Modem Data

Origin

Two (2) sequences of received data from V.29, 9600 bps modems are provided. The first sequence, in data1.mat , is a short block of training data, of about 1.5 seconds, where the modem goes through a carrier synchronizing procedure, followed by a known PN sequence of symbols. The second sequence, in data2.mat, is about 4.75 seconds of "random" data. Both sequences are T/2 sampled at 4800 Hz. The carrier has been removed to the limits of practical implementation, but some offset remains. The power level has been normalized to about unity. The data was obtained over a PBX line with a well behaved bandpass response, starting a gradual rollup at about 1100 Hz and a gradual rolloff at about 2300 Hz (the carrier is at about 1700 Hz).

Matlab code

The code provided below is used to load a modem received sequence and to plot its power spectral density. Check Cornell University Blind Equalization Research Group for a demonstration of blind channel equalization of the received data.

 

%%% 
clear
load data1
 
% Plot rcvd signal
figure(1)
plot(data,'.');
 
% Plot PSD of signal
figure(2)
[P,F]=psd(data);
semilogy(F*1700,fftshift(P));
xlabel('Power Spectrum Magnitude (dB)');
ylabel('Frequency');

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10/10/96