JP2009260799A - Delay detection and demodulation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform excellent reception, against the effect of code interference or phasing, in a narrow-band minimum shift keying (MSK) modulation system. <P>SOLUTION: A delay detection and demodulation device comprises: a phase detecting means 10 for detecting and outputting phase data from a received phase modulation signal; a 2-bit delay detecting means 20 for outputting phase difference data by subtracting phase data preceding to, by two symbols, the phase data outputted from the phase detecting means 10; a data temporary determination means 40, to which the phase difference data from the 2-bit delay detecting means 20 are input, for comparing data subsequent by one symbol with a prescribed threshold and implementing hard determination; and a data determination means 30, to which the phase difference data from the 2-bit delay detecting means 20 are input, for comparing data previous and subsequent by one symbol with the prescribed threshold in accordance with a determination result of the data temporary determination means 40 and performing soft determination and hard determination. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a delay detection demodulator used in, for example, digital mobile communication.

  In the delay detection demodulator, as disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 9-116588), not only the influence of fading but also a bit error rate in a Gaussian transmission path (that is, a transmission path that receives Gaussian noise). As a method to improve the deterioration of characteristics, “In the detection means, the phase difference data is input and the noise component is detected by comparing the phase difference data with the reference value, and the correction value is set based on the detected noise component. In addition, it is described that a correction circuit for correcting the phase difference data output after one symbol of the phase difference data with a set correction value is provided.

Japanese Patent Laid-Open No. 9-116588 (FIG. 1, abstract)

In digital mobile communications, it is necessary to limit the signal bandwidth for effective use of frequency, and a Gaussian low-pass filter (ie, Gaussian function is used for the MSK (Minimum Shift Keying) modulation method with a wide occupied bandwidth. In a narrow band modulation signal such as GMSK (Gaussian-filtered Minimum Shift Keying) that has passed through the filter), even if a delay detection demodulator such as that disclosed in Patent Document 1 is used, it can be used outside the Gaussian transmission line. There is a problem that the influence of intersymbol interference (also referred to as intersymbol interference) that causes the reception error rate characteristic degradation is large.
Intersymbol interference (intersymbol interference) is a phenomenon in which the next bit is affected by what the previous bit is.

As a system that is not easily affected by intersymbol interference and enables efficient detection, “a 2-bit delay detection that demodulates by performing 1-bit differential encoding on a transmission data string among delay detections” Are known.
The 2-bit delay detection method is described in, for example, the IEICE Transactions on '82 / 10 Vol.J65-B No.10 p1253 “Error rate characteristics of differentially encoded GMSK 2-bit delay detection method”. .
However, when 2-bit delay detection is applied to a narrow-band MSK modulation scheme, the effect of intersymbol interference increases due to the use of a filter, so that the reception error rate characteristic is greatly degraded.

  The present invention has been made to solve the above-described problems, and delay detection that can reduce the effects of fading, intersymbol interference, etc., even for an MSK modulation scheme limited to a narrow band. An object of the present invention is to provide a demodulator (delay detection demodulator).

  A delay detection demodulator according to the present invention includes a phase detection unit that detects and outputs phase data from a received phase modulation signal, and subtracts phase data two symbols before from the phase data output from the phase detection unit. 2-bit delay detection means for outputting phase difference data and data provisional determination means for inputting the phase difference data from the 2-bit delay detection means and comparing the data after one symbol with a predetermined threshold value to make a hard decision Then, the phase difference data from the 2-bit delay detection means is input, and soft decision and hard decision are made by comparing the data before and after one symbol with a predetermined threshold according to the decision result of the data temporary decision means. And a data determination means for performing.

According to the present invention, even when the eye pattern is vertically asymmetric, such as the MSK modulation method limited to a narrow band, and the identification threshold value cannot be set to the center, the threshold value can be selected using the preceding and succeeding symbol determination results. Better characteristics can be obtained than when the threshold value is set with an eye pattern considering all patterns (that is, in the case of GMSK 2-bit delay detection).
Therefore, it is possible to provide a delay detection demodulator that can reduce the influence of fading, intersymbol interference, etc., even with respect to the MSK modulation scheme limited to a narrow band.
The “eye pattern” is described in, for example, “CQ Publisher, Wireless Communication and Digital Modulation / Demodulation Technology Chapter 5”.

Embodiment 1
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram conceptually showing an overall configuration of a data receiving system using a delay detection demodulator (delay detection demodulator) according to the present invention.
As shown in FIG. 1, this system includes a receiving antenna 100 that receives an RF signal, a receiving device 200 that performs amplification, band limitation, frequency conversion, and the like on the RF signal received by the receiving antenna 100 and outputs an IF signal. An IF signal output from the receiving device 200 is input, and a delay detection demodulator (delay detection demodulator) 300 that outputs determination values (soft decision data and hard decision data) described later is included.
The decision values (soft decision data, hard decision data) output from the delay detection demodulator 300 are input to a decoder (not shown) and used for subsequent data processing.

FIG. 2 is a diagram illustrating an internal configuration of the delay detection demodulator 300.
In FIG. 2, a phase detector (phase detector) 10 detects the phase data of the IF signal input from the receiving apparatus 200 and outputs the phase data.
The phase data output from the phase detection unit 10 is input to a 2-bit delay detection unit (2-bit delay detection means) 20 to perform delay detection.
It is assumed that the transmission data sequence that is an RF signal input to receiving apparatus 200 is modulated with a data sequence that has been subjected to 1-bit differential encoding.
The 2-bit delay detection unit 20 subtracts the phase data two symbols before from the phase data output from the phase detection unit 10 and outputs phase difference data.

The phase difference data output from the 2-bit delay detection unit 20 is input to a data determination unit (data determination unit) 30 and a data temporary determination unit (data temporary determination unit) 40 described later.
FIG. 3 is a diagram illustrating the configuration of the data determination unit 30, and FIG. 4 is a diagram illustrating the configuration of the data provisional determination unit 40.
The phase difference data input to the data determination unit 30 shown in FIG. 3 is obtained by subtracting the threshold selected by the first data determination unit 32 and outputting a determination value (soft determination data). The subsequent decoding process is performed.

A threshold selection method in the first data determination unit 32 will be described.
First, a hard decision is performed on the data one symbol before input to the first data determination unit 32 and input to the first threshold setting unit 33.
Further, the data temporary determination unit 40 shown in FIG. 4 performs hard determination on the data after one symbol, and inputs the determination result to the first threshold setting unit 33.
That is, the threshold value for the symbol for which soft decision is to be performed is selected from the hard decision result of one symbol before and after the symbol for which soft decision is to be performed.

“Hard decision” is for judging whether “0” or “1” for 1-bit data. If the value is larger than the set threshold, “1” is set. If there is, it is determined as “0”.
Further, “soft decision” refers to making an ambiguous decision by setting a plurality of threshold values and increasing the number of decision values.

The determination values (that is, the soft determination data and the hard determination data) output from the data determination unit 30 are used for data error correction and the like in a subsequent device (not shown).
Moreover, since the determination result by the 2nd data determination part of the data temporary determination part 40 is a temporary determination, it is only a hard determination.
Further, the bit variation range to be determined is determined by the pattern of data before and after the determination (arrangement of “0” and “1”).
Compared to the data provisional determination unit 40 using only the past 1 bit, the data determination unit 30 using the past and future 2 bits has a larger amount of information. Therefore, the data determination unit 30 having the first threshold setting unit 33 can narrow down the variation range of the bit to be determined.

When 2-bit delay detection is performed by the narrow band MSK modulation method, the eye pattern has a vertically asymmetrical characteristic, so the threshold value must be set to a value shifted from the center.
For this reason, the reception error rate characteristic is deteriorated as compared with the MSK modulation method in which band limitation is not performed.
However, focusing on one symbol before and after, since there is a limited phase difference transition depending on the data pattern, it is possible to set a threshold other than a value shifted from the center that is considered in the entire narrowband MSK modulation system. .
Therefore, it is possible to reduce the degradation of the reception error rate characteristic as compared with the 2-bit delay detection by the narrow band MSK modulation method.

In the data temporary determination unit 40 illustrated in FIG. 4, the second threshold setting unit 43 of the data determination unit performs a hard determination that creates a data determination result to be used under threshold selection conditions.
Data obtained by the 2-bit delay detection is input to the data determination unit and is also input to the data temporary determination unit 40.
The data temporary determination unit 40 gives a delay amount that is one symbol smaller than that of the data determination unit 30, and the data determination unit 30 generates data after one symbol for the symbol for which the soft decision is performed.

The second threshold value setting unit 43 inputs data one symbol before the hard decision data by the temporary data decision unit 40, selects a threshold value from the value, and performs a hard decision.
The result of the hard decision is output to the data decision unit 30.

As described above, in the case of the narrow band MSK modulation scheme, the eye pattern is asymmetrical in the vertical direction, so the threshold setting unit 1 also selects the threshold value to compare with the case where the threshold value is fixed, Reduce characteristic deterioration.
However, unlike the threshold setting unit 2, only the data one symbol before is used, so that the transition of the phase difference is different, and the selectable threshold value is different from the threshold setting unit 2.

Regarding the value provided in the threshold setting unit, in the case of the MSK modulation method, the eye pattern that is vertically asymmetric differs depending on the degree of band limitation, and therefore the optimum threshold value changes.
For example, it is possible to estimate a data transition range from past and future data patterns and to select a threshold value when determining data.
As described above, by allowing the threshold to be adjusted, a delay detection demodulator corresponding to various situations can be realized.

  As described above, the delay detection demodulator according to the present embodiment detects the phase data from the received phase modulation signal and outputs the phase data from the phase data output from the phase detection means 10. The 2-bit delay detection means 20 for subtracting the phase data before the symbol and outputting the phase difference data, and the phase difference data from the 2-bit delay detection means 20 are input, and the data after the 1 symbol is compared with a predetermined threshold value and hard. The phase difference data from the data temporary determination means 40 for performing the determination and the 2-bit delay detection means 20 are input, and the data before and after one symbol are compared with a predetermined threshold according to the determination result of the data temporary determination means 40. And data determination means 30 for performing soft determination and hard determination.

Therefore, according to the present embodiment, even when the eye pattern is vertically asymmetric, such as the MSK modulation method limited to a narrow band, and the discrimination threshold cannot be set to the center, the threshold value is set using the preceding and succeeding symbol determination results. Since it can be selected, better characteristics can be obtained than when the threshold value is set with an eye pattern considering all patterns (that is, in the case of GMSK 2-bit delay detection).
That is, the effects of fading, intersymbol interference, and the like can be reduced even for the MSK modulation scheme limited to a narrow band.

The present invention can be applied to other than the MSK modulation method. For example, a data transition range may be estimated from past / future data patterns, and a threshold used for data determination may be selected.

  The present invention is useful for realizing a delay detection demodulator that can reduce the influence of fading, intersymbol interference, etc., even for an MSK modulation scheme limited to a narrow band.

It is a figure which shows notionally the whole structure of the data reception system using the delay detection demodulator concerning this invention. 2 is a diagram illustrating an internal configuration of a delay detection demodulator according to Embodiment 1. FIG. It is a figure which shows the structure of a data determination part. It is a figure which shows the structure of a data provisional determination part.

Explanation of symbols

10 Phase detector (phase detector)
20 2-bit delay detection unit (2-bit delay detection means)
30 Data judgment part (data judgment means)
31 1 Symbol Delay Unit 32 First Data Determination Unit 33 First Threshold Setting Unit 40 Data Temporary Determination Unit (Data Temporary Determination Unit)
41 Second Data Determination Unit 42 1 Symbol Delay Unit 43 Second Threshold Setting Unit 100 Receiving Antenna 200 Receiving Device 300 Delay Detection Demodulating Device

Claims (2)

Phase detection means for detecting and outputting phase data from the received phase modulation signal; and
2-bit delay detection means for subtracting phase data two symbols before from the phase data output from the phase detection means and outputting phase difference data;
Temporary data determination means for inputting the phase difference data from the 2-bit delay detection means and performing a hard decision by comparing the data after one symbol with a predetermined threshold;
Data on which the phase difference data from the 2-bit delay detection means is input, and soft decision and hard decision are made by comparing the data before and after one symbol with a predetermined threshold according to the decision result of the data provisional decision means A delay detection demodulator comprising a determination unit.   2. The delay detection demodulator according to claim 1, wherein a data transition range is estimated from past and future data patterns, and a threshold value used for data determination can be selected.

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