Power spectral density characteristics of MCSK based impulse radios in UWB communications

This paper studies the power spectral density (PSD) characteristics of ultra wideband (UWB) signals modulated by M-ary code shift keying (MCSK)/binary pulse position modulation (BPPM) and MCSK/binary pulse amplitude modulation (BPAM), which we refer to as MCSK based impulse radios (IRs). MCSK/BPPM is a recently proposed UWB modulation format that can achieve a high data rate without affecting pulse shaping and further improve the bit-error-rate (BER) performance subject to the same signal energy per bit. The MCSK/BPPM increases the effective time hopping (TH) code period by randomly selecting a TH code from a set of M distinct codes per user. This selection smooths the continuous spectrum and suppresses the discrete spectral components, which is desired for real implementation. For a complete PSD evaluation of MCSK based IRs, also the PSD of MCSK/BPAM is studied. The analysis shows that MCSK/BPPM and MCSK/BPAM systems achieve improved PSD characteristics over the conventional TH-BPPM and TH-BPAM systems. Suggestions are also made to improve the PSD characteristics of conventional TH systems.