Question in usrp transmitter example

[petroldevil]

In the usrp transmitter example:
what is the exact packet structure?

what is the padding samples? and how it differs from padding bits? and what is the fuction of the padding bits?

what is the function of the blank frame

thanks in advance

[PatJamSim]

Hello petroldevil,

I was unable to find a "usrp transmitter example."  I know we have quite a few NI examples for USRP, but none of them go by that name.

What example are you referring to?  What is its exact name?  Is it part of the NI Example Finder, or from the online Community, or perhaps from some other source?

[petroldevil]

USRPPacketTxRx

[PatJamSim]

The packet is structured as follows, in bits:

The packets are padded because the transmitter and receiver are not sharing any timing information, which means data could potentially be lost.  By adding padding samples, we are able to ensure that when the packet is received, none of the data will be lost at the front and back of the transmitted frame.  Take a look at this thread, which discusses this in more depth.

If you take a look at the block diagram of the USRP Packet Transmitter VI, you'll see a case structure that determines when to send packets to the receiver.  If the case structure reads the queue of samples to be sent as empty, it will instead send a blank frame matching the size specified in the above snippet.  The blank frame is used as an empty packet to ensure the connection is not lost.  If we were to simply not send any packet, then the receiver might assume that the connection was lost when instead we are simply not sending anything.  By sending an empty packet, the receiver knows the connection is still active, and can wait for a packet of actual data.