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thinkpad - Laptop wireless networking options: 1x1 vs 2x2


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



Answer



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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