Method and system for channel allocation in a radio system

This invention relates to a method by which the radio capacity is dynamically allocated to packet radio service and circuit-switched service in a TDMA system, in which the duplex communications between the base stations and the mobile stations take place within time intervals on predetermined channels. The invention also relates to a mobile communication system according to the method.

Most of the current cellular networks offer circuit-switched service for speech and data. The incident frequency band is assigned to these forms of service with equal priority for all. The network does not consider whether the capacity is used for the transmission of voice or data.

In the case of data services in burst form, circuit switching does not utilize the channel optimally. Therefore, cellular networks have used radio services in packet form in addition to existing circuit-switched services. Since an existing radio band cannot be widened, the packet radio services must be fitted to the same band as the circuit-switched services. Thus, one has to take some capacity from the circuit-switched services for the packet radio services.

In TDMA cellular systems, the radio band is usually divided into several frequency bands (FDMA, Frequency Division Multiple Access), and each frequency band is further divided into several time intervals. The logical channels are transmitted in the physical time intervals of the radio interface. In circuit-switched cellular systems, all time intervals are used for control signaling and circuit-switched communications.

The object of the invention is to provide a method which allows more efficient utilization of the capacity of the radio channel. The objective is a method to be used in determining the number of time intervals to be allocated partly for packet radio service and partly for circuit-switched service. According to the invention, this is done by means of the characterizing part of claim 1 by dynamically allocating more capacity, i.e. more time intervals for the form of service that requires it in each case.

This issue has been discussed previously in some patents. Among these may be mentioned, for example, EP-26 11 27, which describes a time-divided telecommunications system in which the spectrum is utilized relatively efficiently by dividing narrowband channels on radio frequency into at least two channels for transmitting coded speech signals and

519 392 provide duplex transmission. However, this document does not deal with dynamic allocation of capacity nor packet radio services per se.

U.S. Patent 4,887,265 discloses a packet radio coupled cellular system. In this system it is possible to connect several data calls to the same radio channel, while preserving the radio spectrum. Mainly, however, the document applies to criteria for connection. It does not deal with the dynamic allocation of capacity for packet radio and circuit-switched services.

According to the invention, a first number of time intervals for packet radio service and a second number of time intervals for circuit-switched service are assigned. If e.g. the need for communications within packet radio service increases, information about this is obtained by a request indicated by a mobile station or by measuring the communications performed by the base station, this information being used as a criterion when additional time intervals are assigned to this service. Such a request can be sent from the mobile station to the base station on a message - ie. signaling channel (eg in connection with connection signaling) or a communication channel, or it can be, for example, transmission of a short message. The request can also be broadcast on a packet radio channel. The capacity required for each service is monitored within the Base Station System (BSS), which as is known consists of Base Transceiver Station (BTS) and the Base Station Controller (BSC), from which information is transmitted to the mobile station regarding the channel configuration. , i.e. the allocation of radio capacity (the channel used by the respective service).

In the basic state, all time intervals on a channel can be assigned to packet radio service as the circuit-switched service does not require capacity. In this case, the circuit-switched service is assigned one or more available time intervals, when a request for this comes, for example, from the mobile station during connection signaling. The base station (base station controller BSC) interprets the request for connection signaling and then disconnects the channel used by the packet radio service and assigns it for circuit-switched service. Alternatively, packet radio service in the base state may be assigned a predetermined minimum number of time intervals, and as packet radio communications increase, they are assigned additional time intervals. As the number of time intervals for packet transmission increases, one must of course reduce the same number of time intervals for the circuit-switched service on the same channel.

519 392

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In a preferred embodiment of the invention, the packet radio service in the basic state has been assigned a predetermined minimum number of time intervals, so that this minimum number is adjusted based on economic factors of importance to the communications and / or the operator. The control can be connected to the results of the communication measurement at the base station, so that automatic adjustment is obtained. Alternatively, the operator can perform adjustment manually, and it can be based on historical communication data.

In sparsely populated areas, or when it is known that the packet radio traffic of the TDMA cell is small or temporary, all time intervals on the channel serving this cell can be assigned to the circuit-switched service. When a need for temporary packet radio communications arises, information about this is transmitted to the base station via e.g. a message channel within the circuit-switched service or another signaling channel, communication channel or short message transmission. For this purpose, a special message can also be determined, which the mobile station requesting the service sends to the base station. Preferably, however, existing message requests are used, e.g. part of a connection message with as small changes as possible, whereby previous services also work.

According to a preferred embodiment, the service can be assigned additional time intervals from the same frequency band, so that the maximum number of time intervals assigned to the service corresponds to the number of time intervals on the band. The service can alternatively be further assigned time intervals from another channel.

Preferred embodiments of the invention are set out in the dependent claims. The invention is described in more detail by way of example and with reference to the figure, which illustrates the time intervals in a TDMA frame.

The goal is thus a procedure that is used partly in packet radio service and partly in circuit-switched service for determining the number of time intervals to be used. The same mechanism can be used in parallel for FDMA bands and also for only one frequency band. On control channels within packet radio service directed towards the mobile stations, the radio channels assigned to packet-switched service must be allocated very often in order for the mobile stations to be informed of the channels currently in force.

519 392

In packet radio cellular systems, such as a GPRS (General Packet Radio Service) system, which can be standardized for GSM / DCS 1800 systems, some of the channels must be allocated for packet radio communications. Then the simplest way is for one or more time intervals to be assigned permanently for packet radio communications, and the other time intervals to be assigned for circuit-switched service. However, the capacity can be distributed even more smoothly on circuit-switched service and packet radio communications. The attached figure illustrates the TDMA frame for a carrier within the GSM / DCS 1800 system. The upper row shows the TDMA frame MS RX received by the mobile station and the lower row the transmission frame MS TX, which is time-shifted with respect to it. The figure shows a time interval in each transmission direction assigned to the packet radio service GPRS. The other time intervals have been allocated for circuit-switched connections CS (Circuit Switched).

Within the TDMA systems, packet radio service is completely new compared to methods that share a common frequency band, such as an Aloha-based protocol. In TDMA radio systems that use packet service, several users usually share a time interval (a frequency band) on the carrier both in the direction of the base station and towards the mobile station. As in GSM / DCS 1800 systems, the GRPS channel could be assigned a time interval among eight intervals on a 200 kHz carrier. Within this selected time interval, approximately 25 kbit / s could be transmitted.

The capacity for a time interval may be insufficient. Then the operator could assign the packet radio service another time interval, and even all time intervals on a 200 kHz radio carrier.

As several time intervals are available, they can be used either together or separately. In common use, the time intervals on the same carrier form a transmission reserve capacity, which is shared by the mobile stations among themselves. One and the same mobile station can use several time intervals to achieve higher data rate for packet transmission. In separate use, each time interval constitutes a separate physical packet transmission channel, and such channels are assigned to the mobile station in a cell so that the communications are evenly distributed. The distribution can, for example, be controlled in the same way as the mobile stations in a GSM system are divided into separate call groups.

In each case, both for shared and separate use of time intervals, growing packet radio traffic in a cell can be better served by assigning packet radio service additional time intervals as needed.

519 392

Example 1

We investigate a situation in which circuit-switched connections are not used. In this case, all time intervals for packet radio service are assigned. The requirements regarding timing of the packet radio channel are extremely strict. When the mobile station sends a request for transmission of packets, the base station system must assign a time interval for this mobile station within a few hundred milliseconds or even faster. For this reason, there must always be channel capacity available for packet radio service.

In a cellular system, the connection time is much slower. Normally, connection takes place in about 3 - 5 seconds. When the base station detects signaling needed for connection of a circuit-switched connection starting from or terminated in the mobile station, one of the packet radio channels can be assigned for such a circuit-switched call. Usually, the maximum transmission time within the same allocation is limited for packet radio service. A reasonable assumption is that the sowing time is less than 1 s. If transmission takes place on all packet radio channels or only one of them, the transmission of the packet is terminated before the same channel must be assigned to circuit-switched service. However, a number of time intervals must be reserved for packet radio service, so that they are always available for this service and a certain minimum level of service can be guaranteed in the cell. This can be a parameter that is regulated on the base station. The operator can regulate this parameter on the basis of the amount of traffic and financial calculations. When a circuit-switched call is ended, the channel is released again for packet radio service.

With this algorithm, one can achieve fast packet transfer without interfering with circuit-switched communications. The capacity of the circuit-switched traffic can be increased when the number of time intervals allocated for packet radio service is higher than the minimum capacity specified by the parameter.

The regulation of the above-mentioned parameters could of course be automated, for example on the basis of the traffic demand measured by the base station, as explained below.

In normal operation, all channels on a carrier (in GSM eight time intervals, ie channels in a burst) are reserved for packet radio services (GPRS). The signaling channels may be on a separate carrier or in certain assigned time intervals, and the logic channels on the packet radio (GPRS) carrier. The mobile stations use conventional signaling within the mobile telephone system for

519 392 connection. The Base Station System (BSS) detects through the connection signaling that a call is coming to the cell. The base station detects this after the mobile station has sent it a Channel Request, which the Base Transceiver Station (BTS) signals to the Base Station Controller (BSC) in a Channel Required message. The base station's control unit within the base station system checks whether there are free communication channels, whereby the channel used by the packet radio service is released for circuit-switched calls that follow. If a free communication channel is found, the mobile station is assigned the free channel as soon as it needs it. Otherwise, a new assignment of the packet radio channel is started and the channel is assigned to the circuit connection as soon as it is needed.

The base station system needs a channel before it sends an assignment request message to the mobile station. The system has plenty of time to perform a new assignment of the channel before the assignment request message is sent. During the time between the assignment request message and the channel requirement message, signaling takes place on the signaling channel, whereby the channel used by packet radio service can be used until the channel requirement message is transmitted. When the channel is used for circuit-switched service and the circuit-switched call is ended, the channel is free and reassigned for packet radio service.

The base station system keeps the mobile station informed of the distribution of radio capacity, ie. sends the mobile station information about which channels are used by each service (ie sends information about so-called.

channel configurations).

The control of capacity and release of a channel between packet radio and circuit-switched service according to the invention may be particularly necessary in connection with switching, ie. when the mobile station comes from one cell within the area of ​​another cell, in which e.g. all channels are used by packet radio service. Then the capacity check and re-assignment of the channel is performed as above, preferably after the base station system has received a notification of the transfer request and before the base station system sends acknowledgment of the request to the mobile station. In other respects, the handover procedure has been defined in the specifications for mobile communication systems, and is therefore known to a man of the trade union, and is thus not explained in more detail here.

519 392

Example 2

As a second alternative, the following situation is examined. A certain minimum level of service is required in any cell. For example, a time interval could always be reserved for packet radio service. The other time intervals are used for circuit-switched services or are available. The base stations measure the amount of communications transmitted on the packet radio channel. The assignment behavior of a channel in a cell must of course be examined carefully before application, for example on the basis of traffic measurements of the cell in question or with the aid of history data obtained from corresponding cells elsewhere. The channel has a certain percentage limit, and with a higher degree of utilization, the channel is overloaded and the service level drops. If the utilization rate of the channel reaches this limit value, another time interval must be reserved for communications. This can be applied for up to eight time intervals within one and the same GSM carrier and even for several carriers.

As the utilization rate of a channel decreases and reaches another, lower level, any of the time intervals used by packet radio service may be released.

The algorithm according to this second alternative gives higher priority for packet radio service, and circuit-switched service can use the capacity not needed for packet radio service.

The definition of threshold values ​​can be based on long-term monitoring of communications. It can alternatively be sliding, so that the threshold values ​​are updated regularly with the help of measurement results obtained during a certain period.

Example 3

As a further alternative, the following cases are examined. A cell always offers a certain level of basic service, which can be extremely low. The mobile station may request some time intervals, either one or more, of the channel management blocks. Based on this request, the base station assigns packet radio service additional time intervals. A channel must of course be assigned to the mobile station very quickly. Then you can not immediately reserve additional channels. The mobile station is assigned a base channel. During the request to send the following packets, the network has had sufficient time to allocate the packet radio service several channels. Then the mobile station can be assigned the additional capacity it requested in the book, ie. additional time intervals for transmission.

519 392

Example 4

Below you will find an alternative. In rural areas, it may be too much to assign packet radio service even a time interval or part of a time interval, if there is only one mobile station in the area, which transmits data once a week. In this case, no base capacity needs to be reserved for packet radio service.

When the mobile station needs to send packet data, it sends a message to the network. When no available packet radio channels are available, the message can be transmitted on conventional signaling channels used for circuit-switched services.

The message can also be sent on other signaling channels, communication channels or in the form of a short message.

Example 5

Examples 1 and 2 above can be used in combination, so as to ensure a fair distribution of the packet radio services between the circuit-switched service and the packet radio service. This means that each service form is assigned a certain number of channels according to a semi-fixed principle, and the service forms use other channels by using a combination of the algorithms in examples 1 and 2, so that blocking of packet radio service can be avoided. The base station sends information to the mobile station on the control channels so that they can compete for the channels and that mobile stations that use low-priority packet radio service are not given access to the network until more channels are available again.