Journal of Global Positioning Systems (2007)
Vol.6, No.2:98-107
Interfer ence and Regulatory Aspects of GNSS Pseudolites
S. Martin, H. Kuhlen, and T. Abt
EADS Astrium GmbH, Germany.
Abstract. Galileo, the European Satellite Navigation
System, is currently under development. Even before first
satellites of the co nstellation are launched, Galileo signals
will be provided throug h ground based Navigation Signal
Generators for the investigation of signal performance
and characteristics. These low power devices, called
Pseudolites (Pseudo-Satellites), will transmit signals
equivalent to those which are transmitted by the in-orbit
satellites. However, from the regulatory point of view
they are not providing Radionavigation Satellite Service
(RNSS) as defined in International Tele communication
Union (ITU) Radio Regulations but "something else".
This has to be investigated, because it is expected that
Pseudolites (PLs) will, beyond their roles to evaluate
signal performances in the early phase of the program,
significantly extend the navigation service availability
into areas where the critical RF propagation of direct line
of sight to satellites is blocked. Sound experience over
many years has already been gained worldwide through
the research with GPS Pseudolites. Galileo will introduce
sophisticated and ambitiou s new signal schemes initiatin g
new designs for innovative Pseudolite solutions. Old and
new signals will coexist for many years to come.
Currently there are various projects ongoing to develop
Pseudolites for Galileo. A practicable regulatory
framework, taking specific operational conditions of
Pseudolites into account, has to be developed by the
regulatory author ities to encourage the impl ementation of
Pseudolite-networks on one side. Bu t, at the same time, it
is important to set strict rules for the implementation to
avoid harmful interferences created by Pseudolites to
RNSS and other radio receivers operated in the vicinity of
a Pseudolite-network. The creation of a clear regulatory
framework has eventually to provide the planning
security for Pseudolite-network operators and RNSS-
provider considering service guarantees. Pseudolites, as
well as other means to achieve a nearly seamless service
availability have b een an essential element of the Galileo
system architecture from its early system studies. In the
Galileo architecture, PLs are defined as a sub-group of
the so-called Local Elements. Technically speaking,
Pseudolites are low power transmitters that either
transmit or repeat (Synchrolites) RNSS-equivalent
signals on the same frequency bands allocated to RNSS
as defined in the ITU-R Radio Regulations. The creation
of a regulatory framework for the operation of
Pseudolites, which is yet undefined, has recently received
a growing attention in the spectrum engineering working
groups and frequency management groups of the
European Conference of Postal and Telecommunications
Administrations (CEPT). So far, PLs are operated under
experimental license only. In order to prepare inputs to
this process, the performance requirements in typical
application scenarios have been investigated. This paper
presents initial considerations and preliminary results of
investigations performed on the interference properties of
general GNSS Pseudolites. It proposes a concept for
typical scenarios that can serve as generic Pseudolite
network architectures to be considered in the on-going
process to determine a regulatory framework for future
operational networks.
Keywords: GPS, Galileo, GNSS, Pseudolites,
Interference.
1 Introduction
Over the past two decades, Pseudolites have been
developed and investigated for a wide variety of
applications. At the b eginning they were u sed to test GPS
signals and the GPS user equipments when no in-orbit
satellites were available. Then their usage has evolved to
augmentation of GPS and even for pseudolite-only indoor
navigation systems (Wang, 2002).
Currently there are GPS pseudolites available which can
broadcast L1- or L2-signals. From the regulatory point of
view all tests and investigations have been performed
with special temporary experimental licenses.
Interference issues were investigated when particularly
necessary but in general licensing process has been
defined so far to authorize the operational use of GPS
Pseudolites. This is because a Pseudolite that is not
consciously adjusted and carefully maintained can very

Martin et al.: Interference and Regulatory Aspects of GNSS Pseudolites 99
quickly turn into a jammer interferer), inhibiting any
navigation service in a large area around the beacon.
In the course of development of the Galileo satellite
navigation systems, Pseudolites were defined as part of
the Galileo architecture namely as "Local Elements". The
future operator of Galileo system (Concessionaire)
considers offering service guarantees. Thus it is of
growing importance to investigate the frame conditions
for controlled implementation and operation of GNSS
Pseudolites.
The approach presented here proposes the following
steps:
• Definition of generic Pseudolite application
scenarios for all RNSS systems to provide the
technical backgro und an d basis for regulatio n;
• Definition of corresponding architecture
parameters and specifications describing these
scenarios;
• Investigations of their regulatory constraints and
possible categories for regulations (service
definition):
o Develop methodologies to investigate
interference scenarios of Pseudolites
with RNSS;
o Dito develop methodologies to analyse
their interference scenario with other
services;
• Consideration by the relevant regulatory working
groups at regional and international level (ITU-R);
• Invite Administrations to consider new allocations
for Pseudolites.
The objective of the entire efforts should be to define a
well balanced process that encourages on one side the
implementation of Pseudolites keeping on the other side
the operators of RNSS networks and national
administrations in the loop. The cost and complexity of
administrative efforts are also to be kept in mind.
2 Scenario Definitions
In order to assess the various environments where
pseudolites can be used, a classification has to be made.
Over the past twenty years, numerous scenarios for
pseudolites have been described in literature as
• Aeronautical applications
• Indoor applications
• Urban and Local GNSS augmentation
• Harbor entrance and docking
• Open pit mining
• …
Each scenario has its specific environmental and
propagation conditions which require a thorough
treatment of the use of pseudolites.
For the subsequent investigations, two basic scenarios are
proposed, which are considered representative for a wide
range of applications:
Scenario 1: "areas where RNSS satellite signals are
partially available", such as in urban
canyons, but also in aeronautical
applications
Scenario 2: "Indoor", where signals from RNSS satellites
are blocked.
The above classification is important in view of the
definition of regulatory constraints and interference
issues between Pseudolites and Radio Navigation
Satellite Services (RNSS) and Pseudolites and other
services as explained later on.
The main system parameters defining a Pseudolite
network are:
• Carrier frequencies
• Effective Isotropic Radiated Power (EIRP)
• Antenna characteristics
• Pulse shaping
• Applied duty cycle
• Number of Pseudolite transmitters
• Locations
The scenari os a r e d e f i ned as follows :
Scenario 1 - U rb a n and Local Scenario
The purpose of using pseudolites in an urban or local
environment is augmentation of GNSS by extending its
service availability into the areas where satellite signals
are not available with a sufficient RF power level for
reliable tracking.
In addition the impaired geometrical distribution of the
visible satellites leads to a degraded positioning
performance.
In terms of propagation characteristics it is difficult to
define a generic urban or local scenario because
multipath effects, shadowing and reflections vary
significantly in the different environments such as narrow
streets with multi-storey buildings or wide open places
with surrounding buildings. Also the service areas that
are targeted for navigation service augmentation (e.g. to
provide location based services) vary with highly specific
scenarios ranging from a few hundreds square meters to a
few tens of square kilometers. With regard to the
regulatory frame conditions, aeronautical applications
with pseudolites are also part of this category. It is also

100 Journal of Global Positioning Systems
important if a Pseudolite network is dedicated for
permanent or short-term operations, e.g. during an event
with mass attractions (sports, commerce, fairs, and
others).
The most critical case so far is the implementation of a
mobile Pseudolite network, particularly in densely
populated areas.
Fig. 1 Different urban and local en vi ronments
Altmayer (1998) has investigated the impact of a dual
pseudolite system in a medium sized street environment.
The tests were conducted with a continuous-wave
pseudolite, i.e. without pulsing. For the positioning tests,
the experiments with various antenna diagrams were
performed to achieve a balanced power flux density over
the entire service area. It turned out that shaping the
antenna diagram can reduce the degrading impacts of the
near-far or hot spot problem. Significant improvements
mitigating multipath impacts in various environments
through the use of optimised antenna diagrams has been
investigated by several studies (Kee et al., 2000; Martin,
1999).
Thus special attention must be paid to the proper radio
frequency planning in the urban scenarios to avoid
performance degradations or loss of services caused by
the near far problem and the impact of multipath
propagations.
A very critical area is the transition zone from outdoor to
indoor as shown in Fig. 2 because the navigation
performance is affected by the potential interference from
Pseudolites and direct satellite signals. The figure gives a
typical scenario where the user is approaching a building
via an open square with perfect satellite coverage
followed by a canopy with degraded satellite visibility
and then entering the building with almost no satellites
available. The goal for pseudolite usage under these
conditions is to provide uninterrupted signal sources for
position calculation.
Fig. 2 Typical transition area from in-door to outdoor positioning
A typical Urban and Local scenario can be characterized
by:
Carrier frequencies
In the past Pseudolites were mostly developed to
complement with the GPS L1-signal. Only a few dual
frequency pseudolites have been developed. It can be
assumed that future Pseudolites will b e applied to operate
in all the allocated RNSS frequency bands. In particular
Pseudolites that support the Galileo signals will become
available to improve the service availabilities in all the
three main user communities targeted by the system.
Exact carrier frequencies correspond to the carrier
frequencies transmitted by the satellites. The Galileo
carrier frequencies for each band are provided in Fig. 10.
Transmitter power
The effectively transmitted RF power is defined at the
antenna input. In the case of a pulsed transmitter, the RF
power is reduced by an adjustable duty cycle. The
optimum duty cycle has to be determined by careful
adjustments. The finally transmitter average RF power of
a pulsed GNSS pseudolite is red uced by
PDCPloss log20
=
(1)
where PDC is the pulsed duty cycle. The impact of a duty
cycle on the overall performance has been investigated in
(Stansell, 1986; SC-159 RTCA, 2000)
Focusing on Galileo in particular it is assumed that the
received signal at the maximum distance from the
Pseudolite has to be in the same order as the receive
power contribution of a single Galileo satellite, i.e. -128
dBm. Then the received peak power at the user's antenna
at maximum distance is
][log20128
max_,, dBmPDCP distrecPSL
−
−
=
(2)
Open place
Narrow street

Martin et al.: Interference and Regulatory Aspects of GNSS Pseudolites 101
The maximum transmit power of a pseudolite can be
calculated with
⎥
⎦
⎤
⎢
⎣
⎡
⋅
−= dist PEIRP distrecPSLPSL
π
λ
4
log20
max_,, (3)
with λ = 0.19m e.g. for the Galileo L1-signal.
Fig. 3 depicts the required transmitter power for up to a
maximum distance of 500m with a duty cycle of 2%.
050100 150 200 250 300 350 400 450500
-60
-50
-40
-30
-20
-10
0
Pseudoli te E IRP [dBm]
Dis t anc e [ m ]
Fig. 3 Pseudolite EIRP for an urban scenario
Pulse patterns and duty cycles
Most of the pseudolites that have been used for indoor
applications so far are operated with duty cycles. In this
case Pseudolites contribute to the navigation solution in
the receiver only for a fraction of the period while the rest
of the period is left for satellite reception if available.
Different pulsing schemes and pulse duty cycles were
used. There are currently two pulsing schemes
recommended by the maritime and the aeronautical
standards RTCM (Stansell, 1986) and RTCA (SC-159
RTCA, 2000), respectively.
In general the pulse duty cycles vary from (1/11) 2% to
20% (Kee et al., 2000).
Antennas
Basically there are two antenna types which can be used
to transmit Pseudolite signals: Patch antennas and helical
antennas. Both can provide right-hand circular
polarization using the same polarisation as the satellite
transmissions. The main differentiator between both is
the gain and pattern. Patch antennas have a hemispherical
shaped antenna diagram with an almost uniform gain
whereas helical antennas have a directional diagram and
higher gain.
Considerations for optimising Pseudo lite antennas can be
found in (Kee et al., 2000) and (Martin, 1999).
Number of Pseudolites
The number of Pseudolites actually implemen ted at a site
depends on the purpose to be achieved and the overall
propagation characteristic of the desired service area.
Pseudolites in Scenario 1 are assumed to augment the
associated GNSS system. In this case, it is not necessary
to ensure visibility of at least four Pseudolites for a full
positioning capability. The number of implemented
equipments should be driven to avoid hot spots. In other
words, a distributed network of low power devices would
be better than the implementation of a few high power
transmitters.
Aeronautical Environment (special case of scenario 1
Applications of Pseudolites in the aeronautical
environment can be seen as a special case of pseudolite
usage. The operations area extends wider than in an urban
scenario and several parameters which influence the
regulatory treatment differ from an urban usage.
In an aeronautical environment pseudolites are used for
precision approach and landing purposes (CAT II/III).
Until a short time ago they have been part of the LAAS
concept (RTCA DO246/C, 2005). Pseudolites have been
removed from the latest version of the RTCA DO246/C
because of missing regulations w.r.t. the airborne
receivers and the unsolved concerns about jamming
caused by pseudolites.
The main benefit of using pseudolites is an increased
availability for precision approaches. For robust
navigation performance, GPS Wideband signals have
been chosen. Pulsing of the signals was foreseen.
Investigations have been done e.g. by several researchers
(e.g., van Dierendonck et al., 1997; Lee et al., 2004;
Bartone, 19 9 9).
Coverage Area
When pseudolites are used for precision approach,
landing and rollout on runway, a horizontal coverage area
of 100m to 20NM (37km) is necessary. Most of the
airport approaches are conducted with a glide path angle
of 3°. Therefore the vertical coverage is set to 5°, taking
into account a safety margin for signal acquisition and
steep approaches.
3°5°
20N
M
Touchdown point
Fig. 4 Airport pseudolite coverage for precision approach
Besides a wide area coverage pseudolite reception while
on the runway and during taxi is necessary. Thus the
antenna pattern has to be shaped to fulfill this
requirement.

102 Journal of Global Positioning Systems
Antenna characteristic of widely used dB Systems Inc.
Multipath Limiting Antenna (MLA) dBs 200A.
Fig. 5 Vertical antenna diagr am of dBs 200A MLA (RIPA-2)
Fig. 6 Top view of antenna pat t ern (RIPA-2)
Transmitter power
The same formula used in the previous section can be
applied. A typical scenario for aviation comprises an
airport and its associated airspace and corridors for
approach and landing. To improve the navigation
conditions Pseudolite signals should have coverage up to
20NM. At the periphery of the services area the received
signal level must be in the order of the regular GPS
wideband sig n al s , i.e. ab out - 13 3 dBm.
The Pseudolite signal is pulsed with a 2% duty cycle.
That leads to a peak EIRPAPL of 38.75 dBm (7.5 watts)
and an average EIRP of 21.75 dBm (150 mW) (van
Dierendonck et al., 1997).
If the computation is performed with Galileo L1
minimum receiver power of -128 dBm this gives Fig. 7.
00.5 11.5 22.5 33.5 4
x 10
4
-60
-50
-40
-30
-20
-10
0
10
20
30
40
Ps eudol ite E I RP [ dB m]
Dis t anc e [ m ]
Fig. 7 Peak EIRP for aeronautical PSL usage
Siting
The location of Pseudolites, particularly in the radio
environment of an airport requires careful interference
analysis and site planning to ensure a good cooperative
performance of the space and round component. Bartone
et al. (2002) showed that placing a pseudolite with a
lateral and advanced offset to the runway gives best
results in terms of coverage and the received power.
Fig. 8 Pseudolite location for landing application
Scenario 2 - I nd oor scenari o
Several studies have been conducted to investigate indoor
positioning with GPS pseudolites (Kee et al., 2000;
Barnes et al., 2004).
A typical scenario comprises four or more Pseudolites in
a room or hall where they are used to determine the
position and track one or more mobile receivers. Usually
these systems operate in a stand alone mode without
additional GNSS satellite signals. These systems can be
synchronized or asynchronous.
The main differentiator to the urban and local scenario
with respect to regulatory issues is that the indoor
Pseudolite systems are assumed not to interfere with

Martin et al.: Interference and Regulatory Aspects of GNSS Pseudolites 103
outdoor GNSS systems. Thus from the regulatory point
of view they could be treated differently from the outdoor
pseudolite systems. The main criterion in this respect
would be that the aggregate power flux density created by
the internal Pseudolites outside the building is
"insignificant", and thus, does not create harmful
interference to the receivers used in the neighbourhood of
the building.
Admittedly, the protection threshold for "insignificance"
remains yet to be determined. Its determinatio n must take
typical receiver performance parameters into account that
the receivers will have in the different market segments,
ranging from consumer products to high-end equipment
for geodesy, safety of life or governmental usages.
Typical parameters for which appropriate values are to be
determined to precisely describe the conditions for an
indoor s cenario are:
Carrier frequencies
Again it is assumed that all the GNSS frequency bands
will be used in order to cover all the existing and
upcoming GNSS services. This also includes GPS L5,
Galileo PRS and Galileo CS.
Transmitter power (EIRP)
The transmitter power was chosen to cover the specific
area and taking into account the pulsing scheme. Usually
power levels are computed according to the scheme given
in the following section. Unfortunately most of the more
complex calculation methods are only valid for distances
above 200m (e.g. models of Okumura, Hata or Walfisch-
Ikegami).
A rough assumption gives an EIRP of -60dBm to -
30dBm for a pulsed signal with 2% duty cycle and a
coverage di stance of up to 40m.
Pulse patterns and duty cycles
In general the same parameters as given in Scenario 1
hold also for this scenario.
Antennas
Most researchers had used helical antennas in the past to
overcome extensive indoor multipath problems. In
contrast to the patch antennas, helical antennas can be
easily shaped to have a more directional diagram and thus
avoid multipath due to lateral reflectors. In a typical
indoor scenario, pseudolite antennas are mounted under
the ceiling or around the corners of a room. These are
quite unfavorable places concerning signal propagation
and reflections. Patch antennas radiate in a hemispherical
diagram thus emitting into nearby reflectors like walls or
ceiling creating multipath. A custom made helical
antenna with a well shaped beam pattern reduces these
influences and prevents multipath.
Number of Transmitters
Depending on the area size and the operating area at least
4 pseudolites have to be installed. Usually in order to
overcome signal blockage more than 4 (up to 6 or 7) are
used for a certain area.
Summary of scenario characteristics
The following table summarizes the above mentioned
parameters for both scenarios.
Table 1: Summary of both scena rios
Local/Urban Indoor
Carrier freq. GPS + Galileo GPS + Galileo
EIRP up to +39dBm -60dBm to - 30dBm
Pulse duty
cycle variable 1/11, 2%-20% variable 1/11, 2%-20%
Antenna omni directional directional
# of
Pseudolites < 4 4 or more
Both scenarios probably could be dealt with by
considering different regulatory constraints. While the
outdoor situation would have to consider a more specific
case by case analysis on the power flux density
distribution created by (pulsed) Pseudolites, respectively,
while the indoor case might be regulated with a
simplified procedure. Standardised low power devices
(type approved) could be used as long as their sole indoor
applicatio n s would be legally enfo rced.
3 Interference issues
Since the very first use of Pseudolites the users have to
deal with an effect caused by the CDMA (wideband)
nature of the GNSS signals. Spread spectrum signals like
GPS and Galileo signals are vulnerable to interference
caused by spread spectrum in-band transmissions (or
intentional jamming in a hostile scenario) due to the
limited signal dynamic range of the correlation properties
(receiver RF front-end and correlators). This effect,
where the receive power level varies significantly with
the distance to a Pseudolite, is also known as "Near-Far"
problem, while satellite signals show an almost constant
power level due to their "nearly equal" distance to a
receiver. Most of the navigation receivers are designed
for maximum sensitivity but not for large dynamic
ranges. This holds for participating receivers (Pseudolites
receivers) as well as for non-participating receivers since
it is of great importance to ensure that the same receivers
can be used - outside and inside the areas augmented by
Pseudolites.
Many ideas have been studied to mitigate th e interference
problems caused by pseudolites, which include, such as
carrier frequency offset (Parkinson et al., 1996), use of
better adapted spreading codes (Ndili, 1994), pulsing of

104 Journal of Global Positioning Systems
the Pseudolites sign al (Cobb, 1997) and pu lse blanking of
a participating receiver. Although many of these ideas
provide a good potential for successful interference
mitigation they unfortunately require major modifications
to GNSS receivers.
So far, it can be con cluded that only pulsing of the signal
provides a certain level of interference mitig ation without
the need to modify the receiver and it will also prevent a
non-Pseudolites receiver from b ei ng un d ul y int er f ered.
Based on the studies carried out on this topic so far,
basically two pulse patterns have been found for GPS
signals (Stansell, 1986, SC-159 RTCA, 2000).
For the Galileo system these GPS pulse patterns appear
less applicable due to largely different signal structures of
the Galileo signal. Therefore, dedicated studies were
performed for Galileo to determine optimized Pseudolite
pulsing schemes. On of these is reported in Abt et al.
(2007).
4 Regulatory Issues
Local, global or regional regulation?
Pseudolites have been exp lained as terrestrial dev ices that
make extended or augmented navigation services
available over some limited local areas differing in terms
of "indoor" or "wider" area coverage.
Authorizations to operate these devices are usually
granted under national legislation by the national
regulatory authorities. This describes the present status
quo.
However, looking into the future perspectives of these
devices to enable a wide variety of innovative
applications in commercial, scientific, military and other
application segments certainly raises the need to search
for a common international approach in defining equal or
at least similar regulatory conditions to operate these
devices. Transparent regulatory frame conditions would
provide valuable planning security for all the parties
involved: pseudo lite manufacturers, system implementers
as well as the operators of the RNSS-systems.
Due to the fact that these devices have a potential to be
applied in large quantities, worldwide, it is of utmost
importance to agree on appropriate rules for their
implementation before their implementations get out of
control. Particularly when RNSS providers, for instance
the future Concessionaire of the European RNSS system
Galileo, might intend to offer their service guarantees,
they must rely on the legal conditions that ensure service
availabilities which are not potentially restricted by the
harmful interferences caused by pseudolites.
On the other hand it is apparently in the interest of the
entire global GNSS-provider community to extend their
(inter-operable) highly accurate navigation and timing
services into urban canyons and indoor environments.
One important element of a seamless provision of
navigation and timing services is the fact that ideally the
same user receivers could be used from outdoor to
indoor. Therefore, from the regulatory point of view, only
the co-frequency pseudo lites are of prime concern.
In summary, the regulation of Pseudolites is a local
(national) affair; however, it has an international impact.
Appropriate regulations that are eventually shared
worldwide would enable common high standards and
allow attractive navigation and timing services to the
advantages for both the navigation providers and the
users.
Regulatory Rules and Players
All of the about 200 sovereign countries in the world
develop, and agree mutually with in a formal
administrative process, the use of any Hertz of the
technically useful frequency spectrum. Frequencies are
natural resources and their use is an element of
sovereignty in each country. Frequency bands are
allocated to generic services such as e.g. to the
Radionavigation Satellite Service (RNSS), independent
of any particular systems, technologies, manufacturers or
brands. Decisions are taken one by one at the highest
level in World Radiocommunication Conferences (WRC)
every three to four years.
All the frequency allocations and the criteria for use of
the spectrum are agreed, actually word by word, and
published in the new edition s 18 month after the end of a
WRC as the Radio Regulations by the
Radiocommunication Sector (ITU-R) of the International
Telecommunication Union (ITU) in Geneva. The last
conference was convened in Geneva, Switzerland, from
22 Oct. to 19 Novem ber 20 0 7.
The rules published with the Radio Regulations are
periodically transferred into national legislations in each
of the ITU Member States. Immediately after a WRC a
Conference Preparatory Meeting (CPM) defines the new
agenda items for the following Conference. The
agreement on still open or new issues, as agreed by a
CPM leads to the detailed investigations in the Task
Groups, the Working Parties, and other entities with
relevant competences covering all the aspects of radio
communications. In a number of cases where positions on
allocations or use of spectrum differ, they are reflected by
splitting the world into three Regions as shown in Fig. 9.
Also shown in Fig. 9 are the regional groups of Member
State Administrations that advocate regional interests and
organize study group structures (Working Groups, Project
Teams) that meet in time coherently to working sessions

Martin et al.: Interference and Regulatory Aspects of GNSS Pseudolites 105
at the ITU-R identifying their particular interests on
agenda items and subjects.
AP T
ATU
CITEL
LAS
CEPT
AP TAP T
ATUATU
CITELCITEL
LASLAS
CEPTCEPT
Fig. 9 Regional Groups of administrations considering regulatory
frames
The conferences of regional Administrations comprise
CITEL (Inter-American Telecommunication
Commission, Washington, DC), CEPT (European
Conference of Postal and Telecommunications
Administrations), ATU (African Telecommunication
Union), LAS (League of Arab States), and APT (Asian-
Pacific Telecommunication Gr ou p ).
Additional allocations of frequency bands to the Radio
Navigation Satellite Service (RNSS) were made at
WRC2000 in Istanbul, Turkey. All RNSS-allocations as
published in the latest edition of the Radio Regulations
are shown in Fig. 10. The WRC2003 decided on rules for
use of the allocated spectrum. These rules ensure the
sharing among RNSS-systems and between RNSS and
other services allocated to the bands.
In the lower two of the four bands shown in Fig. 10, the
allocation of RNSS is co-primary with other radio
services (ARNS, RLS, RNS, a. o.). Pseudolite-network
planners have to keep this constraint in mind. Also shown
in Fig. 10 is the fractional use of the allocated RNSS
spectrum by the Galileo system as well as GPS and
Glonass.
With the variety of multiplexed signals transmitted by
Galileo in the bands as shown in Fig. 11, three main user
groups are primarily addressed with the signals offered
that are optimized to their needs, respectively identified.
Target user groups are in (1) the private and commercial
market segments, (2) the safety-of-life segments
comprising aeronautical, railway, and maritime
applications, as well as (3) the governmental public
regulated services.
It is assumed that Pseudolites would be attractive in each
of these segments. It is therefore essential that the rules
are developed for each of the allocated bands, because
each band introduces different sharing conditions. The
two main groups to share with are the terrestrial radio
navigation systems DME/TACAN in the aeronautical
radio navigation service (ARNS) and the complex group
of civil and military radars in radio location/navigation
services (RLS, RNS).
Regarding the regulation to protect the systems in the
ARNS from the signals in the RNSS, two dedicated ITU-
R Recommendations (M.1639 and M.1642) were
developed and eventually endorsed by the ITU-R (prior
to WRC03). While one document explains the detailed
derivation of the protection limit for ARNS, the other
provides the second procedure and algorithms to
determine the actually aggregate power flux density from
all navigation satellites. Similar recommendations for
other service compatibilities are presently under
consideration in the ITU-R Working Party 8D.
As mentioned before, the signals provided by Galileo in
the different bands are shown in Fig. 11. GPS, Glonass
and a number of other potential RNSS providers have
published further systems that intend to utilize the bands
in a similar way, most of them have co-frequency with
the corresponding Galileo signals.
Sharing the frequencies in this manner fosters the use of
common, particularly mass-market, low cost receivers
since they all could operate with a unique RF-front-end.
GPS GLONASS
1240 1256 12601300MHz
E6
1217 1164
E5B
L5 L2 G2
For Sa fety-of- Life Services
GALILEO GALILEO GPS/ GALILEO
E5A
GPS/ GALILEOGLONASS
15631587 15931610 MHz 1559
G1 L1 C1
5030 MHz5000 5010
Uplink
ARNS (DME/TACAN)
ITU-R Rec.sM.1639 and M.1642RNS/ RLS/ EE SS (WPR, civ+milradar)
Indicates use of
spectrum by GALILEO
E5
RNSS/ ARNS
GPS GLONASS
1240 1256 12601300MHz
E6
1217 1164
E5B
L5 L2 G2
For Sa fety-of- Life Services
GALILEO GALILEO GPS/ GALILEO
E5A
GPS/ GALILEOGLONASS
15631587 15931610 MHz 1559
G1 L1 C1
5030 MHz5000 5010
Uplink
ARNS (DME/TACAN)
ITU-R Rec.sM.1639 and M.1642RNS/ RLS/ EE SS (WPR, civ+milradar)
Indicates use of
spectrum by GALILEO
E5
RNSS/ ARNS
Fig. 10 Frequency bands allocated to RNSS
Power level E6-( A): -155 dB W
Power level E6-(B): -158dBW
Power level E6-(C): -158dBW
Power level (A): -155dBW
Power level (B): -158dBW
Power level (C): -158dBW
Power level E5a-I: -158dBW E5b-I: -158 dBW
Power level E5a-Q: -158dBW E5b-Q:-158 dBW
1260 1300
1278,750 MHz
E6
G/Nav
BOC(10,5)
C/Nav
BPSK(5)
1000 sps+ Pilot
A
B + C
x sps
E5E5a
1164 1215
E5b
I
Q
,
1191,795 MHz1191,795 MHz1207,140
Pilot Pilot
Alt- BOC-
1176,450
F/ Nav
50 spsI/ Nav 250 sps
1559 1594 MHz
1575,420MHz
L1(E1)
G/Nav
BOCcos(15,2.5)
x sps
I/ Nav
BOC(1,1)
250 sps+ Pilot
A
B + C
51 MHz 40 MHz 35 MHz
Power level E6-( A): -155 dB W
Power level E6-(B): -158dBW
Power level E6-(C): -158dBW
Power level (A): -155dBW
Power level (B): -158dBW
Power level (C): -158dBW
Power level E5a-I: -158dBW E5b-I: -158 dBW
Power level E5a-Q: -158dBW E5b-Q:-158 dBW
Power level E6-( A): -155 dB W
Power level E6-(B): -158dBW
Power level E6-(C): -158dBW
Power level (A): -155dBW
Power level (B): -158dBW
Power level (C): -158dBW
Power level E5a-I: -158dBW E5b-I: -158 dBW
Power level E5a-Q: -158dBW E5b-Q:-158 dBW
1260 1300
1278,750 MHz
E6
G/Nav
BOC(10,5)
C/Nav
BPSK(5)
1000 sps+ Pilot
A
B + C
x sps
G/Nav
BOC(10,5)
C/Nav
BPSK(5)
1000 sps+ Pilot
A
B + C
x sps
E5E5a
1164 1215
E5b
I
Q
,
1191,795 MHz1191,795 MHz1207,140
Pilot Pilot
Alt- BOC-
1176,450
F/ Nav
50 spsI/ Nav 250 sps
I
Q
,
1191,795 MHz1191,795 MHz1207,140
Pilot Pilot
Alt- BOC-
1176,450
F/ Nav
50 spsI/ Nav 250 sps
1559 1594 MHz
1575,420MHz
L1(E1)
G/Nav
BOCcos(15,2.5)
x sps
I/ Nav
BOC(1,1)
250 sps+ Pilot
A
B + C
G/Nav
BOCcos(15,2.5)
x sps
I/ Nav
BOC(1,1)
250 sps+ Pilot
A
B + C
51 MHz 40 MHz 35 MHz
Fig. 11 Use of bands by Galileo
Developing the rules for the Pseudolite operations
Each of the published or operational RNSS systems
provides signals targeting at specific user groups:
consumer, professional, military, aviation, just to mention
a few. Thus, a wide variety of pseudolites will be
developed. Important will be how much efforts are
dedicated to the careful system design, performance
monitoring and maintenance of the devices in operation.

106 Journal of Global Positioning Systems
The Galileo system intends to provide the services that
are tailored to three distinct user groups. Each group is
expected to show their interests in the implementation of
Pseudolites and to optimize their signal provision in a
given local area. Particularly the pseudolite segment
supporting consumer market installations in exhibition
plazas, train stations, shopping malls, and alike, will
presumably be the largest group of users showing great
uncertainties in the implementation and maintenance of
these pseudolite devices.
In other cases, neighboring pseudolite implementers may
not consult each other to investigate the overall
compatibility. Or pseudolite implementations for
different user groups (governmental, commercial) may
not have sufficient information about the other's planning
because of classified or proprietary restrictions. All this
supports the need for a formalistic procedure before any
transmission should occur.
This exposes the fundamental dilemma of the situation:
On one hand, it is in the interest of (at least) the Galileo
system operator to encourage as many pseudolite
networks as possible to achieve a good overall user
perception of the Galileo services. On the other hand,
without a (costly) transparent administrative control
instrument, the situation wou ld be quickly out of control.
But, without a cadastre or an otherwise realistic control
instrument of the implemented installatio ns it would soon
be difficult to guarantee any service qualities by the
satellite navigation service operators.
It can be expected, that particularly from low cost sites
(due to equipment quality, maintenance period, etc.),
sooner or later interfering signals could turn an advantage
into its opposite. Granted service guarantees in particular
in those areas could turn into a major cost (service
agreement contracts) and/or nuisance factors.
From the regulatory point of view pseudolites are
terrestrial devices. They are not operating in the RNSS
even if their transmission schemes and protocols are very
similar to those transmitted by the RNSS satellites. The
allocations in th e Radio Regulations provide in the lo wer
and upper band the opportunity to operate pseudolites in
the aeronautical service (ARNS) but not for other
purposes.
Besides formalistic reasons, there is a significant
difference between the RNSS and what pseudolites
provide in technical terms. Different to navigation
satellites, pseudolites could create large differences in the
effectively radiated RF power flux density when a
receiver moves from a location close to the pseudolite
transmitter towards the edge of the coverage. This move
leads to an unbalance of the receive power from space
and from the pseudolite.
Moving with a receiver towards the Pseudolites service
area results in great changes of local signal strength'
while the satellite signal strength remains almost constant
and equal within a defined range. The dynamic range of
an RNSS receiver is normally fairly low because the
receivers are optimized for highest sensitivities to provide
best possible service availability. In the presence of
strong and weak signals the receiver creates
intermodulation products that raise the noise floor which
in turn can lead to a degradation of positioning
performance.
In other words, the assumptions for a maximum pfd that
form the basis for an additional and co-primary RNSS
allocation differ from what pseudolites now would
actually create.
From the regulatory point of view the following questions
need to be answered: (1) What is the radio navigation
service provided by a Pseudolite? (2) What are the
reasonable constraints to protect the RNSS and other
services in the bands to ensure radio compatibility for all
the users? (3) How to regulate (license, monitor, arbitrate,
etc.) their implementation?
Studies are presently underway to investigate some
typical technical scenarios that are representative for a
particular group of applications. Two basic scenarios
were determined so far that provide a clear distinction:
(1) indoor with no (i.e. below threshold) power flux
densities to the world outside and (2) outdoor where
navigation receivers at least can receive marginally some
of the satellite signals.
For the case of indoor, a simplified procedure might be
applied. This could be ensured e.g. by a commercial-off-
the-shelf Pseudolites approved as a low power device and
authorized for indoor uses only.
The next steps on the journey
CEPT has taken the initiative to in v estigate th e regulatory
frame conditions in more detail. Working Group
Spectrum Engineering in its project team 39 has started to
investigate the technical conditions for the operation of
Pseudolites and has invited WG Frequency Management
(WG FM) and WG Regulatory Affairs (WG RA) to
investigate corresponding administrative and legal
aspects.
Studies in the band 1164-1215MHz comprise
compatibility analysis with RNSS and ARNS, in the band
1215-1300MHz sharing with RNSS, RNS, RLS, Space
Research, Earth Exploration Satellite Service, and the
Amateur Radio and Amateur Radio Satellite Service. In
the band 1559-1610MHz sharing with RNSS and ARNS
is required while the Fixed Service allocation is
terminated and is of less significance in the long run.

Martin et al.: Interference and Regulatory Aspects of GNSS Pseudolites 107
The main reason for this article is to invite interested
parties to collaborate and contribute to this analysis. The
Global Navigation Satellite Service as the entirety of all
RNSS systems eventually will be provided as a joint
effort of all the RNSS providers to the advantage of
global user commun ities. Pseudolites can and should play
a significant role in the seamless provision of positioning
and timing services extended into the areas where the
physical propagation conditions would otherwise not
guarantee reliable signal reception.
Final remark
The work reported here is the result of several discussions
with many colleagues in companies and administrations
as well as in the Galileo program. The issues raised here
are quite difficult in terms of finding a solution which
equally is acceptable to regulators, system operators,
Pseudolites-provide rs and the user communities.
Interested study groups are encouraged to complement
the on-going investigations in support of the regulatory
process.
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