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Transcript of 3G HSPA with High Speed Vehicles.pdf
7/30/2019 3G HSPA with High Speed Vehicles.pdf
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3G HSPA for Broadband Communications with High
Speed VehiclesSantiago Tenorio
#1, Paul Spence
*2, Beatriz Garriga
#3, Javier López
#4, Aitor García
#5, Miguel Arranz
#6
#Vodafone Technology Networks, Vodafone SpainIsabel Colbrand, 22, Madrid, Spain1
*McLaren Electronic Systems
Woking, Surrey, GU21 4YH, United [email protected]
Keywords: HSPA, Doppler, Mobility, High Speed, Telemetry, Formula 1
Abstract— This paper presents a proof of concept for acontinuous superior quality Broadband Vehicularcommunication system enabled through 3G HSPA in very high
speed mobility scenarios (beyond 300 km/h), suitable fortelemetry applications in trains, emergency vehicles and motorsport events. The system is quite unique as radio transmission fortelemetry services under extreme speed conditions requires notonly superior Quality of Service guarantees but must also be ableto satisfy these performance requirements under extreme andarbitrarily demanding environments as are typical during anye.g. Formula 1 racing event.
Issues related to the Doppler Effect and abrupt changes of theserving HSPA channel are analyzed and addressed here.
Conclusions show how a special 3G network design can help tomitigate Doppler Effect impacts. The processes carried out byboth the UE and the network to cope with this high speedenvironment has proven essential to sustain the service in these
conditions, as it has the use of suitable receiver Types in the UE.Using derived guidelines and conclusions, a unique system hasbeen developed, built and tested in a Formula 1 environmentwith very promising results.
I. BACKGROUND
3rd
Generation Partnership Project (3GPP) has standardized
WCDMA-based packet-switched air interfaces for both
downlink and uplink called High-Speed Downlink Packet
Access (HSDPA) and High-Speed Uplink Packet Access
(HSUPA) respectively [1]. Under conditions where the signal
strength on the source cell is rapidly deteriorating (as in highspeed scenario) it can occur that the UE may not be able to
reliably decode the necessary mobility information, the
Service Cell Change (SCC) and Radio Resource Control
(RRC) message(s) from the source cell leading to a call drop.
An attempt to re-establish the call as defined in the standard
[2] under these extreme speed conditions is also a challenge as
verified in live testing environment.
Other known standard mobile communication systemsencounter equal or worse technical challenges as for instance
for any Orthogonal Frequency Division Multiplex (OFDM)
based system, frequency offsets, phase noise, and Doppler in a
time varying channel quickly result in a significant degraded
performance. In addition, this is coupled with impact from
inter-carrier interference (ICI) between the OFDM sub-carriers
and increasing complexity in the carrier estimation.This paper addresses the challenge of utilising and optimising
an existing commercial 3G HSPA Broadband system forcommunication to very high speed vehicles. As the main
immediate objective, this activity sought to establish aworking baseline for a new generation of telemetry systems
suitable for high speed applications and delivers a Proof of Concept in a Formula 1 environment.
In this paper, we introduce the setup utilised and the resultsobtained from several tests performed in different high speed
scenarios covering controlled environments.
II. EQUIPMENT DESCRIPTION
The UTRAN network was provided by a 3G equipment
manufacturer using products and features commercially
available.
Five types of devices were tested [3]
Type 1 Receiver, cat 8 HSDPA and cat 5 HSUPA
Type 2 Receiver, cat 8 HSDPA and cat 5 HSUPA
Type 3 Receiver, cat 8 HSDPA and cat 5 HSUPA Type 3 Receiver, cat 10 HSDPA and cat 6 HSUPA
Type 3 Receiver, cat 14 HSDPA and cat 6 HSUPA
III. SCENARIO DESCRIPTION
All testing took place in a high speed circuit - IDIADA - in the
north east of Spain. A dedicated 3G network was installed in
the 2.1GHz band using four Nodes B covering the entire
circuit, and in addition a compact RNC and CORE network
978-1-4244-2519-8/10/$26.00 ©2010 IEEE
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was also installed on-site. Two of the sites covered the curves
in the circuit and were located in a strategic position in order to avoid Doppler Effect impact. The remaining two sites were
installed close to the straight sections of the track - “straights”
- to fully analyse the Doppler Effect.
For coverage purposes, 20m masts were used. Sites in the
curves and straights had tri-sector and bi-sector design with
65º and 33 º cross-polar antenna beam width respectively.
Fig. 1 Test scenario, IDIADA circuit
IV. DOPPLER SHIFT AND MOVILITY ANALYSIS
Several tests were carried out to measure and quantify theimpact of both Doppler spread and mobility management
limitations in extreme conditions i.e. a high speed vehicle.
Particular attention was given to the evaluation of data service
performance itself, in particular measuring the throughput, the
RTT (Round Trip Time), and the effect of cell change when
the vehicle was traveling across two or more cells at speeds of
around 250km/hr and beyond.
A) DOPPLER SHIFT IMPACT
The main affection of high speed scenario is Doppler shift,
also known as Doppler Effect. This effect is the change infrequency in of a wave for an observer moving relative to the
source of the waves.
For waves that propagate in a medium, such as radio waves,
the velocities of the observer and of the source are relative to
the medium in which the waves are transmitted. Doppler shift
follows the next formula, also represented in the figure 2:
θ cos××= vC
f f d
θ: angle between UE mobility and signal propagationdirections
v: vehicle rateC: radio spread rate
f: carrier frequency
Fig. 2 Doppler shift components
The main outcomes regarding Doppler Effect on HSPA
performance are:
In downlink, in neither RSCP nor Ec/No no significant
degradation was detected. The HSDPA throughput loss
was 16% in the worst case
In uplink, the BLER and retransmission rate critically
increases at speeds beyond 180km/h where throughput
drops to almost 0kbps if no Doppler compensationfunctionality is activated in the node B
Figure 3 shows the effect of Doppler Speed on HSUPA UL
data traffic. As speed increases the number of retransmissionsincreases impacting on throughput.
Fig. 3 CAT6 HSUPA UL throughput degradation above 180km/h
Figure 4 shows the effect of Doppler Speed on HSDPA DL
data throughput depending on the UE receiver Type. Type 3
receiver achieved the best performance under different speeds ,and Type 2 showed the biggest throughput degradation of
around 16% respect to 30km/h. Regarding HSDPA coverage
loss measured by CQI, all devices showed similar degradation
trend at high speeds i.e. approximately 1.2dB less compared to
low speeds.UE Receiver Type: --- Type 3 ---Type 2 ---Type 1
20
21
22
23
24
25
26
27
30 Km/h 50 Km/h 80 Km/h 120 Km/h 150 Km/h 180 Km/h 220 Km/h 250 Km/h
dot lines CQI / continious lines MAC throughput
C Q I
2000
2500
3000
3500
4000
4500
5000
5500
6000
k b p s
Fig. 4 CAT8 HSDPA DL throughput and CQI vs. receiver type and
Doppler Speed
To mitigate the effect of Doppler shift in user performance, thefollowing algorithms were implemented in the network side:
1) Frequency offset estimation
2) Frequency offset compensation
There are different methods to perform frequency offset
estimation and compensation - although most of them arevendor proprietary algorithms.
Figure 5 shows the HSUPA throughput gain with a Doppler
shift compensation algorithm on. At 250Km/h, there is no
Car Speed
Doppler Speed
HSUPA Throughput
Retransmission Number
UE Power Headroom
-180 Km/h
180 Km/h
0,5 Mbps
5 Mbps
0
7
20 dB
65 dB
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throughput degradation comparing to 80 and 150km/h cases.
Regarding UE power, 17dB less is required to get 3.7Mbpsmore if Doppler shift compensation is put in place.
Fig. 5 CAT6 HSUPA Throughput and Remaining available power in theUE vs. Doppler speed
B) MOBILITY IMPACT
Current 3G network mobility processes are optimized to
operate at medium-low speed mobility (<150km/h) so under
high speed scenarios a different parameterization and design is
needed.
• Soft handover: New target cell addition time is about
400~800ms (from new cell detection by UE till activeset cell update complete message). Additionally,
HSDPA DL service requires cell change when a new
target cell becomes x-dB’s better than the actual cell
level in terms of EcNo. This process takes usually a
longer period of time since physical channel
reconfigurations must be performed in the UE. Theaverage time required to perform such action is about
1.2~3.3s with 1.75s the average and 0.71s the standard
deviation (from new cell change condition detection by
UE till physical channel reconfiguration complete
message). This broad range is due to the fact that many
3G vendors implement specific timers to avoid ping
pong effect during HSDPA cell change. A full HSDPAcell change procedure requires soft handover plus cell
change actions. Figure 6 shows the average distance
traverse during the cell addition, cell deletion and
HSDPA Reference Cell Change event depending on the
speed. The minimum total overlap distance required
between 2 cells would be around 260m at 300Km/h,
345m if being more conservative.
DISTANCE REQUIRED FOR SHO AND HSDPA CELL CHANGE
0
50
100
150
200
250
300
30 50 80 120 150 180 220 250 300 350
Speed (Km/h)
D i s t a n c e ( m )
Cell addition Cell deletion HSDPA Cell Change
Note: Time to trigger 1a: 100ms; Time to trigger 1b: 640ms; Time
Fig. 6 Distance per event
• Inter frequency and Inter system handover: The
process takes approximately 1.4s ~ 2s in case of inter
frequency handover and 1.4s in case of intersystem
handover under normal conditions.
• Cell reselection: When camped on a cell, the mobile
shall regularly search for a better cell according to the
cell reselection criteria. Cell reselection failure was
frequently detected in high speed scenarios because UE
has changed cells before the cell reselection timer expires.
Performance improvement in high speed mobility scenarios
requires:
1. Avoid inter frequency and inter system handover to
reduce call drop rate and zero throughput periods.
2. Make usage of single cell configurations to avoid
handover and ping pong effect due to pilot pollution as
much as possible. This impact increases proportionately at higher speeds. Figure 7 represents
HSDPA performance when changing cell on a polluted
area. The CQI, HS-SCCH success rate and HS-DSCH
BLER degradation are bigger at high speed impactingon throughput
Fig. 7 Pilot Pollution effect on HSDPA performance vs. speed
3. Optimize network design maximizing handover
overlapping distance taking into account high speeds4. Optimize parameters to accelerate UE decisions and
network reaction (e.g. accelerate 1A trigger, to make
0.5 Mbps
6.9 Mbps
15
30
50%
100%
0%
30%
SC 1
SC 25
Reference Cell
CQI
HS-SCCH Success rate
BLER HS-DSCH
MAC HSDPA Throughput
Reference Cell
CQI
HS-SCCH Success rate
BLER HS-DSCH
MAC HSDPA Throughput
Pilot Pollution at 250 Km/h Pilot Pollution at 50 Km/h
Physical UL Throughput (Mbps)
4.5
3.7
0.4
4.0 4.0 4.1
0
1
2
3
4
5
80Km/h 150Km/h 250Km/h
Average Power Headroom (dB)
33.0 31.2
14.2
30.9 32.136.0
0
10
20
30
40
80Km/h 150Km/h 250Km/h
DOPPLER Feature Off DOPPLER Feature On
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difficult to trigger 1B configuration…)
5. To optimize cell reselection timers (“Treselection”,“Qoffset” and “Qhyst”) and reduce the system
information update time. Additionally, call
reestablishment timers should be optimized.
Figure 8 shows MAC HSDPA throughput variation during cell
change by modifying 1d event reporting parameters (target
cell signal level strength over serving cell level “Hys1d” andtime to satisfy the threshold “Ttrig”) when triggering fast,
medium or slow cell change procedures. As seen on the figure,
being reactive and trying to be on the best cell always or
conservative delaying cell change procedure are not the bestoptimization implementations to improve performance.
3.3
3.5
3.7
3.1
3.2
3.3
3.4
3.5
3.6
3.7
Fast: Hys1d = 2 dB; Ttrig = 320 msec
Medium: Hys1d = 3 dB; Ttrig = 200 msec
Slow: Hys1d = 4 dB; Ttrig = 320 msec
T H R O U G H P U T ( M b p s )
Fast HSDPA Cell Change Medium HSDPA Cell Change Slow HSDPA Cell Change
Fig. 8 HSDPA Performance comparison during cell change with
different mobility optimization strategies
To avoid mobility issues and increase UL capacity, a feature
offered by several infra vendors called Multi-RRU has been
tested. This feature permits several physical cells to work as a
single cell for down link transmission and as independent cells
for up link reception
The following benefits are obtained from the use of this
feature in high speed scenarios:
• Reduction of number of handovers controlled by the RNC
• Flexibility on the coverage area of one cell to adapt the
network design to specific high speed scenarios needs
• Enhancement of the uplink capacity (Throughput increase)
due to different sector RTWP management
• Downlink diversity gain in the overlap coverage area of
different RRU's.
0
1
2
3
4
5
6
7
8
9
10
A p p l i c a t i o n t h r o u g h p u t ( M p b s )
Stat ic UE Mobile UE Total UL Cel l Bandwidth Fig. 9 MRRU feature performance
Figure 9 shows the effect of the feature on uplink cell capacity,
when both users are located in the overlap area of both sectors
the traffic in UL is shared between both (4.5Mbps) but when
each user is located under the coverage area of a different
physical cell the throughput increase as they don’t have to
share common resources (around 4.5Mbps each)
V. HIGH SPEED PERFORMANCE IN AN OPTIMIZED
NETWORK
A) HSDPA PERFORMANCE (250 KM/H)
Figure 10 shows a HSPA/HSPA+ performance comparison
among CAT8, CAT10 and CAT14 devices at 250Km/h. Both
CAT10 and CAT14 devices benefit from 15 codes usage with
QPSK modulation and the Enhanced Layer 2 3GPP feature,thus improving the HS-DSCH BLER. The benefit of using 15
codes with a new advance 3GPP Release 7 receiver type is
significant with up to 88% more throughput achieved withonly 5 more codes available. The reason for this is not only the
number of codes available but also the improved HSDPA
coverage measured by the CQI which is 3dBs better due toimproved receiver type. CAT14 HSPA+ 64QAM device only
gets 6% more throughput than CAT10. This is due to the fact
that there was an Iub limitation and the maximum achievable
throughput was 16Mbps (although Iub limitations aside, a
peak of 21.8Mbps would have been possible).
Fig. 10 CAT8, CAT10 and CAT14 HSDPA/HSPA+ performancecomparison at 250km/h
However, the main conclusion is that utilizing this Rx Type in
the UE permitted 64QAM modulation to be utilized in up to27% of samples with the BLER measured as below the BLER
target of 10%. 64QAM modulation is not affected negatively
with high speed
B) HSUPA PERFORMANCE (310 KM/H)
Figure 11 shows a HSUPA performance comparison among
CAT5 and CAT6 devices at 310Km/h. The CAT5 device
achieved high and stable throughput providing 1.8Mbps on
average as measured at the physical layer (10% below the
Boths user in
same sector
Boths user in
same sector
Boths user in
different sectors
5.06.2
9.7
24.4
4.6
10
13 14
28
810.5
15.014.6
26.5
8.2
Average
MAC
Throughput
(Mbps)
Peak MAC
Throughput
(Mbps)
Average
code
Average CQI Average
BLER (%)
CAT8
CAT10
CAT14
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maximum throughput). The CAT6 device provided more
unstable throughput but did achieve 4.1Mbps on average (29% below the maximum throughput). Using the CAT6 device
required around 8.6dBs more power compared to the CAT5
device to achieve 127% more throughput
-0.7
1.8
7.9
4.1
Tx Power (dBm) HSUPA Physical Throughput
[Mbps]
CAT5 CAT6
Fig. 11 HSUPA performance
UL Cell capacity with multi-user was assessed at 250km/h.
For this purpose, 6 CAT5 HSUPA devices were placed in the
same car performing UDP uploads. For each of the users a
100kbps UL Guaranteed Bit Rate (GBR) was setup in the
Node B and 2 different maximum UL RTWP increase levelsrelative to background noise were analysed: 30dB and 10dB.
Figure 12 shows the results obtained. The UL cell throughput
is slightly degraded by around 15% with a low RTWP increase
but the GBR is achieved 92% of the time whilst only 45.8%
was reached in the other case. Achieving 100% GBR would
require an even lower RTWP increase allowance.
0.3%2.8% 1.0%
21.2%
6.7%
30.2%
92.0%
45.8%
0.00
0.50
1.00
1.50
2.00
2.50
ROT 10dB ROT 30dB ROT 10dB ROT 30dB ROT 10dB ROT 30dB ROT 10dB ROT 30dB
3 4 5 6
H S U P A T h r o u g h p u t C A T 5 ( M b p s )
0%
20%
40%
60%
80%
100%
T i m e s a m p l e s ( % )
% Time Samples Total UL Application Throughput
Simultaneous Users
Fig. 12 Average HSUPA application user throughput vs. number of
satisfied users with GBR
C) ROUND TRIP TIME RESULTS (250 KM/H)
Figure 13 shows the Round Trip Time performance
comparison for CAT5 and CAT6 HSUPA devices when
sending 64bytes ping packets at 250Km/h. As seen in thefigure, CAT6 HSUPA device achieves 8ms lower RTT values
on average (-17%) comparing to CAT5 device. Besides, both
average and standard deviation RTT values increase critically
when the CAT5 device was in soft handover.
47
102
158
39 49 44
11
164
264
1132
9
0
50
100
150
200
250
300
1 2 3
Number of cells in active set
R T T ( m s )
Avg RT T Cat 5 Avg RT T Cat 6 Stand Deviation RT T Cat 5 Stand Deviation RT T Cat 6
Fig. 13 Round Trip Time variation with soft handover for CAT8
HSDPA/CAT5 and CAT6 HSUPA devices
The Round Trip Time of a HSUPA CAT5 device was alsomeasured via simulating load in addition to another CAT5
device performing FTP uploads at 310Km/h. On average, the
RTT value in loaded conditions increased from 59ms to 80ms
(35% increase).
VI. CONCLUSIONS
The trial in IDIADA demonstrated that the 3GPP HSPA
technology works with only a slight degradation at speeds
beyond 300km/h.
A Doppler shift compensation feature is required in the node Bwhen the UE moves at speeds over 180km/h to avoid
throughput degradation. No significant Doppler effect has
been seen on the UE side.
HSPA performance enhances in single cell configuration with
a multi RRU feature improves uplink cell capacity.
Ad-hoc optimization and design solution(s) are mandatory toavoid cell change ping pong effect due to pilot pollution.
Inter-cell overlapping distances over 300m are recommended
to avoid HSPA performance loss due to lack of soft handover or cell change time availability.
Network performance is improved using “HSPA+”
CAT14/HSUPA CAT6 devices in comparison to legacy
devices i.e. better downlink and uplink throughput, round trip
times were achieved and adapted better to the coverage and
radio environment.
VII. ACKNOWLEDGEMENTS
The authors would like to acknowledge Qualcomm, Huaweiand ZTE Corporation for facilitating the necessary UE,
network infrastructure and related support, and in particular to
the Vodafone McLaren Mercedes Racing Team for their support and access to their high-end engineering facilities.
VIII. REFERENCES
[1] 3GPP Rel-7 and Rel-8 White Paper (3G Americas).www.3gamericas.org
[2] 3GPP TS 25.331 V8.9.0 Radio Resource Control (RRC); ProtocolSpecification.
[3] 3GPP TR 25.101 V9.0.0 (2009-05) User Equipment (UE) radiotransmission and reception (FDD).