A method for indicating a multi-slot channel in a TDMA radio-system

The invention relates to a method for identifying a channel with a plurality of time slots in a TDMA (Time Division Multiple Access) radio system, in which the radio channel normally consists of a time slot in frames which consist of several consecutive time slots.

In TDMA radio systems, like many current small-area digital mobile radio communication systems, the radio channel is normally assigned to a time slot in frames which are transmitted at radio frequency and which consist of several consecutive time slots. Current TDMA mobile communication systems and their radio terminals are designed so that traffic channels and control channels of various types can be formed in them. E.g. In a GSM system, channels of different types such as a traffic channel and an associated control channel can share in the capacity of the same time slot. Some systems already allow the simultaneous assignment of more than one channel. The GSM system also allows two traffic channels to be assigned simultaneously at half rate. As new services have developed, it has been found that, in order to achieve higher transmission capacity in a radio channel, TDMA radio systems and their radio terminals should preferably be designed so that they allow channels with multiple time slots to be easily established and used. The invention is particularly concerned with achieving this potential improvement.

Document EP-A-0 399 611 discloses a solution to the above mentioned improvement and it describes a system for quickly assigning multiple duplex voice channels to a radio terminal in order to achieve higher data speed in data message transmission from the radio terminal. The basic idea of ​​the system described is that the terminals keep records of the use and quality of the duplex voice channels, and any additional voice channels required are, whenever necessary, allocated directly to a data message transmission on the basis of the data in this record keeping. The radio terminal can also use data supplied by the base station and the system control unit on the availability of the voice channels, and in this context the paging or voice generation message generated by the base station can contain data on the number of duplex voice channels required and / or the number of the proposed channels. However, this system does not basically make it possible to assign successive physical channels. The configuration according to this description is characterized in that special measures are taken to make several voice channels quickly available for fast data transmission. The description only mentions signaling in passing, stating that guidance data on the number of channels required and suggestions for channels to be assigned can be signaled to the radio terminal, the general impression being that there is separate signaling for additional data transmission, deviating from normal Operation, acts. In contrast, it is the purpose of the invention to specifically provide for signaling when assigning a channel with a plurality of time slots, without increasing or complicating the signaling compared to that in normal operation.

The process of creating a channel between a radio terminal in a TDMA radio system and the base station serving it generally requires a large amount of signaling. In the GSM system for which the preferred embodiment of the invention is given, signaling involves transmitting a message or a message element describing the channel to the radio terminal. This message element, which is referred to as the channel description information element in the GSM system, defines the channel parameters such as the channel type and the time slot used. Accordingly, when two traffic channels at half speed (TCH / H) are assigned simultaneously in the GSM system in the above-mentioned case, signaling includes transmitting an information element describing the respective channel to each channel. When a connection is to be established over several time slots, signaling is very inexpedient in that each time slot is assigned separately, as if it were a separate channel.

The invention is based on the object of providing a method for identifying a channel with a plurality of time slots, in which the amount of signaling is not increased compared to that required for describing a channel using a time slot.

This problem is solved by the teaching of the attached claim 1. The core of the method according to the invention is that the required number of consecutive times2

AT 407 318 B slots in a frame is assigned to a channel with several time slots.

The invention is applicable, for example, to a channel description information element relating to channel assignment signaling in the GSM system, the element defining the channel type and the subchannel being replaced by a code in which the first digits identify the channel as a channel with several time slots and the last digits the Specify the number of time slots to be included. Accordingly, the time slot number in the same octet of the information element identifies the first time slot of the channel with several time slots.

The invention is described in detail below with reference to an exemplary embodiment and to FIG. 1 of the accompanying drawings, which is a schematic view of an element of channel description information used in GSM signaling. The message element, which is always present when it is required when signaling to a radio terminal, supplies the parameters for the channel to be set up.

Figure 1 illustrates four 8-bit octets in the information element identified above. Bits # 8 ... 1 are indicated at the top of the figure, and octets 1-4 are indicated at the right edge of the figure. The bits no. 7 ... 1 element formed in octet 1 CDIEI (Channel Description Information Element Identifier = identifier for the channel description information element) is an identifier that informs the radio terminal that the message element concerned, which is contained in the signaling message consisting of optional message elements, is a Is channel description information element. With regard to the exemplary embodiment of the invention described here, an essential part of the information element consists of a second octet in which the CHT element (channel type and TDMA offset) formed by bits no The element TN formed by bits no. 3 ... 1 (timeslot number) identifies the timeslot number. As can be seen from the reproduction of octets 3 and 4, the content of the information element can vary. Octet 3 begins with a training sequence code TSC and its bit no. 5 determines whether frequency hopping is to be used (H = 1) or not (H = 0). If the frequency hopping procedure is to be used, the element ΜΑΙΟ (Mobile Allocation Index Offset), which continues into the following octet, sets the point from which the frequency hopping procedure begins, and the terminating element HSN (Hopping Sequence Number) of octet no 4 indicates the jump sequence number. If frequency hopping is not used, bits no.4 and no.3 are in octet no. 3 to reserve, and the element ARFCN (Absolute Radio Frequency Channel Number), which occupies the end of octet no. 3 and octet no. 4, identifies the radio frequency by indicating its number.

The element CHT formed by bits # 8 ... 4 in octet # 2 is discussed below. A number of examples are given of the meaning of its code and the code used to assign the multi-time slot channel.

Bits

87654

00001 TCH / F + ACCHs

0001T TCH / H + ACCHs

001TT SDCCH / 4 + SACCH / C4 or CBCH (SDCCH / 4)

01TTT SDCCH / 8 + SACCH / C8 or CBCH (SDCCH / 8) nnn channel with several time slots

TCH / F and TCH / H denote a traffic channel at full or half rate, ACCH denotes generally associated control channels, SDCCH denotes an independent control channel, SACCH denotes a slowly allocated control channel and CBCH denotes a cellular radio channel. The bits marked with T identify the binary-coded sub-channel number.

In this embodiment of the invention, the channel with multiple time slots is closed

The beginning of the element CHT is identified by the bit combination 11, which was previously within the

AT 407 318 Β

GSM specification is not assigned to any other purpose. The three remaining bits in the element CHT, which are marked with n above, are used to form a binary code which identifies the number of time slots in the channel with several time slots. Three bits can be used to identify eight different values, which is sufficient to define all possible channels with multiple timeslots in a GSM system where a frame contains eight timeslots.

The exemplary embodiment currently considered to be optimal has been described above with reference to a GSM system. In the case of a GSM system, other embodiments are also conceivable, wherein a channel with a plurality of time slots can be assigned to a radio terminal without the need for additional signaling compared to normal assignment and definition of a channel using a single time slot. The person skilled in the art recognizes that in other radio systems which operate according to the TDMA principle, similar or different embodiments of the method according to the invention for allocating a channel with a plurality of time slots are possible within the scope of the appended claims.