LTE L11 Throughput Troubleshooting TechniquesSlide title In
CAPITALS 44 pt Slide subtitle 20 pt
LTE L11 Throughput Troubleshooting Techniques
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Slide title In CAPITALS 44 pt Slide subtitle 20 pt
Introduction
Why learn about Throughput Troubleshooting
LTE provides data, lots of data
Throughput is shared in time and frequency
Users notice throughput problems
Learn to isolate the domain causing throughput degradation
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Data throughput is the main driver for 3G and 4G network.
It is more important than ever to know the factors affecting
throughput degradation
This module will present an analysis of various domains which cause
throughput degradation
At the end of the module the course participant will have the key
knowledge to enable them to isolate problem causing domains and
perform a complete LTE RAN and end-to-end analysis of throughput
problems.
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Scope and objectives
Pinpoint causes of throughput degradation clearly within domains
through theory, traces and practical examples
Objectives
Scope
Slide title In CAPITALS 44 pt Slide subtitle 20 pt
> Overview
Agenda
Overview
Slide title In CAPITALS 44 pt Slide subtitle 20 pt
LTE RBS User plane Overview
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LTE RBS User Plane Overview
User plane visualisation
User Plane Domains
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This course aims to explore the throughput troubleshooting
possibilities for the LTE RAN.
End user throughput degradation is very visible to end customers
and operators alike. Hence these problems are sensitive in
nature.
Throughput investigations involve many different nodes and
protocols.
A coordinated approach to troubleshooting is then beneficial to
isolating the problem.
Of note is that we subdivide the throughput analysis into several
smaller domains:
Radio Domain - Specifically concerned with the radio interface and
the L1/L2 protocols.
Transport Domain - This domain is concerned with the northbound IP
network that connects the LTE RBS to the Core Network.
e2e Domain - This domain is concerned with the end-2-end aspects of
throughput. It focus’ on what the user experiences.
The user protocols are presented here for clarity and
reference.
Note: the core interfaces are not explored in this course.
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Data Flow over Air (RBS/UE)
CRC
Payload
Payload
Payload
CRC
Header
Header
Header
Payload
Payload
Payload
Header
Header
Header
PDCP
Header
PDCP
Header
PDCP
Header
PDCP
RLC
MAC
RLC
Header
RLC
Header
RLC
Header
MAC
Header
MAC
Header
Uses sequence numbers.
Support ROHC (not in L10) - shown in diagram with reduction of
header size.
Direct mapping to an RLC SDU.
RLC:
Segments and Concatenates.
Uses HARQ for fast retransmission (RLC handles overall payload
reliability)
Multiplexes multiple RLC PDUs (SRB and/or DRB)
Mapped to Transport Block (1-2 TB per TTI depending on the CWs
supported)
The combination of hybrid-ARQ and RLC attains a good combination of
small roundtrip time and a modest feedback overhead where the two
components complement each other. Thus, the two-level structure
combines the best of two worlds – fast retransmissions due to the
hybrid-ARQ mechanism and reliable packet delivery due to the
RLC.
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network assumptions
Node alarms verified
MO status
Cell availability
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Release Limitations
L11A contains some limitations that directly affect end user
throughput
One SE per TTI in UL and DL (in L11A GA)
Each cell is treated individually, so there could be up to 3 users
simultaneously in an eNB
SIB is scheduled the same as user data, so nothing can be scheduled
at the same time as SIB
DUL user plane capacity limited to 150 Mbps (20MHz)
100PRBs UL, 150 PRBs DL.
16QAM UL (up to MCS24)
MCS28 disabled in DL by default (requires CFI=1 also)
Fixed CFI (number of OFDM symbols for PDCCH)
Default is CFI=2 for 5MHz and less.
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Slide title In CAPITALS 44 pt Slide subtitle 20 pt
Initial Checks
Initial checks
Network changes & Basic troubleshooting
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Before we investigate any throughput issues, it is best to rule out
the most obvious and basic issues that might affect end user
throughput.
This checklist aims to provide some items that should be
checked/ruled out prior to detailed radio or transport network
investigations.
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NW Changes and Basic Troubleshooting
Network/node changes can affect network throughput
Some common examples include:
RBS parameter changes (all MOs under ENodeBFunction, system
constants, EricssonOnly hidden parameters, e.g.
DataRadioBearer)
IP address plan changes
DNS updates
Basic troubleshooting checks include:
MO health status
Planned network changes can cause throughput issues if implemented
incorrectly (or untested).
A history (verbal) of network changes should always be requested
prior to beginning investigations
The listed Moshell commands are considered important inputs prior
to commencing more detailed investigations.
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PC/Server Settings
Confirm the end user PC settings:
Laptop specification can impact throughput (processors, memory, USB
bus, HDD speed, plugged into AC power, etc)
MTU settings in PC (1360 optimal for eNB in L11A to prevent
fragmentation)
Throughput monitors (e.g. Netpersec, only good for downlink UDP
measurements, uplink must be measured at receiving side for
UDP)
TCP enhancements in Vista (experimental), Vista should
“auto-tune”.
Confirm server settings:
FTP server configuration
Linux TCP setting/guide
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Laptop specs:
Some laptops may not provide the necessary power to run high
throughput
The OS and hardware specifics can reduce the achievable throughput
in these cases
If possible, test throughput with other PCs to benchmark the UE/PC
performance
MTU of 1360 avoids IP fragmentation/reassembly (process that
requires many resources and causes delay)
Use appropriate Application
UE Categories
5 UE Categories are defined in 3GPP TS 36.306
The UE-Cat is sent in the UE Capability Transfer procedure (RRC
UECapabilityInformation)
The COLI ue command provides detailed capability info ( KO ) for
connected UEs
DL
UL
UE Category
Maximum number of DL-SCH transport block bits received within a
TTI
Maximum number of bits of a DL-SCH transport block received within
a TTI
Total number of soft channel bits
Maximum number of supported layers for spatial multiplexing in
DL
Category 1
UE Category
Maximum number of bits of an UL-SCH transport block transmitted
within a TTI
Support for 64QAM in UL
Category 1
Highlight UL limitation in L10A (16QAM max)
Highlight Rx div assumed
General Comment on Charts:
Column 1 defines total bits received. Simply multiply these by
1000ms/sec for throughput on L1.
For DL chart:
Soft channel bits: Defines the total number of soft channel bits
available for HARQ processing.
COLI command for UE cap.
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UE Subscriber profile
End User (EPS User) subscription data is stored in the HSS
The EPS User Profile data is identified by its IMSI number
The profile consists of:
RAT frequency selection priority
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ODB - The type of ODB applied to the EPS User.
APN Replacement - Domain name to replace the APN OI when
constructing the Packet Data Network (PDN) Gateway (GW) Fully
Qualified Domain Name (FQDN), upon which to perform a Domain Name
System (DNS) resolution.
Charging - Charging Characteristics associated to the overall EPS
User Profile, according to 3GPP TS 32.299.
AMBR - Aggregate maximum bandwidth of the overall Internet Protocol
(IP) flow associated to the EPS User Profile.
RAT - The Subscriber Profile Identity for RAT/frequency
priority.
APN - Information on all the APNs associated to the EPS User
Profile.
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RBS Parameters RN
RN MO parameters:
(nrOfSymbolsPdcch) (Control Region Size) NOTE: currently controlled
by SC38 in L11A
noOfUsedTxAntennas controls whether OLSM MIMO is used (2) or
not.
partOfRadioPower NOTE: this is the % part of RU capability
independent of SectorEquipmentFunction::confOutputPower
settings
pZeroNominalPucch some UEs need this to be increased or ACK/NACKs
are not received successfully on PUCCH.
pZeroNominalPusch some UEs need this to be increased from default
or lots of errors seen on PUSCH
SectorEquipmentFunction=Sx
DataRadioBearer
Various parameters for RLC status reporting and retransmission.
Should be set to recommended values.
MACConfiguration
xxMaxHARQTx – enable (>1) or disable (1) HARQ. Recommended to
use 4 HARQTx.
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ChannelBandwidth tied to license - > BW = more RBs and higher
payload
PDCCH ranges from 1-3 OFDM symbols. Less provides more symbols for
PDSCH. Currently controlled by system constant number 38 in
L11A
Rx/Tx Antenna - Multiple for Rx and Tx diversity and Spatial
Multiplexing.
pZeroNominalPucch – Some UEs need this to be increased to get
successfully ACK/NACK reception in eNB. However it could cause
neighbour cell interference.
pZeroNominalPusch – Some UEs need this to be increased for eNB to
successfully decode PUSCH transmission.
CyclicPrefix - can limit the number of OFDM symbols. Sizes cater
for different cell sizes. Smaller = more OFDM symbols.
Sector
conf
fqBand
RBS PARAMTERS TN
TN MO parameters:
GigabitEthernet=1
actualSpeedDuplex – if you see half-duplex, it could be a problem
with auto-negotiation
dscpPbitMap (QoS mapping from L3 to L2)
IpInterface=2 (rec. MO id for Signalling and Payload)
vLan/vid (true/false and vlan id)
IpAccessHostEt=1
IpSyncRef (if NTP synchronisation is used)
syncStatus should be OK
nodeSystemClock should be in LOCKED_MODE.
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Enabled Features
The following features directly impact end user throughput
Downlink/Uplink Baseband Capacity
64-QAM DL / 16-QAM UL
To quickly check active licenses (including states):
moshell> inv
Channel Bandwidths:
64-QAM DL / 16-QAM UL:
These features provide higher capacity modulation types for the DL
and UL respectively. More bits/symbols are supported, hence greater
transport block sizes (throughput rates).
Dual Antenna DL Performance Package:
Provides two radio transmission modes: Transmit Diversity and Open
Loop Spatial Multiplexing (OLSM).
OLSM is an antenna technology that can effectively double the
available throughput in the air interface.
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Expected Throughput (Simplified)
This reference shows the expected L1 downlink throughput for
different antenna/radio configurations.
Knowing what L1 throughput to expect in ideal conditions for
different radio configurations is extremely important.
Some inputs to radio setup are thus defined as:
Cyclic Prefix in use
Scheduling Blocks (= 2 RBs)
Configured Control Region Size
Frequency Bandwidths
L1 throughput will include overheads, so expected user throughput
is less than this.
DL SB to Bit calculation
DL Scheduling Block (SB) -> Bit calculation (Normal
CyclicPrefix)
Tx Diversity
2x2 MIMO
Resource Elements (RE) per Resource Block (7 OFDM symbols x 12
SubCarriers)
84
168
168
336
16
32
1
2
3
1
2
3
RE per CRS (OFDM*12 - 4 RS Tx) (OFDM*12 - 8 RS MIMO)
8
20
32
16
40
64
144
132
120
288
264
240
288
264
240
576
528
480
576
528
480
1152
1056
960
864
792
720
1728
1584
1440
20 MHz => 100 RB (64 QAM)
86.4
79.2
72
172.8
158.4
144
64.8
59.4
54
129.6
118.8
108
43.2
39.6
36
86.4
79.2
72
21.6
19.8
18
43.2
39.6
36
76
64
52
152
128
104
Identify the domain
Further analysis required:
Analysis steps to perform:
Single UE call scenario
Optionally use a radio monitor (e.g. TEMS)
Decide - Radio or Transport analysis:
Radio issues provide more control for LTE RAN analysis
Transport issues blend/carry-on towards core elements
*
Steps:
Avoid multi-use and mobility cases. Selective tracing in baseband
is currently limited.
Take logs from a controllable location e.g. on S1 using Wireshark
or internal tools.
Aside from the node logs, we should obtain as many logs as possible
(e.g. TEMS, Routers, Switches, etc).
Iperf is a flexible client/server tool. It runs on multiple
operating systems and can change roles (between
server/client)
UDP allows us to test the pipes and avoids TCPs congestion control
algorithms (which complicate analysis)
TCP will be covered later for completeness
Decide
Radio:
Transport:
?What of cell throughput? - i.e. why only 1 UE
?Is iperf the best tool for the job? Why not Ixia or
<vendor>?
Slide title In CAPITALS 44 pt Slide subtitle 20 pt
Radio Analysis
Radio Analysis
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Radio Analysis
Ericsson’s LTE Baseband provides a detailed mechanism for tracing
the complete L1 and L2 interaction, including MAC scheduling
decisions and L1 decoding results.
Using this information we can further isolate the cause of the
problem and pinpoint either:
UE problem
Scheduling abnormality
eNB northbound problem
S1 user plane
RADIO ANALYSIS
To perform targeted radio analysis, it’s useful to know radio
aspects specific to the following traffic scenarios:
Downlink
Uplink
*
We’ll start by presenting an overview of the Uplink and Downlink
Radio Analysis Areas
Following that, we’ll deep dive into downlink analysis followed by
uplink analysis
The analysis will consist of theory relevant to the area combined
with signals and traces to view the behaviour in a live
system
Finally a few slides show post-processing tools available for
traces to simplify analysis.
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Radio Analysis - Downlink
Areas of analysis for Downlink:
CQI (Channel Quality Index) and RI (Rank Indicator) reported from
UE.
Transmission Mode: MIMO (tm3) vs. TxD (tm2) vs. SIMO (tm1)
MCS vs. number of assigned PRBs vs. assignable bits in
scheduler
UE Scheduling percentage of TTIs (how often is the UE
scheduled)
CFI (number of OFDM symbols for PDCCH) vs. MCS vs. %
scheduling
HARQ
These are the fundamental areas of analysis for downlink:
CQI and RI provides us the SINR/antenna layer reception reports
from the UE point of view
Transmission modes 1 (SIMO),2 (Transmit Diversity) and 3 (Open Loop
Spatial Multiplexing) are supported by the eNB in L11A.
Understanding the relationship between chosen MCS, assigned PRBs
and assignable bits in the scheduler are important for sorting core
network issues/UE issues from air interface issues
Scheduling percentage means the amount of TTIs (typically measured
per second) that the UE was scheduled. This is also related to the
resources allocated for PDCCH (control channels)
PDCCH CFI impacts the % TTI scheduling but also reduces the maximum
MCS achievable.
HARQ will be presented using tracing. Check also the Uplink HARQ
for more detailed theoretical explanation.
RLC retransmissions will be touched on briefly, including how to
trace RLC status messages and some parameters involved.
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Radio Analysis – Uplink
Uplink scheduling overview
PHR (Power Headroom Report) – is the UE at maximum power?
Cell bandwidth vs. maximum allowable PRBs
Link Adaptation
HARQ (less important, because we can measure SINR)
*
These are the fundamental areas of analysis for uplink:
We’ll begin this section with an overview of uplink
scheduling
BSR is the mechanism the UE uses to inform the eNB about the amount
of data waiting in its RLC buffers
PHR is the mechanism the UE uses to inform the eNB about remaining
power at the transmitter (or power limitations)
The number of PRBs available for uplink scheduling has some 3GPP
specified limitations which different from downlink. This means
that, for example, the maximum number of PRBs (for a single UE)
able to be scheduled in 5MHz is 20 and not 23 (with 2 reserved for
PUCCH).
Link adaptation inputs for uplink vary from downlink. One
difference is the CQI (estimate of SINR) is not needed because the
eNB can itself measure SINR of PUSCH transmissions.
PDCCH collisions can occur with SIB/downlink transmissions as
downlink and uplink grants are both scheduled using the same PDCCH
resources.
The theory of HARQ in uplink is presented.
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Radio Analysis DL – CQI/RI and TM
The eNB needs knowledge of the SINR conditions of downlink
transmission to a UE in order to select the most efficient MCS/PRB
combination for a selected UE at any point in time.
Channel Quality Index (CQI):
Informs eNB of current channel conditions as seen at UE
Directly maps to 3GPP defined modulation/code rate (TS36.213 Table
7.2.3-1)
Defined as the highest coding rate the UE could decode at 10% BLER
on HARQ rv=0 transmission
CQI 1-6 map to QPSK
CQI 7-9 map to 16QAM
CQI 10-15 map to 64QAM
Rank Indicator (RI)
Is a feedback mechanism from UE to eNB
Informs eNB whether UE can successfully decode RS from 1 or 2 (or
more) antennas.
eNB scheduler uses this feedback to transmit with either:
*
Radio analysis DL – CQI/RI and TM
The UE measures DL channel quality and reports to eNodeB in the
form of Channel Quality Information (CQI)
The average CQI (periodic-CQI reporting) for the whole band
(wide-band CQI) is reported periodically on PUCCH (or on PUSCH if
user data is scheduled in that TTI) with configured
periodicity.
Sub-band CQI (aperiodic-CQI reporting) is reported when requested
by the eNB. This report is for the PDSCH. Report sent on
PUSCH.
CQI polling is triggered on demand by eNB based on DL traffic
activity.
When 2 antennas are configured, Rank Indicator is also reported.
Precoding Matrix Indicator (PMI) also reported in case of
transmission mode 4 (not in L11A).
CQI
Periodic CQI reports are WCQI only.
Sent on PUCCH (unless PUSCH data is scheduled, in which case it’s
multiplexed onto PUSCH).
Aperiodic CQI reports (eNB must specifically request aperiodic CQI
report in the uplink grant) include RI+WCQI+SCQI
(NOTE: may be requested periodically by the eNB)
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Radio Analysis DL – CQI/RI and TM
In order to transmit with MIMO (OLSM) we should check the
following:
eNB cell is configured with two working transmit antennas.
Check EUtranCellFDD::noOfUsedTxAntennas > 1
L11A GA (default) system constant SC125:3 means that tm3 is used in
case 2 TX antennas are defined.
If only one TX antenna is configured, then tm1 is used
In order to force Transmit Diversity (i.e. prevent OLSM), SC125:2
must be set
UE CQI/RI report from UE shows RI > 1
Rank 1: TxDiversity (transmission mode 2, tm2)
Rank 2: MIMO (Open Loop Spatial Multiplexing in L11A) (transmission
mode 3, tm3)
mtd peek -ta ulMacPeBl -signal LPP_UP_ULMACPE_CI_UL_L1_MEAS2_DL_IND
-dir OUTGOING
This signal (from L1 to MAC scheduler) shows the reported CQI and
RI
(also shows HARQ ACK/NACK for downlink data transmission)
(also shows rxPowerReport and timingAdvanceError)
*
EUtranCellFDD::noOfTxAntennas may be configured as 0 or 2 to
support MIMO (0 means automatically detect number of transmit
antennas available).
Default system parameters in L11A are for open-loop spatial
multiplexing (MIMO), otherwise known as tm3. If only one transmit
antenna is configured, the system will automatically switch to
SIMO.
Therefore it’s possible to switch between SIMO and MIMO using MOM
parameters.
It’s not possible to configure transmit diversity without using
system constants (SC125:2) in L11A.
Rank Indicator is the only way that eNB switches between:
RI=2 OLSM (tm3) and
RI=1 Transmit Diversity (tm2)
Slide title 30 pt Text 18 pt Bullets level 2-5 16 pt !"#
$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~¡¢£¤¥¦§¨©ª«¬®¯°±²³´¶·¸¹º»¼½ÀÁÂÃÄÅÆÇÈËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿŒœŠšŸƒˆ˜–—‘’‚“”„†‡•…‰‹›⁄€™−≤≥
cfrPusch { cfrInfo { ri = 2, cfrLength = 22, cfrFormat = 4,
cfrValid = 1, cfrExpected = 1, cfrCrcFlag = 1 }, cfr[] = [61440, 0,
0, 0] as hex: [f0 00 00 00 00 00 00 00] }
Radio Analysis DL – CQI/RI and TM
LPP_UP_ULMACPE_CI_UL_L1_MEAS2_DL_IND UpUlMacPeCiUlL1Meas2DlIndS
{
cfrPucch { cfrInfo { ri = 0, cfrLength = 4, cfrFormat = 0, cfrValid
= 1, cfrExpected = 1, cfrCrcFlag = 1 }, cfr[] = [0, 0] as hex: [00
00 00 00] }
cfrFormat=0 is a WCQI report only (ignore RI)
Valid report if cfrValid=1,cfrExpected=1,cfrCrcFlag=1
mtd peek -ta ulMacPeBl -signal LPP_UP_ULMACPE_CI_UL_L1_MEAS2_DL_IND
-dir OUTGOING
cfrFormat=4 is a SCQI + RI report
WCQI is first half octet (f => 15). Octets thereafter are
subband CQI reports for each RBG.
A number of subband CQIs follow (see next slide)
cfrPusch { cfrInfo { ri = 2, cfrLength = 18, cfrFormat = 4,
cfrValid = 1, cfrExpected = 1, cfrCrcFlag = 1 }, cfr[] = [48969,
49152, 0, 0] as hex: [bf 49 c0 00 00 00 00 00] }
Rank Indicator = 2 (indicates UE can decode both antenna
streams)
WCQI = 11. 5MHz bandwidth means 4PRBs subbands.
SCQI = F49C = 11 11 01 00 10 01 11 00
*
We only show the relevant parts of the signal content here for
presentation purposes.
The top example is WCQI on PUCCH (periodic CQI report)
Middle example is aperiodic CQI report on PUSCH including
RI+WCQI+SCQI where all reported subbands have same value as WCQI
(15). This is the best possible channel quality report available,
CQI15 is maximum.
Bottom example is aperiodic CQI report on PUSCH including
RI+WCQI+SCQI with variable SCQI reports as indicated. The subbands
only indicate an offset from the WCQI value (this case 11). So, for
example, subband PRBs 0-3 are CQI 10 or less and so on.
Slide title 30 pt Text 18 pt Bullets level 2-5 16 pt !"#
$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~¡¢£¤¥¦§¨©ª«¬®¯°±²³´¶·¸¹º»¼½ÀÁÂÃÄÅÆÇÈËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿŒœŠšŸƒˆ˜–—‘’‚“”„†‡•…‰‹›⁄€™−≤≥
Radio Analysis DL – SCQI Visualisation
From the previous slide, SCQI is visualised here..
For 5MHz, each RBG is 4 PRBs wide (except for SCQI group 7)
SCQI is given relative to WCQI which was 11 in this example
f
0 1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18 19 20
21 22 23 24
5 MHz
SCQI PRBs: 0-3 -1, 4-7 -1, 8-11 +1, 12-15 0, 16-19 +2, 20-23 +1, 24
-1
Sub-band 1 2 3 4 5 6 7
CQI value ( 10 10 12 11 13 12 10 )
*
Radio analysis DL – CQI/RI and TM
cfrFormat = 4 consists of:
4 bit Wideband CQI (i.e. CQI across whole bandwidth)
Up to 13 subband CQI differentials (depends on bandwidth of
cell)
Subband CQI (3GPP TS36.211 Ch 7.2.1)
RBG width depends on bandwidth:
3 & 5MHz – subband width 4 PRBs
10MHz – subband width 6 PRBs
15 & 20MHz – subband width 8 PRBs
Subband Differential mapping, see table below:
*
Radio analysis DL – CQI/RI and TM
7 possible cfrFormats defined in L11A.
Typically see reports cfrFormat 0 and 4 as described
previously
Note that PMI is not yet used (requires tm4)
cfrFormat
Radio analysis DL – CQI/RI and TM
Transmission Mode and MCS can be traced out with the
following:
ULMA4/UpcDlMacCeFt_DL_SCHEDULER LEVEL2 cellId=12 : Selected SE and
HARQ: rnti=61 bbUeRef=201327456 HARQ idx=1 tbs={7992 0} mcs={18 0}
noOfSBs={4294443008 0} rv={0 1} ndi={0 0} rmGbits={21600 0}"
MCS for each codeword. In this case, tm2 so only one MCS
listed.
lhsh gcpu01024 te e trace4 UpcDlMacCeFt_DL_SCHEDULER
LPP_UP_DLMACPE_CI_DL_UE_ALLOC_IND (330) UpDlMacPeCiDlUeAllocIndS
{
prbList[] = [4294443008, 0, 12, 0]dec
[ff f8 00 00 00 00 00 00 00 00 00 0c 00 00 00 00]hex
commonTb { newDataFlag = 1, tbSizeInBytes = 999, l1Tb { rvIndex =
0, modType = 2 (UPDLMACPEMode64Qam), nrOfRateMatchedBits = 21600,
rmSoftBits = 1237248 } }
PRB list in RBGs, for 5MHz RBG size is 2. fff8 corresponds to 25
PRBs (last PRB is 1 less).
MCS is a combination of tbSize and modType.
999 bytes = 7992 bits then put into TS36.213 Table 7.1.7.2.1-1 for
NPRB=25. That gives ITBS of 16.
Convert ITBS to MCS using Table 7.1.7.1-1.
mtd peek -ta dlMacPeBl -signal LPP_UP_DLMACPE_CI_DL_UE_ALLOC_IND
-dir INCOMING
-filter {(U16SIG)8,NEQ,(U16)0x00}
*
There are two possible traces for viewing MCS+TM+PRBs+HARQ info.
They both show the same information in a different format:
lhsh gcpu01024 te e trace4 UpcDlMacCeFt_DL_SCHEDULER
This trace show everything on one line. Transmission mode is not
explicitly stated.
mtd peek -ta dlMacPeBl -signal LPP_UP_DLMACPE_CI_DL_UE_ALLOC_IND
-dir INCOMING -filter {(U16SIG)8,NEQ,(U16)0x00}
This is the signal between MAC and L1 informing all the HARQ
information.
prbResourceIndicatorType will be explained in the next slide
Slide title 30 pt Text 18 pt Bullets level 2-5 16 pt !"#
$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~¡¢£¤¥¦§¨©ª«¬®¯°±²³´¶·¸¹º»¼½ÀÁÂÃÄÅÆÇÈËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿŒœŠšŸƒˆ˜–—‘’‚“”„†‡•…‰‹›⁄€™−≤≥
Radio Analysis DL – CQI/RI and TM
RBG for Resource Allocation Type 0
Defined in 3GPP TS36.213 Ch 7.1.6.1
One bit used to represent a certain number of consecutive
PRBs
1.4MHz is RBG size 1
3 & 5MHZ is RBG size 2
10MHz is RBG size 3
15 & 20MHz is RBG size 4
*
Resource Allocation Types vary between system bandwidths to reduce
the required message size for larger bandwidths.
Larger bandwidths use larger RBG sizes.
Slide title 30 pt Text 18 pt Bullets level 2-5 16 pt !"#
$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~¡¢£¤¥¦§¨©ª«¬®¯°±²³´¶·¸¹º»¼½ÀÁÂÃÄÅÆÇÈËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿŒœŠšŸƒˆ˜–—‘’‚“”„†‡•…‰‹›⁄€™−≤≥
Radio analysis DL – CQI/RI and TM
Example of switching transmission modes based upon RI
(bfn:3352, sfn:280, sf:5.47, bf:128)
ULMA4/UpcDlMacCeFt_DL_SCHEDULER LEVEL2 cellId=12 : Selected SE and
HARQ: rnti=61 bbUeRef=201327456 HARQ idx=1 tbs={7992 0} mcs={18 0}
noOfSBs={4294443008 0} rv={0 1} ndi={0 0} rmGbits={21600 0}"
TM=2 transmission with MCS 18
cfrPusch { cfrInfo { ri = 2, cfrLength = 18, cfrFormat = 4,
cfrValid = 1, cfrExpected = 1, cfrCrcFlag = 1 }, cfr[] = [48969,
49152, 0, 0] as hex: [bf 49 c0 00 00 00 00 00] }
Rank Indicator = 2 received from UE. eNB will now switch to tm3
(OLSM MIMO) transmission
WCQI 11 + SCQI.
bfn:3352, sfn:280, sf:6.47, bf:131) ULMA4/UpcDlMacCeFt_DL_SCHEDULER
LEVEL2 cellId=12 : Selected SE and HARQ: rnti=61 bbUeRef=201327456
HARQ idx=0 tbs={5736 5736} mcs={13 13} noOfSBs={4294443008 0} rv={0
0} ndi={0 1} rmGbits={14400 14400}"
25 PRBs as according to previous example
*
This example shows a switch between tm2 and tm3 based upon RI=2
aperiodic CQI report reception.
Slide title 30 pt Text 18 pt Bullets level 2-5 16 pt !"#
$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~¡¢£¤¥¦§¨©ª«¬®¯°±²³´¶·¸¹º»¼½ÀÁÂÃÄÅÆÇÈËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿŒœŠšŸƒˆ˜–—‘’‚“”„†‡•…‰‹›⁄€™−≤≥
Radio Analysis DL – Assignable Bits
If UE is sending with high CQI (in the range 10-15) and RI=2 but
throughput is still very low, then the next check should be
assignable bits.
Assignable bits means the amount of data in the downlink buffer
available for the scheduler to schedule for this UE.
A classic symptom of low assignable bits is that the UE is
scheduled with a high MCS but a low number of PRBs.
The scheduler always attempts to send with the highest possible MCS
and least number of PRBs so that left-over PRBs could be assigned
to another UE.
*
Radio Analysis DL – Assignable Bits
Possible causes for low assignable bits:
RLC STATUS messages are not being received fast enough and RLC
buffers are full.
Until RLC STATUS ACK messages are received, already transmitted RLC
SDUs are kept in memory in UE and/or eNB
Check for RLC DISCARDs but low (or 0) assignable bits
Data received from core network is not enough to fill the RLC
buffers in eNB.
Check that non-TCP based traffic is not being sent with too large
packet size. For iperf based traffic, recommended size 1360 bytes
(default is 1470).
Set MTU of 1360 in UE (or UE laptop).
RLC DISCARDs will trigger TCP congestion control and lower
thpt.
In L11A the default RLC buffer size per RB is 750 IP packets
Trace discards with lhsh gcpu00768 te e all
UpDlPdcpPeFt_DISCARD
Discards on UDP traffic will not affect throughput
*
Radio Analysis DL – Assignable Bits
ULMA3/UpDlPdcpPeFt_DISCARD TRAFFIC_ABNORMAL Discarding DL PDCP PDU
due to exceeding limits. maxBufferedPacketsInRlc=751
totalNumNonAckedDrbPackets=751 cellId=12 bbUeRef=201327456
bbBearerRef=201327458 receiveFromTeid=3779046158 payloadLength=1506
bytes incl GTP-U header. hoState=0"
750 is default PDCP/RLC buffer per UE in eNB (L11A)
TRAFFIC_ABNORMAL corresponds to trace1. Traffic discards for UDP
are normal, but for TCP traffic it will cause severe throughput
degradation
ULMA4/UpcDlMacCeFt_DL_SCHEDULER LEVEL3 cellId=12 : Selected SE and
PQ: rnti=61 bbUeRef=201327456 PQ lcid=1 assignableBits=0
minPduSize=56 selectedHarq=0"
ULMA4/UpcDlMacCeFt_DL_SCHEDULER LEVEL3 cellId=12 : Selected SE and
PQ: rnti=61 bbUeRef=201327456 PQ lcid=2 assignableBits=0
minPduSize=56 selectedHarq=0"
ULMA4/UpcDlMacCeFt_DL_SCHEDULER LEVEL3 cellId=12 : Selected SE and
PQ: rnti=61 bbUeRef=201327456 PQ lcid=3 assignableBits=8554024
minPduSize=56 selectedHarq=0"
LCID 3 is for the default bearer. LCID 1 and 2 for SRB
About 1MByte of data available for scheduling. Check for low value
of assignable bits which indicates e2e problems affecting data
available to schedule on air for eNB. Low assignable bits for UDP
traffic may indicate MTU problems.
lhsh gcpu00768 te e all UpDlPdcpPeFt_DISCARD
lhsh gcpu01024 te e trace4 UpcDlMacCeFt_DL_SCHEDULER
*
Radio Analysis DL – CFI and Scheduling
Another cause of low (or lower than expected) throughput is that
the UE is not being scheduled in every TTI.
This may be caused by:
Limitations in current scheduler implementation
3GPP defined compromises between control channel efficiency and
scheduling efficiency (especially for lower number of users)
L11A software has some limitations to be aware of:
Only one SE per TTI is supported in L11A
SIBs are scheduled in the same was a user data (i.e. they are sent
to the scheduler).
When a SIB is transmitted, no user data can be transmitted in the
DL at the same time (using default parameters).
It is possible to use (System Constant) SC43 to enable 2SE/TTI in
DL
*
System Constant SC43 controls the number of SE/TTI in the downlink.
The default value of SC43 is 1 in L11A GA, however it is possible
for lab testing to set SC43:2 and have 2 SE/TTI in the
downlink.
System constant definition for L11A GA is found at
http://cdmweb.ericsson.se/WEBLINK/ViewDocs?DocumentName=1%2F19059-HRB105500&Revision=PE2-10
Slide title 30 pt Text 18 pt Bullets level 2-5 16 pt !"#
$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~¡¢£¤¥¦§¨©ª«¬®¯°±²³´¶·¸¹º»¼½ÀÁÂÃÄÅÆÇÈËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿŒœŠšŸƒˆ˜–—‘’‚“”„†‡•…‰‹›⁄€™−≤≥
Radio Analysis DL – CFI and Scheduling
SIBs require PDCCH resources
Typically SIBs consume 4 or 8 CCEs of PDCCH resources.
If a UE is in good SINR conditions, the scheduler may allocate only
one CCE for that UE.
In that case, because of limited positions in PDCCH, it is quite
likely that a PDCCH collision occurs (especially in low system
bandwidths)
If a UE is in bad SINR conditions, the scheduler may allocate a
large number of CCEs for that UE (2 or 4 or 8 CCEs)
Depending on the configured CFI there may only be common search
space available or it may still collide with other PDCCH
users.
*
When the UE is in good SINR, only one CCE is used for PDCCH
transmission
In this case, a CCE index is calculated per subframe and may be at
the beginning of a SIB (8 CCEs). In this case, up to 6 consecutive
slots will be attempted. All of these will overlap with SIBs and
then PDCCH collision has occurred for all possible search
spaces.
When the UE is in bad SINR, many CCEs may be allocated
Large CCEs have limited possible search spaces and a collision may
be unavoidable when SIB is scheduled or when other downlink users
are scheduled.
Slide title 30 pt Text 18 pt Bullets level 2-5 16 pt !"#
$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~¡¢£¤¥¦§¨©ª«¬®¯°±²³´¶·¸¹º»¼½ÀÁÂÃÄÅÆÇÈËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿŒœŠšŸƒˆ˜–—‘’‚“”„†‡•…‰‹›⁄€™−≤≥
Radio Analysis Dl – HARQ
Each transport block transmission is represented as a HARQ
process.
Each HARQ process data is held in memory until NDI is toggled (i.e.
New data is to be sent).
This allows fast retransmission of erronerously received
data.
The schedulers representation of an HARQ process is as
follows:
Feedback status
MCS – modulation and coding scheme
RV – redundancy version. HARQ has 4 redundancy versions, rv0, rv2,
rv3, rv1.
NDI – New Data Indicator (physical layer bit toggled for new
data).
Do not confuse with newDataFlag which is scheduler internal flag
where 1 means new data and 0 means retransmission.
Number of transmission attempts (max 4 transmissions in L11A
default paramters)
In case of rank 2 spatial multiplexing there are 16 HARQ process
per UE instead of 8, but there are two processes that share the
same ID
*
4 redundancy versions exist for HARQ and they are used in the
following order the order RV0, RV2, RV3, RV1.
In case > 4 transmissions are configured, the cycle repeats,
e.g. RV0, RV2, RV3, RV1, RV0, RV2, RV3, RV1, etc
Default is for 4 HARQ transmissions on L11A
Increasing the default number of transmissions means that RLC
parameters also need to be modified and will require larger RLC
buffers
In case one CW is ACKed and one CW is NACKed then the eNB
retransmits BOTH CWs (even though one was received
successfully).
L11A does not send new data on one branch and retransmission on
another.
Another solution could be to send the NACKed CW using transmit
diversity (but L11A does not do this).
Slide title 30 pt Text 18 pt Bullets level 2-5 16 pt !"#
$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~¡¢£¤¥¦§¨©ª«¬®¯°±²³´¶·¸¹º»¼½ÀÁÂÃÄÅÆÇÈËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿŒœŠšŸƒˆ˜–—‘’‚“”„†‡•…‰‹›⁄€™−≤≥
Radio Analysis Dl – HARQ Example
The following slides will show an example of tracing out downlink
HARQ
Initial downlink grant is sent with rv=0 (MIMO, 2 codewords)
SFN 280/subframe 8
SFN 281/subframe 2 (DL Grant + 4TTI)
First retransmission sent with rv=2
SFN 281/subframe 6 (8 TTI past initial transmission is earliest
occasion)
HARQ ACK received on both code words
SFN 282/subframe 0 (DL Grant ReTx + 4TTI)
*
Radio Analysis Dl – HARQ DL Grant
LPP_UP_DLMACPE_CI_DL_UE_ALLOC_IND (330) UpDlMacPeCiDlUeAllocIndS
{
prbList[] = [4294443008, 0, 12, 0]dec
[ff f8 00 00 00 00 00 00 00 00 00 0c 00 00 00 00]hex
swapFlag = 0
commonTb { newDataFlag = 1, tbSizeInBytes = 717, l1Tb { rvIndex =
0, modType = 1 (UPDLMACPEMode16Qam), nrOfRateMatchedBits = 14400,
rmSoftBits = 1237248 } }
macTb { dlHarqProcessId = 0, nrOfMacCtrlElem = 0 }
rlcTb { nrOfBearer = 1, bearerAlloc[0] { bbBearerRef = 201327458,
lcid = 3, rbScheduledSizeInBytes = 717 } }
}
...
SFN/subframe where DL PDSCH will occur. PDCCH DL Grant sent at same
sfn/subframe.
RNTI, TM, used PRBs (same for both code words)
If re-transmission, this indicates if CW0 and CW1 swapped
layers
newDataFlag indicates if it is new data or not
HARQ redundancy version. rv0 used for initial transmission, rv2,
rv3, rv1 used for re-transmission.
HARQ process number. 8 HARQ processes exist in FDD LTE L11A.
CW1 defined here.
Radio Analysis Dl – HARQ FEEDBACK (NACK/NACK)
LPP_UP_ULMACPE_CI_UL_L1_MEAS2_DL_IND (431)
UpUlMacPeCiUlL1Meas2DlIndS {
timingAdvanceError { timingAdvanceError = 1 }
}
}
}
SFN/subframe +4 from DL grant (i.e. where the HARQ ACK/NACK is
received from UE).
HARQ NACK received for DL HARQ Process 0 on both code words.
*
Radio Analysis Dl – HARQ ReTX
LPP_UP_DLMACPE_CI_DL_UE_ALLOC_IND (330) UpDlMacPeCiDlUeAllocIndS
{
prbList[] = [4294443008, 0, 12, 0]dec
[ff f8 00 00 00 00 00 00 00 00 00 0c 00 00 00 00]hex
swapFlag = 0
commonTb { newDataFlag = 0, tbSizeInBytes = 717, l1Tb { rvIndex =
2, modType = 1 (UPDLMACPEMode16Qam), nrOfRateMatchedBits = 14400,
rmSoftBits = 1237248 } }
macTb { dlHarqProcessId = 0, nrOfMacCtrlElem = 0 }
rlcTb { nrOfBearer = 0 }
commonTb { newDataFlag = 0, tbSizeInBytes = 717, l1Tb { rvIndex =
2, modType = 1 (UPDLMACPEMode16Qam), nrOfRateMatchedBits = 14400,
rmSoftBits = 1237248 } }
SFN/subframe where DL PDSCH will occur. PDCCH DL Grant sent at same
sfn/subframe.
RNTI, TM, used PRBs (same for both code words)
Same as previous transmission
HARQ redundancy version. rv2 is used for first retransmission
HARQ process number (same as before)
CW1 defined here.
Radio Analysis Dl – HARQ FEEDBACK (ACK/ACK)
LPP_UP_ULMACPE_CI_UL_L1_MEAS2_DL_IND (431)
UpUlMacPeCiUlL1Meas2DlIndS {
timingAdvanceError { timingAdvanceError = 0 }
}
}
}
SFN/subframe +4 from DL grant (i.e. where the HARQ ACK/NACK is
received from UE).
HARQ ACK/ACK received for DL HARQ Process 0 on both code
words.
*
Radio Analysis DL – RLC
RLC retransmissions are triggered:
When HARQ fails to transmit a transport block within the maximum
number of configured retransmissions
Default number of HARQ transmissions is 4 in L11A
If RLC STATUS messages are not received within the time frames
configured
RLC STATUS messages are sent between peer nodes (eNB and UE) to
inform about lost RLC packets. They can be traced out using
mtd peek -ta dlRlcPeBl -si
UP_DLRLCPE_FI_STATUS_FOR_DL_TRAFFIC_IND
Check:
ACK_SN should be increasing, otherwise RLC buffers are not
released
NACK_SN indicates RLC retransmissions (occasionally is OK)
DataRadioBearer::tStatusProhibit governs how often RLC STATUS
messages may be generated, default is 25ms in L11A.
*
Radio Analysis DL – RLC
RLC PDU {
ACK_SN = 743
}
}
Indicates the SN (Sequence Number) of the last successfully
received RLC packet
NACK_SN indicates RLC retransmissions (HARQ failures)
0xd4205d4f=(sfn:324, sf:5.33, bf:212):
UP_DLRLCPE_FI_STATUS_FOR_DL_TRAFFIC_IND (343)
UpDlRlcPeRlcStatusForDlTrafficIndS {
RLC PDU {
ACK_SN = 787
}
}
Check that ACK_SN is increasing or RLC buffers not released
*
Radio Analysis – Uplink
Uplink scheduling overview
PHR (Power Headroom Report) – is the UE at maximum power?
Cell bandwidth vs. maximum allowable PRBs
Link Adaptation
HARQ (less important, because we can measure SINR)
*
These are the fundamental areas of analysis for uplink:
We’ll begin this section with an overview of uplink
scheduling
BSR is the mechanism the UE uses to inform the eNB about the amount
of data waiting in its RLC buffers
PHR is the mechanism the UE uses to inform the eNB about remaining
power at the transmitter (or power limitations)
The number of PRBs available for uplink scheduling has some 3GPP
specified limitations which different from downlink. This means
that, for example, the maximum number of PRBs (for a single UE)
able to be scheduled in 5MHz is 20 and not 23 (with 2 reserved for
PUCCH).
Link adaptation inputs for uplink vary from downlink. One
difference is the CQI (estimate of SINR) is not needed because the
eNB can itself measure SINR of PUSCH transmissions.
PDCCH collisions can occur with SIB/downlink transmissions as
downlink and uplink grants are both scheduled using the same PDCCH
resources.
The theory of HARQ in uplink is presented.
Slide title 30 pt Text 18 pt Bullets level 2-5 16 pt !"#
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Radio Analysis UL – UPlink Scheduling
UL
eNodeB
Channel sounding
UL grant
Uplink Scheduling consists of the following components:
(if a UE has no PUSCH resources allocated) SR is sent by UE to eNB
in order to request UL grant for BSR transmission
UL grant sent by eNB to UE. Initial buffer size in UL grant is set
to size of BSR report + size of small ping/VoIP packet (to improve
latency).
UE transmits BSR + data (in case data is small enough to fit in the
initial UL grant buffer size allocated)
UL grant based upon BSR is allocated to UE (according to existing
UL demands and link adaptation parameters)
UE transmits data on PUSCH according to UL grant
Channel sounding DMRS and SRS (not used in L11A) are used so that
eNB can understand channel response across PUSCH and schedule UE
accordingly.
Slide title 30 pt Text 18 pt Bullets level 2-5 16 pt !"#
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macCtrlElementList[0] {
}
Radio Analysis Ul – BSR
Buffer Status Report (BSR) is used to inform the eNB of the current
data waiting for transmission in the UE (3GPP TS36.213 Ch.
6.1.3.1)
Values ranges from 0 up to >15000 bytes using 64 index
values.
e.g. index 0 for BS=0, index 1 for 0 < BS <= 10 and so
forth.
Can be traced out through LPP_UP_ULMACPE_CI_UL_MAC_CTRL_INFO_IND.
Expect to see high values for maximum UL throughput. Low values
indicate UE/laptop problem.
Type of MAC report, this case short BSR (6)
LSB 6 bits are the BSR index (this case >150000 bytes)
MSB 2 bits is the LCID
*
Radio Analysis UL – PHR
Power Headroom Report (PHR) is used to inform the eNB of the
remaining transmit power available at the UE. (3GPP TS36.321 Ch.
6.1.3.6)
Defined as difference between configured maximum UE output power
and estimated power used for PUSCH transmission
Reports a index value similar to BSR with values between -23 up to
40 dB
PH values are close to (or less than) 0 means the UE is power
limited
Ideally we look for positive values somewhat greater than 0
*
Radio Analysis UL – PHR
}
Type of MAC report, this case PHR (3)
PHR value of 55 which corresponds to 32 <= PH < 33. In this
case there is no power limitation on the UE side.
PH Index values <= 23 indicates the UE has reached maximum
transmission power
Negative values indicate the UE was power limited
See 3GPP TS36.133 Ch 9.1.8.4 for index mapping
*
Radio Analysis UL – PUCCH and PUSCH
PUCCH takes a minimum 1 PRB on each side of the uplink band for
uplink control signalling, reducing the size of PUSCH
E.g. 5MHz bandwidth, 25 PRBs available. Minimum 2 PRBs for
PUCCH.
23 PRBs available for PUSCH
0
1
2
3
4
5
6
7
8
9
PUSCH – Used for UE data scheduling and UL RA msgs
PUCCH – Semi-static allocation of CQI, SR, ACK/NAK
PUCCH – Semi-static allocation of CQI, SR, ACK/NAK
PUCCH
PUCCH
PUSCH
Radio Analysis UL – PRB Limitations
Due to 3GPP specified design limitations in the UL it is not always
possible to utilise all free PRBs for UL transmissions
3GPP TS36.211 Ch 5.3.3 defines the following formula for the number
of PRBs on PUSCH for a single transmission:
Where a, b and c are integers.
For 5MHz:
23 PRBs are available for PUSCH (2 allocated to PUCCH)
Max number of PRBs for a single PUSCH transmission is 20
PRBs.
This corresponds to a=2, b=0 and c=1 (i.e. 3 PRBs are unavailable
to be used).
In L11A, 3 PRBs would be unused (only one SE/TTI possible).
*
Radio Analysis UL – Link Adaptation
Goal: Select MCS for a certain allocation size to maintain the
target BLER (10%) for the first transmission
Inputs to Uplink Link Adaptation are:
UL interference power:
LPP_UP_ULMACPE_CI_UL_L1_MEAS2_UL_IND outgoing from ulMacPeBl
LPP_UP_ULMACPE_CI_UL_MAC_CTRL_INFO_IND outgoing from
ulMacPeBl
cellStatusReportInd(interferencePower (-125 .. -80dB)
Input to Link Adaptation
Radio Analysis UL – Link Adaptation
LPP_UP_ULCELLPE_CI_CELL_STATUS_REPORT_IND
UpUlCellPeCiCellStatusReportIndS {
sfn = 456
subFrameNo = 3
interferencePower = -1170
High values here (>-104)
rxPwr = -95.6dBm over those PRBs (pZeroNominalPusch= -96dBm)
= ~22.9dB
Radio Analysis UL – Link Adaptation
L11A supports up to MCS 24 in the uplink by default
MCS21-24 are defined as 64QAM
However, according to 3GPP TS36.213 Ch 8.6.1 if a UE does not
support 64QAM then 16QAM can be used for MCS21-24.
Check that MCS24 is selected. If not, check link adaptation inputs
for problems
In UL, the eNB itself can directly measure SINR of the received
signal
Therefore CQI is not necessary for UL transmission
*
Radio Analysis UL – Link Adaptation
Check for:
Could there be some external interferer?
Are the values of pZeroNominalPusch in neighbour cells too
high?
rxPower too low
PHR shows UE at maximum Tx power
Is EUtranCellFDD::pZeroNominalPusch too high causing UE to exceed
maximum transmit power?
Closed-loop power control TPC ignored by UE?
Low values of SINR
Is EUtranCellFDD::pZeroNominalPusch too low?
*
Radio Analysis UL – PDCCH
Time (ms)
Radio Frame
PDCCH carries both the UL (PUSCH) assignment and DL (PDSCH)
assignment.
In case many PDCCH CCEs are used for DL transmission (e.g. SIB with
8 CCEs) it may be that UL grant is not possible to be scheduled in
this TTI for a single UE!
PUSCH
DL subframe (current)
PDSCH
PDCCH
*
Radio Analysis UL – PDCCH
Downlink (PDSCH) assignments
Uplink (PUSCH) grants
In case of a downlink SIB transmission, 8 CCEs of PDCCH may be used
for downlink grant.
To reduce processing load when decoding PDCCH, 3GPP defines
particular search spaces within PDCCH depending on:
Number of CCEs for grant
Number of CCEs for PDCCH
RNTI of the UE
Depending on these parameters, it may not be possible to allocate a
PDCCH uplink grant resource and therefore the UE may not be able to
be scheduled every TTI even if there are unused PUSCH
resources.
See 3GPP TS36.213 Ch 9.1.1
*
Radio Analysis UL – PDCCH
Search space for 1 CCE completely overlaps 8 CCE search
space.
*
Radio Analysis UL – HARQ
LTE defines uplink with synchronous HARQ to reduce PDCCH signaling
load and simplify the uplink HARQ processing
Example 1, successfully received PUSCH data:
Subframe n: UL grant sent to UE
Subframe n+4: PUSCH data received (rv=0)
Subframe n+8: ACK sent, UL grant with New Data Indicator
toggled
Subframe n+12: new PUSCH data received (new HARQ process)
Example 2, HARQ retx:
Subframe n+4: PUSCH data received (rv=0)
Subframe n+8: NACK sent, NO UL grant is signaled on PDCCH
*
Radio Analysis UL – HARQ ReTx
Postponed reTx
PUCCH
PUCCH
PRACH
Radio Analysis UL – HARQ
Because of the synchronous nature of Uplink HARQ, the following
scheduling priority is used:
Random Access Message 3 (RRC Connection Request). Scheduled 6
subframes before, special case.
Non-adaptive HARQ retransmission
Adaptive HARQ retransmission
New Data transmission
Non-adaptive means no UL grant is explicitly scheduled for the
retransmission
Adaptive means that scheduling collision occurred (e.g. collision
with PRACH) and an explicit UL grant was signalled to:
Move the allocated PRBs to another part of the UL spectrum
*
Radio Analysis – Traffic Abnormal
TRACE1 in baseband is defined as TRAFFIC_ABNORMAL. It should be
used to trace out abnormal conditions in baseband processing.
Normally the output gives a good description of the problem
encountered
Some useful TRAFFIC_ABNORMAL traces:
*
Radio Analysis – Post-Processing Tools
3GPP has specified L1 messages in order to reduce the bits required
for transmission on the air interface.
These formats can be difficult to read
For this reason, many values in the traces are presented in formats
which require conversion to human readable formats, for
example:
PRBs allocated in DL/UL grant messages
PHR values
BSR values
MIMO HARQ feedback, etc..
Tools exist to perform these conversions and compact the data
presentation to the end user
One such tool is bbfilter or scheduling_filter.pl
Check the flowfox web page for details
*
Radio Analysis – bbfilter Downlink
$ cat decoded_dl_log.log | ./bbfilterv2.2 -bw 5 –dl
sfn|sf|mode|dlModul|mcs1|mcs2|prb|Ndf|Tbs1|Tbs2|AssBits|Harq|dlBler|cqi|ri|
280| 4|TxDi| 64QAM | 16 | 0 |25 | Y|7736| 0|8771784| | | 11|
2|
280| 5| | | | | | | | | |A | 0% | | |
280| 6|TxDi| 64QAM | 18 | 0 |25 | Y|7992| 0|8764088|A | 0% | |
|
280| 7|TxDi| 64QAM | 18 | 0 |25 | Y|7992| 0|8756144|A | 0% | |
|
280| 8|Mimo| 16QAM | 13 | 13 |25 |Y Y|5736|5736|8748192|A | 0% | |
|
280| 9|Mimo| 16QAM | 13 | 13 |25 |Y Y|5736|5736|8736760| | | |
|
281| 0|Mimo| 16QAM | 12 | 12 |25 |Y Y|4968|4968|8737384|A | 0% | |
|
281| 1|Mimo| 16QAM | 13 | 13 |25 |Y Y|5736|5736|8763568|N | 0% | |
|
281| 2|Mimo| 16QAM | 13 | 13 |25 |Y Y|5736|5736|8776208|N N | 2% |
| |
281| 3|Mimo| 16QAM | 13 | 13 |25 |Y Y|5736|5736|8800856|N N | 4% |
| |
281| 4|Mimo| 16QAM | 13 | 13 |25 |Y Y|5736|5736|8825504|N N | 6% |
| |
281| 5|TxDi| 16QAM | 30 | 0 |25 | N|7992| 0|8862160|N N | 8% | |
|
281| 6|Mimo| 16QAM | 30 | 30 |25 |N N|5736|5736|8862200|N N | 10% |
| |
281| 7|Mimo| 16QAM | 30 | 30 |25 |N N|5736|5736|8862200|A A | 10% |
| |
HARQ ACK/NACK refers to the transmission 4 subframes earlier!
NOTE: Format modified to fit on slide, only example!
*
Here we present an example of trace parses.
This example is a modified output of bbfilter –dl which summaries a
number of traces onto one line.
Note how RI=2 is reported then transmission changes from
TxDiversity to MIMO.
BLER rates are approximate values.
Slide title 30 pt Text 18 pt Bullets level 2-5 16 pt !"#
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Radio Analysis – bbfilter Uplink
$ cat decoded_ul_log.log | ./bbfilterv2.2 -bw 5 –ul
sfn|sf|rxPwrPus|prb|ulTpc|sinr|ulModul|mcs|ndf|ul bsr |phr |ul tbs|
ul crc |har|ulBler|
266| 6| -95.6 | 48| 0:1 | 22 | 16QAM | 23| Y | | | 25456| | A | 2%
|
266| 7| -95.6 | 48| 0:1 | 22 | 16QAM | 24| Y | | | 25456| | A | 2%
|
266| 8| -95.6 | 48| 0:1 | 22 | 16QAM | 24| N | | | 25456| ERR 3182|
N | 5% |
266| 9| -95.6 | 48| 0:1 | 23 | 16QAM | 24| Y | | | 24496| | A | 5%
|
267| 0| -95.7 | 48| 0:1 | 22 | 16QAM | 24| Y |>150000 | | 24496|
| A | 5% |
267| 1| -95.8 | 40| 0:1 | 22 | 16QAM | 24| Y | | | 21384| | A | 5%
|
267| 2| -95.6 | 48| | 23 | 16QAM | 24| Y | | | 25456| | A | 5%
|
267| 3| -95.6 | 48| 0:1 | 22 | 16QAM | 24| Y | | | 25456| | A | 4%
|
267| 4| -95.6 | 48| 0:1 | 22 | 16QAM | 23| Y | | | 25456| | A | 4%
|
267| 5| -95.6 | 48| 0:1 | 22 | 16QAM | 23| Y |>150000 | | 25456|
| A | 4% |
267| 6| -95.6 | 48| 0:1 | 23 | 16QAM | 24| N |>150000 | | 25456|
| A | 4% |
267| 7| -95.6 | 48| 0:1 | 23 | 16QAM | 24| Y | | | 25456| | A | 4%
|
267| 8| -95.6 | 48| 0:1 | 22 | 16QAM | 24| Y | | 32 | 24496| | A |
4% |
UL BSR and PHR values decoded
NOTE: Format modified to fit on slide, only example!
*
Here we present an example of trace parses.
This example is a modified output of bbfilter –ul which summaries a
number of traces onto one line.
BSR and PHR are decoded into human readable formats along with
PRBs.
BLER rates are approximate values.
Slide title 30 pt Text 18 pt Bullets level 2-5 16 pt !"#
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Radio Analysis - Summary
CQI / RI (Rank Indicator) reported from UE.
Transmission Mode (MIMO, TxD, SIMO)
MCS vs. number of assigned PRBs vs. assignable bits in
scheduler
UE Scheduling percentage of TTIs (how often is the UE
scheduled)
PDCCH CFI and scheduling impacts
HARQ
BSR (Buffer Status Report)
PHR (Power Headroom Report) – is the UE at maximum power?
Cell bandwidth vs. maximum allowable PRBs
Link Adaptation
HARQ (less important, because we can measure SINR)
*
These are the fundamental areas of analysis for downlink:
CQI and RI provides us the SINR/antenna layer reception reports
from the UE point of view
Transmission modes 1 (SIMO),2 (Transmit Diversity) and 3 (Open Loop
Spatial Multiplexing) are supported by the eNB in L11A.
Understanding the relationship between chosen MCS, assigned PRBs
and assignable bits in the scheduler are important for sorting core
network issues/UE issues from air interface issues
Scheduling percentage means the amount of TTIs (typically measured
per second) that the UE was scheduled. This is also related to the
resources allocated for PDCCH (control channels)
PDCCH CFI impacts the % TTI scheduling but also reduces the maximum
MCS achievable.
HARQ will be presented using tracing. Check also the Uplink HARQ
for more detailed theoretical explanation.
RLC retransmissions will be touched on briefly, including how to
trace RLC status messages and some parameters involved.
These are the fundamental areas of analysis for uplink:
We’ll begin this section with an overview of uplink
scheduling
BSR is the mechanism the UE uses to inform the eNB about the amount
of data waiting in its RLC buffers
PHR is the mechanism the UE uses to inform the eNB about remaining
power at the transmitter (or power limitations)
The number of PRBs available for uplink scheduling has some 3GPP
specified limitations which different from downlink. This means
that, for example, the maximum number of PRBs (for a single UE)
able to be scheduled in 5MHz is 20 and not 23 (with 2 reserved for
PUCCH).
Link adaptation inputs for uplink vary from downlink. One
difference is the CQI (estimate of SINR) is not needed because the
eNB can itself measure SINR of PUSCH transmissions.
PDCCH collisions can occur with SIB/downlink transmissions as
downlink and uplink grants are both scheduled using the same PDCCH
resources.
The theory of HARQ in uplink is presented.
Slide title In CAPITALS 44 pt Slide subtitle 20 pt
Transport Analysis
Transport Analysis
Several Transport Network topologies (L2/L3) provide great
flexibility in design
Several router redundancy methods are supported
Transport network dimensioning provides insights into the peak
provisioning on the S1 link
The LTE RBS is a QoS enabler, providing end user and transport
network QoS differentiation
*
Transport Topology
*
This diagram shows the different transport network topologies
supported in the LTE RAN.
RBS A is connected directly to a Layer 2 network (Net A) which also
provides direct connectivity to the SGW and MME. Connectivity to
the OSS-RC O&M router R3 is achieved via router R7.
RBS B is connected to a Layer 2 network (Net C) and is routed to
the core network and OSS-RC via routers R2 and R4.
RBS C is connected to a small on-site Layer 2 network and has its
first hop router R6 at the RBS site.
RBS A, B and C have only Layer 3 connectivity to each other. Other
RBSs not shown in the figure may possibly have Layer 2 connectivity
to each other.
The network must be designed so that only one IP address exists for
the next hop router.
This is achieved by placing a router between the RBS and the MME
and SGW pools.
In the case of multiple next hop routers between the RBS and the
MME and SGW pools, Router Path Supervision (RPS) can be used or the
routers can share one IP address using the Virtual Router
Redundancy Protocol (VRRP), for example.
The same setup is required for OSS-RC, if COMINF is not placed at
the same site as the SGW and MME.
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Transport Topology
No strict requirements on using a L2 switched or L3 routed LTE RAN
transport network
No specified topology requirement
A router is required in the network, but LTE RAN transport network
does not have to be L3
Network design is important (number of hops for L3 vs. size of
broadcast domain for L2)
This topology flexibility could complicate troubleshooting efforts
depending on the nodes involved (say 3PP support is required)
*
The RBS network does not need to follow a topology method like full
meshed, partial mesh or point to point.
This ensures that the network is flexible and allows for expansions
using any topology methodology.
When using a Layer 2 Transport Network (such as Carrier Ethernet),
a router is still required at the CN sites.
The transport dimensioning then plays an important role in ensuring
end user data rates.
QoS is also important considering the different types of traffic
supported in the network.
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Transport configuration
A 2 VLAN configuration is recommended (separating O&M and
Transport):
O&M VLAN
The DU supports the following Internet Protocol (IP) logical
interface configurations:
One IPv4 interface for S1, X2, SoIP and O&M IP traffic
Two IPv4 interfaces (on the same GE port): one IPv4 interface for
S1, X2, and SoIP traffic, and one IPv4 interface for O&M
traffic.
VLAN configuration is required when deploying more than one IP
logical interface on the same GE transport network port.
When applicable, each IP interface must be configured on a separate
VLAN.
Router Path Supervision (RPS)
*
RPS is a CPP function (it can be used in products that have CPP as
a platform).
The optional Router Path Supervision function supervises the IP
(layer 3) connections towards a number of configured routers and
decides which one should currently be used as the default router.
I.e. it provides a default router redundancy function.
The router redundancy may be handled by the routers themselves
using a router redundancy protocol, e.g. Virtual Router Redundancy
Protocol
(VRRP). In case the routers are using some redundancy protocol, the
RPS function may have to be turned off in order to avoid
interference.
If RPS is turned off, router 0 will be used as default
router.
Up to three default routers per IP interface can be supervised.
This is done by periodically sending ICMP Echo Requests (with TTL =
1) and a unique IP id field of 0xFFFF to all the routers and
awaiting an ICMP Echo Reply in return.
The default prioritization of the routers, in descending order,
is:
• Router 0 (first preferred default router)
• Router 1 (second preferred default router)
• Router 2 (third preferred default router)
The time between echo requests, as well as the maximum time until
the corresponding echo reply should be received, is configurable.
An echo request not being replied to within the stipulated time is
regarded as a failure, which results in measures as described
below.
If the first default router is considered lost by the RBS, it will
automatically switch to the next router (priority in order of
assignment via attributes).
Note that this allows for redundancy only (not a hot standby
solution).
Router recovery time is determined by when RBS notices the
router/link is down to when another router is selected -> can be
in the order of seconds.
The RPS function is fully configurable via the IpInterface MO (num
of failed pings, max wait for ping reply, num pings before ok,
etc).
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virtual router redundancy protocol (VRRP)
LTE RBS supports VRRP (a router redundancy protocol)
VRRP uses an election method to assign responsibility for a virtual
router to one of the VRRP routers on a LAN
The Master VRRP router controls the IP address(es) associated with
a virtual router and forwards packets sent to these IP
addresses
If the Master fails, one backup VRRP router will act as the virtual
router
LTE RBS is transparent to the process, it does not directly
participate in VRRP
Master
Backup
eNB
eNB
eNB
*
Either RPS or VRRP can be used, but not both router redundancy
features at the same time.
Hence RPS must be turned off in order to use VRRP.
Transport Dimensioning
Dimensioning of the northbound transport network will impact
achievable end user throughput rate
LTE RBS transport network dimensioning process (mobile
backhaul):
Dimensioning is based on payload only!
Determine bandwidth needed for last mile
Determine cell thpt in a loaded network and avg. cell thpt during
busy hour
Calculate agg. bandwidth required in mobile backhaul
*
As assumed, the Radio network inputs are required when dimensioning
the transport network.
The dimensioning process includes:
1. Determining the bandwidth required for the last mile to the
eNodeB by using selected cell peak rate and the transport overhead
to calculate the required bandwidth.
2. Determining the values of Average cell throughput during busy
hour and Cell throughput in a loaded network. The values can be
based either on input from the radio network dimensioning or from
simulations.
3. Calculating the aggregate bandwidth required in the mobile
backhaul, using bandwidth requirements for the last mile and
variants of cell throughput.
Signalling for S1 and X2, together with operation and maintenance
data, generate a relatively small amount of data and are not
considered when dimensioning the backhaul.
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