function [ltmps, alpha, w] = channel (ps, pf_d, pSNR)

    global model; 
    lfd_s=5000;

    ltaps = 1; lpow = 1; llags = 1;
    if (strcmp(model.multipath, 'none') ~= 1)
	ltaps = gen_multipath(model.multipath);
	llags = find (ltaps ~= 0);
	lpow = ltaps (llags);
    end
    lnpaths = size(llags, 2);

    alpha = ones(lnpaths, model.n_t);
    w = zeros(lnpaths, model.n_t);

    if (model.fading == 1)
	alpha = gen_rayleigh(max(pf_d), lfd_s, model.n_t, lnpaths);
	P_alpha = sum(alpha.^2, 2) / model.n_t,
	alpha = alpha ./ repmat(sqrt(P_alpha), [1 model.n_t]);
    end

    if (model.noise == 1) w = wgn(lnpaths, model.n_t, 1, 'complex'); end
    N_f = 10^(-pSNR / 20)
    w = w * N_f;

    ltmps = repmat(ps, [lnpaths 1]) .* alpha + w;
    ltmp = zeros(lnpaths, model.n_t + size(ltaps, 2));
    for lp = 1:lnpaths
	ltmp(lp,llags(lp):model.n_t + llags(lp) - 1) = ltmps(lp,:) * lpow(lp);
    end
    ltmps = sum(ltmp(:,1:model.n_t), 1);

end