Synchronizing apparatus

Abstract: The synchronizing apparatus includes a block (102) for detecting a code (103) from an input signal (13), a block (105) for detecting from the code the variable points of the code at several times as high as the symbol rate, a block (107, 108, 114 0 -114 N-1 ) for calculating a histogram of the detected variables of the code to time, and a block (108, 122) for deciding that the phase number at which the calculated histogram takes the maximum value is a symbol synchronization point. This synchronizing apparatus detects the zero-cross points of an intermediate frequency band signal (103) at N times as high as the symbol rate. It also calculates a histogram of detected time (0 to N-1). The time (0 to N-1) at which the histogram is the maximum within a predetermined detected time is selected as a symbol clock, and thereby symbol synchronization is established.

Description: The present invention relates to synchronizing apparatus for use in the receiver of digital communication system. Description of the Related Art Digitalization in communication has remarkably advanced lately and is still progressing. In this digital communication, the receiving side needs means for pulling frame synchronization in with high speed and high precision. A conventional synchronizing apparatus for pulling-in of synchronization employs a PLL (phase-locked loop) as described in "HOW TO USE PLL-IC" (written by Tuneyasu Hata and Kazuaki Furukawa, and published by Akiba, pp. 20-32, November 1976). This apparatus has a digital VCO (voltage-controlled oscillator) 1 for finally producing a signal synchronized with an input signal under the control of PLL, a binary quantizing phase comparator 2 for comparing the phase of the input signal with the phase of the output signal from the digital VCO 1, and producing data of +1 or -1 as a result of the comparison, and a sequential loop filter 3 for counting the output signal from the binary quantizing phase comparator 2 and supplying a correction signal to the digital voltage-controlled oscillator 1 when the count exceeds a certain value (N). The binary quantizing phase comparator 2 includes a phase comparator 4 for comparing the phase of the input signal with the phase of the output signal from the digital VCO 1, and a quantizer 5 for quantizing the result from the comparator into a binary value. The digital VCO 1 includes a fixed oscillator 6 for oscillating at a fixed frequency, a pulse addition/removal circuit 7 for adding or removing a pulse to or from the output of the fixed oscillator 6 when the sequential loop filter 3 generates the output signal, and a frequency divider 8 for dividing the frequency of the output signal from the fixed oscillator 6 to or from which the pulse has been added or removed. In this synchronizing apparatus, the phase comparator 4 of the binary quantizing phase comparator 2 compares the phase of the input signal with the phase of the output signal from the digital VCO 1. The quantizer 5 produces a value of -1 when the phase of the output signal from the digital VCO 1 is larger than that of the input signal, or when the output signal is ahead of the input signal, but it produces a value of +1 when it is smaller than that, or when the output signal is behind the input signal. The sequential loop filter 3 counts the output from the quantizer 5, and supplies to the pulse addition/removal circuit 7 the correction signal for controlling a pulse to be removed when the count arrives at +N, or for controlling a pulse to be added when the count reaches -N. Therefore, in this synchronizing apparatus used as a frame synchronizer, when the phase of the output signal from the digital VCO 1 shifts in the positive or negative direction relative to the phase of the frame synchronizing signal, the sequential loop filter 3 supplies the first correction signal N frames after the start of pulling-in of synchronization. When the correction signal is supplied to the digital VCO 1, the pulse addition/removal circuit 7 inserts a pulse in the output signal from the fixed oscillator 6 or removes it therefrom in response to this correction signal. Since the oscillation frequency of the fixed oscillator 6 is selected to be R times as high as the input frequency in order that the quantized value for phase control can be reduced, the output signal from the fixed oscillator 6 in which a pulse has been inserted or from which a pulse has been removed by the pulse addition/removal circuit 7 is supplied to the frequency divider 8 where its frequency is divided by R, and the frequency-divided signal is produced from the output end of the digital VCO 1. When there is still a phase difference between the output signal from the digital VCO 1 and the input signal even after the insertion or removal of a pulse, the above operations are repeated, and finally the output signal from the digital VCO 1 is controlled so that the phase difference between the output signal from the digital VCO 1 and the input signal can be minimized. In this apparatus, if  is the initial phase difference at the time of pulling-in of frame synchronization, the time in which the phase pulling-in is caused within error δ is given by the following equation (1) . T 0 = {(-δ) R /360}× N where 360°/R is the phase change in one cycle. The average time in which the frame synchronization is established is derived from Eq. (1) as in the following equation (2). Here, if it is assumed that δ=180/R, the frequency for comparison is 50 Hz, or the frame frequency of full rate of PDC, and the oscillation frequency of the fixed oscillator 6 is 12.6 kHz, then R=252 can be obtained, and thus the average pull-in time is 62.5 × N, or 3.125 seconds. However, since the above conventional synchronizing apparatus employs an analog PLL, it is easily affected by temperature change, timing aging and environmental variation such as voltage fluctuation. In addition, after synchronization is locked by an alternating pattern for synchronization, synchronization holding by use of information symbol is made unstable by the information symbol pattern. EP-A-0 480 165 discloses a method for selecting a retiming signal from a plurality of local clock signals such that the retiming signal occurs in time near a minimum number of data edge transitions sorted using a histogram. GB-A-2 253 122 discloses a synchronizing apparatus comprising means for detecting a code from an input signal, means for detecting from said code the variable points of said code at several times as high as a symbol rate, means for calculating a histogram of said detected variable points, and means for deciding that a phase number, at which said histogram takes the maximum value, is a symbol synchronizing point. Means for controlling, if the histogram takes the maximum value, are supposed to compare that value with another one in order to decide that it is or is not the maximum value. SUMMARY OF THE INVENTION It is an object of the present invention to provide a high-performance synchronizing apparatus all formed of digital circuits to have high resistance to environmental change irrespective of whether the transmitted symbol pattern is an alternating pattern for synchronization or information symbol that has no random property. According to the invention, there is provided a synchronizing apparatus that is all formed of digital circuits, detects the zero-cross points of a received signal of IF band at N times as high as the symbol rate, and establishes the optimum symbol synchronization from the histogram to the detected time. Therefore, in the present invention, since the histogram of the zero-cross points is detected, erroneous operation is not caused even when zero-cross points do not successively occur during some symbol periods in any symbols like information symbol. In addition, when the burst length is short or when the clock precision is very high, synchronization can be established and held by a small number of symbols, and thus low power consumption can be achieved by stopping the synchronizing circuit. Moreover, even when the burst length is long or when the clock precision is low, synchronization can be detected in information symbols, and thus synchronization tracking can be realized by the addition of simple circuits. The first synchronizing apparatus according to the present invention includes means for detecting a code from an input signal, latch means for detecting from the code the variable points of the code at several times as high as the symbol rate, means for calculating a histogram of the detected variable points of the code to time, and means for deciding that the phase number at which the calculated histogram first exceeds a threshold is a symbol synchronization point and that when the histogram does not exceed the threshold within a certain detected period, the phase number at which the calculated histogram takes the maximum value is a symbol synchronization point. In other words, the zero-cross points of a signal of IF band are detected at N times as high as the symbol rate, a histogram to the detected time (0 to N-1) is calculated, the time (0 to N-1) at which the histogram exceeds the threshold within a certain detected period is selected as a symbol clock, and when the histogram does not exceed the threshold within the certain detected period, the time (0 to N-1) at which the histogram takes the maximum value is selected as the symbol clock, thereby quickly establishing the symbol synchronization. The second synchronizing apparatus according to the present invention is one according to the first synchronizing apparatus, wherein after synchronization establishment, timing correction is performed by calculating the histogram at a position, a certain phase unit before and after the synchronization establishment point, and detecting the associated phase number. In other words, after the symbol synchronization establishment, the zero-cross points of a signal of IF band are detected at N times as high as the symbol rate, and the histogram to the detected time (0 to N-1) is calculated. At this time, when the time at which the histogram exceeds a threshold is before the synchronization establishment time (k: 0≤ k ≤ N-1), the symbol synchronization point is corrected to proceed by one clock (1/(N × f s )), and when the time at which the histogram exceeds the threshold is after that, the symbol synchronization point is corrected to be receded by one clock (1/(N × f s )). If the time at which the histogram exceeds the threshold is equal to the synchronization establishment point, no correction is made. Thus, correct symbol synchronization can be established. The third synchronizing apparatus according to the present invention is one according to the second synchronizing apparatus, wherein when the frequency precision is known to be low, the phase number detection is made more frequently to follow the synchronization, and when the frequency precision is known to be high, the phase number detection is made less frequently. Thus, after the symbol synchronization is established, the synchronization correction frequency is controlled in accordance with the burst length and clock precision, so that the consumption power can be reduced. The fourth synchronizing apparatus according to the present invention is one according to any one of the first to third synchronizing apparatus for acquiring synchronization by use of data after A/D conversion, wherein when the difference between the times necessary for signals to reach the synchronizing circuit and the A/D converter causes a more serious problem than use of analog data before A/D conversion (particularly when the symbol rate is high), a desired accurate synchronization point can be detected. The fifth synchronizing apparatus according to the present invention is one according to the fourth synchronizing apparatus, wherein when the synchronizing signal is a sine wave of which the phase is changed 180 degrees at each symbol, each of the absolute values of in-phase and quadrature signals, or I, Q signals of the sampled data after A/D conversion is added, and after the addition, a more accurate one of both sums is selected, so that a desired correct synchronization position can be detected even if there is delay in the analog circuits. The sixth synchronizing apparatus according to the present invention is one according to the fourth synchronizing apparatus, wherein when the synchronizing signal is a sine wave of which the phase is changed 180 degrees at each symbol, the absolute values of the sampled data after A/D conversion are added and used without separating the sampled data into the I and Q signals, so that the circuits can be smaller-sized than in the seventh synchronizing apparatus and that a desired correct synchronization position can be detected even if there is delay in the analog circuits. The seventh synchronizing apparatus according to the present invention is one according to the fifth or sixth synchronizing apparatus, wherein when the synchronizing signal is a sine wave of which the phase is changed 180 degrees at each symbol, calculation is made for the sum of the absolute values of each of the I and Q signals of the sampled data after A/D conversion at four times as high as the symbol rate, selection is made for a pair of adjacent maximum values of a larger level one of the I and Q signals of which the levels are previously determined, calculation is again made for the sum of the absolute values of the larger level signal of the sampled data sampled at an intermediate sampling timing rate therebetween, the resulting three values are compared, and synchronization is acquired by determining the timing for the largest value. Thus, a desired correct synchronization position can be detected even if there is delay in the analog circuits. The eighth synchronizing apparatus according to the present invention is one according to the fifth or sixth synchronizing apparatus, wherein when the synchronizing signal is a sine wave of which the phase is changed 180 degrees at each symbol, calculation is made for the sums of the absolute values of the sampled data after A/D conversion, sampled at four times as high as the symbol rate without separating the sampled data into I and Q signals, selection is made for a pair of two adjacent maximum values of the sampled data, calculation is again made for the sum of the absolute values of the sampled data sampled at an intermediate sampling timing rate therebetween, the resulting three values are compared, and the timing for the largest one is determined, thereby acquiring synchronization. Thus, a desired correct synchronization position can be detected even if there is delay in the analog circuits. The ninth synchronizing apparatus according to the present invention is one according to the seventh or eigth synchronizing apparatus, wherein selection is made for a pair of two adjacent minimum values, calculation is again made for the sum of the absolute values of the sampled data sampled at an intermediate sampling timing rate therebetween, the resulting three values are compared, and synchronization is acquired by determining the timing for the smallest one. Thus, the precision is higher than in the ninth or tenth synchronizing apparatus, and a desired correct synchronization position can be detected even if there is delay in the analog circuits. In this case, the correct synchronization timing is 1/2 symbol after the above synchronization acquisition timing. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of a conventional synchronizing apparatus. Fig. 2 is a block diagram of a receiver including a synchronizing apparatus of a first comparative example. Fig. 3 is a block diagram of the synchronizing apparatus of the first comparative example. Figs. 4A-4I are a timing chart useful for explaining the operation of the synchronizing apparatus shown in Fig. 3. Fig. 5 is a block diagram of a phase number detector shown in Fig. 3. Fig. 6 is a block diagram of a phase number detector included in a synchronizing apparatus of a second comparative example. Fig. 7 is a block diagram of a phase number detector included in a synchronizing apparatus of a first embodiment of the present invention. Fig. 8 is a block diagram of a synchronizing apparatus of a second embodiment of the present invention. Fig. 9 is a block diagram of a receiver including a synchronizing apparatus of a third embodiment of the present invention. Fig. 10 is a block diagram of a receiver including a synchronizing apparatus of a fourth embodiment of the present invention. Fig. 11 is a block diagram of a phase detection circuit included in a synchronizing apparatus of a fifth embodiment of the present invention. Fig. 12 is a block diagram of a phase detection circuit included in a synchronizing apparatus of a sixth embodiment of the present invention. Fig. 13 is a flowchart for showing a phase detection procedure in a synchronizing apparatus of a seventh embodiment of the present invention. Fig. 14 is a flowchart for showing a phase detection procedure in a synchronizing apparatus of an eigths embodiment of the present invention. Fig. 15 is a flowchart for showing a phase detection procedure in a synchronizing apparatus of a ninth embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS (First comparative example) Fig. 2 shows the receiver of a digital mobile communication system having the synchronizing apparatus of the first comparative example. This receiver includes an antenna 11, an RF unit 12 for converting the frequencies of a received high-frequency signal from the antenna 11 down into an intermediate frequency band (IF band) of a received analog signal 13, an analog-to-digital converter (A/D converter) 14 for converting the received analog signal 13 from the RF unit 12 into a received digital signal 15, a demodulator 16 for demodulating the digital received signal 15 from the A/D converter 14 to thereby produce received data 17, a synchronizing circuit 18 for establishing symbol synchronization on the basis of the received analog signal 13 from the RF unit 12, and a timing unit 20 for generating a timing signal 21, on the basis of a phase 19 of a symbol clock from the synchronizing circuit 18, to control the sampling timing in the A/D converter 14, the demodulation timing in the demodulator 16 and the output timing of the received data 17. The synchronizing circuit 18 has, as shown in Fig. 3, a comparator 102, a D-flip-flop 105, a selector 107, a controller 108, N counters 114 0 -114 N-1 , and a phase number detector 122. The comparator 102 detects a code 103 from the received analog signal 13 of IF band from the RF unit 12. The D-flip-flop 105 detects the variable points of the code 103 detected by the comparator 102 with the precision of a clock 104 from the outside, and establishes symbol synchronization on the basis of the detected variable points of the code. The frequency of clock 104 is N times as high as the symbol clock frequency f s , or is f s × N. The controller 108 generates a control signal 109 for switching the contact positions of the selector 107 in accordance with the clock 104 from the outside. The selector 107 changes its contact position in response to the control signal 109 from the controller 108. Thus, the output signal 106 from the D-flip-flop 105 is distributed to the N counters 114 0 -114 N-1 in accordance with the clock number (, or the time t 0 -t N-1 ) of the clock 104. The content of each of the N counters 114 0 -114 N-1 is incremented each time it receives the output signal 106 from the D-flip-flop 105. Thus, the output signals 118 0 -118 N-1 from the N counters 114 0 -114 N-1 indicate histograms of the variable points of the code at the N detected time points. The phase number detector 122 selects the maximum one of the output signals 118 0 -118 N-1 from the N counters 114 0 -114 N-1 (that is, the time, of the N detected time points, at which the histogram of the variable points of the code is the maximum), thus detecting the phase 19 of the symbol clock. The detected symbol clock phase 19 is supplied to the timing unit 20 (see Fig. 2). The operation of the synchronizing circuit 18 will be described with reference to Figs. 4A-4I. The phase detection is made at, for example, four times the symbol rate (namely, four times the symbol clock frequency f s ). Thus, as shown in Fig. 4A, there are four phases P 0 -P 3 within each symbol time. Fig. 4A illustrates the shape of the clock 104 having N times the symbol clock frequency f s (f s × N). When the received signal code 103 as shown in Fig. 4B is supplied from the comparator 102 to the D-flip-flop 105, the code 103 is received at the leading edge of clock 104. Thus, the output signal 106 from the D-flip-flop 105 has a waveform synchronized with the leading edge of the clock 104 as shown in Fig. 4C. In this example, the output signal 106 from the D-flip-flop 105 has a pulse waveform which rises at time t 1 , t 5 corresponding to phase P1 and then falls off at time t 3 corresponding to phase P 3 . The control signal 109 generated from the controller 108 on the basis of the clock 104 has such waveforms as shown in Figs. 4D-4I at times t 0 -t 5 . Therefore, at time t 1 , the D-flip-flop 105 is connected to the counter 114 1 corresponding to time t 1 since the selector 107 is switched to the associated contact position by the control signal 109 (see Fig. 4E) from the controller 108. As a result, the counter 114 1 is incremented in its contents by the leading edge of the output signal 106 from the D-flip-flop 105. At time t 5 , the D-flip-flop 105 is again connected to the counter 114 1 corresponding to time t 5 since the selector 107 is switched to the associated contact position by the control signal 109 (see Fig. 4I) from the controller 108. Consequently, the counter 114 1 is again incremented in its contents by the leading edge of the output signal 106 from the D-flip-flop 105. The phase number detector 122 shown in Fig. 3 has, as illustrated in Fig. 5, a maximum value detection circuit 302 for detecting the maximum one of the output signals 118 0 -118 N-1 from the N counters 114 0 -114 N-1 and producing the counter number (from 0 to N-1) corresponding to the counter with the detected maximum value as the symbol clock phase 19, and a timer 304 for measuring time on the basis of the clock 104 from the outside and generating a control signal 305 for controlling the maximum value detection circuit 302 to start its operation. Therefore, the phase number detector 122 selects the time, of the N detected time points, at which the histogram of the variable points of code 103 provides the maximum. As described above, since the synchronizing apparatus of this embodiment can all be formed of digital circuits as seen from the synchronizing circuit 18, it is possible to detect the zero-cross points of the received signal of IF band at N times as high as the symbol rate and thereby to establish the optimum symbol synchronization from the histogram at the detected time points. In addition, since the histogram detection is made at the zero-cross points, no erroneous operation is caused even if zero-cross points do not occur sequentially over several symbols like information symbol. (Second comparative example embodiment) The synchronizing apparatus of the second comparative embodiment is different from that of the first comparative example in that when any one of the counts of the N counters 114 0 -114 N exceeds a predetermined threshold, a phase number detector 112 1 produces as the symbol clock phase 19 the counter number of the counter having that count. Therefore, in the synchronizing apparatus of this embodiment, the symbol synchronization can be established earlier in the high-precision receiving environment than in the first embodiment of the invention in which the symbol synchronization is established after the lapse of a constant detected time as described above. The phase number detector 122 1 of the synchronizing apparatus of this embodiment has, as shown in Fig. 6, N comparators 402 0 -402 N-1 for comparing a certain threshold and the output signals 118 0 -118 N-1 from the N counters 114 0 -114 N-1 (see Fig. 3) and for producing output signals 403 0 -403 N-1 when the output signals 118 0 -118 N-1 respectively exceed the certain threshold, an OR circuit 404 for calculating the logical sum of the output signals 403 0 -403 N-1 from the N comparators 402 0 -402 N-1 , a counter number signal generator 410 for generating a counter number signal 411 indicating the counter numbers (from 0 to N-1) of the N counters 114 0 -114 N-1 on the basis of the clock 104 from the outside, and a D-flip-flop 407 for latching the counter number signal 411 from the counter number signal generator 410 in response to an output signal 405 from the OR circuit 404. Here, since the N counters 114 0 -114 N-1 are associated with the particular phase points of the symbol clock, respectively (see Figs. 4A-4I), the output signal from the D-flip-flop 407 indicates the symbol clock phase 19. In the phase number detector 122 1 , when any one of the output signals 118 0 -118 N-1 from the N counters 114 0 -114 N-1 is larger than a predetermined threshold, the OR circuit 404 produces the output signal 405, and the D-flip-flop 407 latches the associated counter number. Consequently, the synchronizing apparatus of this comparative example can detect the symbol clock phase 19 earlier than that of the first comparative example. (First embodiment) The synchronizing apparatus of the first embodiment of the present invention is different from those of the first and second comparative examples in that the phase number detector is formed by a combination of the phase number detectors shown in Figs. 5 and 6. Thus, the synchronizing apparatus of this embodiment can establish the symbol synchronization earlier in a high-precision receiving environment, and even under a low-precision receiving environment, it can establish the symbol synchronization after the lapse of a constant detected time. A phase number detector 122 2 in the synchronizing apparatus of this embodiment has, as shown in Fig. 7, a maximum value detection circuit 512 for detecting the maximum one of the output signals 118 0 -118 N-1 from the N counters 114 0 -114 N-1 (see Fig. 3) and producing an output signal 513 indicative of the counter number (from 0 to N-1) of the counter associated with the detected maximum value, a timer 502 for measuring time on the basis of the clock 104 from the outside and generating a first control signal 504 for controlling the maximum value detection circuit 512 to start its operation and a second control signal 503 for controlling a selector 514 to switch, N comparators 507 0 -507 N-1 for comparing a certain threshold with the output signals 118 0 -118 N-1 from the N counters 114 0 -114 N-1 , and producing output signals 508 0 -508 N-1 when the output signals 118 0 -118 N-1 respectively exceed the certain threshold, an OR circuit 509 for calculating the logical sum of the output signals 507 0 -507 N-1 from the N comparators 508 0 -508 N-1 , a counter number signal generator 530 for generating a counter number signal 531 indicating the counter numbers (from 0 to N-1) of the N counters 114 0 -114 N-1 on the basis of the clock 104 from the outside, a D-flip-flop 510 for latching the counter number signal 531 from the counter number signal generator 530 in response to an output signal 521 from the OR circuit 509, and a selector 514 for selecting any one of the output signal 513 from the maximum value detection circuit 512 and an output signal 511 from the D-flip-flop 510 in response to the second control signal 503 from the timer 502. The timer 502 of the phase number detector 122 2 measures time on the basis of the clock 104, and generates the second control signal 503 for controlling the selector 514 to select the output signal 511 from the D-flip-flop 510 until the lapse of a certain detected time and to select the output signal 513 from the maximum value detection circuit 512 after the lapse of the certain detected time. Therefore, when any one of the output signals 118 0 -118 N-1 from the N counters 114 0 -114 N-1 exceeds the predetermined threshold within a constant detected time, the OR circuit 509 produces the output signal 521, thus controlling the D-flip-flop 510 to latch the associated counter number. Then, this counter number is supplied as the symbol clock phase 19 through the selector 514 to the outside. Thus, the synchronizing apparatus of this embodiment can detect the symbol clock phase 19 earlier in a high-precision receiving environment than that of the first embodiment. When any one of the output signals 118 0 -118 N-1 from the N counters 114 0 -114 N-1 does not exceed the threshold within a constant detected time, the time, of the N detected time points, at which the histogram of the variable points of the code 103 is detected to be the maximum by the maximum value detection circuit 512 is supplied as the symbol clock phase 19 through the selector 514 to the outside. Thus, the synchronizing apparatus of this embodiment can establish the symbol synchronization even in a low-precision receiving environment after the lapse of a constant detected time. (Second embodiment) The synchronizing apparatus of the second embodiment of the present invention is different from those in the first comparative example in that the symbol synchronization is corrected after its establishment in association with the time at which the histogram exceeds a certain threshold. In other words, in the synchronizing apparatus of this embodiment, after the establishment of symbol synchronization the zero-cross points of the received signal of IF band are detected at N times as high as the symbol rate, and the histogram of the detected zero-cross points (from 0 to N-1) is calculated. When the time at which the histogram exceeds a certain threshold is before a time k (0≤k≤N-1) at which synchronization has been established, the symbol synchronization is corrected to be one clock (1/(N × fs)) before. When the time at which the histogram exceeds a certain threshold is after the time k (0≤k≤N-1) at which synchronization has been established, the symbol synchronization is corrected to be one clock (1/(N × f s )) after. When the time at which the histogram exceeds a certain threshold is equal to the time k (0≤k≤N-1) at which synchronization has been established, the symbol synchronization is not corrected. The operation of the synchronizing apparatus of this embodiment after the establishment of symbol synchronization will be described with reference to Fig. C. After the symbol synchronization has been established, as in the synchronizing apparatus of the first to third embodiments, a comparator 702 detects a code 703 from a received analog signal 701 of IF band. When the detected code 703 is supplied from the comparator 702 to a D-flip-flop 705, the code 703 is hit by the leading edge of a clock 704. Thus, an output signal 706 from the D-flip-flop 705 has a waveform synchronized with the leading edge of the clock 704. In addition, a controller 708 generates a control signal 709 in response to the clock 704 and supplies it to a selector 707. Thus, the control signal 709 controls three counters 713 k-1 , 713 k , 713 k+1 corresponding to the time points k-1, k, k+1 of the zero-cross points of code 703 to be incremented in their counts through the selector 707. When any one of the time points of the zero-cross points of code 703 is the time k at which synchronization has been established, the three counters 713 k-1 , 713 k , 713 K+1 are all incremented. A phase number detector 719 continuously produces a symbol clock phase 720 at which synchronization has been established. However, when the symbol clock phase after the establishment of synchronization detected as in one of the first to third embodiments is behind the symbol clock phase 720 at which synchronization has been established, this symbol clock phase 720 is delayed by one clock time of clock 704, and supplied to the outside as the new symbol clock phase 720. When the detected symbol clock phase after the detected establishment of synchronization is ahead of the symbol clock phase 720 at which synchronization has been established, this symbol clock phase 720 is advanced by one clock time of clock 704, and supplied to the outside as the new symbol clock phase 720. When the detected symbol clock phase after the detected establishment of synchronization is equal to the symbol clock phase 720 at which synchronization has been established, the symbol clock phase 720 at which synchronization has been established is supplied to the outside as it is. Here, since the symbol clock phase corresponds to time, when the detected time is before the time k at which synchronization has been established (namely, it is time k-1), the symbol synchronization is corrected to be one clock (1/(N × f s )) before. When the detected time is after the time k at which synchronization has been established (namely, it is time k+1), the symbol synchronization is corrected to be one clock (1/(N × f s )) after. When the detected time is equal to the time k at which synchronization has been established, the symbol synchronization is not corrected. Accordingly, the synchronizing apparatus of this embodiment is able to establish correct symbol synchronization by ± 1 clock timing correction after the establishment of synchronization. (Third embodiment) The synchronizing apparatus of the third embodiment of the present invention is different from that of the second embodiment in that timing correction is made after the establishment of synchronization in accordance with the burst length and clock precision. The receiver including the synchronizing apparatus of this embodiment has, as shown in Fig. 9, an antenna 801, an RF unit 802, an analog-to-digital converter (A/D converter) 804 for converting a received analog signal 803 of IF band into a received digital signal 805, a demodulator 806 for demodulating the received digital signal 805 to thereby produce received data 807, a synchronizing circuit 808 for establishing symbol synchronization on the basis of the received analog signal 803, and a timing unit 810 for generating a timing signal 811 on the basis of a phase 809 of symbol clock from the synchronizing circuit 808, thereby controlling the sampling timing in the A/D converter 804, the demodulation timing in the demodulator 806 and the output timing of received data 807. From the above construction point of view, this receiver seems to be similar to that including the synchronizing apparatus of the fourth embodiment (see Fig. 2). However, it is different from the receiver including the synchronizing apparatus of the fourth embodiment in that a timing correction parameter 812 for setting the frequency of the timing correction implementation is supplied from the outside to the timing unit 810, an indication signal 813 for indicating the start of timing correction is supplied from the timing unit 810 to the synchronizing circuit 808, and the synchronizing circuit 808 makes timing correction on the basis of the indication signal 813. In the receiver including the synchronizing apparatus of this embodiment, after the establishment of symbol synchronization the timing unit 810 generates the indication signal 813 indicative of the start of timing correction in accordance with the burst length and clock precision indicated by the timing correction parameter 812, and the synchronizing circuit 808 makes timing correction after the establishment of symbol synchronization in accordance with the generated indication signal 813. Thus, the timing correction implementation frequency can be controlled, and the consumption power can be reduced. (Fourth embodiment) The receiver including the synchronizing apparatus of the fourth embodiment of the present invention is different from that including the synchronizing apparatus of the third embodiment in that as shown in Fig. 10, a received digital signal 1005 from an analog-to-digital converter 1004 is supplied to a synchronizing circuit 1008 in place of a received analog signal 1003 from an RF unit 1002. In other words, the receiver including the synchronizing apparatus of this embodiment has an antenna 1001, the RF unit 1002, the analog-to-digital converter (A/D converter) 1004 for converting the received analog signal 1003 of IF band into the received digital signal 1005, a demodulator 1006 for demodulating the received digital signal 1005 to thereby produce received data 1007, the synchronizing circuit 1008 for establishing symbol synchronization on the basis of the received digital signal 1005, and a timing unit 1010 for generating, in accordance with a symbol clock phase 1009 from the synchronizing circuit 1008, a timing signal 1011 for controlling the sampling timing in the A/D converter 1004, the demodulation timing in the demodulator 1006 and the output timing of received data 1007. A timing correction parameter 1012 for setting the timing correction execution frequency is supplied from the outside to the timing unit 1010, and an indication signal 1013 indicative of the start of timing correction is supplied from the timing unit 1010 to the synchronizing circuit 1008, causing the synchronizing circuit 1008 to make timing correction. In the case where the received analog signal 1003 is used for synchronization, if there is a time difference between the time in which the received analog signal 1003 is transmitted from the RF unit 1002 to the A/D converter 1004 and the time in which the received analog signal 1003 is transmitted from the RF unit 1002 to the synchronizing circuit 1008, or if the A/D converter 1004 has a large conversion delay, the symbol synchronization established in the synchronizing circuit 1008 may be sometimes deviated away from the correct state. Particularly at a high symbol rate, this deviation greatly affects the quality of the received data 1007. However, in the receiver including the synchronizing apparatus of this embodiment, the synchronizing circuit 1008 is able to establish symbol synchronization by use of the received digital signal 1005 fed from the A/D converter 1004, and the received digital signal 1005 is supplied from the A/D converter 1004 to the demodulator 1006. Therefore, if the timing unit 1011 generates an optimum timing signal to the data sequence, the demodulator 1006 can maintain the most suitable timing. (Fifth embodiment) The receiver including the synchronizing apparatus of the present seventh embodiment of the present invention is different from that of the fourth embodiment in that a phase detection circuit shown in Fig. 11 is provided as part of the synchronizing circuit 1008 and timing unit 1010. This phase detection circuit has a first analog-to-digital converter (A/D converter) 1103 for converting an analog in-phase signal (I signal) 1101 into a digital in-phase signal, a second analog-to-digital converter (A/D converter) 1104 for converting an analog quadrature signal (Q signal) 1102 into a digital quadrature signal, a first absolute value integrator 1105 for integrating the digital in-phase signal over a certain time, a second absolute value integrator 1106 for integrating the digital quadrature signal over a predetermined time, a first register 1107 in which the output signal from the first absolute value integrator 1105 is stored, a second register 1108 in which the output signal from the second absolute value integrator 1106 is stored, a discriminator 1109 for detecting synchronization by use of the output signal from the first register 1107 and the output signal from the second register 1108, and a timing generation unit 1110 for generating a sampling timing signal for the first and second A/D converters 1103, 1104, a reset signal for the first and second absolute value integrators 1105, 1106, and a storage destination switching signal for the first and second registers 1107, 1108. To the timing generation unit 1110 are supplied the decision result from the discriminator 1109 and a synchronization start timing signal 1111 from the outside. This phase detection circuit operates at the synchronization pulling-in time as part of the synchronizing circuit 1008 and timing unit 1010 of the receiver including the synchronizing apparatus of the sixth embodiment. When the synchronization start timing signal 1111 is supplied from the outside to the timing generation unit 1110, the timing generation unit 1110 generates the sampling timing signal indicative of timing for each symbol having a given initial phase and supplies it to the first and second A/D converters 1103, 1104. Thus, the analog in-phase signal (I signal) 1101 and the analog quadrature signal (Q signal) 1102 are converted from analog to digital form. Then, the absolute values of the output digital signals from the first and second A/D converters are integrated by the first and second absolute value integrators 1105, 1106 over a predetermined time, respectively. The integrated values from the first and second integrators 1105, 1106 are stored in the first and second registers 1107, 1108, respectively. Thereafter, the timing generation unit 1110 supplies a sampling timing signal for each symbol having a different initial phase to the first and second A/D converters 1103, 1104, and the same operations are repeated. After the integrated values are obtained for some initial phases, all the integrated values stored in the first and second registers 1107, 1108 are supplied to the discriminator 1109, where the most probable integrated value is selected. The decision result indicative of the timing of the selected integrated value is supplied to the timing generation unit 1110. In the synchronizing apparatus of this embodiment having such phase detection circuit, the optimum timing can be obtained without consideration of delay in the analog circuits. (Sixth embodiment) The receiver including the synchronizing apparatus of the eighth embodiment of the present invention is different from that of the fourth embodiment in that a phase detection circuit shown in Fig. 12 is provided as part of the synchronizing circuit 1008 and timing unit 1010. This phase detection circuit has a first analog-to-digital converter (A/D converter) 1203 for converting an analog in-phase signal (I signal) 1201 into a digital in-phase signal, a second analog-to-digital converter (A/D converter) 1204 for converting an analog quadrature signal (Q signal) 1202 into a digital quadrature signal, an absolute value integrator 1205 for integrating the digital in-phase signal and the digital quadrature signal over a certain time, a register 1207 for storing the output signal from the absolute value integrator 1205, a discriminator 1209 for detecting synchronization by use of the output signal from the register 1207, and a timing generation unit 1210 for generating a sampling timing signal for the first and second A/D converters 1203, 1204, a reset signal for the absolute value integrator 1205, and a storage destination switching signal for the register 1207. To the timing generation unit 1210 are supplied a decision result from the discriminator 1209 and a synchronization start timing signal 1211 from the outside. This phase detection circuit operates at the synchronization pulling-in time as part of the synchronizing circuit 1008 and timing unit 1010 of the receiver including the synchronizing apparatus of the sixth embodiment. When the synchronization start timing signal 1211 is supplied from the outside to the timing generation unit 1210, the timing generation unit 1210 generates the sampling timing signal indicative of timing for each symbol having a given initial phase and supplies it to the first and second A/D converters 1203, 1204. Thus, the analog in-phase signal (I signal) 1201 and the analog quadrature signal (Q signal) 1202 are converted from analog to digital form. Then, the absolute values of the output digital signals from the first and second A/D converters are integrated by the absolute value integrator 1205 over a predetermined time. The integrated values from the integrator 1205 are stored in the register 1207. Thereafter, the timing generation unit 1210 supplies a timing signal for each symbol having a different initial phase to the first and second A/D converters 1203, 1204, and the same operations are repeated. After the integrated values are obtained for some initial phases, all the integrated values stored in the register 1207 are supplied to the discriminator 1209, where the most probable integrated value is selected. The decision result indicative of the timing of the selected integrated value is supplied to the timing generation unit 1210. In the synchronizing apparatus of this embodiment having such phase detection circuit, the optimum timing can be obtained without consideration of delay in the analog circuits. In addition, the synchronizing apparatus of this embodiment can be smaller-sized than that of the seventh embodiment. (Seventh embodiment) The receiver including the synchronizing apparatus of the seventh embodiment of the present invention establishes symbol synchronization according to the phase detection procedure (synchronization acquisition procedure) shown in Fig. 13. The receiver including the synchronizing apparatus of this embodiment has the same construction as that of the fifth embodiment. When the synchronization acquisition procedure is started at step 1301, the initial phase counter content i , the level integrated value L i of in-phase signal and the level integrated value L q of quadrature signal are all reset to 0 (at step 1302). Here, the initial phase counter content i can indicate five different initial phases (0-4) in order to divide the symbol time by four and finally to obtain one-eighth precision. The level integrated values L i , L q are absolute value addition variables for the levels of in-phase signal side and quadrature signal side. When the initial phase counter content i is zero, the initial phase is set at an arbitrary value, and the analog in-phase signal and analog quadrature signal are sampled (at step 1303). Then, the integration number-of-times counter content j, which is the contents of a counter for counting the number of times of integrating the absolute values, and p i [i], p q [i], which are variables for calculating the integration of the absolute values of the in-phase signal and quadrature signal, are all set to zero (at step 1304). At steps 1305 to 1307, the absolute value | I| of the in-phase signal is added to the variable p i [i], the absolute value | Q| of the quadrature signal is added to the variable P q [i], the absolute value | I| of the in-phase signal is added to the level integrated value L i , and the absolute value |Q| of the quadrature signal is added to the level integrated value L q . These operations are repeated N number of times of integration. Then, 1 is added to the initial phase counter content i (at step 1308), and if the initial phase counter content i after addition is less than 4(at steps 1309, 1310), the initial phase is deviated 1/4 by 1/4 (at step 1303). Thereafter, the operations of steps 1304 to 1307 are repeated. If the initial phase counter content i is larger than 4 at step 1310, the level integrated value L i and the level integrated value L q are compared with each other (at step 1311). Then, four variables r [0]-r [3] which are the addition of two successive sampling point levels are calculated depending on the results of comparison between the level integrated values L q and L i as follows (steps 1312, 1313). (1) When the level integrated value L i is larger than the level integrated value L p (at step 1312), the variables r [0]- r[4] are calculated by use of variables p i [i]: r [0]= p i [0] + p i [1] r [1]= p i [1] + p i [2] r [2]= p i [2] + p i [3] r [3]= p i [3] + p i [0] (2) When the level integrated value L q is larger than the level integrated value L i (at step 1313), the variables r [0]- r [3] are calculated by use of variables p q [i]: r [0]= p q [0] + p q [1] r [1]= p q [1] + p q [2] r [2]= p q [2] + p q [3] r [3]= p q [3] + p q [0] Thereafter, the maximum one of the calculated variables r [0]- r [3] is selected, and variables p x , p y are found (at step 1314). If the variable r [1] of the variables r [0]- r [3] calculated at step 1312 is the maximum, the timing of variable p i [1] and variable p i [2] can be decided to be most probable, and thus variable p x =variable p i [1], and variable p y =variable p i [2]. At step 1315, the final initial phase can be found by use of variables p x , p y . In the above example, since the most suitable point seems the timing of either variable p i [1], variable p i [2] or the intermediate point, the intermediate timing is found as the final initial phase. At step 1303, the initial phase is changed to the final initial phase found at step 1315, and the operations at the steps 1304 to 1309 are repeated. Then, at step 1316, the level integrated value L i and level integrated value L q are compared with each other. If the level integrated value L i is larger than the level integrated value L q , the largest one of the variables p x , p y , and p i [4] is selected (at step 1317). If the level integrated value L q is larger than the level integrated value L i , the largest one of the variables p x , p y , and p q [4] is selected (at step 1318). Since the timing point at which the selected variable is sampled can be considered to be the most probable synchronization position, that timing is employed as the initial phase (at step 1319), and the synchronization acquisition operation ends (at step 1320). (Eighth embodiment) The receiver including the synchronizing apparatus of the eighth embodiment of the present invention establishes symbol synchronization according to the phase detection procedure (synchronization acquisition procedure) shown in Fig. 14. The receiver including the synchronizing apparatus of this embodiment has the same construction as that of the sixth embodiment. When the synchronization acquisition procedure is started at step 1401, the initial phase counter content i is set at 0 (at step 1402). Here, the initial phase counter content i can indicate five different initial phases (0-4) in order to divide the symbol time by four and finally to obtain one-eighth precision. When the initial phase counter content i is zero, the initial phase is set at an arbitrary value, and the analog in-phase signal and analog quadrature signal are sampled (at step 1403). Then, the integration number-of-times counter content j , which is the contents of a counter for counting the number of times of integrating the absolute values, and p [i], which is a variable for calculating the integration of the absolute values of the in-phase signal and quadrature signal, are all set to zero (at step 1404). At steps 1405 to 1407, the absolute value | I| of the in-phase signal and the absolute value | Q| of the quadrature signal are added to the variable p [i]. These operations are repeated N number of times of integration. Then, 1 is added to the initial phase counter content i (at step 1408), and if the initial phase counter content i after addition is less than 4 (at steps 1409, 1410), the initial phase is deviated 1/4 by 1/4 (at step 1403). Thereafter, the operations of steps 1404 to 1407 are repeated. If the initial phase counter content i is larger than 4 at step 1410, four variables r [0]- r [3] which are the addition of two successive sampling point levels are calculated by use of variables p [i] as follows (at step 1413): r [0]= p [0] + p [1] r [1]= p [1] + p [2] r [2]= p [2] + p [3] r [3]= p [3] + p [0] Thereafter, the maximum one of the calculated variables r [0]- r [3] is selected, and variables p x , p y are found (at step 1414). If the variable r [1] of the variables r [0]- r [3] calculated at step 1413 is the maximum, the timing of variable p [1] and variable p [2] can be decided to be most probable, and thus variable p x =variable p [1], and variable p y =variable p [2]. At step 1415, the final initial phase can be found by use of variables p x , p y . In the above example, since the most suitable point seems the timing of either variable p [1], variable p [2] or the intermediate point, the intermediate timing is found as the final initial phase. At step 1403, the initial phase is changed to the final initial phase found at step 1415, and the operations at the steps 1404 to 1410 are repeated. If the initial phase counter content i after addition is larger than 4 at step 1409, the largest one of the variables p x , p y , and p [4] is selected (at step 1417). Since the timing point at which the selected variable is sampled can be considered to be the most probable synchronization position, that timing is employed as the initial phase (at step 1419), and the synchronization acquisition operation ends (at step 1420). (Ninth embodiment) The receiver including the synchronizing apparatus of the ninth embodiment of the present invention establishes symbol synchronization according to the phase detection procedure (synchronization acquisition procedure) shown in Fig. 15. The receiver including the synchronizing apparatus of this embodiment is an improvement in the performance of the phase detection procedure in the receiver including the synchronizing apparatus of the eighth embodiment. When the synchronization acquisition procedure is started at step 1501, the initial phase counter content i is set at 0 (at step 1502). Here, the initial phase counter content i can indicate five different initial phases (0-4) in order to divide the symbol time by four and finally to obtain one-eighth precision. When the initial phase counter content i is zero, the initial phase is set at an arbitrary value, and the analog in-phase signal and analog quadrature signal are sampled (at step 1503). Then, the integration number-of-times counter content j, which is the contents of a counter for counting the number of times of integrating the absolute values, and p [i], which is a variable for calculating the integration of the absolute values of the in-phase signal and quadrature signal, are all set to zero (at step 1504). At steps 1505 to 1507, the absolute value | I| of the in-phase signal and the absolute value | Q| of the quadrature signal are added to the variable p [i]. These operations are repeated N number of times of integration. Then, 1 is added to the initial phase counter content i (at step 1508), and if the initial phase counter content i after addition is less than 4 (at steps 1509, 1510), the initial phase is deviated 1/4 by 1/4 (at step 1503). Thereafter, the operations of steps 1504 to 1507 are repeated. If the initial phase counter content i is larger than 4 at step 1510, four variables r [0]- r [3] which are the addition of two successive sampling point levels are calculated by use of variables p [i] as follows (at step 1513): r [0]= p [0] + p [1] r [1]= p [1] + p [2] r [2]= p [2] + p [3] r [3]= p [3] + p [0] Thereafter, the minimum one of the calculated variables r [0]- r [3] is selected, and variables p x , p y are found (at step 1514). If the variable r [1] of the variables r [0]- r [3] calculated at step 1513 is the minimum, the timing of variable p [1] and variable p [2] can be decided to be most probable, and thus variable p x =variable p [1], and variable p y =variable p [2]. At step 1515, the final initial phase can be found by use of variables p x , p y . In the above example, since the most suitable point seems the timing of either variable p [1], variable p [2] or the intermediate point, the intermediate timing is found as the final initial phase. At step 1503, the initial phase is changed to the final initial phase found at step 1515, and the operations at the steps 1504 to 1510 are repeated. If the initial phase counter content i after addition is larger than 4 at step 1509, the smallest one of the variables p x , p y , and p [4] is selected (at step 1517). Since the timing point at which the selected variable is sampled can be considered to be the most probable synchronization position, 1/2 symbol behind that timing is employed as the initial phase (at step 1519), and the synchronization acquisition operation ends (at step 1520). Although the synchronizing apparatus of the tenth embodiment selected the largest one of the variables p x , p y and p [4] at step 1417, the smallest one thereof changes more quickly, and thus the synchronizing apparatus of this embodiment has higher detection precision. Since the minimum value, or detection position is located 1/2 symbol away from the symbol discriminated point, the timing is finally shifted that amount. The phase detection procedure in the synchronizing apparatus of this embodiment can be applied to the synchronizing apparatus of the ninth embodiment.

Claims: A synchronizing apparatus comprising: means (102) for detecting a code (103) from an input signal (13); latch means (105) for detecting from said code (103) the variable points of said code at several times as high as a symbol rate; means (107, 108, 114 0 -114 N-1 ) for calculating a histogram of the detected variable points of said code to time; and means (108, 122 2 , (502, 507 0 -507 N-1 , 509, 510, 512, 514, 530)) for deciding that a phase number at which said calculated histogram first exceeds a threshold is a symbol synchronization point, characterized in that , when there is no phase number at which said calculated histogram exceeds said threshold within a certain detected time, a phase number at which said calculated histogram takes the maximum value is a symbol synchronization point. A synchronizing apparatus according to claim 1, wherein after synchronization establishment, timing correction is performed by calculating said histogram at a position a certain phase unit before and after said synchronization establishment point, and detecting said associated correct phase number. A synchronizing apparatus according to claim 2, wherein when the precision of frequency is known to be low, said phase number detection is more frequently made to follow synchronization, but when the precision of frequency is known to be high, said phase number detection is less frequently made. A synchronizing apparatus according to any one of claims 1 to 3, wherein synchronization acquisition is performed by use of analog-to-digital converted data. A synchronizing apparatus according to claim 4, wherein when a synchronizing signal is a sine wave of which the phase is changed 180 degrees at each symbol, the absolute values of said analog-to-digital converted sampled data of in-phase and quadrature signals are added, respectively, and a more accurate one of said sums is selected. A synchronizing apparatus according to claim 4, wherein when a synchronizing signal is a sine wave of which the phase is changed 180 degrees at each symbol, the absolute values of said analog-to-digital converted sampled data of in-phase and quadrature signals are added. A synchronizing apparatus according to claim 5 or 6, wherein when said synchronizing signal is a sine wave of which the phase is changed 180 degrees at each symbol, calculation is performed for the sums of the absolute values of each of said in-phase and quadrature signals in said sampled data sampled at four times as high as a symbol rate, selection is made for a pair of adjacent maximum values of a larger one of said in-phase and quadrature signals of which the levels are previously determined, calculation is again performed for the sums of the absolute values of said sampled data sampled at an intermediate timing therebetween, the resulting three values are compared, and the timing for the largest one is determined, thereby acquiring synchronization. A synchronizing apparatus according to claim 5 or 6, wherein when said synchronizing signal is a sine wave of which the phase is changed 180 degrees at each symbol, calculation is performed for the sum of the absolute values of said sampled data of said in-phase and quadrature signals sampled at four times as high as a symbol rate, selection is performed for a pair of adjacent maximum values of said sum, calculation is performed for the sum of the absolute values of said sampled data sampled at an intermediate timing rate therebetween, the three resulting values are compared, and the timing for the largest one is determined, thereby acquiring synchronization. A synchronizing apparatus according to claim 7 or 8, wherein a pair of adjacent minimum values are selected, calculation is again performed for the sum of the absolute values of said sampled data sampled at an intermediate timing therebetween, the resulting three values are compared, and the timing for the smallest one is determined, thereby acquiring synchronization.

Inventors: HIRAMATSU KATSUHIKO, SUDO HIROAKI, UESUGI MITSURU, HIRAMATSU, KATSUHIKO, SUDO, HIROAKI, UESUGI, MITSURU
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1997
Main classification: H04L7
IPC codes: H04L7, H04L27