QAM modulation technique using verilog

Hi all Thanks for your feedback. i found some coding bout this. But seems like got error in certain line. Anyone expert to debug this?

module qam16(in,out);

input [0:3] in;

output out;

voltage in,out;

parameter real freq = 1.0 from (0:inf);

parameter real ampl = 1.0, thresh = 2.5;

parameter real tdelay = 0 from [0:inf),

ttransit = 1/freq;

real x,y,phi;

integer row,col;

analog

begin

row = 2*(V(in[3]) > thresh + V(in[2]) > thresh);

col = 2*(V(in[1]) > thresh + V(in[0]) > thresh);

x = transition(row-1.5,tdelay,ttransit);

y = transition(col-1.5,tdelay,ttransit);

phi = 2 * `M_PI * freq * $realtime();

V(out) <+ ampl * (x * cos(phi) + y * sin(phi));

end

endmodule

Thanks.

-John-