Modulation Methods/OFDM for 4G Networks - Revision history

Guenter at 13:43, 30 January 2023

2023-01-30T13:43:08Z

Guenter at 16:35, 23 January 2023

2023-01-23T16:35:02Z

Hwang at 11:50, 19 January 2023

2023-01-19T11:50:42Z

Hwang at 11:43, 19 January 2023

2023-01-19T11:43:23Z

Hwang at 11:43, 19 January 2023

2023-01-19T11:43:05Z

Hwang at 11:37, 19 January 2023

2023-01-19T11:37:28Z

Reed at 14:02, 9 April 2022

2022-04-09T14:02:15Z

Guenter at 14:57, 31 January 2022

2022-01-31T14:57:25Z

Guenter at 12:58, 20 January 2022

2022-01-20T12:58:18Z

Guenter at 12:55, 20 January 2022

2022-01-20T12:55:41Z

@@ Line 35: / Line 35: @@
 *and&nbsp; "frequency-dependent attenuation"&nbsp; (&nbsp; "frequency selective fading").
 <br clear=all>
-[[File:EN_Mod_T_5_7_S2_2neu.png |left|frame| Description of time-dependent and frequency-dependent attenuation '''KORREKTUR: arises''']]
+[[File:EN_Mod_T_5_7_S2_2neu.png |left|frame| Description of time-dependent and frequency-dependent attenuation]
 <br><br>The table on the left shows the respective descriptive quantities.&nbsp;  Please note: &nbsp;

@@ Line 35: / Line 35: @@
 *and&nbsp; "frequency-dependent attenuation"&nbsp; (&nbsp; "frequency selective fading").
 <br clear=all>
-[[File:Mod_T_5_7_S2_2neu2.png |left|frame| Description of time-dependent and frequency-dependent attenuation '''KORREKTUR: arises''']]
+[[File:EN_Mod_T_5_7_S2_2neu.png |left|frame| Description of time-dependent and frequency-dependent attenuation '''KORREKTUR: arises''']]
 <br><br>The table on the left shows the respective descriptive quantities.&nbsp;  Please note: &nbsp;

@@ Line 35: / Line 35: @@
 *and&nbsp; "frequency-dependent attenuation"&nbsp; (&nbsp; "frequency selective fading").
 <br clear=all>
-[[File:Mod_T_5_7_S2_2neu2.png |left|frame| Description of time-dependent and frequency-dependent attenuation]]
+[[File:Mod_T_5_7_S2_2neu2.png |left|frame| Description of time-dependent and frequency-dependent attenuation '''KORREKTUR: arises''']]
 <br><br>The table on the left shows the respective descriptive quantities.&nbsp;  Please note: &nbsp;

@@ Line 10: / Line 10: @@
 *$\rm TDMA/FDMA$, see &nbsp;[[Examples_of_Communication_Systems/Allgemeine_Beschreibung_von_GSM|$\rm GSM$]]&nbsp; ("Global System for Mobile Communications"),&nbsp; and
 *$\rm CDMA$, see &nbsp;[[Examples_of_Communication_Systems/Allgemeine_Beschreibung_von_UMTS|$\rm UMTS$]]&nbsp; ("Universal Mobile Telecommunications System").
 *Another name often used synonymously with&nbsp; "4G"&nbsp; is &nbsp;[[Mobile_Communications/General_Information_on_the_LTE_Mobile_Communications_Standard|$\rm LTE$]]&nbsp; ("Long Term Evolution").&nbsp; Like &nbsp;[https://en.wikipedia.org/wiki/WiMAX $\text{WiMAX}$]&nbsp; ("Worldwide Interoperability for Microwave Access"),&nbsp; LTE uses &nbsp;[https://www.techtarget.com/searchnetworking/definition/orthogonal-frequency-division-multiple-access-OFDMA &nbsp;$\rm OFDMA$]&nbsp; ("Orthogonal Frequency Division Multiple Access")&nbsp; as its multiple access method.

@@ Line 9: / Line 9: @@
 As a first example,&nbsp; let's now take a look at the fourth-generation&nbsp; $\rm (4G)$&nbsp; mobile communications networks,&nbsp; which are the successors to the earlier mobile communications networks based on
 *$\rm TDMA/FDMA$, see &nbsp;[[Examples_of_Communication_Systems/Allgemeine_Beschreibung_von_GSM|$\rm GSM$]]&nbsp; ("Global System for Mobile Communications"),&nbsp; and
-*$\rm CDMA$, see &nbsp;[[Examples_of_Communication_Systems/Allgemeine_Beschreibung_von_UMTS|$\rm UMTS$]]&nbsp; ("Universal Mobile Telecommunications System")
+*$\rm CDMA$, see &nbsp;[[Examples_of_Communication_Systems/Allgemeine_Beschreibung_von_UMTS|$\rm UMTS$]]&nbsp; ("Universal Mobile Telecommunications System").
 *Another name often used synonymously with&nbsp; "4G"&nbsp; is &nbsp;[[Mobile_Communications/General_Information_on_the_LTE_Mobile_Communications_Standard|$\rm LTE$]]&nbsp; ("Long Term Evolution").&nbsp; Like &nbsp;[https://en.wikipedia.org/wiki/WiMAX $\text{WiMAX}$]&nbsp; ("Worldwide Interoperability for Microwave Access"),&nbsp; LTE uses &nbsp;[https://www.techtarget.com/searchnetworking/definition/orthogonal-frequency-division-multiple-access-OFDMA &nbsp;$\rm OFDMA$]&nbsp; ("Orthogonal Frequency Division Multiple Access")&nbsp; as its multiple access method.

@@ Line 14: / Line 14: @@
 have replaced them.
-*Another name often used synonymously with&nbsp; "4G"&nbsp; is &nbsp;[[Mobile_Communications/General_Information_on_the_LTE_Mobile_Communications_Standard|$\rm LTE$]]&nbsp; ("Long Term Evolution").&nbsp; Like &nbsp;[https://en.wikipedia.org/wiki/WiMAX WiMAX]&nbsp; ("Worldwide Interoperability for Microwave Access"),&nbsp; LTE uses &nbsp;[https://www.techtarget.com/searchnetworking/definition/orthogonal-frequency-division-multiple-access-OFDMA &nbsp;$\rm OFDMA$]&nbsp; ("Orthogonal Frequency Division Multiple Access")&nbsp; as its multiple access method.
+*Another name often used synonymously with&nbsp; "4G"&nbsp; is &nbsp;[[Mobile_Communications/General_Information_on_the_LTE_Mobile_Communications_Standard|$\rm LTE$]]&nbsp; ("Long Term Evolution").&nbsp; Like &nbsp;[https://en.wikipedia.org/wiki/WiMAX $\text{WiMAX}$]&nbsp; ("Worldwide Interoperability for Microwave Access"),&nbsp; LTE uses &nbsp;[https://www.techtarget.com/searchnetworking/definition/orthogonal-frequency-division-multiple-access-OFDMA &nbsp;$\rm OFDMA$]&nbsp; ("Orthogonal Frequency Division Multiple Access")&nbsp; as its multiple access method.
 *The main difference between a pure&nbsp; "$\rm  multiplexing \; method$"&nbsp;  $($TDM,&nbsp; FDM,&nbsp; CDM,&nbsp; OFDM$)$&nbsp; and a&nbsp; "$\rm multiple \; access \; method$"&nbsp;  $($TDMA,&nbsp; FDMA,&nbsp; CDMA,&nbsp; OFDMA$)$&nbsp; is the user separation realized by resource allocation.&nbsp;  In the case of OFDMA,&nbsp; this means that not only time slots&nbsp; (TDMA)&nbsp; or spreading codes&nbsp; (CDMA)&nbsp; are allocated to the individual subscribers,&nbsp; but also different and&nbsp; "preferably"&nbsp; orthogonal subcarriers.
-*The realization of a suitable allocation mechanism is a non-trivial problem which can only be dealt with very superficially here.&nbsp; It makes sense that a method is not limited to only one&nbsp; (physical)&nbsp; layer,&nbsp; but works across layers.&nbsp; The term&nbsp; "layer"&nbsp; is to be understood here in the sense of the&nbsp; [https://en.wikipedia.org/wiki/OSI_model OSI reference model].&nbsp;
+*The realization of a suitable allocation mechanism is a non-trivial problem which can only be dealt with very superficially here.&nbsp; It makes sense that a method is not limited to only one&nbsp; (physical)&nbsp; layer,&nbsp; but works across layers.&nbsp; The term&nbsp; "layer"&nbsp; is to be understood here in the sense of the&nbsp; [https://en.wikipedia.org/wiki/OSI_model $\text{OSI reference model}$].&nbsp;
-*This is also necessitated by the changing requirements of a mobile communications network.&nbsp; Whereas&nbsp; '''connection-oriented'''&nbsp; services such as voice telephony were in the foreground at the beginning of mobile communications,&nbsp; today&nbsp; '''packet-oriented'''&nbsp; applications such as&nbsp; "Voice over IP" (VoIP),&nbsp; "video telephony"&nbsp; or&nbsp; "mobile data services"&nbsp; represent the main traffic load and are the cause of the increased demand on the available data rates.
+*This is also necessitated by the changing requirements of a mobile communications network.&nbsp; Whereas&nbsp; &raquo;'''connection-oriented'''&laquo;&nbsp; services such as voice telephony were in the foreground at the beginning of mobile communications,&nbsp; today&nbsp; &raquo;'''packet-oriented'''&laquo;&nbsp; applications such as&nbsp; "Voice over IP" (VoIP),&nbsp; "video telephony"&nbsp; or&nbsp; "mobile data services"&nbsp; represent the main traffic load and are the cause of the increased demand on the available data rates.
 ==Some characteristics of mobile radio systems==
 <br>
-First of all,&nbsp; the special features of the mobile radio channel will be discussed very briefly.&nbsp; The figure shows a typical mobile radio scenario.&nbsp; More detailed information on this subject can be found in the book &nbsp;[[Mobile_Communications/Distance_Dependent_Attenuation_and_Shading|Mobile Communications]].
+First of all,&nbsp; the special features of the mobile radio channel will be discussed very briefly.&nbsp; The figure shows a typical mobile radio scenario.&nbsp; More detailed information on this subject can be found in the book &nbsp;[[Mobile_Communications/Distance_Dependent_Attenuation_and_Shading|"Mobile Communications"]].
 [[File:EN_Mob_T1_1_S1.png |right|frame| Characteristics of the mobile communications channel]]
@@ Line 42: / Line 42: @@
 *The coherence bandwidth &nbsp;$f_{\rm coh}$&nbsp; is not the reciprocal of the coherence time &nbsp;$T_{\rm coh}$,&nbsp; although one might assume this due to comparable naming.
-* $f_{\rm coh}$&nbsp; is a parameter for the frequency-dependent attenuation and results as the reciprocal of the &nbsp;[https://en.wikipedia.org/wiki/Delay_spread delay spread].
+* $f_{\rm coh}$&nbsp; is a parameter for the frequency-dependent attenuation and results as the reciprocal of the &nbsp;[https://en.wikipedia.org/wiki/Delay_spread $\text{delay spread}$].
-* $T_{\rm coh}$&nbsp; on the other hand,&nbsp; describes the time-dependent attenuation and is the reciprocal of the &nbsp;[https://en.wikipedia.org/wiki/Fading Doppler spread].
+* $T_{\rm coh}$&nbsp; on the other hand,&nbsp; describes the time-dependent attenuation and is the reciprocal of the &nbsp;[https://en.wikipedia.org/wiki/Fading $\text{Doppler spread}$].
 <br clear=all>
 ==Determination of some OFDM parameters==
@@ Line 89: / Line 89: @@
-The aim of a suitable&nbsp; '''scheduling procedure'''&nbsp; is now,
+The aim of a suitable&nbsp; &raquo;'''scheduling procedure'''&laquo;&nbsp; is now,
 *transmit only when the channel is good,&nbsp; and
 *to serve other subscribers during the dips in attenuation.
-The gain in system throughput that can be achieved in this way is often referred to as&nbsp; [https://en.wikipedia.org/wiki/Diversity_scheme "multi-user diversity gain"].&nbsp;
+The gain in system throughput that can be achieved in this way is often referred to as&nbsp; [https://en.wikipedia.org/wiki/Diversity_scheme $\text{multi-user diversity gain}$].&nbsp;
 The diagram on the right shows the procedure.&nbsp; The blue line represents the desired &nbsp;"riding on the peaks"&nbsp; for the case of eight participants&nbsp; (eight fading processes).&nbsp;

@@ Line 2: / Line 2: @@
 {{Header
 |Untermenü=Multiple Access Methods
-|Vorherige Seite=Realisierung von OFDM-Systemen
+|Vorherige Seite=Implementation of OFDM Systems
-|Nächste Seite=Weitere OFDM–Anwendungen
+|Nächste Seite=Further OFDM Applications
 }}
 ==Multiplexing vs. multiple access methods==

@@ Line 37: / Line 37: @@
 *and&nbsp; "frequency-dependent attenuation"&nbsp; (&nbsp; "frequency selective fading").
 <br clear=all>
-[[File:Mod_T_5_7_S2_2neu.png |left|frame| Description of time-dependent and frequency-dependent attenuation]]
+[[File:Mod_T_5_7_S2_2neu2.png |left|frame| Description of time-dependent and frequency-dependent attenuation]]
 <br><br>The table on the left shows the respective descriptive quantities.&nbsp;  Please note: &nbsp;
@@ Line 82: / Line 82: @@
 [[File: P_ID1652__Mod_T_5_7_S4a_ganz_neu.png |right|frame| Multi-user diversity gain from [Vie17]<ref>Viering, I.:&nbsp; System Aspects in Communications.&nbsp; Lecture manuscript, Lehrstuhl für Nachrichtentechnik, TU München, 2017.</ref>. &nbsp; &nbsp; <br>We thank Ingo Viering for permission to use the diagram.]]
-[[File:P_ID1653__Mod_T_5_7_S5_neu.png |right|frame| Cross-layer scheduler '''KORREKTUR''': higher layers ...]]
+[[File:EN_Mod_T_5_7_S5.png |right|frame| Cross-layer scheduler]]
 *In principle,&nbsp; it can be said that the robustness decreases with increasing &nbsp;${\rm log_2}(M)$,&nbsp; since this reduces the spacing of the possible signal space points.

@@ Line 94: / Line 94: @@
-The gain in system throughput that can be achieved in this way is often referred to as &nbsp; [https://en.wikipedia.org/wiki/Diversity_scheme "multi-user diversity gain"].&nbsp;
+The gain in system throughput that can be achieved in this way is often referred to as&nbsp; [https://en.wikipedia.org/wiki/Diversity_scheme "multi-user diversity gain"].&nbsp;
 The diagram on the right shows the procedure.&nbsp; The blue line represents the desired &nbsp;"riding on the peaks"&nbsp; for the case of eight participants&nbsp; (eight fading processes).&nbsp;
@@ Line 100: / Line 100: @@
 <br>When implementing a channel-adaptive scheduler,&nbsp; however,&nbsp; information from higher layers should also be included,&nbsp; since long waiting times &nbsp; (large delays)&nbsp; must be avoided depending on the &nbsp;"Quality of Service"&nbsp; $\rm (QoS)$&nbsp; requirements and traffic type.&nbsp; The diagram on the right shows a schematic representation of such a &nbsp; "cross–layer approach".&nbsp;
 *The scheduler is located in the MAC layer&nbsp; ("Medium Access Control Layer")&nbsp; and communicates with the other&nbsp; (not necessarily neighboring)&nbsp; layers.&nbsp; It should be noted that this approach contradicts the modularity principle envisaged in the OSI model.
-*A similar approach has already been implemented as part of the extension of the UMTS network to include the&nbsp;[[Examples_of_Communication_Systems/Weiterentwicklungen_von_UMTS#High.E2.80.93Speed_Downlink_Packet_Access|$\rm HSDPA$]]&nbsp; ("High Speed Downlink Packet Access") standard,&nbsp; which has increased the maximum data rate in the 3G network&nbsp; (downstream)&nbsp; from&nbsp; $\text{384 kbit/s}$&nbsp; to the theoretical value&nbsp; $\text{ 14.4 Mbit/s}$.
+*A similar approach has already been implemented as part of the extension of the UMTS network to include the&nbsp;[[Examples_of_Communication_Systems/Weiterentwicklungen_von_UMTS#High.E2.80.93Speed_Downlink_Packet_Access|$\rm HSDPA$]]&nbsp; ("High Speed Downlink Packet Access") standard,&nbsp; which has increased the maximum data rate in the 3G network&nbsp; (downstream)&nbsp; from&nbsp; $\text{384 kbit/s}$&nbsp; to the theoretical value&nbsp; $\text{14.4 Mbit/s}$.

← Older revision		Revision as of 12:55, 20 January 2022
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−	The gain in system throughput that can be achieved in this way is often referred to as  [https://en.wikipedia.org/wiki/Diversity_scheme multi-user diversity gain].	+	The gain in system throughput that can be achieved in this way is often referred to as   [https://en.wikipedia.org/wiki/Diversity_scheme "multi-user diversity gain"].

	The diagram on the right shows the procedure.  The blue line represents the desired  "riding on the peaks"  for the case of eight participants  (eight fading processes).		The diagram on the right shows the procedure.  The blue line represents the desired  "riding on the peaks"  for the case of eight participants  (eight fading processes).