Linear adaptive transmitter-receiver structures for asynchronous CDMA systems

Abstract

An asynchronous code-division multiple access (CDMA) system with adaptive transmitters and receivers is considered. It is assumed that the adaptive receiver and transmitter have no knowledge of the signature waveforms and timing of other users. The concept of adaptive transmitter is based on feedback information from the comsponding receiver. The information obtained from the receiver is used to calculate the optimum transmitter signature. The signatures are adaptively adjusted according to the MSE criterion during the training period as well as during data transmission.CDMA systems employing the adaptive transmitters in the presence of multiple access interference achieve the matched filter bound with no interference. The proposed CDMA system are tested by simulation over a channel with multiple access interference and additive white gilussian noise. Recently proposed CDMA schemes [4] sugest usage of the same bandwidth for forward link and reverse link.This concept of communication allows the transmitter in forward link to 'know' in advance conditions of propagation and channel parametars based on information received in reverse link. The information obtained from the receiver is used to calculate the optimum signature for the respective transmitter. The signatures are adaptively adjusted according to the MSE criterion of optimality during the training period as well as during the data transmission. The rest of the paper is organized as follows. The system model is defined in section 2. In section 3 the proposed model is analyzed and the optimum solution for Vol. 6. NO. I January -February 1995 L l Predrag B. Rapajic, Branlia S. Vucetic

Wireless systems and interference avoidance

“…The filter is equivalent to forming in the decorrelated space and then renormalizing where is the eigenvalue matrix of . It is known that codewords might be adapted for single users to obtain better mean square error (MSE) performance [30], [31]. The following theorem, proven in [9], [30], and [32] shows that the MMSE algorithm is indeed an interference avoidance algorithm.…”

“…However, has a full set of eigenvectors so there exists an additional set of eigenvectors each of which is orthogonal to the . If , is one such eigenvector, then it must also be an eigenvector of since (30) With no loss of generality, let us assume that the first eigenvectors of , are exactly these and that the corresponding eigenvalues are exactly the . 5 Since the eigenvectors collectively span and the eigenvectors comprise the orthogonal complement of the , we can expand the in , as…”

Interference Avoidance for Wireless Systems

“…' Interference avoidance was originally introduced in the context of ''chip-based'' DS-CDMA systems [11] and minimum mean-square error (MMSE) receivers, but was subsequently developed in a general signal space [12][13][14] framework [15,16] which makes them applicable to a wide variety of communication scenarios. Related methods for transmitter and receiver adaptation have also been used in the CDMA context for asynchronous systems [17] and systems affected by multipath [18].…”

Codeword optimization for uplink CDMA dispersive channels

“…We also note the work of Kasturia et al [13] and Lechleider [14] that propose codeword design methods for block transmissions suited for multicarrier modulation systems. More recently, in the context of multiuser detection, methods for transmitter and receiver adaptation [20] have also been used for nonideal channels, although not for a multicarrier modulation framework in particular. Here, we note the work of Rajappan and Honig [19] and that of Concha and Ulukus [3].…”