PN code acquisition using nonparametric detectors in DS/CDMA systems
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 aswhereIn (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 iswhereWe 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 , and T under the null hypothesis H0. We assume that N is even. From the fact that
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]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.
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2012, Signal ProcessingCitation 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.
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2007, Proceedings of the 2007 IEEE International Conference on Mechatronics and Automation, ICMA 2007