ERROR CONTROL CODING

• Error Control Coding Solution Pdf
• Error Control Coding In Digital Communication Ppt

1. Mention is the properties of cyclic codes

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Linearity property

The sum of any two code word is also a valid code word

Cyclic property

Every cyclic shift of a valid code vector produces another valid code vector.

2. Define hamming distance.

The hamming distance between two code vectors is equal to the number of elements in which they differ. For example, let the two code words be,

X = (101) and Y= (110) These two code words differ in second and third bits. Therefore the hamming distance between X and Y is two.

3. What is meant by transparency with respect to line codes

The line code is said to be transparent if the synchronization between the transmitter and receiver is maintained for any type of input data sequence.

4. Define hamming distance and calculate its value for two code words 11100 and11011

The hamming distance between two code vectors is equal to the number of elements in which they differ. For example, let the two code words be,

X = (11100) and Y= (11011)

D= 2 These two code words differ in second and third bits. Therefore the hamming distance between X and Y is two.

5.What is convolution code? How is it different from block codes?

Fixed number of input bits is stored in the shift register & they are combined with the help of mod 2 adders. This operation is equivalent to binary convolution coding.

6.State any four desirable properties of line code

·The PAM signal should have adequate timing content,

·The PAM signal should immune to channel noise and interference

·The PAM signal should allow error detection and error correction

·The PAM signal should be transparent to digital data being transmitted

7.Find the hamming distance 101010 and 010101.If the minimum hamming distance of a (n,k) linear block code is 3, what is its minimum hamming weight?

d(x₁,x₂)=x₁ exor x₂ =111111

d(x₁,x₂)=6

Dmin=3 then Wmin=dmin=3

8. What is meant by syndrome of linear block code?

The non zero output of the produce YHT is called syndrome & it is used to detect errors in y. Syndrome is denoted by S & given as,

S=YHT

9. What is convolutional code? Explain the fundamental difference between block codes and convolutional codes.

Block codes takes‟k‟ number of bits simultaneously form „n‟-bit code vector. This code vector is also called block. Convolutional code takes one message bits at a time and generates two or more encoded bits. Thus convolutional codes generate a string of encoded bits for input message string.

10. What is hamming distance?

The hamming .distance .between .two code vectors .is equal to the number .of elements in which they differ. For example, let the two code words be,

X = (101) and Y= (110)

These .two code words differ in second and third bits.Therefore .the .hamming distance between X and Y is two.

11. Define code efficiency.

The code efficiency is the ratio of message bits in a block to the transmitted bits for that block by the encoder i.e.,

Code efficiency= (k/n)

k=message bits

n=transmitted bits.

12.What are the error detection and correction capabilities of hamming codes ?

The minimum distance (dmin) of hamming codes is „3‟. .Hence it can be used to detect double errors or correct single errors. Hamming codes are basically linear block codes with dmin =3.

13.What is meant by linear code?

A code is linear if modulo-2 sum of any two code vectors produces another code vector. This means any code vector can be expressed as linear combination of other code vectors.

14. What is meant by cyclic codes?

Cyclic codes are the subclasses of linear block codes. They have the property that a cyclic shift of one codeword produces another code word.

15. How syndrome is calculated in Hamming codes and cyclic codes?

In hamming codes the syndrome is calculated as,

S=YH^T

Here Y is the received and H.is the transpose of parity check matrix

16. What is difference between block codes and convolutional codes?

Block codes takes‟k‟ .number of bits simultaneously form „n‟-bit .code vector. This code vector is also called block. Convolutional code takes one message bits at a time and generates two or more encoded bits. Thus convolutional codes generate a string of encoded bits for input message string.

ERROR CONTROL CODING – IMPORTANT TERMS

Properties of cyclic codes:

Linearity property

The sum of any two code word is also a valid code word

Cyclic property

Every cyclic shift of a valid code vector produces another valid code vector.

Hamming distance.

The hamming distance between two code vectors is equal to the number of elements in which they differ. For example, let the two code words be,

X = (101) and Y= (110) These two code words differ in second and third bits. Therefore the hamming distance between X and Y is two.

Transparency with respect to line codes:

The line code is said to be transparent if the synchronization between the transmitter and receiver is maintained for any type of input data sequence.

Hamming distance:

The hamming distance between two code vectors is equal to the number of elements in which they differ. For example, let the two code words be,

X = (11100) and Y= (11011)

D= 2 These two code words differ in second and third bits. Therefore the hamming distance between X and Y is two.

Convolution code:

Fixed number of input bits is stored in the shift register & they are combined with the help of mod 2 adders. This operation is equivalent to binary convolution coding.

Properties of line code:

·The PAM signal should have adequate timing content,

·The PAM signal should immune to channel noise and interference

·The PAM signal should allow error detection and error correction

·The PAM signal should be transparent to digital data being transmitted

Syndrome of linear block code:

The non zero output of the produce YHT is called syndrome & it is used to detect errors in y. Syndrome is denoted by S & given as,

S=YH^T.

Convolutional code:

Block codes takes‟k‟ number of bits simultaneously form “n”-bit code vector. This code vector is also called block. Convolutional code takes one message bits at a time and generates two or more encoded bits. Thus convolutional codes generate a string of encoded bits for input message string.

Code efficiency:

The code efficiency is the ratio of message bits in a block to the transmitted bits for that block by the encoder i.e.,

Code efficiency= (k/n) k=message bits

n=transmitted bits.

Error detection and correction capabilities of hamming codes:

The minimum distance (dmin) of hamming codes is „3‟. .Hence it can be used to detect double errors or correct single errors. Hamming codes are basically linear block codes with dmin =3.

Linear code:

A code is linear if modulo-2 sum of any two code vectors produces another code vector. This means any code vector can be expressed as linear combination of other code vectors.

Cyclic codes:

Cyclic codes are the subclasses of linear block codes. They have the property that a cyclic shift of one codeword produces another code word.

syndrome is calculated in Hamming codes and cyclic codes:

In hamming codes the syndrome is calculated as,

S=YH^T

Here Y is the received and H.is the transpose of parity check matrix

Block codes and convolutional codes:

Block codes takes ‟k” .number of bits simultaneously form “n”-bit .code vector. This code vector is also called block. Convolutional code takes one message bits at a time and generates two or more encoded bits. Thus convolutional codes generate a string of encoded bits for input message string.

Error Control Coding Solution Pdf

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Sends a control code to a service.

To specify additional information when stopping a service, use theControlServiceEx function.

Syntax

Parameters

hService

A handle to the service. This handle is returned by theOpenService orCreateService function. Theaccess rights required for this handledepend on the dwControl code requested.

dwControl

This parameter can be one of the following control codes.

This value can also be a user-defined control code, as described in the following table.

lpServiceStatus

A pointer to a SERVICE_STATUS structure thatreceives the latest service status information. The information returned reflects the most recent status thatthe service reported to the service control manager.

The service control manager fills in the structure only whenGetLastError returns one of the following errorcodes: NO_ERROR, ERROR_INVALID_SERVICE_CONTROL,ERROR_SERVICE_CANNOT_ACCEPT_CTRL, orERROR_SERVICE_NOT_ACTIVE. Otherwise, the structure is not filled in.

Return value

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero. To get extended error information, callGetLastError.

Am to pm conversion amplifier. The following error codes can be set by the service control manager. Other error codes can be set by theregistry functions that are called by the service control manager.

Remarks

The ControlService function asks the ServiceControl Manager (SCM) to send the requested control code to the service. The SCM sends the code if the servicehas specified that it will accept the code, and is in a state in which a control code can be sent to it.

Error Control Coding In Digital Communication Ppt

The SCM processes service control notifications in a serial fashion—it will wait for oneservice to complete processing a service control notification before sending the next one. Because of this, a callto ControlService will block for 30 seconds if anyservice is busy handling a control code. If the busy service still has not returned from its handler function whenthe timeout expires, ControlService fails withERROR_SERVICE_REQUEST_TIMEOUT.

To stop and start a service requires a security descriptor that allows you to do so. The default securitydescriptor allows the LocalSystem account, and membersof the Administrators and Power Users groups to stop and start services. To change the security descriptor of aservice, seeModifying the DACL for a Service.

The QueryServiceStatusEx function returns aSERVICE_STATUS_PROCESS structurewhose dwCurrentState and dwControlsAccepted members indicatethe current state and controls accepted by a running service. All running services accept theSERVICE_CONTROL_INTERROGATE control code by default. Drivers do not accept control codesother than SERVICE_CONTROL_STOP andSERVICE_CONTROL_INTERROGATE. Each service specifies the other control codes that itaccepts when it calls the SetServiceStatus functionto report its status. A service should always accept these codes when it is running, no matter what it isdoing.

The following table shows the action of the SCM in each of the possible service states.

Examples

For an example, see Stopping a Service.

Requirements

See also