Pulse or digital communications – Equalizers
Reexamination Certificate
1997-04-04
2002-03-05
Chin, Stephen (Department: 2634)
Pulse or digital communications
Equalizers
C375S231000, C375S232000, C375S341000, C375S347000
Reexamination Certificate
active
06353630
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention is directed to a method for the parameterization of a reception means of a radio system with allocated antenna means and with a pre-filter and to such a reception means or, respectively, a radio station with at least one reception means.
In a radio system, information is transmitted from a transmitting radio station to a receiving radio station. This information arrives at the receiving radio station in the form of reception signals. Due to various external influences, the reception signals reach the receiving radio station over a plurality of transmission paths. The signal components corresponding to the various transmission paths arrive at the receiving radio station at successive points in time. There is then the problem in the receiving radio station of equalizing these signal components, which can also be influences by further noise components, of correcting the errors and decoding the transmitted information.
Proakis,“Digital Communications”, 1989, pp.593-595 discloses pre-filters that suppress noise components in the reception signals, particularly adjacent channel interference, in a reception means before the detection. A pre-filer is composed of delay elements in which the reception signals are delayed in steps. The reception signals with different delay are respectively weighted with a filter coefficient and are subsequently summed up. The filter coefficients, however, are permanently prescribed, and the pre-filter is part of an equalizer, whereby the detector is fashioned as a simple threshold decision unit.
Further parameters are defined within the reception means for the evaluation of the reception signals. For example, these parameters are channel coefficients known from W. Koch,“Optimum and sub-optimum detection of coded data disturbed by time-varying intersymbol interference”, IEEE Proceedings 1990, pp. 1679-84. These channel coefficients used in a channel model serve the purpose of suitably superposing various signal components of a reception signal that arrive after one another.
It is also known to supply the antenna data acquired from the reception signals by transmission into the base band and analog-to-digital conversion as well as the channel coefficients to a detector that equalizes the antenna data and undertakes the error correction. The symbols of the signals reconstructed in the output of the detector are subsequently decoded in a decoder, for example a Viterbi decoder.
It is known from mobile radiotelephone systems (see M. Mouly, M.-B. Pautet,“The GSM System for Mobile Communication”, 49. rue Louise Bruneau, F-91120 Palaiseau, France, 1992, pp. 231-237) to utilize what are referred to as training sequences in order to equalize receiving radio stations. At predetermined points in time, the transmitting radio station transmits a sequence of digital data that are known to the receiving radio station, i.e. whose data are present undistorted in the receiving radio station.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for the parameterization of a reception means as well as such a reception means or, respectively, radio station in a radio system that enable an adjustable and improved immunity to disturbance.
In a radio system, a reception means with pre-filter is parameterized in that the filter coefficients of the pre-filter are adjustable, and a matching of the pre-filter to a given demand for immunity to disturbance ensues adaptively during the operation of the reception means together with the determination of channel coefficients. It is thus possible to do justice to modified reception conditions. Such a parameterization of the reception means proves advantageous precisely in radio systems since the conditions in the radio channel change fast. For example, training sequences known in radio systems are suitable for setting the filter coefficients.
According to an advantageous development of this inventive method, received reception signals are converted into digital signals in the reception means and are delayed by steps in the adaptive pre-filter belonging to the reception means; the differently delayed reception signals are respectively weighted with filter coefficients and superposed. The reception means also contains a channel model with which the radio channel between transmitting and receiving radio station can be simulated. The channel model is thereby characterized by channel coefficients with which the channel model is matched to the real radio channel. The channel model represents, for example, a filter with finite pulse response. The antenna data and the specific channel coefficients are supplied to a detector for equalization and error correction of the antenna data that is contained in the reception means.
During a training sequence, the signals represent received test data that are additionally present undisturbed in the reception means. Antenna data allocatable to the received test data and model quantities derived from the channel model supplied with the test data are supplied to an arithmetic unit. The filter coefficients for the suppression of received noise quantities and the channel coefficients for the equalization of the differences in running time of various signal components of a reception signal are now simultaneously determined in the arithmetic unit, which likewise belongs to the reception means. To that end, an algorithm is utilized that undertakes the minimization of the deviation of antenna data of the training sequence and model quantities of the training sequence. The determined filter coefficients and channel coefficients can subsequently also be used for the evaluation of the signals outside the training sequence. When processing digital reception signals, it is possible to realize pre-filter, channel model and arithmetic unit in a digital signal processor, additional circuit-oriented outlay being reduced as a result thereof.
The combination of adaptive pre-filter and channel model as well as the simultaneous calculation of the parameters for the filter coefficients and the channel coefficients in an arithmetic unit creates a significant improvement of the functioning of the reception means with respect to the reconstruction of transmitted information. The parameters required for setting the reception means can be determined in common with a simple algorithm. The secondary condition must thereby be noted that the trivial solution with filter coefficients and channel coefficients set to the value zero is precluded. A corresponding secondary condition is to be provided in the algorithm
Dependent on the plurality of delay elements of the adaptive pre-filter, an improved noise signal suppression ensues both for noise sources in adjacent channels as well as in the proper channel, particularly sine-shaped noise sources. The number of sine noise sources that can be completely eliminated corresponds to the number of filter coefficients minus one. The adaptive pre-filter produces a clear improvement of the reception quality, as a result whereof, given employment of the radio station in a radio system, a gain in system capacity also derives, for example in mobile radiotelephone systems due to the greater density of mobile stations thereby enabled.
According to further developments of the subject matter of the invention, the algorithm for determining the filter coefficients and channel coefficients is fashioned such, upon exclusion of the trivial solution, that a plurality of sets of filter coefficients are present in the reception means with which the received test data are respectively evaluated and, subsequently, the channel coefficients are determined with a minimum deviation from antenna data and model quantities. The solution with the least deviation, i.e. the appertaining filter coefficients and specific channel coefficients thereto, is selected and serves for the parameterization of the reception means. This solution reduces the calculating outlay to the determination of the channel coefficients, whereas the filter coefficients are select
Chin Stephen
Liu Shuwang
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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