U.S. patent application number 13/347206 was filed with the patent office on 2012-05-03 for antenna device for a radio base station in a cellular telephony system.
Invention is credited to Ulrika Engstrom, Martin Johansson, Sven Petersson.
Application Number | 20120108297 13/347206 |
Document ID | / |
Family ID | 36615200 |
Filed Date | 2012-05-03 |
United States Patent
Application |
20120108297 |
Kind Code |
A1 |
Petersson; Sven ; et
al. |
May 3, 2012 |
ANTENNA DEVICE FOR A RADIO BASE STATION IN A CELLULAR TELEPHONY
SYSTEM
Abstract
The invention discloses an antenna device for a radio base
station in a cellular telephony system, which comprises a first and
a second input connection for a first (D1) and a second (D2) data
stream, and a first and a second polarization former, one for each
of said data streams. The device also comprises a first and a
second antenna of respective first and second polarizations, and
one amplifier each. The device also comprises a first and a second
combiner, so that the outputs from the polarization formers may be
combined as input to each of the first and second antennas.
Inventors: |
Petersson; Sven; (Savedalen,
SE) ; Johansson; Martin; (Molndal, SE) ;
Engstrom; Ulrika; (Goteborg, SE) |
Family ID: |
36615200 |
Appl. No.: |
13/347206 |
Filed: |
January 10, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11722993 |
Jun 27, 2007 |
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PCT/SE2004/002040 |
Dec 30, 2004 |
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13347206 |
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Current U.S.
Class: |
455/562.1 |
Current CPC
Class: |
H03F 3/24 20130101; H01Q
1/246 20130101; H01Q 23/00 20130101; H01Q 21/245 20130101; H04B
7/10 20130101; H04B 7/0617 20130101; H04B 7/0413 20130101; H04B
2001/0408 20130101; H04B 7/0408 20130101 |
Class at
Publication: |
455/562.1 |
International
Class: |
H04W 88/00 20090101
H04W088/00 |
Claims
1. An antenna device for a radio base station in a cellular
telephony system, the device comprising a first and a second input
connection for a first and a second data stream; a first and a
second polarization former, one for each of said data streams; and
a first and a second antenna of respective first and second
polarizations, the antennas also comprising one amplifier each,
wherein the device additionally comprises a first and a second
combiner, so that the outputs from the polarization formers may be
combined as input to each of the first and second antennas.
2. The antenna device of claim 1, in which each of the first and
second antennas each comprise at least one radiation element which
have the same phase centers.
3. The antenna device of claim 1, in which each of the first and
second polarization formers deliver two outputs, which can then be
combined as input to said first and second antennas.
4. The device of claim 1, in which said polarization formers can
split an incoming data stream into two data streams and output said
two data streams with a phase difference between them, a first of
said data streams being used as input to a first of said combiners,
and a second of said data streams being used as input to a second
of said combiners.
5. The antenna device of claim 1, in which at least one of the
first or second antennas additionally comprises at least one more
radiation element of the same polarization as the first antenna
element of that antenna, the device additionally comprising a beam
former for that antenna, said beam former being connected by its
outputs to at least two of the radiation elements in said antenna,
said beam former using as its input one of said data streams output
from said polarization formers.
6. The device of claim 5, in which said beam former can split an
incoming data stream into two data streams and output said two data
streams with a phase difference between them, a first of said data
streams being used as input to a first of said combiners, and a
second of said data streams being used as input to a second of said
combiners
7. The antenna device of claim 4, additionally comprising input
connections for at least a third data stream, the device also
comprising a first additional beam former for said at least third
data stream, said input connection connecting the data stream to
said first additional beam former, the outputs from said beam
former being used as input to at least two of said combiners.
8. The device of claim 7, also comprising an additional
polarization former for said at least third data stream, as well as
a second additional beam former for said at least third data
stream, said third data stream being used as input to said
additional polarization former, a first output of which is used as
input to the first additional beam former and a second output of
which is used as input to the second additional beam former.
9. The device of claim 1, wherein the first polarization is of a
different polarization as the second polarization.
10. The device of claim 9, wherein the first polarization and the
second polarization are orthogonal to each other.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 11/722,993, filed Jun. 27, 2007, which was the National Stage
of International Application No. PCT/SE2004/002040, filed Dec. 30,
2004, the disclosures of which are incorporated herein by
reference.
TECHNICAL FIELD
[0002] The present invention discloses an antenna device for a
radio base station in a cellular telephony system. The device
comprises a first and a second input connection for a first and a
second data stream, and a first and a second polarization former,
one for each of said data streams, as well as a first and a second
antenna of respective first and second polarizations.
BACKGROUND ART
[0003] In known radio base stations for cellular telephony
networks, there is a number of so called radio chains, each radio
chain comprising a power amplifier, which may itself be comprised
of a number of amplifiers which are connected so as to have a
common input port and a common output port. Each radio chain will
typically also comprise one or more antenna elements, which may be
a part of a larger antenna with more antenna elements, such as an
electrically steerable array antenna.
[0004] In future radio base stations, it would be an advantage if
the stations could support both so called BF-transmission (beam
forming), where typically one data stream is transmitted to each
user, as well as so called MIMO-transmissions (Multiple Input,
Multiple Output), where a plurality of data streams are transmitted
to each user.
[0005] The antenna requirements for BF-transmissions are quite
different from those of MIMO-transmissions, so a conventional way
of designing a radio base station which would be capable of both
would be to have separate antennas for each case, as well as
separate radio chains for each antenna or a switching device
between the power amplifier resource and the antennas.
[0006] Since MIMO and BF would typically not be used
simultaneously, this design would lead to a radio base station with
poor usage of power amplification resources, as well as a radio
base station with quite voluminous equipment, neither of which is
desirable.
DISCLOSURE OF THE INVENTION
[0007] As discussed above, there is a need for an antenna device
for a radio base station in a cellular telephony system that could
be used in a versatile fashion for either MIMO or BF, or possibly
both at the same time.
[0008] This need is addressed by the present invention in that it
discloses an antenna device for a radio base station in a cellular
telephony system, comprising a first and a second input connection
for a first and a second data stream, and a first and a second
polarization former, one for each of said data streams.
[0009] The device of the invention also comprises a first and a
second antenna of respective first and second polarizations, as
well as one amplifier for each of the antennas. The device
additionally comprises a first and a second combiner, so that the
outputs from the polarization formers may be combined as inputs to
each of the first and second antennas.
[0010] Suitably, each of the first and second antennas each
comprise one or more radiation elements which can have the same
phase center.
[0011] By means of the invention, as will become more apparent from
the following detailed description, a more efficient use of the
amplifiers is made possible, due in part to the use of the
polarization formers and the combiners of the device.
[0012] Since antennas of different polarizations are used for
transmitting one and the same signal, as will be explained in more
detail in the following, the signals will be combined in the air
after transmission into resulting polarizations. In this way, the
signal losses associated with more traditional types of signal
combining are avoided.
[0013] Beamforming can also be carried out in certain embodiments
of the device of the invention, since, in said embodiments, at
least one of the first or second antennas additionally comprises at
least one more radiation element of the same polarization as the
first antenna element of that antenna, the device additionally
comprising a beamformer for that antenna.
[0014] Thus, by means of the invention, either beamforming or MIMO
transmission, or possibly both, can be carried out by means of the
same physical equipment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The invention will be described in more detail in the
following, with reference to the appended drawings, in which:
[0016] FIGS. 1 and 2 show background art, and
[0017] FIG. 3 shows different polarizations and their combinations,
and
[0018] FIG. 4 shows a basic embodiment of an antenna device,
and
[0019] FIG. 5 shows a first basic embodiment of the invention,
and
[0020] FIGS. 6-9 show various embodiments of the invention which
utilize beam forming.
EMBODIMENTS
[0021] FIG. 1 shows a system 100 which serves to illustrate some of
the components used in the invention: a data stream D1 is to be
transmitted to a user of a cellular telephony network. In order to
achieve this, the device 100 comprises a first antenna 130, in this
case comprised of a single antenna element of a certain
polarization, in this case vertical polarization, as indicated in
the drawing. The single antenna element 130 may be replaced by more
antenna elements of the same polarization, but will here be shown
and referred to as a single element.
[0022] The antenna element 130 is associated with a power amplifier
120, in order to amplify the signal to a desired level before the
transmission. As indicated by a dashed line, the antenna 100 might
also comprise more radiation elements, suitably of another
polarization. In this case, since no such additional antenna
elements are comprised in the antenna, the dashed line is
terminated with a "0". These additional antenna elements may, in
similarity to the antenna element 130, also be replaced by more
antenna elements of the same polarization, but will here be shown
and referred to as a single element.
[0023] The device 100 also comprises a so called Polarization
Former (PF) 110, which serves to shape the composite polarization
of the transmitted signal if the antenna comprises antenna elements
of different polarizations. Since the antenna of FIG. 1 only
comprises a single antenna element, the PF essentially serves no
function in the device shown, but is still shown in the
drawing.
[0024] As indicated, however, the PF can divide the incoming data
stream, in this case D1, between antenna elements of different
polarizations, and then subject the divided data streams to a
multiplication function which will be elaborated upon later in this
description. In the present case, the data stream which would go to
the "non-existent" antenna element at the end of the dashed line is
multiplied by zero.
[0025] In conclusion, the entire data stream D1 in FIG. 1 is
transmitted by the vertically polarized antenna element 130, after
being amplified by a power amplifier 120.
[0026] For the sake of clarity, FIG. 2 shows how a second data
stream, D2, is transmitted by means of a device 200 similar to the
device 100 of FIG. 1: all of the components of the device 100 are
present in the device 200, so they will not be described at depth
again here. However, the antenna element 230 of the device 200 is
of a different polarization than the one in FIG. 1, in this case
the polarization is horizontal. Accordingly, D2 is transmitted with
horizontal polarization from the antenna 230 after having been
amplified by a power amplifier 220.
[0027] FIG. 3 illustrates the effect of transmitting signals of
different polarizations simultaneously: a first signal is
transmitted with vertical polarization ("V"), and a second signal
is transmitted with horizontal polarization ("H"). If the two
signals are transmitted "in phase", i.e. with no phase shift
between them, the composite signal as seen by a viewer who is
standing in front of and looking at the antenna will be combined
into the polarization referred to as "X" and shown as
+45.degree..
[0028] However, if a phase shift of 180.degree. is introduced into
one of the signals, e.g. the signal which is transmitted with
horizontal polarization, the composite signal seen in the same
"front view" as described above will be combined into the
polarization referred to as "Y", and shown as -45.degree..
[0029] It should be pointed out that the two polarizations
described here, i.e. horizontal and vertical, are merely examples:
any two polarizations may be used, and the two polarizations used
need not be orthogonal to each other, although this is preferred.
Also, the phase shifts introduced need not be
0.degree./180.degree., if other composite polarizations are
desired, other phase shifts which will give the desired composite
polarizations may be used, e.g. 0.degree./+90.degree., giving
circular polarization.
[0030] Thus, as seen in FIG. 3, by introducing a phase shift in one
of two signals transmitted in different polarizations, any desired
resulting polarization may be achieved.
[0031] FIG. 4 shows a basic embodiment of an antenna device 400 of
the invention: the main difference between the device 400 shown in
FIG. 4 and the devices 100, 200, shown previously is that the
device 400 comprises an antenna with two radiation elements 430,
432.
[0032] As with the previous example, each of the two antenna
elements 430, 432, may also symbolize a larger number of elements
of the same polarization. This will be true of other embodiments
shown and described later in this text as well--one antenna
elements may symbolize a larger number of elements.
[0033] The first antenna element is vertically polarized, and the
second antenna element 432 is horizontally polarized, but the two
antenna elements have the same phase center.
[0034] A general principle which applies to a device of the
invention can be pointed out here: In order to create a certain
desired resulting polarization using two antennas of different
inherent polarizations, there must be a desired phase relation
between the signals transmitted by the antennas. One condition for
achieving this is that the two antenna elements have the same phase
center.
[0035] The device also comprises one power amplifier 420, 422, per
radiation element and polarization in the antenna. Thus, in this
example, there are two power amplifiers.
[0036] The device 400 also comprises the polarization forming (PF)
device 410 shown previously. The PF-device shown in FIG. 4 divides
the incoming data stream D1 into two equal streams, each of which
is to be transmitted via one of the antennas 430, 432. Thus, there
will be one data stream on each of the two polarizations used.
[0037] As shown in FIG. 3 and described above, the PF can, by
introducing a phase shift into one of the D1-streams, achieve a
certain composite polarization between the signals transmitted by
the two radiation elements 430, 432.
[0038] As illustrated by the parenthesis in the PF-function in FIG.
4, the PF-function in this case does not introduce any phase shift
into either of the signals going to the separate antenna elements,
each signal is merely multiplied by a factor 1, as indicated by the
numerals in the parenthesis. Thus, the composite polarization
achieved by the signals in this example will be the one shown as
+45.degree. in FIG. 3.
[0039] FIG. 5 shows an embodiment of a device 500 of the invention:
the device 500 comprises input connections for two data streams D1
and D2. For each of said data streams, the device 500 comprises one
polarization former 510, 511. In addition, the device 500 comprises
two antennas each comprising one radiation element where the two
elements have different polarizations, in this case one 530 of
vertical polarization and one 532 of horizontal polarization.
[0040] Each of the radiation elements 530, 532, is associated with
one power amplifier, 520, 522.
[0041] Each of the polarization formers (PF:s) 510, 511, will split
its respective data stream into two separate streams, and can
create a phase shift between the two separate streams, for example
by multiplying one of the streams with a complex number, exp
(-jn*.pi.), where n is an integer, positive or negative.
[0042] Naturally, the same can be achieved by multiplying both of
the separate streams by complex numbers if the desired phase
difference is maintained between the two complex numbers. Another
way of achieving a phase difference is to introduce a delay into
one of the data streams.
[0043] Thus, the output from each of the PF:s 510, 511, will be two
streams containing the same data, but with a desired phase relation
between them.
[0044] As indicated in FIG. 5, an example of the use of the two
PF:s is that the PF which is used for the first data stream D1
doesn't introduce a phase difference between the two separate
streams into which D1 is split, i.e. the PF 510 carries out a
multiplication of the "D1-streams" by the PF-factors (1,1), as
indicated by the numerals (1,1) in the parenthesis in the PF 510 in
FIG. 5. Accordingly, the output from PF 510 is a first and a second
stream of D1, with no phase shift between them.
[0045] The other PF in the device 500, the PF 511, on the other
hand, introduces a phase difference between the two data streams
into which D2 is split, in this case a phase shift of 180.degree.
between the two D2-streams which are output from the PF 511.
[0046] Thus, the output from PF 511 is a first and a second
D2-stream, with a phase difference of -180.degree. between them,
which is also indicated by the numerals (1,-1) in the parenthesis
in the PF 511 in FIG. 5.
[0047] As shown in FIG. 5, the device 500 also comprises a first
515 and a second 516 combiner, which are used to combine the
outputs from the polarization formers, to form inputs to each of
the first 530 and second 532 antenna elements via respective power
amplifiers 520, 522.
[0048] Thus, one of the two output streams from each PF 510, 511,
is input to one of the combiners. This means that to the first
combiner 515, the input is the first "D1-stream" and the first
"D2-stream", and for the second combiner 516, the input is the
"second Di-stream" and the second "D2-stream".
[0049] Consider now the two D1-streams: both D1-streams will pass
through a respective power amplifier 520, 522, and will be
transmitted from separate antennas 530, 532, having different
polarizations, one being vertical and the other being horizontal.
The two D1-streams will thus be combined in the air after being
transmitted in the way shown in FIG. 3, i.e. in the manner referred
to as +45.degree., since no phase shift was introduced by the
PF:s.
[0050] If, instead, the two D2-streams are considered, the
following will be realized: the first and second D2-streams will
also pass through the first 515 and second 516, combiners
respectively, as well as the respective first 520 and second 522
power amplifiers and antenna elements 530, 532.
[0051] However, the PF 511 introduced a phase shift of 180.degree.
between the two D2-streams. Due to this phase shift, the two
D2-streams will after transmission combine in the way referred to
as -45.degree. in FIG. 3.
[0052] Accordingly, the device 500 of FIG. 5 will transmit in two
effective polarizations, one of which is -45.degree. and the other
is +45.degree., with one data stream D1, D2, on each of these
polarizations.
[0053] Since both data streams, or, to be more correct, both the
first and second outputs from the two PF:s 510, 511, are input to
the power amplifiers 520, 522, the power amplifier resources are
shared between the data streams D1 and D2. If the amplifier
resources, in terms of maximal output power, of one amplifier is
denoted as P, the total amplifier resources used is 2P.
[0054] FIG. 6 shows a further embodiment 600 of a device according
to the invention: the embodiments shown previously have only
comprised one antenna element per polarization, vertical and
horizontal. As shown in FIG. 6, it is entirely possible to instead
have two antenna elements in one or (as shown in FIG. 6) both of
the polarizations. The two antenna elements for each polarization
constitute an array antenna.
[0055] Thus, the numerals 630 and 632 in FIG. 6 refer to array
antennas with two elements per polarization, vertical and
horizontal. Naturally, the number of radiation elements per
polarization can be varied in a more or less arbitrary way.
[0056] As is well known within antenna theory, with two or more
radiation elements in one and the same polarization, it is possible
to perform so called beam forming, i.e. to influence the shape of
the resulting radiation pattern in that polarization by weighting
the signals which are fed to the respective radiation element.
[0057] The device 600 comprises means for beam forming, one beam
former (BF) 652 for the first data stream D1, and a second beam
former 656 for the second data stream D2. Additional beam formers,
which will be described later in this text, are indicated with
dashed lines, and referred to by the numbers 650, 654.
[0058] As indicated in FIG. 6, each of the two output data streams
from each of the two PF:s 610, 611, is used as input to one beam
former 652, 656. In this example, the PF multiplies one of the
outgoing data streams by zero, so there is only one effective data
stream output from each PF in this example.
[0059] The BF splits each incoming data stream into parallel data
streams, and introduces a phase shift (and possibly an amplitude
difference) between the output data streams, in this case two.
[0060] As shown in FIG. 6, using the BF 652 as an example, two data
streams D1 are output from the BF, with the described phase shift
between them. These two data streams D1 are each used as input to
one of the radiation elements in one of the polarizations, in this
case the vertically polarized elements 630. Each radiation element
is also equipped with one combiner 615 and one PA 620.
[0061] Thus, the output from the vertical "array antenna" 630 will
be one resulting beam with a desired shape, used for transmitting
data stream D1.
[0062] In a similar manner, the horizontal "array antenna" 632 will
generate one resulting beam with a desired shape, used for
transmitting data stream D2.
[0063] It can be seen that although the polarization formers 610,
611, are comprised in the device 600 shown in FIG. 6, they
essentially serve no purpose in the device, since each data stream
is only connected to one of the array antennas 630, 632. To
illustrate this further, the "horizontal branch" output of the PF
610 is multiplied by zero, as is the "vertical branch" output of
the PF 611. Thus, the effect achieved by the embodiment of FIG. 6
may also possibly be achieved by connecting the data streams D1-D4
directly to the respective beam formers.
[0064] FIG. 7 shows a further development 700 of the device
introduced in FIG. 6: the difference is that in the device 700, all
of the beam formers 750, 752, 754, 756, are employed.
[0065] As can be seen in FIG. 7, the first data stream D1 is input
to the first polarization former 710, where it is split up into two
equal streams, with, in this case, no phase shift being introduced
between them. One of the two "in phase" D1 streams is used as input
to a vertical beamformer 752, and the other D1 stream is used as
input to a horizontal beamformer 750. Vertical and horizontal in
this context means that the output from the beamformer will be used
as input to an array antenna of that polarization.
[0066] In a similar manner, the second data stream D2 is input to
the second polarization former 711, where it is split up into two
equal streams, with, in this case, a phase difference of
180.degree. between them. The "in phase" D2-stream is used as input
to a vertical beamformer 754, and the "-180.degree. " D2-stream is
used as input to a horizontal beamformer 756.
[0067] The device of FIG. 7 also comprises a first array antenna,
730, with two vertically polarized radiation elements, and a second
array antenna 732 with two horizontally polarized elements. The two
array antennas have the same phase center. Each radiation element
is associated with a combiner 715, 716, and a power amplifier 720,
722. In total, there are thus four transmission chains in the
device 700, each comprising a combiner, an amplifier and a
radiation element.
[0068] Each beam former 750, 752, 754, 756, will also output a
first and a second data stream, which are used in the following
way: The two outputs from the vertical beam former 752 associated
with D1 are used as respective inputs to the two transmission
chains of the vertical array antenna 730, and the two outputs from
the horizontal beam former 750 associated with D1 are used as
respective inputs to the two transmission chains of the horizontal
array antenna 732.
[0069] Similarly, the two outputs from the vertical beam former 754
associated with D2 are used as respective inputs to the two
transmission chains of the vertical array antenna 730, and the two
outputs from the horizontal beamformer 756 associated with D2 are
used as respective inputs to the two transmission chains of the
horizontal array antenna 732.
[0070] As a result, each transmission chain in the device 700 is
used by both streams D1 and D2. The D1-streams transmitted by the
horizontal array antenna 732 and the D1 streams transmitted by the
vertical array antenna 732 have had no phase shift introduced by
the PF 710, and will thus combine in the air after transmission
into the polarization shown as +45.degree. in FIG. 3.
[0071] Conversely, the D2-streams transmitted by the horizontal
array antenna 732 and the D2-streams transmitted by the vertical
array antenna 730 have had a phase shift of -180.degree. introduced
by the PF 711, and will thus combine in the air after transmission
into the polarization shown as -45.degree. in FIG. 3. Typically, BF
752=BF 750, and BF 756=BF 754.
[0072] An important issue is the flexibility of this configuration:
In FIG. 6 power resources are dedicated for each data stream, while
in FIG. 7 the entire power resource is shared by both streams
(pooled power resource). A pooled resource can be shared equally or
unequally between the data streams in a device of the invention.
Further, the air combining of signals eliminates the combining loss
commonly associated with a pooled power resource.
[0073] Also, the beams generated by the array antennas 730, 732,
can have been given a desired beam shape by the beamformers 750,
752, 754, 756.
[0074] FIG. 8 shows a further embodiment 800 of the invention. As
shown in this embodiment, the number of data streams used in a
device of the invention need not be restricted to two: in the
embodiment 800, as an example of this, four data streams D1-D4 are
used.
[0075] Each data stream D1-D4 is used as input to a PF, 810-813,
which has the same function as the PF:s described previously. Thus,
the PF:s 810-813 split an incoming data stream into two, and
applies a phase shift and possibly a difference in amplitude
between the two data streams.
[0076] In order to facilitate the understanding of the embodiment
800 of the invention, each PF 810-813 in FIG. 8 is shown as
multiplying one of the outgoing data streams by zero, so that there
is only one data stream output from each PF. Thus, the effect
achieved by the embodiment of FIG. 8 may also possibly be achieved
by connecting the data streams D1-D4 directly to the respective
beam formers.
[0077] Each output data stream from each PF is used as input to a
respective beam former, BF, 852-856. The BF:s of the embodiment 800
have the same function as those BF:s previously described, and will
thus not be described in detail again here. However, each BF will
split an incoming data stream into a first and a second output data
stream.
[0078] Each of the first and second output data streams from each
of the BF:s 852-856 is used as input to one of the transmission
chains in the device, as shown in FIG. 8. The difference between
the embodiment 800 and those embodiment shown previously is that
two "beamformed" data streams D1-D2 and D3-D4 respectively, are
combined as input to the same transmission chains after having
passed through a PF where they are subjected to the same
polarization forming function.
[0079] As can be seen in FIG. 8, the first and the second data
streams D1 and D2, for example, are subjected to the polarization
forming function (1,0) by their respective PF:s.
[0080] After the beam forming, the resulting first data streams
D1.sub.1, D2.sub.1, formed from each of D1 and D2 are combined as
input to the same transmission chains, as is also the case with the
resulting second data streams D1.sub.2, D2.sub.2, formed from each
of D1 and D2.
[0081] As the polarization functions are the same for data streams
D1 and D2, the beam forming function BF(D1), BF(D2), to which each
of the data streams D1, D2, is subjected, must be unique for that
data stream. Thus, after transmission, there will be one D1-beam
and one D2-beam, both with the same polarization, but sufficiently
different to support MIMO transmissions.
[0082] Similarly, the two data streams D3 and D4 are subjected to
the same polarization forming function (0,1), and are then used as
input to the same transmission chains. After transmission, there
will be one D3-beam and one D4-beam, both with the same
polarization, but sufficiently different to support MIMO
transmissions.
[0083] FIG. 9 shows a further development 900 of the device of FIG.
8: one difference between the embodiments 900 and 800 is that in
the embodiment 900, the power amplifier resources are pooled.
[0084] Thus, in this embodiment, four data streams D1-D4 are input
to the device. Each data stream D1-D4 is input to a polarization
former, which splits the input data stream into a first and a
second output data streams. The first output data stream from each
polarization former is used as input to a first beam former BF, and
the second output data stream from each polarization former is used
as input to a second beam former BF.
[0085] Accordingly, considering the incoming data stream D1 as an
example, this data stream is, after polarization forming and beam
forming, split into a first and a second D1-stream from a beam
former for vertical polarization BF(D1, V), and a first and a
second D1-stream from a beam former for horizontal polarization,
BF(D1, H).
[0086] The first and second D1-streams for vertical polarization
are input to a first and second transmission chain, respectively,
in an antenna for vertical polarization.
[0087] In said first and second transmission chains in the antenna
for vertical polarization, the first and second D1-streams are
combined with first and second streams respectively, from the input
data streams D2, D3 and D4.
[0088] As indicated in FIG. 9, the polarization forming functions
for D1 and D2 are the same, as are the polarization forming
functions for D3 and D4, respectively. As pointed out in connection
with FIG. 8, two data streams which have the same PF-function and
which are input to the same antenna must have passed through
different beamforming functions in order to support MIMO
transmission. Streams to be transmitted via horizontally polarized
elements are treated accordingly.
[0089] The invention is not restricted to the examples of
embodiments shown above, but may be varied freely within the scope
of the appended claims.
[0090] One possible variation, for example, could be to use
beamformers which split an incoming data stream into four output
data streams instead of two, as shown above. Each of the four
output data streams would be connected to separate antenna elements
in an array antenna, which would create a narrower beam with higher
gain. Naturally, this principle can be expanded upon, so that
beamformers with even more outputs can be envisioned.
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