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WO2003017494A1 - Procede et dispositif de synchronisation de frequence - Google Patents

Procede et dispositif de synchronisation de frequence Download PDF

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Publication number
WO2003017494A1
WO2003017494A1 PCT/DE2002/002885 DE0202885W WO03017494A1 WO 2003017494 A1 WO2003017494 A1 WO 2003017494A1 DE 0202885 W DE0202885 W DE 0202885W WO 03017494 A1 WO03017494 A1 WO 03017494A1
Authority
WO
WIPO (PCT)
Prior art keywords
frequency
oscillator
reference frequency
range
base station
Prior art date
Application number
PCT/DE2002/002885
Other languages
German (de)
English (en)
Inventor
Christian Steinbauer
Original Assignee
Siemens Aktiengesellschaft
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens Aktiengesellschaft filed Critical Siemens Aktiengesellschaft
Publication of WO2003017494A1 publication Critical patent/WO2003017494A1/fr

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L7/00—Arrangements for synchronising receiver with transmitter
    • H04L7/02—Speed or phase control by the received code signals, the signals containing no special synchronisation information
    • H04L7/033—Speed or phase control by the received code signals, the signals containing no special synchronisation information using the transitions of the received signal to control the phase of the synchronising-signal-generating means, e.g. using a phase-locked loop
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03J—TUNING RESONANT CIRCUITS; SELECTING RESONANT CIRCUITS
    • H03J1/00—Details of adjusting, driving, indicating, or mechanical control arrangements for resonant circuits in general
    • H03J1/0008—Details of adjusting, driving, indicating, or mechanical control arrangements for resonant circuits in general using a central processing unit, e.g. a microprocessor
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03J—TUNING RESONANT CIRCUITS; SELECTING RESONANT CIRCUITS
    • H03J7/00—Automatic frequency control; Automatic scanning over a band of frequencies
    • H03J7/02—Automatic frequency control
    • H03J7/04—Automatic frequency control where the frequency control is accomplished by varying the electrical characteristics of a non-mechanically adjustable element or where the nature of the frequency controlling element is not significant
    • H03J7/06—Automatic frequency control where the frequency control is accomplished by varying the electrical characteristics of a non-mechanically adjustable element or where the nature of the frequency controlling element is not significant using counters or frequency dividers
    • H03J7/065—Automatic frequency control where the frequency control is accomplished by varying the electrical characteristics of a non-mechanically adjustable element or where the nature of the frequency controlling element is not significant using counters or frequency dividers the counter or frequency divider being used in a phase locked loop
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00—Automatic control of frequency or phase; Synchronisation
    • H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
    • H03L7/16—Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop
    • H03L7/18—Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop using a frequency divider or counter in the loop
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L7/00—Arrangements for synchronising receiver with transmitter
    • H04L7/04—Speed or phase control by synchronisation signals
    • H04L7/10—Arrangements for initial synchronisation

Definitions

  • the present invention relates to a method and a device for frequency synchronization of a mobile station with a base station, in particular under extreme temperature conditions.
  • the mobile station To carry out a transmission in the field of mobile communication, the mobile station must be synchronized with the base station.
  • the base station sends signals on the frequency carrier of the Broadcast Control Channel (BCCH) that allow a mobile station to transmit or
  • BCCH Broadcast Control Channel
  • the base station Adapt the reception frequency to a reference frequency specified by the base station.
  • the base station sends a so-called frequency correction burst (FB) in the GSM system, by means of which the mobile station can determine the frequency offset with respect to the base station.
  • FB frequency correction burst
  • This frequency correction burst consists of a predefined bit sequence from which the GMSK modulator (Gaussian Minimum Shift Keying) used in the GSM system generates a pure sinusoidal signal. This then corresponds to an unmodulated carrier (frequency channel) shifted with respect to the reference frequency. In the GSM system, the shift is 67.7kHz.
  • GMSK modulator Gausian Minimum Shift Keying
  • the digital signal processor can then calculate back to the reference frequency.
  • This reference frequency is then produced by means of a frequency synthesis circuit.
  • the output frequency f_out of the frequency synthesis circuit shown in FIG. 1 should match the reference frequency specified by the base station.
  • the terms presented here are not limited to the GSM system; the term “mobile station” also includes a terminal or, in general, any mobile unit in a communication network.
  • the term “base station” is generally understood to mean a central facility in a communication network.
  • the simplified concept of a frequency synthesis circuit can now be seen in FIG.
  • the heart of the frequency synthesis circuit is a PLL (Phase Locked Loop).
  • the PLL has a frequency / phase comparator PD, a filter LF, a high-frequency oscillator HFO and a divider D.
  • the externally fed oscillator frequency of an oscillator crystal VCXO is compared with the frequency in the PLL loop by means of the phase / frequency comparator PD.
  • the filter LF the so-called loop filter, serves to filter out undesired high-frequency components.
  • the high frequency oscillator HFO is used to synthesize the high frequency.
  • the high frequency is divided down by means of the divider D in order to approximate it to the external, that is to say produced outside of the PLL, oscillator frequency of the VCXO, so that they can be compared with one another by means of the phase / frequency comparator.
  • the oscillator frequency is also divided down using a further divider D2 in order to be able to use technologically simple, energy-saving and inexpensive components in the PLL due to the lower input frequency.
  • the frequency f_out on the high-frequency side is specified as a reference frequency by the base station.
  • f_out is produced on the basis of the input frequency f_in, which is given by the oscillator frequency.
  • f_in the oscillator frequency, can be varied by changing the voltage on the oscillator VCXO.
  • the oscillator crystal is already calibrated at room temperature during manufacture. For this, the voltage is measured, the is necessary to achieve a certain oscillator frequency. This happens at only a few calibration points in order to keep the costs as low as possible. For the sake of simplicity, this procedure is explained when using three calibration points:
  • the calibration values for frequency f_min at the minimum tuning voltage, center frequency f_c at medium tuning voltage and frequency f_max at maximum absorption voltage are determined. Only the value f_c is used for the frequency synchronization; the other calibration values for the oscillator frequencies f_min and f_max are used to approximate the frequency behavior of the oscillator in a limited voltage range.
  • the reference frequency is now generated on the basis of the center frequency f_c of the oscillator, for example 13 MHz, or by means of the oscillator frequency divided by the divider D2.
  • the disadvantage here is that the oscillator frequency depends not only on the voltage applied, but also on other factors, in particular the temperature.
  • the oscillator crystal is therefore adjusted in relation to the calibration created during production if there is a different temperature than that which was assumed during the calibration.
  • a different tuning voltage is therefore required at the oscillator crystal to generate f_c than that which was determined during the calibration. To do this, the tuning voltage is now varied by the voltage value associated with f_c.
  • the temperature in the mobile station is measured, for example, using a thermistor and using a corresponding appropriate temperature compensation algorithm compensates for the temperature-dependent error of the oscillator crystal VCXO.
  • this method is complex on the one hand, and on the other hand the temperature compensation itself or precisely does not provide the desired result, in particular at the limits of the temperature range of approximately 0 to 55 ° C. which is considered normal.
  • the main reasons for this are:
  • Hertz / volt which is used in the temperature compensation algorithm to compensate for frequency deviations, changes over temperature, which means that a curve in which the oscillator frequency is plotted against the tuning voltage has a different course for different temperatures having. To take this into account, these curves would have to be stored for different temperatures in order to determine the tuning slope as a function of the tuning voltage, oscillator frequency and temperature.
  • the main disadvantages of frequency synchronization are that temperature compensation must take place and the algorithm for temperature compensation is complex; furthermore, that this temperature compensation algorithm delivers unsatisfactory results, especially in the case of deviations from the room temperature; and that the components used must be of high quality and therefore also have a high price. It is therefore an object of the present invention to simplify the frequency synchronization of a mobile station with a base station and to enable it in particular even in the case of non-standard temperature conditions.
  • a movable unit for example a mobile station, is synchronized with a central unit, for example a base station, with respect to the frequency in which the central unit emits signals which indicate the reference frequency which it predefines.
  • these signals are processed to set the reference frequency and the reference frequency is searched for by segmenting all or part of the available frequency range and searching for the reference frequency in at least one frequency range segment.
  • the search for the reference frequency is ended when the reference frequency has been found by the mobile station. This avoids unnecessary bills.
  • the mobile station contains an oscillator device with an oscillator, by means of which an oscillator frequency is provided. The frequency range in which the reference frequency is searched is changed by changing the oscillator frequency.
  • oscillator also includes the oscillator crystal itself, as well as capacitance diodes, transistors and the like.
  • Another development provides for the frequency range in which the reference frequency is searched to be selected or also changed as a function of external parameters.
  • the search for the desired reference frequency can thus be shortened if, for example, there is a relationship between external parameters and the frequency behavior of the oscillator.
  • a corresponding device has an oscillator circuit, by means of which an externally predetermined reference frequency is synthesized.
  • This oscillator circuit has an oscillator which provides an oscillator frequency, on the basis of which the reference frequency is searched for.
  • the oscillator frequency is changed by means of a processor unit in the device if the search for the reference frequency with the current oscillator frequency has been unsuccessful.
  • a new search for the reference frequency is then carried out based on the changed oscillator frequency.
  • FIG. 1 is a schematic representation of a frequency synthesis circuit with its essential components, in particular the oscillator crystal VCXO
  • Figure 2 shows the ranges in which the oscillator frequency is varied in order to search for the reference frequency.
  • FIGS. 2a and 2b show the windows W1 and W1, W2 and W3, within which the tuning voltage U, which is applied to the oscillator VCXO, is varied in order to achieve the desired oscillator frequency.
  • the tuning voltage U is plotted on the lower axis in FIG. 2a. If the value of the tuning voltage is U (f_c), then according to the calibration, the oscillator crystal has the center frequency f_c. As already explained at the beginning, the calibration usually takes place at three frequency values, to which a voltage is then assigned. The two other calibration points are here designated U (f_max), which characterizes the maximum tuning voltage, and U (f_min), which characterizes the minimum tuning voltage.
  • U (f_max) which characterizes the maximum tuning voltage
  • U (f_min) which characterizes the minimum tuning voltage.
  • the oscillator crystal can be tuned to a maximum within this range, which means that there is a calibration in this voltage range.
  • the deviation relates to that of the oscillator crystal assigned oscillator frequency of, for example, 13 MHz.
  • the deviation from this should ideally be zero Hz, the absolute frequency as reference point should be 13 MHz.
  • the reference frequency transmitted by the base station is also obtained.
  • the frequency synchronization behavior of the mobile station changes accordingly.
  • the signal energy received in the digital signal processor for evaluation decreases in a non-linear manner over the frequency shift due to the power density distribution of the GMSK modulated received signal used for example in GSM, so that the synchronization behavior gradually deteriorates until finally no synchronization at all from a certain frequency shift is more possible. This is the case when the synchronization signal of the base station can no longer be received or can be meaningfully evaluated.
  • the frequency of the reference oscillator is then outside the capture range of the automatic frequency correction control, ie the range within which frequency shifts can be compensated.
  • the capture range and thus the maximum permissible frequency offset of the oscillator is determined by the quality of the detector used. algorithm as well as the signal conditions at the receiving location
  • the frequency synchronization can nevertheless take place.
  • the control loop of the automatic frequency correction (AFC) will change the value of the tuning voltage U (f_c) step by step according to a certain algorithm until the frequency error is less than a certain threshold value, which depends on the mobile radio system used.
  • FIG. 2b An exemplary embodiment of the method according to the invention is shown in FIG. 2b.
  • the tuning voltage is not only varied in a window by the tuning voltage U (f_c) for the center frequency, but further windows are used on the basis of the other values of the tuning voltage, which were set during the calibration.
  • the window W1 is defined analogously to the case shown in FIG. 2a.
  • two further windows W2 and W3 were defined on the basis of the minimum tuning voltage and the maximum tuning voltage. Due to the overlap of two adjacent windows it is guaranteed that the desired oscillator frequency is found in any case.
  • the tuning voltage which leads to a value of the oscillator frequency of 13 MHz for the oscillator crystal VCXO, be marked as point OS.
  • the tuning voltage determined by means of the calibration and temperature compensation achieves a value shifted from the target oscillator frequency of 13 MHz.
  • this value has such a shift with respect to the target oscillator frequency that it no longer lies within the first window W1, the capture range, and consequently the base station can no longer be determined by the search algorithm previously used.
  • the divider D2 has a division ratio of 65, that is to say the input frequency f_in is 200 kHz.
  • the division ratio of D is 1880MHz / 200kHz.
  • 65 * (1880MHz / 0.2MHz) 37.6kHz in the high-frequency range, which corresponds to about a fifth of the bandwidth of a GSM channel.

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Stabilization Of Oscillater, Synchronisation, Frequency Synthesizers (AREA)
  • Oscillators With Electromechanical Resonators (AREA)

Abstract

La présente invention concerne un procédé et un dispositif de synchronisation de fréquence entre une station mobile et une station de base. La synchronisation de fréquence est également possible dans le cas d'un désaccordage important du cristal oscillateur étant donné que le domaine de recherche est choisi de façon correspondante.
PCT/DE2002/002885 2001-08-10 2002-08-06 Procede et dispositif de synchronisation de frequence WO2003017494A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE2001139467 DE10139467A1 (de) 2001-08-10 2001-08-10 Verfahren und Vorrichtung zur Frequenzsynchronisation
DE10139467.5 2001-08-10

Publications (1)

Publication Number Publication Date
WO2003017494A1 true WO2003017494A1 (fr) 2003-02-27

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WO (1) WO2003017494A1 (fr)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4272729A (en) * 1979-05-10 1981-06-09 Harris Corporation Automatic pretuning of a voltage controlled oscillator in a frequency synthesizer using successive approximation
US5552749A (en) * 1995-06-26 1996-09-03 Motorola, Inc. Method for automatically compensating for accuracy degradation of a reference oscillator
US5696468A (en) * 1996-02-29 1997-12-09 Qualcomm Incorporated Method and apparatus for autocalibrating the center frequency of a voltage controlled oscillator of a phase locked loop

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6175722B1 (en) * 1998-01-23 2001-01-16 D.S.P.C. Technologies Ltd. Initial frequency synchronization mechanism

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4272729A (en) * 1979-05-10 1981-06-09 Harris Corporation Automatic pretuning of a voltage controlled oscillator in a frequency synthesizer using successive approximation
US5552749A (en) * 1995-06-26 1996-09-03 Motorola, Inc. Method for automatically compensating for accuracy degradation of a reference oscillator
US5696468A (en) * 1996-02-29 1997-12-09 Qualcomm Incorporated Method and apparatus for autocalibrating the center frequency of a voltage controlled oscillator of a phase locked loop

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
HODGES M R L: "THE GSM RADIO INTERFACE", BRITISH TELECOM TECHNOLOGY JOURNAL, LONDON, GB, vol. 8, no. 1, 1990, pages 31 - 43, XP000575496 *

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Publication number Publication date
DE10139467A1 (de) 2003-02-27

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