Examples of Communication Systems/Entire GSM Transmission System - Revision history

Guenter at 14:10, 20 February 2023

2023-02-20T14:10:45Z

Guenter at 14:09, 20 February 2023

2023-02-20T14:09:09Z

Hwang at 19:53, 6 February 2023

2023-02-06T19:53:58Z

Hwang at 19:52, 6 February 2023

2023-02-06T19:52:32Z

Hwang at 19:51, 6 February 2023

2023-02-06T19:51:23Z

Hwang at 19:50, 6 February 2023

2023-02-06T19:50:23Z

Hwang at 19:48, 6 February 2023

2023-02-06T19:48:13Z

Hwang at 19:47, 6 February 2023

2023-02-06T19:47:27Z

Hwang at 19:40, 6 February 2023

2023-02-06T19:40:07Z

Hwang at 19:36, 6 February 2023

2023-02-06T19:36:14Z

@@ Line 123: / Line 123: @@
 Regarding the last two blocks in the graph,&nbsp; it should be noted:
-[[File:EN_Bei_T_3_4_S6_v4.png|right|frame|Receiver-side data processing for GSM '''KORREKTUR: synthesized''' <br><br><br><br><br>]]
+[[File:EN_Bei_T_3_4_S6_neu.png|right|frame|Receiver-side data processing for GSM<br><br><br><br><br>]]
 *The decoding method is not prescribed by the GSM specification, but is left to the individual network operators. The performance depends on the error correction algorithm used.

← Older revision		Revision as of 14:09, 20 February 2023
Line 79:		Line 79:


−	[[File:~~EN_Bei_T_3_4_S3~~.png\|right\|frame\|Interleaving in GSM speech signals ~~'''KORREKTUR: odd bits from'''~~]]	+	[[File:EN_Bei_T_3_4_S3_v2.png\|right\|frame\|Interleaving in GSM speech signals]]

	For a speech channel,  the interleaver works in the following way:		For a speech channel,  the interleaver works in the following way:

@@ Line 123: / Line 123: @@
 Regarding the last two blocks in the graph,&nbsp; it should be noted:
-[[File:EN_Bei_T_3_4_S6_v4.png|right|frame|Receiver-side data processing for GSM <br><br><br><br><br>]]
+[[File:EN_Bei_T_3_4_S6_v4.png|right|frame|Receiver-side data processing for GSM '''KORREKTUR: synthesized''' <br><br><br><br><br>]]
 *The decoding method is not prescribed by the GSM specification, but is left to the individual network operators. The performance depends on the error correction algorithm used.

@@ Line 114: / Line 114: @@
 #These&nbsp; $244$&nbsp; bits are doubled to&nbsp; $488$&nbsp; bits by a convolutional encoder of rate&nbsp; $1/2$&nbsp; as in speech channels.&nbsp; Two encoded symbols are generated per incoming bit,&nbsp; e.g. according to the generator polynomials&nbsp; $G_0(D) = 1 + D^3 + D^4$&nbsp; $($red marks in the second graph$)$&nbsp; and&nbsp; $G_1(D) = 1 + D + D^3 + D^4$.<br><br>
 #The following interleaver expects as output&nbsp; &ndash; just like a&nbsp; "speech interleaver" &ndash; only&nbsp; $456$&nbsp; bits per frame.&nbsp; Therefore,&nbsp; from the&nbsp; $488$&nbsp; bits at the output of the convolutional encoder still&nbsp; $32$&nbsp; bits at the positions&nbsp; $15 \cdot j \cdot 4 \ \ ( j = 1$, ... ,&nbsp; $32)$&nbsp; are removed&nbsp; $($"puncturing"$)$.<br><br>
-#Since data transmission is less time-critical than speech transmission,&nbsp; a higher interleaving degree is chosen here.&nbsp; The&nbsp; $456$&nbsp; bits are distributed over up to&nbsp; $24$&nbsp; interleaver blocks&nbsp; of&nbsp; $19$&nbsp; bits each,&nbsp; which would not be possible for vspeech services for reasons of real-time transmission.<br><br>
+#Since data transmission is less time-critical than speech transmission,&nbsp; a higher interleaving degree is chosen here.&nbsp; The&nbsp; $456$&nbsp; bits are distributed over up to&nbsp; $24$&nbsp; interleaver blocks&nbsp; of&nbsp; $19$&nbsp; bits each,&nbsp; which would not be possible for speech services for reasons of real-time transmission.<br><br>
 #Then the&nbsp; $456$&nbsp; bits are split into four consecutive&nbsp; "normal bursts"&nbsp; and sent.&nbsp; When packing in the bursts,&nbsp; groupings of even and odd bits are again formed,&nbsp; similar to interleaving in the speech channel.

@@ Line 112: / Line 112: @@
 #The data bit rate of &nbsp; $9.6\ \rm kbit/s$ &nbsp; is first increased in the&nbsp; "Terminal Equipment"&nbsp; of the mobile station through non-GSM specific channel encoding  by&nbsp; $25\%$&nbsp; to &nbsp; $12\ \rm kbit/s$ &nbsp; to allow error detection in circuit-switched networks.<br><br>
 #In data transmission,&nbsp;  all bits are equivalent,&nbsp; so unlike speech channel coding, there are no classes.&nbsp; The&nbsp; $240$&nbsp; bits&nbsp; per&nbsp; $20 \rm ms$ time frame are combined together with four tailbits&nbsp; "$0000$"&nbsp; to form a single data frame.<br><br>
-#These&nbsp; $244$&nbsp; bits are doubled to&nbsp; $488$&nbsp; bits by a convolutional encoder of rate&nbsp; $1/2$&nbsp; as in speech channels.&nbsp; Two encoded symbols are generated per incoming bit,&nbsp; e.g. according to the generator polynomials&nbsp; $G_0(D) = 1 + D^3 + D^4$&nbsp; $($red marks in th second graph$)$&nbsp; and&nbsp; $G_1(D) = 1 + D + D^3 + D^4$.<br><br>
+#These&nbsp; $244$&nbsp; bits are doubled to&nbsp; $488$&nbsp; bits by a convolutional encoder of rate&nbsp; $1/2$&nbsp; as in speech channels.&nbsp; Two encoded symbols are generated per incoming bit,&nbsp; e.g. according to the generator polynomials&nbsp; $G_0(D) = 1 + D^3 + D^4$&nbsp; $($red marks in the second graph$)$&nbsp; and&nbsp; $G_1(D) = 1 + D + D^3 + D^4$.<br><br>
 #The following interleaver expects as output&nbsp; &ndash; just like a&nbsp; "speech interleaver" &ndash; only&nbsp; $456$&nbsp; bits per frame.&nbsp; Therefore,&nbsp; from the&nbsp; $488$&nbsp; bits at the output of the convolutional encoder still&nbsp; $32$&nbsp; bits at the positions&nbsp; $15 \cdot j \cdot 4 \ \ ( j = 1$, ... ,&nbsp; $32)$&nbsp; are removed&nbsp; $($"puncturing"$)$.<br><br>
 #Since data transmission is less time-critical than speech transmission,&nbsp; a higher interleaving degree is chosen here.&nbsp; The&nbsp; $456$&nbsp; bits are distributed over up to&nbsp; $24$&nbsp; interleaver blocks&nbsp; of&nbsp; $19$&nbsp; bits each,&nbsp; which would not be possible for vspeech services for reasons of real-time transmission.<br><br>

← Older revision		Revision as of 19:50, 6 February 2023
Line 79:		Line 79:


−	[[File:EN_Bei_T_3_4_S3.png\|right\|frame\|Interleaving in GSM speech signals]]	+	[[File:EN_Bei_T_3_4_S3.png\|right\|frame\|Interleaving in GSM speech signals '''KORREKTUR: odd bits from''']]

	For a speech channel,  the interleaver works in the following way:		For a speech channel,  the interleaver works in the following way:

@@ Line 49: / Line 49: @@
 Uncoded radio data transmission leads to bit error rates in the percentage range.&nbsp; However,&nbsp; with&nbsp; [[Channel_Coding|$\text{channel coding}$]]&nbsp; some transmission errors can be detected or even corrected at the receiver.&nbsp; The bit error rate can thus be reduced to values smaller than&nbsp; $10^{-5}$.
-First,&nbsp; we consider GSM channel encoding for speech channels,&nbsp; assuming as speech encoder the&nbsp; [[Examples_of_Communication_Systems/Voice_Coding#GSM_Fullrate_Vocoder|$\text{Full Rate Codec}$]].&nbsp;  The channel coding of a speech frame of&nbsp; $20\ \rm ms$&nbsp; duration is done in four consecutive steps according to the diagram.
+First,&nbsp; we consider GSM channel encoding for speech channels,&nbsp; assuming as speech encoder the&nbsp; [[Examples_of_Communication_Systems/Speech_Coding#GSM_Full_Rate_Vocoder|$\text{Full Rate Codec}$]].&nbsp;  The channel coding of a speech frame of&nbsp; $20\ \rm ms$&nbsp; duration is done in four consecutive steps according to the diagram.
 From the description in chapter&nbsp; [[Examples_of_Communication_Systems/Voice_Coding|"Speech Coding"]]&nbsp; it can be seen that not all&nbsp; $260$&nbsp; bits have the same influence on the subjectively perceived speech quality.

← Older revision		Revision as of 19:47, 6 February 2023
Line 39:		Line 39:
	These are transmitted within a time slot of duration  $T_{\rm Z} = T_{\rm burst}$  by means of the  modulation method  "GMSK".  This results in the gross data rate  $270.833 \ \rm kbit/s$.		These are transmitted within a time slot of duration  $T_{\rm Z} = T_{\rm burst}$  by means of the  modulation method  "GMSK".  This results in the gross data rate  $270.833 \ \rm kbit/s$.

−	At receiver side there are in reverse order the blocks  "demodulation" – "burst de-composition" – "de-cryption" – "de-interleaving" – "channel decoding" – "speech decoding".	+	At the receiver side there are in reverse order the blocks  "demodulation" – "burst de-composition" – "de-cryption" – "de-interleaving" – "channel decoding" – "speech decoding".

@@ Line 9: / Line 9: @@
 ==Speech and data transmission components==
 <br>
-On the right you can see the block diagram of the GSM transmission system at the transmitting end,&nbsp; which
+On the right you can see the block diagram of the GSM transmission system at the transmitting end,&nbsp; which is
 *suitable for both digitized speech signals &nbsp;$($sampling rate:&nbsp; $8 \ \rm kHz$,&nbsp; quantization:&nbsp; $13$ bit &nbsp; ⇒ &nbsp; data rate:&nbsp; $104 \ \rm kbit/s)$

@@ Line 20: / Line 20: @@
 #Speech signals are compressed by speech coding by factor&nbsp; $8$ &nbsp; &rArr; &nbsp; from&nbsp; $104 \ \rm kbit/s$&nbsp; to&nbsp; $13 \ \rm kbit/s$.&nbsp; The bit rate given in the graph is for the full rate codec,&nbsp; which delivers  exactly&nbsp; $260$&nbsp; bits per speech frame&nbsp; $($duration&nbsp; $T_{\rm R} = 20\ \rm ms)$&nbsp;.
-#The&nbsp; '''AMR codec'''&nbsp; delivers in highest mode&nbsp; $R_{\rm B}=12.2 \ \rm kbit/s$ &nbsp; &rArr; &nbsp; $244$&nbsp; bits per speech frame.&nbsp; However,&nbsp; the speech codec must also transmit additional information regarding the mode &nbsp; &rArr; &nbsp; so the data rate before channel coding is&nbsp; $13 \ \rm kbit/s$&nbsp;.
+#The&nbsp; &raquo;'''AMR codec'''&laquo;&nbsp; delivers in highest mode&nbsp; $R_{\rm B}=12.2 \ \rm kbit/s$ &nbsp; &rArr; &nbsp; $244$&nbsp; bits per speech frame.&nbsp; However,&nbsp; the speech codec must also transmit additional information regarding the mode &nbsp; &rArr; &nbsp; so the data rate before channel coding is&nbsp; $13 \ \rm kbit/s$&nbsp;.
-#Task of the dashed&nbsp; '''Voice Activity Detection'''&nbsp; is to decide whether the current speech frame actually contains a speech signal or just a  pause during which the power of the transmit amplifier should be turned down.
+#Task of the dashed&nbsp; &raquo;'''Voice Activity Detection'''&laquo;&nbsp; is to decide whether the current speech frame actually contains a speech signal or just a  pause during which the power of the transmit amplifier should be turned down.
-#By&nbsp; '''channel coding'''&nbsp; redundancy is added again to allow error correction at the receiver &nbsp; &rArr; &nbsp;   the channel encoder&nbsp; outputs&nbsp; $456$&nbsp; bits per frame,&nbsp; resulting in the data rate&nbsp; $22.8 \ \rm kbit/s$&nbsp;. The more important bits are specially protected.
+#By&nbsp; &raquo;'''channel coding'''&laquo;&nbsp; redundancy is added again to allow error correction at the receiver &nbsp; &rArr; &nbsp;   the channel encoder&nbsp; outputs&nbsp; $456$&nbsp; bits per frame,&nbsp; resulting in the data rate&nbsp; $22.8 \ \rm kbit/s$&nbsp;. The more important bits are specially protected.
-#The&nbsp; '''interleaver'''&nbsp; scrambles the resulting bit sequence to reduce burst error influence.&nbsp; The&nbsp; $456$&nbsp; input bits are split into four time frames of&nbsp; $114$&nbsp; bits each.&nbsp; Thus,&nbsp; two consecutive bits are always transmitted in two different bursts.
+#The&nbsp; &raquo;'''interleaver'''&laquo;&nbsp; scrambles the resulting bit sequence to reduce burst error influence.&nbsp; The&nbsp; $456$&nbsp; input bits are split into four time frames of&nbsp; $114$&nbsp; bits each.&nbsp; Thus,&nbsp; two consecutive bits are always transmitted in two different bursts.
-#A&nbsp; '''data channel'''&nbsp; &ndash; marked in red in the figure &ndash; differs from a speech channel&nbsp; $($marked in blue$)$&nbsp; only by the different input rate&nbsp; $(9.6 \ \rm kbit/s$&nbsp; instead of&nbsp; $104 \ \rm kbit/s)$&nbsp; and the use of a second,&nbsp; outer channel encoder instead of the speech encoder.
+#A&nbsp; &raquo;'''data channel'''&laquo;&nbsp; &ndash; marked in red in the figure &ndash; differs from a speech channel&nbsp; $($marked in blue$)$&nbsp; only by the different input rate&nbsp; $(9.6 \ \rm kbit/s$&nbsp; instead of&nbsp; $104 \ \rm kbit/s)$&nbsp; and the use of a second,&nbsp; outer channel encoder instead of the speech encoder.
 The components highlighted in green apply equally to speech and data transmission.
-&rArr; &nbsp; The first common system component for speech and data transmission in the block diagram of the GSM transmitter is the&nbsp; '''&raquo;encryption&laquo;''',&nbsp; which is intended to prevent unauthorized persons from gaining access to the data.&nbsp; There are two fundamentally different encryption methods:
+&rArr; &nbsp; The first common system component for speech and data transmission in the block diagram of the GSM transmitter is the&nbsp; &raquo;'''encryption'''&laquo;,&nbsp; which is intended to prevent unauthorized persons from gaining access to the data.&nbsp; There are two fundamentally different encryption methods:
-*'''&raquo;Symmetric encryption&laquo;''':&nbsp; This knows only one secret key,&nbsp; which is used both for encrypting and enciphering the messages in the transmitter and for decrypting and deciphering them in the receiver.&nbsp; The key must be generated prior to communication and exchanged between the communication partners via a secure channel.&nbsp; The advantage of this encryption method used in conventional GSM is that it works very quickly.
+*&raquo;'''Symmetric encryption'''&laquo;:&nbsp; This knows only one secret key,&nbsp; which is used both for encrypting and enciphering the messages in the transmitter and for decrypting and deciphering them in the receiver.&nbsp; The key must be generated prior to communication and exchanged between the communication partners via a secure channel.&nbsp; The advantage of this encryption method used in conventional GSM is that it works very quickly.
-*'''&raquo;Asymmetric encryption&laquo;''':&nbsp; This method uses two independent but matching asymmetric keys.&nbsp; It is not possible to use one key to calculate the other.&nbsp; The&nbsp; "public key"&nbsp; is publicly available and is used for encryption.&nbsp; The&nbsp; "private key"&nbsp; is secret and used for decryption.&nbsp; In contrast to the symmetric encryption methods,&nbsp; the asymmetric methods are much slower,&nbsp; but also offer higher security.
+*&raquo;'''Asymmetric encryption'''&laquo;:&nbsp; This method uses two independent but matching asymmetric keys.&nbsp; It is not possible to use one key to calculate the other.&nbsp; The&nbsp; "public key"&nbsp; is publicly available and is used for encryption.&nbsp; The&nbsp; "private key"&nbsp; is secret and used for decryption.&nbsp; In contrast to the symmetric encryption methods,&nbsp; the asymmetric methods are much slower,&nbsp; but also offer higher security.
-&rArr; &nbsp; The second green block is the&nbsp; '''&raquo;burst composition&laquo;''',&nbsp; where there are different burst types.&nbsp; In a&nbsp; "normal burst"&nbsp; the&nbsp; $114$&nbsp; encoded,&nbsp; scrambled and encrypted bits are mapped to&nbsp; $156.25$&nbsp; bits by&nbsp; $($duration&nbsp; $T_{\rm burst} = 576.9 \ \rm &micro; s)$&nbsp; adding the&nbsp; "guard period",&nbsp; signaling bits,&nbsp; etc.
+&rArr; &nbsp; The second green block is the&nbsp; &raquo;'''burst composition'''&laquo;,&nbsp; where there are different burst types.&nbsp; In a&nbsp; "normal burst"&nbsp; the&nbsp; $114$&nbsp; encoded,&nbsp; scrambled and encrypted bits are mapped to&nbsp; $156.25$&nbsp; bits by&nbsp; $($duration&nbsp; $T_{\rm burst} = 576.9 \ \rm &micro; s)$&nbsp; adding the&nbsp; "guard period",&nbsp; signaling bits,&nbsp; etc.
 These are transmitted within a time slot of duration&nbsp; $T_{\rm Z} = T_{\rm burst}$&nbsp; by means of the&nbsp; modulation method&nbsp; "GMSK".&nbsp; This results in the gross data rate&nbsp; $270.833 \ \rm kbit/s$.
@@ Line 47: / Line 47: @@
 ==Encoding for speech signals==
 <br>
-Uncoded radio data transmission leads to bit error rates in the percentage range.&nbsp; However,&nbsp; with&nbsp; [[Channel_Coding|Channel Coding]]&nbsp; some transmission errors can be detected or even corrected at the receiver.&nbsp; The bit error rate can thus be reduced to values smaller than&nbsp; $10^{-5}$.
+Uncoded radio data transmission leads to bit error rates in the percentage range.&nbsp; However,&nbsp; with&nbsp; [[Channel_Coding|$\text{channel coding}$]]&nbsp; some transmission errors can be detected or even corrected at the receiver.&nbsp; The bit error rate can thus be reduced to values smaller than&nbsp; $10^{-5}$.
-First,&nbsp; we consider GSM channel encoding for speech channels,&nbsp; assuming as speech encoder the&nbsp; [[Examples_of_Communication_Systems/Voice_Coding#GSM_Fullrate_Vocoder|"Full Rate Codec"]].&nbsp;  The channel coding of a speech frame of&nbsp; $20\ \rm ms$&nbsp; duration is done in four consecutive steps according to the diagram.
+First,&nbsp; we consider GSM channel encoding for speech channels,&nbsp; assuming as speech encoder the&nbsp; [[Examples_of_Communication_Systems/Voice_Coding#GSM_Fullrate_Vocoder|$\text{Full Rate Codec}$]].&nbsp;  The channel coding of a speech frame of&nbsp; $20\ \rm ms$&nbsp; duration is done in four consecutive steps according to the diagram.
 From the description in chapter&nbsp; [[Examples_of_Communication_Systems/Voice_Coding|"Speech Coding"]]&nbsp; it can be seen that not all&nbsp; $260$&nbsp; bits have the same influence on the subjectively perceived speech quality.
@@ Line 56: / Line 56: @@
 *Therefore,&nbsp; the data are divided into classes according to their importance: &nbsp; The&nbsp; $50$&nbsp; most important bits form the&nbsp; "Class 1a",&nbsp; other&nbsp; $132$&nbsp; are assigned to&nbsp; "Class 1b"&nbsp; and the remaining&nbsp; $78$&nbsp; bits result in the less important&nbsp; "Class 2".
-*In the next step,&nbsp; a three-bit long&nbsp; [[Examples_of_Communication_Systems/Methods_to_Reduce_the_Bit_Error_Rate_in_DSL#Cyclic_Redundancy_Check|"Cyclic Redundancy Check"]]&nbsp; $\rm (CRC)$&nbsp; checksum is calculated for the&nbsp; $50$&nbsp;  class 1a bits using a feedback shift register.&nbsp; The generator polynomial for this CRC check is:
+*In the next step,&nbsp; a three-bit long&nbsp; [[Examples_of_Communication_Systems/Methods_to_Reduce_the_Bit_Error_Rate_in_DSL#Cyclic_Redundancy_Check|$\text{Cyclic Redundancy Check}$]]&nbsp; $\rm (CRC)$&nbsp; checksum is calculated for the&nbsp; $50$&nbsp;  class 1a bits using a feedback shift register.&nbsp; The generator polynomial for this CRC check is:
 :$$G_{\rm CRC}(D) = D^3 + D +1\hspace{0.05cm}. $$
@@ Line 98: / Line 98: @@
 <br>
 For GSM data transmission,&nbsp; each subscriber only has a net data rate of&nbsp; $9.6\ \rm kbit/s$&nbsp; available.&nbsp; Two methods are used for error protection:
-*'''&raquo;Forward Error Correction&laquo;'''&nbsp; $\rm (FEC)$&nbsp; is implemented at the physical layer by applying convolutional codes.
+*&raquo;'''Forward Error Correction'''&laquo;&nbsp; $\rm (FEC)$&nbsp; is implemented at the physical layer by applying convolutional codes.
-*'''&raquo;Automatic Repeat Request&laquo;'''&nbsp; $\rm (ARQ)$&nbsp; where defective packets that cannot be corrected are re-requested at the link layer.
+*&raquo;'''Automatic Repeat Request'''&laquo;&nbsp; $\rm (ARQ)$&nbsp; where defective packets that cannot be corrected are re-requested at the link layer.
@@ Line 138: / Line 138: @@
-== Exercises for the chapter==
+== Exercise for the chapter==
 <br>
 [[Aufgaben:Exercise_3.7:_GSM_System_Components|Exercise 3.7: GSM System Components]]