On Discrete Sufficient Statistics for Asynchronous Band-limited CDMA Systems

The problem of generating discrete sufficient statistics for statistical signal processing in Code Division Multiple Access (CDMA) systems is considered in context of the underlying channel bandwidth restrictions. In most analyses of CDMA systems, the derivation of discrete sufficient statistics is facilitated by first relaxing the bandwidth constraints on the noise and the signaling waveforms in the corresponding continuoustime system model. The validity of this approach is evaluated. In particular, it is shown that relaxing bandwidth constraints in the above fashion can produce inaccurate discrete system models that lead to anomalous results for signal processing in asynchronous CDMA systems. This is illustrated by considering the performance analyses of conventional matched filter detection, minimum mean squared error (MMSE) detection, and delay acquisition in these systems. The role of chip-matched filtering in generating accurate discrete sufficient statistics is also explored. Th..

On Discrete Sufficient Statistics for Detection in Asynchronous Band-limited CDMA Systems

The problem of generating discrete sufficient statistics for statistical signal processing in Code Division Multiple Access (CDMA) systems is considered in context of the underlying channel bandwidth restrictions. In most analyses of CDMA systems, the derivation of discrete sufficient statistics is facilitated by relaxing the bandwidth constraints on the noise and the signaling waveforms. It is shown that relaxing the constraints on the signaling waveforms can produce inaccurate discrete system models leading to anomalous results for detection in asynchronous CDMA systems. This is illustrated by considering the performance analyses of matched filter detection and minimum mean squared error (MMSE) detection. The role of chip-matched filtering in generating accurate discrete sufficient statistics is also explored. 1 Introduction In standard analyses of communication systems, the generation of sufficient statistics for detection /estimation at the receiver is facilitated by relaxing the..

Multiple-Access Interference Resistant Acquisition for CDMA Systems with Long Spreading Sequences

The problem of estimating the propagation delay of a new user in a (coded) DS/CDMA system in the presence of multiple access interference (MAI) is considered. MAI resistant acquisition schemes are developed for a general CDMA system without the constraint that the spreading sequences of the users repeat every symbol period. It is assumed that the spreading sequences and delays of the interfering users are known. However, knowledge of their amplitudes (which would need estimation) is not assumed, and their unreliable code-symbol estimates are not used. Under this scenario, the optimum maximum-likelihood (ML) scheme is derived. An approximation to the ML scheme, the AML scheme, is also presented for the situation where the chip timing is known a priori. The performance of the AML scheme is analyzed using a Gaussian approximation. Simulations show that the approximation is reasonably accurate, and that the AML performance is close to that of the ML scheme. Comparisons are also made with t..

of the Forward Link Only (FLO) Air Interface. The FLO Air

Abstract—This paper provides an overview of the physical laye