function [range, range_idx] = get_range(s_T, s_R, r_0)
    global T_r delta_t len c range_t;

    % 只取第一个 T_r 的数据计算
    range_N = T_r / delta_t;
    s_T_first = [s_T(1:range_N), zeros(1, len - range_N)];
    s_R_first = [s_R(1:range_N), zeros(1, len - range_N)];

    s_T_fft = fft(s_T_first, len);
    s_R_fft = fft(s_R_first, len);

    % 发射信号和回波信号做相关
    p = ifft(s_R_fft .* conj(s_T_fft));
    norm_p = real(p).^2 + imag(p).^2;
    [~, range_idx] = max(norm_p);

    range = range_t(range_idx) * c / 2;
    % fprintf("predict range = %f\n", range);
    % fprintf("origin range = %f\n", r_0);
    % fprintf("err = %f\n", range - r_0);
    % fprintf("\n");
end