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I'm a beginner on WARP and am working on this project that involves turning on/off the carrier sensing. The goal is to examine how RTS/CTS works on solving the hidden node problem. I call the set_phy_cs_thresh() method under WlanExpNode class to switch on/off the carrier sensing (https://warpproject.org/docs/mango-wlan … rts_thresh). However, I have no idea what the argument to this function stands for.
One experiment setup is: two STAs sending packets to the AP at the same time. As I set threshold to 10 for every node that is involved in the transmission, the experiment usually goes wrong and prints "WARNING: Transport timeout. Requesting missing data". The experiment seems to stop, but actually the blinking LED on the nodes indicate that there is still data transmission between them. In this case nodes can't be initialized unless I switch off the WARP boards and switch on again. As I set threshold to 100 or 1000, this sometimes happens.
Can you give any insight on this topic? Thanks!
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If you look at how the value is used in the low level MAC, you can see that the value is a measure of RSSI (i.e. received signal strength). You can get a sense of the mapping of received power to RSSI here (basically, it is a lookup table based on the frequency band you are in). The PHY itself keeps a running sum of RSSI values (i.e. PHY_RX_RSSI_SUM_LEN number of values) and the threshold is used to determine when the PHY senses the medium as busy or as free.
The "Transport timeout" warning indicates there is an issue transferring data from the node to the host. You should check your Ethernet cables and Ethernet switch to make sure that everything is working properly. To debug this further, which version of the reference design are you using? Also, does the node print anything out over the UART when it runs into a problem?
I would also suggest that you take a look at the Investigating Hidden Nodes and RTS/CTS Access app note.
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I'm using the Mango_802.11_RefDes_v1.3.0. I checked the Ethernet connections and they all work well. When the problem occurs, the UART usually stops updating the Tx/Rx data from the nodes.
Thanks for your help!
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You'll have to provide more details about your setup and the behaviors you're observing. The "transport timeout" warning suggests there are problems in your wlan_exp setup- either in the configuration of your PC/NIC, the Ethernet switch or the ETH B connections at the nodes. It would be helpful to know details of these. It would also be helpful to know the exact UART output during your wlan_exp experiment.
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