EP2645474A1

EP2645474A1 - Distributed antenna system, building structure, vehicle, and communication system thereof

Info

Publication number: EP2645474A1
Application number: EP12305367.0A
Authority: EP
Inventors: Heinz-Dieter Hettstedt; Gurgen Harutyunyan; Alexander Thomas; Axel Schroeder; Erhard Mahlandt
Original assignee: Alcatel Lucent SAS
Current assignee: Alcatel Lucent SAS
Priority date: 2012-03-29
Filing date: 2012-03-29
Publication date: 2013-10-02

Abstract

The present invention relates to a distributed antenna system (2) for exchanging radio frequency signals between at least one user equipment (22a) and at least one transceiver unit (6, 8) coupled to the distributed antenna system (2). The distributed antenna system (2) contains at least two radiating waveguides (10, 12). Each of the at least two radiating waveguides (10, 12) comprises an inner longitudinal hollow space and forms a part of a respective radio frequency transmission channel between the at least one transceiver unit (6, 8) and the at least one user equipment (22a) and can be operated independently of further radiating waveguides. The radiating waveguides (10, 12) are configured to radiate and/or receive the radio frequency signals with a first polarization and a second polarization, respectively, and the first polarization is different from the second polarization. The invention further relates to a building structure, to a vehicle and to a communication system (3).

Description

FIELD OF THE INVENTION

The invention relates to a distributed antenna system for transmitting and receiving radio frequency signals from and to one or several user equipments.

BACKGROUND

Different communication standards such as 3GPP LTE (3GPP = 3rd Generation Partnership Project, LTE = Long Term Evolution), a WLAN (WLAN = Wireless Local Area Network) as defined by IEEE 802.11 (IEEE = Institute of Electrical and Electronics Engineers) or HSPA+ (further generation of HSPA = High Speed Packet Access) propose a MIMO transmission scheme (MIMO = multiple input multiple output) to improve data throughput from the backhaul network to the user equipment and backwards.
For a MIMO transmission scheme a sender unit and a receiver unit comprises at least two antennas, respectively, whereby a plurality of independent radio channels may be established between the devices. The sender unit and the receiver unit comprise signal processing means to make use of said different RF transmission channels.
It is further known to provide an isotropic antenna fixed to one point inside an elongated building structure such as a railway tunnel for providing radio coverage within the tunnel. This configuration has several drawbacks due to decreased coverage.

SUMMARY

The way of providing coverage, when a user equipment moves away from the isotropic antenna effects a reliable transmission and a data throughput of radio frequency signals between the antenna and the user equipment.
Therefore, it is an object of the present invention to provide an improved distributed antenna system which enables the use of a MIMO transmission scheme for the transmission and/or reception of radio frequency signals, particularly within building structures, vehicles and other confined spaces impeding radio frequency wave propagation.
This object is achieved by a distributed antenna system according to claim 1.
The invention enables MIMO communication along guided routes outside buildings but also inside an elongated building structure, in particular inside a railway tunnel or a road tunnel. Thus, a particularly efficient communication between the user equipment and a transceiver over the distributed antenna system may be accomplished, because the inventive distributed antenna system can advantageously support multiple simultaneous communication paths to establish radio frequency transmission channels allowing data rates even above the theoretical Shannon limit. Thus, high data rate applications such as mobile TV (TV = television) inside a funnel environment are feasible for high-density passenger trains, such as metro trains. The different polarizations provide a parameter to identify/distinguish between the different radio frequency transmission channels by the user equipment and by the antenna system itself. I.e., a first MIMO channel may be realized with signals being radiated from a first radiating waveguide with a first polarization, whereas a second MIMO channel may be realized with signals being radiated from a second radiating waveguide with a second polarization.
According to a preferred embodiment, the first polarization is substantially orthogonal to the second polarization. Therefore, the at least first and second radiating waveguides are configured to emit and receive radio frequency signals independently of each other. This feature, in addition to the usage of more than one radiating waveguide, provides a further parameter to create and identify different radio frequency transmission channels supported by the antenna system.
According to a further embodiment, the at least first and second radiating waveguides run substantially into the same direction and/or are at least in sections aligned parallel to each other. Advantageously these configurations allow a continuously substantially equal coverage for example along the elongated building structure. Furthermore, the radiation power level can be reduced for user equipments moving along the at least two radiating waveguides if a smooth radio frequency signal field strength distribution along the radiating waveguides is provided. Further, due to different positions of radiating openings within the radiating waveguides, the radio frequency transmission properties of different radio frequency channels enabled by the radiating waveguides can be tuned, e.g. to achieve different delay characteristics.
According to a further preferred embodiment, the at least first and second radiating waveguides are lengthwise arranged adjacent to each other.
In a further embodiment, one or several first radiating waveguide(s) of the at least two radiating waveguides comprise(s) first slots and a longitudinal axis of each of the first slots is aligned substantially perpendicular to a longitudinal axis of the one or several first radiating waveguide(s). Therefore, the one or several first radiating waveguide(s) running along a horizontal direction can emit radio frequency signals with a horizontal polarization.
According to a further embodiment, one or several second radiating waveguide(s) of the at least two radiating waveguides comprise(s) second slots and a longitudinal axis of each of the second slots is aligned substantially transversely to a longitudinal direction of the one or several second radiating waveguide(s). The one or several second radiating waveguide(s) running along a horizontal direction therefore can radiate and/or receive radio frequency signals with a different polarization as the radio frequency signals radiated and/or received by the one or several first radiating waveguide(s).
A transverse orientation of slots within a radiating waveguide is also possible. It is further possible to provide one specific radiating waveguide with different types of slots. Of course, more than two radiating waveguides may also be provided to form a distributed antenna system according to an embodiment. According to the adjacent arrangement of the first and second radiating waveguides, the distance between the radiating waveguides can be substantially constant along the radiating waveguides and can be equal to or greater than e.g. a diameter of a radiating waveguide. Advantageously, the adjacent arrangement allows an easy installation of the distributed antenna system while still providing the multichannel capability to implement a MIMO transmission scheme. E.g., the adjacent arrangement of radiating waveguides may be mounted to a building wall by means of standoffs, which define a predetermined spacing between the wall and the radiating waveguides.
According to an even further preferred embodiment, two or more radiating waveguides comprise elliptical cross sections and each casing of the two or more radiating waveguides comprises a corrugation. Such a geometrical structure of the radiating waveguides allows an eased installation of the distributed antenna system, because each radiating waveguide may be installed as a whole piece by rewinding the radiating waveguide from a coil and by allowing also an installation on curved walls. Preferably, the at least first and second radiating waveguides are arranged on a height above a floor corresponding to a region of a window of a passing vehicle, in particular a train or a car, or corresponding to a region of a head of a passing person. Thereby, the first and second radiating waveguides provide coverage in the area of a user equipment. So the distance between the radiating waveguides and the user equipment is reduced and persons are less exposed to electromagnetic radiation.
In a further embodiment, a building structure comprises one or several of the distributed antenna systems and the at least two radiating waveguides are arranged on a side wall or on a ceiling inside the building structure or a first one of the at least two radiating waveguides is arranged on a first side wall and a second one of the at least two radiating waveguides is arranged on a second side wall opposite to the first side wall inside the building structure. This configuration provides coverage in a cross section of the building structure which is especially adapted for a user equipment with antennas on top of a passing vehicle. Preferably, the building structure is an elongated building structure such as a railway tunnel or a road tunnel. The configuration with at least two radiating waveguides at opposite side walls provides coverage from both sides of the elongated building structure and therefore the configuration provides reliability of the communication between the two radiating waveguides and the user equipment. For example, one broken radiating waveguide does not lead to a complete collapse of the communication, as the other radiating waveguide can still be operated.
In an even further embodiment, a vehicle comprises one or several of the distributed antenna systems and the at least two radiating waveguides are arranged on a side wall or on a ceiling inside the vehicle or a first one of the at least two radiating waveguides is arranged on a first side wall and a second one of the at least two radiating waveguides is arranged on a second side wall opposite to the first side wall inside the vehicle. Thereby, the distributed antenna system can be also used in vehicles such as planes, busses, cars, trains or metros.
According to a further embodiment, a communication system comprises the one or several distributed antenna systems and the communication system further comprises a host unit and at least two radio frequency transceiver units, each of the at least two radiating waveguides is connected to a respective transceiver unit, and the host unit coordinates the transmission and/or reception of radio frequency signals by the at least two radiating waveguides.
Preferably, the host unit of the distributed antenna system is configured to transmit and/or receive radio frequency signals according to a multiple-input multiple-output transmission scheme.
In a further preferred embodiment, the host unit is connected to a backhaul network, and the host unit is configured to receive downlink data from the backhaul network and to transmit corresponding radio frequency downlink signals by means of the at least two radiating waveguides, and the host unit is configured to receive radio frequency uplink signals by means of the at least two radiating waveguides to transmit corresponding uplink data to the backhaul network.

BRIEF DESCRIPTION OF THE FIGURES

The embodiments of the invention will become apparent in the following detailed description and will be illustrated by accompanying figures given by way of non-limiting illustrations.

Figure 1 schematically depicts a block diagram of a distributed antenna system.
Figure 2 schematically depicts different embodiments of an arrangement of a first and a second radiating waveguide inside an elongated building structure.
Figure 3a schematically depicts the first radiating waveguide in a side view.
Figure 3b schematically depicts the second radiating waveguide in a side view.
Figure 4 schematically depicts the first and the second radiating waveguide in a cross-sectional view.

DESCRIPTION OF THE EMBODIMENTS

Figure 1 schematically depicts a block diagram of a distributed antenna system 2 according to an embodiment. The distributed antenna system 2 comprises exemplarily a first radiating waveguide 10 and a second radiating waveguide 12. Alternatively, the distributed antenna system 2 may comprise three, four or more radiating waveguides.
The first radiating waveguide 10 and the second radiating waveguide 12 are hollow conductors with an elongate casing and an inner longitudinal hollow space. The casing may be a metal material such as copper or aluminium or a plastic material with an inner conductive coating such as copper or aluminium. A communication system 3 comprises the distributed antenna system 2, a host unit 4 and a first and a second transceiver unit 6 and 8. The host unit 4 is e.g. connected to a backhaul network 14.
The distributed antenna system 2 is configured to receive downlink data from the backhaul network 14 via the host unit 4, to create according RF (radio frequency) downlink signals and to transmit the RF downlink signals from the first and the second radiating waveguides 10 and 12 to at least one user equipment (not shown) using preferably a MIMO transmission scheme. Therefore, the distributed antenna system 2 is configured to exchange RF signals between one of the user equipments and one or both of the transceiver units 6, 8 coupled to the antenna system 2. Each of the radiating waveguides 10 or 12 forms a part of a respective RF transmission channel between one of the transceiver units 6, 8 and one of the user equipments. Each of the radiating waveguides 10 and 12 can preferably be operated independently and therefore can transmit and/or receive a distinctive/different RF signal.
RF signals generated and/or forwarded by the transceiver units 6 or 8 to the radiating waveguides 10, 12 are transmitted via the radiating waveguides 10, 12 in a per se known manner and may be radiated from the radiating waveguides 10, 12 to free space via openings or slots of the elongate casing of the radiating waveguides 10, 12. Thus, an RF signal channel between the transceivers 6, 8 and a user equipment comprises a portion of radiating waveguide-guided RF transmission and a further portion of free space RF transmission, namely after said RF signal portions leave the radiating waveguides 8, 10. The user equipment comprises preferably at least two antennas to receive and/or transmit the different RF signals emitted by the radiating waveguides 10, 12. For instance, the different RF signals emitted by the radiating waveguides 10, 12 may each comprise a specific polarization.
According to an embodiment, the distributed antenna system 2 is configured to receive RF uplink signals from the user equipment by means of the first and the second radiating waveguides 10 and 12, again using preferably a MIMO transmission scheme, to generate according uplink data via the transceiver units 6 and 8 and the host unit 4 and to transmit the respective uplink data to the backhaul network 14. The host unit 4 is configured to coordinate the generation and reception of the RF signals in the transceiver units 6 and 8. The first and the second radiating waveguides 10 and 12 are arranged in different locations and/or emit and receive RF signals featuring different polarizations for example. The host unit 4 and/or the user equipment may comprise processing means e.g. for analysing and combining received RF signals in order to provide for spatial diversity, to apply interference cancellation, and the like.
Advantageously, the host unit 4 establishes different RF transmission channels in parallel (i.e., simultaneously) using the same RF spectrum for spatial multiplexing, i.e. by employing different polarizations.
Figure 2 schematically depicts different embodiments of an arrangement of the two radiating waveguides 10 and 12 shown in Figure 1 inside an elongated building structure 16 such as a railway tunnel in a cross section. Of course the depicted scenario is not restricted to railway tunnels and is also applicable to other types of tunnels for example street tunnels, to elongated or large buildings such as airports, shopping malls or to outside scenarios for example along guided routes.
The first radiating waveguide 10 and the second radiating waveguide 12 extend outside a vehicle 18 along the elongated building structure in a moving direction of the vehicle 18. The vehicle 18 may be for example a train coach, a car or another vehicle with a closed cage.
Inside the railway tunnel 16 according to Fig. 2, it is further shown a cross-section of the train 18. Side windows 20 of the train 18 are arranged on each side of the train 18. The side windows 20 are preferably made of material without or with few electromagnetic screening capability, preferably glass which does not prevent RF signals to pass from one side to the other.
User equipment 22a comprises a first antenna 24a to receive and transmit preferably horizontally polarized RF signals and a second antenna 26a to receive and transmit preferably vertically polarized RF signals. The longitudinal axis of the first antenna 24a is arranged substantially perpendicular to the longitudinal axis of the second antenna 26a. The user equipment 22a is preferably a cell phone which can reside at different positions of a passenger area 28 inside the train 18. The user equipment 22a is exemplarily expected to be positioned by the user on the same level in z-direction as the side windows 20. More user equipments are not shown for simplification.
The train 18 may further contain a radio access network node 22 preferably on a roof of the train 18. The radio access network node 22 may be for example an onboard base station such as a femtocell or a relay station. The radio access network node 22 comprises for example a first antenna 24b and a second antenna 26b at an outside of the train 18. The longitudinal axis of the first antenna 24b and the longitudinal axis of the second antenna 26b are arranged preferably perpendicular to each other. The radio access network node 22 may further comprise a third antenna 28b and a fourth antenna 29b inside the train 18. The longitudinal axis of the third antenna 28b and the longitudinal axis of the fourth antenna 29b are arranged preferably perpendicular to each other. The radio access network node 22 preferably provides a train radio service.
Two main embodiments exist how radio frequency signals can be transmitted between the user equipment 22a and the radiating waveguides 10, 12 preferably using a MIMO transmission scheme.
According to a first main embodiment, the radiating waveguides 10A and 12A of the distributed antenna system 2 are arranged on a ceiling 30 of the railway tunnel 16 at a first position A. As shown, the radiating waveguides 10A and 12A are mounted to the ceiling 30 preferably with a distance to the ceiling 30 by means of a distance element or stand-off, respectively. In such a case, first radio frequency signals are transmitted between the radiating waveguides 10A, 12A and the first and second antenna 24b, 26b of the radio access network node 22 and second radio frequency signals are transmitted between the third and fourth antenna 28b, 29b of the radio access network node 22 and the user equipment 22a. Thereby, the radio access network node 22 may work as a user equipment with respect to the distributed antenna system 2 and the communication system 3 and may further work as a base station or relay station towards the user equipment 22a.
According to a second main embodiment, a direct communication between the distributed antenna system 2 and the user equipment 22a is applied. Therefore, the radiating waveguides 10B and 12B may be arranged on a first side wall 32 of the railway tunnel 16 at a second position B. According to the positions A and B, the at least first and second radiating waveguides 10A and 12A, 10B and 12B are lengthwise arranged adjacent to each other with a predefined distance between each other. The predefined distance between the radiating waveguides can range from about 2 cm up to several meters, usually depending on wavelength of the employed RF signals. A minimum distance is preferably in a range of a half of a wavelength of the RF signals to be radiated by the radiating waveguides 10, 12. Regarding a predefined wavelength range, which could be applied to the arrangement of the two radiating waveguides 10, 12, the minimum distance may be preferably adapted to a half of a wavelength of the lower bound of the predefined wavelength range. For a relaxation of installation requirements a preferred minimum distance is several centimetres.
In particular, the first and the second radiating waveguides 10B and 12B may be arranged on a height above a floor 36 of the railway tunnel 16. According to a preferred embodiment, the radiating waveguides 10B and 12B run along an x-direction and on a level in z-direction above the floor 36 corresponding to the level of the windows 20 of the train 18.
In yet another embodiment, a first radiating waveguide 10C is attached to the first side wall 32 according to a position C1 and a second radiating waveguide 12C is attached to a second side wall 34 according to a position C2. The positions C1 and C2 are arranged on a height above the floor 36 inside two planes parallel to the xy-plane and limited in z-direction by the top and bottom edge of one of the windows 20. In further alternative embodiments without moving vehicles but with moving persons, the radiating waveguides 10, 12 may be arranged on a height above a floor corresponding to an average addendum of humans.
The different embodiments are not restricted to a usage of the two radiating waveguides 10 and 12 and also more than two radiating waveguides may be applied for increasing a data throughput and reliability of the distributed antenna system.
According to further embodiments, which are not shown in Figure 2 for simplification, the vehicle 18 may contain two or more radiating waveguides either at an inner surface of the ceiling of the vehicle 18 or at one or both inner side walls of the vehicle 18. In such a case, the two or more radiating waveguides are applied for example instead of the third and fourth antenna 28b, 29b for a communication with the user equipment 22a preferably using a MIMO transmission scheme. In such a case, the vehicle 18 may be for example a train, a metro, a bus, a car, an airplane or another vehicle with a closed cage.
Figure 3a schematically shows a longitudinal section of the first radiating waveguide 10 in a side view. The casing of the first radiating waveguide 10 may preferably contain a corrugation 10c for allowing a bending of the first radiation waveguide 10. The casing of the first radiating waveguide 10 features first slots 38. A longitudinal axis of each of the first slots 38 along the z-direction is aligned perpendicular to a longitudinal axis of the first radiating waveguide 10 along the x-direction. The first slots 38 are arranged in a first group 38a, 38b, 38c and a second group 38d, 38e, 38f along the longitudinal axis of the first radiating waveguide 10. For example, the first radiating waveguide 10 is configured to transmit and receive RF signals featuring a first polarization, wherein the first polarization is a horizontal polarization assuming that the first radiating waveguide 10 extends in a horizontal direction. A mathematical analyses and synthesis of radiating waveguides, which are also known as slotted waveguide array antennas is given for example in "Theoretical design/synthesis of slotted waveguide arrays", A.J. Sangster et al., IEE Proceedings, vol. 136, Pt. H, No. 1, February 1989.
Figure 3b schematically shows a longitudinal section of the second radiating waveguide 12 in a side view. The casing of the second radiating waveguide 12 may preferably also contain a corrugation 12c for allowing a bending of the second radiation waveguide 12. The casing of the second radiating waveguide 12 comprises second slots 42a, 42b, 42c and third slots 44a, 44b, 44c. A longitudinal axis of each of the second slots and the third slots is aligned parallel to xz-plane (i.e., transverse to the longitudinal axis of the radiating waveguide 12).
The second radiating waveguide 12 thus emits and receives RF signals featuring a second polarization, which is different from the first polarization realized by the first radiating waveguide 10 (Fig. 3a). Preferably, the second polarization is a vertical polarization assuming that the second radiating waveguide 12 also extends in a horizontal direction.
A theoretical description of radiating waveguides as shown in Figure 3a and 3b is given for example in sections 3 and 4 of the following document: "Theoretical synthesis and experimental measurements of slotted waveguide feeding systems for 2.45 GHz industrial microwave heating installations", S. Stan
ulovi
, Thesis, Institut für Hochleistungsimpuls- und Mikrowellentechnik, Fakultät für Elektrotechnik und Informationstechnik, Universität Karlsruhe (TH) Forschungszentrum Karlsruhe GmbH, Karlsruhe, 2006.
The RF signals emitted by the first and second radiating waveguides 10 and 12 thus comprise different polarizations which enables different independent RF channels to be achieved that support a MIMO transmission scheme between the user equipment 22a and the radio access network node 22 and the transceivers 6, 8.
Preferably, the first and second radiating waveguides 10 and 12 are configured for broad-band signal transmission, whereby multiple RF bands can simultaneously be transmitted over a single radiating waveguide 10 or 12.
Of course, the inventive distributed antenna system 2 is not restricted to two radiating waveguides 10, 12; it can also comprise more than two radiating waveguides.
According to another embodiment, the first radiating waveguide 10 can be used only for the transmission of RF signals and the second radiating waveguide 10 can be used only for the reception of RF signals.
A further aspect of the present invention is given by a method to operate the distributed antenna system 2, wherein a first RF band, preferably adjacent to a second RF band, is transmitted via the first radiating waveguide 10 to terminals, and wherein at least the second RF band is received via the second radiating waveguide 12, too.
Generally, the at least two radiating waveguides 10 and 12 advantageously establish at least two independent RF transmission channels which may e.g. be employed to enable MIMO transmission schemes. Due to the combination of a distributed antenna concept using the radiating waveguides and the at least two independent RF transmission channels enabled by said at least two radiating waveguides, MIMO schemes may ideally be supported even in tunnels and other structures impeding signal propagation of RF signals having non-vanishing bandwidths.
According to a further embodiment, a pair of first and second radiating waveguides 10 and 12 is used to provide cross-polarization, especially horizontal and vertical, for suppressing cross-coupling between two RF transmission channels for a 2x2 MIMO system, meaning two antennas on transmitter side to emit and two antennas on receiver side to receive, or to provide the ability of diversity.
Figure 4 schematically depicts the first or the second radiating waveguide 10, 12 in a cross-sectional view at a longitudinal position of one of the slots 38, 42, 44. A cross section of the first and the second radiating waveguide 10, 12 may be for example rectangular, circular or elliptical. Preferably, the cross section is elliptical as shown in Figure 4. The casing 11 of the first and/or the second radiating waveguide 10, 12 is preferably covered with a coating 13 such as polyethylene. The slot 38, 42, 44 provides an opening from the hollow space 14 to an outer face of the casing 11 for enabling a radiation of downlink radio frequency signals from the radiating waveguide 10, 12 and for enabling a reception of uplink radio frequency signals which have been transmitted from the user equipment 22a or from the antennas 24b, 26b of the radio access network node 22. The coating 13 preferably encloses the casing 11 and the slot 38, 42, 44. This means, the opening may be preferably only present in the casing 11 and not in the coating 13
Wave propagation inside an elliptical radiating waveguide is different to a further wave propagation inside a coaxial radiating cable. Inside the coaxial radiating cable the radio frequency signals propagate by a TEM wave. In comparison to that, the radio frequency signals propagate inside the radiating waveguides 10, 12 propagate by a HC11 mode. By adapting the geometrical cross-sectional dimensions to a frequency range of the propagating radio frequency signals such as 4 to 10 GHz or 3 to 40 GHz and due to a non-existent solid dielectric material, the radiating waveguides provide much lower propagation losses in this frequency range than coaxial radiating cables.
The description and drawings merely illustrate the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.
Functional blocks denoted as "... unit" or "means for ..." shall be understood as functional blocks comprising circuitry that is adapted for performing a certain function, respectively. Hence, a "means for s.th." may as well be understood as a "means being adapted or suited for s.th.". A means being adapted for performing a certain function does, hence, not imply that such means necessarily is performing said function (at a given time instant).
The functions of the various elements of the communication system 3 shown in Figure 1, may be provided through the use of dedicated hardware as well as the through the use of hardware capable of executing software in association with appropriate software. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared. Moreover, explicit use of the term "processor" or "controller" should not be construed to refer exclusively to hardware capable of executing software, and may implicitly include, without limitation, digital signal processor (DSP) hardware, network processor, application specific integrated circuit (ASIC), field programmable gate array (FPGA), read only memory (ROM) for storing software, random access memory (RAM), and non volatile storage. Other hardware, conventional and/or custom, may also be included. Similarly, any switches shown in the Figures are conceptual only. Their function may be carried out through the operation of program logic, through dedicated logic, through the interaction of program control and dedicated logic, or even manually, the particular technique being selectable by the implementer as more specifically understood from the context.
It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative circuitry embodying the principles of the invention.

Claims

Distributed antenna system (2) for exchanging radio frequency signals between at least one user equipment (22a) and at least one transceiver unit (6, 8) coupled to said distributed antenna system (2), said distributed antenna system (2) comprising at least two radiating waveguides (10, 12), wherein each of said at least two radiating waveguides (10, 12) comprises an inner longitudinal hollow space, wherein each of said at least two radiating waveguides (10, 12) forms a part of a respective radio frequency transmission channel between said at least one transceiver unit (6, 8) and said at least one user equipment (22a) and can be operated independently of further radiating waveguides, wherein the radiating waveguides (10, 12) are configured to radiate and/or receive said radio frequency signals with a first polarization and a second polarization, respectively, and wherein said first polarization is different from said second polarization.
Distributed antenna system (2) according to claim 1, wherein said first polarization is substantially orthogonal to said second polarization.
Distributed antenna system (2) according to any of the preceding claims, wherein said at least two radiating waveguides (10, 12) are at least in sections arranged substantially in parallel to each other.
Distributed antenna system (2) according to any of the preceding claims, wherein said at least two radiating waveguides (10, 12) are lengthwise arranged adjacent to each other.
Distributed antenna system (2) according to any of the preceding claims, wherein at least one (10) of said at least two radiating waveguides comprises first slots (38), and wherein a longitudinal axis of each of said first slots (38) is aligned substantially perpendicular to a longitudinal axis of said at least one (10) of said at least two radiating waveguides.
Distributed antenna system (2) according to any of the preceding claims, wherein at least one further (12) of said at least two radiating waveguides comprises second slots (42), and wherein a longitudinal axis of each of said second slots (42) is aligned substantially transversely to a longitudinal axis of said at least one further (12) of said at least two radiating waveguides.
Distributed antenna system (2) according to any of the preceding claims, wherein said at least two radiating waveguides (10, 12) comprise elliptical cross sections and wherein each casing (11) of said at least two radiating waveguides (10, 12) comprises a corrugation (10c, 12c).
Distributed antenna system (2) according to any of the preceding claims, wherein said at least two radiating waveguides (10, 12) are arranged on a height above a floor (36) corresponding to a region of a window (20) of a passing vehicle (18) or corresponding to an average addendum of a passing human.
A building structure (16) comprising at least one distributed antenna system (2) according to any of the preceding claims, and wherein said at least two radiating waveguides (10, 12) are arranged on a side wall (32) or on a ceiling (30) inside said building structure (16) or wherein a first one of said at least two radiating waveguides (10, 12) is arranged on a first side wall (32) and a second one of said at least two radiating waveguides (10, 12) is arranged on a second side wall (34) opposite to said first side wall (32) inside said building structure (16).
Building structure (16) according to claim 9, wherein said building structure (16) is a railway tunnel or a road tunnel.
A vehicle (18) comprising at least one distributed antenna system according to any of the preceding claims 1 to 8, and wherein said at least two radiating waveguides are arranged on an inner side wall of said vehicle (18) or on an inner surface of a ceiling of said vehicle (18) or a first one of said at least two radiating waveguides is arranged on a first inner side wall and a second one of said at least two radiating waveguides is arranged on a second inner side wall opposite to said first inner side wall of said vehicle (18).
Vehicle (18) according to claim 11, wherein said vehicle is a plane, a bus, a car, a train or a metro.
Communication system (3) comprising at least one distributed antenna system (2) according to any of the preceding claims 1 to 8, wherein said communication system (3) further comprises a host unit (4) and at least two radio frequency transceiver units (6, 8), wherein each of said at least two radiating waveguides (10, 12) is connected to a respective transceiver unit (6, 8), and wherein said host unit (4) coordinates the transmission and/or reception of radio frequency signals by said at least two radiating waveguides (10, 12).
Communication system (3) according to claim 13, wherein said host unit (4) of said distributed antenna system (2) is configured to transmit and/or receive radio frequency signals according to a multiple-input multiple-output transmission scheme.
Communication system (3) according to claim 13 or 14, wherein said host unit (4) is connected to a backhaul network (14), and wherein said host unit (4) is configured to receive downlink data from said backhaul network (14) and to transmit corresponding radio frequency downlink signals by means of said at least two radiating waveguides (10, 12), and wherein said host unit (4) is configured to receive radio frequency uplink signals by means of said at least two radiating waveguides (10, 12) to transmit corresponding uplink data to said backhaul network (14).