Abstract:
The present invention relates generally to the field of signaling of information, and particularly to a method and a system for signaling information in transmission systems. 
     Methods for signaling information in transmission systems do have certain disadvantages, like the use of an additional channel for signaling or the use of a large number of bits for signaling. 
     The present invention facilitates highly protected and highly reliable signaling requiring only a minimum of bits by inserting an individual signaling information into individual frames and by additionally partitioning signaling information and inserting the partitioned signaling information into different frames, i. e. spreading the signaling information.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority of European Patent Application No. 98305811.6, which was filed on Jul. 21, 1998. 
   TECHNICAL FIELD 
   The present invention relates generally to the field of signaling of information, and particularly to a method and a system for signaling information in transmission systems. 
   BACKGROUND OF THE INVENTION 
   In transmission systems like radio networks, e. g. digital cellular radio networks according to the GSM-standard (Global System for Mobile communications), not only user data, e. g. encoded speech signals, are transmitted but also various information necessary for the operation of the network. The transmission of these information often is referred to as signaling. Signaling messages allow the fixed part of the network to discuss management of several issues either related to the user, e. g. call in progress indications, or concerning technical aspects of the communication, e. g. preparation and execution of a handover, with the mobile part of the network. The establishment and the release of a call also require signaling exchanges. In addition, signaling exchanges are even needed in cellular radio networks between fixed components of the network and mobile stations when no communication or call is in progress. 
   In order to transmit signaling information in parallel with the transmission of a user data flow, GSM offers two possibilities. Each traffic channel (TCH) for transporting the user data has an associated low rate channel, used for the transport of signaling called slow associated control channel (SACCH). It is used for non-urgent procedures, mainly the transmission of the radio measurement data needed for the decisions concerning handover. Other needs of associated signaling, e. g. authentication or the command to handover, make use of the TCH itself, called fast associated signaling. For fast associated signaling a so called stealing flag is used, which indicates that a part of the information or data contained in the indicated TCH frame contains signaling information. The stealing flag indicates that either the first half or the complete TCH frame contains signaling information. 
   The known methods for signaling information in a radio network do have certain disadvantages, like the use of an additional channel, e.g. the SACCH channel. It is another disadvantage, that if the traffic channel itself is used, at least half of the bits of each TCH frame are used for signaling and therefore are no longer available for the transmission of user data. It is a further disadvantage that signaling information being transmitted within one frame is susceptible to errors being caused by bad transmission conditions. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide a method for signaling of information. It is the aim of the inventive method under consideration to avoid the drawbacks known from the state of the art. 
   The object is achieved by providing a method for signaling of information in a frame based transmission system, whereat the signaling information contains information necessary for the operation of the transmission system, having steps of inserting signaling information related to individual frames into said individual frames, and 
   partitioning signaling information and inserting said partitioned signaling information into different frames. 
   It is an other object of the present invention to provide a system for signaling of information. It is the aim of the inventive system under consideration to avoid the drawbacks known from the state of the art. 
   The object is achieved by providing a frame based transmission system for signaling of information, whereat the signaling information contains information necessary for the operation of the transmission system, having means for coding and decoding of data, means for handling the coded data in frame format, and means for transmitting and receiving the frames, characterized by 
   means for inserting and evaluating signaling information into and from individual frames related to said individual frames, and 
   means for partitioning signaling information and inserting and evaluating said partitioned information into and from different frames 
   It is advantage of the present invention, that if facilitates highly protected and highly reliable signaling requiring only a minimum of bits. It is another advantage of the present invention, that it easily allows the detection of the signaling bits as the synchronization already available from the transmission system and the frame structure of the transmission system is used for the signaling information. 
   The present invention will become more fully understood from the detailed description given hereinafter and further scope of applicability of the present invention will become apparent. However, it should be understood that the detailed description is given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The following detailed description is accompanied by drawings of which 
       FIG. 1  represents a data structure for signaling information according to this invention, 
       FIG. 2  represents a signaling example according to the data structure of  FIG. 1  in greater detail, and 
       FIG. 3  represents a schematic diagram of a system for signaling information according to this invention. 
   

   DETAILED DESCRIPTION 
   Following, the inventive method and system for signaling of information are explained with reference to a cellular radio network according to the GSM standard. However, it should be understood, that the present invention also is applicable to other transmission systems. The GSM standard is well known, see e.g., “The GSM System for Mobile Communications”, M. Mouly, M.-B. Pautet, Palaiseau, 1992, ISBN 2-9507190-0-7, which is incorporated by reference herein. 
   The information which is signaled characterizes different codec modes for coding and decoding source coded user data, i. e. speech, in this example and will be referenced as adaptive multi-rate coding (AMR). The AMR principle is used for modeling a transmission system that shows graceful degradation in case of deteriorated transmission conditions. If the transmission conditions deteriorate the bit rate used for transmission of source coded user data, e. g. speech, is decreased and the bit rate used for channel coding, i. e. the protection of the user data, is increased. Several AMR modes can be used, depending on the deterioration of the transmission conditions. In the moment there are defined four modes plus two additional modes for expansion. Greater detail of AMR can be found in “Adaptive Multi-Raten Sprachcodierung für zukünftige GSM-Systeme”, Karl Hellwig, ITG-Fachtagung 3.-5. March 1998, Aachen, ITG-Fachbericht 146, pages 173-176, which is incorporated by reference herein. Other signaling aspects of AMR, e. g. signaling for the selection of one of the available channel types, half rate or full rate, will not be explained in the following, as these aspects are not relevant for the understanding of the present invention. 
     FIG. 1  shows data structure for signaling information according to the present invention, especially information on the AMR coding mode called coding mode in the following. The structure shown represents the signaling from the fixed part of the radio network to the mobile part, i.e. data are transmitted from the fixed part to the mobile part. User date, i.e. speech, is being source coded in a speech coding step  101  using one mode of available modes for speech coding according to the selected coding mode. By example, six different coding modes can be used. In this case three bits are necessary for coding the six different coding modes. When the transmission is started the pre-selected coding mode can be the coding mode offering the lowest bit rate for speech. The coding mode can be changed if necessary as will be explained later. According to the selected coding mode the speech coded data from step  101  is channel coded together with at least one additional bit derived from a multi-frame signaling step  102  in a channel coding step  104 , forming speech and multi-frame signaling bits  106 . The additional bit from step  102  is a part of the three bit information used for coding additional signaling information. In the present example it represents the six different coding modes available or measurement information. In this example it takes three frames within a multi-frame of six frames, as e.g. defined and used according to the GSM standard, to transmit the coding mode information as within each frame only one of three bits is transmitted, thus providing additional protection for the transmitted coding mode information. Due to the fact that the one bit used per frame is in addition protected by the channel coding step  104 , total protection is further increased. 
   For each data frame actual coding mode bits are generated in an actual mode signaling step  100  according to the coding mode selected for the data frame. As explained above, for characterizing the coding mode three bits are used. The coding mode bits derived from step  100  are channel coded in a channel coding step  103 . For channel coding e. g. eleven additional bit are used in this example to form fourteen actual mode bits  105 . In a frame formatting and interleaving step  107  the actual mode bits  105  and the speech and multi-frame bits  106  are formatted and interleaved for a transmission step T. As the bits added for signaling are inserted into the data frame structure of the transmission system, the synchronization for the added bits is automatically provided by using the given synchronizing mechanisms. 
   After transmission of the bits a de-interleaving step  108  is used to recover actual mode bits  109  and speech and multi-frame signaling bits  110 . From the actual mode bits  109  in a channel decoding step  111  the three bits for actual mode signaling  112  are recovered. From the speech and multi-frame signaling bits  110  in a channel decoding step  113  the source coded user data  114 , e. g. speech, and the multi-frame signaling  115  are recovered. 
   If, instead of the above described transmission direction from the fixed part of the radio network to the mobile part (downlink), the transmission direction is reversed to the direction from the mobile part to the fixed part of the network (uplink), the actual mode bits  105  also contain the coding mode used for the respective frame as coded in the mobile part, but the multi-frame signaling bits  102  transmitted in three consecutive frames contain a quality measurement of the downlink, as measured by the mobile part at reception thereof. For the measured quality of the downlink eight different levels can be assigned as three bits are used for multi-frame signaling. 
   All above used steps of coding, decoding, transmission etc. are per se well known and are explained e. g. in greater detail in the above mentioned documents. 
   Looking now to  FIG. 2 , the data structure for signaling as explained above will be explained in greater detail.  FIG. 2  shows the signaling for nine consecutive data frames  0  to  8 . In the example shown it is assumed that the fixed part of the network and the mobile part use the same coding mode for the transmission of data in downlink and uplink, this is also referred to a symmetrical operation. It should be noted that it is also possible that the fixed part of the network uses a coding mode for the downlink different from the coding mode used by the mobile part for uplink. In this case an actual mode signaling codeword for the downlink is different in general compared to an actual mode signaling codeword for the uplink. The table of  FIG. 2  has in its first column the frame number of the transmitted data frame; in its second column the three bit actual mode codeword used for signaling of the coding mode for the downlink; in its third column the multi-frame signaling bit used for characterizing the coding mode command for the uplink sent in the downlink; in its fourth column the three bit actual mode codeword used for signaling of the coding mode for the uplink; in its fifth column the multi-frame signaling bit of the uplink used for characterizing the transmission quality of the downlink as received and measured by the mobile part; and in its sixth column the action regarding change of used coding mode. 
   For the first three frames  0  to  2  the actual coding mode is Mode  3 , characterized by bit sequence 010, for both the codewords of downlink and uplink. As no change of coding mode is necessary for the next three frames  3  to  5  the sequence of the multi-frame signaling bits of the downlink also is 010, Mode  3 . In the example shown in the first frame  0  the least significant bit (LSB) is transmitted while the most significant bit (MSB) is transmitted in the third frame  2 . In the same way the quality measurement is signaled in the uplink, LSB in the first frame  0 , MSB is the third frame  2 . The sequence 110 as shown in  FIG. 2  is an assumed value and merely for explanation. Within the consecutive three frames  3  to  5  it is signaled that the frames  6  to  8  will have a different coding mode. To accomplish this the bit sequence of the multi-frame signaling bits is changed to 001 to represent Mode  2 . For the frames  6  to  8  Mode  2  is used as coding mode. 
   The coding modes used both in downlink and uplink are determined by the fixed part of the network. To determine the coding modes the transmission quality of downlink and uplink are analyzed. The quality of the uplink is measured by the fixed part of the network, the quality of the downlink is—as explained above—measured by the mobile part and transmitted to the fixed part of the network using the multi-frame signaling bits of the uplink. 
   The decoding mode used in the fixed part of the network for the data received from the mobile part is determined by the actual mode signaling codeword contained in the uplink. For error checking the received codeword can be compared to a determined codeword of a previous frame, as the code mode can not change during three frames. The decoding mode used in the mobile part for the frames received from the fixed part of the network is determined by the actual mode signaling codeword contained in the downlink. In symmetrical operation, i. e. the same mode is used for downlink and uplink, the received codeword of the downlink can be compared to the mode command sent previously on the downlink during three previous frames. In that way, a very high protection for the signaled modes used for coding and decoding is achieved with a small number of bits, which is important as using different modes for coding and decoding would lead to a destruction of the user data. In case of symmetrical operation, as mentioned above, several strategies can be applied by using the proposed coding scheme of actual code mode word and the partitioned code mode bits. In case of error for, e. g. several frames, either the previous coding mode transmitted in the partitioned code mode bits can be kept for uplink and downlink or the coding mode can be decreased towards more channel coding protection of the speech bits. 
     FIG. 3  is a schematic diagram of a system for signaling information according to this invention. A fixed part of the network  1  and a mobile part  2  are depicted. Both parts have a source coder/decoder  10 ,  20 , e.g. for speech, a first channel coder/decoder  11 ,  21 , a coding mode means  12 ,  22 , a second channel coder/decoder  13 ,  23 , a formatting and interleaving/de-interleaving means  14 ,  24 , a transceiver  15 ,  25 , and an antenna  16 ,  26 . Several other elements are used in the fixed part of the network  1  and the mobile part, e.g. an equalizer is used within the transceivers  15  and  25 , for the sake of an easier understanding of the present invention these elements are not shown as they are not relevant for this invention. For greater detail of the radio network reference is made to the mentioned state of the art. 
   For downlink transmission, i. e. in case the fixed part  1  transmits data frames to the mobile part  2 , user data, e. g. speech, is coded by speech coder  10  using a coding mode as indicated by coding mode means  12 . The output of speech coder  10  is channel coded by channel coder  11 . As explained above, to the output of speech coder  10  at least one bit is added which is part of the multi-frame signaling bits. The additional bit is being generated by the coding mode means  12  according to the used coding mode for the next frames. The coding mode means  12  also generates the three actual mode bits, as explained above. The actual mode bits are channel coded by channel coder  13 , e. g. a block coder. The outputs of channel coders  11  and  13  are fed to the formatting and interleaving means  14  which forms a data frame for transmission, e. g. a transmission frame according to the above mentioned GSM standard. The transmission frame then is transmitted from transmitter  15  and antenna  16 . At the mobile part  2  the transmitted signal, i. e. the transmission frame, is received by antenna  26  and receiver  25 . The transmission frame is de-interleaved by the de-interleaver  24 . The channel coded actual mode bits are coupled to the channel decoder  23 . The decoded actual mode bits are fed to the coding mode means  22 . The coding mode means  22  provides information on the coding mode used in each frame to the channel decoder  21  and to the speech decoder  20  for decoding each individual frame. 
   As explained above with reference to  FIGS. 1 and 2 , the coding mode used at the side of the fixed part  1  of the network for coding the frame which is processed now at the mobile part  2  is identified by the coding mode means  22  analyzing the actual coding mode bits as well as the multi-frame signaling bits, which in this example are transmitted one bit each in subsequent frames. As also explained above, the synchronization for bits added for signaling is automatically provided by using the given frame structure. 
   For uplink transmission, i. e. the mobile part  2  transmits data frames to the fixed part  1  of the network data, e. g. speech, is coded by the speech coder  20  using a coding mode as indicated by coding mode means  22 . The output of speech coder  20  is channel coded by channel coder  21 . As explained above, to the output of speech coder  20  at least one bit is added which is part of the multi-frame signaling bits. The additional bit is being generated by the coding mode means  22  according to the reception quality as estimated for the downlink from measurements in the mobile part  2  and the fixed 1 part of the network. The coding mode means  22  also generates the three actual mode bits indicating the coding mode used for coding of the actual frame, as explained above. The actual mode bits are channel coded by channel coder  23 , e. g. a block coder. The outputs of channel coders  21  and  23  are fed to the formatting and interleaving means  24  which forms a data frame for transmission, e. g. a transmission frame according to the above mentioned GSM standard. The transmission frame then is transmitted from transmitter  25  and antenna  26 . At the fixed part  1  of the network the transmitted signal, i. e. the transmission frame, is received by antenna  16  and receiver  15  which e. g, also measures the quality of the uplink, The transmission frame is de-interleaved by the de-interleaver  14 . The channel coded actual mode bits are coupled to the channel decoder  13 . The decoded actual mode bits are fed to the coding mode means  12 . The coding mode means  12  provides information on the coding mode used in each frame to the channel decoder  11  and to the speech decoder  10  for decoding each individual frame. 
   As explained above with reference to  FIGS. 1 and 2 , the coding mode used at the side of the mobile part  2  for coding the frame which is processed now at the fixed part  1  of the network is identified by the coding mode means  12  analyzing the actual coding mode bits as well as the previously decided coding mode for the uplink. As mentioned before, the coding modes for uplink and downlink are decided at the side of the fixed part  1  of the network based on the transmission quality for uplink and downlink. As also explained above, the synchronization for bits added for signaling is automatically provided by using the given frame structure.