function [kc, valid, Zf] = frame_timing(Z, bins_timing_pilots, sym_per_frame, Zi)

N = length(Z);

if (~isfield(Zi, 'valid'))
    Zi = struct('valid', 1, 'Zk', []);
end

if 1
    valid = 0;
    kc = 0;
    if ~isempty(Zi.Zk)
        Xk = Z .* conj(Zi.Zk);
        if 0
            plot(0:length(Xk)-1, abs(Xk), '-*'); grid;
            pause (0.01); 
        end
        valid = 1;
        kc = mean(abs(Xk));
    end
    Zi.Zk = Z;
end
Zf = Zi;