Elsevier

Signal Processing

Volume 80, Issue 4, April 2000, Pages 731-736
Signal Processing

PN code acquisition using nonparametric detectors in DS/CDMA systems

https://doi.org/10.1016/S0165-1684(99)00164-4Get rights and content

Abstract

In this paper, we propose to use a new nonparametric noncoherent detector for PN code acquisition in DS/CDMA systems. Because this detector is nonparametric, we can decide the threshold of the detector without first having to estimate the variance of time-varying interference. We compare the single-dwell scheme using the proposed detector with that using the conventional detector. From the simulation results, it is clear that the DS/CDMA system with the proposed detector has better performance than that with the conventional detector when the exact estimation of the interference variance is not possible.

Zusammenfassung

In diesem Artikel schlagen wir vor, einen neuen, nichtparametrischen, nichtkohärenten Detektor zur Erfassung von PN Codes in DS/CDMA Systemen zu benutzen. Da es sich um einen nichtparametrischen Detektor handelt, können wir seine Schwelle ohne vorhergehende Schätzung der Varianz der zeitveränderlichen Störung festlegen. Wir vergleichen die single-dwell Methode, die den vorgeschlagenen Detektor benutzt mit der konventionellen Methode. Anhand der Simulationsergebnisse wird deutlich, daß das DS/CDMA System mit dem vorgeschlagenen Detektor bessere Ergebnisse liefert, als mit dem konventionellen Detektor wenn eine exakte Schätzung der Störvarianz nicht möglich ist.

Résumé

Dans cet article, nous proposons d'utiliser un nouveau détecteur non cohérent non paramétrique pour l'acquisition de codes PN dans des systèmes DS/CDMA. Parce que ce détecteur est non paramétrique, nous pouvons décider du seuil de ce détecteur sans avoir à estimer d'abord la variance de l'interférence variant dans le temps. Nous comparons le schéma à retard unique en utilisant le détecteur proposé avec celui utilisant le détecteur conventionnel. Des résultats de simulation, il est clair que le système DS/CDMA avec le détecteur proposé a de meilleures performances que celui avec le détecteur conventionnel lorsque l'estimation exacte de la variance des interférences n'est pas possible.

Introduction

Before the receiver and transmitter in a direct sequence code division multiple access (DS/CDMA) system start communicating each other, the receiver must first synchronize the local despreading pseudonoise (PN) code sequence to the incoming spreading PN code sequence. The synchronization process generally consists of two steps: code acquisition and tracking. The code acquisition is a process of successive decisions wherein the final goal is to bring the two code sequences into (at least) coarse time alignment within a fraction g of the chip duration Tc. After the successful code acquisition, a code tracking loop is used to synchronize the two code sequences even more accurately. In this paper, we consider the code acquisition problem [2], [6], [7], [8], [9].

The basic unit in any acquisition receiver is the decision-making device, that is, a detector. In the conventional parametric detectors, we should estimate the variance of interference to decide the threshold [3], [4]. Yet, estimating the variance of time-varying interference exactly may not be possible in many cases. In this paper, we propose to use a new nonparametric noncoherent detector for PN code acquisition in DS/CDMA systems. We can decide the threshold of the detector without first estimating the variance of the interference, because this detector is nonparametric [1], [5].

Section snippets

System description

Let us consider the noncoherent biphase-shift keying (BPSK) demodulator in DS/CDMA systems. Without loss of generality, we assume that the transmitted data is +1 for the code acquisition. Assuming that the kth user is the desired user, we can describe the input r(t) of the BPSK demodulator for the kth user asr(t)=i=1Ku[2Eici(t+τi)cos(2πf0t+φi)]+n(t),whereci(t)=1Tcn=−∞ai(n)[U(t)−U(t−Tc)].In (1), Ku is the number of users, Ei is the ith user's energy per chip, ci(t) is the ith user's pulse

Nonparametric detector analysis

In this section, we assume that the carrier phase φk is constant over the N chips and g=1. The test statistic of the proposed nonparametric noncoherent detector for the kth user isT(ykI,ykQ)=i=1Nsgn(ykI(i))+i=1Nsgn(ykQ(i)),wheresgn(z)=1ifz⩾0,−1ifz<0.We denote the first and second terms in the right-hand side of (6) by T1 and T2, respectively.

We first calculate the probability mass functions (pmf 's) of T1,T2, and T under the null hypothesis H0. We assume that N is even. From the fact that Pr{yk

Simulation results

In this section, we compare the single-dwell scheme without the verification mode using the proposed detector with that using the conventional detector. As a performance measure, we use the time elapses prior to acquisition, which will be called the code acquisition time Tacq. When the timing error is uniformly distributed, the average code acquisition time of the single-dwell scheme without the verification mode is [7]E{Tacq}=1+(1+KPFA)L−12(2−PD)td/PD,where K is the penalty time factor, L is

Conclusions

In this paper, we proposed to use a new nonparametric noncoherent detector for PN code acquisition in DS/CDMA systems. We showed that we could decide the threshold of the detector without estimating the variance of time-varying interference, because this detector was nonparametric. From the simulation results, we observed that the DS/CDMA system with the proposed detector had better performance than that with the conventional detector when the exact estimation of the interference variance was

Acknowledgements

This research was supported by Korea Research Foundation (KRF) under a 1998 Grant, for which the authors would like to express their thanks. The authors also wish to thank the anonymous reviewers for their constructive suggestions and comments.

References (9)

There are more references available in the full text version of this article.

Cited by (10)

  • Permutation tests for nonparametric detection

    2012, Signal Processing
    Citation Excerpt :

    Applications of rank tests to radar detection can be found in [20–24] and references therein. Other rank applications to (wireless) communications are, for example, in [25–29] and references therein. Finally, although rank tests have been applied to detection [16–29], the more general family of permutation tests has seldom been applied to radar detection [30–35], at least, as far as the authors know.

  • A method of PN code acquisition using signed-rank-based nonparametric detector in multiplicative noise

    2010, Dianzi Yu Xinxi Xuebao/Journal of Electronics and Information Technology
  • A approach to DS-SS signal acquisition using larger step and serial acquisition algorithm

    2007, Proceedings of the 2007 IEEE International Conference on Mechatronics and Automation, ICMA 2007
View all citing articles on Scopus
View full text