SELF CONFIGURING AND OPTIMISATION OF CELL NEIGHBOURS IN WIRELESS TELECOMMUNICATIONS NETWORKS
The present invention relates to a cellular communications network and in particular to the problem of identifying cells for neighbour lists, or handover candidates when the cells are identified by a limited number of non-unique identities. The present invention includes a method for a radio base station, wherein the base station receives reports from one ore more terminals in neighbour cells quality and non-unique identities. The match is sought in a neighbour cell list non-unique identity with a unique cell identity. If the match cannot be made without ambiguity, the base station orders the terminal to detect the unique cell identity. If the reason for the ambiguity is the particular cell is not included in the neighbour cell it is included when its unique identity has been established. The uniquely identified cell is used if a handover is decided.
This application is a continuation of U.S. application Ser. No. 13/084,884, filed Apr. 12, 2011, which is a continuation of U.S. application Ser. No. 11/773,752, filed on Jul. 5, 2007, which claims the benefit of International Application No. PCT/EP2007/01737, filed Feb. 28, 2007, the disclosures of which are incorporated herein by reference.
FIELD OF INVENTION
The present invention relates to self-configuring and optimisation of cell neighbours in wireless telecommunications networks.BACKGROUND OF THE INVENTION
A base station 2 contains a number of receivers and transmitters to give radio coverage for one or more cells. Each base station 2 is connected to a network “backbone”, or core network infrastructure (not shown), which enables communications between base stations and other networks. The example system of
An important concept in such a network is the cell and its neighbours. During a call a mobile terminal 4 typically is moved in the geography, and when so doing leaves a first cell and enters a new cell that neighbours the first cell. The cell may be changed several times and the process of changing the cell that supports a radio link with the terminal is called handover. A list of the known neighbours, the so called “neighbour cell set”, is important both for the network 1 and for the mobile terminal 4 to enable reliable handover between cells. The network 1 can store information relating to a set of neighbour cells for each cell in the system. Evaluation of the best cell for supporting a radio link with the mobile terminal is based upon measurements made by the terminal on the serving cell and on other cells than the serving cell. The neighbour cell list is needed for mapping measurements and handover decisions to a target cell identity and possibly applying specific parameters or rules for the target cell. It will be readily appreciated that the cell boundaries are not sharply defined, but will in practice be somewhat blurred as the range of the base stations will overlap with one another.
In existing systems, the mobile terminal, 4, detects and measures cell operating parameters for neighbouring cells by measuring on their broadcast channels. One measured operating parameter is a cell non-unique identifier which typically consists of a physical layer identifier such as a scramble code which is non uniquely assigned to the cell. Operating parameters also relates to the signal quality of the neighbour cell such as signal strength, signal quality and timing information. When the quality of a neighbour cell is considered better than the current serving cell, a handover from the serving cell to the chosen neighbour cell is executed by the network. The neighbour cell then becomes the serving cell for the mobile terminal.
Typically in a WCDMA (wideband code division multiple access) system, the mobile terminal detects Common Pilot Channel (CPICH) transmissions from surrounding cells, in order to determine id (scramble code) and timing information.
When the mobile reports the neighbour cell signal quality measurements to the network, the cells' respective identities become important. Typically, cell identities are reused for more than one cell. The reuse of identities means that cells may be confused with one other, since the serving cell may have neighbour cells sharing the same identity information.
In the cells are also broadcasted unique cell identities. The unique cell identity is carried on the network layer. Its main use is for special purpose terminals, that are used by an operator of the system for testing and tracing of problems in the network. The unique cell identity is not repeated as often as the non-unique cell identity and is more complicated for a terminal to detect. This is in contrast to the physical layer, that is physical data needed for supporting the radio link. Since the cells' physical layer identifiers are non-unique, populating and maintaining the neighbour cell sets can never be fully automatic. Human efforts are needed to resolve conflicts where the serving cell has multiple neighbours using the same non-unique identifier. A further problem is handover failures owing to the candidate cell has been incorrectly identified.SUMMARY OF THE PRESENT INVENTION
The aim of the present invention is to secure handovers to be performed to the right cell. It solves the problem with a method for a radio base station or for a node controlling a radio base station serving a first cell and comprises the steps of, receiving from a terminal a non-unique cell identity of a second cell and a measure on the quality of the second cell, determining if the second cell can be unambiguously identified by the information in a neighbour cell list, and if ambiguity in the second cell identity is determined, ordering the terminal to identifying and reporting on the unique second cell identity, and associating the non-unique identity with the unique identity.
In a first embodiment ambiguity on the second cell identity is identified if the non-unique cell identity is not included in the neighbour cell list. The association is then made by including the second cell non-unique cell identity and the unique cell identity in the neighbour cell list. In a second embodiment ambiguity on the second cell identity arises if two unique cell identities in the neighbour cell list have the same non-unique identity. The association with the unique cell identity with the non-unique cell identity is then made for the specific radio link with the terminal for a period. The period is typically started with the signal strength of the second cell exceeded a predefined threshold value, and ending when a handover is performed or the second cell signal strength decreases under a second threshold value.
The invention also relates to a radio base stations or a node controlling radio base stations and that is adapted for performing the method.
The invention also includes a method for mobile stations that measures the signal quality on broadcast channels in other cells than the first cell, detects the non unique cell identity on broadcast channels with a quality exceeding a threshold value, transmitting information on the signal quality and second cell non-unique identity to the serving cell and upon receiving a command, detecting the unique cell identity on a broadcast channel and transmitting the unique cell identity.
The invention further relates to a mobile station adapted for performing the method.
An advantage of the present invention is that creation and or updating of a neighbour cell list can be made automatically by the system based on the measurements and cell identity information received from the terminals. Thereby, it is not necessary for humans to plan and maintain the neighbour cell lists.
The basic problem of the present invention is to make a positive identification of a neighbouring cell that is ambiguously detected by a mobile terminal. The ambiguity may arise when a cell, not previously detected, is reported by a mobile terminal, or when two or more cells share the same non-unique cell identity and the two cells. An ambiguity will then arise on what cell that has been measured.
The problem exists in several systems, for example GSM, WCDMA and eUTRAN. In GSM and WCDMA a list of neighbour cells is created for each cell in the system by a human or at least controlled by a human. In so doing any collisions in the non-unique cell identities of the neighbours should be detected and possibly solved by reallocating the non-unique cell identities. It is cumbersome to establish and update the NCL (neighbour cell list) and the allocations of non-unique cell identities, especially when the capacity of a network is increased by the addition of further cells.
For WCDMA and eUTRAN it is desired that the NCL can, if not be completely created automatically, at least be updated automatically by the system based on measurements made by terminals on cells other than the cell serving the terminal. For that reason the present inventions is in particular important for the WCDMA and eUTRA, however, it may well be implemented also in other systems such as the GSM.
The inventions will primarily be implemented in a network node that handles the NCL and decides on handovers. In the eUTRAN this is the task of the eNodeB which is a base station, in the GSM it is the BSC (Base Station Controller) and in the WCDMA it is the RNC (Radio Network Controller) that handles the NCL. Both the BSC and the RNC have the functions of controlling the base stations and their operation on the various cells of the networks, and the term base station controller in this application refers to a node having the functions of the BSC or the RNC.
There are several reasons why the ambiguity may arise in the match between non-unique cell identity and the unique cell identity. The first, and basic reason is the second cell is not included in the NCL. Another reason is the NCL includes an indicator of suspected ambiguity. The indicator may have been added to the NCL prior to the method is being performed. The reason may be handovers to the identified cell have failed. The failure may be detected as terminals have re-established contact with the first cell as serving cell during handover processes, or the target cell has not sent notification to the first cell as serving cell. A further reason for ambiguity is two or more unique cell identities share the same non-unique cell identity.
If the reason for the ambiguity is that the second cell with its unique and non unique cell identities is not included in the NCL they are added to it in the last associating step, 207.
The base station frequently receives, 202, reports from the terminal on measures made on other cells, and then not only the second cell. When the base station has received, 206, the second cell unique identity as detected by the terminal it shall not instruct the terminal to detect the second cell unique identity when again receiving, 202, a quality measure from the terminal, not even if the ambiguity in the NCL is maintained. Therefore, the associating step, 207, shall associate the unique cell identity with the non-unique cell identity for this particular terminal for a specific period or as long as the signal quality of the second cell exceeds a predefined threshold. The association with the particular terminal is not made in the NCL, instead a temporary NCL is used.
As long as the second cell unique cell identity is associated with the terminal, if handover to the second cell is decided it will be directed via the associated second cell unique identity. Thereby the second cell will be instructed to prepare a handover of the terminal, before the terminal itself is instructed to make a handover to the second cell.
In addition to the requirement of ambiguity in the match of unique cell identity to the non-unique cell identity, the further requirement of the second cell quality measure exceeding a threshold value can be added before the terminal is instructed to detect the second cell unique identity. The reason for adding the further requirement is to avoid expense of the terminal performing the detection. The unique cell identity is transmitted from base stations at a much less frequent interval than the physical layer identity. In order to receive and decode this information, the mobile terminal 4 may have to shortly interrupt its communication with the serving cell.
Moreover, some filtering of the measurement data may be needed before the second cell is added to the NCL in the associating step 207. For example the second cell is not included until it has been reported by two or more mobile terminals. Thereby avoiding adding a distant cell that was detected under exceptional propagation conditions, for example from a mobile terminal 4 located in an aircraft.
Additionally in step 207, cell lookup maps the unique cell identity (UCID) to the address of the realising node of that cell. For example, in LTE, this can be an ordinary DNS, mapping the cell identity to an IP address. The IP address in turn points to the RBS realising the cell.
The terminal 4 scans the spectrum to find broadcast channels of potential neighbour cells. The ability to detect and measure a broadcast channel depends on the sensitivity of the hardware in the terminal transceiver and of the broadcast channel power relative to the interference level. A further prerequisite for detecting the second cell identity of the potential neighbour cell in step 303 may be added, and that be the broadcast channel reception quality as detected in step 302, exceeds a threshold value. If the non-unique cell identity is not detected, the second cell is of course not informed to the network, in step 304.
The CID detector 47, the UCID detector 48, and the request receiver 49 are preferably implemented as SW modules, however, they may alternatively be implemented in hardware or in a combination of the two.
Interactions with the user of the device take place using the man machine interface 44, which can include a key pad, microphone, loudspeaker and display device, for example.
Typically the controller will also decide on handovers from the serving base station to a target base station serving the second cell, or which of the other cells that temporary will function as second cell.
In an alternative to the base station described with reference to
However, base stations 2 and mobile terminals 4 which operate in accordance with the present invention are adapted to carry out the method of the invention as described below with reference to
Making use of unique cell identifiers (UCID) means that there is unambiguous information relating to the identity of the neighbour cells, and so confusion regarding those neighbouring cells is removed. Using the fast and low-resource demanding non-unique cell identity for most of the measurements, facilitates efficient resource usage within mobile terminals 4 and rapid handover to the neighbour cells. The mobile terminal 4 is only requested to retrieve the more cumbersome unique cell identifier when a new neighbour is detected, or when an audit of the relation between the non-unique and unique cell identity seems appropriate.
All cell relations can be continuously evaluated. Inputs to that evaluation are mobile terminal reports and events, network events and operator input. The result of the evaluation is that the cell or cell relations will retain different properties. This can also be seen as the cell relation being in different states.
The major advantage of embodiments of the present invention is that it removes the need for manual involvement within the process of maintaining neighbour sets. The operator can decide to fully neglect the concept of neighbours and let the system take care of the neighbour cell definitions.
1. A method for a radio base station or for a base station controller connected to a radio base station and controlling it wherein the radio base station serves a first cell of a plurality of cells in a wireless telecommunications system, the method comprising the steps of:
- communicating with a mobile terminal in the first communications cell;
- receiving from the mobile terminal a quality measure on a second cell and a non-unique identification of the second cell;
- retrieving a neighbour cell list for the first cell, to match a unique-cell identification with the non-unique cell identity, and if ambiguity in the match arises instructing the mobile terminal to determine the unique cell identity of the second cell;
- receiving unique cell identifier information relating to the second communications cell from the mobile terminal; and
- associating the non-unique cell identity with the unique cell identity.
2. A method as claimed in claim 1, wherein ambiguity arises when the second cell non-unique identity is not included in the neighbour cell list.
3. A method as claimed in claim 1, wherein ambiguity arises if the second cell non-unique cell identity is included in the neighbour cell list with information on suspected ambiguity of identification.
4. A method as claimed in claim 1, wherein ambiguity arises if two unique cell identities in the list shares the same non-unique cell identity.
5. A method as claimed in claim 2, wherein in said associating step said second cell non-unique and unique cell identities is added to the neighbour cell list.
6. A method as claimed in claim 3 or 4, wherein in said associating step said second cell non-unique and unique cell identities is associated with the communication with the terminal for a period.
7. A method as claimed in claim 3 or 4, wherein in said associating step said second cell non-unique and unique cell identities are associated with the communication with the terminal as long as the quality measure exceeds a first threshold level
8. A method as claimed in claim 3, wherein information on suspected ambiguity is added to a non-unique cell identity if one or more handovers from the first cell to a cell with the non-unique cell identity has/have been unsuccessful.
9. A method as claimed in claim 1, wherein the quality measure is at least one of;
- signal strength measurement, a signal quality measurement, or timing information.
10. A method as claimed in claim 1, wherein the instructing step is performed on the further condition of the second cell quality measure exceeds a second threshold value.
11. A method as claimed in claim 1, wherein the instructing step is performed on the further condition the second cell is determined to be a handover candidate.
12. A method as claimed in claim 1, comprising the further steps of:
- broadcasting a non-unique identity of the first cell, in a first information layer intended for carrying information for supporting the physical connection with the terminals;
- broadcasting a unique identity of the first cell on an information layer higher then the first layer.
13. A radio base station for providing communication in a first cell with at least one terminal and comprising:
- a radio transceiver;
- a controller including or being connected to a database that includes a neighbour cell list and including a NCL utility, the controller being arranged for receiving via the transceiver reports from the terminal on measured reception quality on other cells than the first cell, including the other cells non-unique cell identities, further arranged for matching the non-unique cell identities with corresponding unique cell identities by retrieving the neighbour cell list, the NCL utility arranged for initiating an instruction being sent to the terminal for identifying and reporting on the unique cell identity of a non-uniquely identified cell if ambiguity arises in the matching, the NCL utility further being arranged for associating the non-unique cell identity and the unique cell identity as reported by the terminal 14. A method for a mobile terminal, 4, in a cellular telecommunications network, the method comprising:
- communicating, 301, over a first link in a first cell;
- measuring, 302, a signal quality of a channel broadcasted in a second cell;
- detecting, 303, a non-unique cell identity broadcasted in the second cell:
- reporting, 304, the measured second cell signal quality and the identified non-unique identity over the first radio link;
- receiving, 305, an instruction over the first radio link to detect a second cell unique identity;
- detecting, 306 the unique cell identity broadcasted in the second cell;
- reporting, 307, the unique second cell identity by transmission over the first radio link.
15. The method of claim 14, wherein the non-unique second cell identity is detected in a first layer carrying physical information.
16. The method of claim 14, wherein the unique second cell identity is detected in a second layer higher than the first layer.
17. A mobile terminal for communicating with a first radio base station in a first cell and performing measures on the reception quality from other cells, and comprising:
- a radio transceiver,
- a controller arranged for identifying a non-unique cell identity of the respective other cells and report to the first radio base station with the quality measures, and further arranged for controlling the transceiver to identify a unique cell identity of one or more of the other cells in response to an instruction received from the first radio base station.
18. The mobile terminal of claim 17, wherein the controller includes a CID detector for identifying the non-unique cell identity.
19. The mobile terminal of claim 17, wherein the controller includes a UCID detector for identifying the unique cell identity.
20. A radio base station controller with an interface for connecting to at least one radio base station and its transceiver and comprising:
- a controller including or being connected to a database that includes a neighbour cell list and including a NCL utility, the controller being arranged for receiving via the transceiver reports from at least one terminal on measured reception quality on other cells than the first cell, including the other cells non-unique cell identities, further arranged for matching the non-unique cell identity with a unique cell identity by retrieving the neighbour cell list, the NCL utility arranged for initiating an instruction being sent to the terminal for identifying and reporting on the unique cell identity of a non-uniquely identified cell if ambiguity arises in the matching, the NCL utility further being arranged for associating the unique cell identity as reported by the terminal with the non-unique cell identity.
International Classification: H04W 24/00 (20090101);