GB2468730A

GB2468730A - Cellular telecommunications system cell site

Info

Publication number: GB2468730A
Application number: GB0909714A
Authority: GB
Inventors: Andrew Dunkin; Paul Edwards; Peter Cosimini
Original assignee: Vodafone Group PLC
Current assignee: Vodafone Group PLC
Priority date: 2009-03-16
Filing date: 2009-06-08
Publication date: 2010-09-22
Also published as: GB0904482D0; GB0909714D0

Abstract

A cell site 20 comprises an antenna element 62 with a first cross-polar antenna 63A and a base station 30. Transmit (downlink) signals and receive (uplink) signals are transmitted between the antenna 63A and the base station 30 via conventional feeder cables 44A,44B. To improve the capacity of the cell site the antenna element 62 is modified to include a second cross-polar antenna 63B. Receive (uplink) signals from the second cross-polar antenna 63B are converted into optical signals by RF to optical conversion unit 64 and transmitted via a fibre optic cable 66 to optical to RF conversion unit 67 mounted at the base station 30. The capacity of the cell site is increased by providing a dual cross-polar antenna unit that provides four receive paths in total. The requirement for additional feeder cables is avoided by transmitting the data from the two additional antenna receive paths via a fibre optic cable 66.

Description

CELLULAR TELECOMMUNICATIONS SYSTEM CELL SITE

The present invention relates to a cellular telecommunications system cell site including an antenna device and a base station, and to a method of improving the performance of such a cellular telecommunications system cell site.

Conventionally cellular telecommunications system cell sites used in 2G (GSM) and 3G (UMTS) cellular telecommunications networks employ a single cross-polar antenna. Receive and transmit data at the cell site is transmitted between a base station and the antenna via RF electrical feed cabling. Many thousands of these "legacy" macro cell sites are provided. To add additional capacity to cellular networks and to support new technology such as Long Term Evolution (LTE), higher frequencies are likely to be used. Higher frequencies have higher propagation losses. In order to provide adequate radio coverage at higher frequencies, further cell sites can be provided, although this is expensive. It is difficult to modify existing cell sites to support further antennae or antennae with additional capacity as this may incur increased cell site rental costs, require planning approval or may result in the antenna supporting-tower weight capacity being exceeded.

According to a first aspect of the present invention, there is provided a cellular telecommunications system cell site including an antenna device, a base station, and RF electrical feed cabling connecting the antenna device to the base station and for carrying transmit data in the downlink direction, wherein a fibre optic connection is provided for connecting the antenna device to the base station and for carrying receive data in the uplink direction.

In the embodiments the capacity of the cell site to carry receive data in the uplink direction is enhanced by providing the fibre optic connection. This capacity enhancement is provided without the disadvantages of adding further RF electrical feed cabling. The fibre optic connection may comprise a single or multiple fibre optic cables. The fibre optic cable or cables are much lighter, smaller and less expensive than RF electrical feed cabling.

The RF electrical feed cabling may, in addition to carrying transmit data in the downlink direction, also carry receive data in the uplink direction. If the antenna is a multi-path antenna, the antenna device may be arranged to send receive data from one of the paths in the uplink direction via the RF electrical feed cabling and to send receive data from another of the paths in the uplink direction via the fibre optic connector.

Alternatively, the RF electrical feed cabling may only transmit data in the downlink direction (i.e. the RF electrical feed cabling does not carry receive data in the uplink direction), and instead the fibre optic connection carries all the receive data in the uplink direction. It can be advantageous to cariy all the receive data in the uplink direction by the fibre optic connection as this allows a antenna tower-mounted amplifier that is conventionally provided to be eliminated.

Further, in such an arrangement, because all the receive data in the uplink direction received by the base station have been carried by the common fibre optic connection, none of the receive data are subject to the loss associated with conventional transmission via the RF electrical feed cabling.

The antenna device may comprise a dual cross-polar antenna having four paths.

Such a dual cross-polar antenna may be provided at a cell site in a radome that is indistinguishable from the radome used to carry a single cross-polar antenna of the type typically employed in 2G and 3G cellular telecommunications networks. The dual cross-polar antenna will provide enhanced capacity, which is particularly advantageous as it counteracts the poorer coverage provided when a base station is operated at a higher frequency band. The operation of base stations at a higher frequency band will become more common when LTE networks are implemented.

The antenna device may include an RF to optical converter for converting radio signals received by the antenna device into a form suitable for being conveyed by the fibre-optic connection. An amplifier for amplifying signals carrying the transmit data in the downlink direction and the RF to optical converter may be accommodated in a common housing. This common housing may be a radome of the antenna device, which provides a particularly neat appearance.

The base station may also include an optical to RF converter for converting signals to from the fibre optic connection into RF signals for processing by an RF unit of the base station. Alternatively, the fibre optic connection may be coupled to a baseband unit of the base station for direct processing thereby (thus avoiding processing by the RF units).

The cell site may serve a plurality of cellular telecommunications network operators (for example, separate legal entities). The fibre optic connection may be arranged to carry receive data in the uplink direction for each of the network operators.

The present invention also provides a method of improving the performance of a cellular telecommunications system cell site as defined in the claims.

For a better understanding of the present invention, the embodiments will now be described with reference to the accompanying drawings in which: Figure 1 is a diagrammatic drawing of key elements of a mobile telecommunications network; Figure 2 is a diagrammatic drawing of a cell site and three cells served by that cell site; Figure 3 is a schematic drawing of a conventional cell site comprising an antenna element and a base station; Figure 4 is a schematic drawing of a cell site in accordance with a first embodiment of the invention in which a dual cross-polar antenna is provided and in which the received signals from the second cross-polar antenna are conveyed by a fibre optic cable to the base station; Figure 5 is a modification of the Figure 4 embodiment in which the functions of the tower mounted amplifier and tower mounted RF to optical conversion unit are combined into a single unit; Figure 6 is a modification of the Figure 4 embodiment in which the tower mounted amplifier and the RF to optical conversion unit are embedded within the radome of the antenna element; Figure 7 is a schematic drawing, a further embodiment of the invention in which the fibre optic cable terminates directly into the baseband unit of a base station; Figure 8 is a schematic drawing of a yet further embodiment of the invention in which received signals from the dual cross-polar antenna are all transmitted by a fibre optic cable to the base station, with only the transmit signals being transmitted via conventional feeder cables; Figure 9 is a detailed view of the RF to optical converter unit of Figure 8; Figure 10 is a schematic view of another embodiment of the invention in which a cell site is shared by two separate cellular telecommunications network operators; and Figure 11 is a detailed view of the RF to optical converter unit of Figure 10.

In the drawings like elements are generally designated with the same reference

S sign.

Key elements of a mobile telecommunications network, and its operation, will now briefly be described with reference to Figure 1.

Each base station (BS) corresponds to a respective cell of its cellular or mobile telecommunications network and receives calls from and transmits calls to a mobile terminal in that cell by wireless radio communication in one or both of the circuit switched or packet switched domains. Such a subscriber's mobile terminal is shown at 1. The mobile terminal may be a handheld mobile telephone.

In a GSM mobile telecommunications network, each base station comprises a base transceiver station (BTS) and a base station controller (BSC). A BSC may control more than one BTS. The BTSs and BSCs comprise the radio access network.

In a UMTS mobile telecommunications network, each base station comprises a node B and a radio network controller (RNC). An RNC may control more than one node B. The node B's and RNC's comprise the radio access network.

In the proposed LTE mobile telecommunications network, each base station comprises an eNode B. The base stations are arranged in groups, and each group of base stations is controlled by a Mobility Management Entity (MME) and a User Plane Entity (UPE).

Conventionally, the base stations are arranged in groups and each group of base stations is controlled by one mobile switching centre (MSC), such as MSC 2 for base stations 3, 4 and 5. As shown in Figure 1, the network has another MSC 6, which is controlling a further three base stations 7A, 8 and 9. In practice, the network will incorporate many more MSCs and base stations than shown in Figure 1. The base stations 3, 4, 5, 7A, 8 and 9 each have dedicated connection to their MSC 2 or MSC 6 -typically a cable connection.

The MSCs 2 and 6 support communications in the circuit switched domain -typically voice calls. Corresponding SGSNs 16 and 18 are provided to support communications in the packet switched domain -such as GPRS data transmissions. The SGSNs 16 and 18 function in an analogous way to the MSCs 2 and 6. The SGSNs 16, 18 are equipped with an equivalent to the VLRs 11, 14 used in the packet switched domain.

Each subscriber to the network is provided with a smart card or SIM which, when associated with the user's mobile terminal identifies the subscriber to the network.

The SIM card is pre-programmed with a unique identification number, the "International Mobile Subscriber Identity" (IMSI) that is not visible on the card and is not known to the subscriber. The subscriber is issued with a publicly known number, that is, the subscriber's telephone number, by means of which callers initiate calls to the subscriber. This number is the MSISDN.

The network includes a home location register (HLR) 10 which, for each subscriber to the network, stores the IMSI and the corresponding MSISDN together with other subscriber data, such as the current or last known MSC or SGSN of the subscriber's mobile terminal.

When mobile terminal 1 is activated, it registers itself in the network by transmitting the IMSI (read from its associated SIM card) to the base station 3 associated with the particular cell in which the terminal 1 is located. In a traditional network, the base station 3 then transmits this IMSI to the MSC 2 with which the base station 3 is registered. In a network using the functionality described in 3GPP TS 23.236, the base station follows prescribed rules to select which MSC to use, and then transmits this IMSI to the selected MSC.

MSC 2 now accesses the appropriate storage location in the HLR 10 present in the core network 140 and extracts the corresponding subscriber MSISDN and other subscriber data from the appropriate storage location, and stores it temporarily in a storage location in a visitor location register (VLR) 14. In this way, therefore the particular subscriber is effectively registered with a particular MSC (MSC 2), and the subscriber's information is temporarily stored in the VLR (VLR 14) associated with that MSC.

Each of the MSCs of the network (MSC 2 and MSC 6) has a respective VLR (14 and 11) associated with it and operates in the same way as already described when a subscriber activates a mobile terminal in one of the cells corresponding to one of the base stations controlled by that MSC.

\Vhen the subscriber using mobile terminal 1 wishes to make a call, they enter the telephone number of the called party in the usual manner. This information is received by the base station 3 and passed on to MSC 2. MSC 2 routes the call towards the called party. By means of the information held in the VLR 14, MSC 2 can associate the call with a particular subscriber and thus record information for charging purposes.

The functionality just described may also apply to the proposed LTE mobile telecommunications network, with its eNode Bs performing the functionality of the base stations and the MME/UPE performing the functionality of the MSCs/VLRs. It is also to be appreciated that the functionality just described is one example of a network in which the embodiments of the invention may be implemented.

Each base station is coupled to an antenna device. The base station and antenna device form a cell site 20 as shown in Figure 2. The cell site 20 provides radio coverage to each of cells 22A,22B and 22C. Typically, the cell site 20 will only provide radio coverage for a portion of each of the cells 22A,22B and 22C. Other portions of each of the cells 22A,22B and 22C are provided with radio coverage and by other cell sites (not shown). Each of these portions of the cell 22A,22B,22C is referred to as a sector. The antenna device of the cell site 20 comprises three separate antenna elements, each of which is arranged to provide radio coverage to a respective one of the cells 22A,22B and 22C.

Figure 3 shows a known arrangement of a base station and antenna device. The antenna device has a single element for providing radio coverage to a particular sector of a cell. The cell site 20 comprises a base station 30 including RF units 32 and a baseband unit 34. The base station 30 is powered by DC power system 36 which is coupled to AC power supply 38. The base station 30 is coupled to the core network 140 via transport equipment 40. The antenna element 42 comprises a single cross polar antenna 43 within a radome 41 which provides two antenna paths. The antenna element 42 is coupled to the base station 30 via two RF electrical feeder cables, 44A and 44B. First feeder cable 44A transmits data in the downlink between the base station 40 and the antenna element 42 and receives data in the uplink between the antenna element 42 and the base station 40 for a first antenna path. The second feeder cable 44B transmits data between the base station 30 and the antenna element 42 in the downlink and receives data from the antenna element 42 to the base station 30 in the uplink for a second antenna path.

The two antenna paths provide two receive paths and two transmit paths.

The first feeder cable 44A is connected to the antenna element 42 via a first flexible jumper 46A, and is connected to the base station 30 via a second flexible jumper 48A. The second feeder cable 44B is connected to the antenna element 42 via a third flexible jumper 46B, and is coupled to the base station 30 via a fourth flexible jumper 48B.

The antenna element 42 is supported by an antenna tower, shown schematically at 50. The feeder cables 44A and 44B are also supported by the antenna tower 50.

Typically, when the cell site is operating in the 1800MHz frequency band or above a tower mounted amplifier 52 is provided for each cell as close to the antenna element 42 for that cell as possible, normally at the head of the tower 50 to amplify the received signals from the antenna element 42 before they pass through the feeder cables 44A,44B. The tower mounted amplifier 52 reduces the impact of losses caused by the passive system comprising the feeder cables 44A,44B and any associated combining equipment, which losses can be several decibels. The provision of a tower mounted amplifier 52 can improve the overall uplink performance of the cell site 20.

In Figure 3 each of the antenna paths of the cross-polar antenna 43 is fed from the antenna via a first RF connection 45A and a second RF antenna connection 45B.

Each of these RF connections carries transmit (downlink) communications and receive (uplink) connections to/from one path of the cross-polar antenna 43.

What ha s b een described thus far is a conventional cellular/mobile telecommunications network.

For LTE networks it is proposed that cell sites will operate at a higher frequency band of 2.6GHz, which will reduce the coverage area of the cell site. As discussed above, at higher frequency bands the propagation losses are higher.

One solution to this problem would be to add further cell sites, but this would incur significant additional costs and take a considerable time to implement.

Another solution is to employ more advanced antenna solutions, such as four-way receive diversity antennae -for example, a dual cross polar antenna that provides four antenna paths (in contrast to the single cross polar antenna that provides two antenna paths illustrated in Figure 3).

A problem with implementing an antenna element with four antenna paths is that four feeder cables would conventionally be required (in contrast to the two feeder cables 44A,44B shown in Figure 3 for the two antenna paths).

Changes and/or additions to antennae and related feeder systems at existing cell sites present major challenges. These challenges include: -Increased site rental costs, as site landlords typically base rental payments on the number of antennae and feeders installed.

-The addition of an antenna may require planning permission.

-The addition of antennae may increase the perceived environmental impact of a cell site, which may cause objections from members of the public.

-The existing towers used to support current antennae and feeder cables are at or near their capacity and are unable to support significant additional hardware, such as additional antennae and feeder cables.

By replacing a conventional single cross polar antenna, that provides two antenna paths, with a dual cross polar antenna that provides four antenna parts, which improves radio coverage, the requirement to provide additional antennae at a cell site can be avoided. However, as mentioned above, the dual cross polar antenna will conventionally require four feeder cables, one for each antenna path, and this may require increased rental payments, planning permission and/or may exceed the support capacity of the antenna tower.

Embodiments of the present invention now to be described in detail provide an advantageous arrangement for adapting existing legacy macro base stations to use four-way receive diversity antennae without requiring the addition of further feeder cables and thereby avoiding the problems of increased rental payments, planning permission and tower support capacity. However, it should be appreciated that the invention is applicable to different antenna designs and is not limited to four-way receive diversity antennae, or any particular antennae with a predetermined number of antenna paths.

In the embodiments a fibre optic cable is used at an existing legacy cell site (like that shown in Figure 3) to carry the signals of one or more antenna paths between the antenna element and the base station. Fibre optic cables are considerably smaller and more discreet, and hence are easier to install within or outside an existing tower structure. Fibre optic cables are also significantly cheaper than conventional RF feeder cables (which can cost �20,000 for a 20 metre cable).

Further, fibre optic cables do not suffer from the intrinsic signal losses that occur in passive RF feeder cables, which is particularly advantageous when handling very low power receive signals which can occur in cellular telecommunications systems.

According to a first embodiment of the invention, as shown in Figure 4, the cell site 20 of Figure 3 is modified such that the single cross polar antenna 42 of Figure 3 is replaced with a dual cross-polar antenna element 62 within radome 61 and comprising a first cross polar antenna 63A and a second cross-polar antenna 63B. The first antenna path of the first cross-polar antenna 63A is coupled to the RF unit 32 of the base station 30 via first flexible jumper 46A, first feeder cable 44A and second flexible jumper 48A. The second antenna path from the first cross-polar antenna 63A is connected to the RF unit 32 of the base station 30 via third flexible jumper 46B, second feeder cable 44B and fourth flexible jumper 48B. Each of the antenna paths of the first cross-polar antenna 63A carries communications in the transmit (downlink) direction and in the receive (uplink) direction. The tower mounted amplifier 52 receives data via RF connections 45A,45B and amplifies received data before it passes along the feeder cables 44A,44B to the RF unit 32 of the base station 30.

The two antenna paths from the second cross-polar antenna 63B are coupled by RF first and second connections 46A,468 to an RF to optical conversion unit 64 which converts the RF signals from the antenna paths into signals suitable for transmission on the fibre optic cable 66.

At the base station 30 end of the fibre optic cable 66 an optical to RF conversion unit 67 is provided to convert the optical signals transmitted by the fibre optic cable 66 back into RF signals for transmission to the RF units 32 of the base station 30 via a fifth flexible jumper 68A and sixth flexible jumper 68B. By converting the optical signals back into RF signals in the same band as the RF signals received by the RF to optical conversion unit 64 from the second cross-polar antenna 63B, there is no requirement for the base station 30 to be modified to handle optical signals.

The RF to optical conversion unit 64 and the optical to RF conversion unit 67 may operated in accordance with the OBSAI or CIPRI standards. The base band unit 34 may be adapted to interpret the optical signals transmitted in accordance with the OBSAI or CIPRI standards.

The RF to optical conversion unit 64 is provided with a DC bias connection 70 from the first flexible jumper 46A. The optical to RF conversion unit 67 receives power from the DC power system 36 that also powers the base station 30.

In the first embodiment the fibre optic cable 66 carries two receive (uplink) connections of the two antenna paths provided by the second cross-polar antenna 63B. This supports the four-way receive diversity functionality of the dual cross-polar antenna 62 whilst not requiring additional heavy and expensive antenna feeders to be provided.

Figure 5 shows a modification of the Figure 4 embodiment in which the tower-mounted amplifier 52 and the RF to optical conversion unit 64, which is also mounted on the tower, are combined into a single passive-optical tower-mounted amplifier unit 70 that supports the transmission of data from the first cross-polar antenna 63A along the conventional passive feeder cables 44A,44B and also the transmission of two receive signals from the RF connectors 65A,65B received from the second cross-polar antenna 63B for transmission along the fibre optic cable 66. Other elements of the cell site of Figure 4 that are not modified are not shown.

Figure 6 shows a further modification of the first embodiment in which the tower-mounted amplifier 52 and the RF to optical conversion unit 64 are embedded within the radome 61 of the antenna element 62. This provides the tower mounted components with a neater appearance whilst still avoiding the need for more than the two conventional feeder cables 44A,44B. The additional received signals from the second cross-polar antenna 63B are conveyed to the base station 30 via the fibre optic cable 66. In the Figure 6 arrangement the tower mounted amplifier 52 and RF to optical conversion unit 64 may be combined into a single unit, like the unit 70 of Figure 5, but which is housed within the radome 61.

Figure 7 shows a further embodiment of the invention in which the optical interface is terminated directly into the baseband unit 34 of the base station 30 for the uplink receive path data from the second cross-polar antenna 63B. This allows the optical to RF conversion unit 67 to be omitted but does require modification to the base station 30 to allow the direct insertion of optical signals to the baseband unit 34.

Figures 8 and 9 show another embodiment of the invention in which a single passive to optical tower-mounted amplifier unit 74 is coupled to each of the RF connectors 45A,45B,65A,65B. The unit 74 receives transmit (downlink) data via the feeder cables 44A,44B in the conventional manner. However, the receive (uplink) data from the RF connectors 45A,45B is not transmitted via the feeder cables 44A,44B, in contrast to the earlier embodiments. Instead, all the received signals from the RF connectors 45A,45B,65A,65B are converted into optical signals for transmission down fibre optic cable 66. The optical signal is received by the optical to RF conversion unit 76 and from there is converted into four separate RF signals representing the RF signals received from each of the RF connectors 45A,45B,65A,65B. These four RF signals are transmitted from the optical to RF conversion unit 76 via connectors 68A,68B,68C,68D and are then received by the RF units 32 of the base station 30 and are then processed in the conventional way.

The base station 30 is configured to provide non duplexed RF connections, i.e. separate transmit and receive connections. The base station 30 supports two transmit streams for MIMO (Multiple Input, Multiple Output) and 4.way receive diversity.

An advantage of this embodiment is that the tower mounted amplifier 52 of Figures 3 to 7 can be omitted as the receive (uplink) signals are transmitted by the fibre optic cable 66 and therefore do not stiffer from the losses associated with conventional transmission via the feeder cables 44A,44B. A further advantage of this embodiment is that all the receive (uplink) signals follow the same optical path and will therefore be better balanced as they will all undergo identical conversion and transport processes to reach the base station 30 prior to processing.

The common receive path removes the need for calibration between the four received signals that would potentially be required due to any differences introduced by them having travelled down either optical or passive RF paths as in the previous embodiments.

In a modification of this embodiment, the fibre optic cable 66 terminates directly into the baseband unit 34, as in the Figure 7 embodiment.

Figure 9 shows an enlarged view of the unit 74 and the inputs to and the outputs from that unit 74. The receive (uplink) signals from the (e.g. 50) RF connectors 45A,45B are separated from those connectors by respective duplexer units 78A,78B and are passed to RF to optical converter processor 80, where they are converted into optical signals for transmission by the fibre optic cable 66, together with the receive (uplink) signals received via the (e.g. 50) RF connectors 65A,65B. The downlink transmit signals from the base station 30 pass along the feeder cables 44A,44B through the duplexer units 78A,78B and along the RF connectors 45A,45B to the first cross-polar antenna 63A for transmission.

Figures 10 and 11 show an additional embodiment of the invention in which a single dual cross-polar antenna element 62 is shared by two different cellular telecommunications network operators.

In this embodiment a single dual cross-polar antenna element 62 is shared by a base station 30 of a first operator, operator A, and a base station 30B of a second operator, operator B. Each of the base stations 30A,30B comprises RF units 32 and a baseband unit 34 as in the previous embodiments. A DC power system and transport equipment is also provided for each of the base stations 30A,30B but this is not shown in Figures 10 and 11 for the sake of simplicity. In this embodiment the first feeder cable 44A is coupled to the base station 30A by flexible jumper 48A and allows transmit data to be sent in the downlink direction to a first of the cross-polar antennae 63A via a flexible jumper 46A and which also passes (unchanged) through RF to optical converter unit 84 and RF connector 45A.

Similarly, transmit data in the downlink direction from the base station 30B is transmitted via a flexible jumper 48B, feeder cable 44B and flexible jumper 46B, and (unchanged) through RF to optical converter unit 80 and RF connector 45B to the second cross-polar antenna 63B. In this embodiment the cell site provides network A with a single transmit path and network B with a single transmit path.

This allows two network operator base stations 30A,30B to be serviced by a single antenna element 62 without requiring the addition of any further feeder cables to the two feeder cables present at a conventional legacy macro base station.

Receive data in the uplink direction are transmitted along two paths from the first cross-polar antenna 63A to the RF to optical converter unit 84 via RF connector 45A and RF connector 65A. Similarly, receive data in the uplink direction from the second cross-polar antenna 63B is transmitted to the RF to optical converter unit 84 along two paths via the RF connector 45B and RF connector 65B.

The RF to optical converter unit 84 is operable to receive the two RF signal channels from the first cross-polar antenna 63A and the two RF signal channels from the second cross-polar antenna 63B and to convert these into optical signals for transmission along fibre optic cable 66. Optical to RF conversion unit 87 receives the optical signals transmitted via the fibre optic cable 66 and converts them back into four RF signal channels corresponding to the four RF channels received from the cross-polar antennae 63A,63B. The two RF receive channels derived from the first cross-polar antenna 63A are transmitted to the RF units 32 of base station 30A of network operator A via respective flexible jumpers 68A and 68B. The two RF receive channels received from the second cross-polar antenna 63B are transmitted to the RF unit 32 of the base station 30B of the network operator B via respective flexible jumpers 68C and 68D. Each base station 30A,30B is configured for non-duplex RF connection to its feeder cable 44A,44B, respectively.

The first cross-polar antenna 63A of the first network operator A and the second cross-polar antenna 63B of the second network operator B may be movable independently by Remote Electrical Tilt (RET) in order to tailor the coverage area and bandwidth distribution provided by the cross-polar antenna of each network operator according to the particular requirements of that network operator. RET varies these aspects by varying the lengths of the antenna elements within the radome 61. This enables a cross-polar antenna to be tilted electrically by about 10 degrees. A connection (not shown) between each of the base stations 30A and 30B to an RET controller (not shown) for each of the cross-polar antennae 63A and 63B is provided for signalling the required tilt adjustments.

Figure 11 shows an enlarged view of the RF to optical conversion unit 84 and the inputs to and the outputs from the unit 84.

The receive (uplink) signal from the connector 45A, from the cross-polar antenna 63A of the first network operator A, is separated from that connector by first duplexer unit 78A and is passed to RF to optical converter processor 80, where it is converted into an optical signal for transmission via the fibre-optic cable 66.

Similarly, the receive (uplink) signal from the connector 45B, from the second cross-polar antenna 63B of the second network operator B is separated from that connector by a second duplexer unit 78B and is passed to the RF to optical converter processor 80, where it is converted into an optical signal for transmission by the fibre optic cable 66. The receive (uplink) signal from each of RF connectors 65A and 65B (from the first and second cross-polar antennae 63A and 63B respectively) are passed directly to the RF to optical converter processor 80, where they are converted into optical signals for transmission by the fibre optic cable 66. The transmit (uplink) signal from the base station 30A of the first network operator A passes along the first feeder cable 44A through the first duplexer unit 78A and along the connector 45A to the first cross-polar antenna 63A for transmission. Similarly, the transmit (uplink) signal from the base station 30B of the second network operator B passes along the second feeder cable 44B through the second duplexer unit 78B and along the connector 45B to the second cross-polar antenna 63B for transmission.

The embodiment of Figures 10 and 11 enables, for example, 2 UMTS (3G) network operators to share two feeder cables 44A and 44B for legacy macro base station and a single radorne 61. Each network operator is provided with a single transmit path and two receive paths.

The embodiments described are by way of example only. It should be understood that variations to the embodiments are possible. For example, the RF to optical converter units 74 and 84 may be embedded within the radome 61.

In the embodiments described the fibre optic cable 66 supports the transmission of up to four receive paths in the uplink direction. The fibre optic cable may support the transmission of a larger number of receive paths. For example, if the cell site serves multiple sectors of multiple cells, a corresponding number of receive paths may be transmitted via a single fibre optic cable 66 after RF to optical conversion.

Embodiments of the invention provide a solution for existing cell sites to be adapted to support new radio technologies in addition to those they currently support. By using optical fibres to carry radio signals between newly installed antennae and the base stations, existing cell sites can be adapted in a relatively cheap and non-disruptive manner to support additional antennae and technologies.

Embodiments of the invention use fibre optic interfaces and technology already existing in current remote radio head technology and typically comply with OBSAT or CIPRI standards. As such the costs to achieve their incorporation into tower mounted amplifiers which exist at a considerably lower price point is achievable.

Claims

CLAIMS1. A cellular telecommunications system cell site including an antenna device, a base station, and RF electrical feed cabling connecting the antenna device to the base station and for carrying transmit data in the downlink direction, wherein a fibre optic connection is provided for connecting the antenna device to the base station and for carlying receive data in the uplink direction.
2. The cell site of claim 1, wherein the antenna device comprises a multi-path antenna.
3. The cell site of claim 1 or 2, wherein the RF electrical feed cabling is also arranged to carry receive data in the uplink direction.
4. The cell site of claim 2 and 3, wherein the antenna device is arranged to send receive data from one of said paths in the uplink direction via the RF electrical feed cabling and to send receive data from another of said paths in the uplink direction via the fibre optic connector.
5. The cell site of claim 1 or 2, wherein the RF electrical feed cabling only carries transmit data in the downlink direction, and wherein the fibre optic connection carries all the receive data in the uplink direction.
6. The cell site of any one of claims 1 to 5, wherein the antenna device comprises a dual cross polar antenna having four paths.
7. The cell site of any one of claims 1 to 6, wherein the antenna device comprises a four-way receive diversity antenna.
8. The cell site of any one of claims 1 to 7, wherein the antenna device includes an RF to optical converter for converting radio signals received by the antenna device into a form suitable for being conveyed by the fibre optic connection.
9. The cell site of claim 8, wherein said antenna device comprises an amplifier for amplifying signals carrying the transmit data in the downlink direction, and wherein the amplifier and the RF to optical converter are accommodated in a common housing.
10. The cell site of claim 9, wherein said common housing comprises a radome of the antenna device.
11. The cell site of claim 8,9 or 10, wherein the base station includes an optical to RF converter for converting signals from the fibre optic connection into RF signals.
12. The cell site of claim 8,9 or 10, wherein the fibre optic connection is coupled to a baseband unit of the base station for direct processing thereby.
13. The cell site of any one of claims 1 to 12, wherein the cell site serves a plurality of network operators and wherein said fibre optic connection is arranged to carry receive data in the uplink direction for each of the network operators.
14. A method of improving the performance of a cellular telecommunications system cell site having an antenna device, a base station, and RF electrical feed cabling connecting the antenna device to the base station and for carrying transmit data in the downlink direction, the method including providing a fibre optic connection which connects the antenna device to the base station and carries receive data in the uplink direction.
15. The method of claim 14, wherein the RF electrical feed cabling also carries receive data in the uplink direction.
16. The method of claim 15, wherein the antenna device comprises a multi-path antenna, the method including sending receive data from one of said paths in the uplink direction via the RF electrical feed cabling and sending receive data from another of said paths in the uplink direction via the fibre optic connection.
17. The method of claim 14, wherein the RF electrical feed cabling only carries transmit data in the downlink direction, and wherein the fibre optic connection carries all the receive data in the uplink direction.
18. The method of any one of claims 14 to 17, wherein the cell site serves a plurality of network operators and wherein said fibre optic connection carries receive data in the uplink direction for each of the network operators.
19. A cell site substantially as hereinbefore described with reference to and/or substantially as illustrated in any one of or any combination of Figures 4 to 11 of the accompanying drawings.

20 A method substantially as hereinbefore described with reference to and/or substantially as illustrated in any one of or any combination of Figures 4 to 11 of the accompanying drawings.