Wireless communication systems and radios

Abstract

We propose a technology that can effectively suppress inter-channel interference when OFDM-based transmission and reception are performed between opposing wireless devices. [Solution] The radio 300 sets the center frequency of the radio used for transmission and reception under a channel arrangement in which subchannels are orthogonal to each other throughout the entire bandwidth including its assigned channel and adjacent channels, such that the orthogonality between the subchannels in its own channel and the subchannels in adjacent channels is maintained.

Description

Technical Field

[0001] The present invention relates to a wireless communication system that performs transmission and reception in an OFDM (Orthogonal Frequency Division Multiplexing) manner between wireless devices facing each other.

Background Art

[0002] Conventionally, a wireless communication system in which one-to-one or one-to-N wireless devices perform transmission and reception facing each other has been put into practical use. Such a wireless communication system is used, for example, as a relay line or an entrance line for broadband transmission applications. In addition, in order to suppress the influence of reflected waves, it is used in applications of long-distance high-speed transmission using the OFDM (Orthogonal Frequency Division Multiplexing) method.

[0003] In this specification, the channel assigned to the wireless device that is the subject of explanation is referred to as the "own channel", the channel adjacent to the own channel is referred to as the "adjacent channel", and the channel further adjacent to the adjacent channel is referred to as the "next adjacent channel".

[0004] Examples of the prior art in the technical field related to the present invention include the following. For example, in Patent Document 1, a base station device measures the reception level from an arbitrary subscriber base station and transmits it to the subscriber base station. The subscriber base station stores an optimal reception level in advance, and adjusts the transmission power according to the difference between the reception level transmitted from the base station device and the optimal reception level.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Problems with conventional wireless communication systems will be explained with reference to Figures 1 and 2. Figure 1 shows an example configuration of a radio 100 used in a conventional wireless communication system. In a conventional wireless communication system, the radios 100 shown in the figure are arranged in a line-of-sight environment so as to face each other in a one-to-one or one-to-many configuration, and transmission and reception are performed between the opposing radios 100 using OFDM wireless technology.

[0007] The radio 100 comprises an antenna 110, a radio unit 120, and a baseband (BB) unit 130. The radio unit 120 includes a transmitting unit 121 and a receiving unit 122 that perform transmission and reception processing, and a transmitting / receiving switching unit 123 that performs a transmit / receive switching operation to selectively connect the transmitting unit 121 or the receiving unit 122 to the antenna 110. The BB unit 130 includes a modulation unit 135 and a demodulation unit 136 that perform modulation and demodulation processing related to primary modulation, an IFFT unit 133 and an FFT unit 134 that perform IFFT (Inverse Fast Fourier Transform) and FFT (Fast Fourier Transform) processing of OFDM signals related to secondary modulation, and a GI insertion unit 131 and a GI deletion unit 132 that perform GI (Guard Interval) insertion and deletion processing. Furthermore, the radio 100 is equipped with a timing synchronization unit 141 for controlling the timing of the transmit / receive switching by the transmit / receive switching unit 123.

[0008] Figure 2 shows an example of the channel arrangement and frequency spectrum of an OFDM signal in a conventional wireless communication system. In Figure 2, five channels, CH0 to CH4, are shown as an example of the channel arrangement and frequency spectrum of an OFDM signal.

[0009] In conventional OFDM systems, each radio implements OFDM within the bandwidth of its own channel. That is, each subchannel constituting the OFDM signal is orthogonal only within its own channel, and orthogonality with the subchannels of adjacent channels is not ensured. Therefore, to suppress interference with adjacent channels, it was necessary to secure a wide guard band between adjacent channels, as shown in Figure 2. However, securing a wide guard band between channels degrades frequency utilization efficiency.

[0010] Furthermore, even with a guard band in place, interference due to leakage power cannot be avoided. Therefore, as a countermeasure against leakage power, it was necessary to ensure sufficient separation distance between radio units. However, ensuring separation distance between radio units hinders the installation and operation of multiple wireless communication systems in the same area. In addition, long-distance transmission requires high transmission power and high antenna gain, which in turn generates large amounts of leakage power. Therefore, achieving long-distance transmission presents the problem of needing to ensure separation distance over a wider area.

[0011] Furthermore, while wireless communication systems like those described above often utilize the quasi-millimeter wave band (3GHz to 30GHz) or millimeter wave band (30GHz to 300GHz) for high-speed transmission over a wide bandwidth, these frequency bands have a problem in that they are susceptible to attenuation of radio waves due to moisture during precipitation such as rain and snow. To address this problem, a method is being considered that maintains a constant communication channel capacity by changing the channel bandwidth to compensate for radio wave attenuation caused by precipitation, etc. However, changing the channel bandwidth may disrupt the orthogonality of subchannels, raising concerns that interference with surrounding systems may increase in such cases.

[0012] As described above, conventional wireless communication systems have a problem in that widening the guard band to suppress interference with adjacent channels degrades frequency utilization efficiency. In addition, increasing the transmit power and antenna gain increases leakage power, and it becomes necessary to ensure separation distances by considering leakage power not only from the same channel but also from adjacent channels and the next adjacent channel, which makes it difficult to install a large number of radios and operate the system efficiently.

[0013] This invention has been made in view of the above-mentioned conventional circumstances, and aims to propose a technology that can effectively suppress inter-channel interference when OFDM type transmission and reception is performed between opposing wireless devices. [Means for solving the problem]

[0014] A wireless communication system according to one aspect of the present invention is a wireless communication system that transmits and receives between opposing wireless devices using OFDM wireless technology, characterized in that the wireless device sets the center frequency of the wireless used for transmission and reception such that the orthogonality between the subchannels in its own channel and the subchannels in the adjacent channel is maintained, under a channel arrangement in which the subchannels are orthogonal to each other throughout the entire bandwidth including the channel assigned to it and the adjacent channel.

[0015] Furthermore, in the above-described wireless communication system, the radio may arrange zero subchannels at both ends of its own channel and set the center frequency to the frequency of the middle of the subchannel group excluding the zero subchannel within its own channel.

[0016] Furthermore, in the above-described wireless communication system, the radio may be configured to synchronize the transmission and reception timing with other radios using adjacent channels.

[0017] Also, in the above wireless communication system, the radio may receive signals in a band including its own channel and adjacent channels, extract sub-channels within its own channel from the received signals, and perform demodulation processing.

[0018] Also, in the above wireless communication system, the radio may have a function of changing the bandwidth of its own channel according to changes in the communication environment, and when changing the bandwidth of its own channel, reset the center frequency so that the orthogonality between the sub-channels within its own channel and the sub-channels within the adjacent channels is maintained.

[0019] A radio according to another aspect of the present invention is a radio that performs transmission and reception by OFDM wireless between other radios facing each other. Under a channel arrangement that makes sub-channels orthogonal to each other over the entire band including its own channel assigned to itself and adjacent channels adjacent thereto, the center frequency of the wireless used for transmission and reception is set so that the orthogonality between the sub-channels within its own channel and the sub-channels within the adjacent channels is maintained.

Effect of the Invention

[0020] According to the present invention, it is possible to effectively suppress inter-channel interference when performing OFDM transmission and reception between radios facing each other.

Brief Description of the Drawings

[0021] [Figure 1] It is a diagram showing a configuration example of a radio used in a conventional wireless communication system. [Figure 2] It is a diagram showing an example of channel arrangement and frequency spectrum of an OFDM signal in a conventional wireless communication system. [Figure 3] It is a diagram showing a configuration example of a radio used in a wireless communication system according to an embodiment of the present invention. [Figure 4] It is a diagram showing an example of channel arrangement and frequency spectrum of an OFDM signal in a wireless communication system according to an embodiment of the present invention. [Figure 5] It is a diagram showing an example of the change in the frequency spectrum by simple bandwidth expansion for attenuation compensation due to precipitation. [Figure 6] It is a diagram showing an example of the change in the frequency spectrum by improved bandwidth expansion for attenuation compensation due to precipitation.

Mode for Carrying Out the Invention

[0022] An embodiment of the present invention will be described with reference to the drawings. FIG. 3 shows a configuration example of a wireless device 300 used in a wireless communication system according to an embodiment of the present invention. The wireless communication system in this example is arranged in a line-of-sight environment such that wireless devices 300 as shown face each other one-to-one or one-to-N, and is configured to perform transmission and reception wirelessly by the OFDM method between the opposing wireless devices 300.

[0023] The radio 300 includes an antenna 310, a radio unit 320, a BB unit 330, a timing control unit 340, and a subchannel orthogonalization control unit 350. The radio unit 320 includes a transmitting unit 321 and a receiving unit 322 that perform transmission and reception processing, a transmit / receive switching unit 323 that selectively switches between the transmitting unit 321 and the receiving unit 322 to connect to the antenna 310, and a center frequency control unit 351 that performs control processing of the center frequency of the radio used for transmission and reception. The BB unit 330 includes a modulation unit 335 and a demodulation unit 336 that perform modulation and demodulation processing related to primary modulation, an IFFT unit 333 and an FFT unit 334 that perform IFFT and FFT processing of the OFDM signal related to secondary modulation, a GI insertion unit 331 and a GI deletion unit 332 that perform insertion and deletion processing of GI, a zero / subchannel insertion unit 352 that performs insertion processing of zero / subchannels during transmission, and an adjacent channel deletion unit 353 that performs deletion processing of adjacent channels and zero / subchannels during reception. The timing control unit 340 includes a timing synchronization unit 341 that performs timing synchronization processing related to transmission and reception switching by the transmit / receive switching unit 323, and a peripheral device timing extraction unit 342 that performs processing to extract the transmission and reception timing of peripheral devices (other radios). The subchannel orthogonalization control unit 350 is incorporated into the radio unit 320 and the BB unit 330, and includes the aforementioned center frequency control unit 351, subchannel insertion unit 352, and adjacent channel deletion unit 353.

[0024] In this example of a wireless communication system, the channel arrangement is such that the subchannels are orthogonal to each other across the entire frequency band allocated to the system (i.e., the frequency band containing multiple channels), and each radio 300 uses the subchannels that fit within its own channel for its OFDM signal. In the following explanation, the radio 300 being described may be referred to as "radio 300A," and the other radio 300 that transmits and receives from radio 300A may be referred to as "radio 300B."

[0025] First, let's explain the operation of the 300A radio during transmission. The transmission data from radio 300A to radio 300B is input to the BB unit 330. The transmission data is converted into symbol values ​​that have undergone modulation processing such as QAM (Quadrature Amplitude Modulation) by the modulation unit 335 of the BB unit 330 and placed in the frequency domain. The IFFT unit 333 of the BB unit 330 performs IFFT processing on the signal resulting from the modulation by the modulation unit 335, converting the signal from the frequency domain to the time domain. During this IFFT processing, the IFFT unit 333 receives a data sequence corresponding to the frequency bandwidth of its own channel from the modulation unit 335, and zeros are input from the zero / subchannel insertion unit 352 of the subchannel orthogonalization control unit 350 to the zero / subchannel positions at both ends of its own channel.

[0026] Zero subchannels serve to maintain orthogonality between channels and act as guard bands; they are not used for signal transmission or reception. Subchannels that span across channels or are in the vicinity of them become zero subchannels. The number of zero subchannels between channels is arbitrary; for example, 2 to 3 zero subchannels (zero subcarriers in Figure 4) are placed between channels. More zero subchannels can be placed between channels to suppress inter-channel interference, but it should be noted that this will reduce frequency utilization efficiency.

[0027] The signal after IFFT processing by the IFFT unit 333 is input to the radio unit 320 as a transmission signal after GI insertion by the GI insertion unit 331 of the BB unit 330 to avoid interference with delayed multipath. The transmission signal is then frequency-converted to the radio frequency and amplified to an appropriate level by the transmission unit 321 of the radio unit 320. The frequency conversion by the transmission unit 321 is performed to match the center frequency of the radio to the frequency set by the center frequency control unit 351 of the subchannel orthogonalization control unit 350.

[0028] Here, the center frequency of the radio is set to the frequency of the middle of the group of subchannels within the channel, excluding the zero subchannel. More specifically, the center frequency of the radio is set to the peak frequency of the subchannel closest to the center of the channel's bandwidth, or the intermediate frequency between the two subchannels closest to the center of the channel's bandwidth. As a result, if the bandwidth of the channel is an integer multiple of the bandwidth of the subchannels, the center frequency of the radio coincides with the frequency of the center of the channel's bandwidth; otherwise, the center frequency of the radio and the frequency of the center of the channel's bandwidth do not coincide. By performing this control, it is possible to maintain the orthogonality of subchannels between channels before and after frequency conversion.

[0029] The transmission signal output from the transmitter 321 is input to the antenna 310 via the transmit / receive switching unit 323 and transmitted from the antenna 310 into space. The signal transmitted from the radio 300A reaches the radio 300B via the propagation path and is received by the radio 300B.

[0030] Next, we will explain the operation of the 300A radio receiver during reception. The transmission signal from radio 300B reaches radio 300A via the propagation path and is received by the antenna 310 of radio 300A. Here, antenna 310 is configured to receive signals in the bandwidth including its own channel and adjacent channels. Therefore, the received signal may include not only signals from its own channel but also signals from adjacent channels.

[0031] The received signal is input to the receiving unit 322 via the transmit / receive switching unit 323, where it is amplified to an appropriate level and its frequency is converted to the baseband. The frequency conversion by the receiving unit 322 is performed in the same way as the frequency conversion by the transmitting unit 321, by adjusting the center frequency of the radio to the frequency set by the center frequency control unit 351 of the subchannel orthogonalization control unit 350. This maintains the orthogonality of subchannels between channels before and after frequency conversion.

[0032] The received signal output from the receiver unit 322 has its GI removed by the GI removal unit 332 of the BB unit 330, and then undergoes FFT processing in the FFT unit 334 of the BB unit 330 to convert the time-domain signal into a frequency-domain signal. Through this FFT processing, the time-domain signal is converted into a group of frequency-domain subchannels corresponding to adjacent channels and the current channel, including the zero subchannel. Here, the adjacent channel removal unit 353 of the subchannel orthogonalization control unit 350 removes or replaces with zero the zero subchannels at both ends of the current channel and the subchannels corresponding to adjacent channels, thereby extracting only the subchannel group excluding the zero subchannel within the current channel, and disabling the adjacent channels and zero subchannels. This makes it possible to separate and reduce the influence of power leaked into adjacent channels and zero subchannels, which were mixed in the time domain, in the frequency domain.

[0033] The signal after FFT processing is input to the demodulation unit 336 of the BB unit 330 and the peripheral device timing extraction unit 342 of the timing control unit 340. The demodulation unit 336 performs demodulation processing on the signal after FFT processing, corresponding to the modulation processing by the modulation unit 335. This makes it possible to demodulate the transmission data from radio 300B to radio 300A.

[0034] The peripheral device timing extraction unit 342 extracts the synchronization signal of the adjacent channel from the signal after FFT processing and outputs the synchronization signal to the timing synchronization unit 341. Based on the synchronization signal of the adjacent channel obtained by the peripheral device timing extraction unit 342, the timing synchronization unit 341 controls the radio unit 320 so that the transmission and reception timing is synchronized with other radios using the adjacent channel. That is, the transmit / receive switching unit 323 of the radio unit 320 switches the connection of the transmit unit 321 or the receive unit 322 to the antenna 310 according to the instructions of the timing synchronization unit 341. This improves the accuracy of the orthogonality of subchannels between channels. It is also possible to synchronize by other methods; for example, each radio 300 may be equipped with a GNSS (Global Navigation Satellite System) receiver to synchronize the time.

[0035] Figure 4 shows an example of the channel arrangement and frequency spectrum of the OFDM signal in the wireless communication system of this example. As shown in the figure, the wireless communication system of this example employs a channel arrangement in which subchannels are orthogonal to each other across the entire bandwidth encompassing multiple channels (CH0 to CH4). In Figure 4, 20 subchannel groups are assigned to each of CH0 to CH4. In addition, two zero subchannels are inserted between CH0 and CH1 and between CH3 and CH4, and three zero subchannels are inserted between CH1 and CH2 and between CH2 and CH3.

[0036] When subchannels are orthogonalized across the entire bandwidth encompassing multiple channels, the bandwidth of a channel may not be an integer multiple of the bandwidth of its subchannels. In radios assigned such channels, the center frequency used for transmission and reception is set to a frequency different from the frequency at the center of the channel's bandwidth. In the example in Figure 4, for channels other than CH2, i.e., channels CH0, CH1, CH3, and CH4, the center frequency used for transmission and reception does not coincide with the frequency at the center of the channel's bandwidth (the channel center in the diagram).

[0037] As described above, in the wireless communication system of this example, the radio 300 sets the center frequency of the radio used for transmission and reception under a channel arrangement in which subchannels are orthogonal to each other throughout the entire bandwidth including its assigned channel and adjacent channels, such that the orthogonality between the subchannels in its own channel and the subchannels in adjacent channels is maintained. More specifically, the radio 300 places zero subchannels at both ends of its own channel and sets the center frequency of the radio to the frequency of the middle of the group of subchannels excluding the zero subchannels within its own channel.

[0038] This allows for the maintenance of subchannel orthogonality not only within the same channel but also with adjacent channels, effectively suppressing interference with adjacent channels and the next adjacent channel. Consequently, the required spacing between radios can be shortened, increasing the density of radio installations and enabling more efficient system operation. Furthermore, it allows for more effective utilization of finite frequency resources.

[0039] Next, as a variation of the wireless communication system in this example, we will describe a configuration that expands the bandwidth to compensate for attenuation due to precipitation. As mentioned above, when using the quasi-millimeter wave band or millimeter wave band for high-speed transmission over a wide bandwidth, these frequency bands have the problem of being susceptible to attenuation of radio waves due to moisture during precipitation such as rain and snow. To address this problem, a method has been considered in which the channel bandwidth is changed in accordance with changes in the communication environment to maintain a constant communication channel capacity in order to compensate for the attenuation of radio waves caused by precipitation, etc.

[0040] However, simply expanding the channel bandwidth can disrupt the orthogonality of subchannels, raising concerns about increased interference with surrounding systems. Figure 5 shows an example of frequency spectrum changes due to simple bandwidth expansion for precipitation attenuation compensation. In the example in Figure 5, CH2 is simply expanded to twice the bandwidth of CH3, but the subchannels within CH2' after bandwidth expansion lose their orthogonality with the original CH2 and CH3. Therefore, even if the subchannels of the original CH1 and CH2 are orthogonal, and the subchannels of the original CH3 and CH4 are orthogonal, the subchannels within CH2' after bandwidth expansion will lose their orthogonality with the adjacent subchannels in CH1 and CH4. Thus, simply expanding the channel bandwidth by twice, four times, etc., changes the arrangement of subchannels before and after bandwidth expansion, disrupting the orthogonality between subchannels in the system.

[0041] Therefore, the radio 300' according to this modified example not only has a function to change the channel bandwidth in accordance with changes in the communication environment in order to compensate for radio wave attenuation caused by rain, etc., but is also configured to readjust the center frequency of the radio used for transmission and reception so that the orthogonality between the subchannels in the same channel and the subchannels in the adjacent channel is maintained when the bandwidth of the own channel is changed. That is, after bandwidth expansion, the radio 300' readjusts the center frequency of the radio to the frequency of the group of subchannels excluding the zero subchannel in the same channel and performs transmission and reception. At this time, the number of zero subchannels placed at both ends of the own channel may be increased or decreased as needed.

[0042] Figure 6 shows an example of frequency spectrum changes due to improved bandwidth expansion for precipitation attenuation compensation. In the example in Figure 6, CH2 is expanded to twice the bandwidth of CH3, and the radio center frequency is readjusted so that the orthogonality between the subchannels in the expanded CH2' and the adjacent subchannels in CH1 and CH4 is maintained. This makes it possible to suppress the effects of channel bandwidth expansion.

[0043] Here, channel bandwidth changes can be controlled by various methods, and the method is not limited. For example, the radio 300' may change the channel bandwidth in response to instructions from the user. As another example, the radio 300' may measure the communication quality of the received signal and change the channel bandwidth if a change in the communication environment is detected from the results. As yet another example, the radio 300' may calculate the attenuation of radio waves in the transmission path from the change in the level of received power and change the channel bandwidth if a change in the communication environment is detected from the results. As yet another example, the radio 300' may provide information such as communication quality and radio wave attenuation to a central control station and change the channel bandwidth in response to instructions from the central control station.

[0044] Although embodiments of the present invention have been described above, these embodiments are merely illustrative and do not limit the technical scope of the present invention. The present invention can take many other embodiments, and various modifications such as omissions and substitutions can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention as described herein, and are included in the scope of the invention and its equivalents as described in the claims.

[0045] Furthermore, the present invention can be provided not only as the devices described above or as systems composed of such devices, but also as methods executed by these devices, programs for a processor to realize the functions of these devices, and storage media for storing such programs in a computer-readable manner. [Industrial applicability]

[0046] This invention can be used in a wireless communication system that performs OFDM-type transmission and reception between opposing wireless devices. [Explanation of symbols]

[0047] 100: Radio, 110: Antenna, 120: Radio unit, 121: Transmitter, 122: Receiver, 123: Transmitter / Receiver switching unit, 130: BB unit, 131: GI insertion unit, 132: GI deletion unit, 133: IFFT unit, 134: FFT unit, 135: Modulation unit, 136: Demodulation unit, 141: Timing synchronization unit, 300: Radio, 310: Antenna, 320: Radio unit, 321: Transmitter, 322: Receiver, 323: Transmitter / Receiver switching unit, 330: BB unit, 331: GI insertion unit, 332: GI deletion unit, 333: IFFT unit, 334: FFT unit, 335: Modulation unit, 336: Demodulation unit, 340: Timing control unit, 341: Timing synchronization unit, 342: Peripheral timing extraction unit, 350: Subchannel orthogonalization control unit, 351: Center frequency control unit, 352: Zero subchannel insertion unit, 353: Adjacent channel deletion unit

Claims

1. In a wireless communication system that transmits and receives data between opposing wireless devices using the OFDM method, The wireless communication system is characterized in that, under a channel arrangement in which subchannels are orthogonal to each other throughout the entire bandwidth including the channel assigned to the wireless device and adjacent channels, the center frequency of the wireless used for transmission and reception is set such that the orthogonality between the subchannels in the channel and the subchannels in adjacent channels is maintained.

2. In the wireless communication system according to claim 1, The wireless communication system is characterized by having zero subchannels at both ends of its own channel, and setting the center frequency to the frequency of the middle subchannel group excluding the zero subchannel within its own channel.

3. In the wireless communication system according to claim 1, The wireless communication system is characterized by the wireless device synchronizing the transmission and reception timing with other wireless devices using adjacent channels.

4. In the wireless communication system according to claim 1, The wireless communication system is characterized by receiving signals in a bandwidth that includes its own channel and adjacent channels, and extracting subchannels within its own channel from the received signals and performing demodulation processing.

5. In the wireless communication system according to any one of claims 1 to 4, The wireless device has a function to change the bandwidth of its own channel in response to changes in the communication environment, and when the bandwidth of its own channel is changed, the center frequency is reset so that the orthogonality between the subchannels within its own channel and the subchannels within the adjacent channel is maintained.

6. In a radio that transmits and receives signals using OFDM radio with other opposing radios, A radio characterized by setting the center frequency of the radio used for transmission and reception, under a channel arrangement in which subchannels are orthogonal to each other throughout the entire bandwidth including the channel assigned to itself and adjacent channels, such that the orthogonality between the subchannels in the own channel and the subchannels in adjacent channels is maintained.

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