FI94202C - Radio channel allocation method - Google Patents

Description

94202

Radio channel allocation method

The invention relates to a method for allocating radio channels for a cellular radio system comprising remote radio stations and a plurality of fixed radio stations spaced apart in the geographical area 5 of the radio system, each having a plurality of traffic channels and a single paging channel. a group of classified radio channels from which the remote station searches for a paging channel in the normal paging procedure, and a second group of radio stations stored in an updatable manner through the paging channels, which can also be used as paging channels, and from which the remote station searches for a paging channel does not produce results.

In cellular radiotelephone systems, communication between the fixed radio network and radiotelephones takes place on 20 radio channels (transmission and reception frequency pairs). Radio channels used for user data transmission, such as voice or data transmission, are called traffic channels. In radio systems in accordance with standard MPT 1343 or equivalent published by the English Department of Trade and Industry (DT1), the radio channel reserved for signaling between the fixed network and the radiotelephone is also called the paging channel. The paging channel further identifies the system and base station location, providing a kind of beacon for radiotelephones looking for a suitable paging channel for their use.

In the two paging channel paging sequences defined by the MPT1343 standard, the NH sequence (Normal hunt sequence) and the CH sequence (Comprehensive hunt sequence) radiotelephone examines a number of channels in search of a suitable paging channel (base station) when the old one is lost or the telephone is switched on. In the NH sequence, the radiotelephone traverses all radio channels classified as paging channels. In the CH sequence, the radiotelephone traverses radio channels, which are usually traffic channels but can also be in call-5 channel usage.

NH channels are permanently programmed into the radio. It is possible for the radio system to add a new radio channel to this list of NH channels or to remove a radio channel from it with special signaling messages.

10 A large trunking system can have up to more than a thousand radio channels, of which, in principle, an arbitrary number can be radio channels belonging to the CH sequence. However, the list of NH channels stored in the radiotelephone can usually contain a maximum of 32 channels. In this case, it is important in the system-15 that an attempt is made to keep the total number of paging channels as close as possible to the number of NH channels in order to minimize the paging times of the paging channels of the radiotelephones.

One known solution for this is to define a radio channel for each of the 20 base stations, which belongs to the group of NH channels. However, this cannot always be done, and the system will have to change the paging channels of the base stations over time, for example due to faults in the channel equipment. In this case, a new * * radio channel that is currently available is taken as a new paging channel, which can act as a paging channel. The selected channel is often other than the NH channel. Over time, several of the paging channels in the system may be CH channels, extending the paging channel paging sequences.

30 If an NH paging channel is deleted from a base station in the system and that channel is not in paging channel use in any other part of the system, the system must send deletion messages on all paging channels. If, in turn, a radio channel which is not used elsewhere in the system is assigned to a base station as a new paging terminal, it should be communicated to all radiotelephones. If there are many channel changes and the channels are arbitrarily allocated as paging channels, the above-mentioned messages generate a lot of load on the paging channels.

The object of the invention is to alleviate the above-mentioned problems.

This is achieved by the allocation method according to the invention, characterized in that a) when changing the paging channel of a fixed radio station, a radio channel permanently belonging to said first group is allocated to the fixed radio station as a new paging channel whenever such is available to the base station, b) if the second paging channel of the fixed station is a radio channel, 15 said radio channel is temporarily transferred to said first group and the group change is notified to the remote stations via paging channels, c) permanently restoring the radio channel of the first group to a fixed radio station as soon as it is available to the base station, and d) when the radio channel is temporarily transferred to the first group is released from paging channel usage, the radio channel is returned to the second group and the group change is notified via paging channels to the remote stations.

The basic idea of the invention is to remain in the state of the system, in which only NH channels are the paging channels, by means of the classification of radio channels and their reservation arrangements.

The radio channels of the system are classified into groups, the first of which consists of the channels to be studied in the NH sequence and the second in the CH sequence. The system favors the channels of the first group in the «paging channel use. If, for one reason or another, the channel of the second group has to be selected as the paging channel, it is temporarily added to the first group-35 and the group change is notified to the radiotelephones. In this case, the system always tries to restore the channel permanently belonging to the first group as the paging channel, so that the size of the group does not increase and the NH sequence is not extended.

Thanks to the invention, the radio system uses almost exclusively the channels belonging to the NH channel set as a paging channel. In this case, the radiotelephones find the paging channels quickly and the paging channels do not need to send signaling about changes in the channel categories.

However, if a CH channel has to be taken as a paging channel, the solution of the invention is more likely to provide information to the radiotelephone than before, because the number of NH channels is limited to a few ten and the method according to the invention has a higher probability of staying within this limit.

The invention will now be described in more detail by means of an exemplary embodiment with reference to the accompanying drawing, in which Figure 1 illustrates a radio system in which the invention can be applied, and Figure 2 illustrates the connection between a radiotelephone exchange and a base station.

Figure 1 shows a trunking-type cellular radiotelephone system in which the geographical area covered by the system is divided into smaller radio areas, i.e. radio cells C1, C2 and C3, so that adjacent cells preferably overlap in their edge areas. The cells are assigned certain frequency channels for voice connections, so that at least cells close to each other have different frequencies in use at the same time. Each cell C1, C2 30 and C3 has at least one fixed multichannel transceiver apparatus BS1, BS2 and BS3, referred to herein as a base station. All base stations BS1, BS2 and BS3 are connected by fixed connections, such as cables, to a radiotelephone exchange MX, which thus controls a plurality of base stations BS, and / or to a system controller CP, which controls the operation of the entire system. A system of this type is described, for example, in GB patent application 2165127 with cross-references.

The radio system has at its disposal predetermined radio frequencies, i.e. radio channels (transmission and reception channel pairs), for voice or data connections, on which the base stations BS are in radio communication with the mobile radio stations, i.e. the radiotelephones MS, which are mobile in the cells. The radio call center MX allocates these radio channels to the support-10 stations on a call-by-call basis. with a dynamic allocation principle so that the same frequencies are not used simultaneously by adjacent base stations that could interfere with each other.

Figure 2 illustrates the connection between the radio exchange 15 and the base station BS. The radiotelephone exchange MX includes a plurality of base station interface units (BSIUs), each of which acts as a link between the call control computer CCC (Channel Control Computer) and the base station radio channel unit ChU (Channel Unit). Each base station BS has a plurality of radio channel units ChU, each comprising a radio transceiver. The CCC of the call control computer of the radiotelephone exchange MX allocates free radio channels, radio channel units ChU and base station interface units BSIU for each call involving one or more of the exchange's own mobile radiotelephone MS MS. For each call, the radiotelephone exchange MX can force the channel unit ChU to operate on a particular radio channel of its choice in order to perform the above-mentioned dynamic allocation.

30 The interface unit BSIU has four main functions: to control access to the associated radio channel, to convert and forward messages between the radio units, i.e. the channel units ChU and the call control computer CCC, to connect the exchange's voice paths to the radio channel and to control and monitor the base station. One BSIU controls one channel 94202 6, which may be either a traffic channel or a control channel (paging channel) used by the system for control signaling, such as call set-up signaling. In both cases, the BSIU receives messages from the call control information-5 machine CCC, monitors the 4-wire voice and signaling connection between the exchange and the base station, and sends CCC monitoring data regarding the transmitter, base station, and transmission line states to the call control computer.

In the paging channel mode, the BSIU may operate as a dedicated paging channel, a non-dedicated paging channel, or a time division paging channel. The paging channel is a radio channel reserved for signaling between the fixed network and the radiotelephone for call set-up, radiotelephone registration, transmission of status and data messages, and broadcasting of network information to the radiotelephone. Each radiotelephone, i.e. mobile radio station, responds to the paging signal of only one base station to which it is currently registered and signals back to the system (exchange) only through this base station during the reception of 20 paging signals. During a call, the radio does not normally receive or transmit on the paging channel.

The radiotelephone leaves the paging channel (base station) according to MPT1343, for example, when the number of invalid words ··, 25 exceeds a set limit or a much better, * * adjacent paging channel is known.

The paging channel search is performed mainly according to MPT1343. The base station BS transmits an SYS code on the paging channel, by means of which the radiotelephone MS identifies the system. The SYS code includes an AREA code that tells the radiotelephone MS the calling area (the central area of a particular mobile switching center MX) and whether re-registration is required. The MPT 1343 specifies five different paging procedures or sequences: 35 Assuming paging procedure RCC (Resuming • · 7 94202 a control channel sequence), in which the MS returns after a call to the same paging channel it has previously listened to if the system has not instructed it to take another paging channel .

5 A single call channel search procedure SCH (Single Chan nel hunt sequence) in which a mobile switching center MX can command an MS for a specific paging channel. This procedure is also used when the MS is turned on and the previously used paging channel and base station location number is retrieved from memory.

10 If the RCC or SCH search fails, the preferred search procedure PH (Preferential hunt procedure) is performed, in which the channels stored in the data table of the neighboring base stations (ASD table) are first checked. For the study, those base stations are selected whose field strength of the caller-15 wool is higher than LI. If the paging channel is not found in the ASD table (or the table is empty), all paging channels in the system are checked. In this procedure, only the paging channel that does not require re-registration is accepted (same AREA code as for the old 20 paging channels).

If the PH search fails, the MS is turned on, or the previous paging channel is lost, the normal search procedure NH (Normal hunt sequence) is performed, in which the channels in the ASD table are initially checked. If the paging channel cannot be found in the -25 dy ASD table, all paging channels in the channel table are checked in the dedicated system. Using the threshold levels L2, LI, and LO in the same manner as in the PH search procedure. All AREA codes are accepted in this procedure.

30 If the NH search fails, an extended search procedure CH (Comprehensive hunt sequence) is performed, which goes through all the channels in the channel table, including those classified as traffic channels. This search is performed using the threshold levels L2, L1 and LO in the same way as in the NH search.

94202 8

In the MX memory of each mobile switching center and in the memory of each radiotelephone MS, a channel table is kept listing all the radio channels used by the system (usually up to 250). The radiotelephone channel table contains a control byte for each channel, where each bit b0-b7 indicates whether the corresponding specification is valid. Such determinations include, for example, control channel (bO), free channel (b1), forbidden channel (b6), measured channel (b7), channel included in the extended search-10 procedure (b2), simplex channel for direct MS-MS use (b3) , a simplex channel for the pager (b4) and a time division paging channel (b5). Bit b5 corresponding to the time division paging channel indicates that this channel is a time division paging channel in some part of the system. If I got elsewhere this channel is a dedicated paging channel or traffic channel.

When the radio is switched on, the channel table is read from non-volatile memory into RAM. The radio system can change a few bits in the channel-20 table stored in RAM with BCAST signaling messages. These changes are only valid until the power is turned off. The following are a few examples of BCAST messages: BCAST (sysdef = 00000), Announce CC. This message indicates more paging channels in the channel table.

•• .25 BCAST (sysdef = 00001), Withdraw CC. By saying this, the paging channels are taken out of the channel table.

. BCAST (sysdef = 00100), Adjacent site CC. This message indicates the paging channels of adjacent base station locations and indicates that it is a time division or dedicated paging channel. The channel number and the corresponding SYS code are stored in the data table (ASD table) of the neighboring base stations. This table is cleared when the paging channel is accepted. The channels in the ASD table are checked first when the paging channel search starts.

35 BCAST (sysdef = 00101), Vote now advice. With this

Il «M k Ul> I 1 i Bl l • · 9 94202 The racket is notified to the mobile station MS of the active adjacent paging channels in the dedicated system.

The radiotelephone MS scans the channel table so that the next paging channel to be measured is randomly selected.

5 When the MS measures a channel that is not a time division paging channel (b6 = 0), it marks the channel with "measured" information (bit b7-1), so that this channel is not re-measured during the same paging procedure. Time division paging channels (b6 * = 1) are measured time and time again because it is not possible to know which base station BS using this paging channel is currently transmitting. In this way, an attempt is made to listen to the paging channels of all base stations.

According to the invention, the radio system aims to use only channels which are fixedly programmed in radiotelephones as NH channels (bO = 1) as paging channels.

To this end, the radio channels of the system are classified into groups, the first of which consists of the channels studied in the NH sequence (b0 = 1) and the second in the CH sequence (b2 = 1). In paging channel use, the system favors the channels of the first group 20 so that when the paging channel of the base station is changed, a radio channel permanently belonging to said first group is allocated to the base station as a new paging channel whenever such is available to the base station. If, for one reason or another, the channel of the second group 25 has to be selected as the paging channel, it is temporarily added to the first group (set to b2 = 0, bO = 1) and the group change is notified to the radiotelephones by an Announce CC message. In order not to increase the size of the NH channel group and to lengthen the NH sequence, the system always tries to restore the channel permanently belonging to the first group as the paging channel as soon as it is available to the base station. Similarly, as soon as a radio channel temporarily transferred to the first group is released from paging channel use, the radio channel is returned to the second group (set to b0 = 0 and b2 = 1) and the group change is notified to the radiotelephones via paging channels.

10 94202 so that the group size does not increase and the NH sequence does not lengthen. This is done, for example, by checking that the BSIU of each faulty channel unit is rehabilitated to see if it can be used for paging channels.

In one embodiment of the invention, radio channels that can only be used as traffic channels are also prioritized for traffic channel use by placing them in the third and fourth channel groups. In this case, the aim is to select a channel belonging to the third group 10 as the traffic channel. If no free traffic channel is found in the third group, the channels in the second group are examined. If no free channel is found in the second group, the channels in the first group are examined. Finally, the channels of the fourth group are examined. In this way, the channels suitable as the paging channel are kept free of traffic channel use for as long as possible.

The figures and the related description are intended to illustrate the present invention only. The details of the method according to the invention may vary within the scope of the appended claims.

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Claims (2)

11 94202 A method for allocating radio channels for a cellular radio system, comprising remote radio stations (MSI, 5 MS2, MS3) and a plurality of fixed radio stations (BS1, BS2, BS3) spaced apart in a geographical area covered by the radio system, each having a plurality of traffic channels and one paging channel; the remote station (MS) permanently storing in the memory 10 a first group of radio channels primarily classified as paging channels of the cellular radio system, among which the remote station searches for a paging channel in a normal paging procedure, and a second group of which the remote station searches for a paging channel in an extended paging procedure if the normal paging procedure does not produce a result, 20 characterized in that a) a fixed line when changing the paging channel of a radio station (BS), a radio channel permanently belonging to said first group is allocated to the fixed radio station (BS) as a new paging channel whenever such is available to the base station, b) if a radio channel belonging to another group has to be temporarily allocated as a paging channel of the fixed radio station (BS), to said first group and notifying the group change via paging channels to the remote stations (MS), c) permanently restoring the radio channel of the first group to the fixed channel (BS) as soon as it is available to the fixed radio station, and 35 d) when temporarily transferring to the first group - 12 94202 ty the radio channel is released from the paging channel usage, the radio channel is returned to the second group and the group change is notified to the remote stations (MS) via the paging channels. A method according to claim 1, characterized in that only radio channels classified as traffic channels are placed in the third and fourth groups of radio channels, and that the aim is to select a channel belonging to the third group, then a channel of the second group, then channels of the first group, and last, the channel of the fourth group is examined. • · • • t 94202 13