KR101714009B1 - Apparatus and method of traceback having minimized decoding delay time - Google Patents

Abstract

A method and apparatus are provided for backtracking data in a communication system. The method comprises the steps of initiating storage of data in a first TBM which is one of a plurality of trace back memories (TBMs) constituting a memory, a step of backwardly presetting the previous TBM of the first TBM Performing reverse tracking during a tracking length, performing a decoding operation to extract decoding information of data stored in a previous TBM of a TBM in which backtracking is performed, and after decoding of data is completed in the first TBM, And starting to store the data in the second TBM which is the TBM from which the information is extracted. According to the present invention, in a system using a Viterbi decoder, a memory required for backtracking is optimally configured, a minimum memory can be used without using a large amount of computation, and a decoding delay time can be minimized.

Description

[0001] APPARATUS AND METHOD OF TRACEBACK HAVING MINIMIZED DECODING DELAY TIME [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reverse tracking apparatus and method, and more particularly, to a reverse tracking apparatus and method for minimizing a decoding delay time.

In general, it is desirable that the performance of the circuit be maintained at or above a desired level while the Viterbi decoder remains low in power consumption. Thus, there is a need for an energy efficient method and structure for implementing a Viterbi decoder.

Viterbi decoders have many applications. For example, a Viterbi decoder may determine a symbol stream that is considered most likely to have been transmitted by a remote transmitter based on the symbol stream received by the receiver in the communication system. Or other applications in data storage systems, disk drives, and the like.

A wireless communication system for transmitting data using a convolutional encoder is restored using a Viterbi decoder. In order to find a similar decoding row, the wireless communication system has a memory that stores selected data in various states going on using the received information. These memories store information because they are tracked over a period of time.

Various methods for efficiently managing memory have been implemented, but information storage and extraction operations are performed in several memories in consideration of time efficiency. It is also possible to use a method to update the information of all data every hour to use minimum memory, but this requires too much computation. In addition, there is a method of performing backward tracking and decoding while advancing backward tracking and decoding of backward tracking while writing to a shift register and shifting memory in the opposite direction, but there is an inconvenience that a memory must be shifted for backward tracking.

There is a need for an efficient backtracking device and backtracking method that effectively uses the memory and completes backtracking and decoding using the same clock and does not shift the memory.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a backtracking method and a memory for preventing a large amount of computation from being required while using a minimum amount of memory.

It is another object of the present invention to provide a method of optimally dividing a backtrace memory and simultaneously operating a plurality of divided memories.

It is another object of the present invention to provide an efficient memory structure having a minimum decoding delay time for back-tracking decoding streams.

According to an aspect of the present invention, a method for backtracking data in a communication system includes initiating storage of data in a first TBM, which is one of a plurality of back trace memories (TBMs) constituting a memory, Performing backward tracking for a predetermined backward trace length backward from the previous TBM of the first TBM, performing decoding operation for extracting decoding information of data stored in the previous TBM of the backward tracking TBM And starting to store the data in the second TBM, which is the TBM from which the decoding information is extracted, after the data is stored in the first TBM.

The size or the number of each of the plurality of TBMs may be determined in consideration of a time for storing a survival path in the memory and a time for performing backtracking in one TBM.

The size N of each of the plurality of TBMs may be determined to be the smallest integer value among the integer values satisfying "N? T / N + 1" based on the trailing length T.

And performing a second backtrace for the backtrack length forward from the previous TBM of the second TBM.

And performing a decoding operation of extracting decoding information of data stored in a previous TBM of a section in which the second backtrace is performed.

The step of performing the backtrace may be performed in a plurality of TBMs based on the backtrack length and the size of each of the plurality of TBMs.

Wherein if the backtrack length is greater than the sum of the sizes of previous TBMs of the first TBM, performing the backtracking comprises traversing back to the beginning of the memory and then backward from the end of the memory ) Followed by backtracking.

Initiation of storage of the data may be performed at the same time as performing the backtracking.

Initiation of the storage of the data may be performed at the same time as performing the decoding operation.

The communication system may be a WLAN system using a 5/6 code rate.

Wherein the step of initiating storage of the data comprises selecting a survival path of one of the survival paths of all states stored in the memory, storing the survival path of all the states in the first TBM, And updating the data including the tracking path every predetermined update timing.

Wherein the step of starting the storage of the data includes storing only a survival path selected from surviving paths of all states stored in the memory in the first TBM, To update the data.

According to another aspect of the present invention, a backtracking apparatus starts storing data in a first TBM, which is one of a plurality of back trace memories (TBMs) constituting a memory, And performing a decoding operation to extract decoding information of the stored data from the TBM previous TBM in which the backward tracking is performed, and after decoding of the data is completed in the first TBM, And a back trace unit for starting to store data in the second TBM which is the TBM from which the information is extracted.

According to another aspect of the present invention, a Viterbi decoder includes a branch value calculator for receiving coded data and preliminarily calculating branch values in all cases, a path selector for performing operations with the calculated branch value, and a memory (TBM), which is one of a plurality of traceback memories (TBMs), through a calculation of the path selection unit, Performs a decoding operation of extracting decoding information of stored data from the TBM previous TBM in which the backward tracking is performed, and after storing the selected path through the operation of the path selecting unit in the first TBM, And a back tracking unit for starting storage of another path selected through the operation of the path selecting unit in the second TBM that is the extracted TBM.

A first-in-last-out (FILO) buffer unit or a Last-In-First-Out (LIFO) buffer unit for changing the order of backward-tracked information.

The path selector may include a parallel ACS (Add Compare Select) using Radix-4.

The path selector may include a parallel ACS (Add Compare Select) using Random-16.

According to the present invention, in a system using a Viterbi decoder, a memory required for backtracking is optimally configured, a minimum memory can be used without using a large amount of computation, and a decoding delay time can be minimized.

In addition, according to the present invention, it is possible to perform back-tracking at the same clock rate while writing in the memory, and reverse state tracking can be performed by obtaining previous state information based on the contents of the memory without shifting the memory.

1 is a flowchart showing an example of a method of receiving and decoding a signal at a receiving end of a communication system to which the present invention is applied.
2 shows an example of a Viterbi decoder to which the present invention is applied.
Fig. 3 relates to a ladix-4 structure to which the present invention is applied.
Fig. 4 relates to a ladix-16 structure to which the present invention is applied.
FIG. 5 shows an example of storing the survival path value, performing backward tracking, and outputting decoded data.
6 shows an example of a backtrace memory to which the present invention is applied.
FIG. 7 shows an example of a backtrace memory to which the backtracking method according to the present invention is applied.
8 is a flowchart illustrating an operation of a backtracking apparatus for performing backtracking in the backtracking memory of FIG. 7 according to the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Also, in order to clearly illustrate the present invention in the drawings, portions not related to the present invention are omitted, and the same or similar reference numerals denote the same or similar components.

1 is a flowchart showing an example of a method of receiving and decoding a signal at a receiving end of a communication system to which the present invention is applied.

The receiving end receives the data encoded by the generating polynomial from the transmitting end of the system (S100).

The decoder (for example, a Viterbi decoder) included in the receiver selects an optimal path from among all possible paths based on the generated polynomial (S105) state (S110), and one of them is selected through backtracking to restore the data (S115).

2 shows an example of a Viterbi decoder to which the present invention is applied.

Referring to FIG. 2, the Viterbi decoder includes a branch metric unit (BMU), a path metric unit (PMU), and a trace back unit (TBU) A first-in-last-out (FILO) buffer unit or a Last-In-First-Out (LIFO) buffer unit for changing the order of the traced back information. In addition, it may further include a backtrace memory in which backtracking is performed.

The branch value calculator receives the encoded data and precomputes branch values in all cases. The branch value in the case of being calculated according to the number of data to be input is changed. For example, if k pieces of coded data to be input are k, 2 ^k different values are calculated. That is, when there are four coded data to be input, a total of 16 (2 ⁴ ) branch values are calculated.

The path selection unit performs an operation on the calculated value and may include an ACS (Add Compare Select) unit. 4 or a radix-16 structure as shown in FIG. 3 or FIG. If the constraint length is C, the operation is performed on 2 ^C-1 states. If the constraint length is C, the state of the previous state The branch value is added to the path value of the previous state and compared and selected for every branch that can be in the current state.

The comparison and the selected value are updated with the path value in the current state in the backtrace memory. The current state is the number of 2 ^C-1 cases, and each state is updated each time according to the input. If the updated state is called the current state, the result of adding the path value of the previous state that can be updated to the current state and the branch value coming from the previous state to the current state is obtained for every possible previous state, do. The selected minimum value is updated to the current path value.

Fig. 3 relates to a Radix-4 structure to which the present invention is applied. This is the case where the constraint length is 3 and the state is 4 (= 2 ³ -1).

Referring to FIG. 3, when the current state is "X00 ", when the state has the ladix 4 structure, the state X00 is changed from the previous states" 00X ", "01X "," And the branch value when the state changes to the state value of the previous state are added to the path value of the previous state, respectively. Then, one of the four paths having the minimum path value is selected. This is because it indicates that the difference between the input encoded data and the predicted encoding value according to the state transition is a similar sequence having a high probability of being small.

Fig. 4 relates to a Radix-16 structure to which the present invention is applied. This is the case where the constraint length is 5 and the state is 16 (= 2 ^5-1 ) individuals.

Referring to FIG. 4, in the case of having a lexix-16 structure, if the current state is "X0000 ", 16 previous states" 0000X ", "0001X ", ... , And branch values when the state changes from "1111X" to " X0000 " are respectively added to the path value of the previous state. Then, one of the 16 paths having the minimum path value is selected.

In this manner, the minimum path value selected by the path selection unit is stored in the backtrack memory for each state.

On the other hand, the backtracker finds the most similar decoding sequence in backtracking memory through backtracking.

There are two methods of performing backtracking while storing the survival path value in the backtracking unit, and decoding data can be outputted by performing backtracking. Here, the survival path value refers to the minimum path value selected by the path selection unit.

First, there is a method of selecting a selected survival path in all states at every point in time, storing the selected survival path in a backtrace memory, and updating previous information according to a path selected by the path selection unit.

FIG. 5 shows an example of storing the survival path value, performing backward tracking, and outputting decoded data.

Referring to FIG. 5, after a certain time has passed, one state can be read to simply determine the state at time "t-T". Here, "t" refers to a time instant and "T" refers to a traceback depth.

Updates the path information of all states to new path information, and outputs the information stored at the time point "tT" in the path information of the previous state as decoded data according to the selected path. At this point, the size of the backtrace memory needed is (state variable (2 ^C-1 ) * T). Also, after a certain traceback length, it has a minimum demodulation delay time at which demodulation occurs upon input. However, hardware complexity is high and power consumption is high in the process of updating the survival path of all memories at every point in time.

Second, only the selected survivor path at every time point is stored, and after a certain time, the previous state is tracked through the stored survival path value in any state, There is a way to get the data. In this case, since there is no need to update all the information at every time point, the hardware complexity is low and the power consumption is reduced. The demodulation delay time is more than doubled in the process of storing the selected survivor path in the backtrack memory and in the backtracking process.

In this case, since the backward tracking is performed using the survival path value obtained from the information input at each point in time, a backtrace memory larger than the backward tracking length is used for time efficiency, and a plurality of read multiple pointers Can be operated. Here, the read multiple pointer refers to a pointer that allows a plurality of read pointers to simultaneously perform a read operation in a plurality of memory spaces. Next, in Fig. 6, it can be seen that the read operation is performed simultaneously at three points.

6 shows an example of a backtrace memory to which the present invention is applied.

Referring to FIG. 6, when a traceback length is T, a plurality of read pointers (three in the case of FIG. 6) are placed, and data is continuously stored (Write: WR) (TakeBack: TB).

The storage memory is divided into (2 * the number of the lead pointers), and in the case of FIG. 6, 2 * 3 pieces are stored.

The size of each storage memory is T / (number of read pointers -1) and T / (3-1) in FIG. 6.

The size of the entire memory in the case of (2 * read pointer number) * T / (the number of the read pointer 1) * 2 Since ^C-1, FIG. 6 (2 * 3) * T / (3-1) * 2 C- ¹ . The size of the confinement field (C) is variable. It is desirable to use sufficient memory for smooth storage and decoding.

FIG. 7 shows an example of a backtrace memory to which the backtracking method according to the present invention is applied.

Referring to FIG. 7, the back trace memory is divided into a plurality of TBMs (TBM ₁ , ..., TBN _{n + 2 in} FIG. 7). The size of each TBM is N, and N is the time required to fill one TBM in terms of time.

Each TBM updates all path information at every point in time. The new path information selected in the previous state and the corresponding tracking path information are updated together. At this time, updating the tracking path information means updating not only the selected new path information but also all the path information necessary for the backward tracking of the previous state. However, this update is performed in one TBM.

When updating of the path information is completed for one TBM, the path information is updated in the same manner for the next TBM. During the update operation for the next TBM, the previous TBM no longer performs the update operation. That is, an update operation is performed for all states only for one TBM at a time.

The size of the traceback memory of Figure 7 is (a TBM of size (N)) * ^(1-C 2) * (n + 2), T is an n * N, which (T * 2 ^{C- 1} ) + (the size of one TBM) * (2 ^C-1 ) * (2).

When the size of one TBM is N, the time taken to store the data in one TBM is at least N clocks and the back-tracking is performed in another TBM during the N clock which is written (WR) to the TBM The path information is updated on one clock and the next TBM is read.

In this manner, the n pieces of TBM information are read with one read pointer, the back trace is performed during the n clock, and the decoding is performed on the next clock to obtain the decoded data.

The product of the size of the TBM and the number of TBMs (N * n) must be greater than or equal to the traceback length T. That way, you can do backtracking properly. If T / N is an integer, the number of TBMs (n) required for backtracking is selected as T / N. If T / N is not an integer, then n is greater than T / N and is chosen as the nearest integer.

For example, the criterion for dividing the traceback length (T) by n TBMs and determining the size (N) of one TBM is N .

The traceback is a method of reading the information of the TBM to obtain the path information of the corresponding state, obtaining the next state information therefrom, searching for the next TBM corresponding to the next state, and obtaining the path information of the next TBM.

If the minimum value of N satisfying the condition of Equation (1) is found and the memory is efficiently divided in the tracing process, the decoding delay time can be minimized. If N is too large, there is a lot of path information to be updated in one TBM, so power consumption may be large.

But can also be applied to a system requiring a long traceback length such as a system using a 5/6 code rate among a wireless LAN system (for example, an IEEE 802.11n system).

In Equation (1), when the trailing length (T) is 90, the size (N) of the TBM is the minimum value of 10. That is, when N is 10, it satisfies the condition of Equation (1) and has a minimum total memory size and minimum delay time.

In this case, one TBM size is 10 * 2 ^C-1 , T is 90, the number n of TBMs for tracing back is 9, and the total memory size is 10 * 2 ^{C-1 *} (9 + 2).

On the other hand, when T is 100, the minimum value of N satisfying the condition of Equation (1) is 11. In this case, since one TBM size is not divided by an integer by T / N, a proximity constant is used. (N) is 10 and the total memory size is 11 * 2 ^C-1 * (10 + 2) since the size of N * n must be greater than or equal to 100, to be.

If T is 100 and N is 12, if n is an integer, the total memory size is 12 * 2 ^C-1 * (9 + 2) to be.

In addition, if T is 100 and N is 13, if n is an integer, the total memory size is 13 * 2 ^C-1 * (8 + 2) to be.

Here, when N is 11 and N is 12, the total memory size is the same. When N is 13, the total memory size is smaller than when N is 11 or 12. However, the memory update of TBM may be advantageous because the N is 11, since N is 12 or 13, which uses less hardware.

8 is a flowchart illustrating an operation of a backtracking apparatus for performing backtracking in the backtracking memory of FIG. 7 according to the present invention. When the data is stored in the backtrace memory, the backtracking device reuses the memory after decoding the stored data, thereby reducing the decoding delay and efficiently reusing the memory.

The backtracking device starts storing data in the first TBM, which is one of a plurality of TBMs constituting the backtrace memory (S800). Simultaneously or immediately thereafter, backtracking is performed in the previous TBM of the first TBM (S805). Tracebacks may be performed in a plurality of TBMs depending on the size (N) of the TBM and the value of the traceback length (T). If the traceback length is greater than the size of the previous TBM of the first TBM, backtracking continues from the end of the traceback memory backwards.

Simultaneously with or immediately after the backtracking is performed, a decoding operation of extracting decoding information of the stored data at the TBM previous TBM in which the backward tracking is performed is performed (S810). That is, back-tracking and decoding operations are performed in different TBMs at the same time (or immediately after) the data is stored.

After the storage of the data is completed, if the backtracking device continuously tries to perform the backtracking (S815), the storage of data is started in the next TBM (second TBM) of the first TBM (S820). The second TBM may be a TBM that extracts decoding information in a previous traceback operation. That is, the data is stored in the memory that has been decoded in the previous traceback operation. Since the data is obtained through decoding, it can be reused as a memory for storing data.

As with the previous traceback operation, backtracking is performed in the previous TBM of the second TBM, and backtracking may be performed in a plurality of TBMs according to the traceback length (T) value. If the size of the previous TBM of the first TBM is smaller than the tracing length, tracing continues from the end of the tracing memory.

In the previous traceback operation, backtracking is performed by the amount corresponding to the traceback length starting from the TBM in which the data was stored. In addition, a decoding operation is performed to extract decoding information of the stored data in the previous TBM of the section in which the backward tracking is performed. The TBM for performing the decoding operation is the last TBM among the plurality of TBMs performing backward tracking in the previous backward tracking operation.

For example, assuming that the backtrace memory is composed of a total of n + 2 TBMs, the backtracking device starts storing data in the (n + 2) th TBM. The storage of the data may be updating the path information or updating the survivor transition information. At the same time (or after the start of storage of data), backtracking is performed in the second TBM to the (n + 1) th TBM, which is a plurality of TBMs before the (n + 2) th TBM. Tracking is performed on a total of n TBMs, and the magnitude of the product of each TBM size (N) and the number of TBMs (n) is equal to or longer than the reverse tracking length (T). The backtracking device extracts the decoding information from the first TBM before completing the storage of data in the (n + 2) th TBM. Delay is reduced because it performs decoding and storing and backtracking of data at the same time.

In order to continue tracing back, after the storage of data in the (n + 2) th TBM is completed, the first TBM from which the decoding information is extracted starts to store data. At the same time (or after the start of storage of data), backtracking is performed in the third TBM to the (n + 2) th TBM. Again, traceback is performed on a total of n TBMs. Further, the backtracking device extracts the decoding information from the second TBM before completing the storage of the data in the first TBM.

The above embodiment can be applied to the backward tracking memory of FIG. First, after data is stored in n + 1 TBMs during (n + 1) * N clocks, data is stored in TBM _{n + 2} and back tracking is started in TMB ₂ to TBM _{n +1} . Then, decoding information is extracted from TBM ₁ before the data is stored in TBM _{n + 2} . When the data is stored in TMB _{n + 2} , the memory moves the storage space to TBM ₁ for the next N clocks and starts storing the data. Hayeoteumeuro immediately extract the decoded information from the TBM ₁ for the previous N is clock data is stored in the TBM _{n +2} for, performing a storage of the data back from the decoded information extracted TBM ₁ to re-use the memory.

In the same way, after the data is stored in TMB ₁ , the memory moves the storage space to TBM ₂ for the next N clocks and starts storing the data. Hayeoteumeuro extracts the decoded information from the TBM ₂ during the immediately preceding clock is N ₁ stored for TBM, The Save in TBM ₂ to re-use the memory.

Sequentially, when the storage is completed in TMB ₂ , the memory moves to the TBM ₃ and starts storing. Hayeoteumeuro extracts the decoded information from the TBM ₃ during the immediately preceding clock TBM N ₂ for storage, it is stored in that the TBM ₂ to re-use the memory.

This course is taught in TMB ₄ , TMB ₅ , ... . By storing the decoded data in the decoded memory, the memory can be efficiently used and the decoding delay time can be reduced.

In the above-described exemplary system, the methods are described on the basis of a flowchart as a series of steps or blocks, but the present invention is not limited to the order of the steps, and some steps may occur in different orders . It will also be understood by those skilled in the art that the steps shown in the flowchart are not exclusive and that other steps may be included or that one or more steps in the flowchart may be deleted without affecting the scope of the invention.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

Claims (20)

A method for backtracking data in a communication system,
Initiating storage of data in a first TBM which is one of a plurality of trace back memories (TBMs) constituting a memory;
Performing backtracking for a predetermined backtrack length backward from a previous TBM of the first TBM;
Performing a decoding operation to extract decoding information of data stored in a previous TBM of an interval in which the backward tracking is performed; And
And after the storage of the data in the first TBM is completed, starting to store data in the second TBM, which is the TBM from which the decoding information is extracted. The method according to claim 1,
Wherein the size or the number of each of the plurality of TBMs is determined in consideration of a time for storing the data in the memory and a time for performing backtracking in one TBM. The method according to claim 1,
The size (N) of each of the plurality of TBMs is calculated using the backtrack length (T)
Quot; N > / N + 1 ". The method according to claim 1,
Further comprising performing a second traceback during the traceback length forward from a previous TBM of the second TBM. 5. The method of claim 4,
Further comprising performing a decoding operation of extracting decoding information of data stored in a previous TBM of an interval in which the second backtrace is performed. The method according to claim 1,
Wherein performing the backtrace comprises:
Wherein the backtracking is performed in a plurality of TBMs based on the backtrack length and the size of each of the plurality of TBMs. The method according to claim 1,
If the traceback length is greater than the sum of the sizes of the previous TBMs of the first TBM,
Wherein the step of backtracking comprises performing a backtracking to the beginning of the memory and then backtracking from the end of the memory backward. The method according to claim 1,
Wherein initiating storage of data in the first TBM is performed concurrently with performing the backtracking. The method according to claim 1,
Wherein starting to store data in the first TBM is performed at the same time as performing the decoding operation. The method according to claim 1,
The communication system includes:
Wherein the wireless LAN system uses a 5/6 code rate. delete delete A first TBM, which is one of a plurality of back trace memories (TBMs) constituting a memory, and performs back trace for a predetermined back trace length from the previous TBM of the first TBM A decoding operation of extracting decoding information of the stored data from the previous TBM of the section in which the backward tracking is performed is performed, and a second TBM, which is the TBM in which the decoding information is extracted after the data is stored in the first TBM, And a back trace section for starting storage. 14. The method of claim 13,
Wherein the size or number of each of the plurality of TBMs is determined in consideration of a time for storing the data in the memory and a time for performing backtracking in one TBM. 14. The method of claim 13,
The back-
And performs a second backtrace during the backtracking length forward in a previous TBM of the second TBM. 16. The method of claim 15,
The back-
And performs a decoding operation of extracting decoding information of data stored in a previous TBM of a section in which the second backtrace is performed. A branch value calculation unit for receiving the coded data and preliminarily calculating branch values in all cases;
A path selector for performing an operation on the calculated value; And
A first TBM, which is one of a plurality of back trace memories (TBMs) constituting a memory, stores a selected path through an operation of the path selecting unit, and stores a predetermined back trace length from the previous TBM of the first TBM Performing a backward tracking while performing a backward tracking and performing a decoding operation of extracting decoding information of stored data in a previous TBM of a section in which the backward tracking is performed, And a backtrace unit for starting storage of another path selected through the operation of the path selection unit in a second TBM that is a TBM from which the decoding information is extracted. 18. The method of claim 17,
A first-in-last-out (FILO) buffer unit or a last-in-first-out (LIFO) buffer unit for changing the order of the traced back information. 18. The method of claim 17,
Wherein the path selecting unit comprises:
And a parallel ACS (Add Compare Select) using Radix-4. 18. The method of claim 17,
Wherein the path selecting unit comprises:
And a parallel ACS (Add Compare Select) using the radix-16.

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