JP5583797B2 - Transmitting apparatus and communication system - Google Patents

Description

  The present invention relates to a transmission apparatus and a communication system that perform modulation according to line conditions.

  For example, in wireless communication, there is an adaptive modulation technique that changes the coding rate for error correction and the number of modulation multi-values according to the line condition (signal-to-noise power ratio: S / N) that fluctuates due to the influence of the propagation environment. Used. By selecting an optimum modulation method according to the S / N of the line by this adaptive modulation technique, the frequency can be used efficiently without disconnecting the line.

  In particular, in satellite communication, the frequency band and transmission power of the communication satellite are limited. Therefore, as described in Non-Patent Document 1, an optimal modulation method is assigned according to the S / N status of each line. This increases the total transmission capacity and the number of lines accommodated.

FIG. 6 shows a configuration example 1 of a conventional transmission apparatus.
In FIG. 6, the modulation means 31 has a configuration corresponding to adaptive modulation in which the coding rate R for error correction and the modulation multilevel number M are variable. The modulation signal output from the modulation means 31 is filtered by the filter 32 and transmitted from the antenna 34 via the amplifier 33. At this time, the clock rate Fs and the filter characteristic (roll-off coefficient α) are fixed to make the occupied bandwidth (Fs (1 + α)) constant. The bit rate is represented by R × M × Fs.

  Here, the higher the coding rate R and the modulation multilevel number M, the higher the frequency utilization efficiency (the number of bits that can be transmitted at 1 Hz), but the higher the required S / N. On the other hand, when the required S / N is lowered, the coding rate R and the modulation multi-level number M may be reduced. However, since the transmission speed is lowered, the clock rate Fs is set to realize the same transmission speed. It is required to increase.

  However, the occupied bandwidth Fs (1 + α) changes with the change of the clock rate Fs. In Non-Patent Document 1, depending on the usage status of the satellite repeater, when the bandwidth usage rate is higher than the usage rate of the repeater power, a communication method with a high required S / N is selected for a new user, and vice versa. On the other hand, when the usage rate of the repeater power is higher than the usage rate of the bandwidth, the communication method with a low required S / N is selected and the power of the satellite repeater is satisfied while allocating many bandwidths to satisfy the required transmission rate. And the band is used in a balanced manner.

JP 2011-176679 A

Nakahira et al., Proposal of dynamic multi-carrier link control that maximizes bandwidth and transmission power of repeater in mobile satellite communication system, IEICE Transactions 2012/5 Vol.J95-B No.5, pp. 662-676 Masuno et al., Performance improvement of self-spectrum reproduction equalization using soft replica in spectrum decomposition / compression transmission, IEICE, Satellite Communication Society, SAT2012-19, pp.7-12

  In the conventional adaptive modulation technique, the coding rate R is generally selected from 1/2, 2/3, 3/4, 5/6, 7/8, etc., and the modulation multilevel number M is a natural number (BPSK: M = 1, QPSK: M = 2, 8PSK: M = 3, 16QAM: M = 4, etc.), both of which are discrete.

  FIG. 7 shows the relationship of frequency utilization efficiency to S / N of a line in a conventional configuration. Here, when the coding rate R is 1/2, 2/3, 3/4, 5/6, 7/8 and the modulation multilevel number M is selected as 1, 2, 3, 4 respectively, This is a plot of frequency utilization efficiency (number of bits that can be transmitted at 1 Hz) when an optimum parameter is selected against S / N, and Shannon's theorem is used for calculation. Thus, since the parameters are discrete, it can be confirmed that the frequency utilization efficiency is stepped.

  Regarding the increase of the clock rate, since a frequency slot composed of a fixed band is generally defined, the data string is serial-parallel converted into the number of subcarriers as shown in FIG. Frequency conversion is appropriately performed so that modulation, filtering, and bands do not overlap (Patent Document 1). Since a plurality of subcarriers are used, the clock rate also becomes an integral multiple according to the number of frequency slots, which is also discrete.

  When the modulation scheme is optimized according to the communication path, it is ideal that the request S / N matches the S / N of the communication path. When a modulation scheme having a low request S / N with respect to the S / N of the communication path is selected, surplus power is used. Further, in order to maintain the transmission speed, it is necessary to cope with the problem by increasing the number of carriers, so that not only power but also a band is used extra.

  That is, in order to select an optimum modulation method according to the communication path, it is required that the frequency utilization efficiency is not stepwise but continuous with respect to the S / N of the line. It should be noted that the relationship between the required S / N and the frequency utilization efficiency needs to increase monotonously.

  An object of the present invention is to provide a transmission apparatus and a communication system that realizes an adaptive modulation technique in which frequency use efficiency changes continuously with respect to S / N of a line.

The present invention relates to a modulation means for modulating a transmission signal at a coding rate R for error correction, a modulation multi-level number M, and a clock rate Fs, and outputting a modulation signal having a bit rate R × M × Fs, and roll-off. coefficient alpha, has a filter characteristic of the pass band width as a clock rate Fs, and a filter for filtering a modulated signal, according to the condition of the line of S / N, sign-rate R, modulation level M, and using the adaptive modulation technique the clock rate Fs to set each discretely varied, the transmission device for transmitting a modulated signal of occupied bandwidth Fs (1 + alpha), the modulation means are discretely set Instead of the clock rate Fs, the transmission signal is modulated using a clock rate Fs ′ (Fs ′> Fs) that continuously changes at a value larger than the clock rate Fs , and the bit rate R × M × Fs ′ is continuously changed. To change The filter removes the sideband component of the modulated signal whose occupied band has increased Fs ′ / Fs times as the discretely set clock rate Fs increases from the clock rate Fs ′ to the clock rate Fs ′ by filtering. In this configuration , the occupied bandwidth of the modulation signal is reduced to Fs (1 + α), and the bit rate R × M × Fs ′ of the modulation signal is continuously obtained using the clock rate Fs ′ that continuously changes by the modulation means. The frequency utilization efficiency with respect to the S / N of the line is continuously changed by reducing the occupied bandwidth of the modulation signal to Fs (1 + α) by the filter while changing.

  A communication system according to the present invention includes the transmission device according to the first invention and a reception device that receives a modulated signal in which a part of the signal component is lost due to sideband component deletion and restores the transmission signal by error correction. .

  The communication system of the present invention receives the modulated signal in which part of the signal component is lost due to the deletion of the sideband component and the transmission apparatus of the first invention, and restores the transmitted signal by error correction and equalization processing Device.

  The transmission apparatus of the present invention can continuously change the frequency use efficiency, which has been discrete with respect to the S / N of the line so far, and can effectively use the transmission power and bandwidth in wireless communication. As a result, the total transmission capacity of the communication system can be increased.

It is a figure which shows the Example structure of the transmitter of this invention. It is a figure which shows the transmission signal spectrum in a prior art and this invention technique. It is a figure which shows the structural example 1 of the receiver corresponding to the transmitter of this invention. It is a figure which shows the structural example 2 of the receiver corresponding to the transmitter of this invention. It is a figure which shows the relationship of the frequency utilization efficiency with respect to S / N of the line | wire in this invention. It is a figure which shows the structural example 1 of the conventional transmitter. It is a figure which shows the relationship of the frequency utilization efficiency with respect to S / N of the line | wire in a conventional structure. It is a figure which shows the structural example 2 of the conventional transmitter.

FIG. 1 shows the configuration of an embodiment of the transmission apparatus of the present invention.
In FIG. 1, the transmission apparatus according to the present embodiment is assumed to be a wireless transmission apparatus, and includes a modulation unit 11, a filter 32, an amplifier 33, and an antenna 34.

  A feature of the present invention is that, in order to realize an adaptive modulation technique in which the frequency utilization efficiency changes continuously with respect to the S / N of the line, the coding rate R for error correction, modulation for the input data string In the modulation means 11 of the multi-valued number M, a modulation in which the continuously changing clock rate Fs ′ (Fs ′> Fs) is used and the occupied band increases as the clock rate Fs increases from the clock rate Fs ′. The sideband component of the signal is deleted and transmitted using a filter having the same occupied bandwidth Fs (1 + α) as in the conventional configuration.

FIG. 2 shows a transmission signal spectrum in the prior art and the technique of the present invention.
In the conventional transmission apparatus, when the assigned occupied bandwidth is Fs (1 + α), a filter with a clock rate Fs, a roll-off coefficient α, and a passband width Fs is used.

  The transmission apparatus of the present invention uses a filter 32 having the same occupied bandwidth Fs (1 + α) as that of the conventional transmission apparatus to filter and transmit a signal modulated at the clock rate Fs ′ (Fs ′> Fs). Become. Accordingly, since the filter characteristic is modulated at a fast clock rate, a signal from which a part of the signal component (hatched part) is deleted is transmitted. At this time, it is necessary to increase the power density so as to compensate for the lost power.

  The bit rate at this time is R × M × Fs ′, and the clock rate Fs ′ can be selected continuously. Further, since the occupied bandwidth is not different from Fs (1 + α), the frequency use efficiency is improved by an amount proportional to Fs ′. In this example, an example of a single carrier is shown. However, in the transmission method using a plurality of subcarriers as in the prior art shown in FIG. 8, the clock rate Fs ′ (Fs '> Fs) may be used for modulation.

FIG. 3 shows a configuration example 1 of a receiving apparatus corresponding to the transmitting apparatus of the present invention.
In FIG. 3, the receiving apparatus includes an antenna 21, an amplifier 22, a filter 23, and demodulation means 24. The signal received by the antenna 21 is input to the filter 23 via the amplifier 22, and the filtered signal is demodulated by the demodulation means 24. At this time, although a part of the signal component of the transmission signal is missing, the transmission data is restored by the error correction capability in the demodulation means 32.

  Here, FIG. 4 shows a configuration example 2 to which the equalizing means 25 for equalizing the signal component missing on the transmission side is applied in order to increase the required S / N. The equalization means 25 is a self-spectrum reproduction (ASR) type using a sub-spectrum replica that generates inter-symbol interference caused by sub-spectrum suppression described in Non-Patent Document 2, for example, by temporary demodulation decoding. Compensation is performed by an equalization method.

  The clock rate Fs' in the present invention is a value exceeding 1 times Fs. However, when the ratio increases, the lost signal component increases, and the equalization capability at the time of reception is limited. Therefore, for example, when (1) R = 3/4, M = 2, and Fs = 1 (MHz / s), the bit rate is 1.5 Mbps, and (2) R = 5/6, M = 2, Fs = 1. In the case of (MHz / s), two modulation schemes having a discrete relationship such that the bit rate is 1.67 Mbps are complemented (R = 3/4, M = 2, 1 <Fs ′ <1.11 (MHz / s), The bit rate is preferably 1.5 to 1.67 (MHz / s).

  In this way, by continuously changing the clock rate Fs ′, as shown in FIG. 5, the frequency utilization efficiency that changes continuously instead of the conventional step shape is realized with respect to the S / N of the line. it can. For example, it can be confirmed that the improvement effect is particularly high in the S / N immediately before the frequency utilization efficiency is improved by the conventional technique, as in the vicinity of S / N = 1.6 dB of the line in FIG.

DESCRIPTION OF SYMBOLS 11, 31 Modulation means 21 Antenna 22 Amplifier 23 Filter 24 Demodulation means 25 Equalization means 32 Filter 33 Amplifier 34 Antenna

Claims (3)

Modulation means for modulating a transmission signal at a coding rate R for error correction, a modulation multi-level number M, and a clock rate Fs, and outputting a modulation signal having a bit rate R × M × Fs;
A filter having a filter characteristic in which a roll-off coefficient is α, a pass bandwidth is the clock rate Fs, and filters the modulated signal;
With
Depending on the circumstances of the line S / N, with the sign-rate R, the modulation level M, and the adaptive modulation technique clock rate Fs you set respectively discretely varied, occupied band In a transmission device that transmits a modulation signal having a width Fs (1 + α) ,
The modulation means modulates the transmission signal using a clock rate Fs ′ (Fs ′> Fs) that continuously changes at a value larger than the clock rate Fs instead of the discretely set clock rate Fs. The bit rate R × M × Fs ′ is continuously changed,
The filter removes by filtering the sideband components of the modulated signal whose occupied band has increased Fs ′ / Fs times as the discretely set clock rate Fs increases to the clock rate Fs ′. , The occupied bandwidth of the modulation signal is reduced to Fs (1 + α) ,
While continuously changing the bit rate R × M × Fs ′ of the modulation signal using the clock rate Fs ′ that continuously changes by the modulation means, the occupied bandwidth of the modulation signal by the filter is changed to Fs ( The frequency utilization efficiency with respect to the S / N of the line is continuously changed by reducing to 1 + α) . A transmission device according to claim 1 ;
A communication system comprising: a receiving device that receives a modulated signal in which a part of a signal component is lost due to deletion of the sideband component, and restores the transmission signal by error correction. A transmission device according to claim 1 ;
A communication system comprising: a receiving device that receives a modulated signal in which a part of a signal component is lost due to deletion of the sideband component, and restores the transmission signal by error correction and equalization processing.

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