JPH0222583B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a TDMA (time division multiple access) transmitter suitable for satellite communication systems. In particular, the present invention relates to a transmitter for burst-like polyphase phase-offset communication that also has means for forming a prefix word and a subsequent information word at the beginning of a burst-like signal in TDMA employing an offset PSK modulation method. Here, "offset PSK modulation method" means that the timing of bit change in at least one series among N-1 data series input to the N-phase phase modulator (N is a positive integer) is , refers to a phase modulation method whose timing is significantly different from that of other sequences.

In communications using the offset PSK modulation method, even if a signal is passed through a transmission path that has a nonlinear response with little envelope variation in its modulated wave, it is rarely affected by its nonlinear characteristics. Therefore, this method can be used in a satellite communication system, and the amplifier on the satellite (transponder) tower can be used at saturation level, thereby making effective use of transmission power and reducing system costs.

However, compared to conventional PSK modulation, the circuit is more complex due to the addition of an offset modulation circuit, the envelope fluctuation is reduced because the signal is transmitted at the saturation level, and the signal-to-noise ratio is not good in normal communication systems. . For these reasons, several problems still need to be solved in order to put the Offset PSK modem into practical use. Among these, the configuration of the preamble word placed at the beginning of the burst signal is extremely important in making it possible to realize a modulation/demodulation circuit.

In a burst communication method used in a communication system such as a satellite communication system, a transmission operation is performed only when transmitting information. Therefore, there are advantages that the required power can be reduced and that communication can be performed between a large number of transmitting and receiving stations using the same satellite and the same frequency band.

In offset PSK communication, information is transmitted by offset PSK modulating a carrier wave, and the information is expressed in the form of a relative phase change of the carrier wave. Demodulation of such an offset PSK signal is performed by comparing the phase of the offset PSK modulated signal with the phase of a reference carrier wave. Therefore, when demodulating an offset PSK modulated signal,
It is necessary to recover the reference carrier wave from the received signal on the receiving side. Simultaneously, a timing signal is also required to reproduce the digital information transmitted from the demodulated output, and this must also be extracted from the received signal.

Therefore, in bursty offset PSK communications, the reference carrier and timing signal must be regenerated for each received burst. However, such reference signals such as a reference carrier wave and a timing signal are not reproduced instantaneously with the arrival of a burst, but are generally accompanied by a certain time delay.
The time required to reproduce this reference signal is called acquisition. Since no reference signal has been established during this acquisition time, no information can be transmitted. Therefore, at the leading edge of the burst, a preamble word (preamble word, a synchronization word to promote the establishment of a reference signal) that does not contain communication information that lasts for a time corresponding to the acquisition time is used. This method includes a word for identifying a transmitting station and is sometimes called a prefix word, but here only a word for synchronization is called a prefix word.) followed by an information word. is used. In such communication using bursts consisting of prefix words and information words, it is required to make the prefix words as short as possible in order to improve communication efficiency. That is, the performance required of the prefix is to reliably transmit information regarding the reference carrier wave and information regarding the timing signal within a short period of time. Furthermore, as an additional performance requirement, it is desirable to include information for detecting the boundary between the prefix part and the information word part of the burst on the receiving side.

Shorten the acquisition time of reference carrier wave regeneration,
Moreover, from the standpoint of reducing the phase jitter, it is convenient for the prefix to be unmodulated, but the timing signal cannot be extracted from the unmodulated signal. One approach that is usually taken is to divide the prefix into two parts in time, one in which the signal is unmodulated and dedicated to establishing the reference carrier, and the other to the 0, π, 0, π... This method applies deep modulation such as this to help establish a timing signal. This method requires a margin for the acquisition time of both the reference carrier wave and the timing signal, so it is not an effective method especially when there is a demand for shortening the prefix. Another method is to apply appropriate phase modulation over the entire prefix, extract the timing signal from this, and
In parallel with this, there is a method of establishing a reference carrier wave from the PSK signal. The method of extracting a reference carrier wave from an offset PSK modulated wave using this PSK modulated signal as a prefix uses a circuit that combines means for removing phase modulation components and means for reducing phase jitter. Furthermore, this method of extracting a timing signal from a modulated signal uses a circuit that combines means for removing a carrier wave component and means for reducing phase jitter.

Means for reducing phase jitter can be roughly divided into methods using a phase synchronization circuit and methods using a band pass filter. The former makes it easy to make the equivalent noise band extremely narrow and has a large jitter reduction effect, but has the disadvantage that the acquisition is more uncertain than the latter. In the latter case, on the other hand, the acquisition is reliable, but it is difficult to narrow the equivalent noise bandwidth.

In addition, methods for removing phase modulation components include the so-called inverse modulation method, in which an inverse modulator is used to convert an offset PSK modulated signal into a continuous signal, and a multiplier is used to multiply the PSK signal by twice its phase number. , a so-called multiplication method in which the frequency is lowered again after removing the modulation component, and a baseband multiplier that operates similar to the inverse modulator of the inverse modulation method.
The so-called Costas method is well known. The disadvantage of these methods of extracting a reference carrier from a PSK signal is that the signal-to-noise ratio deteriorates,
The jitter of the reference carrier wave increases, and the acquisition time increases as the input signal-to-noise ratio worsens.

A method for removing the carrier wave component and extracting the timing signal is to use an envelope detector to extract only the bit (information unit corresponding to binary modulation) fluctuation component of the modulated wave, which corresponds to one bit unit. There is a method of extracting the timing signal by a delay detection method in which the timing signal is multiplied by a signal delayed by a delay time, or the same delay detection method using a delay circuit in units of 1/2 bit.

As methods for removing phase jitter in the extracted timing signal, in addition to the method using the phase synchronization circuit described above and the method using a bandpass filter, there is also a method that uses a variable phase shifter to automatically adjust the phase of the reference timing signal. There are methods such as tracking the timing detection phase.

Also, when considering the feasibility of these circuits, the unique characteristics of the offset PSK modulation system must be taken into account. For example, offset PSK modulated waves are often used at the saturated output of nonlinear circuits, so if the envelope detection method is used, the envelope detector output will be close to DC, and the fluctuations in the detection output due to bit changes will be reduced. Very little timing information is extracted. For this reason, the use of a 1-bit or 1/2-bit delayed detection method is more advantageous than one in which timing information of bit changes is extracted by phase detection, which is not directly related to envelope fluctuations.

It is an object of the present invention to improve and compensate for the drawbacks of the conventional methods described above, to obtain a reproduction reference carrier wave and a timing signal with short acquisition time and little phase jitter, and furthermore, to make it possible to obtain a reproduction reference carrier wave and a timing signal with a short acquisition time and with little phase jitter. It is an object of the present invention to provide a transmitting device that generates a burst-like phase modulation signal that can clearly detect boundaries between parts.

The present invention uses phase α and phase β (α and β are arbitrary phases, however, β−α≠0, π) as a prefix to the carrier wave.
means for performing two-phase phase modulation so as to alternately take
means for performing N-phase phase offset modulation so that the carrier wave has a phase of 2π/Ni (N: positive integer, i=0, 1, 2...N-1) corresponding to the transmission signal as an information word. It is characterized by:

This will be explained in detail below using the drawings. Unless otherwise specified, the embodiments described herein have N=4 and offset time=1/2T (T being the reciprocal of the symbol period or timing frequency).

FIG. 1 is a block diagram showing one embodiment of the present invention. 1 is a carrier wave oscillation source, and its oscillation output is supplied to a two-phase phase modulator 2 or a four (N) phase phase modulator 4 via a changeover switch 6. 2
Phase modulator 2 has a period of 2T applied from terminal 3.
is controlled by a rectangular wave signal of α,
Performs phase modulation of β.

The four-phase phase modulator 4 corresponds to the transmission code applied to the terminal pair 5, 5', and outputs 0, π/2, π, 3π/
Performs four-phase phase modulation. At this time, terminal pair 5,
Since there is a time offset in 5', the timing of the four-phase phase modulation is shifted by the offset time. Either of the outputs of these modulators is linked to the changeover switch 6, passes through the switch 6' controlled by the control signal from the terminal 7, and passes through the gate circuit 8.
join. Gate circuit 8 is controlled by a gate on/off control signal from terminal 9. The output of gate circuit 8 is taken out from terminal 10 as a transmission signal. The control signal applied to the terminal 7 connects the switches 6, 6' to the lower terminal in the prefix word part, and connects the switches 6, 6' to the upper terminal in the information word part. Further, the gate on/off control signal applied to the terminal 9 is a control signal for turning on the gate for a predetermined time to perform burst transmission.

The operation of this device will be explained using the waveform diagram shown in FIG. 2 and the vector diagram shown in FIG. 3.

FIG. 2a shows the structure of the transmitted signal, in which a burst is formed from a prefix word part 11 and an information word part 12. In this transmission signal, the prefix part is subjected to two-phase phase modulation, and the information word part is subjected to four-phase phase offset modulation. An example of the phase change is shown in the waveform diagram of FIG. 2b. In the prefix word part, the phases α and β are taken alternately, and in the information word part, the phase takes any value among 0, π/2, π, and 3π/2. However, in Fig. 2b, the input signal terminal pair 5, 5' to the 4-phase phase modulator 4 has 1/2
Since it has a temporal offset of T time,
Phase changes of 0, π/2, π, and 3π/2 appear every 1/2T time.

This switching of the modulation format between the prefix word part and the information word part is performed by a control signal applied to terminal 7, and the waveform of the control signal is shown by waveform 14 in FIG. 2c. Further, waveform 15 shows the waveform of the gate on/off signal applied to terminal 9. As is clear from the waveform 13, the possible phases of the prefix word part and the information word part are different, so it is easy to detect this boundary on the receiving side.

When the phase relationship shown by waveform 13 is expressed in a vector diagram, it becomes as shown in FIG. 3. The phase of the prefix word part is represented by vectors 16, 17, and the phase of the information word part is represented by vectors 18, 19, 20, 21. As is clear from this vector diagram, vector 16 can be divided into vectors 22 and 23. Also, vector 17 is vector 22
It can be divided into 24 parts. Therefore, the phase in the prefix portion can be considered as the sum of vector 22, which is continuous in time and represents a component having the same phase as vector 18, and vectors 23 and 24, which occur alternately in time. From a signal containing such a continuous component, the continuous component, that is, the reference carrier wave, can be extracted directly using a phase synchronization circuit or a narrow band pass filter, without using a phase modulation component removal circuit as described above. .

Here, since the vectors 23 and 24 have equal lengths and opposite directions, when applied to a narrow band pass circuit such as a phase synchronization circuit, they are averaged and disappear. It is extremely desirable to be able to extract the reference carrier wave from the prefix portion without removing the phase modulation component in this way from the viewpoint of its phase jitter and acquisition characteristics. In addition, in order to continuously extract the reference carrier wave from the information word part, it is necessary to switch the state of the reference carrier detection circuit so as to have a phase modulation component removal function, but at this point, the reference carrier wave has already been detected. has been established, the noise band of a phase-locked circuit or narrow bandpass filter can be made sufficiently narrow without considering the acquisition time. Therefore, deterioration of the signal-to-noise ratio caused by the phase modulation component removal circuit can be adequately coped with.

FIG. 4 shows a specific configuration of a four-phase phase offset modulator (circuit 4 in FIG. 1). Of the two data series input to the input signal terminal pair 5, 5', only one data series passes through the circuit 25 that delays by 1/2T time, is amplified by the amplifiers 26, 26', and then undergoes four-phase phase modulation. Input to the 2 input terminals.

In FIG. 5a, waveforms 39 and 40 show specific examples of two series of data input to the input signal terminal pair 5 and 5'. Furthermore, waveforms 41 and 42 show two series of data input to the two input terminals of the four-phase phase modulator.

FIG. 5b shows the movement of the four-phase phase offset modulated signal in a vector diagram in correspondence with the previous two series of data waveforms 41 and 42. From Figure 5b, the maximum amplitude value of the vector is √2:1 (10log√2=3dB), and this four-phase phase offset modulation phase is not easily affected by passing through a nonlinear transmission path. is easily understood. Although the example of FIG. 5 shows the case where the offset time is 1/2T, it can be implemented in the same way for other offset times and has the same effect.

FIG. 6 is a block diagram showing another embodiment of the invention. Components 1, 4, 5, 7, 8, 9, 10
are the same as the components shown in FIG. In this embodiment, the output of the carrier wave oscillation source 1 is divided into two by a branch circuit 28, one of which is supplied to the four-phase phase offset modulator 4 and the other to the gate circuit 27. In addition, each output is connected to a coupling circuit 29
After being coupled, the signals are guided to the gate circuit 3.

The operation of this device will be explained using the vector diagram in FIG. In this device, in the prefix part, terminal pair 5,
A code is added to 5' so that the modulation phase of the four-phase phase offset modulator 4 becomes -π/2, +π/2, -π/2, +π/2, . The output of the four-phase phase offset modulator 4 at this time is expressed as the vector 3 in FIG.
Indicated by 0.31. At the same time, in the prepositional part,
A gate circuit 27 controlled by a control signal applied to terminal 7 is in an on state and allows the carrier wave to pass through. This gate circuit output is shown by vector 32 in FIG. The outputs of the four-phase phase offset modulator 4 and the gate circuit 27 are connected to a coupling circuit 29.
is combined with The resulting vectors 33 and 34
A signal represented by is obtained from the output terminal 10 via the gate circuit 3. In this way, the output is α
α, which takes the phase of and β alternately and constitutes a prepositional word,
The value of β can be changed by changing the magnitude of vectors 30 and 31.

Next, in the information word part, the gate circuit 27 is turned off and the carrier wave is not passed, and the four-phase phase offset modulator 4 transmits 0, π/2, π/2, Performs four-phase phase modulation of π and 3π/2. The four-phase phase offset modulated signal maintains the same phase relationship even when passing through the coupling circuit, and is obtained from the output terminal 10 via the gate circuit 3. As a result, the phase of the signal obtained from the terminal 10 becomes, for example, a waveform 13 in FIG.

In this embodiment, as shown in the vector diagram of FIG. 7, the prefix word part has a larger amplitude than the information word part. Furthermore, in the vector diagram of FIG. 5, the amplitude is smaller in the prefix word part than in the information word part. Due to the saturation characteristics within the transmitting/receiving device, the repeating device, and the transmission path, such changes in amplitude are constant at the input end of the receiving device and do not adversely affect the demodulation characteristics. This is because, as mentioned earlier, the offset modulation method was devised for communication using a transmission path with saturation characteristics, and is also used for communication using such a transmission path. be.

FIG. 8 is a block diagram showing the configuration of still another embodiment of the present invention. Components 1, 4, 5,
Components 7, 8, 9, and 10 are the same as those shown in FIG. 1, so their explanation will be omitted. In this embodiment, all outputs of the carrier wave oscillation source 1 are applied to a four-phase phase modulator 4, and the output of this modulator 4 is outputted through a (0, -π/4) phase modulator 34 and a gate circuit 8. terminal 1
Appears to 0. In this device, in the prefix portion, a code is added to the terminal pair 5, 5' so that the modulation phase of the four-phase phase modulator 4 becomes 0, π/2, 0, π/2, . . . .

The outputs of the four-phase phase modulator 4 at this time are shown by vectors 35 and 36 in FIG. At the same time, in the prefix part, the modulation phase of the phase modulator 34 (0, -π/4) controlled by the control signal applied to the terminal 7 becomes -π/4, and the vector from the terminal 10 becomes -π/4. Signals represented by 37 and 38 are obtained. Therefore, in the prefix part, the phases are -π/4, +π/4,
-π/4, +π/4... (α=π/4,
β=−π/4). Next, in the information word part, (0, -
π/4) The modulation phase of the phase modulator 34 becomes 0,
The four-phase phase modulator 4 outputs 0, π/2, π,
Performs 3π/2 four-phase phase modulation. The structure of the transmission signal obtained from the terminal 10 in this way is shown in FIG.
The phase becomes, for example, as shown in waveform 13 in FIG. 2b.

FIG. 10 is a block diagram showing the configuration of still another embodiment of the present invention. Components 1, 4, 5,
8, 9, and 10 are the same components as in FIG. In this embodiment, all outputs of the carrier wave oscillation source 1 are applied to a four-phase phase modulator 4;
The output passes through the gate circuit 8 and appears at the output terminal 10. In this device, by driving the four-phase phase modulator 4 in a linear region, it is possible to obtain a code in which the modulation phase becomes α, β, α, β, . . . in the prefix portion. The relationship between the output of the four-phase phase modulator 4 and the drive waveform at this time is shown in FIG.
The two series of data input to terminal pair 5, 5' are
This is shown in waveforms 39 and 40 in Figure a. Further, a time offset of 1/2T is given to the data series shown by waveform 40, and the two series of data directly input to the two input terminals of the four-phase phase modulator 4 are shown as waveforms 41 and 42.

The vectors corresponding to the information words in the waveforms 41 and 42 at this time are shown in the vectors 18, 19, and 2 in FIG.
0 and 21, and the vectors corresponding to the prefix words are shown as vectors 43 and 44. A vector 18 corresponding to an information word is expressed as a combination of vectors 45 and 46 corresponding to high levels of waveforms 41 and 42 of the data series. Similarly, vector 19 is a combination of vectors 47 and 46 corresponding to the low level of data series 41 and the high level of data series 42, and vector 2
0 is a combination of vectors 47 and 48 corresponding to the low level of data series 41 and 42, and vector 21 is a combination of vectors 47 and 48 corresponding to the high level of data series 41 and the low level of 42.
It is expressed as a composite of 5,48. A vector 43 corresponding to the prefix word is a vector 49 equivalent to the prefix word part of the data series 41 and a vector 49 corresponding to the prefix word part of the data series 41.
It is a composite vector with a vector 50 equivalent to the high level of the prefix part of 2. Similarly, the vector 44 is equal to the vector 49 and the vector 51 which is equal to the low level of the prefix part of the data series 42.
It is expressed as a composite vector.

As shown in the example in Figure 1, the four-phase phase offset modulation burst signal generated by the transmitter shown in this example is continuously transmitted by a phase synchronization circuit or a narrow band pass filter without using a phase modulation component removal circuit. A component, ie, a reference carrier wave, can be extracted. However, the phase of the continuous component (reference carrier wave) obtained in this case is ± different from the reference carrier wave obtained using the phase modulation component removal circuit from the following information word.
Since the phase changes by π/4i (i=1, 3, 5, 7), ±π/4i (i=1, 3,
It is necessary to provide 5 and 7) modulators in the demodulation circuit. Further, bit timing information is extracted from the prefix portion by the envelope detection method or the delay detection method, as described in the previous embodiment.

In addition, in this example, 4 of the waveforms 41 and 42 in FIG.
The prefix part and the information word part of the data directly input to the two input terminals of the phase modulator 4 have different amplitudes, but if they are the same, α=π/4j (j=1, 3, 5, 7), β=α±
π/2, but in this case, of course, it is possible to construct a transmitter for a four-phase phase offset modulation burst signal including a reference carrier wave for acquisition and a prefix from which a bit timing signal can be extracted.

As explained above, according to the present invention, it is possible to obtain a reference carrier wave and a bit timing signal with little phase jitter in a short acquisition time on the receiving side, and furthermore, it is possible to obtain a reference carrier wave and a bit timing signal with little phase jitter in a short acquisition time. A transmitting device is obtained which is capable of generating burst-like polyphase phase offset modulated signals that can be detected. The device of the present invention is particularly effective when used as a transmitting device for satellite communications.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention. FIG. 2 is a waveform diagram showing the phase relationship of transmission signals in the embodiment of FIG. 1. FIG. 3 is a vector diagram showing the phase relationship of transmission signals in the embodiment of FIG. 1. FIG. 4 is a diagram showing a specific configuration of the four-phase phase modulator shown in FIG. 1. FIG. 5 is a diagram showing a specific example of two sequences input to the four-phase modulator 4' and showing time-series vector changes corresponding to data. This FIG. 5 also corresponds to the data input and vector diagram of the other embodiment shown in FIG. FIG. 6 is a block diagram showing another embodiment of the invention. FIG. 7 is a vector diagram showing the phase relationship in the prefix portion of the transmission signal of the embodiment of FIG. 6. FIG. 8 is a block diagram showing the configuration of still another embodiment of the present invention. FIG. 9 is a vector diagram showing the phase relationship in the prefix portion of the transmission signal in the embodiment of FIG. 8. FIG. 10 is a block diagram showing still another embodiment of the invention. The vector diagram of the prefix part of the transmitted signal in this example is as shown in Figure 5b.
It is necessary to install a phase modulator. 1... Carrier wave oscillation source, 2... Two-phase phase modulator, 3...
Control signal input terminal, 4, 4'...four-phase phase modulator,
5, 5'... Control signal input terminal pair, 6, 6'... Selector switch, 7... Control signal input terminal, 8... Gate circuit, 9... Control signal input terminal, 10... Transmission signal output terminal, 25... 1 series a circuit for delaying the data by a predetermined offset time, 26, 26'...amplifier;
27... Gate circuit, 28... Branch circuit, 29... Coupling circuit, 34... (0, -π/4) phase modulator.

Claims (1)

[Claims] 1. Phase α and phase β (where α and β are β−α≠0,
PSK alternately takes arbitrary phases that are π)
2π/Ni (where N is a positive integer, i=0, 1, 2...N
-1) a second means for performing N-phase offset PSK modulation so that the phase changes in a time unit different from the time unit of the phase change in the first means; Connection method transmitting device.