A New MSINR Guided Concurrent Multimodulus Adaptive Array (MSINR-GCMMARY) for Enhanced Performance of MC-CDMA Uplink

摘要

Multi-Carrier Code-Division Multiple-Access (MC-CDMA) scheme has been proposed [1] as an efficient transmission scheme. It combines CDMA scheme and Orthogonal Frequency Division Multiplexing (OFDM) technique, so that ISI can be reduced at high data rates. OFDM systems are sensitive to carrier frequency offsets (CFO) due to the relative motion between the transmitter and the receiver or the mismatch between transmit-and-receive oscillators due to drifts from their nominal frequencies. CFO results in loss of orthogonality among the subcarriers and induces intercarrier interference (ICI). In addition, it causes continuous phase rotation and smearing of the signal constellations, especially in high QAM modulation, and hence severe performance degradation. The performance and capacity of MC-CDMA can be further improved by using adaptive antenna arrays at base stations [2]. A blind adaptive beamforming algorithm based on the Maximum Signal-to-Interference-and-Noise Ratio (MSINR) criterion was suggested in [2]. Such a blind algorithm suffers from the phase ambiguity problem. On the other hand, blind multi-modulus array (MMARY) adaptive beam-forming [3]-[4] can be used to recover all co-channel signals without using a reference signal and without assuming prior knowledge of the array direction characteristics. The MMARY overcomes the phase ambiguity problem and it can also handle high order signal constellations. The main drawback of the MMARY is that it extracts the incident signal which has the dominant power (which may not be the desired signal) at the output of the array while nulling other signals [4]-[5]. In this paper, we suggest the use of an adaptive array algorithm that combines a MMA adaptation with the MSINR adaptation. The resultant algorithm is named the MSINR-GMMARY array which combines the best features of both algorithms to yield a more robust adaptation criterion when used in MC-CDMA systems.