WO2013097888A1 - A node in a line-of-sight wireless communication link - Google Patents

A node in a line-of-sight wireless communication link Download PDF

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Publication number
WO2013097888A1
WO2013097888A1 PCT/EP2011/074119 EP2011074119W WO2013097888A1 WO 2013097888 A1 WO2013097888 A1 WO 2013097888A1 EP 2011074119 W EP2011074119 W EP 2011074119W WO 2013097888 A1 WO2013097888 A1 WO 2013097888A1
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Prior art keywords
node
antennas
local oscillator
processing unit
signal processing
Prior art date
Application number
PCT/EP2011/074119
Other languages
French (fr)
Inventor
Dan Weinholt
Ove Thomas Emanuelsson
Carmelo Decanis
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Telefonaktiebolaget L M Ericsson (Publ)
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Priority to PCT/EP2011/074119 priority Critical patent/WO2013097888A1/en
Publication of WO2013097888A1 publication Critical patent/WO2013097888A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/12—Supports; Mounting means
    • H01Q1/125—Means for positioning
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/52—Means for reducing coupling between antennas; Means for reducing coupling between an antenna and another structure
    • H01Q1/521—Means for reducing coupling between antennas; Means for reducing coupling between an antenna and another structure reducing the coupling between adjacent antennas
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q21/00—Antenna arrays or systems
    • H01Q21/24—Combinations of antenna units polarised in different directions for transmitting or receiving circularly and elliptically polarised waves or waves linearly polarised in any direction
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q21/00—Antenna arrays or systems
    • H01Q21/28—Combinations of substantially independent non-interacting antenna units or systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/10—Polarisation diversity; Directional diversity

Definitions

  • the present invention relates to a node in a line-of-sight wireless communication link.
  • the node comprises at least a first antenna and a second antenna, adjacent antennas being mounted at a certain distance from each other.
  • the node further comprises a signal processing unit and a local oscillator.
  • the local oscillator is arranged for demodulating received signals from a first frequency, the signals being received by the antennas at the first frequency.
  • the demodulated signals are handled by the signal processing unit.
  • Line-of-sight (LOS) radio links have been used for decades, and are normally used to transfer information in analog or digital form, primary in digital form nowadays.
  • SNR signal to noise ratio
  • FEC- schemes Forward Error Correction
  • Another way to increase capacity in a LOS radio link is to use polarization discrimination over the same point-to-point connection, which will double the capacity. This technique has been in use for a long time.
  • LOS-MIMO Multiple Input Multiple Output
  • the placement of N transmit and N receive antennas is used to create different transmission distance which allows to separate N different information streams.
  • LOS-MIMO is used in the frequency range of microwave radio links, approximately 1 - 80 GHz,
  • the mounting distance between the antennas may in practice become significantly large in case of fairly low frequency and/or fairly large distances (5-50 km).
  • the node comprises at least a first antenna and a second antenna, adjacent antennas being mounted at a certain distance from each other.
  • the node further comprises a signal processing unit and a local oscillator.
  • the local oscillator is arranged for demodulating received signals from a first frequency, the signals being received by the antennas at the first frequency.
  • the demodulated signals are handled by the signal processing unit.
  • the signal processing unit and the local oscillator are positioned in a common housing, and the antennas are connected to the local oscillator. The distance between adjacent antennas is adjustable.
  • the wireless communication link is of the type LOS-MIMO.
  • the antennas are connected to the local oscillator by means of corresponding adjustable or flexible connections.
  • Each adjustable or flexible connection may for example be in the form of a flexible waveguide or in the form of a coaxial cable.
  • Adjustable antenna distance allows adaption to different hop length.
  • Figure 1 shows a schematic top view of a radio link
  • Figure 2 shows a schematic side view of a radio link node.
  • the radio link L comprises a first node 1 and a second node 10.
  • the first node 1 comprises a first antenna 2 and a second antenna 3, which antennas 2, 3 are mounted at a certain distance d from each other.
  • the second node 10 comprises a corresponding third antenna 1 1 and fourth antenna 12 which are mounted at a certain distance d from each other the mounting distance d being approximately the same for the nodes 1 , 10.
  • the first antenna 2 is arranged to communicate with the third antenna 1 1 and the fourth antenna 12, and the second antenna 3 is also arranged to communicate with the third antenna 1 1 and the fourth antenna 12.
  • the link distance D-i is the distance between the first antenna 2 and the third antenna 1 1 as well as between the second antenna 3 and the fourth antenna 12. Although this is not shown in the schematic Figure 1 , the link distance Di is much greater the mounting distance d, the link distance Di for example being in the order of thousands of meters, and the mounting distance d being in the order of tenths of meters or even less.
  • interfering distance D 2 is the distance between the first antenna 2 and the fourth antenna 12 as well as between the second antenna 3 and the third antenna 1 1 .
  • M is an integer 0, 1 , 2, ...
  • c Speed of light (approximately 3x10 m/s)
  • f Carrier frequency (Hz)
  • ⁇ Carrier wavelength (m).
  • the first node 1 comprises a signal processing unit 4 and a local oscillator 5.
  • the local oscillator 5 is arranged to demodulate the received signal having a first carrier frequency f-i , either by direct demodulation (homodyne receiver), or via one or several intermediate frequencies, for example a second frequency f 2 (heterodyne or super-heterodyne receiver).
  • the signals that are received by the first antenna 2 and the second antenna 3 at the first frequency fi and the demodulated signals are handled by the signal processing unit 4.
  • the signal processing unit 4 and the local oscillator 5 are positioned in a common housing 6, where the antennas 2, 3 are connected to the local oscillator 5. Furthermore, the mounting distance d between the adjacent antennas 2, 3 is adjustable.
  • the housing 6 may comprise all radio components of the first node 1 , and also a modem.
  • the wireless LOS communication link L is of the type LOS-MIMO, LOS- Multiple Input Multiple Output.
  • An interface 9 to the signal processing unit 4 may be in the form of a radio interface 9 for a re-modulated intermediate frequency, the radio interface may then constitute an interface to the node 1 .
  • an interface 9 to the signal processing unit 4 may be in the form of a data interface, the data interface may then constitute an interface to the node 1 .
  • the antennas 2, 3 may be connected to the local oscillator 5 by means of corresponding adjustable or flexible connections 7, 8.
  • the adjustment functionality is indicated with dash-dotted lines in Figure 2.
  • a LOS-MIMO concept is restricted to a combination of frequency and hop distance that results in reasonable antenna mounting distance d ⁇ 2m, which makes it possible to combine the radios of prior art into one unit in the housing 6.
  • This approach allows the use of the same local oscillator 5 for down- conversion for both antennas 2, 3, which removes the problem of differential phase noise which will drastically reduce system implementation complexity, in addition to reduced cost due to only one local oscillator.
  • the present invention allows adjustment of the distance between the antennas 2, 3, it is possible to avoid units that are designed for a specific hop distance.
  • the complete radio is housed in one unit that is mounted to actual mechanical support as one separate unit, and the distance between the antennas 2, 3 is adjustable.
  • the adjustable or flexible connections 7, 8 may for example be in the form of a flexible waveguides or in the form of coaxial cables.
  • the antennas may be separated vertically, as indicated in Figure 2, but may also be separated horizontally.
  • the antennas 2, 3 and the housing 6 are shown attached to a mast 13 by means of a holding means 14, which holding means 14 for example may be in the form of one or two metal beams that are attached to the mast 13.
  • the interface 9 may comprise a coaxial cable or an optical fiber.
  • the antennas 2, 3; 1 1 , 12 may be arranged to receive and transmit signals by means of orthogonal polarizations.
  • orthogonal polarizations For example, two 2x2 LOS-MIMO systems may be used simultaneously if they are separated by means of orthogonal polarizations. If the antennas are provided with a respective OMT (OrthoMode Transducer), the same physical antenna may be used.
  • the number of antennas at each node 1 , 10 may vary, but should be at least two, and be the same number at each node 1 , 10 in a wireless communication link L according to the above.

Abstract

The present invention relates to a node (1) in a line-of-sight wireless communication link (L). The node (1) comprises at least first (2) and second (3)antennas mounted at a certain distance (d) from each other. The node (1) further comprises a signal processing unit (4) and a local oscillator (5). The local oscillator (5) is arranged for demodulating received signals by the antennas (2,3) having a first frequency (fi). This approach reduces differential phase noise compared to individual local oscillators for each antenna. The demodulated signals are handled by the signal processing unit (4). The signal processing unit (4) and the local oscillator (5) are positioned in a common housing (6), and the antennas (2, 3) are connected to the local oscillator (5), where furthermore the distance (d) between adjacent antennas (2, 3) is adjustable. Accordingly, nodes designed for a specific hop distance are avoided.

Description

TITLE
A node in a line-of-sight wireless communication link TECHNICAL FIELD
The present invention relates to a node in a line-of-sight wireless communication link. The node comprises at least a first antenna and a second antenna, adjacent antennas being mounted at a certain distance from each other. The node further comprises a signal processing unit and a local oscillator. The local oscillator is arranged for demodulating received signals from a first frequency, the signals being received by the antennas at the first frequency. The demodulated signals are handled by the signal processing unit.
BACKGROUND
Line-of-sight (LOS) radio links have been used for decades, and are normally used to transfer information in analog or digital form, primary in digital form nowadays. There is an upper bound for the amount of digital data that can be reliably transmitted in a specified bandwidth and signal to noise ratio (SNR) called "Shannon limit". A lot of research has been performed in order to reach this limit by using advanced FEC- schemes (Forward Error Correction). Another way to increase capacity in a LOS radio link is to use polarization discrimination over the same point-to-point connection, which will double the capacity. This technique has been in use for a long time.
One more technique that has been discussed but not yet commercially used is spatial discrimination in a LOS-MIMO (Multiple Input Multiple Output) system. In this case, the placement of N transmit and N receive antennas is used to create different transmission distance which allows to separate N different information streams. When LOS-MIMO is used in the frequency range of microwave radio links, approximately 1 - 80 GHz,
The mounting distance between the antennas may in practice become significantly large in case of fairly low frequency and/or fairly large distances (5-50 km).
In present systems, there is a problem with high performance requirements for phase noise for the local oscillators in order to reduce the differential phase noise. There is thus a need for a LOS radio link, preferably a LOS-MIMO radio link, where the phase noise problems are reduced.
SUMMARY
It is an object of the present invention to provide a LOS radio link were the problem with differential phase noise is alleviated.
Said object tis obtained by means of a node in a line-of-sight wireless communication link. The node comprises at least a first antenna and a second antenna, adjacent antennas being mounted at a certain distance from each other. The node further comprises a signal processing unit and a local oscillator. The local oscillator is arranged for demodulating received signals from a first frequency, the signals being received by the antennas at the first frequency. The demodulated signals are handled by the signal processing unit. Furthermore, the signal processing unit and the local oscillator are positioned in a common housing, and the antennas are connected to the local oscillator. The distance between adjacent antennas is adjustable.
According to an example, the wireless communication link is of the type LOS-MIMO. According to another example, the antennas are connected to the local oscillator by means of corresponding adjustable or flexible connections. Each adjustable or flexible connection may for example be in the form of a flexible waveguide or in the form of a coaxial cable.
More examples are disclosed in the dependent claims.
A number of advantages are obtained by means of the present invention, for example:
Only one unit is needed to realize one side of a LOS radio link hop.
- Differential phase noise problems are avoided by means of an uncomplicated implementation of a common local oscillator.
Adjustable antenna distance allows adaption to different hop length.
Less expensive node. BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described more in detail with reference to the appended drawings, where:
Figure 1 shows a schematic top view of a radio link; and
Figure 2 shows a schematic side view of a radio link node. DETAILED DESCRIPTION
With reference to Figure 1 , schematically showing a top view of a LOS (Line Of Sight) radio link L, the radio link L comprises a first node 1 and a second node 10. The first node 1 comprises a first antenna 2 and a second antenna 3, which antennas 2, 3 are mounted at a certain distance d from each other.
The second node 10 comprises a corresponding third antenna 1 1 and fourth antenna 12 which are mounted at a certain distance d from each other the mounting distance d being approximately the same for the nodes 1 , 10. The first antenna 2 is arranged to communicate with the third antenna 1 1 and the fourth antenna 12, and the second antenna 3 is also arranged to communicate with the third antenna 1 1 and the fourth antenna 12.
The link distance D-i is the distance between the first antenna 2 and the third antenna 1 1 as well as between the second antenna 3 and the fourth antenna 12. Although this is not shown in the schematic Figure 1 , the link distance Di is much greater the mounting distance d, the link distance Di for example being in the order of thousands of meters, and the mounting distance d being in the order of tenths of meters or even less.
It is well known that in order to keep interference levels low, the mounting distance should be adapted to the link distance such that interfering signals may be arranged to cancel each other, which will be discussed below. There is an interfering distance D2, which is the distance between the first antenna 2 and the fourth antenna 12 as well as between the second antenna 3 and the third antenna 1 1 .
Pythagoras theorem then yields:
Figure imgf000006_0001
The preferred mounting distance should be
Figure imgf000006_0002
where M is an integer 0, 1 , 2, ...
For M = 0
(2)
Figure imgf000006_0003
The difference in path length from one antenna to the two other antennas is D2 which means that, inserting (1 ) into (2): ^ = ^ + d2 - D, = D, (3)
Figure imgf000007_0005
But since
d/D « 1
and since there is a known approximation for the case
Figure imgf000007_0001
when x« 1 , the expression (3) above may be written as
Figure imgf000007_0002
Since
Figure imgf000007_0003
an approximation for the distance d between the antennas may be written as
Figure imgf000007_0004
In the above,
c = Speed of light (approximately 3x10 m/s), f = Carrier frequency (Hz), and
λ = Carrier wavelength (m).
With reference to Figure 2, schematically showing a part of the first node 1 , the first node 1 comprises a signal processing unit 4 and a local oscillator 5. The local oscillator 5 is arranged to demodulate the received signal having a first carrier frequency f-i , either by direct demodulation (homodyne receiver), or via one or several intermediate frequencies, for example a second frequency f2 (heterodyne or super-heterodyne receiver). The signals that are received by the first antenna 2 and the second antenna 3 at the first frequency fi and the demodulated signals are handled by the signal processing unit 4.
According to the present invention, the signal processing unit 4 and the local oscillator 5 are positioned in a common housing 6, where the antennas 2, 3 are connected to the local oscillator 5. Furthermore, the mounting distance d between the adjacent antennas 2, 3 is adjustable. Thus the housing 6 may comprise all radio components of the first node 1 , and also a modem.
Preferably, the wireless LOS communication link L is of the type LOS-MIMO, LOS- Multiple Input Multiple Output.
An interface 9 to the signal processing unit 4 may be in the form of a radio interface 9 for a re-modulated intermediate frequency, the radio interface may then constitute an interface to the node 1 .
Then, for example, an interface 9 to the signal processing unit 4 may be in the form of a data interface, the data interface may then constitute an interface to the node 1 .
In order to obtain an adjustable mounting distance d, the antennas 2, 3 may be connected to the local oscillator 5 by means of corresponding adjustable or flexible connections 7, 8. The adjustment functionality is indicated with dash-dotted lines in Figure 2. By means of the present invention, a LOS-MIMO concept is restricted to a combination of frequency and hop distance that results in reasonable antenna mounting distance d < 2m, which makes it possible to combine the radios of prior art into one unit in the housing 6. This approach allows the use of the same local oscillator 5 for down- conversion for both antennas 2, 3, which removes the problem of differential phase noise which will drastically reduce system implementation complexity, in addition to reduced cost due to only one local oscillator.
Since the present invention allows adjustment of the distance between the antennas 2, 3, it is possible to avoid units that are designed for a specific hop distance.
Thus, as a summary, the complete radio is housed in one unit that is mounted to actual mechanical support as one separate unit, and the distance between the antennas 2, 3 is adjustable.
It is conceivable that a corresponding arrangement is present at the second node 10 as well.
The present invention is not limited to the above, but may vary freely within the scope of the appended claims.
For example, the adjustable or flexible connections 7, 8 may for example be in the form of a flexible waveguides or in the form of coaxial cables. The antennas may be separated vertically, as indicated in Figure 2, but may also be separated horizontally. In Figure 2, the antennas 2, 3 and the housing 6 are shown attached to a mast 13 by means of a holding means 14, which holding means 14 for example may be in the form of one or two metal beams that are attached to the mast 13.
The interface 9 may comprise a coaxial cable or an optical fiber. The antennas 2, 3; 1 1 , 12 may be arranged to receive and transmit signals by means of orthogonal polarizations. For example, two 2x2 LOS-MIMO systems may be used simultaneously if they are separated by means of orthogonal polarizations. If the antennas are provided with a respective OMT (OrthoMode Transducer), the same physical antenna may be used.
The number of antennas at each node 1 , 10 may vary, but should be at least two, and be the same number at each node 1 , 10 in a wireless communication link L according to the above.

Claims

1 . A node (1 ) in a line-of-sight, LOS, wireless communication link (L), the node (1 ) comprising at least a first antenna (2) and a second antenna (3), adjacent antennas being mounted at a certain distance (d) from each other, the node (1 ) further comprising a signal processing unit (4) and a local oscillator (5), the local oscillator (5) being arranged for demodulating received signals from a first frequency (f-i ), the signals being received by the antennas (2, 3) at the first frequency (f-i ), the demodulated signals being handled by the signal processing unit (4), characterized in that the signal processing unit (4) and the local oscillator (5) are positioned in a common housing (6), and that the antennas (2, 3) are connected to the local oscillator (5), where furthermore the distance (d) between adjacent antennas (2, 3) is adjustable.
2. A node according to claim 1 , characterized in that the antennas (2, 3) are arranged to receive and transmit signals by means of orthogonal polarizations.
3. A node according to any one of the claims 1 or 2, characterized in that the wireless communication link (L) is of the type LOS-MIMO, LOS-Multiple Input Multiple Output.
4. A node according to any one of the previous claims, characterized in that the antennas (2, 3) are connected to the local oscillator (5) by means of corresponding adjustable or flexible connections (7, 8).
5. A node according to claim 4, characterized in that each adjustable or flexible connection (7, 8) is in the form of a flexible waveguide or in the form of a coaxial cable.
6. A node according to any one of previous the claims, characterized in that an interface (9) to the signal processing unit (4) is in the form of a data interface, the data interface constituting an interface to the node (1 ).
7. A node according to any one of the claims 1 -5, characterized in that an interface (9) to the signal processing unit (4) is in the form of a radio interface (9) for a re-modulated intermediate frequency (f2), the radio interface constituting an interface to the node (1 ).
PCT/EP2011/074119 2011-12-28 2011-12-28 A node in a line-of-sight wireless communication link WO2013097888A1 (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
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WO2016206750A1 (en) * 2015-06-25 2016-12-29 Telefonaktiebolaget Lm Ericsson (Publ) Interference mitigation in multiple input multiple output systems
WO2017167352A1 (en) * 2016-03-29 2017-10-05 Telefonaktiebolaget Lm Ericsson (Publ) Rotatable antenna arrangement for los-mimo

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2016206750A1 (en) * 2015-06-25 2016-12-29 Telefonaktiebolaget Lm Ericsson (Publ) Interference mitigation in multiple input multiple output systems
WO2017167352A1 (en) * 2016-03-29 2017-10-05 Telefonaktiebolaget Lm Ericsson (Publ) Rotatable antenna arrangement for los-mimo
CN108886193A (en) * 2016-03-29 2018-11-23 瑞典爱立信有限公司 Rotary antenna device for LOS-MIMO
US10547355B2 (en) 2016-03-29 2020-01-28 Telefonaktiebolaget Lm Ericsson (Publ) Rotatable antenna arrangement for LOS-MIMO
CN108886193B (en) * 2016-03-29 2021-04-09 瑞典爱立信有限公司 Rotatable antenna arrangement for LOS-MIMO

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