How to change your drone's Wi-Fi channel

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How to change your drone's Wi-Fi channel

Post by ShellDude » 27 Dec 2013, 07:44

AR.Pro can change the channel of your drone's Wi-Fi network. This is useful when the default drone channel is in use by other networks. The below video demonstrates how it works.


Direct link: http://www.youtube.com/v/woIqop1faq8

Wifi Analyzer is cool (free) Google Play app you can use to monitor wireless networks in your vicinity.

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Re: How to change your drone's Wi-Fi channel

Post by garrock » 27 Dec 2013, 16:04

Too bad the AR Drone cannot report what it sees as WiFi channel-traffic along with RSSI's.
That too could then become warning information to the pilot; avoid loosing link.
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Re: How to change your drone's Wi-Fi channel

Post by ShellDude » 27 Dec 2013, 17:20

It would require a little bit of work (and bandwidth) but certainly doable.

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Re: How to change your drone's Wi-Fi channel

Post by VAdroneflier » 28 Dec 2013, 15:30

By conducting tests in a room shielded from all external WiFi signal sources except for those from my own equipment, I found that the ARDrone2 apparently surveys the WiFi environment at power-up and always selects channel 1 in the absence of any competing signal sources. If channel one is already in use (and no others), then the drone picks channel 2. If more than one channel is already in use, the drone picks a remaining open channel if any exist.

Out in the wild where many uncontrolled signal sources may exist simultaneously in the flying area, WiFi Analyzer shows that the drone tends to pick the least cluttered channel at power-up. However, having selected its preferred operating channel, the drone does not later jump to a more open or unused channel if/when competing signals suddenly appear on the chosen channel. In other words, the drone does NOT engage in a frequency hopping strategy like modern 2.4 gHz radios and receivers do to maintain interference-free command links. That is unfortunate. Parrot engineers and firmware programmers could have easily provided that capability if they had chosen to do so.

Can you, as a competing flight control program author/developer, implement an automated WiFi channel hopping capability?

If so, that would be much better than simply providing an initial manual channel selection capability which does not protect against competing signal sources that suddenly appear during flight.

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Re: How to change your drone's Wi-Fi channel

Post by garrock » 28 Dec 2013, 16:22

VAdroneflier wrote:... at power-up and always selects channel 1 in the absence of any competing signal sources. If channel one is already in use (and no others), then the drone picks channel 2. If more than one channel is already in use, the drone picks a remaining open channel if any exist.
That is interesting... perhaps Parrot made a change. Previously, the drone chose Channel 6 first, If it sensed too much traffic there then it blindly chose Channel 1.
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Re: How to change your drone's Wi-Fi channel

Post by pawelsky » 28 Dec 2013, 16:38

garrock wrote:
VAdroneflier wrote:... at power-up and always selects channel 1 in the absence of any competing signal sources. If channel one is already in use (and no others), then the drone picks channel 2. If more than one channel is already in use, the drone picks a remaining open channel if any exist.
That is interesting... perhaps Parrot made a change. Previously, the drone chose Channel 6 first, If it sensed too much traffic there then it blindly chose Channel 1.
I don't think that was a rule to chose 6 first, but based on the wifi setup script the only allowed channels were 1 and 6

Code: Select all

RANDOM_CHAN=auto
[...]
# Allowing ACS to select only channels 1 & 6
wmiconfig -i $NETIF --acsdisablehichannels 1
iwconfig $NETIF channel $RANDOM_CHAN
iwconfig $NETIF rate auto
iwconfig $NETIF commit
So VAdroneflier's finding looks interesting indeed

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Re: How to change your drone's Wi-Fi channel

Post by ShellDude » 28 Dec 2013, 18:53

I could fairly easily upload an execute a deamon based script, yes. With a couple hooks I could also provide a UI showing current channel and neighbors.

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Re: How to change your drone's Wi-Fi channel

Post by baadabing » 29 Dec 2013, 03:06

garrock wrote:Too bad the AR Drone cannot report what it sees as WiFi channel-traffic along with RSSI's.
That too could then become warning information to the pilot; avoid loosing link.
Yes, a smarter, more powerful and focused wifi access point on the drone might do the trick. Have you seen any wifi mod that don't need to be soldered to the motherboard?

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Re: How to change your drone's Wi-Fi channel

Post by garrock » 29 Dec 2013, 16:53

baadabing wrote:... Have you seen any wifi mod that don't need to be soldered to the motherboard?
I have not seen anything worth noting.

The weakest link is the drones WiFi transmit power (its ability to send downlink information). Not so much its ability to receive (its receiver circuit receive sensitivity specified in dB).

This setup gets me out to a Kilometer (3280 feet) and back: the above setup also with an External Antenna mod on the drone.
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Re: How to change your drone's Wi-Fi channel

Post by pawelsky » 29 Dec 2013, 18:11

baadabing wrote:
garrock wrote:Too bad the AR Drone cannot report what it sees as WiFi channel-traffic along with RSSI's.
That too could then become warning information to the pilot; avoid loosing link.
Yes, a smarter, more powerful and focused wifi access point on the drone might do the trick. Have you seen any wifi mod that don't need to be soldered to the motherboard?
Every repeater (small enough for AR.Drone to carry) will not require soldering.

I've been playing witn TP-LINK MR3020 and I've been getting stronger signal than from Drone itself. Did not fly with it, only tested indoors.

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Re: How to change your drone's Wi-Fi channel

Post by ShellDude » 29 Dec 2013, 18:13

Enclosed is the simplicity of the wifi channel change command:

Code: Select all

iwconfig ath0 channel %d commit
Here's its man page:

http://www.linuxcommand.org/man_pages/iwconfig8.html" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

Unfortunately I'm coming up empty doing any kind of scan at the moment:

Code: Select all

# iwlist ath0 scan
ath0      Interface doesn't support scanning : Operation not supported

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Re: How to change your drone's Wi-Fi channel

Post by ShellDude » 29 Dec 2013, 19:21

A couple more updates:

The atheros adapter will NOT scan for neighboring networks in infrastructure (AP) mode. There is a channelselector binary that is used but it ALWAYS goes to channel 6 in AP mode. Once the AP is established that's it… there's no further access beyond the scope of the AP established… however you scan still fallout of AP mode.

Switching to a managed client (I'm sure adhoc would work similarly) you once again get scan access:

Code: Select all

# iwlist ath0 scanning    
ath0      Scan completed :
          Cell 01 - Address: 84:1B:5E:39:1E:28
                    ESSID:"SHELLWLAN"
                    Mode:Master
                    Frequency:2.412 GHz (Channel 1)
                    Quality=37/94  Signal level=-58 dBm  Noise level=-95 dBm
                    Encryption key:on
                    Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 18 Mb/s
                              24 Mb/s; 36 Mb/s; 54 Mb/s; 6 Mb/s; 9 Mb/s
                              12 Mb/s; 48 Mb/s
                    IE: IEEE 802.11i/WPA2 Version 1
                        Group Cipher : CCMP
                        Pairwise Ciphers (1) : CCMP
                        Authentication Suites (1) : PSK
                    Protocol:IEEE 802.11g
                    Extra:bcn_int=200
                    IE: Unknown: <REMOVED>
          Cell 02 - Address: 86:1B:5E:39:1E:29
                    ESSID:"SHELLWLAN-GUEST"
                    Mode:Master
                    Frequency:2.412 GHz (Channel 1)
                    Quality=37/94  Signal level=-58 dBm  Noise level=-95 dBm
                    Encryption key:off
                    Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 18 Mb/s
                              24 Mb/s; 36 Mb/s; 54 Mb/s; 6 Mb/s; 9 Mb/s
                              12 Mb/s; 48 Mb/s
                    Protocol:IEEE 802.11g
                    Extra:bcn_int=200

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Re: How to change your drone's Wi-Fi channel

Post by ShellDude » 29 Dec 2013, 19:24

So to go back to the original question about dynamically hopping channels:

In the one mode where the drone should be able to hop channels (AP/INFRA) it currently cannot because there's no visible way to do peer network scans. In all other modes where it is pointless you have full visibility but since it is the access point's responsibility to swap channels you're SOL.

Also, we could build a script to haphazardly hop channels in AP mode, but I suspect that would lead to bad results considering that any clients (i.e. your phone) would have to keep up with the channel changes reactively which would introduce a ton of latency.

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Why only American Wi-Fi channels

Post by DerShu » 15 May 2014, 08:47

Is the Linux OS on the AR.Drone 2 limited to only American WiFi channels or is that limitation just in AR.Pro? If it is just an AR.Pro limitation would it be possible to have access to all the world wide WiFi channels in a future AR.Pro release?

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