[256 QAM Material is provided for technical discussion and reference purpose only]
Huawei Technologies Co.,
Ltd.
Product Name
Security Level
LTE
INTERNAL
Product Version
Pages
eRAN11.1
Total 25 pages
DL 256QAM Feature introduction
For Internal Use Only
Prepared By
Sanjeev Kumar Sharma (emp ID: 00702301)
Date
Huawei Technologies Co., Ltd.
All rights reserved
2018-06-26
[256 QAM Material is provided for technical discussion and reference purpose only]
Contents
1. Background
2. Solution Introduction
3. Impact Analysis
4. Activation Guide
5. Verification
1. Background
•
3GPP R12 introduce the higher order modulation scheme 256QAM
( Quadrature Amplitude Modulation) in DL , with 8bits per symbol .
•
The DL efficiency gain is up to 33% in theory ( vs. 64QAM in the same
high radio condition).
In order to get the 256QAM gain, higher SINR is required. Obtain the proportion
of downlink MCS indexes greater than 26 and less than 29 in traffic statistics of
current system without 256QAM, a higher proportion indicates greater
improvements provided by DL 256QAM
[256 QAM Material is provided for technical discussion and reference purpose only]
64QAM
256QAM
UE Capability Information
To support 256 QAM, a couple of new IEs are added to UE Capability
Information message as shown below. (This is understandable. Almost every
new feature is added in 3GPP, those features has been added to UE capability
informatoin. If you see UE capability information supporting all the latest feature
as of now (May 2015), you would already see super long UE Capability
Information message.. I am not sure how long the message will get as the
technology evolves even further)
[256 QAM Material is provided for technical discussion and reference purpose only]
CQI Table
As in MCS table, CQI table is also redefined for 256 QAM. As shown in the table
below, you would notice that the total number of CQI value stay same but the
modulation mapping to each CQI index is redefined in 256 QAM (Table 7.2.3-2)
[256 QAM Material is provided for technical discussion and reference purpose only]
Then how can UE figure out which table it has to apply when it is reporting
CQI ? It is instructed by Network via an RRC message as shown below.
[256 QAM Material is provided for technical discussion and reference purpose only]
MCS index DL
[256 QAM Material is provided for technical discussion and reference purpose only]
256QAM, order 8 (MCS index 20 -27)
[256 QAM Material is provided for technical discussion and reference purpose only]
MCX Index UL
[256 QAM Material is provided for technical discussion and reference purpose only]
UE Category support 256QAM
[256 QAM Material is provided for technical discussion and reference purpose only]
Physical Channel modulation schemes
2. Solution Introduction
Table switching concept (Old and new CQI Table)
For CQI new and old table the mechanism used is
Good radio condition = MCS 26, poor radio condition = MCS 11.
The difference between the two thresholds (MCS) is to prevent Ping-Po
ng switch. When old table is being used and MCS>= 26, new CQI table will be
adopted. When new CQI table is being used and MCS<=11, old CQI table will be
adopted.
[256 QAM Material is provided for technical discussion and reference purpose only]
DL 256QAM CQI Table Configure Strategy
Indicates the configuration policy of the CQI table with the MCS of 256QAM. The
configuration policies include fixed configuration and adaptive configuration.
If this parameter is set to FIX_CONFIG(FIX_CONFIG), the CQI table with the
MCS of 256QAM is fixedly configured for UEs supporting 256QAM in downlink
scheduling. If this parameter is set to
ADAPTIVE_CONFIG(ADAPTIVE_CONFIG), the CQI tables with MCSs of
256QAM or other than 256QAM can be adaptively configured for UEs supporting
256QAM based on channel quality in downlink scheduling. This parameter takes
effect only when the Dl256QamSwitch option of the Dl256QamAlgoSwitch
parameter is selected. This parameter applies only to LTE FDD and LTE TDD.
FIX_CONFIG, ADAPTIVE_CONFIG
Recommended: ADAPTIVE_CONFIG
When this parameter is set to FIX_CONFIG, the downlink data rate of QPSK UEs
supporting 256QAM decreases, but the signaling overhead is reduced. When this
parameter is set to ADAPTIVE_CONFIG, the downlink data rate of QPSK UEs
supporting 256QAM increases, but the signaling overhead also increases.
DL 256QAM CQI Table Adaptive Period
Indicates the adaptive handover period of the CQI table with the MCS of
256QAM. This parameter takes effect only when the
Dl256QamCqiTblCfgStrategy parameter is set to
ADAPTIVE_CONFIG(ADAPTIVE_CONFIG). This parameter applies only to LTE
FDD and LTE TDD.
1~1000s
Recommended value:10
[256 QAM Material is provided for technical discussion and reference purpose only]
A smaller value of this parameter results in better performance in tracing channel
quality changes based on adaptive configurations of the CQI table, higher
downlink data rate, and a larger number of RRC connection reconfigurations. A
larger value of this parameter results in the opposite effects.
CQI Table Setting
After 3GPP introduced DL 256QAM, a total of two CQI tables are available. An
eNodeB can either adaptively select a CQI table or use a fixed CQI table during
DL scheduling. This is determined by the
CellDlschAlgo.Dl256QamCqiTblCfgStrategy parameter.

If this parameter is set to ADAPTIVE_CONFIG, the eNodeB adaptively
selects a CQI table for 256QAM-capable UEs based on channel quality.
If channel quality deteriorates for 256QAM-capable UEs, the eNodeB
switches to the CQI table without 256QAM, maintaining the DL rate of
QPSK-based services on the UEs. Therefore, this setting is
recommended.
As the eNodeB must use RRC signaling to notify UEs of the CQI table
used, this setting increases RRC signaling overhead.

If this parameter is set to FIX_CONFIG, the eNodeB always uses the CQI
table with 256QAM for 256QAM-capable UEs.
The CQI table with 256QAM references fewer low-order TBSs (TBSs
with indexes 1, 3, 5, 7, and 9 are not supported) than the CQI table
without 256QAM. Therefore, this parameter setting may result in a
decrease in the DL rate of QPSK-based services for 256QAM-capable
UEs.
DL 256QAM-related Scheduling Process
[256 QAM Material is provided for technical discussion and reference purpose only]
END
1. The eNodeB checks whether the DL 256QAM switch is on.

If the Dl256QamSwitch option of the
CellAlgoSwitch.Dl256QamAlgoSwitch parameter is selected, the
eNodeB performs 2.

If the Dl256QamSwitch option of the
CellAlgoSwitch.Dl256QamAlgoSwitch parameter is deselected,
the eNodeB selects QPSK, 16QAM, or 64QAM for the UE based on
channel quality.
2. The eNodeB checks whether the UE supports DL 256QAM.
The implementation of DL 256QAM requires that UEs be of categories
11 to 14, comply with 3GPP Release 12 or later, and support DL
256QAM.

If the UE supports DL 256QAM, the eNodeB performs 3.
[256 QAM Material is provided for technical discussion and reference purpose only]

If the UE does not support DL 256QAM, the eNodeB selects QPSK,
16QAM, or 64QAM for the UE based on channel quality.
3. The eNodeB checks whether adaptive CQI table selection has been
enabled.

If adaptive selection has been disabled, the eNodeB selects the
CQI table with 256QAM for the UE.

If adaptive selection has been enabled, the eNodeB periodically
determines whether to use the CQI table with 256QAM or the CQI
table without 256QAM for the UE based on channel quality. The
period is specified by the
CellDlschAlgo.Dl256QamCqiTblAdpPeriod parameter.

If this parameter is set to a smaller value, the eNodeB tracks
channel quality changes more frequently for adaptive CQI table
selection, resulting in a higher DL rate. However, RRC
connection reconfiguration messages are sent more frequently.
This increases the probability of service drops.

If this parameter is set to a larger value, the eNodeB tracks
channel quality changes less frequently for adaptive CQI table
selection, resulting in a lower DL rate. However, RRC
connection reconfiguration messages are sent less frequently.
This reduces the probability of service drops.
4. The eNodeB performs scheduling based on channel quality and the
selected CQI table.
NOTE:
The highest-order modulation scheme for evolved multimedia
broadcast/multicast service (eMBMS) in the DL is 64QAM. Therefore, the MCS
table without 256QAM is used during scheduling of eMBMS services.
DL 256QAM Accessory Algorithm
The DL 256QAM accessory algorithm performs noise equalization for baseband
signals. It takes effect during the transmission time intervals (TTIs) where
256QAM is selected as the modulation scheme for DL scheduling. This algorithm
optimizes the error vector magnitude (EVM) for 256QAM-based modulation at
the eNodeB and improves the performance of DL 256QAM-based demodulation.
This algorithm is controlled by the Dl256QamAccessorySwitch option of the
CellAlgoSwitch.Dl256QamAlgoSwitch parameter. In addition, this algorithm
takes effect only when the following conditions are met:

The rank for the UE on which DL 256QAM takes effect is less than or
equal to 2, and the MCS index is greater than or equal to 25. In addition,
the UE is scheduled together with UEs that are using other modulation
schemes during the same TTI.
[256 QAM Material is provided for technical discussion and reference purpose only]

The eNodeB is a macro base station.

The cell bandwidth is greater than or equal to 5 MHz.

The radio frequency (RF) module that serves the cell is configured to work
for LTE FDD only, with a single carrier, and at its nominal power.
Modulation: DL/UL QPSK, DL/UL 16QAM, DL 64QAM
Benefit Analysis
This feature increases spectral efficiency by enabling eNodeBs to dynamically
select appropriate modulation schemes for UEs based on channel quality. When
TBS index 26A is selected for TM9-capable UEs in the cell center, the DL peak
throughput of these UEs increases by 2%–5%.
DL 256QAM benefits
DL 256QAM offers the following benefits:

Increased DL spectral efficiency and therefore DL throughput for UEs in
the cell center

Increased DL peak cell throughput
The level of these increases varies depending on radio channel quality, the error
vector magnitude (EVM) of RF signals sent by eNodeBs, and the EVM of signals
received by UEs. The increases range from 0% to 30% when radio conditions
are favorable and the use of DL 64QAM has achieved the network capacity limit.
You may infer that the limit has been reached when MCS 28, the largest index,
has been selected for downlink transmission on a large proportion (for example,
more than 30%) of occasions. Therefore, it is recommended that DL 256QAM be
enabled in this situation.
The DL 256QAM accessory algorithm further increases the DL throughput of DL
256QAM-capable UEs by decreasing the EVM of RF signals sent by eNodeBs.
The level of the increase is affected by network load, UE service type, radio
channel quality, the original EVM of RF signals sent by eNodeBs, and the EVM
of signals received by UEs. The maximum amount is up to 5%.
NOTE:
Enabling the DL 256QAM accessory algorithm when DL 256QAM has been
enabled does not change the peak throughput that can be achieved using DL
256QAM.
When TBS index 33A is selected for TM9-capable UEs in the cell center, the DL
peak throughput of these UEs increases by 3%–5%.
Network Impact

Impact on DL UE throughput in special scenarios
[256 QAM Material is provided for technical discussion and reference purpose only]
Due to non-linear TBSs introduced in 3GPP specifications, using DL
256QAM instead of DL 64QAM may decrease the throughput of UEs at
locations where the SINR reaches a certain value.
For example, assume that cell bandwidth is 20 MHz and there is one
PDCCH symbol per subframe. If the eNodeB uses the CQI and MCS
tables without 256QAM for a UE at a location where the SINR reaches a
certain value, the eNodeB may select DL 64QAM and TBS index 26,
which indicates a TBS of 75,376 bits. In this case, no block error occurs.
However, if the eNodeB uses the CQI and MCS tables with 256QAM, the
eNodeB has to select TBS index 29 because TBS index 26 is
unavailable. TBS index 29 indicates a TBS of 73,712 bits. In this
scenario, there will be block errors, resulting in a decrease of
approximately 4% in throughput when DL 256QAM is in use.

Impact on the average CQI and average MCS index
When adaptive selection of CQI tables takes effect:

The number of CQI reports sent by UEs for which DL 256QAM is
used is measured by counters L.ChMeas.DL.256QAM.CQI.DL.0–
L.ChMeas.DL.256QAM.CQI.DL.15, as well as by counters
L.ChMeas.CQI.DL.0–L.ChMeas.CQI.DL.15. In the 3GPP-defined
CQI table with 256QAM, the CQI value corresponding to each
specific modulation scheme is lower than that in the CQI table
without 256QAM. As a result, the average CQI value calculated by
using counters L.ChMeas.CQI.DL.0–L.ChMeas.CQI.DL.15
decreases slightly.

The number of times certain MCSs are selected for these UEs is
measured by counters L.ChMeas.PDSCH.DL.256QAM.MCS.0–
L.ChMeas.PDSCH.DL.256QAM.MCS.31. Therefore, the average
MCS value calculated by using counters L.ChMeas.PDSCH.MCS.0–
L.ChMeas.PDSCH.MCS.31 decreases slightly.
The decreases are determined by the proportion of times DL 256QAM is
selected. The higher the proportion, the larger the decreases.

Impact on other relevant counters
The DL 256QAM accessory algorithm causes an increased value of the
L.Traffic.DL.SCH.256QAM.TB.bits counter.
3. Impact Analysis
 Positive Impact ：improve downlink throughput, up to ~30%
[256 QAM Material is provided for technical discussion and reference purpose only]
The 256QAM terminal throughput gain versus SINR is dependent on the
actual channel characteristic, such as fading path, correlation, etc. and
the rank number.
 Negative Impact ：Minor, only few RRC message for CQI/MCS table
alteration will be added.
4. Activation Guide
Activation Guide
 Dependency on Hardware/NEs/ Transimission
 Only supported for UBBPd/UBBPe due to higher baseband
overhead requirement.
 Only supported for V3/V6 RRU module
 Macro,BTS3911E, LampSite supported.
 R12 UE, Category 11~14. and supporting DL-256QAM function
 Dependency on other Features
 LBFD-002025 Basic Scheduling
 LOFD-001015 Enhanced Scheduling
 LBFD-001006 AMC
 License
 Fea
ture
ID
 Fea
ture
Na
me
 Model
 License
Control
Item
 NE
 S
al
e
s
U
[256 QAM Material is provided for technical discussion and reference purpose only]
ni
t
 LE
OF
D110
301
 DL
256
QA
M
 LLT1256
QAM01
 256QAM
(FDD)
 eN
ode
B
 p
er
C
el
l
 Activate Dl 256QAM:

MML: MOD CELLALGOSWITCH: LOCALCELLID=0,
Dl256QamAlgoSwitch=Dl256QamSwitch-1;
 Deactivate Dl 256QAM:

MML: MOD CELLALGOSWITCH:LOCALCELLID=0,
Dl256QamAlgoSwitch=Dl256QamSwitch-0;
 KEY parameter adjustment
The CQI Table configure strategy and adaptive period can be configured as
below.
 MML: MOD CELLDLSCHALGO: LOCALCELLID=0,
Dl256QamCqiTblCfgStrategy=ADAPTIVE_CONFIG;
 MML: MOD CELLDLSCHALGO: LOCALCELLID=0,
Dl256QamCqiTblAdpPeriod = 10;
Activation Observation
Use either of the following measures to observe whether DL 256QAM has taken
effect:

Tracing and monitoring functions of the U2000
1. On the U2000 client, start a Uu interface tracing task in a cell as follows:
Choose Monitor > Signaling Trace > Signaling Trace Management.
Then in the navigation tree on the left, choose Trace Type > LTE >
Application Layer > Uu Interface Trace. Set task parameters to create
the task.
2. Enable a DL 256QAM-capable UE to access the cell, where DL
256QAM has been activated, from the cell center. Start File Transfer
Protocol (FTP) download to the UE.
[256 QAM Material is provided for technical discussion and reference purpose only]
3. Check the RRC_CONN_RECFG message among the traced Uu
messages. If the CQI-ReportConfig IE in the message has the value
altCQI-Table, DL 256QAM has taken effect.

Counters
Monitor the following counters. If the value of any counter is greater than
0, DL 256QAM has taken effect.
Table 6-4 Counters related to DL 256QAM
To verify whether DL TBS index optimization has taken effect, perform the
following steps:
1. Start a Uu interface tracing task on the U2000 client as follows: Choose
Monitor > Signaling Trace > Signaling Trace Management. Then in the
navigation tree on the left, choose Trace Type > LTE > Application
Layer > Uu Interface Trace. Set task parameters to create the task.
2. When the DL 256QAM feature has taken effect, run the MOD
CELLALGOSWITCH command to enable DL TBS index optimization.
3. Check the RRC_CONN_RECFG message in the Uu interface tracing result.
If the PDSCH-Config IE in the message contains the PDSCHConfigDedicated-v1280 IE whose value is a33, DL TBS index optimization
has taken effect when DL 256QAM is used.
Benefit Monitoring
Average DL UE throughput = (L.Thrp.bits.DL –
L.Thrp.bits.DL.LastTTI)/L.Thrp.Time.DL.RmvLastTTI
Compare the average DL UE throughput values before and after the DL 256QAM
feature is activated to determine the feature benefit. The higher the proportion of
times DL 256QAM is selected, the greater the benefit.
Other Monitoring
Before activating the DL 256QAM feature, operators can predict the proportion of
times the DL 256QAM modulation scheme will be selected by calculating the
total proportion of times MCSs 27 and 28 indicating DL 64QAM have been
selected. This is because, according to 3GPP TS 36.213, these two values are
expected to be similar. Note that the UEs for which MCS 28 has been selected
will benefit the most from the DL 256QAM feature.
After the DL 256QAM feature is activated in a cell, the probabilities of DL UE
throughput in high throughput ranges and the average DL throughput in the cell
will increase with the proportion of times DL 256QAM is selected during
scheduling.
[256 QAM Material is provided for technical discussion and reference purpose only]

Proportion of times DL 256QAM has been selected during scheduling
Proportion =
L.Traffic.DL.SCH.256QAM.TB/(L.Traffic.DL.SCH.256QAM.TB +
L.Traffic.DL.SCH.64QAM.TB + L.Traffic.DL.SCH.16QAM.TB +
L.Traffic.DL.SCH.QPSK.TB)

Probability of DL UE throughput in each throughput range
Probability of DL UE throughput in throughput range n (n = 0–9) =
L.Thrp.DL.BitRate.Samp.Indexn/sum(L.Thrp.DL.BitRate.Samp.Index0 to
L.Thrp.DL.BitRate.Samp.Index9)

Average DL throughput in a cell
Throughput = L.Thrp.bits.DL/L.Thrp.Time.Cell.DL.HighPrecision
5. Verification
›
›
256QAM scheduling ratio =
L.Traffic.DL.SCH.256QAM.TB/(L.Traffic.DL.SCH.256QAM.TB+
L.Traffic.DL.SCH. 64QAM.TB+ L.Traffic.DL.SCH.16QAM.TB+
L.Traffic.DL.SCH.QPSK.TB)
›
downlink user throughput = L.Thrp.DL.User(Mbit/s)
=( L.Thrp.bits.DL (bit) - L.Thrp.bits.DL.LastTTI )/
L.Thrp.Time.DL.RmvLastTTI *1024*1024*1000.
New counters introduced
Counter ID
Counter Name
1526739662 L.ChMeas.DL.256QAM.CQI.DL.x(x=0~15)
Number of wideband CQI reports with the value of 0 w
1526739682 L.ChMeas.PDSCH.DL.256QAM.MCS.x(x=0~31) Number of times MCS index 0 is scheduled on the PU
1526739656 L.Traffic.DL.SCH.256QAM.TB
Number of TBs initially transmitted on the downlink S
1526739657 L.Traffic.DL.SCH.256QAM.TB.bits
Number of bits of TBs initially transmitted on the dow
1526739658 L.Traffic.DL.SCH.256QAM.TB.Retrans
Number of TBs retransmitted on the downlink SCH in
1526739659 L.Traffic.DL.SCH.256QAM.TB.Retrans.bits
Number of bits of TBs retransmitted on the downlink S
1526739660 L.Traffic.DL.SCH.256QAM.ErrTB.Ibler
Number of downlink error TBs after initial transmissio
1526739661 L.Traffic.DL.SCH.256QAM.ErrTB.Rbler
Number of downlink error TBs after the maximum num
[256 QAM Material is provided for technical discussion and reference purpose only]