The equivalent path model for evaluating multi-carrier CDMA transmission characteristics under multi-path fading environment exceeding guard interval

摘要

MC-CDMA, which is based on OFDM and CDMA, is a major candidate for systems beyond IMT-2000. A time-domain spreading MC-CDMA system that has consecutive pilot symbols can achieve high quality channel estimation in fast fading environments. Furthermore, it is known that time-domain spreading MC-CDMA is suited to the use of AMC (adaptive modulation and channel coding). MC-CDMA based on OFDM generally has a guard interval (GI), which is a cyclic prefix to avoid the intersymbol interference (ISI) and interchannel interference (ICI) caused by delay paths. The receiving characteristics of MC-CDMA are significantly degraded by ISI and ICI when there are delayed paths that exceed the GI. To accurately estimate the transmission characteristics, we need an accurate delay profile model that well reflects actual delay profiles. The existing model is, however, very complicated, so it cannot be used in computer simulations. We propose an extremely simple equivalent path model for time-domain code spreading MC-CDMA; it consists of just two paths but its transmission characteristics are reasonable if the delay profile has paths that exceed GI. Computer simulation results validate the proposed model. Moreover, we consider a parameter to characterize the model with which we transform an arbitrary path model into the equivalent path model.