HK1029244A - Cell selection based on user profile in cellular radio system - Google Patents

Description

Selecting a cell based on a profile of a user in a wireless cellular system

The present invention generally relates to the selection of a cell in which a terminal of a wireless cellular system operates. In particular, the invention relates to the optimization of the selection of cells in a system in which cells provide a plurality of data transmission functions, and the ability of terminals to utilize these data transmission functions is terminal-specific.

A wireless cellular system comprises fixed base stations, each having a coverage area, and terminals that are mobile with respect to the base stations and their coverage areas. The coverage area is also referred to as a cell. This patent application takes a mobile phone as an example of a terminal. When the mobile phone is powered on, it will in this or that way try to find the strongest base station signal and register with the so-called Location Area (LA) represented by the base station in question. Registration means that the mobile phone informs the mobile phone network via the base station: it can be paged to the base station in question over its entire positioning area. In idle mode, the mobile phone periodically receives messages sent by the base station to detect paging messages indicating an incoming call and other messages sent to it. At the same time, the mobile telephone observes the power of signals from other nearby base stations so that the base stations can be quickly exchanged when needed.

In prior art wireless cellular systems, the base stations are substantially similar in communication characteristics; in other words, the same type of service is obtained from the network regardless of which cell the mobile phone is operating in. An exception to this rule is the arrangement in which a mobile phone is typically directed to operate in cells belonging to a particular Home Area (Home Area) or to avoid certain so-called handover cells, which prioritizes the order of the cells. In the home area arrangement, a fixed geographical home area is set for the mobile telephone by means of a contract between the subscriber and the operator maintaining the wireless cellular system. When the mobile phone is operating in a cell of the home area, it may receive a discount on the normal call price or other benefits.

In prior art wireless cellular systems, the terminals are also very similar in communication characteristics. The system typically specifies only one air interface, the specifications of which relate to the timing of transmission and reception, the available frequency, and the data transmission rate or bit rate as it is known.

EBU (european broadcasting union) and ETSI (european telecommunications standards institute) detail the cell selection functionality in GSM (global system for mobile communications) and its extended DSC1800 (digital communications system at 1800 MHz) in the standards ETS 300535(GSM 03.22) and ETS 300578 (GSM 05.08). In general, the same method can be applied to other digital wireless cellular systems. Cell selection is also discussed in finnish patent application FI-970855(Nokia MobilePhones Oy).

In the search for a new mobile communication system, known as a third generation mobile communication system, it has been found that the known method does not always control the selection of cells in the best possible way. The third generation systems include UTMS (universal mobile telecommunications system) and FPLMTS/IMT-2000 (future public land mobile telecommunications system/2000 MHz international mobile telecommunications). It is planned that in the new system, the mobile terminal will have 3 to 4 operating environments, characterized by the size of the cell and the movement or positioning mode of the terminal. These operating environments are: vehicle environments (macrocells, kilometers), pedestrian environments (microcells, hundreds of meters), office environments (nanocells) and/or picocells, meters), and possibly satellite environments (megacells, hundreds of kilometers). The latter means that the base station communicating with the terminal is located on a satellite or that there is a satellite link between the base station and the terminal although it is on the ground. The size of the cell and the mobility of the terminal provide different possibilities for the implementation of error free communication in different operational environments, which is reflected in the bit rate. Office environments may provide up to 2Mbit/s of communication, while in vehicular environments one may have to be satisfied with a maximum of 144 kbit/s.

If each terminal is trying to select the cell that provides the fastest possible communication all the time, it is easy to see that the number of terminals directed to the "fast" cell is so large that their simultaneous random access requests will cause collisions and connection failures. After a connection with the first base station has been established and the terminal and the first base station have agreed on a certain service level, the connection can be handed over to a base station having cells which at least partly overlap with the cells of the first base station and the capacity conditions are better able to accommodate the connection in question. However, handover increases the signalling load of the network and therefore it is better if a connection can be established with a suitable base station from the outset.

From the patent document US-4916728 (Blair) a method is known in which a mobile phone is able to operate in the network of several operators. To enable selection of the most favorable network, the mobile telephone checks several received frequencies, decodes from the signal it receives a System Identification (SID) code, and adjusts to a frequency, the SID code of which indicates the most favorable operator. The data of the different operators is stored in the memory of the mobile phone, so that in this arrangement the various mobile phones respond to the information sent by the base station in different ways. However, since all base stations in a given operator's network transmit the same SID code, in this approach, the mobile phone cannot be made to operate in a different manner except for the selection for the operator.

In the system referred to in PCT patent document WO-95/24809(Motorola Inc.), the switching centre uses a flag sent by the mobile terminal to decide whether the mobile terminal is entitled to a certain service in a given area. If there are geographical and/or mobile-phone specific restrictions for the service, the switching centre may refuse to provide any service to the mobile phone in the area or may grant the application of a specific service, such as for example a data transfer service. However, in order to change the provision of granted services, the mobile phone must migrate, since the restrictions are always the same in a certain area. Thus, in this method, when the mobile phone or other terminal of the wireless cellular system is stationary, it is not possible to influence the cell selection or reselection.

A multi-level home billing method for a Mobile phone of a wireless cellular system is known from finnish patent application FI-952965 and the corresponding european patent document EP-749254 a1(Nokia Mobile Phones Oy), wherein a binary alphabet sequence is stored in the Mobile phone. Each base station transmits its own specific binary identification code at regular intervals, and the mobile phone selects certain bits from the letter sequence transmitted from the base station to perform a logical operation with the stored binary letter sequence as a mask. If the logical operation yields the correct result, the mobile phone concludes that it is located in the home area or in another area where a certain regional service is available. By using different logical operations it is possible to compose several separate or hierarchical areas with each other where the mobile phone is able to obtain different services from the wireless cellular system. Again, this is not a very suitable method for prioritizing cells, since the service is regional, and the service offered changes only when the mobile phone is moving.

In addition to the above methods, there are known methods and systems in which a mobile telephone or other wireless cellular system terminal is able to detect whether it is operating in a device-specific prioritized cell and to inform the user of this fact. However, none of the prior art systems are able to direct a terminal to use a suitable cell if there are available cells with different capacities.

It is an object of the present invention to provide a method and apparatus for optimizing cell selection when there are available cells of different capacity and/or when the terminal's ability to utilize different cell services varies from terminal to terminal.

The purpose of the invention is realized by the following modes: statistics on communication events are gathered and predictions are made for the next connection based on the gathered statistics and/or characteristics of the terminal.

The method according to the invention is characterized in that it comprises the following steps:

● the terminals receive information about the service level they provide from the base station of the cell of the wireless cellular system,

● terminal makes a prediction of which service level will be needed for the next connection, and

● the terminal selects a cell in which the service level provided by the base station matches the prediction made by the terminal.

The invention also relates to a terminal of a wireless cellular system, the terminal being characterized in that it comprises: means for making a prediction of the level of service required in the next connection and means for selecting a cell such that the level of service provided by the base station in the selected cell matches the prediction described above.

Furthermore, the invention relates to a wireless cellular system, characterized in that it comprises:

● at least in one of the base stations, means for transmitting a control message indicating the level of service offered by the base station in question,

● at least in one terminal

● are used to make predictions about the level of service that may be needed in the next connection and

means for storing it on a storage medium, and

● for comparing the prediction stored on the storage medium with the base station provided

Means for making cell selection on a traffic level basis.

The base station sends control messages at regular intervals to all terminals within the cell area, including information about the base station and its operation. Such control messages may be used to convey information about the bit rate provided by the cell, as well as other parameters defining the capabilities of the base station. The terminal selects one of the overlapping cells that provides a bit rate that matches the prediction of the next required bit rate for the user. Preferably, the prediction is made based on a profile of the user, i.e. statistics on past connections and bit rates used therein. The prediction also shows the terminal's own ability to use different service levels provided by the base station. The decision on cell selection is based on the most restrictive of the three factors: a user, a terminal, and a network. As a limiting factor, the user means that the user has used the offered possibilities to a limited extent only in the past, while the user profile indicates that only a less high level of service may be required in the next connection. By terminal is meant, as a limiting factor, that if the terminal is not able to use the service level of the best base stations (i.e. those providing the highest service level), the system will preferably try to select a cell in which the service level provided by the base station does not exceed the level that the terminal is able to use. As a limiting factor, the network means that when only cells providing a very limited service level are available, the system tries to select a cell that best matches the user profile and terminal capabilities.

The invention will be explained in more detail with reference to preferred embodiments, which are shown by way of example, and the accompanying drawings, in which:

figure 1 shows a base station subsystem and control messages,

figure 2 illustrates the gathering of statistics made by a terminal,

figure 3 illustrates a first example of operation of an embodiment according to the present invention,

figure 4 illustrates a second example of operation according to an embodiment of the present invention,

figure 5 illustrates a third example of operation according to an embodiment of the present invention,

figure 6 illustrates a method according to an embodiment of the invention,

figure 7 illustrates a terminal of a wireless cellular system according to an embodiment of the present invention,

in fig. 1, a first base transceiver station 10(BTS) acts as a base station for a macrocell 11 and provides a terminal with a bit rate of at most 144kbit/s in a single data connection. The second base transceiver station 12 is the base station of the office system in the picocell 13 providing a bit rate of up to 2048kbit/s for the terminal in a single data connection. Both base stations transmit control messages 14 at regular intervals, which comprise, among other data, information about the service provisioning of the base station, i.e. what services the terminal can use through the base station.

One representative factor for the service provision of a base station is the maximum bit rate provided by the base station. The base stations may be divided into pico-level, micro-level, macro-level and macro-level according to the size of the cell so that a given level of base stations provides a bit rate typical of that level. The invention is not limited to the number of definitions of the different levels. Rank information may be conveyed in a variety of ways in control messages sent by the base station. In the classification based on the size of the cell, a practical manner may be applied in which a "00" value of a specific dual bit field indicates a picocell, a "01" value indicates a microcell, a "10" value indicates a macrocell, and a "11" value indicates a macrocell. The classes may also directly indicate the maximum bit rate provided by the base station, for example as in the following table:

table 1: examples of base station ranking

Rank name	Maximum bit rate
		Stage 1	64kbit/s
Stage 2	144kbit/s
		Stage 3	384kbit/s
Stage 4	512kbit/s
		Stage 5	1024kbit/s
Stage 6	2048kbit/s

It is not important in what form, or on what channel, the rank information of the base station is communicated to the terminal. When using the ranking according to table 1, the GSM 2+ base station can also serve as a level 1 or level 2 base station for future multimode terminals. By "multimode terminal" is meant a terminal capable of acting as a terminal of more than one wireless cellular system, depending on the services available in the different systems.

Figure 2 schematically shows a terminal 20 comprising a user's personal SIM (subscriber identity module) card 21. SIM cards are well known as a small size storage medium that holds information about a user and his mobile user agreements in electronic form. According to the invention, the terminal 20 stores information on the connections that have been made between the terminal and the base station on the SIM card 21 or other storage medium accessible to it. The information stored may relate to the class of base station used, the type of connection (voice, video, data, other), the type of service (bit rate, etc.), the particular service employed, and/or another factor representative of the service used in the connection. The information on the SIM card continues to be maintained even if the power of the terminal is turned off; if the information is stored in the volatile memory of the terminal, the information will disappear after the power is turned off. In fig. 2, information is shown as a table including a time column 22a in which the time of connection is stored and a bit rate column 22b in which the bit rate used for connection is used. For clarity, only one profile is shown in the figure. The size of the available memory space determines how much information of the connection can be kept in the table 22 and for each connection. The more connections the information is kept in the table, the more statistical material is used, on the basis of which the terminal can predict what type of connection will be needed next. On the other hand, it may be convenient to save only information about the most recent limited number of connections, since the most recent connections best represent the needs of the user at the time of connection, and if the user changes his or her habits, the statistics will adapt quickly to the new situation. The data in table 22 may be referred to as a user profile.

In addition to the amount of data held in the table, the prediction algorithm also has an effect on the prediction. An exemplary algorithm is to calculate the average of all values in column 22b, which represents the average bit rate of all connections that have been made. The algorithm uses the calculated mean value as a prediction value, thus assuming that the required bit rate in the next connection is equal to the mean value of the bit rates of the past connections. The most recent connection may be mathematically weighted when calculating the average, if desired. If the average falls between two values representing a particular existing bit rate, it is usually a cost to select the next value that is higher than the calculated value and corresponds to a certain existing bit rate value (e.g., one in the right column of table 1) as the prediction. Instead of an average value, the predicted value may be based on a typical value of the values in the column 22b, i.e. the most used bit rate. Alternative methods are also disclosed. The present invention is not limited to the algorithm for calculating the predicted value, and an appropriate approach can be conveniently selected by a trial and error method. The algorithm may also be learning-capable, meaning that both the success rate factors of past predictions and the perceived regularity of the user connection requirements influence the calculation of the predicted values.

In the embodiment according to fig. 2, the terminal follows the following principles in the selection of the cell:

a) when the terminal is powered on, it registers through a suitable base station; the invention does not limit the choice of base station at this stage.

b) In the idle state, the terminal attempts to camp on a cell whose maximum available bit-rate v indicated in the control message sent by the base station satisfies the condition:where T is a pre-calculated by the terminalMeasured values, and the base station digits that the terminal can receive are labeled from 1 to n,

c) the terminal tries to avoid those cells that have a higher bit rate than what is predicted to be needed from the terminal; while in such a cell, the end war attempts to select another cell,

d) the terminal tries to avoid those cells that have a higher bit rate than the terminal can reach; while in such a cell, the end war attempts to select another cell,

e) depending on the terminal's capabilities (e.g., its maximum bit rate) and the prediction it makes, a terminal that is not in the best cell may attempt to select another cell.

It is not essential to the invention what specific algorithm is employed in the terminal to implement the principles listed above. It is also not necessary to implement all the principles from a) to e) described above in an algorithm in order to be within the scope of the invention, since any one of the conditions from b) to e) may implement the idea of the invention alone, according to which the selection of a cell is based on a user profile formed on the basis of previous connections, the capabilities of the terminal and/or the service level provided by the available base stations.

Fig. 6 illustrates an embodiment of a method according to the invention, applying all the features from a to e above. The terminal is powered on in step 101. In step 102, the microprocessor operating the control terminal checks in memory whether there is a user profile representing a previous connection. If so, a prediction value for the service level required in the next connection is calculated in step 103 on the basis of the subscriber profile. If there is no user profile in the memory, a value representing the terminal capabilities, such as the maximum bit rate of the terminal, is retrieved in step 104 and the predicted value is equal to this value. In step 105, it checks whether the base station whose transmission can be received by the terminal includes a base station matching the predicted value. If so, the terminal selects a base station that best matches the predicted value in step 106. If not, the terminal selects the most suitable available base station in step 106 and keeps looping through steps 105 and 107 until it finds at least one base station that matches the prediction. The terminal that has selected a base station according to the prediction will monitor the quality of the connection in step 108. If the connection with the selected base station becomes too weak, the terminal returns to step 105 to find a new base station. However, if the quality of the connection remains good, the terminal remains in the loop formed by steps 108 and 109. The operation is interrupted when the terminal is switched off, which is not shown in the figure.

An example of base station selection (or cell selection) is provided according to the scenario of fig. 3, where the user terminal 30 is a terminal of a complete third generation wireless cellular system, capable of bit rates of up to 2048-kbit/s in high speed data transmission, whereas the user only needs to have his equipment mainly for making ordinary calls. The terminal collects data of the connections established by the user from the table 31 so that the data can indicate that the vast majority of the connections made by the user are ordinary telephones using a bit rate of at most 64 k-kbit/s. According to the above principle c), the terminal tries to select the base station 32 belonging to level 1 in the ranking of table 1 in the idle state. The cell may even be a cell in compliance with the current GSM 2+ phase so that despite the new terminal the user uses the GSM system instead of the new third generation wireless cellular system, the base station 33 of which provides a bit rate of 2048-kbit/s. In this example, the limiting factor on the selection of cells is the user whose previous selection was represented in his user profile.

Fig. 4 illustrates another exemplary scenario in which the terminal 40 does not gather the user profile as such, but rather uses cell selection information 41 regarding the terminal capabilities stored in its memory in the selection of a cell according to item d) above. If, for example, the terminal is able to support a maximum bit rate of 512kbit/s, it will preferably select cells belonging to the levels 1 to 4 in the ranking according to table 1. Only base stations 43 and 44 belonging to levels 5 and 6 are available at location 42, and terminal 40 then selects one of them so as not to deprive the user of the communication service entirely. The terminal tries to find a cell belonging to a level from level 1 to level 4 all the time. The terminal detects at location 46 the transmission of base station 47 belonging to level 3 in addition to base station 45 of level 6 and switches into the cell of base station 47. Thus, in this example, the limiting factor on the selection of cells is the terminal's capabilities.

Fig. 5 provides a third example to illustrate this situation, where either the user profile 51 gathered by the terminal 50 or the terminal capability information recorded in the memory of the terminal predicts: the required bit rate in the next connection corresponds to the 5 th base station (bit rate of 1024 kbit/s) according to table 1 above. However, at location 52, only the level 2 base station 53 is available, and the terminal 50 has selected it. The limiting factor for the selection of a cell at the moment is the positioning of the network, and more specifically of the coverage areas of the base stations of different levels at the area where the terminal operates. When the terminal moves up to position 54 (where available there is a base station 55 of level 5 and a base station 56 of level 6) the terminal selects the former.

Since the terminal knows the maximum bit rate of the current cell in the idle state, it can also convey this piece of information to the user. In fig. 2, the display 23 of the terminal 20 may optionally contain an active flag or other notification to the user of the maximum bit rate of the current cell. This can be more visualized by simple graphical marks, e.g. drawn as ordinary phones, cameras and computers, instead of numbers representing bit rates or text describing the type of connection.

Fig. 7 shows a terminal of a wireless cellular system, which can be used in a wireless cellular system according to the invention. The terminal contains the components typical of prior art mobile communication devices such as a microphone 71, a keypad 72, a display 73, an earphone 74, an antenna 70, an antenna switch or duplex switch 79, and a control module 75 which controls the operation of the terminal. Typically, the control module 75 may be implemented with a Micro Control Unit (MCU) or a Digital Signal Processor (DSP). Furthermore, in fig. 2, a transmitting module 77 and a receiving module 78 are shown, which in fig. 7 are more smart than the terminals of the second generation digital wireless cellular system; for example, they can transmit data at different bit rates. From the planning for third generation wireless cellular systems, the skilled person knows how such a more general transmitting and receiving module can be implemented. The transmit module 77 contains speech coding, channel coding, scrambling and modulation, and RF transmit functions. Accordingly, the receive module 78 includes RF receive functions, demodulation, descrambling, channel decoding, and speech decoding. If the video telephony function is added to the terminal as in the figure, the sending module 77 must have video coding in addition to the speech coding, it receives video images from the camera connected to the device; and the receive module 78 must have video decoding capability so that the decoded video images are sent to the display 73 or a separate video display (not shown). The control module 75 also controls the user interface of the terminal.

In the terminal according to fig. 7, the invention mainly relates to the operation of the control module 75 and the memory 76. Information about the capabilities of the terminal has been programmed into the memory 76 of the terminal before the terminal is put into use. The control module 75 collects data representing connections that have been made and stores them in the memory 76 as a user profile. Under the control of the control module 75, the terminal receives control messages from different base stations via the antenna 70, the duplex switch 79 and the receiving module 78. When a prediction needs to be made for the next possible service level, the control module 75 reads the user profile data (or terminal capability information) from the memory 76 and estimates the prediction value. Under the control of the control module 75, the terminal transmits a registration or switching request through the transmission module 77, the duplex switch 79 and the antenna 70.

The maximum bit rate provided by the base station in the cell in which the terminal is located, or the maximum bit rate of any one cell that the terminal can select at a given moment, does not have to be consistent with the prediction of the next required bit rate by the terminal. Some users may be interested in knowing the estimated value of the terminal and whether it is close to the available resources. A function can be programmed on the terminal by which the user can check what the predicted value for the next bit rate for the terminal is. The user may even be provided with the opportunity to manually alter the prediction.

The prediction estimated by the terminal may not always be valid. A user who has been making ordinary telephone calls for a long time may suddenly make a video call or establish a high speed data connection. Based on its prediction, the terminal is then likely to select a cell with too low a capacity for the connection required by the user, which means that the terminal must soon select a new cell, if any. The end terminal preferably receives and stores data representing the data transfer capabilities of other cells in the neighborhood. Based on the stored data, the terminal can quickly change cells as needed.

In the above we describe how the terminal monitors the distribution of the required bit rate based on the user profile it gathers and makes the cell selection accordingly, almost solely using the bit rate as a cell-specific variable parameter. However, the invention can be generalized to apply any cell-specific variable factor, such as the availability of a certain service. If a service is only available through a certain base station, the terminal may monitor whether the user frequently uses the service and avoid or favor the base station providing that particular service based on the results of the monitoring. All factors that are specific to the base station on which the selection of a cell can be made within the scope of the invention may be referred to collectively as "traffic class".

Claims (12)

1. A method of selecting a cell (11, 13) in a wireless cellular system, characterized in that it comprises the steps of:

a terminal (20) receives from a base station (10, 12) of a wireless cellular system information (14) about the level of service provided by the base station,

the terminal makes a prediction (103, 104) of which class of service level will be required in the next connection, and

the terminal selects (106, 107) a cell in which the level of service provided by the base station corresponds to the prediction made by the terminal.

2. A method as claimed in claim 1, characterized in that the terminal, which is powered on, first selects (107) a cell on the first basis, after which the terminal adjusts (106) the selection of the cell on the basis of whether the service level provided by the base station matches the prediction made by the terminal.

3. The method of claim 1, characterized in that the terminal selects a cell in which the level of service provided by the base station is at least as good as the level of service required by the prediction made by the terminal, which is at the same time the lowest of the levels of service provided by the base stations that the terminal is able to receive its transmission.

4. The method of claim 1, characterized in that the terminal indicates (24) to the user the service level provided by the cell selected by the terminal.

5. The method of claim 1, characterized in that the terminal holds information (22) about past connections between the base station of the wireless cellular system and the terminal, and said prediction is made in such a way that it corresponds to a typical connection defined by the information about past connections.

6. The method of claim 5, characterized in that the terminal stores said information in one of the following storage media: SIM card (21), memory circuit providing semi-permanent storage.

7. A method as claimed in claim 1, characterized in that the terminal uses as the prediction (104) information about the maximum service level that it can utilize itself.

8. The method of claim 7, characterized by in a situation (107) in which the terminal receives information on the service levels provided by the base stations indicating that the service levels of all base stations in question exceed the level that the terminal can utilize, the terminal selecting a cell in which the service level provided by the base station is higher than the level that the terminal can utilize, and then the terminal attempting (105, 106) to change to a cell in which the service level provided by the base station is not higher than the level that the terminal can utilize.

9. A terminal (20) of a wireless cellular system comprising means for receiving control messages transmitted by base stations, means for selecting a cell, and memory means (21), characterized in that it comprises means (22) for making a prediction of the service level required for the next connection, and means (75, 77, 79, 70) for selecting a cell such that the service level provided by a base station in the cell matches the prediction.

10. Terminal of claim 9, characterized in that it comprises indication means (23) for communicating to the user an announcement (24) of the service level based on a control message sent by a base station of the wireless cellular system

11. A terminal as claimed in claim 8, characterised in that the indicating means comprises a display (23) and graphic indicia (24) depicting different service levels which can be selectively displayed on the display.

12. A wireless cellular system comprising terminals (20) and base stations (10, 12) providing various service levels, characterized in that it comprises:

means in at least one base station for transmitting a control message (14) for describing the service level of the base station in question, and

at least in one terminal

For making a prediction (22) of the most likely required service level for the next connection and

means for storing it in a storage medium (21), and

for services based on predictions stored on a storage medium and provided by a base station

Between levels. Means for comparing to select a cell.