SPC11-2: Blind Multiuser Detection in Multirate CDMA Transmissions Using Fluctuations of Correlation Estimators

Abstract

This paper deals with the problem of blind multiuser detection in multirate direct-sequence code division multiple access (DS-CDMA). Direct-Sequence Spread Spectrum (DS-SS) signals are well-known for their low probability of interception: their statistics are similar to those of a noise; furthermore, they are usually transmitted below the noise level. Here, the method based on the fluctuations of autocorrelation estimators, previously described in a single user context [1], is extended to multiusers. From the variable spreading length technique, we will evidence an increase of these periodical fluctuations and, on average, a relationship between their peak amplitudes and sequence lengths. A theoretical analysis will show that detection is possible, even with a very low signal-to-noise ratio (SNR) at the detector input. This approach will be illustrated with experimental results. The assessment of symbol periods allows one to start the synchronization process proposed recently in [2], [3], which also permits the determination of the number of interfering users in each group of users transmitting at the same symbol period, thus, conversely at the same data rate.

Blind MC-DS-CDMA Parameters Estimation in Frequency Selective Channels

“…Thus, we derive the improved blind scheme [10], [11] to the case of MC-DS-CDMA transmission through a frequency selective channel which leads to a low computational cost, as shwon in Table I. Furthermore, combined with the blind source separation approach described in [14], the proposed scheme can be easily extended to the case of MIMO-MC-CDMA transmissions.…”

“…Only fluctuations due to the noise are uniformly distributed over all values of τ [10], [11]. Assuming a receiver filter with a flat frequency response in [−B W /2, +B W /2] ( B W > W in practice) and zero outside.…”

“…In this paper, we consequently extend the fast and efficient blind detection scheme based on the analysis of estimators of autocorrelation fluctuations previously successfully applied to DS-CDMA transmission [10], [11] to the case MC-DS-CDMA systems. We further demonstrate its efficiency in a frequency selective fading channel since it is insensitive to phase and frequency offsets.…”

Blind chip rate estimation in multirate CDMA transmissions using multirate sampling at slow flat fading channels

“…For blind bit rate estimation, we use fluctuation of correlation estimator [9]. To compute the fluctuations, we divide the received signal into M temporal windows with duration of T F for each window.…”

The blind periodic estimation of the pseudo noise sequence in multi-rate DS/CDMA transmissions

“…Therefore, in view of the multi-rate CDMA parameter estimation is particularly important. In [2], the method of using multi-rate sampling was proposed to estimate chip rate in multi-rate CDMA transmissions, [3] proposed a fluctuations of correlation algorithm to estimate periodic of the PN sequence in multi-rate DS/CDMA systems, [4] used FastICA to estimate the spreading sequence ,but the prior knowledge of the PN sequence period had already been acquired, [5] proposed a synchronization method based on Frobenius Square Norm Behaviour, and [6] also used eigenvalue decomposition to estimate the spreading sequence of multi-rate DS/CDMA.…”