Wireless communication system

Abstract

The present disclosure relates to a wireless communication system. The wireless communication system comprises a transmission device and a reception device. The transmission device is configured so as to implement processing for transmitting the same signal in parallel over a plurality of frequency channels. The reception device is configured so as to execute: processing for receiving the plurality of signals transmitted in parallel as a plurality of reception signals; processing for detecting degraded reception signals among the plurality of reception signals; and processing for synthesizing only the non-degraded reception signals.

Description

wireless communication system

[0001] The present disclosure relates to wireless communication systems.

[0002] In wireless communications, there is a technology that reduces the degradation of reception level due to fading by combining or selecting received signals. To achieve long-distance transmission using this technology, it is necessary to increase the transmission output.

[0003] Takaaki Ichikawa, "A Study on Diversity Systems in Digital Wireless Communications," Doctoral Dissertation, Osaka University, July 31, 2000.

[0004] However, to avoid radio wave interference with other systems, legal limits are imposed on transmission output, meaning that depending on the transmission distance, it may not be possible to increase the transmission output to the required level.

[0005] To solve the above-mentioned problems, Non-Patent Document 1 discloses a technology using a space diversity (SD) receiving method. In this technology, the same signal is transmitted multiple times and received by multiple receiving devices. Therefore, by selecting a received signal whose reception level has not decreased due to fading from the received signals received by the multiple receiving devices, it is possible to reduce the decrease in reception level.

[0006] However, in the above-mentioned technology, by using multiple receiving devices located at different locations, it is possible to obtain a received signal with an undiminished reception level. In other words, when there is only one receiving device, there is a problem that the decrease in reception level may not be sufficiently reduced.

[0007] In order to solve the above-mentioned problems, an object of the present disclosure is to provide a wireless communication system that can achieve long-distance transmission without increasing transmission output.

[0008] An aspect of the present disclosure is preferably a wireless communication system comprising a transmitting device and a receiving device, wherein the transmitting device is configured to perform a process of transmitting the same signal in parallel over multiple frequency channels, and the receiving device is configured to perform a process of receiving the multiple parallel-transmitted signals as multiple received signals, a process of detecting degraded received signals from the multiple received signals, and a process of combining only non-degraded received signals.

[0009] According to aspects of the present disclosure, long-distance transmission can be achieved without increasing the transmission output.

[0010] 1 is a diagram illustrating an example configuration of a wireless communication system according to a first embodiment of the present disclosure. FIG. 2 is a block diagram illustrating functions of a wireless communication system according to the first embodiment of the present disclosure. FIG. 3 is a diagram illustrating a hardware configuration of a transmitting device according to the first embodiment of the present disclosure. FIG. 4 is a diagram illustrating a hardware configuration of a receiving device according to the first embodiment of the present disclosure. FIG. 5 is a diagram illustrating waveform changes of a signal according to the first embodiment of the present disclosure. FIG. 6 is a diagram illustrating waveform changes of a signal according to a first comparative example. FIG. 7 is a diagram illustrating waveform changes of a signal according to a second comparative example. FIG. 8 is a diagram illustrating an example of a co-channel arrangement. FIG. 9 is a diagram illustrating an example of an interleaved arrangement. FIG. 10 is a diagram illustrating an example of XPIC processing. FIG. 11 is a diagram illustrating waveform changes of a signal according to a second embodiment of the present disclosure. FIG. 12 is a diagram illustrating waveform changes of a signal according to a comparative example.

[0011] 1 is a diagram illustrating a configuration example of a wireless communication system according to a first embodiment of the present disclosure. The wireless communication system 100 includes a transmitting device 10. The transmitting device 10 has a transmitting antenna 12. The transmitting device 10 and the transmitting antenna 12 are connected using a feeder line 11.

[0012] The transmitting device 10 performs wireless communication with the receiving device 30. The receiving device 30 has a receiving antenna 32. The receiving device 30 and the receiving antenna 32 are connected by a power feeder 31.

[0013] 2 is a block diagram showing functions of the wireless communication system according to the first embodiment of the present disclosure. First, in the transmission device 10, the input unit 13 receives a user signal input by a user. That is, the input unit 13 has a function of connecting the user and the wireless communication system 100 by transmitting a user operation to the transmission device 10.

[0014] The input unit 13 transmits the received user signal to the framing unit 14. The framing unit 14 performs buffering and packetization of the received user signal.

[0015] The framing unit 14 transmits the processed signal to the modulation unit 15. The modulation unit 15 performs modulation processing on the received signal.

[0016] The modulator 15 transmits the processed signal to the branching unit 16. The branching unit 16 performs signal branching processing on the received signal. The signal branching processing is a process of determining multiple frequency channels to be used for transmitting the processed signal. This signal branching processing makes it possible to transmit the same signal in parallel on multiple frequency channels.

[0017] In this disclosure, it is also assumed that multiple frequency channels utilize cross-polarized waves at the same frequency, as will be described later.

[0018] Here, a case is shown in which signal branching processing is performed to use vertically polarized waves (V polarization) and horizontally polarized waves (H polarization) at frequencies f1, f2, and f3 as frequency channels used to transmit processed signals. The frequency channel allocation pattern determined in this manner is called co-channel allocation. Details of co-channel allocation will be described later.

[0019] The branching unit 16 transmits the processed signals to RF units 17av, 17ah, 17bv, 17bh, 17cv, and 17ch. Each RF unit generates a transmission signal by modulating the received signal so that it can be transmitted using a specific frequency channel.

[0020] For example, the RF unit 17av modulates the received signal so that it can be transmitted using V-polarized waves of frequency f1, or the RF unit 17ah modulates the received signal so that it can be transmitted using H-polarized waves of frequency f1.

[0021] Similarly, RF unit 17bv modulates the received signal so that it can be transmitted using V-polarized waves with frequency f2, and RF unit 17bh modulates the received signal so that it can be transmitted using H-polarized waves with frequency f2. RF unit 17cv modulates the received signal so that it can be transmitted using V-polarized waves with frequency f3, and RF unit 17ch modulates the received signal so that it can be transmitted using H-polarized waves with frequency f3.

[0022] The RF units 17av, 17ah, 17bv, 17bh, 17cv, and 17ch transmit the modulated signals to the transmitting antenna 12. The transmitting antenna 12 transmits a signal made up of the received six transmission signals to the receiving antenna 32.

[0023] The receiving antenna 32 transmits a signal consisting of six received signals to RF units 33av, 33ah, 33bv, 33bh, 33cv, and 33ch. Each RF unit performs automatic gain control (AGC) processing using an amplifier and monitoring processing of the carrier-to-noise ratio (C / N) for the received signal.

[0024] The C / N monitoring process is realized by detecting received signals whose C / N has deteriorated due to, for example, radio interference or fading. Received signals detected as deteriorated are excluded from the received signals to be combined in the signal combining process described below. The C / N monitoring process may be realized, for example, by detecting a received signal as deteriorated if its C / N is below a specific threshold.

[0025] For example, the RF unit 33av processes a received signal transmitted using V-polarized waves of frequency f1, while the RF unit 33ah processes a received signal transmitted using H-polarized waves of frequency f1.

[0026] Similarly, RF unit 33bv processes received signals transmitted using V-polarized waves of frequency f2, and RF unit 33bh processes received signals transmitted using H-polarized waves of frequency f2. RF unit 33cv processes received signals transmitted using V-polarized waves of frequency f3, and RF unit 33ch processes received signals transmitted using H-polarized waves of frequency f3.

[0027] The RF units 33av, 33ah, 33bv, 33bh, 33cv, and 33ch transmit the processed signals to the in-phase adjustment unit 34. The in-phase adjustment unit 34 detects the phase of each received signal. Furthermore, the in-phase adjustment unit 34 performs in-phase adjustment processing so that the phases of the detected signals are in-phase. Specifically, the in-phase adjustment unit 34 selects a carrier to be adjusted and shifts the phase of each signal.

[0028] The in-phase adjustment unit 34 transmits the processed signal to the combiner 35. The combiner 35 performs signal combining processing for the received signals. The combiner 35 preferably performs cross polarization interference compensation (XPIC) processing. The XPIC processing will be described later.

[0029] The combiner 35 transmits the processed signal to the demodulator 36. The demodulator 36 performs demodulation processing, carrier selection processing, and XPIC processing on the received signal.

[0030] The demodulation unit 36 ​​transmits the processed signal to the deframing unit 37. The deframing unit 37 performs a buffer removal process on the received signal.

[0031] The deframing unit 37 transmits the processed signal to the output unit 38. The output unit 38 outputs the received signal. That is, the output unit 38 has a function of connecting the user and the wireless communication system 100 by making the user signal transmitted to the receiving device 30 operable by the user.

[0032] The transmitter 10 also includes a monitoring control unit 18. The monitoring control unit 18 receives alarms from each unit and controls each unit. For example, the monitoring control unit 18 receives alarms from the modulation unit 15 and each RF unit. The monitoring control unit 18 also controls the framing unit 14, the modulation unit 15, and each RF unit.

[0033] The receiving device 30 further includes a monitoring control unit 39. The monitoring control unit 39 receives alarms from each unit and controls each unit. For example, the monitoring control unit 39 receives alarms from each RF unit, the in-phase adjustment unit 34, and the demodulation unit 36. The monitoring control unit 39 also controls each RF unit, the in-phase adjustment unit 34, the demodulation unit 36, and the deframing unit 37.

[0034] The monitoring control unit 18 and the monitoring control unit 39 may be connected to each other when the transmitting device 10 and the receiving device 30 are synchronously controlled. In this case, the monitoring control unit 18 and the monitoring control unit 39 may have a function to control each other.

[0035] 3 is a diagram illustrating a hardware configuration of a transmission device according to the first embodiment of the present disclosure. Each function of the transmission device 10 may be partially or entirely configured by hardware such as a programmable logic device (PLD) or a field programmable gate array (FPGA), or may be configured as a program executed by a processor such as a CPU.

[0036] For example, the transmitting device 10 can be realized using a computer and a program, and the program can be recorded on a storage medium or provided via a network.

[0037] 3, the transmitting device 10 has an input unit 108, an output unit 101, a communication unit 102, a CPU 103, a memory 104, and an HDD 105 connected via a bus 106, and functions as a computer. The transmitting device 10 is also capable of inputting and outputting data to and from a computer-readable storage medium 107.

[0038] The input unit 108 is, for example, a keyboard and a mouse, etc. The output unit 101 is, for example, a display device such as a display.

[0039] The communication unit 102 is, for example, a communication interface that communicates with a wireless device to be controlled.

[0040] The CPU 103 controls each component of the transmitting device 10 and performs predetermined processing, etc. The memory 104 and the HDD 105 store data, etc.

[0041] The storage medium 107 is capable of storing programs and the like that cause the transmitting device 10 to execute the functions of the transmitting device 10. Note that the architecture that configures the transmitting device 10 is not limited to the example shown in FIG.

[0042] 4 is a diagram illustrating a hardware configuration of a receiving device according to the first embodiment of the present disclosure. Each function of the receiving device 30 may be partially or entirely configured by hardware such as a programmable logic device (PLD) or a field programmable gate array (FPGA), or may be configured as a program executed by a processor such as a CPU.

[0043] For example, the receiving device 30 can be realized using a computer and a program, and the program can be recorded on a storage medium or provided via a network.

[0044] 4, the receiving device 30 has an input unit 300, an output unit 301, a communication unit 302, a CPU 303, a memory 304, and an HDD 305 connected via a bus 306, and functions as a computer. The receiving device 30 is also capable of inputting and outputting data to and from a computer-readable storage medium 307.

[0045] The input unit 300 is, for example, a keyboard and a mouse, etc. The output unit 301 is, for example, a display device such as a display.

[0046] The communication unit 302 is, for example, a communication interface that communicates with a wireless device to be controlled.

[0047] The CPU 303 controls each unit constituting the receiving device 30 and performs predetermined processing, etc. The memory 304 and HDD 305 store data, etc.

[0048] The storage medium 307 is capable of storing programs and the like that cause the receiving device 30 to execute the functions of the receiving device 30. Note that the architecture that configures the receiving device 30 is not limited to the example shown in FIG.

[0049] 5 is a diagram illustrating waveform changes of a signal according to the first embodiment of the present disclosure. Hereinafter, in the diagrams illustrating waveforms, the horizontal axis represents frequency, the waveforms shown above the horizontal axis represent V polarization, and the waveforms shown below the horizontal axis represent H polarization.

[0050] Transmission waveform 2 is the waveform of six transmission signals transmitted by the transmitting antenna 12 according to this embodiment. Transmission waveform 2 is composed of waveforms of transmission signals 21v, 21h, 22v, 22h, 23v, and 23h. Note that these six transmission signals all have the same transmission power as transmission signal 21, which will be described later.

[0051] Transmission signal 21v shows the waveform of a transmission signal transmitted using V-polarized waves of frequency f1. Transmission signal 21h shows the waveform of a transmission signal transmitted using H-polarized waves of frequency f1. Similarly, transmission signal 22v shows the waveform of a transmission signal transmitted using V-polarized waves of frequency f2, transmission signal 22h shows the waveform of an H-polarized wave of frequency f2, transmission signal 23v shows the waveform of a V-polarized wave of frequency f3, and transmission signal 23h shows the waveform of an H-polarized wave of frequency f3.

[0052] The received waveform 4a is the waveform of a signal transmitted from the transmitting antenna 12 and received by the receiving antenna 32. The received waveform 4a is made up of the waveforms of received signals 41v', 41h', 42v, 42h, 43v, and 43h.

[0053] The C / N ratio of the received signals 42v, 42h, 43v and 43h is 20 dB. The received signals 41v' and 41h' are degraded by the influence of the interference waves 8v and 8h.

[0054] The composite received waveform 6 is a waveform of a signal obtained by combining a portion of the received signals that make up the received waveform 4a by the receiving device 30. Specifically, the composite received waveform 6 is a waveform of a signal obtained by combining received signals 42v, 42h, 43v, and 43h, which are received signals that have not been degraded by the influence of interference waves.

[0055] The composite received waveform 6 is composed of the waveform of a composite received signal 61. The C / N of the composite received signal 61 is 26 dB.

[0056] In order to demonstrate the effect of the first embodiment of the present disclosure, signal waveform changes according to comparative examples are shown. Fig. 6 is a diagram showing signal waveform changes according to a first comparative example. The first comparative example shows an example in which a transmitting device 10, which is 30 km away from a receiving device 30, transmits one signal on one frequency channel.

[0057] The transmission waveform 20 is the waveform of a signal transmitted by the transmission antenna 12 according to this embodiment. The transmission waveform 20 is composed of the waveform of a transmission signal 21.

[0058] The received waveform 40 is the waveform of a signal transmitted from the transmitting antenna 12 and received by the receiving antenna 32. The received waveform 40 is composed of the waveform of a received signal 41.

[0059] 7 is a diagram showing signal waveform changes according to a second comparative example, which illustrates an example in which a transmitting device 10, which is 60 km away from a receiving device 30, transmits one signal over one frequency channel.

[0060] The transmission waveform 20 is the waveform of a signal transmitted by the transmission antenna 12 according to this embodiment. The transmission waveform 20 is composed of the waveform of a transmission signal 21.

[0061] The received waveform 40a is the waveform of a signal transmitted from the transmitting antenna 12 and received by the receiving antenna 32. The received waveform 40a is composed of the waveform of a received signal 41a.

[0062] The C / N ratio of the received signals 41 and 41a will now be described. The free space propagation loss Ls when transmitting a signal from the transmitting device 10 to the receiving device 30 is generally expressed by Equation 1, where d is the wireless section distance [m] and λ is the wavelength [m].

[0063]

[0064] Here, the free space propagation loss in the first comparative example is L ｓ１ , the free space propagation loss in the second comparative example is L ｓ２The wireless section distance in the first comparative example is 30 km, and the wireless section distance in the second comparative example is 60 km. That is, the wireless section distance in the second comparative example is twice the wireless section distance in the first comparative example. As a result, Equations 2 and 3 hold true.

[0065]

[0066]

[0067] As described above, when the wireless section distance is doubled, the free space propagation loss increases by 6 dB.

[0068] Here, the first and second comparative examples use a wireless communication system capable of wireless communication up to 30 km. Furthermore, it is assumed that the required C / N ratio to ensure line quality is 26 dB. The ensured line quality here is, for example, a BER of 1×10 －６ Since the wireless section distance in the first comparative example is 30 km, the C / N ratio of the received signal 41 is 26 dB.

[0069] On the other hand, the wireless section distance in the second comparative example is 60 km. As described above, the free space propagation loss in the second comparative example is 6 dB greater than the free space propagation loss in the first comparative example. Therefore, the C / N ratio of the received signal 41 a is 20 dB.

[0070] As described above, the free space propagation loss increases as the distance between wireless sections increases, resulting in a decrease in the C / N ratio of the received signal, making it impossible to ensure line quality.

[0071] In order to ensure line quality, one possible method for increasing the C / N ratio of the received signal is to increase the transmission output. However, the space in which wireless communication is carried out is shared with other users. Therefore, in order to avoid radio wave interference with other systems, legal limits on transmission output are set. In other words, depending on the transmission distance, it may not be possible to increase the transmission output to the required strength.

[0072] On the other hand, in order to ensure line quality, it is possible to avoid increasing the distance between wireless sections. However, in long-distance communications targeting remote islands or mountainous areas, wired communications are difficult, and wireless communications are necessary. Therefore, it may become necessary to increase the distance between wireless sections.

[0073] Furthermore, Non-Patent Document 1 discloses a technique using an SD reception method to ensure line quality. This technique compensates for fading using SD reception in a fixed microwave system. This SD reception involves installing multiple receiving antennas in locations with low spatial correlation. As a result, the multiple receiving antennas can mutually compensate for distortion in the received signal waveform. Therefore, this SD reception is not intended to ensure line quality when the wireless section distance is long.

[0074] Furthermore, when applying the SD reception described above, it is necessary to install multiple large and heavy antennas at high locations such as steel towers. These antennas must be placed at high altitudes and require the operation of waveguides for long periods of time. Therefore, applying the SD reception described above poses the problem of expensive equipment construction costs and long construction periods.

[0075] As described above, various problems arise when trying to maintain line quality when the wireless section distance is increased. Signal waveform changes according to this embodiment, which solve these problems, will be described with reference to FIG.

[0076] First, the transmitting device 10 transmits the same signal in parallel over six frequency channels. Specifically, by performing signal branching processing, six transmission signals 21v, 21h, 22v, 22h, 23v, and 23h that transmit the same signal are transmitted in parallel.

[0077] The receiving device 30 receives the six transmission signals transmitted in parallel from the transmitting device 10 as received signals 41v', 41h', 42v, 42h, 43v, and 43h. The receiving device 30 also performs C / N monitoring processing on the six received signals to detect degraded received signals. Here, the received signals 41v' and 41h', which have been degraded by the influence of the interference waves 8v and 8h, are detected as degraded received signals.

[0078] Furthermore, the receiving device 30 excludes from the combined signals any received signals detected as degraded in the signal combining process, so that the receiving device 30 can combine only the undegraded received signals 42v, 42h, 43v, and 43h.

[0079] The C / N ratio of the combined received signal 61 acquired by the receiving device 30 at this time will be described in detail. In this embodiment, the received signals are subjected to in-phase adjustment processing before signal combining processing, so the acquired combined received signal is a combined received signal obtained by in-phase combining. Table 1 shows the relationship between the number of received signals to be in-phase combined, C / N, and the wireless section distance at which free space propagation loss can be compensated for by in-phase combining.

[0080]

[0081] As described above, by combining four received signals, it is possible to compensate for free space propagation loss when the wireless section distance is doubled. In this embodiment, by combining four undegraded received signals, it is possible to increase the C / N by 6 dB. In other words, the C / N of the combined received signal 61 becomes 26 dB. As a result, the receiving device 30 can compensate for free space propagation loss even when the wireless space distance from the transmitting device 10 is doubled to 60 km.

[0082] As described above, in this embodiment, the same signal is transmitted in parallel over a plurality of frequency channels, thereby realizing long-distance transmission without increasing the transmission output.

[0083] The technology used in this embodiment will be described in detail below. Fig. 8 is a diagram showing an example of a co-channel arrangement. Here, as an example of a co-channel arrangement, an arrangement pattern of frequency channels used in fixed stations in the 11 GHz band is shown.

[0084] Transmission signal 21v is a transmission signal that uses V polarization with a frequency of 10.730, and transmission signal 21h is a transmission signal that uses H polarization with a frequency of 10.730. Similarly, transmission signal 22v is a transmission signal that uses V polarization with a frequency of 10.790, and transmission signal 22h is a transmission signal that uses H polarization with a frequency of 10.790. Thereafter, transmission signals 23v and 23h, 24v and 24h, 25v and 25h, 26v and 26h, 27v and 27h, and 28v and 28h are transmission signals that use V polarization and H polarization, respectively, with frequencies that increase by 0.060.

[0085] 9 is a diagram showing an example of an interleaved arrangement, in which an arrangement pattern of frequency channels used in fixed stations in the 15 GHz band is shown as an example of an interleaved arrangement.

[0086] Transmission signal 21v is a transmission signal that uses V polarization with a frequency of 14.460. Similarly, transmission signal 22h is a transmission signal that uses H polarization with a frequency of 14.500. Thereafter, transmission signals 23v, 24h, 25v, 26h, 27v, and 28h are transmission signals that alternately use V polarization and H polarization with frequencies that increase by 0.040 each.

[0087] Advantages and disadvantages of co-channel arrangement will be described with reference to Figures 8 and 9. As described above, co-channel arrangement is an arrangement pattern of frequency channels that uses V polarization and H polarization at the same frequency. On the other hand, interleaved arrangement is an arrangement pattern of frequency channels that uses V polarization and H polarization alternately. In other words, interleaved arrangement is an arrangement pattern of frequency channels that does not use V polarization and H polarization simultaneously at the same frequency.

[0088] Electromagnetic waves are waves that propagate parallel to the electric and magnetic fields, with the electric and magnetic fields perpendicular to each other. Radio waves whose electric field plane is perpendicular to the ground are V-polarized waves, and radio waves whose electric field plane is horizontal to the ground are H-polarized waves.

[0089] Wireless communication using co-channel allocation utilizes cross-polarized waves at the same frequency. Therefore, wireless communication using co-channel allocation can utilize more frequency channels than wireless communication that does not utilize cross-polarized waves at the same frequency. In other words, wireless communication using co-channel allocation has the advantage of being able to effectively utilize radio frequency resources.

[0090] On the other hand, wireless communication using co-channel allocation can be subject to interference in received signals due to leakage components from different polarizations. This interference is called cross-polarization interference. Wireless communication using co-channel allocation has the disadvantage that line quality can be degraded due to cross-polarization interference.

[0091] Cross Polarization Discrimination (XPD) is an index that indicates the magnitude of cross-polarized interference. The smaller the XPD value, the greater the interference from the opposite polarization. The smaller the XPD of a transmitting antenna, the more interference from the opposite polarization occurs when transmitting a signal. Therefore, if the XPD of a receiving antenna is smaller than the appropriate value, the signal will be subjected to interference from the opposite polarization when received, resulting in degradation of the received signal.

[0092] In wireless communications using cross-polarized waves at the same frequency, such as those using co-channel arrangements, the antenna's ability to separate V-polarized waves and H-polarized waves is called XPD performance. Because V-polarized waves and H-polarized waves at the same frequency cannot be separated by a filter or a demultiplexer, this new performance index is provided.

[0093] However, even if an antenna with high XPD performance separates the X and H polarizations, it is not possible to completely eliminate cross-polarization interference. Therefore, co-channeling is used in wireless communication systems where the amount of interference due to cross-polarization interference and interference noise other than cross-polarization interference is within an acceptable range and the required C / N ratio can be ensured overall. Co-channeling is widely used, especially in fixed microwave communications.

[0094] 10 is a diagram showing an example of XPIC processing. XPIC processing is a technique generally used in co-channel wireless communication systems for the purpose of eliminating cross-polarized interference. As described above, the wireless communication system according to this embodiment preferably performs XPIC processing.

[0095] First, the transmitting antenna 12 transmits a transmission signal 21v and a transmission signal 21h. The transmission signal 21v and the transmission signal 21h are transmitted using V-polarized waves and H-polarized waves at the same frequency.

[0096] The receiving antenna 32 receives the transmission signal 21v as a reception signal 41v. At this time, cross-polarized interference occurs due to poor XPD performance of the transmitting or receiving antenna, fading, or other factors. This cross-polarized interference generates a leakage signal 50v. The leakage signal 50v is a signal that leaks into the H polarization from the transmission signal 21v, which uses V polarization.

[0097] Similarly, the receiving antenna 32 receives the transmission signal 21h as a reception signal 41h. At this time, cross-polarized interference occurs due to poor XPD performance of the transmitting or receiving antenna, or due to the effects of fading, etc. This cross-polarized interference generates a leakage signal 50h. The leakage signal 50h is a signal that leaks into the V polarization from the transmission signal 21h that uses the H polarization.

[0098] The receiving device 30 performs XPIC processing using compensation signals generated based on the received signals 41v and 41h. The compensation signals may be generated by detecting the contamination signals 50v and 50h when the in-phase adjustment unit 34 performs signal synthesis processing, for example. As a result, the receiving device 30 can obtain received signals 81v and 81h from which the effects of the contamination signals 50v and 50h have been removed.

[0099] The wireless communication system according to this embodiment uses a co-channel arrangement to achieve long-distance transmission. However, wireless communication using the co-channel arrangement may cause C / N degradation due to cross-polarized interference. When C / N degradation occurs, bit errors generally occur in the wireless communication line.

[0100] In particular, in this embodiment, when C / N ratio degradation occurs, it becomes necessary to combine more received signals to compensate for free space propagation loss. In other words, when C / N ratio degradation occurs, it becomes difficult to realize long-distance transmission, which is an advantage of this embodiment.

[0101] As described above, XPIC processing has the effect of removing interference signals generated by cross-polarized interference in wireless communication using co-channel arrangement. Therefore, it is preferable that the wireless communication system according to this embodiment performs XPIC processing to minimize effects other than C / N degradation due to free space propagation loss.

[0102] 11 is a diagram illustrating signal waveform changes according to a second embodiment of the present disclosure. In the first embodiment, the plurality of frequency channels used for parallel transmission of each transmission signal are a group of adjacent frequency channels. This embodiment differs from the first embodiment in that the plurality of frequency channels used for parallel transmission of each transmission signal are set such that a certain interval is created between adjacent frequency channels.

[0103] Transmission waveform 3 is the waveform of six transmission signals transmitted by the transmitting antenna 12 according to this embodiment. Transmission waveform 3 is composed of waveforms of transmission signals 21v, 21h, 24v', 24h', 27v, and 27h. Note that these six transmission signals all have the same transmission power as transmission signal 21.

[0104] Transmission signal 21v shows the waveform of a transmission signal transmitted using V-polarized waves of frequency f1. Transmission signal 21h shows the waveform of a transmission signal transmitted using H-polarized waves of frequency f1. Similarly, transmission signal 24v' shows the waveform of a transmission signal transmitted using V-polarized waves of frequency f4, transmission signal 24h' shows the waveform of an H-polarized wave of frequency f4, transmission signal 27v shows the waveform of a V-polarized wave of frequency f7, and transmission signal 27h shows the waveform of an H-polarized wave of frequency f7.

[0105] Furthermore, the transmission signals 24v' and 24h' are degraded by the influence of an interference wave 8 that spreads over a wide frequency band.

[0106] The received waveform 5 is the waveform of a signal transmitted from the transmitting antenna 12 and received by the receiving antenna 32. The received waveform 5 is made up of the waveforms of the received signals 41v, 41h, 44v', 44h', 47v, and 47h.

[0107] The C / N ratio of the received signals 41v, 41h, 47v and 47h is 20 dB. The received signals 44v' and 44h' are degraded by the influence of the interference wave 8 that spreads over a wide frequency band.

[0108] The composite received waveform 6 is a waveform of a signal obtained by combining parts of the received signals that make up the received waveform 5 by the receiving device 30. Specifically, the composite received waveform 6 is a waveform of a signal obtained by combining received signals 41v, 41h, 47v, and 47h, which are received signals that have not been degraded by the influence of interference waves.

[0109] The composite received waveform 6 is composed of the waveform of a composite received signal 61. The C / N of the composite received signal 61 is 26 dB.

[0110] To illustrate the effects of the second embodiment of the present disclosure, a signal waveform change according to a comparative example is shown. Fig. 12 is a diagram illustrating signal waveform changes according to the comparative example. The comparative example illustrates an example in which a transmitting device 10, which is 60 km away from a receiving device 30, transmits six signals using a group of adjacent frequency channels.

[0111] The transmission waveform 3a is the waveform of six transmission signals transmitted by the transmitting antenna 12 according to this embodiment. The transmission waveform 3a is composed of the waveforms of transmission signals 21v, 21h, 22v', 22h', 23v', and 23h'. Note that all of these six transmission signals have the same transmission power as the transmission signal 21.

[0112] Transmission signal 21v shows the waveform of a transmission signal transmitted using V-polarized waves of frequency f1. Transmission signal 21h shows the waveform of a transmission signal transmitted using H-polarized waves of frequency f1. Similarly, transmission signal 22v' shows the waveform of a transmission signal transmitted using V-polarized waves of frequency f2, transmission signal 22h' shows the waveform of an H-polarized wave of frequency f2, transmission signal 23v' shows the waveform of a V-polarized wave of frequency f3, and transmission signal 23h' shows the waveform of an H-polarized wave of frequency f3.

[0113] Furthermore, the transmission signals 22v', 22h', 23v', and 23h' are degraded by the influence of an interference wave 8 that spreads over a wide frequency band.

[0114] The received waveform 5a is the waveform of a signal transmitted from the transmitting antenna 12 and received by the receiving antenna 32. The received waveform 5a is made up of the waveforms of the received signals 41v, 41h, 42v', 42h', 43v', and 43h'.

[0115] The C / N ratio of the received signals 41v and 42h is 20 dB. The received signals 42v', 42h', 43v', and 43h' are degraded by the influence of an interference wave 8 that spreads over a wide frequency band.

[0116] The composite received waveform 6a is a waveform of a signal obtained by combining parts of the received signals that make up the received waveform 5a by the receiving device 30. Specifically, the composite received waveform 6a is a waveform of a signal obtained by combining received signals 41v and 41h, which are received signals that are not degraded by the influence of interference waves.

[0117] The combined received waveform 6 is composed of the waveform of the combined received signal 61a, which has a C / N ratio of 23 dB.

[0118] Each transmission signal in this comparative example is transmitted using a group of adjacent frequency channels. Because the interference wave 8 spreads across a wide frequency band, it affects multiple frequency channels. As a result, four of the six transmission signals in this comparative example are degraded. In other words, only two received signals are not degraded by the interference wave.

[0119] Therefore, referring to Table 1, the C / N value of the combined received signal 61a according to this comparative example is 23 dB. In other words, the receiving device 30 according to this comparative example cannot compensate for the free space propagation loss when the wireless space distance from the transmitting device 10 is doubled to 60 km.

[0120] On the other hand, in this embodiment, each transmission signal is set so that there is a fixed interval between adjacent frequency channels. Therefore, even if the interference wave 8 spreads over a wide frequency band, it only affects one frequency channel. As a result, in this embodiment, only two of the six transmission signals are degraded. In other words, four reception signals are secured that are not degraded by the influence of the interference wave.

[0121] Therefore, referring to Table 1, the C / N value of the combined received signal 61 according to this embodiment is 26 dB. That is, the receiving device 30 according to this embodiment can compensate for free space propagation loss even when the radio space distance from the transmitting device 10 is doubled to 60 km.

[0122] As described above, in this embodiment, adjacent frequency channels are set to have a fixed interval between them, which makes it possible to reduce the influence of interference waves that spread across a wide frequency band.

[0123] Although the present disclosure has described an aspect in which a wireless communication system includes one receiving device, the present disclosure is not limited to this and may include a plurality of receiving devices having the same functions.Furthermore, the present disclosure has described an aspect in which a wireless communication system includes one transmitting device, the present disclosure is not limited to this and may include a plurality of transmitting devices having the same functions.

[0124] 10: Transmitting device 30: Receiving device 100: Wireless communication system

Claims

1. A wireless communication system comprising a transmitting device and a receiving device, wherein the transmitting device is configured to perform a process of transmitting the same signal in parallel over multiple frequency channels, and the receiving device is configured to perform a process of receiving the multiple parallel-transmitted signals as multiple received signals, a process of detecting any degraded received signals from the multiple received signals, and a process of combining only the undegraded received signals.

2. The wireless communication system according to claim 1, wherein said plurality of frequency channels utilize cross-polarized waves at the same frequency.

3. The wireless communication system of claim 1, wherein said plurality of frequency channels is a group of adjacent frequency channels.

4. A wireless communication system according to claim 1, wherein the plurality of frequency channels are set so that a fixed interval is created between adjacent frequency channels.

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