WO2002045450A1

WO2002045450A1 - A method for determining neighboring cells in a communication network

Info

Publication number: WO2002045450A1
Application number: PCT/EP2000/011890
Authority: WO
Inventors: Volker Wille
Original assignee: Nokia Corporation
Priority date: 2000-11-28
Filing date: 2000-11-28
Publication date: 2002-06-06
Also published as: AU2001226697A1

Abstract

The present invention proposes a method for determining neighboring cells in a communication network, the communication network consisting of a plurality of N cells each being defined by a transceiver device (BS) adapted to communicate with at least one transceiver terminal device (MS) in a respective cell, which plurality of N cells is composed of a serving cell of interest in which at least one transceiver terminal device (MS) actively communicates with said transceiver device (BS) defining said cell of interest, a maximum number of X neighboring cells to said serving cell of interest, to which neighboring cells a handover for a moving transceiver terminal device (MS) can be effected, and a number of N-X-1 surrounding cells surrounding said serving cell of interest and to which surrounding cells no handover for a moving transceiver terminal device (MS) can be effected, the method comprises the steps of: selecting (S41) one of said N cells of said network as a serving cell of interest, commanding (S42) said at least one transceiver terminal device (MS) communicating with said transceiver device (BS) defining said cell of interest to measure signals transmitted by the respective transceiver devices of said plurality of N cells other than the cell of interest, processing (S43) said measurement results to obtain a result indicating a reliability for a successful handover to a respective one of said plurality of N cells other than the cell of interest, evaluating (S44) the obtained indication of reliability and establishing a ranking for said plurality of N cells other than the cell of interest, and selecting (S45) a maximum number of X neighboring cells to said serving cell of interest, to which neighboring cells a handover for a moving transceiver terminal device (MS) can be effected, based on the ranking of reliability.

Description

TITLE OF THE INVENTION

A method for determining neighboring cells in a communication network

FIELD OF THE INVENTION

The present invention relates to a method for determining neighboring cells in a communication network.

BACKGROUND OF THE INVENTION

Generally, communication networks such as for example the GSM network or any other mobile communication network are established as cellular communication networks.

Fig. 1 shows a schematic overview of a cell arrangement of a cellular communication network. As shown therein, the communication network consists of a plurality of N cells. Each cell is defined by a transceiver device BS_1, ..., BS7, or generally BS_N, adapted to communicate with at least one transceiver terminal device MS in a respective cell of the network, as shown in Fig. 2. The illustrated details of a part of the network cell arrangement in Fig. 1 as shown in Fig. 2 are representative for the whole network. The plurality of base stations is controlled by a base station controller device BSC (not shown in Figs. 1 and 2) .

In GSM systems, neighbor definitions are required for each cell of the network in order to define to which of the surrounding cells a call can be handed over (i.e. to which cell a handover procedure may be performed successfully) . Traditionally, the neighbor identification process is based on propagation predictions. These predictions are analyzed and those cells that are closest in propagation terms (not necessarily in geographical terms) are defined as neighboring cells (also called defined adjacencies). For example, up to 32 defined adjacencies can be defined.

For the present specification it is to be noted that each cell Cl, ..., C19, ..., C_N of the plurality of cells of the network can represent a serving cell of interest in which at least one transceiver terminal device MS actively communicates with said transceiver device BS defining said cell of interest. In Fig. 1, cell Cl is marked by bold printing and underlining as representing a current serving cell of interest. All other cells of the network C2, ..., C19, ..., C_N are referred to as surrounding cells. A surrounding cell is thus any cell in the vicinity of a serving cell (or source cell) . A surrounding cell may be a defined or an undefined cell. An undefined cell (undefined adjacency) is any cell that is not defined as a defined adjacency for a particular serving cell of interest. A defined cell (defined adjacency) is a target cell for a handover procedure for a serving cell of interest. Apparently, the same cell may constitute a defined cell for one cell of interest while constituting an undefined cell for another cell of interest.

Based on above mentioned propagation predictions, the identification of those cells that should be defined as neighboring cells is not very accurate. Inaccurate neighbor cell definition, however, results in calls being handed to cells which are not ideal from a radio-link point-of-view. Thus, call quality is degraded and calls might even be dropped.

Incorrect neighbor definition occurs particularly in those environments where the prediction of radio wave propagation is highly inaccurate. These conditions include dense urban areas, such as city centers, and in-building environments. For example due to the lack of information on the building structure and building material it is almost impossible to predict whether a radio wave will penetrate into a building or to which extent the walls of the building will block the propagation of the radio wave. If the signal from an outside cell can penetrate into a building with an in-building cell, then this out-door cell should be defined as a neighboring cell for the in-building cell and vice versa.

Definition of the correct neighboring cells is necessary as only a limited number of neighboring cells can be created. If a cell is not defined as a neighboring cell, then calls can not be handed to that cell. Hence each incorrectly defined cell will potentially disable handovers (HOs) to a more suitable cell.

As a consequence the call is handed to another cell which is offering non-optimal call quality.

An analysis carried out by the applicants and concerning the propagation-prediction based neighbor definitions on a large number of cells in actual networks has shown the inaccuracy of the current propagation prediction based method. Hence, the above described problems of non-optimal cell selection or even call dropping in case of handover will occur, so that a new approach of identifying the required neighboring cell is needed.

A possible new approach has been outlined in PCT patent application No. WO 99/02004. In this application, a mobile communications system is described, in which a base station, as is conventional, directs mobile stations within its cell to make measurements on channels used by neighboring cells. The base station also directs the mobile stations to make measurements on an additional channel not used by a neighboring cell. The additional channel is changed regularly. Measurements made on the additional channel are useful when assessing the potential impact of changes to the frequency reuse plan.

However, the idea as described in this prior art document is described on a high level without going into any details concerning the implementation in practice.

SUMMARY OF THE INVENTION

Hence, it is an object of the present invention to provide a method for determining neighboring cells in a communication network which is free of the above drawbacks while being readily applicable.

According to the present invention, this object is, for example, achieved by a method for determining neighboring cells in a communication network, the communication network consisting of a plurality of N cells each being defined by a transceiver device adapted to communicate with at least one transceiver terminal device in a respective cell, which plurality of N cells is composed of a serving cell of interest in which at least one transceiver terminal device actively communicates with said transceiver device defining said cell of interest, a maximum number of X neighboring cells to said serving cell of interest, to which neighboring cells a handover for a moving transceiver terminal device can be effected, and a number of N-X-l surrounding cells surrounding said serving cell of interest and to which surrounding cells no handover for a moving transceiver terminal device can be effected, the method comprises the steps of: selecting one of said N cells of said network as a serving cell of interest, commanding said at least one transceiver terminal device communicating with said transceiver device defining said cell of interest to measure signals transmitted by the respective transceiver devices of said plurality of N cells other than the cell of interest, processing said measurement results to obtain a result indicating a reliability for a successful handover to a respective one of said plurality of N cells other than the cell of interest, evaluating the obtained indication of reliability and establishing a ranking for said plurality of N cells other than the cell of interest, and selecting a maximum number of X neighboring cells to said serving cell of interest, to which neighboring cells a handover for a moving transceiver terminal device can be effected, based on the ranking of reliability.

According to advantageous further developments of the present invention

- the signals transmitted on the synchronization channel of the respective transceiver devices are monitored;

- a signal strength of the received signals is measured;

- a frame erasure probability for the received signals is measured;

- the reliability for a successful handover to a respective one of said plurality of N cells other than the cell of interest is judged on the basis of the sum of the signal strengths of signals received by said at least one transceiver terminal device from said respective one of said plurality of N cells other than the cell of interest; - the reliability for a successful handover to a respective one of said plurality of N cells other than the cell of interest is (additionally or alternatively) judged on the basis of the number of said at least one transceiver terminal device which received signals from said respective one of said plurality of N cells other than the cell of interest;

- the reliability for a successful handover to a respective one of said plurality of N cells other than the cell of interest is judged on the basis of the average signal strength level of the signals received by said at least one transceiver terminal device from said respective one of said plurality of N cells other than the cell of interest.

- the reliability for a successful handover to a respective one of said plurality of N cells other than the cell of interest is (additionally or alternatively) judged on the basis of the standard deviation of signal strength level of the signals received by said at least one transceiver terminal device from said respective one of said plurality of N cells other than the cell of interest;

- the reliability for a successful handover to a respective one of said plurality of N cells other than the cell of interest is judged on the basis of the sum of the frame erasure probability of said at least one transceiver terminal device which received signals from said respective one of said plurality of N cells other than the cell of interest;

- said selection is effected such that those cells are selected as neighboring cells that are evaluated to have a reliability ranking between the highest and the highest minus X reliability;

- cells evaluated as having a reliability ranking below a predetermined threshold are prevented from being selected as neighboring cells; and - a cell currently defined as a neighboring cell is replaced by a cell currently not defined as a neighboring cell, if the reliability ranking of the cell currently not defined as a neighboring cell is higher than the reliability ranking of the cell currently defined as a neighboring cell. Accordingly, stated in other words, the proposed method to identify neighboring cells resides in utilizing mobile station measurements, which are collected in the base station controller BSC. Conventionally, in an active mode, mobile stations are able to report the signal level of the serving cell and that of the strongest six surrounding cells (defined or undefined adjacencies) . According to the present invention, a two stage process is implemented such that first, the conditions are created under which mobile stations measure and report the signal level from all surrounding cells, and thereupon these signal level measurements are subjected to an appropriate analysis (evaluation) which enables to establish a ranking of all surrounding cells (defined and undefined adjacencies) . Based on this ranking it is relatively easy to decide which surrounding cells should be defined (selected) as neighboring cells.

When compared to the current process of neighbor definition, the proposed method is advantageous as two important factors are included in the data that is being analyzed: • 1) influences such as radio wave propagation and path loss, and * 2) subscriber density and subscriber mobility within cell's of the network.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further objects and advantages of the present invention will become more fully apparent upon referring to the enclosed drawings, in which

Fig. 1 shows a schematic overview of a cell arrangement of a cellular communication network; Fig. 2 illustrates details of a part of the cell arrangement in Fig. 1, representative for the whole network;

Fig. 3 shows a flowchart of the method according to the invention; and

Fig. 4 depicts a graph of reliability information versus cell number as used according to the present invention for ranking establishment and neighbor cell selection.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention is subsequently described in greater detail with reference to the drawings.

Note that in connection with the present invention, certain conditions have to be created for mobile stations MS present within a respective cell of interest to provide useful measurements for deriving a reliability information (such as for example signal level) from all surrounding cells. If these conditions are not created, then mobile stations will provide measurement results that are not sufficient to create a ranking of all surrounding cells and thus identify the most suitable neighboring cells.

The main requirement is that mobile stations are forced to measure all surrounding cells. This is normally not the case as in normal operation mobiles only carry out measurements on those cells that are already defined as a neighboring cell. Hence the system has to have the ability to ensure that mobiles do measure all surrounding cells.

Note that the expression "all cells" as used herein does not necessarily mean all cells of the entire network, but is intended to mean all cells of which a measurement result can still be obtained in a certain cell of interest. Thus,

"all cells" means "all surrounding cells" from which a terminal transceiver device such as a mobile station MS still receives any measurable signal.

This can for example be achieved by providing mobiles with a list of frequencies used on all surrounding cells (i.e. a frequency reuse pattern) . Normally this list contains only the frequencies of the adjacent cells. This task is achieved most efficiently in conditions when the channels that are used on the surrounding cells are already known. For example if these cells can only use a fixed number of channels (as opposed to the entire frequency band used by the operator) , then it is possible to inform the mobile stations of exactly which channels to measure and hence ensure that all surrounding cells are being measured.

The analysis/evaluation of the mobile measurements at the network side (base station controller BSC or network management system NMS) will create a ranking of the surrounding cells on the basis of which it is possible to determine those cells that are 'closest' to the analyzed cell in terms of radio wave propagation, i.e. which cells should be defined as handover HO targets. This ranking can also be thought of as the ranking of surrounding cells based on signal reliability.

An indication for the reliability may for example be signal 'strength'. In this context 'strength' refers to both the actual signal level from a surrounding cell and/or to the number of times that this surrounding cell was measured (i.e. could still be received) by the mobile station population of the analyzed cell within a given time interval. Both factors (signal 'strength' and/or number of measurement samples) can be considered when establishing the ranking of surrounding cells. Nevertheless, other measurement results apart from signal strength may be used for evaluation of the reliability, as will be set out herein after in greater detail. Generally, any statistical data on received signals suitable to establish a reliability information may be used.

The individual method steps will be described with reference to Fig. 3 of the drawings.

The process of neighbor determination starts in a step S40. Subsequently, in step S41, a serving cell of interest is selected by the base station controller BSC. Any cell of the communication network may be selected as a serving cell of interest. Also, after the process of neighbor determination has been conducted for one cell of interest, the process is repeated for another cell selected as a cell of interest, until the neighbor cells for a desired number of cells and/or all network cells have been determined.

Upon selection of a cell of interest, the process proceeds to step S42. In step S42, the base station controller via the base station BS of the cell of interest, commands the transceiver device terminals and/or mobile stations MS present and communicating in/via said selected cell to measure surrounding cells. Particularly, all surrounding cells from the base stations of which a signal may still be received and measured are monitored by this measurement. A respective mobile station MS may conduct these measurements in a parallel manner or in a serial/cyclic manner. The thus obtained measurement results are obtained for each measurable surrounding cell in a number corresponding to the number of mobile stations MS communicating in/via the cell of interest, if all the mobile stations within the cell of interest can receive signals from a respective measurable surrounding cell. The number of measurement results may, however, be smaller than the number of mobile stations MS present within the cell of interest, as it may be expected that not every mobile station can receive signals from each surrounding cell.

These numerous measurement results from the at least one and/or plural mobile stations MS are, step S43, received and processed at the base station controller BSC. In a subsequent step S44, the base station controller BSC evaluates the reliability of the measurement results and based thereupon establishes a ranking of the surrounding cells. Based on the thus established ranking of cells, in step S45, the neighbor cells for the cell of interest are selected by the base station controller BSC. The process or an individual cell of interest then ends in step S46.

Fig. 4 depicts a graph of reliability information versus cell number as used according to the present invention for ranking establishment and neighbor cell selection. For the example graph shown in Fig. 4 it is assumed that cell number Cl highlighted in Fig. 1 by bold and underlined printing has been chosen as a specific serving cell of interest. Consequently, the surrounding cells to cell Cl are as shown in Fig. 1 and Fig. 4, the cells C2 to C19. These cells C2 to C19 are assumed to be the cells from which mobile stations MS within the cell Cl receive signals that can still be measured. As shown in Fig. 4, for each surrounding cell C2 to C19 a reliability has been evaluated which indicates the reliability of a respective cell for a successful handover performed to the respective cell.

As indicated in the example illustrated in Fig. 4, cells number 2, 3, 4, 5, 7, and 8 have the highest reliabilities of all cells C2 to C19. Based on the value of reliability information, a ranking of the cells is established to be in the order of cell 2, 3, 5, 4, 7, and 8. All other cells have a reliability which is below a reliability threshold indicated in Fig. 4 to be "5". A reliability threshold means that cells having a reliability below said threshold will not be considered for neighbor cell selection. Note that the value for a reliability threshold may be defined by the network operator. Also, no threshold may be defined, if desired, i.e. the use of a reliability threshold is optional.

Now, assuming a situation in which none of the surrounding cells has previously been selected as neighbor cell to cell Cl, the reliability evaluation and ranking as explained above with reference to Fig. 4 will be used to select cells 2, 3, 4, 5, 7, and 8 as neighbor cells for cell Cl.

On the other hand, assuming that in a previous neighbor selection process for cell Cl, the cells C2 to C7 were selected as neighbor cells, then neighbor cell C6 will be replaced by the new neighbor cell C8, since the reliability / ranking of cell C8 is higher than the one for cell Cβ in this situation (provided that the ranking of cells C2 to C5 and C7 has not changed in relation to the other cells since the previous neighbor selection process) .

Note that more than one neighbor cells may be replaced by other cells as a result of the selection, if the ranking of more than one cell has changed to be lower than the ranking of others. Also, in replacing / redefining neighbor cells, the reliability threshold can be taken into account. Also, the number of neighbor cells need not necessarily be six, but may be different from six. Thus, as set out above, based on this ranking it is straightforward to determine which surrounding cells should be defined as neighboring cells. Based on this ranking operators are able to decide how many of the surrounding cells should be defined as neighboring cells as well as to establish up to which level of 'reliability' surrounding cells should be defined as neighboring cells.

Subsequently, it will be set out in greater detail, on the basis of which data measured by the mobile stations MS and processed by the base station controller BSC, the reliability information is evaluated and the ranking is established.

It is to be noted that the signals transmitted on the synchronization channel (SCH) of the respective transceiver devices and/or base stations are monitored / measured by the mobile stations (transceiver terminal devices) . Every base station BS (or base transceiver station) broadcasts the synchronization channel SCH in time slot zero of the broadcast control channel traffic channel BCCH-TRX. The SCH contains the absolute value of the frame number of a base station, which is time dependent, and the base station identity code BSIC for identification purposes of the base station.

The base station identity code is an identifier for a base station, although the BSIC does not uniquely identify a single base station, since the BSIC has to be reused a couple of times within a respective PLMN (public land mobile network) . By using the BSIC it is enabled that a mobile station may identify and distinguish between surrounding cells (defined or undefined adjacent cells), even if the base stations in these surrounding cells use the same BCCH frequency. Due to the BSIC being broadcasted within the SCH, the mobile station are not required to establish a connection to a base station BS to learn the BSIC.

The BSIC is composed of the base station color code BCC and the network color code NCC. The BCC is a 3-bit-long parameter of the BSIC used to distinguish among different (8) training sequence codes that one base station may use on common control channels CCCH and to distinguish between surrounding base stations without the need for the mobile station MS as a transceiver terminal device to register to any other base station. The network country code NCC is a code also of a length of 3 bits that identifies the PLMN to which the base station belongs.

Nevertheless, although the present invention is described with reference to an example that the mobile stations conduct their measurements on the data transmitted on the SCH channel, other data transmitted on other channels is also applicable for the purpose of the present invention. The main requirement is that the measured data can be allocated to the sending/broadcasting base station from which they origin.

First data source:

No. 1 undefined adjacencies measurement

BCC NCC BCCH Sum of Samples Sum of DL Signals

Table 1 : First data source - undefined cells

Table 1 displays the data available for undefined adjacent cells of a particular cell (cell of interest) . The name of the BSC measurement that provides the information is called "undefined adjacencies measurement". This data has been labeled as No. 1 to be distinguishable from the further data sources to be explained later. These two pieces of information are shown in the top line of Table 1. Numbering and measurement name will also be provided for the other sources of data in the subsequent sections.

The second row of Table 1 describes the column headers for the data that is available. These are labeled "BCC, NCC, BCCH, Sum of samples and sum of DL signals". As explained above, BCC and NCC together constitute the BSIC. Information from up to 32 of the surrounding cells populates this table with respective information from undefined cells that were measured by the mobile stations while connected to the analyzed cell of interest. This means that table 1 will have up to 32 additional rows, each row containing the identification (BSIC=BCC+NCC) for a specific one of the base stations, the used BCCH of said base station, the sum of samples received in the analyzed cell of interest from said respective cell, i.e. the number of mobile stations which received a signal from said cell, and the sum of the downlink (DL) signals, i.e. the sum of the signal levels received from the number of mobile stations (stated in other words, the signal strength of a signal received by each mobile station is accumulated to obtain a sum of the received signals) .

The ranking of such undefined adjacencies is based on ordering the data according to predetermined ordering schemes to be defined by the network operator. For example, the data may be ordered by the highest value in the column "sum of DL signals". This sorting identifies from which undefined cell the 'highest amount' of signal level (or accumulated energy) was received. This cell is thus considered to represent the strongest of the undefined cells in relation to the analyzed cell. Depending on the number of vacancies in the neighbor cell list of the analyzed cell, the 'strongest' X cell(s) can then be defined as adjacencies. In this context X is user definable and specifies how many cells should be defined as adjacencies (for example six).

Alternatively the cell with the highest number in the column "sum of samples" can also be used as the strongest surrounding cell as well. In this case the ranking is based on the number of signal level samples that mobiles received from the surrounding cell.

Still further, both alternatives mentioned above may be combined. For example, in case values in the column "sum of samples" are identical, the base station of these base stations for which the value in the column "sum of DL signals" is highest is judged to represent the "strongest" base station, i.e. the one having the highest reliability and thus having a higher ranking than the others. Nevertheless, the sequence of applying the above mentioned two criteria may also be inverted so that the value indicated in the column "sum of samples" may be referred to in order to take a decision on the reliability/ranking of surrounding cells having an identical value of "sum of DL signals" .

Second data source:

Table 2 : . Second data source - - for undefined cells

No. Defined Adjacent Cell 2b Measurement

BCC NCC BCCH Avg sig level "std dev" sum of samples

Table 3 : Second data source - de ined cells Tables 2 and 3 represent that data (obtained in measurements named No. 2a and 2b) will be available for undefined and defined cells, respectively. The data for the undefined cells will be obtained as well as the data for the defined cells is provided. The column names for these measurements are: "BCC, NCC, BCCH, avg sig level, std dev, sum of samples".

The data fields BCC, NCC, BCCH and sum of samples has already been explained above, so that only the newly defined data fields and the data contained therein are explained. The data field "avg sig level" contains the average signal level of those signals received by a purality of mobile stations receiving signals from the surrounding (defined and/or undefined cells). The average signal level may be deducted from the measurement No. 1 by calculating "avg sig level" = "sum of DL signals" / "sum of samples". Additionally, the value "std dev" is provided which is the standard deviation of the (strength/level) of evaluated signals.

As the same data is provided for both defined and undefined cells it is possible to rank both sets of adjacencies in order to establish a common ranking for both cell groups. This combining of data from undefined and defined cells was not possible with the data described in the previous section as that data was only provided for undefined cells. If an undefined cell is stronger than a defined cell, then these will change places. I.e. the defined cell becomes undefined and vise versa.

The ranking of surrounding cells is based on the "sum of samples" which is multiplied by the "Avg sig level"

"sum of samples" * "Avg sig level" In addition, this formula can also be altered to include the counter "std dev". This is achieved by adding "Avg sig lev" and "std dev" before the multiplication with the "sum of samples"

"sum of samples" * ("avg sig level" + "std dev")

Both methods evaluate the 'total accumulated power' from a surrounding cell by the mobiles of the analyzed cell. This means that the higher the 'accumulated power' from a surrounding cell, the stronger that cell.

Alternatively, the ranking may be based on evaluating the average signal level alone. For example, the cell/base station for which the highest average signal level is measured by the mobile stations within the cell of interest is judged to be most reliable. Additionally, in case more than one base station has the same value of "avg sig level", the value of "std dev" could additionally be taken into account. Namely, in case of identical average signal value for more than two cells, the cell for which the smallest value of standard deviation has been determined could be judged to be more reliable and therefore be assigned a higher ranking as compared to the other cells having the identical average signal value.

Third Data Source:

Table 4 : Third data source - for undefined cells

Table 5 : Third data source - for defined cells

Tables 4 and 5 represent that also in a third measurement type data will be available for undefined and defined cells, respectively. As the names of these measurements have not been fixed, these are referred to here only by numbering, i.e. No. 3a and/or No. 3b. By combining both sets of data it is possible to determine the ranking of all surrounding cells (defined and undefined) . If an undefined cell is stronger than a defined cell, then these will change places. I.e. the defined cell becomes undefined and vise versa. The columns are labelled "BCC, NCC, BCCH, Sum of FEP".

The data fields BCC, NCC, and BCCH has already been explained above, so that only the newly defined data field and the data contained therein are explained. The data field "FEP" contains the value indicating the frame erasure probability which is obtained under the assumption that a measured cell transmits on the same frequency as the cell of interest.

With these measurements the ranking of the measured cells will be based on the value of the column "Sum of FEP", where FER stands for Frame Erasure Probability. This value represents the potential frame erasures that would have been occurred if the source cell (analysed cell/ cell of interest) and the surrounding cell were using the same frequency. The counter contains the sum of all FEP. Thus the higher the FEP value, the stronger/reliable the adjacent cell. To arrive at the number of erased frames, the C/I (channel interference ratio) measured by mobiles is converted into the frame erasure value and this value is accumulated for each (C/I) measurement reported by the mobiles of the analyzed cell. It is worth pointing out that in this method the hopping mode is also included in establishing the FEP value.

Although several kinds of data usable for evaluating the reliability of a measured cell have been described above, the present invention is not limited thereto. Other data such as the bit error ratio BER, and/or the average value of bit error ratios, and/or the standard deviation of bit error ratios may be applied for evaluating the reliability and establishing a ranking of surrounding cells, whether representing already defined or still undefined adjacencies. Generally, any statistical data on received signals suitable to establish a reliability information may be used. Also, measured data may be applied in combination in order to evaluate the reliability/ ranking of surrounding cells. As a combination, any permutation of data is conceivable. Also, a combination of a new data item for reliability evaluation/ranking establishment is

Accordingly, as has been described above, the present invention proposes a method for determining neighboring cells in a communication network, the communication network consisting of a plurality of N cells each being defined by a transceiver device (BS_1, ..., BS_N) adapted to communicate with at least one transceiver terminal device (MS) in a respective cell, which plurality of N cells is composed of a serving cell of interest in which at least one transceiver terminal device (MS) actively communicates with said transceiver device (BS) defining said cell of interest, a maximum number of X neighboring cells to said serving cell of interest, to which neighboring cells a handover for a moving transceiver terminal device (MS) can be effected, and a number of N-X-l surrounding cells surrounding said serving cell of interest and to which surrounding cells no handover for a moving transceiver terminal device (MS) can be effected, the method comprises the steps of: selecting S41 one of said N cells of said network as a serving cell of interest, commanding S42 said at least one transceiver terminal device (MS) communicating with said transceiver device (BS) defining said cell of interest to measure signals transmitted by the respective transceiver devices of said plurality of N cells other than the cell of interest, processing S43 said measurement results to obtain a result indicating a reliability for a successful handover to a respective one of said plurality of N cells other than the cell of interest, evaluating S44 the obtained indication of reliability and establishing a ranking for said plurality of N cells other than the cell of interest, and selecting S45 a maximum number of X neighboring cells to said serving cell of interest, to which neighboring cells a handover for a moving transceiver terminal device (MS) can be effected, based on the ranking of reliability.

Although the present invention has been described herein above with reference to its preferred embodiments, it should be understood that numerous modifications may be made thereto without departing from the spirit and scope of the invention. It is intended that all such modifications fall within the scope of the appended claims.

Claims

1. A method for determining neighboring cells in a communication network, the communication network consisting of a plurality of N cells each being defined by a transceiver device (BS_1, ..., BS_7,..., BS_N) adapted to communicate with at least one transceiver terminal device (MS) in a respective cell, which plurality of N cells is composed of a serving cell of interest in which at least one transceiver terminal device (MS) actively communicates with said transceiver device (BS) defining said cell of interest, a maximum number of X neighboring cells to said serving cell of interest, to which neighboring cells a handover for a moving transceiver terminal device (MS) can be effected, and a number of N-X-l surrounding cells surrounding said serving cell of interest and to which surrounding cells no handover for a moving transceiver terminal device (MS) can be effected, the method comprises the steps of: selecting (S41) one of said N cells of said network as a serving cell of interest, commanding (S42) said at least one transceiver terminal device (MS) communicating with said transceiver device (BS) defining said cell of interest to measure signals transmitted by the respective transceiver devices of said plurality of N cells other than the cell of interest, processing (S43) said measurement results to obtain a result indicating a reliability for a successful handover to a respective one of said plurality of N cells other than the cell of interest, evaluating (S44) the obtained indication of reliability and establishing a ranking for said plurality of N cells other than the cell of interest, and selecting (S45) a maximum number of X neighboring cells to said serving cell of interest, to which neighboring cells a handover for a moving transceiver terminal device (MS) can be effected, based on the ranking of reliability.

2. A method according to claim 1, wherein the signals transmitted on the synchronization channel (SCH) of the respective transceiver devices are ^'monitored.

3. A method according to claim 1, wherein a signal strength of the received signals is measured.

4. A method according to claim 1, wherein a frame erasure probability for the received signals is measured.

5. A method according to claim 3, wherein the reliability for a successful handover to a respective one of said plurality of N cells other than the cell of interest is judged on the basis of the sum of the signal strengths of signals received by said at least one transceiver terminal device from said respective one of said plurality of N cells other than the cell of interest.

6. A method according to claim 3 or 5, wherein the reliability for a successful handover to a respective one of said plurality of N cells other than the cell of interest is judged on the basis of the number of said at least one transceiver terminal device which received signals from said respective one of said plurality of N cells other than the cell of interest.

7. A method according to claim 3, wherein the reliability for a successful handover to a respective one of said plurality of N cells other than the cell of interest is judged on the basis of the average signal strength level of the signals received by said at least one transceiver terminal device from said respective one of said plurality of N cells other than the cell of interest .

8. A method according to claim 3 or 7, wherein the reliability for a successful handover to a respective one of said plurality of N cells other than the cell of interest is judged on the basis of the standard deviation of signal strength level of the signals received by said at least one transceiver terminal device from said respective one of said plurality of N cells other than the cell of interest.

9. A method according to claim 4, wherein the reliability for a successful handover to a respective one of said plurality of N cells other than the cell of interest is judged on the basis of the sum of the frame erasure probability of said at least one transceiver terminal device which received signals from said respective one of said plurality of N cells other than the cell of interest .

10. A method according to claim 1, wherein said selection is effected such that those cells are selected as neighboring cells that are evaluated to have a reliability ranking between the highest and the highest minus X reliability.

11. A method according to claim 10, wherein cells evaluated as having a reliability ranking below a predetermined threshold are prevented from being selected as neighboring cells.

12. A method according to claim 10, wherein a cell currently defined as a neighboring cell is replaced by a cell currently not defined as a neighboring cell, if the reliability ranking of the cell currently not defined as a neighboring cell is higher than the reliability ranking of the cell currently defined as a neighboring cell.