Difference between revisions of "Aufgaben:Exercise 3.2Z: Components of the GSM System"

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[[File:EN_Bei_Z_3_7.png|right|frame|GSM system components]]
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The diagram shows the entire GSM transmission path,  with the transmitter on the left and the receiver on the right.
  
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[[File:EN_Mob_A_3_2_Z.png|right|frame|GSM system components]]
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The illustration refers only to speech transmission.  In GSM data transmission,  only the top block  $($speech encoder or decoder$)$  is replaced by another channel encoder or decoder  $($concatenation of two channel codes$)$.
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The diagram shows the entire transmission path of the GSM,  
 
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*On the left side the transmitter,
 
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*on the right side the receiver.
 
  
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The two respective lowest system components were already treated in detail in the exercises for the chapter  [[Examples_of_Communication_Systems/Radio_Interface|"Radio Interface"]].
  
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The representation only refers to voice transmission. In GSM data transmission, only the uppermost block (speech encoder or decoder) is replaced by another channel encoder/decoder (concatenation of two channel codes).
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In this exercise,  on the other hand,  some basic properties are queried from
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*Speech encoders and speech decoders,
  
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This task deals with some basic properties of
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*convolutional encoder and convolutional decoder,
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*speech coder and speech decoder,
 
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*Convolution encoder and convolution decoder,
 
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*Interleaver and de-interleaver and
 
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*Encryption and decryption.
 
  
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*interleaver and de-interleaver,  and
  
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*encryption and decryption.
  
  
  
  
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<u>Hint:</u>
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*The exercise belongs to the chapter&nbsp; [[Mobile_Communications/Similarities_Between_GSM_and_UMTS|"Similarities between GSM and UMTS"]].
  
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*Reference is also made to the chapter&nbsp;  [[Mobile_Communications/Characteristics_of_GSM|"Characteristics of GSM"]].
  
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''Notes:''
 
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*The task belongs to the chapter&nbsp; [[Mobile_Communications/Gemeinsamkeiten_von_GSM_und_UMTS|Gemeinsamkeiten von GSM und
 
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UMTS]].
 
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*Reference is also made to the chapter&nbsp;  [[Mobile_Communications/Die_Charakteristika_von_GSM|Die Charakteristika von GSM]].
 
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===Questionnaire===
 
  
 
<quiz display=simple>
 
<quiz display=simple>
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{Which statements are true for speech encoding/decoding?
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{Which statements apply to speech coding or decoding?
 
 
|type="[]"}
 
|type="[]"}
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+ They are components of source coding.
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+ These are source coding components.
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- They are components of channel coding.
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- They are components of channel coding.
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- The speech coder adds redundancy.
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- Redundancy is added by the speech encoder.
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+ The speech coder removes redundancy.
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+ Redundancy is removed by the speech encoder.
  
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{Which statements apply to the convolutional encoder/decoder?
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{Which statements are true for the convolutional encoder or decoder?
 
|type="[]"}
 
|type="[]"}
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- These are components of the source coding.
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- They are components of source coding.
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+ These are components of the channel coding.
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+ They are components of channel coding.
 
+ Redundancy is added by the convolutional encoder.
 
+ Redundancy is added by the convolutional encoder.
 
- Redundancy is removed by the convolutional encoder.
 
- Redundancy is removed by the convolutional encoder.
  
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{What statements apply to the interleaver and de-interleaver?
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{Which statements are true for the interleaver and de-interleaver?
 
|type="[]"}
 
|type="[]"}
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- The Interleaver adds redundancy.
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- The interleaver adds redundancy.
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+ The de-interleaver is used to distribute bundling errors.
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+ The interleaver is used to distribute bundle errors.
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- The interleaver is most important in the AWGN channel.
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- The interleaver has the most significance for the AWGN channel.
  
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{What statements apply to encryption and decryption?
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{Which statements are true for encryption and decryption?
 
|type="[]"}
 
|type="[]"}
 
+ Both serve data security in the sense of data protection.
 
+ Both serve data security in the sense of data protection.
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- These components are used for error correction.
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- These components are for error correction.
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- The encryption adds redundancy.
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- Encryption adds redundancy.
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+ GSM usually uses symmetric encryption.
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+ GSM mostly uses symmetric encryption.
 
</quiz>
 
</quiz>
  
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===Sample Solution===
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===Solution===
 
{{ML-Kopf}}
 
{{ML-Kopf}}
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'''(1)'''&nbsp; Correct are the&nbsp; <u>answers 1 and 4</u>:
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*The goal of speech coding is data compression and thus redundancy reduction.
  
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'''(1)'''&nbsp; The answers <u>1 and 4</u> are correct:
 
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*The goal of speech coding is to compress data and thus reduce redundancy.
 
 
*This is a typical task of source coding.  
 
*This is a typical task of source coding.  
  
  
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'''(2)'''&nbsp; The answers <u>2 and 3</u> are correct:
 
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*Convolutional coding is a form of channel coding that enables the receiver (decoder) to detect and possibly correct errors.
 
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*The channel coder adds (meaningful) redundancy to this, while the speech coder removes irrelevant redundancy.
 
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*In many cases, both components are implemented together or at least closely coordinated
 
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*This is called &bdquo;common source&ndash; and channel coding&rdquo;.
 
  
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'''(3)'''&nbsp; Only the answer <u>2</u> is correct:
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'''(2)'''&nbsp; Correct are the&nbsp; <u>answers 2 and 3</u>:
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*The convolution decoder has big problems if the transmission errors do not occur statistically independent, but bundled.  
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*Convolutional coding is a form of channel coding by which the receiver&nbsp; (convolutional decoder)&nbsp; is enabled to detect and possibly correct errors.
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*Task of Interleaver and De&ndash;interleaver is to break up such bundle errors and distribute them over a longer period of time.  
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*The redundancy is not changed by this procedure.  
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*The channel encoder adds (meaningful) redundancy for this purpose,&nbsp; while the speech encoder removes irrelevant redundancy.
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*In the AWGN&ndash;channel, bit errors occur statistically independently, so that interleaver and de&ndash;interleaver can be dispensed with.  
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*Often both components are implemented together or at least closely coordinated.&nbsp; This is then referred to as&nbsp; "joint source and channel coding".
 +
 
 +
 
 +
 
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'''(3)'''&nbsp; Only&nbsp; <u>answer 2</u>&nbsp; is correct:
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*The convolutional decoder has major problems when the transmission errors are clustered rather than they are statistically independent.
 +
 +
*The task of interleaver and de-interleaver is to break up such bunching errors and spread them over a larger time period.
 +
 +
*The redundancy is not changed by this procedure.
 +
 +
*In the AWGN channel,&nbsp; bit errors occur statistically independently,&nbsp; so interleaver and de-interleaver can be omitted.  
  
  
  
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'''(4)'''&nbsp; The answers <u>1 and 4</u> are correct:
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'''(4)'''&nbsp; Correct are the&nbsp; <u>answers 1 and 4</u>:
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*Encryption and decryption &ndash; the counterpart on the receiving side &ndash; serve only to protect user data against unauthorized access.  
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*Encryption and decryption&nbsp; (the counterpart on the receiving side)&nbsp; are used solely to protect user data from unauthorized access.
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*They are not used for error correction and do not add redundancy.  
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*A distinction is made between symmetric and asymmetric encryption. GSM mainly uses the first variant.  
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*They are not used for error correction,&nbsp; nor do they add redundancy.
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*A distinction is made between symmetric and asymmetric encryption.&nbsp; GSM predominantly uses the first variant.
  
  
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[[Category:Exercises for Mobile Communications|^3.2 Similarities between GSM and UMTS
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[[Category:Mobile Communications: Exercises|^3.2 Similarities between GSM and UMTS
 
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Latest revision as of 18:26, 30 January 2023


GSM system components

The diagram shows the entire GSM transmission path,  with the transmitter on the left and the receiver on the right.

The illustration refers only to speech transmission.  In GSM data transmission,  only the top block  $($speech encoder or decoder$)$  is replaced by another channel encoder or decoder  $($concatenation of two channel codes$)$.

The two respective lowest system components were already treated in detail in the exercises for the chapter  "Radio Interface".

In this exercise,  on the other hand,  some basic properties are queried from

  • Speech encoders and speech decoders,
  • convolutional encoder and convolutional decoder,
  • interleaver and de-interleaver,  and
  • encryption and decryption.



Hint:


1

Which statements are true for speech encoding/decoding?

These are source coding components.
They are components of channel coding.
Redundancy is added by the speech encoder.
Redundancy is removed by the speech encoder.

2

Which statements are true for the convolutional encoder or decoder?

They are components of source coding.
They are components of channel coding.
Redundancy is added by the convolutional encoder.
Redundancy is removed by the convolutional encoder.

3

Which statements are true for the interleaver and de-interleaver?

The interleaver adds redundancy.
The interleaver is used to distribute bundle errors.
The interleaver has the most significance for the AWGN channel.

4

Which statements are true for encryption and decryption?

Both serve data security in the sense of data protection.
These components are for error correction.
Encryption adds redundancy.
GSM mostly uses symmetric encryption.


Solution

Solution

(1)  Correct are the  answers 1 and 4:

  • The goal of speech coding is data compression and thus redundancy reduction.
  • This is a typical task of source coding.


(2)  Correct are the  answers 2 and 3:

  • Convolutional coding is a form of channel coding by which the receiver  (convolutional decoder)  is enabled to detect and possibly correct errors.
  • The channel encoder adds (meaningful) redundancy for this purpose,  while the speech encoder removes irrelevant redundancy.
  • Often both components are implemented together or at least closely coordinated.  This is then referred to as  "joint source and channel coding".


(3)  Only  answer 2  is correct:

  • The convolutional decoder has major problems when the transmission errors are clustered rather than they are statistically independent.
  • The task of interleaver and de-interleaver is to break up such bunching errors and spread them over a larger time period.
  • The redundancy is not changed by this procedure.
  • In the AWGN channel,  bit errors occur statistically independently,  so interleaver and de-interleaver can be omitted.


(4)  Correct are the  answers 1 and 4:

  • Encryption and decryption  (the counterpart on the receiving side)  are used solely to protect user data from unauthorized access.
  • They are not used for error correction,  nor do they add redundancy.
  • A distinction is made between symmetric and asymmetric encryption.  GSM predominantly uses the first variant.


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