high speed uplink packet access (hsupa) vs uplink interference
TRANSCRIPT
HSUPA VS Uplink InterferenceDocument
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High Speed Uplink Packet Access
(HSUPA)
VS
Uplink Interference
PRINCIPLE & TEST REPORT
With CASE STUDY
Huawei Technologies Co., Ltd.
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Dec 2010
Contents
1 PRINCIPLE...................................................................................................4
1.1 High Speech Uplink Packet Access (HSUPA).......................................................4
1.2 Uplink Interference...................................................................................................5
1.3 HSUPA VS Uplink Interference...............................................................................7
1.4 HSUPA Phase 1(TTI 10ms) and Phase 2(TTI 2ms)...............................................9
2 TEST REPORT.........................................................................................10
2.1 Simulation Result from HQ Test Lab...................................................................10
2.2 HSUPA Load Test Result from Customer-xxx’s Test bed...................................11
3 CASE STUDY............................................................................................18
3.1 Problem Description...............................................................................................18
3.2 Problem Analysis...................................................................................................20
3.3 Solutions and Recommendations...........................................................................23
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HSUPA VS Uplink Interference
Abstract:
This technical paper aims to give the readers the understanding about the relationship of
the HSUPA service and the uplink interference (3GPP terminology is RTWP, Received
Total Wideband Power).
The basic principle, test reports and case study from live network are included here to
give a clear view on how the HSUPA service impact on the uplink performance and how
to optimize the network to gain a maximum benefit of HSUPA.
Since HSPA service is widely used in the market, with a good understanding of this
topic, the engineer will be able to operate and optimize the network well.
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1 PRINCIPLE
1.1 High Speech Uplink Packet Access (HSUPA)
HSUPA is introduced within release 6 of the 3GPP specifications. It allows increased individual
connection throughputs, increased total cell throughputs and reduced round trip times.
In Huawei system (RAN10.0), the HSUPA data channel (E-DPDCH) can support either a 2 or 10
ms TTI.
- HSUPA Phase 1, 10ms TTI offers the benefit of improved physical layer performance
over R99, peak rate is 2 Mbps.
- HSUPA (Phase 2), 2ms TTI offers the benefit of reduced system delays and higher
potential throughput, peak rate is 5.76 Mbps.
(HSUPA TTI is configured via RNC MML command,
SET CORRMALGOSWITCH: MapSwitch=MAP_HSUPA_TTI_2MS_SWITCH-1;)
Release 7 of 3GPP specification introduces the possibility of using 4 level Pulse Amplitude
Modulation (4PAM) which equivalent to 16QAM to increase the maximum achievable throughput,
peak rate is 11.5 Mbps. (support in Huawei RAN12.0).
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1.2 Uplink Interference
In the WCDMA system, all the cells share the same frequency, which is beneficial to improve the
system capacity. However, co-frequency multiplexing causes interference among the users.
The Received Total Wideband Power (RTWP) on the uplink is the sum of all user signals and the
channel noise.
Uplink Interference Composition is as follow;
Noise Floor include of thermal noise and Noise Figure (NF) of the system.
K :Boltzmann constant, 1.38×
T :Kelvin temperature, normal temperature: 290 K
W:Signal bandwidth, WCDMA signal bandwidth 3.84MHz
NF: Hardware (NodeB/UE) dependency, typical value of macro NodeB =3 dB
If no other external factors e.g. external interference (from illegal sources), hardware issue. The
main factor that impact on Uplink interference is Traffic Load which includes traffic load from the
users of the cell and adjacent cells.
The relationship between uplink load and uplink interference (Noise Rise) is as below,
( = Load factor)
NFWTKPN )**log(10
KJ /10 23
1
1 1
11 1
TOTN
N ULj
INoiseRise
P i L
RTWP (Received Total Wideband Power)
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UL load is affecting the noise level at the Node B receiver (Noise Rise).
• A typical value of cell load for dimensioning ranges from 30% to 70 %
• 50% is a good compromise between the number of sites and the offered capacity.
• Too high uplink noise level cause cell shrink (reduction of coverage), breathing effect.
The relationship between Noise Rise and RTWP (Received Total Wideband Power),
From previous page,
RTWP (Received Total Wideband Power) dB = Noise Floor (Pn) + Noise Rise (Iown + Iother)
Example, (“Noise Floor” is often called as “Background Noise")
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- Without TMA : Noise Floor (dBm) = Thermal Noise(KTB,room temperature = -108dBm) +
Equivalent Noise Figure (Feeder Loss + NF_B; NF_BS- depends on Node B type, Huawei
typical value around 2.0 dB)
Noise Floor (dBm) = -108 + (0.5+ 2.0) = -105.3 dBm
With 75% Uplink Load (Noise Rise=6 dB), RTWP (dBm) = -105.3 + 6 = 99.3
- With TMA: Equivalent Noise Figure will be reduced due to TMA.
Example: NF Without TMA: (0.5+2.0) dB = 2.5dB , NFWith TMA : 1.2 dB
(calculated from the formula above)
Noise Floor (dBm) = -108 + (1.2) = -106.7 dBm ,
With 50% Uplink Load (Noise Rise =3 dB) - RTWP(dBm) = -106.7+3=-103.7
dBm
1.3 HSUPA VS Uplink Interference
HSUPA service allows the users to achieve higher throughput on uplink but in the same time also
increase significant interference which causing the reduction of cell user access number and
impact on the overall performance.
It is great important to balance between the achievable throughput and system performance on
the uplink. Therefore, Huawei systems apply the Load Control mechanisms to control the level of
uplink interference in each service phase.
Equivalent Noise Figure
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(More detail about Load Control Algorithms, please refer to “Load Control Feature Document)
Load Control algorithms are different between HSUPA and R99 UL as follows:
1. Call Admission Control (CAC):
For HSUPA, PBR-based decision is used to check whether the QoS requirement of
existing users is fulfilled. The QoS is measured on the basis of the Provided Bit Rate
(PBR) of the users. If the QoS requirement is fulfilled, new users are allowed to access
the network.
2. Load Control (LDR) :
-UL R99 is controlled by UL LDR trigger threshold if UL UU LDR algorithm is switch on.
-HSUPA, its scheduling is controlled by Maximum Target Uplink Load Factor and the
real uplink load contributed by none scheduled EDCH users.
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ADD CELLHSUPA: CellId=[Cellid], MaxTargetUlLoadFactor=75;
1.4 HSUPA Phase 1(TTI 10ms) and Phase 2(TTI 2ms)
To ensure that the HSUPA user can access the cell, the minimum GBR (Guarantee Bit
Rate) is recommended. When set the GBR need to consider the trade-off between user
throughput and cell user number.
High GBR High user throughputHigh Uplink Interference Lower cell user number
Low GBR Low user throughput Low Uplink Interference Higher cell user number
If GBR set in RNC =64kbps
(1) 2ms HSUPA
Minimum Throughput=MAX ( one RLC pdu -bit rate , GBR ) =
MAX (320bit/2ms ,64kpbs )=160kbps
(2) 10ms HSUPA
Minimum Throughput=MAX ( one RLC pdu-bit rate , GBR )
=MAX (320bit/10ms ,64kpbs ) =64kbps
If GBR not set in RNC
(1) 2ms HSUPA
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Minimum Throughput =MAX ( one RLC pdu-bit rate , GBR )
=MAX (320bit/2ms ,0kpbs )=160kbps
(2) 10ms HSUPA
Minimum Throughput =MAX ( one RLC pdu-bit rate , GBR )
=MAX (320bit/10ms ,0kpbs ) =32kbps
To sum up, with different HSUPA TTI, 2ms and 10ms , the minimum guaranteed throughput of
user is vary 160kbps vs 64kpbs / 160kbps vs 32kbps. So, when the uplink load is limited, the
number of user that can access the cell is different (HSUPA TTI=2ms serve less number of user
per cell due to higher guaranteed throughput which generating higher uplink interference).
2 TEST REPORT
2.1 Simulation Result from HQ Test Lab
HSUPA 2ms TTI- single antenna simulation (GBR=64kbps, MaxTargetUlLoadFactor
=75%)
FTP user number (simultaneously upload) is limited at 8 due to the limited capacity of air
interface (uplink interference).
UploadofAntenna %( )
Throughputkbps( )
CAT5 8 74. 43 1215. 63CAT6 8 86. 07 1163. 18
UENumber1RX_Antenna
用户等级
HSUPA 10ms TTI- single antenna simulation (GBR=64kbps, MaxTargetUlLoadFactor
=75%)
FTP user number (simultaneously upload) is limited at 20 due to the limited capacity of air
interface (uplink interference).
UploadofAntenna %( )
Throughputkbps( )
CAT5 20 76. 50 1100. 00
UENumber1RX_Antenna
用户等级
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2.2 HSUPA Load Test Result from Customer-xxx’s Test bed
Cell throughput and cell user number are significantly improved especially on HSUPA
Phase2 (TTI 2ms.) when implemented new features in RAN 12.0-Interference
Cancellation(IC) and Adaptive Retransmission.
Interference Cancellation Feature(IC) aims to reduce the UL interference among users
and increase the UL system capacity.
Adaptive Retransmission Feature( (Dynamic NHR) enables the system to dynamically
change the retransmission rate upon the Cell Load and UE Tx Power.
- When cell load and UE Transmit Power are limited, the retransmission rate will
be increased. Increasing the retransmission time requires less UE Tx power thus
lower uplink interference.
- When cell load and UE Transmit Power are less, the retransmission rate will be
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decreased to completely utilize the resources and increase the effective rate of
UE.
Retransmission UE Transmit Power *
Eb/N0 * Coverage * UL Interference*
UE peak throughput peak
Cell Throughput (Multi-users)
Max User Number
Large low low large low low high more
Small high high small high high low less
*At the same effective rate of UE
(Please refer to the comparisons charts of Large and Small Retransmission performance in
next pages).
Summary HSUPA Load Test Result
Test Case Antenna UserNumber Cell Load(%) Cell Tput(Mbps) Cell Load(%) Cell Tput(Mbps) Cell Load(%) Cell Tput(Mbps)1 60% 1.90 50% 1.90 50% 1.982 75% 1.25 75% 2.00 75% 2.303 75% 0.92 75% 1.80 75% 2.204 77% 0.90 75% 1.40 75% 2.005 77% 1.28 75% 1.40 75% 1.906 77% 1.26 75% 1.40 75% 1.907 75% 1.09 75% 1.40 75% 1.708 77% 1.05 75% 1.40 75% 1.709 75% 1.30 75% 1.70
10 75% 1.20 75% 1.6011 75% 1.10 75% 1.5012 75% 1.00 75% 1.4013 75% 0.99 75% 1.4014 80% 0.95 75% 1.3015 90% 1.10 75% 1.3016 92% 1.00 78% 1.20
TTI=10ms + IC (RAN12)
TTI=10ms + IC+Adaptive Retransmission (RAN12)
TTI=10ms (RAN11)
11RX
(Indoor Case)
Test Case Antenna UserNumber Cell Load(%) Cell Tput(Mbps) Cell Load(%) Cell Tput(Mbps) Cell Load(%) Cell Tput(Mbps)1 70% 2.20 75% 3.50 75% 3.902 75% 1.50 75% 2.20 75% 3.003 75% 1.09 75% 2.00 75% 2.404 75% 1.10 75% 1.50 75% 1.905 75% 0.91 75% 1.20 75% 1.906 75% 0.98 75% 1.20 75% 1.807 96% 1.16 75% 1.10 75% 1.608 100% 1.20 92% 1.20 75% 1.509 100% 1.10 75% 1.30
10 75% 1.2011 75% 1.1012 75% 1.1013 90% 1.0014 100% 0.951516
21RX
(Indoor Case)
TTI=2ms (RAN11)
TTI=2ms + IC (RAN12)
TTI=2ms + IC+Adaptive Retransmission (RAN12)
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Test Case Antenna UserNumber Cell Load(%) Cell Tput(Mbps) Cell Load(%) Cell Tput(Mbps) Cell Load(%) Cell Tput(Mbps)1 50% 1.80 40% 1.98 40% 1.982 75% 2.70 60% 3.90 60% 3.903 75% 2.25 75% 3.00 75% 3.904 75% 2.55 75% 3.00 75% 3.205 75% 2.15 75% 3.00 75% 3.006 75% 1.95 75% 2.40 75% 3.007 75% 1.95 75% 2.00 75% 2.808 75% 1.88 75% 2.40 75% 2.409 75% 1.95 75% 2.50 75% 2.50
10 75% 1.76 75% 2.20 75% 2.5011 75% 2.00 75% 2.5012 75% 2.00 75% 2.3013 75% 2.20 75% 2.3014 75% 1.50 75% 2.1015 75% 1.70 75% 1.9016
TTI=10ms (RAN11)
TTI=10ms + IC (RAN12)
TTI=10ms + IC+Adaptive Retransmission (RAN12)
32Rxs
(Outdoor Case)
Test Case Antenna UserNumber Cell Load(%) Cell Tput(Mbps) Cell Load(%) Cell Tput(Mbps) Cell Load(%) Cell Tput(Mbps)1 75% 3.70 70% 4.40 70% 4.402 75% 2.20 75% 5.00 75% 5.403 75% 1.85 75% 4.00 75% 4.204 75% 1.90 75% 3.20 75% 4.005 75% 1.96 75% 2.50 75% 3.506 75% 1.98 75% 2.20 75% 2.607 75% 1.68 75% 1.90 75% 2.308 75% 1.71 75% 1.80 75% 2.309 75% 1.70 75% 2.20
10 75% 1.90 75% 2.2011 80% 1.80 75% 1.9012 85% 2.00 75% 2.0013 100% 1.80 75% 1.8014 75% 1.7015 75% 1.7016
42Rxs
(Outdoor Case)
TTI=2ms (RAN11)
TTI=2ms + IC (RAN12)
TTI=2ms + IC+Adaptive Retransmission (RAN12)
Test Case 1: HSUPA TTI=10ms – 1Rx Antenna without Rx-Diversity (Indoor Case)
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Test Case 2: HSUPA TTI=2ms – 1Rx Antenna without Rx-Diversity (Indoor Case)
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Test Case 3: HSUPA TTI=10ms – 2 RXs Antenna with Rx-Diversity (Outdoor Case)
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Test Case 4: HSUPA TTI=2ms – 2 RXs Antenna with Rx-Diversity (Outdoor Case)
Reference Charts from HQ (Simulation Result)
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Large Retransmission compared with Small Retransmission(10ms TTI)
0
500
1000
1500
2000
2500
3000
3500
4000
1 2 3 4 5 10 15 20 25 30 35 40 45 50 51 52 53User Nmuber
Cell
thro
ughput
0
20
40
60
80
100
120
Cell
Load
Cel l Throughput Smal l Ret ransmi ssi on Cel l Throughput Large Ret ransmi ssi onCel l Load Smal l Ret ransmi ssi on Cel l Load Large Ret ransmi ssi on
Large Retransmission Compared with SmallRetransmission (2ms TTI)
0
500
1000
1500
2000
2500
3000
3500
4000
4500
1 2 3 4 5 10 15 16 17 20 25 29User Number
Cel
l Thr
ough
put
0
20
40
60
80
100
120
Cel
l Loa
d
Cel l Throughput Large Ret ransmi ssi on Cel l Throughput Smal l Ret ransmi ssi onCel Load Smal l Ret ransmi ssi on Cel l Load Large Ret ransmi ssi on
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-In light cell load, small retransmission can give users higher throughput than large
retransmission.
-In medium and heavy cell load, large retransmission can achieve much more user
numbers and cell throughput than small retransmission; the gain can be 20% ~30%. (Based
on user numbers)
To achieve a maximum balance between cell capacity and peak rate of single user in uplink
(2ms TTI bring the higher peak rate of single user, while 10ms TTI can bring the
higher cell capacity). The operator can deploy another new feature (RAN12.0), HSUPA
TTI Auto Reconfiguration together with Adaptive Retransmission.
If the following condition has been fulfilled, this UE’s TTI switch from 2ms to
10ms: “The Uu Load on Congestion Status” & “the UE’s bit rate < Rate threshold for
2ms to 10ms If both of the following conditions are fulfilled, this UE’s TTI switch from 10ms to
2ms: “the UE’s bit rate > Rate threshold for 10ms to 2ms. ” UE Power is not limited. (If the 6A1 have been reported, the 6B2 shall be
reported after that.)
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3 CASE STUDY
3.1 Problem Description
Based on the customer’s feedback in 3G Network (RAN10.0) of Operator XXX, the customers
had the difficulties to access the network ,sometime can access network but the data throughput
is very low and the connections frequently dropped. This problem is appeared at operator’s office
and nearby areas.
Symptoms:
-Based on the Statistic, we observed same pattern of high RTWP and PS drop in all cells that
circled in red.
-These cells are located in the same areas, nearby operator’s office.
-The highest RTWP appeared in Indoor cell, CHAMCHURI_C35-1 and the level of the uplink
interference of other outdoor cells reduce upon the distant from this indoor cell.
- Uplink interference (RTWP) increase very high reached the maximum value at -55 dBm during
working hour (10:00 – 17:30 hrs) on working day.
-We also conducted the FTP download and upload at the Indoor cell, both give a very low
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throughput.
Operator’s Office
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Mean RTWP vs HSDPA Drop Rate (CHAMCHURIC35-1)
Mean RTWP vs Mean number of HSPA user
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3.2 Problem Analysis
Initially, we suspect that the uplink interference causing from the external source which may
illegally use in the operator’s building. This assumption was based on the interference pattern
that occurred in many cells in the same time.
In the first place, we did not expected that the issue related to traffic load due to based on
statistic, found that at the same number of HSUPA users, the RTWP didn’t always high.
(Maximum =20 HSUPA users per cell, the HSUPA user number is limited by Maximum HSUPA
user number setting at RNC)
Troubleshooting Steps, we had proposed 2 troubleshooting steps as below
(1) Use Spectrum Analyzer to search for External Interference source in operator’s building
(2) Conduct Field Test (FTP upload) and open RNC LMT online trace measurement in the
Indoor Cell
Results
(1) There was no external interference detected by Spectrum Analyzer
(2) Based on the field test (FTP upload) and RNC LMT online measurement of indoor cell,
we detected huge increment of RTWP when R99 test user doing the FTP upload (the
test user only can get R99 service due to HSUPA user number already hit maximum 20
based on the setting).
Test Steps
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(1) Condition before start FTP upload test, based on RNC LMT online measurement of
indoor cell, the HSUPA user was always at 20 (HSDPA user number was more
than 20) with the RTWP above -95 dBm.
(2) We started FTP Upload on R99 (from Genex Probe, observed the average
throughput was around 300kbps) and the sudden increment of RTWP upto -55
dBm was observed via online measurement. (We randomly checked the RTWP of
nearby outdoor cells, their RTWP also increased accordingly).
(3) Next, we started FTP Upload on HSUPA (from Genex Probe, observed the very
low throughput, most of the time was 0 kbps) during that time observed no
increment of RTWP via online measurement.
(4) We checked the Load Control parameters setting of this indoor cell; found that the
LDR (Load Reshuffling) didn’t turn-on. This is the reason why RNC still
scheduled bit rate to R99 users although current uplink load was high (above -95
dBm).
(5) For HSUPA user, the scheduling is based on Maximum Target Uplink Load
Factor which set to 75%, thus the bit rate was not scheduled to HSUPA user
consequently no increment of RTWP.
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(6) We recommended to turned-on LDR (UL: BE RATE REDUCTION) for Indoor Cell
and monitor. Based on statistic after turn-on LDR, there was some improvement on
RTWP and PS drop but not on data throughput. However, high RTWP still
observed during peak hour but at shorter period than before.
Genex Probe
Online Measurement (LMT)
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(7) We suspect there might be some issue with HSUPA service as well (We
implemented the HSUPA Phase2 (TTI 2ms) in this network) .Thus, we conducted
the HSUPA Load Test, to check how many HSUPA user (simultaneous FTP
upload) that the cell can support.
From the test result, shown that for indoor case (with 1 Rx antenna), only
maximum 7 simultaneous upload users can supported. If the HSUPA user number
is exceed 7, will cause over-high RTWP. (Please refer to test result in previous
session)
We got confirmation from HQ that this is product limitation, the performance
of HSUPA Phase 2 with 1Rx antenna is limited and only can be improved
with new features (refer to previous sessions) in RAN12.0.
3.3 Solutions and Recommendations
We provided the following recommendations to operators upon this issue as follows,
(1) To turn-off the HSUPA phase 2 in current network and implement it later when
upgraded from RAN10.0 to RAN12.0 with Interference Cancellation and Dynamic NHR
features enabled.
(2) To upgraded capacity of indoor site by adding 2nd carrier. This is to improve user
experience especially on data throughput.
(3) To turn-on Load Control (LDR) to control the interference level which generated from
R99 users.
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