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

[email protected]

[email protected]

[email protected]

[email protected]

[email protected]

*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 3 Receiver, cat 8 HSDPA and cat 5 HSUPA Type 3 Receiver, cat 10 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



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



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



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



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).

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