Wave transmission lines and networks – Automatically controlled systems
Reexamination Certificate
2001-02-20
2003-04-08
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Automatically controlled systems
C333S126000, C333S132000
Reexamination Certificate
active
06545559
ABSTRACT:
This invention relates essentially to a tuning method of the kind stated in the preamble of claim
1
, and a system performing the method.
The invention relates to tuning of a combiner filter in an antenna near system for base station equipment. The invention relates to radio communication systems. In particular it relates to an antenna near system having products designed for combining transmitted power, where multiple carrier frequencies are used, for radio base station equipment.
BACKGROUND
Mobile radio telephony communication systems have grown immensely during the last years. Operators are currently facing severe problems regarding available transmit and receive frequency spectrum allocation. This is a general capacity problem. In conjunction with these problems the number of base station antennas must be minimised. The later is not only due to installation costs but also due to environmental aspects.
Therefore, high market demands have developed for radio base equipments able to use few antennas and still provide high traffic capacity, i.e. serve many calls simultaneously, as well as a limited use of the frequency spectrum.
STATE OF THE ARTS
Base station manufacturers often use filter combiners as the antenna near products of the base station in order to design base station equipment meeting the market demand for high capacity, few antennas and reasonable frequency spectral use. A combiner filter is a kind of adjustable band-pass filter. The filter combiners use filters to combine several transmit carriers towards the mobile stations to one and the same antenna. In order to make the system reasonably manageable for the operators, these filters usually have an automated tuning function, so that each filter can tune to the specific transmit carrier assigned to this particular combiner filter. A number of tuneable combiner filters are connected to one antenna.
PROBLEM
The intrinsic problem with filter combiners arises from the following fundamental conflict:
Operators want to have a narrow channel spacing, low loss and low loss variation. However, the filters cannot be designed to have perfect channel response and perfect out-of-band isolation, i.e. perfect attenuation between the channels.
For example, there are fairly broad band transmit signals in a GSM system to deal with. In particular, this is a problem for GSM EDGE, i.e. high speed data transmission. Narrow filters allowing for narrow channel spacing will impair on the transmitted signal quality.
Filters will drift in temperature. Therefore, once tuned there will still be a need to readjust them. Readjustments could also be needed by other reasons. A degrading of the transmitted signal by an inaccurate re-tuning process is not allowed during this process. The margin for tuning inaccuracy will be very small for a system, which allows a reasonable tight channel spacing.
RELATED ART
In U.S. Pat. No. 5,757,247 a system is described for adjusting a combiner filter. A RF (radio frequency) sample signal is derived proportional to the power of the input of the combiner filter. In one embodiment a sample of the output from the combiner filter is derived. The signals are down converted. The signal obtained has a DC component, which is removed. The signal strengths of the down converted signals are detected. The centre frequency of the combiner filter is adjusted on basis of the detected signal strengths.
OBJECTS
An object of the invention is to provide a tuning system, which will significantly enhance the performance regarding tuning accuracy of current combining systems.
Another object of the invention is to provide a tuning method or system, which will improve the readjustment of the filters when drifted in temperature and/or for some kind of time related changes.
INVENTION
A very precise tool for evaluating how the filters are tuned is obtained by performing a spectral analysis of the transmitted signal before the filter combining system and compare it with a spectral analysis of the outgoing signal from the filter combining system. This method allows for compensation of the measurement system characteristics, such as variation of response within a channel. Hence a clear picture of the true impact of the filter combining system can be derived.
The invention relates on a tuning method or system for a combiner filter in an antenna near system for base station equipment. The combiner filter is connected to a radio transmitter and is intended to have a centre frequency tuned to the carrier frequency of the radio transmitter. The transmitted signals related to the combiner filter are compared with each other. The system is characterized by means to perform a spectral analysis of each of the transmitted signals and compare the spectral analysis results regarding magnitudes and/or phases of the signals; and control means tuning the combiner filter based on the analysis in an iteration procedure until the combiner filter is tuned according to predetermined conditions.
The transmitted signals are preferably signals related to the input and the output of the combiner filter. Sampling means could sample the signals during a predetermined time interval for transfer into frequency domain. Comparing means could provide the spectral analysis of the transmitted signals regarding magnitudes and/or phases and compare the individual magnitudes and/or phases of predetermined frequencies with each other. A measuring circuitry could provide a pre-calibration of the signals in relation to an internal response of the circuitry and correction of the spectral comparison with the internal response.
Down converting means could convert the signals to a video frequency level. Gain controllable amplifier means could amplify each of the down converted signals before comparing them. Signal evaluation means could retrieve control the amplifiers means based on the signal magnitudes of the signals to be compared.
Evaluation means could perform a discrete Fourier transform or FIR filter analysis of the signals to be compared and correlate and/or error estimate their individual spectral density. FIR filter banks or analogue filter banks could perform the evaluation. The evaluation means could divide the signals (magnitudes and/or phases) related to the input and the output of the combiner filter in at least two frequency bands symmetrically around a centre frequency for the combiner filter. The tuning means could tune the combiner filter in iterative steps until the divided signals at the input and the output of the combiner filter are as near to each other as possible. The frequency bands could two, one on each side of the centre frequency, and then the evaluation means provides the ratio between Pfwd(low)/Pi(low) and compare it with the ratio Pfwd(high)/Pi(high), where Pi(low) is a low part below and Pi(high) is a high part above the centre frequency f
0
.of a representation of the input to the combiner filter, Pfwd(low) is a low part below and Pfwd(high) a high part above the centre frequency F
0
of a representation of the output to the combiner filter. Alternatively, the frequency bands could be several on each side of the centre frequency, and the evaluation circuitry compare products of all the spectral components Pfwd(low) and Pi(low) with products of Pfwd(high) and Pi(high). The evaluation means could perform a Fast Fourier transform calculation of the signals and make a correlation of the individual spectral density of the signals. The evaluation means could comprise FIR filter banks or analogue filter banks. Instead, the evaluation means could perform an error estimation of the magnitudes and/or phases of the signals.
The system could be adapted to radio communication systems, for example global system for mobile telephony (GSM) systems or digital advanced mobile telephone service (DAMPS). Switching means could switch, for supervision purpose after tuning, from the signal representation of the output of the combiner filter to a signal (Prefl) related to a reflected signal from the antenna, to which the output of the combiner filter is transmitted.
T
Ahl Torbjörn
Cullbom Peter
Nixon & Vanderhye P.C.
Pascal Robert
Takaoka Dean
Telefonaktiebolaget LM Ericsson (publ)
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