KR100238322B1 - Viterbi detection method and device - Google Patents

Abstract

The Viterbi detection method and apparatus according to the present invention determine a target to be decoded according to the transfer function of various optical channel models, store the result in a register, and detect the Viterbi using the stored decoding target information. An overflow control section is provided between the add-compare-selection section and the state evaluation amount memory to prevent the overflow of the circuit and to operate at high speed. The present invention is applied to a high-speed optical storage medium, it is possible to detect the EFM-modulated signal even with a simple equalizer, and because of the RLL characteristics of the EFM modulation, various states and branches can be removed, thereby reducing the hardware. .

Description

Viterbi detection method and apparatus

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal recovery apparatus for a high speed optical disc, and more particularly, to a Viterbi detection method and apparatus capable of detecting a high speed EFM modulated signal with a simple equalizer without the need for a highly accurate equalizer.

In general, the characteristics of the optical channel depend on the characteristics of the optical pickup apparatus. The characteristics of the optical pickup are similar to those of the low pass filter. Upon detection bit by bit, the magnitude of the signal level must be detected in order to be restored to the original data stream. At this time, if the optical disk rotates at a high speed, the waveform of the output signal is distorted. In addition, in a high density recording medium such as a digital versatile disk (DVD), noise component increases in the read signal due to crosstalk between adjacent tracks. Therefore, to compensate for such distortion, a high performance digital or analog equalizer is needed.

In a conventional high speed optical disk signal recovery apparatus, a signal output from an optical pickup is restored to an original signal by performing level detection through an expensive analog equalizer. The analog equalizer compensates the waveform of the signal output from the optical pickup, and the compensated analog signal is detected on a bit by level level in the level detector and restored to the original signal. In this case, in the high speed optical disc player, the distortion of the signal output from the optical pickup becomes severe and requires a highly sophisticated analog equalizer, which leads to an increase in manufacturing cost.

Especially in high speed optical systems such as 30x CD-ROM or 4.5x DVD ROM / RAM, the optical output's analog output expects an ideal response due to distortion due to intersymbol interference (ISI) rather than at low speed playback. Difficult to do

The technical problem to be solved by the present invention is to solve the above-mentioned problems, without the need for a high-precision equalizer when playing a high-speed high-density optical disk, it is possible to increase the operation speed with a simple equalizer, and efficiently beater for several optical channel models It is to provide a Viterbi detection method capable of detecting rain.

Another technical problem to be solved by the present invention is to solve the above-mentioned problems, the high speed and high-speed optical disk playback without the need for a high-precision equalizer, it is possible to increase the operation speed with a simple equalizer, and efficiently for various optical channel models A Viterbi detection apparatus capable of detecting Viterbi is provided.

1 is a block diagram of a PRML system to which the Viterbi detection apparatus of the present invention is applied.

2 shows a trellis diagram of a fiber channel model.

3 is a circuit diagram illustrating an example of the overflow controller of FIG. 1.

4 shows a diagram of the passage memory of FIG.

5A and 5B are diagrams showing a cell structure constituting a passage memory when the branch is two and the one.

6A, 6B, and 6C are graphs showing signal ratios according to transfer functions of respective channel models.

FIG. 7 is a circuit diagram illustrating an example of the branch quantity calculator of FIG. 1.

8 is a graph illustrating frequency response curves of the transfer functions of each channel model.

<Description of the symbols for the main parts of the drawings>

20 ... branch calculator, 30 ... addition-compare-selection

40 ... overflow controller, 50 ... state evaluation memory

60 ... path memory.

According to an aspect of the present invention, there is provided a Viterbi detection method comprising: (a) determining an optical channel model to be decoded; (b) receiving data read out from the optical pickup and calculating absolute values with respective state reference values; (c) on the basis of the respective branching amounts calculated using the calculated absolute values, the Euclidean distance is obtained by adding the two previous state evaluation quantities and the branching quantities respectively to the current state, and the added 2 Comparing the two values with each other, selecting a smaller value of the two values to determine a new state evaluation amount and generating a passage selection signal; (d) preventing an overflow by using a difference between the largest value and the smallest value of the determined state evaluation amount converged to a predetermined value; (e) storing the determined overflow prevented new state estimate and sending the stored output to the previous state estimate in step (c); And (f) receiving the path selection signal from step (c) and decoding the original signal using a register exchange structure.

In another embodiment, the present invention may allow step (d) to come after step (e).

Preferably, in the optical channel model determination step (a), a model to be decoded is determined according to a transfer function of various optical channel partial response models, and the information is stored in a register.

Preferably, the overflow prevention step (d) is characterized in that when a is the bit width of the branch amount, the difference between the largest value and the small value of the state evaluation amount is always less than 2 ^{a + 2} .

Preferably, the overflow prevention step (d) is characterized by bitwise and gating the most significant bit or another bit.

Viterbi detection apparatus according to another aspect of the present invention for achieving the above object is a register for determining and outputting the optical channel model to be decoded; A branch quantity calculation unit which receives the read data from the optical pickup and calculates the absolute value of each state reference value; On the basis of the respective branch amounts calculated using the calculated absolute values, the Euclidean distance is obtained by adding the two previous state evaluation amounts and the branch amounts to the current state, and the two added values are obtained. An adder-compare-selector for comparing each other, selecting a smaller value of the two values to determine a new state evaluation amount and generating a passage selection signal; An overflow control unit using a difference between the largest value and the smallest value of the determined state evaluation amount converges to a predetermined value; A state evaluation amount memory unit for storing the determined new overflow evaluation state evaluation amount and transmitting the stored output to a previous state evaluation amount of the addition-compare-selecting unit; And a passage memory that receives a passage selection signal from the add-compare-selection section and removes a predetermined number of states and branches using a register exchange structure.

As another embodiment, the present invention may allow the overflow control unit to be connected between the output end of the state evaluation amount memory and the input end of the addition-compare-selection unit.

Preferably, the model to be decoded is selected according to the transfer function of various optical channel partial response models according to the value of the register unit.

Preferably, when the overflow control unit a denotes the bit width of the branch amount, the difference between the maximum value and the minimum value of the state evaluation amount is less than 2 ^{a + 2} .

Preferably, the overflow controller bitwise and gates the most significant bit or another bit.

Hereinafter, a preferred embodiment of the Viterbi detection method and apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

The optical channel can be modeled with a simple partial response (PR) characteristic, and the Viterbi detector can be designed using this. Here, the partial response means extracting information from several adjacent data symbols and restoring one symbol. That is, one data symbol passes through the channel and affects several adjacent data symbols. This characteristic can be used for data symbol recovery.

The characteristics of the optical channel are determined by the density of data symbols, the interval between tracks, the characteristics of the optical pickup, and the characteristics of the modulation scheme used. In fact, it is almost impossible to model a transfer function that fully includes these properties. Even if it is possible, it is almost impossible to create a circuit that perfectly recovers a signal with such a complex transfer function. Therefore, the method of finding the most similar and concise transfer function to the characteristics of the channel and compensating the difference between the modeled characteristics and the actual characteristics through the equalizer is considered to be most desirable, and the partial response maximum response for high-speed optical media reproduction is most desirable. A Viterbi detection method and apparatus for a partial response maximum likelihood (PRML) system have been developed.

1 is a block diagram of a PRML system to which the Viterbi detection apparatus of the present invention is applied, and a block enclosed by a dotted line shows the Viterbi detection apparatus 100 according to the present invention. In Fig. 1, the analog signal output from the optical pickup 2 is converted into a digital signal by the A / D converter 4, and the converted digital signal is the characteristic of the actual channel and the target model characteristic of the Viterbi detection apparatus 100. The equalizer 6 is inputted to the Viterbi detecting apparatus 100 through the equalizer 6 to compensate for the difference between the and. In this case, as shown in FIG. 1, the output of the equalizer 6 may also be output as a signal that does not pass through the Viterbi detection device 100 and used for other purposes.

Viterbi detection apparatus 100 according to the present invention, as shown in the drawings, a register 10, a branch metric calculator (BMC) 20, an add-compare-select; An ACS 30, an overflow controller (OCC) 40, a state metric memory (SMM) 50, and a path memory (PM) 60. The Viterbi detection apparatus 100 is similar to the structure of a general Viterbi decoder, but the Viterbi detection apparatus of the present invention detects the original data stream from unintentionally encoded channel data based on channel modeling. It is different from non-decoders. The Viterbi detection apparatus 100 for the optical channel has a very simple transfer function, a small number of states, and a small hardware size, but requires a fast clock speed and continuous output data. ) And an overflow control logic 40 to prevent an overflow of the condition evaluation amount.

The optical channel modeling applied to the present invention will be described below. Fiber channels are characterized by pit-land density, track density, pickup performance, and modulation transfer functions. As mentioned above, in practice it is almost impossible to fabricate a complete model of the optical channel, and even if it is possible to fabricate a detector with a complete delivery function, it is hardly feasible. Therefore, an optical channel model having a transfer function that compensates the difference between the real model and the evaluation model using the uncomplicated equalizer closest to the channel characteristics can be modeled using a simple convolutional decoder as shown in Equation 1. .

F (z) = 1 + kz + kz ² + z ³ , where k is a positive real value

In this model, the k value depends on the characteristics of the optical pickup and the state of the optical disk. The value of k should be determined according to the ratio of the 3T signal (T is the period of the signal) and the 4T signal of the signal input to the actual Viterbi decoder. Here, the 3T signal is a signal in which data stored on the disk does not undergo signal switching, that is, switching from +1 to -1 or from -1 to +1 for 3T. The relationship between this ratio and k must satisfy Equation 2 below.

Level _3T : Level _4T = k: k + 1

Since only 1 and -1 data are recorded on the disk, the output of a channel having the transfer function of Equation 1 may have five signal levels (+ high, + middle, 0, -middle, -high). As a result, this value becomes a reference value in the BMC 20 of FIG. The ± middle value may be adjusted to the 3T signal level, and the ± high value may be adjusted to the 4T signal level.

In the present invention, transfer functions for various optical channel models are used, which are shown in Table 1, and their frequency response characteristics are shown in FIG.

Model Transfer function PR (1,1,1,1) when k = 1.0 F (z) = 1 + z + z ² + z ³ when k = 2.0, PR (1,2,2,1) F (z) = 1 + 2z + 2z ² + z ³ when k = 3.0, PR (1,3,3,1) F (z) = 1 + 3z + 3z ² + z ³

As shown in Fig. 8, there is no significant difference in the frequency domain, but there is a significant difference between the partial response characteristics in the time domain.

6A, 6B, and 6C show ratios of 3T and 4T signals according to the transfer function of the optical channel model, and each point represents a time point at which quantization is performed and a signal size at that time. As can be seen from Figures 6a, 6b and 6c, it can be seen that the 3T level and the 4T level is different, and the model of PR (1, 1) is insufficient to explain the characteristics of the channel, it is applied in the present invention It doesn't work.

The transfer functions above have a constraint length of 4, so we have 8 states of 2 ^k-1 . However, the data coded by the EFM method is limited to the signal conversion interval of more than 3T. Therefore, the trellis diagram of the optical channel based on this characteristic is as shown in FIG. Here, the reference value should be scaled to fit the range of the input signal. The trellis diagrams of PR (1,1,1,1) and PR (1,3,3,1) are similar, and because of the EFM characteristics, the number of states is 2, The number of quarters decreased by eight. As a result, the minimum distance between symbols increases to increase the error correction capability.

Referring back to FIG. 1, the Viterbi detection method and apparatus according to the present invention will be described in more detail.

The Viterbi detection method of the present invention first determines the optical channel model to be decoded according to the transfer function of the optical channel model. The data read out from the optical pickup are input to calculate the absolute value of each state reference value. On the basis of the respective branch amounts calculated using the calculated absolute values, the Euclidean distance is obtained by adding the two previous state evaluation amounts and the branch amounts to the current state, respectively, and the two added values Compare each other, select the smaller of the two values to determine the new condition evaluation amount and generate the passage selection signal. If the number of states that transition to one state is one, determine the new state estimate by adding the previous state estimate and the branching amount. The difference between the largest value and the smallest value of the determined state evaluation amount is converged to a predetermined value. The determined overflow prevented new state estimate is stored and the stored output is sent to the previous state estimate of the addition-compare-selection step. The path selection signal from the add-compare-selection step is received, and the original signal is recovered and output using a register exchange structure. In the present embodiment, the model to be decoded depends on the setting of the register value and is configured to allow Viterbi detection for the transfer function of various optical channel partial response models.

The BMC 20 of the Viterbi detection apparatus 100 of the present invention calculates each branch metric with the input data. That is, the BMC 20 receives data read out from the optical pickup and calculates an absolute value with each state reference value. The absolute value of these two values is the Euclidean distance. In this case, in the present invention, the optical channel has a transfer function of Equation 1 and is designed to calculate the branching amount for the k value. As shown in FIG. 7, an example of the BMC 20 unit includes five signal levels (+ high, + middle, and the like) of the reference value converter 22 and the input data and the state reference value so that decoding can be performed on several channel models. And absolute value calculators 242, 244, 246, 248, and 250 that calculate and output 0, -middle, and -high. In this structure, the branch amount is 5 bits wide and has a range of +15 to -16. However, due to the problem of the reliability range of the A / D converter 4, it is limited to be calculated in the range of +12 to -12. Here, the + high value is set to 12, -high is set to -12, and since the change in k is the change in the + middle and -middle values, the gain of the input signal of the A / D converter 4 is adjusted as k. It should be possible. This gain should be adjusted until the peak level of the 4T signal reaches + high. As shown in Table 2 below, four transfer functions are used in the present invention.

middle level k 6 1.0 7 1.4 8 2.0 9 3.0

Levels higher than the peak of the 4T signal never occur in Equation 1, but the peaks of the signals longer than the actual 5T may be larger than the peak of the 4T signal. Levels higher than the peaks of these 4T signals are meaningless in terms of transfer functions and must be clipped. Before the divergence calculation, levels higher than 12 are clipped to 12 and levels lower than -12 are clipped to -12.

The register 10 sends the stored register value to the Viterbi detection device 100 to determine a model to decode. A general Viterbi detector performs a function only for one target model, but the Viterbi detection apparatus of the present invention, as described above, has a register for determining and storing one model as a register value among several target models. The value of the register is set so as to correspond to the model of, so that k is changed accordingly (register value ≠ k), and the decoding target model is changed according to the k value of Equation (1).

The ACS 30 normally operates in three steps, and based on one branching amount calculated using the input data, the Euclidean distance is added by adding the two previous state evaluation amounts and the branching amounts to the current state. Obtain each. Next, the two added values are compared with each other, and the smaller of the two values is selected to determine the new condition evaluation amount. The determined state evaluation amount 34 is transmitted to the SMM 40, the branch information selected, that is, the passage selection signal 32 is transmitted to the PM (60). The ACS 30 cannot have a pipelined structure since the previous result should be reflected directly in the current calculation. Therefore, it must operate within only one clock cycle. The operation speed becomes slower as the bit width of the state evaluation amount becomes longer. The minimum bit width of the state evaluation amount is appropriately determined by the bit width of the branch amount and the overflow control logic to be described later. As shown in FIG. 2, the ACS 30 is used only in the states (-1, -1, -1) and (+ 1, + 1, + 1) due to the RLL characteristic of the EFM code.

The SMM 50 stores the new state evaluation amount generated in the ACS 30. State estimator memory consists of flip-flops.

The OVC 40 prevents an overflow of the state evaluation amount memory. The Viterbi detection device must continuously process infinite input data. Status estimates continue to increase because they continue to accumulate previous status estimates and selected branching quantities. The state quantitative value converges to a value without the difference between the largest value and the smallest value growing indefinitely. This is because a small value is always selected from two state evaluation quantities which transition to one state. The difference between the state evaluation amount having the largest value and the state evaluation amount having the smallest value among the operations of the Viterbi detector having the trellis diagram of FIG. 2 satisfies the inequality of Equation 3 below.

SM _max -SM _min <2 ^{a + 2} (where a is the bit width of the branch amount)

In the Viterbi detector, because overflow control must occur with ACS operation every clock, high speed operation is required. In the present invention, as shown in FIG. 3, a bitwise AND gating method capable of operating at a simple and high speed is used.

If Equation 3 is satisfied and the number of bits of the state evaluation amount is set to a + 2, a time point at which the most significant bit of all the state evaluation amounts becomes 1 before overflow occurs. Therefore, in this case, setting all of them to 0 yields the same result as subtracting 2 ^{a + 2} for all condition estimates. That is, if a = 5, the most significant bit (MSB) must all be 1 before overflow occurs, and in this case, through the NAND gate as shown in FIG. When the input value is all 1, it outputs 0 to prevent overflow. The bits other than the MSB are transmitted to the SMM 50 using the NAND gate signal and the respective AND gates. Here, in the case of 8-bit SMM (50), six of the SMM (1), SMM (2), ..., SMM (6) is present independently. If the OVC 40 is between one input terminal of the ACS 30 and the output terminal of the SMM 50, the number of bits of the state amount is increased by 1, but both problems of hardware simplification and high speed processing can be solved at the same time. have.

The PM 60 basically uses a register exchange structure, but some states and branches can be removed from the general branch structure by the RLL characteristic of the EFM modulation code. The structure of the PM is as shown in Fig. 4, and its length is generally known to be close to the theoretical performance when used about 5-6 times the constraint field k. In this case, PM length was set to 24 based on 6 times k. However, since the ACS section is removed due to the removal of some branches, the data stored in the first three stages of PM are always constant, and thus this portion is removed. In addition, since the data of all states converge to one value at the final stage of the PM, unnecessary parts are removed. 5A and 5B illustrate respective cell structures constituting the PM. A cell in which two branches meet as shown in FIG. 4 is shown in FIG. 5A, and a cell connected to only one branch is shown in FIG. 5B. It was. The cell structure where two branches meet includes a multiplexer 62 which receives an upper branch signal and a lower branch signal and selectively outputs the channel signals according to the passage selection signal 32, and under the control of the clock CLK by receiving the output of the multiplexer 62. A flip-flop 64 for outputting stored data is provided, and the cell structure having only one branch has a flip-flop 66 for storing and outputting branch signals according to a control clock without a multiplexer.

So far, the position of the OVC 40 in the Viterbi detector structure has been described as being between the output end of the ACS 30 and the input end of the SMM 50. However, in another embodiment, the position of the OVC is determined by the position of the ACS 30. It can be designed to be between the input terminal and the output terminal of the SMM 50, the operation description in this case is similar to the other and will be omitted. In this case, however, the bit width of the SMM 50 must be increased by one. In addition, the AND gate in OVC 40 may take other bits as well as the most significant bit.

As described above, the Viterbi detection method and apparatus according to the present invention can be applied to a high speed optical storage medium, and can detect an EFM modulated signal using a simple equalizer. Branches can be eliminated, which has the effect of reducing hardware. The use of the Viterbi detector of the present invention eliminates the use of sophisticated equalizers, thereby reducing manufacturing costs and increasing the operating speed by using an overflow controller. In addition, Viterbi can be detected for several channel models, enabling efficient response to channel changes.

Claims (16)

In the Viterbi detection method applied to a signal recovery device of a high speed optical disc, (a) determining a fiber channel model to decode; (b) receiving data read out from the optical pickup and calculating absolute values with respective state reference values; (c) on the basis of the respective branching amounts calculated using the calculated absolute values, the Euclidean distance is obtained by adding the two previous state evaluation quantities and the branching quantities respectively to the current state, and the added 2 Comparing the two values with each other, selecting a smaller value of the two values to determine a new state evaluation amount and generating a passage selection signal; (d) preventing an overflow by using a difference between the largest value and the smallest value of the determined state evaluation amount converged to a predetermined value; (e) storing the determined overflow prevented new state estimate and transmitting the stored output as a previous state estimate in step (c); And (f) receiving the path selection signal from step (c), and removing a predetermined number of states and branches using a register exchange structure. The Viterbi detection method according to claim 1, wherein in the step (a), a model to be decoded is determined and stored according to a transfer function of various optical channel partial response models. The Viterbi detection method according to claim 1, wherein in step (d), when a is a bit width of a branch amount, the convergence is 2 ^{a + 2} . The Viterbi detection method of claim 1, wherein the step (d) comprises bitwise and gating the most significant bit or another bit. In the Viterbi detection method applied to a signal recovery device of a high speed optical disc, (a) determining a fiber channel model to decode; (b) receiving data read out from the optical pickup and calculating absolute values with respective state reference values; (c) on the basis of the respective branching amounts calculated using the calculated absolute values, the Euclidean distance is obtained by adding the two previous state evaluation quantities and the branching quantities respectively to the current state, and the added 2 Comparing the two values with each other, selecting a smaller value of the two values to determine a new state evaluation amount and generating a passage selection signal; (d) storing the determined overflow prevented new state estimate and transmitting the stored output; (e) preventing overflow by using a difference between the largest value and the smallest value of the stored state evaluation amount converged to a predetermined value and outputting the previous state evaluation amount of step (c); And (f) receiving the path selection signal from step (c), and removing a predetermined number of states and branches using a register exchange structure. 6. The Viterbi detection method according to claim 5, wherein in the step (a), a model to be decoded is determined and stored according to a transfer function of various optical channel partial response models. 6. The Viterbi detection method according to claim 5, wherein in step (e), when a is the bit width of the branch amount, the convergence is 2 ^{a + 2} . 6. The Viterbi detection method of claim 5, wherein the step (e) comprises bitwise and gating the most significant bit or another bit. A Viterbi detection device applied to a signal recovery device of a high speed optical disc, A register for determining and storing and outputting an optical channel model to be decoded; A branch quantity calculation unit which receives the read data from the optical pickup and calculates the absolute value of each state reference value; On the basis of the respective branch amounts calculated using the calculated absolute values, the Euclidean distance is obtained by adding the two previous state evaluation amounts and the branch amounts to the current state, respectively, and the two added values An adder-compare-selector for comparing each other, selecting a smaller value of the two values to determine a new state evaluation amount and generating a passage selection signal; An overflow control unit for preventing an overflow by using a difference between the largest value and the smallest value of the determined state evaluation amount converged to a predetermined value; A state evaluation amount memory unit for storing the determined new overflow evaluation state evaluation amount and transmitting the stored output to a previous state evaluation amount of the addition-compare-selecting unit; And And a passage memory which receives a passage selection signal from said add-compare-selection section and removes a predetermined number of states and branches by using a register exchange structure. The Viterbi detection apparatus according to claim 9, wherein the register unit determines and stores a model to be decoded according to a transfer function of various optical channel partial response models. 10. The Viterbi detection apparatus according to claim 9, wherein the overflow control unit converges to 2 ^{a + 2} when a is a bit width of a branch amount. 10. The Viterbi detection apparatus of claim 9, wherein the overflow controller bitwise and gates the most significant bit or another bit. A Viterbi detection device applied to a signal recovery device of a high speed optical disc, A register for determining and storing and outputting an optical channel model to be decoded; A branch quantity calculation unit which receives the read data from the optical pickup and calculates the absolute value of each state reference value; On the basis of the respective branching amounts calculated using the calculated absolute values, the Euclidean distance is obtained by adding the two previous state evaluation amounts and the branching amounts respectively to the current state, and the added two values are obtained. An adder-compare-selector for comparing each other, selecting a smaller value of the two values to determine a new state evaluation amount and generating a passage selection signal; A state evaluation amount memory unit for storing the new state evaluation amount and transmitting the stored output; An overflow control unit for preventing an overflow by using a difference between the largest value and the smallest value of the transmitted state evaluation amount converged to a predetermined value and then transmitting the previous state evaluation amount of the addition-compare-selection unit; And And a passage memory which receives a passage selection signal from said add-compare-selection section and removes a predetermined number of states and branches by using a register exchange structure. The Viterbi detection apparatus according to claim 13, wherein the register unit determines and stores a model to be decoded according to a transfer function of various optical channel partial response models. The Viterbi detection device according to claim 13, wherein the overflow control unit converges to 2 ^{a + 2} when a is a bit width of the branch amount. The Viterbi detection apparatus of claim 13, wherein the overflow controller bitwise and gates the most significant bit or another bit.

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