Wireless communication system, wireless communication method, centralized control device, and wireless communication program

Abstract

Provided is a wireless communication system that, while utilizing a non-linear region of an amplifier, does not cause erroneous transmission of data to occur even in a dense environment and ensures a high data rate. The present invention includes a plurality of base stations 20 and terminal stations 22. A base station 20-1 is provided with a transmission signal amplifier having a variable transmission power, the base station 20-1 providing specification relating to the input / output characteristics of the transmission signal amplifier to a terminal station 22-1 and providing transmission power to the terminal station 22-1. The terminal station 22-1 estimates the constellation of signal points on the basis of the transmission power and the specification, detects coordinate points of a reception signal in constellation coordinates, and detects interference power received from base stations 20-2 and 20-3 that are not communication partners with the terminal station 22-1. Furthermore, a reception point at which the effect of the interference power is reflected is calculated for the coordinate point, and the likelihood that the reception point is the signal point is calculated. A symbol represented by the reception signal is then identified on the basis of the result of calculating said likelihood.

Description

[Technical field]

[0001] The present disclosure relates to a wireless communication system, a wireless communication method, a centralized control device, and a wireless communication program, and more particularly to a wireless communication system, a wireless communication method, a centralized control device, and a wireless communication program that use a single carrier multilevel modulation scheme. [Background technology]

[0002] Non-Patent Document 1 below discloses a technique related to a wireless communication system using a single-carrier multi-level modulation scheme. In wireless communication using a single-carrier multi-level modulation scheme, the higher the transmission power, the higher the SNR (Signal to Noise Ratio) can be.

[0003] On the other hand, amplifiers for transmission signals generally exhibit linear input / output characteristics when the input power is low, but exhibit nonlinear characteristics when the input power is high. For this reason, in wireless communications, the higher the transmission power, the more likely distortion will occur in the transmission signal.

[0004] The above-mentioned Non-Patent Document 1 discloses a technique for keeping the transmission power within the linear region of the amplifier in order to avoid the influence of such distortion. In this case, since distortion is not superimposed on the transmission signal, the signal can be correctly processed in the receiving device, and erroneous transmission of data can be effectively prevented.

[0005] Furthermore, a technique for avoiding the problem of distortion caused by an increase in transmission power is disclosed in the following Patent Document 1. When, for example, an APSK (Amplitude and Phase-Shift Keying) technique is used as a modulation method, in a region where the input power is large, a phase shift occurs in the transmission signal due to a change in the AM / PM characteristics. Patent Document 1 discloses a technique for dealing with such a phase shift.

[0006] FIG. 1 is a diagram for explaining an overview of the technology disclosed in Patent Document 1. More specifically, FIG. 1 shows a constellation corresponding to 32APSK. In 32APSK, 32 symbols, indicated by circles or circles in the diagram, are defined by changing the amplitude and phase of the transmission signal. More specifically, four symbols are defined on the first inner circumference 10, twelve on the second inner circumference 12, and sixteen on the outermost circumference 14.

[0007] Patent Document 1 discloses that one or more pilot signals 16 are arranged on each of the first inner circumference 10, the second inner circumference 12, and the outermost circumference 14. The positions of the pilot signals 16 are shared by the transmitting device and the receiving device. Therefore, the receiving device can detect the phase shift occurring on each concentric circle based on the shift between the position of the pilot signal 16 actually received and the previously shared position.

[0008] Then, for example, when a signal belonging to the first inner circumference 10 is received, the phase shift occurring in the first inner circumference 10 is reflected in that signal. When a signal belonging to another concentric circle is received, the phase shift is corrected in the same manner. With this method, even if a phase shift occurs in the received signal in an area with high transmission power, the shift can be properly corrected to prevent erroneous transmission of data. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] High-Speed ​​Satellite Mobile Communications: Technologies and Challenges, MOHAMED IBNKAHLA, QUAZI MEHBUBAR RAHMAN, AHMED IYANDA SULYMAN, HISHAM ABDULHUSSEIN AL-ASADY, JUN YUAN, AND AHMED SAFWAT, p312-339, PROCEEDINGS OF THE IEEE, VOL. 92, NO. 2, February 2004 [Patent documents]

[0010] [Patent Document 1] JP 2017-59889 A Summary of the Invention [Problem to be solved by the invention]

[0011] However, the technology of Non-Patent Document 1 solves the distortion problem by abandoning the use of the non-linear region of the amplifier. In other words, this technology does not allow the amplifier to fully demonstrate its inherent capabilities, which goes against the essential requirement of using large power without excessive capital investment.

[0012] Furthermore, the transmitting device and the receiving device may be placed in a dense environment. In such an environment, in addition to the signal from the transmitting device of the communication partner, interference power from other cells may reach the receiving device. In an environment where interference power from other cells reaches, the influence of the interference power makes it easy for the receiving device to misrecognize data. The technology of the above-mentioned Non-Patent Document 1 cannot provide any solution to the problem caused by such interference power.

[0013] In the technology of Patent Document 1, a transmitting device needs to transmit to a receiving device at least the same number of pilot signals as the number of concentric circles that make up a constellation. The environment of the communication path of a wireless signal is not always constant. For this reason, the pilot signals need to be transmitted frequently, preferably for each data communication flow.

[0014] The technique described in Patent Document 1 is further forced to transmit a larger number of pilot signals when, for example, QAM (Quadrature Amplitude Modulation) is used as the modulation method. That is, as described in Patent Document 1, if the modulation method is APSK, multiple symbols arranged on concentric circles can be corrected with one common phase shift. Therefore, the number of pilot signals required for multiple symbols arranged on concentric circles is one.

[0015] In contrast, in the case of QAM, the symbols in the constellation are arranged in a lattice pattern. For example, 4 x 4 = 16 or 8 x 8 = 64 symbols are arranged in a lattice pattern on the constellation. In this case, even if one pilot signal can be shared by several symbols, it is necessary to prepare a large number of pilot signals in order to properly correct all symbols.

[0016] If a large number of pilot signals are transmitted and received for each communication flow, the data rate will inevitably decrease. In this regard, the technology described in Patent Document 1 enables the use of large power commensurate with the amplifier's capacity, but there is still room for improvement in terms of data rate.

[0017] Furthermore, the technique described in Patent Document 1 also fails to provide any solution to the above-mentioned problem caused by interference power from other cells that occurs in a dense environment.

[0018] The present disclosure has been made in consideration of the above-mentioned problems, and has a first object to provide a wireless communication system that utilizes the nonlinear region of an amplifier, does not cause erroneous data transmission, and ensures a high data rate, even in a dense environment.

[0019] A second object of the present disclosure is to provide a wireless communication method that utilizes the nonlinear region of an amplifier, does not cause erroneous data transmission, and ensures a high data rate even in a dense environment.

[0020] A third object of the present disclosure is to provide a centralized control device that can instruct multiple transmitting devices placed in a dense environment to use transmission power that satisfies desired communication quality while utilizing the nonlinear region of the amplifiers provided in the transmitting devices.

[0021] A fourth object of the present disclosure is to provide a wireless communication program for realizing a centralized control device that can instruct multiple transmitting devices placed in a dense environment to use transmission power that satisfies a desired communication quality while utilizing the nonlinear region of the amplifiers provided in the transmitting devices. [Means for solving the problem]

[0022] In order to achieve the above object, a first aspect is a wireless communication system including a plurality of base stations and terminal stations that perform wireless communication using a single-carrier multi-level modulation scheme, The base station, A transmission signal amplifier having a variable transmission power is provided, providing specifications regarding input / output characteristics of the transmission signal amplifier to the terminal station; and a process of providing the terminal station with a transmission power used for data transmission. The terminal station, a signal point estimation process for estimating a constellation of signal points based on the transmission power and the specifications; A process of detecting a coordinate point on a constellation coordinate of a received signal; A process of detecting interference power received from a base station that is not a communication partner; A process of calculating a reception point in which the influence of the interference power is reflected on the coordinate point; A process of calculating a likelihood between the reception point and the signal point; It is preferable that the signal processing device is configured to execute a process of identifying an intended symbol of the received signal based on a result of the likelihood calculation.

[0023] A second aspect is a wireless communication method using a plurality of base stations and a terminal station that perform wireless communication using a single carrier multi-level modulation scheme, The base station includes a transmission signal amplifier having a variable transmission power; providing specifications relating to input / output characteristics of the transmission signal amplifier from the base station to the terminal station; providing the terminal station with a transmission power used by the base station for data transmission; a signal point estimation step in which the terminal station estimates a constellation of signal points based on the transmission power and the specifications; The terminal station detects a coordinate point on a constellation coordinate of a received signal; a step of detecting interference power received by the terminal station from a base station that is not a communication partner; A step of the terminal station calculating a reception point in which the influence of the interference power is reflected on the coordinate point; A step in which the terminal station calculates a likelihood between the reception point and the signal point; The terminal station identifies a symbol intended by the received signal based on a result of the likelihood calculation; It is preferable that the present invention includes the following:

[0024] A third aspect is a central control device for controlling a wireless communication system including a plurality of base stations and terminal stations that perform wireless communication using a single-carrier multi-level modulation scheme, the base station is provided with a transmission signal amplifier having a variable transmission power, and is configured to execute a process of providing specifications relating to input / output characteristics of the transmission signal amplifier to the terminal station, and a process of providing a transmission power used for data transmission to the terminal station; The terminal station is configured to execute the following processes: estimating a constellation of signal points based on the transmission power and the specifications; detecting a coordinate point on a constellation coordinate of a received signal; detecting interference power received from a base station that is not a communication partner; calculating a reception point in which the coordinate point reflects an influence of the interference power; calculating a likelihood between the reception point and the signal point; specifying a symbol intended by the received signal based on a result of the likelihood calculation; and calculating an error rate of the received signal; A process of changing a pattern of transmission power for the plurality of base stations; collecting said error rates corresponding to each of said patterns; It is preferable that the wireless communication device is configured to execute a process of determining a command for transmission power to be given to each of the plurality of base stations so that all of the collected error rates satisfy a predetermined requirement.

[0025] A fourth aspect is a wireless communication program for implementing the central control device according to the third aspect, The centralized control device includes an arithmetic processing unit, A process of changing a pattern of transmission power for the plurality of base stations; collecting said error rates corresponding to each of said patterns; determining a transmission power command to be given to each of the plurality of base stations so that all of the collected error rates satisfy a predetermined requirement; It is preferable that the program include a program for executing the above. Effect of the Invention

[0026] According to the first to fourth aspects, it is possible to prevent erroneous data transmission and ensure a high data rate even in a dense environment while utilizing the nonlinear region of the amplifier. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 is a diagram for explaining an overview of the technology disclosed in Patent Document 1. [Diagram 2] FIG. 1 is a diagram for explaining an overall configuration of a wireless communication system according to a first embodiment of the present disclosure. [Diagram 3] FIG. 2 is a diagram for explaining the configuration of a base station to be compared with the base station according to the first embodiment of the present disclosure. [Figure 4] 1 is a diagram showing input / output characteristics of an amplifier built into a base station. [Diagram 5] FIG. 13 is a diagram showing how distortion occurs in a constellation as the transmission power increases. [Figure 6] FIG. 1 is a diagram showing a schematic representation of the effect of interference power from other cells on the accuracy of a reception point. [Figure 7] FIG. 2 is a block diagram for illustrating a configuration of a base station according to the first embodiment of the present disclosure. [Figure 8] FIG. 2 is a block diagram for illustrating a configuration of a terminal station according to the first embodiment of the present disclosure. [Figure 9] FIG. 2 is a diagram for explaining a method in which a terminal station calculates likelihoods for reception points in the first embodiment of the present disclosure. [Figure 10] FIG. 2 is a diagram for explaining a method in which a terminal station reflects interference power from other cells in a likelihood in the first embodiment of the present disclosure. [Figure 11] 5 is a flowchart illustrating an example of a process flow executed by the central control device in the first embodiment of the present disclosure to control the transmission power of a base station. [Figure 12] 11 is a flowchart illustrating a modified example of the flow of processing executed by the central control device in the first embodiment of the present disclosure to control the transmission power of a base station. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Embodiment 1 [Overall configuration of the first embodiment] Fig. 2 shows an overall configuration of a wireless communication system according to the first embodiment of the present disclosure. As shown in Fig. 2, the wireless communication system according to the present embodiment includes base stations 20-1 to 20-3. Hereinafter, when there is no need to distinguish between them, they will be referred to as "base station 20" with the subscripts omitted.

[0029] 2 shows terminal stations 22-1 to 22-3 that are in communication with each of the base stations 20. When there is no need to distinguish between these, they will also be referred to as "terminal stations 22" with the subscripts omitted from the reference numerals.

[0030] More specifically, Fig. 2 shows a state where the terminal station 22-1 is located near the boundary between the communication areas of three base stations 20. In the situation shown in Fig. 2, the terminal station 22-1 establishes communication with the base station 20-1, as shown by the solid arrow in the figure. In addition, the terminal station 22-1 receives interference power from other cells, as shown by the dashed arrow in the figure.

[0031] The wireless communication system of this embodiment also includes a centralized control device 24. The centralized control device 24 controls the three base stations 20 shown in Fig. 2 and can command the transmission power to each of them. The centralized control device 24 can also receive information such as a bit error rate (BER) or a symbol error rate (SER) from the terminal stations 22 via the base stations 20. Hereinafter, for convenience, the error rate handled in this embodiment will be referred to as the BER, but the present disclosure is not limited to this, and the SER may be handled instead of or together with the BER.

[0032] [First problem addressed by the first embodiment] 3 is a block diagram for explaining the configuration of a base station 26 to be compared with the base station 20 in this embodiment. The base station 26 of the comparative example includes an information bit generator 28. The information bit generator 28 generates information bits to be transmitted to the terminal station 22. The information bit generator 28 may include an error correction coding function or an interleaving function.

[0033] The information bits generated by the information bit generation unit 28 are provided to a data signal modulation unit 30. The data signal modulation unit 30 modulates the provided information bits into a data signal. As a modulation method, for example, quadrature amplitude modulation (QAM) or APSK, which can be used for a single carrier multi-level modulation method, can be considered.

[0034] The data signal generated by the data signal modulation unit 30 is provided to a digital-to-analog conversion unit 32. The digital-to-analog conversion unit 32 converts the digitally modulated data signal into an analog transmission signal.

[0035] The transmission signal generated in the digital-to-analog conversion unit 32 is provided to a transmission signal amplifier 34. The transmission signal amplifier 34 amplifies the transmission signal and provides it to an antenna 36. The transmission signal is then transmitted from the antenna 36 to the terminal station 22 in the form of a wireless signal.

[0036] 4 shows the input / output characteristics of the transmission signal amplifier 34. As shown in FIG. 4, the output power (vertical axis) of the transmission signal amplifier 34 is proportional to the input power (horizontal axis) P B In the smaller region, it is proportional to the input power. And, when the input power is P B In the following, the region where the two are proportional to each other is referred to as the "linear region," and the region where the proportional relationship between the two is lost is referred to as the "nonlinear region."

[0037] Figure 5 shows how distortion occurs in an 8x8=64QAM constellation as the transmission power increases. In the 64QAM modulation method, 64 symbols arranged in a grid pattern are defined by changing and adjusting the amplitude of two independent carrier waves. Hereinafter, the points on the constellation coordinates where each of the 64 symbols is defined are referred to as "signal points." Also, the points on the constellation coordinates of each data signal that is actually transmitted are referred to as "reception points."

[0038] In the linear region of the transmission signal amplifier 34, the reception points form a constellation without distortion, as shown on the left side of FIG. 5 (transmission power P1). On the other hand, in the nonlinear region of the transmission signal amplifier 34, the reception points form a constellation without distortion, as shown on the right side of FIG. 5 (transmission power P N As shown in FIG. 1, distortion is superimposed on the constellation at the receiving point.

[0039] The terminal station 22 calculates the likelihood of each reception point included in the transmission signal with respect to nearby signal points, and recognizes each reception point as one of 64 symbols based on the result. The likelihood calculation can be performed, for example, by a method described in the following document.

[0040] On the Optimality of Bit Detection of Certain Digital Modulations, Marvin K. Simon and Ramesh Annavajjala, p299-307, IEEE TRANSACTIONS ON COMMUNICATIONS, VOL. 53, NO. 2, FEBRUARY 2005

[0041] If the terminal station 22 performs the likelihood calculation using the signal points that make up a distortion-free constellation, the reception points generated in the linear region can be correctly recognized. However, the reception points generated in the nonlinear region cannot be correctly recognized because they are shifted from their original positions on the constellation. For this reason, if the transmission signal amplifier 34 uses the nonlinear region, the terminal station 22 may misrecognize data.

[0042] In the base station 26 of the comparative example, if the transmission power is limited to the linear region of the transmission signal amplifier 34, it is possible to prevent distortion of the constellation at the receiving point. Therefore, if such a limitation is imposed, it is possible to prevent misrecognition of data at the terminal station 22. However, in that case, a situation may occur in which the amplification capability of the transmission signal amplifier 34 cannot be fully utilized.

[0043] Therefore, in this embodiment, the relationship between the transmission power used by the transmission signal amplifier 34 and the distortion occurring in the constellation is grasped in advance, and the relationship is shared between the base station 20 and the terminal station 22 at the start of communication. For example, the specifications of the transmission signal amplifier 34 are shared at the start of communication, and during communication, the base station 20 notifies the terminal station 22 of the transmission power, and the terminal station 22 regenerates the constellation corresponding to the transmission power and calculates the likelihood. With this method, even if distortion occurs in the constellation in the nonlinear region, misrecognition of data caused by the distortion can be effectively suppressed.

[0044] [Second problem focused on by the first embodiment] Next, a second problem that the present embodiment focuses on will be described. Fig. 6 is a diagram showing the influence of interference power from other cells on the accuracy of a reception point. Specifically, Fig. 6 shows a distorted constellation reproduced by the terminal station 22 and a reception point 38 of a signal received by the terminal station 22, which are superimposed on each other. The likelihood of the reception point 38 is calculated based on the Euclidean distance between several signal points 40 located in the vicinity of the reception point 38. The signal point 40 for which the greatest likelihood is calculated is recognized as the intended signal of the reception point 38. For this reason, in order to correctly recognize the data, it is desirable that the position of the reception point 38 is not blurred.

[0045] As described above, in the situation shown in Fig. 2, in addition to the signal from the base station 20-1, which is the communication partner, the terminal station 22-1 also receives interference power from the other base stations 20-2 and 20-3. Under such circumstances, the amplitude and phase of the signal arriving at the terminal station 22-1 from the base station 20-1 fluctuates due to the interference power. The reception point 38 shown in Fig. 6 shows how the actual position has become blurred due to the influence of such fluctuations.

[0046] In Fig. 6, the shading of the figure showing reception point 38 simulates the probability distribution of the amplitude and phase of the signal that constitutes the reception point. When reception point 38 is in such a state, if the coordinates at a certain time are specified as the coordinates of reception point 38 for likelihood calculation, the coordinates will contain errors. If the likelihood calculation is performed based on the coordinates, the nearest signal point 40 will be misidentified, which may result in data misidentification.

[0047] In this embodiment, to prevent such data misidentification, the error caused by the interference power is equally superimposed on the position of the reception point 38, and then the likelihoods for all adjacent signal points are calculated. This prevents the likelihood for a specific signal point from becoming erroneously large or small, effectively avoiding data misidentification in the terminal station 22.

[0048] [Features of the first embodiment]

[0049] Fig. 7 is a block diagram for explaining the configuration of base station 20 in this embodiment. In Fig. 7, the same elements as those included in base station 26 of the comparative example (see Fig. 3) are denoted by the same reference numerals, and the explanation thereof will be omitted or simplified.

[0050] The base station 20 in this embodiment includes a transmission unit shown in the upper part of Fig. 7. Here, the information bit generator 28 in the base station 26 of the comparative example is replaced with an information bit generator 42. The information bit generator 42 included in this embodiment generates information bits related to the specifications of the base station 20 at the stage when communication between the base station 20 and the terminal station 22 is started. Specifically, the modulation method used by the base station 20 and the input / output characteristics of the transmission signal amplifier 34 (see Fig. 4) are converted into information bits.

[0051] The information bits thus generated are transmitted from the base station 20 to the terminal station 22 at the stage when communication between the base station 20 and the terminal station 22 is started. Therefore, in this embodiment, at the stage when communication between the two is started, the modulation method used by the base station 20 and the input / output characteristics of the transmission signal amplifier 34 are shared between the two.

[0052] The base station 20 in this embodiment includes a transmission power control unit 44 in front of the transmission signal amplifier 34. The transmission power control unit 44 controls the transmission power so as to obtain a desired communication quality.

[0053] The transmission power control unit 44 can control the transmission power based on the result of the information processing that it has executed. The transmission power control unit 44 may also receive commands related to the transmission power from the centralized control device 24, and in that case, controls the transmission power according to the received commands. The control commands of the transmission power control unit 44 are provided to the transmission signal amplifier 34 and also to the transmission power information notification unit 46.

[0054] The transmission power information notifying unit 46 provides a command value for the transmission power to the information bit generating unit 42. The information bit generating unit 42 then generates bit information on the current transmission power and includes the information in the transmission data. As a result, the base station 20 of this embodiment transmits a transmission signal including information on the transmission power set by the transmission power control unit 44 to the terminal station 22.

[0055] The base station 20 includes a receiving section shown in the lower part of Fig. 7. This receiving section includes a received signal amplifier 48 that receives a received signal from the antenna 36. The received signal amplifier 48 amplifies the received signal with an appropriate gain and provides the amplified signal to an analog-to-digital converter 50.

[0056] The analog-to-digital converter 50 is a block for demodulating an analog received signal into a digital signal. The signal digitized by the analog-to-digital converter 50 is provided to a data signal equalizer 52.

[0057] The data signal equalization unit 52 is a block that obtains an estimated value of a transmission signal by inversely calculating information on the amplitude and phase of the channel response. A training signal is exchanged between the base station 20 and the terminal station 22 prior to a data signal. The contents of the training signal are shared in advance between the base station 20 and the terminal station 22. Therefore, the base station 20 can detect the influence caused by the communication channel based on the actually received training signal. Specifically, the data signal equalization unit 52 reflects the training result in the data signal received from the terminal station 22, thereby generating a data signal in which the influence caused by the communication channel is offset.

[0058] The data signal generated by the data signal equalization unit 52 is provided to the likelihood calculation unit 54. The likelihood calculation unit 54 calculates the likelihood of a signal point on a constellation stored therein for a reception point indicated by the data signal, and recognizes the signal point for which the highest likelihood is obtained as the symbol intended by the current reception point.

[0059] The signal symbolized by the likelihood calculation unit 54 is provided to an information bit detection unit 56. The information bit detection unit 56 detects received bits from the symbolized signal. The information bit detection unit 56 may also have an error correction decoding function and an interleaving function in accordance with the information bit generation unit 42, as necessary.

[0060] 8 is a block diagram for explaining the configuration of the terminal station 22 in this embodiment. The terminal station 22 includes, in most parts, elements that function substantially in the same way as the elements included in the base station 20.

[0061] Specifically, the transmitting section of the terminal station 22 has a configuration for functioning substantially similarly to the transmitting section of the base station 20, except that the transmission power control section 64 does not receive commands from the centralized control device 24. Also, the receiving section of the terminal station 22 has a configuration for functioning substantially similarly to the receiving section of the base station 20, except for the other-cell interference estimation section 78, the likelihood calculation section 80, and the information bit detection section 82.

[0062] The other-cell interference estimation unit 78 detects the magnitude of interference signals received from base stations 20 other than the communicating base station 20. Information on the detected interference signals is provided to a likelihood calculation unit 80 and also to an information bit generation unit 58 to be fed back to the base station 20.

[0063] The likelihood calculation unit 80 calculates the likelihood for the reception point based on the transmission power of the base station 20 and the interference power from other cells. Specifically, the likelihood calculation unit 80 first identifies the constellation of the received signal based on the specification information of the base station 20 acquired at the start of communication and the current transmission power received together with the data signal (see FIG. 5).

[0064] The modulation method used by the base station 20 and the input / output characteristics of the transmission signal amplifier 34 are known to the terminal station 22. If these pieces of information are known, and if the transmission power actually used is known, the constellation of the received signal, including that accompanied by distortion, can be reproduced. After completing this process, the likelihood calculation unit 80 next uses the selected constellation to perform likelihood calculation for the reception point 38 reflecting the training result.

[0065] Fig. 9 is a diagram for explaining an overview of likelihood calculation in this embodiment. The left side of Fig. 9 shows an overview of likelihood calculation when the transmission power is P1. In this case, the constellation of the received signal is free of distortion, with each of the signal points 40 properly arranged in a lattice pattern. The likelihood calculation unit 54 refers to the constellation and calculates the likelihood for some of the signal points 40 located near the reception point 38, using a normal distribution for the Euclidean distance between the two. Then, the signal point 40 for which the largest likelihood is obtained is adopted as the symbol corresponding to that reception point 38.

[0066] The right side of Fig. 9 shows the case where the transmission power is P N 1 shows an overview of the likelihood calculation when the constellation of the received signal includes a shift at each of the signal points 40 due to the nonlinearity of the transmission signal amplifier 34. The likelihood calculation unit 54 refers to the constellation with the shift and calculates the likelihood for the reception point 38 in the same manner as above. Then, based on the result, the symbol represented by the reception point 38 is identified.

[0067] Fig. 10 is a diagram for explaining a method for reflecting the influence of interference power from other cells in the likelihood. Hereinafter, as an example, a case will be described in which the likelihood is calculated for signal points of a distortion-free constellation used in 16QAM (Quadrature Amplitude Modulation).

[0068] In this embodiment, the likelihood calculation unit 80 of the terminal station 22 defines a reception point in the format of z=si+n+I, where si is the coordinate point represented by the received signal, n is the additive noise, and I is a factor representing interference power from other cells. Since the factor of interference power I is added to the coordinate point si together with the additive noise n, the Euclidean distance from the reception point z is wider for all signal points compared to the case where the interference power I is not taken into consideration.

[0069] Therefore, when the effect of interference power is small, a relatively large likelihood is obtained for all signal points located around reception point z. Then, the signal point showing the maximum likelihood among them is recognized as the symbol. In this case, misrecognition of data due to interference power is unlikely to occur.

[0070] When the influence of interference power is large, a relatively small likelihood is obtained for all signal points located around reception point z. The signal point showing the maximum likelihood among them is recognized as the symbol. In this case, the likelihood is also uniformly reduced, so misrecognition of data due to interference power is unlikely to occur.

[0071] As described above, according to the wireless communication system of the present embodiment, the base station 20 can use the nonlinear region of the transmission signal amplifier 34 to transmit a high-power transmission signal. Furthermore, by transferring the specifications of the transmission signal amplifier 34 to the terminal station 22 at the start of communication, the terminal station 22 can reproduce a distorted constellation corresponding to the nonlinear region without the need for subsequent provision of large amounts of information. Then, by performing a likelihood calculation using the constellation, it is possible to prevent data from being erroneously recognized even for a transmission signal using a nonlinear region. Furthermore, since the factor of the interference power I from other cells is added to the additive noise n to calculate the likelihood, it is possible to prevent only the likelihood of a specific signal point from becoming large or small due to the influence of the interference power. Therefore, according to the wireless communication system of the present embodiment, it is possible to ensure a high data rate without causing erroneous data transmission even in a dense environment while utilizing the nonlinear region of the transmission signal amplifier 34.

[0072] In this embodiment, the information bit detector 82 of the terminal station 22 has the same function as the information bit detector 56 of the base station 20, and also has a function of converting information about the bit error rate (BER) of the signal into bits. The BER information is then provided to the information bit generator 58 of the transmitting section.

[0073] The information bit generator 58 of the terminal station 22 performs bit generation processing to include BER information in a transmission signal in order to provide the BER information to the communication partner base station 20. In this manner, in this embodiment, the terminal station 22 provides the base station 20 with information on the BER achieved by the transmission power currently being used by the base station 20.

[0074] The BER information provided to the base stations 20 is provided to the centralized control device 24. Then, the centralized control device 24 controls the transmission power of each base station 20 based on the BER information so as to realize overall optimization of communications involving the base stations 20 under its control.

[0075] [Control by centralized control device] In this embodiment, the centralized control device 24 includes an arithmetic processing unit and a memory device. The memory device stores a program to be executed by the arithmetic processing unit. The program can be installed in the centralized control device 24 by downloading. The program may also be installed in the centralized control device 24 via a recording medium on which the program is recorded.

[0076] Fig. 11 is a flow chart for explaining an example of the process executed by the centralized control device 24 according to the above program. The routine shown in Fig. 11 is repeatedly started at a predetermined interval while communication is being performed in any of the base stations 20 under the control of the centralized control device 24.

[0077] In the routine shown in Fig. 11, first, the transmission power for each of the subordinate base stations 20 is set (step 100). As an example, it is assumed that there are three base stations 20 under the control of the centralized control device 24, and each base station 20 has a function of switching the transmission power between four levels. In this step 100, an initial setting transmission power pattern is set according to a predetermined rule.

[0078] When the process of step 100 is completed, the set transmission power is commanded to all of the subordinate base stations 20. As a result, communication using the transmission power set by the centralized control device 24 is started in the subordinate base stations 20.

[0079] When communication is started, BER information is provided to the subordinate base station 20 from the communicating terminal station 22. The central control device 24 collects the BER information via the base station 20 (step 102).

[0080] Next, it is determined whether the collected BER meets the preset required conditions (step 104). For example, it is determined whether the error rate BER is equal to or less than a required threshold for all communications involving the subordinate base station 20. If it is determined that the BER is equal to or less than the required threshold, it can be determined that the current transmission power pattern is appropriate. In this case, the transmission power is maintained and the current routine is terminated.

[0081] On the other hand, if it is determined in step 104 that the BER does not satisfy the requirement, it can be determined that the current transmission power pattern does not achieve the overall optimum. In this case, it is next determined whether or not the search has been completed for all combinations of transmission power (step 106). If there are three base stations 20 and four levels of transmission power, 3 It is determined whether the search for all 64 combinations has been completed.

[0082] If it is determined that all combinations have been searched, the current routine is terminated and the processing from step 100 onwards is started anew. On the other hand, if it is determined that the exhaustive search has not been completed, the transmission power pattern is changed according to a predetermined rule (step 108). Thereafter, the transmission power pattern is changed and the processing from step 102 onwards is repeated until a BER clear determination is made in step 104.

[0083] When the transmission power of one base station 20 is increased, the SNR of the base station 20 is improved, but the distortion of the constellation becomes large. In addition, the interference power caused by the base station 20 becomes large. On the other hand, when the transmission power of one base station 20 is decreased, the SNR of the base station 20 deteriorates, but the distortion of the constellation and the interference power caused by the base station 20 become small. As a result, the increase or decrease in the transmission power of one base station 20 gives advantages and disadvantages to the quality of the communication related to the base station 20 and the communication related to the other base stations 20. In this embodiment, a pattern of transmission power that realizes the overall optimization can be found by repeatedly trying various transmission power patterns.

[0084] [Modification of the first embodiment] In the above routine shown in Fig. 11, the pattern search is terminated when a transmission power pattern that satisfies the desired BER requirement is found. However, the present disclosure is not limited to this. For example, the search may be continued even after the condition that satisfies the BER requirement is found, to find an optimal transmission power pattern.

[0085] Fig. 12 is a flow chart for explaining the flow of processing executed by the central control device 24 to realize the operation of the above-mentioned modified example. In Fig. 12, steps for executing the same processing as the steps shown in Fig. 11 are given the same reference numerals, and their explanations are abbreviated or simplified.

[0086] 12, the process of step 106 is executed following step 102. Then, until it is determined in step 106 that the search has ended, the transmission power pattern is changed (step 108) and the BER is repeatedly obtained (step 102).

[0087] When the search for all combinations is completed and the determination in step 106 is affirmative, the optimal transmission power pattern is then selected (step 110). Specifically, from the BER results accumulated by repeating step 102, a combination is selected in which all communications meet the requirements and the total BER is minimized. Then, when the selected transmission power pattern is instructed to each of the base stations 20, the current routine is terminated.

[0088] According to the above process, it is possible to find a transmission power pattern that satisfies the requirements of all communications executed under the control of the centralized control device 24 and provides the best communication quality to the entire wireless communication system. Therefore, according to the above modification, it is possible to ensure a higher data rate than in the first embodiment.

[0089] In the above-mentioned first embodiment, the base station 20 provides the terminal station 22 with the specifications of the transmission signal amplifier 34 at the start of wireless communication. However, the present disclosure is not limited to this. For example, the base station 20 may store the terminal station 22 to which the specifications have been provided, and the terminal station 22 to which the specifications have been provided may store the information. Then, for the second and subsequent communications between the two parties, the exchange of the specifications may be omitted.

[0090] In the above-mentioned first embodiment, the base station 20 provides the terminal station 22 with information on the modulation method used for wireless communication together with the specifications of the transmission signal amplifier 34. However, the present disclosure is not limited to this. For example, when the modulation method used for communication between the base station 20 and the terminal station 22 is determined in advance, provision of the information on the modulation method can be omitted. [Explanation of symbols]

[0091] 20, 20-1~20-3 base station 22, 22-1 to 22-3 Terminal station 24 Centralized control device 34, 68 Transmitting signal amplifier 42, 58 Information bit generator 44, 64 Transmission power control section 46, 66 Transmission power information notification unit 54, 80 Likelihood calculation section 78 Other cell interference estimation unit 82 Information bit detection unit

Claims

1. A wireless communication system including a plurality of base stations and terminal stations that perform wireless communication using a single-carrier multi-level modulation scheme, The base station, A transmission signal amplifier having a variable transmission power is provided, providing specifications regarding input / output characteristics of the transmission signal amplifier to the terminal station; and a process of providing the terminal station with a transmission power used for data transmission. The terminal station, a signal point estimation process for estimating a constellation of signal points based on the transmission power and the specifications; A process of detecting a coordinate point on a constellation coordinate of a received signal; A process of detecting interference power received from a base station that is not a communication partner; A process of calculating a reception point in which the influence of the interference power is reflected on the coordinate point; A process of calculating a likelihood between the reception point and the signal point; and a process of identifying an intended symbol of the received signal based on a result of the likelihood calculation.

2. A central control device that commands a transmission power of each of the plurality of base stations, The terminal station, Calculating an error rate of the received signal; providing the error rate to the base station; The centralized control device includes: A process of changing a combination of transmission powers set for each of the plurality of base stations; an error rate collection process of collecting the error rates corresponding to each of the combinations via the base station; 2. The wireless communication system according to claim 1, further comprising: a command determination process for determining a transmission power command to be given to each of said plurality of base stations based on said collected error rates.

3. the error rate collection process includes a process of collecting error rates for all communications involving the base stations under the control of the centralized control device, The command determination process includes: determining whether the error rate satisfies a predetermined requirement; A process of searching for a combination of transmission powers that satisfies all of the predetermined requirements for the error rates; 3. The wireless communication system according to claim 2, further comprising a process of instructing the plurality of base stations to change their transmission power in accordance with the combination obtained as a result of the search.

4. the error rate collection process collects the error rates for all combinations of transmission powers that can be taken by the plurality of base stations; The command determination process includes: selecting an optimal combination according to a predetermined rule from among combinations of transmission powers that satisfy all of the predetermined requirements for the error rates; The wireless communication system according to claim 3 , further comprising a process of instructing the plurality of base stations to change their transmission power in accordance with the optimum combination.

5. A wireless communication method using a plurality of base stations and terminal stations that perform wireless communication using a single carrier multi-level modulation scheme, comprising: The base station includes a transmission signal amplifier having a variable transmission power; providing specifications relating to input / output characteristics of the transmission signal amplifier from the base station to the terminal station; providing the terminal station with a transmission power used by the base station for data transmission; a signal point estimation step in which the terminal station estimates a constellation of signal points based on the transmission power and the specifications; The terminal station detects a coordinate point on a constellation coordinate of a received signal; a step of detecting interference power received by the terminal station from a base station that is not a communication partner; A step of the terminal station calculating a reception point in which the influence of the interference power is reflected on the coordinate point; A step in which the terminal station calculates a likelihood between the reception point and the signal point; The terminal station identifies a symbol intended by the received signal based on a result of the likelihood calculation; A wireless communication method comprising:

6. A step of a centralized control device instructing each of the plurality of base stations to control a transmission power; said terminal station calculating an error rate of a received signal; changing a combination of transmission powers set for each of the plurality of base stations by the centralized control device; said centralized controller collecting said error rates corresponding to each of said combinations; determining a command for transmission power to be given to each of the plurality of base stations based on the collected error rates by the centralized control device; The wireless communication method according to claim 5 , comprising:

7. A central control device for controlling a wireless communication system including a plurality of base stations and terminal stations that perform wireless communication using a single-carrier multi-level modulation scheme, the base station is provided with a transmission signal amplifier having a variable transmission power, and is configured to execute a process of providing specifications relating to input / output characteristics of the transmission signal amplifier to the terminal station, and a process of providing the terminal station with a transmission power used for data transmission; The terminal station is configured to execute the following processes: estimating a constellation of signal points based on the transmission power and the specifications; detecting a coordinate point on a constellation coordinate of a received signal; detecting interference power received from a base station that is not a communication partner; calculating a reception point in which the coordinate point reflects an influence of the interference power; calculating a likelihood between the reception point and the signal point; specifying a symbol intended by the received signal based on a result of the likelihood calculation; and calculating an error rate of the received signal; A process of changing a combination of transmission powers set for each of the plurality of base stations; collecting the error rates corresponding to each of the combinations; and determining a command for transmission power to be given to each of the plurality of base stations so that all of the collected error rates satisfy a predetermined requirement.

8. A wireless communication program for implementing the central control device according to claim 7, The centralized control device includes an arithmetic processing unit, A process of changing a combination of transmission powers set for each of the plurality of base stations; collecting the error rates corresponding to each of the combinations; determining a transmission power command to be given to each of the plurality of base stations so that all of the collected error rates satisfy a predetermined requirement; A wireless communication program including a program for executing the above.

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