function [hN,N] = uwb_sv_cnvrt_ct( h_ct, t, np, num_channels, ts )
% convert continuous-time channel model h_ct to N-times oversampled discrete-time samples
% h_ct, t, np, and num_channels are as specified in uwb_sv_model
% ts is the desired time resolution
% 
% hN will be produced with time resolution ts / N.
% It is up to the user to then apply any filtering and/or complex downconversion and then
% decimate by N to finally obtain an impulse response at time resolution ts.

min_Nfs = 100; % GHz
N = max( 1, ceil(min_Nfs*ts) );  % N*fs = N/ts is the intermediate sampling frequency before decimation
N = 2^nextpow2(N); % make N a power of 2 to facilitate efficient multi-stage decimation
% NOTE: if we force N = 1 and ts = 0.167, the resulting channel hN will be identical to
% the results from earlier versions that did not use continuous-time.
Nfs = N / ts;
t_max = max(t(:));  % maximum time value across all channels
h_len = 1 + floor(t_max * Nfs);  % number of time samples at resolution ts / N
hN = zeros(h_len,num_channels);
for k = 1:num_channels
  np_k = np(k);  % number of paths in this channel
  t_Nfs = 1 + floor(t(1:np_k,k) * Nfs);  % vector of quantized time indices for this channel
  for n = 1:np_k
    hN(t_Nfs(n),k) = hN(t_Nfs(n),k) + h_ct(n,k);
  end
end