JPH04177931A - Communication system - Google Patents

Abstract

PURPOSE:To eliminate phase uncertainty without deteriorating a BER by combining a phase rotation circuit and a frame synchronizing circuit and switching a phase for each prescribed time till a unique word(UW) is detected. CONSTITUTION:A transmitter has a UW insertion circuit 21 and a modulator 23 and inputs a multiplexed input data signal 101 to the UW insertion circuit 21 and a UW is inserted to a head of each frame. A receiver is provided with a demodulator 24, a phase rotation circuit 11 and a frame synchronizing circuit 12 and a data signal received by the receiver is inputted at first to the demodulator 24, in which the signal is demodulated. Then the demodulated data signal is inputted to the phase rotation circuit 11, which selects sequentially the phase of the demodulated data signal for each prescribed time to some ways of demodulation phases to be expected. The frame synchronizing circuit 12 detects the unique word from the data signal. Thus, the phase uncertainty is eliminated without deteriorating the BER(Bit Error Rate).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a communication system using a time division multiplex communication system, and particularly to a communication system used for satellite communication.

[Background Art] Today, various communication or broadcasting services using communication satellites or broadcasting satellites are being put into practical use one after another.

In such services, a large amount of information (
Time division multiplexing, which multiplexes and broadcasts channels (channels), is often used. When using this time division multiplexing method, in order to correctly separate the desired channel on the receiving device side, the transmitting device generally sets up a frame like the one shown in Figure 3 on the time axis, and starts the frame at the beginning of the frame. A code with a strong autocorrelation called a unique word (hereinafter referred to as UW) is inserted into. On the receiving device side, if this UW is detected and frame synchronization is established, the desired channel can be separated. Therefore, in order to stably establish frame synchronization and receive a desired channel, it is important to correctly detect the UW.

In the conventional satellite communication system, as shown in FIG. It has a synchronization circuit 25 and a frame synchronization circuit 26.

The operation of this communication system will be explained below.

The multiplexed input data signal 101 is input to the UW inserter circuit 21. The UWW input circuit 21 inserts a UW at the beginning of each frame of the input data signal 101. The data signal with the UW inserted is input to the differential encoding circuit 22. The differential encoding circuit 22 performs differential conversion of data signals.

The differentially converted data signal is input to the modulator 23,
It is phase modulated and sent to the satellite line 27 as a transmission signal.

The transmission signal transmitted via the satellite line 27 is demodulated by the demodulator 24. The demodulated data signal is differentially inversely converted and decoded by the differential decoding circuit 25. The decoded transmission signal is input to a frame synchronization circuit, where UW is detected and synchronization is established.

The synchronized transmission signal is output from the frame synchronization circuit as an output signal 102, and data of a desired channel can be obtained in a subsequent circuit.

Generally, in satellite communications, a synchronous detection demodulation method is often used. In this method, the demodulated signal demodulated by the demodulator 24 includes phase uncertainty. However, this phase uncertainty is solved by providing a differential encoding circuit 22 on the transmitting side and a differential decoding circuit 25 on the receiving side.

Furthermore, if there is an empty channel in the multiplexed signal, the transmitted data is often the same (fixed data) for each frame. Here, if the fixed data happens to have the same bit arrangement as the UW, an erroneous detection will occur when the frame synchronization circuit 26 detects the UW. When false detection of a UW occurs, incorrect frame timing is established, making it impossible to receive data on the desired channel. To prevent this, conventionally, as a simple method of hardware configuration, a method has been used in which a UW pattern and a UW pattern in which all bits of the UW pattern are inverted are alternately inserted every frame.

[Problem to be solved by the invention] However, when using a differential encoding circuit and a differential decoding circuit as in conventional communication systems, although phase uncertainty can be removed, error data is included. If the error is doubled, the BER (Bt t Err
There is a problem that the performance (or Rate) deteriorates.

An object of the present invention is to provide a communication system that can eliminate phase uncertainty without degrading the BER.

Another object of the present invention is to provide a communication system that does not cause false detection of UW.

[Means for Solving the Problems] According to the present invention, there is provided a communication system for transmitting and receiving a transmission signal in which frames are configured on a time axis and a plurality of pieces of information are time-division multiplexed, wherein A unique word having a predetermined bit arrangement is inserted at the beginning of each of the signals, phase modulation is performed, and the transmission signal is output, and the receiving device receives and demodulates the transmission signal, and then detects the unique word. In a communication system that establishes frame synchronization, the transmitting device includes unique word insertion means for inserting the unique word at the beginning of each of the frames, and phase modulation means for performing phase modulation, and the receiving device includes demodulating means for obtaining a demodulated signal from the signal;
a phase rotation means for switching the phase of the demodulation signal at a predetermined angle at predetermined intervals until a frame synchronization signal is input; A communication system is obtained, comprising a frame synchronization means for detecting, establishing frame synchronization, and outputting the frame synchronization signal.

[Example] The present invention will be described in detail below with reference to the drawings. In addition,
Components that are the same as those in the prior art are given the same numbers and their explanations will be omitted.

FIG. 1 shows a block diagram of an embodiment of the present invention.

The transmitter of this embodiment includes a unique word (UW) insertion circuit 21 and a modulator 23.

The multiplexed input data signal 101 is sent to the UW insertion circuit 21
is input, and a UW is inserted at the beginning of each frame. Here, the UW has two types of patterns with different bit arrangements, and these 2N types of UWl and UW2 are inserted alternately every frame.

The input data signal with UWI and UW2 inserted is modulator 2.
3 and undergoes phase modulation (for example, two-phase phase modulation, four-phase phase modulation, etc.).

The phase modulated data signal is sent to satellite line 27.

The receiving device includes a demodulator 24, a phase rotation circuit 1, and a frame synchronization circuit 12.

The data signal received by the receiving device is then input to the demodulator 24 and demodulated. Here, the demodulated data signal includes phase uncertainty.

Next, the demodulated data signal is input to the phase rotation circuit 11. The phase rotation circuit 11 has a timer (not shown) and sequentially switches the phase of the demodulated data signal to several expected demodulation phases at predetermined time intervals.

In other words, in the case of a two-phase phase modulation method, there are two types (phase difference 180
°), 4 types for 4-phase phase modulation method (phase difference 90'
phase). The predetermined time is a time during which at least two unique words can be detected in the frame synchronization circuit.

The data signal output from the phase rotation circuit 11 is input to the frame synchronization circuit 12. The frame synchronization circuit 12 detects a unique word from the data signal. The frame synchronization circuit 12 detects the same bit arrangement as one of the two unique words (UWI or UW2),
When the bit arrangement of the other unique word (UW2 or UWI) is detected at the position where the unique word one frame later would be detected, it is assumed that frame synchronization has been established, and the frame synchronization signal is transferred to the transfer rotation circuit 11. Output to. Upon receiving this frame synchronization signal, the transfer rotation circuit 11 stops the timer and also stops the phase switching.

In this way, phase uncertainty can be removed by switching the phase until two types of unique words are detected in the frame synchronization circuit. Furthermore, since unique words with two different bit arrangements are used, even if consecutive data signals of the same pattern happen to be the same as the bit arrangement of the unique word, there will be no false detection.

In addition, when UW patterns and UW patterns are inserted alternately as in the conventional case, in the case of two-phase phase modulation,
If the phase is shifted by 180', the detected unique words will be UW patterns and UW patterns alternately, so even though all the data is inverted, it will be judged as correct data. As in the example,
If two different bit arrays, UWI and UW2, are used, such false detection will not occur.

In this way, frame synchronization is established for the output signal 10.
2 is output from the frame synchronization circuit 12.

Note that the bit patterns of the above two types of unique words may be completely different, but for example, if the unique word is divided into the first half and the second half, and the bit pattern of only the second half is alternately inverted every frame, The configuration of the frame synchronization circuit becomes simple.

[Effects of the Invention] According to the present invention, a phase rotation circuit and a frame synchronization circuit are combined, and the phase is switched at predetermined time intervals until UW can be detected, thereby eliminating phase imbalance without deteriorating the BER. Determinism can be removed.

In addition, two types of UW are inserted alternately every frame,
By establishing frame synchronization when two types of UWs are detected, false detection of UWs can be eliminated.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a communication system according to an embodiment of the present invention, FIG. 2 is a block diagram of a conventional communication system, and FIG. 3 is a configuration diagram of a data signal. DESCRIPTION OF SYMBOLS 11... Transfer rotation circuit, 12... Frame synchronization circuit, 21... UW insertion circuit, 22... Differential encoding circuit, 23... Modulator, 24... Demodulator, 25... ...Differential decoding circuit, 26...Frame synchronization circuit.

Claims (1)

[Claims] 1. A communication system for transmitting and receiving a transmission signal in which frames are configured on a time axis and a plurality of pieces of information are time-division multiplexed, wherein a transmitter includes a predetermined signal at the beginning of each frame. A communication system that inserts a unique word having a bit arrangement, performs phase modulation, and outputs the transmission signal, and a receiving device receives and demodulates the transmission signal, and then detects the unique word to establish frame synchronization. In the transmitting device, the transmitting device includes unique word inserting means for inserting the unique word at the beginning of each of the frames, and phase modulating means for performing phase modulation, and the receiving device obtains a demodulated signal from the transmitted signal. demodulating means; phase rotating means for switching the phase of the demodulated signal at a predetermined angle at predetermined intervals until a frame synchronization signal is input; and the phase-rotated demodulated signal output from the transfer rotating means. and frame synchronization means for detecting the unique word of the frame synchronization, establishing frame synchronization, and outputting the frame synchronization signal. 2. The communication system according to claim 1, wherein the unique word insertion circuit alternately inserts two types of unique words having different bit arrangements every frame.