WO2015036034A1

WO2015036034A1 - Vertical tilting

Info

Publication number: WO2015036034A1
Application number: PCT/EP2013/069009
Authority: WO
Inventors: Bernhard Wegmann
Original assignee: Nokia Solutions And Networks Oy
Priority date: 2013-09-13
Filing date: 2013-09-13
Publication date: 2015-03-19

Abstract

A technique, comprising: operating a plurality of first cells and a second cell in parallel, wherein the first cells are operated via respective ones of a plurality of antenna arrays at an antenna site; and said second cell is operated via antenna arrays at said same antenna site at a different degree of vertical tilting to said first cells; wherein said plurality of first cells and said second cell are operated via the same time-frequency resources; and wherein operating said second cell comprises making transmissions for said second cell substantially simultaneously via more than one antenna array at said antenna site.

Description

Description Title

VERTICAL TILTING

Usage of several radiation beams with different vertical tilting can be used to increase the transmission capacity of a serving area served by a group of one or more antenna arrays at an elevated antenna site.

Antenna arrays operated at the same time-frequency resources may be employed in close proximity to each other, such as on the same antenna mast, where the antenna arrays are typically configured to exhibit substantially complementary radiation patterns/beams, and are used to operate different cells. The inventors for the present application have observed that employing several radiation beams with different vertical tilting at an antenna array group can in fact reduce the overall performance of the antenna group as a whole.

It is an aim of the present invention to increase the effectiveness of employment of several radiation beams with different vertical tilting in a group of antenna arrays.

There is hereby provided a method, comprising: operating a plurality of first cells and a second cell in parallel, wherein the first cells are operated via respective ones of a plurality of antenna arrays at an antenna site; and said second cell is operated via antenna arrays at said same antenna site at a different degree of vertical tilting to said first cells; wherein said plurality of first cells and said second cell are operated via the same time-frequency resources; and wherein operating said second cell comprises making transmissions for said second cell substantially simultaneously via more than one antenna array at said antenna site.

According to one embodiment, operating said second cell comprises making transmissions for said second cell substantially simultaneously via more than one of said plurality of antennas via which said first cells are operated.

According to one embodiment, the tilting comprises electrical tilting.

According to one embodiment, the first cells have coverage areas located outwards of the coverage area of the second cell.

According to one embodiment, the method comprises operating said first cells at a lower degree of vertical tilting than said at least one second cell.

According to one embodiment, each of said plurality of antenna arrays comprises a plurality of radiating elements, each radiating element associated with a respective transceiver element; and the phase and/or amplitude at which a signal is transmitted from any one of said radiating elements is individually configurable with respect to the phase and/or amplitude at which said signal is transmitted from any other one of said radiating elements. According to one embodiment, the method comprises controlling the transmission of a signal for one of said first cells and a signal for said second cell from one of said plurality of antenna arrays via the same time-frequency resource, wherein said controlling comprises controlling the transmission of said first cell signal from said plurality of radiating elements for said antenna array according to a set of phases and/or amplitudes different to those employed for the transmission of said second cell signal from the same plurality of radiating elements.

According to one embodiment, each of said first and second cells has a respective Cell Id.

According to one embodiment, said operating said first cells and said at least one second cell comprises transmitting respective reference signals identifying the respective cells.

According to one embodiment, operating said second cell comprises transmitting in parallel from each of said more than one antenna arrays reference signals commonly indicating the same Cell Id.

According to one embodiment, the more than one antenna arrays used to operate the second cell comprise active antenna systems.

There is also hereby provided an apparatus comprising: a processor and memory including computer program code, wherein the memory and computer program code are configured to, with the processor, cause the apparatus to: operate a plurality of first cells and a second cell in parallel; operate the first cells via respective ones of a plurality of antenna arrays at an antenna site; operate said second cell via antenna arrays at said same antenna site at a different degree of vertical tilting to said first cells; operate said plurality of first cells and said second cell via the same time-frequency resources; and make transmissions for said second cell substantially simultaneously via more than one antenna array at said antenna site.

According to one embodiment, the memory and computer program code are further configured to, with the processor, cause the apparatus to: make transmissions for said second cell substantially simultaneously via more than one of said plurality of antennas via which said first cells are operated.

According to one embodiment, the tilting comprises electrical tilting.

According to one embodiment, the memory and computer program code are further configured to, with the processor, cause the apparatus to operate said first cells at a lower degree of vertical tilting than said at least one second cell.

According to one embodiment, each of said plurality of antenna arrays comprises a plurality of radiating elements, each radiating element associated with a respective transceiver element, and wherein the phase and/or amplitude at which a signal is transmitted from any one of said radiating elements is individually configurable with respect to the phase and/or amplitude at which said signal is transmitted from any other one of said radiating elements.

According to one embodiment, the memory and computer program code are further configured to, with the processor, cause the apparatus to: control the transmission of a signal for one of said first cells and a signal for said second cell from one of said plurality of antenna arrays via the same time-frequency resource, and control the transmission of said first cell signal from said plurality of radiating elements for said antenna array according to a set of phases and/or amplitudes different to those employed for the transmission of said second cell signal from the same plurality of radiating elements.

According to one embodiment, operating said first cells and said at least one second cell comprises transmitting respective reference signals identifying the respective cells.

According to one embodiment, the memory and computer program code are further configured to, with the processor, cause the apparatus to transmit in parallel from each of said more than one antenna arrays reference signals commonly indicating the same Cell Id for said second cell. According to one embodiment, the more than one antenna arrays used to operate the second cell comprise active antenna systems.

There is also hereby provided an apparatus comprising: means for operating a plurality of first cells and a second cell in parallel, wherein the first cells are operated via respective ones of a plurality of antenna arrays at an antenna site; and said second cell is operated via antenna arrays at said same antenna site at a different degree of vertical tilting to said first cells; wherein said plurality of first cells and said second cell are operated via the same time-frequency resources; and wherein operating said second cell comprises mak- ing transmissions for said second cell substantially simultaneously via more than one antenna array at said antenna site.

There is also hereby provided a computer program product comprising program code means which when loaded into a computer controls the computer to: operate a plurality of first cells and a second cell in parallel, wherein the first cells are operated via respective ones of a plurality of antenna arrays at an antenna site; and said second cell is operated via antenna arrays at said same antenna site at a different degree of vertical tilting to said first cells; wherein said plurality of first cells and said second cell are operated via the same time-frequency resources; and wherein operating said second cell comprises mak- ing transmissions for said second cell substantially simultaneously via more than one antenna array at said antenna site.

Embodiments of the present invention are described in detail hereunder, by way of example only, with reference to the accompany drawings, in which: Figure 1 schematically illustrates an example of the distribution of antenna arrays by which macro cells are operated in a cellular network;

Figure 2 schematically illustrates a vertical sectorisation technique according to which the respective coverage areas at ground level for two signals transmitted substantially simultaneously from an elevated active antenna array are distinguished by using different degrees of electrical tilting for each signal;

Figure 3 schematically illustrates an example of the respective coverage area of cells in an example technique; Figure 4 schematically illustrates the transmission of baseband signals for a plurality of cells from a baseband unit to an active antenna system in an example technique; and

Figure 5 schematically illustrates a baseband unit and active antenna system for one antenna array used in an example technique.

Figure 1 illustrates part of the architecture of one non-limiting example of a cellular communication system in which the below-described technique can be implemented. The same kind of technique can also be implemented in other examples. Some possible variations include, but are not limited to, the following: the antenna array groups may consist of two antenna arrays or comprise more than three antenna arrays; there can be varia- tions in cell range both between cells operated from the group of antenna arrays and/or between cells operated from different antenna array groups/antenna mast sites; the inner cell mentioned below may be operated from different antenna arrays to the ones used for operating the outer cells; there may be two or more inner cells; the inner cell may have a combination of main lobes that point in different directions to those of the outer cells; the electrical tilting mentioned below may be used in combination with some degree of mechanical tilting.

The exemplary cellular communication system includes a plurality of antenna masts/poles at respective sites 3 each supporting three active antenna arrays 2a, 2b, 2b. Each group of three active antenna arrays 2a, 2b, 2c at each antenna mast site 3 is connected to a respective baseband unit (BBU) 4 via a high speed serial link such as an optic fibre link 6. Each BBU 4 is connected to a core network 8 for the cellular communication system.

Figure 2 only shows 4 antenna mast sites 3, but a cellular communication system could typically comprise thousands of antenna mast sites.

As discussed below, the group of antenna arrays 2 at each antenna mast site 3 are used to operate a respective set of macro cells. The cellular communication system may also include other elements, such as for example, additional radio access nodes operating cells having relatively small coverage areas, such as femto or pico cells, within the coverage area of the macro cells.

The cellular communication system may be used for communicating with user devices (UEs) 10 via wireless interfaces. Only a small number of UEs 10 are shown in Figure 1 , but a cellular communication system would typically serve a very large number of UEs 6. Some examples of user devices (UEs) include mobile phones, smart phones, portable media players, tablets and other portable computer devices etc.. The UE 10 may be any device capable of at least receiving radio signals transmitted via cells operated by the antenna arrays 2. UE 10 may, for example, be a device designed for tasks involving human interaction such as making and receiving phone calls between users, and streaming multimedia or providing other digital content to a user. Non-limiting examples include a smart phone, and a laptop computer/notebook computer/tablet computer/ e-reader device provided with a wireless interface facility.

Figure 5 schematically illustrates an example of elements for the active antenna system 2, and the baseband unit 4 that, in this non-limiting example, provides baseband signals to the active antenna system(s) 2 and the other active antenna systems at the same antenna mast site 3.

The active antenna array 2 includes an array of dipole elements (radiating elements) 12 located forwards of one or more reflector trays 14. Each dipole element 12 is connected to a respective transceiver 16. Each transceiver 16 incorporates an upconvertor, a power amplifier, a low noise amplifier, a downconvertor and a duplexer. The active antenna array 2 also comprises a processor 18 that controls each of the transceivers to generate and transmit radio frequency signals representing the baseband signals received from base- band unit 4 at port 22. The high speed serial link 6 between the BBU 4 and the active antenna array may, for example, be one defined by the Common Public Radio Interface (CPRI), or Open Base Station Architecture Initiative (OBSAI). The one or more memory or data storage units 20 are used for storing data, parameters and/or instructions for use by processor 18. The baseband unit 4 also comprises one or more processors 26 for generating baseband signals for output to the active antenna arrays 2 via port 24. The BBU 4 also comprises a port 30 for receiving data from e.g. the core network 8. The one or more memory or data storage units 28 at BBU 4 are used for storing data, parameters and/or instructions for use by the one or more processors 26 at BBU 4.

The memories 20, 28 may be implemented using a suitable data storage technology, such as, for example, semiconductor based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The data processors 18, 26 may, for example, include one or more of microprocessors, digital signal processors (DSPs) and processors based on a multi-core processor architecture.

References below to processors 18, 26 controlling the operation of other elements of the BBUs 4 and the active antenna arrays 2 refer to the processors operating in accordance with program code stored at memories 20, 28.

It would be appreciated that the apparatus shown in Figure 5 described above may comprise further elements which are not directly involved with the embodiments of the inven- tion described hereafter.

As discussed in more detail below, in this non-limiting example, four cells are operated via the same time-frequency resources from each group of 3 active antennas at each antenna mast site. In other words, in this non-limiting example, the frequency reuse factor for the group of four cells is 1 .

The antenna arrays are mechanically (e.g. by appropriate spacing of the dipole elements (radiating elements) 12) and/or electrically configured to achieve horizontal beamforming by which the antenna arrays exhibit highly anisotropic radiation patterns. The set of three antenna arrays 2 are configured such that they exhibit substantially complementary radiation patterns. There can be some overlap between the radiation patterns to provide total coverage and ensure good hand-off performance, and the overlap typically occurs at about e.g. -10dB from maximum gain. The undesirable effects of interference between signals transmitted from different antenna arrays in these areas of overlap can be eliminated or reduced for transmissions to and/or from UEs 10 in these areas of overlap by e.g. the use of known correction techniques such as forward error correction and/or the use of intelligent resource allocation algorithms to coordinate transmissions from the group of antenna arrays.

In addition to the horizontal beamforming described above, electrical vertical tilting is used to focus the energy of different signals from the same antenna array 2 (via the same time- frequency resources) at different degrees of vertical tilt. This is schematically illustrated for one antenna array in Figure 2, which schematically illustrates the forward part of radiation pattern in a vertical plane for two signals 50, 52 transmitted from the same antenna array 2 at different degrees of vertical tilting from a horizontal plane, wherein the degree of vertical tilting from the horizontal plane may also include a component provided by mechanical tilting. As illustrated in Figure 2, the respective coverage areas of the two signals 50, 52 at a level below the antenna array 2 (e.g. ground level) can be distinguished by the use of different degrees of electrical vertical tilting (optionally in combination with a common degree of mechanical vertical tilting).

Different degrees of electrical tilting for two signals transmitted simultaneously from the same antenna array 2 are achieved using a different combination of phases for the transmission of the signal from the set of radiating elements 12. For example, for a signal having the lowest degree of electrical tilt (zero degrees), the signal may be transmitted from each radiating element with the same phase. For a signal having a higher degree of electrical tilt, one or more differences would be introduced in the relative phase at which the signal is transmitted from one or more radiating elements 12 of the antenna array 2 compared to one or more other radiating elements 12 of the same antenna array 2.

This electrical tilting is used to operate inner and outer cells via the same time-frequency resources from the same antenna array 2, and increase the capacity of the antenna array 2 for those time-frequency resources. The signals for three cells operated at the same time-frequency resources are transmitted from respective ones of the three antenna arrays 2 at the same antenna mast site 3 at a relatively small degree of vertical electrical tilt; and the signals for a fourth cell also operated via the same time-frequency resources are transmitted in parallel from all three antenna arrays at a relatively large degree of vertical electrical tilt. There may be some variation in the degree of vertical electrical tilt between the three outer cell signals, and there may be some variation in the degree of vertical electrical tilt for the fourth cell signals between the three antenna arrays; but the degree(s) of vertical electrical tilt for the outer cell signals is less than the degree(s) of vertical electric tilt used for the fourth cell signals. The radiation patterns/coverage areas at ground level for each of the four cells are schematically illustrated in Figure 3. The difference in the degree of electrical tilting for the fourth, inner cell may be configured such that each of the three cells operated at relatively low degrees of electrical tilt have coverage areas 40, 42, 44 at ground level that are each approximately equal in size to the coverage area 46 at ground level of the fourth, inner cell operated from all three of the antenna arrays at a relatively high degree of electrical tilt. This can be advantageous for sharing traffic between cells in a balanced manner.

There may be some overlap both (i) between each of the radiation patterns/coverage areas at ground level of the three outer cells and the radiation pattern/coverage area at ground level of the fourth, inner cell, and (ii) between the radiation pattern/coverage area at ground level for any one of the outer cells and the radiation pattern/coverage area at ground level of the two remaining outer cells. The undesirable effects of interference between signals transmitted from different antenna arrays in these areas of overlap can be eliminated or reduced for transmissions to and/or from UEs 10 in these areas of overlap by known techniques such as forward error correction and/or the use of intelligent resource allocation algorithms to coordinate transmissions for the 4 cells operated from the group of antenna arrays 2 on the same antenna mast.

For downlink transmissions, the processor at the baseband unit 4 for the four cells operated via the group of three antenna arrays 2 at the same antenna mast site 3 controls the generation and transmission via the optical fiber link 6 to the three antenna arrays 2 of baseband signals for each of the four cells. As illustrated schematically in Figure 4, the baseband signals BB1 , BB2, BB3 for the 3 outer cells are transmitted to respective ones of the three antenna arrays 2 of the antenna array group, and the baseband signal BB4 for the fourth, inner cell is transmitted to all of the three antenna arrays 2 of the antenna array group.

At each antenna array 2, the processor controls the set of transceivers 16 to generate ra- dio frequency signals representing the received baseband signals for the two cells operated via that antenna array 2. The relative phase and/or amplitude of the radio frequency signals generated at each transceiver 16 (and transmitted from the respective dipole elements 12 of that antenna array) are controlled so as to achieve the different levels of electrical tilt for the radiation patterns of the signals for the two cells operated via that antenna array 2.

The inventors for the present application have observed that operating a fourth, inner cell via all three antenna arrays 2a, 2b, 2c at a relatively high degree of electrical tilting can deliver better overall system performance than operating three individual inner cells at a relatively high degree of electrical tilting from respective antenna arrays 2a, 2b, 2c of the antenna array group. In more detail, the inventors have observed that the use of relatively high degrees of electrical tilting can result in a marked increase in the lateral overlap (particularly in the close vicinity of the antenna mast site) between the back lobes/side lobes for one radiation pattern for one antenna array and the main lobe for the radiation pattern of another antenna array in the same antenna array group leading to uncontrollable interference between cell signals in one or more regions relatively close to the antenna mast site 3. The inventors have observed that the reduction in the number of cells operated via the same time-frequency resources by the antenna array group at the antenna mast site 3 (i.e. from six cells to four cells) can be more than compensated for by (i) a reduction in the amount of interference mitigation required to effectively operate the set of cells via the an- tenna array group, and/or (ii) a reduction in the number of handovers between cells operated via the same antenna array group . In other words, the inventors have observed that an improvement in overall performance can be achieved by adopting less densification and instead simultaneously employing the inner radiation patterns (i.e. relatively steep beam tilting) from more than one of the antenna arrays for a single cell (super cell).

The three outer cells and the fourth, inner cell each have respective cell identifiers (Cell Ids). The operation of the three outer cells and the fourth, inner cell involves transmitting reference signals from which UEs 10 can identify the cell to which the reference signal relates, i.e. reference signals from which UEs 10 can determine the Cell Id for the cell to which the reference signal relates.

The fourth cell may be switched on and off according to the level of demand for communication services and/or number of UEs in the overall coverage area of the antenna array group. Accordingly, there may be times when the group of three antenna arrays is used to operate three cells without also being used to operate the fourth cell.

The above description relates to the example of an antenna array group comprising three antenna arrays, but the same kind of technique is also applicable to similar antenna array groups comprising any number of active antenna arrays. Generally, for an antenna array group comprising n antenna arrays, the above-described technique involves operating at least one respective cell via each of the n antenna arrays, and operating at least one extra cell via two or more of the n antenna arrays (and more specifically via all n antenna arrays). Other possible variations include, but are not limited to, the following: there can be variations in cell range both between cells operated from the group of antenna arrays at the same antenna mast site 3 and/or between cells operated from different antenna array groups/antenna mast sites 3; the inner cell mentioned above may be operated from different antenna arrays to the ones used for operating the outer cells; there may be two or more inner cells; the inner cell may have a combination of main lobes that point in different directions to those of the outer cells; the electrical tilting mentioned above may be used in combination with some degree of mechanical tilting.

One specific, non-limiting example of a variation is to provide at the same antenna mast site 3 antenna arrays for operating the inner cell and other antenna arrays for operating the inner super cell. This variation also involves transmitting the inner super cell signals at a degree of vertical tilt greater than that at which the outer cell signals are transmitted.

The program code mentioned above may include software routines, applets and macros. Program code may, for example, be copied into the one or more memories 20, 28 from any apparatus-readable non-transitory data storage medium. Computer program codes may be coded by a programming language, which may be a high-level programming language, such as objective-C, C, C++, C#, Java, etc., or a low-level programming language, such as a machine language, or an assembler. The program code may be stored in a computer readable medium, such as a memory unit or magnetic or optical disk and it may be a non-transitory medium. The program code may also be loadable from a server, host or another suitable resource.

Alternatively, some of the above-described functions or other functions performed at the active antenna array 2 or baseband unit 4 may be implemented by one or more application specific integrated circuits (ASICs), chip sets, field programmable gate arrays

(FPGAs), photonic integrated circuits, etc..

The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.

Programs, such as those provided by Synopsys, Inc. of Mountain View, California and Cadence Design, of San Jose, California automatically route conductors and locate components on a semiconductor chip using well established rules of design as well as libraries of pre stored design modules. Once the design for a semiconductor circuit has been completed, the resultant design, in a standardized electronic format (e.g., Opus, GDSII, or the like) may be transmitted to a semiconductor fabrication facility or "fab" for fabrication.

In addition to the modifications explicitly mentioned above, it will be evident to a person skilled in the art that various other modifications of the described embodiment may be made within the scope of the invention.

Claims

1. A method, comprising: operating a plurality of first cells and a second cell in parallel, wherein the first cells are operated via respective ones of a plurality of antenna arrays at an antenna site; and said second cell is operated via antenna arrays at said same antenna site at a different degree of vertical tilting to said first cells; wherein said plurality of first cells and said second cell are operated via the same time-frequency resources; and wherein operating said second cell comprises making transmissions for said second cell substantially simultaneously via more than one antenna array at said antenna site.

2. A method according to claim 1 , wherein operating said second cell comprises making transmissions for said second cell substantially simultaneously via more than one of said plurality of antennas via which said first cells are operated.

3. A method according to claim 1 or claim 2, wherein the tilting comprises electrical tilting.

4. A method according to any preceding claim, wherein the first cells have coverage areas located outwards of the coverage area of the second cell.

5. A method according to any preceding claim, comprising operating said first cells at a lower degree of vertical tilting than said at least one second cell.

6. A method according to any preceding claim, wherein each of said plurality of an- tenna arrays comprises a plurality of radiating elements, each radiating element associated with a respective transceiver element, and wherein the phase and/or amplitude at which a signal is transmitted from any one of said radiating elements is individually configurable with respect to the phase and/or amplitude at which said signal is transmitted from any other one of said radiating elements.

7. A method according to claim 6, comprising controlling the transmission of a signal for one of said first cells and a signal for said second cell from one of said plurality of antenna arrays via the same time-frequency resource, wherein said controlling comprises controlling the transmission of said first cell signal from said plurality of radiating elements for said antenna array according to a set of phases and/or amplitudes different to those employed for the transmission of said second cell signal from the same plurality of radiating elements.

8. A method according to any preceding claim, wherein each of said first and second cells has a respective Cell Id.

9. A method according to any preceding claim, wherein said operating said first cells and said at least one second cell comprises transmitting respective reference signals identifying the respective cells.

10. A method according to any preceding claim, wherein operating said second cell comprises transmitting in parallel from each of said more than one antenna arrays refer- ence signals commonly indicating the same Cell Id.

1 1 . A method according to any preceding claim, wherein the more than one antenna arrays used to operate the second cell comprise active antenna systems.

12. An apparatus comprising: a processor and memory including computer program code, wherein the memory and computer program code are configured to, with the pro- cessor, cause the apparatus to: operate a plurality of first cells and a second cell in parallel; operate the first cells via respective ones of a plurality of antenna arrays at an antenna site; operate said second cell via antenna arrays at said same antenna site at a different degree of vertical tilting to said first cells; operate said plurality of first cells and said second cell via the same time-frequency resources; and make transmissions for said second cell substantially simultaneously via more than one antenna array at said antenna site.

13. An apparatus according to claim 12, wherein the memory and computer program code are further configured to, with the processor, cause the apparatus to: make transmissions for said second cell substantially simultaneously via more than one of said plurality of antennas via which said first cells are operated.

14. An apparatus according to claim 12 or claim 13, wherein the tilting comprises electrical tilting.

15. An apparatus according to any of claims 12 to 14, wherein the first cells have coverage areas located outwards of the coverage area of the second cell.

16. An apparatus according to any of claims 12 to 15, wherein the memory and com- puter program code are further configured to, with the processor, cause the apparatus to: operate said first cells at a lower degree of vertical tilting than said at least one second cell.

17. An apparatus according to any of claims 12 to 16, wherein each of said plurality of antenna arrays comprises a plurality of radiating elements, each radiating element associ- ated with a respective transceiver element, and wherein the phase and/or amplitude at which a signal is transmitted from any one of said radiating elements is individually configurable with respect to the phase and/or amplitude at which said signal is transmitted from any other one of said radiating elements.

18. An apparatus according to claim 17, wherein the memory and computer program code are further configured to, with the processor, cause the apparatus to: control the transmission of a signal for one of said first cells and a signal for said second cell from one of said plurality of antenna arrays via the same time-frequency resource, and control the transmission of said first cell signal from said plurality of radiating elements for said antenna array according to a set of phases and/or amplitudes different to those employed for the transmission of said second cell signal from the same plurality of radiating elements.

19. An apparatus according to any of claims 12 to 18, wherein each of said first and second cells has a respective Cell Id.

20. An apparatus according to any of claims 12 to 19, wherein said operating said first cells and said at least one second cell comprises transmitting respective reference signals identifying the respective cells.

21 . An apparatus according to any of claims 12 to 20, wherein the memory and computer program code are further configured to, with the processor, cause the apparatus to transmit in parallel from each of said more than one antenna arrays reference signals commonly indicating the same Cell Id for said second cell.

22. An apparatus according to any of claims 12 to 21 , wherein the more than one antenna arrays used to operate the second cell comprise active antenna systems.

23. An apparatus comprising: means for operating a plurality of first cells and a second cell in parallel, wherein the first cells are operated via respective ones of a plurality of antenna arrays at an antenna site; and said second cell is operated via antenna arrays at said same antenna site at a different degree of vertical tilting to said first cells; wherein said plurality of first cells and said second cell are operated via the same time-frequency resources; and wherein operating said second cell comprises making transmissions for said second cell substantially simultaneously via more than one antenna array at said antenna site.

24. A computer program product comprising program code means which when loaded into a computer controls the computer to: operate a plurality of first cells and a second cell in parallel, wherein the first cells are operated via respective ones of a plurality of antenna arrays at an antenna site; and said second cell is operated via antenna arrays at said same antenna site at a different degree of vertical tilting to said first cells; wherein said plurality of first cells and said second cell are operated via the same time-frequency resources; and wherein operating said second cell comprises making transmissions for said second cell substantially simultaneously via more than one antenna array at said antenna site.