RE: Audio from microphone and modulation, basic questions

[eriym]

Hello,

I am using Labview communications and plan to use the USRP2901 for wireless transmission later.

For now, I am trying to acquire audio data from my microphone and then transform it into bits and input this into the PSK modulation. To acquire the sound data I was told to use the "Continuous sound input" from Labview's examples and also for the PSK modulation, I want to use the transmitter "PSK Tx" that is also an example in Labview comms.

I am a beginner with labview and feel that I lack some basic understanding, so here are my questions:

- I know that IQ Rate means the sampling frequency (sample rate)

- I know that PSK modulation maps Bits into Symbols (BPSK maps 1 bits into 1 symbol, QPSK maps 2 bits into 1 symbol..)

- I understand the bits that get transformed into symbols part, however where are the "samples" in all of this? I always hear about samples however I don't see their role here. In which stage of the modulation chain, are we working with samples?

- What does "1 frame of data" in all of this mean? does a frame contain symbols, or samples? 

- I hear my teacher talking about "us wanting to use 8bits" which means 8bits in 1 byte of data I think, but why 8bits? and where in my labview examples am I supposed to specify this "8bits"

- Finally, how do I choose an IQ rate and also "number of samples/channel" ? does it have a relation to which type of modulation am I using?

Thank you!!

[Chan82 · Accepted solution]

Hi eriym,

From my understanding,

- I know that IQ Rate means the sampling frequency (sample rate)

--> Yes

- I know that PSK modulation maps Bits into Symbols (BPSK maps 1 bits into 1 symbol, QPSK maps 2 bits into 1 symbol..)

--> From Wikipedia, the modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted. In this case, digital information (Bits) is transformed into the discrete signal which varies some properties of a carrier signal. (https://en.wikipedia.org/wiki/Modulation)

- I understand the bits that get transformed into symbols part, however where are the "samples" in all of this? I always hear about samples however I don't see their role here. In which stage of the modulation chain, are we working with samples?

--> In mod_Continuous BB-PSK generation.gvi, the actual PSK modulation is performed. In this stage, bits are converted to PSK symbols then the tx filter is applied. Each sample of generated sequence from this process is the sample what you say.

- What does "1 frame of data" in all of this mean? does a frame contain symbols, or samples?

--> In PSK Tx.gvi example of LabVIEW Communications, a certain sample sequence is transmitted again and again. A frame means this sample sequence to be transmitted.

- I hear my teacher talking about "us wanting to use 8bits" which means 8bits in 1 byte of data I think, but why 8bits? and where in my labview examples am I supposed to specify this "8bits"

--> I believe that "8bits" means the resolution of the audio data from your microphone. In PSK transmission, the number of bits to be modulated at once is important. You can choose any modulation order if you want.

- Finally, how do I choose an IQ rate and also "number of samples/channel" ? does it have a relation to which type of modulation am I using?

--> I think the IQ rate is the design parameter you should choose. With the given total bits, if you change IQ rate, the symbol rate will be also changed. But USRP will be able to transmit PSK signals.

Thanks

[eriym]

Hello,

Thank you for your detailed reply, this has helped a lot.