TECHNICAL FIELD

[0001] The present invention relates to a mobile communication system, a base station, and a mobile communication terminal for carrying out a packet transmission according to the spread ALOHA system, in a radio communication that employs the code division multiple access (CDMA) system. Particularly, this invention relates to a retransmission control method to be used when a data error has occurred in a reception packet.

BACKGROUND ART

[0002] A conventional retransmission control method that has been used when a data error has occurred in a reception packet will be explained below. According to a radio communication that employs the CDMA system as a communication system, the information to be transmitted is diffused by different codes to channels so that the information on the plurality of channels can be multiplexed in the same frequency. As a method of high-speed transmitting one call information by utilizing this characteristic, there is a multi-code transmission (multiple transmission) method that carries out a high-speed transmission by allocating a plurality of codes (channels, codes) to one call. By this method, the information can be transmitted faster than when the information is transmitted using one channel.

[0003] FIG. 17 is a diagram showing an example of a multi-code transmission using a conventional mobile communication terminal. FIG. 17 ( a ) shows a normal transmission when a multiplex number M=4. FIG. 17 ( b ) shows a retransmission when a retransmission multiplex number M′=4 (M=4). FIG. 17 ( c ) shows a retransmission when a retransmission multiplex number M′=3 (M=4). FIG. 17 ( d ) shows a retransmission when a retransmission multiplex number M′=2 (M=4). FIG. 17 ( e ) shows a retransmission when a retransmission multiplex number M′=1 (M=4).

[0004] When a plurality of codes are used simultaneously in the normal transmission as shown in FIG. 17 ( a ) (corresponding to A), for example, it is possible to transmit one call information at a speed of a plurality of times faster than when this call information is transmitted by one channel. When the retransmission multiplex number M′=4 as shown in FIG. 17 ( b ), one call information uses four codes at the same time (corresponding to C). In this case, it is possible to transmit the call information at a speed four times faster than when this call information is transmitted using one channel as shown in FIG. 17 ( e ) (corresponding to F). When the retransmission multiplex number M′=3 as shown in FIG. 17 ( c ), one call information uses three codes at the same time (corresponding to D). In this case, it is possible to transmit the call information at a speed three times faster than when this call information is transmitted using one channel as shown in FIG. 17 ( e ) (corresponding to F). When the retransmission multiplex number M′=2 as shown in FIG. 17 ( d ), one call information uses two codes at the same time (corresponding to E). In this case, it is possible to transmit the call information at a speed two times faster than when this call information is transmitted using one channel as shown in FIG. 17 ( e ) (corresponding to F). In FIGS. 17 ( a ) to ( e ), portions denoted by PR are preambles B. The PR is a signal having a constant length consisting of a clock synchronization signal that is necessary for a demodulation processing, for example.

[0005] Sometimes codes that have been allocated to terminals cannot achieve a state that the codes are completely orthogonal with each other. Therefore, when the number of terminals used for simultaneous transmission increases, interference corresponding to this mutual relationship occurs. As a result, a data error occurs in the reception packet. When data errors as shown in FIGS. 17 ( b ), ( c ), ( d ) and ( e ) (corresponding to an X mark in the drawings) have occurred, each mobile communication terminal carries out a packet transmission (retransmission) with a random time interval. Based on this, each mobile communication terminal can avoid a collision with high probability, so that a plurality of mobile communication terminal can share one radio channel.

[0006] Thus, according to a conventional practice, there has been proposed a retransmission method in which the retransmission multiplex number M′ is set to a smaller value than the multiplex number M during a normal transmission, in the multi-code transmission. In the case of carrying out a multi-code transmission, a packet signal length becomes 1/multiplex number when the same volume of information is transmitted without carrying out a multiplexing. In this case, total power after the multiplexing is set constant regardless of the multiplex number.

[0007] FIG. 18 is a diagram showing an example of a multi-code transmission in the conventional mobile communication terminal disclosed in Japanese Patent Application Laid-Open (JP-A) No. 10-233758. Specifically, FIG. 18 ( a ) shows a case in which the multiplex number during a normal transmission is set as M=2 (corresponding to G- 1 and G- 2 in FIG. 18 ( a )). When a transmission error has occurred (corresponding to an X mark), this mobile communication terminal carries out a packet transmission again with a random time interval, in a similar manner to that as described above. For example, FIG. 18 ( b ) and ( c ) show two kinds of retransmission methods in multi-code transmission: a method (b) of carrying out two multiplex transmission during both the normal transmission and the retransmission, and a method (c) of not carrying out a multiplexing during the retransmission.

[0008] FIG. 19 is a diagram showing a simplified state of the diagrams shown in Japanese Patent Application Laid-Open (JP-A) No. 10-233758. Throughput characteristics of the two kinds of packet retransmission methods shown in FIGS. 18 ( b ) and ( c ). In FIG. 19 , throughput in the vertical axis shows a product of an average traffic and a packet success probability. When the throughput is larger, it is possible to transmit more information. In other words, when the throughput is larger, it is possible to accommodate more users. On the other hand, the channel traffic in the horizontal axis shows an average number of terminals during a transmission to a radio channel (a call volume including retransmission). FIG. 19, a dotted line and a solid line show the throughput characteristics of FIGS. 18 ( b ) and ( c ) respectively. According to the conventional retransmission control method, it has been possible to obtain the throughput shown in FIG. 19 by carrying out the controls shown in FIGS. 18 ( b ) and ( c ) respectively.

[0009] According to the conventional retransmission control method, when the channel traffic is small as shown in FIG. 18 , that is, when the channel traffic is smaller than a threshold value th3, it is possible to obtain optimum throughput by the control of (c). On the other hand, when the channel traffic is relatively large, that is, when the channel traffic is larger than the threshold value th3, it is possible to obtain optimum throughput by the control of (b). As explained above, according to the conventional retransmission control method, there has been a problem in that in order to obtain always-optimum throughput, it is necessary to select a retransmission method of either (b) or (c) based on the channel traffic. Further, there has been a problem that it is impossible to accurately measure channel traffic in the actual devices because of the interference and others.

[0010] It is an object of the present invention to provide a mobile communication system, a base station, a mobile communication terminal, and a retransmission control method, capable of obtaining always optimum throughput under the existence of any channel traffic.

DISCLOSURE OF INVENTION

[0011] In order to achieve the above object, according to a first aspect of the present invention, there is provided a mobile communication system for carrying out a packet transmission based on the spread ALOHA system, the mobile communication system comprising: a base station (corresponding to a base station 2 in an embodiment to be described later) that measures an uplink interference value of a transmission path when a data error has occurred in reception packets multiplexed by plurality, generates a retransmission request signal of a packet format based on the measured uplink interference value, and then transmits the retransmission request signal to a mobile communication terminal that has transmitted the erroneous packet; and a mobile communication terminal (corresponding to a mobile station 1 ) that outputs multiplexed transmission data as a transmission packet during a normal transmission, automatically divides the transmission data into parallel signals according to a retransmission multiplex number based on the retransmission request signal when the retransmission request signal has been received, further multiplexes the parallel signals to generate a transmission packet for retransmission, and outputs the transmission packet to the base station.

[0012] According to the above aspect, a retransmission multiplex number is determined based on a measured uplink interference value. Therefore, it is possible to change the multiplex number at the retransmission time according to the uplink interference value. Further, it is possible to obtain a mobile communication system capable of obtaining optimum throughput under the existence of any channel traffic.

[0013] Further, according to a second aspect of the invention, there is provided a mobile communication system of the above aspect, wherein the base station generates a retransmission request signal of a packet data format including the uplink interference value, and transmits the retransmission request signal to the mobile communication terminal that has transmitted the erroneous packet, and the mobile communication terminal extracts the uplink interference value from the received retransmission request signal, compares the uplink interference value with a predetermined threshold value having a plurality of stages, and determines a retransmission multiplex number according to the uplink interference value based on a result of this comparison.

[0014] According to the above aspect, the mobile communication terminal compares the uplink interference value with a predetermined threshold value having a plurality of stages based on the uplink interference value measured by the base station, and determines a retransmission multiplex number according to the uplink interference value.

[0015] Further, according to a third aspect of the invention, there is provided a mobile communication system of the above aspect, wherein the base station generates a retransmission request signal of a packet data format including the uplink interference value, and transmits the retransmission request signal to the mobile communication terminal that has transmitted the erroneous packet, and the mobile communication terminal extracts the uplink interference value from the received retransmission request signal, compares the uplink interference value with a predetermined threshold value, does not multiplex the retransmission data when the uplink interference value is lower than the threshold value, and determines a retransmission multiplex number to be in the same number as the multiplex number during a normal transmission when the uplink interference value is equal to or higher than the threshold value.

[0016] According to the above aspect, the mobile communication terminal compares the uplink interference value with a predetermined threshold value based on the uplink interference value measured by the base station, and determines whether the retransmission data is to be multiplexed or not based on a result of this comparison.

[0017] Further, according to a fourth aspect of the invention, there is provided a mobile communication system of the above aspect, wherein the base station generates a retransmission request signal of a packet data format including the uplink interference value, and transmits the retransmission request signal to the mobile communication terminal that has transmitted the erroneous packet, and the mobile communication terminal extracts the uplink interference value from the received retransmission request signal, obtains a probability for determining a retransmission multiplex number based on the uplink interference value, generates a random number of 0 or 1 based on this probability, does not multiplex the retransmission data when the random number is 0, and determines a retransmission multiplex number to be in the same number as the multiplex number during a normal transmission when the random number is 1.

[0018] According to the above aspect, the mobile communication terminal obtains a probability for determining a retransmission multiplex number based on the uplink interference value measured by the base station, and determines the retransmission multiplex number based on this probability.

[0019] Further, according to a fifth aspect of the invention, there is provided a mobile communication system of the above aspect, wherein the base station compares the uplink interference value with a predetermined threshold value having a plurality of stages, determines a retransmission multiplex number according to the uplink interference value based on a result of this comparison, generates a retransmission request signal of a packet data format including the retransmission multiplex number, and transmits the retransmission request signal to the mobile communication terminal that has transmitted the erroneous packet, and the mobile communication terminal extracts the retransmission multiplex number from the received retransmission request signal, and retransmits the transmission data according to the retransmission multiplex number.

[0020] According to the above aspect, the base station compares the measured uplink interference value with a predetermined threshold value having a plurality of stages, and determines a retransmission multiplex number according to the uplink interference value based on a result of this comparison. The mobile communication terminal retransmits the transmission data based on the received retransmission multiplex number.

[0021] Further, according to a sixth aspect of the invention, there is provided a mobile communication system of the above aspect, wherein the base station compares the uplink interference value with a predetermined threshold value, does not multiplex the retransmission data when the uplink interference value is lower than the threshold value, determines a retransmission multiplex number to be in the same number as the multiplex number during a normal transmission when the uplink interference value is equal to or higher than the threshold value, generates a retransmission request signal of a packet data format including the retransmission multiplex number, and transmits the retransmission request signal to the mobile communication terminal that has transmitted the erroneous packet, and the mobile communication terminal extracts the retransmission multiplex number from the received retransmission request signal, and retransmits the transmission data according to the retransmission multiplex number.

[0022] According to the above aspect, the base station compares the measured uplink interference value with a predetermined threshold value, and determines whether the retransmission data is to be multiplexed or not based on a result of this comparison. The mobile communication terminal retransmits the transmission data based on the received retransmission multiplex number information.

[0023] Further, according to a seventh aspect of the invention, there is provided a mobile communication system of the above aspect, wherein the base station obtains a probability for determining a retransmission multiplex number based on the measured uplink interference value, generates a random number of 0 or 1 based on this probability, does not multiplex the retransmission data when the random number is 0, determines a retransmission multiplex number to be in the same number as the multiplex number during a normal transmission when the random number is 1, generates a retransmission request signal of a packet data format including the retransmission multiplex number, and transmits the retransmission request signal to the mobile communication terminal that has transmitted the erroneous packet, and the mobile communication terminal extracts the retransmission multiplex number from the received retransmission request signal, and retransmits the transmission data according to the retransmission multiplex number.

[0024] According to the above aspect, the base station obtains a probability for determining a retransmission multiplex number based on the measured uplink interference value, determines a retransmission multiplex number based on this probability, and determines a retransmission multiplex number according to the measured uplink interference value. The mobile communication terminal retransmits the transmission data based on the received retransmission multiplex number information.

[0025] Further, according to an eighth aspect of the invention, there is provided a mobile communication system of the above aspect, wherein the base station obtains a probability for determining a retransmission multiplex number based on the measured uplink interference value, generates a retransmission request signal of a packet data format including the probability, and transmits the retransmission request signal to the mobile communication terminal that has transmitted the erroneous packet, and the mobile communication terminal extracts the probability from the received retransmission request signal, generates a random number of 0 or 1 based on this probability, does not multiplex the retransmission data when the random number is 0, and determines a retransmission multiplex number to be in the same number as the multiplex number during a normal transmission when the random number is 1.

[0026] According to the above aspect, the base station obtains a probability for determining a retransmission multiplex number based on the measured uplink interference value. The mobile communication terminal determines a retransmission multiplex number based on the received probability information, and retransmits the transmission data.

[0027] Further, according to a ninth aspect of the present invention, there is provided a base station for carrying out a packet transmission based on the spread ALOHA system, wherein the base station measures an uplink interference value of a transmission path when a data error has occurred in reception packets multiplexed by plurality, generates a retransmission request signal of a packet format based on the measured uplink interference value, and then transmits the retransmission request signal to a mobile communication terminal that has transmitted the erroneous packet.

[0028] According to the above aspect, a retransmission multiplex number is determined based on a measured uplink interference value. Therefore, it is possible to change the multiplex number at the retransmission time according to the uplink interference value.

[0029] Further, according to a tenth aspect of the present invention, there is provided a base station of the above aspect, the base station comprising: a data detecting unit (corresponding to spectrum despreading demodulators 22 - 1 to 22 -J, demodulators 23 - 1 to 23 -J, and a data detector 24 ) that despreads and demodulates the received packet, extracts user data from a demodulated data signal thereby to always monitor a data error in the reception packets, and measures an uplink interference value when there has been a data error; a retransmission request generating unit (corresponding to a traffic control signal generator 25 ) that generates a retransmission request signal based on the measured uplink interference value; and a transmitting unit (corresponding to a spectrum spreading modulator 26 , a carrier generator 27 , and a transmitter 28 ) that converts the retransmission request signal into a packet format, and outputs the retransmission request signal in the packet format.

[0030] According to the above aspect, the base station transmits a retransmission request signal including a measured uplink interference value to a mobile communication terminal. Therefore, it is possible to omit the arithmetic processing for determining a retransmission multiplex number at the base station, which can simplify the structure of the apparatus.

[0031] Further, according to an eleventh aspect of the invention, there is provided abase station of the above aspect, wherein the base station generates a retransmission request signal of a packet data format including the uplink interference value, and transmits the retransmission request signal to the mobile communication terminal that has transmitted the erroneous packet.

[0032] According to the above aspect, the mobile communication terminal determines a retransmission multiplex number based on the uplink interference value measured by the base station.

[0033] Further, according to a twelfth aspect of the invention, there is provided a base station of the above aspect, wherein the base station compares the uplink interference value with a predetermined threshold value having a plurality of stages, determines a retransmission multiplex number according to the uplink interference value based on a result of this comparison, generates a retransmission request signal of a packet data format including the retransmission multiplex number, and transmits the retransmission request signal to the mobile communication terminal that has transmitted the erroneous packet.

[0034] According to the above aspect, the base station compares the measured uplink interference value with a predetermined threshold value having a plurality of stages, and determines a retransmission multiplex number according to the uplink interference value based on a result of this comparison. The mobile communication terminal retransmits the transmission data based on the received retransmission multiplex number.

[0035] Further, according to a thirteenth aspect of the invention, there is provided a base station of the above aspect, wherein the base station compares the uplink interference value with a predetermined threshold value, does not multiplex the retransmission data when the uplink interference value is lower than the threshold value, determines a retransmission multiplex number to be in the same number as the multiplex number during a normal transmission when the uplink interference value is equal to or higher than the threshold value, generates a retransmission request signal of a packet data format including the retransmission multiplex number, and transmits the retransmission request signal to the mobile communication terminal that has transmitted the erroneous packet.

[0036] According to the above aspect, the base station compares the measured uplink interference value with a predetermined threshold value, and determines whether the retransmission data is to be multiplexed or not based on a result of this comparison. The mobile communication terminal retransmits the transmission data based on the received retransmission multiplex number.

[0037] Further, according to a fourteenth aspect of the invention, there is provided a base station of the above aspect, wherein the base station obtains a probability for determining a retransmission multiplex number based on the measured uplink interference value, generates a random number of 0 or 1 based on this probability, does not multiplex the retransmission data when the random number is 0, determines a retransmission multiplex number to be in the same number as the multiplex number during a normal transmission when the random number is 1, generates a retransmission request signal of a packet data format including the retransmission multiplex number, and transmits the retransmission request signal to the mobile communication terminal that has transmitted the erroneous packet.

[0038] According to the above aspect, the base station obtains a probability for determining a retransmission multiplex number based on the measured uplink interference value, determines a retransmission multiplex number based on this probability, and determines a retransmission multiplex number according to the measured uplink interference value. The mobile communication terminal retransmits the transmission data based on the received retransmission multiplex number information.

[0039] Further, according to a fifteenth aspect of the invention, there is provided a base station of the above aspect, wherein the base station obtains a probability for determining are transmission multiplex number based on the measured uplink interference value, generates a retransmission request signal of a packet data format including the probability, and transmits the retransmission request signal to the mobile communication terminal that has transmitted the erroneous packet.

[0040] According to the above aspect, the base station obtains a probability for determining a retransmission multiplex number based on the measured uplink interference value. The mobile communication terminal determines a retransmission multiplex number based on the received probability information, and retransmits the transmission data.

[0041] Further, according to a sixteenth aspect of the invention, there is provided a mobile communication terminal for carrying out a packet transmission based on the spread ALOHA system, wherein the mobile communication terminal outputs multiplexed transmission data as a transmission packet during a normal transmission, automatically divides the transmission data into parallel signals according to a retransmission multiplex number determined based on the retransmission request signal when the retransmission request signal has been received, further multiplexes the parallel signals to generate a transmission packet for retransmission, and outputs the transmission packet to the base station.

[0042] According to the above aspect, a retransmission multiplex number is determined based on a measured uplink interference value. Therefore, it is possible to obtain the mobile communication terminal capable of changing the multiplex number at the retransmission time according to the uplink interference value.

[0043] Further, according to a seventeenth aspect of the invention, there is provided a mobile communication terminal of the above aspect, the mobile communication terminal comprising: a series-parallel converting unit (corresponding to a deserializer 4 ) that converts the internally generated transmission data into parallel signals according to a predetermined multiplex number; a transmitting unit (corresponding to spectrum spreading modulators 7 - 1 to 7 -M, an adder 8 , a carrier generator 9 , and a transmitter 10 ) that spreading modulates the plurality of parallel signals, multiplexes the modulation signals by a predetermined method, and outputs the multiplexed modulation signals as a transmission packet; a retransmission request detecting unit (corresponding to an spectrum despreading demodulator 13 , a demodulator 14 , and a data detector 15 ) that receives a retransmission request signal in the packet format, and despreads and demodulates this signal thereby to detect the retransmission request signal; and a control unit (corresponding to a control section 16 ) that decides a multiplex number of the parallel signals used by the series-parallel converting unit, based on the retransmission request signal.

[0044] According to the above aspect, the mobile communication terminal that has received a retransmission request signal determines a multiplex number based on this signal, automatically converts the transmission data into parallel signals, and then multiplexes the parallel signals. Based on this arrangement, it is possible to take a plurality of values for the multiplex number at the mobile communication terminal. Further, it is not necessary to change over the series-parallel converting unit by a changeover switch or the like when the multiplex number is changed over. Therefore, it is possible to simplify the structure of the apparatus.

[0045] Further, according to an eighteenth aspect of the invention, there is provided a mobile communication terminal of the above aspect, wherein the mobile communication terminal extracts an uplink interference value from the received retransmission request signal, compares this uplink interference value with a predetermined threshold value having a plurality of stages, and determines the retransmission multiplex number according to the uplink interference value based on a result of this comparison.

[0046] According to the above aspect, the mobile communication terminal compares the uplink interference value with a predetermined threshold value having a plurality of stages, and determines the retransmission multiplex number according to the uplink interference value based on a result of this comparison.

[0047] Further, according to a nineteenth aspect of the invention, there is provided a mobile communication terminal of the above aspect, wherein the mobile communication terminal extracts the uplink interference value from the received retransmission request signal, compares the uplink interference value with a predetermined threshold value, does not multiplex the retransmission data when the uplink interference value is lower than the threshold value, and determines a retransmission multiplex number to be in the same number as the multiplex number during a normal transmission when the uplink interference value is equal to or higher than the threshold value.

[0048] According to the above aspect, the mobile communication terminal compares the uplink interference value with a predetermined threshold value based on the uplink interference value measured by the base station, and determines whether the retransmission data is to be multiplexed or not based on a result of this comparison.

[0049] Further, according to a twentieth aspect of the invention, there is provided a mobile communication terminal of the above aspect, wherein the mobile communication terminal extracts the uplink interference value from the received retransmission request signal, obtains a probability for determining a retransmission multiplex number based on the uplink interference value, generates a random number of 0 or 1 based on this probability, does not multiplex the retransmission data when the random number is 0, and determines a retransmission multiplex number to be in the same number as the multiplex number during a normal transmission when the random number is 1.

[0050] According to the above aspect, the mobile communication terminal obtains a probability for determining a retransmission multiplex number based on the uplink interference value measured by the base station, and determines the retransmission multiplex number based on this probability.

[0051] Further, according to a twenty-first aspect of the invention, there is provided a mobile communication terminal of the above aspect, wherein the mobile communication terminal extracts the retransmission multiplex number from the received retransmission request signal, and retransmits the transmission data according to the retransmission multiplex number.

[0052] According to the above aspect, the base station determines a retransmission multiplex number based on a measured uplink interference value, and the mobile communication terminal carries out a retransmission based on the determined retransmission multiplex number.

[0053] Further, according to an twenty-second aspect of the invention, there is provided a mobile communication terminal of the above aspect, wherein the mobile communication terminal extracts the probability from the received retransmission request signal, generates a random number of 0 or 1 based on this probability, does not multiplex the retransmission data when the random number is 0, and determines a retransmission multiplex number to be in the same number as the multiplex number during a normal transmission when the random number is 1.

[0054] According to the above aspect, the base station obtains a probability for determining a retransmission multiplex number based on the measured uplink interference value. The mobile communication terminal determines a retransmission multiplex number based on the received probability information, and retransmits the transmission data.

[0055] Further, according to a twenty-third aspect of the present invention, there is provided a retransmission control method for controlling a retransmission between a mobile communication terminal and a base station in a mobile communication system for carrying out a packet transmission based on the spread ALOHA system, the retransmission control method comprising: a retransmission request signal transmission step (corresponding to FIG. 4 , FIG. 11 , FIG. 13 , FIG. 14 , and FIG. 15 ) of measuring an uplink interference value of a transmission path when a data error has occurred in reception packets multiplexed by plurality, generating a retransmission request signal of a packet format based on the measured uplink interference value, and then transmitting the retransmission request signal to a mobile communication terminal that has transmitted the erroneous packet; and a retransmission step (corresponding to FIG. 5 , FIG. 7 , FIG. 9 , FIG. 12 , and FIG. 16 ) of automatically dividing the transmission data into parallel signals according to a retransmission multiplex number based on the retransmission request signal when the retransmission request signal has been received, further multiplexing the parallel signals to generate a transmission packet for retransmission, and outputting the transmission packet to the base station.

[0056] According to the above aspect, a retransmission multiplex number is determined based on a measured uplink interference value. Therefore, it is possible to change the multiplex number at the retransmission time according to the uplink interference value. Further, it is possible to obtain a retransmission control method capable of obtaining optimum throughput under the existence of any channel traffic.

[0057] Further, according to a twenty-fourth aspect of the invention, there is provided a retransmission control method of the above aspect, wherein the retransmission request signal transmission step is for generating a retransmission request signal of a packet data format including the uplink interference value, and transmitting the retransmission request signal to the mobile communication terminal that has transmitted the erroneous packet (corresponding to FIG. 4 ), and the retransmission step is for extracting the uplink interference value from the received retransmission request signal, comparing the uplink interference value with a predetermined threshold value having a plurality of stages, and determining a retransmission multiplex number according to the uplink interference value based on a result of this comparison (corresponding to FIG. 5 ).

[0058] According to the above aspect, at the retransmission step, the uplink interference value is compared with a predetermined threshold value having a plurality of stages. A retransmission multiplex number is determined according to the uplink interference value, based on the uplink interference value measured at the retransmission request signal transmission step.

[0059] Further, according to a twenty-fifth aspect of the invention, there is provided a retransmission control method of the above aspect, wherein the retransmission request signal transmission step is for generating a retransmission request signal of a packet data format including the uplink interference value, and transmitting the retransmission request signal to the mobile communication terminal that has transmitted the erroneous packet (corresponding to FIG. 4 ), and the retransmission step is for extracting the uplink interference value from the received retransmission request signal, comparing the uplink interference value with a predetermined threshold value, not multiplexing the retransmission data when the uplink interference value is lower than the threshold value, and determining a retransmission multiplex number to be in the same number as the multiplex number during a normal transmission when the uplink interference value is equal to or higher than the threshold value (corresponding to FIG. 7 ).

[0060] According to the above aspect, at the retransmission step, the uplink interference value is compared with a predetermined threshold value and it is determined whether the retransmission data is to be multiplexed or not, based on the uplink interference value measured at the retransmission request signal transmission step.

[0061] Further, according to a twenty-sixth aspect of the invention, there is provided a retransmission control method of the above aspect, wherein the retransmission request signal transmission step is for generating a retransmission request signal of a packet data format including the uplink interference value, and transmitting the retransmission request signal to the mobile communication terminal that has transmitted the erroneous packet (corresponding to FIG. 4 ), and the retransmission step is for extracting the uplink interference value from the received retransmission request signal, obtaining a probability for determining a retransmission multiplex number based on the uplink interference value, generating a random number of 0 or 1 based on this probability, not multiplexing the retransmission data when the random number is 0, and determining a retransmission multiplex number to be in the same number as the multiplex number during a normal transmission when the random number is 1 (corresponding to FIG. 9 ).

[0062] According to the above aspect, at the retransmission step, a probability for determining a retransmission multiplex number is obtained and the retransmission multiplex number is determined using this probability, based on the uplink interference value measured by the base station.

[0063] Further, according to a twenty-seventh aspect of the invention, there is provided a retransmission control method of the above aspect, wherein the retransmission request signal transmission step is for comparing the uplink interference value with a predetermined threshold value having a plurality of stages, determining a retransmission multiplex number according to the uplink interference value based on a result of this comparison, generating a retransmission request signal of a packet data format including the retransmission multiplex number, and transmitting the retransmission request signal to the mobile communication terminal that has transmitted the erroneous packet (corresponding to FIG. 11 ), and the retransmission step is for extracting the retransmission multiplex number from the received retransmission request signal, and retransferring the transmission data according to the retransmission multiplex number (corresponding to FIG. 12 ).

[0064] According to the above aspect, at the retransmission request signal transmission step, the measured uplink interference value is compared with a predetermined threshold value having a plurality of stages, and a retransmission multiplex number according to the uplink interference value is determined based on a result of this comparison. At the retransmission step, the transmission data is retransmitted based on the received retransmission multiplex number.

[0065] Further, according to a twenty-eighth aspect of the invention, there is provided a retransmission control method of the above aspect, wherein the retransmission request signal transmission step is for comparing the uplink interference value with a predetermined threshold value, not multiplexing the retransmission data when the uplink interference value is lower than the threshold value, determining a retransmission multiplex number to be in the same number as the multiplex number during a normal transmission when the uplink interference value is equal to or higher than the threshold value, generating a retransmission request signal of a packet data format including the retransmission multiplex number, and transmitting the retransmission request signal to the mobile communication terminal that has transmitted the erroneous packet (corresponding to FIG. 13 ), and the retransmission step is for extracting the retransmission multiplex number from the received retransmission request signal, and retransferring the transmission data according to the retransmission multiplex number (corresponding to FIG. 12 ).

[0066] According to the above aspect, at the retransmission request signal transmission step, the measured uplink interference value is compared with a predetermined threshold value, and whether the retransmission data is to be multiplexed or not is determined based on a result of this comparison. At the retransmission step, the transmission data is retransmitted based on the received retransmission multiplex number information.

[0067] Further, according to a twenty-ninth aspect of the invention, there is provided a retransmission control method of the above aspect, wherein the retransmission request signal transmission step is for obtaining a probability for determining a retransmission multiplex number based on the measured uplink interference value, generating a random number of 0 or 1 based on this probability, not multiplexing the retransmission data when the random number is 0, determining a retransmission multiplex number to be in the same number as the multiplex number during a normal transmission when the random number is 1, generating a retransmission request signal of a packet data format including the retransmission multiplex number, and transmitting the retransmission request signal to the mobile communication terminal that has transmitted the erroneous packet (corresponding to FIG. 14 ), and the retransmission step is for extracting the retransmission multiplex number from the received retransmission request signal, and retransferring the transmission data according to the retransmission multiplex number (corresponding to FIG. 12 ).

[0068] According to the above aspect, at the retransmission request signal transmission step, a probability for determining a retransmission multiplex number is obtained based on the measured uplink interference value, a retransmission multiplex number is determined based on this probability, and a retransmission multiplex number is determined according to the measured uplink interference value. At the retransmission step, the transmission data is retransmitted based on the received retransmission multiplex number information.

[0069] Further, according to a thirtieth aspect of the invention, there is provided a retransmission control method of the above aspect, wherein the retransmission request signal transmission step is for obtaining a probability for determining a retransmission multiplex number based on the measured uplink interference value, generating a retransmission request signal of a packet data format including the probability, and transmitting the retransmission request signal to the mobile communication terminal that has transmitted the erroneous packet (corresponding to FIG. 15 ), and the retransmission step is for extracting the probability from the received retransmission request signal, generating a random number of 0 or 1 based on this probability, not multiplexing the retransmission data when the random number is 0, and determining a retransmission multiplex number to be in the same number as the multiplex number during a normal transmission when the random number is 1 (corresponding to FIG. 16 ).

[0070] According to the above aspect, at the retransmission request signal transmission step, a probability for determining a retransmission multiplex number is obtained based on the measured uplink interference value. At the retransmission step, a retransmission multiplex number is determined based on the received probability information, and the transmission data is retransmitted.