JPH0630069A - Qam transmission system by multi-subcarrier - Google Patents

Abstract

PURPOSE:To provide a digital transmission system with high power efficiency and profitability by comparing the symbol of a dedicated subcarrier by arranging in a vector opposite to the synthetic vector of the subcarrier of another symbol. CONSTITUTION:Symbol synthesis is applied to the information symbols (SO, S8, Sa or S4, Sc, Se) of received subcarriers 1-5 at a reception side similarly as at a transmission side. When coincidence between the information symbol (S2 or S6) nearest to the symbol {-(S0+S8+Sa) or -(S4+Sc+Se)} symmetric to the synthetic symbol in spatial fashion and a reception symbol (S2 or S6) received by the subcarrier (m) for power control is obtained, it is decided that all the information symbols of received subcarriers are correct. When noncoincidence is obtained, it is decided that an error exists in the information symbol of the subcarrier, and the communication of correct data is performed by a means such as re-transmission, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-subcarrier QAM transmission system, and more particularly to a multi-subcarrier QAM transmission system capable of securing a highly reliable multiplex radio line even with frequency selective fading.

[0002]

2. Description of the Related Art Generally, a mobile multiplex radio communication system, as shown in FIG. 2, has a frequency f of a plurality of subcarrier signals.
1, f2 ... fm are set and the frequency-multiplexed signal is transmitted. Also, individual subcarriers are modulated by time division multiplexed signals, and the subcarriers are arranged with a frequency distribution having a certain power spectrum.

Conventionally, when a QAM multiplex modulation system in which time division multiplexing is applied to this type of multi-subcarrier is applied, 16
Each signal arrangement of the QAM modulated signal is represented as shown in FIG. That is, the maximum amplitude signal points S6, S8,
Sa, S2, signal points S1, S4, Sc, S of the second amplitude
9, Sb, Sf, S6, S3, and S5, Sd, Sc, S7 having the same phase as the maximum amplitude signal point are arranged as the signal points of the third amplitude. Now, when the signal points shown in FIG. 3A are time-division-multiplexed with respect to each of the subcarriers 1 to m, the symbols S0 to S9 and Sa to Sf become the multiplexed signal arrangement shown in FIG. . This symbol arrangement is first arranged so that the maximum amplitude signal points are arranged as synchronization words and pilots, and then the information data is selected so as to form an amplitude and phase arrangement with less interference with each other.

Since each subcarrier signal is modulated by such a signal point arrangement, the power spectrum distribution at a certain point of the maximum amplitude signal points of the synchronization word and pilot becomes large because the power spectrum is concentrated on each subcarrier. The power spectrum distribution in the area of information data is relatively small. Here, the subcarrier m also transmits information data like the other subcarriers 1, 2, and 3. For transmission error correction of these digital modulation methods, a method is used in which information bits are encoded and transmitted according to a predetermined rule and then decoded on the receiving side. At this time, if it is possible to judge that the received multiple information bits are clearly correct, there is a coding method that enables more accurate error correction (for example, Reed-Solomon code). There is a transmission method to do.

Also in the case of a transmission system of a plurality of subcarriers, if the information symbols of a plurality of subcarriers are concentrated in the same signal space, the power spectrum of the digital signal is widened, and transmission with a high output peak power is performed. I needed a machine. In the case of QAM, the accuracy of the linearity of the amplitude of the digital signal is required, so a transmitter with a large difference between the average power and the peak power is technically sophisticated and expensive in price.
In addition, there are problems such as deterioration of power efficiency.

[0006]

In the transmission error correction method of the digital modulation signal in the above-mentioned conventional QAM transmission method using multi-subcarriers, the signal reception level is input and the error determination of the information symbol is made by the signal reception. The correspondence between the level and the transmitted information symbol must be taken exactly. The signal reception level detection circuit
Normally, a semiconductor and a capacitor are combined to cause a delay time. On the other hand, the transmission time of the information symbol becomes shorter as the transmission speed becomes faster, and the delay time of the signal reception level cannot be ignored, which makes it difficult to adopt high precision error correction.

Further, since a symbol vector is provided for each subcarrier, which is a characteristic of the multi-subcarrier QAM system, and the power spectrum of the digital signal is determined by the combined vector, the information symbols of a plurality of subcarriers become neighboring information symbols. There is a drawback in that an advanced and expensive transmitter with low power efficiency must be used in order to cope with the expansion of the power spectrum caused by the concentration.

[0008]

In the QAM transmission method using multi-subcarriers according to the present invention, a plurality of subcarriers whose frequencies differ by the occupied band of the subcarriers are QAM-modulated separately, and then frequency-multiplexed Q is used.
In the AM transmission system, one or a plurality of subcarriers among a plurality of subcarriers is used as a dedicated subcarrier for transmitting control symbols for power control and error detection, and information symbols of other plurality of subcarriers for transmitting information are used. Vectors are combined for each transmission order, and the combined vector and the vector of the dedicated subcarrier are opposite to each other, or are transmitted so that they are the closest combination of vector information symbols.

[0009]

The present invention will be described below with reference to the drawings. Figure 1
Shows a configuration diagram of a communication slot according to an embodiment of the present invention, and corresponds to a symbol of a signal point of 16QAM in FIG. FIG. 3B is a combined vector diagram for explaining the operation principle of this embodiment.

Next, the operation of this embodiment will be described with reference to FIGS. 1 and 3B. Here, the subcarriers 1 to 3 send information data, but the subcarrier m is used as a dedicated subcarrier in order to cancel a combined vector of powers of the subcarriers 1 to 3 described later. Now subcarriers 1-3
The three types of transmission patterns will be described with reference to the combined vector of 1 and the position of the symbol to be canceled by the subcarrier m. The time slot of the symbol of interest is taken as an example of the first column of sync words in FIG. In FIG. 3B, (1) The first cymbal (S0) of the synchronization word of the transmission subcarrier 1 when the combination of information symbols matches the signal space
And the first symbol (S
8), the combined symbol (S0 + S
8) is obtained. Next, when the first symbol (Sa) of the synchronization word of subcarrier 3 and the combined symbol (S0 + S8) are combined, the combined three symbols (S0 + S8 + Sa) becomes a signal space equal to the information symbol (S8). Therefore, the symbol to be inserted into the subcarrier m on the transmission side is a symbol (S2) that is signal-space symmetric to the symbol (S8).
And In this case, the symbol combination of all the subcarriers is “0”, and the power spectrum is the minimum.

(2) Transmission when information symbol combination does not match the signal space Although not shown, when the information symbol (S4) of subcarrier 1 and the information symbol (Sc) of subcarrier 2 are combined, Q is obtained.
A composite symbol (S4 + Sc) is obtained on the axis. Next, when the information symbol (Se) of the subcarrier 3 and the combined symbol (S4 + Sc) are combined, the combined symbol (S4 + Sc + Se) of 3 symbols does not match the signal space of a general information symbol.

In this case, the symbol to be inserted into the subcarrier m on the transmitting side is the symbol (S6) closest to the symbol (-(S4 + Sc + Se)) which is signal spatially symmetric with the combined symbol. Therefore, at this time, the symbol combination of all subcarriers does not become "0", so the power spectrum is not the minimum.

(3) Information symbol error detection on the receiving side On the receiving side, the received information symbols (S0, S8, Sa or S4, Sc, Se) of subcarriers 1 to 3 are symbol-combined in the same manner as the transmitting side, A symbol (-(S0 + S8 + Sa)) or-(S
4 + Sc + Se)) closest to the information symbol (S2 or S6) and the received symbol (S2 or S6) received by the power control subcarrier m, it is determined that each information symbol of all the received subcarriers is correct. To do. If the symbols do not match, it is determined that the information symbol of the subcarrier has an error, and correct data communication can be realized by means of retransmission or the like.

[0014]

As described above, according to the present invention, the symbols of the dedicated subcarriers are arranged in the vector opposite to the composite vector of the subcarriers of other symbols for comparison, and therefore highly accurate error correction is possible. Therefore, there is an effect that it is possible to perform highly efficient data communication with few transmission errors. Moreover, since the information symbols of a plurality of subcarriers can be vector-distributed, the peak power is reduced, and there is an effect that a digital transmission method with high power efficiency and high economical efficiency can be realized.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a communication slot according to an embodiment of the present invention.

FIG. 2 is a frequency allocation diagram of subcarriers common to this embodiment and a conventional example.

FIG. 3 is a QAM signal point constellation diagram (a) and a vector composition diagram (b) of the present embodiment.

FIG. 4 is a configuration diagram of a conventional communication slot.

[Explanation of symbols]

 1, 2, 3, 4 subcarriers S0 to S9, Sa to Sf QAM signal point symbols

Claims (2)

[Claims] 1. In a QAM transmission system using multiple subcarriers, wherein a plurality of subcarriers whose frequencies are different only in an occupied band of the subcarriers are QAM-modulated separately and then frequency-multiplexed, one or a plurality of subcarriers among the plurality of subcarriers. Is used as a dedicated subcarrier for transmitting control symbols for power control and error detection, and information symbols of a plurality of other subcarriers for transmitting information are vector-combined in each transmission order, and the combined vector and the dedicated subcarrier are The QAM transmission method using multi-subcarriers is characterized in that the vector is transmitted in such a manner that the vector is the opposite vector or is the combination of the closest vector information symbols. 2. A control symbol inserted into a dedicated subcarrier and an information symbol inserted into another subcarrier at a receiver, which receives the plurality of subcarriers and the dedicated subcarrier sent from a transmitter side. From the composite vector of
2. The QAM transmission system with multi-subcarriers according to claim 1, further comprising means for detecting the presence or absence of a transmission error in the received information symbol and performing high precision error correction.