JPH0927832A - Multi-carrier transmission method and its device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce deterioration of the transmission quality on the occurrence of fading by arranging a frequency of plural carriers sending coding data so as not to cause simultaneous attenuation in a frequency selective fading. SOLUTION: Plural carriers C1-Cn being components of a channel are arranged at a frequency interval so as not to receive simultaneously the attenuation by frequency selective fading. When the frequency selective fading such as a reception electric field R takes place, a large attenuation is caused in the carrier C2. However, since the other carriers C1, C3 to Cn of the channel have frequencies sufficiently apart from the frequency of the carrier C2, the probability of simultaneously level reduction for the other carriers is very small on the occurrence of level reduction of the carrier C2 due to the frequency selective fading. Thus, accurate data decoding by the error correction processing is attained with respect to coded data and the deterioration of the transmission quality due to the frequency selective fading is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multicarrier transmission method and apparatus for distributing and transmitting individual bits of one digital data to a plurality of channels having different frequencies.

[0002]

2. Description of the Related Art In a multi-carrier transmission system, as shown in FIG. 2, a plurality (n) of carriers C1 to Cn having different frequencies are used as one channel, and one digital data to be transmitted is bit by bit. The carriers C1 to Cn are disassembled and simultaneously modulated by the respective bits and transmitted.
When there are a plurality of pieces of digital data to be transmitted, a method of using the above channels in a time division manner is used according to their time series. Furthermore, a system is constructed by arranging a plurality of the above-mentioned channels at different frequencies and FDM-multiplexing them. As an example of such a system, in Japan, a medium zone type MCA (Multi Chan) having a service area of a radius of 20 to 30 km using the 800 MHz band is used.
nel access) system has been put to practical use.

[0003]

In wireless communication,
So-called frequency-selective fading occurs, which causes large attenuation and phase distortion in a relatively narrow frequency range. For example, when frequency selective fading as shown by the reception electric field R in FIG. 2 occurs, the carriers C1, C2, C3, C
4 and C5 have a particularly large level decrease and phase distortion (since level decrease and phase distortion occur at the same time, they are simply referred to as level decrease below). However, in the conventional multi-carrier transmission system, since each bit of the same digital data is assigned to the carriers C1 to Cn in the same time slot, a pulse error is generated on the receiving side by the number of collected bits in one digital data. Therefore, there is a problem that the error correction process becomes difficult and the transmission quality is deteriorated.

An object of the present invention is to eliminate the above-mentioned problems of the prior art, and to provide a multicarrier transmission method and an apparatus therefor in which the transmission quality is less deteriorated when frequency selective fading occurs.

[0005]

According to the present invention, each of a plurality of carriers forming one channel is modulated by each bit forming transmission digital data and transmitted, and the receiving side demodulates the carrier. In a multi-carrier transmission method in which the obtained bit signals are combined to reproduce digital data, a plurality of carriers forming the one channel are arranged at frequency intervals such that they are not simultaneously attenuated by frequency selective fading. Disclosed is a multicarrier transmission method characterized by the arrangement.

According to the present invention, the transmitted digital data is encoded data which is encoded by using an encoding method having an error correction function, and the reproduced digital data is encoded by the encoding method on the receiving side. Disclosed is a multicarrier transmission method characterized by performing error correction by a corresponding decoding method and performing decoding.

[0007]

By arranging the frequencies of a plurality of carriers for transmitting one piece of encoded data so that attenuation does not occur at the same time due to frequency selective fading, it is highly possible that a plurality of bit errors occur in one piece of encoded data. Get smaller. Therefore, an accurate decoding process can be performed by the error correction process, and the transmission quality can be improved.

[0008]

EXAMPLES The present invention will be described in detail below with reference to examples. FIG. 3 is a block diagram showing an embodiment of the multicarrier transmission apparatus according to the present invention. In the figure, the encoder 1 divides the transmission data for each encoding length and encodes it, and then encodes the next n-bit-length encoded data series A1, A2,
Is generated.

[Number 1] _{A 1 = (a 11, a} 12, ··· a 1n) A 2 = (a 21, a 22, ··· a 2n) · · · A m = (a m1, a m2, · .. a _mn ) .. .. where a _ij (i, j = 1, 2, ...) Is the j-th bit of the encoded data A _i . This encoded data A ₁ , A
₂ ... When input transmission data is one time series, the time series data is divided into coding lengths and sequentially coded. When the input transmission data is a plurality of time-series data, the data separated from each time-series data for each encoding length is sequentially and cyclically extracted and encoded.

The multicarrier interleave circuit 2 is
Each bit forming the encoded data A _i shown in (Equation 1) is separated and distributed so as to correspond to each carrier of one channel. For the sake of simplicity, it is assumed that the length (bit number) n of one encoded data is equal to the number of carriers in one channel. At this time, in the conventional case, the bits a _{i1 to} a _in of the encoded data A _i are distributed so as to correspond to the carriers C1 to Cn of FIG. 2, respectively.
However, in the present embodiment, the carriers forming one channel are arranged so that there are m carrier intervals as shown in FIG. Then, the above bits a _{i1 to} a _in are assigned to the carriers arranged in this way.

The multi-carrier transmitter 3 modulates each of the carriers C1 to Cn in FIG. 1 with each of the bit signals a _{i1 to} a _in assigned as described above, and transmits from the antenna 4.

On the receiving side, the received wave from the antenna 5 is input to the multi-carrier receiving section 6, where each carrier is demodulated and bit signals are taken out, and the multi-carrier deinterleave circuit 7 collects each coded data. Is converted into a received word. This received word is the encoder 1
Since it is the received data corresponding to the output encoded data,
Decoding processing including error correction is performed by the demultiplexer 8 and the received data is extracted.

In the above-described embodiment, the operation when the frequency selective fading occurs will be described below.
Now, if frequency selective fading as shown by the reception electric field R in FIG. 1 occurs, a large attenuation occurs in the carrier C2. However, since the other carriers C1 and C3 to Cn forming the same channel as the carrier C2 are sufficiently separated from the carrier C2 in frequency, when the level decrease occurs due to the frequency-selective fading of the carrier C2, the probability of receiving the level decrease at the same time is extremely high. small. Therefore,
Among the bits constituting the digital data transmitted using the carriers C1 to Cn, that is, the encoded data, only the error rate of the bits transmitted by the carrier C2 becomes large, and the probability that other bits are erroneous at the same time is extremely high. small. For this reason, it is possible to accurately restore data for this one encoded data by error correction processing, and it is possible to prevent deterioration of transmission quality due to frequency selective fading.

Further, in general, the duration of frequency selective fading is much longer than the duration of one piece of encoded data to be transmitted. Therefore, a plurality of pieces of encoded data transmitted by carriers C1 to Cn in FIG. Then it is affected by frequency selective fading. However, in each of the coded data, the occurrence of bit error is limited to 1 bit as described above, so that the transmission quality can be similarly maintained for the time series data.

In the multi-carrier transmission system, a plurality of channels are FDM-multiplexed and used, but it is easy to arrange the carriers in each channel as shown in FIG. FIG. 4 shows an example of the arrangement, and the channel 1 is composed of carriers C11, C12, ... C1n,
Channel 2 is composed of carriers C21, C22, ... C2n. The same applies hereinafter, and the channel m is composed of carriers Cm1, Cm2, ..., Cmn. According to this carrier arrangement, each carrier in the same channel is m
Since they are arranged with carrier intervals separated, the quality of digital data transmitted using each channel when frequency selective fading occurs can be improved in the same manner as described with reference to FIG.

Furthermore, in the carrier arrangement examples of FIGS. 1 and 4, the carriers of one channel are arranged at equal intervals, but this does not necessarily have to be at equal intervals. Each carrier in the same channel is not simultaneously attenuated by frequency selective fading,
Clearly, any suitable spacing arrangement is sufficient.

Further, in the above description, the number of carriers per channel and the coded data length are the same number n, but the present invention can be applied even if they are different. That is, in this case, when each bit of the encoded data is distributed to each carrier, the bit string distributed to the specific carrier is not necessarily the bit at the specific position of the encoded data. Therefore, except in the case where the length of the encoded data is many times the number of carriers in one channel,
Since the probability that a plurality of bits of one encoded data will be in error at the same time due to frequency selective fading is small, the same improvement effect can be obtained.

[0017]

According to the present invention, it is possible to reduce the deterioration of the digital data transmission quality due to the frequency selective fading in the multi-carrier transmission system.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of carrier arrangement in a multicarrier transmission method of the present invention.

FIG. 2 is an explanatory diagram of carrier arrangement in a conventional multicarrier transmission method.

FIG. 3 is a block diagram showing a configuration example of a multicarrier transmission device of the present invention.

FIG. 4 is a diagram showing an example of multi-channel carrier allocation in the multi-carrier transmission method of the present invention.

[Explanation of symbols]

 1 Encoder 2 Multi-carrier interleave circuit 3 Multi-carrier transmitter 6 Multi-carrier receiver 7 Multi-carrier de-interleave circuit 8 Decoder

Claims (4)

[Claims] 1. A plurality of carriers constituting one channel are modulated by respective bits constituting transmission digital data and transmitted, and a receiving side synthesizes bit signals obtained by demodulating the carriers. In a multi-carrier transmission method for reproducing digital data, a plurality of carriers constituting the one channel are arranged at frequency intervals so as not to be simultaneously attenuated by frequency selective fading. Carrier transmission method. 2. The multicarrier transmission method according to claim 1, wherein the frequency intervals of a plurality of carriers forming the one channel are equal intervals. 3. The transmission digital data is coded data that is coded using a coding method having an error correction function, and at the receiving side, the reproduced digital data is decoded corresponding to the coding method. The multicarrier transmission method according to claim 1 or 2, wherein error correction is performed by a coding method and decoding is performed. 4. A coding unit for coding transmission data by a coding method having an error correction function to generate coded data, and each bit signal forming the coded data in one channel. Bit distribution means for allocating to a plurality of channels arranged at frequency intervals that are not simultaneously affected by attenuation due to frequency selective fading, and the carrier corresponding by the bit signal distributed by the means. A multi-carrier transmitting unit for modulating and transmitting the modulated carrier, a receiving unit for receiving and demodulating the transmitted modulated carrier and extracting a bit signal, and combining the bit signals extracted by the unit. Bit synthesizing means for generating digital data, and error correction processing for digital data synthesized by the means Multicarrier transmission apparatus characterized by comprising a composite means for generating a reception data by performing.