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US6526531
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https://patentimages.storage.googleapis.com/fb/6f/fd/7ffd6da1e593b6/US6526531.pdf
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Title: Threshold detection for early termination of iterative decoding.Claims: What is claimed is: 1. In a signal processing application a method of decoding an encoded frame comprising the steps of:a) decoding during a current iteration of iterative decoding the encoded frame to provide a decoded frame including decoded data and decoded error detection information;b) calculating a parity value from the decoded data;c) comparing the parity value with the decoded error detection information to determine if the data passes a parity check;d) if the decoded data passes the parity check1) terminating iterative decoding to provide the decoded data of the current iteration; otherwise if the decoded data does not pass the parity check2) calculating a difference of errors between the decoded frame of the current iteration and a decoded frame of a previous iteration;e) terminating iterative decoding in accordance with an error rate measure based on the difference calculated for the decoded frame of the current iterationwherein the error-rate measure indicates either i) achieving a relative maximum bound for bit-error rate or ii) a relative minimum difference in errors for iterative decoding between the previous and current iterations. 2. The invention as recited in claim 1 wherein for step e) the relative maximum bound is a bit-error-rate threshold for the decoded frame and step e) terminates iterative decoding by comparing the bit-error-rate threshold with the calculated difference for the decoded frame of the current iteration. 3. The invention as recited in claim 1 wherein step e) terminates iterative decoding based on the comparison between i) the difference of errors calculated for a decoded frame of the previous iteration and ii) the difference in errors calculated for the decoded frame of the current iteration when the comparison indicates an increase in bit-error rate for iterative decoding by the current iteration. 4. The invention as recited in claim 1 wherein step e) terminates iterative decoding after repeating steps a) through e) for a total number N iterations of the iterative decoder and further comprises the steps of:f) tracking each difference calculated in step e) of an iteration of the decoder; andg) providing the decoded frame of the iteration corresponding to a relatively minimum difference in errors as decoded data. 5. The invention as recited in claim 1 wherein steps a) through e) are performed when the current iteration for iterative decoding either meets or exceeds an intermediate iteration threshold. 6. The invention as recited in claim 1 wherein the method of steps a) through e) are implemented as program steps by at least one processor in an integrated circuit. 7. The invention as recited in claim 1 wherein the method of steps a) through e) are implemented by a processor of a transceiver operating in accordance with a code-division multiple-access telecommunication standard. 8. In a signal processing application a method of decoding an encoded frame comprising the steps of:a) decoding during a current iteration of iterative decoding the encoded frame to provide a decoded frame of data;b) calculating a difference between the decoded frame of the current iteration and a decoded frame of a previous iteration the difference related to the number of errors in the decoded frame of the current iteration;c) terminating iterative decoding based on an error rate measure by comparing the difference calculated for the decoded frame of the current iteration with a difference calculated during the previous iteration wherein the difference calculated during the previous iteration is related to the number of errors in the decoded frame of the previous iteration. 9. The invention as recited in claim 8 wherein for step c) iterative decoding is terminated when the error-rate measure indicates an increase in bite error rate for iterative decoding between the previous and current iterations. 10. The invention as recited in claim 8 wherein for step c) iterative decoding is terminated after a number N of iterations of the iterative decoder as an error-rate measure and further comprises the steps off) tracking each difference calculated in step b) of an iteration of the decoder; andg) providing the decoded frame of the iteration corresponding to a relatively minimum difference in errors as decoded data. 11. The invention as recited in claim 8 wherein steps a) through c) are performed when the current iteration for iterative decoding exceeds an intermediate iteration threshold. 12. The invention as recited in claim 8 wherein the method of steps a) through c) are implemented as program steps by at least one processor in an integrated circuit. 13. The invention as recited in claim 8 wherein the method of steps a) through e) are implemented by a processor of a transceiver operating in accordance with a code-division multiple-access telecommunication standard. 14. In a signal processing application a circuit for iterative decoding of an encoded frame of data the circuit comprising:an iterative decoder decoding during a current iteration the encoded frame to provide a decoded frame having decoded data and decode error detection information; anda processor comprising:a parity check module calculating a parity value for the decoded data;a threshold detector comparing the parity value with the decoded error detection information to determine if the decoded data passes a parity check; andwherein if the data passes the parity check the processor terminates decoding by the iterative decoder to provide the data of the current iteration as a decoded frame; otherwise if the data does not pass the parity checkthe processor calculates the difference of errors between the decoded frame of the current iteration and a decoded frame of a previous iteration; and terminates decoding by the iterative decoder in accordance with an error rate measure based on the difference calculated for the decoded frame of the current iterationwherein the error-rate measure indicates either i) achieving a relative maximum bound for bit-error rate or ii) a relative minimum difference in bit-error-rate for iterative decoding between the previous and current iterations. 15. The invention as recited in claim 14 wherein the relative maximum bound is a bit-error-rate threshold for the decoded frame and the processor terminates iterative decoding by comparing the bit-error-rate threshold with the calculated difference for the decoded frame of the current iteration. 16. The invention as recited in claim 14 wherein the processor terminates iterative decoding based on the comparison between i) the difference of errors calculated for a decoded frame of the previous iteration and ii) the difference in errors calculated for the decoded frame of the current iteration when the comparison indicates an increase in bit-error rate for iterative decoding by the current iteration. 17. The invention as recited in claim 14 wherein the processor terminates iterative decoding after a total number N iterations of the iterative decoder and the processor further:1) tracks the difference calculated for each iteration of the decoder; and2) provides the decoded frame of the iteration corresponding to a relatively minimum difference in errors as decoded data. 18. The invention as recited in claim 14 wherein the processor calculates the difference when the current iteration for iterative decoding either meets or exceeds an intermediate iteration threshold. 19. The invention as recited in claim 14 wherein the circuit is embodied in an integrated circuit. 20. The invention as recited in claim 14 wherein the circuit is embodied in a transceiver operating in accordance with a code-division multiple-access telecommunication standard. 21. In a signal processing application a circuit for iterative decoding of an encoded frame of data the circuit comprising:an iterative decoder decoding during a current iteration the encoded frame to provide decoded data and decode error detection information; anda processor calculating a difference between the decoded frame of the current iteration and a decoded frame of a previous iteration the difference related to the number of errors in the decoded frame of the current iteration;wherein the processor terminates iterative decoding based on an error rate measure by comparing the difference calculated for the decoded frame of the current iteration with a difference calculated during the previous iteration wherein the difference calculated during the previous iteration is related to the number of errors in the decoded frame of the previous iteration. 22. The invention as recited in claim 21 wherein the processor terminates iterative decoding when the error-rate measure indicates an increase in bite error rate for iterative decoding between the previous and current iterations. 23. The invention as recited in claim 21 wherein iterative decoding is terminated after a number N of iterations of the iterative decoder as an error-rate measure and the processor further:1) tracks each difference calculated for an iteration of the decoder; and2) provides the decoded frame of the iteration corresponding to a relatively minimum difference in errors as decoded data. 24. The invention as recited in claim 21 wherein the circuit is embodied in an integrated circuit. 25. The invention as recited in claim 21 wherein the circuit is embodied in a transceiver operating in accordance with a code-division multiple-access telecommunication standard. 26. A computer-readable medium having stored thereon a plurality of instructions the plurality of instructions including instructions which when executed by a processor cause the processor to implement a method of decoding an encoded frame the method comprising the steps of:a) decoding during a current iteration of iterative decoding the encoded frame to provide a decoded frame including decoded data and decoded error detection information;b) calculating a parity value from the decoded data;c) comparing the parity value with the decoded error detection information to determine if the data passes a parity check;d) if the decoded data passes the parity check1) terminating iterative decoding to provide the decoded data of the current iteration; otherwise if the decoded data does not pass the parity check2) calculating a difference of errors between the decoded frame of the current iteration and a decoded frame of a previous iteration;e) terminating iterative decoding in accordance with an error rate measure based on the difference calculated for the decoded frame of the current iterationwherein the error-rate measure indicates either i) achieving a relative maximum bound for bit-error rate or ii) a relative minimum difference in errors for iterative decoding between the previous and current iterations. 27. A computer-readable medium having stored thereon a plurality of instructions the plurality of instructions including instructions which when executed by a processor cause the processor to implement a method of decoding an encoded frame the method comprising the steps of:a) decoding during a current iteration of iterative decoding the encoded frame to provide a decoded frame of data;b) calculating a difference between the decoded frame of the current iteration and a decoded frame of a previous iteration the difference related to the number of errors in the decoded frame of the current iteration;c) terminating iterative decoding based on an error rate measure by comparing the difference calculated for the decoded frame of the current iteration with a difference calculated during the previous iteration wherein the difference calculated during the previous iteration is related to the number of errors in the decoded frame of the previous iteration.
Classifications: {'H03M13/2975': 'Judging correct decoding e.g. iteration stopping criteria', 'H03M13/2957': 'Turbo codes and decoding', 'H03M13/09': 'Error detection only e.g. using cyclic redundancy check CRC codes or single parity bit'}
Description:
BACKGROUND: 1. Field of the Invention The present invention relates to decoding of encoded data by a receiver in a telecommunication network and more particularly to reducing the number of iterations of an iterative decoder. 2. Description of the Related Art Many communication systems employ 1) multi-dimensional encoding of data with convolutional codes and 2) iterative decoding of the encoded data due to the relatively high coding gain and simple structure of an iterative decoder. Iterative decoding methods may employ soft-in soft-out decoders for decoding data. In an iterative decoding scheme encoded data is repetitively decoded until a predetermined number of decoding iterations complete. The following may be of use to understand the encoding and decoding methods. A set of binary values u is defined in the Galois field-2(GF(2)) with elements {+1 1} where 1 is the null element under modulo-2 addition. The reliability value or soft value L(u) is the log-likelihood ratio of the binary random values in U and is defined as the (natural) log of the ratio of the probability that the random variable U takes on the value u=+1 (logic 2) to the probability that the random variable U takes on the value u=1 (logic 0). The sign of L(u) is used as a hard decision by a detector or decoder and the magnitude of L(u) is used as a reliability statistic (value) for the hard decision. In an iterative decoding scheme the reliability values based on the information bits are updated at each iteration utilizing the information extracted from the previous iteration. Decoding produces a posteriori reliability values for the output decoded data. The a priori reliability values may either be the null set (logic 0 or 1 depending on definition) for the first iteration (since there is no a priori information) or after the first iteration extrinsic reliability values for the information bits from a previous iteration. The extrinsic reliability values are values based on indirect information contained in the decoded information bits and may be generated from the a posteriori reliability values. In general the a posteriori reliability values and/or the extrinsic reliability values of an iteration are employed as extrinsic information input to a decoder for decoding data during the next iteration. FIG. 1 shows an iterative decoder 100 as may be employed in a turbo decoder of the prior art operating in accordance with for example the CDMA-2000 standard. The iterative decoder receives encoded data that may be formed as follows. A frame of data is encoded with a first block code and a first parity bit XP1 is added to the encoded frame of data. The frame of data is also interleaved with mapping f(*) and encoded with a second block code (which may be equivalent to the first block code) and a second parity bit XP2 is added to the encoded frame of data. The encoded data is combined with the interleaved and encoded data to form a set of systematic bits XS (e.g. using a product code). The iterative decoder includes first and second decoders 101 and 104 interleavers 102 and 109 each applying the mapping f(*) to input data de-interleaver 106 applying the inverse of the mapping f(*) to input data and optional buffers 103 105 107 108 and 110 used to temporarily store values during the decoding process. First and second decoders 101 and 104 apply respective decoding operations D1 (the inverse of the first block code) and D2 (the inverse of the second block code). The iterative decoder completes one iteration as follows. First decoder 101 receives systematic bits XS (via 111) and parity bits XP1 (via 112) of the received frame from for example an external memory 120. First decoder 101 also receives extrinsic information (e.g. both the reliability values (soft-data representing values for the decoded frame of data) and extrinsic reliability values) from buffer 107 (via 114). Extrinsic information for one decoder may be derived from the de-interleaved decoded frame of data from the other decoder and parity bits XP1 and/or and parity bits XP2. For the first iteration the extrinsic information provided to first decoder 101 may be initialized to the null set (logic 0 or 1 depending on definition). First decoder 101 performs decoding operation D1 on the systematic bits XS using the extrinsic information and parity bits XP1 to generate soft data. The soft data from first decoder 101 is then interleaved by interleaver 109 and the interleaved soft data is provided as extrinsic information for second decoder 104 (via 115). Systematic bits XS are also interleaved by interleaver 102. Second decoder 104 receives the interleaved extrinsic information (via 115) the parity bits XP2 (via 113) and the interleaved systematic bits XS (via 116) and performs decoding operation D2 to generate soft data. The soft data from second decoder 104 is then de-interleaved by de-interleaver 106 and provided as the extrinsic information (via 114) for decoding the systematic bits XS in the next iteration by first decoder 101 thus ending a single iteration of decoder 100. Several iterations may be required to generate a decoded frame of data from the systematic bits XS and parity bits XP1 and XP2 to satisfy a predetermined threshold for bit error rate (BER) of the iterative decoder. Half of an iteration is defined to be all the operations around one of the two decoders 101 and 104. After N iterations the turbo decoder combines the extrinsic information from both decoders 101 and 104 with the systematic bits XS from the received frame to form the so called soft outputs against which the decision on the transmitted bits are made. In this iteration process every frame of encoded data requires N iterations to decode thus the number of computations is fixed. In general more iterations of the iterative decoding process result in a lower bit error rate (BER) for the decoded output data. For typical implementations of the prior art turbo decoder of FIG. 1 10 to 20 iterations may be needed for satisfactory BER of a decoded frame when signal-to-noise ratio (SNR) is low. Since the number of computations of a circuit implementing the iterative decoder is directly proportional to the number of iterations required for decoding more iterations generally result in higher power consumption for the circuit. Consequently improving the BER performance of the circuit is generally achieved at the expense of increased power consumption. FIG. 2 shows simulated turbo decoder performance as BER versus SNR for different numbers of iterations for the iterative decoder of FIG. 1. The signals are modulated encoded frames of 20730 bits that are transmitted through a communication channel adding white Gaussian noise to the signal. Referring to FIG. 2 higher numbers of iterations generally result in lower BER for the decoded frame. For relatively high SNR (greater than 0.9 dB in FIG. 2) a point (number of iterations) exists where more iterations do not necessarily result in lower BER. Typical choices for the total number N of decoding iterations are generally between 8 and 12 iterations for moderate to high SNR. However the iterative decoding process may exhibit abnormalities when higher numbers of iterations are employed. For example a plot of the BER curve versus number of iterations may not be monotonically decreasing (i.e. the BER may actually be worse with more iterations); and (ii) given a fixed number of iterations BER may not be monotonically decreasing with the SNR of the input signal. Pathetic decoded frames of data in which errors may grow with more iterations cause the BER abnormality. Methods of the prior art to reduce the number of computations and hence the power consumption in the particular circuit implementation of the iterative decoder focus on comparing the decoded output of two consecutive iterations or occasionally two half iterations. If the decoded output data for the two iterations are sufficiently close to each other (according to a predefined measure) then the iterative decoding process may be terminated. Such predefined measure may simply be a total difference in decoded bits between frames being less than a predefined threshold that provides as error bound in the data of the decoded frame. However some measures of sufficiently close require sophisticated mathematical computation increasing the number of computations required. Second these prior art approaches require two decoded output frames for a decision. Thus even if an iteration produces the correctly decoded frame an iterative decoder must wait for the result of the next iteration to confirm this event resulting in unnecessary computations. Third some measures of sufficiently close may still make an incorrect decision: a decoded frame of data containing errors may pass the sufficiently close test even though the encoded frame would be correctly decoded after further iterations. For some telecommunication standards such as 3G wireless standards cyclic redundancy check (CRC) error correction codes are embedded into encoded data frames. While the CRC codes are employed to detect when a decoded frame includes an error the error detection code in these applications is not employed for the early termination of iterative decoding. The CRC codes employed by the standards have at most 16 bits which is not sufficient to keep the probability of the error event low if used as a measure for early termination of iterative decoding.
SUMMARY: The present invention relates to iterative decoding of an encoded frame of data that includes error detection information employed for tests allowing early termination of iterative decoding. A parity check test for the decoded frame is calculated for the decoded frame and for the first test iterative decoding is terminated if the decoded frame is declared correct. In addition the difference or number of differently decoded bits between decoded frames of two iterations may be tracked after iterative decoding reaches an intermediate iteration threshold. A test determines a coding iteration for which the tracked difference has a relative minimum value. For example the test may track each difference value and select as output decoded frame of data the decoded frame corresponding to the iteration having the minimum difference value. Alternatively the test may determine whether for a particular iteration the difference as a function of iteration is no-longer monotonically decreasing. If after an iteration the number of differently decoded bits is not monotonically decreasing iterative decoding is terminated. Implementations of the present invention reduce or eliminate i) unnecessary computations during iterative decoding and ii) the BER abnormality caused by high numbers of decoding iterations. In accordance with embodiments of the present invention decoding of an encoded frame comprises decoding the encoded frame during a current iteration of iterative decoding to provide a decoded frame including decoded data and decoded error detection information. A parity value is calculated from the decoded data and the parity value is compared with the decoded error detection information to determine if the data passes a parity check. If the decoded data passes the parity check iterative decoding is terminated to provide the decoded data of the current iteration. Otherwise if the decoded data does not pass the parity check a difference of errors between the decoded frame of the current iteration and a decoded frame of a previous iteration is calculated and iterative decoding is terminated in accordance with an error rate measure. The error rate measure employs the difference calculated for the decoded frame of the current iteration wherein the error-rate measure indicates either i) achieving a relative minimum difference value or a relative maximum bound for bit-error rate or a relative minimum in bit-error-rate for iterative decoding between the previous and current iterations. In accordance with other embodiments of the present invention decoding of an encoded frame comprises decoding during a current iteration of iterative decoding the encoded frame to provide a decoded frame of data. A difference between the decoded frame of the current iteration and a decoded frame of a previous iteration is calculated the difference related to the number of errors in the decoded frame of the current iteration. Iterative decoding is terminated based on an error rate measure by comparing the difference calculated for the decoded frame of the current iteration with a difference calculated during the previous iteration wherein the difference calculated during the previous iteration is related to the number of errors in the decoded frame of the previous iteration.
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An iterative decoder decodes a frame of encoded data that includes error detection information and terminates the iterative decoding based on a comparison of the decoded frame with the error detection information. The iterative decoder may have a maximum number of specified iterations but may terminate the number of iterations early under specified conditions. The encoded data includes error detection information for parity check calculation. Error detection information may be in accordance with an error detection code such as a cyclic redundancy check (CRC) code. After each iteration of decoding a parity check is calculated for the decoded frame. Early termination of decoding may occur prior to an intermediate iteration threshold M of iterations when the parity check value of the decoded frame is equivalent to the parity check value calculated from the error detection information. Early termination of decoding after M iterations may also occur when a difference in decoding error between frames is either i) below a minimum error distance threshold or ii) no longer monotonically decreasing.
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US6356213
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https://patentimages.storage.googleapis.com/19/ff/6e/c92329c7a320ec/US6356213.pdf
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Title:System and method for prediction-based lossless encoding.Claims: What is claimed is: 1. A method for signal coding comprising the steps of:a) identifying a segment of a signal for coding;b) determining a first predicted value for a given sample within said identified signal segment as a function of prior sample values;c) comparing an actual value with the first predicted value of said given sample and taking as a primary residual value a difference between said actual and said first predicted values;d) determining a second predicted value as a function of said first predicted value and of a predicted value for said primary residual value;e) taking as a secondary residual value a difference between said primary residual value and a predicted value thereof;f) repeating steps (d) and (e) at least once to find a further predicted value as a function of said first predicted value and of predicted values of said primary and secondary residual values; andg) selecting a predictor value as a statistical function of said first said second and said further predicted values. 2. The method for signal coding of claim 1 wherein said predicted value for said primary residual value is determined as a function of residual values found for prior signal samples. 3. The method for signal coding of claim 1 wherein said selection of said predictor value is made by finding a median of said first said second and said further predicted values. 4. The method for signal coding of claim 1 wherein said selection of said predictor value is made by finding a weighted average of said first said second and said further predicted values. 5. The method for signal coding of claim 1 wherein a residual value to code for said given sample value is determined as a difference between said given sample value and said selected predictor value. 6. The method for signal coding of claim 5 wherein said residual value is further coded for transmission to a receiving location using entropy coding. 7. The method for signal coding of claim 1 wherein said step of determining a first predicted value for a given sample comprises the substeps of:defining a prediction order p as a number of said prior samples on which said predicted value is based;forming a 1p vector representing signal values for a set of p input samples immediately preceding said given sample;determining a set of prediction coefficients for prediction of said given sample said set of prediction coefficients being established as a 1p vector; anddetermining said predicted value as a vector product of said signal value vector and said prediction coefficient vector. 8. The method for signal coding of claim 7 wherein said set of prediction coefficients is determined by adding a product of a scale factor and a set of p preceding signal values to a set of prediction coefficients determined for a signal sample immediately preceding said given sample. 9. The method for signal coding of claim 8 wherein said scale factor is determined by a Least Mean Squares minimization of a defined cost function. 10. The method for signal coding of claim 7 wherein said set of prediction coefficients is determined as a function of prediction coefficients determined for a signal sample immediately preceding said given sample. 11. A method for signal coding comprising the steps of:a) selecting a signal sample for coding;b) defining a prediction order p as a number of prior signal samples for evaluation of a predicted value of said selected signal sample;c) forming a 1p vector representing signal values for a set of p input signal samples immediately preceding said selected signal sample;d) determining a set of prediction coefficients for prediction of said selected signal sample said set of prediction coefficients being established as a 1p vector; ande) determining a first predicted value of said selected signal sample as a vector product of said signal value vector and said prediction coefficient vector; andf) comparing an actual value with said first predicted value for said selected signal sample and taking as a primary residual value a difference between said actual and first predicted values. 12. The method for signal coding of claim 11 wherein said set of prediction coefficients is determined as a function of prediction coefficients determined for a signal sample immediately preceding said given signal sample. 13. The method for signal coding of claim 11 wherein said set of prediction coefficients is determined by adding a product of a scale factor and a set of p preceding signal values to a set of prediction coefficients determined for a signal sample immediately preceding said given signal sample. 14. The method for signal coding of claim 13 wherein said scale factor is determined by a Least Mean Squares minimization of a defined cost function. 15. The method for signal coding of claim 11 including the further steps of:g) determining a second predicted value as a function of said first predicted value and of a predicted value for said primary residual value;h) taking as a secondary residual value a difference between said primary residual value and a predicted value thereof;i) repeating steps g and h at least once to find a further predicted value as a function of said first predicted value and of predicted values of said primary and secondary residual values; andj) selecting a predictor value as a statistical function of said first said second and said further predicted values. 16. The method for signal coding of claim 15 where in said selection of said predictor value is made by finding a weighted average of said first said second and said further predicted values. 17. The method for signal coding of claim 15 wherein a residual value to code for said selected signal sample value is determined as a difference between said selected signal sample value and said selected predictor value. 18. The method for signal coding of claim 17 wherein said residual value is further coded for transmission to a receiving location using entropy coding. 19. The method for signal coding of claim 15 wherein said selection of said predictor value is made by finding a median of said first said second and said further predicted values. 20. The method for signal coding of claim 15 wherein said predicted value for said primary residual value is determined as a function of residual values found for prior signal samples.
Classifications: {'G06T9/004': 'Predictors e.g. intraframe interframe coding', 'H03M7/30': 'Compression; Expansion; Suppression of unnecessary data e.g. redundancy reduction'}
Description:
BACKGROUND: In the storage or transmission of information it is frequently necessary to compress the data content of the information. Typically an information signal waveform (which may be a pure digital signal or a digitized analog signal) will consist of signed 16 bit numbers and there will be significant sample-to-sample correlation. Accordingly a compression utility for these signals will desirably take advantage of the sample-to-sample correlation. For signals which exhibit (or are expected to exhibit) such sample-to-sample correlation compression is commonly achieved through prediction coding where the goal is to use some portion of the preceding set of data to predict the next character in the data stream. The predicted value is then compared with the actual value of the predicted character and a difference between the predicted and actual values is determined. That difference or residual as it is usually denoted which will ordinarily be much smaller in magnitude than the actual character value is then used to code for that actual value. All types of compression fall into one of two categories: lossless and lossy. Lossless compression schemes enable all of the compressed data to be recovered after decompression. Lossy compression on the other hand connotes some loss of data between the original signal and the resultant of the compression/decompression process. In general lossy compression methods are designed with a goal of making the loss of data largely immaterial to the receiving application. Lossy compression methods also generally provide a significantly greater compression ratio than can be obtained with lossless compression methods. In many cases linear prediction has been used in lossy speech coding. For example linear predictive coding (LPC) and adaptive pulse code modulation (ADPCM) both have a prediction component and also provide the foundation for other encoding techniques. Many speech coding standards are based on these. For example Coded Excitation Linear Prediction (CELP) uses LPC and encodes residuals using a codebook of residuals from test speech samples. CCITT Standard G.721 used in digital telephone systems builds on ADPCM (32 kb/s) while CCITT Standard G.728 (16 kb/s) uses a variant of CELP. For music coding on the other hand the dominant form of coding has been based on perceptual and frequency domain characteristicsthe most widely-used method/standard being MPEG. Basically perceptual coding exploits limitations of human hearing to remove inaudible components of audio signals. And because the signal energy is concentrated in only certain areas of the frequency spectrum these parts of the spectrum can be encoded with more resolution than the low-energy parts. Various transforms may be used to indicate what frequencies are contained in the signal and their magnitudes. In the most recent MPEG version (MPEG-4 which is directed primarily to multimedia applications) either the discrete cosine transform (DCT) or the Fourier transform may be used. Since only significant frequencies are coded with perceptual coding (other frequencies being discarded) that coding results in lossy compression. In general the known speech coders do a poor job of encoding music and vice versa although it can be important to be able to compress well both types of signals for certain applications such as for movie sound signals. There are other applications including evidentiary matters where any difference between an original and a reproduced signal is unacceptable and thus lossy encoding cannot be used. Moreover while a lay person may find music which has been subject to lossy encoding to be indistinguishable from the original trained musicians may hear the differences between the original and compressed music and find the lossy encoding to be unacceptable.
SUMMARY: Accordingly it is an object of the invention to provide a lossless coding methodology that effectively encodes both speech and music. To that end a lossless encoding methodology is disclosed based on residual coding techniques and using a modified Least Mean Squares methodology to develop a predictor for a signal to be encoded and a residual as the difference between the signal and its predicted value. After the residual for an input signal segment is obtained according to the method of the invention that method is again applied to the residual value process to develop a second predictor from which a second residual value is obtained. The method is then applied for at least one further iteration to the most recently obtained residual value process to develop a third predictor for the signal to be encoded. A single prediction value is then selected as a statistical representative of those multiple predictor values or as a weighted combination of the multiple predictor values. The residual value to be used for encoding the input signal increment is determined as the difference between the signal value and the selected predictor value. The method of the invention encodes integer-valued digital signals by first obtaining an integer-valued predictor and then coding losslessly the prediction residuals which are also integers.
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A lossless encoding methodology is described based on residual coding techniques and using a modified Least Mean Squares methodology to develop a predictor for a signal to be encoded and a residual as the difference between the signal and its predicted value. After the residual for an input signal segment is obtained according to the method of the invention that method is again applied to the residual value process to develop a second predictor from which a second residual value is obtained. The method is then applied for at least one further iteration to the most recently obtained residual value process to develop a third predictor for the signal to be encoded. A single prediction value is then selected as a statistical representative of those multiple predictor values. The residual value to be used for encoding the input signal increment is determined as the difference between the signal value and the selected predictor value.
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US6388584
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https://patentimages.storage.googleapis.com/f9/af/0c/876a7ee6cfcb52/US6388584.pdf
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Title: Method and apparatus for data compression of network packets.Claims: We claim: 1. A data communications method comprising:dividing the input stream of data into a plurality of packets;identifying a respective packet history state for particular ones of the packets as a function of at least one acknowledgement vector;encoding the particular ones of the plurality of packets as a function of the respective packet history associated therewith; andcompressing the plurality of packets into a compressed data stream. 2. The method of claim 1 wherein the respective packet history state associated with the packet is identified as a function of a plurality of received packets. 3. The method of claim 2 wherein the plurality of received packets represent packets which have been previously received by a receiver without a transmission error. 4. The method of claim 2 wherein each packet has a respective packet header the packet header including at least a history vector which identifies the respective packet history state of the packet. 5. The method of claim 3 wherein the acknowledgement vector is generated by the receiver. 6. The method of claim 3 wherein the acknowledgement vector includes a sequence number of the particular received packet which was last received. 7. The method of claim 4 wherein the packet header includes a sequence number identifying a particular received packet. 8. A method of transmitting a communications stream between a sending location and a receiving location across a communications channel the method comprising:dividing the communications stream into a plurality of packets;identifying a respective packet history state for particular ones of the packets as a function of a first acknowledgement vector the first acknowledgement vector being received by the sending location from the receiving location;encoding the particular ones of the packets as a function of the respective packet history associated therewith each such packet having a packet header associated therewith the packet header including at least a history vector which identifies the respective packet history state of the packet;compressing the plurality of packets into a compressed data stream; andtransmitting across the communications channel the compressed data stream from the sending location to the receiving location. 9. The method of claim 8 wherein the respective packet history state associated with the packet is identified as a function of a plurality of received packets at the receiver location. 10. The method of claim 9 wherein the first acknowledgement vector includes a sequence number of a particular received packet which was last received by the receiving location. 11. The method of claim 9 wherein Lempel-Ziv coding is employed in the compressing the packets. 12. The method of claim 8 further comprising:receiving the compressed data stream at the receiving locationextracting the respective history state associated with the particular ones of the packets; anddecompressing the compressed data stream to recover the plurality of packets the particular ones of the encoded packets being decompressed as a function of the extracted packet history associated therewith. 13. The method of claim 12 further comprising:updating a received packet state as a function of the decompressed packets. 14. The method of claim 13 further comprising:constructing a second acknowledgment vector the second acknowledgement vector confirming a receipt of the decompressed packets by the receiving location; andtransmitting the second acknowledgement vector from the receiver location to the sending location. 15. A method of recovering data from a compressed data stream the method comprising:receiving the compressed data stream the compressed data stream including a plurality of encoded packets;identifying a respective history state associated with particular ones of the encoded packets; anddecompressing the compressed data stream to recover the data; the particular ones of the encoded packets being decompressed as a function of the respective packet history associated therewith. 16. The method of claim 15 further comprising:updating a received packet state as a function of the packets being decompressed. 17. The method of claim 16 further comprising:constructing an acknowledgment vector; andtransmitting the acknowledgement vector from a receiver to a transmitter the receiver and the transmitter exchanging the compressed data stream across at least one communications channel. 18. A data communications apparatus comprising:a receiver for receiving a data stream for transmission by the apparatus the data stream comprising a plurality of packets;a encoder for identifying a plurality of packet history states as a function of at least one acknowledgement vector each packet history state being associated with a respective one of the packets and for encoding the plurality packets as a function of the plurality of history states; anda compressor for compressing the packets into a compressed data stream. 19. The data communications apparatus of claim 18 further comprising:a transmitter for transmitting the compressed data stream across a communication channel. 20. The data communications apparatus of claim 19 wherein the communications channel is part of an Internet. 21. The data communications apparatus of claim 18 further comprising:a decompressor for receiving an input data stream the input data stream including a plurality of compressed packets identifying a respective history state associated with particular ones of the compresses packets and decompressing the plurality of compressed packets the particular ones of the compressed packets being decompressed as a function of the respective packet history associated therewith. 22. The data communications apparatus of claim 21 wherein the decompressor constructs at least one acknowledgement vector for transmission from the data communications apparatus. 23. The data communications apparatus of claim 22 wherein the acknowledgement vector confirms a receipt of the decompressed packets by the data communications apparatus. 24. The data communications apparatus of claim 18 wherein the compressor utilizes Lempel-Ziv coding for the compressing the packets into the compressed data stream. 25. An apparatus for processing a compressed digital signal the compressed digital signal being produced by dividing an input stream of digital data into a plurality of packets; identifying a respective packet history state for particular ones of the packets as a function of at least one acknowledgement vector encoding the particular ones of the packets as a function of the respective packet history associated therewith each packet having a packet header associated therewith the packet header including at least a history vector which identifies the respective packet history state of the packet compressing the encoded packets into the compressed digital signal and applying the compressed digital signal to a communications channel the apparatus comprising:a receiver for receiving the compressed digital signal from the communications channel; anda decompressor for decompressing the received compressed digital signal and recovering the input stream of digital data from the decompressed digital signal. 26. The apparatus of claim 25 wherein the particular ones of the packets are decompressed from the compressed digital signal as a function of the respective packet history associated therewith. 27. The apparatus of claim 26 wherein the decompressor constructs an acknowledgment vector and transmits the acknowledgement vector from a receiver to a transmitter the receiver and the transmitter exchanging the compressed digital signal across the communications channel. 28. The apparatus of claim 27 wherein the compressing the packets operation utilizes Lempel-Ziv coding. 29. The apparatus of claim 27 wherein the decompressor updates the respective history state of the associated packet upon being decompressed. 30. A machine-readable medium having stored thereon a plurality of instructions the plurality of instructions including instructions that when executed by a machine cause the machine to perform of a method of transmitting a communications stream between a sending location and a receiving location across a communications channel by dividing the communications stream into a plurality of packets; identifying a respective packet history state for particular ones of the packets as a function of a first acknowledgement vector the first acknowledgement vector being received by the sending location from the receiving location; encoding the particular ones of the packets as a function of the respective packet history associated therewith each such packet having a packet header associated therewith the packet header including at least a history vector which identifies the respective packet history state of the packet; compressing the plurality of packets into a compressed data stream; and transmitting across the communications channel the compressed data stream from the sending location to the receiving location. 31. The machine-readable medium of claim 30 wherein the respective packet history state associated with the packet is identified as a function of a plurality of received packets at the receiver location. 32. The machine-readable medium of claim 31 including further instructions such that the method further comprises the operations of:receiving the compressed data stream at the receiving locationextracting the respective history state associated with the particular ones of the packets; anddecompressing the compressed data stream to recover the plurality of packets the particular ones of the encoded packets being decompressed as a function of the extracted packet history associated therewith. 33. The machine-readable medium of claim 31 including further instructions such that the method further comprises the operations of:constructing a second acknowledgment vector the second acknowledgement vector confirming a receipt of the decompressed packets by the receiving location; andtransmitting the second acknowledgement vector from the receiver location to the sending location.
Classifications: {'H03M7/3084': 'Compression; Expansion; Suppression of unnecessary data e.g. redundancy reduction using adaptive string matching e.g. the Lempel-Ziv method'}
Description:
BACKGROUND: Conventional data compression techniques and systems encode a stream of digital data into a compressed code stream and decode the compressed code stream back into a corresponding original data stream. The code stream is referred to as compressed because the stream typically consists of a smaller number of codes than symbols contained in the original data stream. Such smaller codes can be advantageously stored in a corresponding smaller amount of memory than the original data. Further the compressed code stream can be transmitted in a communications system e.g. a wired wireless or optical fiber communications system in a corresponding shorter period of time than the uncompressed original data. The demand for data transmission and storage capacity in todays communications networks is ever-increasing. Thus data compression plays an integral role in most modem transmission protocols and communications networks. As is well-known two classes of compression techniques useful in the compression of data are so-called special purpose compression and general purpose compression. Special purpose compression techniques are designed for compressing special types of data and are often relatively inexpensive to implement. For example well-known special purpose compression techniques include run-length encoding zero-suppression encoding null-compression encoding and pattern substitution. These techniques generally have relatively small compression ratios due to the fact that they compress data which typically possesses common characteristics and redundancies. As will be appreciated a compression ratio is the measure of the length of the compressed codes relative to the length of the original data. However special purpose compression techniques tend to be ineffective at compressing data of a more general nature i.e. data that does not possess a high degree of common characteristics and the like. In contrast general purpose compression techniques are not designed for specifically compressing one type of data and are often adapted to different types of data during the actual compression process. Some of the most well-known and useful general purpose compression techniques emanate from a family of algorithms developed by J. Ziv and A. Lempel and commonly referred to in the art as Lempel-Ziv coding. In particular Ziv et al. A Universal Algorithm for Sequential Data Compression IEEE Transactions on Information Theory IT-23(3):337-343 May 1977 (describing the commonly denominated LZ1 algorithm) and Ziv et al. Compression of Individual Sequences Via Variable-Rate Coding IEEE Transactions on Information Technology IT-24(5):530-536 September 1978 (describing the commonly denominated LZ2 algorithm) which are each hereby incorporated by reference for all purposes. The LZ1 and LZ2 data compression schemes are well-known in the art and need not be discussed in great detail herein. In brief the LZ1 (also referred to and known in the art as LZ77) data compression process is based on the principle that a repeated sequence of characters can be replaced by a reference to an earlier occurrence of the sequence i.e. matching sequences. The reference e.g. a pointer typically includes an indication of the position of the earlier occurrence e.g. expressed as a byte offset from the start of the repeated sequence and the number of characters i.e. the matched length that are repeated. Typically the references are represented as <offset length> pairs in accordance with conventional LZ1 coding. In contrast LZ2 (also referred to and known in the art as LZ78) compression parses a stream of input data characters into coded values based on an adaptively growing look-up table or dictionary that is produced during the compression. That is LZ2 does not find matches on any byte boundary and with any length as in LZ1 coding but instead when a dictionary word is matched by a source string a new word is added to the dictionary which consists of the matched word plus the following source string byte. In accordance with LZ2 coding matches are coded as pointers or indexes to the words in the dictionary. As mentioned above the art is replete with compression schemes derived on the basic principles embodied by the LZ1 and LZ2 algorithms. For example Terry A. Welch (see T. A. Welch A Technique for High Performance Data Compression IEEE Computer pp. 8-19 June 1984 and U.S. Pat. No. 4558302 issued to Welch on Dec. 10 1985 each of which is incorporated by reference for all purposes) later refined the LZ2 coding process to the well-known Lempel-Ziv-Welch (LZW) compression process. Both the LZ2 and LZW compression techniques are based on the generation and use of a so-called string table that maps strings of input characters into fixed-length codes. More particularly these compression techniques compress a stream of data characters into a compressed stream of codes by serially searching the character stream and generating codes based on sequences of encountered symbols that match corresponding longest possible strings previously stored in the table i.e. dictionary. As each match is made and a code symbol is generated the process also stores a new string entry in the dictionary that comprises the matched sequence in the data stream plus the next character symbol encounter in the data stream. As will be appreciated and as detailed above the essence of Lempel-Ziv coding is finding strings and substrings which are repeated in the original data stream e.g. in a document to be transmitted. The repeated phrases in the document under compression are replaced with a pointer to a place where they have occurred earlier in the original data stream e.g. document. As such decoding data e.g. text which is compressed in this manner simply requires replacing the pointers with the already decoded text to which it points. As is well-known one primary design consideration in employing Lempel-Ziv coding is determining whether to set a limit on how far back a pointer can reach and what that limit should be. A further design consideration of Lempel-Ziv coding involves which substrings within the desired limit may be a target of a pointer. That is the reach of a pointer into earlier text may be unrestricted i.e. a so-called growing window or may be restricted to a fixed size window of the previous N characters where N is typically in the range of several thousand characters e.g. 3 kilobytes. In accordance with this coding repetitions of strings are discovered and compressed only if they both appear in the window. As will be appreciated the considerations made regarding such Lempel-Ziv coding design choices represent a compromise between speed memory requirements and compression ratio. Compression is a significant consideration in improving network efficiencies. For example when the available computational resources i.e. the data processing requirements are large compared to the available network bandwidth it is most advantageous to compress data packets before transmission across the network. Of course the actual compression scheme must be carefully selected in terms of speed and overall compression. That is a compression scheme which is too slow will reduce network performance and an inefficient compression scheme will limit any potential transmission gains. Further complicating the network efficiency issue is the fact that many packet networks are inherently unreliable. That is current well-known packet networks e.g. the Internet routinely drop packets or reorder packets transmitted through the network thereby causing data transmission errors. For example if the compression scheme introduces certain dependencies between packets and the network thereafter drops or reorders such packets the receiver may not be able to decompress a particular packet if a prior packet is lost due to the interdependencies amongst packets. As such certain well-known approaches are employed to mitigate such problems: (1) Improve network reliability whereby in terms of the Internet a more reliable end-to-end transport layer service can be applied e.g. the well-known Transmission Control Protocol (TCP) to compress packets at the transport level; (2) Stateless compression can be used wherein each packet is compressed independently thereby ensuring that each packet can be decompressed at the receiver; and (3) Streaming compression assumes reliable delivery and employs a reset mechanism when this assumption is violated. More particularly when a packet is lost the receiver discards each subsequent packet until compression is reset. After the reset future packets are not dependent on prior packets and decompression can resume normally. Two well-known streaming-type compression techniques include the Point-to-Point Protocols (PPP) Compression Control Protocol and the IP Header Compression protocol employed for Use Datagram Protocol (UDP) packets. The above-described packet compression schemes are useful in mitigating the problems arising from packet interdependencies however such schemes present certain other complications. For example compressing packets at the transport level requires end-to-end utilization and typically requires a certain level of cooperation by the application during transmission. Similarly while stateless compression provides a degree of robustness the packet independence attribute of stateless compression reduces the realized compression ratio due to the fact that such compression examines the data in a single packet. Thus for example this compression approach cannot remove the large amount of redundancy typically found in network headers of adjacent packets. Further while streaming compression provides greater compression ratios these compression schemes multiply the effect of packet loss in that when one packet is lost in the network this causes the receiver to lose several other packets. For low reliability networks e.g. the Internet this multiplying packet effect reduces the utility of employing streaming compression. Therefore a need exists for a compression technique which provides greater robustness and increased compression ratios without the deleterious effects of prior compression schemes.
SUMMARY: An aspect of the invention is directed to a communications method and apparatus that enables inter-packet compression thereby achieving greater robustness and increased compression ratios without the deleterious effects e.g. the effect of packet loss multiplying of prior compression schemes. In accordance with an aspect of the invention a select history state is employed which is determined as a function of a so-called acknowledgement vector. In accordance with an aspect of the invention the acknowledgement vector contains information with respect to the identification of packets which have been successfully received in a prior transmission over a communications channel. That is in accordance with an aspect of the invention the packet history state is a select history state associated with a respective packet. As such a first side of the communications channel e.g. the transmitter or sender side is furnished and cognizant of certain information about which packets have been successfully received by the second side of the communications channel e.g. the receiver or recipient side. In turn the decompressor is also furnished and cognizant of the select history to allow for efficient decompression of the transmitted compressed packets from the sender. That is decompression occurs as a function of which packets were used as history i.e. the select history state during compression of such packets. As such through select history state and acknowledgement aspects of the invention the compressor and decompressor (at either side of the communications channel) work cooperatively to achieve improved compression across a communications channel. In accordance with the preferred embodiment of the invention the packets are encoded and prefixed with a header that includes at least a history vector such history state identifying the respective history state associated with a packet. Further in accordance with an aspect of the invention the acknowledgment vector is constructed and communicated to the transmitter whereby the specific compression algorithm at the transmitter i.e. sender can limit the history used by the compression algorithm to those packets that are successfully received. Thus in accordance with the preferred embodiment the vector identifying the packets used as the history is included in the compressed packet thereby enabling the receiver to reconstruct the packet history state necessary to decompress the packet. Advantageously in accordance with an aspect of the invention increased robustness and greater compression ratios are achieved with a wide variety of compression methods or communications channel arrangements. That is the principles of the invention are independent of any particular one compression scheme and therefore the advantages of employing the various aspects of invention are realized with a wide variety of compression methodologies and communications channel configurations.
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A method and apparatus for compressing packets that enables inter-packet compression thereby achieving greater robustness and increased compression ratios without the deleterious effects e.g. the effect of packet loss multiplying of prior compression schemes. More particularly a so-called acknowledgment scheme is employed in conjunction with the specific compression algorithm such that the transmitter i.e. sender can limit the history used by the compression algorithm to those packets that are correctly received. In particular a vector identifying the packets used as the history is included in the compressed packet thereby enabling the receiver to reconstruct the packet history state necessary to decompress the packet. Advantageously increased robustness and greater compression ratios are achieved independent of any particular one compression scheme.
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US6452544
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https://patentimages.storage.googleapis.com/4d/a1/95/f2a0e76fcbef17/US6452544.pdf
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Title: Portable map display system for presenting a 3D map image and method thereof. Claims: What is claimed is: 1. A portable map display system comprising:a) a portable map display device comprising:i) a display unit;ii) a self-locator unit for detecting a location of the portable map display device;iii) a direction detector unit for detecting a direction the portable map display device is facing;iv) a map data client for requesting map data concerning an area in a vicinity of the portable map display device said map data request including the detected location of the portable map display device and the detected direction of the portable map display device;v) a receiver unit for receiving the requested map data; andvi) a data processor for processing the received map data for transmitting to the display unit and causing the display unit to present to a user a three dimensional image of the vicinity of the location of the portable map display device with spatial perspective from the detected direction the portable map display device is facing; andb) a map data server for receiving the map data request for retrieving the requested map data using the detected location and the detected direction and for sending the requested map data to the receiver unit of the portable map display device. 2. The portable map display system as recited in claim 1 wherein the portable map display device is implemented in one of a head-worn display Personal Digital Assistant (PDA) and a cellular telephone wherein the direction the portable map display device is facing is a direction a user points the one of a head-worn display PDA and a cellular telephone. 3. The portable map display system as recited in claim 1 wherein the self-locator unit is comprised of one of a Global Positioning System (GPS) device a cellular telephone locating system and a radio frequency (RF) beacon triangulation system. 4. The portable map display system as recited in claim 1 wherein the direction detector unit is comprised of a digital compass. 5. The portable map display system as recited in claim 1 wherein the receiver unit receives map data from one of a server over a computer network a server over a wireless communication link and a local memory storage means. 6. The portable map display system as recited in claim 1 wherein the map data server sends the requested map data to the portable map display device using one of a satellite broadcast system a microwave broadcast system and a digital video broadcasting (DVB) system. 7. The portable map display system as recited in claim 1 further comprising:an additional information server for receiving an additional information request and for sending requested additional information to the portable map display device;wherein the portable map display device further comprises:an additional information client for requesting additional information and for receiving the requested additional information. 8. The portable map display system as recited in claim 1 wherein the portable map display device further comprises:a map object selector unit for selecting by a user map objects displayed in the map image. 9. A method for dynamically producing a map image in a portable map display device comprising:determining a location of the portable map display device;determining a direction that the portable map display device is facing;generating a map data request said map data request including the determined location of said portable map display device and the determined direction that the portable map display device is facing;transmitting the map data request over a communication link to a map data server;generating by the map data server in response to the map data request map data concerning the area in the vicinity of the determined location of said portable map display device in the determined direction that the portable map display device is facing;transmitting by the map data server the generated map data;receiving by the portable map device the generated map data; anddisplaying the generated map data as a three dimensional image of the vicinity of the determined location of the portable map display device with spatial perspective from the determined direction that the portable map display device is facing. 10. The portable map imaging method as recited in claim 9 wherein the portable map display device is implemented in one of a Personal Digital Assistant (PDA) and a cellular telephone the determining the direction that the portable map display device is facing step comprising:determining a direction in which a top end of the portable map display device is pointed. 11. The portable map imaging method as recited in claim 9 wherein the portable map display device is a head-worn display the determining the direction that the portable map display device is facing step comprising:determining a direction of a line of sight of the head-worn display. 12. The portable map imaging method as recited in claim 11 further comprising:detecting an orientation of the line of sight of the head-worn display in respect to an actual horizon; andcorrelating an artificial horizon of the three dimensional map image to correspond to the actual horizon in the line of sight of the head-worn display. 13. A portable map display system comprising:a) a portable map display device comprising:i) a display unit;ii) a self-locator unit for detecting a location of the portable map display device;iii) a direction detector unit for detecting a direction the portable map display device is facing;iv) a receiver unit for receiving map data concerning an area in a vicinity of the detected location of the portable map display device in the detected direction of the portable map display device; andv) a data processor for processing the received map data for transmitting to the display unit and causing the display unit to present to a user a three dimensional image of the vicinity of the location of the portable map display device with spatial perspective from the detected direction the portable map display device is facing wherein the spatial perspective comprises a projected view from a viewpoint upon a map plane said viewpoint having a distance d from the map plane and a view-angle formed by the intersection of the map plane with a plane of the viewpoint;b) an input unit for inputting a destination;c) a destination distance calculator unit for determining the destination distance between the location of the portable map display device and the location of the destination; andd) a spatial perspective component controller unit for changing at least one of distance d and the view-angle of the spatial perspective of the three dimensional image wherein said change is proportionate to a change in the determined destination distance. 14. The portable map display system as recited in claim 13 wherein the user can directly control the spatial perspective component controller unit. 15. The portable map display system as recited in claim 13 wherein the spatial perspective component controller controls the distance d to decrease as the portable map display device approaches the destination. 16. The portable map display system as recited in claim 13 wherein the spatial perspective component controller controls the view-angle to decrease as the portable map display device approaches the destination. 17. The portable map display system as recited in claim 13 wherein the display unit comprises a head-worn display having a viewing portion said viewing portion having a display section onto which the three dimensional image with spatial perspective may be displayed to a wearer of the head-worn display wherein the direction the portable map display device is facing is a direction of a line of sight of the head-worn display. 18. The portable map display system as recited in claim 17 wherein the self-locator unit and the direction detector unit are integrated into the head-worn display. 19. The portable map display system as recited in claim 17 further comprising:an orientation detector unit for detecting an orientation of the line of sight of the head-worn display in respect to an actual horizon;wherein an artificial horizon of the three dimensional map image is correlated to correspond to the actual horizon in the line of sight of the head-worn display. 20. The portable map display system as recited in claim 17 wherein the viewing portion of said head-worn display is comprised of the display section and a transparent section through which light can pass. 21. The portable map display system as recited in claim 17 wherein the viewing portion of said head-worn display is transparent and any part of the viewing portion may act as the display section. 22. The portable map display system as recited in claim 17 wherein a viewing portion of said head-worn display is comprised of two combination lens and display screen units each of said two combination units for one eye of the user. 23. The portable map display system as recited in claim 13 wherein the portable map display device further comprises at least one of the input device the destination distance calculator unit and the spatial perspective component controller. 24. A method for dynamically producing a map image in a portable map display device comprising:determining a location of the portable map display device;determining a direction that the portable map display device is facing;receiving map data concerning an area in a vicinity of the determined location of said portable map display device in the determined direction that the portable map display device is facing;displaying the received map data as a three dimensional image of the vicinity of the determined location of the portable map display device with spatial perspective from the determined direction that the portable map display device is facing wherein the spatial perspective comprises a projected view from a viewpoint upon a map plane said viewpoint having a distance d from the map plane and a view-angle formed by the intersection of the map plane with a plane of the viewpoint;inputting a destination;determining a destination distance between the location of the portable map display device and the location of the destination; andchanging at least one of the distance d and the view-angle of the spatial perspective of the three dimensional image wherein said change is proportionate to a change in the determined destination distance. 25. The portable map imaging method as recited in claim 24 further comprising:changing at least one of distance d and the view-angle of the viewpoint. 26. The portable map imaging method as recited in claim 24 wherein the changing at least one of the distance d and the view-angle step comprises decreasing distance d as the portable map display device approaches the destination. 27. The portable map imaging method as recited in claim 24 wherein the changing at least one of the distance d and the view-angle step comprises decreasing the view-angle as the portable map display device approaches the destination. 28. A method for dynamically producing a map image in a portable map display device comprising:determining a location of the portable map display device;determining a direction that the portable map display device is facing;receiving map data concerning an area in a vicinity of the determined location of said portable map display device in the determined direction that the portable map display device is facing;displaying in the portable map display device of the received map data as a three dimensional image of the vicinity of the determined location of the portable map display device with spatial perspective from the determined direction that the portable map display device is facing;generating an additional information request said additional information concerning at least one map object in the displayed three dimensional map image;transmitting the additional information request over a communication link to an additional information server;generating by the additional information server a response to the additional information request said response having additional information concerning the at least one map object in the displayed three dimensional map image; andtransmitting by the additional information server to the portable map device the created response. 29. The portable map imaging method as recited in claim 28 wherein the generating an additional information request comprises:selecting by a user of the portable map display device at least one map object in the displayed three dimensional map image.
Classifications: {'G01C21/20': 'Instruments for performing navigational calculations', 'G01C21/3635': 'Guidance using 3D or perspective road maps', 'G09B29/10': 'Map spot or coordinate position indicators; Map reading aids'}
Description:
BACKGROUND: 1. Field of the Invention This invention relates to a system and method for providing and displaying map information including a perspective map on a portable map display and in particular a head-worn display. 2. Description of the Related Art Although the past twenty years has seen rapid advances in the art of global positioning and dynamic map generation a user that is navigating an unknown city on foot is still burdened with many problems. For instance traditional paper maps which are still the dominant navigational tool for walking tourists are inconvenient to carry and awkward to repeatedly fold and unfold. Furthermore the user must first locate his or her position on the map a task that is not always simple in order to successfully navigate to another location. There is also the problem of the printed map being up-to-date and showing the information that is relevant to the particular user viewing the map. In addition the user may want additional information which can only be provided by another source such as a guidebook. One solution to this problem is to use a Global Positioning System (GPS) locator in conjunction with a paper map in order to discover ones exact location on the map. However this solution just adds an additional piece of technology to carry operate and use in conjunction with an unfolded map. Another solution to the traditional map problem is to combine Global Positioning System (GPS) technology with digital display technology in order to present the user with a display of a local map with the users location indicated in the display. Examples of this combination include the GPS systems in some boats and new cars as well as the new portable GPS receiver/displays. Some of these devices display an electronic image of a map usually an aerial view with the users position indicated by an icon superimposed on the map image. These electronic maps do solve the problem of showing both the users current location and a map of the surrounding environment but they have their own problems. First obviously the GPS systems embedded in some cars is of no use to a walking tourist. The walking tourist must use some sort of portable (i.e. capable of being carried) device that will not hamper his or her movements. Second when using such a portable device there is the problem of the scale and resolution of the map image. On a hand-held device e.g. a Personal Digital Assistant (PDA) or a Global Positioning System (GPS) receiver/display the display screen often has low resolution and the displayed map often has a large scale. Both of these factors lead to the user being unable to directly relate the displayed information with the objects and sights around him or her. However because of the limitations of a hand-held device this problem is difficult to resolve. If the resolution of the small display screen is increased the user will be unable to see the details because of the small size of the screen. If the size of the screen is increased the size of the hand-held instrument will become larger and thus more difficult to carry. Furthermore when hand-held devices are used it is somewhat disruptive of the walking and/or walking tourist experience. For example to be constantly removing a PDA from ones pocket or bag in order to reassure oneself of ones relative location interrupts the flow of a walking tour. This and the constant focus on a small map in ones hands takes away from the ambience the sights and sounds of the walking experience. Further still let us assume the users PDA which displays local maps with GPS information also has a database of information concerning local sites and eating establishments. If the user wants to access this further information the user most navigate through the information screens of the PDA further removing the user from the appreciation of the surrounding environment. An example of a distracting map device is shown in U.S. Pat. No. 6016606 to Oliver et al. This viewing device looks like a short and squat telescope where the user peers in one end at a map slide continued within lit up by light entering the lens on the other side. Thus its lighting operation is similar to a kaleidoscope. The GPS calculated location of the user is superimposed on the map slide. However continually lifting this device up to the sunlight in order to determine ones location or to determine the location of nearby sites would be a hindrance. Particularly if one could not find an adequate light source. Furthermore this device provides no information concerning local sites eating establishments etc. Therefore the need exists for a portable map viewing device capable of indicating the current location of the user where the scale and resolution of the map image clearly depict the users spatial relationship with the objects shown in the map image. Further there is a need for such a portable map viewing device which is also capable of showing information concerning the surrounding environment. Further still there is a need for such a map viewing device which also does not interfere with the walking or walking tourist experience.
SUMMARY: An object of the present invention is to provide a system and method for a portable map display device that is capable of indicating the current location of the user. Another object of the present invention is to provide a system and method for a portable map display device where the scale and resolution of the displayed map image clearly depict the users spatial relationship with the objects shown in the displayed map image. Another object of the present invention is to provide a system and method for a portable map display device which is capable of showing additional non-map information concerning the surrounding environment. Another object of the present invention is to provide a system and method for a portable map display device which does not interfere with the walking or walking tourist experience. Yet another object of the present invention is to provide a system and method for a portable map display device that displays a perspective map which changes as the user approaches an input destination. These and other objects are accomplished by the system and method according to the present invention. In one aspect the system according to the present invention has a portable map display device that has a display unit a self-locator unit for determining the location of the portable map display device and a direction detector unit for determining a direction the portable map display device is facing. Map data concerning the area in the vicinity of the determined location in the determined direction is retrieved and sent to a receiver unit in the portable map display device. A data processor in the portable map display device processes the received map data in order that the display unit presents a three dimensional image of the portable map display device vicinity with spatial perspective from the detected direction the portable map display device is facing. In another aspect a portable map display system also has a spatial perspective component controller unit for changing at least one component of the viewpoint of the spatial perspective. Components of the viewpoint include a distance d and a view-angle where the spatial perspective is a projected view from the viewpoint onto a map plane and the distance d is from the viewpoint to the map plane and the view-angle is formed by the intersection of the map plane with a plane of the viewpoint. In yet another aspect the method according to the present invention dynamically produces a three dimensional map image in a portable map display device. In such a method the location of the portable map display device and the direction the portable map display device is facing is determined. The portable map display device receives map data concerning the area in the vicinity of the determined location in the determined direction of the portable map display device. This received map data is displayed as a three dimensional image of the vicinity of the portable map display device with spatial perspective from the determined direction that the portable map display device is facing. In still another aspect the method according to the present invention has the additional steps of inputting a destination determining a distance from the destination to the portable map display device and changing the distance d and/or the view-angle of the spatial perspective of the three dimensional image displayed in the portable map display device. The change is proportionate to a change in the determined destination distance. Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood however that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that unless otherwise indicated they are merely intended to conceptually illustrate the structures and procedures described herein.
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A system and method for displaying map data to a person using either a hand-held or head-worn display is described. In one preferred system a head-worn display is used. The location of the person and the direction of the persons view is determined. A map image indicated by the location and direction is presented in the display. This map image is displayed in a three-dimensional perspective view allowing the person to easily associate the objects in the map image with the real objects in the persons field of view. In addition the user may indicate a desired destination and the three-dimensional perspective view will be changed according to the users location relative to the desired destination.
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