International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada / In this paper, a new coherent correlation-loop architecture for tracking direct-sequence spread-spectrum signals is proposed. In the proposed correlation loop model, the mean-square tracking error is minimized by varying the cross-correlation function between the received signal and the locally generated signal. The locally generated signal is produced by passing a replica of the transmitted signal through a linear time-invariant filter, which is termed the VCC filter. The issue of bandwidth of a correlation loop is addressed and a bandwidth definition for comparative purposes is introduced. The filter characteristics to minimize the tracking errors are determined using numerical optimization algorithms. This work demonstrates that the amplitude response of the VCC filter is a function of the input signal-to-noise ratio (SNR). In particular, the optimum filter does not replicate a differentiator at finite signal-to-noise ratio as is sometimes assumed. The optimal filter characteristics and the knowledge of the input SNR can be combined to produce a device that has very low probability of loosing lock.

International Telemetering Conference Proceedings / November 04-07, 1991 / Riviera Hotel and Convention Center, Las Vegas, Nevada / A digital device for rapid acquisition of the initial phase of PN code has been implemented. The principles and results of the experiment are introduced in this paper. The m PN code is modulated on IF with BPSK type. The cycle of PN code P=255 chips. The rate of PN code R=5.1 × 10 chips /s. The IF is not acquired. The shift in Doppler 6 frequency f is within l-4KHz. In these conditions, the phase of PN code can be acquired d within 3 ms and the error of sychronization is less than 0.5 chip.

A wireless local area network (LAN) system is proposed to provide mobility for existing data communication services. This thesis presents a physical layer design for a direct sequence spread spectrum ISM band radio LAN system. This radio system employs spread spectrum communication technology and a differential binary phase shift keying/quadrature phase shift keying (BPSK/QPSK) non-coherent receiver to overcome the adverse indoor wireless environment. Moreover, a variable data rate transmission technique is used to dynamically configure the spread spectrum system according to channel performance. This physical layer incorporates the Zilog Z2000 Evaluation Board performing direct sequence spread spectrum processing, a Grayson 900 MHz radio receiver and a transmitter module which was designed and built at Virginia Tech. The transmitted spectrum occupies a 4 MHz bandwidth in the 900 MHz ISM band and this system supports a data rate of up to 363 Kbits/sec. The spread spectrum system design along with detailed descriptions of hardware and control software development are presented. / Master of Science

A non-coherent PN code tracking loop with multi-user detection and simplified multi-path interference cancellation (MPIC) is proposed for direct sequence spread spectrum communications system. A decorrelator decision-feedback detector (DDFD) is first applied on the incoming signal to mitigate the multi-user interference. Then, a simplified multi-path interference cancellation (MPIC) is further used to increase signal quality. Finally, a modified code tracking loop (MCTL) is adopted for non-coherent PN code tracking. Mathematical expressions of the S-curve and tracking jitter are derived. Mean time to lose lock is also compared with traditional tracking loops. From the numerical results, we know the proposed PN code tracking loop can efficiently mitigate the interference from multi-user and multi-path and improve the performance of code tracking loop.

The technique of direct sequence spread spectrum (DS/SS) has been widely used in commercial mobile communication systems. The efficiency of DS/SS system is highly dependent on the accurate and fast synchronization between the incoming and locally generated PN (pseudo-noise) codes. The code synchronization is processed in two steps, acquisition (coarse alignment) and tracking (fine alignment), to bring the delay offset between the two codes. Conventionally, for code synchronization, most of techniques were proposed based on the correlation property of PN codes. Recently, the different approach, by using the adaptive LMS filtering scheme, has been proposed to reduce the hardware complexity and to improve the performance of code synchronization, especially for a long PN code. In this thesis, a new coherent adaptive code synchronization scheme is proposed, where the adaptive constrained LMS (CLMS) algorithm with the maximum tap-weight (MTW) test method is devised for code acquisition. The statistics of weight vector of the proposed CLMS scheme are derived to evaluate the performance, in terms of mean acquisition time (MAT). Analytical and simulation results verify that the proposed scheme for code acquisition outperforms the one using the conventional LMS filtering schemes, under the integer and non-integer time delay cases. Moreover, the setting of threshold value is derived for code acquisition, which is independent of the values of signal-to-noise ratio (SNR) and time delay. Next, the CLMS scheme is proposed associated with the direct delay estimation (DDE) formula for code tracking. This approach does achieve a good delay-tracking performance, which is verified via computer simulation. Simultaneously, the hardware complexity can further be reduced due to that a code-tracking loop implemented by the interpolation method is not required.

Robust signal acquisition is an important task in DS-SS receivers. The objective of the acquisition is to coarsely estimate the signal parameters such that the succeeding parameter tracking algorithms can be initialized. In particular, acquisition is needed to coarsely synchronize the receiver to the timing and frequency of the received signal. For this purpose mainly data aided and feedforward algorithms are applied. Using the maximum likelihood (ML) criterion, an estimator for the joint estimation of receive timing and frequency offset can be derived which determines the maximum of the Likelihood function over the whole parameter uncertainty region. Due to its high complexity the ML synchronizer is difficult to implement for practical applications. Hence, complexity reduced algorithms need to be derived. This thesis gives a systematic survey of acquisition algorithms and of performance analysis methods for analyzing such algorithms under mobile radio propagation conditions. The exploitation of multiple observations is investigated in order to improve the acquisition performance in terms of false alarm rate and acquisition time. In particular, optimal and suboptimal combining schemes for a fixed observation interval as well as sequential utilization of successive observations resulting in a variable observation length are analyzed. Another possibility to make the signal acquisition more efficient in terms of the acquisition time is to use multi stage acquisition algorithms. One class of those algorithms are the well known multiple dwell algorithms. A different approach is to design acquisition procedures in which the information about the unknown parameters is distributed among several stages such that each stage has to cope with a smaller uncertainty region in comparison to the overall parameter uncertainty. Analysis of multi stage algorithms followed by an extensive discussion of the 3GPP FDD downlink acquisition procedure as an example of a multi stage procedure with distributed information conclude the work. / Die zuverlässige Signalakquisition, die auch als Grobsynchronisation bezeichnet wird, stellt eine wichtige Aufgabe in DS-SS-Systemen dar. Das Ziel hierbei ist es, Schätzwerte fur die Übertragungsparameter derart zu bestimmen, dass die der Grobsynchronisation nachfolgende Feinsynchronisation initialisiert werden kann, d. h. dass die bestimmten Schätzwerte innerhalb des Fangbereiches der Feinsynchronisationsalgorithmen liegen. Insbesondere ist es für die Bestimmung von Synchronisationszeitpunkt und Frequenzversatz sinnvoll, eine Grobsynchronisation durchzuführen. Im Interesse einer begrenzten Komplexität sowie einer möglichst schnellen Akquisition finden vor allem datengestützte und vorwärtsverarbeitende Algorithmen Anwendung. Ausgehend vom Maximum-Likelihood-Kriterium (ML-Kriterium) können geeignete Schätzer für die gemeinsame Bestimmung von Synchronisationszeitpunkt und Frequenzversatz abgeleitet werden. Dabei ist das Maximum der Likelihood-Funktion innerhalb der Parameterunsicherheitsregion zu bestimmen. Aufgrund seiner hohen Komplexität ist der ML-Schatzer fur die Akquisition wenig geeignet; vielmehr müssen aufwandsgünstige Algorithmen mit ausreichender Leistungsfähigkeit gefunden werden. In dieser Arbeit werden verschiedene Algorithmen zur Parameterakquisition systematisierend gegenübergestellt. Weiterführend sind Verfahren zur Verbesserung des Akquisitionsverhaltens bezüglich Fehlalarm-Wahrscheinlichkeit und Akquisitionszeit unter Ausnutzung mehrfacher Beobachtung Gegenstand der Betrachtungen. Insbesondere optimale und suboptimale Verfahren mit fester Beobachtungsdauer sowie die sequentielle Auswertung aufeinander folgender Beobachtungen, bei der sich die Beobachtungsdauer nach der erreichten Entscheidungssicherheit bestimmt, werden analysiert. Als eine weitere Möglichkeit, die Signalakquisition in Bezug auf die Akquisitionszeit effizienter zu gestalten, werden mehrstufige Akquisitionsverfahren diskutiert. Es werden zum einen die häufig genutzten Mehrfach-Dwell-Algorithmen sowie mehrstufige Algorithmen mit verteilter Information betrachtet. Bei Letzteren Algorithmen wird jeder Akquisitionsstufe ein Teil der zur Synchronisation benötigten Information zugeordnet, wodurch sich die Parameter-Unsicherheit für jede einzelne Stufe verringert. Ziel hierbei ist es, durch Erhöhung der Entscheidungssicherheit der einzelnen Stufen die mittlere Akquisitionszeit zu reduzieren. Die Diskussion und die Analyse von mehrstufigen Akquisitionsverfahren bilden den Abschluss der Arbeit, wobei besonders auf die 3GPP-FDD Downlink-Akquisition als ein Beispiel fur mehrstufige Verfahren mit verteilter Information eingegangen wird.

Robust signal acquisition is an important task in DS-SS receivers. The objective of the acquisition is to coarsely estimate the signal parameters such that the succeeding parameter tracking algorithms can be initialized. In particular, acquisition is needed to coarsely synchronize the receiver to the timing and frequency of the received signal. For this purpose mainly data aided and feedforward algorithms are applied. Using the maximum likelihood (ML) criterion, an estimator for the joint estimation of receive timing and frequency offset can be derived which determines the maximum of the Likelihood function over the whole parameter uncertainty region. Due to its high complexity the ML synchronizer is difficult to implement for practical applications. Hence, complexity reduced algorithms need to be derived. This thesis gives a systematic survey of acquisition algorithms and of performance analysis methods for analyzing such algorithms under mobile radio propagation conditions. The exploitation of multiple observations is investigated in order to improve the acquisition performance in terms of false alarm rate and acquisition time. In particular, optimal and suboptimal combining schemes for a fixed observation interval as well as sequential utilization of successive observations resulting in a variable observation length are analyzed. Another possibility to make the signal acquisition more efficient in terms of the acquisition time is to use multi stage acquisition algorithms. One class of those algorithms are the well known multiple dwell algorithms. A different approach is to design acquisition procedures in which the information about the unknown parameters is distributed among several stages such that each stage has to cope with a smaller uncertainty region in comparison to the overall parameter uncertainty. Analysis of multi stage algorithms followed by an extensive discussion of the 3GPP FDD downlink acquisition procedure as an example of a multi stage procedure with distributed information conclude the work. / Die zuverlässige Signalakquisition, die auch als Grobsynchronisation bezeichnet wird, stellt eine wichtige Aufgabe in DS-SS-Systemen dar. Das Ziel hierbei ist es, Schätzwerte fur die Übertragungsparameter derart zu bestimmen, dass die der Grobsynchronisation nachfolgende Feinsynchronisation initialisiert werden kann, d. h. dass die bestimmten Schätzwerte innerhalb des Fangbereiches der Feinsynchronisationsalgorithmen liegen. Insbesondere ist es für die Bestimmung von Synchronisationszeitpunkt und Frequenzversatz sinnvoll, eine Grobsynchronisation durchzuführen. Im Interesse einer begrenzten Komplexität sowie einer möglichst schnellen Akquisition finden vor allem datengestützte und vorwärtsverarbeitende Algorithmen Anwendung. Ausgehend vom Maximum-Likelihood-Kriterium (ML-Kriterium) können geeignete Schätzer für die gemeinsame Bestimmung von Synchronisationszeitpunkt und Frequenzversatz abgeleitet werden. Dabei ist das Maximum der Likelihood-Funktion innerhalb der Parameterunsicherheitsregion zu bestimmen. Aufgrund seiner hohen Komplexität ist der ML-Schatzer fur die Akquisition wenig geeignet; vielmehr müssen aufwandsgünstige Algorithmen mit ausreichender Leistungsfähigkeit gefunden werden. In dieser Arbeit werden verschiedene Algorithmen zur Parameterakquisition systematisierend gegenübergestellt. Weiterführend sind Verfahren zur Verbesserung des Akquisitionsverhaltens bezüglich Fehlalarm-Wahrscheinlichkeit und Akquisitionszeit unter Ausnutzung mehrfacher Beobachtung Gegenstand der Betrachtungen. Insbesondere optimale und suboptimale Verfahren mit fester Beobachtungsdauer sowie die sequentielle Auswertung aufeinander folgender Beobachtungen, bei der sich die Beobachtungsdauer nach der erreichten Entscheidungssicherheit bestimmt, werden analysiert. Als eine weitere Möglichkeit, die Signalakquisition in Bezug auf die Akquisitionszeit effizienter zu gestalten, werden mehrstufige Akquisitionsverfahren diskutiert. Es werden zum einen die häufig genutzten Mehrfach-Dwell-Algorithmen sowie mehrstufige Algorithmen mit verteilter Information betrachtet. Bei Letzteren Algorithmen wird jeder Akquisitionsstufe ein Teil der zur Synchronisation benötigten Information zugeordnet, wodurch sich die Parameter-Unsicherheit für jede einzelne Stufe verringert. Ziel hierbei ist es, durch Erhöhung der Entscheidungssicherheit der einzelnen Stufen die mittlere Akquisitionszeit zu reduzieren. Die Diskussion und die Analyse von mehrstufigen Akquisitionsverfahren bilden den Abschluss der Arbeit, wobei besonders auf die 3GPP-FDD Downlink-Akquisition als ein Beispiel fur mehrstufige Verfahren mit verteilter Information eingegangen wird.

International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California / Several different kinds of signal are transmitted through only one carrier in microwave unified telemetry tracking & control system(MUTTCS), which has replaced separate system to accomplish all TT&C functions, and has been widely used now. This paper analyses the advantages and disadvantages of general subcarrier frequency-division MUTTCS, then the principle and performances of advanced spread spectrum MUTTCS(SS-MUTTCS) are discussed in detail. The inherent ranging ability of PN code and the speciality of spread spectrum modulation realize the complete unification including measurement of range, velocity and angle as well as telemetry, telecontrol and communication functions. At the same time, the contradiction between range and velocity measurement in precision, resolution and measuring range can be solved. With CDMA technology, the signal and equipment of multi-target or multi-station TT&C can be unified easily. SS-MUTTCS operates under low S/N, low threshold, low power spectrum density and wide spectrum range, so it meet the requirements of electronic warfare and ECM, with high performance of safety, security, anti-intercept and anti-interference. Therefore, SSMUTTCS is becoming an important trend of modern vehicle TT&C system.