Frequency shift based multiple access interference canceller for DS-CDMA systems

Abstract

Abstract-The cyclostationary properties of Direct Sequence Spread Spectrum signals are well known. These cyclostationary properties imply a redundancy between frequency components separated by multiples of the symbol rate. In this paper we present a Multiple Access Interference Canceller that explores this property and applies to UMTS-TDD. This frequency domain Canceller acts in the spreaded signal in such way that minimizes the interference and noise at its output (Minimum Mean Squared Error Criterium). The performance is evaluated in two detector configurations: one including the Frequency Shift Canceller (FSC) and the other plus a Parallel Interference Canceller (PIC). The results are benchmarked against the performance of the conventional RAKE detector and the conventional PIC detector.

Frequency shift based multiple access interference canceller for multirate UMTS-TDD systems

“…The conversion method between redundant bands expressed by (14) is the base of the FSC and represents a generalization of the technique developed in [5] where the use of a fixed spreading factor resulted a scalar transformation.…”

“…In the present paper we extend the work of [5] to include the general situation of UMTS-TDD where users with different spreading factors can coexist in the same time slot. This enables the transmission of services with different rates by varying the spreading factor, but the structure of the spreading (channelization times scrambling) in UMTS-TDD lead to codes that extend over several symbols.…”

“…In previous work [5] was defined and implemented the FSC for fixed spreading factor. The results show that considerable This work is being supported by a PhD Grant from PRAXIS XXI, Fundacão para a Ciência e Tecnologia and the projects ASILUM and VISEF improvement is achieved against the RAKE and the FSC even outperforms the PIC for moderate to high values of E b /N 0 .…”

Frequency domain equalizer for multirate UMTS-TDD systems

“…In previous work [5] the Frequency Shift Canceller (FSC) was defined and implemented for a fixed spreading factor. The results have shown that considerable improvement is achieved against the RAKE and the FSC even outperforms the PIC for moderate to high values of E b /N 0 .…”