indoor measurments

8/2/2019 Indoor Measurments

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Measurements for Distributed Antennas in WCDMA Indoor Network

Tero Isotalo, Jarno Niemelä and Jukka Lempiäinen

Institute of Communications Engineering, Tampere University of Technology

P.O.Box 553 FI-33101 TAMPERE FINLAND

Tel. +358 3 3115 5128, Fax +358 3 3115 3808

[email protected], http://www.cs.tut.fi/tlt/RNG/

Abstract— The target of the paper is to provide guidelinesfor indoor antenna selection for passive distributedantenna system or radiating cable implementation.Distributed antenna systems are commonly used forindoor installations, and radiating cables are often used intunnels, airplanes, or similar constricted areas. However,guidelines for optimizing WCDMA indoor networkantenna configuration are lacking in the literature. Inthis paper, the effect of different distributed antenna

configurations on signal quality and system performanceis studied, taking also radiating cable in comparison. Aspecial attention is paid to the future requirements of HSDPA. The measurement results show that planning of distributed antenna system is not very sensitive to theamount of antennas, as long as good coverage can beensured. Also radiating cable can be used, but providinggood coverage requires very dense installation of cables.

Key words: DAS, field measurements, indoor, radiating cable, WCDMA

1. Introduction

The need for macrocellular 3G (3rd generation) net-

works is fast increasing in densely built-up areas. In the

near future, a significant number of high data rate users

are located indoors. Therefore, providing good indoor

coverage and capacity also for indoor users will be an

important topic for network operators. Interference and

coverage limitations prevent efficient usage of outdoor

networks for serving indoor users. Thus, dedicated in-

door systems should be used [1]. Available solutions

for building indoor coverage with dedicated systems are

distributed antenna system (DAS), radiating cables (RC)

[2], or pico base stations [3].

Optimizing the behavior of basic UMTS (universal

mobile telecommunication system) indoor systems is an

up-to-date topic, but the future needs of implementing anHSDPA (high speed downlink packet access) function-

ality should be taken into account when planning new

indoor systems. To take a maximal advantage of the HS-

DPA enabled network, good radio conditions are needed

for high bit rate applications that in indoor emphasizes

the need of dedicated indoor systems [4]. In GSM

indoor system planning, the main target was to ensure

good coverage, whereas optimizing WCDMA (wideband

code division multiple access) indoor system might not

be that straightforward task. Indoor environment may

cause some challenges for WCDMA system due to,

e.g., lack of multipath diversity [5]. Thus, excluding few

simulation related references, e.g., [6], [7], guidelines for

a planning dedicated WCDMA indoor systems can not

be found from the literature.

2. WCDMA Indoor Planning

2.1. Indoor Environment

A system is considered to be a wideband, if the

signals’ transmission bandwidth is much wider than

the coherence bandwidth of the radio channel. The co-

herence bandwidth of macrocellular environment varies

typically between 0.053 MHz and 0.16 MHz, which

is clearly less than the bandwidth of WCDMA system

(3.84 MHz). Therefore, WCDMA system is rather robust

for frequency selective fast fading in typical outdoor

environments due to additional multipath diversity. How-

ever, in indoor environment the coherence bandwidth

can be more than 16 MHz. [5] This leads to WCDMA

signal being flat fading in most of typical indoor envi-

ronments, which might cause some unintended behavior

and lowered the system performance in indoor locations.2.2. Configuration Planning

Due to interference limited nature of WCDMA net-

works [8], the requirement of high throughput for a

single user in the cell edge or in an indoor location

can consume great amount of the downlink transmit

power of the whole cell that naturally affect the available

capacity of the whole cell. High bit rate users are rather

often in positions with high propagation loss, such as

buildings or cars. If outdoor network is not planned to

provide coverage and capacity for indoor users, or some

indoor location is introducing high load to some cells,

a dedicated indoor solution inside the building is worthconsidering for providing good indoor coverage [6], [9].

Different antenna configurations have been studied in

various cellular technologies, i.e., [10], [11]. Moreover,

simulations have been performed to analyze the capac-

ity of a dedicated WCDMA indoor system [6], [7].

However, measurement-based comparison of different

antenna configurations and radiating cable providing

background information and guidelines for planning an

indoor network can not be found in the literature.

There are some possible solutions for building indoor

coverage. Macro/microcellular networks can be planned



in such a manner that in-building coverage is taken

into consideration, which reduces the need for deploying

dedicated indoor systems. However, the high in-building

penetration loss makes it an inefficient solution. Most

typical solution is implementation of independent in-

door base station, with either DAS, RC [12], or even

distributed base station system [4].The indoor environment constitutes a challenge for

radio network planning due to the difficulty to per-

form accurate simulations in indoor environment. In

macrocellular radio network planning, estimating the

propagation of the signal can be based on propagation

models, such as Okumura-Hata. In indoor, simple mod-

els can be used, for instance 3GPP path loss model

for indoor environment [13], but very high accuracies

should not be expected. On the other hand, ray-tracing

or similar accurate models can be exploited, but this

requires very detailed information on the building, which

may lead to higher planning cost. Practical knowledge

on earlier successful installations has been used in GSM

indoor planning, but a part of the phenomena caused by

WCDMA system remain currently undiscovered.

2.3. Indoor Antenna Systems

Distributed antenna system is the most common ap-

proach for providing in-building coverage. Antennas

used in DAS are small discrete antenna elements de-

signed specially for indoor use. Typically they are either

omnidirectional or low gain directional antennas. In a

passive DAS implementation1, signal is transferred from

base station by network of feeder cables, connected

by splitters and tappers. Advantages of DAS are easyplanning and good coverage, while drawbacks include

high installation costs compared to, e.g., indoor pico

cells or outdoor-to-indoor repeaters [14].

Radiating cable (RC), often also called as leaky

feeder, is simply a feeder cable with small holes or

groove in the outer conductor of coaxial cable, and the

signal leaks in a controlled way from the cable. The

end of a radiating cable needs to be either terminated,

or one can install a discrete antenna there. Radiating

cables are typically used in, e.g., tunnel installations.

Due to small EIRP (effective isotropic radiated power)

of RC, it is also a good choice for interference sensitive

environments, such as hospitals and airplanes.

Another possible approach for indoor building an

indoor systems is usage of pico cells; a single pico cell

or a dense enough network of small base stations with,

e.g., in-built omnidirectional antenna in desired area for

indoor coverage.

1Note that the fundamental difference between a passive and anactive DAS is the losses in the feeder lines. However, from antennaconfiguration point of view, this separation cannot be made if coveragetargets can be achieved. Hence, the results of this paper can be appliedto both distributed antenna systems.

3. Measured Quality Indicators

Coverage of a cell is estimated by P-CPICH RSCP

(received signal code power for the primary common pi-

lot channel). Standard deviation (STD) of RSCP caused

by free space attenuation together with slow and fast

fading indicates the smoothness of RSCP in the network.

Large variations in RSCP leads to greater slow fading

margins. Quality of the coverage is indicated by P-

CPICH E c/N 0, the received energy per chip on P-

CPICH divided by the power density in the band. The

P-CPICH E c/N 0 is defined as ratio between RSCP and

RSSI (received signal strength indicator):

E cN 0

=RSCP

RSSI (1)

In addition, interference level is indicated with signal

to interference ratio (SIR) for the P-CPICH:

SIR = SF 256 P P −CPICH

(1− α)P TOT + (I inter + pn)L(2)

where SF 256 is the processing gain for P-CPICH,

P P −CPICH is the transmit power of P-CPICH, α is

the downlink orthogonality factor, P TOT is the total

transmit power of the base station, I inter is the received

inter-cell interference, pn is the received noise power,

and L is the path loss. The instantaneous root mean

square (RMS) delay spread σRMS is evaluated in this

paper from scanner measurement according to following

definition:

σRMS =�

τ 2− τ

2 (3)

where

τ 2 =

ka2kτ 2

k

a2k

(4)

is the mean excess delay and

τ 2 =

ka2kτ k

a2k

(5)

is the mean delay with ak as the amplitude of k th

multipath component and its’ a relative delay of τ k.

4. Measurement Setup

Measurements were conducted in an university build-

ing, in two different environments; open area and of-

fice corridor. Open area environment consisted of an

open 100 m long large corridor, having an open hall

in the other end and being 2 floors in height. The

antennas were located in the 2nd floor level, whereas

the measurements were carried out in the 1st floor level.

Antennas did not have LOS (line-of-sight) between each

others, where as connection between antenna and UE

consisted of a mixture of LOS and NLOS (non-line-

of-sight) connections. The office corridor measurements



2 dBi

EIRP

17.66dBm

CPICH

30dBm

RNC BTS

CPICH

30dBm

RNC BTS

-3 dB

CPICH

30dBm

RNC BTS

-5 dB

CPICH

30dBm

RNC

BTS

-3 dB

-3 dB

-3 dB

60 m

-10.12dB

25 m

-4.22dB

a) 1-Antenna

CPICH

30dBm

RNC

BTS

20m 2.66dB

b) 2-Antenna

c) 3-Antenna

d) 4-Antenna

e) Radiating

Cable

2 dBi

EIRP

14.66dBm

2 dBi

EIRP

12.66dBm

2 dBi

EIRP

11.66dBm

60 m

-10.12dB

60 m

-10.12dB

60 m

-10.12dB

60 m

-10.12dB

25 m

-4.22dB

25 m

-4.22dB

25 m

-4.22dB

Figure 1. System block diagram and antenna configuration scenariosfor open area measurements.

were carried out in a narrow corridor opening to other

corridors, and having various small rooms along. An-

tennas were located in the 2nd floor, and measurements

were conducted in the 1st as well as in the 2nd floor.

Antennas had LOS between each others. Measurement

route in the 2nd floor had almost continuous LOS for

the antennas, whereas measurement route in the 1st floor

had only NLOS connections.

The measurements were carried out in an experimen-

tal WCDMA network, consisting of an RNC/Iub (radio

network controller) simulator running on a PC, and a

commercial WCDMA base station, connected to the

an antenna system. The antenna system consisted of a

feeder cable connected to varying antenna configuration.

The antenna configuration for open area measurements

is shown in Fig. 1, and the configuration for office

corridor measurements is otherwise similar, except the

attenuation in feeder cable is 2.9 dB smaller. Also a 4-

antenna scenario was excluded from measurements in

office corridor.

Depending on the antenna configuration, the signal

was transmitted either directly to an antenna or a RC,or split into 2-4 equal parts (2-3 for office corridor).

Antenna locations are shown in Fig. 2. (a)-(d). Antenna

locations for the office corridor are shown in blue/upper

markings, and for the open area with red/lower mark-

ings. Antennas used for the measurements were omni-

directional indoor antennas with 2 dBi gain. Radiating

cable and feeder cable were 1/2" coaxial cables, and the

length of the radiating cable was 20 m.

Measurement routes are shown in Fig. 2.(e) for the 1st

floor, and Fig. 2.(f) for the 2nd floor. The shorter mea-

surement routes in Fig. 2.(f) are measured underneath

(a) 1-antenna / RC (b) 2-antenna

(d) 4-antenna(c) 3-antenna

(e) Measurement routes, 1st floor (f) Measurement routes, 2nd floor

1<RC

RC 1<

2 2

2 2

4 4 4 4

3 3 3

3 3 3

Figure 2. Antenna positions for 1-4 -antenna and radiating cablescenarios (a)-(d), and measurement routes (e-f). (a)-(d) are locatedon the 2nd floor. Upper/blue markings are for the office corridor andlower/red for the open area.

the radiating cable.

Measurement equipment consisted of a WCDMA UE

and a WCDMA scanner, connected to a radio interface

measurement software. The cell scenario was isolated,

i.e., no inter-cell interference was present and the mea-

surements were conducted in connected mode having a

12.2 kbps speech connection. The measurement routes

were repeated several times in order to increase thereliability of results.

5. Measurement Results

All measured values are are shown in Table 1. For

the open area measurements, E c/N 0 values remain at

the level of −4 dB for all configurations, and moreover

the values are at the same level for all the antenna

configuration. This is natural when the load of the

network is low, and no coverage limitations occur,

i.e., RSCP remains at good level above the thermal

noise floor at the mobile. The RSCP level is improved

when increasing the amount of antennas. However, the

coverage improvement achieved by adding more thantwo antennas is rather small partly due to lower EIRP

(1 dB improvement of having four antennas instead of

two). However, with radiating cable the average RSCP is

clearly lower (13..17 dB difference compared to discrete

antennas). A decrease in STD of the level of RSCP was

expected after increasing the number of antennas, but it

remains almost unchanged in open area environment in

all discrete antenna scenarios. Radiating cable provides

clearly the smallest deviation in RSCP. The average

delay spread in discrete antenna scenarios is between

0.30 µs and 0.33 µs, whereas with radiating cable



Table 1. Idle mode measurement results.Open area 1-antenna 2-antenna 3-antenna 4-antenna RC

E c/N 0 [dB] -4.07 -4.03 -4.14 -4.11 -4.10RSCP [dBm] -60.04 -57.50 -57.43 -56.47 -73.50RSCP STD [dB] 5.93 5.24 5.94 5.67 3.66Delay spread [µs] 0.33 0.30 0.33 0.33 0.39SIR [dB] 21.84 21.93 21.63 22.28 22.01

Office corridor, 2nd floor 1-antenna 2-antenna 3-antenna RC

E c/N 0 [dB] -4.12 -4.10 -4.05 -4.01RSCP [dBm] -45.44 -44.05 -41.74 -67.59RSCP STD [dB] 6.98 6.18 5.34 3.97Delay spread [µs] 0.31 0.29 0.28 0.34SIR [dB] 22.27 21.26 21.40 22.14

Office corridor, 1st floor 1-antenna 2-antenna 3-antenna RC

E c/N 0 [dB] -4.21 -4.12 -4.14 -4.49RSCP [dBm] -69.14 -68.49 -67.27 -90.98RSCP STD [dB] 8.11 5.00 4.39 7.47Delay spread [µs] 0.32 0.30 0.31 0.38SIR [dB] 21.74 21.79 22.79 20.83

17 18 19 20 21 22 23 24 250

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

F ( X )

CDF

1−antenna

2−antenna

3−

antenna4−antenna

RC

Figure 3. CDF of downlink SIR measurements in open area for allantenna configurations.

slightly higher, 0.39 µs. The results indicate that certain

amount of multipath diversity would be available in

the particular measurement scenario. Also SIR values

remain at the level of 22 dB. The CDF (cumulative

distribution function) of SIR in open area is shown

in Fig. 3. Increasing the amount of antennas is not

affecting SIR, since the variations between different

antenna configurations are inside one decibel.

In the office corridor in the 2nd floor, the mea-surements were conducted close to antennas with LOS

conditions. Again, E c/N 0 remains close to −4 dB due

to same reasons mentioned before and the level of RSCP

is again increasing when adding more antennas. There

is an improvement of 1.4 dB when adding a second an-

tenna, and another 2.3 dB when adding a third antenna.

Radiating cable has again clearly the worst average

RSCP. In the office corridor, STD of RSCP is behaving

expectedly, decreasing while increasing the number of

antennas and again, radiating cable provides the smallest

signal level variations. Also the delay spread values

17 18 19 20 21 22 23 24 250

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

F ( X )

CDF

1−antenna

2−antenna

3−

antennaRC

Figure 4. CDF of downlink SIR measurements in office area for allantenna configurations (2nd floor).

follow the ones seen in the open area measurements.

When being very close to the antennas, increasing the

number of antennas seems to have negative effect on

SIR. Moreover, radiating cable provides high values for

SIR.

Measurements in office corridor in the 1st floor repeat

the measurements with same configurations than in the

2nd floor, differing only by added one floor attenuation.

Worsened coverage is affecting E c/N 0; slight decreasewith discrete antennas, and clear decrease with radiating

cable due to coverage constraints. Being still relatively

close to antennas, radiating cable is already almost

unusable with one floor attenuation, discrete antennas

still having adequate RSCP values. Direction is again

the same; increasing the number of antennas improves

RSCP values slightly, while also decreasing signal level

variations (RSCP STD). It is good to notice that with

floor attenuation, signal variations with RC are now at

the same level with 1-antenna scenario, whereas close

to cable radiating cable provided the smoothest cover-



14 16 18 20 22 24 260

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

F ( X

)

CDF

1−antenna

2−antenna

3−antenna

RC

Figure 5. CDF of downlink SIR measurements in office area for allantenna configurations (1st floor).

age. Average delay spread remains at the same level

regardless of floor attenuation. SIR values are clearly

increased when adding more antennas, and radiating

cable is Showing lowest SIR values due to reduced

coverage. The CDF of SIR in the office corridors is

shown in Fig. 4 for measurements under the antennas

(the 2nd floor) and in Fig. 5 for measurements with one

floor attenuation (the 1st floor).

6. Conclusions and Discussion

This paper covers the measurements results for indoor

UMTS network with different antenna configurations.

These antenna configurations consisted of a passive

distributed antenna configuration with one to four om-

nidirectional antenna or of a radiating cable. The results

indicate that the average level RSCP increases if the

amount of antennas is increased in open area indoor

and also in more closed corridor -type of indoor en-

vironment. The increase of RSCP was observed even

though the signal was divided into increasing parts

having lower EIRPs for different antennas. The stan-

dard deviation of RSCP decreases while the amount

of antennas is increased, which means more uniform

signal conditions over the measured area. A radiating

cable provides in general more uniform signal level.

However, in order to achieve a uniform signal level

and adequate coverage, an extremely dense cabling isrequired. The delay spread values for all configuration

were almost the same indicating the balance between

the amount of multipath diversity and loss of downlink

code orthogonality. Without any floor attenuation it was

observed that increasing the number of antennas actually

decreases the SIR. However, with a floor attenuation, the

situation is opposite.

Based on the measurement results, it can be seen that

increasing the amount of antennas in DAS improves

the coverage and smooths the average signal level in

the network, but does not provide significant gain in

signal quality. Hence, the measurement results shows

that the capacity of the network does not change at all

if the number of antennas are increased. Radiating cable

can provide decent quality as long as the coverage is

not limiting. Therefore it can be discussed, whether the

focus of planning WCDMA networks should be more

in coverage than capacity. Future studies will includecomparison of DAS and pico cells in indoors, as well

as measurements with indoor HSDPA implementation.

Acknowledgment

Authors would like to thank Elisa Oyj, European

Communications Engineering (ECE) Ltd, Nemo Tech-

nologies, and Nokia Networks for helpful comments

concerning the measurements, and for enabling the

measurement setup. This work was partly funded by

National Technology Agency of Finland.

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