JP4376658B2 - Base station apparatus, mobile terminal and mobile communication system - Google Patents

Description

  The present invention relates to a mobile communication system in which a modulation scheme is switched according to channel quality when communication is performed between a mobile terminal and a base station, and a base station apparatus and a mobile terminal used in this system. .

  In recent mobile communication systems, as one of means for solving the demand for higher speed of data communication, an adaptive modulation method in which a plurality of modulation methods are prepared and the modulation method is switched according to the line quality has come to be used. I came. Multiple modulation methods with different bit rates are used. For example, BPSK (Binary Phase Shift keying), QPSK (Quadrature Phase Shift keying), 8PSK (8 Phase Shift keying), 16QAM (16 Quadrature) A modulation method such as Amplitude Moduration is used. In a mobile communication system using such an adaptive modulation method, when the channel quality is good, the data transmission speed is increased by switching to a modulation method with a higher bit rate, and when the channel quality is poor, the modulation method with a lower bit rate. The data transmission rate and the transmission error are reduced in the entire communication by switching to the above and lowering the data transmission rate.

Next, the above items will be described with reference to FIG.
FIG. 4 is a block diagram showing a mobile communication system using a conventional adaptive modulation system. The following description is for the adaptive modulation method in the communication direction from the base station 1 to the mobile station 2, but the same is true for the communication direction from the mobile station 2 to the base station 1.
In FIG. 4, in the base station 1, the modulation scheme control unit 11 initially sets the most standard modulation scheme among the plurality of modulation schemes in the transmission baseband processing unit 12. The transmission baseband processing unit 12 modulates transmission data by the above-described modulation scheme, and the transmission RF processing unit 13 converts the modulated signal into an RF signal and transmits it to the mobile station (mobile terminal) 2. .

In the mobile station 2, after the RF signal received by the reception RF processing unit 21 is returned to the baseband signal, the reception baseband processing unit 22 demodulates the original data. Next, the line quality calculation unit 23 calculates the line quality based on the demodulated data. The channel quality changes every moment depending on the installation location and propagation environment of the mobile station 2, and the value is closely related to the data transmission rate that the mobile station 2 can receive. The calculated line quality information is output to the transmission baseband processing unit 24. The transmission baseband processing unit 24 multiplexes the channel quality information into the transmission data of the mobile station 2, and the transmission RF processing unit 25 converts the multiplexed transmission data into an RF signal and transmits it to the base station 1.

  In the base station 1, the reception RF processing unit 14 returns the RF signal including the channel quality information from the mobile station 2 to the baseband signal, and then demodulates the reception baseband processing unit 15. Is extracted and notified to the modulation scheme control unit 11. The modulation scheme control unit 11 determines a modulation scheme to be used for the next transmission data based on the line quality information. That is, the value of the line quality information is compared with the value at the previous transmission, and if the two are different, the modulation scheme is changed, and if the two are the same, the previous modulation scheme is maintained as it is. Through such a series of operations, the base station 1 can transmit data at the maximum data transmission rate that can be received by the mobile station 2 at the present time, and can realize high-speed communication.

FIG. 5 is a flowchart showing processing based on the above operation.
Transmit data with initial setting of modulation method on the transmission side (step S1), compare the line quality sent from the reception side with the previous line quality (S2), and decide to change the modulation method if they are different If it is the same, the decision is made to keep the previous modulation method as it is (S4). In accordance with this determination, a modulation scheme is set (S5), and data modulated by the modulation scheme is transmitted (S6). Data is received on the receiving side (S7), channel quality is calculated (S8), the channel quality information is quantized and multiplexed into data, and transmitted to the transmitting side (S9). The transmission side compares again with the previous line quality (S2), and the same processing is repeated thereafter.

  FIG. 6 shows an example of channel quality and post-quantization channel quality for each modulation method such as BPSK, QPSK, 8PSK, 16QAM.

As a conventional technique, an adaptive modulation scheme transceiver for TDD using an adaptive modulation scheme has been proposed (for example, see Patent Document 1).
Japanese Unexamined Patent Publication No. 9-200282

In step S2 of FIG. 5 described above, when the transmission side compares and determines whether or not the line quality is the same as the previous time, the demodulation method used on the transmission side uses the demodulation method corresponding to the previously used modulation method. In that case, if the line quality is worse than the previous time, demodulation becomes difficult and an error occurs. When this error occurs a predetermined number of times, it is determined that the line quality is different. If the line quality is better than the previous time, the comparison determination is performed after sequentially changing to a modulation method having a higher bit rate until an error occurs.
Since the line quality comparison / determination is performed as described above, the negotiation process between steps S2 to S9 in FIG. 4 is required between the transmission side and the reception side until an error occurs a predetermined number of times and a determination result is obtained. In the meantime, there was a problem that the communication was interrupted and the throughput was lowered.
Accordingly, it is an object of the present invention to solve the above-described problems and reduce a decrease in throughput.

A base station apparatus according to the present invention comprises a communication means for communicating with a mobile terminal, a line quality receiving means for receiving a line quality notified from the mobile terminal, and at least the communication means according to the received line quality comprises a modulation scheme changeover means for switching a modulation scheme to be used to calculate the remaining amount of the transmission data, and the data remaining amount calculation means for controlling the modulation scheme changeover means in accordance with the remaining amount of the transmission data calculated, with, The modulation method switching means does not switch the modulation method regardless of the channel quality when the remaining amount of transmission data is equal to or less than a threshold value .

Further, the mobile terminal according to the present invention is a mobile terminal having communication means for communicating with a base station apparatus, and modulation scheme switching means for switching a modulation scheme in accordance with channel quality notified from the base station apparatus. Data remaining amount calculating means for calculating the remaining amount of transmission data and controlling the modulation method switching means according to the calculated remaining amount of transmission data, the modulation method switching means, wherein the remaining amount of transmission data is a threshold value In the following cases, the modulation method is not switched regardless of the channel quality .

The mobile communication system according to the present invention includes a first communication unit that communicates with a base station apparatus, a channel quality calculation unit that calculates channel quality, and the calculated communication channel that transmits the calculated channel quality to the first communication unit. A mobile terminal provided with a channel quality notification means for notifying to the base station apparatus, a second communication means for communicating with the mobile terminal, and a line quality receiving means for receiving the notified line quality And a modulation scheme switching means for switching at least a modulation scheme used in the second communication unit according to the channel quality, and the modulation scheme according to the calculated remaining amount of transmission data by calculating the remaining amount of transmission data. a mobile terminal that includes a data remaining level calculation means for controlling the switching means, Ri Tona, the modulation scheme changeover means, said time transmitting data remaining is equal to or smaller than the threshold regardless of the channel quality which is the calculated Modulation method Is not performed .

ADVANTAGE OF THE INVENTION According to this invention, in the mobile communication system using an adaptive modulation system, interruption of communication time can be reduced and the fall of a throughput can be reduced.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a mobile communication system based on an adaptive modulation system according to an embodiment of the present invention, and parts corresponding to those in FIG. The transmission data amount calculation unit 16 calculates the remaining amount of transmission data currently being transmitted (for example, the remaining amount of a file being downloaded) and controls the modulation scheme control unit 11 according to the calculation result. . That is, when the remaining amount of transmission data is small, the modulation scheme control unit 11 does not switch the modulation scheme regardless of the channel quality notified from the mobile terminal 2.

  As described above, conventionally, when the channel quality changes, negotiation is required to switch the modulation method, and the throughput decreases during that time. However, when the remaining amount of transmission data is small, the channel quality is Even if it deteriorates, it may be advantageous from the viewpoint of data transmission efficiency of the entire communication to transmit using the same modulation method as it is without performing time-consuming negotiation.

Next, the operation will be described. Note that the transmission baseband processing unit 12 of the base station 1 and the transmission baseband processing unit 24 of the mobile station 2 have, for example, modulation circuits using a plurality of modulation schemes having different bit rates as shown in FIG. In addition, the reception baseband processing unit 14 of the base station 1 and the reception baseband processing unit 22 of the mobile station 2 have demodulation circuits corresponding to the plurality of modulation schemes.
In FIG. 1, first, the modulation scheme control unit 11 of the base station (base station apparatus) 1 initially sets the most standard modulation scheme among the plurality of modulation schemes in the transmission baseband processing unit 12. The transmission data is modulated with the above-described modulation scheme. The transmission RF processing unit 13 converts the modulated signal into an RF signal and transmits it to the mobile station (mobile terminal) 2.

In the mobile station 2, after the RF signal received by the reception RF processing unit 21 is returned to the baseband signal, the reception baseband processing unit 22 demodulates the original data. Next, the line quality calculation unit 23 calculates the line quality based on the demodulated data. The channel quality changes every moment depending on the installation location and propagation environment of the mobile station 2, and the value is closely related to the data transmission rate that the mobile station 2 can receive. The calculated line quality information is output to the transmission baseband processing unit 24. The transmission baseband processing unit 24 multiplexes the channel quality information into the transmission data of the mobile station 2, and the transmission RF processing unit 25 converts the multiplexed transmission data into an RF signal and transmits it to the base station 1.

  In the base station 1, the reception RF processing unit 14 returns the RF signal including the channel quality information from the mobile station 2 to the baseband signal, and then demodulates the reception baseband processing unit 15. Is extracted and notified to the modulation scheme control unit 11. The modulation scheme control unit 11 determines a modulation scheme to be used for the next transmission data based on the line quality information. That is, the value of the line quality information is compared with the value at the previous transmission, and if the two are different, the modulation scheme is changed, and if the two are the same, the previous modulation scheme is maintained as it is. When changing the modulation method, if the line quality is good, switch to a modulation method with a higher bit rate to increase the data transmission speed, and if the line quality is deteriorated, switch to a modulation method with a lower bit rate. Reduce the data transmission rate.

On the other hand, the transmission data amount calculation unit 16 calculates the remaining amount of currently transmitted data, and notifies the modulation scheme control unit 11 of the calculated remaining amount information. The modulation method control unit 11 enables switching of the modulation method if the remaining data amount exceeds the threshold value, and prohibits switching of the modulation method if the remaining data amount is less than the threshold value.

  The above explanation is for the case of the adaptive modulation method in the communication direction from the base station 1 to the mobile station 2, but the mobile station 2 includes the modulation method control unit 11 and the transmission data amount calculation unit 16, and the base station 1 includes By providing the channel quality calculation unit 23, the same as described above is established in the communication direction from the mobile station 2 to the base station 1.

FIG. 2 is a flowchart showing processing based on the above-described operation according to the first embodiment, and processing corresponding to FIG. 5 is assigned the same step number.
In the present embodiment, step S10 is newly provided to perform processing for comparing the remaining amount of transmission data with the threshold value α. First, the transmission side initializes the modulation method and transmits data (S1). The line quality sent from the reception side is compared with the previous line quality (S2). It is checked whether or not the threshold value α is exceeded (S10), and if so, a decision is made to change the modulation method (S3). If not exceeded, a decision is made to maintain the previous modulation scheme (S4). Also, when the line quality is the same as the previous line quality in S2, it is determined to maintain the previous modulation scheme (S4). A modulation scheme is set according to the above determination (S5), and data modulated by the modulation scheme is transmitted (S6). Data is received on the receiving side (S7), channel quality is calculated (S8), the channel quality information is quantized and multiplexed into data, and transmitted to the transmitting side (S9). The transmission side compares again with the previous line quality (S2), and the same processing is repeated thereafter.

According to the present embodiment, the base station 1 can transmit data at the maximum data transmission rate that can be received by the mobile station 2 at the present time by the above-described series of operations, thereby realizing high-speed communication. it can. Further, when the remaining amount of transmission data is small, the switching of the modulation method is prohibited, and thus negotiation is omitted. Therefore, the interruption of communication in the entire communication is reduced, and the reduction in throughput can be reduced.

FIG. 3 is a flowchart showing processing based on the above-described operation according to the second embodiment, and processing corresponding to that in FIG. 2 is given the same step number.
In this embodiment, two threshold values α and β are provided, and accordingly, steps S11 to S15 are newly provided. First, after the transmission side initializes the modulation method and transmits data (S1), the relationship between the current line quality (A) and the previous line quality (B) is examined (S11). If A> B, it is checked whether or not the remaining amount of transmission data exceeds the threshold value α (S12), and if it exceeds, a decision is made to change the modulation method (S13). If not exceeded, a decision is made to maintain the previous modulation scheme (S4). Also, when A = B in S11, it is determined to maintain the previous modulation scheme (S4). If A <B in S11, it is checked whether or not the remaining amount of transmission data exceeds the threshold value β (S14). If not exceeded, a decision is made to maintain the previous modulation scheme (S4). A modulation scheme is set according to the determination of S13, S15, and S4 (S5), and data modulated by the modulation scheme is transmitted (S6). Data is received on the receiving side (S7), channel quality is calculated (S8), the channel quality information is quantized and multiplexed into data, and transmitted to the transmitting side (S9). The transmission side compares again with the previous line quality (S2), and the same processing is repeated thereafter.

  In the present embodiment, whether or not the current line quality (A) is improved, deteriorated or the same as the previous line quality (B) is checked by S11. If they are the same, the modulation scheme is maintained. In the case of improvement, the remaining amount of transmission data is compared with the threshold value α, and in the case of decrease, the remaining amount of transmission data is compared with the threshold value β, and it is determined whether or not to change the modulation method according to each comparison result. Regarding the threshold values α and β, the threshold value β for determining whether to switch the modulation when the channel quality is lowered is preferably smaller than the threshold value α in order to reduce the influence of data retransmission due to a communication error. . That is, since the determination is made when the channel quality is deteriorated, the effect can be obtained even if β is made smaller than α, considering that many errors occur with the same modulation system.

1 is a block diagram showing a mobile communication system using an adaptive modulation system according to an embodiment of the present invention. 3 is a flowchart showing an operation of the mobile communication system according to the first embodiment. It is a flowchart which shows operation | movement of the mobile communication system by 2nd Embodiment. It is a block diagram which shows the mobile communication system by the conventional adaptive modulation system. It is a flowchart which shows operation | movement of the mobile communication system by the conventional adaptive modulation system. It is a block diagram which shows the modulation system and channel quality which are used with the mobile communication system by an adaptive modulation system.

Explanation of symbols

1 Base station 1
DESCRIPTION OF SYMBOLS 11 Modulation system control part 12 Transmission baseband process part 13 Transmission RF process part 14 Reception RF process part 15 Reception baseband process part 16 Transmission data amount calculation part 2 Mobile station (mobile terminal)
21 reception RF processing unit 22 reception baseband processing unit 23 channel quality calculation unit 24 transmission baseband processing unit 25 transmission RF processing unit

Claims (12)

A communication means for communicating with the mobile terminal;
Line quality receiving means for receiving the line quality notified from the mobile terminal;
Modulation scheme switching means for switching at least the modulation scheme used in the communication means according to the received line quality;
Data remaining amount calculating means for calculating a remaining amount of transmission data and controlling the modulation method switching means according to the calculated remaining amount of transmission data ;
Equipped with a,
The base station apparatus, wherein the modulation scheme switching means does not switch the modulation scheme regardless of the channel quality when the remaining amount of transmission data is equal to or less than a threshold value .   The modulation scheme switching means does not switch the modulation scheme when the remaining transmission data is below the first threshold when the current channel quality is improved from the previous channel quality, and the current channel quality is 2. The base station apparatus according to claim 1, wherein when the remaining transmission data is less than a second threshold when the channel quality is lower than the channel quality, the modulation scheme is not switched. The base station apparatus according to claim 2, characterized in that said second threshold value <the first threshold. The modulation scheme, the base station apparatus of any one of claims 1-3, characterized in that the plurality of modulation schemes with different bit rates. In a mobile terminal having communication means for communicating with a base station apparatus, and modulation scheme switching means for switching a modulation scheme in accordance with channel quality notified from the base station apparatus,
Data remaining amount calculating means for calculating the remaining amount of transmission data and controlling the modulation method switching means according to the calculated remaining amount of transmission data ;
The mobile terminal according to claim 1, wherein the modulation scheme switching means does not switch the modulation scheme regardless of the channel quality when the remaining amount of transmission data is equal to or less than a threshold value . The modulation scheme switching means does not switch the modulation scheme when the remaining transmission data is below the first threshold when the current channel quality is improved from the previous channel quality, and the current channel quality is 6. The mobile terminal according to claim 5, wherein when the remaining transmission data is less than a second threshold when the channel quality is lower than the channel quality, the modulation scheme is not switched. The mobile terminal according to claim 6, wherein the second threshold value <the first threshold value. The mobile terminal according to any one of claims 5 to 7 , wherein the modulation scheme is a plurality of modulation schemes having different bit rates. First communication means for communicating with the base station apparatus, line quality calculation means for calculating line quality, and line quality for notifying the calculated station quality to the base station apparatus using the first communication means A mobile terminal comprising a notification means;
Second communication means for communicating with the mobile terminal, line quality receiving means for receiving the notified line quality, and switching a modulation method used in at least the second communication means in accordance with the line quality. A base station apparatus comprising: modulation scheme switching means; and data remaining amount calculation means for calculating the remaining amount of transmission data and controlling the modulation scheme switching means in accordance with the calculated remaining amount of transmission data ;
Tona is,
The mobile communication system, wherein the modulation scheme switching means does not switch the modulation scheme regardless of the calculated channel quality when the remaining amount of transmission data is equal to or less than a threshold value . The modulation scheme switching means does not switch the modulation scheme when the currently calculated channel quality is higher than the previously calculated channel quality and the remaining amount of transmission data is equal to or less than a first threshold, and is currently calculated. 10. The mobile communication system according to claim 9, wherein when the remaining channel quality is lower than the previously calculated channel quality, the modulation system is not switched when the remaining amount of transmission data is equal to or less than a second threshold value. . The mobile communication system according to claim 10, wherein the second threshold value <the first threshold value. The mobile communication system according to any one of claims 9 to 11 , wherein the modulation scheme is a plurality of modulation schemes having different bit rates.

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