JP2011193383A - Radio communication apparatus and local signal processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform reception processing by generating a high-quality local signal which suppresses phase noise, without expanding circuit scale. <P>SOLUTION: A transmitting side transmits a OFDM-modulated radio signal by continuously inserting, in a time direction, a non-modulated pilot symbol into a specific frequency on a frequency axis for transmit data by means of a pilot symbol inserting unit 19. When a receiving side receives the OFDM-modulated radio signal into which a pilot symbol has been inserted similarly to the radio signal, a pilot symbol extracting circuit 14 extracts the pilot symbol from a modulation signal of the received radio signal, a PLL circuit 15 generates a local signal by making the extracted pilot symbol into a reference signal; and a mixer 13 frequency-converts the received radio signal using the local signal. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a wireless communication apparatus and a local signal processing method for performing wireless communication using OFDM (Orthogonal Frequency Division Multiplexing) modulation.

  In recent high-speed transmission communication, not only fixed communication such as a terrestrial digital wireless line but also mobile communication such as a mobile phone and semi-fixed communication such as BWA (Broad Band Wireless Access) are often used. Modulation schemes using the value modulation QAM scheme and the OFDM scheme are used. Recently, not only 64QAM but also 128QAM and 256QAM have been adopted. However, the transmission capacity can be increased by increasing the number of levels, while the interference between symbols becomes relatively large and effective throughput is increased. To affect. Among the causes of intersymbol interference, in addition to deterioration factors in radio channels (for example, fading) and deterioration factors in reception system circuits (for example, NF), there are a plurality of deterioration factors in the transmission system circuit as shown below. (Signal processing accuracy in digital processing unit, quadrature error of modulator, phase noise of local oscillator, nonlinear distortion of AMP, etc.). Of these, the effects of phase noise are mainly due to the performance of the components (phaser, VCO, etc.) that make up the local oscillator, and although improvements could be made by selecting components, this was reduced. There were few proposals for a transmission / reception architecture to do this.

  Conventionally, in order to improve the phase noise of a local oscillator, a low-noise phase shifter and a VCO with good phase noise characteristics are used, and a PLL circuit is designed with a loop filter design that matches the system (demodulator performance). It was. In addition, in order to improve the phase noise characteristics by means of circuit design, there are examples such as setting the cut-off frequency of the loop to a low range, but by doing so, tapping from outside (vibration etc.) There was a negative effect of being weakened by noise.

  Thus, as a known technique for improving phase noise, a technique using a double frequency converter called double conversion has been proposed (see, for example, Patent Documents 1 to 3).

JP 2006-229404 A JP-A-8-107315 Japanese Patent Laid-Open No. 5-206876

  However, the above-described method causes problems such as an increase in circuit configuration and complexity, and an increase in cost.

  The present invention has been made paying attention to the above circumstances, and its object is to generate a high-quality local signal in which phase noise is suppressed without increasing the circuit scale, and to perform reception processing, and It is to provide a local signal processing method.

  In order to achieve the above object, one aspect of the present invention comprises pilot symbol insertion means for continuously inserting unmodulated pilot symbols in a specific frequency on a frequency axis with respect to transmission data in the time direction. A transmitter that transmits a radio signal obtained by OFDM-modulating transmission data in which symbols are inserted, and a radio signal in which the pilot symbol is inserted and OFDM-modulated are received from the communication partner in the same manner as the radio signal, and the received radio signal Distributing means for distributing the first received radio signal to the second received radio signal, and pilot symbol extracting means for extracting and outputting the pilot symbol carrier from the distributed first received radio signal; Local signal generating means for generating a local signal using the carrier as a reference signal, The second received radio signal to provide a radio communication apparatus characterized by comprising: a receiving unit for frequency-converting by.

  According to another aspect of the present invention, there is provided a method for use in a wireless communication apparatus that transmits and receives a wireless signal to and from a communication partner, wherein a non-modulated pilot symbol is timed to a specific frequency on a frequency axis for transmission data. A pilot symbol insertion step of continuously inserting in the direction, transmitting a radio signal obtained by OFDM-modulating transmission data in which the pilot symbol is inserted, and inserting the pilot symbol from the communication partner in the same manner as the radio signal Receiving the received OFDM modulated radio signal, distributing the received radio signal into a first received radio signal and a second received radio signal, and the pilot from the distributed first received radio signal A pilot symbol extracting step of extracting and outputting a symbol carrier; and a local signal using the carrier as a reference signal. And a local signal generation step of generating a signal, said providing a local signal processing method characterized by frequency converting the second received radio signal by a local signal.

  Therefore, according to the present invention, it is possible to provide a radio communication apparatus and a local signal processing method for generating a high-quality local signal in which phase noise is suppressed without increasing the circuit scale and performing reception processing.

1 is a block diagram showing a configuration of a wireless communication device according to a first embodiment of the present invention. The figure which shows the example of pilot symbol insertion of 1st Embodiment. The figure which shows the example of pilot symbol insertion of 2nd Embodiment of this invention. The block diagram which shows the structure of the pilot symbol extraction circuit of the receiving side of 2nd Embodiment. The figure which shows the example of pilot symbol insertion of 3rd Embodiment of this invention. The block diagram which shows the structure of the pilot symbol insertion part of 3rd Embodiment. The flowchart which shows an example of operation | movement of the pilot arrangement | positioning control part of 3rd Embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
In the first embodiment according to the present invention, pilot symbols are allocated on a single fixed frequency (same subcarrier) and used for improving phase noise characteristics.

  FIG. 1 is a functional block diagram showing the configuration of the wireless communication apparatus according to the first embodiment. This wireless communication apparatus has a configuration including a transmission-side block and a reception-side block, but may have a transmission antenna and a reception antenna without sharing transmission / reception antennas.

  This wireless communication apparatus includes a modulation unit 1, a D / A converter 2, a mixer 3, a crystal oscillator 4, a PLL (Phase Locked Loop) circuit 5, a transmission filter 6, an amplification unit 7, and a pilot symbol insertion unit as transmission side blocks. 19 is provided. The reception side block includes a low noise amplifier 10, a divider 11, a delay unit 12, a mixer 13, a pilot symbol extraction circuit 14, a PLL circuit 15, a reception filter 16, an A / D converter 17, and a demodulation unit 18. Furthermore, an antenna duplexer 8 and an antenna 9 that are used together in transmission and reception are provided.

  The operation of the transmission side block will be described. At the time of transmission, the modulation unit 1 modulates transmission data using QAM (Quadrature Amplitude Modulation) and OFDM (Orthogonal Frequency Division Multiplexing) as modulation schemes. Pilot symbol insertion section 19 inserts pilot symbols into transmission data prior to OFDM modulation.

  Further, as will be described later, whether or not to insert a pilot symbol may be determined by referring to a predetermined determination criterion, such as an error state of data obtained by demodulating a radio signal received from the other party by the demodulator 18. Good. FIG. 2 shows an example of pilot symbol insertion according to the first embodiment. For example, as shown in FIG. 2, the pilot symbol insertion unit 19 inserts pilot symbol data that becomes a non-modulated carrier continuously at a single fixed frequency with respect to an OFDM modulated wave of transmission data.

  The signal modulated by the modulation unit 1 is converted into an analog signal by the D / A converter 2, mixed with a local signal generated by the PLL circuit 5 from the reference signal from the crystal oscillator 4 in the mixer 3, and RF (Radio frequency) ) Is converted to a signal. Further, the RF signal is amplified by the amplifier 7 via the transmission filter 6 and then transmitted from the antenna 9 via the antenna duplexer 8.

  Next, the receiving side block will be described. The radio signal received by the antenna 9 passes through the duplexer 8 and is amplified by the low noise amplification unit 10. The amplified radio signal is distributed by the distributor 11 to the delay device 12 and the pilot symbol extraction circuit 14 and output. The pilot symbol extraction circuit 14 extracts a pilot symbol carrier inserted on the transmission side from the radio signal and supplies it to the PLL circuit 15.

  The pilot symbol extraction circuit 14 is notified of the pilot symbol insertion condition from the pilot symbol insertion unit 19 or the extraction condition is set in advance, so that the radio signal in which the pilot symbol is inserted in the same manner as the transmitted radio signal. And then it is possible to extract pilot symbols, ie carriers.

  The PLL circuit 15 operates as a local oscillator that generates and outputs a local signal using the extracted pilot symbol carrier as a reference signal.

  A delay time corresponding to the processing time in the pilot symbol extraction circuit 14 and the PLL circuit 15 is added by the delay device 12 so that the other wireless signal branched is aligned with the reference signal output from the PLL circuit 15. 13 is input.

  Then, the local signal input to the mixer 13 and the radio signal are mixed and converted into a baseband signal to cancel the phase noise.

  That is, the local signal generated from the pilot symbol received from the other party and input to the mixer 13 and the radio signal are generated with the same phase noise at the same timing. Is not output.

  The baseband (OFDM) modulated signal from which the phase noise has been canceled is subjected to waveform shaping and removal of out-of-band components by the reception filter 16 and converted to a digital signal by the A / D converter 17. The demodulator 18 demodulates the received data by performing symbol determination for each subcarrier obtained by FFT (Fast Fourier Transform).

  As described above, in the first embodiment, a pilot symbol on an OFDM signal is converted into an unmodulated signal and inserted into a specific subcarrier on the transmitting side (base station side), and this is inserted on a receiving side (terminal side). By extracting and using as a reference signal of the local oscillator, the same phase noise component as that on the transmission side is held, and the phase noise of the local oscillator on the transmission side can be canceled by frequency conversion by the mixer.

  It is expected that the multi-level modulation system having a large influence of phase noise is applied to a line that requires a large capacity transmission particularly at a short distance. In such a case, as described above, by inserting and transmitting unmodulated pilot symbols continuously at a specific frequency, phase noise is canceled based on the pilot symbols on the receiving side, and throughput is reduced. Can be suppressed. In addition, phase noise can be canceled by transmission and reception without having double frequency conversion and without needing a circuit for generating and superimposing a fixed pilot signal. Therefore, according to the first embodiment, the phase noise characteristics can be improved efficiently without increasing the circuit scale.

(Second Embodiment)
In the second embodiment, a plurality of pilot symbols are inserted on the frequency axis. As a result, in the heterodyne system, it is possible to extract the pilot symbol on the receiving side and simplify the local oscillation unit.

  The configuration of the wireless communication apparatus of the second embodiment is the same as that of FIG. 1 shown in the first embodiment, except for the details of the pilot symbol extraction circuit 14 of the receiving side block. FIG. 3 shows an example of pilot symbol insertion according to the second embodiment.

  FIG. 4A shows an example of the configuration of the pilot symbol extraction circuit 14. The pilot symbol extraction circuit 14 includes a low-pass filter 41, a high-pass filter 42, and a mixer (frequency converter) 43. As shown in FIG. 3, the pilot symbols are preferably inserted on both sides for ease of design of a filter to be extracted. In the configuration of FIG. 4A, two pilot symbols prepared on the frequency axis are extracted using the low-pass filter 41 and the high-pass filter 42, and the difference frequency (f1-f2) is extracted by the mixer 43. The signal is extracted and supplied to the PLL circuit 15 on the receiving side, which is a local oscillator, and used as a reference signal.

  FIG. 4B shows another configuration example of the configuration of the pilot symbol extraction circuit 14. The pilot symbol extraction circuit 14 includes a low-pass filter 41, a high-pass filter 42, a selector 44, and a frequency divider (N / M) 45. In the configuration of FIG. 4B, the low-pass filter 41 and the high-pass filter 42 are switched by the selector 44, and either the pilot symbol of the frequency (f1) or the pilot symbol of the frequency (f2) is divided. 45 is supplied as a reference signal to the PLL circuit 15 via 45.

  The selection condition of the selector 44, the frequency division condition of the frequency divider 45, the pilot symbol insertion destination and the arrangement condition are associated in advance and stored in the memory in the pilot symbol insertion unit 19.

  By configuring in this way, it is possible to extract a pilot frequency difference on the receiving side by arranging a plurality of pilot symbols at specific frequency intervals, and for selecting and setting a specific frequency in a heterodyne system. A circuit becomes unnecessary.

(Third embodiment)
FIG. 5 is a conceptual diagram illustrating an example of pilot symbol insertion according to the third embodiment.

  In FIG. 5, pilot symbols used by each terminal (USER1 to USER4) are an example inserted according to a transmission region or a modulation scheme to which each terminal is assigned.

  In systems such as WiMAX and LTE, the transmission area and modulation method used for each receiving side (terminal) dynamically change according to the setting conditions at the time of link establishment. In other words, what transmission area and modulation method are used are separately negotiated and set by the communication control means (not shown) between the wireless communication apparatus and the terminal when the link is established. Then, pilot symbols (carriers) are extracted from radio signals received under the set conditions. The transmission area setting conditions correspond to the portions surrounded by dotted lines for each terminal (USER1 to USER4) in FIG. 5, and for example, modulation schemes such as 128QAM, 64QAM, and 8QAM are set in each enclosed portion. The These setting conditions are notified from the communication control means to the pilot symbol insertion unit 19 and the like.

  Thus, in the third embodiment, pilot symbols are arranged according to the transmission region and modulation scheme used by each terminal. Furthermore, the pilot symbol arrangement can be dynamically changed by monitoring the reception state on the reception side. The state on the receiving side can be known also on the transmitting side, for example, by having a function of monitoring CRC, ARQ, and the like.

  In a system (TDD system) having the same transmission / reception frequency, the distance to the terminal can be estimated based on the incoming power from the terminal, and the arrangement of pilot symbols can be controlled accordingly. For example, when the incoming power is high, it is possible to improve the throughput by selecting the high multilevel QAM method and using pilot symbols for phase noise cancellation.

  The configuration of the wireless communication apparatus of the third embodiment is the same as that of FIG. 1 shown in the first embodiment, except for the details of the pilot symbol insertion unit 19 of the transmission side block.

  For example, as shown in FIG. 5, a pilot symbol is inserted into a terminal USER4 that exists at a short distance and requires high throughput, while a pilot symbol exists at a terminal USER1 that exists at a long distance and requires low throughput. Is not inserted. The pilot symbol insertion unit 19 monitors received signal quality and selects whether or not to insert a pilot symbol in a radio signal transmitted to the communication partner, or what type of insertion is performed. This determined condition is also notified from the pilot symbol insertion unit 19 to the pilot symbol extraction circuit 14 as pilot setting information. The pilot symbol extraction circuit 14 extracts a pilot symbol from the received radio signal for each transmission region assigned to the communication partner based on the pilot setting information. The PLL circuit 15 generates a local signal from pilot symbols extracted for each transmission region. The mixer 13 mixes the local signal and the radio signal received together with the local signal to perform frequency conversion, thereby canceling the phase noise according to the communication condition of the communication partner.

  FIG. 6 shows a configuration example of the pilot symbol insertion unit 19 of the third embodiment. The pilot symbol insertion unit 19 includes a modulation scheme monitor unit 61, a CRC monitor unit 62, an ARQ retransmission count monitor unit 63, a terminal incoming power monitor unit 64, a pilot symbol arrangement control unit 65, a PHY layer generation unit 66, Is provided.

  Modulation method monitor unit 61, CRC monitor unit 62, ARQ retransmission count monitor unit 63, and terminal incoming power monitor unit 64 are functional means implemented in demodulation unit 18 of the receiving side block, and these monitor information is inserted into pilot symbols. It may be input to the unit 19.

  The pilot symbol arrangement control unit 65 performs pilot symbol arrangement control as follows, for example. FIG. 7 is a flowchart showing an example of the operation of the pilot arrangement control unit of the third embodiment.

  The pilot symbol arrangement control unit 65 first determines whether 64QAM or 256QAM or the like is selected as the multilevel modulation method in the modulation method monitoring unit 61 (step S1). In the determination of step S1, when a multi-level modulation method capable of taking a large amount of data such as 64QAM or 256QAM is selected and a high throughput is required, the terminal incoming power monitor unit 64 determines that the terminal incoming power is higher than the reference value. It is determined whether it is high (step S2).

  If it is determined in step S2 that the incoming power is relatively high, that is, it is determined that there is a terminal at a short distance, the error occurrence rate of the CRC monitor unit 62 and the number of retransmissions of the ARQ retransmission number monitor unit 63 set the respective reference values. It is determined whether it exceeds each (step S3). When the error occurrence rate and the number of retransmissions exceed the reference values in the determination of step S3 and errors occur frequently, it is determined as the influence of the phase noise, and the pilot symbol arrangement control unit 65 determines the effect of the phase noise. A pilot symbol is inserted into the subcarrier of the terminal (step S4).

  After that, the pilot symbol arrangement control unit 65 determines whether or not the ARQ retransmission number monitor unit 63 has decreased the number of ARQ retransmissions due to the insertion of the pilot symbol (step S5). First, the pilot symbol insertion position is optimized (step S6). In this optimization, for example, the order of placement destinations is determined in advance as insertion position candidates, and the operation of placing pilot symbols according to the order is repeated until it is determined in step S5 that the number of ARQ retransmissions has decreased.

  That is, according to the third embodiment, it is possible to dynamically arrange pilot symbols so as to optimize the throughput according to the communication state on the reception side (terminal side).

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

  DESCRIPTION OF SYMBOLS 1 ... Modulator, 2 ... D / A converter, 3 ... Mixer, 4 ... Crystal oscillator, 5 ... PLL circuit, 6 ... Transmission filter, 7 ... Amplifier, 8 ... Antenna duplexer, 9 ... Antenna, 10 ... Low noise amplifier , 11 ... distributor, 12 ... delay, 13 ... mixer, 14 ... pilot symbol extraction circuit, 15 ... PLL circuit, 16 ... reception filter, 17 ... A / D converter, 18 ... demodulation unit, 19 ... pilot symbol insertion unit , 41 ... low pass filter, 42 ... high pass filter, 43 ... mixer, 44 ... selector, 45 ... frequency divider, 61 ... modulation system monitor unit, 62 ... CRC monitor unit, 63 ... ARQ retransmission count monitor unit, 64: Terminal incoming power monitor unit, 65 ... Pilot symbol arrangement control unit, 66 ... PHY layer generation unit.

Claims (10)

Pilot symbol insertion means for continuously inserting unmodulated pilot symbols at a specific frequency on the frequency axis with respect to transmission data in the time direction is provided, and the transmission data into which the pilot symbols are inserted is OFDM (Orthogonal Frequency Division Multiplexing) A transmitter for transmitting the modulated radio signal;
Distribution means for receiving, from the communication partner, a radio signal in which the pilot symbols are inserted and OFDM-modulated in the same manner as the radio signal, and distributing the received radio signal to a first received radio signal and a second received radio signal Pilot symbol extraction means for extracting and outputting the pilot symbol carrier from the distributed first received radio signal, and local signal generation means for generating a local signal using the carrier as a reference signal, A wireless communication apparatus comprising: a receiving unit that converts the frequency of the second received wireless signal using the local signal.   The radio communication apparatus according to claim 1, wherein the pilot symbol insertion unit inserts the pilot symbols at a plurality of frequencies on a frequency axis. The modulation signal includes the pilot symbols corresponding to a plurality of frequencies on the frequency axis,
The radio communication apparatus according to claim 2, wherein the pilot symbol extraction unit extracts a difference frequency corresponding to the pilot symbol.   The radio communication apparatus according to claim 1, wherein the pilot symbol insertion means inserts a pilot symbol according to a transmission area and a modulation scheme of the communication partner.   The pilot symbol insertion means monitors at least one state of a modulation scheme used by the terminal, incoming power, error occurrence rate, and number of retransmissions, and compares the monitoring data with a predetermined reference to determine pilot symbols. The wireless communication apparatus according to claim 4, wherein it is determined whether or not to insert. A method used in a wireless communication device that transmits and receives wireless signals to and from a communication partner,
A pilot symbol insertion step of continuously inserting unmodulated pilot symbols at a specific frequency on a frequency axis with respect to transmission data in a time direction, and transmitting the data into which the pilot symbols are inserted into OFDM (Orthogonal Frequency Division Multiplexing) ) Transmit modulated radio signal,
Distribution of receiving the pilot symbol inserted and the OFDM modulated radio signal from the communication partner in the same manner as the radio signal, and distributing the received radio signal to the first received radio signal and the second received radio signal A pilot symbol extracting step of extracting and outputting the pilot symbol carrier from the distributed first received radio signal, and a local signal generating step of generating a local signal using the carrier as a reference signal. Then, the local signal processing method, wherein the second received radio signal is frequency-converted by the local signal.   The local signal processing method according to claim 6, wherein the pilot symbol insertion step inserts the pilot symbols at a plurality of frequencies on a frequency axis. The modulation signal includes the pilot symbols corresponding to a plurality of frequencies on the frequency axis,
The local signal processing method according to claim 7, wherein the pilot symbol extracting step extracts a difference frequency corresponding between the pilot symbols.   The local signal processing method according to claim 6, wherein the pilot symbol insertion step inserts a pilot symbol according to a transmission region and a modulation scheme of the communication partner.   The pilot symbol insertion step monitors at least one state of a modulation scheme used by the terminal, incoming power, error occurrence rate, and number of retransmissions, and compares the monitoring data with a predetermined reference to compare pilot symbols with pilot symbols. 10. The local signal processing method according to claim 9, wherein whether or not to insert is determined.

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