Effects of Code Design on the Spectral Characteristics of MCSK Based Impulse Radios

Abstract

This paper investigates the effects of code design on the power spectral density (PSD) characteristics of M-ary code shift keying (MCSK) based impulse radios (IRs) used in ultra wideband (UWB) communications. MCSK based IRs are modified IRs that were designed to increase the data rate by randomly selecting a time hopping (TH) code from a set of M distinct TH codes per user. This selection 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 studied in detail in the paper. Accordingly, the trade-off between efficient spectrum shaping and MA capability is discussed for different code design criteria, which should be carefully addressed for real system implementation.