Doppler and multipath properties of quadriphase signal design without co-channel interference nor detection sidelobe for uplink in approximately synchronized cellular CDMA systems

Abstract

Power control or interference cancellation requires a heavy cost for the uplink in mobile CDMA systems. Suehiro (1993, 1994) proposed a 4-phase signal design for approximately synchronized CDMA systems without co-channel interference. In the proposed 4-phase signal design, each user is assigned a carrier frequency, some 4-phase sequence of finite length with pseudo-periodic property and comb-shaped spectrum, and a matched filter for the central large part of the assigned sequence. When the assigned sequence of the comb-shaped spectrum is modulated by the carrier the obtained signal has a comb-shaped spread spectrum. The carriers are assigned to each user so that any two of the users have an orthogonal comb-spectrum to each other. Because each user has a filter which is matched to the central part of the assigned sequence, no user receives co-channel interference near the main detection pulse under the condition of approximate synchronization. The Doppler effect and the multipath properties are simulated. When the carrier frequencies are about 2000 MHz, the signals works almost without co-channel interference under the Doppler shift at 1000 km/h. This result of simulation shows the usefulness of the 4-phase signal design without co-channel interference for an approximately synchronized uplink in cellular CDMA systems.