WO2012016739A1 - Method of operating a base station and base station - Google Patents

Method of operating a base station and base station Download PDF

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Publication number
WO2012016739A1
WO2012016739A1 PCT/EP2011/059544 EP2011059544W WO2012016739A1 WO 2012016739 A1 WO2012016739 A1 WO 2012016739A1 EP 2011059544 W EP2011059544 W EP 2011059544W WO 2012016739 A1 WO2012016739 A1 WO 2012016739A1
Authority
WO
WIPO (PCT)
Prior art keywords
base station
tilt angle
specific
terminal
transmission
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/EP2011/059544
Other languages
French (fr)
Inventor
Hardy Halbauer
Stephan Saur
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Alcatel Lucent SAS
Original Assignee
Alcatel Lucent SAS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Alcatel Lucent SAS filed Critical Alcatel Lucent SAS
Priority to JP2013522152A priority Critical patent/JP5627783B2/en
Priority to KR1020137002633A priority patent/KR101498010B1/en
Priority to US13/813,586 priority patent/US20130130706A1/en
Priority to BR112013003684A priority patent/BR112013003684A2/en
Priority to CN201180031644.1A priority patent/CN102960011B/en
Publication of WO2012016739A1 publication Critical patent/WO2012016739A1/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
    • H04W88/08—Access point devices
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/04—Wireless resource allocation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/04—Wireless resource allocation
    • H04W72/044—Wireless resource allocation based on the type of the allocated resource
    • H04W72/046—Wireless resource allocation based on the type of the allocated resource the resource being in the space domain, e.g. beams
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
    • H04W16/24—Cell structures
    • H04W16/28—Cell structures using beam steering
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/50—Allocation or scheduling criteria for wireless resources
    • H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
    • H04W72/542—Allocation or scheduling criteria for wireless resources based on quality criteria using measured or perceived quality

Definitions

  • the invention relates to a method of operating, a base station for a cellular communications network.
  • invention further relates to a base station for a cellular communications network:.
  • Conventional base stations for cellular communications networks comprise antenna systems having, one or more antennas which either have a fixed beam pattern or which enable an adjustment of a beam pattern in a horizontal direction.
  • the base station comprising at least one antenna system, a beam pattern, of which is controlled at least regarding a tilt angle, and by associating at least one radio resource used for data transmission to and/or from at least one terminal with a specific value for the tilt angle.
  • the inventive principle proposes to use different tilt angle values for different radio resources managed by said base station.
  • specific subframes: of a data transmission are assigned to different values of the tilt angle, i.e., different subframes of an ongoing data transmission are transmitted by the base station, using different tilt angles for respective
  • a sequence of subframes as known from the LTE communications standard may be assigned different tilt angles so that subsequent subframes, each of which may e.g. have a length of 1 ms (millisecond), make use of different tilt angles.
  • specific frequency bands and/or carrier frequencies are assigned to different values of the. tilt angle. That is, the base station may determine to transmit signals scheduled to specific frequency bands and/or subbands with one or more specific tilt angles. It is also possible to assign various carrier frequencies to different tilt angles each- Of course, according to a further embodiment, a combination of the afore mentioned methods of assigning different tilt angles to various subframes, frequency bands, carrier frequencies and possibly also other radio transmission resources is also possible.
  • the base station may be configured to perform some kind of
  • the assignment of radio resources and/or terminals associated with said radio resources to a specific value for the tilt angle is performed depending on at least one of; a specific rule, feedback information provided by said terminal, the
  • a predetermined specific rule may be employed for assigning radio resources to the available tilt angles, for instance, subsequent subframes of an LTE-transmission may alternately be assigned to different available tilt angles. That is, if a maximum of two different tilt angles is available with a specific antenna system, every second subframe is transmitted using the same of said two available tilt angles.
  • a further advantageous variant which relies on feedback information provided by said terminal to the base station for associating radio resources to a specific value for the tilt angle, advantageously enables to optimize the data transmission from the base station to the terminal and vice versa.
  • the feedback information enables the base station to determine a quality of data transmission as can be measured by the mobile terminal in relation to a specific tilt angle used by the base station.
  • the base station comprises information characterizing transmission quality depending on the used tilt angle.
  • neighboring base stations is considered by a base station when associating radio resources with the available tilt angles.
  • neighboring base stations can operate in a coordinated manner regarding the setting of their tilt angles leading to the reduced degree of interference.
  • said feedback information comprises at least one of: information
  • CQI channel quality indication.
  • PMI precoding matrix index
  • information comprises information associating a quality and/or various qualities of transmissipn between the base station and said mobile terminal with the specific tilt angle value and/or multiple specific tilt angle values available, indicating which tilt angle leads: to which transmission quality.
  • the base station transmits information indicative, of a selected tilt angle to said terminal. I.e., the terminal is notified of which tilt angle has been used by the base station for a data transmission to the terminal.
  • information may e.g. be comprised in an additional control field which e.g.
  • the terminal can simply forward the received tilt angle signaling information together with locally determined transmission quality information to the base station without being required to determine which tilt angle has been used by the base station for the respective data transmission.
  • a specific value, for said tilt angle is set by electronically controlling the beam pattern, of said antenna system.
  • the antenna system has an electronically controllable beam pattern, a tilt angle of which may be controlled.
  • a specific value of said tilt angle is set by providing different antennas each of which has a specific tilt angle, which may particularly be a fixed tilt angle., selecting one of the different antennas depending on a desired tilt angle to be set, and transmitting data via said selected antenna.
  • a specific tilt angle which may particularly be a fixed tilt angle.
  • conventional antennas having a fixed tilt angle may be used.
  • a respective number (i.e., two Or more) of antennas having different fixed tilt angles must he provided and selected during operation of the base station depending on the desired tilt angle.
  • a further solution to the object of the present invention is given by a base station according to claim 9 ⁇
  • the base station comprises at least one antenna system, a beam pattern of which can be controlled at least regarding a tilt angle, wherein the base station is configured to associate at least one radio resource used for data
  • Figure 1 depicts a simplified block diagram of a base
  • Figure 2 depicts a simplified block diagram of an antenna system of a base station according to a further embodiment
  • Figure 3 depicts a simplified, flow-chart of a method of operating a base station according to an embodiment
  • Figure 4 depicts an. exemplarysequence of subframes: and associated tilt angles.
  • the base station 100 may serve a number of terminals 20a such as mobile user terminals by maintaining respective data communication sessions in a per se known manner.
  • the base station 100 may operate according to at least one of the. following standards: GSM (Global System for Mobile communications) , UMTS (Universal Mobile
  • the base station 10.0 comprises an antenna system 110, a characteristic beam pattern of which is symbolized by the shape 111.
  • the antenna system 110 may be electronically controlled to reconfigure its beam pattern 111 or at least a direction of the main lobe of beam pattern 111 in which the main lobe's axis 112 extends.
  • the tilt angle ⁇ of the antenna system 110 more precisely of its main lobe 111, which - as can be gathered from Figure l - is defined as the angle between the main lobe's axis 112 and a virtual plane P that is parallel to ground, Can be electronically controlled.
  • the processing means 120 which, also control the basic operation of the base station 100 in a per. se known, manner.
  • the processing means 120 may also be configured to perform the method according to the embodiments explained below with reference to the further Figures .
  • the base station 100 may comprise an antenna system a beam pattern of which cannot be controlled electronically.
  • An antenna system a beam pattern of which cannot be controlled electronically.
  • the antenna system of Figure 2 comprises two different antennas 110a, 110b, each of which is mounted so as to have a specific, preferably fixed, tilt angle with respect to ground plane P.
  • the first antenna 110a has a fixed tilt angle ⁇ a. Consequently, the main lobe 111a of its radiation pattern has a first direction 112a.
  • the second antenna 110b has a fixed tilt angle ⁇ b, which is different from the tilt angle ⁇ a of the first antenna 110a. Consequently, the main lobe 112a of its radiation pattern has a second direction 112b.
  • tilt angle control can be performed as follows: Since there are two different antennas having different (fixed) tilt angles ⁇ a, ⁇ b, in order to set a specific tilt angle, the base station 100 ( Figure 1) or its processing means 1 . 20, respectively, determine which tilt angle to use, and after that, the antenna having the determined tilt angle is selected and used for data transmission, e.g. to the terminal 20a.
  • the number of different tilt angles to be realised with the system according to Figure 2 depends on the overall number of antennas 110a, 110b having different tilt angles .
  • the method To offer increased flexibility regarding the operational characteristics of the base ' station 100, the method
  • a first step 200 at least one radio resource used for data transmission to and/or from at least one terminal 20a.
  • Figure 1 is associated with a specific value for the tilt angle ⁇ .
  • the base station 100 selects a specific tilt angle for a data transmission that can be characterized by using a specific carrier frequency or some other radio resource as defined by the respective communications standard employed by the base station.
  • the base station 100 performs a data transmission using the previously selected specific tilt arigle.
  • specific subframes of a data transmission are assigned to different values of the tilt angle, i.e., different subframes of an ongoing data transmission are transmitted by the base station 100 using different tilt angles for respective subframes.
  • a sequence of subframes as known from the LTE communications standard may be assigned different tilt angles so that subsequent subframes, each of which may e.g. have a length of l ms (millisecond), make use of different tilt angles.
  • Figure 4 shows a sequence of consecutive subframes 0, .. , 9 of an LTE data transmission of said base station 100 along a time axis t.
  • the odd-numbered subframes 1, 3, .. are associated with specific tilt angle ⁇ b, while the even-numbered subframes 0, 2, are associated with the other possible tilt angle ⁇ a,
  • specific frequency bands and/or carrier frequencies are assigned to different values of the tilt arigle. That is, the base station 100 may determine to transmit signals scheduled to specific frequency bands with one or more specific tilt angles. It is also possible to assign various carrier frequencies to different, tilt angles each. Of course, according to a further embodiment, a combination of the afore mentioned methods of assigning different tilt angles to various subframes, frequency bands, carrier frequencies and possibly also other radio transmission resources defined by the communications standard employed by base station 100 is also possible.
  • the base station 100 may be configured to perform an optimization algorithm in order to schedule, the different resources (subframes, frequency bands, carrier frequencies, ..) to the available tilt angles ⁇ a, ⁇ b that can be realized with the antenna system 110.
  • the different resources subframes, frequency bands, carrier frequencies, ..
  • a predetermined specific rule may be employed for assigning radio resources to the available tilt angles ⁇ a, ⁇ b. For instance, as already explained above with reference to Figure 4, subsequent subframes of an LTE transmission may alternately be
  • a further advantageous variant which, relies on feedback information provided by said terminal 20a to the base station 100 for associating radio resources to a specific value, for the tilt angle, advantageously enables to
  • the feedback information enables the base station 100 to determine a quality of data transmission as can be measured by the mobile terminal 20a in relation to a specific tilt angle used by the base station 100. That is, with this
  • the base station 100 comprises information characterizing transmission quality depending on the used tilt angle.
  • neighboring base stations is considered by the base station 100 when associating radio resources with the available tilt, angles ⁇ a, ⁇ b.
  • neighboring base stations can operate in a coordinated manner regarding the setting of their tilt angles leading to the reduced degree of
  • said feedback information comprises at least one of: information
  • CQI channel quality indication
  • MMI precoding matrix index
  • the base station 100 can reliably judge whether assigning specific tilt angles ⁇ a, ⁇ b yields improved results regarding, transmission quality.
  • the base station 100 transmits information indicative of a selected tilt angle ⁇ a, ⁇ b to said terminal 20a. I.e., the terminal 20a is notified of which, tilt angle has been used by the base station 100 for a specific data transmission to the
  • Such information may e.g. be comprised in an additional control field which e.g. comprises some bits, for representing a specific one of the possible tilt value angles ⁇ a, ⁇ b. I.e., for two possible tilt angles ⁇ a, ⁇ b,. only one bit is required in the downlink for performing a corresponding "tilt angle signaling" to the terminal 20a.
  • an additional control field which e.g. comprises some bits, for representing a specific one of the possible tilt value angles ⁇ a, ⁇ b. I.e., for two possible tilt angles ⁇ a, ⁇ b,. only one bit is required in the downlink for performing a corresponding "tilt angle signaling" to the terminal 20a.
  • the terminal 20a can simply forward the received tilt angle signaling information together with its locally determined transmission quality information to the base station 100 without being required to determine itself which tilt angle, has been used by the base station 100 for the respective data transmission.
  • the base station 100 which may also foe referred to as eNB, evolved Node B., in the context of the LTE communications standard, uses different downtilts, i.e. tilt angles, for specific time intervals, e.g. an LTE subframe, for the downlink (DL) transmission.
  • the assignment of the downtilts to the subframes may be done according to a specific rule or order, so that each downtilt is used from time to time.
  • the terminal 20a measures the Precoding Matrix Index (PMI) and the
  • CQI Channel Quality Indication
  • the eNB 100 advantageously can derive the beat suited downtilt angle, to serve a specific terminal 20a, e.g. by comparing the fed back CQI and/or PMI information.
  • A. scheduler of the eNB 100 which may e.g. be implemented by the processing means 120, uses this information to achedule the DL (downlink) transmissions of each user / terminal 20a in subframes. which are dedicated to. the best suited downtilt angle.
  • the eNB 100 within each subframe the eNB 100 sends control information indicating the used downtilt angle.
  • the terminal 20a decodes this information and sends it back together with the CQI/PMI information derived from this subframe. So the eNB 110 knows the relation of used downtilt and the corresponding feedback reporting.
  • a combination of the principles of the above explained embodiments with the technique of coordinated scheduling is also feasible: If also the best companion and/or worst companion PMIs of neighbour base stations (not shown) are measured and the relation to the measurement subframe/used downtilt is known, the schedulers of the base station 100 and its neighbours have all information needed to assign the available resources in an optimized way. The downtilt information thus adds an. additional degree of freedom to existing scheduling algorithms.
  • the base station 100 is equipped with an antenna system 110 realizing a certain number of discrete tilt angles ( "downtilts" ) , e.g. two different downtilts.
  • the number of downtilts is mapped to the number of groups of subframes.
  • two groups of subframes are used, even or odd numbered subframes.
  • the same downtilt is applied.
  • LTE-A subframes are. transmitted with alternating downtilts, odd subframes with the first
  • the terminals 20a receive the common pilots that are transmitted by the base station 1.00 in a per se known manner and measure the CQI and PMI an a per subframe basis. Together with the feedback information (CQI, PMI) , the. terminal 20a feeds back whether the measurement is based, on an even or an odd subframe. In this specific case only 1 additional bit of feedback would be needed, with 2 bits of feedback four different downtilts could be handled. The number of different groups of subframes should be defined and configured in advance.
  • the eNB 100 knows the used downtilt, because it has been notified, correspondingly by the terminal 20a.
  • a "downtilt. control" information is inserted in each subframe., which identifies the currently used
  • the terminal 20a measures the PMI and/or CQI based on a subframe and feeds back these reports together with the control information received in DL within the measurement subframe. Due to this, no additional knowledge on the used downtilt is required on terminal side.
  • each downtilt angle available at the eNB 100 a specific part of the frequency band that may be used for data transmission is assigned.
  • the PMI and CQI measurements of the terminal 20a are performed per frequency subband (measurements down to a width of 6 PRBs (physical resource block) are possible in a 10-MHz LTE system)
  • the reporting is fed back per frequency subband. In this way, the. relation of the measurement with the currently used downtilt can be derived by the eNB 100 without, specific knowledge at the terminal 20a.
  • downtilts can be realized in different ways, e.g.: - using an antenna or antenna system 110 with electronic downtilt control .
  • a synchronized uplink (UL) operation (DL/UL frames starting at the same time) is p-erformed.
  • the proposed solution allows deployment of terminal (i.e., UE-) specific downtilt angles right now by providing a solution feasible with available antennas having fixed tilt angles. Any possibly required additional information on timing relation to be provided by the terminals 20a is not specific to the embodiments, but also helpful and necessary for currently discussed proposals on coordinated scheduling and for joint processing techniques.
  • the inventive principle enables the deployment of advanced inter-cell interference reduction methods already with relatively simple antenna hardware.
  • the embodiments explained above are not limited to base stations 100 of cellular communications networks.
  • the inventive principle of assigning different tilt angles to different transmission resources may rather be applied to any base station having at least one antenna system 110 a tilt angle of which ⁇ or a tilt angle of a main lobe of a corresponding beam pattern) may be. controlled, e.g.
  • the principle may be applied with GSM-; UMTS-, LTE-, and WiMAX- base stations, as well as with base stations, operating according to other existing or future, standards.
  • the application of the inventive principle reduces an effort required for network planning and
  • the base station 100 or its processing means 120 can apply the inventive principle, a decentralized adaptation of the radio access network to changing environments and operating conditions is enabled.
  • the further degrees of freedom gained by the application of the inventive principle may advantageously be employed to improve existing scheduling techniques, e.g. with regard to fairness or spectral efficiency and the like.
  • processor 7 or * Controller' should not be construed, to refer exclusively to hardware capable of executing software, and may
  • DSP digital signal processor
  • ASIC application specific integrated circuit
  • FPGA field programmable gate array
  • ROM read only memory
  • RAM random access memory
  • FIGS any switches shown in the FIGS, are conceptual only. Their function may be carried out through the

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  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Radio Transmission System (AREA)

Abstract

The present invention relates to a method of operating a base station (100) for a cellular communications, network, wherein said base station (100) comprises at least one antenna system (110), a beam pattern of which is controlled at least regarding a tilt angle (θ), wherein at least one radio resource used for data transmission to and/or from least one terminal (20a) is associated with a specific value for the tilt angle (θ).

Description

Title: Method of Operating a Base Station and Base Station
Specification
Field of the Invention
The invention relates to a method of operating, a base station for a cellular communications network. The
invention further relates to a base station for a cellular communications network:.
Background
Conventional base stations for cellular communications networks comprise antenna systems having, one or more antennas which either have a fixed beam pattern or which enable an adjustment of a beam pattern in a horizontal direction.
There is a need to provide a more sophisticated base station and method of operating a base station which offer increased flexibility regarding the operational
characteristics of the base station.
Summary
According to the present invention, regarding the. above mentioned method of operating a base station, this object is achieved by: the base station comprising at least one antenna system, a beam pattern, of which is controlled at least regarding a tilt angle, and by associating at least one radio resource used for data transmission to and/or from at least one terminal with a specific value for the tilt angle.
I.e., the inventive principle proposes to use different tilt angle values for different radio resources managed by said base station.
For instance, according to a preferred embodiment, specific subframes: of a data transmission are assigned to different values of the tilt angle, i.e., different subframes of an ongoing data transmission are transmitted by the base station, using different tilt angles for respective
subframes. For instance, a sequence of subframes as known from the LTE communications standard may be assigned different tilt angles so that subsequent subframes, each of which may e.g. have a length of 1 ms (millisecond), make use of different tilt angles.
According to a further preferred embodiment, specific frequency bands and/or carrier frequencies are assigned to different values of the. tilt angle. That is, the base station may determine to transmit signals scheduled to specific frequency bands and/or subbands with one or more specific tilt angles. It is also possible to assign various carrier frequencies to different tilt angles each- Of course, according to a further embodiment, a combination of the afore mentioned methods of assigning different tilt angles to various subframes, frequency bands, carrier frequencies and possibly also other radio transmission resources is also possible.
Generally, according to a further embodiment, the base station may be configured to perform some kind of
optimization algorithm in order to schedule; the different resources (subframes, frequency bands, carrier frequencies, ..) to the available tilt angles that can be realized with the antenna system.
According to a further preferred embodiment, the assignment of radio resources and/or terminals associated with said radio resources to a specific value for the tilt angle is performed depending on at least one of; a specific rule, feedback information provided by said terminal, the
distance between the base station and the terminal,
scheduling information of neighboring base stations.
According to a simple embodiment, a predetermined specific rule may be employed for assigning radio resources to the available tilt angles, for instance, subsequent subframes of an LTE-transmission may alternately be assigned to different available tilt angles. That is, if a maximum of two different tilt angles is available with a specific antenna system, every second subframe is transmitted using the same of said two available tilt angles.
Of course, other patterns can also be realized.
A further advantageous variant, which relies on feedback information provided by said terminal to the base station for associating radio resources to a specific value for the tilt angle, advantageously enables to optimize the data transmission from the base station to the terminal and vice versa. Preferably, the feedback information enables the base station to determine a quality of data transmission as can be measured by the mobile terminal in relation to a specific tilt angle used by the base station. That is, with this embodiment, the base station comprises information characterizing transmission quality depending on the used tilt angle. Moreover, it is also possible to consider a distance between the base station and a terminal for assigning radio resources to a specific value of the tilt angle.
It is also possible that scheduling Information of
neighboring base stations is considered by a base station when associating radio resources with the available tilt angles. Thus, neighboring base stations can operate in a coordinated manner regarding the setting of their tilt angles leading to the reduced degree of interference.
According to a further preferred embodiment, said feedback information comprises at least one of: information
characterizing a quality of transmission between the base station and the mobile terminal such as e.g. channel quality indication. (CQI) data as used by the LTE standard or precoding matrix index (PMI). information such as also used by the LTE standard. Prom this type of feedback information, the base station can reliably judge whether assigning specific tilt angles yields improved results regarding transmission quality.
According to a further embodiment, said feedback
information comprises information associating a quality and/or various qualities of transmissipn between the base station and said mobile terminal with the specific tilt angle value and/or multiple specific tilt angle values available, indicating which tilt angle leads: to which transmission quality.
According to. a further embodiment, the base station transmits information indicative, of a selected tilt angle to said terminal. I.e., the terminal is notified of which tilt angle has been used by the base station for a data transmission to the terminal. Such information may e.g. be comprised in an additional control field which e.g.
comprises some bits for representing a specific one of the possible tilt value angles, I.e., for two possible tilt angles, only one bit is required in the downlink for performing a corresponding "tilt angle signaling" to the terminal. This advantageously enables the terminal to combine transmission quality information as obtained by the terminal with the information indicative of the. selected tilt angle. Thus, the terminal can simply forward the received tilt angle signaling information together with locally determined transmission quality information to the base station without being required to determine which tilt angle has been used by the base station for the respective data transmission.
According to a further embodiment, a specific value, for said tilt angle is set by electronically controlling the beam pattern, of said antenna system. According to this embodiment, the antenna system has an electronically controllable beam pattern, a tilt angle of which may be controlled.
According to a further preferred embodiment., a specific value of said tilt angle is set by providing different antennas each of which has a specific tilt angle, which may particularly be a fixed tilt angle., selecting one of the different antennas depending on a desired tilt angle to be set, and transmitting data via said selected antenna. I.e., in this embodiment, conventional antennas having a fixed tilt angle may be used. For achieving a variety of
different tilt angles, a respective number (i.e., two Or more) of antennas having different fixed tilt angles must he provided and selected during operation of the base station depending on the desired tilt angle. A further solution to the object of the present invention, is given by a base station according to claim 9· The base station comprises at least one antenna system, a beam pattern of which can be controlled at least regarding a tilt angle, wherein the base station is configured to associate at least one radio resource used for data
transmission to and/or from at least one terminal with a specific value for the tilt, angle.
Further advantageous embodiments of the invention are given in the dependent claims.
Brief Description of the Figures
Further features, aspects and advantages of the present invention are given in the following detailed description with reference to the drawings in which:
Figure 1 depicts a simplified block diagram of a base
station according to an embodiment.
Figure 2 depicts a simplified block diagram of an antenna system of a base station according to a further embodiment,
Figure 3 depicts a simplified, flow-chart of a method of operating a base station according to an embodiment, and
Figure 4 depicts an. exemplarysequence of subframes: and associated tilt angles.
Description of the Embodiments Figure 1 depicts a simplified block diagram of a base station 100 of a cellular communications network. The base station 100 may serve a number of terminals 20a such as mobile user terminals by maintaining respective data communication sessions in a per se known manner. For instance, the base station 100 may operate according to at least one of the. following standards: GSM (Global System for Mobile communications) , UMTS (Universal Mobile
Telecommunications System) , LTE (Long Term Evolution) / LTE Advanced, WiMax {Worldwide Interoperability for Microwave Access) , WLAN {Wireless Local Area Network) . the base station 10.0 comprises an antenna system 110, a characteristic beam pattern of which is symbolized by the shape 111. According to an embodiment, the antenna system 110 may be electronically controlled to reconfigure its beam pattern 111 or at least a direction of the main lobe of beam pattern 111 in which the main lobe's axis 112 extends. I.e., the tilt angle θ of the antenna system 110, more precisely of its main lobe 111, which - as can be gathered from Figure l - is defined as the angle between the main lobe's axis 112 and a virtual plane P that is parallel to ground, Can be electronically controlled. This is e.g. accomplished by the processing means 120 which, also control the basic operation of the base station 100 in a per. se known, manner. Moreover, the processing means 120 may also be configured to perform the method according to the embodiments explained below with reference to the further Figures .
According to a further embodiment, the base station 100 may comprise an antenna system a beam pattern of which cannot be controlled electronically. Such a system is depicted by Figure 2. The antenna system of Figure 2 comprises two different antennas 110a, 110b, each of which is mounted so as to have a specific, preferably fixed, tilt angle with respect to ground plane P.
Presently, the first antenna 110a has a fixed tilt angle θa. Consequently, the main lobe 111a of its radiation pattern has a first direction 112a. The second antenna 110b has a fixed tilt angle θb, which is different from the tilt angle θa of the first antenna 110a. Consequently, the main lobe 112a of its radiation pattern has a second direction 112b.
With the antenna system depicted by Figure 2, tilt angle control can be performed as follows: Since there are two different antennas having different (fixed) tilt angles θa, θb, in order to set a specific tilt angle, the base station 100 (Figure 1) or its processing means 1.20, respectively, determine which tilt angle to use, and after that, the antenna having the determined tilt angle is selected and used for data transmission, e.g. to the terminal 20a.
Obviously, the number of different tilt angles to be realised with the system according to Figure 2 depends on the overall number of antennas 110a, 110b having different tilt angles .
A combination of an electronically controllable antenna system 110 (Figure 1) with the technique as according to Figure 2 is also possible.
To offer increased flexibility regarding the operational characteristics of the base' station 100, the method
explained below with respect to the flow-chart of Figure 3 is performed. In a first step 200, at least one radio resource used for data transmission to and/or from at least one terminal 20a. (Figure 1) is associated with a specific value for the tilt angle θ. I.e, , the base station 100 selects a specific tilt angle for a data transmission that can be characterized by using a specific carrier frequency or some other radio resource as defined by the respective communications standard employed by the base station. In step 210, the base station 100 performs a data transmission using the previously selected specific tilt arigle.
For instance, according to a preferred embodiment,, specific subframes of a data transmission are assigned to different values of the tilt angle, i.e., different subframes of an ongoing data transmission are transmitted by the base station 100 using different tilt angles for respective subframes. For instance, a sequence of subframes as known from the LTE communications standard may be assigned different tilt angles so that subsequent subframes, each of which may e.g. have a length of l ms (millisecond), make use of different tilt angles. Figure 4 shows a sequence of consecutive subframes 0, .. , 9 of an LTE data transmission of said base station 100 along a time axis t. As can also, be gathered from Figure 4, the odd-numbered subframes 1, 3, .. are associated with specific tilt angle θb, while the even-numbered subframes 0, 2, are associated with the other possible tilt angle θa,
According to a further preferred embodiment, specific frequency bands and/or carrier frequencies are assigned to different values of the tilt arigle. That is, the base station 100 may determine to transmit signals scheduled to specific frequency bands with one or more specific tilt angles. It is also possible to assign various carrier frequencies to different, tilt angles each. Of course, according to a further embodiment, a combination of the afore mentioned methods of assigning different tilt angles to various subframes, frequency bands, carrier frequencies and possibly also other radio transmission resources defined by the communications standard employed by base station 100 is also possible.
Generally, according to a further embodiment, the base station 100 may be configured to perform an optimization algorithm in order to schedule, the different resources (subframes, frequency bands, carrier frequencies, ..) to the available tilt angles θa, θb that can be realized with the antenna system 110.
According to a further preferred embodiment, the assignment of radio resources and/or terminals 20a associated with .said radio resources to. a specific value θa, θb for the tilt angle θ is performed depending on at least one of: a specific rule, feedback information provided by said terminal 20a, the distance between the base station 100 and the terminal 20a, scheduling information of neighboring base stations (not shown) .
According to. an embodiment, a predetermined specific rule may be employed for assigning radio resources to the available tilt angles θa, θb. For instance, as already explained above with reference to Figure 4, subsequent subframes of an LTE transmission may alternately be
assigned to different available tilt angles θa, θb. That is, if a maximum of two different tilt angles 8a, θb is available with a specific antenna system 110, every second subframc is transmitted using the same of said two
available tilt angles. Of course, other patterns can also be realized*
A further advantageous variant, which, relies on feedback information provided by said terminal 20a to the base station 100 for associating radio resources to a specific value, for the tilt angle, advantageously enables to
optimize the data transmission from the base station 100 to the terminal 20a and vice versa. Preferably, the feedback information enables the base station 100 to determine a quality of data transmission as can be measured by the mobile terminal 20a in relation to a specific tilt angle used by the base station 100. That is, with this
embodiment, the base station 100 comprises information characterizing transmission quality depending on the used tilt angle.
Moreover, it is also possible to consider a distance between the base station 100 and the terminal 2.0a for assigning radio resources to a specific value of the tilt angle .
It is also possible that scheduling information of
neighboring base stations is considered by the base station 100 when associating radio resources with the available tilt, angles θa, θb. Thus, neighboring base stations can operate in a coordinated manner regarding the setting of their tilt angles leading to the reduced degree of
interference .
According to a further preferred embodiment; said feedback information comprises at least one of: information
characterizing a quality of transmission between the base station 100 and the mobile terminal 20a such as e.g.
channel quality indication (CQI) data as used by the LTE standard or precoding matrix index (MMI) information such as also, used by the LTE standard. From this type of
feedback information,, the base station 100 can reliably judge whether assigning specific tilt angles θa, θb yields improved results regarding, transmission quality.
According to a further embodiment , said feedback
information comprises infprmatipn associating a quality of transmission between the base station 100 and said mobile terminal 20a with the specific tilt angle value θa, θb used for said transmission thus leaving no doubt which specific tilt angle effected a specific quality of transmission.
According to a further embodiment, the base station 100 transmits information indicative of a selected tilt angle θa, θb to said terminal 20a. I.e., the terminal 20a is notified of which, tilt angle has been used by the base station 100 for a specific data transmission to the
terminal 20a. Such information may e.g. be comprised in an additional control field which e.g. comprises some bits, for representing a specific one of the possible tilt value angles θa, θb. I.e., for two possible tilt angles θa, θb,. only one bit is required in the downlink for performing a corresponding "tilt angle signaling" to the terminal 20a. This advantageously enables the terminal 20a to combine transmission, quality information as obtained by the
terminal with the information indicative of the selected tilt angle θa, θb as. delivered by the base station 100.
Thus, the terminal 20a can simply forward the received tilt angle signaling information together with its locally determined transmission quality information to the base station 100 without being required to determine itself which tilt angle, has been used by the base station 100 for the respective data transmission. According to a further embodiment, the base station 100, which may also foe referred to as eNB, evolved Node B., in the context of the LTE communications standard, uses different downtilts, i.e. tilt angles, for specific time intervals, e.g. an LTE subframe, for the downlink (DL) transmission. The assignment of the downtilts to the subframes may be done according to a specific rule or order, so that each downtilt is used from time to time.
Preferably, according to a further embodiment, the terminal 20a measures the Precoding Matrix Index (PMI) and the
Channel Quality Indication (CQI) from the common pilots within each subframe and reports these values to the eNB 100. In addition, to capture a feedback delay which is due to signal propagation effects and processing delays within the components 20a., 100, information on the subframe related to the reporting information (i.e., feedback information.) is transmitted to the eNB 100.
From this information, the eNB 100 advantageously can derive the beat suited downtilt angle, to serve a specific terminal 20a, e.g. by comparing the fed back CQI and/or PMI information.
A. scheduler of the eNB 100, which may e.g. be implemented by the processing means 120, uses this information to achedule the DL (downlink) transmissions of each user / terminal 20a in subframes. which are dedicated to. the best suited downtilt angle.
According to a further embodiment, within each subframe the eNB 100 sends control information indicating the used downtilt angle. The terminal 20a decodes this information and sends it back together with the CQI/PMI information derived from this subframe. So the eNB 110 knows the relation of used downtilt and the corresponding feedback reporting.
According to a further embodiment, a combination of the principles of the above explained embodiments with the technique of coordinated scheduling is also feasible: If also the best companion and/or worst companion PMIs of neighbour base stations (not shown) are measured and the relation to the measurement subframe/used downtilt is known, the schedulers of the base station 100 and its neighbours have all information needed to assign the available resources in an optimized way. The downtilt information thus adds an. additional degree of freedom to existing scheduling algorithms.
According to a further embodiment, the base station 100 is equipped with an antenna system 110 realizing a certain number of discrete tilt angles ( "downtilts" ) , e.g. two different downtilts. The number of downtilts is mapped to the number of groups of subframes. In the present
embodiment, two groups of subframes are used, even or odd numbered subframes. In a downlink direction, for each subframe within a group, the same downtilt is applied. In the embodiment, LTE-A subframes are. transmitted with alternating downtilts, odd subframes with the first
downtilt value, even subframes with the second possible downtilt value. The terminals 20a receive the common pilots that are transmitted by the base station 1.00 in a per se known manner and measure the CQI and PMI an a per subframe basis. Together with the feedback information (CQI, PMI) , the. terminal 20a feeds back whether the measurement is based, on an even or an odd subframe. In this specific case only 1 additional bit of feedback would be needed, with 2 bits of feedback four different downtilts could be handled. The number of different groups of subframes should be defined and configured in advance.
According to a further embodiment, if e.g. an individual subframe number is reported back explicitely together with the measurement feedback to the base station 100, no specific mapping or sequence of downtilts needs to be applied. For each reporting, the eNB 100 knows the used downtilt, because it has been notified, correspondingly by the terminal 20a.
According to a further embodiment, in the downlink
direction, a "downtilt. control" information is inserted in each subframe., which identifies the currently used
downtilt- The terminal 20a measures the PMI and/or CQI based on a subframe and feeds back these reports together with the control information received in DL within the measurement subframe. Due to this, no additional knowledge on the used downtilt is required on terminal side.
According to a further embodiment, to each downtilt angle available at the eNB 100, a specific part of the frequency band that may be used for data transmission is assigned. The PMI and CQI measurements of the terminal 20a are performed per frequency subband (measurements down to a width of 6 PRBs (physical resource block) are possible in a 10-MHz LTE system) The reporting is fed back per frequency subband. In this way, the. relation of the measurement with the currently used downtilt can be derived by the eNB 100 without, specific knowledge at the terminal 20a.
As already explained above, the different tilt angles
( "downtilts") can be realized in different ways, e.g.: - using an antenna or antenna system 110 with electronic downtilt control .
- using multiple antennas 110a, 11.0b per e.NB 100, each having a different downtilt θa, θb. Each subframe
transmission is switched to the appropriate antenna.
- use of multiple antennas. 110a, 110b with different downtilt θa, θb in. combination with additional baseband units (e.g., one baseband unit per antenna). This would also allow allocation of subbands with different downtilt within the same subframe.
Preferably, a synchronized uplink (UL) operation (DL/UL frames starting at the same time) is p-erformed.
The inventive principle employed by the embodiments
advantageously enables to reduce inter-cell interference and therefore increase the spectral efficiency.
The proposed solution allows deployment of terminal (i.e., UE-) specific downtilt angles right now by providing a solution feasible with available antennas having fixed tilt angles. Any possibly required additional information on timing relation to be provided by the terminals 20a is not specific to the embodiments, but also helpful and necessary for currently discussed proposals on coordinated scheduling and for joint processing techniques.
The inventive principle enables the deployment of advanced inter-cell interference reduction methods already with relatively simple antenna hardware. The embodiments explained above are not limited to base stations 100 of cellular communications networks. The inventive principle of assigning different tilt angles to different transmission resources may rather be applied to any base station having at least one antenna system 110 a tilt angle of which {or a tilt angle of a main lobe of a corresponding beam pattern) may be. controlled, e.g.
electronically or on an electromechanical basis or by switching between different antennas 110a, 110b having fixed tilt angles. Typically, the principle may be applied with GSM-; UMTS-, LTE-, and WiMAX- base stations, as well as with base stations, operating according to other existing or future, standards.
Advantageously, the application of the inventive principle reduces an effort required for network planning and
increases network robustness. Moreover,, since the base station 100 or its processing means 120 can apply the inventive principle, a decentralized adaptation of the radio access network to changing environments and operating conditions is enabled.
The further degrees of freedom gained by the application of the inventive principle may advantageously be employed to improve existing scheduling techniques, e.g. with regard to fairness or spectral efficiency and the like.
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 .
The functions of the various elements shown in the Figures, including any functional blocks labelled; as 'processors', may be provided through the use of dedicated hardware as well as hardware capable of executing software in
association with appropriate software. When provided by a pro.ces.soir, 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 processor7 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 FIGS, 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..

Claims

Claims
1. Method of operating a base station (100) for a
cellular communications network, wherein said base station (100) comprises at least one antenna system (110)., a beam pattern of which is controlled at least regarding a till angle (θ) , wherein at least one radio resource used for data transmission to and/or from at least one terminal (20a) is associated with a specific value for the tilt angle (θ) , wherein the assignment of the radio resources, and/or terminals (20a)
associated with said radio resources to specific values for the tilt angle (θ) is performed depending .on feedback information provided by said terminal
(20a) , wherein said feedback information comprises at least information associating a quality of
transmission between said base station (100) and said mobile terminal (20a) with a specific tilt angle value for said transmission.
2. Method, according to claim 1, wherein specific
subframes are assigned to different values of the tilt angle (&) .
3. Method according to one of the preceding claims,
wherein specific fregency bands and/or carrier frequencies are assigned to different values of the tilt angle (θ) .
4. Method according to one of the preceding claims,
wherein the assignment of radio resoui*ces and/or terminals (20a) associated with said radio resources to specific values for the tilt angle (θ) is performed depending on at least one of: a specific rule, feedback information provided by said terminal (20a) , a distance between the base station (100) and a terminal (20a), scheduling information of neighbouring base stations.
5. Method according to claim.4, wherein said feedback
information comprises at least one of : information, characterizing a quality of transmission between said base station (100.) and said mobile terminal (20a;) , information associating a quality of transmission between said base station (100) and. said mobile, terminal (20a) with a specific tilt angle value used for said transmission.
6. Method according to one of the preceding claims,
wherein the base station (100) transmits information indicative of a selected tilt angle to said terminal (20a) .
7. Method according to one of the preceding claims,
wherein a specific value for said tilt angle (θ) is set by: electronically controlling the beam pattern of said antenna system (110) ..
8. Method according to one of the preceding claims,
wherein a specific value for said tilt angle (θ) is set by: providing different antennas (110a, 110b) each of which has a specific tilt angle (θa, θb) , selecting one of said different antennas (1.10a,. 110b) depending on a desired tilt angle to be set,,, and transmitting data via said selected antenna .
9. Base station (100) for a cellular communications
network, wherein said base station (100) comprises at. least one antenna system. (110) , a beam pattern of which can be controlled at least regarding a tilt angle (θ) , wherein said base station (100) is
configured to associate at least one radio resource used for data transmission to and/or from at least one terminal (20a) with a specific value for the tilt angle (θ) , wherein said base station (100) is
configured to perform the assignment of radio
resources and/or terminals (20a) associated with said radio resources to specific values for the tilt angle.
(θ) depending on feedback information provided by said terminal (20a) , wherein, said feedback information comprises at least information associating a quality of transmission between said base station (100) and said mobile terminal (20a) with a specific tilt angle value used for said transmission.
10. Base station (100} according to claim 9, wherein said base station (100) is configured to assign specific sub-frames to different values of the tilt angle (Θ) .
11. Base station (100) according to one of the claims 9 to
10, wherein said base station (100.) is configured to assign specific frequency bands and/or carrier
frequencies to different values of the tilt, angle (θ) .
12. Base station (100) according to one of the claims 9 to
11, wherein said base station (100) is configured to perform the assignment of radio resources and/or terminals (20a) associated, with said radio resources to specific values for the tilt angle (θ,) depending on at least one of: a specific rule, feedback information provided by said terminal (20a) , a distance between the base station (100) and a terminal (20a).,
scheduling information of neighbouring base stations.
13. Base station (100) according to one of the claims 9 to 12, wherein said feedback information comprises at least one of: information characterizing a quality of transmission between said base station (100) and said mobile terminal (20a) , information associating a quality of transmission between said base station (100) and said mobile terminal (20a) with a specific tilt angle value, used for said transmission.
14. Base station (100) according to one of the claims 9 to 13, wherein said base station (100) is configured to transmit information indicative of a selected tilt angle to said terminal (20a)„ 15. Base station (100) according to one of the claims 9 to
14, wherein said base station (100) is configured to set a specific value for said tilt angle (θ) by:
electronically controlling the beam pattern of said antenna system (110).. 16. Base station (100) according to one of the claims 9 to
15, wherein said base station (100) is configured to set. a specific value for said tilt angle (θ) by:
providing different antennas (110a, 110b) each of which has a specific tilt angle (θa., θb) , selecting one of said different antennas (110a, 110b) depending on a desired tilt angle to be set, and transmitting data via said selected antenna.
PCT/EP2011/059544 2010-08-03 2011-06-09 Method of operating a base station and base station Ceased WO2012016739A1 (en)

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US13/813,586 US20130130706A1 (en) 2010-08-03 2011-06-09 Method of operating a base station and base station
BR112013003684A BR112013003684A2 (en) 2010-08-03 2011-06-09 method of operating a base station and base station
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US20130130706A1 (en) 2013-05-23
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BR112013003684A2 (en) 2016-09-06
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