COMBINER FILTER APPARATUS
This invention relates to combiner filter apparatus for transceivers and a
method of use thereof.
Although the following description refers almost exclusively to combiner
filter apparatus for use with transceivers in a wireless communications
network, it will be appreciated by persons skilled in the art that the combiner
filter apparatus of the present invention could be used with transmitters
and/or receivers alone and/or for use in any suitable application.
Mobile phone operators seek to minimise the capital expenditure (capex)
required to build a wireless network as well as minimise the ongoing
operating expenditure (opex). If an operator provides both 2G (2nd
generation mobile communication) and 3G (3rd generation mobile
communication) wireless network services then a way to reduce opex is for
the two networks to share a cell site.
An example of a typical cell site arrangement forming part of a wireless
telecommunications network is shown in figure 1. Such a cell site
arrangement has conventionally been used by a single mobile phone
operator, for a single frequency band and a single wireless network
technology (i.e., 2G or 3G services). The cell site includes a mast 5, at the
top of which is typically mounted an antenna 1 for transmitting and/or
receiving one or more radio frequency signals and optionally a tower
mounted amplifier 9 for amplifying the radio frequency signals. Antenna 1 is
connected via a feeder cable 11 to amplifier 9. A base transceiver station
(BTS) 7 is typically located at the base of the mast 5 and is connected via a
feeder cable 3 to amplifier 9. The BTS 7 typically includes a transceiver that
generates one or more radio frequency signals for transmission to a mobile
phone unit, as well as receiving one or more radio frequency signals from
the mobile phone unit.
In order to minimise capex, wherever possible the hardware relating to the
two different wireless technology service networks share the same cell site,
for example the 2G and 3G services of a particular operator share the same
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mast. If the 2G and 3G services are in different bands (for example 1800
MHz and 2100 MHz respectively), it is known to provide filter combiners
that can be used at the base of the mast to combine signals onto a common
antenna system. Figure 2 shows an example of a typical cell site arrangement
including two BTSs 13, 15 for providing 2G and 3G network services
respectively, each BTS operating in a different radio frequency band. As
previously described, the cell site includes a mast 5 with an antenna 1 and
optionally an amplifier 9 mounted adjacent the top of the mast. The two
BTSs 13, 15 are provided at the base of the mast. In this example, BTS 13
operates at a frequency of 2100MHz and BTS 15 operates at a frequency of
1800MHz. The BTSs 13, 15 are connected via cables 17 to a filter combiner
19 that allows the two BTSs to share common antenna 1. The filter
combiner 19 is connected via cable 3 to the tower mounted amplifier 9 but
could be connected directly to antenna 1. The filter combiner 19, as shown
in figure 4, typically comprises a housing 16 having an antenna port 18 for
connection to antenna 1 or amplifier 9, a first port 20 for connection to the
BTS 15 operating within the 1800MHz frequency band and a second port
22 for connection to the BTS 13 operating within the 2100MHz frequency
band. Filter combiner 19 includes two filters 37, 39, one filter for each radio
frequency band 1800MHz and 2100MHz respectively. An end of the
1800MHz filter 37 is connected to a port of the BTS 13 and an end of the
2100MHz filter 39 is connected to the port of the BTS 15. The opposite
ends of filters 37, 39 are multiplexed together to provide a common signal
path connected to port 18. Each of the filters 37, 39 pass both the transmit
(Tx) and receive (Rx) frequency signals of the respective band through the
same.
Figure 3 shows the signal transmission loss versus the frequency response of
the conventional filter combiner 19 in figure 2. The pass band 21 of the
1800MHz filter 37 is a single contiguous block of spectrum that covers both
the receive (Rx) and transmit (Tx) frequencies from the 1800 MHz band.
The pass band 23 of the 2100MHz filter 39 is a single contiguous block of
spectrum that covers both the receive (Rx) and transmit (Tx) frequencies
from the 2100MHz band.
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Traditionally, mobile phone networks have been independently deployed by
each mobile phone operator resulting in several networks running in parallel
within a particular country. Recently, regulators have allowed and
encouraged mobile phone operators to share portions of their network
infrastructure with each other in order to reduce costs, promote network
roll out and hence improve both network coverage and capacity. A similar
arrangement to that shown in figures 2 -4 can be used for different mobile
phone operators with BTSs operating at different frequencies to achieve
network infrastructure sharing between operators.
Mobile phone networks operate in several regulated bands. For example, in
India services are currently run in the 850 MHz, 900MHz, 1800MHz,
2100MHz and 2300 MHz bands. Within each band, mobile phone systems
use the frequency division duplex (FDD) technique whereby a block of
spectrum is assigned to BTS transmission and a separate block of spectrum,
non-contiguous with the first, is assigned to BTS reception. Typically, the
transmit block of spectrum is higher in frequency than the receive block of
spectrum. The transmit and receive spectrum blocks are subdivided and
allocated in paired spectrum blocks to individual operators. For example, if
operators A and B own spectrum in the same band and operator A’s
spectrum is higher in frequency than operator B’s spectrum, then operators
A’s receive sub band will lie between operator B’s receive and transmit sub
bands. Conventional filter combiners that allow sharing of an antenna
system for base stations that operate in different frequency bands such as
900MHz and 1800MHz, do not allow for the situation of multiple BTSs
operating in the same frequency band sharing a single antenna system.
One solution to the above problem is to use hybrid combiners or 3dB
combiners. Such combiners are broad band, do not include any filtering
means and do not have frequency specific paths within them. However, they
have a significant disadvantage in that they dissipate half (3dB) of the signal
power that passes through them. This is extremely inefficient and
significantly impacts the coverage and capacity of a cell site. An example of a
cell site arrangement using a hybrid combiner is described with reference to
figures 5 and 6.
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The cell site in figure 5 comprises two BTSs 13, 25 operating in the same
frequency band, which in this example is 2100MHz, and which share the
same mast 5, antenna 1 and amplifier 9 arrangement. The BTSs 13, 25 are
connected via cables 17 to a hybrid combiner 27. The hybrid combiner 27 in
turn is connected via a cable 3 to the amplifier 9. The hybrid combiner 27
has two paths; one for each operator and each covering both Receive (Rx)
and Transmit (Tx) signals providing a single pass band response 29, as
shown in figure 6. The signal transmission loss versus frequency response of
the two paths is substantially similar and the transmission loss is greater than
3dB in the 2100MHz band. This means that over half of the power of any
Tx signal that passes through the hybrid combiner 27 is dissipated within it
and the power of any Rx signal that passes through the hybrid combiner is
split in half.
It is therefore an aim of the present invention to provide combiner filter
apparatus that overcomes the above mentioned problems.
It is a further aim of the present invention to provide a method of using
combiner filter apparatus that overcomes the above mentioned problems.
According to a first aspect of the present invention there is provided
combiner filter apparatus for use in a wireless communication system, said
apparatus including first filtering means and at least second filtering means,
an end of the first filtering means multiplexed to an end of the at least
second filtering means to allow connection of the system to a common
antenna system in use, characterised in that each of said first and at least
second filtering means includes at least two filters connected in parallel to
provide at least two non-contiguous pass bands associated with each of the
filtering means.
An advantage of providing combiner filter apparatus where each filter
means or path through the apparatus has at least two non-contiguous pass
bands is that FDD BTSs operating in the same frequency band can be
combined onto a single antenna system in a low loss manner.
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Thus, in the prior art, combiner filter apparatus typically includes a single
filter in each path of the apparatus. For conventional combiner filter
apparatus having two paths defined therethrough for filtering two different
frequency bands, each path having a single filter, this generates two pass
bands; one pass band per path. Each pass band covers both the transmit
and receive frequencies. This is in contrast to the combiner filter apparatus
of the present invention, wherein at least two filters are provided in parallel
per path of the apparatus. For combiner filter apparatus of the present
invention having two paths defined therethrough for filtering radio
frequency signals in the same frequency band, of for example two different
operators, each path having at least two filters connected in parallel, this
generates four pass bands; two non-contiguous pass bands per path. Each
pass band represents the transmit or receive frequencies of a particular
frequency band or operator.
The term filter and/or filtering means used herein refers to any suitable
filtering device which allows transmit and/or receive signals of one or more
frequencies or frequency ranges to pass through it but which attenuates
signals of at least one or more other frequencies or frequency ranges to a
significantly greater extent. In one example, the filter and/or filter means is a
band pass filter.
Preferably, the filters are tuned such that at least one of the pass bands of
the first filtering means lies between at least two of the pass bands of the
second filtering means.
Further preferably the passband associated with the transmission
frequencies of the first filter means lies between the passbands associated
with the receiver and transmission frequencies of the second filter means.
Preferably each of the first and at least second filtering means includes a pair
of filters connected together in parallel.
In one embodiment the wireless communication system includes one base
transceiver station (BTS), a mast and an antenna system. The combiner filter
apparatus of the present invention can allow two different operators to
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share the same BTS, mast and antenna system using the same frequency
band.
In a further embodiment the wireless communication system includes at
least two base transceiver stations (BTSs), a mast and an antenna system.
The combiner filter apparatus of the present invention can allow a single
operator to share two different technologies provided by the two BTSs (i.e.
2G and 3G) using the same mast, antenna system and using the same
frequency band, or two operators to share two BTSs using the same mast,
antenna system and frequency band.
The combiner filter apparatus is preferably provided between the at least
one BTS and the antenna system. The antenna system can include antenna
means and optionally amplifier means.
In one embodiment of the present invention in use, the apparatus is
arranged to allow any or any combination of a first transmit signal to travel
from a first BTS, through the first filtering means and through a multiplexed
junction to antenna means provided as part of the wireless communications
system; a first receive signal travels from the antenna means through the
multiplexed junction and through the first filtering means to the first BTS; a
second transmit signal travels from a second BTS, through the second
filtering means and through the multiplexed junction to the antenna means;
a second receive signal travels from the antenna means through the
multiplexed junction and through the second filtering means to the second
BTS.
In one embodiment the combiner filter apparatus is provided in a housing
and further preferably in a single housing. The housing is typically formed of
such material to allow the same to be weatherproof and to withstand
external environmental conditions, such as heat, cold, rain, snow and/or the
like.
In one embodiment the housing and/or apparatus can be attached,
detachably attached to or integrally formed with an antenna, antenna means,
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mast on which the antenna means is mounted and/or the like, with which
the combiner filter apparatus is used.
In one embodiment the combiner filter apparatus is provided with
mounting means for mounting the apparatus to a suitable support structure.
The support structure could be an equipment rack, a mast, tower a suitable
surface of a building and/or the like. The mounting means could include
any or any combination of suitable mounting means such as one or more
brackets, nuts, bolts, screws, jubilee clips and/or the like.
In one embodiment the apparatus includes further filtering means that allow
further BTSs operating in the same frequency band to share the common
antenna means or system.
In one embodiment the apparatus includes further filtering means that allow
BTSs operating in different frequency bands to share the common antenna
means or system.
The combiner filter apparatus typically has at least two transmit/receive
ports and a common port. The at least two transmit/receive ports typically
allow connection of the first and at least second filtering means to first and
at least second BTSs, and the common port typically allows connection of
the multiplexed end of the first and at least second filtering means to the
common antenna system. The first filtering means typically has a first end
coupled to a transmit/receive port and a second end or multiplexed end
coupled to the common port. The at least second filtering means typically
has a first end coupled to a transmit/receive port and a second end or
multiplexed end coupled to the common port. The coupling of the first and
at least second filtering means to the transmit/receive port and/or the
common port could take place via a common junction, common
transformer and/or the like.
In one embodiment the filters within each filtering means are multiplexed
together and the first and at least second filtering means are then
multiplexed together. In an alternative embodiment the filters of each
filtering means are multiplexed together.
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In one embodiment the combiner filter apparatus is a dual or multi- unit in
that there are at least two separate or independent pairs of filtering means.
For example, the dual unit could include the first and second filtering means
to form a first pair of filtering means and could include third and fourth
filtering means to form a second pair of filtering means. Each filtering
means typically includes at least two filters connected together in parallel.
According to a second aspect of the present invention there is provided a
method of using combiner filter apparatus forming part of a wireless
communications system, said combiner filter apparatus including first
filtering means and at least second filtering means, an end of the first
filtering means multiplexed to an end of the at least second filtering means,
said method including the steps of transmitting and/or receiving signals
through the first filtering means and/or at least second filtering means,
characterised in that each of said first and at least second filtering means
includes at least two filters connected in parallel to provide at least two noncontiguous
pass bands per filtering means.
Preferably each filter within the first and at least second filtering means is
tuned to the required receive and transmit frequency of the sub-pass bands.
According to a yet further aspect of the present invention there is provided
a cell site arrangement including combiner filter apparatus.
A detailed embodiment of the present invention will now be described with
reference to the accompanying figures, wherein:
Figure 1 (PRIOR ART) shows an example of a typical prior art cell site
arrangement forming part of a wireless communication system;
Figure 2 (PRIOR ART) shows an example of a typical prior art cell site
arrangement including two BTSs, each BTS operating in a different
frequency band, sharing a single antenna system, using a conventional filter
combiner;
Figure 3 (PRIOR ART) shows the signal frequency response versus signal
transmission loss of the conventional filter combiner in figure 2;
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Figure 4 (PRIOR ART) is a simplified block diagram showing the
conventional filter combiner in figure 2;
Figure 5 (PRIOR ART) shows an example of a typical prior art cell site
arrangement including two BTSs, each BTS operating in the same frequency
band, sharing a single antenna system, using a conventional hybrid
combiner;
Figure 6 (PRIOR ART) shows the signal frequency response versus signal
transmission loss of the conventional hybrid combiner in figure 5;
Figure 7 (PRESENT INVENTION) shows an example of a typical cell site
arrangement including two BTSs, each BTS operating in the same frequency
band, sharing a single antenna system, using combiner filter apparatus of the
present invention;
Figure 8 (PRESENT INVENTION) shows the signal frequency response
versus signal transmission loss of the combiner filter apparatus in figure 7;
and
Figure 9 (PRESENT INVENTION) is a simplified block diagram showing
the combiner filter apparatus of the present invention.
Referring to figures 7-9, there is illustrated an embodiment of the present
invention that uses combiner filter apparatus 31 in a cell site arrangement of
a wireless mobile network to allow two base transceiver stations (BTSs) 13,
25 operating at the same radio frequency band, which in this example is
2100MHz, to share the same common mast 5, antenna 1 and amplifier 9.
For example, BTS 13 could be owned by a first mobile phone operator A
and BTS 25 could be owned by a second mobile phone operator B.
In particular, figure 7 shows a cell site including a mast 5, at the top of
which is mounted an antenna 1 for receiving and/or transmitting one or
more radio frequency signals therefrom and optionally an amplifier 9 for
amplifying the one or more radio frequency signals. The antenna 1 is
connected to amplifier 9 via a feeder cable 11. A feeder cable 3 connects the
amplifier 9 to one end of the combiner filter apparatus 31. If the amplifier is
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not provided, feeder cable 3 connects antenna 1 to the combiner filter
apparatus 31. Feeder cables 17 connect the combiner filter apparatus 31 to
the two BTSs 13, 25.
Figure 9 shows a simplified block diagram of the combiner filter apparatus
31 of the present invention. The apparatus 31 includes a housing 49 having
a common antenna port 51 which allows apparatus 31 to be connected to
amplifier 9 or antenna 1 via cable 11, a port 53 to allow apparatus 31 to be
connected to operator’s A BTS 13 via cable 17 and a port 55 to allow
apparatus 31 to be connected to operator’s B BTS 25.
The combining apparatus includes first filtering means in the form of a first
pair of filters 41, 43, for filtering the 2100MHz band signals for operator A
and second filtering means in the form of a second pair of filters 45, 47 for
filtering the 2100MHz band signals for operator B. The filters comprising
each filter pair are connected together in parallel.
The filter pair for operator A has filter 41 for passing the frequencies
corresponding to the receive sub band of operator A and filter 43 for
passing the frequencies corresponding to the transmit sub band of operator
A.
The filter pair for operator B has filter 45 for passing the frequencies
corresponding to the receive sub band of operator B and filter 47 for
passing the frequencies corresponding to the transmit sub band of operator
B. Thus, the combiner filter apparatus 31 allows two different mobile phone
operators that are running wireless mobile services in the same frequency
band to share a common antenna system (antenna 1) and cell site.
Figure 8 shows the transmission loss versus the frequency response of the
combiner filter apparatus 31. It can be seen from figure 8 that the result of
providing two pairs of filters connected together in parallel is that two
resulting pass bands 33, 33’ corresponding to the receive (Rx) and transmit
(Tx) bands of the first pair of filters 41, 43 respectively form two separate
non-contiguous blocks of spectrum that cover paired spectrum from within
the receive and transmit spectrum blocks of the 2100MHz band for
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operator A. The two resulting pass bands 35, 35’ of the second pair of filters
45, 47 respectively form two separate non-contiguous blocks of spectrum
that cover paired spectrum from within the receive and transmit spectrum
blocks of the 2100MHz band for operator B. Thus, the pass bands of the
two filtering pairs for the two different operators A and B are interleaved.
The transmission loss of the filters 41-47 is low, typically a few tenths of a
dB. This is a significant improvement compared to the transmission loss of
the hybrid combiner, shown in figure 6.
Thus, it can be seen that the combiner filter apparatus of the present
invention results in one pair of pass bands to cover the paired spectrum
owned by one operator and another pair of pass bands to cover the paired
spectrum owned by a different operator, thus allowing the two operators to
share an antenna system in a low loss manner.
In the event of a network operator requiring one or more further BTSs to
share the antenna system, it is possible to add additional filtering means to
allow this.
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Claims:
1. Combiner filter apparatus for use in a wireless communication
system, said apparatus including first filtering means and at least
second filtering means, an end of the first filtering means multiplexed
to an end of the at least second filtering means to allow connection of
the apparatus to a common antenna system in use, characterised in
that each of said first and at least second filtering means includes at
least two filters connected in parallel to provide at least two noncontiguous
pass bands associated with each filtering means.
2. Combiner filter apparatus according to claim 1 characterised in that
the filters are band pass filters.
3. Combiner filter apparatus according to claim 1 characterised in that
the filters are tuned such that one of the pass bands of the first
filtering means lies between at least two pass bands of the at least
second filtering means.
4. Combiner filter apparatus according to claim 3 characterised in that
the passband associated with the transmission frequencies of the first
filter means lies between the passbands associated with the receiver
and transmission frequencies of the at least second filter means.
5. Combiner filter apparatus according to claim 1 characterised in that
each of the first and at least second filtering means includes a pair of
filters connected together in parallel.
6. Combiner filter apparatus according to claim 1 characterised in that
the wireless communication system in which the apparatus is used
includes at least one base transceiver station, a mast and an antenna
system.
7. Combiner filter apparatus according to claim 1 characterised in that
the wireless communication system in which the apparatus is used
includes at least two base transceiver stations, a mast and an antenna
system.
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8. Combiner filter apparatus according to claim 6 or 7 characterised in
that the apparatus is connected between the base transceiver
station(s) and the antenna system.
9. Combiner filter apparatus according to claim 1 characterised in that
the apparatus is arranged to combine radio frequency signals of the
same frequency band.
10. Combiner filter apparatus according to claim 1 characterised in that
the apparatus allows any or any combination of a first transmit signal
to travel from a first base transceiver station, through the first
filtering means and through a multiplexed junction to antenna means
provided as part of the wireless communications system; a first
receive signal to travel from the antenna means through the
multiplexed junction and through the first filtering means to the first
base transceiver station; a second transmit signal to travel from a
second base transceiver station, through the second filtering means
and through the multiplexed junction to the antenna means; a second
receive signal to travel from the antenna means through the
multiplexed junction and through the second filtering means to the
second base transceiver station.
11. Combiner filter apparatus according to claim 1 characterised in that
the apparatus is provided in a housing.
12. Combiner filter apparatus according to claim 1 characterised in that
the apparatus is attached, detachably attached or integrally formed
with an antenna, antenna means or mast on which the antenna means
is mounted on and which is used with the apparatus.
13. Combiner filter apparatus according to claim 1 characterised in that
the apparatus is provided with mounting means for mounting the
apparatus to a suitable support structure in use.
14. Combiner filter apparatus according to claim 13 characterised in that
the mounting means includes any or any combination of one or more
brackets, nuts, bolts, screws or jubilee clips.
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15. Combiner filter apparatus according to claim 1 characterised in that
the apparatus includes further filter means to allow the apparatus to
be used with further base station transceivers operating in the same
and/or different frequency bands to allow sharing of a common
antenna system.
16. Combiner filter apparatus according to claim 1 characterised in that
the apparatus includes at least two transmit/receive ports and a
common port.
17. Combiner filter apparatus according to claim 1 characterised in that at
least two separate or independent pairs of filtering means are
provided as part of the apparatus.
18. A method of using combiner filter apparatus forming part of a
wireless communication system, said combiner filter apparatus
including first filtering means and at least second filtering means, and
end of the first filtering means multiplexed to an end of the at least
second filtering means, said method including the steps of
transmitting and/or receiving signals through the first filtering means
and/or at least second filtering means, characterised in that each of
said first and at least second filtering means includes at least two
filters connected in parallel to provide at least two non-contiguous
pass bands per filtering means.
19. A cell site arrangement for a wireless communication system
including a combiner filter apparatus according to claim 1.
Dated this 29th day of July, 2013
SAMUEL NIRANAJAN C.J.
OF K & S PARTNERS