Wireless communication device and adaptive modulation method

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

Technical Field

[0001] The present invention relates to a wireless communication device and an adaptive modulation method, and more particularly to a technique suitable for use in satellite communication that utilizes an adaptive modulation method for switching a modulation method based on a propagation environment.

Background Art

[0002] In a wireless communication system, an adaptive modulation method for switching a modulation method based on a propagation environment is used to improve frequency utilization efficiency. In the adaptive modulation method, generally, a receiving station (e.g., a wireless terminal) calculates a line quality based on a received radio wave, feeds back the calculation result of the line quality to a transmitting station (e.g., a satellite or a base station), and the transmitting station selects a modulation method based on the fed-back calculation result of the line quality. In such a method, a change to a modulation method suitable for the propagation environment is made.

[0003] As a communication device using an adaptive modulation method, there is known a communication device including a line quality change direction detection means for detecting a change direction of a line quality based on a received signal, and a modulation method determination means for determining a modulation method used for signal transmission based on a line quality before a change when a change direction of the line quality detected by the line quality change direction detection means is an improvement direction (see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in the conventional adaptive modulation method, the calculation result of the line quality is fed back from the receiving station to the transmitting station. However, the calculation result of the fed-back line quality represents the line quality situation a predetermined time ago, and there is a delay time between the time when the receiving station receives the signal (in other words, the time when the communication situation in the line / propagation path was as per the calculation result of the line quality) and the time when the transmitting station actually switches the modulation method. There are various reasons for the delay time. For example, in the case of a satellite communication system, since communication is carried out via a satellite, the transmission delay of the information signal used for selecting the modulation method is large. Also, the return link for the receiving station to transmit the information used for selecting the modulation method to the transmitting station is often a TDM (abbreviation for Time Division Multiplexing; time division multiplexing) method, so the delay time of the return link varies and is not stable. Due to these reasons, a non-constant delay time occurs in the information serving as the criterion for determining the modulation method. Due to the delay time (also referred to as the "delay of the adaptive modulation control loop") between the time when the receiving station receives the signal (in other words, the time when the communication situation in the line / propagation path was as per the calculation result of the line quality) and the time when the transmitting station actually switches the modulation method, there is a difference between the calculation result of the line quality serving as the criterion for determining the modulation method and the actual line quality at the time of actually switching the modulation method. In particular, when a large change occurs in the propagation environment, there is a problem that an appropriate modulation method cannot be selected, and ultimately, there is a problem that the transmission efficiency is reduced.

[0006] Also, in the method such as in Patent Document 1, the acquisition frequency of the line quality information serving as the criterion for determining the modulation method needs to be sufficiently fine with respect to the occurrence frequency of changes in the propagation environment. That is, it is necessary to acquire information densely, and the frequency at which the receiving station has to transmit the line quality information increases. For this reason, especially when the receiving station is a mobile device, there is a problem that the battery is consumed and the operating time becomes short.

[0007] Therefore, an object of the present invention is to provide a wireless communication device and an adaptive modulation method capable of selecting an appropriate modulation method without increasing the transmission frequency of the line quality information by the receiving station.

Means for Solving the Problem

[0008] In order to solve the above problems, a wireless communication device according to the present invention is a wireless communication device that performs wireless communication using an adaptive modulation method with a device of a communication partner, and is based on combination data of a reception time and a line quality in the device of the communication partner transmitted from the device of the communication partner. It has a modulation method control unit that selects a modulation method to be used at the time of transmission to the device of the communication partner. Shi , The modulation method control unit uses, as components, the actual values of the probabilities of occurrence of each combination of the variation tendency of the line quality in the time period before a certain reception time in the device of the communication partner and the variation tendency of the line quality in the time period after the certain reception time in the past communication performed between the wireless communication device and the device of the communication partner, to form a transition probability matrix, and the variation tendency of the line quality in the time period before the reception time in the device of the communication partner when actually selecting the modulation method for communication. Based on this, the variation tendency of the line quality in the time period after the reception time in the device of the communication partner when actually selecting the modulation method for communication is predicted. Using this, a line quality calculation unit is provided to estimate the line quality at the processing time in the wireless communication device after the reception time in the device of the communication partner when actually selecting the modulation method for communication. It is characterized by this.

[0011] In the wireless communication device according to the present invention, when the modulation method control unit selects the modulation method for actually performing communication, it uses the variation tendency of the line quality in a time zone before the reception time in the device of the communication partner. A first line quality calculation unit that estimates the line quality at the processing time in the wireless communication device after the reception time in the device of the communication partner when selecting the modulation method for actually performing communication. Line quality And a modulation method selection unit that selects the modulation method based on the line quality estimated by the first line quality calculation unit and the line quality estimated by the first line quality calculation unit. It may be configured to include. Before The line quality estimated by the first line quality calculation unit described above Line quality Quality and before The above-mentioned The line quality estimated by the line quality calculation unit described above Line quality Quality and based on the above, it may be provided with a modulation method selection unit that selects the modulation method.

[0012] In the wireless communication device according to the present invention, when the modulation method control unit has elapsed a predetermined time from the time when the wireless communication device last received the combination data transmitted from the device of the communication partner, it is prepared in advance. It may be provided with a reception stagnation countermeasure unit that selects the lowest modulation method among a plurality of modulation methods.

[0013] In the wireless communication device according to the present invention, the transmission period of the combination data may be changed based on the absolute value of the variation tendency of the line quality in a time zone before the reception time in the device of the communication partner when selecting the modulation method for actually performing communication.

[0014] The 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 based on combination data of a reception time and a line quality in the communication partner device transmitted from the communication partner device, the wireless communication device selects a modulation scheme to be used when transmitting to the communication partner device. Shi , The wireless communication device uses, as components, the actual values of the probabilities of occurrence of each combination of the variation tendency of the line quality in the time period before a certain reception time in the device of the communication partner and the variation tendency of the line quality in the time period after the certain reception time in the past communication performed between the wireless communication device and the device of the communication partner, to form a transition probability matrix, and the variation tendency of the line quality in the time period before the reception time in the device of the communication partner when actually selecting the modulation method for communication. Based on this, the variation tendency of the line quality in the time period after the reception time in the device of the communication partner when actually selecting the modulation method for communication is predicted. Using this, the line quality at the processing time in the wireless communication device after the reception time in the device of the communication partner when actually selecting the modulation method for communication is estimated. It is characterized by this.

Advantages of the Invention

[0017] According to the wireless communication device and the adaptive modulation method of the present invention, since the modulation scheme to be used when transmitting to the communication partner device is selected based on the combination data of the reception time and the line quality in the communication partner device transmitted from the communication partner device, the modulation scheme is determined in consideration of the line quality and the time when the line quality was acquired (that is, the reception time in the communication partner device). Therefore, it is possible to perform control assuming two factors: the delay of the adaptive modulation control loop and the variation trend of the line quality, and it is possible to select an appropriate modulation scheme. For example, compared to the case where the modulation scheme is selected assuming a uniform estimation error of the value of the index representing the line quality, it is possible to select a modulation scheme with higher transmission efficiency. According to the wireless communication device 1 and the adaptive modulation method according to the embodiment, it is also possible to select an appropriate modulation scheme without increasing the transmission frequency of the line quality information by the receiving station.

[0018] According to the wireless communication device of the present invention, when the lowest modulation scheme is selected when a predetermined time has elapsed since the wireless communication device last received the combination data transmitted from the communication partner device, the data used for estimating the communication status in the line / propagation path is old, so the difference between the calculation result of the line quality, which is the criterion for determining the modulation scheme, and the actual line quality at the time of actually switching the modulation scheme becomes large. It is possible to avoid a situation where an inappropriate modulation scheme is selected.

[0019] According to the wireless communication device of the present invention, when the transmission period of the combined data is changed based on the absolute value of the variation gradient of the line quality, it is possible to accurately follow the change in the propagation environment that varies greatly in a short time and select an appropriate modulation method. When the change in the propagation environment is slow, traffic can be reduced or the calculation load on the device can be reduced.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0021] Hereinafter, the present invention will be described based on the illustrated embodiments.

[0022] FIG. 1 is a functional block diagram showing a schematic configuration of a wireless communication device 1 according to an embodiment of the present invention. FIG. 2 is a diagram showing an example of operation timing related to wireless communication between the wireless communication device 1 according to the embodiment and a communication terminal 9 which is a communication partner.

[0023] The wireless communication device 1 performs digital wireless communication with the communication terminal 9 via the 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. Note that it is assumed that the wireless communication device 1 and the communication terminal 9 can use a time synchronized with each other by using time information obtained by the clock function of GPS (abbreviation for Global Positioning System; global positioning system).

[0024] In the description of this invention, the "modulation method" means at least one of (narrow sense) modulation methods / modulation levels such as BPSK, QPSK, 16QAM, and 64QAM, and parameters related to coding (for example, coding rate, code length) (note that BPSK is an abbreviation for Binary Phase Shift Keying. QPSK is an abbreviation for Quadrature Phase Shift Keying. QAM is an abbreviation for Quadrature Amplitude Modulation).

[0025] The communication terminal 9 performs predetermined processing such as amplification, frequency conversion, and demodulation on the wireless signal wirelessly transmitted from the wireless communication device 1 and received via the antenna, and obtains communication data transmitted from the wireless communication device 1 (that is, data used for the original communication between the wireless communication device 1 and the communication terminal 9), and calculates the line quality for each frame based on the received symbols.

[0026] The index used as the line quality is not limited to a specific type, and any information that can represent the degree of good / bad communication status in the line / propagation path may be used. Examples of the index used as the line quality include the received level [dB], the carrier-to-noise ratio (that is, the C / N ratio; Carrier to Noise ratio) [dB], and RSSI (abbreviation for Received Signal Strength Indicator).

[0027] The communication terminal 9 generates combined data of, for example, the line quality calculated for each frame and the reception time of the radio signal used for the calculation of the line quality. The value of the index representing the quality of the line (in other words, the degree of good or bad communication status in the line / propagation path) calculated based on the radio signal received at the reception time Tr_n is expressed as "line quality Ctr_n". The subscript n is an identifier for distinguishing a plurality of consecutive time points in time series from each other in time series order, and as consecutive values where the value of the previous time point in time series is smaller, n = 1, 2, 3, ···.

[0028] The time Tt_n is the transmission time when the communication terminal 9 generates the combined data of the reception time Tr_n and the line quality Ctr_n at the communication terminal 9 and transmits it to the wireless communication device 1. The time length (unit: second) from the transmission time Tt_n-1 to the 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).

[0029] The communication terminal 9 generates a transmission frame based on the combined data of the reception time Tr_n and the line quality Ctr_n together with the communication data to be transmitted to the wireless communication device 1 (that is, the data used for the original communication between the wireless communication device 1 and the communication terminal 9), and after performing predetermined processing such as modulation of the transmission frame and conversion into a radio signal, transmits it via the antenna.

[0030] That is, the communication terminal 9 generates and transmits the combined data of the reception time Tr_n and the line quality Ctr_n at the communication terminal 9 at intervals of the cycle time Δt.

[0031] The wireless communication device 1 is a mechanism for performing digital wireless communication with the communication terminal 9 via the satellite 8 using an adaptive modulation method, and mainly includes a reception unit 2, a demodulation unit 3, a modulation method control unit 4, a modulation unit 5, and a transmission unit 6.

[0032] The wireless communication device 1 may further include a control unit composed of a central processing unit (CPU for short) and the like, which has a function of controlling the operations of each part constituting the wireless communication device 1 as needed, and a storage unit composed of a ROM (Read Only Memory for short), a RAM (Random Access Memory for short), etc., which serves as a work area for temporarily storing data, information, etc. generated when the central processing unit performs arithmetic processing related to the selection / determination of the modulation method, or serves as a storage area for storing various information, programs, data, etc.

[0033] The wireless communication device 1 and the adaptive modulation method according to the embodiment are configured to select a modulation method to be used at the time of transmission to the communication terminal 9 based on the combined data of the reception time and the line quality at the communication terminal 9 transmitted from the communication terminal 9.

[0034] In the following description, the time when the wireless communication device 1 starts processing related to the selection / determination of the modulation method using the line quality Ctr_n calculated based on the radio signal received at the reception time Tr_n at the communication terminal 9 and transmitted from the communication terminal 9 is represented as the "processing time Tp_n". The processing time Tp_n may be the time when the wireless communication device 1 receives the radio signal transmitted from the communication terminal 9.

[0035] Also, the time difference between the reception time Tr_n at the communication terminal 9 and the processing time Tp_n at the wireless communication device 1 (that is, Tp_n - Tr_n; specifically, the delay time) is represented as the "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, and therefore the starting point of the time lag Tlag_n is before the transmission time Tt_n from the communication terminal 9 (although not clearly shifted in the figure).

[0036] The receiving unit 2 amplifies and frequency-converts the radio signal wirelessly transmitted from the communication terminal 9 and received via the antenna, and outputs the converted signal.

[0037] 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, extracts the communication data transmitted from the communication terminal 9 (that is, the data used for the original communication between the wireless communication device 1 and the communication terminal 9) as reception data, and extracts and outputs the combined data of the reception time Tr_n and the line quality Ctr_n at the communication terminal 9 transmitted from the communication terminal 9.

[0038] That is, in principle (in other words, if the communication situation in the line / propagation path is good), the wireless communication device 1 receives the combined data of the reception time Tr_n and the line quality Ctr_n at the communication terminal 9 transmitted from the communication terminal 9 at intervals of the cycle time Δt. However, since the transmission delay of the wireless signal from the communication terminal 9 to the wireless communication device 1 is not constant, the timing / time interval at which the wireless communication device 1 receives the wireless signal is not constant, and therefore the time lag Tlag_n is not constant.

[0039] The modulation method control unit 4 is a mechanism for selecting the modulation method 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 line quality Ctr_n at the communication terminal 9 transmitted from the communication terminal 9, and outputting a signal for controlling the switching to the selected modulation method, and includes a first line quality calculation unit 41, a second line quality calculation unit 42, a modulation method selection unit 43, and a reception pause countermeasure unit 44.

[0040] The first line quality calculation unit 41 estimates the value of an index representing the quality of the line (in other words, the degree of good / bad communication situation in the line / propagation path) using the fluctuation slope and time lag of the line quality. The value estimated by the first line quality calculation unit 41 is called the "first propagation path estimated value".

[0041] Specifically, the first line quality calculation unit 41 estimates the first propagation path estimated value C1tp_n according to the following mathematical formula 1. (1) C1tp_n = Ctr_n+(Ctr_n-Ctr_n-1) / (Tr_n-Tr_n-1)×Tlag_n Here, C1tp_n: The first propagation path estimated value at the processing time Tp_n in the wireless communication device 1 Ctr_n: The line quality at the reception time Tr_n in the communication terminal 9 Ctr_n-1: The line quality at the reception time Tr_n-1 in the communication terminal 9 Tlag_n: The time lag between the reception time Tr_n in the communication terminal 9 and the processing time Tp_n in the wireless communication device 1 (Tlag_n = Tp_n - Tr_n)

[0042] "(Ctr_n - Ctr_n-1) / (Tr_n - Tr_n-1)", which corresponds to the variation tendency of the line quality in the above formula (1), may be calculated by the communication terminal 9 and transmitted from the communication terminal 9 to the wireless communication device 1 together with the combined data of the combination of the reception time Tr_n and the line quality Ctr_n in the communication terminal 9.

[0043] That is, the first line quality calculation unit 41 assumes that the variation tendency of the line quality in the time period before the reception time Tr_n in the communication terminal 9 continues in the same way in the time period after the reception time Tr_n, and estimates the line quality (specifically, the first propagation path estimated value C1tp_n) at the time when the time lag Tlag_n has elapsed from the reception time Tr_n (i.e., the processing time Tp_n in the wireless communication device 1).

[0044] The first line quality calculation unit 41 outputs the estimated first propagation path estimated value C1tp_n.

[0045] Here, when the wireless communication device 1 receives new combined data before the predetermined stagnation upper limit time elapses from the time when the wireless communication device 1 last received the combined data transmitted from the communication terminal 9, the first line quality calculation unit 41 performs the process of estimating the first propagation path estimated value C1tp_n.

[0046] On the other hand, if no new combined data is received before the stagnation upper limit time elapses since the wireless communication device 1 last received the combined data transmitted from the communication terminal 9, the first line quality calculation unit 41 does not perform the process of estimating the first propagation path estimation value C1tp_n, and outputs a signal notifying that the stagnation upper limit time has elapsed to the reception stagnation response unit 44. In this case, the processes by the following second line quality calculation unit 42 and the modulation method selection unit 43 are not performed either.

[0047] The stagnation upper limit time is not limited to a specific time length (unit: second). For example, if the data used for estimating the communication status in the line / propagation path is old, there is a risk that the difference between the calculation result of the line quality serving as the criterion for determining the modulation method and the actual line quality when actually switching the modulation method will increase, and ultimately, it may not be possible to select an appropriate modulation method. After considering such factors, it is appropriately set to an appropriate time length. 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.

[0048] As shown in FIG. 3, when the stagnation upper limit time is set to a time length longer than twice the cycle time Δt, and new combined data is received after a time of twice the cycle time Δt has elapsed based on the reception time Tr_n-2 at the communication terminal 9 among the combined data that the wireless communication device 1 last (in other words, immediately before) received (in the example shown in the figure, the combined data of the reception time Tr_n-1 and the line quality Ctr_n-1 at the communication terminal 9 transmitted from the communication terminal 9 at the transmission time Tt_n-1 is received with loss), the first line quality calculation unit 41 uses the combined data that the wireless communication device 1 last (in other words, immediately before) received (in the example shown in the figure, the combined data of the reception time Tr_n-2 and the line quality Ctr_n-2 at the communication terminal 9) to perform the process of estimating the first propagation path estimation value (in the example shown in the figure, C1tp_n).

[0049] In the case of the example shown in FIG. 3, specifically, the first line quality calculation unit 41 estimates the first propagation path estimation value C1tp_n according to the following mathematical formula 2. (Number 2) C1tp_n = Ctr_n+(Ctr_n - Ctr_n-2) / (Tr_n - Tr_n-2)×Tlag_n Here, C1tp_n: The first propagation path estimated value at the processing time Tp_n in the wireless communication device 1 Ctr_n: The line quality at the reception time Tr_n in the communication terminal 9 Ctr_n-2: The line quality at the reception time Tr_n-2 in the communication terminal 9 Tlag_n: The time lag between the reception time Tr_n in the communication terminal 9 and the processing time Tp_n in the wireless communication device 1 (Tlag_n = Tp_n - Tr_n)

[0050] In the example shown in FIG. 3, the stagnation upper limit time is set to a time length slightly longer than twice the cycle time Δt. If the combination data of the reception time Tr_n-1 and the line quality Ctr_n-1 transmitted from the communication terminal 9 at the transmission time Tt_n-1 is followed by the combination data of the reception time Tr_n and the line quality Ctr_n transmitted from the communication terminal 9 at the transmission time Tt_n and is also temporarily lost, the wireless communication device 1 does not receive new combination data before the stagnation upper limit time elapses from the time when the combination data transmitted from the communication terminal 9 was last received. The first line quality calculation unit 41 does not perform the process of estimating the first propagation path estimated value C1tp_n and outputs a signal notifying that the stagnation upper limit time has elapsed to the reception stagnation countermeasure unit 44. Then, the processes by the following second line quality calculation unit 42 and the modulation method selection unit 43 are not performed either.

[0051] The second line quality calculation unit 42 calculates the variation tendency of the line quality in the previous time period and then estimates the variation tendency of the line quality after the time lag by a Markov process to estimate the value of an index representing the line quality (in other words, the degree of good or bad communication status in the line / propagation path). The value estimated by the second line quality calculation unit 42 is called the "second propagation path estimated value".

[0052] Specifically, the second line quality calculation unit 42 estimates the second propagation path estimated value C2tp_n according to the following mathematical formula 3. (Equation 3) C2tp_n = Ctr_n + ΔCtr_n × Tlag_n Here, C2tp_n: The second propagation path estimated value at the processing time Tp_n in the wireless communication device 1 Ctr_n: The line quality at the reception time Tr_n in the communication terminal 9 ΔCtr_n: The estimated value of the variation tendency of the line quality from the reception time Tr_n in the communication terminal 9 to the processing time Tp_n in the wireless communication device 1 Tlag_n: The time lag between the reception time Tr_n in the communication terminal 9 and the processing time Tp_n in the wireless communication device 1 (Tlag_n = Tp_n - Tr_n)

[0053] Among the above mathematical formula 3, the estimated value ΔCtr_n of the variation tendency of the line quality is calculated using the transition probability matrix T.

[0054] As shown in FIG. 4, the transition probability matrix T is the probability value p of each combination of the pre-time variation tendency ΔCbef_n of the line quality (see the following mathematical formula 4) from the reception time Tr_n - 1 to the reception time Tr_n in the communication terminal 9 (in other words, in the previous cycle time Δt) and the post-time variation tendency ΔCaft_n of the line quality (see the following mathematical formula 5) from the reception time Tr_n to the reception time Tr_n + 1 in the communication terminal 9 (in other words, in the subsequent cycle time Δt). ij It is a matrix with (i, j) components. (Equation 4) ΔCbef_n = (Ctr_n - Ctr_n - 1) / (Tr_n - Tr_n - 1) (Equation 5) ΔCaft_n = (Ctr_n + 1 - Ctr_n) / (Tr_n + 1 - Tr_n)

[0055] ΔC in FIG. 4 1 , ΔC 2 , ΔC 3is a value defined as the pre-timepoint variation slope ΔCbef of the line quality and the post-timepoint variation slope ΔCaft of the line quality, which is a negative number, 0, or a positive number, and is actually a specific numerical value.

[0056] The transition probability matrix T is created based on the past communication performance between the wireless communication device 1 and the communication terminal 9. Specifically, the transition probability matrix T is calculated from the pre-timepoint variation slope ΔCbef calculated from the line quality at a certain reception time at the communication terminal 9 and the line quality at the reception time Δt before the certain reception time, and the post-timepoint variation slope ΔCaft calculated from the line quality at the certain reception time at the communication terminal 9 and the line quality at the reception time Δt after the certain reception time. A set of combined data is created, and the transition probability matrix T is created by obtaining the probability distribution of each combination of the pre-timepoint variation slope ΔCbef and the post-timepoint variation slope ΔCaft in the set.

[0057] The transition probability matrix T is stored in, for example, a storage unit and is appropriately read and used by the second line quality calculation unit 42. The transition probability matrix T may be updated as needed.

[0058] Specifically, for example, when the transition probability matrix T is represented as shown in FIG. 4, the estimated value ΔCtr_n of the variation slope of the line quality is calculated according to the following formula 6 using the transition probability matrix T when the pre-timepoint variation slope ΔCbef_n of the line quality from the reception time Tr_n-1 to the reception time Tr_n (in other words, in the previous cycle time Δt) at the communication terminal 9 is less than ΔC. 1 When it is less than, the transition probability matrix T is used and calculated according to the following formula 6. (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 +p14 ×{ΔC 3 +(ΔC 3 -ΔC 2 ) / 2}

[0059] The estimated value ΔCtr_n of the variation slope of the line quality, or the probability value p that is the (i, j) component of the transition probability matrix T ij may be determined based on the value of the post-time variation slope ΔCaft with the largest absolute value among the combinations of the pre-time variation slope ΔCbef and the post-time variation slope ΔCaft when p is equal to or greater than a predetermined transition probability threshold.

[0060] Specifically, for example, when the transition probability matrix T is represented as shown in FIG. 4 and the transition probability threshold is predetermined to be Pthr (specifically, for example, any value in the range of about 0.1 to 0.3), and the pre-time variation slope ΔCbef_n of the line quality from the reception time Tr_n - 1 to the reception time Tr_n in the communication terminal 9 (in other words, in the previous cycle time Δt) is less than ΔC 1 . 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 estimated value ΔCtr_n of the variation slope of the line quality may be set to "ΔC 1 -(ΔC 2 -ΔC 1 ) / 2".

[0061] The second line quality calculation unit 42 estimates the line quality (specifically, the second propagation path estimated value C2tp_n) at the time (i.e., the processing time Tp_n in the wireless communication device 1) when the time lag Tlag_n has elapsed from the reception time Tr_n, after predicting the variation slope of the line quality (i.e., ΔCtr_n) in the time zone after the reception time Tr_n based on the variation slope of the line quality (i.e., ΔCbef_n) in the time zone before the reception time Tr_n in the communication terminal 9 and the transition probability matrix T.

[0062] The second line quality calculation unit 42 outputs the estimated second propagation path estimated value C2tp_n.

[0063] Here, as shown in FIG. 3, when the stagnation upper limit time is set to a time length longer than twice the cycle time Δt, and when new combined data is received after a time of twice the cycle time Δt has elapsed from the reception time Tr_n-2 in the communication terminal 9 among the combined data last (in other words, immediately before) received by the wireless communication device 1 (in the example shown in the figure, the combined data of the reception time Tr_n-1 and the line quality Ctr_n-1 transmitted from the communication terminal 9 at the transmission time Tt_n-1 is reception lost), the second line quality calculation unit 42 uses the combined data last (in other words, immediately before) received by the wireless communication device 1 (in the example shown in the figure, the combined data of the reception time Tr_n-2 and the line quality Ctr_n-2 in the communication terminal 9) to perform the process of estimating the second propagation path estimated value (in the example shown in the figure, C2tp_n).

[0064] In the case of the example shown in FIG. 3, the estimated value ΔCtr_n of the variation slope of the line quality in the above formula 3 is calculated by performing a matrix calculation of the square of the transition probability matrix T and then using the transition probability matrix T 2 in the same procedure as the above formula 6, or in the same procedure as the method of using the above transition probability threshold for the transition probability matrix T 2 is calculated.

[0065] The modulation method selection unit 43 selects a modulation method based on the first propagation path estimation value C1tp_n and the second propagation path estimation value C2tp_n.

[0066] Specifically, the modulation method selection unit 43 first receives the input of the first propagation path estimation value C1tp_n output from the first line quality calculation unit 41 and receives the input of the second propagation path estimation value C2tp_n output from the second line quality calculation unit 42, and identifies the propagation path with the worse line quality among the first propagation path estimation value C1tp_n and the second propagation path estimation value C2tp_n. The propagation path estimation value identified by the modulation method selection unit 43 is referred to as the "specific propagation path estimation value".

[0067] Subsequently, the modulation method selection unit 43 selects a modulation method based on the specific propagation path estimation value. That is, the modulation method selection unit 43 selects a modulation method based on the specific propagation path estimation value, which is the one with the worse line quality among the first propagation path estimation value C1tp_n and the second propagation path estimation value C2tp_n, so as to avoid the risk of misselecting the modulation method due to the estimation error of the value of the index representing the line quality (specifically, the first propagation path estimation value C1tp_n and the second propagation path estimation value C2tp_n).

[0068] Specifically, for example, a correspondence table between the specific propagation path estimation value CS and the modulation method, including a plurality of combinations of the specific propagation path estimation value CS for designating the modulation method according to the magnitude of the specific propagation path estimation value CS and the modulation method, is created in advance, and the modulation method selection unit 43 selects the modulation method according to the correspondence table. The correspondence table between the specific propagation path estimation value CS and the modulation method is stored, for example, in a storage unit and is appropriately read and used by the modulation method selection unit 43.

[0069] An example of the correspondence table between the specific propagation path estimation value CS and the modulation method is shown in FIG. 5. The example shown in FIG. 5 is based on the premise that the better the communication situation in the line / propagation path, the larger the specific propagation path estimation value CS (note that CS in FIG. 5 1 , CS 2 , CS 3 , CS4 is a value determined according to the type of index representing the line quality, and is actually a specific numerical value). The example shown in FIG. 5 also enables the selection of a modulation method with a higher transmission efficiency among a plurality of modulation methods as the communication situation in the line / propagation path is better. Note that a modulation method with a lower transmission efficiency is regarded as lower, and a modulation method with a higher transmission efficiency is regarded as higher.

[0070] The example shown in FIG. 5 is an example of a correspondence table when the modulation method / number of modulation levels is selected according to the specific propagation path estimation value CS. However, the correspondence table between the specific propagation path estimation value CS and the modulation method is not limited to the example shown in FIG. 5. A correspondence table may be created and used in which parameters related to encoding (e.g., coding rate, code length) are selected according to the specific propagation path estimation value CS. Alternatively, a correspondence table may be created and used in which a combination of the modulation method / number of modulation levels and parameters related to encoding (e.g., coding rate, code length) is selected according to the specific propagation path estimation value CS.

[0071] Then, the modulation method selection unit 43 outputs a signal (referred to as a "modulation method control signal") for controlling the switching to the selected modulation method.

[0072] When the reception suspension countermeasure unit 44 receives an input of a signal notifying that the suspension upper limit time has elapsed since the wireless communication device 1 last received the combined data transmitted from the communication terminal 9, which is output from the first line quality calculation unit 41, it selects a predetermined modulation method.

[0073] When the elapsed time since the wireless communication device 1 last received the combination data transmitted from the communication terminal 9 reaches the stagnation upper limit time, that is, when the communication situation in the line / propagation path is poor and the wireless communication device 1 cannot receive the combination data of the reception time Tr_n and the line quality Ctr_n at the communication terminal 9 for a predetermined time. Therefore, the reception stagnation countermeasure unit 44 selects the lowest modulation method among a plurality of modulation methods prepared in advance (specifically, the plurality of modulation methods included in the correspondence table), in other words, the modulation method expected to maximize the value of the index representing the quality of the line (that is, the line quality Ctr_n) (in the example of the correspondence table shown in FIG. 5, BPSK).

[0074] The reception stagnation countermeasure unit 44 outputs a signal (that is, a modulation method control signal) for controlling the switching to the selected modulation method.

[0075] The modulation unit 5 receives the input of the transmission data, which is the communication data to be transmitted to the communication terminal 9 (that is, the data used for the original communication between the wireless communication device 1 and the communication terminal 9), and also receives the input of the modulation method control signal output from the modulation method control unit 4. The modulation unit 5 performs modulation processing on the transmission data while switching the modulation method according to the modulation method control signal to generate a modulation signal, and outputs the modulation signal.

[0076] The transmission unit 6 receives the input of the modulation signal output from the modulation unit 5, performs predetermined processing such as frequency conversion and amplification on the modulation signal, and then wirelessly transmits the processed signal via the antenna.

[0077] According to the wireless communication device 1 and the adaptive modulation method according to the embodiment, since the modulation method to be used at the time of transmission to the communication terminal 9 is selected based on the combined data of the reception time Tr_n and the line quality Ctr_n at the communication terminal 9 transmitted from the communication terminal 9, the modulation method is determined in consideration of the line quality Ctr_n and the time when the line quality Ctr_n was acquired (that is, the reception time Tr_n at the communication terminal 9). Therefore, it is possible to perform control assuming two factors: the delay of the adaptive modulation control loop and the variation tendency of the line quality, and it is possible to select an appropriate modulation method. For example, compared with the case of selecting a modulation method assuming a uniform estimation error of the value of the index representing the line quality, it is possible to select a modulation method with higher transmission efficiency. According to the wireless communication device 1 and the adaptive modulation method according to the embodiment, it is also possible to select an appropriate modulation method without increasing the transmission frequency of the line quality information by the receiving station.

[0078] According to the wireless communication device 1 and the adaptive modulation method according to the embodiment, when the stagnation upper limit time has elapsed since the time when the wireless communication device 1 last received the combined data transmitted from the communication terminal 9, the lowest modulation method is selected. Therefore, it is possible to avoid a situation where the difference between the calculation result of the line quality that is the criterion for determining the modulation method and the actual line quality at the time of actually switching the modulation method becomes large because the data used for estimating the communication situation in the line / propagation path is old, and it is possible to avoid selecting a modulation method that cannot be said to be appropriate.

[0079] As described above, the embodiments of the present invention have been described. However, the specific configuration is not limited to the above embodiments, and even if there are design changes and the like within the scope not departing from the gist of the present invention, they are included in the present invention.

[0080] Specifically, in the above embodiment, when the wireless communication device 1 and the communication terminal 9 are synchronized with each other, the communication terminal 9 transmits the reception time Tr_n at the communication terminal 9 to the wireless communication device 1 by using the synchronized time, and the wireless communication device 1 calculates the time lag Tlag_n (=Tp_n - Tr_n). However, the wireless communication device 1 may calculate the average delay time and determine the time lag Tlag based on the average delay time. Specifically, for example, when the transmission unit 6 of the wireless communication device 1 wirelessly transmits a signal as transmission data, the signal includes time information (specifically, a time stamp of the transmission time from the wireless communication device 1). When the communication terminal 9 receives the signal including the time information together with the communication data, the communication terminal 9 transmits the line quality Ctr_n and the time information to the wireless communication device 1 (note that the reception time Tr_n at the communication terminal 9 is not transmitted). The wireless communication device 1 calculates the time difference between the time information (i.e., the time stamp of the transmission time from the wireless communication device 1) transmitted back from the communication terminal 9 and the reception time, and calculates the average value of the time differences in a predetermined past period, and may set half of the average value of the time differences as Tlag.

[0081] Also, 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. However, the modulation method control unit 4 may include only one of the first line quality calculation unit 41 and the second line quality calculation unit 42. In this case, the modulation method selection unit 43 is not provided, and the modulation method is selected based on the first propagation path estimated value C1tp_n estimated by the first line quality calculation unit 41, or the modulation method is selected based on the second propagation path estimated value C2tp_n estimated by the second line quality calculation unit 42.

[0082] In addition, in the above-described embodiment, the modulation method control unit 4 is provided with the reception pause response unit 44, but the modulation method control unit 4 may not be provided with the reception pause response unit 44. In this case, the pause upper limit 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 estimates the first propagation path estimation value C1tp_n, or the second line quality calculation unit 42 estimates the second propagation path estimation value C2tp_n.

[0083] Also, in the above-described embodiment, the cycle time Δt is made constant, but the cycle time Δt may be changed. For example, when the absolute value of the line quality variation gradient expressed as (Ctr_n - Ctr_n-1) / (Tr_n - Tr_n-1) exceeds a predetermined threshold due to a large change in the propagation environment, the cycle time Δt may be shortened to accelerate the transmission cycle of the line quality information from the communication terminal 9 (specifically, the combination data of the reception time Tr_n and the line quality Ctr_n at the communication terminal 9). Alternatively, the cycle time Δt may be changed (specifically, shortened or lengthened) according to the magnitude of the absolute value of the line quality variation gradient expressed as (Ctr_n - Ctr_n-1) / (Tr_n - Tr_n-1) to change the transmission cycle of the line quality information from the communication terminal 9. Further, when the absolute value of the line quality variation gradient exceeds a predetermined threshold, the communication terminal 9 may perform the transmission process of the line quality Ctr_n or the reception time Tr_n at the communication terminal 9 as the highest priority process. This makes it possible to appropriately select an appropriate modulation method by accurately following the changes in the propagation environment that vary greatly in a short time, and to reduce traffic or the calculation load of the device when the changes in the propagation environment are slow.

Explanation of Reference Numerals

[0084] 1 Wireless communication device 2 Receiver 3 Demodulation unit 4 Modulation method control unit 41 First line quality calculation unit 42 Second line quality calculation unit 43 Modulation method selection unit 44 Reception stagnation countermeasure unit 5 Modulation unit 6 Transmission unit 8 Satellite 9 Communication terminal

Claims

1. A wireless communication device that performs wireless communication using an adaptive modulation method with a communication partner's device, comprising a modulation method control unit that selects a modulation method to be used when transmitting to the communication partner's device based on combined data of a reception time and line quality in the communication partner's device transmitted from the communication partner's device, wherein the modulation method control unit uses, as components, actual values of probabilities of occurrence of respective combinations of a variation tendency of line quality in a time period before a certain reception time in the communication partner's device and a variation tendency of line quality in a time period after the certain reception time in past communication performed between the wireless communication device and the communication partner's device, to form a transition probability matrix, and a variation tendency of line quality in a time period before a reception time in the communication partner's device when actually selecting the modulation method for actual communication, and uses the variation tendency of line quality in a time period after the reception time in the communication partner's device predicted based on these to estimate the line quality at a processing time in the wireless communication device after the reception time in the communication partner's device when actually selecting the modulation method for actual communication, and is provided with a line quality calculation unit. A wireless communication device characterized by the above.

2. The modulation method control unit comprises a first line quality calculation unit that estimates the line quality at a processing time in the wireless communication device after a reception time in the communication partner's device when actually selecting the modulation method for actual communication, using a variation tendency of line quality in a time period before the reception time in the communication partner's device when actually selecting the modulation method for actual communication, and a modulation method selection unit that selects the modulation method based on the line quality estimated by the first line quality calculation unit and the line quality estimated by the line quality calculation unit. The wireless communication device according to Claim 1, characterized by the above.

3. The modulation method control unit is provided with a reception stagnation countermeasure unit that selects the lowest modulation method among a plurality of pre-prepared modulation methods when a predetermined time has elapsed since the time when the wireless communication device last received the combined data transmitted from the communication partner's device. The wireless communication device according to any one of Claims 1 or 2, characterized by the above.

4. Based on the absolute value of the variation trend of the line quality in the time period before the reception time in the device of the communication partner when selecting the modulation method for actual communication, change the transmission period of the combined data. The wireless communication device according to any one of claims 1 to 3, characterized by the above.

5. 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, Based on the combined data of the reception time and the line quality in the device of the communication partner transmitted from the device of the communication partner, select the modulation method used by the wireless communication device when transmitting to the device of the communication partner. The wireless communication device uses, as components, the actual values of the probabilities of occurrence of each of the combinations of the variation trend of the line quality in the time period before a certain reception time in the device of the communication partner and the variation trend of the line quality in the time period after the certain reception time in the past communication performed between the wireless communication device and the device of the communication partner, which is a transition probability matrix, and the variation trend of the line quality in the time period before the reception time in the device of the communication partner when selecting the modulation method for actual communication. Using the variation trend of the line quality in the time period after the reception time in the device of the communication partner when selecting the modulation method for actual communication predicted based on the above, estimate the line quality at the processing time in the wireless communication device after the reception time in the device of the communication partner when selecting the modulation method for actual communication. An adaptive modulation method characterized by the above.

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