HK1021285A - A method and a device to utilise the channels for a cellular system - Google Patents

Description

Method and apparatus for utilizing channels of cellular system

The present invention relates generally to communication arrangements over a channel between a base station and a terminal of a cellular system. More particularly, the present invention relates to efficient utilization of communication capacity contained in a channel.

According to the formal definition of CCITT (international telegraph consultative committee for telephone telegraph), "channels" are the identifying part of the interface. In a cellular system, the radio interface between a base station and a terminal comprises several channels. The downlink paging channel, broadcast control channel, and cell broadcast channel of these channels are the fundamental channels with respect to the present invention. In the following, known embodiments of these channels in the GSM system (global system for mobile communications) are described in order to clarify the background of the invention.

In the GSM system, the radio interface is divided into frequency bands with a bandwidth of 200KHz, time slots with a length of 0.577ms in the time direction, and information is transmitted as bursts in these time slots. The definition of a certain channel represents an indication of those time slots in which information belonging to said channel can be transmitted. The Paging Channel (PCH) and the Access Grant Channel (AGCH) establish a PAGCH entity where the ratio of PCH to AGCH will vary over time. The Broadcast Control Channel (BCCH) is its own channel. The time slots used by the BCCH and PAGCH are defined as follows: there are 51 consecutive frames at the so-called Common Control Channel (CCCH) frequency of the cell, each frame consisting of 8 consecutive time slots, and the first time slot is occupied from each frame. The time slots obtained in this way are numbered from 0 to 51. If so-called full rate PAGCH is used, time slots 2 to 5 belong to the BCCH and time slots 6 to 9,12 to 15,16 to 19,22 to 25,26 to 29,32 to 35,36 to 39,42 to 45 and 46 to 49 belong to the PAGCH. One third rate PAGCH includes only slots 6 through 9,12 through 15, and 16 through 19.

The Cell Broadcast Channel (CBCH) may be set on the same frequency with the BCCH and PAGCH, or on another frequency, or it may even use frequency hopping. It is defined such that when examining a continuous period of 8 51 frames with a total length of about 2 seconds, the CBCH includes 4 groups of 4 slots during this period. Regarding the time slot used by the PAGCH, the time slot used by the CBCH is located such that there is always a time difference of at least a certain minimum length between the burst transmitted in the time slot belonging to the CBCH and the burst belonging to the paging message and transmitted in the time slot belonging to the PAGCH, so that the terminal can receive the burst and the paging message transmitted through the CBCH. The arrangement of the time slots used by the BCCH, PAGCH and CBCH is described in detail in the book "GSM mobile communication system" published by the authors MichelMouly, Marie-bernadite paute, in 1992, for example, by Palaiseau, ISBN 2-9507190-0-7.

All terminals in a certain cell do not receive all paging messages transmitted on a PAGCH, but the terminals have been divided into so-called paging groups, and the paging messages transmitted to these groups have a certain schedule within the PAGCH. The receiver of the terminal is always active when it is in idle mode and tunes to the CCCH frequency when its paging group has a predetermined paging message transmission time. Furthermore the receiver of the terminal is always active and tuned to the CCCH frequency during the BCCH and CBCH.

The receiver of the terminal consumes energy when it is switched on. The receiver should be switched on for as little time as possible so that the charging of the battery of the terminal can be sustained longer.

It is an object of the invention to provide a method by which the receiver of a terminal can reduce the electric power consumption when in idle mode compared to the prior art. It is also an object of the invention to provide an apparatus for using the method of the invention.

The object of the invention is achieved in that the information normally transmitted on the broadcast control channel and on the cell broadcast channel is sent out on the unoccupied part of the paging channel.

The method according to the invention is applicable in cellular systems, where a paging channel for transmitting a request for establishing a downlink connection and a broadcast control channel for transmitting general information for connecting cells of a base station are defined between the base station and a terminal. The method according to the invention is characterized in that: when the data transmission capacity of the paging channel is higher than the total number of data, which has to be transmitted in connection with the request for establishing a downlink connection, general information of the cell connecting the base station is transmitted on the paging channel.

The invention also relates to a base station of a cellular system, characterized in that it comprises means for transmitting general information about the cell of the base station on a paging channel.

The invention also relates to a terminal of a cellular system, characterized in that it comprises means for receiving general information about the cell of the base station on a paging channel.

The paging channel comprises time slots (more generally: during a certain time on a certain frequency) during which the terminal must be in reception mode, irrespective of whether or not in fact the base station has a paging message to send. In accordance with the present invention, the base station may transmit other information on those portions of the paging channel that may otherwise be unoccupied due to a low number of paging messages to be transmitted. The other information is preferably information that is typically transmitted on a broadcast control channel and/or on a cell broadcast channel. When a terminal receives information belonging to the broadcast control channel and/or the cell broadcast channel on the paging channel, it must then receive the same information again on the appropriate broadcast control channel and/or on the cell broadcast channel, but it can switch off its receiver at the transmission time of the other channels and it can save power.

Power savings in the base station are less dominant than in the terminal, so the base station can send the same information well on the unoccupied portion of the paging channel and on the broadcast control channel and/or on the cell broadcast channel.

The invention will be described in more detail below with reference to preferred embodiments provided as examples and to the accompanying drawings, in which:

figure 1 illustrates the principle of the present invention,

figure 2 shows the structure of a paging message known per se,

figure 3 shows how a paging message is placed on the paging channel,

fig. 4 shows a base station of a cellular system according to the invention; and

fig. 5 shows a terminal of a cellular system according to the invention.

In fig. 1, block 100 generally represents the fixed portion or "network" of a cellular system, while block 101 represents a terminal. The network 100 comprises a functional part 102 which generates transmission control data called BCCH data for the GSM system. Likewise the network 100 has a functional part 103 which generates broadcast transmission data or CBCH data, and a functional part 104 which generates paging messages or PCH data. In the terminal 101 there is a system parameter memory 105 which stores the received BCCH data. In addition, the terminal 101 has a provision (Presentation) section 106 for the broadcast transmission, which provides CBCH information messages to the user of the terminal, and a paging message processing section 107, which checks whether a received paging message is intended for this terminal, and if so, it starts a function for establishing a connection requested by the incoming call in the terminal. The network 100 and the terminal 101 are connected by means of three channels 108,109 and 110, which conform to the specifications of the cellular system in question. In the GSM system, the BCCH channel 108, CBCH channel 109 and PCH channel 110 are formed by time slots which, according to this definition, are periodically repeated on the CCCH frequency, as described in the description of the prior art above.

In the network 100 there is always a direct connection from each functional part 102,103 and 104 to the corresponding channel 108,109 and 110, so that the data generated by each functional part 102,103 and 104 is transmitted in the channel belonging to that part. On the other hand, there are also connections from functional parts 102 and 103, which generate BCCH data and CBCH data, to PCH channel 110, but these connections are conditional: BCCH data and/or CBCH data are transmitted on the PCH channel only when there is unoccupied space or when paging messages generated by the PCH portion 104 do not occupy all space on the PCH channel 110.

There is a connection from the PCH channel 110 to the paging message processing section 107 in the terminal 101. There is furthermore a conditional connection from the PCH channel 110 to the system parameter memory 105 and to the broadcast transmission providing part 106, so that data destined for these channels and received on the PCH channel can be delivered to the correct address. The connections from the BCCH channel 108 to the system parameters memory and from the CBCH channel 109 to the broadcast transmission providing part 106 are also conditional or used only if blocks 105 and 106 do not receive the required data over the PCH channel 110.

Fig. 2 shows a paging message as defined in the GSM system standard No. GSM 04.08. The first field of the paging message 200 is a so-called pseudo-length field 201 having a length of one octet or 8 bits. The pseudo-length value in field 201 represents the sum of the lengths of the other fields 203, expressed in octets, between the first field 201 and the last field 202 of the paging message. The other fields 203 are not essential to the invention and their total or pseudo length values may vary between 5 and 22 octets. The last field 202 is a so-called spare octets field and its length is determined by the fact that the sum of the last field and the dummy length value in field 201 must be 22 octets. In other words, the length of the spare octets field 202 may be any integer number of octets between 0 and 17 octets that comprise these values.

The above field lengths are particularly relevant for so-called type 1 paging messages. The standard GSM04.08 also defines paging messages of types 2 and 3, which differ from paging messages of type 1 with respect to length and field usage. However, they also include a spare octet field that can be used in the manner of the embodiments of the invention described below.

The spare octets field 202 in the GSM standard 04.08 is reserved for use in future system extensions. The present invention is one such extension. According to prior art, the base station may send a paging message according to fig. 2, which contains five octets of actual data in field 203 and 7 octets of padding bits, i.e. unoccupied space, in field 202. According to a first embodiment of the invention, the unoccupied space in the field 202 can be utilized by transmitting such data among it, which can be transmitted typically on the BCCH channel or on the CBCH channel.

If the spare octet field 202 of a certain paging message contains information belonging to other channels, an identifier containing this fact must be indicated in the paging message so that the terminal can know its situation. One possibility for establishing the identifier is to use the message type field contained in field 203, but the message type field having a length of one octet is not specifically shown in the figure. Different types of messages can be clearly defined using 8 bits, but at the time of writing this patent application, standard GSM04.08 only retains less than 100 values of the message type field to indicate certain types of messages (e.g., value 00100001 represents a type 1 paging message, value 00100010 represents a type 2 paging message, value 00100100 represents a type 3 paging message, and value 00100111 represents a response to a paging message). The value of the unreserved message type field may be reserved for indicating paging messages whose spare octet field contains information, typically that they belong to the BCCH channel. In addition, the values of the unreserved message type field may be reserved for paging messages containing information on behalf of its spare octet field, which may typically belong to the CBCH channel.

Another possibility to define a paging message identifier to indicate that the spare octet field contains information belonging to other channels is to use the extra capacity included in field 201. The maximum pseudo length of the paging message is 22 octets, so that the maximum value of field 201 is the binary number 00010110 representing the decimal number 22. The three most significant bits in field 201 of the prior art paging message are therefore always zero. In order to use them in a manner according to the invention, the most significant bit of the field 201 is 1, for example if the spare octet field contains information that can generally belong to the BCCH channel, and the second most significant bit of the field 201 is 1 if the spare octet field contains information that can generally belong to the CBCH channel.

Fig. 3 schematically shows time slots 301 belonging to a paging channel and 36 such time slots in 51 consecutive frames, for example in a full rate PAGCH channel of a GSM system. The number of downlink paging messages and the number of capacity allocation messages sent as a reply to an uplink paging message from a terminal will vary depending on how often the users are calling each other. During the quiet period, it may happen that only a few of the 36 slots contain paging messages or capacity allocation messages. These "occupied" time slots are shown in the figure as grey time slots. It may even happen that several frames of 51 frames are used so that the base station does not send any paging messages or capacity allocation messages at all. The main part of the time slot 301 is an unoccupied time slot, shown as a white time slot in the figure. According to another embodiment of the invention, the base station may send messages in these unoccupied time slots, similar to messages sent on the BCCH and CBCH channels according to the prior art. This embodiment may use the spare octets field shown in fig. 2 instead, or both embodiments may be used simultaneously. The use of unoccupied time slots has the advantage over the use of a spare octet field that new messages, which are separately identified, need not be defined, but that prior art messages known per se can be used, which messages are only sent on a different channel than in prior art systems.

Fig. 4 schematically shows a base station 400 of a cellular system, which communicates with the rest of the network via duplex communication links 401 in a manner known per se. The base station 400 includes a parallel transmission section 402 for simultaneous transmission on different frequencies. One of the transmitter parts 402 is the transmitter part of the common control frequency or CCCH frequency of the cell, while part 402 comprises a BCCH part 403, a CBCH part 404 and a PCH part 405 as well as a timing part 406, which control their mutual timing and are used for timing reception of synchronization information from the common control part 407 of the base station. Each portion 403,404 and 405 generates a message according to a specification associated with the corresponding respective channel. Each section 403,404 and 405 is switched in its order to a radio frequency section 408 using the order determined by the timing section 406 which performs the required modulation and up-conversion to convert the transmitted message to a CCCH frequency signal which is provided to a transmit antenna 409. For operation according to the first embodiment of the invention there is a connection from the BCCH part 403 and from the CBCH part 404 to the PCH part so that information normally sent on the BCCH or CBCH can be placed in spare octets of the paging message generated in the PCH part. The second embodiment of the invention requires that the timing part 406 is programmed so that it can connect either the BCCH part 403 or the CBCH part 404 to the radio part 408 when the PCH part 405 does not contain paging messages sent in all PCH slots. From PCH portion 405 to timing portion 406, there may be a connection through which the PCH portion may indicate when there is additional space in the PCH. Furthermore, BCCH portion 403 and CBCH portion 404 may provide data to PCH portion 405 contiguously, so PCH portion 405 only ignores such data if there is not enough room in PCH to send such data. Of course the base station may comprise a number of other parts which are not shown in fig. 4.

Fig. 5 schematically shows a cellular system terminal 500, which shows an antenna 501 of the terminal part, a radio frequency part 502, a channel decoding and demultiplexing part 503, notably a driver 504 and a display 505, a D/a converter 506 and a loudspeaker 507 and a control unit 508. The radio frequency part 502 contains a receiver whose activity and reception frequency can be controlled by a control unit 508. The channel decoding and demultiplexing section 503 transmits voice signals received during a call to the speaker 507 via the D/a converter 506 and all data signals to the control section 508, and text messages received on the CBCH channel are also supplied to the display 505 via the display driver 504. The system parameters transmitted on the BCCH channel are stored in a memory 509 by the control unit 508. In prior art operation, the control portion 508 always switches the receiver in the radio frequency portion 502 to receive on a certain CCCH frequency when the BCCH, CBCH or PCH channel is transmitted again. In addition to the BCCH channels of the own cell, the terminal can prepare for cell reselection by also receiving BCCH channels of other neighboring cells. Of course the terminal may contain a number of other parts not shown in fig. 5, the embodiments provided are not limited with respect to the invention: the same operation can be achieved in other ways as well.

In order for the terminal 500 to be able to operate in a manner according to the invention, the control means 508 must be programmed such that it detects when the data received on the PCH channel represents a regular paging message and when the data received on the PCH channel is such a data that can normally be received on the BCCH and CBCH channels. Furthermore, some criteria have to be programmed in the control means 508, on the basis of which the control means can find out that the data normally sent on the BCCH and/or CBCH channel is sufficiently received on the PCH channel and therefore does not need to be converted at the receiver during reception of the BCCH or CBCH channel. Such programming is a technique known to those skilled in the art. When defining the criterion, for example, the cyclic characteristics of the channel definition can be utilized. Considering a certain period after which the mutual schedule of BCCH, CBCH and PCH channels is repeated in the same way, the control unit 508 can check whether data belonging to the BCCH and/or CBCH channels was received on the PCH channel during the previous corresponding period. If so, data from those channels does not need to be received during this period, which data belongs to those channels and was received on the PCH channel during the previous period. During each cycle when receiving a PCH channel, the control component 508 checks whether it contains data belonging to other channels.

It can be seen that the advantages of the present invention are: during idle mode, the receiver of the terminal is required to be switched on for a period of up to as short as 20%, and therefore the terminal may be switched on for a longer time before its battery has to be recharged accordingly. The operation according to the invention can be arranged by programming the base station and the terminal to operate in a new way without necessarily requiring access to the implementation of their own existing components, which is advantageous in terms of manufacturing technology. Also those terminals that do not support the operation of the invention are still fully available, even if the base station programming works in the way of the invention: the terminals according to the invention simply ignore such messages received on the PCH channel, which are not identified as paging messages intended for them. Accordingly, the terminal according to the invention can also be used in the cells of prior art base stations, since when the terminal does not receive information belonging to the BCCH or CBCH channel on the PCH channel, it receives information on their own channel according to the prior art.

In the above we describe how the invention is primarily intended for use in GSM systems. It is clear, however, that the invention is not limited to any certain system, but that it is applicable to all these cellular systems: there is at least periodically unoccupied space on the paging channel and information belonging to other channels is transmitted in parallel with the paging channel. Examples of other cellular systems are the GSM extended DCS1800 and DCS1900 (digital communication System at 1800/1900 MHz), PDC (personal digital cellular), IS-54 and IS-96 (temporary Standard 54/96), and the third generation proposed future cellular System UMTS (Universal Mobile Telecommunications System). The channel names in this patent application are only examples.

Claims (9)

1. Method for transmitting information from a base station (100,400) to a terminal (101,500) in a cellular radio system in which system a paging channel (110) between the base station and the terminal is defined for transmitting requests for establishing downlink connections and a broadcast channel (108,109) is defined for transmitting general information about the cell of the base station, characterized in that: general information about the cell of the base station is transmitted on the paging channel (110) when the information transmission capacity of the paging channel (110) is higher than the total amount of information about the request to establish a downlink connection that has to be transmitted.

2. A method according to claim 1, characterized in that: when the information transmission capacity of the paging channel is higher than the total amount of information that has to be transmitted about the request to establish a downlink connection, general information about the cell of the base station is transmitted on the paging channel (110) and not on the broadcast channel (108, 109).

3. A method according to claim 1, characterized in that: when the information transmission capacity of the paging channel is higher than the total amount of information that has to be transmitted about the request to establish a downlink connection, general information about the cell of the base station is transmitted on the paging channel (110) in addition to the broadcast channel (108, 109).

4. A method according to claim 1, characterized in that: general information about the base station's cell is in the otherwise unoccupied part (202) of the request to establish a downlink connection, which is sent on the paging channel.

5. A method according to claim 1, characterized in that: in addition to the request for establishing a downlink connection, general information about the cell of the base station is transmitted on the paging channel in other messages transmitted on the paging channel.

6. A method according to claim 1, characterized in that:

the cellular system is one of: GSM, DCS1800, DCS 1900;

the paging channel is one of: PCH, PAGCH; and

the broadcast control channel is one of: BCCH, CBCH.

7. A base station (400) of a cellular system, the base station comprising means for:

for sending (405,408) a request for establishing a downlink connection on a paging channel having a certain data transmission capacity, and

general information about the base station's cell is transmitted (403,404,408) on the broadcast control channel,

characterized in that it comprises means (403,404,408) for transmitting general information about the cell of the base station on the paging channel.

8. A terminal (500) of a cellular system, the terminal comprising means for:

for receiving (502,503,508) a request to establish a downlink connection on the paging channel with a certain information transmission capacity, and

for receiving (502,503,508,504,505,509) information on the broadcast control channel about the cell of the base station,

characterized in that it comprises means (502,503,508,509) for receiving general information about the cell of the base station on the paging channel.

9. A terminal according to claim 8, characterized in that it comprises a control unit (508) and means for receiving information on the paging channel at predetermined intervals on the paging channel, and

a) the control means (508) is arranged to check that the paging channel has been received since a previous time

Whether a certain predetermined time has elapsed since the message about the cell of the base station

During the longer period of time of the operation,

b) arranging for the control unit (508) to temporarily respond to a negative result of step a)

Preventing reception of information on the broadcast control channel.