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DVB-T network planning: A case study for
Greece
ARTICLE in IEEE ANTENNAS AND PROPAGATION MAGAZINE · FEBRUARY 2009
Impact Factor: 1.32 · DOI: 10.1109/MAP.2009.4939022
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DVB T network planning: A case study for
Greece
D. A. Kateros, D. A. Zarbouti, D. C. Tsilimantos, C. I. Katsigiannis, P. K. Gkonis, I. E. Foukarakis
D. I. Kaklamani and I. S. Venieris
National Technical University of Athens
School of Electrical and Computer Engineering
Heroon Polytechniou 9, 15773, Athens, Greece
E mails: dimitris, chkatsig@icbnet.ntua.gr, dzarb, dtsiliman, pgkonis, ifouk@esd.ntua.gr
dkaklam@mail.ntua.gr, venieris@cs.ntua.gr
The terrestrial digital video broadcasting (DVB T) network planning is the main
interest of this article along with a case study for Greece. The basic principles and the
guidelines of the DVB T planning process are presented in conjunction with their application to
the establishment of the Greek DVB T allotment plan. The procedures described in this article
were followed by the authors during the International Telecommunication Union (ITU) DVB T
planning project that concluded with the ITU’s Regional Radiocommunication Conference 2006
(RRC 06) and the Geneva (GE 06) frequency plan for terrestrial digital radio broadcasting.
allotment, compatibility analysis, DVB T, FAP, interference calculation, plan synthesis,
SFN
1
INTRODUCTION
Traditionally, the terrestrial broadcasting planning approach involved the definition of a
number of assignments, each of which consists of the transmitter site specified in terms of
longitude and latitude, as well as the specific transmitter’s characteristics and antenna’s
configuration. These parameters are chosen to ensure acceptable reception or ‘coverage’ of the
desired service in an area associated with, and usually surrounding, the transmitter location.
However, the desired coverage of the assignment was not explicitly taken into account during
the development of the plan and, in principle, could not be determined until the plan was
finalized. This is the approach used for the establishment of the Stockholm (ST 61)
broadcasting plan. On the other hand, a plan must not only provide means to specify ones
right to use a spectrum resource, but more importantly, means to protect its effective
utilization. On this line of thought, it is more essential for a plan to achieve protection of
known service areas, than to specify the characteristics of a number of transmitting sites.
The developments in standardization of digital radio broadcasting systems have introduced
new possibilities regarding the methodology of planning terrestrial broadcasting networks.
The introduction of single frequency networks (SFNs), allows the synchronization of the
transmitters of a confined geographic area, so that they may operate at the same frequency
channel without any destructive interference occurring at the receiver. Therefore, the planning
of digital radio broadcasting networks has gained a degree of flexibility, which allows
transmitter characteristics and placement calibration, as more than one transmitter may be
used to achieve coverage over a given area without depleting spectrum resources. This
approach that has already been employed in recent broadcasting plans, such as the Maastricht
2002 terrestrial digital audio broadcasting (T DAB) plan and the Geneva 2006 DVB T and T
DAB plan [1], allows the simplification of the planning process using a higher level of
abstraction, namely allotments. The actual implementation of the allotment into a set of
assignments can be postponed to a latter stage. In addition, this planning approach is
appropriate for very large scale planning that may comprise regional broadcasting networks
with different degree of design and implementation progress.
The first part of this paper is dedicated to the overview of the basic principles and
guidelines that can be taken into account during the planning process of a DVB T allotment
plan. Due to the different conditions in terms of propagation characteristics, terrain
morphology, demographics, cultural diversity and economics that can be found in various
regions, it is evident that there is no standard methodology for the design and the
implementation of such a plan. In the second part of the paper, we present our planning
experience for the Greek DVB T allotment plan and outline the methodology and decisions
taken towards its establishment. The presented allotment plan is part of the GE 06 digital
terrestrial broadcasting plan [1], whose production was coordinated by ITU and consists of the
broadcasting plans 118 involved countries. Throughout this paper we examine the processes
of designing the allotments, conducting interference analysis and performing the distribution
of available frequency channels between them.
2
DVB T ALLOTMENT PLANNING
2.1 Allotment Area Definition
An allotment is a service area that is intended to be protected against interference. In order
to define an allotment, three parameters must be determined; an ordered set of geographical
positions called ‘test points’, that represent the allotment boundaries, a maximum value for
the acceptable interference level at the allotment test points and means to calculate the
outgoing interference from the allotment. This section outlines the procedure of allotment
boundary definition.
The primary goal of allotment area definition is to ensure its coverage with a single
frequency, as SFNs exhibit self interference limitations. The 8K carrier operational mode of
the DVB T system which is suitable for SFN networks, defines 896 Es useful symbol duration
( ) [2]. In order to compensate for the multi path effect present in the terrestrial broadcasting
environment which leads to inter symbol interference in the presence of echoes, a guard
interval (GI) is assumed. Two transmitters operating in the same SFN network transmit
simultaneously the same symbol. Assuming
corresponds to distance difference
=
⋅
the speed of the propagating signal this
(Table I). The application of a propagation
prediction technique can then identify areas within the intended coverage area that may suffer
from self interference.
The design of allotments is also bound to non technical parameters and criteria, such as
demographics and boundaries, both regional and national. The implementation of an allotment
as an SFN implies the broadcasting of a common set of programs within the allotment.
Consequently, allotments must be efficiently mapped to distinct demographic regions, in order
to account for linguistic diversity or to reflect administrative divisions either international or
within a country. Lastly, allotment areas, as service areas, should be particularly focused on
areas of significant population density. The aforementioned constraints have already been
considered to some extent for the implementation of the analogue TV networks. Therefore,
the planning of digital radio broadcasting services with allotments can benefit greatly building
on this experience.
Another aspect of the allotment definition has to do with the efficient frequency reuse.
There is a straightforward relation between allotment size and the relevant frequency reuse
distance. As the allotment area size decreases with relation to the reuse distance the allotment
network becomes more “spectrum hungry” and the amount of frequency channels that can be
assigned to each allotment area while satisfying interference constraints is reduced. The
spectrum resources are limited, and therefore extremely valuable, so the allotment design
should receive feedback from the evaluation of the interference relations between allotments.
In the framework of the RRC 06, the only suggested method for allotment definition was
the Channel Potential Method [3]. This method describes a procedure for the conversion of
existing analogue assignments to allotment areas for digital broadcasting. The method aims to
design allotment areas that can be mapped to and exhibit a certain degree of compatibility
with the assignments of the agreed analogue broadcasting plans. Thus, its application
facilitates the transition from analogue to digital broadcasting, which is a fairly complex
problem, as it involves not only different technical criteria, but also different transition
timetables between various regions.
Although the method has a significant regulatory usefulness, providing means to convert an
existing and agreed analogue broadcasting plan to a digital one, its application is mostly based
on geometrical criteria, so many technical concerns are raised. Overall, the method is more
suitable for latticed analogue broadcasting networks of landlocked regions and cannot be seen
as a global solution for all cases.
2.2 Compatibility Analysis
The goal of the compatibility analysis process is the assessment of the interference
constraints between the defined allotments. The abstract concept of allotment has to be
associated with specific parameters to represent the required service coverage inside the
allotment as well as the outgoing interference. Two general approaches can be introduced for
the compatibility analysis process, each corresponding to a different progress status
concerning the network design and resulting to a different level of accuracy.
The initial estimation of the environment that the DVB T network will be implemented is
essential in order to define the appropriate propagation model and its parameters. In the
framework of RRC 06 the propagation model employed for terrestrial broadcasting is
described in the recommendation P.1546 [4]. However, it is an empirical, not location specific
model based on measurements that do not consider diffraction losses nor sub path attenuation.
Typical planning software tools include more sophisticated field strength prediction methods
that can be used in conjunction with a terrain digital elevation model (DEM) in order to obtain
more accurate results.
Every network planning process is triggered by the subscriber’s and operator’s needs and
wishes. Therefore, an initial set of parameters that depends on these needs must be defined.
These basic parameters and constraints are described shortly in the followings.
Each allotment of the planning area should be associated with a reception type and a
coverage quality. In DVB T the fixed, the portable (indoor, outdoor) and the mobile are the
supported reception modes while the coverage quality is denoted through the percentage of
locations that the desired service is provided within the service area. The decision about the
reception mode must be followed by the decision concerning the desired throughput.
There exist a large number of different possible DVB T systems (variants) depending on the
choice of modulation type and code rate. For instance, the offered throughput in an 8MHz
channel ranges from 5 (QPSK 1/2) to 30Mbps (64QAM 7/8) according to the selected DVB T
variant and GI. The selection of the DVB T variant is determined taking into account both the
required reception type and the desirable throughput. Apparently, the DVB T variant
determines the minimum signal to noise ratio (SNR) that is required at the receiver end, while
equation (1) indicates the minimum power.
= 10 log (
⋅ ⋅
where = 1.38M10 23 J/K is the Boltzmann’s constant,
)+
(1)
= 2900 K is the absolute temperature,
is the channel bandwidth,
is the receiver noise figure and
case of fixed reception mode. Nevertheless, the
are the feeder losses in the
provides the requirement in a noise
limited planning basis which is not the case for broadcasting networks. Therefore, it is
common practice to introduce a margin in the link budget calculations so as to take into
account the network interference potential during the planning process. In the framework of
GE 06 plan an interference margin (O) of 3dB [5] was considered. Hence, the minimum
required power of (1) becomes:
= 10 log (
)+
⋅ ⋅
+
(2)
Finally, the aforementioned choices lead to the determination of the protection ratio (PR)
value [6]. In essence, the PR value stems from the
and the considered interference
margin, while it provides an estimation of the interfering signals level related to the wanted
ones. Obviously, the PR is strictly bound to the DVB T variant choice together with the
min
calculated in (2). Equation (3) provides the power threshold for acceptable reception in
conformity with the DVB T planning criteria.
≥∑
+
(3)
=1
where
is the interfering power from the
interfering transmitters. Note that the
th
transmitter and
is the total number of
value of (3) along with the antenna effective aperture
and gain provides the minimum required field strength,
,min(
) given in dBEV/m, that
apparently depends on the frequency.
!
"
The above paragraph indicates that there is an important number of possible planning
configurations. ITU in order to minimize them and facilitate the planning process grouped
them into three RPCs [5]. Specifically, the possible combinations of reception mode,
modulation type, code rate and required location coverage probability were grouped according
to the equivalent minimum median field strength required on the receiving location. The
minimum median field strength in frequency is given by:
=
where
is the man made noise,
desired coverage probability and
+
+
+
(4)
is the location correction factor that corresponds to the
are the losses that must be taken into account in relation to
the reception mode. In portable outdoor reception
accounts for losses caused by the building
height while in portable indoor reception there are additional losses for the building
penetration. The
#
values for representative frequencies are given in [5]. The evaluation for
different frequencies is conducted using a field strength correction formula [4].
$
The interference calculations are the final step for the compatibility analysis. In particular,
there are two approaches that can be followed according to the degree of insight concerning
the future allotment implementation as a set of assignments.
2.2.3.1 1st Approach: Specific Transmitting Sites
In case that a substantial subset of the transmitting sites implementing the allotment has
been determined, accurate calculations concerning both the wanted field strength and the
interference potential of each allotment can be performed. In this approach a field strength
prediction method that accounts for terrain morphology is essential.
During the compatibility analysis the total interfering, ∑ =1
and wanted field strength,
,
are calculated at every test point and once again the inequality of equation (3) applies. In order
to obtain a strict estimation of the maximum allowed interference we consider
%
and
we solve the derived equality. The maximum allowable interference at any allotment test point
is then given by:
=
−
(5)
When the criterion of equation (3) falls through then the incompatibility is reported to the
synthesis process. It must be highlighted that the examination of equation (3) at every test
point considers all potential interference sources.
2.2.3.2 2nd Approach: Reference Networks (RNs)
When the specific transmitting site locations corresponding to an allotment have not yet
been determined, there is a need to model the outgoing interference by alternate means. The
method that was proposed by ITU and was adopted in the framework of RRC 06, involved the
definition of generic network structures with geometrical symmetry and homogeneity with
regard to transmitter characteristics, called RNs. The use of RNs for the compatibility analysis
is bound to the use of RPCs since the characteristics of the transmitters at each RN
differentiate according to the RPC. There are four kinds of RNs, each corresponding to a
different wanted reception type and service area characteristics. Their detailed description can
be found in [5]. In addition, the propagation model used for this approach of interference
calculation is the empirical P.1546.
Fig. 1 depicts the RN placement in order to conduct interference calculations between two
allotments. The interfering field strength is evaluated on each allotment test point and the
largest calculated value is considered as the overall interference to the wanted allotment. The
interfering field strength is derived by the summation of the individual field strengths
produced by each transmitter. It is apparent that this method does not take into account
multiple interference situations where the wanted allotment receives harmful interference
levels due to the addition of interfering field strengths from more than one allotments. The
compatibility status (compatible or incompatible) of each pair of allotments is examined by
formula (6) and is reported to the synthesis algorithm.
≤
In the above inequality the
#(
−
− −
) is evaluated with equation (4),
(6)
is the location correction
factor of the interfering allotment and & (&'0) is the antenna discrimination [7] in the case
that the wanted allotment has fixed reception (RPC 1). Note that inequality (3) does not apply
for this approach since it refers to a multiple interference assessment scenario. Equation (5) is
used instead in order to determine the maximum accepted interfering field strength.
The utilization of RNs allows the calculation of the minimum separation distance between
two co channeled allotment areas (reuse distance) [8]. The reuse distances can be calculated
by employing the interference potential curves of P.1546 and by taking into account the
maximum acceptable interference (
()
for each of the wanted and interfering allotment
combinations, i.e. solving the equation (5) for the reference frequency of the band under
consideration.
2.3 Plan Synthesis
Plan synthesis is the procedure of allocating frequency channels to the defined allotment
areas. It can generally be seen as a variation of the frequency assignment problem (FAP). The
basic FAP consists of assignment constraints, interference constraints and an objective or
optimization criterion. The frequency assignment model typically involves a predefined set of
frequency channels f and a set of nodes n requiring frequency channels. For every node , a
subset of the available frequencies f is specified, from which a number of frequencies
( )
(the multiplicity of the node) must be assigned to it. The problem is usually represented by a
graph. Each vertex represents a node and each edge represents an incompatibility between two
nodes for a given pair of frequency channels. A more suitable representation for computer
processing is that of a
x
matrix, where
is number of nodes. Each element , ) of this
matrix is an integer that corresponds to the required channel separation between the and )
nodes.
For digital radio broadcasting systems, adjacent channel interference constraints need not be
taken into account due to the low protection ratios that apply [6]. Consequently, the above
representation is simplified to binary interference constraints. In fact, most models of the
frequency assignment problem found in the literature use binary constraints as input [9].
However, this approach does not take into account multiple interference. In the case of DVB
T planning, multiple interference must be considered since the DVB T system is characterized
by rapid signal degradation from perfect to no reception within a narrow dB margin. On the
contrary the analogue TV systems involve different impairment grades [6] [10]. The
feasibility of possible frequency distributions can be assessed taking into account the results of
the compatibility analysis.
The synthesis algorithm in the case of DVB T allotment planning should account for
additional features. Firstly, existing analogue assignments within the allotment area may
determine specific channels to be assigned to the allotment. Moreover, the channel
distribution between allotment areas must be balanced in order to avoid unfair channel
distributions where very few channels are assigned to ‘difficult’ allotment areas. This
constitutes a problem of many FAP algorithms, observed in [11].
Due to these requirements, algorithms employing heuristic techniques are more appropriate.
The more frequently meta heuristics used are the Simulated Annealing [12], the Taboo Search
[13] and the Genetic Algorithms [14]. Another heuristic approach involves greedy methods
and more specifically sequential algorithms [15].
The procedure led by ITU in RRC 06 involved the submission of requirements from
Administrations (input requirements). This resulted in a synthesis algorithm with the objective
to maximize the number of requirements accepted for entry in the GE 06 Plan [16]. A
sequential algorithm was employed consisting of two steps. In the first one the ordering of the
requirements was conducted. In the second step each requirement was assigned a channel
from its available channel list. A total of three approaches for the first step and of five for the
second one was defined. Out of the fifteen different plans produced by the possible
combinations, the one satisfying the highest number of requirements was selected. The
success of this method relied heavily on the pre coordination of the input requirements by the
Administrations. Specifically, ITU provided means to eliminate the detected incompatibilities
between requirements taking into account the results of the pre coordination procedures
(administrative declarations).
3
GREEK CASE STUDY
Greece is located in the Southeastern Europe with a population of approximately 11 million.
The Greek terrain morphology is extremely complex and diverse, as mountains (almost 60
percent of the land) coexist with the third largest coast line in the world and almost 200
islands, half of which are inhabited. Approximately 97% of households rely on the terrestrial
analogue TV broadcasting networks, while the remaining 3% are satellite subscribers. The
existing terrestrial analogue broadcasting network has been built in an ad hoc manner with
little central planning, a situation which has led to the scarcity of spectrum resources as well
as significant interference problems over a number of service areas. These facts, add
significant difficulties in the establishment of a DVB T plan, as diverse propagation
conditions and existing analogue broadcasting experience need to be carefully taken into
account in order to establish a spectrum efficient plan that will serve adequately the
population needs.
The planning procedure was conducted on behalf of the Greek Ministry of Transport and
Communications, which is the authority responsible for the country’s representation to the
ITU concerning spectrum regulation and management. The ICS Telecom of ATDI was used as
a network planning and propagation prediction software tool. This software allowed the
performance of simulations over a digital elevation model (DEM) representation of Greece
with 50m resolution. The results of these simulations were used to make propagation and
interference calculations and thus calibrate transmitter characteristics, define SFN networks
and conduct a compatibility analysis between the defined allotment areas.
3.1 Allotment Area Definition
In general, the allotment boundaries definition is a gradual process that involves several
refinement steps, each one with different criteria that must be met. The steps that were
followed in the case of the Greek allotment plan are:
1) Examination of the analogue transmitter network and assessment of the existing service
areas
2) Definition and extraction of the “useful sites” of the analogue TV network
3) Grouping of the “useful sites” into SFNs.
4) Examination of the coverage areas of the produced SFNs and initial construction of the
allotment plan.
5) Allotment partitioning, merging and resizing according to received feedback from
compatibility analysis and plan synthesis processes.
At first, the examination of the operating analogue network offered a good estimation of the
service areas that appear in the Greek geographical area. The most important service areas
represented large cities and surroundings or well separated areas by the terrain morphology.
The transmitting sites that corresponded to these service areas were examined and a list of
important terrestrial broadcasting locations was determined. Throughout this paper we denote
these locations as “useful sites”. The majority of the “useful sites” exhibits significant spatial
and demographic coverage and they are located in high altitudes comprising a relatively clear
first Fresnel zone.
Although the resulted “useful sites” from the above constraints were already in use by the
analogue TV network, the respective transmitter characteristics for the DVB T were
determined as a result of simulations performed using ICS Telecom. Table II summarizes the
basic planning parameters in case of Greece. The power thresholds of the minimum required
and maximum allowed interference have been derived by (3) and (5) respectively. Note that
due to the selected reception type there were no feeder losses (
= 0).
According to the aforementioned network parameters adequate choices for the transmitting
power and the antenna configuration were made. During this procedure additional effort was
made in order to reduce the outgoing interference from the envisaged allotment. Table III
provides a transmitter configuration example.
The importance of SFNs was highlighted in the previous section. Therefore, the “useful
sites” were grouped in SFNs. The GI duration was chosen at 224Es, which corresponds to the
maximum time of arrival (ToA) difference between any received signals from the transmitters
within the same SFN. This time interval corresponds to 67 km (see Table I).The initial
grouping of the “useful sites” to SFNs was performed by limiting the distance between two
transmitters to 67 Km, which constitutes a convenient approximation in order to take into
account the aforementioned ToA constraint. It must be noted that the estimation of the
distances between the “useful sites” could not allow for a smaller GI, as it would increase
significantly the number of produced SFNs.
The first allotment plan that was resulted by the former procedure contained 35 allotments.
Nevertheless, a further examination of the SFNs was undertaken since their initial definition
was based on the transmitters’ distance. The examination took place with the ICS Telecom
and for a specific allotment the self inference levels did not allow the future SFN
implementation. As a result the specific allotment was divided into two.
We should note that the transmitter network comprised of the “useful sites” does not
provide full area coverage to the majority of the defined allotments and additional planning
with gap filling transmitters is required; however it is sufficient for planning purposes, for two
reasons. Firstly, it provides substantial population coverage and secondly the outgoing
interference from an allotment is dominantly provoked from the “useful sites”, as they have
significantly larger e.r.p. and effective heights than the envisaged gap fillers.
3.2 Compatibility Analysis
After the initial allotment definition the compatibility analysis took place. As it was
mentioned earlier, in the framework of the RRC 06, ITU used the empirical propagation
model of the recommendation P.1546 due to its simplicity and low computational effort.
However, in our planning there was a need for more accurate field strength calculations, hence
the Fresnel propagation prediction method was chosen. Opposite to the ITU R P.1546, which
does not take into account geometrical attenuation terms such as sub path attenuation and
multi edge diffraction, the Fresnel module included in the ICS Telecom provides several
choices for this purpose.
The diffraction losses were considered through the Deygout method [18] since it is the most
widely used for this kind of planning [19]. Nevertheless, this method usually overestimates
the losses in cases of many obstacles too close to each other, so the more approximate
Bullington method [20] was chosen for the mountainous environment of central and northern
Greece [21][22].
In order for the sub path attenuation to be considered in our studies the standard sub path
attenuation method provided also by ICS was used. The sub path attenuation coefficient used
by ICS is given by (7) and it is added to the total losses calculations.
*
=ρ⋅
(7)
In (8) ρ = (#1 + # 2 + #3 + # 4 ) / # is the proportion of the total path that is located above the first
Fresnel virtual ellipsoid (see Fig. 2) and
is the Deygout correction term given by (8).
= 20 log(75000# ) − 20 log(π +1+2 )
(8)
In (8) # is the distance between the transmitter and receiver, +1 and +2 are the transmitter and
receiver heights respectively and is the operating frequency in MHz.
The compatibility analysis was conducted by calculating the outgoing interference from the
transmitter network of each allotment to the test points of all potentially affected allotments.
This resulted in two kinds of incompatibilities between two allotments, which were classified
as “hard” and “soft” based on the following inequality:
≥
where
+
+
(9)
is the received field strength on each test point from the transmitters of the wanted
allotment,
is the interfering field strength on the same test point,
protection ratio and
is the relevant
is a margin in dB. “Hard” incompatibilities concern allotment pairs for
which inequality (9) falls through for at least one of the examined test points for
= 0. “Soft”
incompatibilities, on the other hand, concern allotment pairs where no “hard” incompatibility
exists and inequality (9) falls through for at least one of the examined test points for = 6.
The “soft” incompatibilities can additively cause the same effect as a “hard”
incompatibility. Fig. 3 summarizes the ‘soft’ and ‘hard’ incompatibilities identified between
the allotments of the final Greek plan for Band IV. These incompatibilities constitute the
constraints to be taken into account during the plan synthesis.
As stated in the previous section, the transmitter network assumed for planning did not
necessarily provide sufficient coverage to the entire allotment area. Therefore, the received
field strength value in some allotment test points was less than the minimum required. To
compensate for this fact, equation (10) was used.
= max {
where
,
}
(10)
is the wanted field strength used for the compatibility analysis on each test point.
3.3 Plan Synthesis
The results of the compatibility analysis are summarized in a matrix C, whose element
)
is
the field strength on the test point from allotment ). C contains all the necessary information
for wanted and interfering field strength values on allotment test points. In order to conduct
the plan synthesis an algorithm employing known meta heuristics was implemented. Details
on the design and performance of the algorithm can be found in [23].
This algorithm has two stages; in the first one, it creates as many mutual compatible
frequency layers as possible. A frequency layer denotes a set of
evenly among all
channels that are distributed
allotments. In the second stage additional frequency channels are allocated
without violating any of the constraints. During this stage provision is taken to preserve
balance to the channel allocation between allotments. This is essential, as the heterogeneous
terrain caused substantial differences between the number of incompatibilities of the
allotments situated in main land and those situated in sea. An additional measure taken to
facilitate the synthesis process was the unification of neighboring allotment areas containing
islands. This led to a final plan of 33 allotments, illustrated in Fig. 3.
Another feature of the implemented algorithm is the possibility to accept as input a
predefined partial channel allocation which remains fixed during the synthesis process. This
was essential in order to allow for the synthesis process to take into account the results of the
coordination procedure that took place between Greece and its neighboring countries during
the preparation activities for RRC 06.
A simple example of the algorithm’s functionality is demonstrated visually in Fig. 4. In this
example a synthesis problem consisting of 5 allotment areas and 10 available frequency
channels is assumed. The graph represents the constraints. Stage 1 includes steps 1 3, while
stage 2 steps 4 7.
Fig. 5 displays the performance of the synthesis algorithm by presenting the CDF of the
number of channels allocated to an allotment area in the case of Greece over 50 independent
runs. Three scenarios are shown:
Compatibility analysis performed by ITU.
Compatibility analysis performed using ICS Telecom and real transmitter network. Plan
synthesis ignores multiple interference.
Compatibility analysis performed using ICS Telecom and real transmitter network. Plan
synthesis considers multiple interference.
Fig. 5 suggests that the outgoing interference prediction method based on reference
networks and ITU R P.1546 propagation model is not suitable for the Greek terrain and
allotment design. The majority of detected incompatibilities, which lead to the poor synthesis
results, can be ignored. This can be attributed to three reasons. Firstly, the employed
propagation model does not take into account terrain morphology and differentiates only
between land and sea paths. Secondly, the careful selection of real transmitter sites and
characteristics further reduces the outgoing interference. Lastly, RN placement as described
earlier may result in placement of transmitters directly on sea (see Fig. 1), which induces
additional calculated interference.
Moreover, the small difference between the CDFs of the two scenarios stemmed from the
compatibility analysis conducted with ICS Telecom indicates that even for the limited number
of the Greek allotments the inclusion of multiple interference calculations may prevent the
acceptance of invalid channel distributions. On the contrary the binary constraints scenario
fails to detect these cases and produces more optimistic results.
3.4 Attiki: an implementation example
The most important allotment with respect mainly to its population is the allotment Attiki
which also includes the city of Athens. Fig. 6 displays the transmitter network assumed for
planning purposes, as well as a possible future implementation for this allotment. As shown,
the SFN network that consists of four transmitters does not provide sufficient coverage of the
allotment (Fig. 6a). The SFN, comprised by 8 transmitters, clearly results to a higher
percentage of allotment coverage (Fig. 6b).
Note that the outgoing interference levels do not substantially increase with the addition of
the four transmitters (see Fig. 6c and 6d). Specifically, no alteration to the constraints
established during the compatibility analysis process takes place. This shows that the
methodology followed resulted to an allotment plan that is possible to be implemented with a
DVB T transmitter network that will serve the future needs of operators and subscribers.
4
CONCLUSIONS
In this paper a methodology for allotment based DVB T planning that builds upon existing
analogue transmitter network experience and infrastructure was introduced. Based on this
methodology it is possible to define the allotment boundaries as well as assess their
interference relation. The degree of flexibility induced to the allotment implementation by
SFNs allows the implementation of a complete transmitter network without violating any of
the initial planning assumptions concerning interference constraints.
The experience of the planning in case of Greece indicates that even in difficult propagation
conditions (warm sea, islands) the proper site selection and transmitters’ configuration can
lead to manageable interference constraints between allotments. Additionally, topographic
decoupling present in mountainous areas can be utilized for the same purpose.
Lastly, the multi interference inclusion in the plan synthesis process led to a more viable
channel allocation. It must be noted that the significance of the multiple interference
consideration increases when the number of allotments included in the planning process
increases (larger countries).
5
ACKNOWLEDGEMENTS
The authors would like to thank Mr. V. Goltsios whose knowledge and experience on the
analog TV broadcasting infrastructure of Greece proved very useful towards the establishment
of the Greek DVB T plan.
6
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TABLE I
MAXIMUM SIGNAL SOURCE – RECEIVER DISTANCE DIFFERENCE
GI=Tg/Tu
1/4
1/8
1/16
1/32
Tg (.s)
224
112
56
28
/s (Km)
67
33.5
16.75
8.375
Figure 1: RN placement in order to conduct interference calculations between two allotment areas.
TABLE II
Basic Network Parameters
Reception Type
DVB T variant
Guard Interval (GI)
Implementation Margin (O)
(
Protection Ratio (PR)
Propagation Model
Receiver height
Portable Outdoor
16 QAM 2/3
¼
3 dB
79dBm
63dBm
16
Fresnel (Bullington)
2m
TABLE III
Transmitter Configuration for site Ymittos (Band IV)
Tx Configuration
Power (Watt)
Antenna Gain
Signal
Modulation
Antenna
Diagram
Analog TV
1000
12 dB
PAL
Analog
DVB T
250
12 dB
DVB 8MHz
16 QAM 2/3
Figure 2: Fresnel zones between transmitter and receiver for sub path attenuation losses calculation.
Figure 3: The final Greek allotment plan along with the “hard” and “soft” constraints graph for Band IV.
Figure 4: A demonstration of the functionality of the synthesis algorithm.
Figure 5: The cumulative distribution function for the number of channels allocated to an allotment area over 50
independent runs.
(a) The wanted field strength produced by the four “useful sites”
(b) The wanted field strength produced by the four “useful sites” and four additional gap fillers
(c) The interfering field strength produced by the four “useful sites”
(d) The interfering field strength produced by the four “useful sites” and four additional gap fillers
Figure 6: Wanted and interfering field strength for allotment Attiki with a network consisting of the four “useful”
sites with which the planning was conducted and with four additional gap filling transmitters.