If an AP encountered RADAR and requires to change channel. And the new channel that AP moved will be announced in channel switch announcement action frame to all clients which are connected to that AP. In this case, does all clients (Stations) required to re associate with the AP with the new channel?
-- An AP shall inform associated STAs that the AP is moving to a new channel and maintain the association by advertising the switch using Channel Switch Announcement elements in Beacon frames, Probe Response frames, and Channel Switch Announcement frames until the intended channel switch time.
--The AP may force STAs in the BSS to stop transmissions until the channel switch takes place by setting the Channel Switch Mode field in the Channel Switch Announcement element to 1.
--The channel switch should be scheduled so that all STAs in the BSS, including STAs in power save mode, have the opportunity to receive at least one Channel Switch Announcement element before the switch.
--The AP may send the Channel Switch Announcement frame in a BSS without performing a backoff, after determining the WM is idle for one PIFS period.
A STA that receives a Channel Switch Announcement element may choose not to perform the specified switch, but to take alternative action. For example, it may choose to move to a different BSS.
--A STA in a BSS that is not the AP shall not transmit the Channel Switch Announcement element
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In dvb:
the receiver has to know which frequency the new transport stream is being broadcast on (and this alone is not trivial). Second, the receiver has to tell the tuner to change to the new frequency.
My question is how the receiver knows which frequency the new transport stream is being broadcast, i mean given a range of frequency (min_freq, max_freq),how the receiver knows the good frequency, what is the mechanism behind.
Each change in DVB is signaled by table version change.
If new transport stream is being broadcast, then new NIT version must be signaled as well.
In NIT table there is a 2nd description loop, in which you can find list of all transport streams in the network. In this loop there are as well descriptors that tells you on which frequency there is each transport stream broadcast.
See delivery_descriptor in NIT table for new added transport stream.
Przemo's hint to the NIT is correct. It is defined in ETSI EN 300 468. That document will also tell you about the delivery system descriptors in the NIT.
how to use AT+CWLAP in esp8266 to get wifi signal strength? I want to get the signal strength which is displayed on the serial monitor and use it in my code in arduino IDE!
After sending the AT+CWLAP command, ESP8266 will answer with a list of all available AP's detected.
The format of the response will be like:
+CWLAP:<ecn>,<ssid>,<rssi>,<mac>,<freq offset,<freq calibration>
where:
<ecn>: indicates the security level, from 0 (OPEN) to 4 (Maximum security level)
<ssid>: it's the ssid of the AP
<rssi>: it's the signal strength, which is indicated in decibel format (e.g. -70)
<mac>: it's the MAC address
<ch>: channel
<freq offset>: ut's the frequency offset of AP，unit：KHz.
<freq calibration>: it's the calibration for frequency offset
So, the <rssi> parameter is what you are interested in.
Maybe, depending on the firmware version of your ESP8266, it's possible that AT+CWLAP command returns a different number of parameters, omitting, for example, the last four.
When a receiving node would like to ACK acknowledge the receipt of a frame, what exactly is it supposed to transmit?
The same frame just with a dominant bit for ACK?
No, every CAN node controller on the bus will usually listen to a message transferred and will automatically check this frame for correctness (CRC).
And it will usually also acknowledge the message by overwriting the recessive ACK=1 ("send" by the transmitter) with a dominant ACK=0 during message transfer. So there is no second message needed to acknowledge the first one.
That's also why you can't have any CAN bus with just one node, because there is no one else to acknowledge and check its sent frames.
Of course, in some controllers these checks can be deactivated or ignored, but not in the common use case.
I am using Corona sdk to create a multiplayer game. Each device sends 15 messages per second containing the position of their character. This results in a choppy movement because some messages take slightly different times to be received and it only sends 15 per second in a 30 fps game. How could I take the difference in the position or rotation of the character from the previous frame to current frame to predict the position if no data is received in the next frame. I am completely open to other solutions too! Thanks!
If the send rate is fixed and known to both parties (sender and receiver), then the receiver can assume it. In that case, dead reckoning is a well-established technique that is easy to apply. For example, if sender sends data every 1/15th second, then receiver can assume that, after the first packet has been received, any other packets will be 1/15th second apart. If something is not received after 1/15th second, then receiver makes a guess as to what the data would be at 1/15th second if it had been received. Then when the packet actually comes, it corrects the guess.
The only thing to guarantee is the order of packets, and delivery. If packets never drop, and always get there in order (i.e., TCP), you're laughing.
If order is guaranteed but some get dropped, then receiver needs to know when drop occurred. I think this could be corrected via a counter that is part of packet. So if receiver gets a packet with counter = X, and next packet has packet = X+2, then receiver knows that the packet was dropped because order is guaranteed, so time delta between the two is 2/15th second.
If no dropping but order not guaranteed, the counter will help there too: your receiver is guaranteed that if X has arrived, X+1 will arrive eventually, so even if it gets X+2, it should save X+2 and wait till X+1 arrives.
Finally, if neither delivery nor order are guaranteed (the case of UDP packets on a WAN), then once more counter is sufficient, but the algorithm changes: if it gets packet with counter=X, and it gets X+2, it could mean that X+1 has been dropped, or will arrive shortly, but there is no way to know. So the receiver could wait a small amount (maybe another 1/15th second) if X+1 hasn't arrived by then, declare it as dropped (so if does eventually arrive it will be ignored).
The near-constant frequency of sender is critical in the above.
I would like to create a DSP plugin which takes an input of 8 channels (the 7.1 speaker mode), does some processing then returns the data to 2 output channels. My plan was to use setspeakermode to FMOD_SPEAKERMODE_7POINT1 and FMOD_DSP_DESCRIPTION.channels to 2 but that didnt work, both in and out channels were showing as 2 in my FMOD_DSP_READCALLBACK function.
How can I do this?
You cannot perform a true downmix in FMODEx using the DSP plugin interface. The best you can do is process the incoming 8ch data, then fill just the front left and front right parts of the output buffer leaving the rest silent.
Setting the channel count to 2 tells FMOD your DSP can only handle stereo signal, setting the count to 0 means any channel count.