JP2001285166A - In-band diversity transmission method - Google Patents

Abstract

(57) [Summary] A diversity method is widely used to prevent an increase in data errors due to fading. In particular, in an in-band diversity method, a sufficient effect is obtained against fading occurring over the entire transmission bandwidth. Was not obtained. For this reason, an object of the present invention is to realize an effective fading countermeasure while utilizing the features of the in-band diversity method. According to the present invention, for example, BPS is applied to two tone signals used in in-band diversity.
Modulation methods having different communication speeds such as K and 16QAM are applied. By changing the communication speed in this manner, transmission with higher redundancy can be performed on the high-speed side, which is resistant to errors, and the lower the transmission speed is, the lower the transmission speed is with respect to the deterioration of the S / N ratio of the line. Since it has an advantageous effect on the rate, the reliability of the line could be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a diversity method for preventing deterioration of communication quality due to fading in a broadcasting format using an HF line. In particular, 1
In a transmission system in which only a frequency band can be used and a frequency diversity function cannot be ensured, the present invention relates to a transmission method for reducing data errors due to fading when an in-band diversity method is used.

[0002]

2. Description of the Related Art Conventionally, when performing in-band diversity, two or more tones of the same modulation method are arranged in a band, and in-band diversity is implemented on the receiving side. FIG. 7 shows two BPSK (Bi-Pha) in one band.
FIG. 7 is a phase space diagram showing an example of a case where se shift keying (two-phase modulation) tones are arranged. That is, two tone signals (binary signals) of tone A and tone B are arranged in one bandwidth BW, and they are arranged in the same modulation method (B
PSK), they are all shown in the same phase space diagram,
They have the same communication speed. In such a conventional method, even if one tone is poorly received due to selective fading and an error occurs in received data, the other tone can be normally received if the other tone is normally received. , Which is higher in so-called selective fading, but avoids errors in received data when non-selective and the entire band is affected by fading. Can not do.

FIGS. 8 and 9 show transmission data (ABCD).
Is shown as an example of the case where is sent as two tones. FIG. 8 shows a case where two BPSK tones are transmitted normally. In this case, the transmission data (ABCD) is correctly received and reproduced. On the other hand, FIG. 9 shows an example in which the entire band is unselective and is affected by fading. Only data (A) is correctly received, and the other data (BCD) is It will be an error. As described above, in the conventional method, only one of a pair of data strings is affected by selective fading as shown in FIG. 8, and the other one can be transmitted correctly without being affected. However, data errors cannot be avoided for fading which is non-selectively affected by the entire band.

[0004]

As described above, in the conventional method, except for a special case such as selective fading, data errors cannot be avoided for normal fading. Therefore, in the present invention,
Provides a transmission method that can prevent data errors even when the inside of the band is temporarily disturbed due to large fading over the entire band, or when the spatial noise always occurs and the signal condition is poor. It is intended to be.

[0005]

In order to achieve the above-mentioned object, in the present invention, in order to perform diversity,
A digital modulation method in which communication speeds are different for a plurality of frequencies in the same band is adopted. The configuration is such that n data blocks that have been time-compressed during the time length corresponding to the data block are arranged in n pieces.
In order to secure the inter-tone synchronization of the data distributed to the tones having different communication speeds in this manner, a first synchronization signal is added to the head of each of the time-compressed data blocks on the high-speed side, and Perform recognition. At the same time, a second synchronization signal is added before the first synchronization signal on the low-speed side in order to synchronize data on the high-speed side and the low-speed side of the communication speed. The configuration is such that a synchronization signal having the same pattern as the synchronization signal is added.

In addition, a configuration is adopted in which an error of a transmitted code is detected, and a code for error detection is added to the end of each of the low-speed and high-speed data blocks in order to select and switch to correct data. , Even if an error occurs, correct data is selected and read out.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, in the conventional transmission method of digital data by the in-band diversity method, the same modulation method (for example, BPSK) is used in one band.
And two or more tones are arranged, and the receiving side performs in-band diversity processing. According to this method, there is a disadvantage that data errors due to fading cannot be avoided as described above. For this reason, in the present invention, different modulation methods are applied to these two tones to transmit at different communication speeds.

Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of the present invention. One of two modulated tones arranged in the same band is BPSK, and the other is 16QAM (16 Quadrature Amplitude Modula).
Option quadrature amplitude modulation). The communication speed of BPSK is 1200 bps, and the communication speed of 16QAM is 4800 bps. That is, 16QAM is B
Since the communication speed is four times as high as that of PSK, the data transmitted on the BPSK side can be repeatedly transmitted four times on the side of the 16QAM modulation method in the same time.
By changing the modulation method in this way, so-called multiple transmission can be performed with a tone having a higher communication speed. FIG. 2 shows an example of a data array in the case of performing this multiple continuous transmission on one high-speed side. As shown in FIG. 2, during the period of sending (ABCD) data once in BPSK, the same data (A
BCD) can be sent four times. That is, communication with higher redundancy can be performed on the high communication speed side, and it is possible to enhance against data errors.

Therefore, in the case of the present method, when fading occurs temporarily in the band on the HF line as shown in FIG. 3 and a reception failure occurs, the conventional method uses data (BCD) as shown in FIG. However, in the present method shown in FIG. 3, since redundancy is provided by 16QAM multiple transmission and data (ABCD) of the first block is transmitted normally, even if fading occurs. Error-free reception is possible without the influence. In order to enable the process of discriminating a data string transmitted correctly as described above, it is necessary to add a data synchronization signal and an error detection code to each data block composed of data (ABCD). As the data synchronization signal, a synchronization pattern having a specific autocorrelation coefficient having a low occurrence probability in the data string may be used, or in some cases, only one bit as a start bit may be used. In addition, as an error detection code, generally used parity bits or CR bits are used.
A cyclic code such as C may be applied.

The synchronization signal and the error detection code should basically be attached to each data block as a unit. Therefore, a synchronization signal for recognizing the head of each block is provided at the head of each block. It may be added, and if necessary, a block end signal may be added at the end.
As the error detection code, a system of block codes processed in block units is suitable, but it goes without saying that convolutional codes can also be applied. Further, data synchronization is required even between the low-speed side and the high-speed side of the communication speed. Therefore, it is necessary to provide another synchronization signal before the synchronization signal provided to the low-speed side data block. .
In this case, the timings of the start portions on the high-speed side and the low-speed side of the communication speed may be matched, and the same pattern of synchronization signal may be used. This situation is shown in FIG. FIG.
(A) shows the data arrangement on the low-speed side and (b) shows the data arrangement on the high-speed side. In the low-speed side (a), the data block DB is composed of a data part D, a synchronization signal S1 and an error detection code E. It has the same configuration as each of the high-speed data blocks DB1 to DBn. The synchronizing signal S2 is for synchronizing the timings of the low-speed side and the high-speed side, and uses a pattern common to both sides. e1 to en are error detection codes for each data block on the high-speed side.

Further, even if no fading occurs, the line condition is continuously bad, and BPSK, 16QA
When the S / N ratio is low for both of the M tones as shown in FIG. 5, the situation of error occurrence is different from the above situation. That is, rather than dropping data in bursts as described above, sporadic errors due to the low S / N ratio of both tone signals occur in both tone signals. However, in this case, a relationship as shown in FIG. 6 is known between the S / N ratio and the bit error rate. From FIG. 6, when the S / N ratio is low, BPSK is more likely to have a code error point. Is known to be advantageous. Therefore, as shown in FIG. 5, when the noise level is high and the S / N ratio of both modulated signals is low over the band, BPSK can receive signals with less errors.

[0012]

According to the present invention, when performing in-band diversity transmission, modulation methods having different communication speeds are used, so that the higher the communication speed and the lower the S / N ratio are for fading. In this case, the lower communication speed works effectively, and data transmission by in-band diversity can be executed stably.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an example of an arrangement of tones in a band and a situation in a phase space of a modulated wave according to the present invention.

FIG. 2 is a data arrangement diagram according to the present invention.

FIG. 3 is a conceptual diagram showing the effect of fading in the present invention.

FIG. 4 is a conceptual diagram showing a situation when the in-band noise level is high.

FIG. 5 is a characteristic diagram showing a relationship between S / N and an error rate in various modulation methods.

FIG. 6 is a phase space diagram showing the arrangement of in-band tones in the conventional method.

FIG. 7 is a transmission pattern diagram in a conventional method.

FIG. 8 is a conceptual diagram showing the effect of fading in a conventional method.

FIG. 9 is a conceptual diagram showing a case where the entire band is affected by fading in the conventional method.

[Explanation of symbols]

 BW: Bandwidth D: Data part DB: Data block DB1 to DBn: High-speed data block E: Low-speed error detection code e1-en: High-speed error detection code S1: Low-speed data block synchronization signal S2: High-speed / low-speed timing Synchronization signal s1 'to sn': High-speed data block synchronization signal

Claims (5)

[Claims] An in-band diversity method for performing communication using a plurality of different frequencies within the same frequency band, wherein digital modulation having a different communication speed is performed for each of the frequencies. Band diversity transmission method. 2. The in-band diversity method according to claim 1, wherein one data block including the first synchronization signal, the error detection code, and the data is assigned to a lower frequency of the communication speed, and An in-band diversity transmission method, characterized in that a data block whose frequency is an integral multiple of the one data block is transmitted within the same time as one block transmission time on the lower side of the communication speed. 3. The in-band diversity method according to claim 2, wherein the time of one data block length on the low-speed side of the communication speed is one word time, and the second word is at least before or after the one word time length. A synchronization signal, wherein the second synchronization signal uses a synchronization signal of the same type as that of the tone at the higher communication speed, and the second synchronization signal is time-compressed at the tone at the higher communication speed. An in-band diversity transmission method characterized by being added to at least one of before and after a plurality of the one data blocks arranged in a group. 4. The in-band diversity method according to claim 1, wherein the reception radio wave intensity is detected to have decreased to a level at which a predetermined normal reception state cannot be ensured, and during this period, the other is detected. The in-band diversity transmission method, wherein if the tone is received normally, it is switched to the tone and the receiving operation is continued. 5. The in-band diversity transmission method according to claim 4, wherein quality degradation of a received radio wave is detected by an error detection code added to each data.