JPH1188455A - System for synchronizing frame - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extract an advance wave position even under multi-path phasing which is generated by plural waves being more than three. SOLUTION: A mutually correlative peak position being leading most in terms of a time in a stipulated time window is detected. The mutually correlative value of a reception signal with a unique word signal is calculated(101) and a threshold value F0 is calculated from its max. value(103). A reception timing in a succeeding frame is corrected so as to permit a first peak position P0 which exceeds the threshold value F0 for the first time to be a synchronizing point in the succeeding frame(112).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio communication device, and more particularly to a frame synchronization method for temporally synchronizing a radio signal transmitted from a communication partner in a multipath fading environment.

[0002]

2. Description of the Related Art As a conventional frame synchronization method, "16Q"
Frame Synchronization Method for Equalizer in High-Speed Data Transmission of AM-TDMA Mobile Radio ", IEICE Communication Spring Conference B-362, 1994.

[0003] In a multipath fading environment, the error rate characteristic is extremely deteriorated due to the influence of intersymbol interference due to a delayed wave. An equalizer is used to remove the influence of the intersymbol interference on the receiving side.

[0004] In order to remove the intersymbol interference by the equalizer and restore the original transmitted signal, it is necessary that information of a direct wave and a delayed wave due to reflection or the like be input to the tap of the equalizer. Therefore, in order to sufficiently bring out the performance of the equalizer, the synchronization position that defines the cutout timing of the received data input to the equalizer is important.

Therefore, usually, the equalizer prepares the number of taps for a time twice as long as the expected delay amount in consideration of the case of synchronizing with the delay wave. However, especially DFE (Decisio
n When the RLS (Recursive Least Squares) algorithm is used as the propagation path estimation algorithm in an equalizer of the type (Feedback Equalizer), the number of taps is reduced as much as possible because the processing amount is proportional to the square of the number of taps There was a request to do so.

[0006] In the above-mentioned literature, it is stated that by using the first wave of received data input to the equalizer as a synchronization point, synchronization with a delayed wave can be avoided and performance can be maintained with a small number of taps.

FIG. 2 shows an example of sampled received I and Q signals 200 after quadrature detection. In FIG. 2, the upper part shows the I signal 201 and the lower part shows the Q signal 202. Generally, a signal prescribed for time synchronization on the transmitting side is inserted in the received signal 200. This predetermined signal is called a unique word signal. FIG. 3 shows an example of the unique word signal. In FIG. 3, a unique word signal 300 is shown.
Is composed of a fixed number of samples.
5 shows a signal 302.

[0008] Received signal 2 sampled at fixed time intervals
By calculating the cross-correlation between 00 and the unique word signal 300, the position of the unique word signal in the received signal is detected. The sampled received I and Q signals are
i (i) and Rq (i) (where 0 ≦ i). Also, the I and Q signals of the unique word signal are represented by Ui (j) and Uq (j), respectively.
(However, 0 ≦ j <N, N is a specified value). From these, the cross-correlation value S (i) between the received signal and the unique word signal
Is shown as in the following Equation 1.

[0009]

(Equation 1)

FIG. 4 shows the cross-correlation value S (i) between the received signal and the unique word signal according to equation (1). In the above conventional example, attention is paid to the two peak positions P1 and P2 of the cross-correlation values shown in FIG. 4, and the leading wave is extracted from the received signal as a synchronization point.

This flow will be described with reference to FIG. The cross-correlation value between the received signal and the unique word signal is calculated (5
01), the cross-correlation maximum value F1 and the time P1 are stored (502). Next, a threshold value F0 is calculated from the maximum cross-correlation value F1 in order to detect whether the received signal waveform is a single wave or a combination of two waves (503). The coefficient TH for calculating the threshold is a constant determined in the system. Further, the second largest cross-correlation value is stored as F2 and the time is stored as P2 (50).
4).

The values of F2 and F0 are compared (505). 2
When the second largest cross-correlation value F2 does not exceed the threshold value F0 (F2 <F0), the received signal is regarded as one wave, and P1 is stored as the synchronization point P0 that defines the reception timing in the next frame ( 508). On the other hand, when F2> F0, it is determined that the received signal consists of two waves, and P1 and P1
The second time position is compared (506). If P1 is temporally earlier than P2, it is determined that P1 corresponds to the direct wave, and P1 is stored as the synchronization point P0 (508). P
When 2 is earlier than P1 in time, it is determined that P2 corresponds to the direct wave, and P2 is stored as the synchronization point P0 (507). At the next frame timing, the reception timing is corrected so as to be at a position one frame time after the stored synchronization point P0 (509). By this means, it is possible to synchronize with the direct wave at the next frame timing, and it is not necessary to assume synchronization with the delay wave, so that the number of taps of the equalizer can be set to at most the delay time. As a result, the processing amount can be reduced by reducing the number of taps of the equalizer.

[0013]

In such prior art, attention is paid only to the maximum value and the second largest value of the cross-correlation value, and a two-wave Rayleigh fading environment is assumed. However, in a real environment, not only the direct wave and only one reflected wave are received. According to the related art, the position of the preceding wave cannot always be extracted in a multipath fading environment generated by a plurality of three or more waves, and there is no guarantee that the desired reception performance can be obtained.

[0014]

In order to solve the above-mentioned problems, it is desirable to employ a method capable of capturing the first wave in time without depending on the number of waves arriving at the receiver. Therefore, in the present invention, the position of the first cross-correlation peak in time within the specified time window is detected.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to FIGS. FIG. 1 is an example of a synchronization acquisition flow according to the present invention. The cross-correlation value between the received signal and the unique word signal is calculated in the same manner as in the conventional example (101). FIG. 4 shows the calculation results. The maximum value F1 of the cross-correlation value is stored (1
02), a value F0 obtained by multiplying F1 by the coefficient TH is calculated as a threshold value (103).

A cross-correlation value position exceeding the threshold value F0 is searched by comparing the cross-correlation value with the value of the threshold value F0 in order from the head of the sample of the received signal (104).
To 107). By this processing, in the example of FIG. 4, the point a is detected as a time position where the threshold value F0 is first exceeded. a
The time position i at the point and the cross-correlation value A are stored.
The cross-correlation value B one sample later (i + 1) is obtained (10
8) Compare with the stored cross-correlation value A (109).
If the cross-correlation value B after one sample is large, it is determined that the first cross-correlation peak position has not been detected yet,
The time position i and the cross-correlation value A are updated to the contents (i + 1, B) one sample later (110), and the same operation is repeated (108 to 110). If the cross-correlation value one sample later in time is smaller, the time position currently stored assuming that the first peak position has been detected is set as the synchronization point in the next frame (111). In the example of FIG. 4, the reception timing is corrected so that the searched first cross-correlation peak position P2 becomes the synchronization point in the next frame.

This process is performed within a prescribed time window after synchronization is acquired in the first frame. The size of the time window can be determined by the system. Since the cross-correlation peak position does not change significantly from frame to frame, synchronization can be reliably acquired with a smaller amount of processing.

When the reception timing is corrected, the timing is not corrected by a necessary correction amount at a time.
An upper limit of the amount of correction for one time may be set (for example, 1/4 symbol time). If the maximum value F1 of the cross-correlation value becomes extremely large due to the multipath fading, the peak value of the preceding wave to be originally captured becomes equal to or less than the threshold value F0, and the delayed wave is captured. Things can happen. By setting the upper limit of the correction amount, large correction of the synchronization position can be prevented. As a result, the data cutout position to the equalizer is not much different from the case where the preceding wave is captured, so that the performance can be prevented from deteriorating.

Next, an example of the configuration of a wireless device according to the present invention will be described with reference to FIG. The received signal 601 received via the antenna 602 is subjected to amplification and frequency conversion by the RF unit 603, and becomes a received IF signal 604. From the reception IF signal 604, an I signal 608 and a Q signal 609 of the reception signal are extracted by a quadrature detector 605 and LPFs 606 and 607 for limiting a reception band. The extracted I signal 608 and Q signal 609 are sampled by A / D converters 610 and 611, converted into digitized reception I signal 612 and reception Q signal 613, and stored in memory 614. The received I signal 612 and the received Q signal 613 stored in the memory 614 calculate a cross-correlation value between the received I signal 612 and the received Q signal 613 with a unique word signal stored in advance.

The temporally leading peak position is extracted from the calculated cross-correlation value as described above, and the synchronization point in the next frame is determined. This synchronization point is notified to the timing management unit 616, and corrects various timings including the reception timing of the wireless device. In the next frame, at the reception timing instructed by the timing management unit 616, the memory 6
The storage of the received signal into the received signal stream 14 is started, and the stored received signal is passed to the equalizer 617 at the subsequent stage, where it is converted into a received bit stream 618.

The following method is also conceivable besides limiting the correction amount of the reception timing based on the cross-correlation peak position detected as described above to a predetermined range. For example, using the method described above, the difference between the cross-correlation peak position P0 detected as shown in FIG. 7 and a predetermined reception position is obtained. The predetermined receiving position is a receiving position that is used as a reference when synchronizing with the base station in the wireless device.
The wireless device adjusts the timing so that the predetermined receiving position matches the unique word signal detecting position from the base station. The frequency of this difference amount is recorded in a database as shown in FIG. The unit of the difference amount in this database is the aforementioned sample unit. From this database,
By dividing the product sum of each difference and the frequency by the sum of the frequencies, the average value of the past differences can be calculated. The reception timing in the next frame may be corrected based on the average value of the past difference amounts.

[0022]

According to the present invention, it is possible to detect a temporally leading cross-correlation peak position without depending on a plurality of arriving wave numbers. This has the effect of reducing the number of taps in the equalizer by making the position of the received data input to the equalizer temporally based on the first cross-correlation peak position.

[Brief description of the drawings]

FIG. 1 is a diagram showing a flow of a frame synchronization method according to the present invention.

FIG. 2 is a diagram illustrating an example of a received signal.

FIG. 3 is a diagram showing an example of a unique word signal.

FIG. 4 is a diagram illustrating an example of a cross-correlation value between a received signal and a unique word signal.

FIG. 5 is a diagram showing a flow of a conventional example.

FIG. 6 is a diagram showing an example of a receiver configuration according to the present invention.

FIG. 7 is a diagram illustrating an example of a difference between a peak detection position and a predetermined reception position according to the present invention.

FIG. 8 is a diagram showing an example of a database relating to a difference amount according to the present invention.

[Explanation of symbols]

101-112: Processing flow in the present invention, 200:
Received sample signal, 201: Received sample I signal, 20
2: reception sample Q signal, 300: unique word signal, 301: unique word I signal, 302: unique word Q signal, 501-509: processing flow in the conventional example, 601: reception signal, 602: antenna, 603:
RF unit, 604: reception IF signal, 605: quadrature detector,
606, 607: LPF, 608: received I signal, 60
9: reception Q signal, 610, 611: A / D converter, 61
2: digitized reception I signal, 613: digitized reception Q
Signal, 614: memory, 615: cross-correlation calculator, 61
6: Timing management unit, 617: Equalization unit, 618: Received bit stream.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Eimatsu Moriyama 4-2-1 Nukikitamachi, Koganei-shi, Tokyo Inside Communications Research Laboratory, Ministry of Posts and Telecommunications

Claims (4)

[Claims] 1. A received signal is sampled at a certain time interval, a specified number of samples are extracted from the sampled signal, and a cross-correlation value between the extracted sample and a known signal having the same number of samples is obtained. Are calculated at regular time intervals, and among the calculated cross-correlation values, cross-correlation values exceeding a prescribed threshold value are selected, and among the selected cross-correlation values, the earliest time-dependent cross-correlation value is selected. A frame synchronization method characterized by sequentially comparing values in a temporally slower direction from a correlation value and performing time synchronization using peak position information of a cross-correlation value detected first. 2. The frame synchronization according to claim 1, wherein a cross-correlation value between the extracted sample and a known signal having the same number of samples is calculated at predetermined time intervals within a specified time range. Method. 3. The method according to claim 1, wherein when time synchronization is performed using peak position information of a cross-correlation value detected first, the amount of reception timing to be corrected is limited to a predetermined range. 3. The frame synchronization method according to 1. 4. When time synchronization is performed using peak position information of a cross-correlation value detected first, a difference amount between the peak position and a predetermined reception position is recorded, and the average of the difference amounts is recorded. 3. The frame synchronization method according to claim 1, wherein the reception timing of the next frame is modified according to the value.