 802.11 channels were never wider than about 20 or 22MHz). Wide channels are fine in the 5GHz band which is a much larger band with a lot more channels and a lot less congestion than the old 2.4GHz band. But in the 2.4GHz band, using wide channels can cause problems because it takes up like two-thirds of the entire band, leaving very little room for things like Bluetooth and neighboring 802.11 networks. Unfortunately, that 1x1 solution is only b/g/n and doesn't say "a", which implies it ONLY supports the small, congested 2.4GHz band.

The 2x2 solution says it supports "a" (802.11a), which only worked in the 5GHz band, which means that radio is 5GHz capable. Since it also lists b and g, you know it's 2.4GHz capable. Also, because it's almost certainly a 2x2:2, it can almost certainly use signaling rates up to 300 megabits per second.

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Please tell me how type of WiFi adapter is related to antennas count? Internal (MiniPCI, MiniPCI-E) b/g adapters usually have 2 antennas connectors, sometimes - 1. Internal b/g/n - 3 antennas connectors. Occasionally n adapters comes with only two antennas. I've checked that usually best connection gives cards with 3 plugs and based on Atheros chips. P.S. +1 for good, comprehensive answer. Thanks. –  George Gaál Aug 16 '11 at 10:56
    
thank you for explaining everything. I did opt for the 2x2. I just completed the order. –  Valamas Aug 16 '11 at 11:49
    
@George that would probably be a good choice for a separate Question, but in short: Even with a single radio, you can have a "main" and an "auxilliary" antenna, to provide "antenna diversity"; in case the main antenna is not in a good place to receive a certain signal, maybe the aux antenna can receive it. MIMO systems are less likely to employ antenna diversity on top of MIMO, so they usually only have one antenna per radio chain, but I've seen designs that have a main and an aux for each radio chain. –  Spiff Aug 16 '11 at 20:54
    
What is “BLT”? _ –  Robert Siemer Mar 27 at 12:51
    
@Robert That was a poor attempt at a humorous analogy. A BLT is a super delicious Bacon, Lettuce, and Tomato sandwich, which is a very popular sandwich in the US. The star of the show is the bacon. –  Spiff Mar 27 at 14:32
  1. There is difference in supported standards. I'm really not sure if you need 802.11a. It is old and obsolete WiFi. Oldest standard I commonly find around is 802.11b
  2. 2x2 says about MIMO configuration. Usually it better is to have 2x2 configuration than 1x1 or 1x2.
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-1 for misinformation. 802.11a actually hit the market 3 years later than 802.11b and provided ~5x the performance, and a less cluttered frequency band. –  Spiff Aug 16 '11 at 5:51
    
@Spiff, I've checked you are right. But 802.11a isn't commonly used anyway. –  George Gaál Aug 16 '11 at 10:50
1  
Actually 802.11a is used all the time by 5GHz N clients as fallback when they get too far away from the AP to sustain N rates, but are still close enough for A rates. And since support for A signifies support for 5GHz, it's definitely something to look for and pay extra for when buying N gear. –  Spiff Aug 16 '11 at 20:51

It refers to the number of wireless antennae - wireless n supports 1,2 or 4. 2x2 means it can send and receive on two antennae at once, and in general can take advantage of MIMO

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-1 for misinformation. Antennas are passive hunks of metal; they don't improve the data rate other than passively improving SNR. You can add a dozen antennas to a radio and you still won't get an higher throughput than the maximum modulation scheme the radio is capable of. The magic of MIMO (and N), is in the number of additional radio chains, not just antennas. Also, 802.11n can do 3 ins and outs too. All the 450mbps N stuff that's come out in the last 18 months is 3x3:3. The 802.11n spec supports up to 4x4:4, but no one is shipping a radio that supports 4 spacial streams yet. –  Spiff Aug 16 '11 at 5:57
    
hm. citation required - in my case wikipedia - which is what i quoted says maximum number of transmit antennas or RF chains in addition for mimo it says is the use of multiple antennas at both the transmitter and receiver to improve communication performance. –  Journeyman Geek Aug 16 '11 at 6:34
    
Talking about the antennas and not the radio chains is like saying coax splitters are what allow you to watch more CATV channels simultaneously. The splitters themselves aren't what makes it happen; you have to hook them up to additional tuners and displays. Same thing with antennas and radio chains (RF chains). Adding a second antenna doesn't do much for you unless you add a second radio chain to transmit/receive a separate data stream on the second antenna. –  Spiff Aug 16 '11 at 7:53
    
If you still need a citation that there are 1-4 radio chains involved, I'll cite the primary source, the standard itself: IEEE 802.11n-2009, Clause 20.3.3, figure 20-2, "Transmitter block diagram". Also 20.3.4 steps "p" through "s". You can download the spec for free here: standards.ieee.org/getieee802/download/802.11n-2009.pdf (You have to select something from the pop-up menu at the bottom of the page and hit "Accept" before the download begins.) –  Spiff Aug 16 '11 at 7:58
    
in which case, since you have a better answer, and its obviously too long to be comments, feel free to post it as such. –  Journeyman Geek Aug 16 '11 at 9:26

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