A modified PN code tracking loop for DS/SS signal in the fast fading channel and strong interference environment

It has been reported that a smart antenna can improve bit error rate (BER) performance significantly in a mobile communications system (Tanaka, S. et al., IEEE JSAC, vol.18, no.8, p.1495-504, 2000). However, the smart antenna has not been applied and analyzed much for the pseudonoise (PN) code tracking loop, which is one of the important aspects in spread spectrum communications receivers. We present a performance analysis of a first order PN-code tracking loop with a smart antenna under a frequency selective fading environment, and show that the smart antenna can also improve the PN code tracking loop significantly, compared to a single antenna element system. We employ the root mean square (RMS) error and mean time to lose lock (MTLL) of the PN code tracking loop as performance criterion.

Pseudonoise (PN) code tracking loops in direct-sequence spread-spectrum systems are often implemented using digital hardware. Performance degradation due to quantization and sampling effects is not adequately characterized by the traditional analog system feedback loop analysis. A low-complexity digital PN code tracking loop with one-bit non-commensurate sampling is analyzed, and the steady-state delay error variance is derived. The results are compared with that of an equivalent analog loop.

In an effort to transmit information over communication channels that contain both Gaussian and non-Gaussian noise components, military and commercial applications frequently rely upon the use of direct sequence spread spectrum (DSSS) techniques. Whilst DSSS is an interference tolerant modulation scheme, situations may be encountered when the processing gain offered by the pseudonoise (PN) spreading code is inadequate. Enhancements to the interference immunity of a DSSS system can be accomplished through the use of signal processing techniques that suppress unwanted interference prior to despreading. To date, the majority of interference suppression techniques developed for DSSS applications, have concentrated on improving detector performance exclusively, and perfect synchronisation between transmitter and receiver is assumed. However, the process of PN code acquisition and tracking within a DSSS receiver is arguably one of the most critical functions within the receiver structure since, if it fails to operate correctly, the wanted signal will not be successfully recovered. An evaluation of the benefits of any interference suppression technique within a DSSS receiver would not be complete without considering at least one level within the synchronisation hierarchy. We examine the improvements in receiver performance, when the process of PN code tracking and detection employs a novel wavelet packet denoising (WPD) procedure for a variety of non-Gaussian channel scenarios.

The cooperative combat of manned/unmanned aerial vehicle combine the advantages of both sides to enhance the combat capability to the greatest extent. The research results show that the cooperative combat of manned/unmanned aerial vehicle needs to solve the availability of the data link between fighters. In the strong interference environment, frequency hopping communication technology is used to prevent enemy electromagnetic interference. However, the traditional frequency hopping technology requires the communication parties to pre-negotiate the frequency hopping spectrum, and the fighters use the pre-negotiated frequency hopping pattern for communication. However, the research shows that it is difficult to exchange frequency hopping parameters between the two sides of the communication, and the availability of the data link is difficult to guarantee in a strong electromagnetic interference environment. Since the communication sequence of the uncoordinated frequency hopping communication can be predicted, a variable speed uncoordinated frequency hopping technique is proposed in this paper to increase the difficulty of reconnaissance and tracking of frequency hopping parameters. Next, we propose an artificial noise co-interference technology that can interfere with the channel communication quality of the enemy, but our signal reception is not affected. Furthermore, we use the zero-sum game model to analyze the electromagnetic confrontation process between the enemy and us. The experimental results show that the variable speed uncoordinated frequency hopping technique and the artificial noise co-interference technology have good anti-interference effects.

The landscape of Global Navigation Satellite Systems (GNSS) signals is undergoing significant change. The parallel development of new, more robust and versatile signals along with two new GNSS systems with global reach is having a dramatic impact on the development of GNSS receivers. Receiver manufacturers are continually developing and implementing unique signal acquisition and tracking algorithms, advanced integrity monitoring algorithms, advanced multipath mitigation algorithms and a host of other enhancements in an effort to improve the performance of GNSS receivers and make their products stand out in a crowded field. The objective of this research is to develop a methodology for comparing the pseudorandom noise (PRN) code tracking performance of various receivers. While the overall performance of a receiver depends on many more factors, effective PRN code tracking is fundamental to the operation of a GNSS receiver. The methodology developed in this research requires three fundamental measurements from the receiver under test – code pseudorange, carrier pseudorange and carrier-to-noise-density ratio (C/No). These measurements are generated by all GNSS receivers but may not always be available to the user. Therefore, this methodology can only be performed on receivers that output these values. This methodology might be useful as a tool to evaluate the suitability of various receivers in certain environments or applications (e.g., weak signal environments, high dynamic environments, unfriendly radio frequency (RF) interference environments, etc.) and also as a means of comparing the relative performance of receivers in those environments or applications. Expectations for the research were that the data collection and analysis techniques would generate code loop tracking jitter plots that closely tracked with theoretical curves. In addition, it was expected that different receivers would yield slightly different jitter plots giving them a unique “signature.” Finally, it was expected that some receivers might incorporate scalar code tracking loops and others might incorporate vector tracking loops. The methodology was developed and refined using three receivers from three popular manufacturers, each with a unique set of capabilities. Raw data was collected from each receiver and processed using purpose built algorithms to estimate the code loop tracking jitter for each signal for each receiver. The code loop tracking observations for each of the three receivers tested were compared with theoretical curves generated using closed form equations published in previous papers. In most cases, the data compared favorably. However, there were some significant outliers that are worthy of additional research and analysis. In addition, the jitter plots for one receiver tested indicated that it used scalar code tracking loops and the jitter plots for the other two receivers indicated that they use vector tracking loops. It appears to be possible to determine if a receiver uses scalar tracking loops or vector tracking loops based on the jitter estimates generated in this research. This research indicated that the methodology might be a useful tool for 2 characterizing GNSS receivers and, eventually evaluating their performance in various environments. However, more data collection and analysis is required to further validate and refine the methodology. Also, more analysis of the signals that yielded “non-conforming” jitter plots should be examined in more detail.

A PN (Pseudonoise) code is often used for ranging systems, measurements or clock transmission, etc. Signal transmission using the PN code is effective even at low SNR. The delay‐lock loop is an effective circuit to detect PN code in such large noise, and is used widely. However, in the discriminator characteristic of conventional DLL, the range where the loop control signal can be gained is extremely narrow. Therefore, if the loop once loses lock for noise or for any reason, a large time is required for resynchronization. To compensate the fault of DLL, this paper proposes the improved DLL (IDLL‐1) with extended range of discriminator characteristic. Tracking performances are evaluated theoretically for a first‐order loop, and experimentally for a second‐order loop. Furthermore, the more improved DLL (IDLL‐2), which consists of IDLL‐1 and simple circuits, is proposed. Performance evaluation is done by experiments and simulations.

Previous satellite telemetry, tracking, and command (TT&C) link analyses [Ref 1, 4] for Space Ground Link Subsystem (SGLS) considered C/No and SNR (or Eb/N0), without including the effects of command turnaround noises. This paper analyzes SGLS services that include the Turnaround Command (TAC) intermodulation (IM) noises in addition to the regular thermal noise. The SGLS pseudorandom noise (PRN) ranging signals use a 500 kHz clock, which is a component (C1) of 1 Mcps PRN long ranging codes (C1, x, a, b, and c codes). Satellite test data shows that running a PRN ranging test with a 500 kHz clock is an acceptable approximation for the PRN case. The difference between PRN and 500 kHz clock ranging is small (same residual carriers of C= −40 dBm for PRN and 500 kHz clock ranging in Figures 1 and 2). This paper shows that the TAC robs power from SGLS signals, degrading their C/No or SNR and link performances. Also test data (Figure 2) is used to show that the TAC IM noises are as predicted by theories in the Appendix, and that they will reduce SGLS C/No and degrade the carrier and ranging acquisition performances. Luckily these TAC IM noises will not affect carrier and ranging tracking performances or telemetry demodulation, because these IM noises are outside of the narrow tracking or detection bandwidths.

In this letter, we propose a new tracking scheme that is robust against multipath fading for pseudonoise (PN) code tracking in direct-sequence-spread spectrum systems. The proposed scheme employs an adaptive filter whose taps are adapted using a block least-mean square algorithm and it results in minimizing the effect of multipath interference on the tracking performance. We show that the mean-squared tracking error performance of the proposed scheme is not affected by the presence of closely spaced paths (e.g., one to three chips), unlike that of conventional delay locked loops. We also show that the tap-weight distribution of the filter provides accurate estimates of the multipath delays. For example, at E/sub b//N/sub 0/=5 dB, 98% of the time the path estimates lie within one sample (1/5 of a chip) from the actual delays. Furthermore, simulation results suggest that multipath delays over a wide range of terminal speeds can be tracked successfully. The proposed scheme is well suited for wideband code-division multiple-access systems where a large number of closely-spaced multipath components need to be tracked and used in RAKE combining.

This paper revisits the interference channels under strong interference and very strong interference, for both discrete memoryless and Gaussian channels. In particular, it is shown that for the classical definitions, while the conditions of strong interference for discrete and Gaussian cases coincide with each other, those of very strong interference are not consistent with each other in terms of mutual information inequalities. Based on this observation, a new class of discrete memoryless interference channels under very strong interference is introduced whose capacity region is characterized. This new class of channels is consistent with the Gaussian interference channel under very strong interference. Moreover, this new class of interference channels is not a subset of any existing classes of discrete memoryless interference channels with known capacity region.

Code tracking performance analysis of GNSS signal in the presence of CW interference

In this paper, training-based estimation of correlated block fading channels in a multiple-antenna, multi-user environment is considered. The linear minimum mean squared error (LMMSE) estimator is presented first. Then the problem of optimally designing the training data set, so as to minimize the mean squared channel estimation error subject to a total transmit power constraint, is addressed. It is shown that the optimal transmission directions are dictated jointly by the eigen-decompositions of the channel and interference covariance matrices. Their roles, in the channel estimation and interference suppression tasks, respectively, are revealed in the optimal transmit beamformer structure. The simulation results demonstrate that the gain in estimation performance from using the optimal training sequence increases considerably with increasing spatial fading correlation, especially in strong interference environments.

In the direct sequence spread spectrum packet radio system, pseudonoise (PN) code synchronization is an essential part which could affect the overall system performance and has to be done in a short time period. In this paper a code phase synchronization device which employs differential detection structure to enhance the overall packet detectability is presented. This device also employs the automatic threshold adaptation technique which was previously presented as a practical scheme to be applied for packet radio communication. However this method called ATC is not suitable for the fading environment which is common in mobile communication. By employing the differential detection structure as its signal preprocessor, the proposed device can still exploit the advantage of ATC and gives significant improvement in terms of packet loss probability in the fast Rayleigh fading channel.

Orthogonal frequency-division multiplexing (OFDM) is robust against frequency selective fading because of the increase of the symbol duration. However, the time-varying nature of the channel causes inter-carrier interference (ICI) which destroys the orthogonal of sub-carriers and degrades the system performance severely. To alleviate the detrimental effect of ICI, there is a need for ICI mitigation within one OFDM symbol. We propose an iterative Inter-Carrier Interference (ICI) estimation and cancellation technique for OFDM systems based on regularized constrained total least squares. In the proposed scheme, ICI aren’t treated as additional additive white Gaussian noise (AWGN). The effect of Inter-Carrier Interference (ICI) and inter-symbol interference (ISI) on channel estimation is regarded as perturbation of channel. We propose a novel algorithm for channel estimation o based on regularized constrained total least squares. Computer simulations show that significant improvement can be obtained by the proposed scheme in fast fading channels.

Satellite-based navigation requires precise knowledge of the structure of the transmitted signals. For GPS, accurate knowledge of the shape of the code correlation peaks is required to ensure no biases are introduced into the position solution. It is generally presumed that all GPS-like satellite signals are virtually identical. However, in 1993 a satellite malfunction introduced significant distortion onto one of the satellite C/A codes. That distortion caused range errors to vary with receiver filter characteristics and code tracking loop implementation. As a result, high-integrity systems such as the Wide Area Augmentation System (WAAS) must implement signal deformation monitors to detect and remove signals that become anomalously distorted. In the future, WAAS will rely on modernized signals from both GPS (L5) and Galileo (E1/L1/E2 and E5A/E5B). This should increase performance for users; however they must still protect against potential signal deformations. Although the International Civil Aviation Organization (ICAO) has agreed on a threat scenario for GPS L1 signals, no such agreement exists for modernized signals. In addition, each of these signals will have different chipping rates and their correlation peak structures will be quite different from that of the GPS C/A code. Their code tracking loop implantations are as yet not well- defined, but may differ somewhat from traditional architectures. An additional complication is the unknown receiver filter characteristics that the new receivers will employ. Each of these factors may render a given signal and/or receiver configuration more or less sensitive to signal deformations. This paper analyzes the range error sensitivity of several modernized signals subjected to distortions of the type considered in the ICAO threat model for signal deformations. To isolate the effects of the signal-in-space deformation errors, it assumes an ideal, wideband receiver filter and basic early-minus-late code tracking implementations for the new codes. It also compares the distortion-induced range errors for the new codes to those currently modeled for the C/A code. Finally, these results are used to motivate threat model refinements and receiver tracking loop constraints that minimize the affects of this error source for the modernized GNSS signals.

Improving tracking accuracy with subcarrier assistance and code monitoring for BOC modulated signal