JP2008236565A - Method and apparatus for detecting head position of radio frame - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect, in simple configuration and within a short time, the head position of a radio frame of OFDM which is constituted of a plurality of symbols and in which a guard interval (GI) is provided in the head of each of symbols, the GI copying data about the number of predetermined samples at a terminal within the present symbol, and the first GI of a leading symbol is longer than the second GI of another symbol. <P>SOLUTION: Regarding an input frame and a signal delaying the input frame for a predetermined length, an auto-correlation is operated for each phase, and that output is integrated at respective times of first and second GIs. At any arbitrary position of a frame, correlation results as many as a number corresponding to a combination of arrays that can be generated within one frame for positions to dispose a symbol having the first GI and a symbol having the second GI are added with respect to the output of each integration value, and the result is stored. The phase of a peak value and a GI length are detected from each of stored correlation results and the head position of the frame can be determined. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a radio frame head position detection method and apparatus, and more particularly to OFDM (Orthogonal Frequency Division Multiplexing) that modulates and transmits an information signal using a plurality of carriers whose frequency components are orthogonal to each other. The present invention relates to a method and an apparatus for detecting the start position of a radio frame.

  In OFDM used in mobile communication, if a collection of a plurality of OFDM symbols is a transmission unit called a frame, it is necessary to extract a frame head position for processing after demodulation.

  FIG. 7 is a configuration example of an OFDM frame. FIG. 7 shows the configuration of an OFDM frame employed in mobile communication. One frame is composed of 3840 samples (samples) in 0.5 ms. In this example, one frame is composed of 7 symbols, These symbols are composed of 552 samples, and the remaining six symbols are composed of 548 samples. At the beginning of each symbol, a GI (guard interval) is provided as a guard interval to prevent intersymbol interference, the guard interval (referred to as GI1) of the leading symbol is 40 samples, and the guard interval length ( 40 samples) is generated by copying (copying) the signal to the head. The guard interval (referred to as GI2) of six symbols other than the head is 36 samples, and is generated by duplicating a signal corresponding to the guard interval length (36 samples) from the end portion of each symbol at the head of each symbol. . In the frame configuration shown in FIG. 7, the horizontal axis represents time and the vertical axis represents frequency distribution, indicating that a plurality of frequencies can be used.

  FIG. 8 is an explanatory diagram of a conventional method using a pilot pattern, and FIG. 9 is a configuration diagram using the pilot pattern. In this conventional example, on the transmission side, a pilot pattern (552 sample length) as shown in B is multiplexed and transmitted with respect to the frame pattern as shown in A in synchronization with the head position of the frame. When such a frame is received, it is assumed that detection of the head position of the frame is started at time t1 (arbitrary time position) as shown in C. In this case, the pilot pattern is notified to the receiving side in advance, and the highest correlation result is shown after the correlation is sequentially performed for each phase of each sample of the received frame by the correlation window of the pilot pattern of 552 samples. This is to detect the correlation start position, and is performed by the configuration shown in FIG.

  In the configuration of FIG. 9, when an OFDM radio signal is received from the receiving antenna 80, it is amplified by the RF amplifier 81, converted to a digital signal by the A / D converter 82, and input to the cross correlator 84. The cross-correlator 84 calculates the cross-correlation between the pilot pattern generated from the pilot replica pattern generator 83, the digital signal from the A / D converter 82, and 552 phases (pilot pattern length). However, the cross-correlation operation is executed continuously for the phase of (552 + 548 × 6) = 3840, and the correlation result for 552 samples is obtained for each phase by the integrator 85, and each obtained integration value is stored in the correlation result storage unit. 86 is stored for each phase, and a total of 3840 phases of correlation result data is obtained. When the peak value is detected by the peak value detection unit 87 from the data for 3840 phases stored in the correlation result storage unit 86, the phase at which the peak value is generated is calculated by the timing calculation unit 88, and the frame head timing is obtained.

  When the head of the frame shown in FIG. 8 is detected with the configuration shown in FIG. 9, the highest correlation result with the pilot pattern (head position) can be obtained at the position shown at time t2 in FIG.

  The methods shown in FIGS. 8 and 9 require a parallel correlator for the pilot pattern, and it is necessary to perform correlation processing with the pilot pattern notified to the receiving side in advance for one continuous frame.

  Further, there is a method of performing two-stage detection as a method that eliminates the correlation between consecutive one frames. That is, in the first stage, the input data is accumulated for 512 samples (delayed by 512 samples), the delayed data and the input data are correlated, and the leading position of the symbol of the input data is detected. After detecting the head position, as a second step, correlation processing with the pilot pattern is performed within a range of ± α with the symbol head position as the center. If the detection by this two-stage method is performed, it is possible to narrow the correlation range with the pilot pattern, but it takes time for processing for the first stage, and it takes a long time if the second stage is included.

In the conventional OFDM technology, a frame timing signal is generated by generating a frame timing signal by detecting a peak using a waveform obtained by performing a piecewise integration in the guard interval by using a null symbol for the correlation in the guard interval. There is a technique for synchronizing frame synchronization signals (see Patent Document 1).
JP 10-313284 A

  The method shown in FIGS. 8 and 9 requires processing time to perform correlation processing with a pilot pattern over one continuous frame, and requires a parallel correlator for the pilot pattern, and further acquires a pilot pattern. There is a problem that needs to be done. Further, the method using the two-step process using the pilot pattern has a problem that it takes a lot of time to detect the symbol head position in the first step.

  The present invention comprises a plurality of OFDM symbols, each having a guard interval obtained by copying (copying) a predetermined number of samples at the end of the data in the symbol at the beginning of each symbol, and the guard interval of the first symbol in the frame being other It is an object of the present invention to provide a method and apparatus for detecting the start position of a radio frame that can detect the start position of an OFDM frame having a configuration longer than the guard interval of a symbol in a short time with a simple configuration.

  FIG. 1 is a diagram illustrating the principle of the present invention. In the figure, the OFDM frame targeted by the present invention consists of n symbols, and an example where n = 7 will be described below. Each symbol has a guard interval obtained by copying data of a predetermined number of samples at the end of the symbol, and the number of samples (40 samples) of the first guard interval (GI1) of the symbol at the head of the frame follows. The frame is longer than the number of samples (36 samples) of the second guard interval (GI2) of 6 symbols. In FIG. 1, a is an input frame, b is a delay signal of an input frame obtained by delaying the frame a by 512 sample times, which is the number of samples excluding the guard interval in each symbol, and c is a frame head detection start position (arbitrary position). The auto-correlation between the input frame a and the delayed input frame b is taken, and the correlation result is integrated by the number of samples of the first guard interval and the number of samples of the second guard interval is integrated. It represents the parallel operation of the second integration d2. The outputs of the first and second integrals are added with integral values to correlate with seven types of patterns shown as e1 to e7 shown in e of FIG. This is because when the detection of the frame head position is started from an arbitrary symbol in the frame, the combination of guard interval lengths that appears when performing the guard interval correlation processing for one frame is a long guard interval (40 samples) and a short guard interval. The following seven combinations (1) to (7), which are combinations of intervals (36 samples).

(1) 40-36-36-36-36-36-36
(2) 36-36-36-36-36-36-40
(3) 36-36-36-36-36-40-36
(4) 36-36-36-36-40-40-36-36
(5) 36−36−36−40−36−36−36
(6) 36−36−40−36−36−36−36
(7) 36-40-36-36-36-36-36
The seven combination patterns for identifying which of the seven guard interval (GI) combinations correspond to e1 to e7 in FIG. In the pattern e1, the first guard interval GI1 (40 sample length) is located at the top (1), and the second guard interval GI2 (36 sample length) is located at the positions (2) to (7). In the pattern e2, the second guard interval GI2 is located at the top (1) to (6), and the first guard interval GI1 is located at (7). In the patterns e3 to e7, the first guard interval GI1 is arranged at the positions (6), (5), (4), (3), (2), and the second guard interval GI2 is arranged at other positions. Pattern.

  GI1 integration and GI2 integration values are added to the seven GI lengths of e1 to e7, and correlation results are added for each phase (two integration values are set in the GI length values of seven combinations) And the correlation result corresponding to each combination for each phase is stored in the storage unit f. This operation is performed for 552 phases (552 sample lengths) corresponding to the length of the symbol including the first guard interval GI1, and the integration value at that time is calculated after the next 552 phases for the same phase. It is added to the value and stored, and is repeatedly executed for one frame period (3840 samples). Thereby, 552 (phase) × 7 (seed) = 3864 pieces of data are obtained in the storage unit f. From this data, the peak value is detected by the processing of the peak value detection g, and the phase and guard interval length (or GI length combination) in which the peak value is detected are detected. A calculation is performed based on the detection result, and the head position of the frame is output.

  In the above description, the example shown in FIG. 1 shows the start detection operation of a frame configuration that differs only in the guard interval length inserted at the head of the frame. However, if the configuration can identify other guard interval positions of the frame, The start position of the frame can be detected by the same principle.

  According to the present invention, the start position of an OFDM frame that is composed of a plurality of symbols and whose guard interval length in a specific (first) symbol is different from the guard interval length of other symbols is detected. It becomes possible to do.

  If the structure of the guard interval of the frame is known, it is possible to detect the frame head position without specifying a pilot pattern for specifying the head or a code of the synchronization channel. The frame head position can be detected in a shorter time than the conventional two-stage method of GI correlation and pilot pattern correlation.

  FIG. 2 is a diagram showing the configuration of the embodiment. In the figure, 10 is an antenna, 11 is a radio frequency (RF) amplification unit, 12 is an A / D conversion unit, 13 is a delay unit, 14 is an autocorrelation unit, and 15-1 is a first guard interval (GI1). ) For the integration of the length (40 samples) of the second guard interval (GI2), and 16-2 for the integration of the length (36 samples) of the second guard interval (GI2). -16-7 are correlation result addition units # 1 to # 7, 17 are constituted by a memory, 552 phases × 7 types = correlation result storage unit storing 3864 correlation results, 18 is a peak value detection unit, 19 Is a timing calculation unit.

  In this embodiment, a radio signal having the OFDM frame configuration shown in FIG. 1 is received from the antenna 10, the radio signal is amplified by the RF amplifier 11, and the output signal is converted to a digital signal by the A / D converter 12. Is done. On the one hand, the digital signal is input to the autocorrelation unit 14 and the other is input to the delay unit 13. The delay unit 13 delays the data length of 512 samples excluding the guard interval in each symbol of the OFDM frame. The output signal from the A / D converter 12 and the delayed output signal from the delay unit 13 are subjected to autocorrelation calculation in the autocorrelation unit 14, and the output is output for 40 samples by the first integration unit 15-1. Integration is performed, and 36 samples are integrated by the second integration unit 15-2. These two integrated values are added by correlation result adding units 16-1 to 16-7 corresponding to the seven combination patterns of each guard interval. This combination pattern is the combination shown in (1) to (7) described in the explanation of FIG. 1, and is shown as e1 to e7 in FIG.

  Correlation result addition values corresponding to the respective phases of the first and second integration units by the correlation result addition units # 1 to # 7 provided corresponding to the combinations of (1) to (7) above are provided for each phase. Stored in the correlation result storage unit 17 for each combination. Thus, when the data for 552 phases (for the head symbol length) is stored in the correlation result storage unit 17, the maximum value is detected by the peak value detection unit 18. When the peak value is detected, the frame start position is calculated by the timing calculation unit 19 based on the phase and the combination pattern type.

  Next, a specific operation example of the embodiment will be described with reference to time charts (part 1) to (part 3) of the embodiment shown in FIGS. FIG. 6 is an example of correlation result addition values for each phase and each combination corresponding to the time chart of the embodiment.

  3 to 5, a is a received signal, b is a received signal delayed by a delay unit of 512 sample times (13 in FIG. 2), c is an autocorrelation start of the received signal a and the delayed received signal b (arbitrary frame) This represents the time (or phase) from the start detection start point), and each numerical value of 0, 1, 2,... Is the time from the start point (phase, corresponding to the number of samples). When autocorrelation is started by the autocorrelation unit (14 in FIG. 2), the output is integrated by 36 samples by the first integration unit (15-1 in FIG. 2), and phase 0, 1, 2,... Shows the state of integration started, 40 samples are integrated in the second integration unit (15-2 in FIG. 2), and phase 0, 1, 2,. Shows the state of integration started. In the case of d1, since the second guard interval is 36 samples, the correlation results of the signals from 0 to 35 starting from the start position are integrated, and then the correlation results of the signals from 1 to 36 are integrated. Thereafter, the same process is sequentially performed for each phase. In the case of e1, the correlation result of the signals from 0 to 39 at the start position is integrated for 40 samples that is the length of the first guard interval, and then the correlation result of the signals from 1 to 40 is integrated. Thereafter, the same integration is performed for each phase.

  FIG. 4 shows the received signal and the delayed received signal following FIG. 3, and d3 and e3 show the integration of 36 samples and the integration of 40 samples when it reaches 550 (samples) from the frame head detection start position. FIG. 5 further shows a state in which the integration of 36 samples and the integration of 40 samples after 3838 samples are executed for a plurality of consecutive phases from the frame head detection start time after the time of FIG.

  FIG. 6 shows a correlation result storage that stores correlation result addition values for combinations 1 to 7 of the GI length arrangement (guard interval combination pattern) for a part of phases 1, 2,. (17 in FIG. 2) is shown. That is, for phase 1, for the GI length sequence of combination 1, the correlation result addition values are “0”, “552”, “1100”, “1648”, “2196”, “2744”, “3292”. An addition value is obtained, and for each GI length sequence of combination 2, addition values of “0”, “548”, “1096”, “1644”, “2192”, “2740”, “3288” are obtained, Similarly, the addition value of the correlation result is obtained for combination 3 to combination 7.

  When the correlation result addition data as shown in FIG. 5 is obtained as 552 phases × 7 types = 3864 data, the peak value of the maximum correlation value is detected, and the type of the phase and guard interval combination ( Or guard interval length) can be detected.

It is a principle explanatory view of the present invention. It is a figure which shows the structure of an Example. It is a figure which shows the time chart (the 1) of an Example. It is a figure which shows the time chart (the 2) of an Example. It is a figure which shows the time chart (the 3) of an Example. It is a figure which shows the example of data of the correlation result addition value corresponding to the time chart of an Example. It is a figure which shows the structural example of an OFDM frame. It is explanatory drawing of the method using a pilot pattern. It is a block diagram using a pilot pattern.

Explanation of symbols

a input frame b delayed signal of input frame c autocorrelation d1 first integration d2 second integration e1 to e7 guard interval combination f storage unit g peak value detection

Claims (3)

It is composed of a fixed number of symbols, and has a guard interval obtained by copying data of a predetermined number of samples at the end of its own symbol at the beginning of each symbol, and the first guard interval of the first symbol of the frame is another symbol In the method for detecting the start position of a radio frame longer than the second guard interval of
An input frame and a signal obtained by delaying the input frame by a predetermined length are input, an autocorrelation operation is performed for each phase, and the output is integrated with the time of the first and second guard intervals,
Corresponds to the combination of the arrangement of the first and second guard intervals that can be generated in one frame at the arrangement position of the symbol having the first guard interval and the symbol having the second guard interval at an arbitrary position of the frame. The number of correlation results is added to the output of each integral value, and the result corresponding to each array combination for each phase is stored.
From the stored correlation results, the phase of the peak value and the guard interval length are detected,
A method of detecting a start position of a radio frame, wherein a start position of a frame is obtained from the detected peak value. In claim 1,
The radio frame is composed of seven symbols,
The delay time of the input frame for taking the autocorrelation is the time obtained by removing the guard interval from the symbol length,
7. A method of detecting a start position of a radio frame, wherein the number of combinations of the first and second guard intervals is seven. It is composed of a fixed number of symbols, and has a guard interval obtained by copying data of a predetermined number of samples at the end of its own symbol at the beginning of each symbol, and the first guard interval of the first symbol of the frame is another symbol In the radio frame head position detection device longer than the second guard interval,
A delay unit for delaying an input frame by a time obtained by removing the guard interval from the symbol length;
An autocorrelation unit that performs autocorrelation by inputting an input frame and a frame delayed by the delay unit;
First and second integration units that receive the output of the autocorrelation unit and integrate the lengths of the first guard interval and the second guard interval;
The outputs of the first and second integrators are input, and the first and second positions that can be detected as arrangement positions of a symbol having a first guard interval and a symbol having the second guard interval at an arbitrary position of the frame. A correlation result adding unit for adding correlation results corresponding to combinations of two guard interval arrays;
A storage unit for storing the output from the correlation result addition unit,
An apparatus for detecting the start position of a radio frame, comprising: detecting a peak value from the storage unit; and detecting a frame head from a phase detected by the peak value.

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