FR2742291A1 - Neighbouring cell monitoring device for mobile communication networks - Google Patents

Abstract

The device examines nearby mobile radio cells to determine the best available cell for communication. A first memory (1) contains a table which includes the present best available cells. A second memory (2) has a list of cells which are to be examined to determine whether signals received from the cell exceed a set level. A third memory (3) includes a table with a table of cells which are to be ignored. A control unit (4) writes (8) cell information to the various tables and removes cell information which is no longer applicable.

Description

Device for monitoring neighboring cells by a mobile station in a cellular mobile radio network.

 The present invention relates to a device for monitoring neighboring cells by a mobile station in a cellular mobile radio network.

 In a cellular radiocommunication network, it is necessary to permanently determine the best serving cell for each mobile station in order, in the case where the current serving cell is not a better cell, to carry out a change of serving cell (or "handover") to the best serving cell thus determined, also called target cell, this in order to optimize in particular the quality of communications and the overall level of interference in the network.

 This target cell is determined, on the network scale, on the basis of various parameters, in particular measurements of reception levels carried out by the mobile stations relative to their serving cell and to neighboring cells, the results of these measurements being transmitted by the mobile stations to the so-called base stations of the serving cells.

 The reception level measurements made by a mobile station relative to the neighboring cells are reception level measurements at predetermined frequencies, also called beacon frequencies, specific to each of these cells and permanently transmitted by the base stations of these cells. .

 Those of the beacon frequencies received by a mobile station, which are actually to be measured, that is to say which actually relate to cells considered to be neighboring, are indicated to the mobile station by the base station of the serving cell of this mobile station.

In addition, to distinguish these beacon frequencies from possible interfering frequencies other than beacon frequencies, the mobile station does not simply perform a reception level measurement, but also searches for characteristic information carried by the signals received at these frequencies ( this information being for example, in a GSM network (Global System for Mobile
Communications ") contained in a particular channel called
FCCH "Frequency Correction Channel").

Furthermore, to distinguish a neighboring cell having a given beacon frequency, from a non-neighboring cell having the same beacon frequency (this case can in particular occur in the case of spectrum allocated to the relatively restricted network, or even at the border between different networks), the mobile station must also carry out a search for characteristic information carried by the signal received at this beacon frequency (this information being for example, in a GSM network, called
BSIC: "Base Station Identity Code" and being contained in a particular channel called SCH "Channel Synchronization").

 In addition, an order of importance is obtained for the measurement results thus obtained, only the highest values (at most six values in the case of a GSM network for example) having to be transmitted to the base station of the waitress cell.

 The operations to be performed in this way by a mobile station are therefore not limited to a simple measurement of reception levels relating to neighboring cells, but are also intended to determine at most N best neighboring cells defined as cells corresponding to signals. received at a higher level and moreover satisfying a validity examination of information carried by the signals picked up at the corresponding frequencies.

The main object of the present invention is to optimize the treatments thus carried out in mobile stations, with a view in particular to
- to make the process of determining better neighboring cells faster, and in particular to react more quickly to the appearance of new candidate cells (that is to say of relatively high level) but not yet examined, this contributing in particular to make this process more efficient in the presence of measurement results fluctuating relatively rapidly over time, which is particularly the case in microcellular networks,
- to make the number of best cells thus determined closest to N at all times, this contributing, at the network level, to facilitate the search for target cells and to reduce the risks of loss of communications.

A subject of the present invention is thus a device for monitoring neighboring cells by a mobile station in a cellular mobile radio network, this device operating on measurements of the levels of signals received from said neighboring cells, and being intended to determine at most N best neighboring cells, defined as cells corresponding to signals received at a higher level and which also satisfy a test of the validity of information carried by these signals, and this device being essentially characterized in that it comprises
- a memory containing a table called the table of the best cells,
- a memory containing a table called cell table to be examined,
- a memory containing a table called table of cells to be ignored,
- means for registering cells in the table to be ignored, cells not satisfying said examination,
- means for registering in the table the best cells, cells satisfying said examination.

Other objects and characteristics of the present invention will appear on reading the following description of an exemplary embodiment, made in connection with the attached drawings in which
FIG. 1 is a block diagram of an example of a device according to the present invention,
- Figures 2 to 5 are tables intended to illustrate various examples of operation of a device according to the present invention.

 The device illustrated in FIG. 1, intended to equip a mobile station, operates on results of measurements of levels of signals received at predetermined frequencies broadcast by the cells close to the server cell of the mobile station considered, these measurement results, denoted R, being provided with a given period known as the measurement period.

This device makes it possible, at each measurement period, to determine at most N best neighboring cells defined as being cells corresponding to signals received at a higher level and which also satisfy a validity examination of information carried by these signals.

This device includes
a memory 1 containing a table called the table of the best cells,
a memory 2 containing a table called table of cells to be examined,
a memory 3 containing a table called the table of cells to be ignored,
- means for registering in the table cells to be ignored cells not satisfying said examination,
- means for registering in the table the best cells, cells satisfying said examination.

 In the example illustrated in FIG. 1, this device further comprises means 4 for registering in the table of cells to be examined, and on the condition that they are not registered in the table of cells to be ignored, cells having a level higher than the lowest of the levels of the cells registered in the table of best cells, or, in the case where the number of cells registered in the table of best cells is less than N, also cells of level lower than this lower level.

According to another exemplary embodiment, not specifically illustrated, this device would also comprise, instead of the means 4,
- means for registering cells in the table to be examined, provided that they are not registered in the table for cells to be ignored,
means for registering in the table of the best cells, cells satisfying said examination, on the condition that they have a level higher than the lowest of the levels of the cells registered in the table of best cells, or, in the case where the number of cells registered in the table of the best cells is less than N, even if they have a level lower than this lower level.

The means 4 for registering cells in the table of cells to be examined comprise, in the example illustrated in FIG. 1
means 5 known as classification, for carrying out a classification in order of importance of the levels received and measured R, and therefore of the corresponding cells,
means 6 known as of comparison, to compare the cells contained in the table of the best cells, with the cells determined by the said classification myens, with a view to determining those of the cells determined by the said classification means, which have a level higher than at most low levels of cells in the table of best cells, or, in the case where the number of cells registered in the table of best cells is less than N, also cells of level lower than this lower level,
means 7 for comparing the cells determined by said comparison means 6 with the cells registered in the table of cells to be ignored, and for not authorizing the registration, in the table of cells to be examined, of cells determined by said means of comparison 6, only if they are not in the table of cells to ignore.

 In the example illustrated in FIG. 1, the means for registering cells in the table of cells to be ignored, and the means for registering cells in the table for the best cells include means 8 for carrying out an examination of the cells of the table cells to be examined, in order to order an inscription, in the table of cells to be ignored, of cells not satisfying said examination, or, in the table of best cells, cells satisfying said examination.

 In the example illustrated in FIG. 1, the means 8 are also used to carry out a re-examination (that is to say a confirmation of validity) of the cells registered in the table of the best cells (knowing, in the case of a GSM network for example, that such a re-examination is considered negative only if it is not satisfied for a fourth consecutive time).

 In addition, in the example illustrated in FIG. 1, means 9 are provided for authorizing an erasure of the table of cells to be ignored.

 In the examples described in the following, various possible examples of the implementation of these means will be given 9.

 In a stable environment, the means 9 may however not be necessary.

 The tables of Figures 2 to 5 are intended to illustrate possible examples of the operation of such a device.

 In these examples, it is assumed that the number of neighboring cells to be monitored is equal to 12 (these neighboring cells being designated by their number, in this case from 1 to 12) and that the number N of best cells is equal to 6, these numerical values corresponding more particularly, for example, to a GSM network.

Each of these tables includes as many rows as successive instants considered, and four columns containing respectively
- the first, denoted MES, the cell numbers arranged in order of importance of reception levels (in this case in descending order) as obtained for the measurement period considered,
- the second, the content of the table MC of the best cells, as obtained at the instant considered,
- the third, the content of the EX table of cells to be examined as obtained at the instant considered.

 - the fourth, the content of the AI table of cells to be ignored, as obtained at the time considered.

 In the examples thus considered, the cells of the table MC of the best cells are further classified in order of importance of reception levels (in this case in decreasing order) and to each cell of the table EX of cells to be examined is associated (although not mentioned in these tables) an indication on the classification of its level compared to that of the cells of the table MC, in order to be able, in the event of inscription in this table MC, to respect the classification inside from this table.

 By way of example, the duration of the measurement period is equal to 470 ms, which more particularly corresponds to the case of a GSM network.

 The table in FIG. 2 corresponds, by way of example, to the case where the table MC of the best cells is, at the initial time t = 0, incomplete (its content being, for example: 1, 2, 3, 4), where the measurement results are fixed from one measurement period to another (the content of the MES column being, for example: 1, 2, 3, 4, 5, 6, 7 , 8, 9, 10, 11, 12) and where the cells of the table MC always satisfy said examination (the examination of these cells not being mentioned in the following furthermore).

For example, at the initial time t = 0, the table EX and the table AI are empty.

 During the second measurement period, cells 5 and 6 are entered in the EX table, and a priority phase of examination of these cells 5 and 6 is started.

In the example considered, before the second period has elapsed, that is to say in this case for t comprised between 470 ms and 940 ms, it is established that cell 5 satisfies said examination, in which case this cell 5 is entered in the MC table and deleted from the EX table, and the examination of cell 6 is started
By way of example, during the third measurement period, that is to say in this case for t comprised between 940 ms and 1410 ms, it is established that cell 6 does not pass said examination, in which case the cell 6 is entered in table AI, and deleted from table EX.

For example, at t = 1410 ms, cell 7 is entered in the EX table, and for t between 1410 ms and 1880 ms, the examination result for cell 7 is positive, in which case cell 7 is listed in the table
MC and deleted from the EX table.

 In the example illustrated, at t = 1880 ms, the table MC being complete, and the table EX being empty, it is considered that the process has reached sufficient stability to erase the table AI.A t = 2350 ms , cell 6 is then again registered in the table EX, and a priority phase of examination of this cell is again started, and so on.

 In this first example, the registration of cells in the EX table aims to make the number of best cells closest to 6, therefore to facilitate the search for target cells at the network level and to reduce the risks loss of communication.

 The registration of cells in the AI table also aims to speed up the process of determining better cells, by avoiding systematically re-examining candidate cells (that is to say of relatively strong reception level) but whose the review has already been negative.

 The table in FIG. 3 corresponds, by way of example, to the case where the table MC is, at the initial time t = 0, complete (its content being by way of example: 1, 2, 3, 4, 5, 6), where the measurement results are fixed from one measurement period to another and include levels higher than the lowest of the levels of the table MC (the content of the column MES being, for example : 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1) and where the examinations carried out on the cells of the MC table are always positive.

 For example, at t = 0, the EX and AI tables are empty.

 At t = 470 ms, cells 12, 11, 10, 9, 8, 7 are entered in the EX table and a priority phase for examining these cells is started.

 For example, for t between 470 ms and 940 ms, the examination of cell 12 is positive. Cell 12 is then entered in the table MC, in place of cell 1.

 As an example, for t between 1410 ms and 1880 ms, the examination of cell 11 is negative. Cell 11 is then erased from table EX, and entered in table AI.

 For example, for t between 2350 ms and 2820 ms, the examination of cell 10 is negative.

 Cell 10 is then erased from table EX, and entered in table AI.

 For example, at the end of a time interval equal to 5 s (which corresponds more particularly to the case of a GSM network), ie at t = 5470 ms, we enter an uninterruptible phase of examination of the cells of the MC table, while cells 9, 8, 7 are still entered in the EX table, that is to say that the examination of these cells has not yet been completed.

 At the end of this phase of examination of the cells of the table MC, in this case at t = 15,470 ms, we again enter a phase of examination of the cells 9, 8, 7 of the table EX.

 In the example considered, if the fate of these cells, namely their registration in the AI table, or their registration in the MC table, is determined during this new phase, then the AI table is deleted, otherwise we re-enter a examination phase of these cells, and so on.

 In this second example, the cells registered in the table EX are therefore cells having a level higher than the lowest of the levels of the cells of the table MC.

 The purpose of registering cells in the AI table is, as in the previous example, to save time in the process of determining better cells, by avoiding systematically re-examining cells for which the examination has already been revealed. negative.

 The table in FIG. 4 corresponds, by way of example, to the case where at the initial time t = 0 the table MC is full (its content being, for example: 1, 2, 3, 4, 5 , 6), and the empty EX and AI tables, where the measurement results are fixed (the contents of the MES column being, for example: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12), and where the examination of one of the cells of the table MC turns out to be negative.

 For example, for t between 0 and 470 ms, the examination of cell 3 is, for example for the nth consecutive time, negative (with n for example equal to 4 in a GSM network). Cell 3 is then removed from the table MC and entered in the table AI.

 Cell 7 is then entered in the EX table (for example at t = 470 ms) and a priority phase for examining this cell is then started.

As an example for t between 940 ms and 1410 ms, the examination of cell 7 is positive, and cell 7 is then deleted from the EX table and entered in the table.
MC.

 In the example considered, the table MC then being complete, and the table EX empty, the process is considered to be stable and therefore the table AI is deleted (for example at t = 1410 ms).

 As in the first example, registering cells in the EX table is intended to make the number of cells in the MC table closest to N.

 As in the first and second previous example, registering cells in the AI table saves time in the process of determining the best cells, by avoiding unnecessarily re-examining cells for which the examination has already been revealed. negative.

 The table in FIG. 5 corresponds, by way of example, to the case where at the initial instant t = 0 the table MC is complete (its content being for example: 1, 2, 3, 4, 5, 6) and empty EX and AI tables, and in the case of measurement results fluctuating from one measurement period to another.

 As an example, at t = 470 ms, the measurement results indicate in decreasing order of levels, cells 1, 2, 3, 4, 5, 7, 8, 9, 10, 11, 12.

Cells 7 and 8 are then entered in the table
EX, and a priority phase of examination of these cells is started.

 For example, at t = 940 ms, the measurement results indicate, in decreasing order of levels, cells 1, 2, 3, 4, 9, 7, 5, 6, 8, 10, 11, 12.

 Cell 8 is then replaced by cell 9 in the EX table.

 Although in the example of embodiment considered, the cells of the table EX are in principle classified in order of importance of reception levels, in this case in decreasing order, in order to allow an examination of these cells in this order, cell 9 is in this case classified after cell 7 in order to continue the unfinished examination of cell 7.

 As an example, for t between 940 ms and 1410 ms, the examination of cell 7 is negative.

 Cell 7 is then deleted from table EX and entered in table AI.

 For example, at t = 1410 ms, the measurement results indicate, in descending order, cells 1, 2, 3, 4, 9, 7, 10, 5, 6, 8, 11, 12.

 Cell 10 is then entered in table EX, in addition to cell 9 for which the examination is continued.

For example, for t between 1410 ms and 1880 ms, the examination of cell 9 is positive, and cell 9 is then erased from the EX table and entered in the table
MC, in this case between cells 4 and 5, the lower level cell 6 being removed from the MC table.

 For example, at t = 1880 ms, the measurement results indicate, in descending order, cells 1, 2, 3, 4, 9, 7, 8, 5, 6, 10, 11, 12.

 Cell 8 is then entered in table EX in place of cell 10.

For example, for t between 1880 ms and 2350 ms, the examination of cell 8 is negative, and cell 8 is then erased from the EX table and entered in the table
HAVE.

 In the example considered, the table MC being complete, and the table EX then being empty, the table AI can be deleted (for example at t = 2350 ms).

 As in the second example, the cells entered in the EX table are cells of level higher than the lowest of the levels of the cells of the table MC.

 As in the previous examples, registering cells in the AI table makes it possible to speed up the process of determining better cells, by avoiding unnecessarily re-examining certain cells.

 It will be noted that in the case considered here of measurement results fluctuating from one measurement period to another, the risk exists that the table EX is never empty, therefore that the table AI is never deleted (if at least, as in the previous examples, the condition for carrying out such an erasure is that the table MC is complete and the table EX empty), and therefore that the examinations which could be carried out on the cells of the table AI are no longer necessarily negative.

 Under these conditions, it will be possible to erase the table AI more frequently.

 For example, this AI table could be erased entirely with a periodicity determined in this case to obtain a better compromise between speed of the process and reliability of the results provided.

 This AI table could also be partially erased with a certain regularity, for example by using to achieve a memory of the type first in-first out, or "FIFO" ("Firs In-First Out"), or by associating with each of the cells stored in this table, a time-out mechanism intended to control the erasure of this cell after a determined time interval.

 It will be understood that the invention is not limited to the operating examples thus described, which constitute only examples among others, intended only to better understand the operation of a device according to the invention.

Claims (4)

 1) Device for monitoring neighboring cells by a mobile station in a cellular mobile radio network, device operating on measurements of signal levels received from said neighboring cells, and being intended to determine at most N best neighboring cells, defined as being cells corresponding to signals received at a higher level and moreover satisfying an examination of the validity of information carried by these signals, device characterized in that it comprises  - a memory (1) containing a table called the best cell table,  - a memory (2) containing a table called table of cells to be examined,  - a memory (3) containing a table called the table of cells to be ignored,  - means (8) for registering in the table cells to be ignored, cells not satisfying said examination,  - Means (8) for registering in the table of the best cells, cells satisfying said examination.  2) Device according to claim 1, characterized in that it further comprises  - means (4) for registering, in the table of cells to be examined, and provided that they are not registered in the table of cells to be ignored, cells having a level higher than the lowest of the levels of the cells registered in the table of best cells, or, in the case where the number of cells registered in the table of best cells is less than N, also cells of level lower than this lower level.  3) Device according to claim 1, characterized in that it further comprises  - means for registering cells in the table of cells to be examined, provided that they are not registered in the table of cells to be ignored,  means for registering in the table of the best cells, cells satisfying said examination, on the condition that they have a level higher than the lowest of the levels of the cells registered in the table of best cells, or, in the case where the number of cells registered in the table of the best cells is less than N, even if they have a level lower than this lower level.  4) Device according to one of claims 1 to 3, characterized in that it further comprises means (9) for authorizing an erasure, in whole or in part, of the memory containing the table of cells to be ignored.