JP2010268396A - Diversity reception device and diversity reception method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the load of arithmetic processing on a DSP etc., and also to reduce a phase adjusting means in size and cost by adjusting phases of the reception signals when synthesis processing on a plurality of reception signals input from a plurality of antennas is performed. <P>SOLUTION: An intensity-phase decision circuit 19 monitors signal intensities of a master signal and a slave signal, and when selection switching between the master signal and the slave signal is determined, the determined selection switching is suspended until a π/4-DQPSK demodulation block 22 which demodulates the master signal and the slave signal whose phases are corrected by phase shift circuits 13 and 14, reports the timing of a symbol decision point acquired on the basis of a preamble. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a diversity receiving apparatus and a diversity receiving method for receiving a radio signal. More specifically, the present invention relates to a diversity reception technique in which an optimum radio signal is selectively selected as a main signal serving as a phase reference from radio signals received from a plurality of antennas.

  When receiving a radio signal, the transmission quality of the received signal deteriorates due to fading caused by fluctuations in transmission characteristics. In particular, in a receiving apparatus such as a land mobile radio station, since a radio signal from a base station arrives from a plurality of transmission paths (multipath) reflected and refracted by surrounding buildings or the like, fading by multipath The received signal fluctuates greatly under the influence of

  In order to overcome such a phenomenon, a diversity reception system is known in which a plurality of antennas are set apart by a predetermined distance in a receiving apparatus, and signals received from each of the plurality of antennas are switched and selected. . For example, π / 4-DQPSK (Differential Quadrature Phase-Shift Keying) is π / 2 by rotating in a direction that increases the phase of the signal vector through one of four angles ± 45 ° and ± 135 °. Modulation that conveys a pair of data bits having a phase difference of (ie, orthogonal). During phase rotation, the signal modulated by π / 4-DQPSK exhibits a frequency shift equal to the rate of phase change, and the data bit pair can be demodulated by measuring this frequency shift. As for the diversity reception method, some proposals have been made conventionally as in Patent Documents 1 to 6 below.

  For example, in Patent Document 1, the phase of two systems of received signals respectively input from two receiving antennas is compared with a reference phase, and the number of data bits that fluctuate in a phase region that cannot be obtained due to fading is measured. The receiving antenna is switched and selected according to the measurement result (see the first embodiment of Patent Document 1 and FIGS. 1 to 4).

  In Patent Document 2, two received signals respectively input from two receiving antennas are detected by converting them to an intermediate frequency by a local oscillator, and the phase difference between the two systems of subcarrier signals extracted from the detected signals. And detecting the two systems of detection signals while controlling the phase of one of the local oscillators according to the phase difference (from the lower right column on the second page of Patent Document 2 to the third page). (See upper right column and FIG. 1).

  Further, in Patent Document 3, after compensating for fading phase distortion of received signals of each system input from two or more antennas, weighting is performed using the envelope level (that is, amplitude) of the received signals of each system. (See the example of Patent Document 3 and FIG. 1).

  In Patent Document 4, a phase shifter that gives a predetermined phase amount to a carrier wave synchronized with reception signals received by a plurality of antennas, and a main reception signal are detected using the carrier wave. The subcarrier signal is detected using the carrier wave, and each detection signal is branched and captured by the synthesis phase control circuit, and the phase amount of the carrier wave controlled by the phase shifter is set to a value at which each detection signal is in-phase synthesized. (See paragraph numbers “0008” to “0010” of Patent Document 4 and FIG. 1).

  In Patent Document 5, a phase error information signal obtained from the identification result of a detection signal after combining two received signals is acquired, and a main detection signal is obtained using a phase shifter for performing a predetermined correction and the phase error information signal. Main signal phase compensation circuit that performs phase compensation of the signal, a sub signal phase compensation circuit that performs phase compensation of the sub detection signal using the output signal of the phase shifter, and a signal synthesis circuit that synthesizes each phase compensation detection signal after phase compensation And the detection phase of each detection signal are compared, and the correction amount of the phase error information signal given to the sub-signal phase compensation circuit is set to a value at which each phase compensation detection signal is in phase (Patent Document 5). (See abstract and Figure 1).

  In Patent Document 6, the amplitude and phase obtained individually from two branches of a radio transmission system to which a modulation method whose carrier phase is variable are applied, and the received wave obtained individually The phase of the vector sum is obtained by an arithmetic operation based on the combination of the difference between the two and the phase difference or the difference between the amplitude and the phase difference and one of these received waves (Patent Document 6). Example and FIG. 4, FIG. 6 to FIG. 9).

Japanese Patent Publication No. 07-071033 Japanese Patent Laid-Open No. 03-239020 Japanese Patent Publication No. 07-118671 Japanese Patent Laid-Open No. 05-235812 JP 05-291992 A Japanese Patent No. 33888938

  FIG. 5 is a diagram for explaining the general concept of multipath when signals are received from two antennas, using the IQ plane. In FIG. 5, the vector V1 is a direct wave (path 1) and the vector V2 is an indirect wave (path 2). A combined wave (path 1 + path 2) of the received signal of vector V1 and the received signal of vector V2 is indicated by vector V3.

  In the case of FIG. 5A, the phase error between the direct wave vector V1 and the indirect wave vector V2 is relatively small. In this case, the amplitude of the vector V3 of the combined wave, that is, the scalar value that is the length of the vector V3 is large. On the other hand, in the case of FIG. 5B, the phase error between the direct wave vector V1 and the indirect wave vector V2 is large. In this case, although the amplitudes of the vector V1 and the vector V2 are large, the amplitude of the vector V3 of the synthesized wave is small.

  From this, the strength (amplitude) of the synthesized signal obtained by synthesizing the two signals means that the phase error between the two signals is small, that is, the normal phase when the phases of the two signals are not multipath. It is necessary to be close to. For this reason, even in the prior arts such as the above-mentioned patent documents, when receiving by the diversity method, a signal having a high strength is selected. However, it has been difficult to fundamentally improve the influence of multipath only by selecting a strong signal. The reason will be described below.

  FIG. 6 is a diagram of a conventional example showing a state in which two systems of signals phase-modulated by the 1 / 4π-DQPSK method are selected while being switched. The timing of sampling the received signal is a quarter of the period of the symbol determination point. That is, if the timing of the symbol decision point period is t, the symbol decision point changes as t = 0, t = 1, t = 2, t = 3..., Whereas the sampling timing for performing orthogonal transformation is t = 0, t = 0.25, t = 0.5, t = 0.75, t = 1, t = 1.25, t = 1.5, t = 1.75, t = 2, and so on. Transition.

  6A shows the change of the vector, that is, the amplitude and phase of the signal received from the antenna 1, and FIG. 6B shows the change of the amplitude and phase of the signal received from the antenna 2. Is. Conventionally, the amplitude of reception signals received from two antennas is constantly monitored in real time, the phase thereof is adjusted, and the two reception signals are combined. FIG. 6C is a diagram showing the presence / absence of antenna switching timing for selecting the main signal for each sampling timing by constantly comparing the signal strengths of the signal received from the antenna 1 and the signal received from the antenna 2. It is.

  Until the timing of t = 0 (until not shown t = −0.25), the signal of the antenna 1 is the main signal. From the timing of t = 0 to the timing of t = 0.25, the signal strength of the antenna 1 is higher than the signal strength of the antenna 2. Therefore, at each timing of t = 0 and t = 0.25, the antenna 1 Selection is maintained as the main signal as it is, and antenna switching (switching of the main signal) is not performed.

  If the signal strength of the antenna 2 becomes larger than the signal strength of the antenna 1 between the timing of t = 0.25 and the timing of t = 0.5, the signal of the antenna 2 is mainly transmitted at the timing of t = 0.5. The antenna is switched so as to obtain a signal. Thereafter, since the signal strength of the antenna 2 is higher than the signal strength of the antenna 1 until the timing of t = 1, the signal of the antenna 2 is used as the main signal as it is at each timing of t = 0.75 and t = 1. The selection is maintained and antenna switching (main signal switching) is not performed.

  However, before the antenna switching (main signal switching), the phase difference between the reception signal of the antenna 1 and the reception signal of the antenna 2 is “+ 135 °”, but the antenna switching (main signal switching) is performed. After being performed, the phase difference between the reception signal of the antenna 1 and the reception signal of the antenna 2 is “+ 20 °”, and a symbol error has occurred. In this case, for example, even if simple phase correction is performed, the influence of the Doppler shift remains, so it is difficult to eliminate the symbol error. For this measure, complicated and high-speed arithmetic processing is performed by phase adjusting means such as a DSP.

  As described above, in the prior arts such as the above patent documents, the amplitudes of received signals received from a plurality of antennas are constantly monitored in real time, that is, at each sampling timing, and the phases thereof are adjusted to synthesize a plurality of received signals. Since the processing is performed, the calculation processing load of the phase adjusting means such as the DSP increases, leading to an increase in the size and cost of the phase adjusting means, and the amplitude change due to the modulation also affects the synthesizing process. There was a problem that it could not be obtained sufficiently.

  The present invention solves the above-described problem, and when adjusting the phases of received signals input from a plurality of antennas to combine a plurality of received signals, the arithmetic processing load of a phase adjusting means such as a DSP It is an object of the present invention to provide a diversity receiving apparatus and a diversity receiving method that reduce the amount of noise and reduce the size and cost of phase adjusting means.

  In order to achieve the above object, a diversity receiver according to the first aspect of the present invention has a symbol identification point for determining each symbol in consecutive symbols, in which symbols representing baseband signals are phase-modulated. A diversity receiving apparatus for receiving radio signals having signals from a plurality of antennas, wherein a plurality of received signals respectively received from the plurality of antennas are sampled at a timing with a period smaller than a period of a symbol determination point, and orthogonal to each other Orthogonal transformation means for orthogonally transforming into a pair of signals and outputting a plurality of systems of digital signals each consisting of the pair of signals, and any one of the plurality of systems of digital signals output by the orthogonal transformation means Selecting means for selecting as a main signal as a phase reference and selecting other signals as sub signals; Phase correction means for correcting the phases of the main signal and the slave signal selected by the selection means, and the selection means monitors the signal strength of the master signal and the slave signal, and Until the predetermined demodulating means for demodulating the main signal and the sub signal whose phase has been corrected by the phase correcting means notifies the timing of the symbol determination point acquired based on the identification signal. Is characterized by waiting for execution of the determined selection switching.

  For example, the phase correction means corrects the phase of the main signal after the selection switching by the phase difference between the main signal and the sub signal immediately before the selection switching, and calculates the phase difference between the main signal and the sub signal at the immediately preceding symbol determination point. The phase of the slave signal may be corrected.

  For example, the selection unit detects the phase of the main signal and the sub signal whose phases are corrected by the phase correction unit based on each pair of signals, and detects the phase of the detected main signal and the phase of the detected main signal. The phase difference from the phase of the slave signal may be calculated, and the phase correction unit may correct the phases of the main signal and the slave signal with the phase difference calculated by the selection unit.

  Further, for example, the selection unit compares the signal strengths of the main signal and the sub signal whose phases are corrected by the phase correction unit, and compares the result of the comparison with respect to a plurality of digital signals output by the orthogonal transform unit. The selection switching or selection maintenance of the main signal and the slave signal may be determined according to the above.

  Further, for example, the selection unit may compare the signal intensities of the main signal and the sub signal whose phases are corrected by the phase correction unit by the sum of the squares of the scalar values of the pair of signals.

  In order to achieve the above object, the diversity reception method according to the second aspect of the present invention is such that a symbol representing a baseband signal is phase-modulated and a predetermined identification is made at a symbol determination point for determining each symbol in successive symbols. A diversity reception method for receiving a radio signal having a signal from a plurality of antennas, wherein a plurality of received signals respectively received from the plurality of antennas are sampled at a timing with a period smaller than a period of a symbol determination point, and orthogonal to each other A first step of orthogonally transforming into a pair of signals and outputting a plurality of systems of digital signals each consisting of the pair of signals, and any one of the plurality of systems of digital signals output by the first step A second signal is selected as a main signal with a phase reference, and another signal is selected as a sub signal. And a third step of correcting the phase of the main signal and the sub signal selected by the second step, and the second step monitors the signal strength of the main signal and the sub signal. When the selection switching between the main signal and the sub signal is decided, the predetermined demodulating means for demodulating the main signal and the sub signal whose phase is corrected by the third step is acquired based on the identification signal. Until the timing of the symbol determination point is notified, execution of the determined selection switching is awaited.

  For example, in the third step, the phase of the main signal after the selection switching is corrected by the phase difference between the main signal and the sub signal immediately before the selection switching, and the phase difference between the main signal and the sub signal at the immediately preceding symbol determination point. Thus, the phase of the slave signal may be corrected.

  Further, for example, the second step detects the phase of the main signal and the sub signal whose phases are corrected in the third step based on each pair of signals, and the phase of the detected main signal and the phase of the main signal are detected. A phase difference with the detected phase of the slave signal may be calculated, and the third step may correct the phases of the main signal and the slave signal with the phase difference calculated by the second step.

  Further, for example, the second step compares the signal strengths of the main signal and the sub signal whose phases are corrected by the third step, and the digital signals of a plurality of systems output by the first step are: Depending on the comparison result, selection switching or selection maintenance of the main signal and the sub signal may be determined.

  Further, for example, in the second step, the signal intensities of the main signal and the sub signal whose phases are corrected in the third step may be compared with the sum of the squares of the scalar values of the pair of signals.

  According to the present invention, the phase of the data is adjusted based on the symbol data pattern and the symbol transition extracted from the reception signals input from the plurality of antennas, and a plurality of reception signals are combined to perform accurate processing. In addition to enabling phase adjustment, the processing load on the phase adjustment means such as a DSP is reduced, and the phase adjustment means can be reduced in size and price.

It is a basic block diagram in the case of combining two systems of signals received from two antennas. It is a block diagram of the diversity receiver in the embodiment of the present invention. It is a figure which shows the state which selects, switching 2 systems of signals which were phase-modulated by the 1/4 (pi) -DQPSK system in embodiment of this invention. It is the figure which compared the bit error rate with respect to an input level with a prior art example and this Embodiment. It is a figure explaining the general concept of multipath in the case of receiving a signal from two antennas using an IQ pole plane. It is a figure of a prior art example which shows the state which selects while switching 2 systems of signals which were phase-modulated by the 1/4 (pi) -DQPSK system.

  Hereinafter, embodiments of a diversity receiving apparatus and diversity receiving method according to the present invention will be described with reference to the drawings, but before that, a method of combining and detecting two received signals will be described. FIG. 1 is a block diagram of a basic circuit in a case where two systems of signals received from two antennas 31 and 32 are combined in the diversity reception method. The two received signals are amplified by the amplifier circuits 33 and 34, and then the phases are corrected by the phase correction circuits (φ) 35 and 36. The two systems of signals whose phases have been corrected are synthesized by the adder 37 and input to the detection circuit 38.

  Theoretically, if the phase difference between the two signals is corrected by the phase correction circuits 35 and 36 and the two signals are in phase, a combined signal with the maximum ratio can be obtained. Is not held on the receiving side, a symbol error may occur as shown in FIG. Therefore, “a signal with a correct reception pattern” means “a signal with a small phase error” and “a signal with a strong signal strength”. Therefore, in order to always obtain a strong signal, an embodiment of the present invention will be described below. A diversity receiving apparatus and a diversity receiving method will be described.

  FIG. 2 is a block diagram showing a configuration of the diversity receiving apparatus according to the embodiment of the present invention. In FIG. 2, the diversity receiving apparatus includes an orthogonal transform unit 100, a diversity unit 200, and a demodulation unit 300.

  The antennas 1 and 2 input received signals to the orthogonal transform unit 100. The received signals from the antennas 1 and 2 include an i signal and a q signal, which are analog signals obtained by orthogonally modulating symbols representing baseband signals by the 1 / 4π-DQPSK system. Each symbol constituting the baseband signal is composed of 2 bits of “00”, “01”, “10”, and “11”. The head of each symbol includes a preamble (identification signal) in which 16 to 32 specific codes “1001” are continued. This preamble represents the timing of symbol determination points for determining each symbol.

  The orthogonal transform unit 100 (orthogonal transform means) performs orthogonal transform on each of the two systems of signals received from the antennas 1 and 2. For this reason, the orthogonal transform unit 100 includes an oscillator 3, a −π / 2 phase shifter 4, and four multipliers (mixers) 5 to 8. The oscillator 3 outputs an oscillation signal having the same frequency as the carrier signal (carrier) of the radio signal input from the antennas 1 and 2. The multipliers 5 and 7 separate the i signal by multiplying the received signal and the oscillation signal, and output them to the diversity unit 200. The multipliers 6 and 8 multiply the received signal by the oscillation signal shifted by 90 ° by the −π / 2 phase shifter 4 to separate the q signal and output it to the diversity unit 200.

  Diversity unit 200 removes unnecessary high-frequency components from the i and q signals of the two systems of received signals output from orthogonal transform unit 100, and converts the I and Q signals that are baseband signals. Extraction, phase shift, intensity determination, and phase determination are performed, and two systems of I signals and Q signals are combined and output to the demodulator 300.

  For this reason, the diversity unit 200 includes LPF (low-pass filter) circuits 9 to 12 including four RRC (root raised cosine) filter circuits, two phase shift circuits 13 and 14, two phase detection circuits 15 and 17, Two intensity detection circuits 16 and 18, an intensity / phase determination circuit 19, and two adders 20 and 21 are provided. Hereinafter, these functions will be described.

  The LPF circuit 9 removes unnecessary high-frequency components of the i signal input from the corresponding multiplier 5 of the orthogonal transform unit 100 and outputs a baseband I signal to the phase shift circuit 13. The LPF 10 removes unnecessary high-frequency components from the q signal input from the corresponding multiplier 6 of the orthogonal transform unit 100 and outputs a baseband Q signal to the phase shift circuit 13. The LPF circuit 11 removes unnecessary high frequency components of the i signal input from the corresponding multiplier 7 of the orthogonal transform unit 100 and outputs a baseband I signal to the phase shift circuit 14. The LPF circuit 12 removes unnecessary high-frequency components from the q signal input from the corresponding multiplier 8 of the orthogonal transform unit 100 and outputs a baseband Q signal to the phase shift circuit 14.

  The phase shift circuits 13 and 14 (phase correction means) include an A / D converter, a clock generation circuit, and other circuits (all not shown), and are analog I signals input from the LPF circuits 9 to 12. And the Q signal are sampled and converted into digital I and Q signals. In this case, sampling is performed at a timing smaller than the cycle of the symbol determination point, for example, a quarter cycle in the present embodiment.

  That is, the A / D converter samples the analog I signal and Q signal by the sampling signal generated by the clock generation circuit, and converts the sampled signal into a digital I signal and Q signal. Therefore, when the timing of the period of the symbol determination point is t, t = 0, t = 0.25, t = 0.5, t = 0.75, t = 1.0, t = 1.25, t = Two sampling I and Q signals from the antenna 1 and the antenna 2 are generated in the phase shift circuits 13 and 14 at a sampling timing of 1.5.

  The phase shift circuit 13 outputs the phase-corrected I signal to the phase detection circuit 15, the intensity detection circuit 16, and the multiplier 20, and also outputs the phase-corrected Q signal to the phase detection circuit 15, the intensity detection circuit 16, and the multiplier. To 21. The phase shift circuit 14 outputs the phase-corrected I signal to the phase detection circuit 17, the intensity detection circuit 18, and the multiplier 20, and the phase-corrected Q signal to the phase detection circuit 17, the intensity detection circuit 18, and Output to the multiplier 21.

The phase detection circuits 15 and 17 detect the phase of the vector of the received signal based on the I signal and the Q signal from the corresponding phase shift circuits 13 and 14, respectively. When the phase of the vector is φ, φ is expressed by the following equation. The phase detection circuits 15 and 17 output the detected phase to the intensity / phase determination circuit 19.
φ = tan ^-1 (Q signal scalar / I signal scalar)

The intensity detection circuits 16 and 18 detect the amplitude of the received signal, that is, the scalar value of the vector based on the I signal and Q signal from the corresponding phase shift circuits 13 and 14, respectively. The scalar value of the vector is represented by the square root of the sum of I ² and Q ² (the sum of the squares of I and Q). However, since the division for calculating the square root requires many calculation steps, the intensity detection circuits 16, 18 Calculates the sum of the squares of I and Q, and outputs the calculation result to the intensity / phase determination circuit 19.

  The intensity / phase determination circuit 19 (selection means) is based on the phases and amplitudes of the two received signals input from the phase detection circuits 15 and 17 and the intensity detection circuits 16 and 18 (actually the sum of squares of I and Q). Thus, the state of the received signal is constantly monitored (at each sampling timing), the main signal and signal selection switching is determined as necessary, and the phase shift circuits 13 and 14 are instructed to perform selection switching. However, even when switching is determined, selection switching is not instructed to the phase shift circuits 13 and 14 in real time of determination, that is, sampling timing. The instruction for selection switching is waited until the next symbol determination point, and selection switching is instructed to the phase shift circuits 13 and 14 when the timing of the symbol determination point is notified from the demodulator 300, as will be described later. . Further, the intensity / phase determination circuit 19 calculates the phase difference Δφ between the phase (φmain) of the main signal and the phase (φsub) of the sub signal input from the phase detection circuits 15 and 17, respectively, and the timing of the symbol determination point Is notified to the phase shift circuits 13 and 14 of the phase difference Δφ.

  The adder 20 adds the two I signals input from the phase shift circuits 13 and 14 and outputs the result to the π / 4-DQPSK demodulation block 22 of the demodulation unit 300. The adder 21 adds the two Q signals input from the phase shift circuits 13 and 14 and outputs the result to the π / 4-DQPSK demodulation block 22 of the demodulation unit 300.

  The π / 4-DQPSK demodulating block 22 (demodulating means) demodulates the added I signal and Q signal for each symbol with reference to a symbol determination point, and a binary symbol consisting of “0” and “1”. Is output to the next stage as a demodulated data string. In this case, a symbol determination point serving as a demodulation reference is detected based on a preamble that is identification information added to the head of each symbol. The timing of the detected symbol determination point is notified to the intensity / phase determination circuit 19.

  The phase shift circuits 13 and 14 select and switch based on the presence / absence of switching instructed for each timing of the symbol determination point from the intensity / phase determination circuit 19 and the phase difference Δφ between the main signal and the sub signal to be notified. The phase of the main signal after selection switching is corrected by the phase difference Δφ between the immediately preceding main signal and the slave signal, and the phase of the slave signal is corrected by the phase difference Δφ between the main signal and the slave signal at the immediately preceding symbol determination point. That is, the phase of the main signal after switching is corrected by the correction amount of the sub signal that has been phase-corrected immediately before switching from the sub signal to the main signal, and the phase of the sub signal is changed to the phase of the main signal at the immediately preceding symbol determination point. Therefore, the phase of the slave signal is corrected by the phase difference Δφ.

  Next, a diversity reception method executed by the diversity receiver of FIG. 2 will be described in detail with reference to FIGS.

  FIG. 3 is a diagram of an IQ pole plane showing a state in which two systems of signals phase-modulated by the 1 / 4π-DQPSK method are selected while being switched in the present embodiment. In FIG. 3, item 1 in the first stage in the vertical direction represents a vector of I and Q signals input from the LPF circuits 9 to 12 to the phase shift circuits 13 and 14 in FIG. 2, and item 2 in the next stage. 2 is a vector of I and Q signals input to the phase detection circuits 15 and 17, the intensity detection circuits 16 and 18, and the adders 20 and 21 from the phase shift circuits 13 and 14 in FIG. The item 3 in the last stage represents a vector of I and Q signals input from the adders 20 and 21 of FIG. 2 to the π / 4-DQPSK demodulation block 22, that is, a combined signal of the antenna 1 and the antenna 2 Represents a vector.

  Further, one of the two received signals from the antennas 1 and 2 is selected as the main signal, the other is selected as the sub signal, and the vector of each item is 1/4 of the period of the symbol determination point. At the sampling timing (t = −0.25, 0, 0.25, 0.5, 0.75, 1.0, 1.25, 1.5...) The determination is made by the intensity / phase determination circuit 19. Hereinafter, the determination process at each sampling timing will be described.

(1) When t = −0.25 (symbol) At this time, it is assumed that the main signal serving as a phase reference is a received signal from the antenna 1 and the slave signal is a received signal from the antenna 2. Further, the phase difference at the time of the previous antenna switching (not shown) (that is, at the time of the selection switching of the main signal and the sub signal immediately before) is “+ 90 °” and It is assumed that the phase difference is “+ 72 °”.

  First, the phase of the vector of the main signal is corrected by the phase shift circuits 13 and 14 with the phase difference “+ 90 °” at the time of the previous antenna switching (when the main signal and the slave signal are selected and switched). The correction is only for the phase, and the amplitude is not corrected. As long as the received signal from the antenna 1 is the main signal, that is, as long as there is no selection switching between the main signal and the sub signal, this correction amount is constant. On the other hand, the vector of the slave signal of the antenna 2 is corrected by the phase difference “+ 72 °” from the main signal at the immediately preceding symbol determination point. However, even if the phase of the subordinate signal vector is corrected, the phase of the main signal and the phase of the subordinate signal are not necessarily the same due to the influence of the Doppler shift. Although signal strength is detected by the strength detection circuits 16 and 18 (in this case, antenna 1> antenna 2), since this timing is not a symbol determination point, the signal strength of the main signal and the slave signal for antenna switching is used. No judgment is made. Item 3 shows the result of adding the vector of the main signal and the vector of the sub signal, that is, the combined vector of the main signal and the sub signal input from the adders 20 and 21 to the π / 4-DQPSK demodulation block 22.

(2) When t = 0 (symbol) Since this is a symbol determination point, the main signal is selectively switched or maintained, and the phases of the main signal and the sub signal are matched. The phase of the slave signal of the antenna 2 output from the phase shift circuit 14 is “+ 207 ° (= 135 + 72)” since the correction of “+ 72 °” is added until immediately before. On the other hand, since the phase of the signal of the antenna 1 output from the phase shift circuit 13 is “+ 180 °”, the phase difference is “−27 ° (= 180−207)”. This value is added to the correction amount “+ 72 °” to obtain the final sub-signal correction amount “+ 45 ° (= −27 + 72)”. That is, the phase difference from the main signal at the immediately preceding symbol determination point is obtained. This value is the same up to the next symbol determination point. Since this timing is a symbol determination point, a scalar value of a vector that is the signal intensity of the main signal and the sub signal is calculated, and a signal having a large scalar value is selected as the main signal. However, since the signal strength in this case is the same as that of the previous symbol determination point with antenna 1> antenna 2, the previous selection is maintained and selection switching is not performed. Item 3 shows a combined vector of the main signal and the sub signal input from the adders 20 and 21 to the π / 4-DQPSK demodulation block 22.

(3) When t = 0.25 to 0.5 (symbol) This case is the same as when t = −0.25 (symbol), and the description thereof is omitted.

(4) When t = 0.75 (symbol) The signal intensity of the antenna 1 and the antenna 2 detected by the intensity detection circuits 16 and 18, that is, the vector scalar, changes from antenna 2> antenna 1, but the symbol Since it is not the determination point, the main signal and the sub signal are not switched, and the current selection is maintained and the process waits until the next symbol determination point.

(5) When t = 1.0 (symbol) Since it is a symbol determination point, the phase shift circuits 13 and 14 change the vector of the antenna 1 as the main signal at the time of the previous antenna switching (selection of the main signal and the sub signal). The phase of the antenna 2 that is the sub signal is corrected with the phase difference “+ 45 °” from the main signal at the immediately preceding symbol determination point. As a result, the phase of the vector of the signal output from the phase shift circuit 14 corresponding to the antenna 2 is “−45 ° (= −90 + 45)”, and the signal output from the phase shift circuit 13 corresponding to the antenna 1 Since the phase of the vector is “−56 ° (= −146 + 90)”, the phase difference between the signal of the antenna 1 and the signal of the antenna 2 is “−11 ° (= −56 − (− 45)”. Is added to the previous correction amount “+ 45 °” to calculate the final sub-signal correction amount “+ 34 ° (= + 45-11).” This correction amount is the main signal at the immediately preceding symbol determination point. And the phase difference.

  Further, at the timing of this symbol determination point, unlike the case of “t = 0 (symbol)”, the vector scalars which are the signal strengths of the antenna 1 and the antenna 2 detected by the strength detection circuits 16 and 18 are 2> The antenna 1 is changed. For this reason, selection switching is performed according to the following procedure so that the signal of the antenna 2 is selected as the main signal until the next symbol determination point, and the signal of the antenna 1 is selected as the sub signal.

  First, after the next sampling timing (when t = 1.25), the phase correction amount on the main signal side for the signal of the antenna 2 is calculated. This is equal to the phase difference with the main signal at the previous symbol determination point, which was performed for the previous antenna switching (selection switching between the main signal and the sub signal), that is, the signal of the antenna 2, and was calculated above. Equal to “+ 34 °”. Then, after the next sampling timing (when t = 1.25), the phase difference from the main signal at the symbol determination point immediately before the signal of the antenna 1 is calculated. This phase difference is “+ 90 °”, which is equal to the previous antenna switching (selection switching between the main signal and the slave signal) that has been performed for the signal of the antenna 1 so far. Item 3 shows a combined vector of the main signal and the sub signal input from the adders 20 and 21 to the π / 4-DQPSK demodulation block 22.

(6) When t = 1.25 to 1.5 (symbol) At the timing of the immediately preceding symbol determination point, the signal of the antenna 2 is selected as the main signal, and the signal of the antenna 1 is selected as the sub signal. The vector of the signal of the antenna 2 that is the main signal is corrected by the phase difference “+ 34 °” at the time of the previous antenna switching (selection switching between the main signal and the sub signal). On the other hand, the signal vector of the antenna 1 which is a slave signal is corrected by the phase correction amount “+ 90 °” of the slave signal until the timing of the next symbol determination point. Item 3 shows a combined vector of the main signal and the sub signal input from the adders 20 and 21 to the π / 4-DQPSK demodulation block 22.

  FIG. 4 is a diagram comparing the bit error rate (BER) with respect to the input level between the conventional example and this embodiment. FIG. 4A shows a measurement result of the BER characteristic in a fading environment of 60 km / h in the conventional example. When a radio signal is received by a single antenna (measurement result of Δ in the figure), the diversity method is shown. FIG. 6 is a diagram comparing the BER with respect to the input level (dB μV / open), comparing with the case where a wireless signal is received (measurement result of ◆ in the figure). FIG. 4B is a measurement result of the BER characteristic in a fading environment of 60 km / h in the present embodiment. When a radio signal is received with a single antenna (measurement result of Δ in the figure), It is a figure which compares the case where a radio signal is received by a diversity system (measurement result of ◆ in the figure), and shows a comparison of BER with respect to an input level (dBμV / open).

  When the reception in the conventional example shown in FIG. 4A and the reception in this embodiment shown in FIG. 4B are compared in the improvement degree between the case of single antenna reception and the case of diversity reception, 1 In the vicinity of% sensitivity, the conventional example is improved by 6 to 7 dB, whereas in the present embodiment, it is improved by 12 dB. In the static characteristics, when the same signal intensity is input, the sensitivity does not change in the conventional example, whereas in the present embodiment, the sensitivity is improved by 10 dB.

  As described above, in the above-described embodiment, the two received signals received from the two antennas 1 and 2 have timings (t = 0, t = 0.25, t = 0.5, t = 0.75, t = 1.0, t = 1.25, t = 1.5...), And orthogonally transforms into a pair of signals orthogonal to each other. An orthogonal transform unit 100 that outputs two systems of digital signals, and one of the two systems of digital signals output by the orthogonal transform unit 100 is selected as a main signal based on a phase reference, and the other signals And a phase shift circuit 13 and 14 for correcting the phases of the main signal and the sub signal selected by the strength / phase determination circuit 19, and an intensity / phase determination circuit. 9 monitors the signal strength of the main signal and the sub signal, and when the selection switching between the main signal and the sub signal is determined, demodulates the main signal and the sub signal whose phases are corrected by the phase shift circuits 13 and 14 Until the π / 4-DQPSK demodulating block 22 notifies the timing of the symbol determination point acquired based on the preamble, it waits for execution of the determined selection switching. Therefore, by adjusting the phase based on the symbol data pattern extracted from the received signals input from the two antennas 1 and 2 and the transition of the symbols, and performing the combining process of the two systems of received signals, accurate Enables phase adjustment and monitors the amplitude of the two signals received from the antennas 1 and 2 in real time, that is, at every sampling timing, and does not adjust the phase. The processing load is reduced, and the phase adjustment means can be reduced in size and price.

  In the above embodiment, the phase shift circuits 13 and 14 correct the phase of the main signal after the selection switching by the phase difference between the main signal and the slave signal immediately before the selection switching, and the main signal and the slave at the immediately preceding symbol determination point. The phase of the slave signal is corrected by the phase difference from the signal. Therefore, it is possible to prevent the occurrence of symbol errors due to phase correction at each sampling timing.

  Further, in the above embodiment, the intensity / phase determination circuit 19 detects the phases of the main signal and the sub signal whose phases are corrected by the phase shift circuits 13 and 14 based on the respective pair of I signal and Q signal. Then, the phase difference between the detected phase of the main signal and the detected phase of the sub signal is calculated, and the phase shift circuits 13 and 14 use the phase difference calculated by the intensity / phase determination circuit 19 to determine the main signal and the sub signal. Correct the phase of the signal.

  Further, in the above embodiment, the strength / phase determination circuit 19 compares the signal strengths of the main signal and the sub signal whose phases are corrected by the phase shift circuits 13 and 14 and outputs them by the orthogonal transform unit 100. For the digital signal of the system, selection switching or selection maintenance of the main signal and the slave signal is determined according to the comparison result. In this case, the intensity / phase determination circuit 19 compares the signal intensities of the main signal and the sub signal whose phases are corrected by the phase shift circuits 13 and 14 with the sum of the squares of the scalar values of the pair of signals. Therefore, since the square root that requires a large number of calculation steps is not calculated, the calculation processing load such as DSP is further reduced, which contributes to further miniaturization and cost reduction.

  The above embodiments are for explaining the present invention, and the present invention is not limited to the above embodiments, and other embodiments and other embodiments that can be considered by those skilled in the art without departing from the scope of the claims. Modifications also belong to the present invention. For example, although the diversity receiver and the diversity reception method in the above embodiment perform reception with two antennas, the antenna configuration in the present invention is not limited to two antennas. A diversity receiving apparatus and a diversity receiving method for receiving signals by using three or more antennas are also included in the present invention.

13, 14 Phase shift circuit 15, 17 Phase detection circuit 16, 18 Intensity detection circuit 19 Intensity / phase determination circuit 20, 21 Adder 22 π / 4-DQPSK demodulation block 100 Orthogonal transformation unit

Claims (10)

A diversity receiving apparatus that receives, from a plurality of antennas, radio signals having a predetermined identification signal at a symbol determination point for determining each symbol in consecutive symbols, wherein symbols representing baseband signals are phase-modulated.
A plurality of systems of received signals respectively received from the plurality of antennas are sampled at a timing with a period smaller than the period of the symbol determination point, and orthogonally transformed into a pair of signals orthogonal to each other, Orthogonal transform means for outputting a digital signal;
Selecting means for selecting any one of the plurality of digital signals output by the orthogonal transform means as a main signal with a phase reference and selecting the other signal as a sub signal;
Phase correction means for correcting the phases of the main signal and the sub signal selected by the selection means;
With
The selection means monitors the signal intensity of the main signal and the sub signal, and when the selection switching between the main signal and the sub signal is determined, the main signal and the sub signal whose phase is corrected by the phase correction means. The diversity receiving apparatus, wherein the predetermined demodulating means to demodulate waits for execution of the determined selection switching until the timing of the symbol determination point acquired based on the identification signal is notified.   The phase correction means corrects the phase of the main signal after the selection switching by the phase difference between the main signal and the sub signal immediately before the selection switching, and the sub signal by the phase difference between the main signal and the sub signal at the immediately preceding symbol determination point. The diversity receiver according to claim 1, wherein the phase of the diversity receiver is corrected.   The selection unit detects the phase of the main signal and the sub signal whose phases are corrected by the phase correction unit based on each pair of signals, and detects the phase of the detected main signal and the phase of the detected sub signal The diversity receiving apparatus according to claim 2, wherein the phase correction unit corrects the phase of the main signal and the sub signal with the phase difference calculated by the selection unit.   The selection unit compares the signal strengths of the main signal and the sub signal whose phases are corrected by the phase correction unit, and determines a plurality of digital signals output by the orthogonal transform unit according to the comparison result. 4. The diversity receiver according to claim 1, wherein selection switching or selection maintenance of the signal and the slave signal is determined.   The said selection means compares the signal strength of the main signal and the sub signal which were phase-corrected by the said phase correction means with the sum of the square of the scalar value of each pair of signals, The selection means of Claim 4 characterized by the above-mentioned. Diversity receiver. A diversity reception method in which a symbol representing a baseband signal is phase-modulated and a radio signal having a predetermined identification signal at a symbol determination point for determining each symbol in successive symbols is received from a plurality of antennas.
A plurality of systems of received signals respectively received from the plurality of antennas are sampled at a timing with a period smaller than the period of the symbol determination point, and orthogonally transformed into a pair of signals orthogonal to each other, A first step of outputting a digital signal;
A second step of selecting any one of the plurality of digital signals output by the first step as a main signal with a phase reference and selecting another signal as a sub signal;
A third step of correcting the phases of the main signal and the slave signal selected in the second step;
Run
In the second step, when the signal strength of the main signal and the sub signal is monitored and the selection switching between the main signal and the sub signal is determined, the main signal and the sub signal whose phases are corrected in the third step are determined. A diversity receiving method characterized by waiting for execution of the determined selection switching until a predetermined demodulating means for demodulating the signal notifies the timing of the symbol determination point acquired based on the identification signal.   In the third step, the phase of the main signal after the selection switching is corrected by the phase difference between the main signal and the sub signal immediately before the selection switching, and the sub signal is corrected by the phase difference between the main signal and the sub signal at the immediately preceding symbol determination point. The diversity reception method according to claim 6, wherein the phase of the signal is corrected.   The second step detects the phase of the main signal and the sub signal whose phases are corrected by the third step based on each pair of signals, and detects the phase of the detected main signal and the detected sub signal The phase difference between the main signal and the sub signal is corrected by the phase difference calculated by the second step, and the third step corrects the phase of the main signal and the sub signal. Diversity reception method.   The second step compares the signal intensities of the main signal and the sub signal whose phases are corrected in the third step, and the digital signal of a plurality of systems output in the first step is compared with the comparison result. 9. The diversity reception method according to claim 6, wherein selection switching or selection maintenance of the main signal and the slave signal is determined accordingly.   The second step compares the signal intensities of the main signal and the sub signal whose phases are corrected in the third step by the sum of the squares of the scalar values of the pair of signals, respectively. The diversity receiving method described in 1.

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