N = 20000;          % # symbols
h = [1 0.45 -0.2];  % channel impulse response
h = h/norm(h);
Le = 20;            % equalizer length
mu = 1E-3;          % step size
snr = 30;           % snr in dB
M = 10;             % oversample rate

tx_type = "bpsk";   % select modulation type here "bpsk" or "fsk"

if strcmp(tx_type, "bpsk")
  s0 = round( rand(N,1) )*2 - 1;     % BPSK signal
  s0M = zeros(N*M,1);                % oversampled BPSK signal
  k = 1;
  for i=1:M:N*M
   s0M(i:i+M-1) = s0(k);
    k ++;
  end
end

if strcmp(tx_type, "fsk")
  tx_bits = round(rand(1,N));

  % continuous phase FSK modulator

  w1 = pi/4;
  w2 = pi/2;
  tx_phase = 0;
  tx = zeros(M*N,1);

  for i=1:N
    for k=1:M
      if tx_bits(i)
        tx_phase += w2;
      else
        tx_phase += w1;
      end
      tx((i-1)*M+k) = exp(j*tx_phase);
    end
  end

  s0M = real(tx);
end

s = filter(h,1,s0M);                % filtered signal

% add Gaussian noise at desired snr

n = randn(N*M,1);
vs = var(s);
vn = vs*10^(-snr/10);
n = sqrt(vn)*n;
r = s + n;          % received signal

e = zeros(N*M,1);   % error
w = zeros(Le,1);    % equalizer coefficients
w(Le)=1;            % actual filter taps are flipud(w)!

yd = zeros(N*M,1);

for i = 1:N*M-Le,
    x = r(i:Le+i-1);
    y = w'*x;
    yd(i)=y;
    e(i) = y^2 - 1;
    w = w - mu * e(i) * y * x;
end

np = 100;           % # sybmols to plot (last np will be plotted); np < N!

figure(1); clf;
subplot(311), plot(e.*e), title('error')
subplot(312), stem(conv(flipud(w),h)), title('equalized channel impulse response')
subplot(313);
plot(1:np,s0M(N-np+1:N),1:np,yd(N-np+1-Le+1:N-Le+1))
title('transmitted and equalized signal'), legend('transmitted','equalized'), axis([0,np,-1.5,2])