A communication system provides one or more physical transmission channels for transmitting data between a data source and a data sink. The transmission channels may be of a wide variety of types, e.g. for cable-conducted transmission using electrical or optical signals or for radio transmission via a radio interface using electromagnetic waves. The text below concerns radio transmission, in particular.
Radio transmission is used in mobile radio systems in order to set up a connection to nonstationary subscriber terminals. A mobile station in a mobile radio system is such a nonstationary subscriber terminal. Within the network coverage, the mobile station can request a connection from any desired locations, or a connection can be set up to the mobile station. The most common mobile radio system is GSM (global system for mobile communications), which was developed for a single service, for voice transmission purposes. The data rate of this service was assumed to be constant. The GSM mobile radio system is called a 2nd generation system.
By contrast, the successive mobile radio generation, the 3rd mobile radio generation, which is currently being standardized in Europe under the name UMTS (Universal System for Mobile Communications), has provision for a plurality of services, which are to be transmitted within a transmission protocol.
The standardization documents ETSI SMG2/UMTS L23 expert group, Tdoc SMG2 UMTS-23 257/98, dated Oct. 6, 1998, Tdoc SMG2 508/98 and Tdoc SMG2 515/98, dated Nov. 16, 1998, give an overview of the present state of development of standardization and, in particular, an overview of the requirements in terms of how a transmission protocol can support the transport of data for a plurality of services.
The use of a common physical channel for transmitting data for a plurality of services presupposes that a unique mapping specification indicates the allocation of the services to different segments of the physical channel. By way of example, a physical channel is defined by a frequency band, a spread code (CDMA code division multiple access) and, if appropriate, a time slot within a frame.
The following terms are used to describe the mapping specification:
Transport Format (TF):
A transport format defines a data rate, a coding, scrambling (interleaving), a data rate adjustment by puncturing and an error protection specification for a transport channel for a service.
Transport Format Set (TFS):
This denotes a set of possible transport formats which are permitted for a specific service.
Transport Format Combination (TFC):
This term indicates a possible combination of the transport formats for the various services which are mapped onto a common physical channel.
Transport Format Combination Set (TFCS):
This denotes a set of possible TFCs as a subset of all TFCs which are permitted for a specific connection.
Transport Format Combination Identifier (TFCI):
This information item indicates the currently used combination of the transport formats within the TFCs.
Examples relating to the transport formats can be found in ETSI SMG2/UMTS L23 expert group, Tdoc SMG2 UMTS-23 257/98, dated Oct. 6, 1998, pp. 14–16.
In order to be able to select the currently used combination of the transport formats for the various services in line with requirements, the TFC needs to be able to be changed and hence the TFCI needs to be signaled regularly. This signaling ties up transmission capacity, however. The greater the number of possible combination options (TFCS), the more capacity is required for signaling.