Power limits for secondary devices operating on TV white spaces

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Analog Integrated Circuits and SignalProcessingAn International Journal ISSN 0925-1030 Analog Integr Circ Sig ProcessDOI 10.1007/s10470-013-0129-4

Power limits for secondary devicesoperating on TV white spaces

Erika P. L. Almeida, Fabiano S. Chaves,Robson D. Vieira & Renato F. Iida

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Power limits for secondary devices operating on TV white spaces

Location specific strategies to be adopted by geo-location databases

Erika P. L. Almeida • Fabiano S. Chaves •

Robson D. Vieira • Renato F. Iida

Received: 19 March 2013 / Revised: 4 July 2013 / Accepted: 29 August 2013

� Springer Science+Business Media New York 2013

Abstract The use of TV white spaces as an alternative to

overcome spectrum scarcity is a huge opportunity for new

telecommunication systems and services. While being

attractive for its desirable propagation characteristics, this

part of the spectrum imposes a major difficulty from design

and regulatory perspectives: how to optimize the use of

spectrum and to ensure the protection of primary users, TV

systems for example, at the same time. This paper dis-

cusses strategies to be adopted by geo-location database

operators to calculate adaptive maximum permitted power

levels for secondary devices, according to permissible

levels of interference into the digital terrestrial television

primary system.

Keywords TV white spaces � DTT broadcasting �Cognitive radio � Unlicensed devices

1 Introduction

Spectrum is a valuable and limited resource shared among

a large number of wireless communication systems. The

increase of the use of wireless technologies as well as the

current—fixed—model of spectrum usage have caused

what is called spectrum scarcity, i.e., the available spec-

trum may not be enough to accommodate the expected

traffic demand for the next years.

In the past few years, a new model for the use of

spectrum has been proposed: the dynamic spectrum access.

In this model, instead of fixed assignment of spectrum for

specific services, frequency bands are assigned to services

or systems according to the demand. In this sense, cogni-

tive radio has emerged as the enabling concept for more

efficient utilization of spectrum, since it is capable of

changing emission characteristics of systems (transmission

frequency, for example), according to the spectral avail-

ability by its location.

The switch off from analog to digital television has freed

up a large amount of frequencies in the Ultra-High Fre-

quency (UHF) band, which has motivated the use of this part

of the spectrum—known as TV white space—on a secondary

basis. Regulatory authorities in different countries are

defining the rules and requirements for secondary usage in

this frequency band. In the United States, for example, the

Federal Communications Commision (FCC) launched the

rules for white spaces in the end of 2010. In Europe, the

European Conference of Postal and Telecommunications

Administrations (CEPT), through the SE43 project team

(responsible for dealing with cognitive radio matters) final-

ized its ECC Report 159 in January 2011, in which technical

and operation requirements were defined for cognitive radio

systems operating on the frequency band 470–790 MHz and

issues requiring further studies were determined.

Two aspects of the operation of white space devices

(WSDs) are crucial to the protection of primary systems and

highly depend on regulatory requirements: the accuracy of

the technique for identification of free channels and the

E. P. L. Almeida (&) � F. S. Chaves � R. F. Iida

Av. Torquato Tapajos, 7200, Colonia Terra Nova, Manaus, AM,

Brazil

e-mail: [email protected]

F. S. Chaves


R. F. Iida


R. D. Vieira

SCS Quadra 01 Bloco F, Ed. Camargo Correa, Brasılia, DF,

Brazil


123

Analog Integr Circ Sig Process

DOI 10.1007/s10470-013-0129-4

Author's personal copy

maximum permitted transmission power. Two techniques

are well known for the identification of spectral opportuni-

ties: spectrum sensing and geo-location database assisted

operation. With spectrum sensing, WSDs try to detect the

presence of incumbent services and determine the poten-

tially available channels. On the other hand, with geo-loca-

tion database, the WSDs need to be aware of their location

and consult a geo-location database in order to determine

which frequencies are available at that location. Initial

studies have shown that spectrum sensing techniques alone

cannot guarantee a reliable identification of available chan-

nels. Therefore, the geo-location database assisted operation

is preferred to provide protection to primary systems.

The geo-location database contains relevant information

about the digital terrestrial television (DTT) system plan-

ning (location of transmitters, used frequencies and prop-

agation characteristics, for example) to determinate

channel availability in different locations. The database

matches the location provided by the WSD with the

information previously available, in order to determine if

there is a transmission opportunity, or not. If there are

available channels, the database must inform the WSD with

the frequency and the maximum permissible transmission

power at that location, so that harmful interference to the

primary system is avoided.

CEPT and FCC recommend the geo-location database

assisted operation as the main method to protect the pri-

mary system. However, the implementation of this data-

base differs in each case. FCC, for example, defined fixed

emission limits for secondary devices [1] based on their

type (fixed or portable) and location regarding the DTT

transmitter: inside or outside its coverage contour. Besides,

FCC does not permit the use of fixed WSDs on the first

adjacent channel inside the coverage area. Some compa-

nies are already providing databases based on FCC rules,

like Spectrum Bridge [2].

On the other hand, CEPT describes on the ECC Report

159 [3] general rules for the calculation of maximum

permitted WSD power, which are more flexible than the

implementation proposed by FCC. In CEPT methodology,

the maximum permitted power varies within the coverage

area according to the degradation caused into the DTT

system. The topics left for further studies in ECC Report

159 have been recently addressed in ECC Report 186 [4],

which includes some content of the present paper.

This paper addresses how a geo-location database based

on CEPT methodology can define limits for WSD trans-

mission power by respecting the interference limits and

protection criteria. Section 2 introduces important param-

eters used in the planning of broadcasting systems in the

band 470–790 MHz. Protection criteria to DTT service

used to set maximum permitted interference are discussed

in Sect. 3. Derivation of upper limits for permissible WSD

transmission power and different database strategies to

calculate the WSD maximum permitted emission limits are

presented in Sects. 4 and 5. Finally, simulation results and

conclusions are presented in Sects. 6 and 7.

2 Broadcasting service in the band 470–790 MHz

When planning DTT systems in VHF/UHF bands some

relevant parameters must be taken into account in order to

guarantee appropriate coverage and protection from inter-

ference. A set of those parameters and planning criteria for

DTT technologies are defined in Recommendation ITU-R

BT. 1368-8 [5].

2.1 Protection of the DTT receiver from interference

From the perspective of the DTT receiver, two parameters are

important to appropriate operation in the presence of inter-

ference: protection ratio (PR) and overloading threshold [5].

The radio frequency PR is defined as the minimum value

of wanted-to-unwanted signal ratio at the receiver input,

usually expressed in decibels, for the achievement of a

target quality, which for digital systems is usually mea-

sured in terms of bit error rate (BER). For digital video

broadcasting—terrestrial (DVB-T) systems, the PR is

measured before the Reed Solomon decoding, considering

a 2 9 10-4 BER [6, 7]. The PR for a given frequency

offset considers the adjacent channel leakage ratio of the

interfering transmitter, as well as the adjacent channel

selectivity of the interfered receiver [3]. In general, PRs are

approximately constant with the variation of the wanted

DTT signal level. This means that for higher wanted signal

level a proportional increased interference is allowed

without harmful effects.

In spite of a higher permissible interference in case of

higher wanted signal levels, at a certain level of interfer-

ence the DTT receiver assumes a non-linear behavior and

begins to lose its ability to discriminate the wanted signal

from the interfering signals at adjacent frequencies. This

interference level is known as overloading threshold (Oth)

and must be avoided at the DTT receiver [6].

2.2 DTT coverage quality

In DTT systems, coverage quality is measured in terms of the

probability with which a DTT receiver operates correctly in a

certain small area (pixel). This quality measure is called

location probability, LP. Then, the DTT coverage area is

composed of all locations where the LP is higher than or

equal to a given target percentage, usually 95 % for fixed

outdoor (FO), portable outdoor (PO), and portable indoor

(PI) DTT reception [7].


123


In the absence of interference, LP corresponds to the

probability of the wanted electric field strength at the DTT

receiver antenna, Ew, being higher than or equal to the

minimum field strength, Emin, associated to the minimum

required signal-to-noise ratio and the noise figure. Interfer-

ence caused by the DTT system itself or by other sources

affects DTT coverage negatively. A general expression for

location probability is given below (in linear domain):

LP ¼ Pr Ew�Emin þXK

k¼1

PRkðDfkÞEik

( ); ð1Þ

where Pr{A} is the probability of event A; Eik is the field

strength at the DTT receiver antenna due to the kth inter-

ference source, and PRkðDfkÞ represents the PR for the fre-

quency offset Dfk between the kth interference (unwanted)

signal and the wanted signal.

Wanted and interference field strengths at the DTT

receiver are commonly modeled as log-normal random

variables with specific mean and standard deviation [3,

Annex 6] i.e.:

– Ew ½dBlV=m� �N ðEwmed; r2wÞ: field strength of the

wanted signal at the DTT receiver antenna, with mean

Ewmed ½dBlV=m� and standard deviation rw [dB];

– Ei½dBlV=m� �N ðEimed; r2i Þ: field strength of the

interference signal at the DTT receiver antenna, with

mean Eimed ½dBlV=m� and standard deviation ri [dB].

Figure 1 shows an example of the variation of the

location probability with the wanted median field strength

Ewmed, in the absence of interference from other DTT

transmitters, i.e.PK

k¼1 PRkðDfkÞEik ¼ 0.

This signal model allows the assessment of the LP,

Eq. (1), through analytical calculation or simulation. A

closed-form expression for LP as a function of Ewmed and

rw is possible for the interference-free case, where a nor-

mal distribution property can be used:

LP ¼ Pr Ew�Eminf g ¼ QEmin � Ewmed

rw

� �; ð2Þ

where Qð�Þ is the Gaussian tail probability function (Q-

function). On the other hand, simulations are required to

assess LP when interference is present, since the sum of

log-normal random variables in (1) is no longer log-normal

distributed and the property used above does not apply.

3 Protection criteria to DTT service

Previous section presented some parameters related to the

operation of DTT systems and its protection against

interference. These parameters must be considered on the

definition of criteria to protect DTT receivers from harmful

WSD interference. Such criteria will define the maximum

permitted transmit power, i.e. the effective isotropically

radiated power (EIRP) of WSDs for non-harmful interfer-

ence to DTT receivers. When assessing the interference

caused by a WSD into the DTT service, two quantities are

important:

– The degradation of the coverage quality of DTT

service;

– The degradation of the ability of DTT receiver to

discriminate the desired signal from interference

signals.

The DTT service coverage quality degradation is

directly related to the location probability, which will be

inevitably reduced in case of secondary devices operation.

In order to take this effect into account, an additional term

needs to be considered in Eq. 1 [3]:

LPWSD ¼ Pr Ew�Emin þXK

k¼1

PRUkEiUkþ PRWSDEiWSD

( );

ð3Þ

where PRWSD is the WSD-to-DTT PR for a given fre-

quency offset, and Ei_WSD is the field strength of the

interference generated by the WSD. The degradation of the

coverage quality of DTT service, is then calculated as:

56.21 61.21 66.21 71.21 76.21 81.21 86.210.95

0.96

0.97

0.98

0.99

1

Ewmed

[dBμV/m]

Loca

tion

Pro

babi

lity

Fixed DTT receptionPortable DTT reception

Fig. 1 Location probability in

the absence of unwanted

emissions from the DTT service


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DLP ¼ LP� LPWSD: For each value of Ewmed a different

value of Eimed (median interfering field strength) is neces-

sary to cause a given degradation in location probability

DLP: This is illustrated in Fig. 2. ECC Report 159 con-

siders three values of DLP: 0.1, 0.5, and 1 %.

The second restriction refers to the degradation of the

ability of DTT receiver to discriminate the desired signal

from interference signals, which is directly related to the

overloading threshold. Using the overloading threshold as

an interference limit, the DTT receiver’s ability to dis-

criminate signals is guaranteed.

An additional protection criterion establishes limits for

the total interference caused by WSDs. Limitation of

interference to broadcasting systems is recommended in

ITU-R BT. 1895 [8], where it is stated that ‘‘the total

interference at the receiver from all radiations and emis-

sions without a corresponding frequency allocation in the

Radio Regulations should not exceed 1 per cent of the total

receiving system noise power’’. This -20 dB maximum

interference-to-noise ratio (I/N) has been discussed during

SE43 Group meetings and I/N B -3 dB has been sug-

gested as protection criterion. Recommendation ITU-R BT.

1895 itself states that interference limitation values must be

used as guidelines, above which compatibility studies of

the effect of radiations and emissions from other applica-

tions and services into the broadcasting service should be

undertaken.

Figure 3 shows the maximum permitted WSD EIRP

using each of the presented protection criterion separately

considering a coexistence scenario consisting of a PO DTT

receiver and a portable WSD operating on the 2nd adjacent

channel. Using the parameters presented in [9]:

PRðDf Þ ¼ 40 dB, path loss = 34.72 dB, Oth = –30.5 dBm

and DTT-Rx antenna gain = 2.15 dBi. In this figure, it can

be noticed that, in spite of the fact that the I/N criterion

meets the limits imposed by the PR and Oth, it impacts

negatively the viability of secondary systems operation in

this frequency band.

The presented protecion criteria are studied in [9], from

which it is concluded that:

– The use of the maximum interference-to-noise based

protection criterion penalizes the efficient use of

spectrum, for not considering the variability of the

DTT coverage quality within its entire operation area.

– The possibility of variable degradation in location

probability is an interesting approach in order to take

advantage of the DTT coverage quality if the over-

loading threshold is also respected.

Given the variability of the DTT coverage within its

operation area, as shown in Fig. 2, tolerable levels of

degradation should be defined prioritizing both the pro-

tection of the DTT service and the viability of secondary

systems operation in this frequency band. Tolerable levels

of DLP are recognized in [3] as an issue requiring further

studies. An optimum degradation level is not expected to

be found, since the decision about the DLP to be adopted is

influenced by several aspects, as the target DTT coverage

quality, the specific characteristics of different regions

(urban, suburban, rural areas), etc. Moreover, political and/

or economic aspects may also play a role on this decision.

In spite of this, upper limits for DLP can be derived by

considering the technical limitations of DTT receivers in

dealing with interference.

4 Upper limits for DLP and WSD EIRP

The operation of white space systems in TV bands causes

additional interference to the primary DTT system and

consequently degrades the original DTT LP. The criterion

considered to protect DTT systems from WSD interference

is the restriction of DLP to acceptable/tolerable levels. As

mentioned, the decision about the DLP level to be adopted

involves several aspects, including subjective ones. No

−30 −20 −10 0 10 20 30 40 50 60

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1

Eimed

[dBμV/m]

Loca

tion

Pro

babi

lity

cons

ider

ing

WS

Ds

Ewmed

ref

Ewmed

ref

+ 10dB

Ewmed

ref

+ 20dB

Ewmed

ref

+ 30dB

Fig. 2 Location probability in

the presence of WSD

interference, considering fixed

DTT reception, for different

values of Ewmed. Ewmedref

represents the median field

strength of the wanted DTT

signal at the edge of the

coverage area, and Eimed is

calculated considering co-

channel protection ratio, PR(0)


123


https://www.researchgate.net/publication/261418226_On_the_protection_criteria_for_the_operation_of_white_space_systems_on_TV_bands?el=1_x_8&enrichId=rgreq-df242622a10a6a862db51d6510ba634b-XXX&enrichSource=Y292ZXJQYWdlOzI2MzI2ODM2NztBUzoxMDMyMTIyNjY4MTk1ODlAMTQwMTYxOTEzMDY4Mg==


solid arguments have been presented so far to define limits

of tolerance regarding DLP.

In this section, we present limits for tolerable DLP; and

consequently for WSD EIRP, based on technical limita-

tions of the DTT receiver in handling interference. In Sect.

2.1, PR and Oth are presented as parameters of protection of

the DTT receiver against interference. Now, we derive

interference limits for appropriate operation of the DTT

receiver by considering PR and Oth. We take into account

statistical variations of wanted and interfering signals,

providing interference limits for the protection of the DTT

receiver for a given percentage of locations. From the

interference limits, we obtain the corresponding maximum

permissible levels of DLP and WSD EIRP. For simplicity,

interference of other DTT transmitters is ignored.

4.1 Limitation imposed by PR

The respect of PR consists in guaranteeing that the signal-

to-interference ratio (SIR) at the DTT receiver antenna is

higher than or equal to the PR. In terms of field strength,

SIR is given by (Ew - Ei), where Ei is the WSD interfer-

ence observed at the DTT receiver. Since Ew and Ei are

log-normal random variables, SIR is also log-normal dis-

tributed, with mean ðEwmed � EimedÞ ½dBlV=m� and stan-

dard deviationffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffir2

w þ r2i

p[dB]. Then, making use of the

normal distribution property, the condition for SIR being

higher than or equal to the PR for a percentage X of

locations in a pixel is represented as follows:

X ¼ Pr Ew � Ei�PRðDf Þf g

¼ QPRðDf Þ � ðEwmed � EimedÞffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

r2w þ r2

i

p !

:ð4Þ

Therefore, the limiting interference median field

strength for the protection of a percentage X of locations

within the pixel with respect to the appropriate protection

ratio PRðDf Þ; EPRimed max; is expressed as a function of the

wanted median field strength Ewmed and wanted and

interfering standard deviations rw and ri as follows:

EPRimed max ¼ Ewmed � PRðDf Þ þ lX

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffir2

w þ r2i

q; ð5Þ

where lX = Q-1(X), with Q�1ð�Þ denoting the inverse of

the Q-function. The term lX

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffir2

w þ r2i

pis the location

correction factor, that takes into account the statistical

variations of both the wanted and the interfering signals.

4.2 Limitation imposed by Oth

The overload of the DTT receiver happens when the

interference power at the front-end of the receiver, IFE,

overcomes a certain level called overloading threshold. IFE

relates to the interference power at the DTT receiver

antenna, I, as follows:

IFE ¼ I � POLþ Ga; ð6Þ

where POL and Ga represent antenna polarization

discrimination and antenna gain (including feeder loss).

Interference I and field strength Ei have the following

relationship for the frequency of operation fMHz given in MHz:

I ¼ Ei � 20 log10ðfMHzÞ � 77:2: ð7Þ

Then, from (6) and (7), IFE is represented as a log-

normal random variable with mean IFEmed = Eimed - 20

log10(fMHz) - 77.2 - POL ? Ga, and standard deviation

ri.

In order to avoid the overload of the DTT receiver, IFE

must be lower than or equal to Oth. Since IFE is log-normal

distributed, the condition for IFE being lower than or equal

to Oth for a percentage X of locations in a pixel is

X ¼ Pr IFE �Othf g ¼ Q �Oth � IFEmed

ri

� �: ð8Þ

The limiting interference median field strength for the

respect of Oth for a percentage X of locations within the

pixel, EOth

imed max; is thus expressed as follows:

61.21 66.21 71.21 76.21 81.21 86.21

−15

−10

−5

0

5

10

15

20

Ewmed

dBμV/mM

axim

um p

erm

itted

EIR

P [d

Bm

]

Limited by Δ LP = 0.1%Limited by I/N ≤ 3 dBLimited by O

th

Fig. 3 Maximum permitted

WSD EIRP according to

different protection criteria:

DLP ¼ 0:1 %; Oth and I/

N B -3 dB


123


EOth

imed max ¼ Oth þ lXri þ POL� Ga þ 20 log10ðfMHzÞþ 77:2;

ð9Þ

where lX = Q-1(X), as previously. In this case the location

correction factor is lXri and takes into account the statis-

tical variations of interference only, since the DTT receiver

overload does not depend on Ew. It is also important to

remark that EOth

imed max does not depend on the PR.

4.3 Overall upper limits for DLP and WSD EIRP

The protection of the DTT receiver against interference for

a percentage X of locations inside the pixel is guaranteed

by the simultaneous respect of PR and Oth. In other words,

the limiting interference field strength at the DTT receiver,

Eimed_max, is given by

Eimedmax¼ min EPR

imed max;EOth

imed max

� �; ð10Þ

with EPRimed max and EOth

imed max given in (5) and (9).

The WSD EIRP upper limit, EIRPmax, is calculated from

Eimed_max as follows:

EIRPmax ¼ Imax þ LOSSþ Aatt þ Adisc; ð11Þ

where Imax is the interference limit at the DTT receiver

which corresponds1 to Eimedmax; LOSS is the propagation

loss between the WSD transmitter and the DTT receiver,

Aatt is the WSD antenna attenuation, and Adisc is the DTT

antenna discrimination. Reference interference scenarios

involving the WSD transmitter and the DTT receiver are

considered, since the actual configuration is usually not

known [3].

The methodology proposed in [3] is used to obtain by

Monte Carlo simulations the curves of both the original LP,

without WSD interference and as a function of Ewmed, and

the resulting LP for different Ewmed levels as a function of

Eimed. The resulting LP of interest is the one obtained with

the limiting WSD interference Eimed_max. The difference

between the original and the resulting LP is considered the

DLP upper limit, i.e. DLPmax; for the protection of the DTT

receiver for a percentage X of locations in the pixel.

5 Strategies to calculate maximum WSD EIRP

Section 4 presented upper technical limits for the degra-

dation of DLP: However, different strategies may be

adopted by National Administrations in order to set the

location specific WSD EIRP. In this section, we present

three strategies to calculate the permitted interference field

strength and the maximum permitted WSD EIRP. Figure 4

shows a representation of each strategy proposed. For the

sake of comparison, we also present in the end of this

section the strategy adopted in the United States according

to FCC rules.

Strategy 1 proposes the division of the coverage area in

layers, defined by the value of the DTT median field

strength at its edges, as in Fig. 4a. This means that Ewmed is

inside the ith layer if Ewmedrefþ ði� 1ÞD�Ewmed

\Ewmedrefþ iD; in which D defines the range of the layer in

terms of minimum and maximum field strengths. Parameter

D may be determined by Administrations, based on the

accuracy of information present at the geo-location data-

base. For each WSD that queries the database for a chan-

nel, the database will match the location provided by this

device with the planned value of Ewmed for that location.

Then, the database maps this location in a layer and returns

to the WSD the available channels and the associated

maximum permitted EIRP for that layer. This strategy is

expected to increase the protection of DTT receivers

against errors at the geo-location database due to uncer-

tainties associated with the information about the DTT

planning, or lack of accuracy of location information given

by the WSD, since the level of wanted median field

strength taken for calculations, Ewmedlayer, is the one esti-

mated to the external edge of the layer, i.e. the lowest one

at that layer. Besides, the computational effort is propor-

tional to the number of layers defined by the database. This

strategy uses a fixed value of DLP in all layers and may be

summarized as follows:

1. WSD sends its location to the geo-location database.

2. The geo-location database maps the received location

in a value of planned Ewmed and the corresponding

layer, which leads to a Ewmedlayer.

3. Using the value of Ewmedlayerand DLP; the database

calculates the interference median field strength for the

layer according to Strategy 1, Est1imedlayer

; so that the

permitted DLP is satisfied.

Strategy 2, represented in Fig. 4(b), also divides the

coverage area in layers, as in Strategy 1, but proposes the

use of different values of DLP in each layer. The value of

DLP inside each layer must respect the maximum permitted

degradation that leads to Eimedmax, in Eq. (10). Albeit giving

more flexibility to the maximum WSD EIRP, this strategy

still guarantees further protection of DTT receivers, since

the division of the DTT coverage area in layers is still

present. Strategy 2 can be summarized in the following:



in a value of planned Ewmed and the corresponding

layer, which leads to a Eimedlayer .

1 Equation (7) translates field strength in [dBlV/m] into interference

in [dBm].


123


3. Using the value of Ewmedlayerand the maximum value of

DLP for the median field strength considered in that

layer, the database calculates the maximum Est2

imedlayerso

that permitted DLP is satisfied.

Strategy 3 is the most flexible strategy, as shown in

Fig. 4(c). Instead of spliting the coverage area in layers, as

in Strategies 1 and 2, this strategy uses the exact value of

planned Ewmed for the location provided by a WSD. For

each value of Ewmed this strategy uses the maximum per-

mitted DLP: This strategy is summarized as:



in a value of planned Ewmed.

3. The database matches the Ewmed with the maximum

permitted DLP and calculates Est3imed so that so that

permitted DLP is satisfied.

With the value of Estiimed calculated for each of the pre-

sented strategies, the database can calculate the maximum

permitted EIRP according to Eq. 11.

FCC’s strategy [1] consists in a fixed assignment of

WSD emission limits based on the device class. There are

two device classes specified:

– Fixed have geo-location capabilities, transmit to one or

more fixed or portable devices.

– Personal or portable devices: may operate in two

modes.

– Mode I in this mode, devices are not required to

incorporate geo-location or database access capabilities

and obtain the list of available channels on which they

can operate from either a fixed or Mode II device that

accesses a database.

– Mode II these devices must incorporate a geo-location

capability.

This strategy can be summarized as follows:

1. WSD receives a list of available channels on which it can

operate. If the device is a fixed device or a personal device

in mode II, it receives the list from the geo-location

database. If it is a personal mode I device, it receives the

list from either a fixed device or a mode II device.

2. Based on its type and location, the device choses an

appropriate emission level:

– Fixed device 36 dBm on vacant channels not

adjacent to occupied TV channels.

– Portable devices 16 dBm on the first channel

adjacent to occupied TV channels or 20 dBm on

vacant channels not adjacent to TV channels.

6 Simulation results and discussion

In this section, two sets of results are presented. In Sect.

6.1, some reasonable assumptions and parameters’ values

are considered for the calculation of Eimedmax and EIRPmax,

and the assessment of the resulting LP and DLPmax by

simulations, according to the content of Sect. 4. Based on

the upper limits Eimed_max and EIRPmax, Sect. 6.2 presents

examples of maximum emission limits based on the strat-

egies presented in Sect. 5.

Fig. 4 Representation of presented strategies. a Strategy 1: coverage area divided in layers with a single DLP level. b Strategy 2: coverage area

divided in layers with distinct DLP levels. c Strategy 3: Permitted DLP levels vary within the coverage area


123


6.1 Upper limits for DLP and WSD EIRP

Considering the absence of specific system characteristics

related to WSDs, the simulations presented in this section

adopts long term evolution (LTE) parameters to perform

compatibility studies, as in [3].

Two types of WSDs are considered: fixed (F) and por-

table (P). For each type of WSD, curves of

EIRPmax; DLPmax and resulting LP are presented for three

DTT reception modes: FO at 10 m above ground level

(agl.), PO, and PI reception at 1.5 m agl. The reference

interference scenarios for the calculation of EIRPmax are

summarized in Table 1. We consider WSD operation on

the 1st adjacent channel to an operating DTT channel, for

which a reasonable value of PR is –30 dB for any reception

mode. Stringent values of Oth [5] are also considered.

For the three DTT reception modes, LP at the coverage

edge is 95 % and increases with Ewmed. Table 2 gives for

each reception mode the reference (minimum) wanted DTT

median field strength, Ewmed ref and the standard deviation

of wanted and interference signals, rw and ri. Ewmed ref at

10 m agl. is 17 dB (free space loss) higher for portable

reception due to height difference. When applicable, wall

effects over the signals are also considered: additional 8 dB

loss and 5.5 dB standard deviation.

The curves in Fig. 5 are obtained for quasi perfect DTT

receiver operation with respect to interference, i.e. pro-

tection of the DTT receiver for 99.9 % of locations

(X = 0.999 in Sect. 4). As a general behavior, EIRPmax

increases with Ewmed from the DTT coverage edge to areas

with better DTT coverage. EIRPmax is first limited by the

PR, since with low or moderate Ewmed, the relevant WSD

interference constraint is the prescribed SIR at the DTT

receiver. With the increase of Ewmed, the interference at the

DTT can approach the Oth and from this point EIRPmax is

constrained to a fixed value. The decaying behavior of

LPmax curves is explained by the impact of the permitted

WSD interference on the original LP. For low LP, even low

WSD interference may cause high LP degradation, while

high LP (high Ewmed) is less susceptible to degradation due

to WSD interference.

For FO DTT reception, EIRPmax varies from about

-12.6 dBm at the coverage edge to 24.75 dBm (limited by

Oth) at locations where Ewmed C 96.21 dBlV/m. The cor-

responding DLPmax decays from 0.91 % to about 0.1 %

(DLP is almost negligible for Ewmed C 126.21 dBlV/m),

where DTT coverage is immune to the 24.75 dBm inter-

ference due to the high Ewmed level. The curve of DTT LP

which results from WSD interference indicates that already

in locations where Ewmed is only 5 dB above Ewmed ref ; the

resulting LP is around 99 %.

If the protection of PO DTT reception is considered,

DLPmax and resulting LP for fixed WSD transmission have

values similar with those protecting FO DTT reception, but

for a different coverage area (Ewmed [ 78.21 dBlV/m at 10

m agl.). As expected, in this case EIRPmax is more

restrictive. The protection of PI DTT reception also

imposes new restrictions in its coverage area: EIRPmax is

about 1.57 dBm at the coverage edge (87.95 dBlV/m at 10

m agl.) and increases until the limit protecting FO DTT,

24.75 dBm, reception for Ewmed � 111 dBlV/m. The cor-

responding DLPmax for PI DTT reception decreases from

0.25 to 0.1 % with the increase of Ewmed.

Fig. 6 shows the corresponding curves for portable WSD

transmission. To protect FO DTT reception, EIRPmax is

limited to -12.7 dBm at the coverage edge and increases

with Ewmed until 14.75 dBm for Ewmed � 86:21 dBlV=m:

DLPmax varies from 0.91 to 0.1 % when entering the DTT

coverage area (almost negligible for Ewmed C 126.21 dBlV/m).

Once more, the resulting LP is at least 99 % for locations

where Ewmed is 5 dB or more above Ewmed ref : If protection of

portable DTT reception is considered, EIRPmax is reduced to

at most -5 dBm in this coverage area.

Similar curves can be traced for other adjacent channels,

where PR and Oth values vary [5]. In general, the curves indicate

Table 1 Reference interference scenarios

Scenario descriptiona,b,c LOSS

(dB)

Aatt

(dB)

Adisc

(dB)

POL

(dB)

Oth

(dBm)WSD DTT d (m)

F FO 20 54.72 0 0 3 -13

F PO 20 55.45 10 0 0 -26

F PI 20 55.45 10 0 0 -26

P FO 20 54.72 0 0 0 -20

P PO 2 34.72 0 0 0 -27

P PI 2 34.72 0 0 0 -27

a Height of fixed WSD is 10 m agl.; height of portable WSD is the

same as the DTT receiver in each scenariob LOSS is calculated with the free space path loss model. Calculations

consider fMHz = 650 MHzc DTT receiver antenna gains are Ga = 9.15 dBi for fixed and

Ga = 2.15 dBi for portable reception

Table 2 DTT coverage requirements and signal parameters setting

DTT reception mode

FO PO PI

Ewmed ref ½dBlV=m� 56.21 61.21a 62.95b

rw [dB] 5.5 5.5 7.78

ri [dB] 3.5 3.5 3.5c

a 78.21 at 10 m aglb 87.95 at 10 m aglc 6.52 for outdoor WSD


123


that the accommodation of a TVWS system with reasonable

transmission powers and acceptable resulting DTT LP may be

possible in significant part of the DTT coverage area.

It is interesting to compare the EIRP limits obtained in

this work, using the proposed strategies, parameters and the

methodology adopted by CEPT, with the ones obtained

under FCC rules (summarized in Sect. 5), noting that there

are differences between WSD out-of-band emission levels

considered in each case [1, 3]. For example, in Fig. 5 it is

shown that fixed devices are able to operate in the first

adjacent channel with EIRP values up to 25 dBm. With

FCC’s strategy, these transmissions would not be allowed

at all, since operation of fixed devices in channels adjacent

to occupied TV channels is not permitted. On the other

hand, portable devices operating in the first adjacent

channel under FCC rules are able to transmit with an EIRP

of 16 dBm, whereas the limits shown in Fig. 6 restrict

portable devices to transmit with up to 15 dBm.

6.2 Maximum EIRP limits according to the proposed

strategies

Based on upper limits of DLP presented on Sect. 6.1 and

the strategies described in Sect. 5, we now present

examples of maximum emission limits based on reference

scenarios. In this paper, we present results for two of the

most restrictive scenarios: fixed WSD transmitter—fixed

DTT receiver and portable WSD transmitter—PO DTT

receiver, whose parameters and protection criteria for 1st

adjacent channel operation are defined in Table 1. In a real

situation, this information is loaded by the geo-location

database every time a device queries for a transmission

opportunity, based on the WSD type provided to the

database. The purpose of using reference geometries at the

geo-location database is to overcome the lack of spatial

information about DTT receivers. Therefore, those geom-

etries represent, in general, worst case situations between

DTT receivers and WSDs, either for the small distance or

alignment of antennas.

Strategy 1 divides the coverage area in layers and con-

siders the same DLP in all of them. Then, the single DLP

level must be lower than the upper limit calculated for each

location within the coverage area (Sect. 6.1). Considering

the protection of 99.99 % of locations, it is adopted DLP ¼0:1 % for both fixed and portable WSD transmission. In

this example, the layers are selected with D ¼ 5 dB:

Depending on the quality of information available at the

database, D can be increased or decreased.

55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130−15−10

−505

1015202530

Ewmed

[dBμV/m] at 10m agl.

Fix

ed W

SD

EIR

Pm

ax [d

Bm

]

55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 1300

0.2%

0.4%

0.6%

0.8%

1%

Ewmed


ΔLP

55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 13094%

95%

96%

97%

98%

99%

100%

Ewmed


Res

ultin

g LP

Protection of fixed outdoor DTT reception

Protection of portable outdoor DTT reception

Protection of portable indoor DTT reception

61.21 dBμV/mat 1.5m outdoor

62.95 dBμV/mat 1.5m indoor

Fig. 5 Fixed WSD

transmission: EIRPmax ð1st adj.

channel), DLPmax and the

resulting LP for the protection

of the DTT receiver from

interference for 99.9 % of

locations


123


From Fig. 7, Strategy 1 may be considered conservative

since the maximum permitted EIRP is far from the upper

limit EIRPmax, especially at the edge of the coverage area.

Additional protection is provided for DTT receivers in this

area, where the DLPmax is higher than the adopted

DLP ¼ 0:1 %.

In opposition to Strategy 1, Strategy 2 considers dif-

ferent values of DLP in each layer. Any value of DLP

below the upper limit DLPmax can be used in this strategy.

Figure 8 shows the case where the adopted DLP levels for

the different layers are equal to the upper limits shown in

Figs. 5 and 6. Increasing the number of layers in this

strategy, the maximum WSD EIRP becomes closer to the

upper limits. Albeit being less conservative than Strategy 1,

Strategy 2 continues providing protection of DTT receiv-

ers, since the value of Ewmed considered in each layer is the

one expected at the edge of the layer, i.e. it is the lowest

inside that layer.

Since Strategy 3 does not divide the coverage area in

layers, neither fixes the value of DLP; it can reach the EIRP

upper limits, if the values of DLP are chosen accordingly.

In Fig. 9, three examples of maximum permitted EIRP

curves are shown according to the percentage of locations

protected. This strategy is more susceptible to errors in the

geo-location database if there is lack of accuracy of the

location information provided by WSDs.

55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130−35−30−25−20−15−10

−505

1015

Ewmed

[dBμV/m] at 10m agl.Por

tabl

e W

SD

EIR

Pm

ax [d

Bm

]

55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 1300

0.2%

0.4%

0.6%

0.8%

1%

Ewmed


ΔLP

55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 13094%

95%

96%

97%

98%

99%

100%

Ewmed


Res

ultin

g LP

Protection of fixed outdoor DTT reception

Protection of portable outdoor DTT reception

Protection of portable indoor DTT reception

61.21 dBμV/mat 1.5m outdoor

62.95 dBμV/mat 1.5m indoor

Fig. 6 Portable WSD

transmission: EIRPmax ð1st adj.

channel), DLPmax and the

resulting LP for the protection

of the DTT receiver from

interference for 99.9 % of

locations

60 70 80 90 100 110 120 130−40

−30

−20

−10

0

10

20

30

Ewmed

dBμV/m

Max

imum

per

mitt

ed E

IRP

[dB

m]

Protection of fixed outdoor DTT receptionStrategy 1 limit for fixed WSDProtection of portable outdoor DTT receptionStrategy 1 limit for portable WSD


EIRP given by Strategy 1


123


There is a trade-off in the selection of the strategy to be

adopted by the geo-location database, specially due to

some sources of uncertainties that can impact on the cal-

culation of upper limits of WSD EIRP. Two parameters are

important to aid the selection of the strategy: accuracy of

the DTT planning information stored at the database and

accuracy of the location information provided by WSDs.

For example, if the information about DTT planning is

incorrect, there is a possibility of miscalculation of the

value of location probability in a given pixel. If this value

is higher than what is observed in practice, the geo-location

database may calculate a higher upper limit of WSD EIRP,

resulting in an incresed probability of interference in the

DTT receivers. Higher upper limits of WSD EIRP can also

be calculated if the location informed by the WSD is wrong

and is mapped into a pixel with higher location probability.

In practice, information about DTT planning and values

of location probability are expected to be known for every

pixel within the country. The size of a pixel is typically

100 m � 100 m: In order to avoid errors due to inacurracy

of the location sent by the WSD, CEPT methodology

already included location accuracy as a minimum

requirement of information to be communicated to the geo-

location database. Therefore, both parameters could be

considered in selecting the appropriate strategy: size of a

pixel and the accuracy of the geo-location technique used

by the WSD. For instance, the global positioning system

provides a worst case pseudorange accuracy of 7.8 m at

95 % confidence level [10], distance that is still within a

pixel area. So, if this technique is used by the WSD, the

database could chose the less conservative strategy, i.e.

Strategy 3. On the other hand, if the WSD uses a less

accurate technique, the database could choose a more

conservative strategy, such as Strategies 1 and 2.

7 Conclusions

In the definition of WSD emission limits, there is a trade-

off between the maximum permitted WSD EIRP and the

protection of DTT receivers. In Europe, although the

methodology to calculate the maximum power is defined in

ECC Report 159, the database implementation and the

upper emission limits are still open issues. This paper

presents viable solutions for database implementation of

the CEPT methodology, respecting upper limits and ref-

erence geometries. Three strategies are proposed in this

work, ranging from a conservative and less complex

approach to a more flexible one, closer to the upper limits.

All presented strategies ensure the required protection and,

60 70 80 90 100 110 120 130−40

−30

−20

−10

0

10

20

30

Ewmed

dBμV/mM

axim

um p

erm

itted

EIR

P [d

Bm

]

Protection of fixed outdoor DTT receptionStrategy 2 limit for fixed WSDProtection of portable outdoor DTT receptionStrategy 2 limit for portable WSD



60 70 80 90 100 110 120 130−40

−30

−20

−10

0

10

20

30

Ewmed

dBμV/m

Max

imum

per

mitt

ed E

IRP

[dB

m]

Fixed WSD, X = 99.90% of locationsFixed WSD, X = 99.95% of locationsFixed WSD, X = 99.98% of locationsPortable WSD, X = 99.90% of locationsPortable WSD, X = 99.95% of locationsPortable WSD, X = 99.98% of locations




123


due to their simplicity, can be implemented in geo-location

databases without increasing significantly the implemen-

tation costs and maintenance.

References

1. Federal Communication Commission. (2008). Second report and

order and memorandum opinion and order, in the matter of

unlicensed operation in the tv broadcast bands additional spec-

trum for unlicensed devices below 900 MHz and in the 3 GHz

band (ET docket 08-260).

2. Spectrum Bridge: Show my white space. (2012). http://whitespaces.

spectrumbridge.com/whitespaces/home.aspx.

3. ECC Report 159. (2011) Technical and operational requirements

for the possible operation of cognitive radio systems in the white

spaces of the frequency band 470–790 MHz (2011). ECC within

CEPT.

4. ECC Report 186. (2013). Technical and operational requirements for

the operation of white space devices under geo-location approach.

http://www.erodocdb.dk/doks/doccategoryecc.aspx?doccatid=4.

5. Recommendation ITU-R BT.1368-8 (2008). Planning criteria for

digital terrestrial television services in the VHF/UHF bands.

6. Draft ECC Report 148. (2010). Measurements on the perfor-

mance of DVB-T receivers in the presence of interference from

the mobile service (especially from LTE). ECC within CEPT.

7. ECC Report 49. (2004). Technical criteria of digital video

broadcasting terrestrial (DVB-T) and terrestrial—digital audio

broadcasting (T-DAB) allotment planning. ECC within CEPT.

8. Recommendation ITU-R BT.1895. (2011). Protection criteria for

terrestrial broadcasting systems.

9. Almeida, E., de S Chaves, F., & Vieira, R. (2012). On the pro-

tection criteria for the operation of white space systems on tv

bands. In 2012 IEEE Wireless Communications and Networking

Conference (WCNC) (pp. 2258–2263). doi:10.1109/WCNC.2012.

6214169.

10. Department of Defense United States of America. (2008). Global

positioning system standard positioning service performance standard.

http://www.gps.gov/technical/ps/2008-SPS-performance-standard.pdf.

Erika P. L. Almeida received

her Telecom Engineer and

M.Sc. degrees from the Uni-

versity of Brasılia (UnB), Bra-

zil, in 2007 and 2010

respectively. She is a researcher

at Nokia Institute of Technol-

ogy, INdT, since 2011, where

she has worked with LTE, white

space concepts and coexistence

issues in TV white spaces.

Current research topics include

Wi-Fi evolution and cognitive

radio networks.

Fabiano S. Chaves received the

B.Sc. degree in electrical engi-

neering and the M.Sc. degree

in teleinformatics engineering

from the Federal University of

Ceara, Brazil, in 2003 and 2005,

and the Ph.D. degree in electri-

cal engineering from the Uni-

versity of Campinas, Brazil, and

the Ecole Normale Superieure

de Cachan, France, in 2010. In

2000, he attended the Universi-

tat Stuttgart, Germany, as part

of a 1-year CAPES/DAAD

Sandwich Graduation Program.

Since 2010 he has been Research Engineer at the Nokia Institute of

Technology, Brazil. His research interests include topics in radio

resource management and signal processing, the application of

automatic control and game theory to communication problems, and

cognitive radio systems.

Robson D. Vieira received

M.Sc. and Ph.D. degrees in

electrical engineering from the

Catholic University of Rio de

Janeiro, Brazil, in 2001 and

2005, respectively. During 2005

to 2010, he was working with

white space concepts, and sup-

porting some GERAN and

802.16 m standardization activ-

ities focused on system perfor-

mance evaluation at INdT.

Since 2010, he is an R&D

technical manager at INdT. His

research interests include Wi-Fi

Evolution, B4G, and cognitive radio networks.

Renato F. Iida received his

Telecom Engineer and M.Sc.

degrees from the University of

Brasılia (UnB), Brazil, in 2002

and 2006, respectively. He is a

researcher at INdT, Brazil, since

2008. He worked in GSM/

EDGE research and radio

resource management using the

OSC technology, TCP/IP net-

working and Location based

services. Current research topic

is development of drivers and

applications for Windows phone

7 and 8.


123


http://whitespaces.spectrumbridge.com/whitespaces/home.aspx

http://whitespaces.spectrumbridge.com/whitespaces/home.aspx

http://www.erodocdb.dk/doks/doccategoryecc.aspx?doccatid=4

http://dx.doi.org/10.1109/WCNC.2012.6214169

http://dx.doi.org/10.1109/WCNC.2012.6214169

http://www.gps.gov/technical/ps/2008-SPS-performance-standard.pdf






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Power limits for secondary devices operating on TV white spaces