On CDMA with space--time codes over multipath fading channels

Abstract

We explore in this paper code division multiple access systems with multiple transmitter and receiver antennae combined with algebraic constellations over a quasi-static multipath fading channel. We first propose a technique to obtain transmit diversity for a single user over quasi-static fading channels by combining algebraic constellations with full spatial diversity and spreading sequences with good cross-correlation properties. The proposed scheme is then generalized to a multiuser system using the same algebraic constellation and different spreading sequences. We also propose a linear multiuser detector based on the combination of linear decorrelation with respect to all users, and the application of the sphere decoder to decode each user separately. Finally, we consider the generalization to multipath fading channels where the additional diversity advantage due to multipath is exploited by the sphere decoder, and a method of blind channel estimation based on subspace decomposition is examined.

Iterative Multiuser Detection and Decoding for DS-CDMA System With Space-Time Linear Dispersion

“…(31)]) does not offer full diversity. Damen et al proposed a class of high-rate full-transmit diversity-based space-time CDMA systems in [23]. However, they actually use space codes instead of space-time codes.…”

“…However, they actually use space codes instead of space-time codes. Note that in [23], N t source data symbols are transformed using a signal space diversity rotation to obtain N t coded symbols, and each of the coded symbols is spread through a signature sequence. Although these spread symbols are over time, the signatures are not spread over multiple data symbols.…”

“…Although these spread symbols are over time, the signatures are not spread over multiple data symbols. The approach in [23] actually limits the potential to exploit time diversity in signal levels.…”

Full-rate, full-diversity space-time codes in asynchronous DS/CDMA with joint sphere decoding and interference suppression

“…Furthermore, when the number of receive antennas is greater than two, it has been shown that the Alamouti scheme loses some multiplexing gain [7], and thus, is not optimal. Applying the diagonal ST codes to DS/CDMA was proposed in [8]. Again, this system has to be synchronous and use orthogonal spreading codes to separate different transmit antennas.…”

“…As far as the diversity-multiplexing tradeoff is concerned [7], we adopt the threaded algebraic space-time (TAST) code recently proposed in [8], which can achieve the full transmission rate as well as maintain the full diversity gain. In asynchronous DS/CDMA, chip-level oversampling is usually followed by an MMSE detector to suppress the MAI [3].…”