Method and system for channel allocation in a radio system

The invention relates to a method by which the radio scope is dynamically divided between the packet radio service and the circuit-switched service in a TDMA (Time Division Multiple Access) system in which bidirectional traffic between base stations and mobile stations takes place in time slots on specified channels. The invention also relates to a mobile telecommunication system which operates according to this method

Most current small zone radio networks offer circuit-switched services for voice and data. The available frequency band is divided between these services, which all have the same priority. The network does not take into account whether the transmission capacity is used for the transmission of voice or data.

When considering burst data services, circuit switching does not make optimal use of a channel. For this reason, packet radio services are used together with existing circuit-switched services in small-area radio networks. Since the existing radio band cannot be expanded, packet radio services must be fitted into the same band as circuit-switched services. Accordingly, the circuit-switched services must be deprived of a certain scope for packet radio services.

In TDMA small area radio systems, a radio band is usually divided into several frequency bands (FDMA = Frequency Division Multiple Access), and each frequency band is further divided into several time slots. Logical channels are transmitted in physical time slots of the radio interface. In circuit-switched small-area radio systems, all time slots are used for controlling signaling and for circuit-switched traffic.

The purpose of the invention is to provide a method by which the scope of a radio channel can be better used. The invention is based on the object of creating a method and a device with which the number of time slots can be determined which are assigned to the packet radio service on the one hand and to the circuit-switched service on the other.

This object is achieved by the method according to the attached claim 1 and by the device according to the attached claim 10. According to the invention, that form of service is dynamically assigned more scope, ie more time slots, which it requires at a specific point in time.

Cases relating to this subject have already been discussed in various patent publications. An example of this is document EP-A-0 261 127, which describes a time division multiplexed telecommunications system in which the spectrum is used in a relatively efficient manner by dividing narrowband radio frequency channels into at least two time slots, one of which is for transmission coded voice signals and the other is used for bidirectional transmission. However, this document does not discuss dynamic allocation of transmission capacity, nor does it discuss packet radio services as such.

U.S. Patent 4,887,265 discloses a packet-switched small zone radio system. In this system, several data calls can be switched to the same radio channel, which saves radio spectrum. However, the publication mainly discusses criteria for call forwarding. It does not discuss the dynamic allocation of transmission volume to packet radio services and circuit-switched services.

According to the invention, a certain basic number of time slots is reserved for packet radio services, as well as a number of time slots for circuit-switched services. If z. If, for example, the traffic demand for packet radio services increases, information about this is obtained via a request displayed by a mobile station or from traffic measurements by the base station, whereupon this information is used as a criterion for assigning more time slots to this service. Such a request may be transmitted from a mobile station to a base station on a messaging or signaling channel (e.g. in signaling establishing a call) or on a traffic channel, or it may e.g. B. be a short message issue. The request can also be transmitted on a packet radio channel. The capacity required for each service is monitored in the base station system (BSS), which in a known manner consists of base transceiver stations (BTS) and base station controller (BSC = Base Station Controller), from where information regarding the channel configurations, ie the assignment of the radio scope (which channel is available for which service) is transmitted to the mobile station.

AT 410 049 B

In the basic mode, all time slots of a channel can be assigned to a packet radio service if circuit-switched services do not require any capacity. In this case, one or more circuit-switched services are allocated when a request for this is received, e.g. B. with call setup signaling from a mobile station. The base station controller interprets the request from all call setup signals and then de-assigns a channel that is assigned for use for a packet radio service and assigns it to a circuit-switched service. Alternatively, in the basic mode, a predetermined minimum number of time slots can be allocated to packet radio services, in which case more time slots are allocated to packet radio traffic if this increases. As the number of timeslots used for packet radio services increases, the same number of timeslots must be deallocated for wired services in the same channel.

In a preferred embodiment of the invention, in the basic mode, a certain minimum number of time slots is allocated to packet radio services, this minimum number being set on the basis of economic considerations such as are important for the traffic and / or the operator. The control can be coupled to results of the traffic measurement as carried out by the base transceiver station, whereby the adjustment is made automatically. Alternatively, the operator can make the adjustment manually and it can be based on historical traffic information and so on.

In sparsely populated areas, or when packet radio traffic is known to be sparse or random in a TDMA zone, all time slots of the channel serving the zone can be allocated to circuit switched services. If by chance a need for packet radio traffic arises, related information is transmitted to the base transceiver station, e.g. B. via the message channel of a circuit-switched service or via another signaling channel, a traffic channel or via short message output. For this purpose, a special message can also be defined which a mobile station requesting the service transmits to the base transceiver station. Preferably, however, existing messages are used for the request, e.g. B. part of a minimally modified call setup message, in which case old services will also work.

According to a preferred embodiment, more slots can be allocated for a service in the same frequency band, so that the minimum number of time slots allocated to the service corresponds to the number of time slots in the band. Alternatively, time slots can also be assigned in another channel for a service.

Preferred embodiments of the invention are claimed in the independent claims. The invention will now be described in more detail with the aid of the following examples with reference to the accompanying figure which shows time slots in a TDMA frame.

It is a method that is used to determine the number of time slots, such as are used on the one hand for packet radio service and on the other hand for circuit-switched service. The same mechanisms can be used in parallel for FDMA bands and, on the other hand, also for only one frequency band. In downlink packet radio control channels, radio channels assigned to packet switching often need to be tagged in order to inform the mobile stations of the currently active channels.

In small packet radio systems such as the GPRS system (General Packet Radio Service), which can be standardized as a GSM / DCS-1800 system, some of the channels must be assigned to the packet radio traffic. In this case, the simplest method is to permanently assign one or more time slots to packet radio traffic and reserve the rest of the time slots for circuit-switched services. However, it is possible to divide the capacity even more flexibly between circuit-switched services and packet radio services. The TDMA frame of a carrier wave according to the GSM / DCS-1800 system is illustrated in the accompanying figure. The upper line shows the TDMA frame MS RX received from a mobile station, and the lower line shows the time-shifted transmission frame MS TX. The figure shows how a time slot is reserved for the packet radio service GPRS in both the downlink and the uplink direction. The rest of the time slots are reserved for circuit switched (CS) calls.

Packet radio service in TMDA systems is quite new in comparison with methods which share a common frequency band, such as according to the Aloha Basic Protocol. In packet transmission

TDMA radio systems using AT 410 049 B generally use multiple users of a carrier wave time slot (frequency band) in both the uplink and the downlink.

In GSM / DCS-1800 systems, a time slot consisting of eight time slots of a radio carrier wave of 200 kHz can be assigned to a GRPS channel. Approximately 25 kbit / s can be transmitted in this selected time slot.

The size of a time slot can be insufficient. In this case, the operator can also assign another time slot or even all time slots of a radio carrier wave of 200 kHz to the packet radio service.

If several time slots are available, their use can be combined or separated. When used in combination, the time slots of the same carrier wave for transmission form a transmission scope pool which is shared by the mobile stations. One and the same mobile station can use these multiple time slots in order to achieve a higher data rate for packet transmission. When used separately, each time slot is a separate physical packet transmission channel and such channels are assigned to the mobile stations in a zone in order to achieve an even distribution of traffic. The distribution can e.g. Be controlled in the same way that mobile stations are divided into separate paging groups in a GSM system.

In both cases, both with shared and separate time slot usage, increasing packet radio traffic in a zone can be better served by assigning more time slots to the packet radio service when the demand increases.

example 1

A situation is examined where no circuit switched connections are in use. In this case, all time slots are assigned to the packet radio service. The requirements regarding the timing of a packet radio channel are very strict. When a mobile station transmits a request to transmit a packet, the base station system must reserve a time slot for that mobile station within a few hundred milliseconds, or even faster. For this reason, channel capacity must always be available for packet radio services.

Calls are set up much more slowly in a small zone radio network. Typically, a call will be established within 3-5 seconds. If the base transceiver station detects signaling such as is required to set up a circuit-switched call originating from a mobile station or ending there, one of the packet radio channels can be reserved for such a circuit-switched structure. Normally, the maximum transmission time within one and the same reservation with the packet radio service is limited. It is reasonable to assume that the transmission time will be less than 1 second. If there is transmission in all or only one of the packet radio channels, the transmission of the packet is completed before the same channel must be assigned circuit-switched use. However, a number of timeslots must be reserved for the packet radio service, these timeslots always being available for this service, so that a certain minimum level is guaranteed for the service in the zone. This can be an adjustable parameter in the base transceiver station. The operator can set this parameter based on the amount of traffic and economic calculations. When a circuit-switched call is completed, that channel is released again for the packet radio service.

Using this algorithm, fast packet transmission can be achieved without disrupting the line-bound traffic. The transmission volume for circuit-switched traffic can be increased if the time slots reserved for packet radio services exceed the minimum transmission volume specified by the parameter.

The setting of the above parameter could also be automated, e.g. Based on the traffic requirements measured by the base transceiver station, as described below.

In a normal operating mode, all channels on a carrier wave (in GSM there are eight time slots or channels in a burst) are reserved for packet radio services (GPRS). The signaling channels can be supplied on a separate carrier wave or in certain specified channels

AT 410 049 B assigned time slots and the logical channels can be on the GPRS carrier waves. Mobile stations use the conventional signaling of the mobile telephone system to set up a call. From a call setup signal, the base station system (BSS) recognizes that a call is arriving in the zone. The base transceiver station (BTS) recognizes this after a mobile station has transmitted a channel request to it, which is communicated in a channel request message from this base transceiver station to the base station controller (BSC). The base station controller of the base station system checks whether there are free traffic channels, whereupon a channel in use for packet radio service is released for circuit-switched calls as follows. When a free traffic channel is found, the mobile station gets a free channel as soon as it needs one. If a free channel is not found, a reallocation for the packet radio channel is started and the channel is put into circuit switched use immediately when required.

The base station system needs a channel before transmitting an assignment request to the mobile station. The system has ample time to reallocate the channel prior to the transmission of the assignment request, within the time between the assignment request and the channel request message, there is a signaling in the signaling channel, in which case the channel in use for the packet radio service can be used until the channel request message is transmitted is. After the channel has been put into use for the circuit-switched service and after the circuit-switched call is completed, the channel is free and is reassigned to the packet radio service.

The base station system keeps the mobile station informed of the division of the radio transmission range, ie it sends information to the mobile station as to which channels are in use for which service (ie it transmits information relating to so-called channel configurations).

The checking of the transmission capacity and the cancellation of a channel assignment between packet radio and circuit-switched services, as they are carried out according to the invention, can especially in the case of a handover, ie when a mobile station from one zone to another, in the z. B. all channels for packet radio service are in use, may be required. In this case, the transmission scope check and the channel reassignment as described above are preferably carried out after the base station system has received a handover request from the mobile station and before the base station system transmits a handover request confirmation to the mobile station. In other respects, the handover procedure is laid down in the specifications of the mobile system and is therefore known to the person skilled in the art, which is why it does not have to be described in more detail here.

Example 2

As another alternative, the following situation is examined. A certain minimum level of service is required in a zone. For example, a time slot could always be reserved for packet radio service. The other time slots are used for circuit-switched services or they are free. The base transceiver stations measure the amount of traffic on the packet radio channel. Before use, the channel allocation behavior in a zone must be carefully examined, e.g. B. on the basis of traffic measurements for the relevant zone or on the basis of historical data such as are obtained from corresponding zones located elsewhere. When a channel is used, there is a certain percentage limit, and when a usage ratio exceeds this, the channel is overloaded and the level of service falls. When the utilization ratio of a channel reaches this value, another time slot must be reserved for the traffic. This can be applied to as many as eight timeslots within a GSM carrier wave and even to multiple carrier waves.

If the utilization ratio of a channel falls and reaches another, lower level, the assignment of one of the time slots in use for packet radio can be canceled.

The algorithm according to this second alternative gives the packet radio service higher priority, and circuit-switched services can use the transmission volume that is not required by the packet radio services.

AT 41 0 049 B

The determination of the threshold values ​​can be based on a long-term tracking of the traffic. Alternatively, a change can be made in that the threshold values ​​are regularly updated by using measurement results as obtained within a specified period of time in the past.

Example 3

The following case is discussed as a further alternative. A certain level of service, which can be quite low, is always offered in a zone. A mobile station can issue a request to the channel control block for a few timeslots, one or more. Based on this request, the base transceiver station assigns multiple time slots to the packet radio service. A channel must be assigned to the mobile station very quickly. In this case, additional channels cannot be reserved immediately. The mobile station receives the basic channel. During an assignment request for the following packet, the network has sufficient time to assign several channels to the packet radio service. Accordingly, the mobile station can immediately receive the additional transmission volume requested by it, that is, a plurality of time slots for the transmission.

Example 4

Another alternative is discussed below. In rural areas the allocation of even a single time slot or part of a time slot for packet radio services can be excessive, e.g. B. in an area where there is only one mobile station that transmits data once a week. In this case, there is no need to reserve a basic scope for packet radio services in the cell.

When the mobile station needs to transmit packet data, it transmits a message to the network for this purpose. Since free packet radio channels are now available, the message can be transmitted on conventional signaling channels such as those used for circuit-switched services. The message can also be transmitted on other signaling channels, traffic channels or as a short message output.

Example 5

Examples 1 and 2 above can be used in combination to ensure that circuit-switched services and packet radio services make fair use of channel transmission scope. This means that a certain amount of channel transmission is assigned to the use by both services according to a semi-fixed principle and use the services of other channels using a combination of the algorithms of Examples 1 and 2 in such a way that congestion situations with regard to packet radio services are under control. The base transceiver station transmits information to the mobile stations via control channels so that they can compete for the channels and also prevent access to the network by mobile stations using low priority packet radio services until more channels are available.