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

Abstract

The present invention carries out spatial multiplexing transmission between a moving MS 10 provided with a plurality of satellite antennas 14 and a ground station including a plurality of ground antennas 16. The MS 10 comprises one or more processor circuits and a memory in which is stored a program that is executed by the processor circuit. The processor circuit detects the direction of each of the plurality of ground antennas 16, sets one of the directions as a desired direction, and sets the other directions as non-desired directions. On the basis of the desired direction and the non-desired directions, a weight vector for strengthening signals from the desired direction and weakening signals from the non-desired directions is calculated. An input vector received by the plurality of satellite antennas 14 is multiplied by the weight vector to thereby generate a desired signal to be regarded as a signal from the desired direction.

Description

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

[0001] This disclosure relates to a wireless communication system, a wireless communication device, a wireless communication method, and a wireless communication program, and in particular to a wireless communication system, a wireless communication device, a wireless communication method, and a wireless communication program that are suitable for realizing spatial multiplexing transmission between a non-terrestrial mobile station such as a satellite and a terrestrial station with an inexpensive configuration.

[0002] Non-Patent Document 1 below proposes utilizing MIMO (Multiple-Input Multiple Output) technology when performing wireless communication between a satellite and a terrestrial base station. MIMO technology involves spatially multiplexing wireless signals by arranging multiple antennas on at least one of the transmitting and receiving sides. This technology significantly increases communication capacity compared to wireless communication using a pair of antennas between the transmitting and receiving sides.

[0003] When wireless signals are transmitted from multiple transmit antennas and received by multiple receive antennas, the multiple transmit signals may arrive at the receive antenna in an interfering state. For this reason, MIMO technology implemented using multiple antennas requires interference compensation technology to separate the interfering signals.

[0004] Interference compensation techniques are roughly divided into transmit precoding and receive interference compensation. Non-Patent Document 2 below discloses a technique related to transmit precoding. Also, Non-Patent Document 3 below discloses a technique related to receive interference compensation.

[0005] A. Knopp, RT Schwarz, D. Ogermann, CA Hofmann and B. Lankl, "Satellite System Design Examples for Maximum MIMO Spectral Efficiency in LOS Channels," IEEE GLOBECOM 2008 - 2008 IEEE Global Telecommunications Conference, 2008, pp. 1-6. Stankovic, Veljko, and Martin Haardt. "Generalized design of multi-user MIMO precoding matrices." IEEE Transactions on Wireless Communications 7.3 (2008): 953-961. Ahmed, Sajid, et al. "Iterative receivers for MIMO-OFDM and their convergence behavior." IEEE Transactions on Vehicular Technology 58.1 (2008): 461-468.

[0006] The above-mentioned non-patent document 1 states that in a line-of-sight environment where a transmitting station and a receiving station are in sight, antenna placement is an important factor for improving transmission capacity. In line-of-sight communications, such as satellite communications, the distance between the transmitter and receiver is long. In this case, installing multiple terrestrial station antennas corresponding to a single satellite at a large distance from each other makes it easier to form multiple channels with low correlation with each other. Therefore, in order to enable MIMO transmission using low-correlation channels via a satellite feeder link, it is effective to connect antennas placed remotely on the ground to a terrestrial base station by wire.

[0007] Satellite communications generally use wideband signals. In such communications, the time allocable to one symbol tends to be short. Therefore, even a small error in reception time can easily cause significant inter-symbol interference.

[0008] In transmit precoding technology, the state of the channel formed between the transmitting antenna and the receiving antenna is first estimated. Based on the estimated channel state, the transmitting station transmits a precoded signal so that the transmitted wave arrives at the receiving antenna with the effects of interference canceled. In this case, the receiving station can receive and demodulate the signals that arrive at each receiving antenna without considering that it is MIMO transmission.

[0009] However, in the uplink of satellite communications, the need to place terrestrial antennas at a distance results in large differences in the transmission path lengths between the transmitting and receiving antennas, which can easily lead to errors in the reception timing of signals arriving at the satellite. While offsetting the transmission timing can be considered to cancel the errors, it is difficult to accurately compensate for the reception time errors because the wireless path between the mobile satellite and the terrestrial antenna is constantly fluctuating. Therefore, in satellite communications that use wideband signals and remotely located terrestrial antennas, significant inter-symbol interference (ISI) is unavoidable, making it difficult to achieve accurate interference cancellation using transmit precoding.

[0010] Next, we consider separation using reception interference compensation. The satellite receiver can perform delay detection and separation processing on signals received from the ground. For this reason, in spatial multiplexing transmission using non-terrestrial mobile stations such as low-earth orbit satellites, it is considered preferable to use reception interference compensation to eliminate the effects of interference.

[0011] Antennas that non-land mobile stations are equipped with include antennas with mechanical tracking mechanisms, such as parabolic antennas, and phased array antennas that achieve electronic tracking mechanisms by controlling the excitation phase of multi-element antennas. In either case, an interference compensation function is required to separate MIMO signals that were not completely removed by the receiver. To achieve interference compensation, a timing compensation function to compensate for the timing delay of the received signal and a digital interference compensation function to estimate the channel state and operate equalization processing are required.

[0012] While such reception equalization methods are expected to significantly improve performance, they also impose a large computational load and consume a lot of power due to delay compensation, channel estimation, weight calculations, etc. Therefore, systems using conventional reception interference cancellation tend to increase equipment costs and are not suitable for low-cost development. In order to realize non-terrestrial mobile communications at lower cost, it is desirable to achieve spatial multiplexing transmission using a simpler interference cancellation mechanism.

[0013] In order to solve the above-mentioned problems, the first object of the present disclosure is to provide a wireless communication system that realizes spatial multiplexing transmission from a fixed station to a mobile station with an inexpensive configuration by using a simple interference compensation mechanism.

[0014] A second object of the present disclosure is to provide a wireless communication device that realizes spatial multiplexing transmission from a fixed station to a mobile station with an inexpensive configuration by using a simple interference compensation mechanism.

[0015] A third object of the present disclosure is to provide a wireless communication method for realizing spatial multiplexing transmission from a fixed station to a mobile station with an inexpensive configuration by using a simple interference compensation mechanism.

[0016] A fourth object of the present disclosure is to provide a wireless communication program for realizing spatial multiplexing transmission from a fixed station to a mobile station with an inexpensive configuration by using a simple interference compensation mechanism.

[0017] In order to achieve the above-mentioned object, a first aspect is a wireless communication system that performs spatial multiplexing transmission between a mobile station that moves and is equipped with multiple antennas, and a fixed station that includes multiple fixed antennas, wherein the mobile station has one or more processor circuits and a memory that stores a program executed by the processor circuit, and the processor circuit is preferably configured to perform the following: a process of detecting the direction of each of the multiple fixed antennas; a process of designating one of the directions as a desired direction and the others as undesired directions; a process of calculating a weight vector that strengthens signals from the desired direction and weakens signals from the undesired directions based on the desired direction and the undesired directions; and a process of generating a desired signal that is considered to be a signal from the desired direction by multiplying an input vector received by the multiple antennas by the weight vector.

[0018] Furthermore, a second aspect is a wireless communication device that functions as a mobile station equipped with multiple antennas and that performs spatial multiplexing transmission between a fixed station including multiple fixed antennas, and that includes one or more processor circuits and a memory that stores a program executed by the processor circuit, and it is desirable that the processor circuit is configured to perform the following: a process of detecting the direction of each of the multiple fixed antennas; a process of designating one of the directions as a desired direction and the others as undesired directions; a process of calculating a weight vector that strengthens signals from the desired direction and weakens signals from the undesired directions based on the desired direction and the undesired directions; and a process of generating a desired signal that is considered to be a signal from the desired direction by multiplying an input vector received by the multiple antennas by the weight vector.

[0019] Furthermore, a third aspect is a wireless communication method for performing spatial multiplexing transmission between a mobile station that moves and is equipped with multiple antennas and a fixed station that includes multiple fixed antennas, and preferably includes the following: the mobile station detecting the direction of each of the multiple fixed antennas; the mobile station designating one of the directions as a desired direction and the others as undesired directions; the mobile station calculating a weight vector that strengthens a signal from the desired direction and weakens a signal from the undesired direction based on the desired direction and the undesired direction; the fixed station transmitting a signal from each of the multiple fixed antennas; and the mobile station generating a desired signal that is considered to be a signal from the desired direction by multiplying an input vector received by the multiple antennas by the weight vector.

[0020] Furthermore, a fourth aspect is a computer-readable wireless communication program for realizing the wireless communication device described in the second aspect, which preferably includes the following program to cause a processor circuit provided in the wireless communication device to execute: a process of detecting the direction of each of multiple fixed antennas installed to realize spatial multiplexing transmission between the multiple antennas provided in the wireless communication device; a process of recognizing one of the directions as a desired direction and the others as undesired directions; a process of calculating a weight vector based on the desired direction and the undesired directions, which strengthens the signal from the desired direction and weakens the signal from the undesired direction; and a process of generating a desired signal that is regarded as a signal from the desired direction by multiplying an input vector received by the multiple antennas by the weight vector.

[0021] According to the first to fourth aspects, by using a simple interference compensation mechanism, spatial multiplexing transmission from a fixed station to a mobile station can be realized with an inexpensive configuration.

[0022] FIG. 1 is a diagram illustrating a configuration of a wireless communication system according to a first embodiment of the present disclosure. FIG. 2 illustrates uplink transmission from a terrestrial antenna to a satellite antenna in the wireless communication system illustrated in FIG. 1. FIG. 3 is a diagram illustrating an overview of general reception interference compensation for eliminating the influence of interference illustrated in FIG. 2. FIG. 4 is a diagram illustrating features of the first embodiment of the present disclosure. FIG. 5 is a schematic diagram of a non-terrestrial mobile station according to the first embodiment of the present disclosure. FIG. 6 is a block diagram illustrating functional configurations of a non-terrestrial mobile station (receiving station) and a terrestrial base station (transmitting station) according to the first embodiment of the present disclosure. FIG. 7 is a flowchart illustrating a flow of processing executed in the first embodiment of the present disclosure. FIG. 8 is a diagram illustrating a configuration of a wireless communication system according to a second embodiment of the present disclosure.

[0023] First Embodiment. [Configuration of First Embodiment] Fig. 1 shows a configuration in which a wireless communication system according to a first embodiment of the present disclosure is realized using a non-terrestrial mobile station (MS: Mobile Station) 10 and a terrestrial base station (GW: Gateway) 12. In this embodiment, the MS 10 is specifically a LEO (Low Earth Orbit) satellite. However, the MS 10 is not limited to a LEO satellite and may be, for example, an unmanned aerial vehicle or the like.

[0024] The MS 10 is equipped with two satellite antennas 14-1 and 14-2. Hereinafter, when there is no need to distinguish between the two satellite antennas, the subscripts of the reference numerals will be omitted and they will be referred to as satellite antennas 14. In this embodiment, the satellite antennas 14 are each configured as a parabolic antenna equipped with an independent mechanical tracking mechanism. The number of satellite antennas 14 is not limited to two, and may be two or more.

[0025] Two ground antennas 16-1 and 16-2 are connected to the GW 12 by wire. Hereinafter, when there is no need to distinguish between the two ground antennas, the subscripts of the reference symbols will be omitted and they will be referred to as the ground antenna 16. Like the satellite antenna 14, the ground antenna 16 is also configured as a parabolic antenna equipped with a mechanical tracking mechanism. Note that the number of ground antennas 16 is not limited to two, and may be two or more.

[0026] The LEO satellites that make up MS10 orbit the Earth in a low Earth orbit (LEO), which is an orbit around the Earth at an altitude of 2,000 km or less. Unlike geostationary Earth orbit (GEO) satellites, LEO satellites are characterized by their constant movement as seen from the Earth's surface. Therefore, to provide continuous service using LEO satellites, it is necessary to launch multiple satellites and provide comprehensive coverage to the entire service area. In particular, to provide global services, it is essential to deploy a satellite constellation orbiting the Earth.

[0027] In order to increase the communication capacity of terrestrial terminals or the number of terrestrial terminals that can be accommodated in services using LEO satellites, it is necessary to increase the capacity of the feeder link lines used for data communication. In order to increase the capacity of the lines, it is desirable to use high frequency bands that enable wideband communication. In this embodiment, for example, the Ka band in the 20 to 30 GHz band or the Q / V band in the 40 to 50 GHz band is used.

[0028] Furthermore, in this embodiment, as a further method for increasing the capacity of a line, multiple-input multiple output (MIMO) technology is utilized, which performs spatial multiplexing transmission using multiple antennas. When MIMO transmission is performed between a satellite and a ground station, a line-of-sight environment is formed between the two, which increases spatial correlation, making it difficult to accurately separate multiplexed transmitted signals.

[0029] It is known that the placement of terrestrial antennas 16 is an important factor in improving transmission capacity in a line-of-sight environment. In this embodiment, the multiple terrestrial antennas 16 that communicate with one MS 10 are placed far apart. This placement allows multiple channels with low correlation to be formed between the MS 10 and the multiple terrestrial antennas 16, thereby increasing the capacity of the line.

[0030] [Issues of the First Embodiment] Figure 2 shows how uplink transmission is performed from the terrestrial antenna 16 to the satellite antenna 14 in the wireless communication system shown in Figure 1. In this embodiment, uplink transmission is performed after a one-to-one correspondence between the terrestrial antenna 16-1 and the satellite antenna 14-1, and a one-to-one correspondence between the terrestrial antenna 16-2 and the satellite antenna 14-2.

[0031] Because the terrestrial antennas 16 are fixed on the ground, the MS 10 can grasp the position of each terrestrial antenna 16. On the other hand, because the movement route of the MS 10 is predetermined, the GW 12 can estimate or predict the position of the MS 10. Therefore, the satellite antenna 14-1 and the terrestrial antenna 16-1 each use their own tracking function to adjust the elevation angle toward the other antenna with which they should have a one-to-one correspondence. The same is true for the satellite antenna 14-2 and the terrestrial antenna 16-2.

[0032] 2, the solid line indicated by the reference numeral 18-1 represents the desired signal transmitted from the terrestrial antenna 16-1 to the satellite antenna 14-1, while the dashed line indicated by the reference numeral 20-1 represents an interference wave, i.e., an undesired signal, which is transmitted from the terrestrial antenna 16-1 and then reaches the satellite antenna 14-2 via a crossing channel.

[0033] The solid line indicated by the reference numeral 18-2 and the dashed line indicated by the reference numeral 20-2 similarly indicate the desired signal traveling from the terrestrial antenna 16-2 to the satellite antenna 14-2 and the undesired signal that reaches the satellite antenna 14-1 via the cross-channel. As shown in Figure 2, even if the terrestrial antenna 16 and the satellite antenna 14 are in one-to-one correspondence, it is not possible to completely eliminate the cross-channel components. For this reason, some kind of interference compensation is necessary to achieve spatial multiplexing transmission that eliminates the effects of interference.

[0034] Hereinafter, when there is no need to distinguish between the two desired signals 18-1 and 18-2, the subscripts of the reference symbols will be omitted and they will be referred to as desired signals 18. Similarly, when there is no need to distinguish between the two undesired signals 20-1 and 20-2, the subscripts of the reference symbols will be omitted and they will be referred to as undesired signals 20.

[0035] Fig. 3 is a diagram for explaining an outline of general reception interference cancellation for eliminating the influence of the interference shown in Fig. 2. In general reception interference cancellation, a unique known signal (UW: Unique Word) is inserted into each transmission signal from the terrestrial antennas 16-1 and 16-2. The MS 10 performs channel estimation by detecting the cross-correlation of the UW included in the received signal, and then performs equalization processing based on the estimation result.

[0036] 3, there are four channel components (2×2) between the two terrestrial antennas 16-1 and 16-2 and the two satellite antennas 14-1 and 14-2. These channel components can be expressed as follows:

[0037]

[0038] After estimating these four channel coefficients by UW cross-correlation detection, the MS 10 obtains the following channel estimation matrix based on the results:

[0039]

[0040] Then, for example, using the Zero Forcing algorithm, the pseudo-inverse of the above channel estimation matrix is ​​generated as follows:

[0041]

[0042] The MS 10 multiplies the received signal X(t) by the pseudo-inverse matrix thus generated to generate a signal y(t) from which the interference component has been cancelled.

[0043] In the configuration of this embodiment, in order to reduce channel correlation when spatial multiplexing transmission is performed in a line-of-sight environment, the terrestrial antennas 16 are placed at a distance, and a large difference is created in the angle of arrival of signals heading to the MS 10 from the multiple terrestrial antennas 16. As a result, differences occur in the propagation distances of signals transmitted from the GW 12 via the terrestrial antennas 16-1 and 16-2, and even if the GW 12 transmits signals at the same timing, the MS 10 receives those signals at different times.

[0044] When the above-described reception interference compensation is applied to the configuration of this embodiment, it becomes necessary to perform delay compensation to prevent degradation of equalization characteristics due to differences in reception timing. Specifically, it becomes necessary to detect the error in the arrival timing of the signals transmitted from the terrestrial antennas 16-1 and 16-2 based on the difference in the peak timing of the UW cross-correlation value, and then perform equalization after reflecting the amount of phase shift due to the timing error in the channel estimation value.

[0045] In addition to processes such as obtaining a channel estimation matrix and generating a pseudo-inverse matrix, detecting signal delays, performing equalization processing, and delay compensation for each signal after equalization requires a large computational load and consumes a large amount of power. Therefore, if we try to cancel the effects of interference using the above method, the circuit scale of the MS 10 will increase, making it difficult to keep development costs and equipment costs low.

[0046] [Features of the First Embodiment] Figure 4 is a diagram illustrating features of the first embodiment of the present disclosure. In this embodiment, as described above, there is a one-to-one correspondence between the satellite antennas 14 and the terrestrial antennas 16. Therefore, the satellite antenna 14-1 receives the desired signal 18-1 from the terrestrial antenna 16-1, and the satellite antenna 14-2 receives the desired signal 18-2 from the terrestrial antenna 16-2. However, because the antenna beam widths extend beyond the reception area of ​​the desired signal 18, the undesired signal 18-2 from the terrestrial antenna 16-2 reaches the satellite antenna 14-1, and the undesired signal 18-1 from the terrestrial antenna 16-1 reaches the satellite antenna 14-2.

[0047] In this embodiment, to address this interference, the receiving station MS 10 achieves equalization of the received signal using a simple technique by combining electronic beamforming with phase and amplitude control. More specifically, the MS 10 generates a 2x2 weight vector W that improves the SINR of the desired signal and eliminates the effects of undesired signals, and multiplies this by the input vector X(t), thereby achieving simple and highly accurate equalization.

[0048] The weight vector W is calculated using pointing direction information acquired by the two satellite antennas 14-1 and 14-2 using their respective tracking mechanisms. For example, if the signal from the terrestrial antenna 16-1 is the desired signal, the pointing direction of the satellite antenna 14-1 is acquired as the direction of the desired signal 18-1, and the pointing direction of the satellite antenna 14-2 is acquired as the direction of the undesired signal 18-2. These direction information pieces are then used to calculate the weight vector W such that the main beam is directed in the direction of arrival of the desired signal 18-1 and the null beam is directed in the direction of arrival of the undesired signals.

[0049] Similarly, when the signal from terrestrial antenna 16-2 is the desired signal, a weight vector W is calculated so that a null beam is directed in the direction of satellite antenna 14-1 and a main beam is directed in the direction of satellite antenna 14-2. By multiplying the input vector X(t) by such a weight vector W, a desired signal can be obtained in which the effects of interference caused by undesired signals are sufficiently suppressed, without complex calculations. Therefore, according to the configuration of this embodiment, a system that achieves high-precision equalization processing with a small circuit scale can be realized at low cost.

[0050] [Example of Equalization Using Weight Vector W] Fig. 5 shows a schematic diagram of the MS 10 in this embodiment. Here, it is assumed that the satellite antennas 14-1 and 14-2 constitute an adaptive antenna based on the least mean square error (MMSE) method. Here, the difference between a reference signal r(t) created by the receiving station as a replica of the desired signal and the actual array output signal y(t) is taken as the error signal e(t). The output signal y(t) is calculated by the adjoint matrix W of the weight vector W. H and the input vector X(t) to the antenna can be expressed as follows:

[0051] y(t)=W H X(t)...(1)

[0052] Therefore, the error signal e(t) is as shown in the following equation (2): The value W that minimizes the error signal e(t) shown in equation (2) is the optimal value Wopt of the weight vector.

[0053] e(t)=r(t)-y(t)=r(t)-W H X(t) ... (2)

[0054] The mean square error of the error signal e(t) can be expressed by the following equation:

[0055] E[|e(t)| 2 ]=E[|r(t) -W H X(t)| 2 ] = E[|r(t) | 2 ] -W T r * xr -W H r xr +W H R xx W... (3)

[0056] However, W T is the transpose matrix of the weight vector W. * means complex conjugate. r xr is the correlation vector between the reference signal r(t) and the input vector X(t), and R xx are correlation matrices of the input vectors. They are respectively defined by the following equation (4).

[0057] r xr = E[X(t)r * (t)] R xx = E[X(t)X H (t)] ...(4)

[0058] The above equation (3) is called the evaluation function of the MMSE standard. This evaluation function is a quadratic function of the weight vector W. The correlation matrix R xx is a positive definite matrix, and W H R xx Since W>0, the extreme value of the evaluation function is the only minimum value.

[0059] Therefore, the mean square error E[|e(t)| 2 The value of the weight vector W that minimizes [ ] can be found by setting the gradient with respect to W to zero, as shown in the following equation.

[0060] ▽w E[|e(t)| 2 ] = 0 ... (5)

[0061] In the above equation (5), ▽w E[|e(t)| 2 ] is the gradient of the mean square error with respect to the weight vector W, and can be expressed by the following equation (6) using vector differentiation.

[0062] ▽w E[|e(t)| 2 ] = -2r xr +2R xx W... (6)

[0063] From the above equations (5) and (6), the optimal value Wopt of the weight vector W is given by the following equation (7).

[0064] Wopt = r xr / R xx =R xx -1 r xr ... (7)

[0065] Below, we will explain a method for detecting a desired signal transmitted from terrestrial antenna 16 using the optimal value Wopt of weight vector W. For convenience, the configuration shown in Figure 5 is assumed to be an MMSE adaptive antenna consisting of two isotropic elements. It is also assumed that a signal s(t) from terrestrial antenna 16-1 arrives from a direction θs relative to the direction perpendicular to the satellite antenna 14 shown in Figure 5, and a signal u(t) from terrestrial antenna 16-2 arrives from a direction θu. Furthermore, it is assumed that satellite antennas 14-1 and 14-2 are spaced apart by approximately half the wavelength of signals s(t) and u(t).

[0066] 5, if signal s(t) is the desired signal 18-1, signal u(t) is an interference signal that affects the former, i.e., an undesired signal 20-2. If desired signal s(t) is substituted for reference signal r(t), input vector X(t) can be expressed by the following equation. Note that the direction θs of signal s(t) and the direction θu of signal u(t) can be detected from the tracking directions of satellite antennas 14-1 and 14-2, respectively.

[0067]

[0068] where n1(t) and n2(t) are the internal noises in the satellite antennas 14-1 and 14-2, respectively. When the input vector X(t) is expressed by the above equation (8), the correlation matrix R xx and the correlation vector r xr are expressed by the following equations (9) and (10), respectively.

[0069]

[0070]

[0071] Therefore, the optimum value Wopt of the above equation (7) is given by the following equation (11).

[0072]

[0073] By applying the optimum value Wopt thus obtained to the above equation (1), the satellite antenna 14 can be given the characteristic of directing a main beam in the θs direction and a null beam in the θu direction. In other words, it is possible to realize the characteristic of generating a received signal y(t) that is extremely little affected by interference from undesired signals u(t) with respect to the input vector X(t) and that exhibits a high SINR with respect to the desired signal s(t). In other words, this optimum value Wopt allows the satellite antenna 14 to receive the input vector X(t) and accurately generate a transmission signal from the terrestrial antenna 16-1.

[0074] Furthermore, if the desired signal and the undesired signal are swapped, and the optimum value Wopt is calculated with u(t) as the desired signal 18-2 and s(t) as the undesired signal 20-1, the direction of the main beam and the direction of the null beam are swapped. Therefore, if such an optimum value Wopt is applied to the above equation (1), it is possible to generate a received signal y(t) from the input vector X(t) that is extremely little affected by interference from the signal s(t) and exhibits a high SINR relative to the signal u(t). In other words, this optimum value Wopt can provide the satellite antenna 14 with the characteristic of receiving the input vector X(t) and accurately generating a transmission signal from the terrestrial antenna 16-2.

[0075] [Functional Configuration of First Embodiment] The functions realized by the components described herein may be implemented in circuitry or processing circuitry including general-purpose processors, application-specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), CPUs (Central Processing Units), conventional circuits, and / or combinations thereof, programmed to realize the described functions. A processor includes transistors and other circuits and is considered to be circuitry or processing circuitry. A processor may also be a programmed processor that executes a program stored in a memory.

[0076] In this specification, a circuit, a "part," a "unit," or a "means" refers to hardware that is programmed to implement a described function or that implements that function, and may be any hardware disclosed in this specification or any hardware that is programmed to implement the described function or that is known to execute that program.

[0077] If the hardware is a processor, which is considered to be a type of circuitry, then the circuitry, "part" or "unit" or "means" is the combination of the hardware and software used to configure the hardware and / or processor.

[0078] Figure 6 is a block diagram for functionally explaining the configuration of the MS 10 functioning as a receiving station and the GW 12 functioning as a transmitting station. Specifically, the configuration shown in Figure 6 can be realized by combining dedicated hardware with a computer system. The computer system includes a processor such as a CPU, memory devices including ROM, RAM, and a hard disk, and various interface devices. The functions of the MS 10 and the GW 12 are realized by the execution of programs stored in the respective memory devices by the respective processors.

[0079] As shown in Figure 6, the GW 12 has the following blocks for processing uplink data to be transmitted to the MA 10. "Parallel / serial conversion unit 30": A block that performs parallel / serial conversion of the bit information of the uplink data. "Transmission signal modulation unit 32": A block that modulates the bit string and converts it into an electrical signal. "Frequency conversion unit 34": A block that converts the electrical signal into a predetermined frequency that should be applied to the radio signal to be sent from the terrestrial antenna 16. "Signal transmission unit 36": A block for transmitting the transmission signal from the terrestrial antenna 16.

[0080] The GW 12 has the following blocks for processing downlink data from the MS 10. "Signal receiver 38": A block for receiving signals that have reached the terrestrial antenna 16. "Antenna directivity controller 40": A block for performing processing to direct the main beam of the terrestrial antenna 16 in a desired direction.

[0081] The MS 10 has the following blocks for processing the uplink data transmitted from the GW 12: "Signal Receiver 42": A block for receiving signals that have reached the MS 10; "Reception Interference Compensator 44": A block for performing interference compensation on the received signal to eliminate the effects of undesired signals and increase the SINR of the desired signal; More specifically, this block generates the received signal y(t) by multiplying the input vector X(t) received by the satellite antenna 14 by the optimal value Wopt of the weight vector W; "Frequency Converter 46": A block for converting the radio signal received by the satellite antenna 14 into an electrical signal of a predetermined frequency; "Received Signal Demodulator 48": A block for demodulating the received signal to produce a bit string; "Serial / Parallel Converter 50": A block for serial / parallel conversion of the electrical signal demodulated into a bit string to generate uplink data; "Antenna Pointing Controller 52": A block for performing processing to direct the main beam of the satellite antenna 14 in the desired direction. "Interference direction detection unit 54": A block that calculates the arrival direction of the desired signal and the arrival direction of the undesired signal from the information on the direction of direction generated by the antenna direction control unit 52. The obtained information on the direction of arrival is provided to the reception interference compensation unit 44. "Signal transmission unit 56": A block that transmits downlink data from the satellite antenna 14 to the terrestrial antenna 16.

[0082] [Operation of First Embodiment] FIG. 7 is a flowchart for explaining the flow of processing executed in the MS 10 functioning as a receiving station and the GW 12 functioning as a transmitting station in this embodiment to realize the above functions.

[0083] The MS 10, functioning as a receiving station, first predicts the direction of the transmitting station, specifically, the direction of each of the one or more terrestrial antennas 16 with which communication should be established (step 100). The positions of the terrestrial antennas 16 are known to the MS 10. The MS 10 also knows its own position using GPS information or the like. This allows the MS 10 to accurately predict the direction of the terrestrial antennas 16. In this embodiment, the direction θs of the terrestrial antenna 16-1 and the direction θu of the terrestrial antenna 16-2 are predicted in step 100.

[0084] Next, the MS 10 performs coarse adjustment control of the pointing of the satellite antenna 14 based on the predicted direction (step 102). The pointing of each satellite antenna 14 is controlled independently by its own tracking mechanism.

[0085] Next, the MS 10 transmits a beacon signal toward the ground antennas 16 (step 104). Specifically, a beacon signal is transmitted from each of the satellite antennas 14 toward each of the ground antennas 16 with which a one-to-one relationship should be established.

[0086] Next, the MS 10 waits for a transmission from the terrestrial antenna 16 and receives the transmitted signal (step 106).

[0087] Then, based on the received signals, fine adjustment control is performed on the direction of each satellite antenna 14 (step 108).

[0088] Next, the desired direction and undesired direction for MS 10 are detected (step 110). For example, if satellite antenna 14-1 is pointed in the θs direction, it can be determined that the signal from terrestrial antenna 16-1 arrives from the θs direction. Also, if satellite antenna 14-2 is pointed in the θu direction, it can be determined that the signal from terrestrial antenna 16-2 arrives from the θu direction. In this case, when the desired signal is the signal from terrestrial antenna 16-1, the desired direction is detected as θs, and the undesired direction is detected as θu. Also, when the desired signal is the signal from terrestrial antenna 16-2, the desired direction is detected as θu, and the undesired direction is detected as θs.

[0089] Next, the MS 10 calculates the optimal value Wopt of the weight vector W shown in equation (11) above based on the detected desired and undesired directions. Then, interference cancellation is performed by multiplying the input vector X(t) received by the satellite antenna 14 by this optimal value Wopt (step 112). Specifically, the MS 10 acquires the transmission signal from the terrestrial antenna 16-1 using the optimal value Wopt with θs as the desired direction, and acquires the transmission signal from the terrestrial antenna 16-2 using the optimal value Wopt with θu as the desired direction.

[0090] Thereafter, the MS 10 sequentially executes the processes of demodulation (step 114), frequency conversion (step 116), serial conversion (step 118), and data recovery (step 120).

[0091] The GW 12, functioning as a transmitting station, first predicts the direction of the receiving station, specifically, the direction of the MS 10 as seen from each of one or more terrestrial antennas 16 that should establish communication with the MS 10 (step 130). The GW 12 is aware of the movement schedule of the MS 10. The positions of each terrestrial antenna 16 are also known to the GW 12. Therefore, the GW 12 can accurately predict the direction of the MS 10 as seen from each terrestrial antenna 16. In this embodiment, in step 130, the direction of the MS 10 as seen from the terrestrial antenna 16-1 is predicted as θs, and the direction of the MS 10 as seen from the terrestrial antenna 16-2 is predicted as θu.

[0092] Next, the GW 12 performs coarse adjustment control of the direction of the terrestrial antennas 16 based on the predicted direction (step 132). The direction of each terrestrial antenna 16 is controlled independently by its own tracking mechanism.

[0093] Next, the GW 12 performs a process of receiving a beacon emitted from the satellite antenna 14 (step 134).

[0094] Then, fine-tuning control is performed on the pointing of each of the ground antennas 16 based on the received beacons (step 136).

[0095] Thereafter, when the GW 12 recognizes the generation of data (step 138), it performs parallel conversion (step 140), modulation (step 142), and frequency conversion (step 144), and then transmits the signal from each terrestrial antenna 16 (step 146).

[0096] As described above, according to the wireless communication system of this embodiment, spatial multiplexing transmission using non-terrestrial mobile stations can be realized by extremely simple processing without estimating channel conditions, compensating for signal delays, etc. Therefore, according to this embodiment, a system that can establish high-quality communications at low development costs can be realized.

[0097] Second Embodiment Next, a second embodiment of the present disclosure will be described with reference to Fig. 8. The wireless communication system of this embodiment is similar to the system of the first embodiment, except that the non-terrestrial mobile station is changed from MS10 to MS60. Also, MS60 is similar to MS10, except that satellite antennas 14-1 and 14-2 are replaced with a satellite antenna 62.

[0098] In the first embodiment described above, a parabolic antenna equipped with a mechanical tracking mechanism is used as the satellite antenna 14. However, antennas applicable to the wireless communication system of the present disclosure are not limited to parabolic antennas. The MS 60 is a phased array antenna and has the function of controlling the beam directionality by controlling the amplitude and phase.

[0099] Even when MS 60 is used, the desired signal from terrestrial antenna 16-1 can be received with high accuracy by using the optimal value Wopt based on the desired direction θs and the undesired direction θu. Furthermore, the desired signal from terrestrial antenna 16-2 can be received with high accuracy by using the optimal value Wopt calculated by interchanging the desired direction and the undesired direction. Therefore, even with the configuration of embodiment 2, it is possible to realize an inexpensive, high-quality system.

[0100] [Modifications of the First and Second Embodiments] In the second embodiment described above, it has been explained that a phased array antenna can be used as the satellite antenna 14, but the present disclosure is not limited to this. It is also possible to use a phased array antenna not only for the satellite antenna 14 but also for the terrestrial antenna 16.

[0101] Furthermore, in the above-described first and second embodiments, the optimal value Wopt of the weight vector W is calculated to improve the SINR of the desired signal and eliminate the influence of undesired signals, but the present disclosure is not limited to this. The optimal value Wopt may be any value that increases the strength of the desired signal and decreases the strength of undesired signals. Furthermore, the optimal value Wopt may be any value that increases the strength of the desired signal or decreases the strength of the undesired signals.

[0102] 10 Non-terrestrial mobile station (MS) 12 Terrestrial base station (GW) 14, 14-1, 14-2 Satellite antenna 16, 16-1, 16-2 Terrestrial antenna 18, 18-1, 18-2 Desired signal 20, 20-1, 20-2 Undesired signal

Claims

1. A wireless communication system that performs spatial multiplexing transmission between a mobile station that moves with a plurality of antennas and a fixed station that includes a plurality of fixed antennas, wherein the mobile station includes one or more processor circuits and a memory that stores a program executed by the processor circuits, and the processor circuits perform a process of detecting a direction of each of the plurality of fixed antennas, a process of designating one of the directions as a desired direction and the others as undesired directions, a process of calculating a weight vector that strengthens a signal from the desired direction and weakens a signal from the undesired direction based on the desired direction and the undesired directions, and a process of generating a desired signal regarded as a signal from the desired direction by multiplying an input vector received by the plurality of antennas by the weight vector.

2. A wireless communication device that functions as a mobile station that moves with a plurality of antennas and performs spatial multiplexing transmission with a fixed station that includes a plurality of fixed antennas, the wireless communication device including one or more processor circuits and a memory that stores a program executed by the processor circuits, and the processor circuits perform a process of detecting a direction of each of the plurality of fixed antennas, a process of designating one of the directions as a desired direction and the others as undesired directions, a process of calculating a weight vector that strengthens a signal from the desired direction and weakens a signal from the undesired direction based on the desired direction and the undesired directions, and a process of generating a desired signal regarded as a signal from the desired direction by multiplying an input vector received by the plurality of antennas by the weight vector.

3. A wireless communication method for performing spatial multiplexing transmission between a mobile station that moves with a plurality of antennas and a fixed station that includes a plurality of fixed antennas, the method comprising: the mobile station detecting the direction of each of the plurality of fixed antennas; the mobile station designating one of the directions as a desired direction and the others as undesired directions; the mobile station calculating a weight vector for strengthening a signal from the desired direction and weakening a signal from the undesired direction based on the desired direction and the undesired directions; the fixed station transmitting signals from each of the plurality of fixed antennas; and the mobile station generating a desired signal regarded as a signal from the desired direction by multiplying an input vector received by the plurality of antennas by the weight vector.

4. A computer-readable wireless communication program for realizing the wireless communication device according to claim 2, the program including: a process for causing a processor circuit included in the wireless communication device to detect the direction of each of a plurality of fixed antennas installed to realize spatial multiplexing transmission between the wireless communication device and a plurality of antennas included in the wireless communication device; a process for causing the direction to be recognized with one of the directions as a desired direction and the others as undesired directions; a process for causing a weight vector for strengthening a signal from the desired direction and weakening a signal from the undesired direction to be calculated based on the desired direction and the undesired directions; and a process for generating a desired signal regarded as a signal from the desired direction by multiplying an input vector received by the plurality of antennas by the weight vector.

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