WO2009071693A1

WO2009071693A1 - Method and device for selecting a femtocell

Info

Publication number: WO2009071693A1
Application number: PCT/EP2008/066941
Authority: WO
Inventors: Takahito Yoshizawa
Original assignee: Thomson Licensing
Priority date: 2007-12-06
Filing date: 2008-12-05
Publication date: 2009-06-11

Abstract

The invention concerns a cellular terminal and method at a cellular terminal for selecting a base station in a cellular network comprising at least one first base station and at least one second base station, wherein the first base station covers a much smaller area than the second base station. The method comprises at a cellular terminal the steps of getting the priority level of the at least one first base station, measuring the signal strength received from the at least one first base station and the at least one second base station, selecting the first base station corresponding to the priority level of the first base stations, and having the highest signal strength, and, if no first base station corresponds to the highest priority level, selecting the second base station having the highest priority level and the highest signal strength.

Description

Method and device for selecting a femtocell

FIELD OF THE INVENTION

The present invention relates generally to cellular base station and femtocell base stations. In particular it relates to method at a cellular device to select a femtocell.

BACKGROUND OF THE INVENTION

This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

A femtocell is a cellular base station that is functionally similar to a macrocell cellular base station, noted a macrocell hereinafter. A femtocell is also called an access point base station. It is adapted to connect cellular handsets to a mobile network. The area covered by a base station is called a cell. When a cellular handset is located in a cell, it can connect to a base station. A femtocell is adapted to cover a much lower cell range than a macrocell. The cell size covered by a macrocell is a macro cell. The cell size covered by a femtocell is a femto cell. A typical use of a femtocell is inside a building to cover areas that are not reached by a macrocell. A cellular service operator provides a plurality of macrocells and femtocells. A handset may be located in multiple cells at the same time. It performs selection between macrocells and / or femtocells. The selection is typically based on the reception power level. The handset selects the base station offering the best radio frequency quality. This selection based on the power level does not permit the handset to explicitly choose a base station among the others. The handset can't select a base station that is not offering the best radio frequency quality. If the handset is located inside several cells, the handset selects the base station providing the best radio frequency quality. The handset does not necessarily select the closer base station.

The present invention attempts to remedy at least some of the concerns connected with the selection of the base station.

SUMMARY OF THE INVENTION The present invention relates to a method, at a cellular terminal for selecting a base station in a cellular network comprising at least one first base station and at least one second base station, wherein the first base station covers a much smaller area than the second base station. The method comprises, at a cellular terminal, the steps of getting the priority level of said at least one first base station, measuring the signal strength received from said at least one first base station and said at least one second base station, selecting the first base station corresponding to the priority level of the first base stations, and having the highest signal strength and if no first base station corresponds to the highest priority level, selecting the second base station having the highest priority level and the highest signal strength.

According to the method of the invention, the cellular terminal selects a first base station not only based on the signal strength but also on the priority level. The selection is performed among the first base stations having the highest priority level only. The cellular network comprises various types of base stations. The base stations belong to the same cellular network. The first type of base station covers a much lower area then the second type of base station. The area covered by a base station is a cell. The cell range of the first type of base station is much lower than the cell range of the second type of base station.

The invention also concerns a method at a cellular terminal for selecting a base station in a cellular network comprising at least one first base station and at least one second base station, wherein the first base station covers a much smaller area than the second base station.

To this end the method comprises, at a cellular terminal, the steps of getting the priority level of said at least one first base station, measuring the signal strength received from said at least one first base station and said at least one second base station and selecting among the at least one first base stations, the base station having the highest priority and the highest signal strength.

According to the method of the invention, the cellular terminal selects a first base station not only based on the signal strength but also on the priority level. The selection is performed among all the first base stations.

And the first base station having the highest priority and the highest signal strength is selected.

According to an embodiment, the method further comprises the step of, if no first base station has been selected, selecting the second base station having the highest priority level and the highest signal strength.

According to an embodiment of the invention, the first base station is a femtocell and the second base station is a macrocell.

According to an embodiment of the invention, the first base station is comprised in a gateway.

According to an embodiment of the invention, the step of getting the priority level comprises indicating the priority level through a user interface.

The invention also relates to a cellular device comprising communicating means for emitting and receiving in a cellular network comprising at least one first base station and at least one second base station, user interfacing means for indicating a priority level of a first base station, and selecting means for selecting the base station according to the priority level and the signal strength.

Certain aspects commensurate in scope with the disclosed embodiments are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood and illustrated by means of the following embodiment and execution examples, in no way limitative, with reference to the appended figures on which: - Figure 1 represents a system compliant with the embodiment;

- Figure 2 is a block diagram of a handset device compliant with the embodiment;

- Figure 3 is a block diagram of a femtocell device compliant with the embodiment; - Figure 4 is a flow chart representing the first part of the reselection algorithm compliant with the embodiment; and

- Figure 5 is a flow chart representing the second part of the reselection algorithm compliant with the embodiment.

In Figures 2 and 3, the represented blocks are purely functional entities, which do not necessarily correspond to physically separate entities. Namely, they could be developed in the form of software, or be implemented in one or several integrated circuits. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The system according to the embodiment is indicated in figure 1. It comprises a handset 1 , which is a cellular terminal that conforms to the Universal Mobile Telecommunication System (UMTS) standards. Of course the skilled person in the art would appreciate that the handset could be any type of cellular terminal such as any type of second, third or fourth generation terminal.

Figure 1 represents a typical case where the handset is located in a macrocell 4 and two femtocells 2 and 3, which are part of a cellular network. The macrocell and the femtocell conform to the same standard, which is the UMTS standard. There are multiple macro cells and femto cells available to the handset. Of course there might be more than one macrocell or/and more than two femtocells available to the handset. The femto cell coverage diameter is typically a few dozen meters. The macro cell coverage diameter is typically several hundreds of meters.

The first femtocell 2 corresponds to the home femtocell. The second femtocell 3 corresponds to the neighbor femtocell. Home and neighbor femtocells are further described hereinafter.

At the handset there is a priority level defined for the femtocells. All the femtocells don't have the same priority level as regards to the handset. Here the first femtocell has a priority higher than the second femtocell.

The handset is represented in figure 2. The handset comprises a communicating module 14 for emitting and receiving in the UMTS network.

The communicating module is adapted to detect the radio signal strengths received on the surrounding cells. The radio signal strengths are indicated to the selecting module 15.

The user interface 13 is adapted to indicate the management information to the end user. In particular it indicates that the handset is connected or not to a femtocell. The user interface also provides means for the end user to indicate the preferred femtocells. The end user may indicate the priority level of some femtocells. It classifies the femtocells per their priority levels. The preferred femtocells get the priority level 1. Another set of femtocells then get a priority level 2 that is lower than the priority 1. And the femtocell that have not been indicated get the priority level 3 that is lower than priority 2. The number of priority levels might be more or less than three. This is configurable at the user interface. The number of priority levels might also be fixed at the terminal. The priority level may also be remotely entered in the handset by the cellular operator. It is indicated to the handset through a configuration file downloaded to the handset through the cellular network. The processor 11 is adapted to execute the programs of the different modules of the handset. The storing module 12 is adapted to store all the data necessary for the modules of the handset. In particular it stores the CeII ID corresponding to the home cell. The subscriber's handset maintains the "home cell" information. The home cell is a femtocell installed at the subscriber's residence. This is the femtocell to which a particular handset identifies the cell to be its associated femtocell.

The home cell is information that identifies the subscriber's femtocell installed at his/her residence. This home cell is the one that the subscriber's handset communicates with when the subscriber is at home. The home cell information is derived from the combination of "cell ID" and "cell type" being transmitted from the cell in the broadcast information.

The handset comprises a selection module 15. The selection module is adapted to select the cell to which the handset connects. The user's handset uniquely identifies the femtocell with which the user's cellular service subscription is associated with (i.e. "my femtocell at home"). This identification distinguishes itself from all macrocells and all other femtocells served by a service provider. Based on this identification, the intended femtocell that the subscriber owns is selected whenever the subscriber is at home and the femtocell coverage is optimized in order to meet end user's expectation with respect to the femtocell coverage within the residential environment. From the base stations (both macrocells and femtocell), "cell ID" information is transmitted in the broadcast information. The "cell ID" uniquely identifies a cell within a cellular operator's network. In addition, the handset uses the "cell type". The "cell type" categorizes the cells into multiple types of cells. One of the types defines the femtocell as one type of cell. Another type of cell is the macrocell.

Based on the "cell ID" and "cell type" information, a femtocell is uniquely categorized as a femtocell and further uniquely identifies itself and differentiates from all other femtocells in a service provider's network.

The femtocell 2 is represented in figure 3. It comprises a communicating module 24 for emitting and receiving in the UMTS network. It also comprises storing module 22 for storing among others the femtocell celljd. The cell type is also stored in the storing module. The storing module is a non volatile memory. The celljd and the cell type are configured during commissioning. Of course the storing module might be a flash memory, wherein the celljd might be managed and updated by the cell operator.

According to the embodiment, the femtocell is a standalone device. Of course the femtocell could be comprised in another device such as a gateway device.

The femtocell accepts connection from the handsets that has the subscription from the same mobile operator from which the femtocell is associated with. In other words, femtocells are sold by a mobile operator, and only the mobile operator subscribers can connect to it.

A pairing mechanism is performed in the subscriber's handset.

This mechanism allows the handset to store the "cell ID" for which the handset uses to identify the presence of "home cell." The pairing operation needs to be done when the femtocell is put into operation so that the handset can correctly identify the femtocell. The exact pairing operation may involve manual operation of the handset, which is out of the scope of the disclosure. Of course the handset can pair to more than one femtocell.

The selection module of the handset performs rove-in and rove- out as described hereinafter.

Rove-in is an action by the handset when it re-selects a femtocell from a macrocell as a subscriber moves from outside to inside the residence in which the femtocell is installed.

When the handset detects the "home cell" to be present with above the minimum radio signal strength, the subscriber's handset attempts to re-select it. This selection is irrespective of the signal strength of other cells in the environment, such as nearby macrocells. By intentionally giving preference to the "home cell" over macrocell(s) in the area, the usage of the in-home femtocell is ensured whenever the subscriber is at home. This also ensures that the intended femtocell that the subscriber owns and installed at his/her residence is used over some other femtocell(s) present in the environment irrespective of its radio signal strength. If the handset does not detect the "home cell" at all or its received radio signal strength is below the minimum level, then the handset attempts to re-select other available cells based on a pre-defined mechanism.

All femtocells are expected to have the same "cell type" value. Therefore, by "cell type" value alone, the handset can not distinguish if it is the one that the handset is supposed to use or not ("my femtocell" versus somebody else's femtocell in the environment). Therefore, this identification avoids unintended re-selection to femtocell(s) that does not belong to the particular subscriber.

Rove-out is an action by the handset when it re-selects a macrocell or another femtocell from the subscriber's femtocell as a subscriber moves from inside to outside the residence in which the subscriber's femtocell is installed. The goal of this mechanism is to maximize the femtocell coverage in the residential environment the subscriber expects. This may include the immediate area around the residence as well (e.g. garage, front door, back porch, etc.). In this case, the handset should stay with the femtocell rather than re-selecting the macrocell or other femtocell. This method re-uses an existing mechanism described in 3GPP TS25-304. This Technical Specification defines a mechanism in which the currently served cell is kept as long as the signal strength from it meets minimum acceptable threshold.

The reselection algorithm that is performed by the section module 15 of the handset 1 is indicated in figures 4 and 5. When camped on a cell, the mobile regularly searches for a better cell according to the cell reselection criteria. If a better cell is found, that cell is selected.

At step S1 the handset is powered on. The handset is not associated to any cell. It performs measurement of all cells in the environment at step S2. The handset measures the signal strength of all the cells in a manner well known per se in the UMTS environment. Of course S2 represents also the case where the handset is associated to a macrocell and performs the signal strength measurement of all surrounding cells.

At step S3, the handset classifies the cells into two lists. A first list comprises the femtocells. The second list comprises the macrocells. Each list orders the cells by the signal strength.

At step S4, the handset verifies whether any of the femtocells is the home cell, and whether it reaches the allowable minimum signal strength. If such a femtocell is identified, the handset performs a reselection procedure, at step S5, to the home cell. If the reselection succeeds, the handset is associated to the femtocell and the procedure is terminated. If it does not succeed, the handset moves to the step S6.

If no femtocell having home cell with the minimum signal required is identified, the handset moves to the step S6. At step S6 the handset performs reselection procedure to the first femtocell in the list. If the reselection succeeds, the procedure is terminated. If it does not succeed, and if there is another femtocell in the list, the handset moves to the step S6. If it does not succeed, and if there is no other femtocell in the list, the handset moves to the step S7.

At step S7, the handset reselects to the first macrocell in the macrocell list. If the reselection succeeds, the procedure is terminated. If it does not succeed, the handset performs reselection to the macrocell following in the list. While reselection does not succeed and there is a macrocell in the list, the handset performs the reselection.

The procedure as indicated at step S6 enables the "community femtocell". This is a situation similar to a public Wi-Fi hotspot service where there's a group of Wi-Fi access points open to public. Here a group of multiple femtocells open to public.

This is opposed to a closed femtocell that permits connection only to a specific set of users. In that case, if at the step S4 the handset does not detect that any of the femtocells is the home cell and/or whether it does not reach the allowable minimum signal strength the handset moves to the step

S7.

The embodiment distinguishes a home femtocell and other femtocells such as neighbor femtocells. The home femtocell has the highest priority. The other femtocells have lower priority than the home femtocell. In the selection procedure, the handset first selects the home femtocell, and then selects the femtocells having lower priority.

More generally the femtocells are classified into different levels of priority. Several femtocells may have the same priority. The priority of femtocells is indicated at the handset as specified hereinabove. The handset then selects the femtocells based on their priority level. The femtocell having higher priority is always selected. The reselection procedure is then performed at step S6 with femtocells classified according to their priority.

When several femtocells have the same priority, the selection is performed on the signal strength level. The femtocell providing the highest signal strength is selected. References disclosed in the description, the claims and the drawings may be provided independently or in any appropriate combination. Features may, where appropriate, be implemented in hardware, software, or a combination of the two. Reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one implementation of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments.

Reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims.

Claims

1. Method at a cellular terminal for selecting a base station in a cellular network comprising at least one femtocell base station, comprising, at the cellular terminal, the steps of:

- Selecting at least one femtocell base station; and

- Assigning a priority level to said femtocell base station, so that said cellular terminal performs cell reselection based on the priority level of the femtocell base station.

2. Method according to claim 1 , characterized in that the step of selecting comprises the step of recording an identifier of said femtocell base station at said terminal.

3. Method according to any one of the preceding claims, characterized in that it further comprises the steps of, when camped on a base station, reselecting the femtocell base station having the highest priority level.

4. Method according to claim 3, characterized in that if more than one femtocell base station have the highest priority level, reselecting the femtocell base station having the highest power level.

5. Cellular device comprising:

- a user interface for selecting a femtocell base station and assigning a priority level to said selected femtocell base station,

- storing means for recording an identifier of said selected femtocell base station and said priority level; and - selecting means for performing cell reselection according to the femtocell base station priority level.