WO2001093459A1

WO2001093459A1 - An arrangement and a method for synchronising a telecommunication network element

Info

Publication number: WO2001093459A1
Application number: PCT/EP2000/005146
Authority: WO
Inventors: Cor Van Der Water
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2000-05-31
Filing date: 2000-05-31
Publication date: 2001-12-06
Anticipated expiration: 2002-11-30
Also published as: EP1410530A1; AU2000255291A1

Abstract

This invention relates to communication devices in general, and more particularly, to a new type of solution for synchronising a telecommunication network element, such as a Radio Fixed Part (RFP), a Wireless Relay Station (WRS) or a Portable Part (PP). The solution according to the invention can be used in cellular mobile communica-tions systems as well as in cellular cordless communications systems such as Digital Enhanced Communications System (DECT).

Description

AN ARRANGEMENT AND A METHOD FOR SYNCHRONISING A TELECOMMUNICATION NETWORK ELEMENT

This invention relates to communication devices in general, and more particularly, to a new type of solution for synchronising a telecommunication network element, such as a Radio Fixed Part (RFP) , a Wireless Relay Station (WRS) or a Portable Part (PP) . The solution according to the invention can be used in cellular mobile communications systems as well as in cordless communications systems such as Digital Enhanced Communications System (DECT) .

The use of wireless telecommunication has exponentially increased. People as users demand more and more wireless applications, that are not only easy and comfortable to use, but also fast and flexible to install and take into use. New wireless telecommunication applications are replacing many of the conventional wireline system applications .

A typical wireless telecommunication system consists of a multitude of network elements communicating with each other. These network elements should be properly synchronised in relation to each other. The air interfaces between the elements can however cause some delays that have to be compensated.

In the following, the prior art solutions will be described in more detail with reference to the accompanying figure 1, which is an illustrative diagram showing a cordless telecommunication system according to prior art.

Figure 1 is an illustrative diagram showing a cordless telecommunication system according to prior art. A cordless telecommunication system according to prior art consists of a Fixed Part 1, such as Central Control Fixed Part (CCFP) 1 and of a number of Radio Fixed Parts (RFPs) 2, 3, 4 communicating with a number of users each having a Portable Part (PP) 8, such as a cordless phone 8. The synchronisation signal of the system is provided by a system clock 5.

In a typical cordless telecommunication system according to prior art there may also be a number of Wireless Relay Stations (WRS) 6, 7, which can for instance be located in the remote areas of the network between the users and a Radio Fixed Part (RFP) 2. Wireless Relay Station (WRS) 6, 7 is seen from the side of a Radio Fixed Part (RFP) 2 as a Portable Part (PP) , and correspondingly WRS 6, 7 is seen from the side of a Portable Part (PP) 8 as a Radio Fixed Part (RFP) .

As the Portable Part (PP) 8, such as a cordless phone 8 is moving around in the network area there can be a need to handover the communication from one RFP 2, 3, 4 (RFP, Radio Fixed Part) to another RFP 2, 3, 4. This handover may also occur between one RFP 2, 3, 4 and one WRS 6, 7 (WRS, Wireless Relay Station) or between one WRS 6, 7 and another WRS 6, 7.

In a cordless telecommunication system according to prior art, such as Digital Enhanced Communications System (DECT), it is required that all RFPs 2, 3, 4 of one Fixed Part 1, such as Central Control Fixed Part (CCFP) 1, transmit synchronously within narrow tolerance in order to support handover between RFPs 2 , 3 , 4.

For a Wireless Relay Station (WRS) 6, 7, having a radio link to a RFP 2 of one Fixed Part 1, it is not obvious how it can accurately synchronise to the RFP 2 in order to allow the Portable Part (PP) 8 to make handovers from WRS

6, ,7, to RFP 2, 3, 4 and back.

The radio link used in this communication may introduce an unknown delay, especially when applying antennas with directional gain, as e.g. in an RLL application (RLL, Radio Local Loop) . In a typical RLL application there can be more than 5 kilometre distance between Wireless Relay Station (WRS) 6, 7, and Radio Fixed Part (RFP) 2, 3, 4 which introduces more than 40 bits of delay.

There are some prior art solutions for synchronising a telecommunication network element such as a Wireless Relay Station (WRS) of a Digital Enhanced Communications System (DECT) . A typical solution is to have an algorithm in the Wireless Relay Station (WRS) to compensate the timing delay experienced by the distance between the Radio Fixed Part (RFP) 2, 3, 4 and the Wireless Relay Station (WRS) 6,

7. The compensation algorithm adjusts the transmitter of the WRS 6, 7 until the RFP 2, 3, 4 receives the signal from WRS 6, 7 well. However, this still does not give an accurate synchronisation of the WRS 6, 7.

The current prior art arrangements for synchronising a telecommunication network element have many disadvantages. The delays make it difficult to accomplish the handovers in the network, thus making the network more unreliable. The arrangements also do not support the optimal use of the radio spectrum.

Although the synchronisation arrangements compensate the timing delay experienced by the distance between the Radio Fixed Part (RFP) 2, 3, 4 and the Wireless Relay Station (WRS) 6, 7, the WRS 6, 7 is not brought into synchronisation in timing with the RFP 2, 3, 4. In order to support handover between the network elements 2-7, network elements have to be placed closer to each other in the network. This is also done to meet the narrow requirements on synchronous transmission within the network .

The enterprises acquiring the cordless telecommunication networks place strict requirements on the performance of the network. The network has to meet the requirements in relation to the required services and to technical performance. There is further a demand for greater flexibility in use than in the prior art networks such as for load sharing and for more flexible handovers . The network should also be easier to upgrade; i.e. the devices in the cordless telecommunication network also have to be easy to update and to re-activate.

From the side of the users of a cordless telecommunication network as well as the enterprises acquiring a network there are also some expectations in regard to the reliability of the network. There should be possibility for the user to move around in the network area i.e. handovers between the network elements have to be arranged in a flexible manner.

In the view of the previously mentioned expectations there so far has not been provided an adequate solution for synchronising a telecommunication network element that would efficiently minimise the delays in the network. There is an increasing demand for a new type of solution for synchronising a telecommunication network element.

The aim of this invention is to overcome the drawbacks of the prior art solutions and to provide new type of solution for synchronising a telecommunication network element .

According to the first aspect of the present invention there is provided an arrangement for synchronising a telecommunication network element comprising at least one synchronising network element, and a number of synchronised network elements, that are communicating with a number of users, some of the users having a Portable device, which is characterised by that the synchronising network element transmits an "Advance Timing" message when receiving a signal from the synchronised network element that is not correctly synchronised to the synchronising network element. There is also provided a method for synchronising a telecommunication network element, which is characterised by that method comprises the steps of measuring a signal from the synchronised network element by the synchronising network element, judging whether the synchronised network element is correctly synchronised to the synchronising network element, and when the synchronised network element is not correctly synchronised to the synchronising network element, transmitting an "Advance Timing" message when receiving a signal from the synchronising network element to the synchronised network element.

In a solution for synchronising a telecommunication network element according to the present invention, the synchronising network element e.g. Radio Fixed Part (RFP) transmits an "Advance Timing" message when receiving a signal from the synchronised network element e.g. Wireless Relay Station (WRS) that is not correctly synchronised to the synchronising network element (e.g. RFP) .

The "Advance Timing" message contains the number of bits that the synchronised network element (e.g. WRS) should shift in timing to arrive at nominal timing in the synchronising network element (e.g. RFP). The "Advance Timing" message also contains information on whether the synchronised network element (e.g. WRS) should shift forward or backward in timing. The information from the "Advance Timing" message can be used by the synchronised network element (e.g. WRS) to compensate exactly half of the bits indicated by the "Advance Timing" message to arrive at nominal timing of the synchronising network element (e.g. RFP) . The synchronised network element (e.g. WRS) can also compensate exactly half of the bits indicated by the "Advance Timing" message, added to the already set timing compensation for the transmission path from the synchronised network element (e.g. WRS) to the synchronising network element (e.g. RFP) .

This way the synchronised network element (e.g. WRS) compensates the delay of the RFP-WRS path and not the delay of the WRS-RFP path. This means that the synchronised network element (e.g. WRS) is synchronous in timing to the synchronising network element (e.g. RFP) . This allows a portable terminal to handover from one network element to the other when it can receive both network elements.

In a solution for synchronising a telecommunication network element according to the present invention, the synchronisation is achieved using an "Advance Timing" message between the synchronising network element e.g. Radio Fixed Part (RFP) and the synchronised network element e.g. Wireless Relay Station (WRS).

A rough synchronisation is achieved between the synchronising network element (e.g. RFP) and the synchronised network element (e.g. WRS) by changing the timing of the synchronised network element (e.g. WRS) by multiple bits, when there is an "Access Request" from synchronised network element (e.g. WRS) to the synchronising network element (e.g. RFP) that remains unanswered. This timing change compensates for the double delay in the path RFP-WRS-RFP. Complete understanding of the arrangement and method of the present invention may be obtained by the preferred embodiments that follow, taken in conjunction with the accompanying drawings, wherein:

Figure 1 is an illustrative diagram showing a cordless telecommunication system according to prior art, Figure 2 is an illustrative diagram showing an arrangement for synchronising a telecommunication network element according to the present invention applied in a Cable DECT environment .

The prior art solutions have been described in drawing 1. In the following, the solution according to the present invention will be described in more detail with reference to the accompanying drawing 2.

Figure 2 is an illustrative diagram showing an arrangement for synchronising a telecommunication network element according to the present invention applied in a Cable DECT environment. An arrangement for synchronising a telecommunication network element in a Cable DECT environment according to the present invention consists of a Fixed Part 9, such as Central Control Fixed Part (CCFP) 9 and of a number of Radio Fixed Parts (RFPs) 10, 11, 12 communicating with a number of users each having a Portable Part (PP) 18, such as a cordless phone 18. The Radio Fixed Parts (RFPs) 10, 11, 12 can also be used to distribute the CATV signals. The synchronisation signal of the arrangement is provided by an internal or external system clock of the Fixed Part (CCFP) 9.

In a Cable DECT environment according to the present invention the RFPs are 10, 11, 12 typically clustered at one central place, where also the CATV signals are distributed. The CATV cables 13 are also used to carry the DECT signal to the user premises, where repeaters 14-17 e.g. Wireless Relay Stations (WRS) 14-17 reside. A repeater 14-17 (e.g. WRS) takes the signal from the cable 13, synchronises itself, and transmits its own cell e.g. DECT Cell back towards the side of the Radio Fixed Parts (RFPs) 10, 11, 12 and Portable Parts (PP) 18.

In an arrangement for synchronising a telecommunication network element in a Cable DECT environment according to the present invention the repeater 14-17 (e.g. WRS) can synchronise itself exactly to the Radio Fixed Parts (RFPs) 10, 11, 12, independent of the length of the CATV cable 13. In a Cable DECT environment according to the present invention handover of Portable Parts (PP) 18 is supported throughout the whole area covered by one CATV sub-system e.g. a whole village.

With the help of the solution according to the present invention all repeaters 14-17 in a Cable DECT telecommunications system will be synchronised, even when the neighbouring repeaters 14-17 are connected via different paths, with cables of different lengths. With the help of the solution according to the present invention increases the mobility of the user, because the handover of Portable Parts (PP) 18 is possible throughout the whole area covered by one CATV sub-system e.g. a whole village.

With the help of the solution according to the invention it is possible to reduce the number of repeaters in the network without reducing service. The solution according to the invention also makes it possible to have an optimal use of the radio spectrum, since all transmitters are synchronised precisely.

The arrangement for synchronising a telecommunication network element according to the present invention can be implemented for example in a large building. In a solution according to the present invention not all the apartments in a large building will need a repeater, when one cell gives coverage throughout the neighbouring apartments . In a solution according to the present invention also redundancy is easily achieved.

In an arrangement according to the present invention the upgrading of the repeater by remote download can be performed more easily. The arrangement does not require the repeater to remain fully operational with one executable load while downloading the next load thus not requiring double memory installation.

In an arrangement according to the present invention the repeater can cease activity, since it can be covered by the neighbouring repeaters . The software can first be downloaded, and then the repeater can be re-activated before the software downloading of the neighbouring repeater.

In a solution according to the present invention reduction of cost can also be achieved from load sharing. Not all of the repeaters in a particular cell need to be configured to support the maximum load on the cell. The surplus load will escape to the adjacent cells, so that the calls will not be lost, while each repeater can be optimally configured.

The solution according to the invention enables an accurate synchronisation fulfilling the requirements and minimising the delays in the network. The solution provides more flexibility to the network whilst ensuring high performance and reliability in the network.

In a solution according to the present invention the required services can be performed efficiently, such as load sharing and flexible handover support between the network elements . In an arrangement according to the present invention the network is easy to upgrade. In the network the network elements can be easily updated and re- activated.

The arrangement for synchronising a telecommunication network element according to the present invention can be implemented for example in a Cable DECT application or in an RLL application. With precise synchronisation provided by the solution according to the invention a repeater in an RLL application can bridge a distance of more than 5000 metres with a directional antenna connected to the repeater (WRS) . With very accurate timing provided by the solution according to the invention a good handover behaviour of the repeater e.g. WRS can be supported.

Claims

WHAT IS CLAIMED IS:

1. An arrangement for synchronising a telecommunication network element comprising - at least one synchronising network element, and a number of synchronised network elements, that are communicating with a number of users, some of the users having a Portable device, characterised in that the synchronising network element transmits an "Advance Timing" message when receiving a signal from the synchronised network element that is not correctly synchronised to the synchronising network element .

2. A synchronisation arrangement according to Claim 1, characterised in that the "Advance Timing" message contains the number of bits that the synchronised network element is to shift in timing.

3. A synchronisation arrangement according to Claim 2, characterised in that the "Advance Timing" message also contains information on whether the synchronised network element is to shift forward or backward in timing.

4. A synchronisation arrangement according to Claim 2 or Claim 3 , characterised in that the information from the "Advance Timing" message is used by the synchronised network element to compensate exactly half of the bits indicated.

5. A synchronisation arrangement according to Claim 2 or Claim 3 , characterised in that the information from the "Advance Timing" message is used by the synchronised network element to compensate exactly half of the bits indicated added to the already set timing compensation for the transmission path from the synchronised network element to the synchronising network element .

6. A synchronisation arrangement according to any of the Claims 1 to 5, characterised in that the synchronising network element is a Radio Fixed Part and that the synchronised network elements are Wireless Relay Stations.

7. An arrangement for synchronising a telecommunication network element in a Cable DECT environment, which comprises a Fixed Part (9) , a number of Radio Fixed Parts (10), (11), (12), which are communicating with a number of users each having a Portable Part (18) , and which Radio Fixed Parts also are used to distribute the CATV signals,

CATV cables (13), which are used to carry CATV signals and also the DECT signal to the user premises, and repeaters (14) -(17), which take the signal from the cable (13), synchronise themselves, and transmit their own cell towards the Radio Fixed Parts (10), (11), (12) and Portable Parts (18) , which synchronisation arrangement is characterised in that the Radio Fixed Part (10) , (11) , (12) , transmits an "Advance Timing" message when receiving a signal from the repeaters (14) -(17) that are not correctly synchronised to the Radio Fixed Part (10), (11), (12).

8. A synchronisation arrangement according to Claim 7, characterised in that the "Advance Timing" message contains the number of bits that the repeater (14) -(17) is to shift in timing.

9. A synchronisation arrangement according to Claim 8, characterised in that the "Advance Timing" message also contains information on whether the repeater (14) -(17) is to shift forward or backward in timing.

10. A synchronisation arrangement according to Claim 8 or Claim 9 , characterised in that the information from the "Advance Timing" message is used by the repeater (14) -(17) to compensate exactly half of the bits indicated.

11. A synchronisation arrangement according to Claim 8 or Claim 9, characterised in that the information from the

"Advance Timing" message is used by the repeater (14) -(17) to compensate exactly half of the bits indicated added to the already set timing compensation for the transmission path from the synchronised network element to the synchronising network element.

12. A synchronisation arrangement according to any of the Claims 7 to 11, characterised in that the repeaters (14) -(17) are Wireless Relay Stations.

13. A synchronisation arrangement according to any of the preceding claims 1-12, characterised in that the arrangement is implemented in an RLL application.

14. A method for synchronising a telecommunication network element, characterised in that the method comprises the steps of measuring a signal from the synchronised network element by the synchronising network element, - judging whether the synchronised network element is correctly synchronised to the synchronising network element, and when the synchronised network element is not correctly synchronised to the synchronising network element, transmitting an "Advance Timing" message when receiving a signal from the synchronising network element to the synchronised network element.

15. A synchronisation arrangement according to Claim 14, characterised in that the "Advance Timing" message contains the number of bits that the synchronised network element is to shift in timing.

16. A synchronisation arrangement according to Claim 15, characterised in that the "Advance Timing" message also contains information on whether the synchronised network element is to shift forward or backward in timing.

17. A synchronisation arrangement according to Claim 15 or Claim 16, characterised in that the information from the "Advance Timing" message is used by the synchronised network element to compensate exactly half of the bits indicated.

18. A synchronisation arrangement according to Claim 15 or Claim 16, characterised in that the information from the "Advance Timing" message is used by the synchronised network element to compensate exactly half of the bits indicated added to the already set timing compensation for the transmission path from the synchronised network element to the synchronising network element.