Pulse or digital communications – Receivers – Particular pulse demodulator or detector
Reexamination Certificate
1999-12-23
2002-05-21
Chin, Stephen (Department: 2734)
Pulse or digital communications
Receivers
Particular pulse demodulator or detector
C375S262000, C375S265000, C714S796000
Reexamination Certificate
active
06393075
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention lies in the telecommunications field. More specifically, the invention relates to a method for processing data received by a receiver, in which data transmitted in successive frames over a transmission link are received. One frame contains a predefined number of bit positions. The received data are processed by means of a maximum a posteriori probability algorithm using metric increments or a maximum likelihood algorithm, whereby the Viterbi algorithm is used. The metric increments for at least one bit position whose value and/or whose so-called reliability value is correlated from frame to frame are thereby calculated in dependence on a current reliability value determined for that bit position. The reliability value is a measure of the probability that the value of the bit position has a predefined value.
A method of this type is known for a Viterbi algorithm, for example from the article “Source-Controlled Channel Decoding” by Joachim Hagenauer in “IEEE Transactions on Communications”, Volume 43, No. 9, September 1995, pages 2449-2457. Substantial parts of the article are also contained in U.S. Pat. No. 5,511,081 to Hagenauer (German patent DE 42 24 214 C2). In particular, formula (21) in the article specifies the calculation of new metrics M
k
(m) from old metrics M
k−1
(m) and an associated metric increment. The index m thereby denotes a specific path and k defines a specific bit position in a frame. A reliability value L(u
k
) is used in calculating the metric M
k
(m). On pages 2454 and 2455 of the article, the so-called HUK algorithm is suggested for the determination of the reliability value L(u
k
). The algorithm is thereby based on an empirical model in which the reliability values L(u
k
) are calculated similar to the so-called points in a German third-party liability insurance for cars. Because of the empirical character, the estimates for the reliability values L(u
k
) are inaccurate. The metric increments are either added to or multiplied by metrics already calculated.
The maximum a posteriori probability algorithm and the maximum likelihood algorithm are algorithms which compare a data sequence transmitted over the transmission link with reference sequences s, and determine the reference sequence s which, with the greatest probability, belongs to the transmitted data sequence. Maximum a posteriori probability means that reference sequence s is selected for which the probability P (s|y) becomes a maximum. The term y represents the received data sequence. Maximum likelihood means that reference sequence s is selected for which the probability P (y|s) becomes a maximum. The transmission link is, for example, a radio channel, a transmission line or else a storage medium from which data are read.
A multiple receiver which is insensitive to noise and has a number of receiving antennas is disclosed in U.S. Pat. No. 5,202,903 to Okanoue (European patent application EP 0 449 327). The received signals are generated by a single transmitted signal, which passes to the antennas via various transmission paths. Branch metrics for the implementation of a Viterbi algorithm are calculated from the received signals from the individual antennas. Before the algorithm is implemented, the branch metrics calculated in relation to the received signals from the individual antennas are weighted and combined. After the Viterbi algorithm has been implemented, this leads to the generation of a symbol sequence which agrees well with a transmitted symbol sequence on which the transmitted signal is based.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method and device for source-controlled channel decoding using a Kalman filter, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which specifies a simple method for determining the reliability values which calculates the current reliability values as far as possible without errors and accurately.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of processing data received by a receiver, which comprises:
receiving data transmitted in successive frames, each containing a predefined number of bit positions, via a transmission link;
processing the received data with a maximum a posteriori probability algorithm using one of metric increments and a maximum likelihood algorithm;
calculating the metric increments for at least one bit position, whose value and/or whose reliability value is correlated from frame to frame, in dependence from a current reliability value determined for the frame being currently processed, whereby the current reliability value is a measure of a probability that the value of the bit position has a predefined value;
determining the current reliability value by using at least one observed reliability value determined for the bit position from a previously processed frame or from the frame being currently processed; and
determining the current reliability value such that a sum formed over several frames of the deviations of an error-free reliability value for the respective frame and of the reliability value determined for the same frame assumes a minimum.
The invention is based on the consideration that the current reliability values could be determined very accurately with an optimization method. However, the difficulty is that reliability values to be used for the optimization are based on an observation which is subject to errors. The errors can be attributed to disturbances during the transmission of the data over the transmission link and to results from the Viterbi algorithm which are subject to errors. Therefore, in the method according to the invention, the target function defined is the sum of the deviations of an essentially error-free reliability value for a frame and of the reliability value determined for the same frame. In this case, the deviation relates to the magnitude of the difference between the actual, error-free reliability value and the determined reliability value. The target function is minimized by the optimization method, so that the reliability values determined in order to implement the Viterbi algorithm approach the error-free reliability values very closely.
In the method according to the invention, the minimization of the target function can be carried out in spite of unknown error-free reliability values, since, in the optimization method, a mathematical model is used which produces a relationship between the reliability values based on the observations and the error-free reliability values. In addition, so-called a priori information is used in the model, that is to say information which is known before the transmission of the data over the transmission link, such as information relating to the correlation of the data or the correlation of the reliability values in successive frames. In this sense, the data source influences the further processing of the data. If the processing is decoding, for example, then one also speaks of source-controlled channel decoding.
In the case of a Viterbi algorithm without iteration, the reliability value based on the observation is generally available only after a delay of one frame. Accordingly, in order to determine the current reliability value, recourse must be had to an observed reliability value which has been determined for the bit position from a frame that has already been processed. If, on the other hand, a Viterbi algorithm with iteration is carried out, then a reliability value based on an observation for the frame currently being processed is already available in the second iteration step. In this case, this observed reliability value is used to determine the current reliability value.
The method according to the invention supplies better results by comparison with the known HUK algorithm, since it can be used to process severely fluctuating source signals, in which the HUK algorithm is not capable of esti
Chin Stephen
Greenberg Laurence A.
Lerner Herbert L.
Liu Shuwang
Siemens Aktiengesellschaft
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