JPH0377703B2 - - Google Patents

Description

[Detailed Description of the Invention] (1) Industrial Application Field The present invention relates to an orthogonal modulation method in digital communication.

(2) Conventional technology Conventionally, BPSK (Binary Phase Shift Keying),
For QPSK (Quadrature Phase Shift Keying) baseband signals, as shown in Figure 1a, if the data is a mark, set it to 1, if it is a space, set it to -1.
An NRZ (Non-Return-to-Zero) code is used. In addition, multivalued ASK (Amplitude Shift
Keying), multi-value PSK, multi-value QAM (Quadrature
Amplitude Shift Keying), etc., the NRZ code is multi-level.

The NRZ code is a code that can efficiently transmit given power, but since the clock for data determination is recovered from the received signal, if the transmitted data contains a long string of 1s or 0s, the clock will be lost. The disadvantage is that playback becomes impossible. Therefore, if there is a possibility that the transmitted data includes a long string of 1's or 0's, it is necessary to scramble the transmitted data in advance to prevent consecutive 1's or 0's.

On the other hand, Manchester code is a coding system that allows easy clock reproduction. As shown in Figure 1b, the Manchester code divides the time slot in the NRZ code into two, and converts 1 in the NRZ code into
1), -1 is set to (-1, 1). In the case of Manchester codes, there is always a rising or falling point (hereinafter referred to as an edge) at the midpoint of one code, so clock reproduction is easy even if marks or spaces are continuous. However, in this case, 1
Since there are two pulses between two codes, this has the disadvantage that twice the frequency band is required compared to the NRZ code when transmitting the same amount of information.

(3) Problems to be Solved by the Invention In the Manchester code, edges always exist at a period equal to the symbol rate, so clock reproduction is easy. However, among two pulses in one code, once the sign of the preceding pulse is determined, the sign of the subsequent pulse is uniquely determined to be the inverted sign of the preceding pulse. Despite this, only 1 bit of information can be transmitted. Therefore, when transmitting the same amount of information as when using the NRZ code, twice the bandwidth is required.

From the above, if one symbol is composed of two pulses with edges within one symbol, and a code that can transmit twice as much information as an NRZ code is used, NRZ
It is thought that it will be possible to perform digital orthogonal modulation in the same band as when using codes and with easy clock recovery.

The present invention relates to an orthogonal modulation method based on this principle.

(4) Means for solving the problem Modulated waves in the present invention are generated as follows.

(1) Convert n-bit data to S/P (serial/parallel).

(2) If the baseband signal has only in-phase components, n-1 bits out of n bits are used, and if orthogonal components also exist, n-2 bits are used to calculate the complex signal.
Generates NRZ code. An example of the generated NRZ code is shown in Figure 2a. However, the length of one symbol is T
(sec).

(3) Divide one symbol of the generated NRZ code into two,
Divided into NRZ slot and information slot. However, whether the first half or the second half of one symbol is used as the information slot depends on the bit information not used in NRZ code generation (1 bit if the baseband signal contains only in-phase components, 2 bits if the baseband signal also includes orthogonal components). Determined based on bits). and,
The signal generated by the NRZ code generator is directly inserted into the NRZ slot, and a predetermined signal or a signal according to the information of the NRZ slot is inserted into the information slot.

For example, if the in-phase or quadrature component NRZ signal has the waveform shown in FIG. 2a, the symbol waveforms generated by the above operations will be of two types, shown in FIG. 2b and c. However, in this case, the information slot has 0
has been inserted.

In addition to inserting a certain value (0 in the figure) into the information slot as shown in Figure 2 b and c, for example, the polarity of the NRZ slot signal is reversed as shown in Figure 2 d. It is also possible to insert a signal whose amplitude is a certain constant value. This may be arbitrarily set based on the requirements of the modulation method, receiver configuration, clock reproduction characteristics, etc.

(4) The complex baseband signal generated by the above operations is orthogonally modulated in the orthogonal modulation section.

(5) Effect FIG. 3 shows a configuration diagram of the present invention.

First, data is divided into n bits (n is the number of bits included in one symbol) in the S/P converter 1. Next, the NRZ code generating section 2 generates a complex NRZ code from n-1 bits of information when the baseband signal includes only in-phase components, and from n-2 bits of information when it also includes orthogonal components.

Furthermore, in the information slot signal generating section 3,
Using 1-bit information if the baseband signal contains only in-phase components, and 2-bit information if it also includes orthogonal components, information slot selection information indicating which time slot is to be used as the information slot is first generated, and the information slot selection information is Generates a signal to be inserted into the

The baseband signal generation section 4 generates a complex baseband signal based on the signals generated by the NRZ code generation section 2 and the information slot signal generation section.

Note that the baseband signal generation section 4 also includes waveform shaping for band limitation. Furthermore, when configuring the present invention using digital signal processing technology, part or all of the NRZ code generation section 1, information slot signal generation section 2, and baseband signal generation section 3 may be configured as one unit. It is possible.

Thereafter, the signal is modulated in the orthogonal modulation section 5 to obtain a transmission signal. Note that the orthogonal modulation section also includes a transmission power amplifier.

(6) Example To explain the above method more specifically,
An example of applying the above concept to QPSK will be explained. Note that in the case of QPSK, n=4.

First, the serial/parallel converter 1 generates 4-bit parallel data. Next, first, a complex NRZ code is generated using 2-bit information.
Therefore, the in-phase and quadrature components each have one of the waveforms shown in FIG. 1a.

Also, the remaining 2 bits of information are used to decide whether the information slot should be placed in the first half or the second half.

Therefore, there are four types of symbol waveforms of in-phase or quadrature components generated in the baseband signal generation section as shown in FIGS. 4a to 4d. However, 0 is inserted into the information slot.

As you can see from the waveforms a to d, when a specific signal is inserted into the information slot, an edge always occurs at the midpoint of the symbol with a period of T (sec), which makes clock reproduction easier. .

In addition, in the case of QPSK, one code is a in Figure 1.
or b. Since the baseband signal is in complex form, one symbol contains two bits of information.

In contrast, in the case of this method, one symbol contains 4 bits of information, but the bandwidth is 2 bits of QPSK.
Since twice as much information is required, the amount of information that can be transmitted in the same band is equal to that of conventional QPSK.

In addition, the present invention uses the same idea to
It can be applied to ASK, multi-value PSK, multi-value QAM, etc.

As an example of application to systems other than QPSK, a method of applying the present invention to 16QAM will be shown. In that case, n=6 and 4
Generates NRZ code using bits and 2
Bits are used to select information slots. In this case as well, if the same band is used, the amount of information that can be transmitted is the same as with conventional 16QAM.

In the case of 16QAM, the in-phase and quadrature components of the baseband signal are one of those shown in FIGS. 5a-d.

On the other hand, when the present invention is applied, the in-phase and quadrature components generated in the baseband signal generation section 4 become one of the components a to h in FIG. 4.

(7) Effects of the Invention When the present invention is used, since an edge always occurs at the center of one symbol, it is possible to obtain a modulated signal whose clock is easily recovered with the same transmission efficiency as when using an NRZ code.

In digital communications, clock recovery characteristics influence error rate characteristics. Therefore, it can be expected that the error rate characteristics will be improved by using this method.

[Brief explanation of drawings]

Fig. 1 shows the symbol waveforms of the NRZ code and the Manchester code, Fig. 2 shows the symbol waveforms when the present invention is used, Fig. 3 shows the configuration of the present invention, and Fig. 4 shows the symbol waveforms when the present invention is used.
Figure 5 shows the waveform pattern of the baseband signal when the present invention is applied to QPSK. Figure 6 shows the waveform pattern of the baseband signal when the present invention is applied to 16QAM. be. In FIG. 3, 1 is an S/P (serial/parallel converter), 2 is an NRZ code generator, and 3 is
4 is a baseband signal generator, and 5 is an orthogonal modulator.

Claims (1)

[Claims] In the case of digital orthogonal modulation that generates one symbol from 1n bits of information, if the baseband signal has only in-phase components,
n if it contains 1 bit of information and also includes orthogonal components.
Using the information of n-2 bits in the bit, NRZ
generate one symbol consisting of a sign
The NRZ code generator and the NRZ code generator generate 1 symbol into 2
divided into two time slots, one of which is
One time slot (hereinafter referred to as NRZ slot) uses the signal generated by the NRZ code generator as is, and the information determined by the information slot signal generator is inserted into the other time slot (hereinafter referred to as information slot). By doing so, the baseband signal generator generates a complex baseband signal having a signal level conversion point at the midpoint of one symbol, and when the baseband signal has only an in-phase component, the information of 1 bit out of n bits is generated. , and if it also includes an orthogonal component, use 2 bits of information out of n bits,
By selecting an information slot and using an information slot signal generation section that generates a signal to be inserted into the information slot, and an orthogonal modulation section that orthogonally modulates the generated baseband signal, clock regeneration is easy, and An orthogonal modulation method that is characterized by generating modulated waves that can be transmitted with the same transmission efficiency as when using NRZ codes.