public class ViterbiDecoder extends Transformer
The decoder finds the most likely data sequence given noisy inputs by searching all possibilities and computing the distance between the codewords they produce and the observed noisy data. The sequence yielding the minimum distance is the decoded output.
There are two choices offered in this actor to compute the distance. If it the parameter softDecoding is set to be false, the input port will accept boolean tokens and compute the Hamming distance. If the parameter softDecoding is set to be true, the input port will accept double tokens and compute the Euclidean distance. The parameter constellation should be a double array of length 2. The first element specifies the amplitude of "false" input. The second element specifies the amplitude of "true" input. At this time, this actor can only handle binary antipodal constellations, but we expect to generalize this.
Soft decoding has lower probability of decoding error than hard decoding. But distance computation for hard decoding is easier, since it is based on bit operations. Moreover, hard decoding can be used when there is no direct observation of the noisy data, but only observations of a bit sequence that may have errors in it. With hard decoding, this actor serves the role of correcting errors. With soft decoding, it serves the role of reducing the likelyhood of errors.
There is some delay between the reading of input data and the production of decoded output data. That delay, which is called the trace-back depth or truncation depth of the decoder, is controlled by the delay parameter, which is required to be a positive integer. On the first delay firings of this actor, the outputs will be false. On each firing, the number of outputs produced is uncodedRate, so the output will have a prefix of delay*uncodedRate false-valued tokens before any decoded bits are produced. Larger values of delay generally reduce the probability of error. A good rule of thumb is to set delay to five times the highest order of all polynomials, provided that the convolutional code is a one that has good distance properties.
For more information on convolutional codes and Viterbi decoder, see the ConvolutionalCoder actor and Proakis, Digital Communications, Fourth Edition, McGraw-Hill, 2001, pp. 471-477 and pp. 482-485, or Barry, Lee and Messerschmitt, Digital Communication, Third Edition, Kluwer, 2004.
Entity.ContainedObjectsIterator| Modifier and Type | Field and Description |
|---|---|
Parameter |
constellation
The constellation for soft decoding.
|
Parameter |
delay
Integer defining the trace back depth of the viterbi decoder.
|
Parameter |
polynomialArray
An array of integers defining polynomials with
binary coefficients.
|
Parameter |
softDecoding
Boolean defining the decoding mode.
|
Parameter |
trellisDecoding
Boolean defining whether the decoder will do trellis decoding.
|
Parameter |
uncodedRate
Integer defining the number of bits produced at the output
in each firing.
|
input, output_typesValid_actorFiringListeners, _initializables, _notifyingActorFiring, _stopRequested_changeListeners, _changeLock, _changeRequests, _debugging, _debugListeners, _deferChangeRequests, _elementName, _isPersistent, _verbose, _workspace, ATTRIBUTES, CLASSNAME, COMPLETE, CONTENTS, DEEP, FULLNAME, LINKSCOMPLETED, NOT_READY, STOP_ITERATING| Constructor and Description |
|---|
ViterbiDecoder(CompositeEntity container,
java.lang.String name)
Construct an actor with the given container and name.
|
| Modifier and Type | Method and Description |
|---|---|
void |
attributeChanged(Attribute attribute)
If the attribute being changed is softDecoding or
trellisDecoding, set input port and constellation
type to be complex if trellisDecoding is true; else
if softDecoding is true, set them to double type;
otherwise set the input port to type boolean.
|
java.lang.Object |
clone(Workspace workspace)
Clone the actor into the specified workspace.
|
void |
fire()
Read n inputs and produce k outputs, where n
is the number of integers in polynomialArray and k
is the value of the uncodedRate parameter.
|
void |
initialize()
Initialize the actor.
|
boolean |
postfire()
Record the datum in buffers into their temporary versions.
|
_containedTypeConstraints, _customTypeConstraints, _defaultTypeConstraints, _fireAt, _fireAt, attributeTypeChanged, clone, isBackwardTypeInferenceEnabled, newPort, typeConstraintList, typeConstraints_actorFiring, _actorFiring, _declareDelayDependency, addActorFiringListener, addInitializable, connectionsChanged, createReceivers, declareDelayDependency, getCausalityInterface, getDirector, getExecutiveDirector, getManager, inputPortList, isFireFunctional, isStrict, iterate, newReceiver, outputPortList, prefire, preinitialize, pruneDependencies, recordFiring, removeActorFiringListener, removeDependency, removeInitializable, setContainer, stop, stopFire, terminate, wrapup_adjustDeferrals, _checkContainer, _getContainedObject, _propagateExistence, getContainer, instantiate, isAtomic, isOpaque, moveDown, moveToFirst, moveToIndex, moveToLast, moveUp, propagateExistence, setName_addPort, _description, _exportMoMLContents, _removePort, _validateSettables, connectedPortList, connectedPorts, containedObjectsIterator, getAttribute, getPort, getPorts, linkedRelationList, linkedRelations, portList, removeAllPorts, setClassDefinition, uniqueName_setParent, exportMoML, getChildren, getElementName, getParent, getPrototypeList, isClassDefinition, isWithinClassDefinition_addAttribute, _adjustOverride, _attachText, _cloneFixAttributeFields, _containedDecorators, _copyChangeRequestList, _debug, _debug, _debug, _debug, _debug, _executeChangeRequests, _getIndentPrefix, _isMoMLSuppressed, _markContentsDerived, _notifyHierarchyListenersAfterChange, _notifyHierarchyListenersBeforeChange, _propagateValue, _removeAttribute, _splitName, _stripNumericSuffix, addChangeListener, addDebugListener, addHierarchyListener, attributeDeleted, attributeList, attributeList, decorators, deepContains, depthInHierarchy, description, description, event, executeChangeRequests, exportMoML, exportMoML, exportMoML, exportMoML, exportMoMLPlain, getAttribute, getAttributes, getChangeListeners, getClassName, getDecoratorAttribute, getDecoratorAttributes, getDerivedLevel, getDerivedList, getDisplayName, getFullName, getModelErrorHandler, getName, getName, getSource, handleModelError, isDeferringChangeRequests, isOverridden, isPersistent, lazyContainedObjectsIterator, message, notifyOfNameChange, propagateValue, propagateValues, removeAttribute, removeChangeListener, removeDebugListener, removeHierarchyListener, requestChange, setClassName, setDeferringChangeRequests, setDerivedLevel, setDisplayName, setModelErrorHandler, setPersistent, setSource, sortContainedObjects, toplevel, toString, validateSettables, workspaceequals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, waitcreateReceivers, getCausalityInterface, getDirector, getExecutiveDirector, getManager, inputPortList, newReceiver, outputPortListisFireFunctional, isStrict, iterate, prefire, stop, stopFire, terminateaddInitializable, preinitialize, removeInitializable, wrapupdescription, getContainer, getDisplayName, getFullName, getName, getName, setNamegetDerivedLevel, getDerivedList, propagateValuepublic Parameter polynomialArray
public Parameter uncodedRate
public Parameter delay
public Parameter softDecoding
public Parameter trellisDecoding
public Parameter constellation
public ViterbiDecoder(CompositeEntity container, java.lang.String name) throws NameDuplicationException, IllegalActionException
container - The container.name - The name of this actor.IllegalActionException - If the entity cannot be contained
by the proposed container.NameDuplicationException - If the container already has an
actor with this name.public void attributeChanged(Attribute attribute) throws IllegalActionException
attributeChanged in class NamedObjattribute - The attribute that changed.IllegalActionException - If uncodedRate,
or delay is non-positive, or any element of
polynomialArray is non-positive.public java.lang.Object clone(Workspace workspace) throws java.lang.CloneNotSupportedException
clone in class TypedAtomicActorworkspace - The workspace for the new object.java.lang.CloneNotSupportedException - If a derived class contains
an attribute that cannot be cloned.NamedObj.exportMoML(Writer, int, String),
NamedObj.setDeferringChangeRequests(boolean)public void fire()
throws IllegalActionException
fire in interface Executablefire in class AtomicActor<TypedIOPort>IllegalActionException - Not thrown in this base class.public void initialize()
throws IllegalActionException
initialize in interface Initializableinitialize in class AtomicActor<TypedIOPort>IllegalActionException - If the parent class throws it.public boolean postfire()
throws IllegalActionException
postfire in interface Executablepostfire in class AtomicActor<TypedIOPort>IllegalActionException - If the base class throws it