Pulse or digital communications – Synchronizers – Frequency or phase control using synchronizing signal
Reexamination Certificate
2001-02-27
2003-11-04
Corrielus, Jean (Department: 2631)
Pulse or digital communications
Synchronizers
Frequency or phase control using synchronizing signal
C370S515000, C375S150000
Reexamination Certificate
active
06643344
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a method for tracking a locally generated spread spectrum signal sequence in order to synchronize the locally generated spread spectrum signal sequence with a corresponding received spread spectrum signal sequence. The invention also relates to a configuration for tracking a locally generated spread spectrum signal sequence.
The method according to the invention can be used with basic spread spectrum methods, such as direct sequence methods. In these methods, a message is modulated with a higher-frequency pseudo-random binary sequence before being transmitted. The receiver can extract the message from the pseudo noise signal produced if the receiver knows the binary sequence.
These methods are used in data communications, position finding and navigation. An important field of use is, e.g. the real-time satellite navigation according to the NAVSTAR GPS system (Navigation System with Timing And Ranging, Global Positioning System), which is described, e.g. by Schrödter, in “GPS Satellite Navigation,” Franzis Verlag, Munich, 1994. For a receiver to be able to identify a transmitter and evaluate its information, it must know a transmitter-specific code (gold code) which is transmitted as a periodic signal sequence of predetermined length. In order to make the code available, all the codes of the transmitters in question are stored in the receiver. Since, furthermore the phase angle of each incoming signal is not known, the match between the received spread spectrum signal sequence and the locally generated spread spectrum signal sequence is established in an acquisition method. The comparison is performed by the correlation function of the signal which becomes almost one when there is synchronization.
Since the transmitter and the receiver are moving relative to one another, the synchronization must be subsequently maintained by correcting the phase of the locally generated spread spectrum signal sequence to the received spread spectrum signal sequence. This is done by regulating the clock of the locally generated spread spectrum signal sequence as a function of the phase deviation found.
It is known to use a so-called delay locked loop (DLL) for this purpose as is described, for example, in Holmes: Coherent Spread Spectrum Systems, Robert E. Krieger, 1990. This method is based on the locally generated spread spectrum signal sequence being phase shifted by the same amount preceding and following the expected punctual times and the received spread spectrum signal sequence being correlated with the spread spectrum signal sequences of this earlier and later time. The results are then subtracted from one another in order to receive the final correlation result.
In this method, it is found that a small phase shift is advantageous to the control characteristic with respect to the noise but that it is disadvantageous in a multiplicity of operating conditions when a good correction of the locally generated spread spectrum signal sequence is to be achieved. The smaller the early/late interval of the closed-loop control, the poorer becomes the dynamic behavior because the tracking can be lost with fast and sudden movements.
In U.S. Pat. No. 5,734,674 to Fenton et al., a method for synchronizing a locally generated spread spectrum signal sequence with a corresponding received spread spectrum signal sequence is described. In this method, a large early/late interval is initially used which covers a large capture range.
In the course of the closed-loop control, this large early/late interval is narrowed down. The actual signal tracking is then done with a small early/late interval. In a very dynamic scenario or with a very noisy initial signal, the closed-loop control may, therefore, lose lock.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method and a configuration for tracking which overcome the above-mentioned disadvantages of the heretofore-known methods and configurations of this general type and which improve the dynamic behavior and, at the same time improve a variance of the distributed results.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of tracking a locally generated spread spectrum signal sequence, the method includes the steps of:
correlating a received spread spectrum signal sequence with a locally generated spread spectrum signal sequence with respect to a synchronization time at a relatively earlier time and a relatively later time in an early/late interval;
subtracting correlation responses from one another;
controlling a clock of the locally generated spread spectrum signal sequence as a function of a result of the subtracting step for synchronizing the locally generated spread spectrum signal sequence with a received spread spectrum signal sequence corresponding to the locally generated spread spectrum signal sequence;
performing correlations based on at least two hierarchically staggered closed-loop controls with different early/late intervals;
providing an early interval of a first one of the at least two hierarchically staggered closed-loop controls having a relatively smaller early/late interval such that the early interval of the first one of the at least two hierarchically staggered closed-loop controls does not become earlier than an early interval of a second one of the at least two hierarchically staggered closed-loop controls having a relatively next-larger early/late interval; and
providing a late interval of the first one of the at least two hierarchically staggered closed-loop controls such that the late interval of the first one of the at least two hierarchically staggered closed-loop controls does not become later than a late interval of the second one of the at least two hierarchically staggered closed-loop controls.
In other words, the object of the invention is achieved by a method for correlating a locally generated spread spectrum signal sequence for synchronization with a corresponding received spread spectrum signal sequence, wherein the latter is correlated with the locally generated spread spectrum signal sequence with respect to the synchronization time at an earlier and a later time in an early/late interval, the correlation responses are subtracted from one another and the clock of the locally generated spread spectrum signal sequence is controlled as a function of the result of the subtraction, wherein correlations are performed through the use of at least two hierarchically staggered closed-loop controls with different early/late intervals and in that the early interval of one closed-loop control having a small early/late interval must not become earlier than the early interval of the other closed-loop control having a next-larger early/late interval and, furthermore, the late intervals of the one closed-loop control having a small early/late interval must not become later than the late interval of the other closed-loop control having a next-larger early/late interval.
According to another mode of the invention, the correlations are performed by starting with a largest one of the early/late intervals; and the correlations are performed with a given one of the early/late intervals smaller than the largest one of the early/late intervals subsequent to reaching a control limit of the largest one of the early/late intervals.
According to yet another mode of the invention, an early time and a late time of a given one of the at least two hierarchically staggered closed-loop controls having a smallest one of the early/late intervals are used for calculating a punctual time.
With the objects of the invention in view there is also provided, a configuration for tracking a locally generated spread spectrum signal sequence, including:
a delay locked loop configuration including filter devices, the delay locked loop configuration comparing locally generated early spread spectrum signal sequences, locally generated punctual spread spectrum signal sequences and locally generated late sprea
Gunzelmann Bertram
Molev-Shteiman Arkadi
Corrielus Jean
Greenberg Laurence A.
Infineon - Technologies AG
Locher Ralph E.
Stemer Werner H.
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