Question about NRZ data, anyone know this either?

[uptonogoode]

I have a baseband which is an NRZ data stream. Its a typical, run-of-the-mill data stream at, say, 100 Mbps. It has a spectrum shaped like a sinc, which begins at zero Hz, and its first null is at a frequency (hz) equal to the data rate (bps).

To transmit wirelessly, the normal thing to do is use a modulation scheme like QPSK, for example. But suppose I dont modulate this, but instead simply up-convert, transmit over some distance, and down-convert.

Question: What bad, unforseen things happen to my signal at the receiver? Can anyone tell me why I shouldn't do this? No one does this, and I have a feeling there are good reasons why. Any smart radio people have answers in a nutshell?

Here are my guesses:

Bandwidth efficiency sucks?
Clock recovery isnt possible?
Baseband spectra has a DC component that wont be recovered?
Receiver LO has no way to phase lock with transmitter LO? But then what happens if not?
All of the above? Or something else?

Thanks a million people. --Upton O Goode

[abhityagi85]

hello dear
wireless medium is the only critera u should look at. First thing is if yo simply wish to test, u can use simple upconverion and downconversion. no probs. but if u look at BER, u will find that for a given SNR, some modulation schemes work better than others. Some have good bandwidth efficiency han others. some has better immunity to fading especially OFDM to say.

Some of the above things may be undesired for u and may certainly affect your decision to choose which one to take.

importantly apart from taht you will have to do some source coding to reduce the redundancy in message. also you will have o introduce some knpwn-redundancy in form of error detectiona nd correction codes.

Whats u decide, tell to me too.
<abhityagi85[at]gmail.com>

[sujanraj]

I think, Key problem associated with your modulation scheme is the DC component and low frequency component of the signal. The wireless channel acts as high pass filter, meaning no dc signal (and low frequency component)will be transmitted. I think this will explain why your signal is like that at the receiver.