DETAILED DESCRIPTION Receiver 100 shown in FIG.
1 is adapted for use in a voiceband data set, or modem.
Although not shown in the FIG.
, receiver 100 may operate under microprocessor control.
Receiver 100 is illustratively used in a communication system employing quadrature-amplitude modulation (QAM).
In particular, four information bits, comprising a so-called data symbol, are communicated once every T=1/2400 sec.
The symbol rate is thus 2400 baud, yielding a binary data transmission rate of 9600 bits per second.
The four bits to be transmitted are encoded into two signal levels, each of which can take on one of the four values +1, -1, +3, -3.
The two signal levels amplitude modulate respective 1800 Hz in-phase and quadrature-phase carrier waves which, in combination, comprise the transmitted QAM signal.
The QAM signal, representing a succession of data symbols transmitted at a rate of 1/T symbols per second, is received by receiver 100 on lead 116.
This passband input signal, r(t), passes to analog input circuitry 120 comprised of a bandpass filter and Hilbert transform circuit.
The output of circuitry 120 is comprised of a Hilbert transform pair r(t) and f(t) derived from the received passband signal.
These are passed to an A/D converter 125 on leads 122 and 123.
A master clock 130 generates 128 master clock pulses every T seconds on lead 131.
These are received by receiver timing generator 135.
The latter counts the pulses on lead 131 and generates timing signals on a number of output leads to control the sequencing of the various signal processing functions within the modem.
One of these leads shown explicitly is lead 136.
The latter extends pulses to A/D converter 125 at a rate which causes A/D converter 125 to generate line samples at p/T samples per second.
The parameter p is illustratively equal to 2.
A/D converter 125 thus generates two complex passband, i.
e.
, modulated, line samples R.
sub.
m and R.
sub.
m ' during the m.
sup.
th receiver symbol interval.
(An alternative way of generating R
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Multiplexer-related 
