JP4490546B2 - In-band diversity transmission method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in a diversity method for preventing quality deterioration of communication contents due to fading in a broadcast format using an HF line. In particular, the present invention relates to a transmission method for reducing data errors due to fading when using an in-band diversity method in a transmission system in which only one frequency band can be used and a frequency diversity function cannot be secured.
[0002]
[Prior 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 performed on the receiving side. FIG. 7 is a phase space diagram showing an example in which two BPSK (Bi-Phase Shift Keying) tones are arranged in one band. That is, two tone signals (binary signal) of tone A and tone B are arranged in one bandwidth BW, and since these are the same modulation method (BPSK), both are shown in the same phase space diagram, It has 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, if one of the other tones is normally received, it can be received normally (generally). Therefore, it is strong against so-called selective fading, but avoids errors in received data when it is non-selective and the entire band is affected by fading. I can't.
[0003]
FIG. 8 and FIG. 9 show examples of cases where transmission data (ABCD) is sent as two tones. FIG. 8 shows a case where two BPSK tones are normally transmitted. In this case, transmission data (ABCD) is correctly received and reproduced. On the other hand, the case of FIG. 9 shows an example of non-selection and the entire band is affected by fading. Only data (A) is correctly received, and the other data (BCD) is It becomes an error. Thus, in the conventional method, selective fading is affected only by one of the pair of data strings as shown in FIG. 8, and correct transmission can be performed without being influenced by the other one. However, an error in data cannot be avoided for fading that is non-selectively affected by the entire band.
[0004]
[Problems to be solved by the invention]
As described above, in the conventional method, data error cannot be avoided for normal fading except for special cases such as selective fading. For this reason, in the present invention, even when the band is temporarily disturbed due to large fading over the entire band, or when the spatial noise always occurs and the signal state is bad, the data error is detected. The object is to provide a transmission method that can be prevented.
[0005]
[Means for Solving the Problems]
In order to achieve the above-described object, in the present invention, in order to perform diversity, a digital modulation method having different communication speeds for a plurality of frequencies in the same band is adopted, and a high-speed communication speed is a low-speed communication speed. The number is n times (n is a positive integer), and n one data block that is time-compressed in the time length of one data block on the low speed side is arranged on the high speed side. In order to ensure synchronization between tones of data distributed to tones having different communication speeds in this way, a first synchronization signal is added to the head of each data block subjected to time compression on the high speed side, and Recognize. At the same time, in order to synchronize data on the high speed side and low speed side of the communication speed, a second synchronization signal is added before the first synchronization signal on the low speed side, and the second synchronization signal is also synchronized with this timing on the high speed side. A synchronization signal having the same pattern as the synchronization signal is added.
[0006]
In addition, an error detection code is added to the tail of each data block on the low-speed side and high-speed side in order to detect an error in the transmitted code and to select and switch to the correct data. Even if it occurs, the correct data is selected and read.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
As described above, in the conventional digital data transmission method using the in-band diversity method, two or more tones according to the same modulation method (for example, BPSK) are arranged in one band, and in-band diversity processing is performed on the receiving side. Met. According to this method, as described above, there is a weak point that an error in data due to fading cannot be avoided. For this reason, in the present invention, different modulation methods are applied to these two tones and transmission is performed at different communication speeds.
[0008]
The present invention will be described below with reference to the drawings.
FIG. 1 shows an embodiment of the present invention, in which one of two modulation tones arranged in the same band is BPSK and the other is 16 QAM (16 Quadrature Amplitude Modulation). is there. The communication speed of BPSK is 1200 bps, and the communication speed of 16QAM is 4800 bps. That is, since 16QAM has a communication speed four times that of BPSK, the data transmitted on the BPSK side can be repeatedly transmitted four times on the 16QAM modulation method side within 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 where this multiple continuous transmission is performed on one high speed side. As shown in FIG. 2, the same data (ABCD) can be repeatedly transmitted four times in 16QAM in a period in which (ABCD) data is transmitted once in BPSK. That is, communication with higher redundancy can be performed on the high-speed communication speed side, and it is possible to enhance against data errors.
[0009]
Therefore, in the case of this method, when fading occurs temporarily in the band on the HF line as shown in FIG. 3 and a reception failure occurs, the data (BCD) is dropped in the conventional method as shown in FIG. However, in the present method shown in FIG. 3, redundancy is provided by 16QAM multiple transmissions, and the first block of data (ABCD) is transmitted normally, so even if fading occurs, there is no effect. It is possible to receive without error. In order to make it possible to discriminate the data string transmitted correctly in this way, it is necessary to add a data synchronization signal and an error detection code to each data block composed of data (ABCD). The data synchronization signal may be a synchronization pattern having a specific autocorrelation coefficient with a low occurrence probability in the data string, or in some cases, only 1 bit as a start bit can be used. Further, as the error detection code, a commonly used cyclic bit such as a parity bit or CRC may be applied.
[0010]
These synchronization signals and error detection codes should basically be attached to each data block as a unit. Therefore, a synchronization signal for recognizing the head portion of the block is given to the head portion of each block, and If necessary, a block end signal may be added at the end. In addition, a block code system processed in units of blocks is suitable as the error detection code, but it goes without saying that a convolutional code can also be applied. Furthermore, data synchronization is necessary between the low speed side and the high speed side of the communication speed, and therefore it is also necessary to add another synchronization signal before the synchronization signal given to the data block on the low speed side. . In this case, the timings of the start portions on the high speed side and the low speed side of the communication speed should be matched, and the same pattern of synchronization signals should be used. This situation is shown in FIG. In FIG. 4, (a) is the low speed side and (b) shows the data arrangement on the high speed side. On the low speed side (a), the data block DB includes the data portion D, the synchronization signal S1, and the error detection code E. And has the same configuration as each of the data blocks DB1 to DBn on the high speed side. The synchronization signal S2 is used for timing synchronization between the low speed side and the high speed side, and uses a common pattern on both sides. e1 to en are error detection codes for each data block on the high speed side.
[0011]
Furthermore, even if fading does not occur, the line condition is continuously bad, and an error occurs when the S / N ratio is low for both BPSK and 16QAM tones in the band as shown in FIG. The situation is different. That is, data is not dropped in a burst manner as described above, but sporadic errors due to the low S / N ratio of both tone signals occur for both tone signals. However, in this case, between the S / N ratio and bit error rate it is known relationship as shown in FIG. 6, FIG. 6, when the S / N ratio is low point towards the BPSK is code error is It is known to be advantageous. Therefore, as shown in FIG. 5, when the noise level is high across the band and the S / N ratio is low for both modulation signals, BPSK can receive with fewer errors.
[0012]
【The invention's effect】
When performing in-band diversity transmission, according to the present invention, modulation methods having different communication speeds are used. The slower 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 in-band frequency allocation and a situation in a phase space of a modulated wave showing an example of an arrangement of in-band tones in the present invention.
FIG. 2 is a data arrangement diagram according to the present invention.
FIG. 3 is a conceptual diagram showing the influence 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 the relationship between S / N and 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 the conventional method.
FIG. 8 is a conceptual diagram showing the influence of fading in the 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 blocks DB1-DBn: High-speed side data block E: Low-speed side error detection code e1-en: High-speed side error detection code S1: Low-speed side data block synchronization signal S2: High-speed / low-speed timing Synchronization signal s1 'to sn': High-speed data block synchronization signal

Claims (4)

In the in-band diversity method for performing communication using a plurality of different frequencies within the same frequency band,
While performing digital modulation having a different communication speed for each frequency,
One data block including the first synchronization signal, error detection code and data is assigned to a frequency on the low speed side of the communication speed, and the frequency on the high speed side of the communication speed is an integral multiple of the one data block and each is the same. An in-band diversity transmission method characterized by transmitting a plurality of data blocks having data contents within the same time as one block transmission time on the lower speed side of the communication speed. "   2. The in-band diversity method according to claim 1, wherein a time of one data block length on a low communication speed side is set to one word time, and a second synchronization signal is provided at least before or after the one word time length. The second sync signal uses a sync signal of the same type as the high-speed tone of the communication speed, and the second sync signal is time-compressed and arranged together in the high-speed tone of the communication speed. An in-band diversity transmission method, wherein the in-band diversity transmission method is added to at least one of before and after the plurality of data blocks.   3. The in-band diversity method according to claim 1, wherein it is detected that the received radio wave intensity has dropped to a level at which a predetermined normal reception state cannot be ensured, and the other tone is normal during this period. An in-band diversity transmission method characterized in that if it is received, it is switched to that and the receiving operation is continued.   4. The in-band diversity transmission method according to claim 3, wherein quality degradation of received radio waves is detected by an error detection code added to each data.

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