JP5220668B2 - Modulation method switching method, data communication apparatus, and data communication system - Google Patents

Description

  The present invention relates to a modulation method switching method, a data communication apparatus, and a data communication system for switching communication data modulation methods.

  Patent Document 1 discloses a wireless reception device that compares the magnitude of a measured error vector with a predetermined threshold and switches a modulation method according to the comparison result.

JP 2004-56499 A

However, when the modulation method is switched based on a comparison between a value such as an error vector and a threshold as in Patent Document 1, an error occurs in communication data due to the switching.
Further, when an error occurs in communication data, the wireless reception device requests retransmission of the communication data, and thus the throughput of communication data that is actually transmitted and received may be reduced.

  The present invention provides a modulation scheme switching method, a data communication apparatus, and a data communication system that can suppress a decrease in communication data throughput caused by switching of the modulation scheme.

A modulation scheme switching method according to a first aspect of the present invention is a modulation scheme switching method when data communication is performed using one modulation scheme selected from a plurality of different modulation schemes. A communication state acquisition step for acquiring a value indicating the communication state of the communication state, and an average value and a standard deviation value of the values indicating the communication state based on the plurality of values indicating the communication state acquired by the communication state acquisition step. The communication state calculation step to be calculated and the value indicating the communication state newly acquired by the communication state acquisition step are within a predetermined variation range determined from the average value and the standard deviation value of the values indicating the communication state. A new modulation scheme for performing the data communication is selected, and a value indicating the communication state newly acquired by the communication state acquisition step indicates the communication state. If the average value of and a predetermined variation range as determined from the standard deviation value, having a selection step of maintaining the modulation scheme selected.

  Preferably, the communication state acquisition step may acquire an error vector magnitude value indicating an error between a received symbol and a true symbol included in the received communication data as a value indicating the communication state.

  Preferably, in the selection step, when the value indicating the communication state newly acquired by the communication state acquisition step is smaller than the average value of the values indicating the communication state within the variation range, the modulation method being selected is selected. When a modulation method with a higher throughput of the communication data is selected, and the value indicating the communication state newly acquired by the communication state acquisition step is larger than the average value of the values indicating the communication state within the variation range, You may select the modulation system whose throughput of the said communication data is lower than the modulation system currently selected.

  Preferably, the selection step may change the variation range by changing a coefficient by which the standard deviation value is multiplied according to a variation in a value indicating the communication state in a unit time.

According to a second aspect of the present invention, there is provided a data communication apparatus, wherein the communication data is transmitted / received by the communication unit by switching a modulation method between a communication unit that transmits / receives communication data to / from another communication unit and a plurality of different modulation methods. An adaptive modulation unit that modulates a communication state, a communication state acquisition unit that repeatedly acquires a value indicating a communication state between the communication unit and the other communication unit, and a plurality of the communication states acquired by the communication state acquisition unit A communication state calculation unit that calculates an average value and a standard deviation value of values indicating the communication state based on the value, and a value indicating the communication state newly acquired by the communication state acquisition unit indicates the communication state A value indicating a communication state newly selected by the communication state acquisition unit when a new modulation method for performing the data communication is selected when the value is within a predetermined variation range determined from an average value and a standard deviation value But, If serial is an average value and a predetermined variation range as determined from the standard deviation of the values indicating the communication state comprises a selection unit for maintaining the modulation scheme selected, the.

  Preferably, the communication unit may transmit and receive communication data by wireless communication with the other communication unit, and the data communication device may be a base station or a wireless communication terminal of a wireless communication system.

  Preferably, when an error occurs in the communication data received by the adaptive modulation unit, a retransmission request unit that requests retransmission of the communication data may be provided.

A data communication system according to a third aspect of the present invention includes a pair of communication units that transmit and receive communication data, and the communication data that the pair of communication units transmit and receive by switching a modulation method between a plurality of different modulation methods. a pair of adaptive modulator for modulating a communication state acquiring unit that repeatedly acquires a value indicating the communication state of the pair of the communication unit, on the basis of a value indicating the plurality of communication status acquired by the communication status acquiring unit A communication state calculation unit that calculates an average value and a standard deviation value indicating the communication state, and a value indicating the communication state newly acquired by the communication state acquisition unit is an average value of the value indicating the communication state And a new modulation method for performing the data communication is selected, and a value indicating the communication state newly acquired by the communication state acquisition unit is a previous value. If the average value and the predetermined variation range, which is determined from the standard deviation of the values indicating the communication state comprises a selection unit for maintaining the modulation scheme selected, the.

  ADVANTAGE OF THE INVENTION According to this invention, the fall of the throughput of communication data resulting from switching of a modulation system can be suppressed.

FIG. 1 is a system configuration diagram of a radio communication system according to an embodiment of the present invention. FIG. 2 is an explanatory diagram of a communication sequence between the base station and the PHS terminal. FIG. 3 is an explanatory diagram of a plurality of modulation schemes of the PHS terminal and the base station. FIG. 4 is a block diagram of a hardware configuration of the PHS terminal of FIG. FIG. 5 is a diagram of an IQ constellation. FIG. 6 is an explanatory diagram of the EVM buffer. FIG. 7 is an explanatory diagram of a data structure example of a multi-value table. FIG. 8 is an explanatory diagram of an example of the data structure of the value reduction table. FIG. 9 is a functional block diagram of the wireless communication system of FIG. FIG. 10 is a flowchart of the modulation system switching process of the PHS terminal of FIG. FIG. 11 is an explanatory diagram of a switching example of the PHS terminal of FIG. FIG. 12 is a flowchart of the modulation system switching process of the comparative example. FIG. 13 is an explanatory diagram of a modulation system switching example in the comparative example of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a system configuration diagram of a wireless communication system 1 according to an embodiment of the present invention.
The wireless communication system 1 in FIG. 1 is a data communication system that transmits and receives communication data via a wireless line.
The wireless communication system 1 includes a PHS (Personal Handy Phone) terminal 2 and a base station 3. The plurality of base stations 3 are connected to the communication network 4.

FIG. 2 is an explanatory diagram showing a sequence of communication data transmitted / received between the base station 3 and the PHS terminal 2. In FIG. 2, time flows from left to right.
The base station 3 and the PHS terminal 2 of the wireless communication system 1 transmit and receive communication data by the TDMA / TDD (Time Division Multiple Access / Time Division Duplex) method.
The base station 3 and the PHS terminal 2 that transmit and receive communication data by the TDD scheme perform bidirectional communication in units of frames configured by four downlink slots 6 and four uplink slots 7.
The downlink slot 6 is a slot for transmitting communication data from the base station 3 to the PHS terminal 2.
The uplink slot 7 is a slot for transmitting communication data from the PHS terminal 2 to the base station 3.
The downlink slot 6 or the uplink slot 7 has header data and payload data. Further, data specifying a data modulation method is included between the header data and the payload data.

The base station 3 assigns the PHS terminal 2 to an unused slot.
In the case of space division multiple access (SDMA), the base station 3 can assign a plurality of PHS terminals 2 to one slot.
Thereby, the some PHS terminal 2 can transmit / receive communication data with each base station 3 using a common frequency band.

FIG. 3 shows a plurality of modulation schemes that can be executed by the PHS terminal 2 and the base station 3.
The PHS terminal 2 or the base station 3 modulates communication data using one modulation method selected in common from a plurality of modulation methods shown in FIG.
FIG. 3 shows six modulation schemes of BPSK, QPSK, 8PSK, 16QAM, 32QAM, and 64QAM. The plurality of modulation schemes in FIG. 3 are a plurality of modulation schemes that can be executed by an adaptive modulation encoding unit 41 described later.
BPSK, QPSK, and 8PSK have different coding rates. 16QAM, 32QAM and 64QAM have different coding rates. PSK and QAM have different modulation schemes.
Further, as shown in FIG. 3, BPSK, QPSK, 8PSK, 16QAM, 32QAM, and 64QAM increase the amount of communication data that can be transmitted / received per frame in that order.
Further, as shown in FIG. 3, BPSK, QPSK, 8PSK, 16QAM, 32QAM, and 64QAM are less resistant to radio errors in that order.

FIG. 4 is a block diagram showing a hardware configuration of the PHS terminal 2 of FIG.
The PHS terminal 2 includes a radio communication unit (RF) 11, an operation unit (KEY) 12, a display unit (DISP) 13, a voice modem unit (MODEM) 14, a CPU (Central Processing Unit) 15, a memory (MEM) 16, and A system bus 17 is provided for connecting them.

The wireless communication unit 11 establishes a communication channel with the base station 3 and transmits / receives communication data to / from the base station 3 using the slots assigned in the communication method of FIG. 2 described above.
The wireless communication unit 11 wirelessly transmits the communication data included in the input signal from the CPU 15 to the base station 3 and outputs a signal including the communication data received from the base station 3 to the CPU 15.

The operation unit 12 has a plurality of operation keys not shown.
The operation keys include, for example, a function key, a power key, a call key, a numeric key, a character key, and a call key. The operation keys are arranged on the surface of the PHS terminal 2.
Then, the operation unit 12 outputs a signal corresponding to the operation key operated by the user to the CPU 15.

The display unit 13 includes an LCD (Liquid Crystal Display Device), an organic EL (Electro-Luminescence) device, and the like that are not shown.
The LCD or the organic EL device has a structure in which a plurality of pixels (Pixels) are arranged in a matrix for each RGB color component, and is arranged on the surface of the PHS terminal 2.
The display unit 13 displays display data included in the signal input from the CPU 15. Thereby, the display part 13 displays the map which shows the present position of the PHS terminal 2, for example.

The voice modem unit 14 is connected to a speaker 18 and a microphone 19.
The voice modem unit 14 samples the voice input to the microphone 19 and outputs a signal including voice data to the CPU 15.
The voice modem unit 14 drives the speaker 18 with voice data included in the input signal from the CPU 15.
As a result, sound corresponding to the sound data is output from the speaker 18.

The memory 16 includes a program that can be read and executed by the CPU 15, data that is read and written by the CPU 15, and the like.
Note that the program stored in the memory 16 may be any program installed on a computer-readable recording medium such as a CD-ROM (Compact Disc Read Only Memory). The program may be a program installed via a transmission medium such as the Internet.

  The data stored in the memory 16 includes, for example, as shown in FIG. 34, a value reduction table (DN_TBL) 35, and modulation scheme data (MOD) 36.

FIG. 5 is a diagram showing an IQ constellation.
The IQ constellation is a diagram illustrating an in-phase component and a quadrature component in the quadrature modulation method.
In FIG. 5, the horizontal axis is the in-phase component, and the vertical axis is the quadrature component.

FIG. 5 also shows four true symbol points 21 to 24 and one reception symbol point 25 in the case of QPSK.
As the mutual interval between the true symbol points 21 to 24 is larger, an error is less likely to occur in the communication data after demodulation.
In the case of BPSK, the two true symbol points become a pair of diagonal true symbol points in FIG.
Therefore, communication data modulated by BPSK is less likely to contain errors in demodulated communication data compared to communication data modulated by QPSK.

An EVM (Error Vector Magnitude) value has a value corresponding to an error between the true symbol point 21 and the received symbol point 25.
The EVM value has a value obtained by normalizing the positional deviation in the IQ constellation between the ideal modulation signal and the measurement modulation signal by the ideal modulation signal.
The EVM value is a measure of communication quality, and the smaller the value, the better the communication quality.
Thus, the EVM value is a value indicating a phase (amplitude) deviation (error) of the received signal that should be originally present.

A reception symbol point 25 of communication data transmitted in an ideal communication state in which no error occurs coincides with the true symbol point 21.
The EVM value increases as the error between the true symbol point 21 and the received symbol point 25 increases.
For example, when the EVM value is a value corresponding to the distance between the true symbol point 21 and the true symbol point 22, the communication data encoded in the true symbol point 21 is the communication data of the true symbol point 22. Will be combined by mistake.
Thus, the received data having a large EVM value is likely to cause an error.

The EVM buffer 31 holds a plurality of EVM values.
The EVM buffer 31 is a FIFO buffer.
FIG. 6 is an explanatory diagram showing changes in data stored in the EVM buffer 31.
The EVM buffer 31 stores n EVM values in n (n is a natural number) buffer memories.
FIG. 6A shows data stored in the EVM buffer 31 at time t.
FIG. 6B shows data stored in the EVM buffer 31 at time t + 1 after time t.
FIG. 6C shows data stored in the EVM buffer 31 at time t + 2 after time t + 1.

Then, the EVM buffer 31 stores new EVM values in a state where a plurality of EVM values are stored as shown in FIG.
Thereby, as shown in FIG. 6B, the EVM buffer 31 stores a value obtained by shifting the value of each buffer memory one by one, and stores a new EVM value in the empty buffer memory.
+ In FIG. 6B, the EVM value “16” stored in the first buffer memory of FIG. 6A is deleted, and a new EVM value “20” is stored in the nth buffer memory.

Similarly, when the next new EVM value is stored, the EVM buffer 31 stores a value obtained by shifting the value of each buffer memory one by one as shown in FIG. Store the new EVM value.
In FIG. 6C, the EVM value “17” stored in the first buffer memory in FIG. 6B is deleted, and the new EVM value “21” is stored in the n-th buffer memory.

The average value data 32 holds an average value of a plurality of EVM values stored in the EVM buffer 31.
For example, when the EVM buffer 31 stores a plurality of EVM values “16, 17,..., 19, 18” in FIG. 6A, the average value data 32 is the latest EVM value “18”. The average value of “16, 17,..., 19” is retained.

The standard deviation value data 33 holds standard deviation values of a plurality of EVM values stored in the EVM buffer 31.
For example, when a plurality of EVM values “16, 17,..., 19, 18” in FIG. 6A are stored in the EVM buffer 31, the standard deviation value data 33 is the latest EVM value “18”. The standard deviation values of “16, 17,...

FIG. 7 is an explanatory diagram showing an example of the data structure of the multilevel table 34.
The multi-value table 34 is a table in which a plurality of modulation schemes in FIG. 3 are associated with a plurality of threshold ranges.
Each threshold range of the multi-value table 34 is compared with the EVM value when the modulation method is multi-valued.
7 has, for example, “5-1” as a threshold range corresponding to 64QAM, “10-6” as a threshold range corresponding to 32QAM, and as a threshold range corresponding to 16QAM. It has “15-11”.

FIG. 8 is an explanatory diagram showing an example of the data structure of the value reduction table 35.
The value reduction table 35 is a table in which a plurality of modulation schemes in FIG. 3 are associated with a plurality of threshold ranges.
Each threshold range of the reduction value table 35 is compared with the EVM value when the modulation method is reduced.
8 has, for example, “1-7” as a threshold range corresponding to 64QAM, “8-12” as a threshold range corresponding to 32QAM, and a threshold range corresponding to 16QAM. It has "13-17".
The threshold range associated with each modulation method in the reduction table 35 has a larger maximum value than the threshold range associated with each modulation method in the multi-value table 34, and overall The numerical value range is large.

The modulation scheme data 36 holds a modulation scheme executed by an adaptive modulation encoding unit 41 (to be described later) of the PHS terminal 2.
The modulation scheme data 36 includes data indicating one modulation scheme selected from the plurality of modulation schemes in FIG.
Further, the modulation scheme data 36 can be updated by the selection unit 44 and the base station 3 described later of the PHS terminal 2.

  The CPU 15 is a computer that reads and executes a program stored in the memory 16, and functions as a processing unit of the PHS terminal 2.

FIG. 9 shows functional blocks implemented in the PHS terminal 2 when the CPU 15 executes the program. FIG. 9 is a functional block diagram of the wireless communication system 1 of FIG.
As shown in FIG. 9, the PHS terminal 2 includes an adaptive modulation and coding unit (AMC) 41, an EVM acquisition unit (EVM) 42, a calculation unit (CAL) 43, a selection unit (SEL) 44, A data communication control unit (CTRL) 45 and an application unit (API) 46 are realized.

The adaptive modulation encoding unit 41 reads the modulation scheme from the modulation scheme data 36.
In addition, the adaptive modulation and coding unit 41 performs coding processing and modulation processing of communication data transmitted and received by the wireless communication unit 11 according to the read modulation scheme.

The EVM acquisition unit 42 acquires the EVM value of the communication data received by the wireless communication unit 11.
In the process of acquiring the EVM value of the received communication data, the EVM acquisition unit 42 re-encodes the communication data decoded by the adaptive modulation and encoding unit 41, for example.
Further, the EVM acquisition unit 42 acquires an EVM value from the error between the re-encoded communication data and the communication data actually input to the adaptive modulation and encoding unit 41.
The EVM acquisition unit 42 adds the newly acquired EVM value to the EVM buffer 31 of the memory.
Accordingly, the plurality of EVM values stored in the EVM buffer 31 are stored in the n latest EVM values.

For example, when QPSK is selected, the EVM acquisition unit 42 re-encodes communication data decoded by the adaptive modulation and coding unit 41 using QPSK, using QPSK.
This re-encoded communication data becomes one of the true symbol points 21 to 24 in FIG.
The communication data actually input to the adaptive modulation and coding unit 41 is the reception symbol point 25 in FIG.
Then, the EVM acquisition unit 42 acquires an EVM value from these symbol points.
In addition, the EVM acquisition unit 42 adds the newly acquired EVM value to the EVM buffer 31 of the memory.

The calculation unit 43 calculates an average value and a standard deviation value from a plurality of EVM values stored in the EVM buffer 31.
For example, the calculation unit 43 calculates the average value and the standard deviation value of EVM (1) to EVM (n-1) in FIG.
In addition, the calculation unit 43 updates the average value data 32 with the calculated average value, and updates the standard deviation value data 33 with the calculated standard deviation value.

The selection unit 44 selects one modulation scheme from the plurality of modulation schemes in FIG. 3 based on various data stored in the memory 16.
Further, the selection unit 44 updates the modulation method data 36 with the selected modulation method.

The application unit 46 realizes, for example, a call function, a browser function, a moving image display function, and the like in the PHS terminal 2.
Then, the application unit 46 generates communication data or a transmission request for communication data in accordance with the operation of the operation unit 12.
The application unit 46 reproduces communication data received by the PHS terminal 2. For example, the application unit 46 outputs the received audio data to the audio modem unit 14 and reproduces the audio.
The application unit 46 outputs the received display data to the display unit and displays an image.

The data communication control unit 45 manages transmission / reception of communication data of the application unit 46.
Then, the data communication control unit 45 outputs the communication data generated by the application unit 46 or the transmission request for communication data to the adaptive modulation and coding unit 41.
In addition, the data communication control unit 45 supplies the communication data demodulated by the adaptive modulation and coding unit 41 to the application unit 46.
Further, when the communication data demodulated by the adaptive modulation and coding unit 41 includes an error, the data communication control unit 45 outputs a request for retransmission of the communication data to the adaptive modulation and coding unit 41 as necessary.
For example, when transmitting / receiving communication data by TCP (Transmission Control Protocol), the data communication control unit 45 outputs a request for retransmission of communication data to the adaptive modulation and coding unit 41.

FIG. 10 is a flowchart of the modulation system switching process in the PHS terminal 2 of FIG.
The switching process in FIG. 10 is executed by the PHS terminal 2 every time the PHS terminal 2 receives communication data of a new downlink slot 6 and the adaptive modulation and coding unit 41 generates newly received communication data, for example. The

When the adaptive modulation encoding unit 41 generates newly received communication data, the EVM acquisition unit 42 acquires the EVM value EVM (n) of the newly received communication data (step S1).
Then, the EVM acquisition unit 42 adds the newly acquired EVM value EVM (n) to the EVM buffer 31 of the memory.
As a result, the newly acquired EVM value EVM (n) is stored in the EVM buffer 31.
The EVM buffer 31 stores n EVM values EVM (n) to EVM (1) from the latest EVM value.

When the newly acquired EVM value EVM (n) is stored in the EVM buffer 31, the calculation unit 43 calculates the average of the plurality of EVM values EVM (1) to EVM (n-1) stored in the EVM buffer 31. A value μ and a standard deviation value σ are calculated (step S2).
Then, the calculation unit 43 updates the average value data 32 and the standard deviation value data 33 with the calculated average value μ and quasi-deviation value σ.
Thereby, the memory 16 stores a plurality of EVM values EVM (1) to EVM (n) including newly acquired EVM values and an average value of the plurality of EVM values EVM (1) to EVM (n−1). μ and the quasi-deviation value σ are stored.

When the new EVM value, average value, and quasi-deviation value are stored in the memory 16, the selection unit 44 selects one modulation method based on various data stored in the memory 16.
The selection unit 44 first determines whether or not the new EVM value EVM (n) is equal to or less than the previous EVM value EVM (n−1) (step S3).

When the new EVM value is equal to or less than the previous EVM value, the selection unit 44 further determines whether or not the new EVM value EVM (n) is within a predetermined variation range equal to or less than the average value μ. (Step S4).
Specifically, the selection unit 44 determines that the new EVM value EVM (n) ranges from the value obtained by subtracting the quasi-deviation value from the average value (μ−Zσ: Z is a constant of a predetermined value) to the average value μ. It is judged whether it is in.

When the new EVM value is within a predetermined variation range equal to or less than the average value, the selection unit 44 further determines whether or not the new EVM value EVM (n) is smaller than the threshold range corresponding to the currently selected modulation method. Is determined (step S5).
The selection unit 44 selects the currently selected modulation method from the modulation method data 36, and acquires the threshold range corresponding to the selected modulation method from the multi-value quantization table 34 of FIG.
Then, the selection unit 44 compares the acquired threshold range with the new EVM value EVM (n), and determines whether or not the new EVM value EVM (n) is smaller than the threshold range.

When the new EVM value is smaller than the threshold range, the selection unit 44 multi-values the modulation method (step S6).
The selection unit 44 selects a modulation method corresponding to the threshold range including the new EVM value EVM (n) in the multi-value table 34 of FIG.
Further, the selection unit 44 updates the modulation method data 36 according to the selected modulation method.

After converting the modulation scheme into multiple values, the selection unit 44 arranges a plurality of EVM values in the EVM buffer 31 (step S7).
Specifically, the selection unit 44 releases the oldest EVM value EVM (1) in the EVM buffer 31 from the memory 16.
The selection unit 44 records the remaining plurality of EVM (2) to EVM (n) in the memory 16 as EVM (1) to EVM (n-1).

In step S4, when the new EVM value EVM (n) is not within a predetermined variation range equal to or less than the average value μ, the selection unit 44 maintains the current modulation method (step S8).
Then, the selection unit 44 arranges a plurality of EVM values in the EVM buffer 31 without updating the modulation scheme data 36 (step S7).

In step S5, when the new EVM value EVM (n) is not smaller than the threshold range corresponding to the currently selected modulation method, the selection unit 44 maintains the current modulation method (step S8).
Then, the selection unit 44 arranges a plurality of EVM values in the EVM buffer 31 without updating the modulation scheme data 36 (step S7).

In step S3, when the new EVM value is not equal to or less than the previous EVM value, the selection unit 44 further determines whether or not the new EVM value EVM (n) is within a predetermined variation range equal to or less than the average value μ. Is determined (step S9).
Specifically, the selection unit 44 determines whether or not the new EVM value EVM (n) is within the range from the value obtained by adding the quasi-deviation value from the average value (μ + Zσ) to the average value μ. .

When the new EVM value is within a predetermined variation range equal to or greater than the average value, the selection unit 44 further determines whether or not the new EVM value EVM (n) is larger than the threshold range corresponding to the currently selected modulation method. Is determined (step S10).
The selection unit 44 selects the currently selected modulation method from the modulation method data 36, and acquires the threshold range corresponding to the selected modulation method from the value reduction table 35 of FIG.
Then, the selection unit 44 compares the acquired threshold range with the new EVM value EVM (n), and determines whether or not the new EVM value EVM (n) is larger than the threshold range.

When the new EVM value is larger than the threshold range, the selection unit 44 decreases the modulation method (step S11).
The selection unit 44 selects a modulation method corresponding to the threshold range including the new EVM value EVM (n) in the reduction table 35 of FIG.
Further, the selection unit 44 updates the modulation method data 36 according to the selected modulation method.

  After decreasing the modulation method, the selection unit 44 arranges a plurality of EVM values in the EVM buffer 31 (step S7).

In step S9, when the new EVM value EVM (n) is not within a predetermined variation range equal to or greater than the average value μ, the selection unit 44 maintains the current modulation method (step S8).
Then, the selection unit 44 arranges a plurality of EVM values in the EVM buffer 31 without updating the modulation scheme data 36 (step S7).

If the new EVM value EVM (n) is not smaller than the threshold range corresponding to the currently selected modulation method in step S10, the selection unit 44 maintains the current modulation method (step S8).
Then, the selection unit 44 arranges a plurality of EVM values in the EVM buffer 31 without updating the modulation scheme data 36 (step S7).

FIG. 11 is an explanatory diagram of an example of switching the modulation scheme in the PHS terminal 2 of FIG.
In FIG. 11, 15 timings from time t = 1 to 15 are illustrated.
As internal data at each timing, the latest EVM value EVM (n), variation range (μ−Zσ), selected modulation method, CRC (Cyclic Redundancy Check) error of communication data or UW (synchronization word) error Presence / absence and cumulative received data amount (bits) are shown.
FIG. 11 shows an example in which the number n of EVM values in the EVM buffer 31 is 11 and the coefficient Z for calculating the variation range is 2.
When the EVM value changes as shown in FIG. 11, the selected modulation scheme is maintained at 32 QAM at all timings t = 1 to 15, and no CRC error or UW error occurs in the communication data.
As a result, the cumulative amount of received data transmitted and received in the period of timing t = 1-15 is 6240 bits.

FIG. 12 is a flowchart of the modulation system switching process of the comparative example.
Each step in FIG. 12 is the same as each step in FIG.
However, when compared with FIG. 10, the flowchart of FIG. 12 does not include steps S4 and S10 for determining whether or not the latest EVM value is within a predetermined variation range.

FIG. 13 is an explanatory diagram of a modulation system switching example in the comparative example of FIG.
Then, when the EVM value changes as shown in FIG. 13, at the timing t = 11, the latest EVM value becomes 5, and the modulation method is changed to 64QAM.
Further, when the latest EVM value returns to 7 at timing t = 12 immediately after that, a CRC error or a UW error occurs in communication data received by the 64QAM modulation method.
Further, because of the CRC error or UW error, the data communication control unit 45 requests retransmission of the communication data at timing t = 13, so that the accumulated received data amount is 5920 bits.
Thus, in the switching process of FIG. 12, the cumulative received data amount is smaller than in the switching process of FIG.

As described above, in this embodiment, the modulation method is switched when the newly acquired EVM value is within a predetermined variation range determined by the average value and the standard deviation of the EVM values.
Therefore, in this embodiment, for example, due to movement of the PHS terminal 2 or multipath fading, the newly acquired EVM value is so small that it is impossible in the actual communication environment of communication data. Even if it fluctuates, the modulation method can be maintained at a method in which a retransmission request of communication data suitable for the actual communication environment of communication data is difficult to occur.
As a result, in this embodiment, the occurrence of communication data errors can be suppressed even if the propagation environment is unstable because the PHS terminal 2 is moving or fading due to multipath occurs.
Further, in this embodiment, since the occurrence of communication data errors is suppressed and the number of retransmissions of communication data is reduced, the amount of communication data transmitted without error per unit time can be increased.
As a result, in this embodiment, it is possible to suppress a decrease in communication data throughput due to switching of the modulation method.

In addition, when a plurality of wireless communication units are actually manufactured, individual differences occur for each wireless communication unit in the signal processing performance of the plurality of wireless communication units.
In this embodiment, even when individual differences occur in such a wireless communication unit, it is possible to select an optimum modulation scheme so as to reduce the number of occurrences of communication data errors in accordance with individual differences in signal processing performance.

In this embodiment, useless switching of the modulation scheme based on a specific EVM value is reduced, and a stable modulation scheme according to the communication environment is maintained.
Therefore, in this embodiment, it becomes difficult to generate a retransmission request, and high-speed data communication can be executed.

  The above embodiment is a preferred embodiment of the present invention, but the present invention is not limited to this, and various modifications or changes are possible.

In the above embodiment, the EVM value is acquired as a value indicating the communication state of data communication.
In addition, for example, a bit error rate value or the like may be acquired as a value indicating the communication state of data communication.

In the above embodiment, it is determined whether or not the newly acquired EVM value is a variation within a certain standard deviation range of the EVM value. That is, in the above embodiment, it is determined whether or not the EVM value is within a certain variation range.
In addition to this, for example, the variation range may be changed by changing the coefficient Z by which the standard deviation value is multiplied according to the variation of the EVM value in unit time.

The wireless communication system 1 of the above embodiment has a PHS terminal 2 as a wireless communication terminal.
In addition, for example, the wireless communication system 1 is a wireless communication terminal including a mobile phone other than the PHS terminal 2, a PDA (Personal Data Assistant) having a communication function, a portable game device having a communication function, a personal computer having a communication function, and the like. You may have as.

In the above embodiment, the PHS terminal 2 which is a kind of wireless communication terminal acquires the EVM value, calculates the fluctuation of the EVM value, and selects the modulation method.
In addition to this, for example, the base station 3 may acquire the EVM value, calculate the fluctuation of the EVM value, and select the modulation method of the adaptive modulation unit.
In addition, the base station 3 has the wireless communication part 11, CPU15, the memory 16, and the system bus 17 which connects these similarly to the PHS terminal 2 of FIG.
When processing is performed in the base station 3, the CPU 15 executes a program stored in the memory 16, thereby causing the base station 3 to have an adaptive modulation encoding unit 41, an EVM acquisition unit 42, a calculation unit 43, a selection unit 44, The data communication control unit 45 may be realized.

  The above embodiment is a data communication system in which the PHS terminal 2 and the base station 3 transmit and receive communication data via a wireless line. In addition to this, in the data communication system, a pair of data communication terminals may transmit and receive communication data via a wired line.

In the above embodiment, the adaptive modulation and coding unit 41, the EVM acquisition unit 42, the calculation unit 43, the selection unit 44, the data communication control unit 45, and the application unit 46 of the PHS terminal 2 are realized in the PHS terminal 2 by software. The
A part or all of these units 41 to 46 may be realized by hardware.

DESCRIPTION OF SYMBOLS 1 ... Wireless communication system (data communication system), 2 ... PHS terminal (wireless communication terminal, data communication apparatus), 3 ... Base station, 11 ... Wireless communication part (communication part), 15 ... CPU (control part), 31 ... EVM buffer, 32... Average value data, 33... Standard deviation value data, 34... Multi-value table, 35. ... EVM acquisition unit (communication status acquisition unit), 43 ... calculation unit (communication status calculation unit), 44 ... selection unit, 45 ... data communication control unit (retransmission request unit), 46 ... application unit, S1 ... communication status acquisition step , S2 ... communication state calculation step, S3 to S6, S8 to S11 ... selection step, EVM value ... error vector magnitude value, Z ... coefficient for multiplying the standard deviation value

Claims (8)

A modulation method switching method when data communication is performed by one modulation method selected from a plurality of different modulation methods,
A communication state acquisition step of acquiring a value indicating a communication state of the data communication;
A communication state calculating step of calculating an average value and a standard deviation value of the values indicating the communication state based on the values indicating the plurality of communication states acquired by the communication state acquiring step ;
When the value indicating the communication state newly acquired by the communication state acquiring step is within a predetermined variation range determined from the average value and the standard deviation value of the values indicating the communication state, a new data communication is performed. A value indicating the communication state newly acquired by the communication state acquisition step is outside a predetermined variation range determined from an average value and a standard deviation value of the values indicating the communication state. A selection step for maintaining the selected modulation scheme ;
A modulation method switching method comprising: The communication state acquisition step includes:
An error vector magnitude value indicating an error between a received symbol and a true symbol included in the received communication data is acquired as a value indicating the communication state .
The modulation method switching method according to claim 1 . The selection step includes
When the value indicating the communication state newly acquired in the communication state acquisition step is smaller than the average value of the communication state within the variation range, the modulation of the communication data having a higher throughput than the selected modulation method Select a method,
When the value indicating the communication state newly acquired by the communication state acquisition step is larger than the average value of the communication state within the variation range, the modulation of the communication data throughput is lower than that of the selected modulation method Select method ,
The modulation method switching method according to claim 2 . The selection step includes
Changing the variation range by changing the coefficient by which the standard deviation value is multiplied according to the variation in the value indicating the communication state in unit time ;
The modulation method switching method according to any one of claims 1 to 3 . A communication unit that transmits and receives communication data to and from other communication units;
An adaptive modulation unit that modulates the communication data transmitted and received by the communication unit by switching a modulation method between different modulation methods;
A communication state acquisition unit that repeatedly acquires a value indicating a communication state between the communication unit and the other communication unit;
A communication state calculation unit that calculates an average value and a standard deviation value of values indicating the communication state based on a plurality of values indicating the communication state acquired by the communication state acquisition unit ;
When the value indicating the communication state newly acquired by the communication state acquisition unit is within a predetermined variation range determined from the average value and the standard deviation value of the values indicating the communication state, the new data communication is performed. A value indicating a communication state newly acquired by the communication state acquisition unit is outside a predetermined variation range determined from an average value and a standard deviation value of the values indicating the communication state. A selection unit for maintaining the selected modulation method ;
A data communication device. The communication unit is
Sending and receiving communication data by wireless communication with the other communication unit,
The data communication device includes:
A base station or a wireless communication terminal of a wireless communication system ;
The data communication apparatus according to claim 5 . When there is an error in the communication data received by the adaptive modulation unit, it has a retransmission request unit that requests retransmission of the communication data ,
The data communication apparatus according to claim 5 or 6 . A pair of communication units for transmitting and receiving communication data;
A pair of adaptive modulators that modulate the communication data transmitted and received by the pair of communication units by switching the modulation method between different modulation schemes;
A communication state acquisition unit that repeatedly acquires a value indicating the communication state of the pair of communication units;
A communication state calculation unit that calculates an average value and a standard deviation value of values indicating the communication state based on a plurality of values indicating the communication state acquired by the communication state acquisition unit ;
When the value indicating the communication state newly acquired by the communication state acquisition unit is within a predetermined variation range determined from the average value and the standard deviation value of the values indicating the communication state, the new data communication is performed. A value indicating a communication state newly acquired by the communication state acquisition unit is outside a predetermined variation range determined from an average value and a standard deviation value of the values indicating the communication state. A selection unit for maintaining the selected modulation method ;
A data communication system.

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