JP2004297118A - Communication terminal, wireless communication system and wireless communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication terminal, a wireless communication system, and a wireless communication method for quickly changing the transmission rate obtained from an ordinary reception state into a lower transmission rate when the reception state of the communication terminal is deteriorated and reducing the delay in data transmission more than in prior arts while reducing the data error rate. <P>SOLUTION: The communication terminal includes: a CIR measurement section 5 for measuring communication quality; a conversion table 61 for specifying a correspondence relation between the communication quality and the transmission rate; and a DRC conversion section 6 that calculates a change in the communication quality, obtains the transmission rate corresponding to the communication quality from the correspondence relation specified by the conversion table 61 when the change is a prescribed value or over, and obtains a transmission rate lower than the transmission rate according to the correspondence relation specified by the conversion table 61 when the change is smaller than the prescribed value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a communication terminal, a wireless communication system, and a wireless communication method.
[0002]
[Prior art]
In recent years, a cdma2000 1x-EV DO system has been developed as a next-generation high-speed wireless communication system. In the cdma2000 1x-EV DO system, the base station switches the modulation scheme of data to be transmitted to the terminal based on information notifying the reception state received from the mobile communication terminal. It is possible to use a high transmission rate with low error resilience at the time, and a low transmission rate with high error resilience when the reception condition is bad.
[0003]
Further, in the cdma2000 1x-EV DO system, a predicted downlink data communication rate directly indicating an extremely accurate data communication rate obtained in consideration of prediction, correction by statistical data such as an error rate of past downlink data transmission, and the like. (DRC; Data Rate Control Bit) is provided on the terminal side as a table, and the terminal notifies the base station of the predicted downlink data communication speed based on this table.
[0004]
For example, the table provided on the terminal side includes a plurality of reception state levels and a transmission rate (DRC) corresponding to each reception state level. The lower the reception level, the lower the transmission rate (DRC). According to this table, it is possible to select a transmission rate with low error resilience but high speed when the reception status of the terminal is good, and a transmission rate with low error but high error resilience when the reception status is bad.
[0005]
Conventionally, in a wireless communication system in which the line quality (reception state) is measured using a pilot signal or the like and the transmission rate is controlled using the line quality and the above table, the measured line quality and the actual A method has been devised in which the table is rewritten when there is a deviation from the line quality at which communication is possible.
[0006]
[Patent Document 1]
JP-A-2002-300644
[Problems to be solved by the invention]
However, in the conventional cdma2000 1x-EV DO wireless communication system, when a transmission rate that can be actually transmitted is lower than a transmission rate (DRC) obtained using the above table, communication data that cannot be received by a terminal is transmitted. An error is recognized by the base station and causes a delay. In addition, since the communication data in which the error has occurred is retransmitted from the base station to the terminal, the data transfer is further delayed. For this reason, data may not reach the terminal and video may be stopped, for example, when performing streaming reproduction that requires real-time performance.
[0008]
Further, in the wireless communication system described in Patent Document 1, when the number of data retransmissions at a base station exceeds a threshold, a table that defines the relationship between line quality and transmission rate is rewritten to reduce the transmission rate. To change. As a result, in the wireless communication system described in Patent Document 1, since data must be retransmitted more times than the threshold value, wasteful data retransmission often occurs, and a rapid response in accordance with a change state of the line quality occurs. It is often difficult to effectively change the transmission rate, and it is often not possible to effectively respond to the actual change in line quality.
[0009]
The present invention has been made in consideration of the above circumstances, and when the reception state is deteriorated in a communication terminal, it is possible to quickly change the transmission rate to a transmission rate lower than the transmission rate normally required from the reception state, It is an object of the present invention to provide a communication terminal, a wireless communication system, and a wireless communication method that can reduce the delay of data transmission while reducing the error rate.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 includes a communication quality measuring unit that measures communication quality, a table that defines a correspondence relationship between the communication quality and a transmission rate, and a change amount of the communication quality. When the change amount is smaller than a predetermined value or more, a transmission rate corresponding to the communication quality is obtained by a correspondence defined in the table, and the change amount is equal to or larger than a predetermined value. A transmission rate conversion unit for obtaining a transmission rate lower than the transmission rate based on the correspondence defined in the table.
[0011]
The transmission rate conversion unit according to claim 2, wherein, when the change amount is equal to or more than a predetermined value, the transmission rate conversion unit obtains a transmission rate lower than a transmission rate defined by the correspondence relation of the table. The correspondence is changed.
[0012]
The invention according to claim 3, wherein the transmission rate conversion unit sets the current communication quality measured by the communication quality measurement unit to a lower communication quality when the change amount is equal to or more than a predetermined value. Is determined by using the table.
[0013]
In the invention according to claim 4, the transmission rate conversion unit obtains a transmission rate corresponding to the current communication quality measured by the communication quality measurement unit from the table when the change amount is equal to or more than a predetermined value. Later, the obtained transmission rate is set to a lower transmission rate.
[0014]
The invention according to claim 5 is characterized in that the communication terminal includes a transmission unit that transmits a transmission rate obtained by the transmission rate conversion unit to a base station.
[0015]
The invention according to claim 6 is a wireless communication system in which the base station switches a modulation scheme of data transmitted to the communication terminal based on a transmission rate transmitted from the communication terminal to the base station, wherein the communication terminal includes: A communication quality measurement unit that measures communication quality, a table that defines a correspondence relationship between the communication quality and the transmission rate, a change function calculation unit that calculates a change amount of the communication quality, and the change amount is larger than a predetermined value. If it is smaller, the transmission rate corresponding to the communication quality is determined by the correspondence defined in the table, and if the amount of change is equal to or greater than a predetermined value, the transmission rate is lower than the transmission rate by the correspondence defined in the table. A transmission rate conversion unit for determining a rate; and a transmission unit for transmitting the transmission rate obtained by the transmission rate conversion unit to the base station, wherein the base station is connected to the communication terminal. At a transmission rate transmitted from, and having a data modulation unit that transmits data to the communication terminal.
[0016]
According to a seventh aspect of the present invention, the communication terminal sequentially measures the communication quality, obtains a transmission rate corresponding to the measured communication quality from a table that defines the correspondence between the communication quality and the transmission rate, and determines the transmission rate. A wireless communication method for transmitting a rate from a communication terminal to a base station and switching a modulation method of data transmitted from the communication terminal to the communication terminal based on the transmission rate; Is calculated, and when the change amount is equal to or more than a predetermined value, a transmission rate lower than a transmission rate based on the correspondence defined in the table is obtained and transmitted to the base station.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a communication terminal according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a communication terminal according to the embodiment of the present invention. The communication terminal sequentially measures the communication quality, obtains a transmission rate corresponding to the measured communication quality by a table that defines a correspondence relationship between the communication quality and the transmission rate, transmits the transmission rate to the base station, It is used in a wireless communication network in which a base station switches a modulation method of data transmitted to the communication terminal based on the transmission rate.
[0018]
The communication terminal includes an antenna 1, a duplexer 2, a reception RF unit 3, a demodulation unit 4, a CIR measurement unit 5, a DRC conversion unit 6, a memory 7, a DRC signal creation unit 8, a modulation unit 9, and a transmission RF unit 10. ing. The CIR measurement unit 5 serves as a communication quality measurement unit, and sequentially measures the reception state of the present communication terminal, that is, the communication quality (for example, received electric field strength, carrier-to-interference ratio = CIR). The CIR measuring unit 5 receives a pilot signal via, for example, the antenna 1, the duplexer 2, and the receiving RF unit 3, and measures the CIR based on the pilot signal.
[0019]
The DRC conversion unit 6 serves as a transmission rate conversion unit, and converts the communication quality (for example, CIR) measured by the CIR measurement unit 5 into a transmission rate (for example, predicted downlink data communication rate (DRC)). . The memory 7 stores at least one communication quality measured by the CIR measuring unit 5. That is, the memory 7 is an area in which the CIRs measured by the CIR measuring unit 5 are sequentially stored. The conversion table 61 is a table that defines the correspondence between the communication quality and the transmission rate.
[0020]
Further, the DRC conversion unit 6 calculates a change function (change function) of the communication quality based on the communication quality stored in the memory 7 and the communication quality sent from the CIR measurement unit 5. As a function. If the calculated change in the communication quality is smaller than the predetermined value, the DRC conversion unit 6 determines the transmission rate corresponding to the communication quality transmitted from the CIR measurement unit 5 according to the correspondence defined by the conversion table 61. If the change amount is equal to or greater than a predetermined value, a transmission rate lower than the transmission rate based on the correspondence defined in the conversion table 61 is determined.
[0021]
The DRC signal creation unit 8 creates a DRC signal based on the transmission rate obtained by the DRC conversion unit 6, and converts the DRC signal into a base station via the modulation unit 9, the transmission RF unit 10, the duplexer 2, and the antenna 1. Send to
[0022]
Next, an example of the operation of the communication terminal will be described.
A signal for measuring circuit quality such as a pilot signal transmitted from the base station is received by the antenna 1, the duplexer 2, and the reception RF unit 3, demodulated by the demodulation unit 4, and sent to the CIR measurement unit 5. CIR measuring section 5 measures the CIR based on the received pilot signal and sends the measurement result to DRC converting section 6.
[0023]
The DRC conversion unit 6 performs a predetermined calculation on the data (CIR) sent from the CIR measurement unit 5 and one or more immediately preceding data (CIR) stored in the memory 7 to calculate the time versus CIR. (For example, an approximate straight line) is calculated. Thus, the amount of change in CIR is calculated.
[0024]
The DRC conversion unit 6 changes the conversion table 61 for converting the CIR into the DRC value when the calculated function slope falls below a certain threshold value, that is, when the radio wave condition becomes worse than a predetermined value. Here, when the radio wave condition deteriorates by a predetermined value or more, the DRC conversion unit 6 converts the CIR into the DRC value by the conversion table 61 without changing the conversion table 61 and then offsets the DRC value. , May be converted to a DRC lower than the normal CIR to DRC conversion value.
[0025]
When the radio wave condition is deteriorated by a predetermined value or more, the DRC conversion unit 6 receives the input from the CIR measurement unit 5 before converting the CIR into the DRC value in the conversion table 61 without changing the conversion table 61. The converted CIR may be changed to a smaller value, and the reduced CIR may be converted to a DRC value by the conversion table 61.
On the other hand, when the gradient of the function obtained by the DRC conversion unit 6 is larger than a predetermined threshold, that is, in a normal state, the CIR is converted into a DRC value using the conversion table 61 as usual.
[0026]
The DRC determined by the DRC converter 6 is sent to the DRC signal generator 8 to be converted into a DRC signal. The DRC signal is modulated by the modulator 9 and then transmitted from the transmission RF unit 10 to the base station via the duplexer 2 and the antenna 1. The base station receives the DRC signal transmitted from the communication terminal, and transmits data such as streaming data to the communication terminal at a transmission rate defined by the DRC signal.
[0027]
FIG. 2 is a diagram illustrating an example of the conversion table 61 in a normal state. The conversion table 61 converts the CIR into a DRC. Here, in CIR1 to CIR6, the communication state is CIR6 and CIR1 is the worst. That is, the communication state is CIR1 <CIR2 <CIR3 <CIR4 <CIR5 <CIR6 (the same applies hereinafter). As for the transmission rates of the DRCs 1 to 6, the DRC 6 is the fastest and the DRC 1 is the slowest. That is, the transmission rate is DRC1 <DRC2 <DRC3 <DRC4 <DRC5 <DRC6 (the same applies hereinafter). In the normal state, for example, when the communication state measured by the CIR measurement unit 5 is “CIR3”, the transmission rate output from the DRC conversion unit 6 is “DRC3”.
[0028]
FIG. 3 shows the conversion table 61 changed from the normal state when the slope of the function calculated by the DRC conversion unit 6 falls below a certain threshold value, that is, when the communication condition becomes worse than a predetermined value. ing. When the communication state is worse than a predetermined value, for example, when the communication state measured by the CIR measurement unit 5 is “CIR3”, the transmission rate output from the DRC conversion unit 6 is “DRC2”. Therefore, the transmission rate is lower than the normal transmission rate shown in FIG.
[0029]
4, when the slope of the function calculated by the DRC conversion unit 6 falls below a certain threshold value, that is, when the communication condition deteriorates by a predetermined value or more, the CIR measurement unit is changed without changing the conversion table 61. 5 shows a method of changing (offset) the CIR inputted by the DRC converter 6 to a smaller value from 5 and converting the reduced CIR into a DRC value in the conversion table 61.
[0030]
For example, in a normal state, when the communication state measured by the CIR measurement unit 5 is “CIR3”, the transmission rate output from the DRC conversion unit 6 is “DRC3”. On the other hand, if the communication condition has deteriorated by a predetermined value or more, when the communication state measured by the CIR measurement unit 5 is “CIR3”, the DRC conversion unit 6 sets “CIR3” to “CIR2” and then sets the conversion table 61 to “CIR2”. With reference to “DRC2” corresponding to “CIR2”, the “DRC2” is output as the transmission rate.
[0031]
FIG. 5 shows a case where the gradient of the function calculated by the DRC conversion unit 6 falls below a certain threshold value, that is, when the communication condition becomes worse than a predetermined value, the conversion table 61 is not changed and the conversion table 61 is not changed. A method of converting the CIR into a DRC value at 61, offsetting the DRC value to a lower value, and converting the DRC value to a DRC lower than a normal CIR to DRC conversion value is shown.
[0032]
For example, in a normal state, when the communication state measured by the CIR measurement unit 5 is “CIR3”, the transmission rate output from the DRC conversion unit 6 is “DRC3”. On the other hand, when the communication status is worse than the predetermined value, when the communication status measured by the CIR measurement unit 5 is “CIR3”, the DRC conversion unit 6 refers to the conversion table 61 and changes “CIR3” to “DIR3”. After that, “DIR3” is offset to “DIR2”, and “DRC2” is output as the transmission rate.
[0033]
Next, a specific communication state will be described. In a conventional communication system, in a situation where the communication state is deteriorating (when the slope of the function calculated by the DRC conversion unit 6 immediately before the conversion exceeds a threshold), for example, 150 kbps in a normal conversion Suppose you requested a transmission rate. However, in actuality, there is a case where the state becomes worse than the conversion prediction and communication can be performed only at 100 kbps. In this case, at least 50 kbits of data cannot be received, and the data is delayed. If a reception error occurs, retransmission control is performed, so that data is further delayed. Also, since data is sent with a DRC value higher than the actual transmission speed, the communication speed is high but the error resilience is low, and the number of transmission errors has increased, resulting in a large data delay. Occurs.
[0034]
On the other hand, according to the above embodiment, in a situation where the communication state is deteriorating (when the slope of the function calculated by the DRC conversion unit 6 immediately before the conversion exceeds the threshold), the normal In the conversion, a transmission rate of, for example, 150 kbps is required, but a transmission rate of, for example, 75 kbps is required. As a result, the transmission rate becomes lower than usual, so that the delay due to the reception error is greatly reduced, and the number of transmission error occurrences is also greatly reduced because the transmission is performed with high error resilience. As a result, according to the above embodiment, the delay due to unnecessary retransmission can be reduced, and data can be transmitted at a higher speed than in the past.
[0035]
Therefore, according to the present embodiment, when the communication state is deteriorating, it is possible to predict the progress of the deteriorating state, to convert the DRC value obtained from the CIR to a value lower than the normal conversion, and to rapidly reduce the Can be prevented from being transmitted from the base station at a transmission rate higher than the transmission rate that can be actually transmitted when the transmission rate is getting worse. Therefore, according to the present embodiment, it is possible to prevent data delay due to the inability of the communication terminal to receive data transmitted from the base station, and further delay due to retransmission control due to inability to transmit data. It is possible to effectively prevent a problem such as a stop of reproduction due to a data delay in content requiring real-time properties.
[0036]
Further, in the present embodiment, since the DRC value is not always lowered, the transmission rate is not narrowed when the radio wave condition is improved or stable.
[0037]
As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to the embodiments, and may include a design change or the like without departing from the gist of the present invention.
[0038]
【The invention's effect】
As described above, according to the present invention, when the reception state of a communication terminal deteriorates, it is possible to quickly change to a transmission rate lower than the transmission rate obtained from the reception state in a normal state, and to reduce the data error. It is possible to reduce the delay of data transmission while reducing the rate.
[0039]
Further, according to the present invention, the amount of change in communication quality is calculated, and the communication terminal changes the transmission rate based on the amount of change, so that when the reception state of the communication terminal deteriorates, unnecessary retransmission of data is performed. Can be reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram of a communication terminal according to an embodiment of the present invention.
FIG. 2 is a diagram showing an example of a conversion table provided in the communication terminal according to the first embodiment.
FIG. 3 is a diagram illustrating an example of a conversion table when a communication condition is deteriorated.
FIG. 4 is a diagram illustrating an example of a conversion method when a communication condition deteriorates.
FIG. 5 is a diagram illustrating an example of a conversion method when a communication condition deteriorates.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Antenna, 2 ... Duplexer, 3 ... Reception RF part, 4 ... Demodulation part, 5 ... CIR measurement part, 6 ... DRC conversion part, 7 ... Memory, 8 ... DRC signal creation part, 9 ... Modulation part, 10 ... Transmission RF section

Claims (7)

A communication quality measuring unit for measuring communication quality;
A table that defines the correspondence between the communication quality and the transmission rate,
A change function calculating unit that calculates a change amount of the communication quality,
If the amount of change is smaller than a predetermined value, a transmission rate corresponding to the communication quality is determined by a correspondence defined in the table. If the amount of change is equal to or more than a predetermined value, a response specified in the table is used. A communication rate conversion unit for obtaining a transmission rate lower than the transmission rate based on the relationship. The transmission rate conversion unit, when the change amount is a predetermined value or more, to change the correspondence of the table so as to obtain a transmission rate lower than the transmission rate defined by the correspondence of the table. The communication terminal according to claim 1. The transmission rate conversion unit, when the change amount is equal to or more than a predetermined value, the current communication quality measured by the communication quality measurement unit as a lower communication quality, the transmission rate corresponding to the low communication quality by the table. The communication terminal according to claim 1, wherein the value is obtained. The transmission rate conversion unit, when the change amount is a predetermined value or more, after obtaining the transmission rate corresponding to the current communication quality measured by the communication quality measurement unit from the table, the obtained transmission rate more The communication terminal according to claim 1, wherein the transmission rate is set to be low. The communication terminal according to any one of claims 1 to 4, wherein the communication terminal includes a transmission unit that transmits a transmission rate obtained by the transmission rate conversion unit to a base station. In a wireless communication system in which the base station switches a modulation scheme of data transmitted to the communication terminal based on a transmission rate transmitted from the communication terminal to the base station,
The communication terminal,
A communication quality measuring unit for measuring communication quality;
A table that defines the correspondence between the communication quality and the transmission rate,
A change function calculating unit that calculates a change amount of the communication quality,
If the amount of change is smaller than a predetermined value, a transmission rate corresponding to the communication quality is determined by a correspondence defined in the table. If the amount of change is equal to or more than a predetermined value, a response specified in the table is used. A transmission rate conversion unit that seeks a transmission rate lower than the transmission rate due to the relationship;
A transmission unit that transmits the transmission rate determined by the transmission rate conversion unit to the base station,
The wireless communication system according to claim 1, wherein the base station includes a data modulation unit that transmits data to the communication terminal at a transmission rate transmitted from the communication terminal. The communication terminal sequentially measures the communication quality, obtains a transmission rate corresponding to the measured communication quality by a table that defines the correspondence between the communication quality and the transmission rate, and transmits the transmission rate from the communication terminal to the base station. And a wireless communication method for switching a modulation method of data transmitted from the base station to the communication terminal based on the transmission rate,
The communication terminal calculates a change amount of the communication quality measured sequentially, and when the change amount is equal to or more than a predetermined value, obtains a transmission rate lower than a transmission rate based on the correspondence defined in the table and obtains the base station. A wireless communication method characterized by transmitting to a wireless communication device.

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