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Difference between revisions of "Mesh/Spectrum"
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Using a frequency analyzer or software-defined radio with a wide frequency range, it's possible to scan the actual frequency usage across the entire range of interest. Elonics 4000 can scan from 64 mhz to 2.2 ghz and only costs about $25. | Using a frequency analyzer or software-defined radio with a wide frequency range, it's possible to scan the actual frequency usage across the entire range of interest. Elonics 4000 can scan from 64 mhz to 2.2 ghz and only costs about $25. | ||
= OpenWRT setup = | |||
== 5 GHz == | |||
Here are some reasonable settings for a point to point or point to multi-point 5 GHz rooftop node: | |||
<pre> | |||
channel 149 | |||
hwmode 11na | |||
htmode HT40 | |||
chanbw 20 | |||
txpower | |||
</pre> | |||
The ath9k driver does not yet have support for a 802.11n-only mode (also known as greenfield). The closest is 802.11n+a. Apparently you can prevent 802.11a nodes from associating somehow. [http://comments.gmane.org/gmane.linux.drivers.ath9k.devel/10735 source]. | |||
I'm not sure how to set the guard interval. The default is likely 800 ns, which we may want to lower for shorter links or heighten for longer links. | |||
= Hardware capabilities = | |||
== 5 GHz == | |||
Data rates for various settings can be looked up in [http://en.wikipedia.org/wiki/IEEE_802.11n-2009#Data_rates this table]. | |||
=== Nanostation M5 === | |||
Assuming 40 MHz channel and 800 ns guard interval: | |||
<pre> | |||
Setting | Speed | Modulation | Tx power | Rx sensitivity | | |||
------------------------------------------------------------------------ | |||
MCS12 | 162 Mbit/sec | 16-QAM | 22 dBm / 157 mW | -84 dBm | | |||
MCS13 | 216 Mbit/sec | 64-QAM | 20 dBm / 100 mW | -79 dBm | | |||
MCS14 | 243 Mbit/sec | 64-QAM | 18 dBm / 63 mW | -78 dBm | | |||
MCS15 | 270 Mbit/sec | 64-QAM | 17 dBm / 50 mW | -75 dBm | | |||
</pre> | |||