Hi
I need your input for AP-6532 CLI configuration. We can see STBC parameter in CLI. === ap6532-21D210(config-device-B4-C7-99-21-D2-10-if-radio1)#st? stbc Configure Space-Time Block Coding (STBC) parameters ap6532-21D210(config-device-B4-C7-99-21-D2-10-if-radio1)#stbc ? none Disable support for STBC tx-only Support only transmit STBC === #The default seems to be disabled. How is this used and in which scenario is this expected to be used? Our partner found out and now want to confirm if this is working in case of the single mesh or (Mesh Connex scenario)? Your input would be greatly appreciated.
4 Replies
Hi Sato The purpose of the transmitting techniques is, as mentioned in my previous post, to increase the receiver ability to detect and process signals at lower SNR. I don't know what kind of issues your end customer is having, if any, but I would recommend a proper site survey to be done, not to rely on these techniques, and have proper SNR, and interference sources removed. If this has been done, I would recommend them to open a support case with their TAC for their region, to find the root cause of their issue. If they have distance problems, you might want to review which antennas are being used, e.g. you might need directional antennas instead of omnidirectional.
As mentioned before, when implementing STBC, the received signal may be improved by 8dB (can yield 69% more range). This applies only to STBC frames, therefore it does not automatically mean an increased BSS size for all STAs. Even if you don't have client access, in your scenario, because of backward compatibility STAs are also required to send a standard non-STBC beacon (referred as primary beacon).
STBC is an optional code to increase robustness for specific scenarios. It is more useful when the number of transmit chains is greater than the number of receiver chains. The AP6532 is a 2 x 3: 2 ,802.11n AP, which means it has more receiving antennas than transmitting. This is useful at lower SNR , because multiple transmit antennas do no improve performance, but multiple receive antennas in this specific case.
Hi Silva-san I really apprecaite your comment. We do not have the issue in the field. This partner wants to know this from our implementation point of view, including the theoritical point of view. So I can be back to them with your input. Thanks again Sato
Hi Sato-san
Information about STBC can be found in the Internet, e.g.:
http://en.wikipedia.org/wiki/Space%E2%80%93time_block_code
STBC is one of the PHY Layer enhancements with 802.11n
In simple words:
STBC transmits different copies of the data stream from different antennas.
Space-time block coding (STBC) and Cyclic Shift Diversity (CSD specified in the standard) are transmitting diversity techniques where the same transmitted data is sent out of multiple antennas.
STBC is possible only between 802.11n devices. CSD can be used also with legacy. The rate of data transmitted is not increased as transmit antennas are added, but receiver ability to detect signals at lower SNR and process them increase.
When implementing STBC, the received signal may be improved by 8dB (can yield 69% more range). This applies only to STBC frames, therefore it does not automatically mean an increased BSS size for all STAs.
STBC beacon frames are sent using the lowest MCS. Because of backward compatibility STAs are also required to send a standard non-STBC beacon (referred as primary beacon).
Although STBC operations increase the range of our BSS for STBC beacons, it will introduce new hidden node problem. To combat this, Dual CTS is used. It sets the NAV in STAs that do not support STBC and STAs that can only associate and communicate use STBC because of their physical distance away from the AP. The 802.11n uses CF-End frame originally defined as part of PCF.
Dual CTS – all non-STBC STAs in the BSS will transmit a RTS to AP at the beginning of every TXOP. AP will then respond with 2 CTS frames (1 in STBC format and other in non-STBC format – the order it depends on STA). It will then use a CF-End (purpose is to set the NAV =0) if STA finishes sending the data before the end of its TXOP. The CF-End is also sent in STBC frame and non-STBC frame. Throughput will be significantly reduced.
I am unsure how this will help you with AP6532s and have not seen this feature highlighted before, just now with the AP8132. See attached data sheet.
Hope the above explanation clarifies the feature for you, and when it would be useful to have it.
Thank you for your input. This was helpful for me to understand STBC, including AP-8132. If AP-6532 is used and configured as the single hop mesh with 11n only, does STBC help from the distance point of view? (AP-6532 is being used as mesh only node without the client acess.)