Beam forming using an antenna arrangement
There is provided mechanisms for beam forming using an antenna array comprising dual polarized elements. A method comprises generating one or two beam ports, wherein the one or two beam ports are defined by combining at least two non-overlapping subarrays. Each subarray has two subarray ports, the two subarray ports having identical power patterns and mutually orthogonal polarization. The at least two non-overlapping subarrays are combined via expansion weights. The expansion weights map the one or two beam ports to subarray ports such that the one or two beam ports have the same power pattern as the subarrays. At least some of the expansion weights have identical non-zero magnitude and are related in phase to form a transmission lobe. The method comprises transmitting signals using said one or two beam ports.
1. An antenna arrangement, comprising:
an antenna array comprising dual polarized elements for beam forming;
processing circuitry configured to cause the antenna array to:
generate one or two beam ports:
wherein the one or two beam ports are defined by combining at least two non-overlapping subarrays;
wherein each subarray has two subarray ports, the two subarray ports having identical power patterns and mutually orthogonal polarization;
wherein the at least two non-overlapping subarrays are combined via expansion weights;
wherein the expansion weights map the one or two beam ports to subarray ports such that the one or two beam ports have the same power pattern as the subarray ports;
wherein at least some of the expansion weights have identical non-zero magnitude and are related in phase to form a transmission lobe;
wherein the expansion weights are collected in an expansion matrix and are determined such that the expansion matrix is spatially white;
transmit signals using the one or two beam ports.
2. The antenna arrangement of claim 1 , wherein the expansion weights map the one or two beam ports to subarray ports such that the one or two beam ports have the same power pattern as the subarrays.
3. The antenna arrangement of claim 1 , wherein:
there are two beam ports; and
the expansion weights are defined to keep the polarization of the two beam ports mutually orthogonal.
4. The antenna arrangement of claim 1 , wherein:
there are two beam ports; and
the expansion weights map the two beam ports to products of powers of 2, 6, or 10 subarrays per dimension.
5. The antenna arrangement of claim 1 , wherein
there is one beam port; and
the expansion weights map the beam port to powers of 2, 6, and/or 10 times 1, 3, or 5 subarrays.
6. The antenna arrangement of claim 1 , wherein the subarrays are further expanded by further expansion weights before defining the one or two beam ports.
7. The antenna arrangement of claim 1 , wherein the expansion weights are determined such that all elements in a matrix defined by the sum of the magnitude squared of the two-dimensional discrete Fourier transform of a first expansion weight matrix applied to a first of the subarray ports and the magnitude squared of the two-dimensional discrete Fourier transform of a second expansion weight matrix applied to a second of the subarray ports have the same value.
8. The antenna arrangement of claim 1 , wherein the expansion weights are determined such that:
|DFT( ea )| 2 +|DFT( eb )| 2 =k·J rc ,
where DFT(ea) and DFT(eb) denote the discrete Fourier transforms of ea and eb, respectively, where ea and eb are the total expansion matrices applied to the subarray ports a and b, respectively, where a is first of the subarray ports, where b is a second of the subarray ports, where k is a constant, and where J rc is an all-one matrix having r rows and c columns.
9. The antenna arrangement of claim 1 , wherein the at least two non-overlapping subarrays together cover all elements of the antenna array.
10. The antenna arrangement of claim 1 , wherein the expansion weights of the at least two sub-arrays are added to generate one of the one or two beam ports.
11. The antenna arrangement of claim 1 , wherein the expansion weights for a port a with a first polarization are determined as:
ea
2
=
[
e
i
π
4
[
1
-
1
]
Z
12
]
,
ea
6
=
[
e
i
π
4
[
3
1
0
0
1
3
]
Z
32
]
,
ea
10
=
[
e
i
π
4
[
-
2
0
-
1
3
0
0
3
-
1
0
-
2
]
Z
52
]
,
where ea m denotes the expansion weights for mapping one beam port of the one or two beam ports to multiples of m subarrays, and where Z rc an all-zero matrix having r rows and c columns.
12. The antenna arrangement of claim 11 , wherein the expansion weights for a port b with a second polarization, orthogonal to the first polarization, is determined as:
eb m =flipud([ ea m (:,2)− ea m (:,1)]*),
where ea m (:,c) denotes column c of ea m , where * denotes complex conjugate, and where flipud(x) reverses the row order of x.
13. The antenna arrangement of claim 1 , wherein the signals comprise at least one of broadcast information and system information.
14. The antenna arrangement of claim 1 , wherein there are two beam ports; and wherein the expansion weights map the one or two beam ports to subarray ports such that the one or two beam ports have the same power pattern as the subarrays, and the two beam ports have mutually orthogonal polarizations in any direction.
15. The antenna arrangement of claim 2 , wherein
there are two beam ports; and
the two beam ports have mutually orthogonal polarizations in any direction.
16. A network node comprising:
an antenna arrangement comprising an antenna array and processing circuitry;
wherein the antenna array comprises dual polarized elements for beam forming;
wherein the processing circuitry is configured to cause the antenna array to:
generate one or two beam ports:
wherein the one or two beam ports are defined by combining at least two non-overlapping subarrays;
wherein each subarray has two subarray ports, the two subarray ports having identical power patterns and mutually orthogonal polarization;
wherein the at least two non-overlapping subarrays are combined via expansion weights;
wherein the expansion weights map the one or two beam ports to subarray ports such that the one or two beam ports have the same power pattern as the subarrays;
wherein at least some of the expansion weights have identical non-zero magnitude and are related in phase to form a transmission lobe;
wherein the expansion weights are collected in an expansion matrix and are determined such that the expansion matrix is spatially white;
transmit signals using the one or two beam ports.
17. An antenna system comprising:
an array of antenna elements:
wherein each antenna element is a sub-array of at least a first and a second radiating antenna element, the first radiating antenna element being connected via feed network to a first subarray port and the second radiating antenna element being connected via feed network to a second subarray port, the first and the second subarray port having mutually orthogonal polarization, and
wherein each subarray port is connected to a radio chain as comprised in a radio array; and
subarray ports accessible to baseband signal processing being linear combinations of the first and second antenna ports of all radiating antenna elements,
wherein the subarray ports accessible to baseband signal processing are fewer than the antenna ports of all radiating antenna elements.
18. The antenna system of claim 17 , further comprising processing circuitry configured to cause the antenna system to form virtual antenna ports in baseband signal processing by matrix multiplications.
19. The antenna system of claim 18 , wherein the virtual antenna port carries common reference signals (CRS), channel state information reference signals (CSI-RS), and UE-specific reference signals and data.
20. A wireless device, comprising an antenna arrangement, the antenna arrangement comprising:
an antenna array comprising dual polarized elements for beam forming;
processing circuitry configured to cause the antenna array to:
generate one or two beam ports:
wherein the one or two beam ports are defined by combining at least two non-overlapping subarrays;
wherein each subarray has two subarray ports, the two subarray ports having identical power patterns and mutually orthogonal polarization;
wherein the at least two non-overlapping subarrays are combined via expansion weights;
wherein the expansion weights map the one or two beam ports to subarray ports such that the one or two beam ports have the same power pattern as the subarray ports;
wherein at least some of the expansion weights have identical non-zero magnitude and are related in phase to form a transmission lobe;
wherein the expansion weights are collected in an expansion matrix and are determined such that the expansion matrix is spatially white;
transmit signals using the one or two beam ports.