Spectral characteristics of M-ary code shift keying based impulse radios: Effects of code design

This paper analyzes the power spectral density (PSD) characteristics of ultra wideband (UWB) signals modulated by M-ary code shift keying (MCSK) that can be combined with binary pulse position modulation (BPPM) and binary pulse amplitude modulation (BPAM), which we refer to as MCSK based impulse radios (IRs). MCSK based IRs are modified IRs that were designed to increase the data rate of conventional IRs by embedding the data on a time hopping (TH) code randomly selected from a set of M distinct TH codes per user. This random selection also results in increased effective TH code period, which helps smoothing the continuous spectrum and suppressing the discrete spectral components. In combination with the random code selection, design of the TH code set for each user is very important for spectrum shaping and multiple access (MA) capability, and is addressed in detail in the paper.