Currently, there are two received sequences available for V.29, 9600 bps modems. The first sequence, A, is a short block of training data (about 1.5 sec), where the modem goes through a carrier synchronizing procedure, followed by a known PN sequence of symbols. The second sequence, B, 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).
See below for received signal eye diagrams and power spectral densities. The pictures were generated using the following Matlab commands:
load data1
% Plot rcvd signal
figure(1)
plot(data,'.');
% Plot PSD of signal
figure(2)
[Paa,F]=psd(data);
semilogy(F*1700,fftshift(Paa));
ylabel('Power Spectrum Magnitude (dB)');
xlabel('Frequency');
