MT7921 dual band WiFi Setup Problem

Installing and Using OpenWrt
1

I've installed OpenWrt 23.05.5 on a x86/64 mini computer.
Network HW:
2 * Ethernet, 1 for WAN, 1 for LAN
wireless AX210NBW for wwan
wireless mt7921 for wlan
L860GL 4G modem

I want to set up dual band operation for mt7921. This device supports DBDC:
dbdc
These statements are from two different manuals. I guess it means that each radio is dedicated to a certain band in DBDC mode.

To set up dual band there must be 2 radios, one for each band, but for this device I see only one radio.

How can I set up dual band (same SSID and password) ?

2

Could you identify like lspci the card you have? For dual-band simultaneous operation you need 2 7921 chips e.g. https://asiarf.com/product/wi-fi-6e-mini-pcie-module-mt7916-aw7916-npd/

3

Thank you for the fast response!

lspci:

04:00.0 Network controller: MEDIATEK Corp. MT7921 802.11ax PCI Express Wireless Network Adapter
        Subsystem: MEDIATEK Corp. MT7921 802.11ax PCI Express Wireless Network Adapter
        Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+
        Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
        Latency: 0, Cache Line Size: 64 bytes
        Interrupt: pin A routed to IRQ 137
        Region 0: Memory at 80100000 (64-bit, prefetchable) [size=1M]
        Region 2: Memory at 80200000 (64-bit, prefetchable) [size=16K]
        Region 4: Memory at 80204000 (64-bit, prefetchable) [size=4K]
        Capabilities: [80] Express (v2) Endpoint, MSI 00
                DevCap: MaxPayload 128 bytes, PhantFunc 0, Latency L0s unlimited, L1 unlimited
                        ExtTag+ AttnBtn- AttnInd- PwrInd- RBE+ FLReset+ SlotPowerLimit 25W
                DevCtl: CorrErr- NonFatalErr- FatalErr- UnsupReq-
                        RlxdOrd+ ExtTag+ PhantFunc- AuxPwr- NoSnoop+ FLReset-
                        MaxPayload 128 bytes, MaxReadReq 512 bytes
                DevSta: CorrErr- NonFatalErr- FatalErr- UnsupReq- AuxPwr- TransPend-
                LnkCap: Port #1, Speed 5GT/s, Width x1, ASPM L0s L1, Exit Latency L0s <2us, L1 <8us
                        ClockPM- Surprise- LLActRep- BwNot- ASPMOptComp+
                LnkCtl: ASPM Disabled; RCB 64 bytes, Disabled- CommClk+
                        ExtSynch- ClockPM- AutWidDis- BWInt- AutBWInt-
                LnkSta: Speed 5GT/s, Width x1
                        TrErr- Train- SlotClk+ DLActive- BWMgmt- ABWMgmt-
                DevCap2: Completion Timeout: Range ABCD, TimeoutDis+ NROPrPrP- LTR+
                         10BitTagComp- 10BitTagReq- OBFF Not Supported, ExtFmt+ EETLPPrefix-
                         EmergencyPowerReduction Not Supported, EmergencyPowerReductionInit-
                         FRS- TPHComp- ExtTPHComp-
                         AtomicOpsCap: 32bit- 64bit- 128bitCAS-
                DevCtl2: Completion Timeout: 50us to 50ms, TimeoutDis- LTR+ 10BitTagReq- OBFF Disabled,
                         AtomicOpsCtl: ReqEn-
                LnkCap2: Supported Link Speeds: 2.5-5GT/s, Crosslink- Retimer- 2Retimers- DRS-
                LnkCtl2: Target Link Speed: 5GT/s, EnterCompliance- SpeedDis-
                         Transmit Margin: Normal Operating Range, EnterModifiedCompliance- ComplianceSOS-
                         Compliance Preset/De-emphasis: -6dB de-emphasis, 0dB preshoot
                LnkSta2: Current De-emphasis Level: -3.5dB, EqualizationComplete- EqualizationPhase1-
                         EqualizationPhase2- EqualizationPhase3- LinkEqualizationRequest-
                         Retimer- 2Retimers- CrosslinkRes: unsupported
        Capabilities: [e0] MSI: Enable+ Count=1/32 Maskable+ 64bit+
                Address: 00000000fee00478  Data: 0000
                Masking: fffffffe  Pending: 00000000
        Capabilities: [f8] Power Management version 3
                Flags: PMEClk- DSI+ D1+ D2+ AuxCurrent=0mA PME(D0+,D1+,D2+,D3hot+,D3cold+)
                Status: D0 NoSoftRst+ PME-Enable- DSel=0 DScale=0 PME-
        Kernel driver in use: mt7921e

I understand that it is necessary to have 2 radios available for concurrent dual band operation (DBDC). According to the manuals I have the mt7921 supports DBDC (see above) and accordingly has 2 radios on board (plus 2 radios for BT).

mt7921 block diagram
mt7921 block diagram591×567 42.3 KB

So unless the manuals do lie the HW should be capable of DBDC with a single chip.
However, maybe the driver cannot handle it. I hope though that it's a matter of settings.

4

Maybe this (rather lengthy) output of iw list may also help:

Wiphy phy1
        wiphy index: 1
        max # scan SSIDs: 4
        max scan IEs length: 482 bytes
        max # sched scan SSIDs: 10
        max # match sets: 16
        Retry short limit: 7
        Retry long limit: 4
        Coverage class: 0 (up to 0m)
        Device supports AP-side u-APSD.
        Device supports T-DLS.
        Available Antennas: TX 0x3 RX 0x3
        Configured Antennas: TX 0x3 RX 0x3
        Supported interface modes:
                 * managed
                 * AP
                 * AP/VLAN
                 * monitor
                 * P2P-client
                 * P2P-GO
        Band 1:
                Capabilities: 0x9ff
                        RX LDPC
                        HT20/HT40
                        SM Power Save disabled
                        RX Greenfield
                        RX HT20 SGI
                        RX HT40 SGI
                        TX STBC
                        RX STBC 1-stream
                        Max AMSDU length: 7935 bytes
                        No DSSS/CCK HT40
                Maximum RX AMPDU length 65535 bytes (exponent: 0x003)
                Minimum RX AMPDU time spacing: No restriction (0x00)
                HT TX/RX MCS rate indexes supported: 0-15
                HE Iftypes: managed
                        HE MAC Capabilities (0x08011a000040):
                                +HTC HE Supported
                                Trigger Frame MAC Padding Duration: 2
                                OM Control
                                Maximum A-MPDU Length Exponent: 3
                                A-MSDU in A-MPDU
                        HE PHY Capabilities: (0x2270ce120dc0b306423f00):
                                HE40/2.4GHz
                                242 tone RUs/2.4GHz
                                Device Class: 1
                                LDPC Coding in Payload
                                HE SU PPDU with 1x HE-LTF and 0.8us GI
                                NDP with 4x HE-LTF and 3.2us GI
                                STBC Tx <= 80MHz
                                STBC Rx <= 80MHz
                                Full Bandwidth UL MU-MIMO
                                Partial Bandwidth UL MU-MIMO
                                DCM Max Constellation: 2
                                DCM Max Constellation Rx: 2
                                SU Beamformee
                                Beamformee STS <= 80Mhz: 3
                                Ng = 16 SU Feedback
                                Ng = 16 MU Feedback
                                Codebook Size SU Feedback
                                Codebook Size MU Feedback
                                Triggered CQI Feedback
                                Partial Bandwidth Extended Range
                                PPE Threshold Present
                                Power Boost Factor ar
                                HE SU PPDU & HE PPDU 4x HE-LTF 0.8us GI
                                20MHz in 40MHz HE PPDU 2.4GHz
                                DCM Max BW: 1
                                Longer Than 16HE SIG-B OFDM Symbols
                                Non-Triggered CQI Feedback
                                TX 1024-QAM
                                RX 1024-QAM
                                RX Full BW SU Using HE MU PPDU with Compression SIGB
                                RX Full BW SU Using HE MU PPDU with Non-Compression SIGB
                        HE RX MCS and NSS set <= 80 MHz
                                1 streams: MCS 0-11
                                2 streams: MCS 0-11
                                3 streams: not supported
                                4 streams: not supported
                                5 streams: not supported
                                6 streams: not supported
                                7 streams: not supported
                                8 streams: not supported
                        HE TX MCS and NSS set <= 80 MHz
                                1 streams: MCS 0-11
                                2 streams: MCS 0-11
                                3 streams: not supported
                                4 streams: not supported
                                5 streams: not supported
                                6 streams: not supported
                                7 streams: not supported
                                8 streams: not supported
                        PPE Threshold 0x39 0x1c 0xc7 0x71 0x1c 0x07
                EHT Iftypes: managed
                        EHT MAC Capabilities (0x0000):
                        EHT PHY Capabilities: (0x0000000000000000):
                        EHT MCS/NSS: (0x):
                        EHT bw=20 MHz, max NSS for MCS 0-7: Rx=0, Tx=0
                        EHT bw=20 MHz, max NSS for MCS 8-9: Rx=0, Tx=0
                        EHT bw=20 MHz, max NSS for MCS 10-11: Rx=0, Tx=0
                        EHT bw=20 MHz, max NSS for MCS 12-13: Rx=0, Tx=0
                HE Iftypes: AP
                        HE MAC Capabilities (0x00011a081044):
                                +HTC HE Supported
                                BSR
                                OM Control
                                Maximum A-MPDU Length Exponent: 3
                                BQR
                                A-MSDU in A-MPDU
                                OM Control UL MU Data Disable RX
                        HE PHY Capabilities: (0x0220ce120000a000000c00):
                                HE40/2.4GHz
                                LDPC Coding in Payload
                                NDP with 4x HE-LTF and 3.2us GI
                                STBC Tx <= 80MHz
                                STBC Rx <= 80MHz
                                Full Bandwidth UL MU-MIMO
                                Partial Bandwidth UL MU-MIMO
                                DCM Max Constellation: 2
                                DCM Max Constellation Rx: 2
                                Partial Bandwidth Extended Range
                                PPE Threshold Present
                                TX 1024-QAM
                                RX 1024-QAM
                        HE RX MCS and NSS set <= 80 MHz
                                1 streams: MCS 0-11
                                2 streams: MCS 0-11
                                3 streams: not supported
                                4 streams: not supported
                                5 streams: not supported
                                6 streams: not supported
                                7 streams: not supported
                                8 streams: not supported
                        HE TX MCS and NSS set <= 80 MHz
                                1 streams: MCS 0-11
                                2 streams: MCS 0-11
                                3 streams: not supported
                                4 streams: not supported
                                5 streams: not supported
                                6 streams: not supported
                                7 streams: not supported
                                8 streams: not supported
                        PPE Threshold 0x39 0x1c 0xc7 0x71 0x1c 0x07
                EHT Iftypes: AP
                        EHT MAC Capabilities (0x0000):
                        EHT PHY Capabilities: (0x0000000000000000):
                        EHT MCS/NSS: (0x):
                        EHT bw=20 MHz, max NSS for MCS 0-7: Rx=0, Tx=0
                        EHT bw=20 MHz, max NSS for MCS 8-9: Rx=0, Tx=0
                        EHT bw=20 MHz, max NSS for MCS 10-11: Rx=0, Tx=0
                        EHT bw=20 MHz, max NSS for MCS 12-13: Rx=0, Tx=0
                Frequencies:
                        * 2412 MHz [1] (20.0 dBm)
                        * 2417 MHz [2] (20.0 dBm)
                        * 2422 MHz [3] (20.0 dBm)
                        * 2427 MHz [4] (20.0 dBm)
                        * 2432 MHz [5] (20.0 dBm)
                        * 2437 MHz [6] (20.0 dBm)
                        * 2442 MHz [7] (20.0 dBm)
                        * 2447 MHz [8] (20.0 dBm)
                        * 2452 MHz [9] (20.0 dBm)
                        * 2457 MHz [10] (20.0 dBm)
                        * 2462 MHz [11] (20.0 dBm)
                        * 2467 MHz [12] (20.0 dBm) (no IR)
                        * 2472 MHz [13] (20.0 dBm) (no IR)
                        * 2484 MHz [14] (20.0 dBm) (no IR)
        Band 2:
                Capabilities: 0x9ff
                        RX LDPC
                        HT20/HT40
                        SM Power Save disabled
                        RX Greenfield
                        RX HT20 SGI
                        RX HT40 SGI
                        TX STBC
                        RX STBC 1-stream
                        Max AMSDU length: 7935 bytes
                        No DSSS/CCK HT40
                Maximum RX AMPDU length 65535 bytes (exponent: 0x003)
                Minimum RX AMPDU time spacing: No restriction (0x00)
                HT TX/RX MCS rate indexes supported: 0-15
                VHT Capabilities (0x339071b2):
                        Max MPDU length: 11454
                        Supported Channel Width: neither 160 nor 80+80
                        RX LDPC
                        short GI (80 MHz)
                        TX STBC
                        SU Beamformee
                        MU Beamformee
                        RX antenna pattern consistency
                        TX antenna pattern consistency
                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 extended NSS: supported
                HE Iftypes: managed
                        HE MAC Capabilities (0x08011a000040):
                                +HTC HE Supported
                                Trigger Frame MAC Padding Duration: 2
                                OM Control
                                Maximum A-MPDU Length Exponent: 3
                                A-MSDU in A-MPDU
                        HE PHY Capabilities: (0x4470ce120dc0b306423f00):
                                HE40/HE80/5GHz
                                242 tone RUs/5GHz
                                Device Class: 1
                                LDPC Coding in Payload
                                HE SU PPDU with 1x HE-LTF and 0.8us GI
                                NDP with 4x HE-LTF and 3.2us GI
                                STBC Tx <= 80MHz
                                STBC Rx <= 80MHz
                                Full Bandwidth UL MU-MIMO
                                Partial Bandwidth UL MU-MIMO
                                DCM Max Constellation: 2
                                DCM Max Constellation Rx: 2
                                SU Beamformee
                                Beamformee STS <= 80Mhz: 3
                                Ng = 16 SU Feedback
                                Ng = 16 MU Feedback
                                Codebook Size SU Feedback
                                Codebook Size MU Feedback
                                Triggered CQI Feedback
                                Partial Bandwidth Extended Range
                                PPE Threshold Present
                                Power Boost Factor ar
                                HE SU PPDU & HE PPDU 4x HE-LTF 0.8us GI
                                20MHz in 40MHz HE PPDU 2.4GHz
                                DCM Max BW: 1
                                Longer Than 16HE SIG-B OFDM Symbols
                                Non-Triggered CQI Feedback
                                TX 1024-QAM
                                RX 1024-QAM
                                RX Full BW SU Using HE MU PPDU with Compression SIGB
                                RX Full BW SU Using HE MU PPDU with Non-Compression SIGB
                        HE RX MCS and NSS set <= 80 MHz
                                1 streams: MCS 0-11
                                2 streams: MCS 0-11
                                3 streams: not supported
                                4 streams: not supported
                                5 streams: not supported
                                6 streams: not supported
                                7 streams: not supported
                                8 streams: not supported
                        HE TX MCS and NSS set <= 80 MHz
                                1 streams: MCS 0-11
                                2 streams: MCS 0-11
                                3 streams: not supported
                                4 streams: not supported
                                5 streams: not supported
                                6 streams: not supported
                                7 streams: not supported
                                8 streams: not supported
                        PPE Threshold 0x39 0x1c 0xc7 0x71 0x1c 0x07
                EHT Iftypes: managed
                        EHT MAC Capabilities (0x0000):
                        EHT PHY Capabilities: (0x0000000000000000):
                        EHT MCS/NSS: (0x):
                        EHT bw <= 80 MHz, max NSS for MCS 8-9: Rx=0, Tx=0
                        EHT bw <= 80 MHz, max NSS for MCS 10-11: Rx=0, Tx=0
                        EHT bw <= 80 MHz, max NSS for MCS 12-13: Rx=0, Tx=0
                HE Iftypes: AP
                        HE MAC Capabilities (0x00011a081044):
                                +HTC HE Supported
                                BSR
                                OM Control
                                Maximum A-MPDU Length Exponent: 3
                                BQR
                                A-MSDU in A-MPDU
                                OM Control UL MU Data Disable RX
                        HE PHY Capabilities: (0x0420ce120000a000000c00):
                                HE40/HE80/5GHz
                                LDPC Coding in Payload
                                NDP with 4x HE-LTF and 3.2us GI
                                STBC Tx <= 80MHz
                                STBC Rx <= 80MHz
                                Full Bandwidth UL MU-MIMO
                                Partial Bandwidth UL MU-MIMO
                                DCM Max Constellation: 2
                                DCM Max Constellation Rx: 2
                                Partial Bandwidth Extended Range
                                PPE Threshold Present
                                TX 1024-QAM
                                RX 1024-QAM
                        HE RX MCS and NSS set <= 80 MHz
                                1 streams: MCS 0-11
                                2 streams: MCS 0-11
                                3 streams: not supported
                                4 streams: not supported
                                5 streams: not supported
                                6 streams: not supported
                                7 streams: not supported
                                8 streams: not supported
                        HE TX MCS and NSS set <= 80 MHz
                                1 streams: MCS 0-11
                                2 streams: MCS 0-11
                                3 streams: not supported
                                4 streams: not supported
                                5 streams: not supported
                                6 streams: not supported
                                7 streams: not supported
                                8 streams: not supported
                        PPE Threshold 0x39 0x1c 0xc7 0x71 0x1c 0x07
                EHT Iftypes: AP
                        EHT MAC Capabilities (0x0000):
                        EHT PHY Capabilities: (0x0000000000000000):
                        EHT MCS/NSS: (0x):
                        EHT bw <= 80 MHz, max NSS for MCS 8-9: Rx=0, Tx=0
                        EHT bw <= 80 MHz, max NSS for MCS 10-11: Rx=0, Tx=0
                        EHT bw <= 80 MHz, max NSS for MCS 12-13: Rx=0, Tx=0
                Frequencies:
                        * 5180 MHz [36] (20.0 dBm)
                        * 5200 MHz [40] (20.0 dBm)
                        * 5220 MHz [44] (20.0 dBm)
                        * 5240 MHz [48] (20.0 dBm)
                        * 5260 MHz [52] (20.0 dBm) (no IR, radar detection)
                        * 5280 MHz [56] (20.0 dBm) (no IR, radar detection)
                        * 5300 MHz [60] (20.0 dBm) (no IR, radar detection)
                        * 5320 MHz [64] (20.0 dBm) (no IR, radar detection)
                        * 5500 MHz [100] (20.0 dBm) (no IR, radar detection)
                        * 5520 MHz [104] (20.0 dBm) (no IR, radar detection)
                        * 5540 MHz [108] (20.0 dBm) (no IR, radar detection)
                        * 5560 MHz [112] (20.0 dBm) (no IR, radar detection)
                        * 5580 MHz [116] (20.0 dBm) (no IR, radar detection)
                        * 5600 MHz [120] (20.0 dBm) (no IR, radar detection)
                        * 5620 MHz [124] (20.0 dBm) (no IR, radar detection)
                        * 5640 MHz [128] (20.0 dBm) (no IR, radar detection)
                        * 5660 MHz [132] (20.0 dBm) (no IR, radar detection)
                        * 5680 MHz [136] (20.0 dBm) (no IR, radar detection)
                        * 5700 MHz [140] (20.0 dBm) (no IR, radar detection)
                        * 5720 MHz [144] (20.0 dBm) (no IR, radar detection)
                        * 5745 MHz [149] (20.0 dBm) (no IR)
                        * 5765 MHz [153] (20.0 dBm) (no IR)
                        * 5785 MHz [157] (20.0 dBm) (no IR)
                        * 5805 MHz [161] (20.0 dBm) (no IR)
                        * 5825 MHz [165] (20.0 dBm) (no IR)
                        * 5845 MHz [169] (disabled)
                        * 5865 MHz [173] (disabled)
                        * 5885 MHz [177] (disabled)
        valid interface combinations:
                 * #{ managed, P2P-client } <= 2, #{ AP, P2P-GO } <= 1,
                   total <= 2, #channels <= 2
        HT Capability overrides:
                 * MCS: ff ff ff ff ff ff ff ff ff ff
                 * maximum A-MSDU length
                 * supported channel width
                 * short GI for 40 MHz
                 * max A-MPDU length exponent
                 * min MPDU start spacing
        max # scan plans: 1
        max scan plan interval: 65535
        max scan plan iterations: 0
        Supported extended features:
                * [ RRM ]: RRM
                * [ SET_SCAN_DWELL ]: scan dwell setting
                * [ BEACON_RATE_LEGACY ]: legacy beacon rate setting
                * [ BEACON_RATE_HT ]: HT beacon rate setting
                * [ BEACON_RATE_VHT ]: VHT beacon rate setting
                * [ FILS_STA ]: STA FILS (Fast Initial Link Setup)
                * [ CQM_RSSI_LIST ]: multiple CQM_RSSI_THOLD records
                * [ CONTROL_PORT_OVER_NL80211 ]: control port over nl80211
                * [ ACK_SIGNAL_SUPPORT ]: ack signal level support
                * [ TXQS ]: FQ-CoDel-enabled intermediate TXQs
                * [ CAN_REPLACE_PTK0 ]: can safely replace PTK 0 when rekeying
                * [ AIRTIME_FAIRNESS ]: airtime fairness scheduling
                * [ AQL ]: Airtime Queue Limits (AQL)
                * [ CONTROL_PORT_NO_PREAUTH ]: disable pre-auth over nl80211 control port support
                * [ SCAN_FREQ_KHZ ]: scan on kHz frequency support
                * [ CONTROL_PORT_OVER_NL80211_TX_STATUS ]: tx status for nl80211 control port support
                * [ BEACON_RATE_HE ]: HE beacon rate support (AP/mesh)
5

It sort of says #channels 2 in combinations, but I dont think wifi scripts accomodate that (?or even check if hostapd could....)

1 Like
6

I agree with you. I think the HW could do it, but the SW doesn't support it.
If so, the driver must be the problem, because any higher level (HW independent) SW allows it with other HW.
I would go so far as to look into the driver sources (if available), but I do not have any technical documentation for the mt7921 (programmer's guide, user manual etc.). And without documentation it is not possible to explore anything.
If someone has technical documentation please provide it to me.

7

The product brief is aimed at commercial OEMs integrating the chip into their Wi-Fi solutions either to be used with a vendor development kit under NDA or proprietary Windows drivers both provided by Mediatek.

Most Linux (open source) drivers don't go beyond getting a basic Wi-Fi client connection operating one radio at a time and maybe one tethering access point using hostapd. That's all the code OpenWrt can make use of for wireless freedom. The "good stuff" isn't in there.

1 Like
8

OK, then the situation is understandable. While not satisfactory.
Yet, if technical documentation would be available as for most other chips the driver could be enhanced over time.
What a pity only a little fraction of the functionality of this device can be used this way.
Anyway, too much of complaining doesn't do well; I will go on to the next issue I have...
Many thanks for the information provided here! :+1:
If anyone reads this and has technical documentation for the mt7921 or alike please provide it.

9

The RF hardware on the board (between the chip and the antenna) must also be built for concurrent operation. This is a bit more expensive than a system that operates on one band at a time, which is typical for the laptop market. If the card is concurrent compatible that will be encoded into the EEPROM and the driver should pick that up and present two radios to the user.

I think that there are very few PCIe or M.2 DBDC compatible cards out there. It was more found in cheap routers, and I really thought that the OpenWrt driver supports it.

1 Like
10

You are probably right.
Seems I have to go with single band operation for the moment. When it turns out that this becomes a hassle in practice, I will get a 'real' DBDC card.

I am just very confused that a company can make statements in their documentation, that their device is DBDC compliant while it is not. Also the block diagram suggests it, while it is not detailed enough to determine whether a tiny little part is missing.
Without detailed technical documentation, which is not available, we will not be able to determine the truth.

When I need to buy a replacement I'll come back and get advice from you which one will be the right one.
:minibus:

11

Try here:
https://w1.fi/cgit/hostap/tree/hostapd/hostapd.conf
Should be along lines of 80+80. Multi band operation is a thing in wifi7, you may have to wait though.

1 Like
12

Thank you for this info.
At least it got me to the info of your former concern whether hostapd can do DBDC. Yes, it does.
From the hostapd documentation:

An AP can only use one band at a time: 2.4GHz OR 5GHz, a so-called "dual-band AP" is just one AP at 2.4GHz and another at 5GHz;

and "what you can do:"

Use 2.4GHz and 5GHz at the same time on the same card. 
This requires a card with two radios though, which is pretty rare (but hostapd supports it) - if the card creates two wlanX interfaces, you might be lucky

I did have a look at hostapd.conf. Since I do not understand much of networking I am a bit lost what you meant. Sorry. :pensive:
I didn't find any hint on concurrent dual band operation, probably because I don't know what to look for.
80+80 is related to bandwidth, as far as I know.
What I want to achieve, however, is a network sending both on 2.4 GHz and 5 GHz with the same SSID and password, so that it looks as one for the client. The actual communication band (and channel) is determined by the transmission conditions and switched automatically.
This is how it looks like at client side (here a smartphone):

1730752089776
17307520897761440×1422 85.3 KB

I hope I did not express my question misleading.

13

After a bit more research I did indeed find some settings in hostapd.conf which need to be set to a different value than default for DBDC operation.
However, more than one radio must be defined before these entries make sense.
So it goes back to the driver not exposing the two radios.

14

You are conflating Mediatek's (wlan) chipset specifications, with that of the actual vendor who manufactured the physical WLAN card you bought. A vendor doesn't need to implement all the potentially possible features the underlying chipset would support, especially in this case, it's both a decision of the (PHY-/ amp) design, as well as the EEPROM/ calibration data encoding.

That aside, mt7921 is a client-centric chipset to begin with (which only has limited AP features and smaller limit on the maximum number of connected clients), 2x2 - which you would reduce to 1x1+1x1 in DBDC mode, which is hardly sensible.

AP-centric mt7915 DBDC cards (again, it depends on the actual card you're buying there as well) with 4x4, respectively 2x2+2x2 in DBDC mode, are a more sensible choice for this purpose, but keep in mind that their power- and cooling requirements are quite different than those of mt7921.

In practice, using a dedicated (OpenWrt supported-) AP is a more sensible solution here - and cheaper.

1 Like
15

Or a slightly older 2-chip m2 mt76 card(while this one indicating 2 channels in each band is properly understood and scripted)

1 Like
16

@slh and @brada4
Thanks for your answers!
Seems that I should buy a different WLAN card.
I will be mostly at home as long as I work on the router, having a prefect connection to the internet anyway. Therefore I will continue to use the mt7921 card in single band mode until finished.
Then, if I see that dual band operation is really necessary, I will buy a suitable card. Of course I will ask you before purchase which one is best.

17

But dont think card is broken or defective, it is just too modern

18

No, mine is not broken as far as I can tell. All functions I use are working as I expect them.
Especially both bands are working. Inside the motorhome perfect, of course, the signal strength to my house is acceptable on 2.4 GHz, really bad on 5 GHz. The RV is a faraday cage, that is.

19

@brada4 ..., it is just too modern

:rofl: yes!