Mean Acquisition Time Performance Research Articles

Interleaving of local code replicas‐based rapid acquisition method for time division data multiplexing long pseudo‐noise‐code signals

In global navigation satellite system, to further improve acquisition and tracking performance and consequently improve anti-jamming capability of long pseudo-noise (PN)-code signals, time division data multiplexing technique is utilised. For the signals, how to avoid possible energy cancellation of odd and even chips and how to quickly test code phases as many as possible in parallel are two keys for rapid acquisition. In this study, an interleaving of local code replicas-based acquisition method is proposed. By interleaving odd-number and even-number chips of local code replicas, the proposed method breaks the intrinsic code phase relation of PN-codes, avoids the possible energy cancellation of odd and even chips, and accelerates the search process by testing more code phases through interleaved chips. The detection and mean acquisition time performance of the proposed method is analysed. It is shown that compared with the previous time-gate method, the proposed method greatly saves computation requirement by taking the advantage of frequency-domain correlation technique over time-domain one. Compared with the L2C-like method, the proposed method enhances the capability of testing code phases in parallel twice at the expense of degrading detection performance. Numerical results demonstrate that when the capability dominates over detection performance the proposed method is more desirable.

Partial-correlation-result reconstruction technique for weak global navigation satellite system long pseudo-noise-code acquisition

In global navigation satellite system (GNSS), the signals are very weak. In particular, when the signals are interfered by other signals or shadowed by heavy vegetation, mountains, buildings etc., they will be significantly attenuated and become much weaker. In the situation, for GNSS pseudo-noise (PN)-code acquisition, detection performance is critical. In the study, to improve the detection performance of the previously published double block zero-padding (DBZP) method for weak GNSS long PN-code signals, the authors propose to reconstruct the correlation results of DBZP. Taking the advantage of utilising the correlation results that correspond to part of received signal aligning with local signal and are discarded by DBZP, the technique expands coherent integration time. The effect of the proposed technique on detection and mean acquisition time performance is analysed. It is shown that after reconstructing correlation results the proposed technique expands coherent integration time to twice, improves detection performance about 1.3 dB and consequently further shortens mean acquisition time, whereas it does not increase the implementation complexity of a GNSS receiver. The technique is also applicable to other GNSS long PN-code acquisition methods such as the previously published direct average method and the overlap average method.

Mapping and overlapping based carrier frequency searching technique for rapid GNSS long PN-code acquisition

In global navigation satellite systems (GNSS), because of the long period and high chip rate of long pseudo-noise (PN) code, the rapid acquisition is hard to accomplish. To speed up search process, in the paper, a mapping and overlapping based carrier frequency searching technique is proposed. By mapping incoming signals of the same interval to different carrier frequency cells and overlapping together the mapped incoming signals that correspond to the same code phase, the technique reduces the number of the cells to be searched. The effect of the technique on detection and mean acquisition time performance is analyzed. It is shown that the technique reduces the cells to be searched and shortens mean acquisition time at the expense of degrading detection performance. The technique is fit to the previously published acquisition methods and is capable of improving their mean acquisition time performance. Numerical and simulation results validate the analysis.

Generalized zero-padding scheme for direct GPS P-code acquisition

Because of the long period and high chip rate of GPS P-code, direct acquisition is challenging. In the letter, the widely used zero-padding scheme (ZPS) for direct GPS P-code acquisition is generalized to investigate the effects of the ZPS on detection performance, parallel searching capability, and mean acquisition time. It is shown that, by adjusting the zeros padded to received signal according to signal to noise ratio, the generalized zero-padding scheme (GZPS) makes a better tradeoff between detection performance and parallel searching capability and further reduces mean acquisition time. The generalized zero-padding scheme can be easily applied to the previously proposed zero-padding method (ZPM) and the direct average method (DAM) to improve their mean acquisition time performance and it does not increase the implementation complexity of a receiver.

Initial and Post-Initial Code Acquisition in the Noncoherent Multiple-Input/Multiple-Output-Aided DS-CDMA Downlink

In this paper, we investigate the issues of both initial and post-initial acquisition schemes in the multiple-input/multiple-output (MIMO)-aided direct-sequence code-division multiple-access (DS-CDMA) downlink when communicating over spatially uncorrelated Rayleigh channels. The associated mean acquisition time (MAT) performance trends are characterized as a function of the number of MIMO elements. Furthermore, we characterize both the initial and post-initial acquisition performance as a function of the relevant system parameters. Our findings suggest that increasing the number of transmit antennas in a MIMO-aided CDMA system results in combining the low-energy noise-contaminated signals of the transmit antennas, which ultimately increases the MAT by an order of magnitude when the signal-to-interference-plus-noise ratio (SINR) is relatively low, regardless of whether single- or multipath scenarios are considered. This phenomenon has a detrimental effect on the performance of Rake-receiver-based synchronization schemes when the perfectly synchronized system is capable of attaining its target bit-error-rate performance at reduced SINR values, as a benefit of employing multiple transmit antennas. Based on our analysis justified by information-theoretic considerations, our acquisition design guidelines are applicable to diverse noncoherent (NC) MIMO-assisted scenarios.

Improved Zero-Padding Method for Rapid Long PN-Code Acquisition

To improve the mean acquisition time performance of the zero-padding (ZP) method, we propose to reduce the code phases searched in coarse acquisition by summing local pseudo-noise (PN) code and down sampling received signal. The detection and mean acquisition time performance of the proposed method is analyzed and compared with that of the zero-padding method. It is shown that the proposed method further reduces the mean acquisition time at the expense of degrading detection performance.

Non-Coherent Code Acquisition in the Multiple Transmit/Multiple Receive Antenna Aided Single- and Multi-Carrier DS-CDMA Downlink

We analyse the characteristics of the Non-Coherent (NC) Multiple Transmit/Multiple Receive (MTMR) antenna aided Multi-Carrier (MC) DS-CDMA downlink employing a serial search based acquisition scheme, when communicating over spatially uncorrelated Rayleigh channels. The associated Mean Acquisition Time (MAT) performance trends are characterised as a function of both the number of antennas and that of the number of subcarriers. It is shown that the employment of both multiple transmit antennas and multiple subcarriers is typically detrimental in terms of the achievable NC acquisition performance, while that obtained by exploiting multiple receive antennas is always beneficial, regardless whether single-path or multi-path scenarios are considered. Based on our results justified by information theoretic considerations, our acquisition design guidelines are applicable to diverse NC MTMR antenna aided scenarios.

Differentially coherent code acquisition in the MIMO-aided multi-carrier DS-CDMA downlink

Both differentially coherent and non-coherent code acquisition schemes designed for the multiple-input multiple-output (MIMO)-aided multi-carrier (MC)-DS-CDMA downlink are analysed, when communicating over uncorrelated Rayleigh channels. The attainable mean acquisition time (MAT) performance is studied as a function of both the number of multiple transmit/multiple receive antennas and that of the number of subcarriers. It is demonstrated that in contrast to the expectations, when the number of multiple transmit antennas and/or that of the subcarriers is increased in both the differentially coherent and the non-coherent code acquisition scenarios, the achievable MAT deteriorates over the entire signal-to-interference plus noise ratio (SINR) per chip (Ec/Io) range considered, except for the scenario of single-carrier (SC)-DS-CDMA using P ¼ 2 transmit antennas and R ¼ 1 receive antenna. As expected, the degree of performance degradation depends upon the specific scheme and the Ec/Io ratio considered, although paradoxically, the correctly synchronised MIMO-aided system is capable of attaining its target bit error ratio performance at reduced SINR values.

Differentially coherent combining for double-dwell code acquisition in ds-cdma systems

The use of differentially coherent combining is proposed to improve the performance of a double-dwell acquisition system by increasing the reliability of a decision in the verification stage. The detection and mean acquisition time performance of the acquisition scheme with the proposed combining scheme is analyzed in frequency-selective Rayleigh fading channels, and compared with that of two previously published double-dwell acquisition schemes based on long correlation intervals and noncoherent combining. It is shown that the proposed acquisition scheme outperforms the previous ones, and that the performance improvement increases as the frequency offset increases.

Acquisition for DS/CDMA systems with multiple antennas in frequency-selective fading channels

A generalized code acquisition scheme for direct-sequence code-division multiple-access systems with multiple antennas is proposed over frequency-selective fading channels. The proposed scheme is developed on the framework of a generalized configuration of multiple antennas and correlators. The nonconsecutive search method is generalized and extended to multiple antenna systems to exploit multipath signals in improving acquisition performance over frequency-selective fading channels. The proposed scheme also adopts a hybrid decision strategy to make effective decisions on acquisition. The mean acquisition time performance of the proposed acquisition scheme is analyzed and evaluated in frequency-selective Rayleigh-fading channels with general multipath delay profiles and spatial-fading correlations. The effects of nonconsecutive search on mean acquisition time are investigated for various channel environments, and the optimal choice of decision strategy is discussed. Furthermore, effects of various configurations of multiple antennas and correlators, decision thresholds, and correlation interval on the performance are also investigated.

Seed accumulating sequential estimation for PN sequence acquisition at low signal-to-noise ratio

The sequential estimation (SE) proposed by Ward for rapid acquisition of pseudo-noise (PN) sequences performs well only at moderate chip signal-to-noise ratios (SNRs). In this paper, a seed accumulating sequential estimation (SASE) method based on accumulated seeds of the received PN sequence is proposed, which performs well at low chip SNR also. The mean acquisition time performance of the SASE method is investigated. Numerical results show that the SASE performs dramatically better than the SE at low chip SNR and the improvement becomes larger as the period of PN sequence increases.

Code acquisition schemes using antenna arrays for DS-SS systems and their performance in spatially correlated fading channels

We propose parallel and serial code-acquisition schemes using antenna arrays for initial acquisition of direct-sequence spread-spectrum signals, which can lower substantially the range of detectable signal-to-noise ratio (SNR) as compared to the corresponding conventional schemes with a single antenna. The proposed schemes use the sum of all the single-antenna decision samples from antenna arrays, corresponding to an identical subsequence of a given pseudonoise code as a decision variable in order to enhance SNR of the resulting signal. We analyze the mean acquisition time performance under an additive white Gaussian noise channel and spatially correlated time-varying flat Rayleigh fading channels by deriving the expressions for the probabilities of detection, missing, and false alarm. We consider two extreme cases of spatial fading correlation among antenna arrays, the case of uncorrelated diversity antennas and the case of perfectly correlated antennas. From numerical results, we see that the acquisition performance of the proposed schemes using antenna arrays becomes improved continually as the number of antennas increases and the performance improvement depends on the degree of spatial fading correlation.

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.

Utilization of multipaths for spread-spectrum code acquisition in frequency-selective Rayleigh fading channels

A novel acquisition scheme that utilizes multipaths to improve the acquisition performance is proposed for frequency-selective fading channels. The proposed acquisition scheme employs nonconsecutive search and joint triple-cell detection. The performance is analyzed in frequency-selective Rayleigh fading channels. Equations for the probabilities of detection and false alarm are derived, and an expression for the mean acquisition time is developed. The mean acquisition time performance of the proposed and conventional acquisition schemes is evaluated and compared. It is found that the proposed acquisition scheme significantly outperforms the conventional one. The effects of various channel parameters such as the number of resolvable paths, the shape of the multipath intensity profile (MIP) and the signal-to-interference ratio (SIR) on acquisition performance are also investigated.

Serial acquisition of DS-CDMA signals in multipath fading mobile channels

This paper compares the mean acquisition time (MAT) performance of two serial search acquisition schemes over frequency-selective multipath Rayleigh fading channels. Both the conventional cell-by-cell detection and the novel joint two-cell detection are characterized. In contrast to the majority of published results considering only one correct timing state (H/sub 1/ cell) in the uncertainty region of the pseudonoise (PN) sequence, this paper analyzes the MAT performance of the serial search acquisition schemes with multiple timing states in the uncertainty region. The MAT performance comparison between the conventional cell-by-cell detection and the joint two-cell detection shows that the latter can achieve an improved acquisition performance at almost the same complexity.

Performance evaluation of spread-spectrum code acquisition using four-state Markov process

A direct sequence serial search acquisition scheme based on the assumption that there are two adjacent in-phase states (H/sub 1/ cells) in the code position uncertainty region, on which the received pseudorandom noise (PN) code and the local despreading PN code signal is coarsely aligned, is presented. To utilise both H/sub 1/ cells, the test statistic is composed of the observation on the couple of adjacent cells by a given type of detector and the acquisition process is modelled by a four-state Markov chain. As an application of this general approach, the noncoherent matched filter detector acquisition of BPSK direct sequence spread-spectrum signals over an additive white Gaussian noise channel is analysed. The mean acquisition time is evaluated for various values of system parameters. The comparisons with that of the conventional cell-by-cell serial search acquisition system show that, at almost the same cost, an improved acquisition performance can be achieved and a more robust mean acquisition time performance against the variation of the threshold can be reached. The proposed scheme can be employed to replace any conventional cell-by-cell PN sequence serial search scheme, provided that the decision variable is changed correspondingly.

Pseudo‐Noise Code Synchronization of Multicarrier DS‐CDMA Systems on Multipath Fading Channels Part I: Analysis of the Serial Search Multiple‐Dwell Acquisition

AbstractPseudo‐Noise (PN) code synchronization is investigated in this and an accompanied paper for multicarrier direct‐sequence code division multiple access (DS‐CDMA) systems on multipath Rayleigh fading channels. In this part, a new analysis is developed to evaluate accurately the mean acquisition time performance of serial search multiple‐dwell acquisition systems. The method is unique in that it can take the correlations due to fading into account, including the correlations among different dwells and carriers. In addition, the effects of system parameters on the acquisition performance such as carrier and user numbers, fading correlations, dwell number and times, and thresholds can be easily evaluated, as compared to computer simulations, and, therefore, facilitating the design of the acquisition subsystem. Our analytical results are verified by computer simulations.

Performance analysis of DSA-based DS/CDMA acquisition

We analyze the acquisition time performance of the distributed sample acquisition (DSA) scheme proposed for a fast DS/CDMA signal acquisition. To analyze the composite acquisition mechanism, we first define several acquisition-related probability parameters which can describe all the essential events in the DSA synchronization, along with the basic states that constitute the eventual DSA state transition diagram. Then, we construct the state transition diagram employing these basic states and the moment generating functions which are entirely based on the above defined probability parameters. Applying this state transition diagram and determining the acquisition-related parameters, we finally analyze the mean acquisition time performance of the DSA.

Effects of cell correlations in a matched-filter PN code acquisition for direct-sequence spread-spectrum systems

Rapid pseudonoise (PN) code acquisition with matched-filter correlators has been very popular in direct-sequence (DS) spread-spectrum systems. Conventionally, the analysis of this acquisition method is based on the assumption that the detections among cells are independent. However, there may be strong correlations among cell detections for the case that the cell size is less than a chip duration. In this paper, the mean acquisition time performance of the acquisition method is analyzed with the cell correlations being taken into account. Numerical results show that depending on the threshold value and other system parameters, the effect of cell correlations may be over 20% of the mean acquisition time for signal-to-noise ratios (SNR) of practical interest. The analytical results are substantiated by computer simulations.

Code acquisition of DS/SS signals in fading channels using an LMS adaptive filter

The mean acquisition time performance for a direct-sequence spread-spectrum (DS/SS) code acquisition technique utilizing a finite impulse response (FIR) least-mean-square (LMS)-adaptive filter is investigated in fading conditions. The optimum tap-weight vector for the adaptive filter is derived and computer simulation results are presented to assess the acquisition performance for the system. It is shown that fading causes a slight degradation to the mean acquisition time (less than 3-dB signal-to-noise ratio (SNR) degradation) which is far less than that incurred by other systems utilizing matched filters (about 10 dB). In frequency selective fading channels, the adaptive nature of the proposed scheme is exploited to acquire the strongest received path and as the paths fade the new strongest available path is acquired.