WO2000064052A1

WO2000064052A1 - Method and system for tuning resonance modules

Info

Publication number: WO2000064052A1
Application number: PCT/SE2000/000716
Authority: WO
Inventors: Björn Johansson; Lennart Larsson; Rolf Folkesson; Fredrik Oskarsson
Original assignee: Allgon Ab
Priority date: 1999-04-16
Filing date: 2000-04-14
Publication date: 2000-10-26
Also published as: EP1171952A1; CN1346541A; SE9901372D0; AU4444900A

Abstract

A method and system involving determination of signal response of a plurality of tunable resonance modules; sensing at least a first primary analogue signal from a first one of said transmitter signals; analog-to-digital converting said first primary analogue signal to form a first digital signal; performing time-discrete operations on said first primary digital signal to determine a first primary signal quantity; comparing sensed signal quantities to form a discrepancy quantity, comparing said discrepancy quantity to said signal response to determine a tuning vector; actuating said tuning means of said first resonance module by said tuning vector to obtain resonance therein for said first transmitter signal; and repetition for each module and for obtaining fed-back tuning.

Description

METHOD AND SYSTEM FOR TUNING RESONANCE MODULES

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to a method and a system for tuning in a fed-back tuning loop a plurality of resonance modules in for instance a radio base station, each resonance module having tuning means, a transmitter connection, and an antenna connection.

Such an arrangement for tuning resonance modules is disclosed in the published PCT Applications Nos PCT/SE92/0004 and PCT/SE97/01125. These publications concern prior technology for a typical field of use of the present invention. They are incorporated herein by reference.

That resonance module in the afore-mentioned documents includes a resonant cavity and a resonance body, the position of which is adjustable by means of a motor to control the resonance frequency of the resonance module. As long as there is a phase difference between high-frequency input and output signals of the resonance module, the arrangement adjusts the position of the resonance body so as to reduce that phase difference.

One of these prior art arrangements includes a voltage controlled oscillator that generates a high-frequency signal which is mixed with the input signal and the output signal in first and second mixers, respectively. Thus, two low-frequency signals are formed, the phase difference of which is a measure of a mistuning of the resonance module. Dependent thereon, the resonance module is tuned by means of the motor to a correct resonance frequency being the frequency of the input signal of the resonance module.

However, such voltage controlled oscillator is a relatively complicated and expensive component, which is required to have high dynamic performance since a relatively wide frequency range has to be scanned in the prior art tuning method.

In the other one of these prior art arrangements the voltage controlled oscillator has been excluded, but the system and method still rely on a rather large number of radio frequency components and other analogue components which inherently involve aging, drift and tolerance. To provide and maintain high performance, such an arrangement becomes relatively expensive.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a method of for tuning resonance module, which method eliminates the problems with RF components, for instance, aging, drift and tolerances. Further objects of the invention are to provide an efficient and accurate method wherein plural resonance modules can be tuned in a sequential process or in a parallel process, wherein multiplexing can be used to reduce required circuitry and get a general hardware platform easy to configure for different frequency bands and access methods, and to provide an efficient and cost- effective system for tuning resonance modules, in particular, for carrying out the method according to the invention.

These and other objects are attained and above-indicated problems are solved by the method and the system according to the appended claims.

Analogue high-frequency input and output signals on the transmitter and antenna connection are sensed and directly converted to digital form for processing in a digital signal processor. A tuning vector is determined for each resonance module based on two such digitally converted signals. A corresponding one of the tuning vectors is applied to each tuning means. The procedure is repeated continously and for each resonance module to provide a fed- back control loop. One particular advantage of the inventive method and system are that they provide the possibility for the system itself to examine its signal environment and adapt to it, for example, when a communication standard is changed or extended.

The inventive method and system are applicable to any type of resonance modules including, but not limited to, cavity resonators, half-wave or quarter-wave resonators, and waveguide resonators.

Further, the inventive method and system can either compare two or more signals sensed at different positions, e.g., sensed original (SI), internal (S2), reflected (S3), and antenna (S4) signals, and/or one or more of these signals sensed at different points in time at different postions of the resonator tuning means .

Further advantageous developments of the invention are set forth in the dependent claims and the detailed description below.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a block diagram of a resonance module tuning system including a plurality of possible sensing positions connected via a possible multiplexor to A/D converter means and a digital signal processor for controlling the tuning means of the resonance module,

Fig. 2 shows a first embodiment of the tuning system of fig. 1 including a multiplexor and a common A/D converter. Fig. 3 shows a second embodiment of the tuning system of fig. 1 including separate A/D converters.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

With reference to fig. 1, a single signal link is shown which is intended for a ulti signal combiner unit (cf. PCT/SE97/01125) intended for a base station in, e.g., a PCS mobile telephone system. In this embodiment of the invention the combiner unit could include four tunable resonance modules each arranged to be connected at one side to an output of a respective transmitter via a respective isolator and at the other side to a common transmitting antenna via a phasing network.

The improved sub-system of fig. 1 for tuning a first resonance module 1 comprises a tunable resonator 2 having tuning means 3, a transmitter connection 4, and an antenna connection 5. The system further comprises an isolator 6, which includes two circulator elements and a sensor P3 for sensing a transmitter signal Tl from a transmitter (not shown) , passing the isolator 6, to the transmitter connection 4 of the resonance module 1. The sensor P3 in the isolator 6 produces an input signal S3 that is essentially a small fraction of the transmitter signal Tl.

The input signal S3 is fed via a first multiplexer (MUX1) 7, the operating sequence of which is to be described further below, to a sampler and analog-to-digital-converter (ADC) 8, which feeds the signal in digital form to a digital signal prosessor (DSP) 9. The DSP 9 processes the digital signal and calculates a tuning vector based thereon containing information on distance and direction for movement of the tuning means 3. The DSP 9 sends a control signal Cl to the tuning means to obtain an intended tuning position, i.e., an intended resonance frequency of the resonance module 1. Additionally to the tuning vector the DSP 9 may assign a tuning speed and acceleration for actuation of the tuning means 3.

The sub-system can include a further sensor P2 arranged inside the resonator 2 for sensing an antenna signal Al or a quantity indicative thereof. This sensed signal S2 is fed via the MUX1 7 and the ADC 8 to the DSP 9 to be compared to signal S3 in order to determine a relative phase difference. That phase difference is a measure of a relative difference between a frequency of the transmitter signal Tl and the frequency to which the resonance module is presently tuned. Signal S2 is essentially a small fraction of the antenna signal Al . Alternatively, the output signal could be sensed by sensor P4 on the antenna connection 5 to produce a signal S4 to be used instead of signal S2. In that case, however, signals originating from other transmitters (none shown) could be more of a problem. In ideal tuning of the resonance module, the phase difference between the transmitter signal Tl on the transmitter connection 4 and the antenna signal Al on the antenna connection 5 would be zero (when compensation for signal travel is taken into account) .

Of course, the real time difference between the measurements is known and determined by the DSP. The sequence of connecting signals (SI - S4) by the MUXl 7 is not critical to the measurement principles.

A description will follow below with reference to figs. 2 and 3, respectively, of two different ways to evaluate differences between a primary and a secondary signal for determining a tuning vector. The examples involve estimation of the quantity of signal phase. However, another possible quantity is signal amplitude.

In fig. 2 the main embodiment indicated in fig. 1 is shown in somewhat greater detail. The primary signal SI derived from the transmitter signal Tl and the secondary signal S2 derived from the antenna signal Al are fed to MUXl 7 and are converted to digital form one at a time in the ADC 8 as the DSP 9 controls the operation of the MUXl 7. When multiplexing the difference in time between samples has to be taken into account.

If the time between sampling SI and S2 is short (in the order of 1/Fs, where Fs is the sampling frequency of the ADC) , it is possible to neglect any phase change in the signals resulting from phase modulation. The phase delay to compensate for (by conventional methods) is then proportional to the swiching cycle in the multiplexing.

If the time between sampling SI and S2 is long (multiplex switching cycle substantially greater than 1/Fs) , the modulation phase change in the signal should be predicted in order to compensate for it. This is performed by a conventional predictor method using primarily sample values of SI, but possibly also feed-back of sample values of S2. The total phase delay to compensate for is then proportional to the the swiching cycle in the multiplexing and the modulation phase change together.

For ease of understanding, the operations in the DSP 9 will be described more fully for the case depicted in fig. 3 where the primary and secondary signals SI and S2 are sampled and converted simultaneously in separate ADC 10 and ADC 11, respectively. The different steps in the DSP operation are:

1. Estimation of the carrier frequency ( = 2 Fc) of signal SI. The estimation is designated . This step is done by discrete fourier transformation.

2. If disturbing signals are present close to signal S2, such signals are removed by applying a suitable band pass filter having characteristics determined by the estimate and design parameters of the system. Signal SI can be filtered by the same or a similar filter in order to alter SI in the same manner as signal S2 is altered in the filtering. This eliminates any unwanted filter influence when comparing SI and S2.

3. Estimate a relative phase from the filtered primary and secondary signals. It is preferable to use a discrete fourier transformation method. 4. Based on the results of the steps 1-3 and a functional model of the resonance module, the filter function of the resonator module can now be changed to according to tuning vector proportional to the relative phase of SI and S2. The tuning means is actuated via a control output of the DSP. When applying the tuning vector, the result of steps 1-3 can be compared to desired values.

To obtain essentially the same performance in the solutions of figs. 2 and 3, a sampling rate at least twice as high is needed in the fig. 2 solution. On the other hand, multiplexing reduces the number of analog-to-digital converters needed.

In the described embodiments, an electrical stepping motor, controlled by a signal Cl from the DSP 9, performs adjustment of a first resonance module by moving via a mechanical link a tuning element in the resonator of the resonance module. The motor itself may set a limit to the speed of adjustment of the resonance module.

Although the invention has been described in conjunction with preferred embodiments, it is to be understood that various modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims. Thus, the invention incorporates any system for carrying out the method defined by the method claims. Although the presently preferred method is disclosed, there are obviously more ways within the inventive scope to combine measurements at one or more of the different signal sensing positions PI, P2, P3, P4 (or others) than explicitly explained herein.

Claims

1. Method for combining to one antenna, a plurality of transmitter signals from a corresponding plurality of radio transmitters operable at variable carrier frequencies, by means of a corresponding plurality of tunable resonance modules and a signal processing means including memory means, each of said resonance modules having tuning means, a transmitter connection, and an antenna connection, said method comprising the steps of:

(a) determining signal response of said tunable resonance modules,

(b) storing information of said signal response in said memory means, (c) deriving a first primary analogue signal from a first one of said transmitter signals, (d) analog-to-digital converting said first primary analogue signal to form a first primary digital signal, (e) selecting a first secondary analogue signal being complementary to said first primary analogue signal,

(f) deriving said first secondary analogue signal from said first one of said transmitter signals,

(g) analog-to-digital converting said first secondary analogue signal to form a first secondary digital signal, (h) performing time-discrete operations on said first primary digital signal to determine a first primary signal quantity, (i) performing time-discrete operations on said first secondary digital signal to determine a first secondary signal quantity, (j) comparing said first primary and secondary signal quantities to form a discrepancy quantity, (k) comparing said discrepancy quantity to said signal response to determine a tuning vector indicative of direction and absolute value for tuning, (1) actuating said tuning means of said first resonance module by said tuning vector to obtain resonance therein for said first transmitter signal, (m) repeating steps (c)-(d) and (f)-(m) for feed back tuning.

2. Method according to claim 1, wherein steps (a) - (m) are carried out for each resonance module by means of multiplexing signals to be processed in time-discrete operations.

3. Method according to claim 1, wherein said analog-to- digital conversion is performed directly at a high frequency of said first transmitter signal.

4. Method according to claim 1, wherein said signal quantities are selected from a group consisting of: signal phase, signal phase change, signal amplitude, and signal amplitude change.

5. Method according to claim 1, further comprising multiplexing and processing further input and output signals of further resonance modules using common measurement circuitry and a common signal processing unit.

6. Method according to claim 1, further comprising parallelly processing further input and output signals of further resonance modules using separate measurement circuitry and a common signal processing unit.

7. Method according to claim 1, wherein primary and secondary signals are obtained at different positions in a signal path.

8. Method according to claim 7, wherein primary and secondary signals are as a set of two of: an original transmitter signal, a signal reflected by said resonance module, a signal within said resonance module, a signal output from said resonance module.

9. Method according to claim 1, wherein primary and secondary signals are obtained at different points in time with intermediate actuation of said tuning means.

10. Method according to claim 1, wherein steps between analogue-to-digital converting and actuating the tuning means further comprise: (i) Estimation of the carrier frequency of said first primary analogue signal, (ii) If disturbing signals are present close to said first secondary analogue signal, removing such signals by applying a band pass filter having characteristics determined by the estimate, (iii) Estimation of a relative phase between the filtered first primary and secondary analogue signals, (iv) Based on the results in (i)-(iii) and said signal response of said resonance module, determining said tuning vector.

11. Method according to claim 1, wherein the operations performed on the primary and secondary signals are adapted in response to any change in characteristics of said transmitter signals to maintain stability in said fed-back tuning .

12. System for tuning at least one tunable resonance module in a radio base station, said tunable resonance module (1) having tuning means (3), a transmitter connection (4), and an antenna connection (5), said system comprising at least one analog-to-digital converter for converting high- frequency measuring signals from at least one of an input signal and an output signal to and from said tunable resonance module, respectively, for calculating by time- discrete operations a tuning vector for controlling said tuning means .

13. System according to claim 12 for carrying out the method of any of the preceding method claims.