U.S. patent application number 12/160139 was filed with the patent office on 2009-01-08 for array antenna arrangement.
Invention is credited to Mats H. Andersson, Sven Anders Derneryd, Anna Barbro Engstrom, Bo Goransson, Martin Nils Johansson, Sven Oscar Petersson.
Application Number | 20090010356 12/160139 |
Document ID | / |
Family ID | 36942378 |
Filed Date | 2009-01-08 |
United States Patent
Application |
20090010356 |
Kind Code |
A1 |
Engstrom; Anna Barbro ; et
al. |
January 8, 2009 |
Array Antenna Arrangement
Abstract
The present invention relates to a wireless communication
system, comprising at least one base station in a communication
cell. The base station is equipped with at least one array antenna
comprising at least two antenna ports which are coupled to
respective at least two corresponding antenna Q elements, where at
leas two of the at least two antenna elements have essentially the
same polarization. The array antenna is arranged for communication
via at least two antenna radiation lobes, each antenna radiation
lobe communicating an information stream to at least one UE (user
equipment) in the cell. According to a certain aspect of the
present invention, in a first mode 0 operation, the array antenna
is arranged for communication via one antenna radiation lobe. The
present invention also relates to a method for performing said
communication.
Inventors: |
Engstrom; Anna Barbro;
(Floda, SE) ; Goransson; Bo; (Sollentuna, SE)
; Johansson; Martin Nils; (Molndal, SE) ;
Andersson; Mats H.; (Goteborg, SE) ; Petersson; Sven
Oscar; (Savedalen, SE) ; Derneryd; Sven Anders;
(Goteborg, SE) |
Correspondence
Address: |
ERICSSON INC.
6300 LEGACY DRIVE, M/S EVR 1-C-11
PLANO
TX
75024
US
|
Family ID: |
36942378 |
Appl. No.: |
12/160139 |
Filed: |
January 4, 2006 |
PCT Filed: |
January 4, 2006 |
PCT NO: |
PCT/EP06/00035 |
371 Date: |
July 7, 2008 |
Current U.S.
Class: |
375/267 |
Current CPC
Class: |
H04B 7/0617 20130101;
H04W 16/28 20130101; H04B 7/0417 20130101; H04B 7/0619 20130101;
H04W 84/042 20130101 |
Class at
Publication: |
375/267 |
International
Class: |
H04B 7/06 20060101
H04B007/06 |
Claims
1-17. (canceled)
18. A wireless communication system comprising: at least one array
antenna adapted to being coupled to at least one base station in a
communication cell; the array antenna having at least two antenna
ports wherein the at least two ports are coupled to respective at
least two corresponding antenna elements where at least two of the
at least two antenna elements have essentially the same
polarization and where, in a first mode of operation, the array
antenna is arranged for communication via one antenna radiation
lobe communicating one information stream to at least one user
equipment (UE) in the cell; and the array antenna having a second
mode of operation arranged for communication via at least two
antenna radiation lobes each antenna radiation lobe communicating
an information stream to the at least one UE in the cell, thus
communicating by means of Multiple Input Multiple Output
(MIMO).
19. The communication system according to claim 18, wherein each
antenna element comprises at least one radiating element.
20. The communication system according to claim 18, wherein each
antenna radiation lobe has a fixed, predetermined azimuth and
elevation directional angle.
21. The communication system according to claim 20, wherein each
antenna radiation lobe is controlled by being turned on or off, and
by distributing different power levels and/or data bit rates in
each information stream feeding the at least two antenna
elements.
22. The communication system according to claim 18, wherein each
antenna radiation lobe is individually controllable in azimuth or
elevation, or both in azimuth and elevation, in such a way that the
communication of the information streams is essentially
optimized.
23. The communication system according to claim 18, wherein the
control of the antenna lobes is performed adaptively, based on
feed-back information from the UE, said feed-back information being
in the form of at least one data bit.
24. The communication system according to claim 23, wherein the
feed-back information is in the form of a Channel Quality Indicator
(CQI) value.
25. The communication system according to claim 18, wherein a total
information stream is fed into the communication system, said total
information stream always being radiated by the antenna elements
utilizing the full area of the antenna element's aperture.
26. The communication system according to claim 18, wherein the
array antenna further comprises dual polarized antenna
elements.
27. The communication system according to claim 26, wherein the
array antenna comprises at least four antenna elements, each
antenna element having a first and second polarization, the
polarizations being essentially de-correlated, the antenna elements
further forming at least two rows and two columns, the rows where
the first polarization of the antenna elements in the first row and
the first polarization of the antenna elements in the second row
are coupled to a beam-forming device, and where the second
polarization of the antenna elements in the first column and the
second polarization of the antenna elements in the second column
are coupled to a beam-forming device, enabling the radiation lobes
formed by the rows having the first polarization, to be controlled
separate from the radiation lobes formed by the columns having the
second polarization, the antenna radiation lobes being incoherently
added in the far-field.
28. A wireless communication system at least one base station in a
communication cell, the base station being coupled to at least one
array antenna, the at least one array antenna comprising: at least
two antenna ports wherein the at least two ports are coupled to
respective at least two corresponding antenna elements, wherein at
least two of the at least two antenna elements have essentially the
same polarization, the array antenna arranged for communication via
at least two antenna radiation lobes, each antenna radiation lobe
communicating an information stream to at least one user equipment
(UE) in the cell, thus communicating by means of Multiple Input
Multiple Output (MIMO).
29. The communication system according to claim 28, wherein each
antenna element comprises at least one radiating element.
30. The communication system according to claim 28, wherein each
antenna radiation lobe has a fixed, predetermined azimuth and
elevation directional angle.
31. The communication system according to claim 30, wherein each
antenna radiation lobe is controlled by being turned on or off, and
by distributing different power levels and/or data bit rates in
each information stream feeding the at least two antenna
elements.
32. The communication system according to claim 28, wherein each
antenna radiation lobe is individually controllable in azimuth or
elevation, or both in azimuth and elevation, in such a way that the
communication of the information streams is essentially
optimized.
33. The communication system according to claim 28, wherein the
control of the antenna lobes is performed adaptively, based on
feed-back information from the UE, said feed-back information being
in the form of at least one data bit.
34. The communication system according to claim 33, wherein the
feed-back information is in the form of a Channel Quality Indicator
(CQI) value.
35. The communication system according to claim 28, wherein a total
information stream is fed into the communication system, said total
information stream always being radiated by the antenna elements
utilizing the full area of the antenna element's aperture.
36. The communication system according to claim 28, wherein the
array antenna further comprises dual polarized antenna
elements.
37. The communication system according to claim 36, wherein the
array antenna comprises at least four antenna elements, each
antenna element having a first and second polarization, the
polarizations being essentially de-correlated, the antenna elements
further forming at least two rows and two columns, the rows where
the first polarization of the antenna elements in the first row and
the first polarization of the antenna elements in the second row
are coupled to a beam-forming device, and where the second
polarization of the antenna elements in the first column and the
second polarization of the antenna elements in the second column
are coupled to a beam-forming device, enabling the radiation lobes
formed by the rows having the first polarization, to be controlled
separate from the radiation lobes formed by the columns having the
second polarization, the antenna radiation lobes being incoherently
added in the far-field.
38. An array antenna arranged for use in a communication system
comprising: at least two antenna ports wherein the at least two
ports are coupled to respective at least two corresponding antenna
elements where at least two of the at least two antenna elements
have essentially the same polarization and where, in a first mode
of operation, the array antenna is arranged for communication via
one antenna radiation lobe communicating one information stream to
at least one user equipment (UE) in the cell; and the array antenna
having a second mode of operation arranged for communication via at
least two antenna radiation lobes each antenna radiation lobe
communicating an information stream to the at least one UE in the
cell, thus communicating by means of Multiple Input Multiple Output
(MIMO).
39. A method for communication of at least one information stream
from a base station array antenna in a communication cell, the base
station array antenna having at least two antenna ports where the
at least two ports are coupled to respective at least two
corresponding antenna elements where at least two of the at least
two antenna elements have essentially the same polarization, in a
first mode of operation comprising the steps of: in a first mode of
operation, communicating one information stream, to at least one
user equipment (UE) in the cell, via one antenna radiation lobe; in
a second mode of operation, communicating at least two information
streams, to the at least one UE in the cell via at least two
antenna radiation lobes.
40. The method according to claim 39 wherein the antenna lobes are
controlled adaptively, using feed-back information from the UE,
said feed-back information being in the form of at least one data
bit.
41. The method according to claim 40, wherein the feed-back uses a
Channel Quality Indicator (CQI) value.
42. The method according to claim 39 wherein dual polarization is
used.
43. A method for communication of at least two information streams
from a base station array antenna in a communication cell, the base
station array antenna having at least two antenna ports where the
at least two ports are coupled to respective at least two
corresponding antenna elements where at least two of the at least
two antenna elements have essentially the same polarization,
comprising the step of: communicating the at least two information
streams, to at least one user equipment (UE) in the cell via at
least two antenna radiation lobes.
44. The method according to claim 43 wherein the antenna lobes are
controlled adaptively, using feed-back information from the UE,
said feed-back information being in the form of at least one data
bit.
45. The method according to claim 44, wherein the feed-back uses a
Channel Quality Indicator (CQI) value.
46. The method according to claim 43 wherein dual polarization is
used.
Description
TECHNICAL FIELD
[0001] The present invention relates to a wireless communication
system comprising at least one base station in a communication
cell, the base station being equipped with at least one array
antenna comprising at least two antenna ports, where the at least
two ports are connected to respective at least two corresponding
antenna elements, where at least two of the at least two antenna
elements, have essentially the same polarization.
[0002] According to a certain aspect of the invention, in a first
mode of operation, the array antenna is arranged for communication
via one antenna radiation lobe, communicating one information
stream to at least one UE (user equipment) in the cell.
[0003] The present invention also relates to a method for
communication of at least one information stream from a base
station array antenna in a communication cell, the base station
array antenna comprising at least two antenna ports, where the at
least two ports are connected to respective at least two
corresponding antenna elements, where at least two of the at least
two antenna elements have essentially the same polarization.
[0004] According to a certain aspect of the invention, in a first
mode of operation, the method comprises the step: communicating one
information stream, to at least one UE (user equipment) in the
cell, via one antenna radiation lobe.
BACKGROUND ART
[0005] The demand for wireless communication systems has grown
steadily, and is still growing, and a number of technological
advancement steps have been taken during this growth. In order to
acquire increased system capacity and user data bit rate for
wireless systems by employing de-correlated propagation paths, MIMO
(Multiple Input Multiple Output) systems have been considered to
constitute a preferred technology for improving the capacity and
the user data bit rate. MIMO employs a number of separate
independent signal paths, for example by means of several
transmitting and receiving antennas.
[0006] Generally, a MIMO system utilizes de-correlated, or at least
essentially de-correlated, transmitted signals. The meaning of the
term "de-correlated signals" in this context is that the radiation
patterns are essentially de-correlated. This is today made possible
by means of spatial separation, i.e. having at least two antennas
separated by 5-10 wavelengths, (calculated from the centre
frequency of the frequency band for which the antennas are
designed), normally in azimuth, in order to achieve low correlation
between the signals at the antenna ports. These at least two
antennas have at least one antenna radiation lobe each.
[0007] It is also possible to combine spatial separation with
polarization separation, where the antennas then also are arranged
for transmission and reception of signals having orthogonal
polarizations.
[0008] A base station in a MIMO system may thus be arranged with a
number of antennas, separated by 5-10 wavelengths, each one of the
base station antennas either being designed for one polarization or
a plurality of essentially de-correlated polarizations, typically
two essentially de-correlated polarizations. These antennas produce
antenna radiation lobes which are de-correlated, either by space or
polarization, or both.
[0009] It is necessary that a user equipment (for example a mobile
phone or a portable computer) is arranged with at least two antenna
ports for communication in a MIMO system.
[0010] A problem with existing MIMO arrangements is that, since an
original information stream is divided into two or more separate
information streams, the SNR (Signal to Noise Ratio) is
deteriorated given a fixed output power. A decreased SNR results in
that the rate of transferred data, the data bit rate, is
decreased.
[0011] Furthermore, the signal path between the base station and
the user equipment may be blocked by a number of objects such as
large buildings in an urban environment, which objects cause a
number of reflections. These reflections may result in that the
signal to noise ratio (SNR) becomes even more deteriorated, and
thus the signals transmitted between the base station and the user
equipment may become more and more noisy the more buildings that
are in the way. It may thus be possible to use MIMO only in the
vicinity of a base station. A good MIMO performance requires good
SNR.
[0012] The traditional MIMO systems, having one information stream
per antenna, are thus afflicted with a disadvantage concerning the
data bit rate between the base station and the user equipment, both
in urban environments and in the countryside, due to the fact that
the base station antenna radiation lobes are spatially separated in
order to obtain essentially de-correlated signals. This means that
the MIMO system is not used optimally, for a given surface area and
output power.
DISCLOSURE OF THE INVENTION
[0013] The objective problem that is solved by the present
invention is to provide an arrangement suitable for a MIMO system,
which arrangement is capable of providing an enhanced communication
between a base station, having at least two antenna ports, and a
user equipment, having at least two antenna ports for communication
via the at least two base station antenna radiation lobes.
[0014] The objective problem is solved by means of a wireless
communication system according to the introduction, where the array
antenna is arranged for communication via at least two antenna
radiation lobes, each antenna radiation lobe communicating an
information stream to the at least one UE (user equipment) in the
cell, thus communicating by means of MIMO (Multiple Input Multiple
Output).
[0015] According to a certain aspect of the invention, this
corresponds to a second mode of operation.
[0016] The objective problem is also solved by means of an array
antenna arranged for use in the communication system.
[0017] Furthermore, the objective problem is also solved by means
of a method according to the introduction, where the method further
comprises the step: communicating at least two information streams,
to the at least one UE (user equipment) in the cell, via at least
two antenna radiation lobes.
[0018] According to a certain aspect of the invention, this
corresponds to a second mode of operation.
[0019] That means that the decrease of SNR due to the dividing of
an original information stream into two or more separate
information streams is more or less recovered by use of array gain,
where furthermore a relatively small amount of information
regarding the channel is required.
[0020] Preferred embodiments are disclosed in the dependent
claims.
[0021] Several advantages are achieved by means of the present
invention, for example: [0022] higher bit rate capacity [0023] easy
installation and lower site costs [0024] a single antenna with
multiple antenna radiation lobes, pointing in different directions
and being sufficiently de-correlated, is used instead of multiple
antennas with single antenna radiation lobes, resulting in that the
antenna surface is used efficiently, taking advantage of the
antenna array gain, the whole antenna surface providing gain for
each radiation lobe.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The present invention will now be described more in detail
with reference to the appended drawings, where
[0026] FIG. 1a shows a schematic top view of the system according
to the present invention;
[0027] FIG. 1b shows a schematic view of a base station array
antenna;
[0028] FIG. 2 shows a schematic side view of an embodiment of the
invention;
[0029] FIG. 3 shows a schematic top view of another embodiment of
the invention;
[0030] FIG. 4 shows a schematic side view of another embodiment of
the invention;
[0031] FIG. 5 shows a schematic top view of yet another embodiment
of the invention; and
[0032] FIG. 6 shows a schematic view of a dual polarized base
station array antenna.
PREFERRED EMBODIMENTS
[0033] As shown in FIG. 1a, a communication system C comprises a
base station 1 arranged for communication in a MIMO (Multiple Input
Multiple Output) system. The base station 1 is placed in such a way
that it covers a communication cell 2. With reference also to FIG.
1b, the base station 1 is equipped with an array antenna 3, which
array antenna 3 in a first embodiment comprises a first 4, second
5, third 6 and fourth 7 antenna element. Each antenna element 4, 5,
6, 7 comprises at least one radiating element. The antenna elements
4, 5, 6, 7 are placed in a first 8 and second 9 row and a first 10
and second column 11, forming a 2.times.2 array antenna 3. The
antenna elements 4, 5, 6, 7 are preferably mutually separated by
approximately 0.5-1 wavelengths (calculated from the centre
frequency of the frequency band for which the antennas are
designed) in a horizontal plane for beam-forming in azimuth and
approximately 0.5-4 wavelengths in a vertical plane for
beam-forming in elevation. In this example, each antenna element 4,
5, 6, 7 is arranged for a single polarization, said polarization
being essentially the same for each antenna element 4, 5, 6, 7.
These antenna elements 4, 5, 6, 7 receive and transmit signals
using the same frequency band, for the uplink and another frequency
band for the downlink if FDD (Frequency Division Duplex) is
utilized, or using the same frequency band, for both the uplink and
the downlink if TDD (Time Division Duplex) is utilized.
[0034] In this first embodiment, the four antenna elements 4, 5, 6,
7 are each one connected to respective first 12, second 13, third
14 and fourth 15 feeding lines via a first P1, second P2, third P3
and fourth P4 respective antenna port, where the feeding lines 12,
13, 14, 15 are connected to a beam-forming device 16 of a
previously known kind, for example a digital beam-forming device.
The beam-forming device 16 is in turn connected to a first 17,
second 18, third 19 and fourth 20 information stream feeding line,
each information stream originating from a total information stream
feeding line 21. The total information stream is divided into the
four information streams by means of a dividing device 22.
[0035] One user equipment (UE) 23 is positioned within the cell 2,
where the user equipment 23 for example is a mobile phone or a
portable computer. It is assumed that the UE 23 is arranged for
reception of four de-correlated signals, in other words it is
assumed that the UE 23 is equipped with four independent antenna
ports (not shown).
[0036] According to the present invention, the radiation lobes 24,
25, 26, 27 are controlled depending on the transmission
circumstances for transmission between the base station 1 and the
UE 23. The control is performed in such a way that an enhanced
communication between the base station 1 and the UE 23 is
obtained.
[0037] In the present embodiment, the beam-forming device 16 is
arranged for controlling the number of output radiation lobes in
such a way that one 24, two 25, three 26 or four 27 radiation lobes
with fixed predetermined directions in azimuth and elevation are
switched on. The number of radiation lobes and which ones that
should be turned on and off is controlled in such a way that an
enhanced communication between the base station 1 and the UE 23 is
obtained.
[0038] In a first mode of operation, communication is performed via
only one radiation lobe, communicating one information stream. Then
the communication system C is not communicating via MIMO. In a
second mode of operation, communication is performed via at least
two antenna radiation lobes 24, 25, 26, 27, each antenna radiation
lobe 24, 25, 26, 27 communicating an information stream. Then the
communication system C is communicating via MIMO.
[0039] Independently on how many radiation lobes that are used, all
the information from the total information stream is always
radiated by the four antenna elements 4, 5, 6, 7, utilizing the
full area of the antenna element's aperture.
[0040] The UE 23, which may be moving relative to the base station
1, continuously provides feed-back to the base station 1 regarding
the highest data bit rate that is currently possible. Based on this
information, the antenna radiation lobes 24, 25, 26, 27 are
adaptively controlled. The adaptive control comprises turning
radiation lobes on and off as well as distributing different power
levels and/or data bit rates in each information stream.
[0041] The feed-back normally comprises relatively limited
information regarding the channel, in its simplest form the
feed-back is only in the form of one data bit. The more information
regarding the channel that is comprised in the feed-back, the
better the adaptive control becomes. It is, however, possible to
achieve an acceptable adaptive control with said relatively limited
information regarding the channel. A typical type of feed-back is a
so-called CQI-value (Channel Quality Indicator) that is well known
in the art.
[0042] In a second embodiment, which also may be implemented with
reference to FIGS. 1a and 1b, the four information streams are fed
to the beam-forming device 16 which here is arranged for
controlling the azimuth and elevation direction for each output
antenna radiation lobe 24, 25, 26, 27. The beam-forming device is
in this example preferably a digital beam-forming device.
[0043] Each one of the four information streams correspond to four
base station antenna radiation lobes, where each one of the lobes
is directed in the direction where the optimal communication with a
certain UE is achieved. The adjustment of the lobes is performed
both in azimuth and elevation. Directing lobes in this way may
affect the signal paths in such a way that they are not essentially
de-correlated, but according to the invention they are
de-correlated to a sufficient degree.
[0044] As in the first embodiment, the UE 23, which may be moving
relative to the base station 1, continuously provides feed-back to
the base station 1 regarding the highest transmission data bit rate
that currently is possible. Based on this information, the
directions of the antenna radiation lobes 24, 25, 26, 27 are
adaptively controlled.
[0045] The main goal of the invention is thus to enhance the
communication, even if it means that the degree of de-correlation
is decreased. De-correlation is then not preserved at the expense
of communication data bit rate for all the embodiments.
[0046] According to the embodiments above, during transmission, the
digital beam-forming device 16 feeds each one of the four
information streams to each one of the antenna ports P1, P2, P3, P4
in the base station array antenna 3 with a certain amplitude
relation and a certain phase relation in order to obtain the
desired antenna radiation lobe directions in azimuth and elevation
for each antenna radiation lobe 24, 25, 26, 27.
[0047] That means that, in the examples, the first information
stream is fed to all four antenna ports P1, P2, P3, P4, having a
certain amplitude relation and a certain phase relation for each
one of the antenna ports P1, P2, P3, P4. This may be performed for
all information streams at the same time, and due to superposition,
four antenna radiation lobes 24, 25, 26, 27 are obtained, one for
each information stream, where each antenna radiation lobe 24, 25,
26, 27 is obtained by means of the four antenna elements 4, 5, 6,
7.
[0048] In the first embodiment, no functionality for changing the
direction of the antenna radiation lobes 24, 25, 26, 27 is
provided, there is only the possibility to turn the antenna
radiation lobes 24, 25, 26, 27, thus pointing in pre-determined
directions, on and off.
[0049] The digital beam-forming described above is in itself
previously known, and will not be described more in detail
here.
[0050] As shown in the side view in FIG. 2, showing an example of
the functionality of the second embodiment, a relatively small
building 28 is positioned in front of a UE 23 and a large building
is positioned behind the UE 23. Three antenna radiation lobes 24',
25', 26' are directed at the UE 23, having essentially the same
directional angle in azimuth, but having different directional
angles in elevation.
[0051] An azimuth directional angle of an antenna radiation lobe is
defined as the angle between a normal extending from the centre of
the antenna's main radiating surface and the azimuth direction of
the antenna radiation lobe. A corresponding definition is valid for
an elevation directional angle of an antenna radiation lobe. The
direction of an antenna radiation lobe is preferably defined as the
direction where the antenna radiation lobe has its maximum signal,
other definitions occur.
[0052] Due to the smaller building 28 partly blocking the path, all
four antenna radiation lobes 24', 25', 26', 27' can not achieve an
optimal communication with the UE 23 by being directed more or less
directly at the UE 23. Therefore, one of the antenna radiation
lobes 27', the fourth antenna radiation lobe in this example, is
instead directed towards the larger building 29 in such a way that
the fourth information stream, which is transmitted by means of the
fourth antenna radiation lobe 27', reaches the UE 23 by means of
reflection in the larger building 29.
[0053] If, for example, the UE 23 clears the smaller building 28,
the fourth lobe 27' is re-directed in such a way that it is
directed at the UE more directly based on the feed-back from the UE
23. Then, all four antenna radiation lobes 24', 25', 26', 27' are
directed at the UE 23, having essentially the same directional
angle in azimuth, but having different directional angles in
elevation in order to provide sufficiently de-correlated
propagation paths.
[0054] As shown in the top view in FIG. 3, showing another example
of the functionality of the second embodiment, a relatively small
building 30 is positioned in front of a UE 23, but there are no
significant buildings behind the UE 23. A relatively large building
31 is positioned on the left side of the UE 23, when looking at the
UE 23 from the base station 1.
[0055] Three antenna radiation lobes 24'', 25'', 26'' are directed
at the UE 23, having essentially the same directional angle in
azimuth, but having different directional angles in elevation (not
shown in FIG. 3 since it is a top view). Due to the smaller
building 30 partly blocking the path, all four antenna radiation
lobes 24'', 25'', 26'', 27'' can not achieve an optimal
communication with the UE 23 by being directed directly at the UE
23. Therefore, one of the antenna radiation lobes 27'', the fourth
antenna radiation lobe in this example, is instead directed towards
the larger building 31 at the left in such a way that the fourth
information stream, which is transmitted by means of the fourth
antenna radiation lobe 27'', reaches the UE 23 by means of
reflection in the larger building 31 at the left, regarded from the
base station 1 point of view.
[0056] In the same way as described previously, the lobe directions
may be altered due to movement of the UE 23 or other circumstances.
This is controlled based on the UE:s feed-back.
[0057] As shown in the side view in FIG. 4, showing yet another
example of the functionality of the second embodiment, a UE 23 is
positioned in the countryside, where there are no buildings. Here,
all the antenna radiation lobes 24''', 25''', 26''', 27''' are
directed at the UE 23, having essentially the same directional
angle in azimuth, but having different directional angles in
elevation. The fourth embodiment illustrates that the present
invention is not directed primarily towards reflections in
buildings, but towards optimizing of the communication between the
base station 1 and the UE 23, irrespective of the surroundings, and
irrespective of if the degree of de-correlation is decreased.
[0058] Of course, there are often more than one UE in the cell.
With reference to FIG. 5, there are a first 23a, second 23b and
third 23c UE in a cell 2. According to the invention, each one of
the UE:s 23a, 23b, 23c in the cell 2 receives a certain time slot
where all the base station antenna radiation lobes (not shown in
FIG. 5) co-operate to optimize the communication between the base
station 1 and a certain UE. During a first time slot, all the base
station antenna radiation lobes co-operate to optimize the
communication between the base station 1 and the first UE 23a.
During a second and third time slot, communication is optimized
between the base station 1 and the second 23b and third 23c UE:s,
respectively, in the same way. How the antenna radiation lobes are
directed for each UE 23a, 23b, 23c depends on the surroundings for
each UE 23a, 23b, 23c, for example if there are buildings (not
shown) present. The procedure according to the above relates to a
time division multiple access (TDMA) system, of course other
systems such as a frequency division multiple access (FDMA) system
or a combination of both, are possible.
[0059] The UE 23 may be equipped with any number of antenna ports,
but in order for the UE 23 to be arranged for a MIMO system, it is
necessary that the UE 23 is equipped with at least two antenna
ports. When communication commences, the base station 1 adapts to
the number of antenna ports available at the UE 23.
[0060] The UE 23 may be equipped with adaptive antennas, which
antennas are electrically controllable in the direction where the
highest data bit rate is achieved. The UE 23 may also be equipped
with means (not shown) for determining which orientation of the UE
23 that provides the best communication properties.
[0061] The invention is not limited to the embodiments described
above, but may vary freely within the scope of the appended claims.
For example, the base station array antenna may have any suitable
configuration of antenna elements, for example 4 columns and 4
rows, forming a 4.times.4 array antenna, thus being arranged for
achieving up to sixteen antenna radiation lobes.
[0062] More generally, the base station antenna is an array antenna
equipped with at least two antenna ports, where the at least two
ports are connected to respective at least two corresponding
antenna elements, where at least two of the at least two antenna
elements have essentially the same polarization.
[0063] Thus, according to the invention, at least two antenna ports
must be comprised in the base station array antenna, the base
station array antenna thus being arranged for radiating two antenna
radiation lobes, which is necessary for MIMO communication.
[0064] However, assuming that the first embodiment is used for the
situation according to FIG. 4, it is conceivable that only one
antenna radiation lobe is switched on, since no more antenna
radiation lobes are necessary to achieve optimal communication
between the base station 1 and the UE 23.
[0065] It is of course conceivable that the second embodiment, with
controllable antenna radiation lobes, may be arranged for turning
antenna radiation lobes off in the same manner as in the first
embodiment.
[0066] The lobes of the base station array antenna 3 according to
the second embodiment of the invention may be controllable in
azimuth only, elevation only, or, as in the embodiments above, both
in azimuth and elevation. As known to those skilled in the art, a
base station array antenna that is controllable in both azimuth and
elevation has to be two-dimensional, i.e. have antenna elements in
both rows and columns.
[0067] For all embodiments, the base station array antenna 3 may
further comprise dual polarized antenna elements, the base station
array antenna 3 thus being arranged for communication via two
essentially orthogonal polarizations, thus doubling the information
stream transmission rate.
[0068] An example of how dual polarized antenna elements can be
arranged is described below with reference to FIG. 6. There, an
array antenna 32 is shown, having a first 33, second 34, third 35
and fourth 36 antenna element. Each antenna element 33, 34, 35, 36
comprises at least one radiating element. The antenna elements 33,
34, 35, 36 are placed in a first 37 and second 38 row and a first
39 and second column 40, forming a 2.times.2 array antenna 32. The
antenna elements 33, 34, 35, 36 are preferably separated by
approximately 0.5-1 wavelengths (calculated from the centre
frequency of the frequency band for which the antennas are
designed) in the horizontal plane for beam-forming in azimuth and
approximately 0.5-4 wavelengths in a vertical plane for
beam-forming in elevation. Each antenna element 33, 34, 35, 36 is
arranged for a first and a second polarization, the polarizations
being essentially de-correlated.
[0069] The antenna elements 33, 34, 35, 36 receive and transmit
signals using the same frequency band, for the uplink and another
frequency band for the downlink if FDD (Frequency Division Duplex)
is utilized, or using the same frequency band, for both the uplink
and the downlink if TDD (Time Division Duplex) is utilized.
[0070] In this example, the first polarization of the first 33,
second 34, third 35 and fourth 36 antenna element is connected to
respective first 41, second 42, third 43 and fourth 44 feeding
lines via respective first P1a, second P2a, third P3a and fourth
P4a antenna ports. In the same way, the second polarization of the
first 33, second 34, third 35 and fourth 36 antenna element is
connected to respective fifth 45, sixth 46, seventh 47 and eighth
48 feeding lines via respective fifth P1b, sixth P2b, seventh P3b
and eighth P4b antenna ports.
[0071] The first 41 and second 42 feeding lines, which are
connected to the first polarization of the antenna elements 33, 34
in the first row 37, are connected to a first power divider 49, and
the second 43 and third 44 feeding lines, which are connected to
the first polarization of the antenna elements 35, 36 in the second
row 38, are connected to a second power divider 50.
[0072] The fifth 45 and seventh 47 feeding lines, which are
connected to the second polarization of the antenna elements 33, 35
in the first column 39, are connected to a third power divider 51,
and the sixth 46 and eighth 48 feeding lines, which are connected
to the second polarization of the antenna elements 34, 36 in the
second column 40, are connected to a fourth power divider 52.
[0073] The first 49 and second 50 power dividers are connected to a
first beam-forming device 53 and the third 51 and fourth 52 power
dividers are connected to a second beam-forming device 54. The
beam-forming devices 53, 54 are of a previously known kind, for
example digital beam-forming devices. The devices 53, 54 may be
combined in one beam-forming device.
[0074] By means of this arrangement, the radiation lobes formed by
the rows 37, 38, having the first polarization, may be controlled
separate from the radiation lobes formed by the columns 39, 40,
having the second polarization. The antenna radiation beams are
incoherently added in the far-field.
[0075] Generally, for all embodiments described, since all antenna
arrangements are reciprocal, all features described as concerning
transmission, are also applicable concerning reception.
[0076] Furthermore, the number of base station array antennas 3,
base station antenna radiation lobes 24, 25, 26, 27 may vary in any
convenient way, provided that the system still is arranged for
MIMO.
[0077] As indicated above, the invention is applicable for an
arbitrary number of UE:s 23; 23a, 23b, 23c. More than one base
station 1 may also be necessary, for example due to the demands for
capacity and/or the layout of the cell 2 environments.
[0078] The base station 1 may be a base station in any wireless
communication system, such as a wireless local area network
(WLAN).
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