JP2023044758A - Wireless communication device and adaptive modulation method - Google Patents

Abstract

To select an appropriate modulation method without increasing the transmission frequency of channel quality information by a receiving station.SOLUTION: A wireless communication device 1 selects a modulation scheme to be used for transmission to a communication terminal 9 on the basis of combination data of a reception time and channel quality at the communication terminal 9 transmitted from the communication terminal 9.SELECTED DRAWING: Figure 1

Description

The present invention relates to a radio communication apparatus and an adaptive modulation method, and more particularly to technology suitable for satellite communications using an adaptive modulation scheme that switches the modulation scheme based on the propagation environment.

2. Description of the Related Art In wireless communication systems, adaptive modulation schemes are used to switch modulation schemes based on the propagation environment in order to improve frequency utilization efficiency. In the adaptive modulation method, the channel quality is generally calculated based on the radio waves received by the receiving station (e.g., wireless terminal), and the result of the channel quality calculation is fed back to the transmitting station (e.g., satellite or base station). Then, the transmitting station selects a modulation scheme based on the feedback channel quality calculation result. With such a method, a change to a modulation method suitable for the propagation environment is performed.

As a communication apparatus using an adaptive modulation method, a line quality change direction detection means for detecting a change direction of line quality based on a received signal, and a line quality change direction detected by the line quality change direction detection means is in the direction of improvement, and modulation scheme determining means for determining the modulation scheme to be used for signal transmission based on the quality of the line before the change is known (see Patent Document 1). .

JP 2005-012684 A

By the way, in the conventional adaptive modulation method, the result of channel quality calculation is fed back from the receiving station to the transmitting station. There is a delay time between the time when the signal is received (in other words, the time when the communication conditions on the line/propagation path are the same as the result of the above-mentioned line quality calculation) and the time when the transmitting station actually switches the modulation scheme. . There are various possible causes for the delay time. For example, in the case of a satellite communication system, communication is performed via a satellite, so the transmission delay of the information signal used for selecting the modulation scheme is large. In many cases, the return link for transmitting the information used for selecting the modulation method from the receiving station to the transmitting station is TDM (abbreviation of Time Division Multiplexing). Time fluctuates and is not stable. Due to these factors, a non-constant delay time occurs in the information that serves as a criterion for determining the modulation scheme. Delay time between the time when the receiving station receives the signal (in other words, the time when the communication condition on the line/propagation path is the same as the result of the above-mentioned line quality calculation) and the time when the transmitting station actually switches the modulation scheme (Also called "adaptive modulation control loop delay"), there is a difference between the calculated channel quality, which is the criteria for determining the modulation method, and the actual channel quality when the modulation method is actually switched. Especially when a change occurs, there is a problem that an appropriate modulation scheme cannot be selected, and furthermore, there is a problem that the transmission efficiency is reduced.

In addition, in the technique disclosed in Patent Document 1, the frequency of acquisition of channel quality information, which is used as a criterion for determining the modulation scheme, must be sufficiently fine with respect to the frequency of occurrence of changes in the propagation environment. That is, it is necessary to acquire information closely, and the frequency with which the receiving station must transmit information on channel quality increases. Therefore, especially when the receiving station is a mobile device, there is a problem that the battery is consumed and the operating time is shortened.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a radio communication apparatus and an adaptive modulation method capable of selecting an appropriate modulation scheme without increasing the frequency of transmission of channel quality information by a receiving station.

In order to solve the above problems, a radio communication apparatus according to the present invention is a radio communication apparatus that performs radio communication with a device of a communication partner using an adaptive modulation method, wherein a signal transmitted from the device of the communication partner is and a modulation method control unit that selects a modulation method to be used for transmission to the communication partner device based on combination data of reception time and line quality in the communication partner device.

In the radio communication apparatus according to the present invention, the modulation method control unit selects the modulation method for actual communication, and the variation in line quality in a time period before the reception time in the communication partner device is Channel quality for estimating the channel quality at the processing time in the wireless communication device after the reception time in the communication partner device when selecting the modulation scheme for the actual communication, using the slope A calculation unit may be provided.

In the wireless communication device according to the present invention, the modulation method control unit controls the reception time of the communication partner device in the past communication between the wireless communication device and the communication partner device. a transition probability matrix, which is a matrix whose components are actual values of probabilities of occurrence of each combination of the slope of channel quality fluctuation in the previous time slot and the slope of channel quality fluctuation in the time slot after the certain reception time; and said actual communication predicted based on the fluctuation slope of the channel quality in a time zone prior to the reception time in said communication partner device when said modulation scheme is selected for actually performing communication. When selecting the modulation method for the actual communication by using the fluctuation slope of the channel quality in the time zone after the reception time in the communication partner device when selecting the modulation method for the purpose of A line quality calculation unit may be provided for estimating line quality at a processing time in the wireless communication device after the reception time in the communication partner device.

In the radio communication apparatus according to the present invention, the modulation method control unit selects the modulation method for actual communication, and the variation in line quality in a time period before the reception time in the communication partner device is A first step of estimating the quality of the line at the processing time in the wireless communication device after the reception time in the communication partner device when selecting the modulation scheme for the actual communication, using the slope. variation in line quality in a time zone before a certain reception time in said communication partner device in past communications between said wireless communication device and said communication partner device a transition probability matrix, which is a matrix whose components are actual values of probabilities of occurrence of each combination of the slope and the variation slope of the line quality in the time zone after the certain reception time; Selecting the modulation method for the actual communication predicted based on the fluctuation slope of channel quality in a time period before the reception time in the communication partner device when selecting the modulation method. The above-mentioned in the communication partner device when selecting the modulation scheme for the actual communication by using the fluctuation slope of the line quality in the time zone after the reception time in the communication partner device at the time a second channel quality calculator for estimating channel quality at a processing time in the wireless communication device after the reception time; and the channel quality estimated by the first channel quality calculator and the second channel quality and a modulation method selection unit that selects the modulation method based on the channel quality estimated by the channel quality calculation unit.

In the radio communication apparatus according to the present invention, the modulation method control unit, when a predetermined time has passed since the radio communication apparatus last received the combination data transmitted from the communication partner apparatus, A reception stagnation handling unit may be provided that selects the lowest modulation scheme from among a plurality of prepared modulation schemes.

The radio communication apparatus according to the present invention selects the modulation scheme for actual communication based on the absolute value of the slope of the line quality fluctuation in the time zone prior to the reception time in the apparatus of the communication partner. A transmission cycle of the combined data may be changed.

Further, an adaptive modulation method according to the present invention is an adaptive modulation method in wireless communication in which an adaptive modulation scheme is used between a wireless communication device and a communication partner device, and a The wireless communication device selects a modulation scheme to be used for transmission to the communication partner device based on combined data of reception time and channel quality in the communication partner device.

In the adaptive modulation method according to the present invention, when the wireless communication device selects the modulation scheme for actual communication, the fluctuation slope of the channel quality in a time period prior to the reception time in the communication partner device is is used to estimate the quality of the line at the processing time in the wireless communication device after the reception time in the communication partner device when selecting the modulation scheme for the actual communication. may

The adaptive modulation method according to the present invention is such that the wireless communication device receives data from a past communication between the wireless communication device and the communication partner device before a certain reception time in the communication partner device. a transition probability matrix, which is a matrix whose components are the actual values of the probabilities of occurrence of each combination of the variation slope of the channel quality in the time zone and the variation slope of the channel quality in the time zone after the certain reception time; To perform the actual communication predicted based on the fluctuation slope of the line quality in the time zone before the reception time in the communication partner device when the modulation method is selected for the actual communication. When selecting the modulation method for actually performing the communication, using the fluctuation slope of the line quality in the time zone after the reception time in the communication partner device when selecting the modulation method The channel quality may be estimated at a processing time in the wireless communication device after the reception time in the communication partner device.

According to the wireless communication device and the adaptive modulation method according to the present invention, it is used at the time of transmission to the device of the communication partner based on the combined data of the reception time and the channel quality in the device of the communication partner transmitted from the device of the communication partner. Since the modulation scheme is selected, the modulation scheme is determined by considering the channel quality and the time when the channel quality is acquired (that is, the reception time at the communication partner device), so the adaptive modulation control loop It is possible to perform control based on two assumptions, the delay and the fluctuation slope of the channel quality, and it is possible to select an appropriate modulation method. It is possible to select a modulation scheme with higher transmission efficiency than when selecting a modulation scheme based on assumptions. According to the wireless communication apparatus 1 and the adaptive modulation method according to the embodiment, it is also possible to select an appropriate modulation method without increasing the frequency of transmission of channel quality information by the receiving station.

According to the radio communication apparatus of the present invention, when a predetermined time has passed since the radio communication apparatus last received the combination data transmitted from the device of the communication partner, the lowest modulation method is selected. In this case, the data used for estimating the communication status of the circuit/propagation path is old, and there is a difference between the calculation result of the circuit quality, which is the criteria for deciding the modulation method, and the actual circuit quality when the modulation method is actually switched. becomes large, and it is possible to avoid a situation in which an inappropriate modulation scheme is selected.

According to the radio communication apparatus according to the present invention, when the transmission period of the combination data is changed based on the absolute value of the slope of the line quality fluctuation, it is possible to accurately respond to changes in the propagation environment that fluctuate greatly in a short period of time. In addition, when the propagation environment changes slowly, the traffic can be reduced and the computational load of the device can be reduced.

1 is a functional block diagram showing a schematic configuration of a wireless communication device according to an embodiment of the present invention; FIG. FIG. 2 is a diagram showing an example of operation timing involved in wireless communication between the wireless communication device and communication terminal in FIG. 1; 4 is a diagram showing another example of operation timings involved in wireless communication between the wireless communication device and the communication terminal in FIG. 1; FIG. 2 is a diagram showing an example of a transition probability matrix used in the wireless communication device of FIG. 1; FIG. 2 is a diagram showing an example of a correspondence table between specific channel estimation values and modulation schemes used in the radio communication apparatus of FIG. 1; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on the illustrated embodiments.

FIG. 1 is a functional block diagram showing a schematic configuration of a wireless communication device 1 according to an embodiment of the invention. FIG. 2 is a diagram showing an example of operation timing involved in wireless communication between the wireless communication device 1 according to the embodiment and the communication terminal 9 as a communication partner.

A wireless communication device 1 performs digital wireless communication with a communication terminal 9 via a satellite 8 using an adaptive modulation method, and a wireless communication system including the wireless communication device 1, the satellite 8, and the communication terminal 9 is configured. be done. The wireless communication device 1 and the communication terminal 9 can use the time synchronized with each other by using the time information obtained by the clock function of GPS (Global Positioning System). Suppose that

The "modulation scheme" in the description of the present invention includes (narrowly defined) modulation schemes such as BPSK, QPSK, 16QAM, and 64QAM, modulation multi-level number, and parameters related to encoding (e.g., encoding rate, code length). (BPSK: abbreviation for Binary Phase Shift Keying; QPSK: abbreviation for Quadrature Phase Shift Keying; QAM: abbreviation for Quadrature Amplitude Modulation).

Communication terminal 9 performs predetermined processing such as amplification, frequency conversion, and demodulation on a radio signal that has been radio-transmitted from radio communication apparatus 1 and received via an antenna, and converts the radio signal to communication data transmitted from radio communication apparatus 1 ( That is, data used for original communication between the radio communication apparatus 1 and the communication terminal 9) is acquired, and the channel quality is calculated for each frame based on the received symbols.

The index used as line quality is not limited to a specific type, and may be any information that can represent the degree of good/bad communication status on a line/propagation path. Indicators used as channel quality include, for example, reception level [dB], carrier to noise ratio (that is, C/N ratio) [dB], and RSSI (abbreviation of Received Signal Strength Indicator). .

The communication terminal 9 generates combined data of, for example, the channel quality calculated for each frame and the reception time of the radio signal used for calculating the channel quality. The value of the index representing the channel quality (in other words, the degree of good/bad communication status in the channel/propagation path) calculated based on the radio signal received at the reception time Tr_n is expressed as “channel quality Ctr_n”. The subscript n is an identifier for distinguishing a plurality of consecutive points in time series from each other in chronological order. ...is.

The time Tt_n is the transmission time at which the communication terminal 9 generates combined data of the reception time Tr_n and the channel quality Ctr_n at the communication terminal 9 and transmits the combined data to the wireless communication device 1 . The length of time (unit: seconds) from transmission time Tt_n-1 to next transmission time Tt_n is called "cycle time Δt" (that is, for example, Δt=Tt_n+1−Tt_n=Tt_n−Tt_n−1).

The communication terminal 9 transmits communication data to the wireless communication device 1 (that is, data used for original communication between the wireless communication device 1 and the communication terminal 9) together with the reception time Tr_n and the line quality Ctr_n. A transmission frame is generated based on the combined data, and after performing predetermined processing such as modulation of the transmission frame and conversion into a radio signal, it is transmitted via an antenna.

That is, the communication terminal 9 generates and transmits combined data of the reception time Tr_n and the channel quality Ctr_n at the communication terminal 9 at intervals of the cycle time Δt.

A wireless communication device 1 is a mechanism for performing digital wireless communication using an adaptive modulation method with a communication terminal 9 via a satellite 8, and mainly includes a receiver 2, a demodulator 3, It has a modulation scheme control section 4 , a modulation section 5 and a transmission section 6 .

The wireless communication device 1 includes a control unit (CPU: abbreviation for Central Processing Unit) having a function of controlling the operation of each unit that configures the wireless communication device 1, and a central processing unit. It serves as a work area for temporarily storing data and information generated when the processing unit performs arithmetic processing related to selection/decision of the modulation method, and stores various information, programs, data, etc. It may further have a storage unit comprising a ROM (abbreviation for Read Only Memory) and a RAM (abbreviation for Random Access Memory) having a function of serving as a storage area for storing data.

The radio communication apparatus 1 and the adaptive modulation method according to the embodiment select the modulation method to be used when transmitting to the communication terminal 9 based on the combination data of the reception time and channel quality at the communication terminal 9 transmitted from the communication terminal 9. Choose, like.

In the following description, processing related to the selection/determination of the modulation scheme by the radio communication apparatus 1 using the channel quality Ctr_n that is calculated based on the radio signal received at the communication terminal 9 at the reception time Tr_n and transmitted from the communication terminal 9 is represented as "processing time Tp_n". The processing time Tp_n may be the time when the wireless communication device 1 receives the wireless signal transmitted from the communication terminal 9 .

Also, the time difference between the reception time Tr_n in the communication terminal 9 and the processing time Tp_n in the wireless communication device 1 (that is, Tp_n−Tr_n; specifically, the delay time) is expressed as “time lag Tlag_n” (see FIG. 2). . Note that the reception time Tr_n at the communication terminal 9 is before the transmission time Tt_n from the communication terminal 9, so the starting point of the time lag Tlag_n (not clearly shifted in the figure) is from the transmission time Tt_n from the communication terminal 9. is also ahead.

The receiving unit 2 amplifies and frequency-converts a radio signal that is radio-transmitted from the communication terminal 9 and received via an antenna, and outputs the converted signal.

The demodulation unit 3 receives the input of the converted signal output from the reception unit 2, performs predetermined processing such as demodulation on the signal, and performs communication data transmitted from the communication terminal 9 (that is, radio communication data). The data used for the original communication between the device 1 and the communication terminal 9) is extracted and output as received data, and the reception time Tr_n at the communication terminal 9 and the line quality transmitted from the communication terminal 9 Extract and output the combined data with Ctr_n.

That is, in principle (in other words, if the communication conditions on the line/propagation path are good), the wireless communication device 1 receives the reception time Tr_n at the communication terminal 9 and the line Receive combined data with quality Ctr_n. However, since the transmission delay of the radio signal from the communication terminal 9 to the radio communication device 1 is not constant, the timing/time interval for receiving the radio signal by the radio communication device 1 is not constant, and therefore the time lag Tlag_n is not constant. .

The modulation scheme control unit 4 selects a modulation scheme to be applied/used at the time of transmission to the communication terminal 9 based on the combined data of the reception time Tr_n and the channel quality Ctr_n at the communication terminal 9 transmitted from the communication terminal 9. A mechanism for outputting a signal for controlling switching to the modulation scheme selected with the first channel quality calculation unit 41, the second channel quality calculation unit 42, the modulation scheme selection unit 43, and A reception stagnation handling unit 44 is provided.

The first channel quality calculator 41 estimates the value of an index representing the quality of the channel (in other words, the degree of good/bad communication status in the channel/propagation path) using the fluctuation slope and time lag of the channel quality. A value estimated by the first channel quality calculator 41 is called a "first channel estimation value".

Specifically, the first channel quality calculator 41 estimates the first channel estimation value C1tp_n according to Equation 1 below.
(Formula 1) C1tp_n = Ctr_n + (Ctr_n - Ctr_n-1) / (Tr_n - Tr_n-1) x Tlag_n
Here,
C1tp_n: First channel estimation value at processing time Tp_n in wireless communication device 1 Ctr_n: Channel quality at reception time Tr_n in communication terminal 9 Ctr_n-1: Channel quality at reception time Tr_n-1 in communication terminal 9 Tlag_n: Communication terminal Reception time Tr_n in 9 and processing time in wireless communication device 1
Time lag with Tp_n (Tlag_n = Tp_n - Tr_n)

"(Ctr_n−Ctr_n−1)/(Tr_n−Tr_n−1)" corresponding to the variation slope of the channel quality in the above Equation 1 is calculated by the communication terminal 9, and the reception time Tr_n at the communication terminal 9 and It may be transmitted from the communication terminal 9 to the wireless communication device 1 together with the combination data with the channel quality Ctr_n.

The first channel quality calculator 41 assumes that the slope of channel quality fluctuation in the time zone before the reception time Tr_n in the communication terminal 9 continues in the same way in the time zone after the reception time Tr_n. The channel quality (specifically, the first propagation path estimation value C1tp_n) at the time when the time lag Tlag_n has passed from the reception time Tr_n (that is, the processing time Tp_n in the wireless communication device 1) is estimated.

The first channel quality calculator 41 outputs the estimated first channel estimation value C1tp_n.

Here, the first line quality calculation unit 41 calculates new combination data before the predetermined delay upper limit time elapses from the time when the wireless communication device 1 last receives the combination data transmitted from the communication terminal 9. When received, a process of estimating the first channel estimation value C1tp_n is performed.

On the other hand, if new combination data is not received before the stagnation upper limit time elapses from the time when the wireless communication apparatus 1 last received the combination data transmitted from the communication terminal 9, the first line quality calculation unit 41 outputs to the reception stagnation handling unit 44 a signal notifying that the stagnation upper limit time has elapsed without performing the process of estimating the first channel estimation value C1tp_n. In this case, neither the processing by the second line quality calculation unit 42 nor the processing by the modulation scheme selection unit 43 described below is performed.

The upper limit of delay time is not limited to a specific length of time (unit: seconds). Considering that the difference between the calculation result and the actual line quality when switching the modulation method may become large, and that it may not be possible to select an appropriate modulation method. , is appropriately set to an appropriate length of time. The stagnation upper limit time is set to a time length within a range of about 1.5 to 4 times the cycle time Δt, for example.

Note that, as shown in FIG. 3, when the stagnation upper limit time is set to a length of time longer than twice the period time Δt, the combination received last (in other words, immediately before) by the wireless communication device 1 When new combination data is received after a period of time twice the cycle time Δt has passed from the reception time Tr_n-2 of the data at the communication terminal 9 (in the example shown in the figure, at the transmission time Tt_n-1 (the combination data of the reception time Tr_n-1 and the channel quality Ctr_n-1 in the communication terminal 9 transmitted from the communication terminal 9 is lost), the first channel quality calculation unit 41 (In other words, immediately before) received combination data (in the example shown in the figure, combination data of reception time Tr_n-2 and channel quality Ctr_n-2 in communication terminal 9) is used to generate the first channel estimation value ( In the illustrated example, a process of estimating C1tp_n) is performed.

In the example shown in FIG. 3, the first channel quality calculator 41 specifically estimates the first channel estimation value C1tp_n according to Equation 2 below.
(Formula 2) C1tp_n = Ctr_n + (Ctr_n - Ctr_n-2) / (Tr_n - Tr_n-2) x Tlag_n
Here,
C1tp_n: first channel estimation value at processing time Tp_n in wireless communication device 1 Ctr_n: channel quality at reception time Tr_n in communication terminal 9 Ctr_n-2: channel quality at reception time Tr_n-2 in communication terminal 9 Tlag_n: communication terminal Reception time Tr_n in 9 and processing time in wireless communication device 1
Time lag with Tp_n (Tlag_n = Tp_n - Tr_n)

In the example shown in FIG. 3, the upper limit of the stagnation time is set to a length of time slightly longer than twice the cycle time Δt, and the reception time Tr_n transmitted from the communication terminal 9 at the transmission time Tt_n−1 If the combination data of reception time Tr_n and line quality Ctr_n transmitted from communication terminal 9 at transmission time Tt_n subsequent to the combination data of -1 and line quality Ctr_n-1 also suffers a reception loss, communication terminal 9 New combination data will not be received before the stagnation upper limit time elapses from the time when the wireless communication device 1 last received the combination data to be transmitted. A signal notifying that the upper limit of the stagnation time has elapsed is output to the reception stagnation handling unit 44 without executing the process of estimating the estimated value C1tp_n. In addition, neither the processing by the second line quality calculation unit 42 nor the processing by the modulation scheme selection unit 43 described below is performed.

The second line quality calculation unit 42 calculates the line quality fluctuation slope in the previous time period, and then estimates the line quality fluctuation slope after the time lag using a Markov process. The value of the index representing the degree of good/bad communication conditions on the propagation path is estimated. A value estimated by the second channel quality calculator 42 is called a "second channel estimation value".

Specifically, the second channel quality calculator 42 estimates the second channel estimation value C2tp_n according to Equation 3 below.
(Formula 3) C2tp_n = Ctr_n + ΔCtr_n x Tlag_n
Here,
C2tp_n: Second channel estimation value at processing time Tp_n in wireless communication device 1 Ctr_n: Channel quality at reception time Tr_n in communication terminal 9 ΔCtr_n: Processing time in wireless communication device 1 from reception time Tr_n in communication terminal 9
Estimated value of slope of channel quality fluctuation over Tp_n Tlag_n: Reception time Tr_n at communication terminal 9 and processing time at wireless communication device 1
Time lag with Tp_n (Tlag_n = Tp_n - Tr_n)

In Equation 3 above, the transition probability matrix T is used to calculate the estimated value ΔCtr_n of the variation slope of the channel quality.

As shown in FIG. 4, the transition probability matrix T is the pre-point fluctuation slope ΔCbef_n (described below (see Equation 4), and the post-time fluctuation slope ΔCaft_n (see Equation 5 below) of the channel quality from the reception time Tr_n to the reception time Tr_n+1 (in other words, at the subsequent cycle time Δt) in the communication terminal 9. It is a matrix whose (i, j) elements are the probability values p _ij of each combination occurring.
(Formula 4) ΔCbef_n = (Ctr_n-Ctr_n-1)/(Tr_n-Tr_n-1)
(Formula 5) ΔCaft_n = (Ctr_n+1-Ctr_n)/(Tr_n+1-Tr_n)

ΔC ₁ , ΔC ₂ , and ΔC ₃ in FIG. 4 are values determined as the pre-point fluctuation slope ΔCbef of the channel quality and the post-point fluctuation slope ΔCaft of the channel quality, and are negative numbers, 0, or positive numbers. is a specific numerical value.

The transition probability matrix T is created based on the results of past communications performed between the wireless communication device 1 and the communication terminal 9 . Specifically, the transition probability matrix T is calculated from the channel quality at a certain reception time in the communication terminal 9 and the channel quality at the reception time before the period time Δt from the certain reception time. , and the post-time fluctuation slope ΔCaft calculated from the line quality at the certain reception time in the communication terminal 9 and the line quality at the reception time after the period time Δt from the certain reception time. , by determining the probability distribution of each combination of the pre-point variation slope ΔCbef and the post-point variation slope ΔCaft in the set.

The transition probability matrix T is stored, for example, in a storage unit, etc., and read by the second channel quality calculation unit 42 as appropriate for use. The transition probability matrix T may be updated as necessary.

Specifically, for example, when the transition probability matrix T is expressed as shown in FIG. 4, the estimated value ΔCtr_n of the fluctuation slope of channel quality is ( In other words, when the pre-instant variation slope ΔCbef_n of the channel quality (at the previous period time Δt) is less than ΔC ₁ , the transition probability matrix T is used to be calculated according to Equation 6 below.
(Equation 6) ΔCtr_n = p ₁₁ ×{ΔC ₁ -(ΔC ₂ -ΔC ₁ )/2}
+ p ₁₂ ×(ΔC ₁ +ΔC ₂ )/2
+ p ₁₃ ×(ΔC ₂ +ΔC ₃ )/2
+p ₁₄ ×{ΔC ₃ +(ΔC ₃ -ΔC ₂ )/2}

The estimated value ΔCtr_n of the variation slope of the channel quality is the variation slope ΔCbef before and after the time _when the probability value pij, which is the (i, j) component of the transition probability matrix T, is equal to or greater than a predetermined transition probability threshold. It may be determined based on the value of the post-time change slope ΔCaft having the largest absolute value among combinations with the change slope ΔCaft.

Specifically, for example, the transition probability matrix T is expressed as shown in FIG. ), the pre-point fluctuation slope ΔCbef_n of the channel quality from the reception time Tr_n−1 to the reception time Tr_n (in other words, at the previous cycle time Δt) in the communication terminal 9 is less than ΔC ₁ and At this time, if p ₁₄ <p ₁₃ <Pthr<p ₁₂ <p ₁₁ and |ΔC ₁ −(ΔC ₂ −ΔC ₁ )/2|>|(ΔC ₁ +ΔC ₂ )/2|, the line The estimated value ΔCtr_n of the quality fluctuation slope may be set to "ΔC ₁ -(ΔC ₂ -ΔC ₁ )/2".

In other words, the second channel quality calculator 42 calculates, from the reception time Tr_n on the basis of the channel quality fluctuation slope (that is, ΔCbef_n) and the transition probability matrix T in the time zone before the reception time Tr_n in the communication terminal 9, After predicting the fluctuation slope of the channel quality in the later time zone (that is, ΔCtr_n), the channel quality (specifically , the second channel estimation value C2tp_n) is estimated.

The second channel quality calculator 42 outputs the estimated second channel estimation value C2tp_n.

Here, as shown in FIG. 3, when the stagnation upper limit time is set to a time length longer than twice the period time Δt, the wireless communication device 1 received last (in other words, just before) When new combination data is received after a period of time twice the cycle time Δt has elapsed from the reception time Tr_n-2 at the communication terminal 9 of the combination data (in the example shown in the figure, the transmission time Tt_n-1 (the combination data of the reception time Tr_n-1 and the channel quality Ctr_n-1 in the communication terminal 9 transmitted from the communication terminal 9 is lost), the second channel quality calculator 42 determines that the wireless communication device 1 Second channel estimation value using the combination data (in the example shown in the figure, combination data of reception time Tr_n-2 and channel quality Ctr_n-2 in communication terminal 9) received last (in other words, just before) (C2tp_n in the example shown in the figure) is estimated.

In the example shown in FIG. 3, the estimated value ΔCtr_n of the variation slope of the channel quality in the above Equation 3 is calculated by squaring the transition probability matrix T and then using the transition probability matrix T ² . It is calculated by the same procedure as the above Equation 6 or by the same procedure as the method of using the above transition probability threshold for the transition probability matrix T ² .

The modulation scheme selection unit 43 selects a modulation scheme based on the first channel estimation value C1tp_n and the second channel estimation value C2tp_n.

Specifically, the modulation scheme selection unit 43 first receives the input of the first channel estimation value C1tp_n output from the first channel quality calculation unit 41, and outputs from the second channel quality calculation unit 42. Receives the input of the second channel estimation value C2tp_n obtained by the second channel estimation value C2tp_n, and specifies which of the first channel estimation value C1tp_n and the second channel estimation value C2tp_n has the worse channel quality. A channel estimation value specified by the modulation scheme selection unit 43 is called a “specific channel estimation value”.

The modulation scheme selection unit 43 then selects a modulation scheme based on the specific channel estimation value. The modulation scheme selection unit 43 selects a modulation scheme based on the specific channel estimation value, which has the worse channel quality, of the first channel estimation value C1tp_n and the second channel estimation value C2tp_n. By making the selection, the selection of the modulation method is erroneous due to the estimation error of the index value representing the quality of the channel (specifically, the first channel estimation value C1tp_n, the second channel estimation value C2tp_n). The modulation method is selected so as to avoid the risk of

Specifically, for example, a specific channel estimation value CS including a plurality of combinations of the specific channel estimation value CS and the modulation method for specifying the modulation method according to the magnitude of the specific channel estimation value CS, and A table of correspondence with modulation schemes is created in advance, and the modulation scheme selector 43 selects a modulation scheme according to the correspondence table. The correspondence table between the specific channel estimation value CS and the modulation scheme is stored in, for example, a storage unit, and is read by the modulation scheme selection unit 43 as appropriate and used.

FIG. 5 shows an example of a correspondence table between specific channel estimation values CS and modulation schemes. The example shown in FIG. 5 is based on the premise that the larger the specific channel estimation value CS, the better the communication conditions in the line/channel (where CS ₁ , CS ₂ , CS ₃ and CS ₄ in FIG. 5 are , a value determined according to the type of index representing the quality of the line, and is actually a specific numerical value). In the example shown in FIG. 5, the better the communication conditions on the line/propagation path, the higher the transmission efficiency among the plurality of modulation schemes. A modulation scheme with low transmission efficiency is ranked lower, and a modulation scheme with high transmission efficiency is ranked higher.

The example shown in FIG. 5 is an example of a correspondence table when the modulation scheme/modulation M-ary number is selected according to the specific channel estimation value CS. However, the correspondence table between the specific channel estimation value CS and the modulation scheme is not limited to the example shown in FIG. A correspondence table in which the code length) is selected may be created and used, or parameters related to modulation scheme/modulation multilevel number and encoding (for example, code A correspondence table may be created and used in which a combination with a conversion rate, code length) is selected.

Then, the modulation scheme selector 43 outputs a signal for controlling switching to the selected modulation scheme (referred to as a "modulation scheme control signal").

The reception stagnation handling unit 44 notifies that the stagnation upper limit time has elapsed since the wireless communication device 1 last received the combination data transmitted from the communication terminal 9, which is output from the first line quality calculation unit 41. A predetermined modulation method is selected when receiving a signal input to be used.

When the stagnation upper limit time has elapsed since the wireless communication device 1 last received the combined data transmitted from the communication terminal 9, that is, the reception at the communication terminal 9 is It is considered that the radio communication apparatus 1 cannot receive the combined data of the time Tr_n and the channel quality Ctr_n for a predetermined period of time. Therefore, the reception stagnation handling unit 44 selects the lowest modulation scheme among a plurality of modulation schemes prepared in advance (specifically, a plurality of modulation schemes included in the correspondence table), in other words, A modulation scheme (BPSK in the example of the correspondence table shown in FIG. 5) that is expected to maximize the value of the index representing quality (that is, channel quality Ctr_n) is selected.

The reception stagnation handling unit 44 outputs a signal for controlling switching to the selected modulation scheme (that is, a modulation scheme control signal).

The modulation unit 5 receives input of transmission data, which is communication data to be transmitted to the communication terminal 9 (that is, data used for original communication between the wireless communication device 1 and the communication terminal 9), receiving a modulation scheme control signal output from a modulation scheme control unit 4, performing modulation processing on the transmission data while switching the modulation scheme according to the modulation scheme control signal to generate a modulated signal, and generating the modulated signal; Output.

The transmitter 6 receives the modulated signal output from the modulator 5, performs predetermined processing such as frequency conversion and amplification on the modulated signal, and transmits the processed signal wirelessly through an antenna. Send.

According to the wireless communication device 1 and the adaptive modulation method according to the embodiment, based on the combination data of the reception time Tr_n and the channel quality Ctr_n at the communication terminal 9 transmitted from the communication terminal 9, Since the modulation scheme to be used is selected, the modulation scheme is determined in consideration of the channel quality Ctr_n and the time when the channel quality Ctr_n is acquired (that is, the reception time Tr_n at the communication terminal 9). It is possible to perform control assuming both the delay of the modulation control loop and the fluctuation slope of the channel quality, and it is possible to select an appropriate modulation method. , it is possible to select a modulation scheme with higher transmission efficiency than when selecting a modulation scheme based on the uniform assumption of . According to the wireless communication apparatus 1 and the adaptive modulation method according to the embodiment, it is also possible to select an appropriate modulation method without increasing the frequency of transmission of channel quality information by the receiving station.

According to the wireless communication device 1 and the adaptive modulation method according to the embodiment, when the stagnation upper limit time has passed since the wireless communication device 1 last received the combination data transmitted from the communication terminal 9, the lowest modulation Since the method is selected, the data used for estimating the communication status on the line/propagation path is old, so the calculation result of the line quality, which is the criterion for deciding the modulation method, and the actual time when the modulation method is actually switched. It is possible to avoid a situation in which the difference with channel quality becomes large, and to avoid a situation in which an inappropriate modulation scheme is selected.

Although the embodiments of the present invention have been described above, the specific configuration is not limited to the above-described embodiments. Included in the invention.

Specifically, in the above-described embodiment, the communication terminal 9 transmits the reception time Tr_n at the communication terminal 9 to the radio communication apparatus 1 using the mutually synchronized time between the radio communication apparatus 1 and the communication terminal 9. While transmitting, the radio communication device 1 calculates the time lag Tlag_n (=Tp_n - Tr_n). The radio communication device 1 calculates the average delay time and calculates the time lag Tlag may be determined. Specifically, for example, when the transmission unit 6 of the wireless communication device 1 wirelessly transmits a signal as transmission data, the time information (specifically, the time stamp of the transmission time from the wireless communication device 1) is added to the signal. and transmit the time information and the line quality Ctr_n when the communication terminal 9 receives the signal including the time information together with the communication data to the wireless communication device 1 (the reception time Tr_n at the communication terminal 9 is not send). The wireless communication device 1 calculates the time difference between the time information sent back to the communication terminal 9 (that is, the time stamp of the transmission time from the wireless communication device 1) and the reception time, An average value of the time differences in the period may be calculated, and half of the average value of the time differences may be set as Tlag.

Further, in the above embodiment, the modulation method control unit 4 includes both the first line quality calculation unit 41 and the second line quality calculation unit 42. Only one of the line quality calculation unit 41 and the second line quality calculation unit 42 may be provided. In this case, the modulation scheme selection unit 43 is not provided, and the modulation scheme is selected based on the first channel estimation value C1tp_n estimated by the first channel quality calculation unit 41, or the second channel A modulation scheme is selected based on the second channel estimation value C2tp_n estimated by the quality calculator 42 .

Further, although the modulation scheme control section 4 is provided with the reception stagnation handling section 44 in the above embodiment, the modulation scheme control section 4 may not be provided with the reception stagnation handling section 44 . In this case, the upper limit of stagnation time is not set, and regardless of the elapsed time since the wireless communication device 1 last received the combination data transmitted from the communication terminal 9, the first line quality calculation unit 41 calculates the first 1 channel estimation value C1tp_n, and the second channel quality calculation unit 42 performs processing for estimating the second channel estimation value C2tp_n.

Further, although the cycle time Δt is constant in the above embodiment, the cycle time Δt may be changed. For example, when the absolute value of the channel quality fluctuation slope represented by (Ctr_n−Ctr_n−1)/(Tr_n−Tr_n−1) exceeds a predetermined threshold due to a large change in the propagation environment, The transmission cycle of the channel quality information from the communication terminal 9 (more specifically, the combination data of the reception time Tr_n and the channel quality Ctr_n in the communication terminal 9) may be shortened by shortening the cycle time Δt. Alternatively, the period time Δt is changed (specifically, shortened The transmission period of the line quality information from the communication terminal 9 may be changed by increasing or lengthening the transmission period. Further, when the absolute value of the slope of the line quality fluctuation exceeds a predetermined threshold value, the communication terminal 9 gives the highest priority to the transmission processing of the line quality Ctr_n and the reception time Tr_n in the communication terminal 9. may This makes it possible to accurately follow changes in the propagation environment, which fluctuate greatly in a short time, and to select an appropriate modulation method. It is possible to reduce the calculation load of

1 wireless communication device 2 receiver 3 demodulator 4 modulation scheme controller 41 first channel quality calculator 42 second channel quality calculator 43 modulation scheme selector 44 reception stagnation countermeasure unit 5 modulator 6 transmitter 8 satellite 9 communication terminal

Claims (9)

A wireless communication device that performs wireless communication with a communication partner device using an adaptive modulation method,
A modulation scheme control unit that selects a modulation scheme to be used for transmission to the communication partner device based on combination data of reception time and channel quality in the communication partner device transmitted from the communication partner device,
A wireless communication device characterized by: The modulation scheme control unit uses the variation slope of the line quality in the time zone before the reception time in the communication partner device when selecting the modulation scheme for actually performing the communication. A line quality calculation unit for estimating the quality of the line at the processing time in the wireless communication device after the reception time in the communication partner device when selecting the modulation scheme to perform
The wireless communication device according to claim 1, characterized by: Fluctuations in line quality in a time period before a certain reception time in the communication partner device in past communications performed between the wireless communication device and the communication partner device by the modulation method control unit A transition probability matrix, which is a matrix whose components are actual values of probabilities of occurrence of each combination of the slope and the variation slope of the line quality in the time zone after the certain reception time, and the transition probability matrix for actually performing communication. When selecting the modulation method for the actual communication predicted based on the fluctuation slope of the line quality in the time zone before the reception time in the communication partner device when selecting the modulation method The reception in the communication partner device when selecting the modulation scheme for the actual communication by using the fluctuation slope of the line quality in the time zone after the reception time in the communication partner device A line quality calculation unit that estimates the quality of the line at the processing time in the wireless communication device after the time,
The wireless communication device according to claim 1, characterized by: The modulation method control unit
The modulation scheme for actually performing communication by using the fluctuation slope of the line quality in a time zone before the reception time in the communication partner device when selecting the modulation scheme for actually performing communication. A first line quality calculation unit that estimates the quality of the line at the processing time in the wireless communication device after the reception time in the communication partner device when selecting;
In the past communication performed between the wireless communication device and the device of the communication partner, the fluctuation slope of the line quality in a time period before a certain reception time in the device of the communication partner and the certain reception time A transition probability matrix, which is a matrix whose components are the actual values of the probability of occurrence of each of the combinations with the fluctuation slope of the channel quality in the later time zone, and when selecting the modulation method for the actual communication said communication partner device when selecting said modulation scheme for said actual communication predicted based on the fluctuation slope of line quality in a time zone before the reception time in said communication partner device of using the fluctuation slope of the line quality in the time period after the reception time in the communication partner device when the modulation method is selected for the actual communication after the reception time a second line quality calculator for estimating the quality of the line at the processing time in the wireless communication device;
a modulation method selection unit that selects the modulation method based on the channel quality estimated by the first channel quality calculation unit and the channel quality estimated by the second channel quality calculation unit; prepare
The wireless communication device according to claim 1, characterized by: The modulation scheme control unit selects a plurality of modulation schemes prepared in advance when a predetermined time has passed since the wireless communication apparatus last received the combination data transmitted from the communication partner device. Equipped with a reception stagnation response unit that selects the lowest modulation method among them,
The wireless communication device according to any one of claims 1 to 4, characterized in that: The transmission cycle of the combination data is changed based on the absolute value of the slope of the line quality fluctuation in the time zone before the reception time in the communication partner device when the modulation method is selected for actual communication. ,
The wireless communication device according to any one of claims 1 to 5, characterized in that: An adaptive modulation method in wireless communication in which an adaptive modulation method is used between a wireless communication device and a communication partner device,
Selecting a modulation scheme to be used by the wireless communication device when transmitting to the communication partner device based on combination data of reception time and line quality in the communication partner device transmitted from the communication partner device;
An adaptive modulation method characterized by: When the wireless communication device selects the modulation scheme for actually performing communication, the slope of line quality fluctuation in a time period before the reception time in the communication partner device is used to perform the actual communication. estimating the quality of the line at the processing time in the wireless communication device after the reception time in the communication partner device when selecting the modulation scheme to perform;
8. The adaptive modulation method according to claim 7, characterized by: Variation slope of line quality in a time period before a certain reception time in the communication partner device in the past communication between the wireless communication device and the communication partner device a transition probability matrix, which is a matrix whose components are actual values of probabilities of occurrence of each of the combination of each of the combination of and the variation slope of the channel quality in the time zone after the certain reception time, and the modulation for actually performing communication When selecting the modulation method for the actual communication predicted based on the fluctuation slope of the line quality in the time zone before the reception time in the communication partner device when selecting the method The reception time in the communication partner device when selecting the modulation scheme for the actual communication by using the fluctuation slope of the line quality in the time zone after the reception time in the communication partner device. Estimate the quality of the line at the processing time in the wireless communication device after
8. The adaptive modulation method according to claim 7, characterized by:

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