Jetson TX2 WIFI AP 40MHz & 80MHz Bandwidth

Robotics & Edge Computing Jetson & Embedded Systems Jetson TX2
1

Hello, we’ve been using the Jetson TX2 in AP mode for a while now and we’ve been limited to using channels 36, 40, 44 and 48 - which is stated as 802.11ac20 in the Jetson TX2 OEM Wireless Compliance Guide;

(https://developer.nvidia.com/jetson-tx1-and-tx2-oem-wireless-compliance-guide)

On the Jetson, we can see that the following channels are available;

		Frequencies:
		* 5180 MHz [36] (0.0 dBm)
		* 5200 MHz [40] (0.0 dBm)
		* 5220 MHz [44] (0.0 dBm)
		* 5240 MHz [48] (0.0 dBm)
		* 5260 MHz [52] (0.0 dBm)
		* 5280 MHz [56] (0.0 dBm)
		* 5300 MHz [60] (0.0 dBm)
		* 5320 MHz [64] (0.0 dBm)

From what I understand, channels 52, 56, 60 and 64 can’t be used in AP mode as they are marked as passive. Is it correct that they can only be used in station mode?

image

However, what I don’t understand is that there are a few more channels available e.g. channels 38 and 46 (802.11ac40) and channel 42 (802.11ac80) stated in the document. However, these channels aren’t visible when doing a iw phy phy0 info. Is this due to the broadcom firmware? how can we enable these channels and use them in AP mode?

image

3

Hi,

Channel 38 and 46 are not primary channel, hence it will not be listed using iw tool and cannot be directly configured for either stations or in AP mode. Wifi channel are 20MHx wide. 40MHz and 80MHz channels are formed by including adjacent channels.

For example, channel 36 in 20MHz mode will only have single 20MHz channel, while channel 36 in 40MHz will include adjacent channel 36, and 38 to form 40MHz channel. Is this case primary would be 36, iw tool only lists primary channel. Same logic applies to form 80MHz channel which will be formed by including 4 20MHz adjacent channels.

That is why you cannot see those channels in iw tool.

1 Like
4

Thanks for the explanation. That makes sense! Would you be able to give some information on how to specify 40MHz/80MHz bandwidth in hostapd config?

5

I am still checking this internally. Looks like we don’t have such setting in hostapd before.

6

@WayneWWW did you manage to get any information on this? I tried adding the following in hostapd.conf for 80MHz but it didn’t work;

vht_oper_chwidth=1
channel=36
vht_oper_centr_freq_seg0_idx=42#

I got a “Failed to set channel for kernel driver” error.

7

Hi @WayneWWW , this is the continuation of issue @JGSandom reported.
when I do “iw list” on the Jetson TX2, I get below hardware capabilities, don’t see HT40, does it mean HT40 is not supported by hardware in AP mode?

Band 2:
	Capabilities: 0x1020
		HT20
		Static SM Power Save
		RX HT20 SGI
		No RX STBC
		Max AMSDU length: 3839 bytes
		DSSS/CCK HT40
8

Hi @WayneWWW , could you please help us understand why HT40 capabilities are not shown with “iw list” in AP mode? How to enable ?

9

Hi,

We tried to enable this with below method.

channel=36
require_vht=1
vht_capab=[SHORT-GI-80][SU-BEAMFORMEE]
vht_oper_chwidth=1
vht_oper_centr_freq_seg0_idx=42

Downloaded the latest hostap source from here, also needed to ignore the return for the secondary channel offset in src/common/hw_features_common.c:578.

Its working without the secondary channel offset, this setting requires [HT40+]/[HT40-] but driver doesn’t support it.

Only 80Mhz is supported here.

10

Hi @WayneWWW , thanks for getting back on this. Do you expect Jetson TX2 AP wifi clients to be able to negotiate to 40/80 MHz bandwidth without the suggested changes ? I see that AP is able to advertise 80Mhz capabilities on air.

Below is the wifi scan dump on client when associated with Jetson TX2 AP:

pi@raspberrypi : ~ $ sudo iw wlan0 scan

BSS 00:04:4b:f8:66:06(on wlan0) – associated

last seen: 4185.558s [boottime]

TSF: 0 usec (0d, 00:00:00)

freq: 5240

beacon interval: 100 TUs

capability: ESS Privacy SpectrumMgmt (0x0111)

signal: -31.00 dBm

last seen: 0 ms ago

SSID: XXXX-YYYY

Supported rates: 6.0* 9.0 12.0* 18.0 24.0* 36.0 48.0 54.0

Country: XT Environment: Indoor/Outdoor

Channels [36 - 36] @ 23 dBm

Channels [40 - 40] @ 23 dBm

Channels [44 - 44] @ 23 dBm

Channels [48 - 48] @ 23 dBm

Channels [52 - 52] @ 23 dBm

Channels [56 - 56] @ 23 dBm

Channels [60 - 60] @ 23 dBm

Channels [64 - 64] @ 23 dBm

Power constraint: 0 dB

TPC report: TX power: 12 dBm

RSN: * Version: 1

  • Group cipher: CCMP
  • Pairwise ciphers: CCMP
  • Authentication suites: PSK
  • Capabilities: 16-PTKSA-RC 1-GTKSA-RC (0x000c)

HT capabilities:

Capabilities: 0x6f

RX LDPC

HT20/HT40

SM Power Save disabled

RX HT20 SGI

RX HT40 SGI

No RX STBC

Max AMSDU length: 3839 bytes

No DSSS/CCK HT40

Maximum RX AMPDU length 65535 bytes (exponent: 0x003)

Minimum RX AMPDU time spacing: 4 usec (0x05)

HT RX MCS rate indexes supported: 0-15

HT TX MCS rate indexes are undefined

HT operation:

  • primary channel: 48
  • secondary channel offset: below
  • STA channel width: any
  • RIFS: 1
  • HT protection: no
  • non-GF present: 1
  • OBSS non-GF present: 0
  • dual beacon: 0
  • dual CTS protection: 0
  • STBC beacon: 0
  • L-SIG TXOP Prot: 0
  • PCO active: 0
  • PCO phase: 0

Extended capabilities:

  • Extended Channel Switching
  • Interworking
  • QoS Map
  • Operating Mode Notification
  • Max Number Of MSDUs In A-MSDU is unlimited

VHT capabilities:

VHT Capabilities (0x0f815832):

Max MPDU length: 11454

Supported Channel Width: neither 160 nor 80+80

RX LDPC

short GI (80 MHz)

SU Beamformer

SU Beamformee

VHT RX MCS set:

1 streams: MCS 0-9

2 streams: MCS 0-9

3 streams: not supported

4 streams: not supported

5 streams: not supported

6 streams: not supported

7 streams: not supported

8 streams: not supported

VHT RX highest supported: 0 Mbps

VHT TX MCS set:

1 streams: MCS 0-9

2 streams: MCS 0-9

3 streams: not supported

4 streams: not supported

5 streams: not supported

6 streams: not supported

7 streams: not supported

8 streams: not supported

VHT TX highest supported: 0 Mbps

VHT operation:

*** channel width: 1 (80 MHz)**
*** center freq segment 1: 42**

  • center freq segment 2: 0
  • VHT basic MCS set: 0x0000

WMM: * Parameter version 1

  • u-APSD
  • BE: CW 15-1023, AIFSN 3
  • BK: CW 15-1023, AIFSN 7
  • VI: CW 7-15, AIFSN 2, TXOP 3008 usec
  • VO: CW 3-7, AIFSN 2, TXOP 1504 usec