PN Code Acquisition Scheme Research Articles

Adaptive Hybrid Acquisition of PN Sequences Based on Automatic Multipath Cancellation in Frequency-Selective Rayleigh Fading Channels

A hybrid PN-code acquisition scheme is proposed and studied for direct sequence code division multiple access communications in frequency-selective Rayleigh fading channels. The most important feature of the proposed system is its ability to dynamically estimate the number of multipath signals that may lie in the reference channel. The basic idea of the considered algorithm is to sort the partial correlations and carry out successive censoring tests by updating the noise estimation until the first path synchronization. Exact expressions for the probability of false alarm and the mean acquisition time are derived. The performances of the proposed system are then studied and compared with those of the adaptive hybrid acquisition processor (AHAP) and the ordered statistic hybrid acquisition processor (OSHAP). The effects of various channel parameters on the acquisition performance, namely the number of resolvable paths, the multipath intensity profile and the signal-to-noise ratio are also investigated. Numerical results show that the proposed acquisition scheme outperforms the conventional ones which are based on AHAP and OSHAP algorithms.

DS/SS code acquisition with joint detection of multiple correct cells using locally optimum test statistics in Rayleigh fading channels

A new PN code acquisition scheme is proposed based on the joint detection of correct cells ( H 1 cells) at which the code phase offset between the locally generated and received PN codes is within a desired small offset. Most of the acquisition schemes which have been proposed assume that there exists one and only one H 1 cell over the uncertainty region. However, in practical systems, there exist multiple H 1 cells. In this paper, using the locally optimum test statistic, the joint decision rule of two H 1 cells is derived for nonselective Rayleigh fading channels. Then, with the proposed acquisition scheme based on the joint decision rule, a closed-form expression of the mean acquisition time is obtained with the state diagram, and the probabilities of detection, missing, and false alarm are derived. The mean acquisition time performance of the proposed acquisition scheme is compared with that of a conventional acquisition scheme in which only an H 1 cell is used for detection at each step. The numerical results show that the proposed scheme not only has better performance but also is more robust to the residual code phase offset variation than the conventional scheme.

A coarse/fine search PN code acquisition scheme

A parallel two-stage acquisition technique is described for direct sequence spread spectrum (DS/SS) range finding applications. The technique offers hardware complexity that scales better with code length than matched filter correlators while providing better performance than sequential detection using comparable hardware.

New PN code acquisition scheme for CDMA networks with low signal-to-noise ratios

A new approach to PN code acquisition is presented and analyzed. A recirculation loop is used to improve probability of synchro cell detection P/sub D/ in each retrace of the code uncertainty region. To further improve P/sub D/ and probability of false alarm P/sub fa/ simultaneously, code diversity (a number of synchro channels in parallel) is used. This is especially effective in the channel with multiple access interference and near-far effect. Typical applications are networks with very low signal-to-noise ratio. Examples are code division multiple access (CDMA) LEO satellite systems experiencing high Doppler or any CDMA network where the number of users is approaching capacity limits. Even if the carrier Doppler is compensated, in any asynchronous LEO satellite network, compensation of code Doppler is not feasible. For this reason, in order to cope with code Doppler (D) and delay (/spl tau/), a modification based on transforming the two-dimensional uncertainty region (D, /spl tau/) into a new uncertainty region (T/sub c/, /spl tau/) will be introduced. Parameter T/sub c/ is the period of the correlation pulses at the output of a sliding correlator. When Doppler rate is present, the three-dimensional uncertainty region (D, R/sub d/, /spl tau/) is transformed into a new one (T/sub c/, R/sub t/, /spl tau/) where R/sub d/ and R/sub t/ are Doppler rate and correlation pulse period change rate, respectively. The main motivation for this work is to find new algorithms suitable for all digital receiver implementation and operation at low signal-to-noise ratios. These algorithms make CDMA techniques feasible for direct communication between LEO satellite and small ground-based user terminals (handsets). A comprehensive performance study of the new PN code acquisition system is presented and discussed. The results obtained demonstrate that, for low signal-to noise ratios, the acquisition time achieved with the new algorithm is one order of magnitude shorter compared with standard techniques known so far.

Noncoherent SPRT-based acquisition scheme for DSSS

A noncoherent sequential PN code acquisition scheme is proposed. The out-of-phase and on-phase sequences are properly modelled to avoid significantly high error probabilities occurring with the conventional SPRT-based acquisition. In addition, data modulation and frequency offset can be effectively overcome using this technique.