WO2000018122A1 - Method and apparatus for shuffling and deshuffling video signals - Google Patents

Method and apparatus for shuffling and deshuffling video signals Download PDF

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Publication number
WO2000018122A1
WO2000018122A1 PCT/US1999/021666 US9921666W WO0018122A1 WO 2000018122 A1 WO2000018122 A1 WO 2000018122A1 US 9921666 W US9921666 W US 9921666W WO 0018122 A1 WO0018122 A1 WO 0018122A1
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WO
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Prior art keywords
shuffling
method
memory
data
lines
Prior art date
Application number
PCT/US1999/021666
Other languages
French (fr)
Inventor
Charles P. Kelly
Douglas N. Nelson
Original Assignee
General Instrument Corporation
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00Television systems
    • H04N7/16Analogue secrecy systems; Analogue subscription systems
    • H04N7/167Systems rendering the television signal unintelligible and subsequently intelligible
    • H04N7/169Systems operating in the time domain of the television signal
    • H04N7/1696Systems operating in the time domain of the television signal by changing or reversing the order of active picture signal portions

Abstract

This invention teaches a video line shuffling method wherein video line displacement is variable and controlled depending upon the distortion in a given system. A series of permutations is applied to the original picture such that lines are shuffled in a controlled manner to achieve line displacement within a desired range. Memory requirements are minimized by utilizing a method whereby a single memory has data written into locations which were read from in a previous step. Where DRAM is utilized for the memory, a write method is employed to eliminate the need for strobing the rows and columns DRAM.

Description

METHOD AND APPARATUS FOR SHUFFLING AND DESHUFFLING VIDEO SIGNALS

BACKGROUND

This invention is related to encoding and decoding of video information, and

more particularly to a method and apparatus for securing the transmission of video

signals so that only authorized subscribers can view transmitted video information.

Systems have been developed for scrambling television signals to secure

transmission of video information. An example of a scrambling technique involves

"block shuffling" wherein a television field consisting of video lines is divided into

several blocks or groups of video lines. The video lines within each block are then

randomly shuffled or scrambled so that the original line sequence is changed to a

new scrambled line sequence within each block. The scrambled video signals are

then transmitted to a receiver along with data relating to a code corresponding to the

order of the randomly shuffled lines in each block. A receiver having a decoder is

utilized at a subscriber location to return the lines within each block to their original

sequence so that a video display of each block recreates the original field.

U.S. Patent No. 5,321,748 discloses a method and apparatus for scrambling

video signals utilizing such a block shuffling technique. A block of video lines is

divided into top and bottom sub block portions. The top and bottom sub block

portions are switched and within each sub block portion, the video lines are

randomly shuffled. This is said to improve masking of the original video

information by increasing the expected value of line displacement. U.S. Patent No. 4,405,942 discloses another method and system for secure

transmission and reception of a video signal wherein parts of the video signal are

delayed in relation to each other to form an encoded video signal. The encoder

utilizes two field memories and a flip flop such that a first field is loaded into one of

the field memories and then before the next field of video information arrives, the

flip flop changes state for loading the next field of video information into the second

field memory.

Several problems exist in that signal distortion effects occur during

transmission. Some of these effects include field tilt or hum caused by cable

amplifiers, nonlinear transmitters, or receiver imperfections. These distortion affects

may change the luminance of lines in a field. Luminance is typically distorted across

the field such that minimal distortion occurs at the top of the field and maximum

distortion occurs at the bottom of the field. For example, line 1 may experience a

low level of distortion while line 500 experiences a high level of distortion. Since

the change in distortion is gradual from the top of the field to the bottom of the field,

it is usually not noticeable when a television signal is transmitted and viewed at a

subscriber's television. When the lines are shuffled, transmitted, and then deshuffled

at a subscriber location, sharp contrasts in luminance between adjacent deshuffled

lines may be visible on the video display. This occurs because the shuffled field is

transmitted and the gradual distortion effect described above is applied during the

transmission. During deshuffling, a line which was transmitted at position 1 with a

low level of distortion may be moved next to a line which was transmitted at position 500 having a high level of distortion creating an undesirable effect which is visible

in the television picture received at the subscriber location. This problem is

exaggerated by increasing the average expected line displacement during the

shuffling process. Therefore, the maximum average line displacement will be

limited by the transmission network causing the distortion. For example, a network

having high distortion can accommodate a smaller average line displacement than

a network having lower distortion. Since increasing average line displacement

improves masking, it is therefore desirable to transmit scrambled signals having the

maximum average line displacement which network distortion permits.

Another problem exists in that systems for encoding or decoding the video

signals typically utilize a plurality of memories for processing. This increases the

number of components necessary to implement such a system and also introduces

unwanted delay in signal processing.

SUMMARY

It is therefore an object of the present invention to provide a method and

apparatus for scrambling and descrambling video signals utilizing a shuffling

technique which is adaptable to a given network for maximizing masking of the

video signal while minimizing undesirable effects of network distortion.

It is a further object of the invention to implement such a system in order to

minimize the number of memory components and delay in signal processing. These and other objects have been achieved by providing a method for video

line shuffling wherein a picture field containing a plurality of lines is first applied to

a shuffling function having a first block size parameter and a first increment

parameter. Next, the shuffled lines are applied to a second shuffling function having

a second block size parameter and a second increment parameter. Memory

requirements are reduced in the deshuffling method by utilizing a single memory and

writing to locations in that memory in a step immediately following a read from the

respective locations. Where the memory device utilized is a DRAM, a method is

presented for refreshing rows and columns of the DRAM without the need for

strobing.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a block representation of the shuffling and deshuffling process.

Figure 2 is a diagram of a recursive function for shuffling or deshuffling lines

of a video field.

Figure 3 is a graph showing input line number versus output line number for

a first shuffling method.

Figure 4 is a graph showing input line number versus output line number for

a second shuffling method.

Figure 5 is a diagram of a video shuffling method having reduced memory

requirements. Figure 6 is a table showing memory write locations for a series of video line

samples.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The video line shuffling method will first be described generally with

reference to Figure 1. A shuffler first applies a permutation P to an original picture

10. The permutation P rearranges the line sequence of the original picture 10 to

form a shuffled picture 20. The shuffled picture 20 is considered to be masked or

secure because if viewed on a monitor or television, the original picture 10 is

unintelligible.

The shuffled picture 20 is transmitted over a network to a set top terminal

having a deshuffler for reconstructing the original picture 10. The deshuffler serves

to apply an inverse permutation F1 to the shuffled picture 20 to create a

reconstructed picture 10'. The deshuffler having the inverse permutation P"1

rearranges the shuffled lines into their original positions to reconstruct the original

picture.

The shuffling method will now be described in greater detail with reference

to Figure 2. The permutation P is defined by a series of shuffling functions g(x).

Each shuffling function g(x) is defined by a pair of shuffle parameters (B, I) where

the B values correspond to a block size and the I values correspond to an increment

within the block. Therefore, if the line number, x is known, each shuffling function

can be described by: g(x,B,D

To complete the permutation, a series of shuffling functions may be applied

to the original picture 10. Figure 2, for example, shows the application of three such

shuffling functions resulting in the permutation defined by:

g(g(g(x,Bl,Il),B2,I2),B3,I3)

where x is the original line number of a given line in a field, Bn is a parameter

defining the block size for a respective shuffling function n, and In is a parameter

defining an increment within the blocks for the respective shuffling function n.

Following a line, for example line 1 , through the permutation, it can be seen that line

1 enters the first shuffling function and exits at position 4. It then exits the second

shuffling function at position 9 and exits the third shuffling function at position 12.

The inverse permutation P Λ is represented by a reverse path traveling from the right

to left side of Figure 2. It should be understood that B and I values can be selected

to achieve a number of different permutations P and inverse permutations P Λ. By

selecting B and I values the permutation P can be designed to limit line

displacement. For example, in Figure 2, B l, B2 and B3are selected so that the

resultant blocks have coincident boundaries HI, H2, H3 at the center of each

shuffling function. The result is that no line will cross the center of the permutation

P thus limiting maximum line displacement to within on half of the picture 10.

Referring now to Figures 3 and 4, results data will be described for two

different permutations applied by the shuffler of Figure 1. It should be understood

that these permutations are shown to illustrate how masking is limited by system distortion. Also, these permutations are different from the permutation presented in

Figure 2. Figure 3 shows a graphical representation of input line versus output line

numbers for a first selected permutation P. The resultant pattern indicates that each

line of the original picture 10 is moved only a small amount in the shuffle picture 20.

This permutation is desirable for systems that have high levels of distortion

introduced during transmission. The reconstructed picture 10' will exhibit only

minor distortion upon reconstruction. This permutation, however, provides a low

level of masking since the lines are shuffled in a pattern along a relatively small

displacement.

Figure 4 shows a graphical representation of input line versus output line

number for a second permutation P. This permutation, exhibits a high level of line

displacement and is suitable for systems containing less distortion. It can be

appreciated that this permutation provides a higher degree of masking since lines are

displaced more than the those of Figure 3.

Video line shuffling/deshuffling methods require the use of memory , typically

random access memory (RAM), for temporarily storing and reading lines during

permutation. Since reducing the number of components in such a system often

reduces the cost, it is desirable to minimize the amount of memory necessary for

performing the shuffling and deshuffling method. Additionally, memory typically

represents a large percentage of the cost associated with a finished terminal

containing the deshuffler. As described in the background section, known

techniques utilize a pair of memories, one memory typically is written to in a cycle while the other memory is typically read from in order to perform the deshuffling.

Figure 5 shows a method of deshuffling utilizing an exemplary single four location

memory. It should be understood that while a four location memory is utilized in this

example in order to simplify the explanation, smaller or larger memories can be

utilized with this method. Also, for ease of explanation, a simplified permutation

M and inverse permutation M"1 will be described. Those reasonably skilled in the

art will appreciate that a more complex permutation such as that shown in Figure 2

could be applied to this method. The memory which will be described is located

within a decoder which is typically part of a set top terminal at a subscriber location.

The shuffler is typically positioned at the head end of a video transmission system.

Beginning at the upper left corner of Figure 5, in the first step, an original

line sequence of 1, 2, 3, 4 has been stored in the memory. A deshuffler reads the

memory in order such that 1 is read from the first position. Next, the shuffler sends

a permutation 2, 3, 1, 4 which is stored in consecutive memory locations as shown

in steps 2-5. Also during this second step, the deshuffler continues to read from the

memory in order such that the second, third and fourth locations are read. During

the fifth step, the deshuffler does not read from the memory. This is because

between steps 5 and 6, the Verticle Blanking Interval (VBI) occurs. This is shown

by way of example to illustrate how an interval is provided between steps for the

VBI. Those skilled in the art will appreciate that while the VBI is shown between

steps 5 and 6 and again between steps 10 and 1, the method can be adapted to

provide this interval between different steps according to timing requirements of any given system. In step 6, the deshuffler reads from memory locations utilizing the

inverse permutation 3, 1, 2, 4. In step 7 the shuffler begins consecutively storing

according to the inverse permutation 3, 1, 2, 4. It should be noticed that in each step

where the shuffler stores a value into a memory location, the deshuffler in the

previous step has read from that same location. Therefore, each memory location is

utilized as soon as it is made available by having been read from It should be noted

that the shuffler sends the inverse permutation M"1 based upon the location number

of the most recently read data in steps 6-10. For example in step 6, a 1 is read from

location 3, therefore in step 7, the shuffler sends a 3 corresponding to the location

number previously read. In step 7 the deshuffler reads 2 from location 1, therefore

the shuffler sends a 1 corresponding to the location number previously read. Based

upon this logic, the inverse permutation 3, 1, 2, 4 is generated.

Another method of reducing cost of the finished terminal is to select lower

cost memory components. For example, DRAM may be suitable from economic and

design requirements perspectives. The use of DRAM as a memory device for the

deshuffler and a novel write method will now be described in greater detail with

reference to Figure 6. First it should be understood that each line of video is

digitally sampled for storage in the memory. In this example, 909 samples are taken

per line. It should also be understood that the number of samples may be selected

according to system design requirements. DRAM is typically arranged to have

locations in rows and columns. In order to refresh a row of DRAM, it is necessary

to either write to or strobe any column in that row. Likewise, in order to refresh any column, it is necessary to write to or strobe any row along that column. It is

necessary to refresh all rows and columns at a minimum time interval prescribed by

the DRAM. In this case, the refresh rate for the selected DRAM is 8 ms. Since

DRAM is required to have its columns and rows refreshed at the refresh rate, they

are typically strobed to maintain the data stored in locations in the associated rows

and columns. A problem is presented in that strobing requires added bandwidth to

send the strobe signals. The following method eliminates the need for the strobe

signals and therefore reduces bandwidth requirements. Write locations are selected

in such a way that rows and columns are written to within a minimum time interval

prescribed by the refresh rate to avoid losing data stored therein and to avoid the

need to strobing the rows or columns.

Referring now to Figure 6, the storage of 909 samples representing video line

0 will be described.. The first 127 samples are written into row 0. Along row 0 of

the DRAM, the samples are written into columns 0 through 127. The samples 128-

255 are next written into row 64, columns 128-225. This pattern continues until

sample 512. The particular DRAM selected for this application utilizes a nine bit

column address having a maximum value of 511. Continuing along video line 0,

samples 512-639 are written into row 256, columns 0-127. It is therefore evident

that the column numbers wrap back to 0 after reaching the maximum value of 511.

Continuing along video line 0, samples 640-767 are written into row 320, columns

128-255. Samples are written at an approximate rate of 14 million samples per

second. This allows 128 lines of 909 samples to be written into DRAM every 8 ms. With each line being written according to Figure 6, this method serves to refresh

each column and each row within the given time interval necessary for the DRAM.

An advantage of the present mvention is that the shuffling method provides

a controlled amount of maximum line displacement which is adjustable depending

upon the distortion present in a given system. This provides for a maximum masking

level within the confines of system distortion.

An additional advantage is that one memory may be utilized to deshuffle a

shuffled picture.

An additional advantage is that where DRAM is utilized for the memory, the

need for strobing or refreshing the memory is eliminated.

It should be understood that while this invention is presented here in the form

of the embodiments shown, the scope of the invention is intended to be limited only

by the following claims.

Claims

What is claimed is:
1. A video line shuffling method comprising the steps of:
applying a first shuffling function to a plurality of lines, the first shuffling
function having a first block size parameter and a first increment parameter;
applying a second shuffling function to the plurality of lines, the second
shuffling function having a second block size parameter and a second increment
parameter.
2. The video line shuffling method of claim 1 wherein line displacement in
each shuffling function is limited to be within a block defined by the respective
block size parameters.
3. The video line shuffling method of claim 2 wherein line displacement
within each block is limited by the increment parameter.
4. The video line shuffling method of claim 1 further comprising the step of
applying a third shuffling function to the plurality of lines, the third shuffling
function having a third block size parameter and a third increment parameter.
5. The video line shuffling method of claim 4 further comprising the step of
applying a series of shuffling functions to the plurality of lines, the series containing at least one shuffling function having a respective block size parameter and a
respective increment parameter.
6. The video line shuffling method of any one of claims 1 to 5 wherein the
block size parameter of one of the shuffling functions defines a block having at least
one boundary coincident with a boundary of a block of another shuffling function.
7. A video line shuffling method utilizing a shuffler at a first location and a
deshuffler having a memory at a second location, the method comprising the steps
of:
sending a first series of data shuffled according to a first permutation from the
shuffler to the deshuffler;
sequentially writing the first series of data into the memory such that data is
written into a memory location immediately after that memory location has been
read,
sending a second series of data according to an inverse of the first permutation
from the shuffler to the deshuffler; and
writing to memory locations defined by the data in the inverse permutation
such that data is written into a memory location immediately after that memory
location has been read.
8. A method of writing data into a memory having C columns and R rows
defining a plurality of memory locations, the method comprising the steps of:
dividing the data into lines wherein each line contains a first length of data;
dividing the lines into subsets each having a second length being smaller that
the first length;
writing each subset into a selected row and column range of the memory such
that each time a subset is written, the selected row is incremented by a value I.
9. The method of claim 8 wherein I is selected so that each row has data
written therein within a minimum selected time interval.
PCT/US1999/021666 1998-09-21 1999-09-20 Method and apparatus for shuffling and deshuffling video signals WO2000018122A1 (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2010086317A1 (en) 2009-01-28 2010-08-05 Telefonaktiebolaget L M Ericsson (Publ) Lightweight streaming protection by sequence number scrambling
WO2013044800A1 (en) * 2011-09-28 2013-04-04 中国移动通信集团公司 Video frame stream processing method, video server and terminal equipment

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1993007716A1 (en) * 1991-09-30 1993-04-15 Thomson Consumer Electronics S.A. Method and apparatus for secure transmission of video signals
US5321748A (en) * 1992-07-02 1994-06-14 General Instrument Corporation, Jerrold Communications Method and apparatus for television signal scrambling using block shuffling

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1993007716A1 (en) * 1991-09-30 1993-04-15 Thomson Consumer Electronics S.A. Method and apparatus for secure transmission of video signals
US5321748A (en) * 1992-07-02 1994-06-14 General Instrument Corporation, Jerrold Communications Method and apparatus for television signal scrambling using block shuffling

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2010086317A1 (en) 2009-01-28 2010-08-05 Telefonaktiebolaget L M Ericsson (Publ) Lightweight streaming protection by sequence number scrambling
US8204217B2 (en) 2009-01-28 2012-06-19 Telefonaktiebolaget Lm Ericsson (Publ) Lightweight streaming protection by sequence number scrambling
WO2013044800A1 (en) * 2011-09-28 2013-04-04 中国移动通信集团公司 Video frame stream processing method, video server and terminal equipment

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