JP2016006939A - Radio communication system, radio communication device, and radio communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio communication device capable of suppressing an impact of adjacent channel interference in OFDM transmission.SOLUTION: In a radio communication system for communicating in accordance with OFDM transmission, an adjacent system causing interference adjusts transmission timing of the system so that delay in reception timing of a signal of the system relative to reception timing of an existing system is within a GI period (a). In addition, it adjusts the period of FFT processing so that the FFT processing of the system is performed within one frame period of the existing system (b).

Description

  The present invention relates to a wireless communication system, a wireless communication apparatus, and a wireless communication method.

  LTE (Long Term Evolution) Release 8 (Rel. 8), which is a wireless communication system standardized by 3GPP (3rd Generation Partnership Project), for example, communicates using a maximum bandwidth of 20 MHz. Can be done.

  In LTE-A (Long Term Evolution-Advanced), which is an advanced version of LTE, the bandwidth supported by LTE is a basic unit in order to realize further high-speed transmission while ensuring backward compatibility with LTE. Carrier Aggregation (CA: Carrier Aggregation) technology that uses multiple bundled component carriers (CC) at the same time is adopted, and wide bandwidth transmission of up to 100 MHz using 5 CC (20 MHz width x 5) can be realized. is there.

  In a communication system using an OFDM (Orthogonal Frequency Division Multiplexing) communication system that is used not only for LTE and LTE-A but also for terrestrial digital broadcasting and the like, such as convolutional coding and turbo coding. Error correction coding is performed, and reliability is ensured by frequency diversity gain. Here, when there are two independent OFDM wireless communication systems, there is a report on a technique for providing a guard band between adjacent channels in order to avoid mutual inter-channel interference (see Patent Document 1).

By the way, in recent years, the demand for mobile communication traffic has increased rapidly with the spread of highly functional portable terminals such as smartphones. In order to cope with such an increase in demand for mobile communication traffic, it is necessary to develop new frequency bands that have not been used so far, in addition to improving frequency utilization efficiency by new wireless communication methods.
For example, as one means for improving frequency utilization efficiency, there is an effective utilization of a frequency band that is free in space and time.

  In general, in a relatively low frequency band (for example, 3 GHz or less) suitable for mobile communication, it is very difficult to secure a continuous bandwidth that can newly accommodate high-speed wireless transmission.

  On the other hand, vacant frequency bands are discretely present between the bands of the existing communication systems. Although the usage situation fluctuates temporally and geographically, there is a possibility that a bandwidth capable of realizing high-speed wireless transmission can be secured if these small vacant frequency bands are flexibly bundled and used.

  For this purpose, unlike existing communication systems, a communication technique that can flexibly cope with transmission band division and transmission in a plurality of frequency bands is required. As one of such communication technologies, Non-Patent Document 1 discloses a wideband discrete OFDM communication system.

  The broadband discrete OFDM communication system is based on OFDM that multiplexes and transmits information on a plurality of relatively narrow-band carriers (subcarriers) that are orthogonal to each other. In the transceiver, IFFT (Inverse Fast Fourier Transform) ) / FFT (Fast Fourier Transform) to perform division for each subcarrier by digital signal processing. At that time, as described above, subcarriers are arranged and transmitted in free frequency bands that exist discretely and are demodulated by bundling those subcarriers in a receiver, thereby performing the above-described multiple discrete free spaces. It has a feature that signal transmission using a frequency band can be performed relatively easily.

  FIG. 14 is a diagram showing the basic concept of such discrete OFDM.

  In discrete OFDM, by arranging subcarriers so as not to interfere with signals of other existing communication systems, communication can be performed without affecting the existing system. As a result, a wireless communication system having a wide required transmission bandwidth can be accommodated by bundling and using discrete free frequencies even in a situation where a bandwidth cannot be secured in a specific frequency band.

JP 2012-169699 A Specification

Keiji Takasaki, Goro Hasegawa, Tatsuo Shibata, "Study on Wideband Discrete OFDM Technology", IEICE Technical Report, vol. 113, no. 57, SR2013-16, pp. 83-89, May 2013

  However, on the receiving side, both the signal of the own system and the signal of the existing system are received together, so that the OFDM signal of the own system to be transmitted and the signal of the existing wireless system adjacent to the signal are non-orthogonal or asynchronous on the frequency axis. If the received signal is received in the state of (2), the spectrum of the existing wireless system signal spreads after FFT and appears as interference in the own system band. This is called “adjacent channel interference”.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a radio communication system, a radio communication apparatus, and a radio that can suppress the influence of adjacent channel interference in OFDM transmission. It is to provide a communication method.

  According to one aspect of the present invention, there is provided a wireless communication apparatus in a wireless communication system that performs communication using an orthogonal frequency division multiplex system, wherein orthogonal frequencies are spread over a frequency region in which the existing wireless system and the respective frequency bands used by the own system are mixed. A receiving unit for receiving a subcarrier signal by division multiplexing transmission, a timing detecting unit for detecting the symbol timing of the existing system, and a Fourier transform in the frame period of the existing system according to the detected symbol timing A timing adjustment unit for adjusting the timing so as to perform, a Fourier transform unit that performs Fourier transform on the received signal from the reception unit at the adjusted timing, and a demodulation process on the output of the Fourier transform unit And a demodulation / decoding processing unit.

  Preferably, the frame in the own system has the same frame length as the frame in the existing system, and the guard interval period is also the same, and the reception timing of the frame in the own system is more guard than the reception timing of the frame in the existing system. Reception is performed in a state of being delayed by a period shorter than the interval period.

  Preferably, the wireless communication system is a system that performs communication by discrete orthogonal frequency division multiplex transmission in which subcarriers are discretely arranged and transmitted in an empty frequency band that is not used in an existing wireless system based on the discrete orthogonal frequency division multiplex method. is there.

  According to another aspect of the present invention, there is provided a wireless communication apparatus in a wireless communication system that performs communication using an orthogonal frequency division multiplexing method, an encoded modulation processing unit that performs modulation processing on a subcarrier of a transmission signal, An inverse Fourier transform unit that performs inverse Fourier transform on the subcarriers modulated in the frequency band to be used; a guard interval addition unit that forms a transmission frame by adding a guard interval to the inverse Fourier transformed signal; The timing information acquisition unit for acquiring the symbol timing information of the existing system on the reception side, and the reception timing of the frame of the own system is the reception timing of the frame of the existing system on the reception side according to the acquired symbol timing. Delayed by a period shorter than the guard interval period from the timing Comprising a transmission timing adjusting section for adjusting a transmission timing and a transmission unit for transmitting the frame by an orthogonal frequency division multiplexing transmission.

  Preferably, the wireless communication system is a system that performs communication by discrete orthogonal frequency division multiplex transmission in which subcarriers are discretely arranged and transmitted in an empty frequency band that is not used in an existing wireless system based on the discrete orthogonal frequency division multiplex method. is there.

  According to still another aspect of the present invention, a wireless communication system that performs communication by orthogonal frequency division multiplex transmission includes a first wireless communication device, and the first wireless communication device performs error correction coding processing on a transmission signal. And an encoded modulation processing unit that performs modulation processing on the subcarrier, an inverse Fourier transform unit that performs inverse Fourier transform on the subcarrier modulated in the frequency band used by the own system, and an inverse Fourier transform. A guard interval adding unit that forms a transmission frame by adding a guard interval to the received signal, a timing information acquiring unit for acquiring symbol timing information of an existing system that is adjacent in frequency on the receiving side, and Depending on the symbol timing, on the receiving side, the frame reception timing of the local system A transmission timing adjustment unit for adjusting the transmission timing so as to be delayed by a period shorter than the guard interval period, and a transmission unit for transmitting a frame by orthogonal frequency division multiplexing transmission. The second wireless communication apparatus further includes a second wireless communication apparatus, and the second wireless communication apparatus receives a subcarrier signal by orthogonal frequency division multiplex transmission over a frequency region in which frequency bands used by the existing wireless system and the own system are mixed. Receiver, a timing detector for detecting the symbol timing of the existing system, and a timing for adjusting the timing to perform Fourier transform in the frame period of the existing system according to the detected symbol timing Adjusted for received signal from adjusting unit and receiving unit A Fourier transform unit for performing a Fourier transform in timing, and performs demodulation processing on the output of the Fourier transform unit, and a demodulation decoding unit that performs error correction decoding on the demodulated signal.

  Preferably, the wireless communication system is a system that performs communication by discrete orthogonal frequency division multiplex transmission in which subcarriers are discretely arranged and transmitted in an empty frequency band that is not used in an existing wireless system based on the discrete orthogonal frequency division multiplex method. is there.

  According to the present invention, it is possible to suppress transmission quality deterioration due to the influence of interference while enabling wireless transmission and reception in a wide band.

It is a functional block diagram which shows the example of a structure of the radio | wireless communications system 1000 of this Embodiment. It is a figure for demonstrating the concept of the interference avoidance at the time of OFDM communication systems adjoining. It is a figure explaining the adjacent channel interference in case the signal of an own system and the signal of the existing radio system are non-orthogonal on a frequency axis. It is a figure which shows the distance from the subcarrier of an existing radio | wireless system (on a frequency), and the magnitude | size of adjacent channel interference. It is a conceptual diagram explaining the conditions which make an own system signal orthogonalize to the existing system signal. It is a conceptual diagram for demonstrating the guard interval (GI: Guard Interval) in an OFDM signal. It is a conceptual diagram for demonstrating the condition where interference is avoided with respect to multi-fading by a guard interval. It is a figure for demonstrating the influence when a timing is later than an existing system. It is a figure for demonstrating the influence when the timing of an existing system is earlier than an own system. In this Embodiment, it is a conceptual diagram explaining control of the reception timing of the signal of the own system with respect to the signal of the existing system. 2 is a functional block diagram for explaining a configuration of a wireless communication apparatus 2000. FIG. It is a functional block diagram for demonstrating the structure of radio | wireless communication apparatus 2000 'which is a modification of the radio | wireless communication apparatus of the receiving side. It is a functional block diagram which shows the structure of the radio | wireless communication apparatus 3000 of the transmission side of a radio | wireless communications system. It is a figure which shows the basic concept of discrete OFDM.

  Hereinafter, configurations of a wireless communication system and a wireless communication apparatus according to an embodiment of the present invention will be described. In the following embodiments, components and processing steps given the same reference numerals are the same or equivalent, and the description thereof will not be repeated unless necessary.

In the following description, a discrete OFDM system will be described as a specific example. However, even in a normal OFDM system that is not discrete, a similar effect can be obtained if there is an adjacent existing system without taking a guard band. Basic configuration of the embodiment)
FIG. 1 is a functional block diagram illustrating an example of a configuration of a wireless communication system 1000 according to the present embodiment.

  In the following configuration, although not particularly limited, each function related to transmission is described as being based on the LTE standard.

  Referring to FIG. 1, in radio communication system 1000, since the frequency band to be transmitted / received is extremely wide, high frequency units corresponding to the respective frequencies are arranged on both the transmission side and the reception side. FIG. 1 shows a configuration in which four systems are arranged as an example. However, a configuration using a broadband high-frequency device that collectively covers the corresponding frequency band may be used.

  In addition, the downlink (downlink) band from the base station to the user terminal and the uplink (uplink) band from the user terminal to the base station are independently secured in a frequency band (FDD: frequency It is possible to employ a (division multiplexing) configuration or a configuration in which the downlink and uplink share the same frequency band and are used at different times (TDD: time division multiplexing).

  On the other hand, since the target frequency is different for each high-frequency unit, the quality of the communication path such as propagation attenuation and Doppler frequency is greatly different.

  Therefore, first, on the transmission side of the wireless communication system 1000, a channel encoder 110 is provided in order to increase frequency use efficiency by transmission according to the quality of the communication path. Each of the channel encoders 110 performs processing such as transmission path error correction coding such as a Turbo code, and interleaving. This channel encoder performs processing such as adaptive modulation according to the communication quality of the target empty frequency band.

  The signal after processing by the channel encoder 110 is provided to the modulation unit 112. Modulation section 112 includes subcarrier mapper 120 and modulator 1124.

  In wireless communication system 1000, IFFT / FFT processing is used to perform signal mapping and demapping to orthogonal subcarriers. A number of IFFT / FFT circuits capable of processing a signal with a predetermined bandwidth are allocated to one high-frequency unit covering a predetermined band, and each point of the IFFT / FFT circuit corresponds to a subcarrier with a predetermined bandwidth. . In addition, the structure which processes using the IFFT / FFT circuit which divided | segmented the subcarrier across several high frequency units collectively may be sufficient. Alternatively, a configuration may be used in which a signal within a band covered by one high-frequency unit is processed by being divided by a plurality of IFFT / FFT circuits.

  The subcarrier mapper 120 arranges modulation data at IFFT points corresponding to subcarriers to be transmitted among the subcarriers of the high frequency unit on the transmission side (for example, base station apparatus).

  Modulator 1124 performs predetermined digital modulation processing on the transmission signal subcarrier mapped by subcarrier mapper 120. For example, QPSK, 16QAM, 64QAM, etc. can be used.

  Thereafter, the IFFT units 130-1 to 130-4 execute IFFT processing for each high-frequency unit, and the D / A converters 132-1 to 132-4 respectively convert the digital signals into analog signals.

  The outputs of the D / A converters 132-1 to 132-4 are mixed with the IF signal from the IF oscillator 133 and the mixers 134-1 to 134-4, and the local oscillators 140-1 to 140-1 corresponding to each frequency band are mixed. The output of 140-4 is mixed by the mixers 136-1 to 136-4.

  In the radio communication system 1000, the target radio frequency (RF) is, for example, 170 MHz to 1 GHz, and it is difficult to ensure an intermediate frequency (IF) that is normally set lower than RF due to the configuration of the radio transceiver. It is. Therefore, in FIG. 1, a configuration using an IF higher than RF is used. A direct conversion method that does not use IF may be employed.

  The functional block 142 is a functional block that executes a function as an FDD duplexer when the FDD is mounted, and executes a function as a TDD switch when the TDD is mounted.

  The signal from block 142 is sent out from antenna 150.

  On the other hand, on the receiving side, the signal received by the antenna 200 is subjected to a function as an FDD duplexer or TDD switch by the function block 202, and then output from the local oscillators 204-1 to 204-4 corresponding to each frequency band. And the mixers 210-1 to 210-4.

  Further, the outputs of the mixers 210-1 to 210-4 are multiplied by the IF signal from the IF oscillator 211 by the mixers 212-1 to 212-4, and analog / digital conversion is performed by the A / D converters 214-1 to 214-4. (A / D conversion) and FFT processing, which is the inverse processing of IFFT processing, is executed in the FFT units 220-1 to 220-4.

  Signals separated for each subcarrier from FFT sections 220-1 to 220-4 are provided to demodulation section 240.

  Demodulator 240 includes demodulator 2402 and subcarrier demapper 230.

  The demodulator 2402 executes a demodulation process that is an inverse process of the process of the modulator 1124.

  For the signal from the demodulator 2402, the subcarrier demapper 230 extracts the data of the corresponding FFT point by the inverse processing of the subcarrier mapper 120. Further, the channel decoder 250 performs deinterleaving processing and error correction decoding processing.

  The configuration on the uplink side is basically the same as the configuration on the downlink side, but the illustration is simplified in FIG.

The feedback channel modulation encoder 280 modulates a control signal that feeds back the reception status of the reception side (for example, mobile station apparatus) to the base station side in order to perform control such as adaptive modulation, and the feedback channel demodulation decoder 180 Such a feedback control signal is demodulated.
(Outline of subcarrier arrangement of this embodiment)
FIG. 2 is a diagram for explaining the concept of interference avoidance when OFDM communication systems are adjacent to each other.

  As shown in FIG. 2 (a), in the wideband discrete OFDM (Wideband Non-Contiguous OFDM: WNC-OFDM) communication system, the free system in the frequency domain of the OFDM signal of the existing system is used to The discrete OFDM signal is communicated.

  In this way, when OFDM systems are arranged side by side in adjacent frequency bands, the OFDM signal has a large side lobe, so if the adjacent system and the subcarriers of its own system are too close to each other, they interfere with each other.

  For this reason, as described in Patent Document 1, it is common to provide a guard band between the adjacent system and the subcarrier of the own system so as not to interfere with each other as shown in FIG. is there. However, with such a configuration, the band utilization efficiency is reduced by the guard band.

Therefore, in the present embodiment, as shown in FIG. 2C, the own system signal is orthogonalized to the existing system signal, so that the guard band can be reduced and the signal can be arranged. With such a configuration, an unused frequency that could not be used in FIG. 2B can be used.
(General theory of interference effects between OFDM signals)
In the following, in order to realize the subcarrier arrangement of the present embodiment, a general theory of the interference effect between OFDM signals will be described as a premise of the description of the configuration in which the own system signal is orthogonalized to the existing system signal.

  FIG. 3 is a diagram for explaining adjacent channel interference when the signal of the own system and the signal of the existing wireless system are non-orthogonal on the frequency axis.

  FIG. 3A shows waveforms on the frequency of the subcarrier of the system and the subcarrier of the existing wireless system, and FIG. 3B shows the case where the adjacent channel interval is changed based on the subcarrier width. The calculation result of the magnitude | size of adjacent channel interference is shown. In FIG. 3B, the calculation is performed assuming that the signal of the own system and the signal of the existing wireless system are synchronized.

  Except for special cases where the frequency separation between the local system and the existing wireless system is a natural number multiple of the subcarrier interval of the local system, the subcarrier interval is the same between the local system and the existing system, and both are synchronized. After the FFT processing of the OFDM receiver, the signal spectrum of the existing wireless system spreads to the corresponding subcarriers of the own system, and interference influence occurs.

  Even in the case where the existing system is a single carrier, interference effects are similarly caused when the existing system is not synchronized or orthogonal to the subcarriers of the own system.

  FIG. 4 is a diagram illustrating the distance (in frequency) from the subcarrier of the existing wireless system and the magnitude of adjacent channel interference.

  In FIG. 4, the horizontal axis represents the subcarrier number (index) of the own system counted from the adjacent channel, and the vertical axis represents the adjacent channel interference level.

  In addition, the parameter indicates the magnitude of the offset of the frequency position between the own system and the existing system when the subcarrier width is used as a unit. f_sc represents a subcarrier interval. For example, 0 indicates that the frequency positions of the own system and the existing system overlap (the interference is the largest), and 7f_sc / 8 indicates a subcarrier interval of 7 / 8 indicates that it is shifted by a width of 8 times.

  As shown in FIG. 4, it can be seen that subcarriers adjacent to the existing system are particularly affected by interference.

Therefore, when OFDM communication is performed by arranging subcarriers of the own system in the vacant frequency of the signal of the existing wireless system, reception quality of the subcarriers to be transmitted is uneven depending on the arrangement of the existing system and the subcarriers of the own system Thus, the effect of the error correction code cannot be sufficiently obtained, and the transmission characteristics are greatly deteriorated.
(Method to orthogonalize own system signal to existing system signal)
Based on the above assumptions, a method for orthogonalizing the own system signal to the existing system signal will be described.

  FIG. 5 is a conceptual diagram for explaining conditions for orthogonalizing the own system signal to the existing system signal.

  As shown in FIG. 5A, when the OFDM signal of the own system and the OFDM signal of another existing system are adjacent in the frequency domain, in order to orthogonalize the own system signal to the existing system signal The following conditions need to be met:

i) Matching of subcarrier intervals (of own system signal and existing system signal) ii) Satisfying orthogonal relationship on frequency axis iii) Matching of symbol length iv) Matching of symbol timing Among these, i) to iii) Is determined as a parameter of the communication method, and therefore it is necessary to make the existing system adjacent to the local system match in advance.
For example, if your system finds a temporally and spatially available frequency band and uses it temporarily, you can receive and analyze an existing system signal, Obtain the parameter information of the existing system, such as by reading it from the own terminal or in an accessible server, and match the parameters of the own system to start using the radio frequency. Etc. are possible.

However, as shown in FIG. 5 (b), the deviation of the symbol timing in the condition iv) changes depending on the difference in distance from the own system base station and the existing system base station, and the timing is adjusted with high accuracy. Generally difficult.
(Effect of symbol timing shift (offset))
As described with reference to FIG. 5, it is difficult to match the symbol timing between the own system and the existing system. Then, next, the influence when the symbol timing is shifted in this way will be described.

  FIG. 6 is a conceptual diagram for explaining a guard interval (GI) in an OFDM signal.

  In general, the guard interval is provided by copying the rear part of a symbol signal having a predetermined length (tg) and adding it to the head part.

  In this way, by performing FFT processing on the receiving side, it is possible to remove interference of delayed waves having a GI length or less by the guard interval.

  FIG. 7 is a conceptual diagram for explaining a situation where interference is avoided with respect to multi-fading by the guard interval.

  That is, FIG. 7 illustrates a situation of avoiding interference when a signal from the same transmitting station causes a shift in arrival time at the receiving station due to the influence of multipath in the transmission path.

  In the receiving station, it is assumed that two delayed waves (delayed wave 1 and delayed wave 2) having different delay times arrive with respect to the preceding wave for multipath fading.

  First, in the receiving station, the OFDM demodulator performs FFT processing in the FFT interval (original symbol interval) excluding the GI of the preceding wave. Between the preceding wave and the delayed wave 1, the delay time is equal to or shorter than the GI length, and the signal waveform of the delayed wave 1 is cyclic in the FFT section of the preceding wave, so that interference by the delayed wave 1 does not occur.

  On the other hand, since the delay time exceeds the GI length between the preceding wave and the delayed wave 2, the signal waveform of the delayed wave 2 is not cyclic in the FFT section of the preceding wave. Occurs.

  FIG. 8 is a diagram for explaining the influence when the timing of the existing system is later than that of the own system.

  In FIG. 8, in particular, as shown in FIG. 5, it is assumed that the use frequency of the own system and the use frequency of the existing system are adjacent to each other. It is assumed that it is close to the frequency and exists in the FFT band of its own system receiver.

  As shown in FIG. 8A, when the timing of the existing system is later than that of the own system and the FFT processing is performed for the symbol period in the own system, the timing offset between the existing system and the own system is within the GI period. Since the FFT interval signal waveform is cyclic, there is no interference with the system.

  On the other hand, as shown in FIG. 8B, when the timing of the existing system is later than that of the own system, when the FFT processing is performed for the symbol period in the existing system, the deviation of the incoming symbol timing between the existing system and the own system. Even within the GI period, since the FFT section signal waveform is not cyclic, interference with the existing system occurs. This is because the period of performing the FFT process of the existing system extends to the signal of the subsequent next symbol, and interference occurs.

  FIG. 9 is a diagram for explaining the influence when the timing of the existing system is earlier than that of the own system.

  As shown in FIG. 9 (a), when the existing system is earlier in timing than the own system, when the FFT processing is performed for the symbol period in the own system, the difference in symbol timing between the existing system and the own system is the GI period. Even within the range, since the FFT interval signal waveform is not cyclic, interference with the existing system occurs. This is because the period during which the FFT processing of the own system extends to the signal of the next symbol following the existing system causes interference.

  On the other hand, as shown in FIG. 9B, when the existing system is earlier in timing than the own system, when the FFT processing is performed for the symbol period in the existing system, the timing offset between the existing system and the own system is within the GI period. Then, since the FFT interval signal waveform is cyclic, interference with the existing system does not occur.

As described above with reference to FIGS. 8 and 9, when the reception timing of the signal of the existing system and the signal of the own system is deviated, interference occurs in the FFT processing in the own system or the existing system.
(Timing control of this embodiment)
FIG. 10 is a conceptual diagram illustrating the control of the reception timing of the signal of the own system with respect to the signal of the existing system in the present embodiment.

  As a premise, it is assumed that both the own system and the existing system that communicate in adjacent frequency bands transmit signals by OFDM transmission. In the following description, it is assumed that the subcarrier interval is the same between the local system and the existing system, the frame length is the same, and the symbol length and the GI period are the same. At this time, it is assumed that the subcarriers of the own system are arranged in a free area where there are no subcarriers of the existing system so as to be orthogonal to the subcarriers of the existing system in terms of frequency.

  As shown in FIG. 10A, by controlling the transmission timing from the own system, with respect to the reception timing in the existing system, the delay of the reception timing of the signal of the own system with respect to the reception timing of the existing system is within the GI period. The transmission timing of the signal from the own system is adjusted so that

  On the other hand, under the condition that the timing of the transmission signal from the own system is controlled as shown in FIG. 10A, in the reception process in the own system, the period during which the FFT process is performed is the end of the symbol period of the existing system. Adjust to finish before. By adjusting in this way, the FFT processing for the own system is executed within one frame period of the existing system, and is not affected by signals from subsequent frames of the existing system.

In this way, by adjusting the transmission timing on the own system side and the FFT processing period in the reception processing of the own system, the interference to the existing system is suppressed, and the interference from the existing system to the own system is also suppressed. It becomes possible.
(Receiver configuration)
FIG. 11 is a functional block diagram for explaining the configuration of wireless communication apparatus 2000.

  FIG. 11 shows the configuration on the receiving side of the configuration of the wireless communication system shown in FIG. 1, particularly focusing on the processing of the baseband signal.

  In the configuration of FIG. 1, the configuration is divided into four systems as an example, but in FIG. 11, the configuration is one system as an example. Referring to FIG. 11, radio communication apparatus 2000 includes an RF unit 206 that performs high-frequency signal processing of a signal received by antenna 200, and an A / D converter 214 that converts an analog signal from RF unit 206 into a digital signal. including.

  The FFT unit 220 removes the guard interval GI from the digitally converted OFDM symbol, and adjusts the timing for performing the FFT processing as described with reference to FIG. 10, and the FFT timing adjustment unit 2202 from the A / D converter 214. The existing system timing detection unit 2206 for detecting the symbol timing of the existing system based on the signal and the FFT processing on the OFDM symbol from which the guard interval is removed to convert the time domain signal into the frequency domain signal FFT processing unit 2204.

  Demodulator 240 includes demodulator 2402 and subcarrier demapper 230. Demodulator 2402 includes a plurality of demappers that perform demodulation processing for each subcarrier on the output from FFT processing section 2204. Each demapper performs demapping on the corresponding subcarrier signal.

  The subcarrier demapper 230 includes a used subcarrier extraction unit 2404.

  The used subcarrier extraction unit 2404 extracts, as a serial signal, a signal corresponding to the own system subcarrier used for the demodulated NC-OFDM transmission output from the demapper.

  As for “signal corresponding to own system subcarrier used for NC-OFDM transmission”, for example, a frequency use information acquisition unit (not shown) uses the own system subcarrier information used for NC-OFDM transmission and the existing radio system. The subcarrier information corresponding to a certain frequency can be obtained. Here, for such “subcarrier information”, for example, corresponding information is acquired by decoding a cognitive pilot channel or a cognitive control channel. Here, the cognitive pilot channel (CPC) is a channel that transmits frequency use information of a specific part of a band in a certain region. A CPC may be placed in that particular band or in an internationally determined frequency band outside that band. For example, the following documents disclose CPC.

Reference: ITU-R M.2225: Introduction to Cognitive Radio Systems in the Land Mobile Service (Section 4.1.1.2)
Note that the demapper may be configured such that only the one corresponding to the own system subcarrier used for NC-OFDM transmission operates.

  The channel decoder 250 receives, as an input, a deinterleaver 2502 that performs deinterleave processing, which is reverse processing of interleaving, on the bit signal output from the used subcarrier extraction unit 2404, and after error correction. And a CRC decoder 2506 that performs error detection by decoding a CRC (cyclic redundancy check) code.

By adopting such a configuration of the radio communication device 2000 on the receiving side, as shown in FIG. 10B, by controlling the timing of the FFT processing of the own system, the existing system for the communication signal of the own system can be controlled. It is possible to suppress the interference.
(Modification of receiver configuration)
FIG. 12 is a functional block diagram for explaining a configuration of a wireless communication device 2000 ′ which is a modification of the receiving-side wireless communication device.

  11 differs from the configuration shown in FIG. 11 in order to detect the symbol timing of the signal of the existing system, independently of the system for receiving the signal of the own system, the antenna 201, the RF unit 207, and the A / D. The point is that the converter 215 is provided.

  The existing system timing detection unit 2206 detects the symbol timing of the existing system based on the signal from the A / D converter 215.

  Since other configurations are the same as those shown in FIG. 11, the same portions are denoted by the same reference numerals, and description thereof will not be repeated.

The configuration of the wireless communication device 2000 ′ in FIG. 12 can also achieve the same effects as the reception-side wireless communication device 2000 shown in FIG.
(Configuration of transmitter)
Hereinafter, the configuration of the transmission side (for example, the base station side) in the wireless communication system shown in FIG. 1 will be described.

  FIG. 13 is a functional block diagram illustrating a configuration of the wireless communication device 3000 on the transmission side of the wireless communication system.

  Referring to FIG. 13, in radio communication apparatus 3000, channel encoder 110 transmits CRC code 1102 that performs CRC coding on transmission data, and a Turbo code or the like for the CRC-coded signal. An error correction encoder 1104 that performs path error correction coding and an interleaver 1106 that performs interleaving processing are included.

  The signal processed by the channel encoder 110 is given to the modulation unit 112, and the subcarrier mapper 120 of the modulation unit 112 modulates the modulated data to the IFFT point corresponding to the subcarrier to be transmitted among the subcarriers of the high frequency unit on the transmission side. Place. At this time, for example, the subcarrier mapper 120 executes modulation data arrangement (subcarrier mapping) based on information from a frequency use information acquisition unit (not shown).

  That is, the frequency usage information acquisition unit is used in the own system subcarrier information and the existing radio system used for NC-OFDM transmission, for example, in the same manner as the frequency usage information acquisition unit (not shown) described in the configuration on the receiver side. The subcarrier information corresponding to the frequency is acquired.

  The used subcarrier adjustment unit 1122 of the subcarrier mapper 120 selects a subcarrier to be subjected to symbol mapping based on own system subcarrier information used for NC-OFDM transmission acquired from the frequency usage information acquisition unit.

  Modulator 1124 of modulation section 112 includes a plurality of mappers that perform modulation processing for each subcarrier. Each mapper performs modulation (mapping) on the constellation for the corresponding subcarrier signal.

  IFFT section 130 generates an IF symbol by adding a guard interval GI to an IFFT processing section 1302 that executes IFFT processing on the output of modulator 1124 and a time domain signal output from IFFT processing section 1302 Based on the symbol timing of the existing system acquired by the GI adding unit 1304 and the existing system timing information acquiring unit 1306, the transmission timing of the transmission frame of the own system is adjusted as shown in FIG. Transmission timing adjustment unit 1308.

  In the wireless communication apparatus 3000 on the transmission side, the existing system timing information acquisition unit 1306 can acquire information related to the symbol timing of the existing system, for example, as feedback information from the receiver side of the own system. . Alternatively, the existing system timing information acquisition unit 1306 is more preferably configured to acquire information related to the symbol timing of the existing system, for example, as feedback information from the receiver operating as the receiver of the existing system. Further, in the wireless communication device 3000 on the transmission side, information on the frame length of the existing system and the length of the GI period is not particularly limited. For example, the information may be held in advance as a table for each frequency band used, Or it is good also as a structure which provides a frequency use information acquisition part and this frequency use information acquisition part acquires with the use frequency of the existing system.

  The D / A converter 132 performs conversion from a digital signal to an analog signal for the signal from the GI adding unit 1304, and the RF unit 135 converts the output of the D / A converter 132 into a high frequency signal. Thus, a transmission signal is transmitted from the antenna 150.

  With the configuration as described above, it is possible to suppress interference from the OFDM signal of the existing system and to suppress interference from the own system to the existing system while improving frequency utilization efficiency.

  Embodiment disclosed this time is an illustration of the structure for implementing this invention concretely, Comprising: The technical scope of this invention is not restrict | limited. The technical scope of the present invention is shown not by the description of the embodiment but by the scope of the claims, and includes modifications within the wording and equivalent meanings of the scope of the claims. Is intended.

  110 channel encoder, 112 modulation unit, 120 subcarrier mapper, 130-1 to 130-4 IFFT unit, 132-1 to 132-4 D / A converter, 133, 211 IF oscillator, 134-1 to 134-4, 136-1 to 136-4, 210-1 to 210-4, 212-1 to 212-4 Mixer, 140-1 to 140-4, 204-1 to 204-4 Local oscillator, 150, 200 Antenna, 180 Feedback Channel demodulation decoder, 214-1 to 214-4 A / D converter, 220-1 to 220-4 FFT unit, 230 subcarrier demapper, 240 demodulator, 250 channel decoder, 280 feedback channel modulation encoder, 1000 wireless communication System, 1302 IFFT processing unit, 1304 GI adding unit, 13 8 transmission timing adjusting section, 1306 the existing system timing information acquisition unit, 2000,200.1,2000.2,3000 wireless communication device, 2202 FFT timing adjuster, 2204 FFT processing unit, 2206 an existing system timing detection unit.

Claims (7)

A wireless communication apparatus in a wireless communication system that communicates by orthogonal frequency division multiplexing,
A receiving unit for receiving a subcarrier signal by the orthogonal frequency division multiplex transmission over a frequency region in which respective frequency bands used by an existing wireless system and the own system are mixed;
A timing detector for detecting the symbol timing of the existing system;
In accordance with the detected symbol timing, a timing adjustment unit for adjusting timing so as to perform Fourier transform in a frame period of the existing system;
A Fourier transform unit that performs Fourier transform on the received signal from the receiving unit at the adjusted timing;
A radio communication apparatus comprising: a demodulation / decoding processing unit that performs demodulation processing on an output of the Fourier transform unit.   The frame in the own system has the same frame length as the frame of the existing system and the same guard interval period, and the reception timing of the frame of the own system is higher than the reception timing of the frame of the existing system. The wireless communication apparatus according to claim 1, wherein reception is performed in a state of being delayed by a period shorter than a guard interval period.   The wireless communication system is a system that performs communication by discrete orthogonal frequency division multiplex transmission in which subcarriers are discretely arranged and transmitted in a vacant frequency band that is not used in an existing wireless system based on a discrete orthogonal frequency division multiplex system. The wireless communication apparatus according to claim 1 or 2. A wireless communication apparatus in a wireless communication system that communicates by orthogonal frequency division multiplexing,
An encoded modulation processing unit that performs modulation processing on a subcarrier of a transmission signal;
An inverse Fourier transform unit that performs an inverse Fourier transform on a subcarrier modulated in a frequency band used by the system;
A guard interval adding unit that forms a transmission frame by adding a guard interval to the inverse Fourier transformed signal;
A timing information acquisition unit for acquiring symbol timing information of the existing system on the receiving side;
According to the acquired symbol timing, on the receiving side, the transmission timing is such that the reception timing of the frame of the own system is delayed by a period shorter than the guard interval period from the reception timing of the frame of the existing system. A transmission timing adjustment unit for adjusting
A wireless communication apparatus comprising: a transmission unit for transmitting the frame by the orthogonal frequency division multiplexing transmission.   The wireless communication system is a system that performs communication by discrete orthogonal frequency division multiplex transmission in which subcarriers are discretely arranged and transmitted in a vacant frequency band that is not used in an existing wireless system based on a discrete orthogonal frequency division multiplex system. The wireless communication apparatus according to claim 4. A wireless communication system for performing communication by orthogonal frequency division multiplex transmission,
A first wireless communication device, wherein the first wireless communication device comprises:
An encoded modulation processing unit that performs error correction coding processing on a transmission signal and modulation processing on subcarriers;
An inverse Fourier transform unit that performs an inverse Fourier transform on a subcarrier modulated in a frequency band used by the system;
A guard interval adding unit that forms a transmission frame by adding a guard interval to the inverse Fourier transformed signal;
A timing information acquisition unit for acquiring information of symbol timing of existing systems that are adjacent in frequency on the receiving side;
According to the acquired symbol timing, on the receiving side, the transmission timing is such that the reception timing of the frame of the own system is delayed by a period shorter than the guard interval period from the reception timing of the frame of the existing system. A transmission timing adjustment unit for adjusting
A transmission unit for transmitting the frame by the orthogonal frequency division multiplexing transmission,
The wireless communication device further includes a second wireless communication device, and the second wireless communication device includes:
A receiving unit for receiving the subcarrier signal by the orthogonal frequency division multiplexing transmission over a frequency region in which the existing wireless system and the frequency band used by the own system are mixed;
A timing detector for detecting the symbol timing of the existing system;
In accordance with the detected symbol timing, a timing adjustment unit for adjusting timing so as to perform Fourier transform in a frame period of the existing system;
A Fourier transform unit that performs Fourier transform on the received signal from the receiving unit at the adjusted timing;
A radio communication system, comprising: a demodulation decoding processing unit that performs demodulation processing on the output of the Fourier transform unit and performs error correction decoding on the demodulated signal.   The wireless communication system is a system that performs communication by discrete orthogonal frequency division multiplex transmission in which subcarriers are discretely arranged and transmitted in a vacant frequency band that is not used in an existing wireless system based on a discrete orthogonal frequency division multiplex system. The wireless communication system according to claim 6.