Examples of Communication Systems/Further Developments of UMTS - Revision history

Maintenance script: Add German interlanguage link

2026-03-16T12:26:15Z

Add German interlanguage link

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	{{Display}}		{{Display}}
			[[de:Beispiele_von_Nachrichtensystemen/Weiterentwicklungen_von_UMTS]]

Guenter at 17:21, 25 March 2023

2023-03-25T17:21:15Z

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	$\text{Example 2:}$		$\text{Example 2:}$
	This graphic is intended to illustrate  how the HARQ process works.  The following steps are to be distinguished:		This graphic is intended to illustrate  how the HARQ process works.  The following steps are to be distinguished:
	[[File:~~EN_Bei_T_4_4_S4b~~.png\|right\|frame\|On the HARQ procedure ~~'''KORREKTUR: ""'''~~]]		[[File:EN_Bei_T_4_4_S4b_v2.png\|right\|frame\|On the HARQ procedure]]
	*Before transmission,  the base station informs the receiver of an upcoming transmission using the  '''HS-SCCH'''  channel,  where the  '''HS-SCCH''' frame has three time slots.		*Before transmission,  the base station informs the receiver of an upcoming transmission using the  '''HS-SCCH'''  channel,  where the  '''HS-SCCH''' frame has three time slots.

Hwang at 10:49, 8 March 2023

2023-03-08T10:49:40Z

← Older revision		Revision as of 12:49, 8 March 2023
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	$\text{Example 2:}$		$\text{Example 2:}$
	This graphic is intended to illustrate  how the HARQ process works.  The following steps are to be distinguished:		This graphic is intended to illustrate  how the HARQ process works.  The following steps are to be distinguished:
	[[File:EN_Bei_T_4_4_S4b.png\|right\|frame\|On the HARQ procedure]]		[[File:EN_Bei_T_4_4_S4b.png\|right\|frame\|On the HARQ procedure '''KORREKTUR: ""''']]
	*Before transmission,  the base station informs the receiver of an upcoming transmission using the  '''HS-SCCH'''  channel,  where the  '''HS-SCCH''' frame has three time slots.		*Before transmission,  the base station informs the receiver of an upcoming transmission using the  '''HS-SCCH'''  channel,  where the  '''HS-SCCH''' frame has three time slots.

Hwang at 10:45, 8 March 2023

2023-03-08T10:45:25Z

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	<br>		<br>
	Another feature of HSDPA is the reduction of packet round-trip delay  $\rm (RTD)$  and the use of  "HARQ":		Another feature of HSDPA is the reduction of packet round-trip delay  $\rm (RTD)$  and the use of  "HARQ":
	*The  »'''round-trip delay'''»  has been reduced by HSDPA to  $\text{70 ms}$  $($compared  $\text{160 ... 200 ms}$  with UMTS R'99$)$,~~»~~ which is of great importance for some applications,  e.g. web browsing.  This reduction was achieved by decreasing the transport block length to about  $2$  milliseconds  $($previously  $\text{10 ms}$  or  $\text{20 ms)}$.		*The  »'''round-trip delay'''»  has been reduced by HSDPA to  $\text{70 ms}$  $($compared  $\text{160 ... 200 ms}$  with UMTS R'99$)$, which is of great importance for some applications,  e.g. web browsing.  This reduction was achieved by decreasing the transport block length to about  $2$  milliseconds  $($previously  $\text{10 ms}$  or  $\text{20 ms)}$.

	*In each Node B,  a  »'''HARQ'''«  $($"Hybrid Automatic Repeat Request"$)$  has been implemented to minimize transmission delays.  This mechanism prevents significant delays from occurring due to retransmission of erroneous blocks.  This is because such delays can be interpreted by TCP protocol as blocking,  which then leads to further delays.		*In each Node B,  a  »'''HARQ'''«  $($"Hybrid Automatic Repeat Request"$)$  has been implemented to minimize transmission delays.  This mechanism prevents significant delays from occurring due to retransmission of erroneous blocks.  This is because such delays can be interpreted by TCP protocol as blocking,  which then leads to further delays.

Guenter at 14:38, 6 March 2023

2023-03-06T14:38:05Z

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	The most important further developments were		The most important further developments were
	[[File:~~EN_Bei_T_4_4_S2~~.png\|right\|frame\|Further development of UMTS between 2000 and 2011<br><br> ~~'''Korrektur''' Spezi...~~]]		[[File:EN_Bei_T_4_4_S1_v2.png\|right\|frame\|Further development of UMTS between 2000 and 2011<br><br>]]
	[[File:EN_Bei_T_4_4_S1.png\|right\|frame\|Characteristics of HSDPA]]		[[File:EN_Bei_T_4_4_S1.png\|right\|frame\|Characteristics of HSDPA]]

Guenter at 15:37, 4 March 2023

2023-03-04T15:37:47Z

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	== Exercises for the chapter==		== Exercises for the chapter==
	<br>		<br>
	[[Aufgaben:Exercise_4.8:_HSDPA_and_HSUPA\|"Exercise 4.8: HSDPA and HSUPA"]]		[[Aufgaben:Exercise_4.8:_HSDPA_and_HSUPA\|Exercise 4.8: HSDPA and HSUPA]]


	{{Display}}		{{Display}}

Guenter at 16:18, 3 March 2023

2023-03-03T16:18:34Z

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	A detailed description of LTE can be found in the fourth main chapter of the book  "[[Mobile Communications]]". However, this was also written in 2011, shortly after its introduction~~. For more recent articles, please refer to the Internet~~.		A detailed description of LTE can be found in the fourth main chapter of the book  "[[Mobile Communications]]". However, this was also written in 2011, shortly after its introduction.

Guenter at 15:59, 3 March 2023

2023-03-03T15:59:27Z

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	The most important further developments were		The most important further developments were
	[[File:EN_Bei_T_4_4_S2.png\|right\|frame\|Further development of UMTS between 2000 and 2011<br><br>]]		[[File:EN_Bei_T_4_4_S2.png\|right\|frame\|Further development of UMTS between 2000 and 2011<br><br> '''Korrektur''' Spezi...]]
	[[File:EN_Bei_T_4_4_S1.png\|right\|frame\|Characteristics of HSDPA]]		[[File:EN_Bei_T_4_4_S1.png\|right\|frame\|Characteristics of HSDPA]]

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	==High–Speed Uplink Packet Access==		==High–Speed Uplink Packet Access==
	<br>		<br>
	Since UMTS R'99, the specifications for the uplink have not been further developed, although bidirectional symmetrical applications have become increasingly important and ever greater demands have been placed on transmission speeds. Until the introduction of Release 6, data rates were between  $\text{64 kbit/s}$  and  $\text{128 kbit/s}$, and up to  $\text{384 kbit/s}$ under ideal conditions.		Since  "UMTS R'99",  the specifications for the uplink have not been further developed,  although bidirectional symmetrical applications have become increasingly important and ever greater demands have been placed on transmission speeds.  Until the introduction of  "Release 6",  data rates were between   $\text{64 kbit/s}$   and   $\text{128 kbit/s}$,  and up to   $\text{384 kbit/s}$   under ideal conditions.

	With UMTS Release 6, ''High-Speed Uplink Packet Access''  (~~'''~~HSUPA~~'''~~)  was defined in 2004 and introduced in 2007. ~~This significantly increased the data rates on the uplink. These are theoretically up to~~  $\text{5.8 Mbit/s}$. In practice - taking into account simultaneous transmission for multiple users and receiver capacity - transmission rates of up to approx.  $\text{800 kbit/s}$  are still achieved.		With  "UMTS Release 6",  "High-Speed Uplink Packet Access"  $\rm (HSUPA)$  was defined in 2004 and introduced in 2007.

	~~The essential improvement by HSUPA is due to~~ the ~~introduction of an additional uplink channel, the  ''Enhanced Dedicated Channel''  ('''E-DCH'''). This minimizes, among other things in~~ the ~~dedicated~~ uplink ~~channels, the impact of applications with highly varying and sometimes very intensive data volumes  (English~~:  ~~''Bursty Traffic'')~~.		This significantly increased the data rates on the uplink:
			*These are theoretically up to  $\text{5.8 Mbit/s}$.

	~~However, although the~~  ~~'''E-DCH'''~~  is a dedicated transport channel, it does not guarantee the subscriber a fixed bandwidth in the uplink direction, as is the case with UMTS R'99. This flexible and efficient allocation of bandwidth depending on channel conditions allows a substantial increase in cell capacity.		*In practice – taking into account simultaneous transmission for multiple users and receiver capacity – transmission rates of up to  $\approx\text{800 kbit/s}$  are still achieved.

	[[File:P_ID3116__Bei_T_4_4_S6_v1.png\|right\|frame\|HSUPA ~~im Überblick~~]]		[[File:P_ID3116__Bei_T_4_4_S6_v1.png\|right\|frame\|Chart of HSUPA]]
	In addition to the new transport channel  ('''E-DCH''')  the following procedures were also introduced in the uplink  ('''HSUPA''')  analogous to the downlink  ('''HSDPA''')  in addition:
	*''Node B Scheduling'',
	*''Hybrid Automatic Repeat Request''  (HARQ).


	The use of HSUPA in the uplink only makes sense if it is combined with HSDPA in the downlink. Their interaction significantly increases the performance of the overall system.		The essential improvement by HSUPA is due to the introduction of an additional uplink channel,  the  "Enhanced Dedicated Channel"  $($'''E-DCH'''$)$.  This minimizes,  among other things in the dedicated uplink channels,  the impact of applications with highly varying and sometimes very intensive data volumes  $($"Bursty Traffic"$)$.

			However,  although the  '''E-DCH'''  is a dedicated transport channel,  it does not guarantee the subscriber a fixed bandwidth in the uplink direction,  as is the case with  "UMTS R'99".  This flexible and efficient allocation of bandwidth depending on channel conditions allows a substantial increase in cell capacity.

			In addition to the new transport channel  '''E-DCH''',  the following procedures were additional introduced in the uplink  $($'''HSUPA'''$)$  analogous to the downlink  $($'''HSDPA'''$)$:
			*"Node B Scheduling",

			*"Hybrid Automatic Repeat Request"  $\rm (HARQ)$.


			The use of HSUPA in the uplink only makes sense if it is combined with HSDPA in the downlink.  Their interaction significantly increases the performance of the overall system.


	==UTRAN Long Term Evolution==		==UTRAN Long Term Evolution==
	<br>		<br>
	~~[[File:EN_Bei_T_4_4_S7.png\|right\|frame\|Von  '''UMTS'''  zu  '''LTE''']]~~		"Long Term Evolution"  $\rm (LTE)$  represents a fourth-generation mobile communications system designed and standardized by the  [http://www.3gpp.org/ $\rm 3gpp$]  in parallel with the various further development phases of UMTS,  in order to meet the ever-increasing demands on future mobile communications systems.  This system is also referred to as  "High Speed OFDM Packet Access"  $\rm (HSOPA)$.  The chart summarizes the development of mobile communications systems from the perspective of 2011.
	''Long Term Evolution''  $\rm (LTE)$  represents a fourth-generation mobile communications system designed and standardized by the  [http://www.3gpp.org/ "3gpp"]  in parallel with the various further development phases of UMTS, in order to meet the ever-increasing demands on future mobile communications systems. This system is also referred to as  ''High Speed OFDM Packet Access''  $\rm (HSOPA)$ .

	~~The chart summarizes the development of mobile communications systems from the perspective of 2011.~~		LTE was developed as a forward-looking alternative to third-generation mobile communications systems.  The basic LTE features of were defined in 2004,  but concrete requirements were not drawn up until 2006.  The first systems began operating in 2011.
	~~<br clear=all>~~
	LTE was developed as a forward-looking alternative to third-generation mobile communications systems. The basic features of ~~LTE~~ were defined in 2004, but concrete requirements were not drawn up until 2006. The first systems began operating in 2011.		[[File:EN_Bei_T_4_4_S7.png\|right\|frame\|From  '''UMTS'''  to  '''LTE'''   <u>Attention please:</u> <br>   The data given here is from  $2011$,  shortly after the LTE launch. <br>   You can find the currently valid LTE features on the Internet. ]]

	Some features of UTRAN-LTE are listed below in bullet points without comment:		Some features of UTRAN-LTE are listed below in bullet points without comment:
	*The ''frequency ranges'' allocated for GSM and UMTS  continue to be used. An extension into the range around  $\text{2600 MHz}$  is planned.		#The frequency ranges allocated for GSM and UMTS  continue to be used.  An extension into the range around  $\text{2600 MHz}$  is planned.
	*Between  $200$  and  $400$  active subscribers can be served simultaneously, which means an increase in  ''cell capacity''  compared to UMTS by a factor of $2$  to $3$~~ ~~.		#Between  $200$  and  $400$  active subscribers can be served simultaneously,  which means an increase in  ''cell capacity''  compared to UMTS by a factor of $2$  to $3$.
	*The range is  $\text{5 km}$  (~~with~~ optimal quality) up to  $\text{100 km}$  (~~with~~ reduced quality). ''Maximum data rates'' are given as  $\text{100 Mbit/s}$  in the downlink and  $\text{50 Mbit/s}$  in the uplink.		#The range is  $\text{5 km}$  $($optimal quality$)$ up to  $\text{100 km}$  $($reduced quality$)$.  Maximum data rates are given as  $\text{100 Mbit/s}$  in the downlink and  $\text{50 Mbit/s}$  in the uplink.
	*The ''delay times'' are reduced to less than  $\text{5 ms}$  for larger bandwidth allocations and to  $\text{10 ms}$  for smaller bandwidth allocations.		#The delay times are reduced to less than  $\text{5 ms}$  for larger bandwidth allocations and to  $\text{10 ms}$  for smaller bandwidth allocations.
	*Bandwidths can be flexibly allocated over a very wide range with  $\text{1.25 MHz}$,  $\text{2.5 MHz}$,  $\text{5 MHz}$,  $\text{10 MHz}$,  $\text{15 MHz}$  and  $\text{20 MHz}$  .		#Bandwidths can be flexibly allocated over a very wide range with  $\text{1.25 MHz}$,  $\text{2.5 MHz}$,  $\text{5 MHz}$,  $\text{10 MHz}$,  $\text{15 MHz}$  and  $\text{20 MHz}$  .
	*The multiple access techniques used are  ''Orthogonal Frequency Division Multiple Access''  (~~'''~~OFDMA~~'''~~)  in the downlink and  ''Single Carrier Frequency Division Multiple Multiplexing''  (~~'''~~SC-FDMA~~'''~~)  in the uplink.		#The multiple access techniques used are  "Orthogonal Frequency Division Multiple Access"  $\rm (OFDMA)$  in the downlink and  "Single Carrier Frequency Division Multiple Multiplexing"  $\text{(SC-FDMA)}$  in the uplink.
	*Despite these ~~multiple~~ innovations, there is compatibility with the mobile communications systems of previous generations and a seamless transition to them is possible.		#Despite these innovations,  there is compatibility with the mobile communications systems of previous generations and a seamless transition to them is possible.

Guenter at 14:48, 3 March 2023

2023-03-03T14:48:25Z

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	*The  »'''round-trip delay'''»  has been reduced by HSDPA to  $\text{70 ms}$  $($compared  $\text{160 ... 200 ms}$  with UMTS R'99$)$,» which is of great importance for some applications,  e.g. web browsing.  This reduction was achieved by decreasing the transport block length to about  $2$  milliseconds  $($previously  $\text{10 ms}$  or  $\text{20 ms)}$.		*The  »'''round-trip delay'''»  has been reduced by HSDPA to  $\text{70 ms}$  $($compared  $\text{160 ... 200 ms}$  with UMTS R'99$)$,» which is of great importance for some applications,  e.g. web browsing.  This reduction was achieved by decreasing the transport block length to about  $2$  milliseconds  $($previously  $\text{10 ms}$  or  $\text{20 ms)}$.

	*In each Node B,  a  "Hybrid Automatic Repeat Request"~~ ~~ $~~\rm (HARQ~~)$  has been implemented to minimize transmission delays.  This mechanism prevents significant delays from occurring due to retransmission of erroneous blocks.  This is because such delays can be interpreted by TCP protocol as blocking,  which then leads to further delays.		*In each Node B,  a  »'''HARQ'''«  $($"Hybrid Automatic Repeat Request"$)$  has been implemented to minimize transmission delays.  This mechanism prevents significant delays from occurring due to retransmission of erroneous blocks.  This is because such delays can be interpreted by TCP protocol as blocking,  which then leads to further delays.

	*Using the HARQ mechanism and with transport block lengths of  $\text{2 ms}$  the transmission delays in HSPDA are less than  $\text{10 ms}$.  This is a crucial improvement over UMTS,  where error detection  $($associated with retransmission$)$  takes approximately  $\text{90 ms}$.		*Using the HARQ mechanism and with transport block lengths of  $\text{2 ms}$  the transmission delays in HSPDA are less than  $\text{10 ms}$.  This is a crucial improvement over UMTS,  where error detection  $($associated with retransmission$)$  takes approximately  $\text{90 ms}$.
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	*In contrast,  HARQ does not further increase the data rate if  $10 \cdot \lg \E_{\rm B}/N_0 > 2 \ \rm dB$.}}		*In contrast,  HARQ does not further increase the data rate if  $10 \cdot \lg \E_{\rm B}/N_0 > 2 \ \rm dB$.}}
	<br clear=all>		<br clear=all>
	~~The following~~ graphic is intended to illustrate  ''how the HARQ process works''. The following steps are to be distinguished:		{{GraueBox\|TEXT=
	*Before transmission, the base station informs the receiver of an upcoming transmission using the  '''HS-SCCH'''  channel, where a  '''HS-SCCH''' frame has three time slots.		$\text{Example 2:}$
	*Control data arrives at the receiver and is evaluated immediately after the arrival of the first  '''SCCH''' time slot.		This graphic is intended to illustrate  how the HARQ process works.  The following steps are to be distinguished:
	*Data transmission on the  '''HS-PDSCH'''  starts as soon as the ~~subscriber~~ has received the first two time slots of the control data block.		[[File:EN_Bei_T_4_4_S4b.png\|right\|frame\|On the HARQ procedure]]
	*Within  $\text{5 ms}$  of receiving a frame of data, the receiver must have decoded the entire frame and checked for errors.		*Before transmission,  the base station informs the receiver of an upcoming transmission using the  '''HS-SCCH'''  channel,  where the  '''HS-SCCH''' frame has three time slots.
	*If the transmission is error free, a positive acknowledgement  ('''ACK''')  is sent upstream, otherwise a  ''Non Acknowledgement''  ('''NACK''')  is sent.
			*Control data arrives at the receiver and is evaluated immediately after the arrival of the first  '''SCCH''' time slot.

			*Data transmission on the  '''HS-PDSCH'''  starts as soon as the user has received the first two time slots of the control data block.

			*Within  $\text{5 ms}$  of receiving a frame of data,  the receiver must have decoded the entire frame and checked for errors.

	~~[[File~~:~~EN_Bei_T_4_4_S4b~~.~~png\|center\|frame\|On the HARQ procedure]]~~		*If the transmission is error-free,
			:*a positive acknowledgement  $($'''ACK'''$)$  is sent upstream,
			:*otherwise a  "non acknowledgement"  $($'''NACK'''$)$  is sent.}}

	Since the HARQ does not send a new frame until the acknowledgement of the already transmitted frames is received, the receiver must be able to manage up to eight HARQs. This guarantees the correct sequence and thereby the correct processing of the data in the higher levels.
			Since the HARQ does not send a new frame until the acknowledgement of the already transmitted frames is received,  the receiver must be able to manage up to eight HARQs. This guarantees the correct sequence and thereby the correct processing of the data in the higher levels.

	{{BlaueBox\|TEXT=		{{BlaueBox\|TEXT=
	$\text{It is also worth mentioning:}$		$\text{It is also worth mentioning:}$  In addition to HARQ,  in  UMTS Release 5  a  »'''Node B Scheduling'''«  was introduced to be able to react quickly to changes in the transmission conditions of individual nodes  $($for example,  due to fading$)$.
			#This scheduling is used to decide which frames are assigned to which transmission channel.
	In addition to HARQ, in ~~the~~  ''UMTS Release 5''  a  '''Node B Scheduling'''  was introduced to be able to react quickly to changes in the transmission conditions of individual nodes (for example, due to fading).		#Priorities are assigned during scheduling.  A frame is only sent when it has the highest priority,  which means that it is most likely to be received correctly.
	*This scheduling is used to decide which frames are assigned to which transmission channel.		#This scheduling makes better use of the available bandwidth and significantly increases cell capacity.}}
	*Priorities are assigned during scheduling. A frame is only sent when it has the highest priority, which means that it is most likely to be received correctly.
	*This scheduling makes better use of the available bandwidth and significantly increases cell capacity.}}


	==Adaptive modulation, adaptive coding and adaptive transmission rate==		==Adaptive modulation, adaptive coding and adaptive transmission rate==
	<br>		<br>
	In HSDPA, the signals are ''adaptively modulated''. This means:		In HSDPA,  the signals are  "adaptively modulated".  This means:
	*Under good transmission conditions, higher-level modulation  (16-QAM ~~or 64-QAM)~~  ~~is used.~~		[[File:EN_Bei_T_4_4_S5.png\|right\|frame\|Adaptive modulation and coding in HSDPA]]
	*In poorer conditions, it is switched to  ~~''Quaternary Phase Shift Keying''  (QPSK) or 4~~-QAM.		*Under good transmission conditions,  a higher-level modulation is used:  $\text{16-QAM}$  or  $\text{64-QAM}$.

			*In poorer conditions,  it is switched to  "Quaternary Phase Shift Keying"  $\text{QPSK}$  or  $\text{4-QAM}$.

	In addition to modulation, the coding as well as the number of  '''HS-DSCH''' channels used simultaneously by a subscriber can be flexibly and quickly  $($all  $\text{2 ms)}$  changed depending on the channel quality. Despite the simultaneous use of adaptive modulation and adaptive coding, the power is always kept constant.

	~~[[File:EN_Bei_T_4_4_S5~~.~~png\|right\|frame\|Adaptive~~ modulation and coding ~~in HSDPA]]~~		In addition to modulation,  the coding as well as the number of  '''HS-DSCH'''  channels used simultaneously by a subscriber can be flexibly and quickly  $($all  $\text{2 ms)}$  changed depending on the channel quality.  Despite the simultaneous use of adaptive modulation and adaptive coding,  the power is always kept constant.

	Power control runs differently in HSDPA than in UMTS R'99:		⇒   Power control runs differently in  "HSDPA"  than in  "UMTS R'99":
	*The transmit power is always adapted to the signal quality, while the bandwidth should be kept as constant as possible.		*The transmit power is always adapted to the signal quality, while the bandwidth should be kept as constant as possible.
	*Only if the power can no longer be increased, the spreading factor is increased and thus the data rate is lowered.		*Only if the power can no longer be increased, the spreading factor is increased and thus the data rate is lowered.


	The maximum achievable data rate depends mainly on the  ''receiver performance''  and on the  ''transport format and resource combinations''  (TFRC).		⇒   The maximum achievable data rate depends mainly on the  receiver performance  and on the  "transport format and resource combinations"  $\rm (TFRC)$.

	In the table, various parameter combinations for modulation and code rate are given and the resulting bit rates can be seen. Not considered ~~here~~ is the ''overhead''.		In the table,  various parameter combinations for modulation and code rate are given and the resulting bit rates can be seen.  Not considered in this table is the  "overhead".
	<br clear=all>		<br clear=all>
	==High–Speed Uplink Packet Access==		==High–Speed Uplink Packet Access==

Guenter at 13:37, 3 March 2023

2023-03-03T13:37:20Z

← Older revision		Revision as of 15:37, 3 March 2023
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	*Using the HARQ mechanism and with transport block lengths of  $\text{2 ms}$  the transmission delays in HSPDA are less than  $\text{10 ms}$.  This is a crucial improvement over UMTS,  where error detection  $($associated with retransmission$)$  takes approximately  $\text{90 ms}$.		*Using the HARQ mechanism and with transport block lengths of  $\text{2 ms}$  the transmission delays in HSPDA are less than  $\text{10 ms}$.  This is a crucial improvement over UMTS,  where error detection  $($associated with retransmission$)$  takes approximately  $\text{90 ms}$.

	In the HARQ procedure, the detection of an error or no error is acknowledged for each individual transport frame. This procedure is referred to as  ~~'''~~Stop and Wait~~'''~~  (SAW).		*In the HARQ procedure,  the detection of  "error"  or  "no error"  is acknowledged for each individual transport frame.  <br>This procedure is referred to as  "Stop and Wait"  $\rm (SAW)$.


	~~[[File:EN_Bei_T_4_4_S4.png\|right\|frame\|Increasing the data rate by HARQ]]~~
	{{GraueBox\|TEXT=		{{GraueBox\|TEXT=
	$\text{Example 1:}$		$\text{Example 1:}$
	The graph shows the achievable data rate as a function of the quotient  $E_{\rm B}/N_0$  (in dB).		The graph shows the achievable data rate as a function of the quotient  $E_{\rm B}/N_0$  $($in dB$)$.
			[[File:EN_Bei_T_4_4_S4.png\|right\|frame\|Increasing the data rate by HARQ]]







			*You can see decisive improvements by the HARQ mechanism,  especially for small  $E_{\rm B}/N_0$  values.


	*~~You can see decisive improvements by the HARQ mechanism~~, ~~especially for small values of~~  ~~$E_{\rm B}/N_0$.~~
	*In contrast, HARQ does not further increase the data rate if  $10 - \lg \E_{\rm B}/N_0 > 2 \ \rm dB$~~ ~~.}}		*In contrast,  HARQ does not further increase the data rate if  $10 \cdot \lg \E_{\rm B}/N_0 > 2 \ \rm dB$.}}
	<br clear=all>		<br clear=all>
	The following graphic is intended to illustrate  ''how the HARQ process works''. The following steps are to be distinguished:		The following graphic is intended to illustrate  ''how the HARQ process works''. The following steps are to be distinguished: