Comparison of time and frequency domain processing of a multi-carrier spread-spectrum system

Multi-carrier spread-spectrum (MC-SS) modulation is a new kind of spread-spectrum modulation[1],[2]. The spreading code is designed in the frequency domain. Hence, the system is dual to a direct-sequence spread-system (DS-SS) where the spreading code is given in the time domain. There exist two different views: the OFDM view and the DS-SS view. Many publications deal with the frequency domain processing. Transmitter and receiver structures are similar to OFDM. Therefore all these implementations use a guard interval to avoid ISI. The disadvantage of this guard interval is the higher hardware complexity and the waste of symbol energy. In the following paper the effect of ISI on a MC-SS system is investigated. Both types of implementation (time or frequency domain) are compared and the dependencies of the performance from the spreading code are demonstrated. It is shown that with proper code selection and a rime domain implementation without guard interval (RAKE receiver) it is possible to outperform equivalent frequency domain receivers with guard interval (MRC).