Abstract:
A method for increasing information throughput in a transmitter of a digital mobile telecommunication system is provided. The method includes the step of implementing error correction with respect to a traffic channel frame having user service information to generate CRC bits for the user service information of the traffic channel frame. The CRC bits are inserted into a control channel frame. The traffic channel frame and the control channel frame having the inserted CRC bits are transmitted at a radio frequency.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to digital mobile telecommunication systems and, more particularly, to a transmitter with increased throughput of user information between a mobile telecommunication terminal and a base station. 
     2. Description of the Related Art 
     A Code Division Multiple Access (CDMA) system sets an n-bit random pattern (spread code) of “0s” and “1s” and transmits a message stream of that pattern and an inverted pattern at a bit rate n times the message bit rate. As the CDMA system transmits a message at the high bit rate, the width of the frequency spectrum is spread. Therefore, the CDMA system is sometimes referred to as a spread spectrum system. 
     A mobile telecommunication terminal, which is a subscriber or personal communication terminal, provides telecommunication services for the user by radio communication with a base station. 
     A conventional transmitter of the mobile telecommunication terminal and the base station in a typical CDMA system is illustrated in FIG.  1 . The transmitter includes a voice encoder  10 , a Cyclic Redundancy Check (CRC) encoder  12 , a tail bit inserter  14 , a Forward Error Correction (FEC) encoder  16 , an interleaver  18 , a symbol repeater  20 , and a digital modulator  22 . 
     In operation, voice or data information coded by voice encoder  10  is applied to CRC encoder  12  and tail bit inserter  14 . The CRC encoder  12  CRC-encodes the applied voice or data information and adds the CRC-encoded result to the voice or data information. The tail bit inserter  14  inserts tail bits (fixed value bits) into the applied voice or data information. The CRC encoder  12  and tail bit inserter  14  perform the above operations in the time unit of a frame. The CRC-encoded result and the tail bits are added to the voice or data information to detect a transmission error of a traffic channel frame upon transmitting or receiving traffic channel data in the time unit of a frame. 
     Referring to FIG. 2, the structure of a traffic channel frame in which the CRC-encoded result and the tail bits are added to the voice or data information by CRC encoder  12  and tail bit inserter  14  is shown. The traffic channel frame is comprised of I data (voice) bits corresponding to the voice information generated by voice encoder  10 , F CRC bits generated by CRC encoder  12  via a polynomial which uses the voice information bits, and T tail bits consisting of “0s”. 
     For example, in an IS-95 system, a traffic channel frame of 9600 bps voice data is comprised of 192 bits during a frame of 20 ms in duration. The 192 bits are employed as follows: 172 voice information bits, 12 CRC bits, and 8 tail bits. A traffic channel frame of 4800 bps voice data is comprised of 96 bits during a frame of 20 ms. The 96 bits are employed as follows: 80 voice information bits, 8 CRC bits, and 8 tail bits. 
     The traffic channel frame illustrated in FIG. 2 is applied to an Radio Frequency (RF) transmitter after being processed by FEC encoder  16 , interleaver  18 , symbol repeater  20  and digital modulator  22 , and carrier-modulated. 
     The FEC encoder  16  is a convolutional encoder for correcting a bit error in the receiver generated during radio transmission. The interleaver  18  is a block interleaver that performs interleaving to prevent a burst error which may be generated on a mobile telecommunication radio transmission channel. The symbol repeater  20  adjusts the symbol rate of the interleaved traffic channel frame. The digital modulator  22  consists of a direct sequence (DS) spread spectrum device, a data modulator, and a digital low pass filter for increasing the efficiency of a frequency band. 
     Meanwhile, the receiver receives the traffic channel frame and corrects an error through a digital demodulator, a de-interleaver, and a Viterbi decoder having a FEC decoding function. The error-corrected voice information is applied to a CRC encoder which is identical to that used in the transmitter. The receiver compares CRC bits obtained by the CRC encoder with CRC bits within the received traffic channel frame. If they are equal to each other, then no errors are considered to be present in the transmitted traffic channel frame. However, if they are not equal, then an error(s) is considered to be present in the traffic channel frame. 
     Thus, the CRC bits are inserted into the traffic channel frame together with the voice information in order to determine whether or not there are errors in the traffic channel frame. As such, the throughput of the voice information is decreased by a number of bits equal to the number of CRC bits. For instance, in the IS-95 system of 9600 bps voice data, since there are 12 CRC bits out of the total 192 bits during the frame time of 20 ms, the throughput of the voice information decreases by 6.25 percent (i.e., 12/192×100). Similarly, in the IS-95 system of 4800 bps voice data, the throughput of the voice information decreases by 8.33 percent (i.e., 8/96×100). 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a transmitter for increasing the throughput of traffic information in a mobile communication system by transmitting CRC bits through a control channel frame. 
     It is another object of the present invention to provide a method for increasing the throughput of traffic information in a mobile communication system by transmitting CRC bits through a control channel frame. 
     In one aspect of the invention, a transmitter for increasing information throughput in a digital mobile telecommunication system is provided. The transmitter includes: means for implementing error correction with respect to a traffic channel frame having user service information to generate CRC bits for the user service information of the traffic channel frame; and means for inserting the CRC bits into a control channel frame, wherein the traffic channel frame and the control channel frame having the inserted CRC bits are transmitted at a radio frequency. 
     In another aspect of the invention, a method for increasing information throughput in a transmitter of a digital mobile telecommunication system is provided. The method includes the steps of: implementing error correction with respect to a traffic channel frame having user service information to generate CRC bits for the user service information of the traffic channel frame; and inserting the CRC bits into a control channel frame, wherein the traffic channel frame and the control channel frame having the inserted CRC bits are transmitted at a radio frequency. 
     These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a conventional transmitter in a direct sequence code division multiple access (DS-CDMA) mobile telecommunication system; 
     FIG. 2 is a diagram illustrating the structure of a traffic channel frame generated by the transmitter of FIG. 1; 
     FIG. 3 is a block diagram of a transmitter in a DS-CDMA mobile telecommunication system according to a preferred embodiment of the present invention; 
     FIG. 4 is a diagram illustrating the structure of a traffic channel frame generated by the transmitter of FIG. 3; and 
     FIG. 5 is a diagram illustrating the structure of a control channel frame generated from the transmitter of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Telecommunication technology has developed from CDMA digital mobile telecommunication systems which provide voice-based information services into future mobile telecommunication systems which provide radio multimedia services including moving pictures and data up to 2 Mbps. One such future mobile telecommunication system is the Future Public Land Mobile Telecommunication System (FPLMTS), which is also referred to as the International Mobile Telecommunication-2000 (IMT-2000). 
     To vary a user data rate and improve the quality of service according to user demands for various services of a mobile telecommunication system, a traffic channel frame is employed for transmitting user service information (voice, data, image, etc.) and a control channel frame associated with the user traffic channel frame is also employed. The control channel frame has the same frame time as the traffic channel frame. The control channel frame and the traffic channel frame are simultaneously transmitted. Although there may be differences according to the type of system employed and the services provided, the control channel frame generally includes a user information data rate corresponding to the traffic channel frame to be transmitted next, FEC and interleaver types and parameters, modulation types and parameters, handover related calculation values, etc. However, while the control channel frame contains a considerable amount of information and parameters in comparison to the traffic channel frame, its throughput is relatively small. As a result, the CRC bits which have been conventionally contained within the traffic channel frame are now contained within the control channel frame which is transmitted together with the traffic channel frame. By containing the CRC bits within the control channel frame in accordance with the present invention, the throughput of user traffic information can be increased. 
     Hereinafter, it is assumed that a mobile telecommunication system for providing voice, data and radio multimedia services is applied to a DS-CDMA system, and uses a traffic channel frame for transmitting the user service information and an independent control channel for transmitting control and signaling information. 
     Referring to FIG. 3, a block diagram of a transmitter in a direct sequence code division multiple access (DS-CDMA) mobile telecommunication system according to the present invention is shown. A user service information provider  30  generates information frames containing user service information such as, for example, voice, data, and image information. The time duration of an information frame generated from provider  30  is equal to a frame for the traffic channel. A tail bit inserter  32  inserts tail bits into the information frame supplied from user service information provider  30  and generates a traffic channel frame with a structure shown in FIG.  4 . The traffic channel frame is comprised of (I+F) user service information bits and T tail bits. A first CRC encoder  42  generates first CRC bits used for detecting an error of the applied information frame. A control and signaling information provider  44  generates control and signaling information associated with traffic control as a control channel frame. A multiplexer (MUX)  46  multiplexes the first CRC bits generated by CRC encoder  42  with the control channel frame generated by control and signaling information provider  44 . A second CRC encoder  48  generates second CRC bits for detecting an error of the control channel frame which has been multiplexed with the first CRC bits of the traffic channel. The second CRC encoder  48  inserts the second CRC bits into the control channel frame. The structure of the control channel frame generated by second CRC encoder  48  is shown in FIG.  5 . The control channel frame is comprised of C control and signaling information bits, F first CRC bits, M second CRC bits, and T tail bits. A first FEC encoder  34  and a second FEC encoder  50  perform error correction coding for correcting a bit error generated on a radio communication channel with respect to the traffic channel frame and the control channel frame, respectively. A first interleaver  36  and a second interleaver  52  prevent a burst error in the traffic channel frame and the control channel frame, respectively. A first symbol repeater  38  and a second symbol repeater  54  equalize the symbol rate of a first digital modulator  40  corresponding to the traffic channel frame and a second digital modulator  56  corresponding to the control channel frame, respectively. The first and second digital modulators  40  and  56  implement DS spread spectrum modulation and data modulation. A digital adder  58  adds the traffic channel frame generated by first digital modulator  40  to the control channel frame generated by second digital modulator  56  in order to simultaneously transmit the traffic and control channel frames. 
     In operation, the traffic channel frame, which contains information such as voice, data, and image information, is simultaneously supplied to tail bit inserter  32  and first CRC encoder  42  from user service information provider  30  in the time unit of a frame. The tail bits are inserted into the traffic channel frame applied to tail bit inserter  32 . The structure of the traffic channel frame generated by tail bit inserter  32  is shown in FIG.  4 . The traffic channel frame consists of the user service information bits which correspond to the time unit of a frame defined by the user service data rate and the system, and the tail bits associated with the FEC encoder used in the system. The number of tail bits is T. Assuming that for the traffic channel a frame is 20 ms in duration (as in the case of IS-95) and also, that the same CRC encoder is used, F CRC bits are transmitted using the control channel frame. Therefore, in the structure of the traffic channel frame according to the present invention, F service information bits can be further transmitted. 
     The traffic channel frame generated by tail bit inserter  32  is coded by first FEC encoder  34  to correct a bit error which may be generated on the radio transmission channel and applied to the first interleaver  36 . The traffic channel frame is interleaved by first interleaver  36  to prevent a burst error, and is then applied to first symbol repeater  38  which equalizes the symbol rate of first digital modulator  40  by repeating symbols. The traffic channel frame generated by first symbol repeater  38  is applied to first digital modulator  40  to perform DS spread spectrum modulation and data modulation. The output of first digital modulator  40  is applied to digital adder  58 . 
     On the other hand, the traffic channel frame is applied to first CRC encoder  42 , and the first CRC bits for the user service information are generated therefrom. The control channel frame having the control and signaling information is generated by control and signaling information provider  44 . The first CRC bits are CRC bits for the traffic channel information. The first CRC bits and the control channel frame are supplied to MUX  46  and multiplexed with each other. The resultant control channel frame generated by MUX  46  is applied to second CRC encoder  48  and the second CRC bits are added thereto, thereby generating the control channel frame with the structure illustrated in FIG.  5 . The second CRC bits are CRC bits for the control and signaling information bits and the first CRC bits. 
     In the structure of the control channel frame, the control and signaling information bits consist of C bits of a user service information data rate corresponding to the traffic channel frame to be transmitted next, FEC and interleaver types and parameters, modulation types and parameters, handover related calculation values and parameters, etc. 
     The control channel frame generated by second CRC encoder  48  is applied to digital adder  58  after processing by FEC encoder  50 , interleaver  52 , symbol repeater  52  and digital modulator  54  in the same manner as described above with respect to the traffic channel frame. However, the number of repeated symbols in second symbol repeater  54  is greater than that in first symbol repeater  38 . This is because the number of control and signaling information bits of the control channel frame is less than the number of user service information bits of the traffic channel frame during the same frame time. Therefore, the symbols of the control channel frame can be repeated more than the symbols of the traffic channel frame. 
     The traffic channel frame and the control channel frame generated by first and second digital modulators  40  and  56 , respectively, are added to each other by digital adder  58 . The added traffic channel frame and control channel frame are RF-modulated and transmitted through a digital-to-analog converter, an RF transmitter and an antenna. 
     As described above, the CRC bits for detecting an error in the user service information are transmitted using a physically independent control channel frame instead of a traffic channel frame. Therefore, the throughput of user service information can be increased by a number of bits equal to the CRC bits which have been eliminated from the traffic channel frame. Since the data rate of the control channel frame is relatively smaller than the data rate of the traffic channel frame during the same frame time, the number of repeated symbols of the control channel frame can be increased. An increase in the number of repeated symbols in the mobile telecommunication system lessens the likelihood of an error being generated on the radio transmission channel. Hence, the CRC bits transmitted by the control channel frame have a lower probability of generating an error than those transmitted by the traffic channel frame of the prior art. Further, since the probability of an error being generated in the control channel frame is very low, the use of the (first) CRC bits transmitted in the control channel frame to detect an error of the traffic channel frame results in increased accuracy in the detection of errors of the traffic channel frame. Thus, by accurately detecting an error of the traffic channel frame, the present invention may be used to increase the quality of the services provided by a mobile telecommunication system. 
     Although illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention.