JP2014007613A - Communication device and communication control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication device and a communication control method, suppressing the selection of an upper-level modulation class more than necessity.SOLUTION: A communication device 101-1 according to the present invention, which performs transmission/reception of data with an opposite communication party 101-2 through a relay device 103-1, includes a control unit for selecting a modulation class when transmitting data to the relay device 103-1, at least on the basis of a transmission state when the self-device transmits data.

Description

  The present invention relates to a communication device and a communication control method.

  As communication methods for realizing high-speed communication between a communication terminal and a base station, LTE (Long Term Evolution), MC-CDMA (Multi Carrier Code Division Multiple Access), WiMAX (Worldwide Interoperability for Microwave Access) (registered trademark), etc. It has been known. Conventionally, a technique called an adaptive modulation (link adaptation) method has been proposed in order to improve communication services in such a communication method.

  The adaptive modulation scheme is a technique for changing the modulation class used in the communication according to the communication status between the communication terminal (mobile station) which is a communication device and the base station (see, for example, Patent Document 1). Based on the signal received from the base station, the communication terminal calculates a CNR (Carrier to Noise Ratio) indicating the quality (propagation quality) of the radio propagation path between the communication terminal and the base station. Then, the communication terminal specifies a modulation class corresponding to the calculated CNR from a predefined MCS (Modulation and Coding Scheme) table. In the MSC table, as the propagation quality is better, that is, as the CNR is larger, a modulation class that can transmit data at higher speed is associated. As a result, if the propagation quality is good, a higher-order modulation class that can achieve high throughput is selected. If the propagation quality is not good, the lower-order modulation class is less likely to break data in order to suppress the occurrence of disconnection. Is selected.

JP 2005-236709 A

  However, the throughput of data communication between the communication terminal and the communication terminal (partner communication terminal) that is the call destination of this communication terminal is not only the propagation quality between the communication terminal and the base station, It is also affected by the congestion status (load status) of the network with the partner communication terminal. Therefore, even if the propagation quality is good, if the network is congested, the throughput may not increase due to the selection of the upper modulation class.

  In such a case, even if a lower modulation class that is not easily affected by noise is selected, the actual throughput is not changed. Therefore, selecting a higher-order modulation class in a situation where the network is congested results in a reduction in error resilience even though the expected throughput of the modulation class cannot be obtained.

  Accordingly, an object of the present invention made in view of the above problems is to provide a communication device and a communication control method that suppress the selection of a higher-order modulation class than necessary.

In order to solve the above-described problems, the invention of the communication device according to the first aspect is as follows:
A communication device that transmits and receives data with a communication partner via a relay device,
The communication apparatus includes a control unit that selects a modulation class for transmitting data to the relay apparatus based on at least a transmission state when the own apparatus transmits data.

  The invention according to a second aspect is the communication apparatus according to the first aspect, wherein the control unit determines the modulation class based on the transmission status and a communication quality value between the relay apparatus. It is characterized by selecting.

  The invention according to a third aspect is characterized in that, in the communication device according to the first or second aspect, the transmission status is a TCP window size.

  The invention according to a fourth aspect is characterized in that, in the communication device according to the third aspect, the control unit corrects the communication quality value based on the TCP window size.

  The invention according to a fifth aspect is characterized in that, in the communication apparatus according to the third aspect, the control unit determines a selectable highest modulation class based on the TCP window size. Is.

  As described above, the solution of the present invention has been described as an apparatus. However, the present invention can be realized as a method, a program, and a storage medium storing the program, which are substantially equivalent thereto, and the scope of the present invention. It should be understood that these are also included.

For example, a communication control method according to a seventh aspect that realizes the present invention as a method is:
In a communication control method in a communication device that transmits and receives data with a communication partner via a relay device, the communication device includes:
The communication control method includes a step of selecting a modulation class for transmitting data to the relay apparatus based at least on a transmission situation when the own apparatus transmits data.

  According to the communication device and the communication control method according to the present invention configured as described above, it is possible to suppress selection of a higher modulation class than necessary.

FIG. 1 is a schematic configuration diagram of a communication system according to the first embodiment of the present invention. FIG. 2 is a functional block diagram showing a schematic configuration of the communication terminal according to the first embodiment of the present invention. FIG. 3 is a flowchart showing processing of the communication terminal according to the first embodiment of the present invention. FIG. 4 is a flowchart showing processing of the communication terminal according to the second embodiment of the present invention.

  Hereinafter, an embodiment in which a communication device of the present invention is applied to a communication terminal will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic configuration diagram of a communication system according to the first embodiment of the present invention. The communication system 100 includes a communication terminal 101 (101-1, 101-2), a base station 103 (103-1, 103-2, 103-3), a router 105, and a core network 107. Yes. The communication partner (call destination) of communication terminal 101-1 is communication terminal 101-2. That is, the communication terminal 101-1 transmits / receives data to / from the communication terminal 101-2 via the base station 103-1, the router 105, the core network 107, and the base station 103-3. Hereinafter, the base station 103-1 that is a direct wireless communication destination with the communication terminal 101-1 is also referred to as a relay device.

  The communication system 100 is a system in which an acknowledgment (ACK) indicating completion of normal reception of the data is transmitted from the communication terminal 101-2 with respect to the data transmitted from the communication terminal 101-1, for example, the TCP protocol. Adopted.

  The communication terminal 101 employs an adaptive modulation scheme that selects a modulation class when data is transmitted to the base station 103. Therefore, the communication terminal 101-1 uses the modulation used for communication with the base station 103-1 according to the communication environment (propagation quality) between the communication terminal 101-1 and the base station 103-1 that is a relay device. Set the class. The communication terminal 101-1 is, for example, a mobile phone terminal or a personal computer.

  The modulation class is determined by a combination of a modulation method and a coding rate (coding rate), for example. The modulation scheme determines the number of bits that can be transmitted in one symbol. For example, BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), 8PSK (8 Phase Shift Keying), 16QAM (16 Quadrature Amplitude Modulation) ), 64 QAM (64 Quadrature Amplitude Modulation). BPSK is a modulation scheme that can transmit 1 bit per symbol. QPSK is a modulation method capable of transmitting 2 bits per symbol. 8PSK is a modulation method capable of transmitting 3 bits per symbol. 16QAM is a modulation method capable of transmitting 4 bits per symbol. 64QAM is a modulation method capable of transmitting 6 bits per symbol. Hereinafter, a modulation scheme having a larger number of bits that can be transmitted in one symbol is referred to as an upper modulation scheme, and a modulation scheme having a smaller number of bits that can be transmitted in one symbol is referred to as a lower modulation scheme. The higher the modulation method, the more easily the data is broken (although it is more susceptible to noise), but the amount of data that can be transmitted at a time increases. On the other hand, the higher the modulation method, the smaller the amount of data that can be transmitted at one time, but the more difficult it is to break the data.

  The coding rate indicates the strength of error correction, that is, the rate at which data bits are allocated. As the coding rate increases, the proportion of data bits in the number of bits transmitted in one transmission increases, and the proportion of coding bits for error correction decreases. In other words, the amount of data that can be transmitted at a time increases, but broken data is difficult to repair. Also, the smaller the coding rate, the smaller the amount of data that can be transmitted, but the higher the possibility that broken data can be repaired.

  For example, in a modulation class in which the modulation method is QPSK and the coding rate is 1/2, 1 bit can be transmitted with 1 symbol (2 [bit / symbol] × 1/2 = 1 [bit / symbol]). Hereinafter, a modulation class having a larger number of bits that can be transmitted in one symbol is referred to as an upper modulation class, and a modulation class having a smaller number of bits that can be transmitted in one symbol is referred to as a lower modulation class.

  The communication terminal 101 grasps the transmission status when the own terminal transmits data. The transmission status is information that reflects whether or not an acknowledgment has been received within a predetermined time for the transmitted data, and is, for example, a TCP window size. The TCP window size indicates the amount of data that the communication terminal 101 can send in one transmission. The TCP window size increases when all acknowledgments for data sent in one transmission within a predetermined time can be received, and decreases when all acknowledgments cannot be received. That is, the TCP window size is updated when a predetermined time elapses after the communication terminal 101 transmits data.

  Whether or not an acknowledgment is received within a predetermined time depends on the network between the communication terminal 101-1 and the communication terminal 101-2 (a network including the base station 103, the router 105, and the core network 107). It is influenced by the congestion situation. As the amount of communication in the network increases and the congestion situation worsens, the communication terminal 101-1 is less likely to receive an acknowledgment from the communication terminal 101-2 within a predetermined time due to data transmission delay, data loss, and the like. Become. As a result, the TCP window size decreases.

  For example, when the base station 103-1 or 103-2 communicates with a plurality of communication terminals (not shown) and a large amount of data is collected from the base station 103-1 or 103-2 to the router 105, the router 105 is congested. May occur. In this case, a delay occurs until the data from the communication terminal 101-1 is sent from the router 105 to the core network 107, or the data from the communication terminal 101-1 is lost at the router 105. Then, the communication terminal 101-1 often fails to receive an affirmative response, and the TCP window size decreases.

  The initial value and increase / decrease amount of the TCP window size can be arbitrarily set based on the specifications of the communication system 100 and the like.

  The router 105 is connected to a plurality of base stations 103-1 and 103-2. The router 105 sends data from a plurality of base stations 103-1 and 103-2 to the core network 107, and connects data from the core network 107 to the communication terminal 101 that is the destination of the data. Sent to the base station 103. The core network 107 is a communication line network that connects base stations.

  FIG. 2 is a functional block diagram showing a schematic configuration of the communication terminal according to the first embodiment of the present invention. The communication terminal 101 of this embodiment includes a communication unit 111, a baseband unit 113, a storage unit 115, and a control unit 117. The communication unit 111, the baseband unit 113, and the storage unit 115 are connected to the control unit 117.

  The communication unit 111 transmits and receives data (wireless signals) to and from the base station 103 via an antenna. The communication unit 111 performs amplification and down-conversion with low noise on the received signal (reception signal) and sends the signal to the baseband unit 113. In addition, the communication unit 111 performs up-conversion and amplification on the signal from the baseband unit 113, and generates a transmission signal. Then, the communication unit 111 transmits the transmission signal to the base station 103 via the antenna.

  The baseband unit 113 demodulates the received signal and extracts the baseband signal by performing AD conversion, fast Fourier transform, and the like on the received signal from the communication unit 111. Then, the baseband unit 113 sends a baseband signal to the control unit 117. The baseband unit 113 modulates the baseband signal by performing inverse fast Fourier transform, DA conversion, and the like on the baseband signal from the control unit 117 based on the modulation class set by the control unit 117. . Then, the baseband unit 113 sends the modulated baseband signal to the communication unit 111.

  The storage unit 115 stores various information such as an adaptive modulation table (hereinafter referred to as an adaptive modulation table), a transmission status (TCP window size), a transmission status threshold, and the like, and also functions as a work memory and the like. .

  The adaptive modulation table is a table indicating a modulation class to be selected corresponding to the communication quality value between the communication terminal 101-1 and the base station 103-1. The communication quality value between the communication terminal 101-1 and the base station 103-1, for example, is a value representing the reception quality of data from the base station 103-1 received by the communication terminal 101-1. The reception quality is, for example, CINR, CNR, SINR (Signal to Interference and Noise Ratio), SNR (Signal to Noise Ratio) or the like. Hereinafter, in this embodiment, it is assumed that the communication quality value is a CINR value. The larger the CINR value, the better the communication quality, that is, the lower the bit error rate of data, and the modulation class with higher throughput can be applied.

  The adaptive modulation table is a look-up table as shown in Table 1 below, for example, and shows the correspondence between the CINR value, which is a communication quality value, and the modulation class. The higher the modulation class, that is, the larger the modulation class number, the greater the number of bits that can be transmitted in one symbol, and the higher the expected throughput (hereinafter referred to as the expected throughput).

  The transmission status threshold is an index indicating the congestion status allowed in the network between the communication terminal 101-1 and the communication terminal 101-2, and is, for example, a value related to the TCP window size. The allowable congestion situation is a congestion situation in which the expected throughput is realized in the modulation class selected based on the adaptive modulation table. Hereinafter, it is assumed that the transmission status threshold is a value related to the TCP window size (TCP window size threshold). Since the TCP window size decreases as the congestion situation worsens, when the TCP window size of the communication terminal 101-1 is equal to or larger than the TCP window size threshold, the expected throughput of the modulation class selected based on CINR is It means to be realized. Also, if the TCP window size is less than the TCP window size threshold, it means that the expected throughput of the selected modulation class is not realized. Note that the realization of the expected throughput is not strictly limited to the fact that the actual throughput (hereinafter referred to as the actually measured throughput) completely matches the expected throughput. For example, the communication terminal 101-1 can determine that the expected throughput is realized if the error range is determined in advance and the actually measured throughput is included in the expected throughput error range.

  The control unit 117 controls and manages the entire communication terminal 101 including each functional block of the communication terminal 101. The control unit 117 is configured as software executed on an arbitrary suitable processor such as a CPU (central processing unit) or a dedicated processor (for example, DSP (digital signal processor)) specialized for each process. You can also. The processing performed by the control unit 117 will be described in detail with reference to FIG.

  Next, processing of the communication terminal 101 will be described using FIG. FIG. 3 is a flowchart showing processing of the communication terminal according to the first embodiment of the present invention. Note that the reference numerals of the functional blocks related to the communication terminal 101-1 will be described by adding 1 to the reference numerals regarding the functional blocks of the communication terminal 101 shown in FIG. 2.

  When base station 103-1 transmits control data such as user data and an acknowledgment from communication terminal 101-2, communication unit 111-1 of communication terminal 101-1 receives data from base station 103-1. (Step S101). The data received by the communication unit 111-1 is demodulated by the baseband unit 113-1 and sent to the control unit 117-1.

  The control unit 117-1 calculates the CINR of the data received by the communication unit 111-1 (Step S102). Then, the control unit 117-1 reads the TCP window size and the TCP window size threshold stored in the storage unit 115-1, and compares these values (step S103).

  When the TCP window size is equal to or larger than the TCP window size threshold (Yes in step S103), when a modulation class is selected from the adaptive modulation table based on CINR, the expected throughput of the modulation class is realized. Therefore, the control unit 117-1 selects the modulation class corresponding to the CINR calculated in step S102 (step S104). Then, the baseband unit 113-1 modulates the baseband signal with the selected modulation class, and the communication unit 111-1 transmits this modulated signal to the base station 103-1.

  In step S103, when the TCP window size is smaller than the TCP window size threshold (No in step S103), when a modulation class is selected based on the adaptive modulation table, the expected throughput of the modulation class is not realized. . Therefore, the control unit 117-1 corrects the calculated CINR (hereinafter referred to as actually measured CINR) to be smaller, and selects a lower modulation class based on the adaptive modulation table ( Step S105).

  For example, the control unit 117-1 can correct the communication quality value by the following equation (1). In Equation (1), CQ means actual measured CINR, CQ ′ means corrected CINR (hereinafter referred to as corrected CINR), TCPwin means TCP window size, and WINprm means TCP window size threshold. Since the TCP window size is less than the TCP window size threshold value, TCPwin / WINprm is less than 1, so the correction CINR is smaller than the actual measurement CINR.

  CQ '= CQ x (TCPwin / WINprm) (1)

  Then, the control unit 117-1 selects a modulation class corresponding to the correction CINR based on the adaptive modulation table (step S104).

  It should be noted that the processing of steps S103 and S105 can be summarized by defining an equation for correcting CINR as the following equation (2). In this case, the control unit 117-1 can select the modulation class corresponding to the correction CINR based on the adaptive modulation table even when the TCP window size is equal to or larger than the TCP window size threshold.

  CQ '= CQ x min (TCPwin / WINprm, 1) (2)

  The function with min (A, B) outputs a smaller value of A and B. In Expression (2), when the TCP window size is equal to or larger than the TCP window size threshold, TCPwin / WINprm is equal to or larger than 1. Therefore, the corrected CINR is the same as the actual CINR, and the TCP window size is less than the TCP window size threshold. In this case, since TCPwin / WINprm is less than 1, the correction CINR is smaller than the actual measurement CINR.

  In the present invention, the formula for correcting CINR is not limited to the formula described above, and any formula can be set as long as the calculated actual CINR is smaller. For example, a weighting factor w (<1) is added, and a CINR correction formula can be determined as in the following formula (3).

  CQ '= CQ x w x min (TCPwin / WINprm, 1) (3)

  As described above, in the present embodiment, the control unit 117-1 of the communication terminal 101-1 includes the TCP window size, which is the transmission status when the communication terminal 101-1 transmits data, and the data from the base station 103-1. The modulation class is selected based on the CINR. The TCP window size fluctuates corresponding to the network congestion state between the communication terminal 101-1 and the communication terminal 101-2 that is the communication partner of the terminal. For this reason, the control unit 117-1 can select a modulation class reflecting the congestion situation by using not only the CINR but also the TCP window size. Therefore, even if the communication quality between the communication terminal 101-1 and the base station 103-1 is good, it is difficult to select a modulation class that is difficult to realize the expected throughput due to network congestion. Thereby, it is possible to suppress selection of a higher-order modulation class than necessary, and it is possible to suppress a reduction in error resistance of the modulated signal.

  In the present embodiment, the control unit 117-1 can use the TCP window size as the transmission status. The transmission status indicates whether or not an acknowledgment for data transmitted by the communication terminal 101-1 has been correctly received. The TCP window size is increased or decreased according to the reception status of the acknowledgment. Therefore, by using the existing TCP window size, the present invention can be realized without constructing in the communication system 100 a mechanism for returning an acknowledgment to transmission data.

  In the present embodiment, the control unit 117-1 can correct the CINR of data from the base station 103-1, based on the TCP window size. The worse the congestion situation, the lower the modulation class that can realize the expected throughput, and the smaller the TCP window size. Therefore, the control unit 117-1 can correct the CINR of the data from the base station 103-1 so that the decrease rate of the CINR becomes larger as the TCP window size becomes smaller. As the value of CINR becomes smaller, the modulation class selected based on the applied modulation table indicating the correspondence between CINR and the modulation class tends to be lower.

(Second Embodiment)
In the first embodiment, the correction of the CINR value according to the network congestion status has been described. In the second embodiment, the highest modulation class that can be selected according to the network congestion status is determined. Will be described.

  A communication system 200 according to the second embodiment includes a communication terminal 201 (201-1, 201-2), a base station 203 (203-1, 203-2, 203-3), a router 205, and a core network. 207. These components are the same as those of the communication terminal 101 (101-1, 101-2), the base station 103 (103-1, 103-2, 103-3), the router 105, and the core network 107 of the first embodiment. Therefore, the description is omitted.

  Similar to the communication terminal 101 of the first embodiment, the communication terminal 201 according to the second embodiment includes a communication unit 211, a baseband unit 213, a storage unit 215, and a control unit 217. Since the functions of the functional units 211, 213, and 215 other than the control unit 217 are the same as the functions of the corresponding functional units of the first embodiment, description thereof will be omitted. Hereinafter, the reference numerals of the functional blocks related to the communication terminal 201-1 will be described by adding 1 to the reference numerals regarding the functional blocks of the communication terminal 201.

  The function of the control unit 217 will be described with reference to FIG. FIG. 4 is a sequence diagram showing processing performed in the communication terminal according to the second embodiment of the present invention. Note that the processing in steps S201 to S204 in FIG. 4 is the same as the processing in steps S101 to S104 in the first embodiment in FIG.

  When the TCP window size is smaller than the TCP window size threshold (No in step S203), the control unit 217-1 determines the highest modulation class that can be selected based on the TCP window size. More specifically, the control unit 217-1 lowers the selectable highest modulation class as the TCP window size is smaller. For example, in the current congestion state indicated by the TCP window size, the highest modulation class among modulation classes capable of realizing a desired expected throughput is set as the highest modulation class.

  For example, when the TCP window size threshold is 100, the control unit 217-1 can determine the relationship between the TCP window size and the highest modulation class as shown in Table 2 below.

  For example, when the window size is 85, the control unit 217-1 restricts the highest modulation class to 3. That is, in a network congestion situation where the window size is 85, it means that the expected throughput is not realized even if four or more modulation classes are selected. Therefore, the correspondence between CINR and modulation class in Table 1 is changed as shown in Table 3 below. At this time, the control unit 217-1 may change and store the adaptive modulation table in the storage unit 215-1.

  Thereby, for example, when CINR is 29, the control unit 217-1 selects the modulation class 3 by the determination process of the highest modulation class (step S204). If the determination process of the highest modulation class is not performed, the modulation class 4 is selected from Table 1.

  As described above, in the present embodiment, the control unit 217-1 of the communication terminal 201-1 determines a selectable highest modulation class based on the TCP window size. As a result, the control unit 217-1 can lower the selectable highest modulation class as the TCP window size decreases. Therefore, a modulation class for which it is difficult to realize the expected throughput due to network congestion becomes difficult to select as the TCP window size decreases. Thereby, it is possible to suppress selection of a higher-order modulation class than necessary, and it is possible to suppress a reduction in error resistance of the modulated signal.

  Although the present invention has been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications and corrections based on the present disclosure. Therefore, it should be noted that these variations and modifications are included in the scope of the present invention.

  For example, functions included in each member, each means, each step, etc. can be rearranged so as not to be logically contradictory, and a plurality of means, steps, etc. can be combined or divided into one. Is possible.

  In the above description of the embodiment of the present invention, the communication terminal selects the modulation class based on the TCP window size indicating the transmission status when the terminal transmits data and the CINR of the data from the base station. However, the present invention is not limited to this embodiment. For example, the communication terminal can select the modulation class based only on the TCP window size. In this case, the communication terminal selects the upper modulation class as the TCP window size increases, and selects the lower modulation class as the TCP window size decreases. The decrease in the TCP window size occurs when the communication terminal cannot receive an acknowledgment. Such a situation is not only when the network congestion situation deteriorates, but also when the modulation class cannot cope with the communication environment between the communication terminal and the base station, and the base station cannot correctly demodulate the signal from the communication terminal. Also occurs. Therefore, the TCP window size can reflect not only the network congestion status but also the communication quality between the communication terminal and the base station. This makes it possible to select a modulation class in consideration of network congestion and communication quality only by using the TCP window size.

  In the above description of the embodiment of the present invention, the relay apparatus is a base station, but the present invention is not limited to this aspect. For example, when there is a device (repeater) that relays a radio signal (data) transmitted and received between the communication terminal and the base station, the repeater can be used as the relay device of the present invention. In this case, the communication terminal calculates the CINR of the data received from the repeater.

  Further, in the above description of the embodiment of the present invention, for example, the meaning of the technical idea of expression such as the TCP window size threshold “greater than” or the TCP window size threshold “less than” is not necessarily a strict meaning. Depending on the specifications of the communication terminal, the meaning when the reference value is included or not included is included. For example, the TCP window size threshold “greater than or equal to” can imply not only when the TCP window size reaches the TCP window size threshold but also when the TCP window size exceeds the TCP window size. In addition, for example, “less than” the TCP window size threshold means not only when the TCP window size falls below the TCP window size threshold, but also when the TCP window size threshold is reached, that is, when the TCP window size threshold falls below the TCP window size threshold. It shall be possible.

100 Communication System 101-1 Communication Terminal (Communication Device)
101-2 Communication terminal (communication partner)
103-1 Base station (relay device)
103-2, 103-3 Base station 105 Router 107 Core network 111 Communication unit 113 Baseband unit 115 Storage unit 117 Control unit

Claims (6)

A communication device that transmits and receives data with a communication partner via a relay device,
A communication apparatus comprising a control unit that selects a modulation class for transmitting data to a relay apparatus based at least on a transmission situation when the own apparatus transmits data.   The communication apparatus according to claim 1, wherein the control unit selects the modulation class based on the transmission status and a communication quality value between the relay apparatus.   3. The communication apparatus according to claim 1, wherein the transmission status is a TCP window size.   The communication apparatus according to claim 3, wherein the control unit corrects the communication quality value based on the TCP window size.   4. The communication apparatus according to claim 3, wherein the control unit determines a selectable highest modulation class based on the TCP window size. In a communication control method in a communication device that transmits and receives data with a communication partner via a relay device, the communication device includes:
A communication control method including a step of selecting a modulation class for transmitting data to a relay device based at least on a transmission situation when the own device transmits data.

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