Patent number 8788921 is assigned to
The following quote was obtained by the news editors from the background information supplied by the inventors: "Various products including hard disk drives utilize a read channel device to retrieve information from a medium and decode and convert the information to a digital data format. Such read channel devices may include data processing circuits including encoder, detector and decoder circuits to encode, detect and decode data as it is stored and retrieved from a medium or transmitted through a data channel, in order to reduce the likelihood of errors in the retrieved data.
"It is important that the read channel devices be able to rapidly and accurately detect the data bits in retrieved or received data samples so they can be decoded. A number of various types of detectors are available to identify the value of encoded data bits as they are retrieved or received, before the detected data is decoded. One such detector is a maximum a posteriori (MAP) detector, which determines the most likely value of each encoded data bit. A typical MAP detector uses a trellis structure to calculate the probability or branch metric for each possible value of a bit or group of bits. A forward pass through the trellis is performed, calculating the probabilities of the possible values, a backward pass through the trellis is performed, again calculating the probabilities of the possible values, and the results of the forward and backward passes are combined to arrive at a decision based on the probabilities.
"Because efforts are continually being made to increase the speed of data processing circuits while reducing their size and complexity, all while operating with increasingly dense storage devices or transmission channels that increase noise, there exists a need in the art for improving data detection in data processing circuits."
In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "Various embodiments of the present invention provide apparatuses, systems and methods for data detection in a detector with soft pruning. For example, a data detector is disclosed that includes a branch metric calculator operable to calculate branch metrics for transitions between states in a trellis for the data detector, and a branch metric offset circuit operable to apply branch metric offsets to the branch metrics to yield soft pruned branch metrics. The branch metric offsets comprise a range of probability values from zero percent to one hundred percent. The branch metric offsets are applied in some embodiments to all transitions, including those from states that originate prohibited transitions and those from states that do not originate prohibited transitions. The branch metric offsets are derived in some instances from conditional state transition probabilities for encoded data at an input of the data detector based on at least one constraint on the encoded data. The soft pruning or application of branch metric offsets is disabled in some embodiments when constraints on encoded data are violated at the input to the data detector. In some cases, the branch metric offset circuit is operable to periodically switch between multiple sets of branch metric offsets. In cases in which the data detector is a maximum a posteriori detector, the branch metric offset circuit is operable to apply the branch metric offsets in a forward detection operation and in a reverse detection operation.
"Other embodiments provide a method of detecting data in a data detector with soft pruning, including calculating a branch metric for each of a plurality of transitions between states in the data detector, applying a branch metric offset to each of the branch metrics to yield soft pruned branch metrics, and calculating hard decisions based on the soft pruned branch metrics. In some instances of the aforementioned embodiments, the branch metric offsets are applied to all transitions in the data detector. Some embodiments also include deriving the branch metric offsets from probabilities of data patterns at an input to the data detector by counting occurrences of each possible pattern in a sliding window applied to a data stream at an output of an encoder upstream of the data detector to yield probabilities of occurrence, grouping the possible patterns and normalizing the probabilities of occurrence by group. Some embodiments also include disabling the application of branch metric offsets when data at an input of the data detector violates constraints upon which the branch metric offsets are based.
"This summary provides only a general outline of some embodiments according to the present invention. Many other objects, features, advantages and other embodiments of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings."
URL and more information on this patent, see: Chang, Wu; Krachkovsky, Victor; Yang, Shaohua; Xia, Haitao. Detector with Soft Pruning. U.S. Patent Number 8788921, filed
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