Apparatus for making a random access to the reverse common channel of a base station in CDMA and method therefor

0001NOTE: More than one reissue application has been filed for the reissue of U.S. Pat. No. 6,614,771. The reissue applications are application Ser. Nos. 11/218,277, filed Sep. 2, 2005, and the current application being filed Dec. 6, 2007, which is a continuation reissue application of application Ser. No. 11/218,277.

BACKGROUND OF THE INVENTION

00021. Field of the Invention

0003The present invention concerns an apparatus for making a plurality of cellular phones randomly access a common channel to transmit data in CDMA (Code Division Multiple Access), and a method therefor.

00042. Technical Background

0005Recently, it has been demanded that the mobile communication system may provide data communication services to enable exchanges of moving image and character data together with those of conventional voiced information during movement. IMT-2000 (International Mobile Telecommunication-2000) is an international project to develop a mobile communication system to enable such data communication services based on an internationally integrated standard. In addition, an effort has been made to achieve high speed data transmission with some limitation in the mobile characteristics, and particularly, the wireless LAN proposed in IEEE 802.11 standard is commercially able to make data transmission at 2 Mbps (Mega bit per sec).

0006Generally, the circuit-switch, which is employed in the present public switched telephone network (PSTN), digital cellular system and personal communication system, is not desirable to make such high speed data transmission because of ineffectively using a limited number of channels. In order to resolve the disadvantages of the circuit-switch, the packet-switch has been proposed to make high speed data transmission in IMT-2000, which is under development for LAN or the standard of the future mobile communication system. The band spread method of CDMA applied to the present digital cellular system has a large communication capacity, and is prevented from external tapping and stabilized to make communications under the multipath environment generated by the radio channels rapidly changed through movement, so that it is widely used in the commercial wireless LAN, CDMA One of LMNQ (Lucent Motorola, Nortel, Qualcomm, Samsung) proposed as the standard of the future IMT-2000, or W-CDMA (Wideband-CDMA) chiefly developed in Europe and Japan.

0007The future IMT-2000 system is to support both voiced data and packet data communications. In this case, it is very ineffective that the packet data is assigned with an exclusive channel as the voiced data. Namely, although the continuous voiced data must be assigned with an exclusive channel, it is desirable for effective use of resources and simplification of the system that the discontinuous small packet data are transmitted through the reverse common channels less than the number of the active terminals. Moreover, if the number of the subscribers is increased, and thus the amount of the data transmitted, the reverse common channels must be necessarily used for the effective use of resources.

0008The ALOHA method is the most effective way of channel access and data transmission through the reverse common channel, and a typical random access, which is developed by Hawaii University in 1970 as a protocol for the wireless network between the islands of Hawaii State. However, such ALOHA suffers the inefficiency of data transmission performed without any timed schedule between the base station and terminals, and network overloaded due to frequent collision of data transmitted by a number of terminals. The slotted ALOHA has been developed to define a standard time between the base station and terminal in order to cope with such problems. This method is to allow the data transmission of a terminal only in a set time, so that the rate of substantial data and thus the transmission efficiency is increased, and the interferences from another terminal is reduced, thereby improving the efficiency of the whole network. However, since the slotted ALOHA makes the data transmission basically in the contention mode, it is impossible to avoid collisions of data transmitted from the terminals. Hence, if there is an additional channel for controlling and transmitting information in the forward link from the base station to the terminals, the base station broadcasts the information of the received data to the terminals in order to avoid such data collision.

0009In the ALOHA system employing CDMA, each terminal uses a different code or the same code with a time offset to avoid data collision. In addition, a preamble signal is firstly transmitted to determine the power to be used for data transmission, and the initial synchronization with the code to use and the tracking of the code synchronization is performed previous to the data transmission, thereby preventing data transmission error. Describing the conventional ALOHA protocol employing CDMA in reference to <figref idref="DRAWINGS">FIG. 1</figref>, a terminal makes an access attempt to transmit data. The access attempt consists of a plurality of access sub-attempts, each of which in turn consists of a plurality of access probe sequences, each of which in turn consists of a plurality of access probes. The access probe consists of a preamble transmitting a pilot channel without any substantial information to evaluate the channel situation and to make the initial synchronization between the codes of the terminal and base station and the tracking of the code synchronization, and an access channel message capsule containing the access information or the user's data following the preamble. In order to transmit an access signal or data through the reverse common channel, a terminal firstly transmits an access probe at a given power level, which must have a minimum value to reduce the interferences affecting the other terminals that transmit data through an exclusive channel or other reverse common channels. Then, the terminal which made an attempt to transmit data with the first access probe waits for a prescribed time interval TA the signal from the base station representing whether the transmitted data is received. If the first access probe fails to reach the base station, the terminal makes another attempt to retransmit the second probe at a power level increased by a given level PI compared to the power level of the first probe after a random time interval RT. If not succeeding in the data transmission through a prescribed number of the access probes of the first access probe sequence, the terminal performs the second access probe sequence after passing an additional random time interval RS.

0010While the conventional ALOHA protocol system employing CDMA can make a stable data transmission in the reverse common channel by performing stably the code synchronization and the tracking thereof with the preamble of a sufficient length even when many data are transmitted through the reverse common channel, the preamble is the signal to establish the code synchronization, and less important and longer than the substantial data. Thus, if the synchronization is exactly acquired in the preamble but with an error in transmission of the substantial data, the preamble should be retransmitted reducing the data transmission efficiency.

SUMMARY OF THE INVENTION

0011It is an object of the present invention to provide an apparatus for making a plurality of cellular phones randomly access a common channel to transmit data in CDMA, which enables the base station to broadcast a signal representing whether it has acquired the synchronization signal of the data received through the reverse common channel or no, so as to prevent the terminals from unnecessarily transmitting data, thereby avoiding interference signals generated in the reverse common channel.

0012It is another object of the present invention to reduce the power used in the terminal to employ an exclusive channel or the reverse common channel to transmit data, and to enable the failed terminal to quickly retransmit data.

0013It is still another object of the present invention to provide an apparatus for making a plurality of cellular phones randomly access a common channel to transmit data in CDMA, which may stably perform the code synchronization and the tracking thereof with a preamble of the same length, and achieve reliable data transmission, and reduce the time taken for transmitting data.

0014It is further another object of the present invention to enable the base station to broadcast the information concerning the state of the channel card to all terminals in real time so as to prevent the terminals from unnecessarily transmitting data.

0015According to the present invention, an apparatus for making a plurality of terminals have a random access to the reverse common channel of a base station in CDMA, comprises code synchronization detection information broadcast means provided in the base station for broadcasting the state information of a channel card in real time for the terminals to recognize the code synchronization detection when the code synchronization of a certain data is acquired through performing the code synchronization of the preambles transmitted from the terminals through the reverse common channel, and data transmission determination means provided in the terminals for making the terminals to have attempted data transmission in the same time slot with the data of the code synchronization detection continue data transmission and the other terminals stop data transmission.

0016According to an aspect of the present invention, each of the terminals comprises a data generator for generating the data transmitted to the base station, a data transmitter for transmitting the data generated from the data generator, a terminal RF signal processor for converting the data from the data transmitter into an RF signal transmitted to the base station and for processing an RF signal received from the base station, a broadcast signal receiver for receiving a broadcast signal from the terminal RF signal processor to determine the data transmission, and data transmission determination circuit for controlling the data transmitter to determine whether to make an attempt of transmitting data or to keep on transmitting the data presently under transmission according to the broadcast signal.

0017When the data transmission determination circuit receives a broadcast signal representing the detection of the code synchronization in a time slot from the base station, it holds the data transmission until receiving a broadcast signal representing the code synchronization not acquired when it does not perform data transmission or keeps on transmitting data when it has attempted the data transmission in the time slot corresponding to the broadcast signal or stops the data transmission performed in the time slot not corresponding to the broadcast signal and holds it until receiving a broadcast signal representing the code synchronization not acquired.

0018Preferably, the data transmission determination circuit determines the data transmission by receiving the broadcast signal representing the detection of the code synchronization in a time slot from the base station, the data transmission being determined by the first or second broadcast signal according as the ratio of the packet length to the slot length is 2 or 4.

0019The data transmitter is preferably designed to have a transmitted data unit consisting of the preamble and user's data, and the power of the preamble is set different from that of the user's data. The data transmitter performs the power control according to the power control bit transmitted after receiving the broadcast signal representing the detection of the received signal synchronization from the base station, and maintains a constant power level regardless of the power control bit transmitted upon receiving the broadcast signal representing the received signal synchronization not acquired from the base station.

0020The base station preferably comprises a base station RF signal processor for receiving the RF signal transmitted from the terminal, a data transceiver for demodulating the signal from the base station RF signal processor to deliver it to an upper hierarchy or another network or vice versa, the data transceiver generating a signal representing whether the received signal synchronization is acquired or no, a detection determination circuit for receiving the resultant signal of the code synchronization used to determine whether the received signal is acquired or no upon completing the preamble of the data transmitted from the data transceiver, a broadcast determination circuit for determining the information to broadcast to the terminals according to the detection of the received signal synchronization recognized by the detection determination circuit, and a broadcast transmitter for controlling the base station RF signal processor to transmit the broadcast signal determined by the broadcast determination circuit at a prescribed power level in a prescribed time.

0021Preferably, the detection determination circuit determines the initial code synchronization and the tracking of the synchronization in a given time before completion of a preamble transmission to make the terminals perform the precise operation in the beginning of the slot. In addition, the detection determination circuit searches the codes around the beginning of each time slot for a duration that may vary from the length of the time slot to the length of the preamble.

0022The broadcast determination circuit determines the broadcast signal only with a single bit representing the detection of the synchronization in the preamble. The broadcast transmitter transmits the broadcast signal determined by the broadcast determination circuit through an additional channel using a different code other than the presently used code at every time of completing the slot. Besides, the broadcast transmitter transmits the broadcast signal determined by the broadcast determination circuit at every time of completing the slot in the punctured form having the power control bit transmitted through the pilot channel and a time offset.

0023The present invention will now described more specifically with reference to the drawings attached only by way of examples.

BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS

0024<figref idref="DRAWINGS">FIG. 1</figref> is a schematic diagram for illustrating the data transmission in ALOHA system employing a common channel in conventional CDMA;

0025<figref idref="DRAWINGS">FIG. 2</figref> illustrates a CDMA network where the inventive apparatus is applied;

0026<figref idref="DRAWINGS">FIG. 3</figref> is a block diagram for illustrating the base station communicating with the terminal according to the inventive apparatus;

0027<figref idref="DRAWINGS">FIG. 4A</figref> is a timing diagram for illustrating the random access to the reverse common channel in the inventive apparatus; and

0028<figref idref="DRAWINGS">FIG. 4B</figref> is a timing diagram for illustrating the random access to the reverse common channel using mini time slots in the inventive apparatus.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

0029Referring to <figref idref="DRAWINGS">FIG. 2</figref>, the subscriber's terminal <b>110</b> transmits a preamble through the reverse common channel to the base station, which performs the code synchronization to receive the data generated from the terminal. CDMA network <b>300</b> controls a plurality of base stations <b>200</b>, <b>210</b>, communicating with other networks. PSTN (Public Switched Telephone Network) <b>400</b> also communicates with the CDMA network <b>300</b> to connect the mobile terminal <b>110</b> with the telephone subscriber. Internet <b>500</b> also communicates with the CDMA network <b>300</b> to connect the terminal <b>110</b> with the Internet subscriber. PSDN (Public Switched Data Network) <b>600</b> communicates with the CDMA network <b>300</b> to connect the terminal <b>110</b> with the PSDN subscriber.

0030The base station <b>200</b> is provided with code synchronization detection information broadcast means for broadcasting the state information of a channel card in real time for the terminals to recognize the code synchronization detection when the code synchronization of a certain data is acquired through performing the code synchronization of the preambles transmitted from the terminals through the reverse common channel. In addition, each terminal <b>100</b> is provided with data transmission determination means for making the terminals to have attempted data transmission in the same time slot with the data of the code synchronization detection continue data transmission and the other terminals stop data transmission.

0031As shown in <figref idref="DRAWINGS">FIG. 3</figref>, the terminal <b>110</b> comprise a data generator <b>111</b> for generating the data transmitted to the base station <b>210</b>, a data transmitter <b>112</b> for transmitting the data generated from the data generator, a terminal RF signal processor <b>113</b> for converting the data from the data transmitter <b>112</b> into an RF signal transmitted to the base station <b>210</b> and for processing an RF signal received from the base station <b>210</b>, a broadcast signal receiver <b>114</b> for receiving a broadcast signal from the terminal RF signal processor <b>113</b> to determine the data transmission, and data transmission determination circuit <b>115</b> for controlling the data transmitter <b>112</b> to determine whether to make an attempt of transmitting data or to keep on transmitting the data presently under transmission according to the broadcast signal.

0032The base station <b>210</b> preferably comprises a base station RF signal processor <b>211</b> for receiving the RF signal transmitted from the terminal <b>110</b>, a data transceiver <b>212</b> for demodulating the signal from the base station RF signal processor <b>211</b> to deliver it to an upper hierarchy or another network or vice versa, the data transceiver <b>212</b> generating a signal representing whether the received signal synchronization is acquired or no, a detection determination circuit <b>213</b> for receiving the resultant signal of the code synchronization used to determine whether the received signal is acquired or no upon completing the preamble of the data transmitted from the data transceiver <b>212</b>, a broadcast determination circuit <b>214</b> for determining the information to broadcast to the terminals according to the detection of the received signal synchronization recognized by the detection determination circuit <b>213</b>, and a broadcast transmitter <b>215</b> for controlling the base station RF signal processor <b>211</b> to transmit the broadcast signal determined by the broadcast determination circuit <b>214</b> at a prescribed power level in a prescribed time.

0033Describing the operation of the inventive apparatus in connection with <figref idref="DRAWINGS">FIGS. 3 and 4</figref>, the data generator <b>111</b> of the terminal <b>110</b> generates the data consisting of a control signal to connect the terminal <b>110</b> with the base station <b>210</b> and a substantial data transmitted by the user of the terminal <b>110</b>. The data may be transmitted through an exclusive channel or the reverse common channel according to the traffic characteristics. In the inventive apparatus, the data is transmitted through the reverse common channel. The data generated from the data generator is determined to be transmitted or not according to the broadcast signal received from the base station <b>210</b>.

0034The hub RF signal processor <b>211</b> of the base station <b>210</b> converts the RF signal into the base band signal transmitted to the data transceiver <b>212</b>, which performs the initial code synchronization and the tracking thereof through the preamble of the data received the reverse common channel. Generally speaking, while the initial code synchronization and the tracking thereof may be determined after completing of the preamble receiving, the probability to achieve the code synchronization may be approximately evaluated by means of the power of the received signal even before completion of the preamble receiving, so that the broadcast signal may be determined prior to completion of the preamble transmission, and therefore the time taken for determining and transmitting the broadcast signal may be reduced, thus making it possible to broadcast in real time. Hence, the effect of broadcasting thus determined broadcast signal to all terminals prevents the interference signals because the other terminals are stopped to transmit data when the code synchronization has been attained.

0035Consequently, the base station <b>210</b> decodes the data received through the reverse common channel to make an error detection, and broadcasts the signal representing the detection of the code synchronization of the received data to the terminals in real time. Namely, the detection determination circuit <b>213</b> transfers the resultant signal of the code synchronization detection of the received signal from the data transceiver <b>212</b> after completion of the preamble to the broadcast determination circuit <b>214</b>, which determines the preparation to demodulate the data according to the signal from the data transceiver <b>212</b> representing demodulation such as the signal of the synchronization detection and the output signal of the detection determination circuit <b>213</b>.

0036Then, the broadcast transmitter <b>215</b> transmits the information representing the detection of the code synchronization instead of PCB (Power Control Bit) at the boundary of the time slot in order to transmit in real time the broadcast signal determined by the broadcast determination circuit <b>214</b> as transmitting PCB through the pilot channel. The possible time delay, as described above, may occur before transmission of the preamble, and therefore the prepared broadcast signal is broadcast before the beginning of the time slot to prevent the performance degradation.

0037The terminals <b>110</b> determines the subsequent operations depending on the information of the code synchronization received from the base station <b>210</b>. When the base station <b>210</b> transmits the signal representing the detection of the code synchronization of the data transmitted through the reverse common channel in a specific time slot, the terminals that have not transmitted data must hold until the completion of transmitting the acquired data while the terminals that have attempted data transmission in the corresponding time slot keep on transmitting the data. Of course, the terminals that have attempted data transmission in the other time slots must stop the transmission until the completion of transmitting the acquired data.

0038<figref idref="DRAWINGS">FIG. 4A</figref> illustrates the example of attempting the data transmission using the beginning of the time slot determined by the system time set in the system. In this case, it is assumed that the length of the preamble necessary for the code synchronization for the data transmission is twice the data length. The time taken for a single data transmission consists of a plurality of time slots. The terminal <b>110</b> including the data newly generated or to be retransmitted before the beginning of the first time slot S₀performs the data transmission in the first time slot interval S₀-S₁. As shown in <figref idref="DRAWINGS">FIG. 4A</figref>, the five data are simultaneously transmitted, and in the next time slot interval S₁-S₂are transmitted two data through the reverse common channel to the base station. Hence, the total of the data transmitted in the second time slot interval is seven.

0039Firstly, it is assumed that the base station performs the initial code synchronization and the tracking thereof by detecting one of the five data transmitted in the first time slot interval S₀-S₁. This assumption may be taken valid because the data are acquired different in power level or transmission delay even if transmitted simultaneously according to the distance between the base station <b>200</b> and the terminal <b>110</b>. Therefore, as shown in <figref idref="DRAWINGS">FIG. 4A</figref>, the detection of the data transmitted at the beginning of the first time slot S₀is recognized by the base station <b>200</b> at the beginning of the third time slot S₂, transmitted to all the terminals. Then, the terminal <b>110</b> determines the next operation according to the broadcast signal received through the terminal RF signal processor <b>113</b> and the broadcast signal receiver <b>114</b>. Namely, receiving the broadcast signal, the terminals that have made the data transmission at the beginning of the first time slot S₀keep on transmitting data, performing closed loop power control by using the PCB transmitted from this time. Since the previous PCB is invalid due to the preamble not acquired, the closed loop power control of the preamble prior to broadcasting the synchronization detection signal may cause abrupt change to the power generated from the terminal <b>110</b>.

0040In the mean time, the terminals that have made data transmission at time points other than the beginning of the first time slot stop the transmission to attempt retransmission in the time slot at which the next not acquired signal is transmitted. On the other hand, if the broadcast signal represents the synchronization not acquired, the terminal does not perform an additional operation, keeping on carrying out the operation done in the previous time slot interval. In this way, the base station may achieve more precise demodulation of the acquired data because of reduced signal interference, transmitting data in the increased power without degradation of the overall system performance. Namely, the data acquired from the preamble may be stably demodulated, so that the time taken for the transmission is reduced and the transmission efficiency is improved.

0041<figref idref="DRAWINGS">FIG. 4B</figref> illustrates the data transmission procedure where the length of the time slot is more reduced. The length of the preamble for the code synchronization is twice the data length as in <figref idref="DRAWINGS">FIG. 4A</figref>. In this case, each time slot is divided into a plurality of smaller time slots, so that the number of the terminals <b>110</b> is reduced for a time slot. A data is transmitted in the beginning of the first time slot S_0-0, and two data in the beginning of the next time slot S_0-1, so that the amount of the data transmitted at the beginning of each time slot is reduced, thus increasing the probability of detecting in the preamble compared to the case of <figref idref="DRAWINGS">FIG. 4A</figref>.

0042Consequently, the data transmitted in the second time slot S_0-1is acquired by the base station <b>200</b> to broadcast the detection signal to the terminal <b>110</b> in the time slot S_2-1of completing the preamble. Receiving the detection signal, the terminals that have performed data transmission in the beginning of the second time slot S_0-1, keep on transmitting data while the terminals that have performed data transmission in the other time slots stop transmission, holding until the time slot S_3-1of receiving the signal not acquired from the base station, and thus the terminals that have not performed data transmission. Compared to <figref idref="DRAWINGS">FIG. 4A</figref> where two of seven terminals stop transmission, the five terminals stop data transmission, and therefore it will be noted that the reduced slot secures the stable data transmission with reduced signal interference. Thus, the reduced slot length reduces the probability of transmitting data in the same time slot, so that there is increased the nubmer of the terminals stopping unnecessary transmission after detection of the preamble. This increases the stability of data transmission, decreasing the signal interference in the terminals using the exclusive channel or other reverse common channels. However, since the signal broadcast from the base station <b>200</b> to the terminal <b>110</b> is determined by the signal received from the terminal, it is required that the slot length is maintained over a prescribed level to minimize the disadvantages caused by the transmission delay or multi-path. Namely, if the slot length is reduced below the prescribed level to reduce the level of the interference signal, the performance of the overall system is degraded because of increasing the frequency of the signal interference. Hence, it is desirable to select the slot length that may reduce the level of the signal interference with minimizing the disadvantages caused by the transmission delay and multi-path.

0043In another aspect of the present invention, a method for making a plurality of terminals have a random access to the reverse common channel of a base station in CDMA, comprises the steps of broadcasting from the base station the state information of a channel card in real time for the terminals to recognize the code synchronization detection when the code synchronization of a certain data is acquired through performing the code synchronization of the preambles transmitted from the terminals through the reverse common channel, and making the terminals to have attempted data transmission in the same time slot with the data of the code synchronization detection continue data transmission and the other terminals stop data transmission.

0044Preferably, the step of making the terminals transmit data comprises the steps of generating the data transmitted to the base station, transmitting the data to the base station, converting the data into an RF signal transmitted to the base station and processing a broadcast RF signal received from the base station, receiving the converted broadcast RF signal to determine the data transmission, and determining whether to make an attempt of transmitting data or to keep on transmitting the data presently under transmission according to the broadcast signal.

0045Preferably, the step of broadcasting in the base station comprises the steps of receiving the RF signal transmitted from the terminal, demodulating the signal from the base station RF signal processor to deliver it to an upper hierarchy or another network or vice versa, and generating a signal representing whether the received signal synchronization is acquired or no, receiving the resultant signal of the code synchronization used to determine whether the received signal is acquired or no upon completing the preamble of the data transmitted, determining the information to broadcast to the terminals according to the detection of the received signal synchronization, and controlling the base station to transmit the broadcast signal at a prescribed power level in a prescribed time.

0046Describing the operation of the inventive method in connection with <figref idref="DRAWINGS">FIG. 4</figref>, the data generator of the terminal generates the data consisting of a control signal to connect the terminal with the base station and a substantial data transmitted by the user of the terminal. The data generated from the data generator is determined to be transmitted or not according to the broadcast signal received from the base station.

0047The hub RF signal processor of the base station converts the RF signal into the base band signal transmitted to the data transceiver, which performs the initial code synchronization and the tracking thereof through the preamble of the data received the reverse common channel. Generally speaking, while the initial code synchronization and the tracking thereof may be determined after completing of the preamble receiving, the probability to achieve the code synchronization may be approximately evaluated by means of the power of the received signal even before completion of the preamble receiving, so that the broadcast signal may be determined prior to completion of the preamble transmission, and therefore the time taken for determining and transmitting the broadcast signal may be reduced, thus making it possible to broadcast in real time. Hence, the effect of broadcasting thus determined broadcast signal to all terminals prevents the interference signals because the other terminals are stopped to transmit data when the code synchronization has been attained.

0048Consequently, the base station <b>210</b> decodes the data received through the reverse common channel to make an error detection, and broadcasts the signal representing the detection of the code synchronization of the received data to the terminals in real time. Namely, the detection determination circuit transfers the resultant signal of the code synchronization detection of the received signal from the data transceiver after completion of the preamble to the broadcast determination circuit, which determines the preparation to demodulate the data according to the signal from the data transceiver representing demodulation such as the signal of the synchronization detection and the output signal of the detection determination circuit. Then, the broadcast transmitter transmits the information representing the detection of the code synchronization instead of PCB at the boundary of the time slot in order to transmit in real time the broadcast signal determined by the broadcast determination circuit as transmitting PCB through the pilot channel.

0049The terminals determine the subsequent operations depending on the information of the code synchronization received from the base station. When the base station transmits the signal representing the detection of the code synchronization of the data transmitted through the reverse common channel in a specific time slot, the terminals that have not transmitted data must hold until the completion of transmitting the acquired data while the terminals that have attempted data transmission in the corresponding time slot keep on transmitting the data. Of course, the terminals that have attempted data transmission in the other time slots must stop the transmission until the completion of transmitting the acquired data.

0050<figref idref="DRAWINGS">FIG. 4A</figref> illustrates the example of attempting the data transmission using the beginning of the time slot determined by the system time set in the system. Since the preamble and data constitute a transmission data unit, the performance depends on the power and length of the preamble. Hence, if the transmission data unit is greater than twice the time slot, the inventive effect is achieved, or otherwise, the effect not obtained. The present invention sets the time slot smaller than the conventional time slot to improve the performance. The time taken for a single data transmission consists of a plurality of time slots. The terminal including the data newly generated or to be retransmitted before the beginning of the first time slot S₀performs the data transmission in the first time slot interval S₀-S₁. As shown in <figref idref="DRAWINGS">FIG. 4A</figref>, the five data are simultaneously transmitted, and in the next time slot interval S₁-S₂are transmitted two data through the reverse common channel to the base station. Hence, the total of the data transmitted in the second time slot interval is seven.

0051Firstly, it is assumed that the base station performs the initial code synchronization and the tracking thereof by detecting one of the five data transmitted in the first time slot interval S₀-S₁. This assumption may be taken valid because the data are acquired different in power level or transmission delay even if transmitted simultaneously according to the distance between the base station and the terminal. Therefore, as shown in <figref idref="DRAWINGS">FIG. 4A</figref>, the detection of the data transmitted at the beginning of the first time slot S₀is recognized by the base station at the beginning of the third time slot S₂, transmitted to all the terminals. Then, the terminal determines the next operation according to the broadcast signal received through the terminal RF signal processor and the broadcast signal receiver. Namely, receiving the broadcast signal, the terminals that have made the data transmission at the beginning of the first time slot S₀keep on transmitting data, performing closed loop power control by using the PCB transmitted from this time. Since the previous PCB is invalid due to the preamble not acquired, the closed loop power control of the preamble prior to broadcasting the synchronization detection signal may cause abrupt change to the power generated from the terminal.

0052In the mean time, the terminals that have made data transmission at time points other than the beginning of the first time slot stop the transmission to attempt retransmission in the time slot at which the next signal not acquired is transmitted. On the other hand, if the broadcast signal represents the synchronization not acquired, the terminal does not perform an additional operation, keeping on carrying out the operation done in the previous time slot interval. In this way, the base station may achieve more precise demodulation of the acquired data because of reduced signal interference, transmitting data in the increased power without degradation of the overall system performance. Namely, the data acquired from the preamble may be stably demodulated, so that the time taken for the transmission is reduced and the transmission efficiency is improved.

0053<figref idref="DRAWINGS">FIG. 4B</figref> illustrates the data transmission procedure where the length of the time slot is more reduced. The length of the preamble for the code synchronization is twice the data length as in <figref idref="DRAWINGS">FIG. 4A</figref>. In this case, each time slot is divided into a plurality of smaller time slots, so that the nubmer of the terminals is reduced for a time slot. A data is transmitted in the beginning of the first time slot S_0-0, and two data in the beginning of the next time slot S_0-1, so that the amount of the data transmitted at the beginning of each time slot is reduced, thus increasing the probability of detecting in the preamble compared to the case of <figref idref="DRAWINGS">FIG. 4A</figref>.

0054Consequently, the data transmitted in the second time slot S_0-1is acquired by the base station to broadcast the detection signal to the terminal in the time slot S_2-1of completing the preamble. Receiving the detection signal, the terminals that have performed data transmission in the beginning of the second time slot S_0-1keep on transmitting data while the terminals that have performed data transmission in the other time slots stop transmission, holding until the time slot S_3-1of receiving the signal not acquired from the base station, and thus the terminals that have not performed data transmission. Compared to <figref idref="DRAWINGS">FIG. 4A</figref> where two of seven terminals stop transmission, the five terminals stop data transmission, and therefore it will be noted that the reduced slot secures the stable data transmission with reduced signal interference. Thus, the reduced slot length reduces the probability of transmitting data in the same time slot, so that there is increased the nubmer of the terminals stopping unnecessary transmission after detection of the preamble. This increases the stability of data transmission, decreasing the signal interference in the terminals using the exclusive channel or other reverse common channels. However, since the signal broadcast from the base station to the terminal is determined by the signal received from the terminal, it is required that the slot length is maintained over a prescribed level to minimize the disadvantages caused by the transmission delay or multi-path. Namely, if the slot length is reduced below the prescribed level to reduce the level of the interference signal, the performance of the overall system is degraded because of increasing the frequency of the signal interference. Hence, it is desirable to select the slot length that may reduce the level of the signal interference with minimizing the disadvantages caused by the transmission delay and multi-path

0055Thus, the base station broadcasts a signal representing the detection of the synchronization of the data transmitted through the reverse common channel to all terminals to selectively stop unnecessary data transmission, preventing the reverse common channel from being affected by the unnecessary signal interference. This reduces the signal interference in the radio channel to decrease the power used by the terminal performing data transmission through the exclusive or reverse common channel. In addition, the terminals failed in data transmission through the reverse common channel may expediently perform retransmission, reducing delay time. Hence, the inventive apparatus may be properly applied to a high speed data transmission system such as IMT-2000.