EP0934674A1

EP0934674A1 - Method and format conversion device for continuous format conversion of atm cells with user information into message blocks of a radio interface of a digital radio network

Info

Publication number: EP0934674A1
Application number: EP97910249A
Authority: EP
Inventors: Thomas Zimmermann
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1996-10-24
Filing date: 1997-10-02
Publication date: 1999-08-11
Also published as: KR20000052760A; WO1998018284A1; JP2001502507A

Abstract

A method for continuous format conversion of ATM cells with user information into message blocks of a radio interface of a digital radio network with mobile or stationary subscribers linked by radio. Within the message blocks, control blocks with a fixed amount of bits for addressing and control of user data blocks are provided, the message blocks are subdivided into a sufficiently fine sub-frame, and starting times of the user data blocks within a message block are specified in the control blocks. Alternatively, fixed starting times of the user data blocks are specified.

Description

description

Method and format conversion device for the continuous format conversion of ATM cells with useful information in radio blocks of a radio interface of a digital radio network

The invention relates to a method and a format conversion device for the continuous format conversion of ATM (Asynchronous Transfer Mode) cells with useful information in radio blocks of a radio interface of a digital radio network.

As known from R.Händel, "Evolution of the Networks with ATM", telcom report 17 (1994), No. 1, pp. 8-11, future broadband networks, such as broadband ISDN, will be based on the ATM principle. A number of new services will be possible in these networks.

The currently existing mobile radio systems such as GSM (Global System for Mobile Communications) are not designed for ATM traffic. The DECT (Digital European Cordless Telephone) wireless telephony system has not previously been intended for broadband ATM traffic, but rather has been designed for a wireless subscriber connection for voice transmission mainly for use in rooms.

The invention is based on the object of specifying a conversion method with which ATM cells can be transmitted to mobile or radio-connected stationary subscribers with the best possible use of the radio blocks defined in the radio interface.

According to the invention, this object is achieved by the method according to the features of claim 1 or 3 and the format conversion device according to the features of claim 15 solved. Further developments of the invention result from the subclaims.

According to one embodiment of the invention, there is a continuous format conversion of ATM cells with useful information into radio blocks of a radio interface of a digital radio network with mobile or stationary subscribers connected via radio by transmitting user data blocks within the radio blocks, organization blocks with a fixed amount in the radio blocks of bits for addressing and

Organization of user data blocks are provided, the radio blocks are subdivided into a sufficiently fine sub-grid, and start times of the user data blocks within a radio block are defined in the organization blocks.

By defining the start times for the user data blocks within a radio block, a flexible utilization of the bit rate of the radio system is possible. The sub-grid - defined by bit positions, defined fractions of bit positions or multiples of bit positions - makes it possible to keep dead times of the user data blocks within a radio block to a minimum.

According to an advantageous embodiment, a fixed number of bits of the respective user data block is assigned

Organizational channel operated via which all data required for the implementation of ATM cells are exchanged during the connection. This enables easy-to-use in-band signaling.

An alternative method according to the invention for the continuous format conversion of ATM cells into radio blocks provides to create useful data blocks for the transmission of the useful information within the radio blocks and to fix fixed start times of the useful data blocks. Due to the fixed start times of the user data blocks, the signaling effort reduced. One or more possible start times can be specified.

It is advantageous to offer several types of radio blocks with different bit rates for the ATM cells within the radio system. For example, a radio block type is used for information transmission if the bit rate of the user data block is greater than or equal to the bit rate of the ATM cells. Alternatively, a radio block type with the next higher permissible bit rate is used for transmission if the bit rate of the user data blocks of a traffic relationship is lower than the bit rate of the ATM cells.

According to a further advantageous embodiment, the user data blocks are only partially filled with user information of the ATM cells if the bit rate of the user data blocks of a traffic relationship is greater than the bit rate of the ATM cells.

Furthermore, it is possible to combine several radio blocks into a user channel if the bit rate of the user data blocks of a traffic relationship is lower than the bit rate of the ATM cells. The bit rate available to the subscriber is thus increased in accordance with the requirements of the AT transmission. Several radio blocks are combined by multiplexing into one channel, by occupying several radio blocks in a TDMA (time division multiple access) system, by several parallel channels of the same frequency in a CDMA (code division multiple access) system or by several parallel channels of different types Frequency in a FDMA (frequency division multiple access) system.

In order to make new services, such as voice transmission, data services and information services, usable for mobile terminals, according to a development of the invention, ATM cells are transmitted via an ISDN or broadband ISDN transmission system and are fed to a base station for the radio system. The invention is explained in more detail below on the basis of exemplary embodiments.

The mobile communication system shown in FIG. 1 is a radio network based on the known GSM mobile radio system, which consists of a multiplicity of mobile switching centers MSC which are networked with one another or which provide access to a fixed network or other network PSTN. Furthermore, these mobile switching centers MSC are each connected to at least one base station controller BSC. Each base station controller BSC in turn enables a connection to at least one base station BS. Such a base station BS is a radio station which can set up a communication link to mobile stations MS via a radio interface. Such a radio connection to a mobile station MS is shown as an example in FIG.

The radio interface between base station BS and mobile station MS is organized according to the time-division multiplex method. For example, eight time slots are provided on a carrier frequency, which can be used for different communication connections and for organizing the radio interface. If a base station also provides several carrier frequencies, there is also a frequency division multiplex.

According to the invention, a format conversion of ATM cells transmitted by the fixed network PSTN into the radio blocks of the radio interface is to take place. This conversion takes place in a format conversion device FU, which is assigned to the base station controller BSC. The format conversion device FU can alternatively also be implemented in a mobile switching center MSC or in an independent coding conversion device. The technical implementation of such format conversion devices FU are known to the person skilled in the art from the corresponding specialist literature. The method according to the invention for converting the format of ATM cells with useful information into radio blocks of a radio interface for future mobile radio standards such as FPLMTS (Future Public Land Mobile Telecommunications System) and UMTS (Universal Mobile Telecommunications System) is particularly relevant. These planned systems can be designed in accordance with the radio network according to FIG. 1, as shown below, in order to handle ATM traffic. It is also envisaged to enable the transmission of ATM cells with bit rates up to 2 Mbit / s in so-called wireless access networks (AN), that is, the subscriber connection to a stationary subscriber via a radio interface that uses, for example, a CDMA radio transmission method.

The structure of these digital radio networks is in J.Oudelaar, "Evolution toward UMTS", PIMRC 94, 5th IEEE International Symp. On Personal, Indoor and Mobile Radio Communications, The Hague, NL, September 18-22, 1994, p.852 -856, and

M.Lenti, H. Hageman "Paging in UMTS", RACE Mobile Telecommunication Workshop, Vol. 1, Amsterdam, NL, May 17-19, 1994, pp. 405-410. The radio transmission takes place between a stationary base station and a mobile station or a second base station instead.

The most important criterion for assessing the transmission quality of a radio channel is the bit error rate BER as a function of the signal-to-noise ratio S / N. A specific signal-to-noise ratio is required for a specific bit error rate BER and vice versa. In order not to exceed a certain bit error rate, the signal-to-noise ratio must not fall below a certain value. In order to reduce the bit error rate for a given signal-to-noise ratio, error-reducing and automatically controlled repetition methods, the so-called called automatic repetition request procedure = ARQ procedure.

A known technique for reducing the bit error rate is represented by error correction methods (FEC = Forward Error Correction). Convolutional coding methods with a bit rate increase of approximately 1: 2 are typically used in this field in mobile radio.

The transmission signals from the mobile station and base station in a mobile radio network are typically divided into defined structures of radio blocks (AIP = Air Interface Packet) according to the design of the radio interface. This also applies to the existing GSM and DECT mobile radio systems, which as TDMA systems handle several connections on one RF carrier. This means that other connections are processed between the radio blocks of a traffic relationship and thus pauses occur between the radio blocks of a traffic relationship which depend on the number of total connections per carrier. Other systems use CDMA methods, in which many traffic relationships with spread signals are transmitted simultaneously and without gaps in a continuous sequence and without pauses. The uncoded basic scheme of the radio block structure is the same for both types of transmission.

A radio block AIP with the duration T _AIP consists of three parts: the user data block N _PLD , which contains the data to be transmitted (user information - for example voice information) and possibly an organizational block, the preamble T3 _mR , the

Contains synchronization and control data, and the remaining block ^N _TAIL I which is provided for error protection (FEC) and possibly for the TDMA method at least partially for signalless switching times (eg switching the transmitter on and off, time reserve and protection time). Furthermore, two types of AIP radio blocks are now to be considered, which are provided for example in an AN concept:

Type 1: All AIP radio blocks have the same length of time, eg T _AIP = 5 ms. The preamble is 6 bits long and the remaining block is zero. The difference between possible AIP radio blocks is that the number of bits that make up the user data block (information part) depends on the bit rate of the service to be transmitted, see Table 1.

Type 2: All AIP radio blocks have the same number of bits, e.g. 160 useful bits, a preamble of 15 bits and a remaining block of 6 bits. They differ in their duration, see Table 2, according to the bit rates of the participants to be transmitted. It should be noted that to implement an ISDN connection, it is necessary to combine two channels with 64 Kbit / s each and one channel with 16 Kbit / s by multiplexing.

There are two types of ATM cells, a normal and a shortened ATM cell. In order to transmit shortened ATM cells via radio interfaces, it is expedient, as is known from European Patent EP 0 616 480, to transmit only 16 bits = 2 bytes of the ATM preamble. Therefore, the shortened ATM cell consists of a total of 400 bits (48 + 2 = 50 bytes) instead of 424 bits (53 bytes) for the normal ATM cell.

In order to transmit ATM cells via radio interfaces, the block formats must be converted. One possibility according to the invention is the cell division of the ATM cells.

When using the ATM cell division, the shortened ATM cells are divided into parts of equal size and distributed evenly over the radio blocks AIP. Tables 6 and 7 show the Properties for the previously discussed two groups of AIP radio blocks. For the first group of radio blocks AIP with the same duration and for example 360 bit useful information, a shortened ATM cell with a length of 50 bytes = 400 bits, as shown in FIG. 2, is divided into two parts of 200 bits each and each Part of a radio block assigned to AIP. This means that only 200 of the 360 available bits can be used for each AIP radio block, resulting in a 44.4% share of empty bits.

For the second group of radio blocks AIP with the same number of 160 useful bits, for example, three radio blocks AIP with a transmission capacity of 480 bits are required for a shortened ATM cell of 400 bits. The empty bit content is now 1 - 400/480 = 0.167 or 16.7%. The other properties are shown in Table 7.

Due to the fact that the radio blocks AIP currently defined in radio interfaces only partially fit to shortened ATM cells according to their size, the cell division scheme is less efficient in these cases.

The implementation of the format of ATM cells in AIP radio blocks should in principle be carried out continuously and as quickly as possible. If e.g. If the useful bit rate of the radio subscriber is the same as the useful bit rate of the ATM subscriber, the radio blocks AIP are completely filled. If not, the radio blocks AIP are only partially filled, depending on the data rate and the start times of the ATM cells. In order to find the start time of a shortened ATM cell in a radio block AIP, additional information must be transmitted within the radio block AIP.

Two groups of AIP radio blocks are now considered. Table 3 shows the various parameters of the first group of AIP radio blocks, which have the same length of time and were presented in Table 1. The second column shows the start information of the shortened radio block AIP inserted in the user information. For example, to address a position within 180 bits, an 8 bit address is required. This means that 4.4% of the transmission capacity has been allocated for this purpose and only 172 bits can be used within 5 ms for the transmission of ATM data in the user data block. This results in a maximum ATM bit rate that can be transmitted via the radio path of 172 bits / 5 ms = 34.4 Kbit / s. However, the maximum permissible ATM subscriber bit rate is already reduced again by the factor 48: (48 + 2) bytes = 384: 400 bits = 0.96 without the use of ARQ for the transmission of shortened ATM cells. In this case it is 33,024 Kbit / s and is listed in Table 3, last column.

Table 4 shows various parameters of the second group of radio blocks AIP, which have an equal number of bits and were presented in Table 2. In order to address a position within the user information, an address of 8 bits is required. This means that 5% of the transmission capacity has to be used for addressing. As a result, only 152 bits can be used for the transmission of ATM data; at an ATM bit rate of 3.8 Kbit / s. This requires an AIP radio block with a duration of 152 bits / 3.8 kbps = 40 ms. Here, too, is the maximum allowable

ATM subscriber bit rate for the transmission of shortened ATM cells without the use of ARQ reduced by the factor 0.96 to 3.648 Kbit / s and listed in the last column of Table 4.

For an unrestricted implementation scheme for ATM cells in radio blocks AIP of any radio interfaces, according to one embodiment of the invention, a sub-grid is used within the user data block (information part) of the radio blocks to perceive any start times. The format conversion of the ATM cells into the structures of the radio blocks AIP thus takes place without a time delay. A fixed amount of bits per AIP radio block is used for addressing and organizing the format conversion.

When using an unrestricted implementation scheme, each radio block AIP has in its information part a fixed, temporal sub-grid of positions at which a shortened ATM cell can begin. This sub-grid always starts at the beginning of an information section. Since only multiples of this sub-grid can be used to start a data transfer, a sufficiently fine-grained sub-grid is required.

In order to find the beginning of a shortened ATM cell in data detection, less addressing effort is required than in the continuous conversion scheme described above. However, a few bits per radio block are required to continuously identify the sub-grid positions. During the transmission, a minimal signal delay in the size of an element of the sub-grid must be accepted for reasons of the intermediate storage which is necessary in principle.

When using a grid length of 8 bits for the first group of radio blocks AIP, the parameters are created, which are set out in Table 5. For a user data block of 180 bits, for example, a 5 bit address is required for the continuous identification of the sub-grid. 175 bits are thus available for the user information. The largest number that can be divided by 8 bits = 1 byte among the number 175 (= 180 available bits - 5 addressing bits) is the number 168, which has a difference of 175 - 168 = 7 empty bits. Compared to the continuous implementation scheme described above, the properties of this unrestricted implementation scheme are more favorable for the last three types with a useful information of 360, 720 and 1440 bits. If you apply the unrestricted conversion method with a sub-grid size of 8 bits to the radio blocks AIP shown in Table 2 with a constant number of bits, 3 bits with an address of 5 bits, i.e. a total of 8 bits, result in a useful information of 160 bits. Since this is again 5% of the useful information, in this example the properties are the same compared to the continuous conversion process.

Basically, the unrestricted implementation method has the advantage that the ATM cells arriving from the ISDN network in the radio network are only inserted into the radio transmission protocol with a delay of up to 8 bits.

According to the invention, it is further proposed to use a fixed number of bits of the user data block as the assigned organizational channel for the transmission of all data accompanying the connection.

For the first group of radio blocks AIP with the same duration T _AIP , a sub-block of, for example, 20 bits per radio block for each radio block type can be introduced as an assigned organization channel for the organization of the format conversion. The effective bit rate of this organizational channel is 20 Bit / 5 ms = 4 Kbit / s based on the assumptions made. Table 8 shows the properties for this example.

By using the implementation with a permanently assigned organizational channel, the properties in Table 8 are only marginally less favorable than with continuous implementation in Table 3. However, there is a clear subdivision into useful information and organizational information, which proves to be very advantageous when handling the format implementation.

The unrestricted implementation method for ATM cells in radio blocks has the following advantageous properties: If the subscriber bit rate of the radio subscriber is less than or equal to the permissible ATM bit rate of one of the available radio block types, this radio block type is used. In this case, the radio blocks are filled with shortened ATM cells, as described above.

If the ATM subscriber bit rate is lower than the permissible ATM bit rate of the lowest available radio block type, the radio blocks are only partially filled with useful information, depending on the data rate of the ATM cells.

When the ATM subscriber bit rate exceeds the allowable bit rate of a radio block type, the radio block type with the next higher allowable ATM bit rate is used for transmission.

If the required transmission rate is higher than the maximum bit rate that can be transmitted in the radio blocks, several types of radio blocks can be combined to form a useful channel in order to realize higher transmission rates. This can be done either by multiplexing in one channel, by occupying several radio blocks in a TDMA system, by several parallel channels of the same frequency in a CDMA system or by several parallel channels of different frequencies in an FDMA system.

Table 1

Table 2

Table 3

Table 5

Table 6

Table 7

Claims

claims

1. Method for continuous format conversion of ATM cells with useful information in radio blocks (AIP) of a radio interface of a digital radio network with participants connected via radio, where

- User data blocks (N _PLD ) are transmitted within the radio blocks (AIP), - Organization blocks (N _HDR ) are provided in the radio blocks (AIP) with a fixed amount of bits for addressing and organizing the user data blocks (N _PLD ), and

- The radio blocks (AIP) are subdivided into a sufficiently fine sub-grid, in which start times of the user data blocks (N _PLD ) within a radio block (AIP) are defined in the organizational blocks (N _HDR ).

2. The method according to claim 1, in which a fixed number of bits of the respective user data block (N _PLD ) is operated as an assigned organizational channel, via which all data required for converting ATM cells are exchanged during the connection.

3. Method for the continuous format conversion of ATM cells with user information in radio blocks (AIP) of a radio interface of a digital radio network with subscribers connected via radio, user data blocks (N _PLD ) for transmitting the user information being provided within the radio blocks (AIP), and fixed starting times the user data blocks (N _PD ) are defined.

4. The method according to claim 3, wherein the user data blocks (N _PLD ) of the radio blocks (AIP) are divided into a sufficiently fine sub-grid, and Starting times of the user data blocks (N _PLD ) within a radio block (AIP) can be defined.

5. The method according to any one of the preceding claims, in which several radio block types are offered with different bit rates for the ATM cells.

6. The method according to claim 5, in which a radio block type is used for data transmission if the bit rate of the user data blocks (N _PLD ) of a traffic relationship is greater than or equal to the bit rate of the ATM cells.

7. The method according to claim 5, in which a radio block type with the next higher permissible bit rate is used for transmission if the bit rate of the user data blocks (N _PLD ) of a traffic relationship is smaller than the bit rate of the ATM cells.

8. The method according to claim 5, wherein the user data blocks (N _PLD ) are only partially filled with user information of the ATM cells if the bit rate of the user data blocks (N _PLD ) of a traffic relationship is greater than the bit rate of the ATM cells.

9. The method according to claim 5, in which a plurality of radio blocks (AIP) are combined to form a user channel if the bit rate of the user data block (N _PLD ) is lower than the bit rate of the ATM cells.

10. The method according to claim 9, wherein the combination is carried out by multiplexing into one channel.

11. The method according to claim 9, wherein the combination is carried out by occupying several radio blocks (AIP) in a TDMA system.

12. The method according to claim 9, wherein the combination is carried out by several parallel channels of the same frequency in a CDMA system.

13. The method according to claim 9, wherein the combination is carried out by several parallel channels of different frequencies in an FDMA system.

14. The method according to any one of the preceding claims, in which the ATM cells are transmitted by an ISDN or broadband ISDN transmission system.

15. Format conversion device (FU) for the format conversion of ATM cells with useful information in radio blocks (AIP) of a radio interface of a digital radio network with subscribers connected via radio, with user data blocks (N _PLD ) being transmitted within the radio blocks (AIP), and the format conversion device (FU) is designed such that - organization blocks (N _HDR ) are provided in the radio blocks (AIP) with a fixed amount of bits for addressing and organizing the user data blocks (N _PD ), - that the radio blocks (AIP) are sufficient sub-grid are divided, - that start times of the user data blocks (N _PLD ) within a radio block (AIP) are defined in the organizational blocks (N _HDR ).