JP3046786B2 - Multi-carrier signal transmission device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for multicarrier signal transmission used in digital radio communication. The present invention relates to OFDM (Orthogonal Frequency Division).
Multiplexing). In particular, the present invention relates to a technique for adjusting the maximum amplitude of a multicarrier signal to a predetermined value.

[0002]

2. Description of the Related Art A conventional multi-carrier signal transmission apparatus having means for suppressing the maximum value of a multi-carrier signal is shown in FIG.
This will be described with reference to FIG. FIG. 4 is a block diagram of a main part of a conventional multicarrier signal transmission device. This multicarrier signal transmission device uses OFDM.

[0003] A multi-carrier signal generation unit 10 is repeatedly input with a transmission bit sequence having a certain finite length, and generates and outputs a multi-carrier signal corresponding to the input sequence. When the OFDM is applied, the multi-carrier signal generation unit 10 converts the serial / parallel conversion circuit 11 and the inverse DFT (Inver
se Discrete Fourie Transform) circuit 12 and parallel-serial conversion circuit 13 (for example,
References: SBWeinstein, et.al, "Data Transmission b
y Frequency-Division Fourier Transform, "IEEE Tran
s.on Communications, vol. 19, No. 5, October 1971). The multicarrier signal is supplied to the inverse DFT circuit 12
A symbol is added for each inverse Fourier transform performed by

[0004] In order to suppress the maximum value of the multicarrier signal output from the multicarrier signal generation unit 10, a clipping unit 50 that clips the maximum amplitude of the multicarrier signal is used in the related art.

In this case, the output of the clipping unit 50 is
Assuming that s (t) is an output of the multicarrier signal generation unit 10 given as a baseband complex signal, A is a maximum amplitude specified value, and u (t) is an output of the clipping unit 50, s (t)> A: u (t) = A × (s (t) / | s
(T) |) s (t) ≦ A: It is given as u (t) = s (t).

[0006]

In the transmission of a multicarrier signal, it is often necessary to suppress the maximum value of the multicarrier signal in order to ease the required back-off value of the signal amplifier. In the related art, the maximum amplitude of the transmission signal is suppressed by clipping of the clipping unit 50.

Since the clipping operation in this case is a kind of non-linear signal conversion, mutual interference between the carriers in the multicarrier signal is caused, and the error rate is reduced even in a transmission path having a good carrier signal power to noise power ratio. Becomes difficult.

That is, for a portion where the amplitude of the multi-carrier signal exceeds a predetermined value, only that portion is forcibly suppressed by clipping. This causes mutual interference between them and causes a code error.

Further, when the bit patterns of the respective carriers of the multicarrier signal are the same or approximate, the maximum amplitude value of the multicarrier signal becomes extremely large because the maximum amplitude portions of the respective carriers overlap. There is. If the maximum amplitude generated in this way is forcibly suppressed by clipping, the mutual interference between the carriers will be large, and the accompanying effect on the bit error rate will also be large.

The present invention has been made in such a background, and a multi-carrier signal capable of suppressing the maximum amplitude to a predetermined value or less without causing mutual interference between each carrier and a code error. It is an object to provide a transmission device. The present invention provides a multi-carrier signal transmission device that can reduce the probability that the maximum amplitude locations of each carrier overlap when a multi-carrier signal is generated from a plurality of bit sequences having the same or similar bit patterns. Aim.

[0011]

SUMMARY OF THE INVENTION A multicarrier signal transmission apparatus according to the present invention detects a maximum value of a multicarrier signal for each symbol, and outputs a corresponding multicarrier signal for each symbol in accordance with the magnitude of the maximum value. The most main feature is that the maximum value of the multicarrier signal is suppressed by uniformly suppressing the positions other than the positions.

The suppression is performed by multiplying the amplitude by a constant. This constant multiplying operation is a linear operation and does not cause mutual interference between carriers in a multicarrier signal which is found in the prior art using clipping. Therefore, a floor phenomenon in the code error characteristic does not occur.

Further, by adding a different start symbol for each burst of each bit sequence, the start symbol of the transmission burst can be made different for each burst.

For this reason, in OFDM, an extremely large maximum amplitude portion may appear at a specific portion of a multicarrier signal due to, for example, overlapping of the maximum amplitude portion of each carrier. By adding a symbol, it is possible to avoid a situation where an extremely large maximum amplitude is fixedly generated for a specific bit sequence. For example, as an error compensation technique, a retransmission technique for transmitting the same information transmission bit (A
This is effective when the bit sequences are the same or similar, such as when RQ (Automatic Repeat Request) is used. Further, the present invention can be applied to a case where differential encoding is used.

As described above, it is necessary to prevent an extremely large maximum amplitude from being generated in a part of the multicarrier signal.
By suppressing the maximum value by the above-mentioned constant multiplication operation, the maximum amplitude can be suppressed to a predetermined value or less without causing mutual interference between carriers and a code error.

That is, the present invention relates to a multi-carrier signal transmission device, which receives a bit sequence and generates a multi-carrier signal divided for each symbol in accordance with the bit sequence. Means for suppressing the maximum amplitude from exceeding a predetermined value. It is a feature of the present invention that the suppressing means includes means for detecting the maximum amplitude of the multicarrier signal for each symbol, and this multiplying means so that the maximum amplitude does not exceed the predetermined value according to the detection result. Means for uniformly suppressing the amplitude of the carrier signal for each symbol including a portion other than the maximum amplitude.

Further, it is desirable to have means for adding a different start symbol to the head of each bit sequence.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram of a main part of a multicarrier signal transmission apparatus according to a first embodiment of the present invention.
FIG. 2 is a block diagram of a main part of a multicarrier signal transmission apparatus according to a second embodiment of the present invention.

The present invention relates to a multi-carrier signal transmission apparatus, which receives a bit sequence and generates a multi-carrier signal divided for each symbol in accordance with the bit sequence. A multi-carrier signal transmission device including a maximum amplitude suppression unit 15 for inputting and suppressing the maximum amplitude thereof so as not to exceed a predetermined value.

Here, a feature of the present invention is that the maximum amplitude suppressing section 15 includes a symbol-by-symbol maximum value detecting section 20 for detecting the maximum amplitude of the multicarrier signal for each symbol.
In accordance with the detection result, a symbol-by-symbol maximum value suppression unit 30 that evenly suppresses the amplitude of the multicarrier signal for each symbol including a portion other than the maximum amplitude so that the maximum amplitude does not exceed the predetermined value. Including.

Further, the second embodiment of the present invention includes a burst-based variable start symbol adding section 40 for adding a different start symbol to the head of each bit sequence.

[0022]

【Example】

(First Embodiment) A first embodiment of the present invention will be described with reference to FIG. A bit sequence is input to the multicarrier signal generation unit 10, and a multicarrier signal corresponding to the bit sequence is generated and output. The multi-carrier signal generator 10
Are configured in the same manner as in the prior art using OFDM.

The output of the multi-carrier signal generator 10 is
The maximum value (maximum amplitude or maximum power) of the multicarrier signal input to the maximum value detection unit 20 for each symbol and output from the multicarrier signal generation unit 10 is determined for each symbol (O
(Every inverse Fourier transform in FDM).

The maximum value suppression unit 30 for each symbol
Based on the maximum value information detected by the maximum value detection unit 20 for each symbol, a multicarrier signal u (t) whose maximum value is suppressed for each symbol is output.

When s (t) is the output of the multicarrier signal generator 10 given as a baseband complex signal, A is the maximum amplitude specified value, and Adet is the detected maximum amplitude, the maximum value suppression unit 30 for each symbol The output u (t) is: s (t)> A: u (t) = A × (s (t) / | A
det |) s (t) ≦ A: It is given as u (t) = s (t). Alternatively, the output u (t) may be a signal having the amplitude A, and u (t) = A × (s (t) / | Adet |).

The multicarrier signal transmission apparatus according to the first embodiment of the present invention suppresses the maximum value of the multicarrier signal by a linear operation. In other words, instead of clipping only the waveform at the maximum amplitude point as in the related art, suppression is performed equally for each symbol including the point other than the maximum amplitude point. Therefore, distortion due to non-linear signal conversion does not occur in the output waveform.

Therefore, there is no mutual interference between carriers in the multicarrier signal. Therefore, the bit error rate characteristics do not deteriorate. When OFDM is used, the probability of occurrence of a symbol having a large peak value is low. Therefore, by suppressing the maximum value for each symbol, a good average signal-to-noise ratio can be realized. As an effect of the first embodiment of the present invention, AWGN (Aditive White Gaussi
FIG. 3 shows the bit error rate characteristics in an anisotropic communication channel. The horizontal axis indicates Eb / No, and the vertical axis indicates the bit error rate. As shown in FIG. 3, the effect of the present invention is clear.

(Second Embodiment) A multicarrier signal transmission apparatus according to a second embodiment of the present invention will be described with reference to FIG. The multicarrier signal transmission apparatus according to the second embodiment of the present invention is based on the premise that differential encoding is used. It has a variable start symbol adding unit 40 for each burst. Therefore, a different start symbol is added for each wireless transmission burst, and even when the information bits to be transmitted are the same, the bit sequence of each carrier transmitted by OFDM is different. Therefore, it is possible to avoid occurrence of an extremely large maximum amplitude that is fixedly generated in a multicarrier signal for a certain transmitted bit sequence.

As a result, it is possible to prevent code errors from concentrating on a specific sequence (combination) of information transmission bits, and in particular, as an error compensation technique, a retransmission technique for transmitting the same information transmission bit. (ARQ: Automatic Re
peat Request) can be used to improve the throughput.

[0030]

As described above, according to the present invention,
The maximum amplitude can be suppressed to a predetermined value or less without causing mutual interference between carriers and a code error. In addition, for example, when a multicarrier signal is generated from a plurality of bit sequences having the same or similar bit patterns, it is possible to reduce the probability that the maximum amplitude portions of each carrier overlap.

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of a multicarrier signal transmission apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a main part of a multicarrier signal transmission apparatus according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a bit error rate characteristic in an AWGN communication channel.

FIG. 4 is a block diagram of a main part of a conventional multicarrier signal transmission device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Multicarrier signal generation part 11 Serial-parallel conversion circuit 12 Inverse DFT circuit 13 Parallel-serial conversion circuit 15 Maximum amplitude suppression part 20 Maximum value detection part for every symbol 30 Maximum value suppression part for every symbol 40 Variable start symbol addition part for every burst 50 Clipping section

Continued on the front page (56) References “Study of Peak Power Reduction Method for Wideband Microcell OFDM System”, IEICE Technical Report, October 17, 1997, Vol. 97, no. 323, p. 103-110, RCS97-143 (58) Fields investigated (Int. Cl. ⁷ , DB name) H04J 11/00 H04B 1/04

Claims (2)

(57) [Claims] 1. A means for inputting a bit sequence and generating a multi-carrier signal divided for each symbol in accordance with the bit sequence, and suppressing the input of the multi-carrier signal so that the maximum amplitude does not exceed a predetermined value. A multicarrier signal transmission device comprising: a means for detecting the maximum amplitude of the multicarrier signal for each symbol; and the maximum amplitude does not exceed the predetermined value according to the detection result. Means for evenly suppressing the amplitude of the multicarrier signal including a portion other than the maximum amplitude for each symbol. 2. The multicarrier signal transmission apparatus according to claim 1, further comprising means for adding a different start symbol to the head of each bit sequence.