Communication system for transmission between ATM network and mobile radio system.

IS 2 157 207 T3

DESCRIPTION

Communication system for transmission between an ATM network and a mobile radio system.

This invention relates to communication systems and, more especially, relates to mobile radio communication systems of the kind in which an asynchronous transfer mode (ATM) network is used to support a mobile communication system. by radio.

The principles of ATM operation are well known to those skilled in the art and are described in Patent Application GB-A2268359, published on 01.05.94, which should be consulted in this case.

In European Patent Application No. 0 426 269 A1, published on 05.08.91, a system for mobile communications is described having a plurality of base stations and users. Each base station has an associated interface unit that organizes the voice information into packets and includes header information regarding user addresses and destinations. The movement of the various users is tracked by the interface units passing control blocks between interface units. The information stored within the base station interfaces allows user movement between base stations without loss of communication.

In ATM systems, data is transmitted over a network in small packets or cells, each of which consists of 48 octets of user significant data (known as the information field) and 5 octets of network significant data (known as header). The term "significant user data", when used in this specification, is intended to include any type of information that passes through the network and includes voice and / or signaling. The header of an ATM cell contains a plurality of fields as follows. Two fields comprise the Virtual Path Identifier (VPI) and the Virtual Channel Identifier (VCI) which are used to route cells through the ATM network. Therefore, the combination of the VPI and VCI fields defines each interface connection identity. Another field comprises header error control (HEC) data that is used to detect and correct errors in the header. Another field contains Generic Flow Control (GFC) data that is used to control user access and is not used within the network. Other fields include the useful load type indicator data (PTI) and the cell loss priority data (CLP) that are important for the transmission of data through an ATM network.

It was understood that, to pass ATM cells from a fixed ATM network to a mobile terminal through a radio network, measures must be taken for the transmission of at least part of the header data as well as the information field. One method of transporting ATM cells over a radio interface between a fixed ATM network and a mobile cellular radio terminal is to transport the entire 53-byte cell. However, as it was understood, this circumstance imposes a great load of headend information on the mobile radio system, which from now on will be called consumed resource. This total consumed resource occupies approximately 10% of the available bandwidth that could be used in a more productive way to allow more mobile users to be accommodated by the system.

Consequently, an object of the present invention is to provide a communication system that includes an interface between a fixed ATM network and a mobile radio system in which the resource consumed is reduced.

According to one aspect of the present invention, a communication system is provided for data transmission from an ATM network to a mobile radio system that comprises an interface device coupled between them, which is operative to suppress the header of each cell. of ATM that enters the referred system from the network, VPI and VCI data; a translator device that responds to the VPI and VCI data to properly encode the data so that the code corresponds to a CDMA code or, as a variant, the code corresponds to a TDMA timing system, said code comprising the rest of each cell from which the aforementioned VPI and VCI data has been suppressed, so the translation device is available to correlate the VPI and VCI data either to the appropriate CDMA code or, as a variant, to an appropriate interval or intervals of a TDMA system, and further comprising a second translator device that responds to codes belonging to user addresses and arranged to correlate the CDMA code or, as a variant, the interval or intervals of the TDMA system to produce the corresponding VPI and VCI data, and means to recombine this VPI and VCI data with data comprising the remainder of the cell from which it had been deleted, to thereby produce complete cells suitable for transmission from said system to a mobile terminal.

It will be understood that, for the transmission of data in the opposite direction, (that is, in the "uplink") a similar process will take place.

To further reduce resource consumption at the start, other fields can be removed from the header and used to form the basis for adaptation of the rest of the cell before being transmitted to the mobile radio system, carrying out an appropriate reconstitution process. to reintroduce fields, whereby the ATM cells are sufficiently reconstituted before being reintroduced into the ATM system.

For example, the HEC and GFC header fields can be removed from each cell along with the VPI and VCI fields to produce both an information field and a truncated header, which are transmitted through the mobile radio system using an indicated code. by the VPI / VCI data, the fields being reconstituted to produce a complete cell with the appropriate header information before being transmitted through the ATM system.

Some embodiments of the invention were described below, by way of example only, taking as reference the drawings ad2

ES 2 157 207 T3 together, in which:

Figure 1 is a block diagram, somewhat schematic, of a communication system according to an embodiment of the invention, and in which:

Figure 2 is a block diagram, somewhat schematic, of a communication system according to an alternative embodiment of the invention.

Referring now to Figure 1, the communication system comprises a mobile radio system, represented within a dashed line 1, which comprises a transmitter 2 that was in communication with a plurality of mobile units, and a receiver 3 that was in communication. with a plurality of transmitters, not illustrated. The cells, coming from an ATM network, are fed by a line 4 to a unit 5 that serves to suppress VPI and VCI data fields from the headend. The information field and the residual head of each cell are then fed, by line 6, to the radio transmitting equipment 2. The data from the VPI and VCI fields is fed from unit 5, by line 7, to a Translator 8 used to transfer the data from the VPI and VCI fields to the corresponding CDMA code data that is fed, by a line 9, to the transmitter equipment 2.

The rest of each cell, which comprises the information field and the residual header, from which the VPI and VCI data have been suppressed, is transmitted to an appropriate address to a module, as indicated by the VPI and VCI data. .

Rather, the signals received within the mobile radio system at the receiving equipment 3 are translated into a second porter 10 to produce VPI and VCI codes corresponding to the CDMA code used in the system. This VPI and VCI data is then combined in a unit 11 with the rest of the appropriate cell, so that it can be transmitted, over a line 12, to the mobile terminal.

Therefore, it was understood that a significant reduction in resource consumption was achieved by correlating the ATM header connection information (VPI + VCI) in the CDMA code used for the radio path. In practice, when the connection is established, or when a mobile is affiliated with a new cell, the fixed part of the network, characteristically the base station, assigns the CDMA code that must be used for that connection within a cell. particular radio cell. Subsequently, all ATM cells, transmitted on the connection, are carried out in the specified CDMA code. If more than one connection was required between a particular mobile and a base station, a separate CDMA code was assigned for each additional connection.

In the operation of the system previously described in relation to figure 1, each cell of the ATM cell flow in line 4 consists of a 48-byte information field plus a 5-byte header and conforms to the relevant standards. of CCITT. The VPI and VCI fields are removed from the header and the residual header, plus the information field, is sent to the radio equipment. At the same time, the VPI and VCI values ​​are translated into the CDMA code value to be used by the radio interface and this code value is also sent to the radio equipment. The radio equipment then uses the code required to transmit the residual header of the information field of the ATM cell over the radio paths, as described above in connection with the drawings. At the receiver, the reverse process is applied: the value of the CDMA code, used for transmission, is transferred to the corresponding VPI / VCI combination that is added to the information received by the radio interface to reconstitute the original ATM cell. .

Additional resource consumption savings can be achieved by making use of the error detection and correction capabilities of a digital radio system. AND^orThese generally provide a more powerful error control device than what can be provided by the HEC. Therefore, the HEC field is not required on the radio interface and can be suppressed. Furthermore, since the GFC is only important in the user interface without appropriate terminal equipment, it is not necessary to transmit it over the radio interface. Therefore, it is only essential to transmit the PTI and CLP fields over the radio path.

Referring now to figure 2, an improved communication system will be described below, in which the parts corresponding to figure 1 bear the same numerical indications. In general, an ATM cell flow contained empty filler cells and it is assumed that these were suppressed prior to the process carried out in the arrangement described below with reference to Figure 2. However, for each cell that is not empty, the following operations are carried out. In transmitter 2, the HEC and GFC fields are suppressed by a unit 13 and the VPI and VCI fields are translated to provide a CDMA code that is used for the transmission of the rest of the cell, that is, the field of information and a truncated header.

At receiver 3 a VPI and VIC portion of the header is reconstructed, the GFC field is given a default value, and the HEC field is recalculated before reconstituting the outgoing stream. The ATM cells in the outflow are arranged to conform to the appropriate CCITT standards. Those skilled in the art will appreciate that empty cells are properly reinserted to ensure that there is a continuous flow of cells at the exit interface.

Although the invention has been illustrated with respect to a CDMA radio access technique, it is understood that it generally has application to other radio access techniques, such as, for example, time-division multiple access (TDMA). Using TDMA, once a slot (or a plurality of slots) has been assigned to be used for a particular connection, a correlation similar to that described with respect to Figures 1 and 2 above can be performed. However, instead of correlating CDMA codes, the correlation

ES 2 157 207 T3 corresponds to appropriate ranges.

It will be understood that an important advantage of the systems according to the present invention is that a significant reduction is achieved in the amount of data that must be transmitted over a radio interface with each ATM cell. Using VPI / VCI to CDMA code mapping will reduce resource consumption from about 10% to about 5%. The introduction of additional savings may have applications to reduce even more the consumption of the resource up to approximately 1%. These improvements will add considerably to the efficiency of the radio system operation and will facilitate the inclusion of more mobile users.