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CC3120: 802.11b/g channels

DINESH SUNDAR
Prodigy 50 points
Part Number: CC3120
Other Parts Discussed in Thread: CC3135

We are using the 802.11g channel for high bit rate in CC3120 and we need to forcefully off the 802.11b channel to avoid low bitrates in CC3120.

Could you please help us how to forcefully off the 802.11 b Channel ?

  • 0
    TI__Guru 63006 points

    unfortunately we don’t have such configuration in the simplelink devices.

  • 0 in reply to Kobi Leibovitch
    Prodigy 70 points

    Hi Kobi.

    Are we unable to de-activate particular bitrates so they are not available/advertised during wireless handshake with AP?

    Here is a bit of background for this question:

    We have a wireless product using CC1352 as main micro and CC3120 as 2.4GHz wifi radio. One of our customers claims this product cannot successfully establish a connection with their AP when the lower-bitrate (802.11b bitrates) are disabled on the AP (forcing our product to negotiate to higher bitrates); but that the product does establish a connection with their AP as long as the lower bitrates (802.11b) are enabled (allowing our product to negotiate to lower bitrates if necessary). Further, they claim that once the connection is established, they can then turn the lower bitrates (802.11b) off and the connection remains in-tact.

    Our internal testing does not reproduce the customer's issue. The product successfully negotiates a connection with our APs even with the lower-bitrates disabled on the AP. We have success even at distances over 75ft and through walls. Our request here to disable lower bitrates on the CC3120 was to show that our product can connect and never use lower bitrates. We also would like to disable lower bitrates if it is possible to change the bitrate of the Probe Request packets (see #3 below).

    Can you provide any documentation or further information for the following:

    1. Is it accurate to say that during the wifi negotiation process, the CC3120 will advertise support for all 802.11b/g/n bitrates, and that the available bitrates for wifi TX packets, after negotiation, will be whatever bitrates are supported by both the CC3120 and the AP?

    2. What parameters (maybe RSSI?) and what thresholds for these parameters are used to determine the specific bitrate chosen for a particular CC3120 transmit.

    3. Our Wireshark wifi captures have shown that negotiation starts with Probe Request from CC3120 and Probe Response from AP. Probe Request from CC3120 is always at 1Mbps; and Probe Response from AP is always at the bitrate selected as "Default" on the AP. Is Probe Request at 1Mbps as expected? If we were to disable the 802.11b bitrates (which includes 1Mbps), would the CC3120 Probe Request packet than transmit at a different bitrate (perhaps the lowest supported 802.11g bitrate)?

    Overall, we are trying to gain an understanding of the CC3120 wifi connection negotiation algorithms to better support our customers as they voice concerns with our wireless performance using the CC3120.

    Thank you for any additional help and/or information you can provide.

    Best Regards.

    Dan

  • 0 in reply to Dan Cross
    TI__Guru 63006 points

    Depending on how the AP behaves when the B rates are disabled (whether it affects the reception or just the transmission) - it can impact the connection.

    1. the assumption is correct

    2. For data packets - we have an internal (inside the NWP) rate adaptation algorithm that combines several inputs to generate the initial rate for a packet - then a backoff will be applied (so failure to get an ACK on specific rate will trigger a retransmission in a lower rate). It is common to send pre-connection management frames (such as probe request) in the lower ("basic") rates. Probe request will be sent using 1Mbps on 2.4GHz band (it will be 6Mpbs on 5GHz in cc3135) - so AP without no B support can be impacted.

    The behavior in which the AP ignores B frames sent to it is not typical and this issue is not common.

    As said, unfortunately there is no standard way to control this from the host. Only way is using the transceiver mode where the host control the rate of sent packet but it requires some stack on the host (maybe some sort of scan in transceiver mode, i.e. sending prob-req and receiving prob-res/beacons, and then switching to standard station mode for connecting using the desired BSSID will work).