Design and performance analysis of UWB TH-MA scheme using multi-code based PPM

In this paper, we propose an UWB time-hopping multiple-access (TH-MA) scheme using multi-code based PPM. The multi-code signal, which is generated by spreading the desired user´s M transmitting bits with M orthogonal codes, is pulse-position modulated. At the receiver, the received signal is demodulated through two stages. In the first stage, the multi-code based PPM signal is demodulated through the Bayes decision rule. Then, in the second stage, the demodulated multi-code signal is de-spreaded by using the M orthogonal spreading codes that are used in the transmitter. The BER performance and bit transmission rate (R_b) of the proposed scheme is analyzed. Numerical results show that the proposed scheme has a much higher bit transmission rate than the conventional PPM scheme as M increases and also has better BER performance than the conventional PPM scheme in the same bit transmission case because it can achieve an additional spreading gain.