Qing Zhou Francis C. M. Lau Analytical performance of M-ary time-hopping orthogonal PPM UWB systems under multiple access interference. 1780-1784 2008 56 IEEE Transactions on Communications 11 http://dx.doi.org/10.1109/TCOMM.2008.070016 db/journals/tcom/tcom56.html#ZhouL08