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LTE10, LTE11, LTE571
LTE10, LTE11, LTE571
Nidia Couto - nidia.couto@nsn.com
Nidia Couto - nidia.couto@nsn.com
The latest version of this NEI can
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LT
LTE10 E10 --EPS EPS bearebearers for crs for conversational voiceonversational voice
LT
LTE1E11 -1 -Robust HeadeRobust Header Compressior Compressionn
LT
RL20 - LTE10 - EPS bearers for conversational voice
Table of Cont ents
1
Introduction
Motivation and Feature OverviewMain Menu
NEI Contact: Nidia Couto / Dawid Czarnecki
2
Interdependencies
Interdependencies with Other Features and Functions3
Technical Details
Functionality and Implementation, Message Flows5
Dimensioning Aspects
Dimensioning Impacts and Examples4
Configuration Management
ParametersMain Menu
•
Two new QCI bearers:
─ QCI1 bearer for transmission of voice packets
─ QCI5 bearer dedicated for IMS signaling
•
O&M switch (schedulType) allows to define whether QCI5 bearer carries IMS signaling or not
─ If IMS signaling is not specified for QCI5, the bearer is weighted according to QCI-specific relative weight (schedulWeight on
qciTab5)
Techni cal Details
LTE10 - EPS bearers for conversational voice - IMS signaling Table of Contents
IMS
–
IP Multim edia Subsystem
IP Multimedia Subsystem is an access-independent architecture that enables various types of multimedia services
to mobile-users using common Internet-based protocols.
If schedulType is not set for signaling, QCI5 is weighted as a
Main Menu
•
To ensure QoS for voice calls, both target bit rate and delay have to be maintained
‒
The Flexi BTS takes the GBR signaled via S1 interface into account for Radio Resource Management ( Admission
Control and Scheduler ).
The maximum GBR for EPS bearers with QCI 1 is limited by qci1GbrLimit (default: 250kbps). EPS bearers with GBR value
higher than this will be rejected by eNB.
•
Admission Control
‒
Due to QoS restrictions, two new thresholds for GBR bearers are introduced to radio admission control
GBR threshold for new calls: maxNumQci1Drb
GBR threshold for incoming calls: addNumQci1DrbRadioReasHo, addNumQci1DrbTimeCriticalHo
•
Scheduler
‒
Dynamic scheduling is applied for EPS bearers with QCI 1
‒
The uplink and downlink scheduler use the GBR delay budget for its scheduling decisions. The delay budget can
be configured by the operator (delayTarget, schedulBSD, schedulWeight)
‒
Non-GBR data transmission might be reduced in order to achieve the GBR for voice users
‒
Voice service (as based on GBR bearers) is not subjected to rate capping functions
Techni cal Details
LTE10 - EPS bearers for conversational voice –Impacts on RRM
Main Menu
Configuration Management
LTE10 –Parameters related to Radio Admission Control
Table of Contents
QCI1-specific
parameters for different
bandwidths
Carrier BW 20MHz 15MHz 10MHz 5MHz max PRBs 100 PRBs 75 PRBs 50 PRBs 25 PRBs
used PRBs for UL-signaling (PUCCH)
19 see RRM.2691 17 see RRM.2691 10 see RRM.2691 8 see RRM.2691
Parameter step sizerange, defaultvalue step sizerange, defaultvalue step sizerange, defaultvalue step sizerange, defaultvalue
maxNumQci1Drb 0…600 step 1 100 0…500 step 1 100 0…400 step 1 100 0…200 step 1 75 addNumQci1DrbRadioReasHo 0…600step 1 40 0…500step 1 30 0…400step 1 15 0…200step 1 15 addNumQci1DrbTimeCriticalHo 0…600 step 1 40 0…500 step 1 30 0…400 step 1 20 0…200 step 1 15
O&M thresholds for RAC interaction with BM and MM for 10 MHz*
MOC Modifiableby Abb reviat ed name Values Descr ipt ion
LNCEL Operator maxNumQci1Drb range: 0-400, step: 1default: 100 (for 10MHz band) Threshold for the maximum number of established QCI1-GBR-DRBs in the cell
LNCEL Operator addNumQci1DrbRadioReasHo range: 0-400, step: 1default: 15 (for 10MHz band)
Additional margin for the maximum number of active GBRs in the cell accessing the cell via handover with HO-cause "HO desirable for radio reasons". This margin is added to the threshold maxNumQci1Drb.
LNCEL Operator addNumQci1DrbTimeCriticalHo range: 0-400, step: 1default: 20 (for 10MHz band)
Additional margin for the maximum number of active GBRs in the cell accessing the cell via hand over with HO-cause: "Time Critical HO". This margin is added to the threshold maxNumQci1Drb.
Values for RL40. For earlier releases the number of QCI1
DRBs is limited to 150 in 5MHz and 200 in other BWs.
Main Menu
GSM/LTE RF sharing at 1800 MHz
•
Only UL considered (limiting link)
•
Short retransmission delay in LTE allows for several
HARQ retransmissions within acceptable delay budget
(50..70ms total packet delay at the air interface)
–
With the cost of reducing capacity as each retransmission
will require a new scheduler allocation.
•
Lowering AMR codec rate will also increase the cell range
• Gain from RoHC already included in the calculations
LTE10
–
Coverage Aspects
No impact on coverage –Using retransmissions , HARQ gain can bring ~5dB improvement in LiBu
Table of Contents
Results slightly worse than GSM (7dBm higher power).
Further improvement can be achieved after considering the gains of packet segmentation
Main Menu
VoIP capacity example:
•
Due to the big number of small packets being sent, the
bottleneck for VoIP users is not on on U-Plane, but on
C-Plane
–
Each allocation requires a PDDCH grant
–
For non cell edge users, grants can be reduced by
aggregating multiple packets (max 3, subjected to delay
target) and sending them all at once
–
For user at the cell edge, each retransmission requires a
separate PDCCH grant, reducing the number of supported
users
LTE10
–
Capacity Aspects
No impact on Cell Throughput –Number of UEs limited due to PDCCH resources
Table of Contents
Alt ho ug h more r etrans mi ss io ns im prove robustness and coverage, increased PDCCH usage may lead to VoIP capacity degradatio n.
Ass um pt io ns
• VoIP codec AMR12.2
• 10MHz BW
• 3 PDCCH symbols • PDCCH Alpha = 0.8
Such calculations can be performed
HARQ Gain (3 retransmissions)
RL20 - LTE11 - Robust Header Compression
Table of Cont ents
1
Introduction
Motivation and Feature OverviewMain Menu
NEI Contact: Nidia Couto / Dawid Czarnecki
2
Interdependencies
Interdependencies with Other Features and Functions3
Technical Details
Functionality and Implementation, Message Flows6
Dimensioning Aspects
Dimensioning Impacts and Examples5
Benefits and Gains
Simulation, Lab and Field FindingsMain Menu
•
The robust header compression (RoHC) function compresses the header of IP packets for the EPS
bearer with QCI 1
•
RoHC is supported for IPv4 and IPv6.
•
The following RoHC profiles are supported (3GPP R8):
‒ ROHC uncompressed (RFC 4995)
‒ ROHC RTP (RFC 3095, RFC 4815)
‒ ROHC UDP (RFC 3095, RFC 4815)
‒
Those RoHC profiles must be supported by all IMS-voice
capable UEs (3GPP TS 36.306)
•
Operation takes place between 3rd and 2
ndOSI layer
Introduction
LTE11 - Robust Header Compression Table of Contents
320bits
Main Menu
Techni cal Details
LTE11 - Robust Header Compression –Exemplification
Table of Contents
Field predictable in the course of transmission –
“Destination IP”
IP/UDP/RTP header consisting of predictable and
unpredictable fields -subjected to compression
MAC header, RLC header, VoIP payload, CRC checksum - not subjected
to compression 10.0.0.10 10.0.0.10 10.0.0.10 10.0.0.10 10.0.0.10 10.0.0.10 6 3 7 0 1 8 “from now on assume Destination IP is 10.0.0.10” 10.0.0.10 6 3 7 0 1 8 x Unpredictable field
Context - information about all fields that are predictable and their change patterns sent in the beginning of transmission to allow header compression
Uncompressed transmission
Compressed transmission
Initial transmission, “context” is initialized so that next transmissions can be
compressed
In the course of transmission header fields initialized in context do not have to be
Main Menu
Benefits and Gains
LTE11 - Robust Header Compression –Exemplary Call
Table of Contents
Source:
10 minutes of 12.2 kbps AMR coded VoIP call wit h talk spu rt/silent p eriod alternating every 1 second
(SID packets excluded)
ROHC header type Field description ROHC header bits Samples Samples [%] IR To initialize the context of the decompressor 504 8 0,01% IR-DYN To initialize the dynamic part of the context 120 1500 1,00% R-0 To signal 6 LSBs of RTP Sequence Number 24 118961 79,31% R-0-CRC To update reference value of RTP SN 32 17625 11,75% R-2 To signal more LSBs of the RTP SN 40 6000 4,00% R-2-Ext3 Sent when compressor does not receive ACK for R-0-CRC 56 1500 1,00% R-0-ACK Used by decompressorto acknowledge received R-0-CRC or R-2-Ext3 packets 40 4406 2,94%
TOTAL 150000 100,00%
Uncompressed header volume
IPv4/UDP/RTP packet overhead is 40 bytes
15000 packets x 40B x 8b = 4.8 x 10
7bits
Compressed header volume
RoHC headers sizes are given in the table
504 x 8 + 120 x 1500 + … + 40 x 4406 = 4.1 x 10
6bits
Main Menu
Representative transmission
LTE11 - Robust Header Compression Table of Contents
RoHC Header Size Distribution
75% 80% 85% 90% 95% 100% 24 32 40 56 120 504 C D F
RoHC header size [bits]
0% 20% 40% 60% 80% 100% 504 120 24 32 40 56 40 P D F
RoHC header si ze [bits]
98%
98% of RoHC headers si ze is smaller or equal to
40 bits
For link budget purp oses RoHC header size is assumed to
be 40 bits
Main Menu
Dimensioning Aspects
LTE11 - Robust Header Compression –Impact on Coverage
Table of Contents
• Enhanced Pedestrian A 5Hz (EPA05) • Equipment parameters:
– Tx Power: eNB 40W / UE 23 dBm
– Antenna Gain: eNB 18 dBi / UE 0 dBi
– Feeder Loss: DL 0.4 dB / UL 0.4 dB(feederless)
– Noise Figure: eNB 2.2 dB / UE 7 dB
• Other features:
– eNB: 2 Tx antennas, 2 Rx antennas (2x2 MIMO)
– UE: 1 Tx antenna, 2 Rx antennas (MRC)
– DL F-domain Scheduler: channel-aware
– UL F-domain Scheduler: channel-unaware
• Additional margins:
– Interference margin for 50% load (~ 1…2dB)
– 2.5 dB gain against shadowing
• IP/UDP/RTP header - 320 bits • TTI bundling –off
RL20@10MHz(12.2 kbps, no RoHC)
RL20@10MHz(12.2 kbps, RoHC)
• Enhanced Pedestrian A 5Hz (EPA05) • Equipment parameters:
– Tx Power: eNB 40W / UE 23 dBm
– Antenna Gain: eNB 18 dBi / UE 0 dBi
– Feeder Loss: DL 0.4 dB / UL 0.4 dB(feederless)
– Noise Figure: eNB 2.2 dB / UE 7 dB
• Other features:
– eNB: 2 Tx antennas, 2 Rx antennas (2x2 MIMO)
– UE: 1 Tx antenna, 2 Rx antennas (MRC)
– DL F-domain Scheduler: channel-aware
– UL F-domain Scheduler: channel-unaware
• Additional margins:
– Interference margin for 50% load (~1…2dB)
– 2.5 dB gain against shadowing
• RoHC header - 40 bits • TTI bundling - off
DL 171 dB*
UL 150 dB*
Propagation
• Operating Band
– FD-LTE: 2100 MHz
• COST 231 Hata 2-slope propagation model with – Antenna height NB: 30m
– Antenna height MS: 1.5m
• Clutter dependent figures(Dense Urban / Urban / Suburban / Rural)
– Std. dev.: 9 / 8 / 8 / 7 [dB]
– Cell area prob.: 94.4 / 94.0 / 94.0 / 89.9 [%]
DL 171.5 dB*
UL 153 dB*
3dB gain due to less bandwidth needed
per user (lower MCS used)
RL30 - LTE571 - Controlled UL packet segmentation
Table of Cont ents
1
Introduction
Motivation and Feature OverviewMain Menu
NEI Contact: Nidia Couto / Dawid Czarnecki
2
Interdependencies
Interdependencies with Other Features and Functions3
Technical Details
Functionality and Implementation, Message Flows5
Dimensioning Aspects
Dimensioning Impacts and ExamplesMain Menu
•
Packet Segmentation Algorithm is used as an extension to
Link Adaptation for Uplink coverage improvement
‒
The enhancement in coverage comes at the cost of cell
throughput
‒
Due to increased number of time allocations per packet,
PDCCH load also increases
•
Packet segmentation is not an event-triggered mechanism, it
is done automatically and only for UEs with poor radio
channel
‒
LTE571 is simply an enhancement to the existing,
non-configurable packet segmentation mechanism on Layer 2
Introduction
LTE571 - Controlled UL packet segmentation Table of Contents
TTIs m m+1 L2 SDU 304b Packet segmentation TTIs L2 SDU 152b m m+1 m+2 RLC MAC RLC MAC L2 SDU 152b 1/2 2/2 RLC MAC
Total energy per packet = 22.67dBm
Total energy per packet = 25.37dBm
Increased robustness by spreading the packet in
time domain
Padding Padding Padding
Higher overhead
16b
Main Menu I TBS N PRB 1 2 3 4 5 6 7 8 0 16 32 56 88 120 152 176 208 1 24 56 88 144 176 208 224 256 2 32 72 144 176 208 256 296 328 3 40 104 176 208 256 328 392 440 4 56 120 208 256 328 408 488 552 5 72 144 224 328 424 504 600 680 6 88 176 256 392 504 600 712 808 7 104 224 328 472 584 712 840 968 8 120 256 392 536 680 808 968 1096 9 136 296 456 616 776 936 1096 1256 10 144 328 504 680 872 1032 1224 1384
What happens with allocation when UE conditions are getting worse
(LTE571 di sabled)
1. Initially user is in good radio conditions sothere’sno need for segmentation. It occupies the minimum number of PRBs needed to transmit its data with given MCS
2. As radio conditions worsen, AMC decreases MCS order and, consequently, more PRBs are occupied
3. MAX_NUM_PRB (from ATB) is reached and whole packet can no longer be sent at once 4. Packet is segmented. Original packet size is split into 2 packets (240b and 64b plus
header). First part is sent with limit from ATB (256b TBS), second part with the lowest possible number of PRBs to ensure transport of 80b packet (144b TBS, remaining filled with padding).
5. As radio conditions worsen MCS order drops (AMC) and PRB usage increases 6. Further increase of #PRBs not possible - MAX_NUM_PRB (from ATB) would be
exceeded. Segmentation needed.
7. Packet is segmented again –304 bits are distributed into 3 segments (2 segments of 152b and 1 segment of 56b). 8. As MCS cannot be further decreased, ATB has to reduce the
number of PRBs, increasing segmentation
9. Packet will be segmented as much as needed to fit into the available allocation.
10. Once MAX_NUM_PRB is reduced to 1, UE will send only RLC+MAC headers and no data
Packet Segmentation when LTE571 is disabled
LTE571 - Controlled UL packet segmentation Table of Contents
– 1 segment – 2 segments – 3 segments – 5 segments – 8 segments – 19 segments – headers only
Worsening radio conditions
Ass um pt io ns
• RLC SDU size = 304 bits
• RLC + MAC header = 16 bits
88 MAX_NUM_PRB (from ATB) MAX_NUM_PRB (from ATB) 56
Without LTE571, allocation of single PRB is allowed. This way only headers are
transmitted
32 32
Main Menu I TBS N PRB 1 2 3 4 5 6 7 8 0 16 32 56 88 120 152 176 208 1 24 56 88 144 176 208 224 256 2 32 72 144 176 208 256 296 328 3 40 104 176 208 256 328 392 440 4 56 120 208 256 328 408 488 552 5 72 144 224 328 424 504 600 680 6 88 176 256 392 504 600 712 808 7 104 224 328 472 584 712 840 968 8 120 256 392 536 680 808 968 1096 9 136 296 456 616 776 936 1096 1256 10 144 328 504 680 872 1032 1224 1384
What happens with allocation when UE conditions are getting worse
(LTE571 enabled)
1. Initially user is in good radio conditions sothere’sno need for segmentation. It occupies the minimum number of PRBs needed to transmit its data with given MCS
2. As radio conditions worsen, AMC decreases MCS order and, consequently, more PRBs are occupied
3. MAX_NUM_PRB (from ATB) is reached and whole packet can no longer be sent at once 4. Packet is segmented. Original packet size is split into 2 packets (240b and 64b plus
header). First part is sent with limit from ATB (256b TBS), second part with the lowest possible number of PRBs to ensure transport of 80b packet (144b TBS, remaining filled with padding).
5. As radio conditions worsen MCS order drops (AMC) and PRB usage increases 6. Further increase of #PRBs not possible - MAX_NUM_PRB (from ATB) would be
exceeded. Segmentation needed.
7. Packet is segmented again –304 bits are distributed into 3 segments (2 segments of 152b and 1 segment of 88b). 40b padding need to be added to fulfill ulsMinTbs.
8. As MCS cannot be further decreased, ATB has to reduce the number of PRBs, increasing segmentation
9. Once the minimum number of PRBs is reached (ulsMinRbPerUe >MAX_NUM_PRB), no further segmentation is possible, even if MAX_NUM_PRB is reduced.
10. UE will keep been allocated ulsMinRbPerUe and sending at least ulsMinTbs bits of data
Packet Segmentation when LTE571 is enabled
LTE571 - Controlled UL packet segmentation Table of Contents
– 1 segment – 2 segments – 3 segments – 5 segments
Worsening radio conditions
Ass um pt io ns
• RLC SDU size = 304 bits
• RLC + MAC header= 16 bits
88
MAX_NUM_PRB (from ATB)
New parameters introduc ed
• ulsMinTbs = 72 bits
• ulsMinRbPerUe = 4
LTE571 stablishes a minimum TBS and PRB number to control generated
overhead
MAX_NUM_PRB (from ATB)
Main Menu
ELSE:
redBwMinRbUl <= PRB
UE<= min(redBwMaxRbUl, PRB
BSR, MAX_NUM_PRB)
redBwMinRbUl<= PRB
UE<= min(redBwMaxRbUl, MAX_NUM_PRB)
redBwMinRbUl<= PRB
UE<= min(redBwMaxRbUl, MAX_#_PRB_SR, MAX_NUM_PRB)
PRB assignment
–
New condit ion intro duced
LTE571 - Controlled UL packet segmentation Table of Contents
IF ulsMinRbPerUe >= MAX_NUM_PRB :
PRB
UE= max( redBwMinRbUl, PRB_ulsMinTbs, ulsMinRbPerUe)
Minimum number of PRBs per UE
(LTE571)
Ordinary Scheduled UEs
Candidate Set 3 UEs
UEs having Scheduling Request scheduled
max(redBwMinRbUl, PRB_ulsMinTbs) <= PRB
UE<= min(redBwMaxRbUl, PRB
BSR, MAX_NUM_PRB)
max(redBwMinRbUl, PRB_ulsMinTbs) <= PRB
UE<= min(redBwMaxRbUl, MAX_NUM_PRB)
max(redBwMinRbUl, PRB_ulsMinTbs) <= PRB
UE<= min(redBwMaxRbUl, MAX_#_PRB_SR, MAX_NUM_PRB)
Without LTE571
If LTE571 is enabled, PRB allocation is limited by ulsMinRBPerUe, whenver
MAX_NUM_PRB is too small
Number of PRBs based on min TBS and MCS order
(LTE571)
Numberof PRBs based on min TBS and MCS order
(LTE571)
redBwMinRbUl - Minimum number of PRBs assigned in UL
redBwMaxRbUl - Maximum number of PRBs assigned to a UE scheduled in UL
Without LTE571 upper limit for PRB allocation is always coming from ATB
Main Menu
•
Sending packet segments in consecutive TTIs allows more energy per voice packet to be
aggregated, increasing coverage
•
The coverage gain achieved with packet segmentations grows with each segmentation
operation, as well as L2 overhead
‒ However the gain does not grow linearly, the smaller the segment, the lower the gain
Dimensioning Aspects
LTE571 - Controlled UL packet segmentation –Coverage Gain
Table of Contents
Packet segmentation can provide up to ~5 dB coverage gain (by sacrific ing capacity) Real gains will depend on used codec, Link Adap tat io n set ti ng s and nu mb er of seg men tatio ns
Ass um pt io ns
• ulsMinTbs = 72 bits
• minRbPerUe = 4
• VoIP codec = AMR12.2
• UE Tx power = 23dBm
•
Depending on E-ULLA settings and the desired
configuration, ul sMinRBPerUe and ulsMinTbs
have to be set accordingly
Simulations performed by System Architecture suggest following values as most optimized*:
ulsMinRBPerUe = 3
ulsMinTbs = 104
Main Menu
•
Since the maximum number of supported VoIP users depends
mostly on PDCCH resources, it significantly drops with the increase
of segmentation order
‒
Each segment (and HARQ retransmission) will require a new PDCCH
allocation and a new PHICH in DL (for transmission of ACKs/NACKs
per segment).
•
The higher the achieved coverage gain, the greater is the capacity
loss, which is why the most robust configurations are generally not
used
Dimensioning Aspects
LTE571 - Controlled UL packet segmentation –Capacity Loss
Table of Contents
Gain pr ovided by packet segmentation c omes
at the cost of the cell capacity
Assu mp ti on s*
• ulsMinTbs = 72 bits • minRbPerUe = 4
• VoIP codec = AMR12.2
• UE Tx power = 23dBm
• 10 MHz Bandwidth