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Does operating an 802.11a/b/g/n wireless access point in mixed mode decrease its effective range?

Posted on 2011-02-10
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I'm planning a wireless deployment for our small two-level nursing home.  I need to support our own laptops which all have 802.11n WLAN cards as well as visitor's laptops which will certainly include folks with 802.11b/g cards.

I'm presently considering deploying the HP MSM410 access point, which supports 802.11a/b/g/n. It has a single radio.

Will the presence of 802.11g devices decrease the effective range of my access points for N clients?  For example, suppose I assume I will only have Wireless-N clients and space my access points further apart to take advantage of 802.11n's increased range.  Then, someone with a 802.11g device connects to one of my APs.  Will that AP's range be decreased for all clients, including N?  Or will N clients experience the same coverage, and G devices experience coverage gaps between the APs (because they were spaced for N, not G)?

Or...does the increased range of 802.11n benefit 802.11b/g clients as well?
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Question by:TWAINdriver
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by:sharkbot221984
ID: 34867019
In short yes and no.  The 802.11 g/b will benefit from the greater range of the N device but not to the extent that an N receiving device would.  Think of b, b benefits from using a g router over a b only router, but you operate at only the 11 mbps limit of b, and are more likely to lose conneciton at a given distance than a g device.  Likely you would run into the G device running at slower speeds than an N device at the equivalent distance.  The further you get away from the signal source you may still have connection, but at reduced transmission speeds.  There are many factors that could influence the quality of the signal in your building, such as other devices operating at the 2.4/5GHz range that your access point will operate at (cordless phones, microwaves etc.)  Ideally a site survey should be conducted and that would tell you where you should place the access points for nominal coverage for both n/g devices.
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rfc1180 earned 250 total points
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>I'm presently considering deploying the HP MSM410 access point, which supports 802.11a/b/g/n. It has a single radio.

all of which have different modulation algorithms and more specifically technology (802.11n and MIMO). Using a single radio and 802.11g client will experience slower network performance connected to an 802.11b router than to an 802.11g router, this is a give as the connection is limited by the speed of the 802.11b router; however, when both 802.11b and 802.11g clients are connected to an 802.11g router, the performance of the 802.11g clients can suffer. In the worst case, all 802.11g clients will slow down to have the same network speed as the 802.11b clients (Using the same modulation for the link). This is the same for other 802.11 standards clients. If you want a solid, dependable wifi network, use all the same clients.

Billy
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by:TWAINdriver
ID: 34909592
Please forgive my brief abscense.  Thanks for the responses so far.

Both of your comments indicate that, at the least, b/g clients will 1) Experience a slower connection speed as their distance from the AP increases, and 2) Their presence may negatively affect the connection speed of N devices using the same AP.

sharkbot221984> The 802.11 g/b will benefit from the greater range of the N device but not to the extent that an N receiving device would.

If I understand correctly, you're saying that: 1) b/g devices should maintain a link further from an N access point than they would from a G-only AP, and that 2) Nevertheless, N devices will maintain a link at even greater distances than G devices (perhaps, assuming only N-clients are present).  Are my interpretations correct?

rfc1180> In the worst case, all 802.11g clients will slow down to have the same network speed as the 802.11b clients (Using the same modulation for the link).

Would an AP with dual radios solve this problem, assuming I can restrict b/g clients to one radio and N clients to the other?

I do intend to perform a site survey, but am just trying to have an idea of what my AP placement might need to look like before I get into this.
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by:rfc1180
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>Would an AP with dual radios solve this problem, assuming I can restrict b/g clients to one radio and N clients to the other?


Correct, Radio A: 802.11b, Radio B 802.11g; However, if you can afford it, avoid 802.11b at all costs. Use OFDM (802.11g). If you however have clients that have only 802.11b, then there is not much you can do, if the user base is low, disable 802.11b and force 802.11g and upgrade the clients have have 802.11b only cards; also, yes, you can do 802.11n as well; 802.11b/g on Radio A, and 802.11n on Radio B.

Also, just a little 2 cents on the 802.11n range, it does not increase by much to have a significant change. 802.11n still uses 2.4Ghz or 5.8Ghz; 802.11 uses a wider bandwidth spacing (40Mhz), spatial diversity to allow the performance to increase to 300Mbps and limited exposure to multipath fading which gives you a little bit more range, but again, not that you will notice.

Billy
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by:TWAINdriver
ID: 34910118
rfc1180> Also, just a little 2 cents on the 802.11n range, it does not increase by much to have a significant change. 802.11n still uses 2.4Ghz or 5.8Ghz; 802.11 uses a wider bandwidth spacing (40Mhz), spatial diversity to allow the performance to increase to 300Mbps and limited exposure to multipath fading which gives you a little bit more range, but again, not that you will notice.

So you're saying, even in a N-only environment, the useable range of the AP isn't all that much better than a G environment?  If so, that's pretty significant to me.  My primary need is range, not throughput as I have a few users with low bandwidth requirements spread out over a large area.
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by:rfc1180
ID: 34910192
> My primary need is range, not throughput as I have a few users with low bandwidth requirements spread out over a large area.

Correct, it is still the same output power, gain of the antennas and frequency; you get a little better range based on the spatial diversity, MIMO, and other factors/variables. Nothing you will notice, it is a marketing term that is over exaggerated.

Billy
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by:sharkbot221984
sharkbot221984 earned 250 total points
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I have noticed better performance from a G client with an N router over a G only router at the same distance - nothing that blew my mind, maybe 20% increase at best (and not sustained)  Enough to somewhat satisfy my needs and enough to not justify converting the G client to N as well.

Depending on the AP you choose, and it's firmware abilities (or ability to flash with better firmware) you could futz around with booting output power, swapping out different antennae, or you could just build to G range expectations with N equipment and have good cell overlap so you don't wind up with any dead zones.
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by:TWAINdriver
ID: 34910761
You both have been a tremendous help.  Thank you.
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by:rfc1180
ID: 34911014
>maybe 20% increase at best (and not sustained)
yeah, it will vary depending on the individual; what I think is not much increase maybe different from another engineer. This also is also considering the vendor, make, and model of choice, RF environment, etc.

Good Luck
Billy
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by:TWAINdriver
ID: 34911181
Understood.  Clearly the wireless survey is the best (and only) way to know for sure what to expect out of one's environment.
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by:rfc1180
ID: 34911243
absolutely!
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