Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR OPTIMIZING THE POSITIONING OF HIGH SENSITIVITY
RECEIVER FRONT-ENDS IN A MOBILE TELEPHONY NETWORK AND
RELATED MOBILE TELEPHONY NETWORK
The present invention generally relates to the field of mobile telephony and
particularly to a mobile telephony network with access of the CDMA type ("Code
Division Multiple Access"), hence W-CDMA or CDMA 2000 or UMTS. More
particularly, the present invention relates to a method for optimizing the
to positioning of high sensitivity receiver front-ends in a mobile telephony
network
and to a related mobile telephony network.
In a mobile telephony network, geographic areas are subdivided into a
plurality of cells. The network traffic in each cell is handled by a Base
Transceiver
Station for transmitting and/or receiving radio signals (voice and/or data)
to/from
mobile terminals. Such base transceiver stations can be equipped with receiver
front-ends inserted downstream of a transceiver antenna, whose main function
is to
select and amplify the radio signals that are within the frequency range
useful for
communication and to attenuate all other potentially interfering signals.
Typically, communication from the mobile terminal to the base transceiver
2o station (up-link chamzel) is characterized by radio signals having rather
low power.
Such radio signals are therefore subject to degradation in the presence of
noise.
As disclosed in US 6,263,215, in order to increase significantly the signal-to-
noise ratio and hence the sensitivity of base transceiver stations in
receiving the
radio signals transmitted by the mobile terminals, the stations can be
equipped with
cryogenic receiver front-ends.
As described in M.I. Salkola "CDMA Capacity- Can You Supersize That?",
2002 IEEE Wireless Communications and Networking Conference Record.
WCNC 2002 (Cat. No. 02TH8609) vol. 2 pp. 768-73, the application of cryogenic
receiver front-ends to the base transceiver stations has a direct impact on
the
3o performance of the mobile telephony network because it makes it possible to
increase its capacity.
Moreover, as described in D. Jedamzik; R. Menolascino; M. Pizarroso; B.
Salas; "Evaluation of HTS sub-systems for cellular base stations" 1999 IEEE
Transactions on Applied Superconductivity" vol. 9 no. 2 pt. 3 pp. 4022-5,
there are
two scenarios where an operator, in the case of a GSM-type network, can fmd
interesting the characteristics of base transceiver stations equipped with
front-ends
made with superconducting materials. These two scenarios correspond to a
coverage-limited scenario (low traffic cases where coverage is the limiting
factor)
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and a capacity-limited scenario (high traffic environment where the offered
traffic
is the limiting factor). The coverage-limited scenario corresponds to a rural
environment, where the greater sensitivity of base transceiver stations
equipped
with front-ends made with superconducting materials makes it possible to
obtain
an expansion of the coverage area of individual cells. The capacity-limited
scenario corresponds to an urban enviromnent, where the base transceiver
station
equipped with front-ends made with superconducting materials would allow a
tighter frequency reuse as a result of the better isolation between carries it
provides.
l0 For each of these two scenarios, two network designs are produced and
analyzed in a comparative manner. The first network design is totally composed
of
standard base transceiver stations and the second network design is totally
composed of base transceiver stations equipped with front-ends made with
superconducting materials.
Results are presented for a GSM-1800 type network. In particular, these
results show that the network operator can choose to employ different
advantages;
for example a reduction in the number of base transceiver stations in rural
areas by
24% or an increased capacity in urban areas, with a simultaneous reduction of
carriers by 30%.
2o However, the aforementioned paper fails to provide a well defined meaning
for the terms "urban" and "rural".
Moreover, the Applicant has observed that the advantages listed in the paper,
in particular for the urban area, are connected to the improved spectral
selectivity
of base transceiver stations equipped with front ends made with
superconducting
material with respect to standard base transceiver stations. An improved
spectral
selectivity is particularly significant in the case of a GSM network.
In the remainder of the present description and claims we shall define as high
sensitivity receiver front-end a front end having a total noise figure of less
than 2
dB, more preferably less than 1 dB, still more preferably less than 0.7 dB.
Preferably, the lugh sensitivity receiver front-end is mounted a short
distance from
the transceiver antenna. Preferably, the high sensitivity receiver front-end
comprises at least a filter and an amplifier mutually connected in cascade
arrangement. Preferably, the filter and the amplifier operate at cryogenic
temperatures. The filter preferably comprises superconducting materials.
The Applicant, however, has observed that if an operator has a number of
high sensitivity receiver front-ends that is lower than the number of cells
into
which the mobile telephony network is subdivided, the operator must be able to
select a criterion for positioning said receiver front-ends in such a way as
to
maximize network performance.
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Advantageously, the Applicant has found that according to a criterion for
positioning a smaller number of high sensitivity receiver front-ends than the
number of cells into which a network is subdivided, in such a way as to
maximize
the performance of the network itself, each cell of the network is preferably
assigned a first or a second category, based on a traffic expectation
constructed
from cartographic/morphological information so that the number of first
category
cells is approximately equal to the number of high sensitivity receiver front-
ends.
The Applicant has also observed that by positioning the high sensitivity
receiver
front-ends available to the operator substantially in all cells belonging to
the first
to category, the traffic collected by the network can be maximized.
More specifically, a method for optimizing the positioning of high sensitivity
receiver front-ends within a mobile telephony network 1 of the CDMA type
comprising a plurality of cells 2, includes the steps of: defining a first and
a second
cell indicator V~ell, V2; defining a first and a second threshold value L and
L2;
comparing said first cell indicator V~e» with a first threshold value L and
said
second cell indicator V2 with a second threshold value LZ; associating with a
first
category a plurality of first cells 2a, each of said first cells 2a having
said first cell
indicator V~ell greater than said first threshold value L or said second cell
indicator
Va greater than said second threshold value L2; positioning a plurality of
high
sensitivity receiver front-ends 5 substantially in all said plurality of first
cells Za.
The method according to the invention can further comprise the steps of
associating with a second category a plurality of second cells 2b, each of
said
second cells 2b having said first cell indicator V~e» smaller than said first
threshold
value L and said second cell indicator Va smaller than said second threshold
value
L2; positioning a plurality of low sensitivity receiver front-ends
substantially in all
said plurality of second cells 2b.
Advantageously, the step of defining for each cell 2 a first and a second cell
indicator V~~», V2 comprises the steps of associating with said first cell
indicator
V~e» cartographic/morphological characteristics indicative of a traffic
expectation
3o for each cell 2; associating with said second cell indicator V2
cartographic/morphological characteristics indicative of a traffic expectation
for
each cell 2 and of an expanse of geographic area whereon each cell 2 stands.
Moreover, the step of defining a first and a second threshold value L and L2
comprises the step of selecting a pair of values for said first and second
threshold
value L and L2 in such a way that said plurality of first cells 2a is
substantially
equal in number to said plurality of high sensitivity receiver front-ends 5
and that
said plurality of second cells 2b is substantially equal to the difference
between
said plurality of cells 2 and said plurality of first cells 2a.
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Advantageously, said pair of values comprises a first and a second value that
meet the condition whereby the ratio between said first value and said second
value is roughly equal to 1/15 ~ 0.005.
Another aspect of the present invention relates to a CDMA mobile telephony
network 1 comprising a plurality of cells 2. The plurality of cells 2 includes
a
plurality of first cells 2a associated to at least 90% of a plurality of high
sensitivity
receiver front-ends 5, each first cell 2a having a first cell indicator V~en
greater
than a first threshold value L or a second cell indicator VZ greater than a
second
threshold value.
to Moreover, the mobile telephony network 1 according to the invention
comprises a plurality of second cells 2b associated to a plurality of low
sensitivity
receiver front-ends, each second cell 2b having said frst cell indicator V~ell
smaller
than said first threshold value L and said second cell indicator V2 smaller
than said
second threshold value L2.
Advantageously, the first cell indicator V~ell is associated to
cartographic/morphological characteristics indicative of a traffic expectation
for
each cell 2 while the second cell indicator VZ is associated to
cartographic/morphological characteristics indicative of a traffic expectation
for
each cell 2 and of an expanse of geographic area whereon each cell 2 stands.
Furthermore, each high sensitivity receiver front-end 5 is inserted between a
transceiver antenna 4 and a base transceiver station 3.
In a preferred embodiment, the high sensitivity receiver front-end 5 is a
cryogenic receiver front-end.
In detail, the cryogeuc receiver front-end comprises a cryostat 11 that
encloses at least a band-pass type filter 12 and a low noise amplif er 13.
Preferably, the band-pass filter 12 is obtained with a technology based on
high
critical temperature superconducting materials.
According to an additional aspect of the present invention, each high
sensitivity receiver front-end 5 is inserted between a transceiver antenna 4
and a
base transceiver station 3, said high sensitivity receiver front-end 5
comprising at
least a first and a second band-pass filter 25, 26 between which is inserted a
low
noise amplifier 27.
The cryogenic receiver front-end 5 can be mounted along the antenna lead-in
in such a way as to minimize the overall noise figure of the receiver chain.
More preferably, the cryogenic receiver front-end 5 is mounted at such a
distance that losses due to antenna lead-in are negligible with respect to the
noise
figure introduced by the cryogenic receiver front-end 5.
Preferably, said cryostat 11 operates at cryogenic temperatures lower than
200 K, more preferably lower than 100 K.
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Moreover, preferably, the cryostat 10 operates at cryogenic temperatures
higher than 60 K.
In particular, the number of the plurality of cells 2 that form the mobile
telephony network 1 is greater than a predetermined value.
. Preferably, said predetermined value is greater than 100, more preferably it
is greater than 500, yet more preferably it is greater than 1000.
The characteristics and advantages of the present invention shall become
more readily apparent from the description, set out hereafter, of an
embodiment
provided purely by way of non limiting example with reference to the
accompanying drawings, in which:
- Figure 1 is a schematic representation of a best server portion of a W-
CDMA mobile telephony network;
- Figure 2 is a schematic representation of a preferred embodiment of a high
sensitivity receiver front-end for use in the network of Figure 1; and
- Figure 3 is a schematic representation of an additional embodiment of a
high sensitivity receiver front-end used in the network of Figure 1;
- Figure 4 shows a flow chart relating to the implementation of the method
according to the invention.
With reference to Figure 1, the method for optimizing the positioning of high
sensitivity receiver front-ends in a mobile telephony network according to the
invention is applied to a mobile telephony network 1, or to a portion thereof,
with
access of the CDMA type, and in particular of the W-CDMA or CDMA 2000 or
IJMTS type. For the sake of simplicity, Figure 1 does not show the so-called
soft
handover areas, because they are not essential for the purposes of the present
invention. hi particular, the term soft handover area means the area in which
a
mobile terminal simultaneously maintains active connections with more than one
cell.
More in detail, the mobile telephony network 1 comprises a plurality of cells
2 (for instance more than 100, preferably more than 500 and yet more
preferably
more than 1000). The network traffic present in each cell 2 is handled by a
base
transceiver station 3 (or B-node) for transmitting and/or receiving radio
signals
(voice and/or data) to/from mobile terminals, such as cellular telephones,
PDAs,
computers, etc. The base transceiver station 3 comprises a number of
transceiver
antennas 4 equal to the number of cells 2 that the station is to serve.
In the mobile telephony network 1 it is advantageous for the operator to be
able to position a number of high sensitivity receiver front-ends smaller than
the
plurality of cells 2, in order to maximize the performance of the network.
As Figure 2 shows, a high sensitivity receiver front-end 5 is typically
inserted between a transceiver antenna 4 and the base transceiver station 3.
More
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specifically, a receiver front-end is defined as having high sensitivity if
the overall
noise figure of the receiver chain from the transceiver antenna 4 to the base
transceiver station 3 is less than 2 dB, more preferably less than 1 dB, yet
more
preferably less than 0.7 dB. In a preferred embodiment, the high sensitivity
receiver front-end 5 comprises one or more devices operating at cryogenic
temperatures. In this case, the high sensitivity receiver front-end 5 will be
indicated as cryogenic receiver front-end. In detail, the cryogenic receiver
front-
end 5 comprises a first node 6 coupled to the transceiver antenna 4 and a
second
node 7 coupled to the base transceiver station 3. In detail, in the first node
6 the
to signal coming from the transceiver antenna 4 is split into two distinct
signals, a
transmission signal and a reception signal. In the second node 7 the two
transmission and reception signals present at the end of the two chains of
transmission and reception are rejoined. The resulting signal is then sent to
the
base transceiver station 3. Between the first and the second node 6, 7 are
inserted a
transmission branch 8 in which the transmission signal passes and a reception
branch 9 in which the reception signal passes. The transmission branch 8
comprises a transmission filter 10 while the reception branch 9 comprises a
cryostat 11 that encloses a band-pass filter 12 and a low noise amplifier
(LNA) 13,
mutually connected in cascade arrangement. Preferably, the cryostat 11
comprises
an additional band-pass filter 14. Alternatively, the band-pass filter 14 can
be
positioned outside the cryostat 11. Preferably, the band-pass filter 12 and
the
additional band-pass filter 14 are constructed with a technology based on High
critical Temperature Superconductors (HTS). Moreover, the cryostat 11 operates
at
cryogenic temperatures ranging between 60 K and 200 K and, more preferably,
between 60 K and 100 K.
The cryogenic receiver front-end 5 is preferably mounted at such a distance
from the transceiver antenna 4 that the losses due to the antenna lead-in are
negligible relative to the noise figure introduced by the receiver front-end
itself.
Preferably, said distance is no greater than 1 m. Less preferably, the
cryogenic
receiver front-end 5 can be placed in the most accessible position along the
antenna lead-in in such a way as to reduce in any case the overall noise
figure of
the receiver chain.
More in detail, a cryogenic receiver front-end and the process for its
manufacturing are described in US patent application 2002053215.
Advantageously, cryogenic receiver front-ends have a reduced noise figure
(no more than 2 dB, more preferably no more than 1 dB, yet more preferably no
more than 0.7 dB). By way of comparison, the noise figure of traditional base
transceiver stations usually exceed 2.5 dB.
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All this translates into an increase of from 1 dB to 10 dB of the sensitivity
of
the base transceiver station 3 with respect to the sensitivity of traditional
base
transceiver stations.
In a less preferred embodiment, shown in Figure 3, the high sensitivity
receiver front-end 5 (where the term "high sensitivity" in this case means a
noise
figure of less than 2 dB and more preferably less than 1.5 dB) is mounted at a
short
distance from the transceiver antenna 4 in order to avoid losses due to
antenna
lead-in (Tower Mounted Amplifier or TMA). The high sensitivity receiver front-
end 5 comprises a first node 20 coupled to the transceiver antenna 4 and a
second
to node 21 coupled to the base transceiver station 3. In the first node 20 the
signal
coming from the transceiver antenna 4 is split into two distinct signals, a
transmission signal and a reception signal. The second node 21 rejoins the
transmission and the reception signals present at the end of the two chains of
transmission and reception. The resulting signal is then sent to the base
transceiver
i5 station 3. Between the first and the second node 20, 21 are inserted a
transmission
branch 22 and a reception branch 23. The transmission branch 22 comprises a
transmission filter 24 while the reception branch 23 comprises a first and a
second
band-pass filter 25, 26 of a traditional type, between which is inserted a low
noise
amplifier 27 not operating at cryogenic temperatures.
2o The method according to the invention will now be described with reference
to the flow chart shown in Figure 4. In detail, the flow chart of Figure 4
represents
a classification algorithm CLASS that operates a classification at the level
of the
individual cells 2. Each cell 2 is defined as the set of pixels (elements of
territory,
typically having dimensions in the order of SOm x SOm) which, for a particular
25 type of service provided by the mobile telephony network 1, constitute the
best
server area of the transceiver antenna 4 serving that cell. In particular, the
term
"best server area" means the location of the pixels in which the transceiver
antemia
4 guarantees a field level necessary (electromagnetic requirement) for the
delivery
of that particular type of service and greater than the field level provided
by any
30 other bordering transceiver antenna.
It is important to note that the classification algoritlun CLASS makes use of
a pixel weighting factor pp which can assume a finite number of values (by way
of
indication, between 1 and 100) based on cartograpluclmorphological
information.
For each pixel, one has:
35 pp = MAX (Pd, Pm~Ps)
where:
pd is a factor that takes into account the built-up percentage of the pixel
(i.e. the
percentage of the surface of the pixel covered by constructions having a
height
exceeding 3 m) and it can assume, by way of indication, values included in the
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range 1-100;
pm is a factor that takes into account the morphology of the pixel and it can
assume. by wav of indication_ the valnPC chnwn in tahlP 1 cet not hPln~zm
T a of environment Value of factor pm
Urban 20
Suburban 15
Industrial area 10
Thickly wooded area 1
Thinly wooded area and meadow 2
with trees
O en area with vegetation and 2
damp areas
Bare area 1
Glacier 1
Water 2
TABLE 1
It is important to specify that, in this context, an enviromnent is considered
urban when buildings, roads, and artificially covered surfaces (buildings
whose
height is less than or equal to 3 m, parking lots, courtyards, streets, etc.)
occupy
more than 80% of the total surface considered. On the other hand, an
environment
is considered suburban when buildings, roads, and artificially covered
surfaces
to (low buildings, parking lots, etc.) occupy between 50% and 80% of the total
surface.
Additionally, ps is a factor that takes into account the presence of
communication infrastructures such as railroads, highways and thoroughfares
and
it can assume, by wav of indication_ the values shown in tahl~ 7. cPt n"t
hPlnw
Starting data item Value of ps
Highway 60
Highway + thoroughfare
Hi hway + thorou hfare + railroad
Thoroughfare 30
Thoroughfare + railroad
Railroad 20
is TABLE 2
For each cell 2 the Applicant has defined the following dimensions:
Np = number of pixels that make up an individual cell 2 (area of the
individual cell
2);
pp; = value assumed by the pixel weighting factor pp;
20 Np(pp;) = number of pixels for which the pixel weighting factor pp assumes
the
value pp;.
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Starting from the above dimensions, the Applicant has subsequently defined
a first and a second cell indicator, respectively V~elt and VZ, represented by
the
following expressions:
_ 1 loo
cell - N ~l-I PpiNp (Ppi)
P
1 100
100 ~-s PP=NP (Ppl )
where the first cell indicator V~en provides an evaluation normalized to the
area of
the value of the cell 2 considered in terms of factor pp and indicatively it
can
assume values within the 1-100 range, while the second cell indicator VZ
considers
in absolute sense, i.e. wholly independently from the dimensions of the area,
only
the values of the factor pp that exceed 2. The Applicant has observed that
values of
the factor pp that are smaller than or equal to 2 distinguish pixels with a
low level
of interest in terms of traffic potentially offered. The range of values
assmned by
this second cell indicator VZ, in the absence of normalization, cannot be
defined a
priori (except for the minimum value, which is 3).
The Applicant has also observed that high values of the first cell indicator
V~ell (in particular greater than or equal to 20) are associated to cells 2
with high
presence of elements that distinguish an urban terntory or with cells 2 with
morphological characteristics (highways, thoroughfares, railroads) that are
comparable in terms of traffic potentially offered (and hence, of traffic to
be
handled). However, normalization to the area tends to lower the value of the
first
cell indicator V~elt associated to the cells 2 which, while including some
pixels with
typically urban characteristics, have a rather extensive area, typical of
substantially
open areas.
The Applicant has thus introduced the second cell indicator V2, through
which values are assigned to the cells 2 that extend mainly on open areas but
also
include areas with small towns or segments of roads or railroads.
The Applicant has also observed that the combined use of these two cell
indicators V~e» and V2 assures an adequate classification of the cells 2.
With reference again to the flow chart of Figure 4, the classification
algorithm CLASS assigns to the cells 2 preferably a first and a second
category.
3o In particular, the first category comprises a plurality of first cells 2a
having
the first cell indicator V~el1 greater than a first threshold value L or the
second cell
indicator VZ greater than a second threshold value La, while the second
category
comprises a plurality of second cells 2b having the first cell indicator V~ell
smaller
than the first threshold value L and the second cell indicator V2 smaller than
the
second threshold value L2.
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The Applicant has observed that the first and the second threshold value L
and L2 can preferably be chosen from any pair of values that meets the
following
condition:
_L __ 1 ~ 0.005
LZ 15
The optimal pair of values will be the one for which the plurality of first
cells
2a is substantially equal (where the term "substantially" means more or less
10%)
to the plurality of high sensitivity receiver front-ends 5 available to the
operator.
Consequently, the plurality of second cells 2b will be substantially equal
(where
the term "substantially" means more or less 10%) to the difference between the
plurality of cells 2 that compose the mobile telephony network l and the
plurality
to of first cells 2a.
According to the method of the present invention, at least 90% of the
plurality of high sensitivity receiver front-ends 5 available to the operator
is then
associated to the plurality of first cells 2a belonging to the first category
while the
plurality of second cells 2b of the second category is equipped with low
sensitivity
receiver front-ends, where the term "low sensitivity" means that the overall
noise
figure exceeds 2.5 dB.
Hereafter, the performance of the mobile telephony network 1 is analyzed in
terms of offered traffic recovered (as a function of the expansion of the best
server
area) using the method according to the invention.
2o To perform this analysis, the Applicant considered a mobile telephony
network 1 able to cover a portion of the Italian territory. The considered
network
comprised a nmnber of cells 2 equal to 2171. The Applicant, moreover,
hypothesized that the number of high sensitivity receiver front-ends 5
available to
the operator was equal to 1208.
With regard to the geographic area examined, two distinct portions of the
territory were identified: the first one refers to a portion of territory
around a city
and the second one refers to a portion of terntory not including any cities.
The electromagnetic parameters (frequency, power, antenna) in use are those
of the UMTS standard
3o The Applicant then selected for the threshold values L and LZ the pair of
values (10, 150). Using this pair of values (10, 150) a subdivision of the
2171 cells
2 is achieved that assigns to the first category a number of first cells 2a
equal to
1208 (hence, equal to the number of high sensitivity receiver front-ends 5
available
to the operator) and to the second category a number of second cells 2b equal
to
963.
According to the method of the present invention, the 1208 first cells 2a are
then equipped with the high sensitivity receiver front-ends 5 (in this case,
the term
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"high sensitivity" means a noise figure of 0.7 dB) whilst the 963 second cells
2b
are equipped with low sensitivity receiver front-ends (in tlus case, "low
sensitivity" means a noise figure of 2.7 dB). The results obtained in terms of
offered traffic are shown in column 1 of table 3, set out below.
Offered
traffic
Erl)
Level of electromagneticHigh sensitivityHigh sensitivityHigh sensitivity
field receiver receiver receiver
dB~V/m front-ends 5 front-ends 5 front-ends 5
in the 1208 in 405 urban in 405 rural
cells 2 belongingsites (1188 cells)sites (983 cells)
to the
first cate or
41 29980 29857 29973
49 27668 27465 27562
57 23107 22867 22427
61 19502 19270 18544
67 13499 13367 12579
TABLE 3
It should be noted that the offered traffic is measured in Erlangs. In detail,
the Erlang is the measure of the mean daily traffic intensity which in terms
of
offered traffic corresponds to the mean number of potential connections
to simultaneously active.
Moreover, the offered traffic was calculated for best server areas referred to
five different types of service corresponding to five different levels of
electromagnetic field, set out below:
~ 41 dBp,V/m Voice 13 kb/s with earphone;
~ 49 dB~.V/m Voice 13 kb/s without earphone / in car with earphone;
~ 57 dB~,V/m Data 144 kb/s in car;
~ 61 dB~.V/m Data 64 kb/s indoors;
~ 67 dB~,V/m Data 384 kb/s indoors.
Columns 2 and 3 of Table 3 instead show the results obtained by applying to
the mobile telephony network 1 a classification algorithm that operates at
site level
(site being defined as the location of the pixels served by a single base
transceiver
station 3) and not at the level of individual cells 2 as is instead the case
for the
classification algoritlun CLASS. In particular, the sites are classified as
urban sites
and rural sites.
Operating on the same geographic area defined previously, the classification
of "urban" was assigned to all 405 sites, corresponding to a number of cells 2
equal to 1188, that are located within the portion of territory around the
city and
that of "rural" to the remaining 405 sites, corresponding to a number of cells
2
equal to 983, of the portion of terntory not including cities.
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The results shown in column 2 of Table 3 relate to the case in which all 40S
urban sites (i.e. all 1188 cells 2) are equipped with the high sensitivity
receiver
front-ends 4 whilst the 405 rural sites (i.e. all 983 cells 2) are equipped
with the
low sensitivity receiver front-ends.
The results shown in column 3 of Table 3 instead relate to the case in which
all 405 rural sites are equipped with the high sensitivity receiver front-ends
4
whilst all 40S urban sites are equipped with the low sensitivity receiver
front-ends.
As can be observed comparing the columns of Table 3, the increase in terms
of offered traffic obtained using the method according to the invention
depends on
l0 the field level considered. Comparing columns 1 and 2 of table 3, the
increase in
terms of monthly Erlangs ranges from a minimum of I23 Erl for the field level
of
4I dB~.V/m to a maximum of 240 Erl for the field level of 57 dB~,V/m.
On the other hand, comparing columns 1 and 3 of table 3, the increase in
terms of offered traffic obtained using the method according to the invention
ranges from a minimum of 7 Erl for the field level of 41 dB~.V/m to a maximum
of
958 Erl for the field level of 61 dB~,V/m.
In general, it can be stated that by applying the method according to the
invention to the mobile telephony network 1 an increase in the traffic offered
by
the entire network is obtained and hence an increase in the capacity of the
network
2o that ranges from a minimum of 7 Erl to a maximum of 958 Erl.
The Applicant has determined that the increase in offered traffic is
maintained substantially stable even varying by ~ 10% the pair of threshold
values
L and Lz and/or equipping with tha high sensitivity receiver front-ends 4 at
least
90% of the plurality of first cells 2a.
Moreover, it is important to specify that the increase in terms of offered
traffic was obtained using a band-pass filter 12 having a bandwidth of about
60
MHz. This means that the advantages highlighted herein are not linked to the
improved spectral selectivity of the base transceiver stations as stated by
Jedamzik
et al. in particular for the urban area. An improved spectral selectivity is
particularly significant in the case of a GSM network, like the one used for
the
simulations described in the article, where it is important to reduce
interference
due to the adjacent channels. In the case of a network of the CDMA type, and
in
particular of the UMTS type, like the mobile telephony network according to
the
invention, the advantages described above in terms of offered traffic are
independent and additional with respect to any advantages deriving from the
reduction of the interference due to the adjacent channels. In the example of
the
network 1 described, any adjacent channels are not eliminated by the band-pass
filter 12.
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The Applicant has also conducted an additional analysis in which the portion
of mobile telephony network 1 considered comprised a number of cells 2 equal
to
1188. In particular, the geographic area examined corresponds to a portion of
territory around a city. The Applicant has also hypothesized that the operator
had
available a number of high sensitivity receiver front-ends 4 equal to 10% or
to
50% or to 80% of the total number of cells 2 considered, i.e. equal to 119,
594 and
950 respectively. For each of the configurations considered, the Applicant
then
identified a. na.ir ~f threshe~ld values T, and T~° as shown in Table 4
set out below:
Threshold ValuesFirst configurationSecond configurationThird configuration
10% - 119 50% - 594 80% - 950
L 41.8 21.2 10.8
L2 627 318 162
TABLE 4
to In particular, using the pair of values (41.8; 627), a subdivision of the
1188
cells 2 is reached that assigns to the first category a number of first cells
2a equal
to 119 (hence equal to the number of high sensitivity receiver front-ends 5
available to the operator in this first configuration); using the pair of
values (21.2;
318), a subdivision of the 1188 cells 2 is reached that assigns to the first
category a
number of first cells 2a equal to 594 (equal to the number of high sensitivity
receiver front-ends 4 available to the operator in tlus second configuration);
using
the pair of values (10.8; 162) a subdivision of the 1188 cells 2 is reached
that
assigns to the first category a number of first cells 2a equal to 950 (equal
to the
number of high sensitivity receiver front-ends 5 available to the operator in
this
2o third configuration).
According to the method of the present invention, in the first configuration
the 119 first cells 2a identified axe then equipped with the high sensitivity
receiver
front-ends 5 available while the remaining 1069 second cells 2b are equipped
with
low sensitivity receiver front-ends; in the second configuration, the 594
first cells
2a identified are equipped with the available high sensitivity receiver front-
ends 4
while the 594 second cells 2b are equipped with low sensitivity receiver front-
ends; in the third configuration, the 950 first cells 2a identified are
equipped with
the high sensitivity receiver front-ends 4 available while the 238 second
cells 2b
are equipped with low sensitivity receiver front-ends.
3o It should be specified that the noise figure values for the high
sensitivity
receiver front-ends 5 and the low sensitivity receiver front-ends are the same
as
those used for the previously analyzed case.
The results obtained in terms of offered traffic are shown in Table 5 set out
below; the offered traffic was calculated for the five different types of
service
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corresponding to the five different levels of electromagnetic field considered
previously.
The comparison was conducted with the case in which all 1188 cells 2 are
equipped with low sensitivity receiver front ends (column 1) and with the case
in
which all 1188 cells 2 are equipped with high sensitivity receiver front-ends
(column 5).
Offered traffic (Erll
Level of 1188 cells 119 cells 594 cells 950 cells 1188 cells
2 2 2 2 2
electromagneticequipped equipped equipped equipped equipped
with with with with with
field low sensitivityhigh sensitivityhigh sensitivityhigh sensitivityhigh
sensitivity
dB~V/m receiver receiver receiver receiver receiver
front- front- front- front- front-
ends ends ends ends ends
41 20032 20042 20085 20150 20182
49 18951 18981 19099 19243 19314
57 15922 16097 16601 16882 16992
61 13287 13530 14191 14520 14637
67 9096 9317 I 9948 10284 I 10415
TABLE 5
1o Comparing column 1 with columns 2, 3, 4, and 5, one notes that for the
first
two levels of electromagnetic field, the increase in offered traffic obtained
with the
configurations 10%, 50%, 80% with respect to the gain in offered traffic
obtained
with the configuration in which all cells 2 are equipped with high sensitivity
receiver front-ends is smaller than the percentage of high sensitivity
receiver front
ends used.
In particular, for the level 41 dB~, V/m, with 10% of high sensitivity
receiver
front-ends installed the gain is 10 Erl corresponding only to 6.6% of the 150
Erl
gained by equipping all 1188 cells 2 with high sensitivity receiver front-
ends. Vice
versa for high field levels (corresponding to high-value service types) this
situation
2o is definitely inverted. In particular for the level 67 dB~, V/m, with 10%
of high
sensitivity receiver front-ends installed, the gain is already 16% of what
would be
obtained equipping all 1188 cells 2 with high sensitivity receiver front-ends.
Moreover, Table 6 shows the results obtained in terms of mean recovered
offered traffic (in Erlangs) per installed high sensitivity receiver front-
end.
Mean recovered offered traffic (Erll
Level of 1188 cells 119 cells 594 cells 950 cells 1188 cells
2 2 2 2 2
electromagneticequipped equipped equipped equipped equipped
with with with with with
field low sensitivityhi h sensitivityhigh sensitivityhi h sensitivityhigh
sensitivity
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dB~V/m receiver receiver receiver receiver receiver
front- front- front- front- front-
ends ends ends ends ends
41 0 0.080 0.089 0.124 0.126
49 0 0.250 0.249 0.307 0.306
57 0 1.471 1.143 1.010 0.901
61 0 2.047 1.523 1.299 1.137
67 0 1.857 1.435 1.251 1.111
TABLE 6
The data provided in Table 6 show that for high field levels the mean traffic
recovered per installed receiver front-end increases for configurations 10,
50, 80
with respect to the configuration with all lugh sensitivity receiver front-
ends
installed.
