JPH04364621A - Signal transmitter - Google Patents

Abstract

PURPOSE:To switch a line while the quality of a transmission signal is kept by starting the transmission of a standby line when the quality of the transmission signal of an active line is degraded and switching the line when synchronization is taken. CONSTITUTION:When a bit error rate reaches a prescribed rate or above, as soon as a line switching signal is sent to a line switching device 10 and a frame synchronization detector 9, the signal transmission in a standby line is started. Then the detector 9 implements frame synchronization based on a transmission signal sent through the standby line and after the frame synchronization in the standby line is confirmed, the switching device 10 is used to switch the line. Since the active line and the standby line are switched between a transmission frame and a frequency, the active and standby lines are switched without causing error correction disabling state of the signal caused when the switching is implemented in the frame of the transmission signal.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal transmission system using a plurality of lines.

0002

2. Description of the Related Art In a wireless communication system such as a digital microwave communication system, a communication system including a plurality of lines is constructed as shown in FIG. 4 in order to prevent deterioration of transmitted information due to propagation distortion caused by fading. For example, if a signal is transmitted using a certain working line and the quality of the signal transmitted over that communication line deteriorates, signal transmission on the protection line is started and the transmitted signal is synchronized with the working line. Once established, the working line is switched to the protection line to prevent the quality of the transmitted signal from deteriorating.

By the way, in the case of signal transmission by phase modulation, there are two methods: a method of determining the phase of the signal and performing decoding by transmitting a reference phase to the receiving means, and a method of transmitting the reference phase to the receiving means. There is a method of transmitting only the signal and decoding the signal.

In the former method, the problem of phase rotation between different lines does not occur because information is transmitted while constantly checking the reference phase on the receiving side. It is necessary to add the reference phase signal to the transmission information, encode it, and transmit it. However, according to this method, the reference phase information must be transmitted in addition to the information that should be transmitted, which reduces the transmission efficiency of the transmitted information. Therefore, the latter method, which allows the transmission signal to be decoded without sending reference phase information, is superior in terms of transmission efficiency.

However, when signal transmission is performed using a modulation method such as PSK or QAM, the modulated transmission signal does not include reference phase information, and when the transmission signal is demodulated by a receiving device, the phase is uncertain. Sexual issues arise. This will be explained below.

[0006] The receiving device generates reference transport information independently from the received carrier wave. Therefore, there is a possibility that a shift in transmission may occur between demodulated received signals between the working line and the protection line. Figure 5 (
A) shows the transport deviation due to QPSK modulation. Let the 2-bit demodulated signals of the two lines at the same clock be XY and X'Y', respectively. When an XY signal is demodulated on one of the lines, if a phase shift occurs between these lines, the demodulated signal rotates depending on the magnitude of the phase shift. This situation will be explained using the diagram shown in FIG.

Even if the (0,0) signal is demodulated on the working line, the (0,0) signal is not necessarily demodulated on the protection line. Due to phase uncertainty, each of the (0,1), (1,1), and (1,0) signals may be demodulated due to the difference in phase rotation. For demodulated signals with such phase rotation, error correction can be performed on the code frames of each demodulated signal as shown in (1) and (2) of FIG. 5(B). However, if the codes of demodulated signals with different phase shifts rotate within the same frame (see 5(B)(3)), error correction cannot be performed.

Therefore, when a plurality of lines are used in parallel, even if the same signal is transmitted, demodulation is performed on each line, and demodulated signals having different phase components may be transmitted. If line switching is performed in this transmission state, there is a risk that codes with different phase states may exist within the same frame, making it impossible to perform correct error correction, resulting in interruption of communication.

[0009] To prevent this, in a diversity communication system, a method is adopted in which lines are switched after demodulating, error correcting, and decoding the received signal on two lines, a working line and a protection line, respectively. Even if the transmission signal has a phase rotation, the same information can be obtained by decoding it, so by switching the line once the decoded signal is obtained for each line, the line can be switched without interrupting communication. Ta.

0010

[Problems to be Solved by the Invention] As stated above, when transmitting signals by switching multiple lines, switching must be performed after performing error correction decoding and decoding operations for each line. , due to phase uncertainty, line switching could not be performed properly. SUMMARY OF THE INVENTION An object of the present invention is to provide a signal transmission device having a line switching means that solves the problem of phase uncertainty. [Structure of the invention]

[0011]

[Means for Solving the Problems] The present invention provides a transmitting device comprising an encoder, an error correction encoder, and a modulator, a transmission line system comprising a working line and at least one protection line, and a demodulator. a frame synchronization detector for detecting frame synchronization of a code word from a signal demodulated by the demodulator; an error correction decoder for performing error correction based on the signal output from the frame synchronization detector; The present invention provides a signal transmission device having a receiving device including a line switcher that performs line switching based on a signal from the error correction decoder.

0012

[Operation] In the present invention, when the quality of the transmission signal deteriorates on the working line, signal transmission on the protection line is started, and when frame synchronization is detected on the protection line, the code word of the transmission signal is Switch the line between frames.

When switching between the working line and the protection line, the line can be switched without the inconvenience of not being able to correct errors due to line switching within a single frame of a transmission signal.

[0014]

[Example] Regarding the signal transmission device based on the drawings below,
explain.

FIG. 1 is a block diagram showing the configuration of a signal transmission device according to the present invention. An input terminal 1, an encoder 2, an error correction encoder 3, and a modulator 4 constitute a transmitter. Further, a receiving device is constituted by demodulators 7 and 8, a frame synchronization detector 9, a line switch 10, an error correction decoder 11, a decoder 12, and an output terminal 13.

Next, the operation of this embodiment will be explained. On the transmitting side, a transmission signal is input from input terminal 1. A transmission signal inputted from an input terminal is encoded by an encoder 2, subjected to error correction encoding by an error correction encoder 3, and then modulated and the signal is transmitted from a transmitter. On the receiving device side, after demodulating the received signal, it performs frame synchronization detection, passes through a line switch, performs error correction processing in an error correction decoder, encodes it, and outputs it to an output terminal.

In this system, the line switching operation is performed by the following operation. The error correction decoder 11 performs error correction on the transmitted signal, and also has a function of comparing the transmission signal input to the error correction encoder with the transmission signal after error correction. Detect the bit error rate of the previous transmission signal. When this bit error rate is smaller than a certain value, it is determined that transmission is being performed in good condition and no line switching operation is performed. However, when the bit error rate exceeds a certain value, it is determined that it is necessary to change the line.
At the same time as sending a line switching signal to the line switching device 10 and frame synchronization detector 9, signal transmission on the protection line is started. Then, a frame synchronization detector detects frame synchronization based on the transmission signal transmitted through the protection line, and after confirming that frame synchronization has been achieved on the protection line, the line switching device 10 executes line switching.

[0018] In a signal transmission device having a line switching device as described above, switching between the working line and the protection line is performed between frames of the transmission signal, so that when switching occurs within the frame of the transmission signal, Switching between the working line and the protection line can be carried out without causing a state in which errors in the resulting signal cannot be corrected. In addition, in conventional systems, the error correction decoder and decoder were provided independently for each line, which tended to complicate the system, but with the present invention, error correction and decoding can be performed after line switching. By performing this operation, the number of error correction decoders and decoders can be reduced, and the system configuration can be simplified. The above description is an example of the case where the spatial diversity method is adopted. Next, a line switching method when employing a frequency diversity communication system will be explained.

FIG. 2 shows its configuration. In the frequency diversity system, signals are transmitted using different frequencies on the working line and the protection line, so it is necessary to prepare for line switching on the transmitter side as well. For this reason, the transmitter is provided with a line controller. When the signal error rate on the working line increases and line switching becomes necessary, a line switching signal is sent to the receiving device's line switcher and frame synchronization detector, and a line switching signal is sent through the control feedback line. It is also sent to the line controller of the transmitter. When the line controller of the transmitter receives the line switching signal, it starts signal transmission through the protection line and completes preparations for line switching. Even when line switching is implemented using this method, the same effects as in the previous embodiment can be obtained.

FIG. 3 shows another configuration example of a receiving apparatus applicable to the above two embodiments. In this configuration, the signal demodulated on the working line and the signal demodulated on the protection line are input to the line switch, and the signal from the line switch is input to the frame synchronization detector and the error correction decoder. Another feature is that a control circuit receives signals from a frame synchronization detector and an error correction decoder, and the signals from this control circuit are input to a line switch.

The operating principle of this receiving device will be explained. When the current circuit is in operation, the signal demodulated from the current channel is input to the error correction decoder and frame synchronization detector via the line switch. The frame synchronization detector checks whether the line is frame synchronized and sends a frame synchronization signal to the error correction decoder and control circuit. The error correction decoder performs an error correction operation on the transmission signal, and the error-corrected transmission signal is input to the decoder. The error correction decoder detects the bit error rate of the transmission signal by comparing the transmission signal before and after error correction, and sends this bit error signal to the control circuit.

The control circuit functions to generate signals for line switching. If the bit error rate exceeds a certain value, it is determined that line switching is necessary, and signal transmission on the protection line is started in preparation for line switching. Furthermore, the control circuit constantly monitors the frame synchronization signal from the frame synchronization detector for the working line. Normally, signal processing on the working line and signal processing on the protection line operate with the same reference clock, so when frame synchronization is achieved on the working line, it is considered that frame synchronization is also achieved on the protection line. Therefore, if frame synchronization is achieved for the working line, it becomes possible to switch between the working line and the protection line between frames.

[0023] Therefore, signal transmission on the protection line is started,
When the control circuit determines that the frame synchronization of the working line is achieved, a line switching signal is input to the line switching device to realize line switching. Since the receiving device shown in this embodiment can perform line switching without detecting frame synchronization on the protection line, there is no need to perform frame synchronization detection operation for each line, and there is no need to provide multiple frame synchronization detection circuits. A circuit can be constructed.

The receiving apparatus shown in this embodiment can also be applied to a spatial diversity system, and in that case, the number of transmitting antennas may be one. Furthermore, by providing a feedback line for control and providing a line controller on the transmitter side, it is also possible to apply the frequency diversity method.

[0025]

Effects of the Invention As explained above, in the present invention, even in a communication device that switches between a working line and a protection line, a signal transmission device that can switch lines without deteriorating the quality of the transmitted signal is provided. can be provided.

[Brief explanation of drawings]

[Figure 1] System configuration diagram showing one embodiment of the present invention

[Figure 2] System configuration diagram showing another embodiment of the present invention

[Fig. 3] System configuration diagram showing one embodiment of a receiving device used in the configuration of the present invention

[Figure 4] System configuration diagram showing conventional technology

[Figure 5]
Diagram showing the relationship between code phase rotation and error correction

[Figure 6]
Diagram showing the relationship between phase shift between lines and rotation of demodulated signal

[Explanation of symbols]

2 Encoder 3 Error correction encoder 4 Modulator 7, 8 Demodulator 9 Frame synchronization detector 10 Line switch 11 Error correction decoder 12 Decoder

Claims (4)

[Claims] 1. A transmitting device comprising an encoder, an error correction encoder, and a modulator, and a transmission line system comprising a working line and at least one protection line for transmitting signals from the transmitting device. , a demodulator that demodulates the signal transmitted via the transmission line system, a frame synchronization detector that detects frame synchronization of a code word from the signal demodulated by the demodulator, and a frame synchronization detector output from the frame synchronization detector. an error correction decoder that performs error correction based on the error-corrected signal; a decoder that decodes the error-corrected signal; and a line switch that performs line switching based on the signal from the error-correction decoder. 1. A signal transmission device comprising: a receiving device. 2. The line switching device is configured to switch the line between a codeword frame and a codeword frame immediately following the codeword frame based on a signal from the frame synchronization detector. The signal transmission device according to claim 1, characterized in that: 3. The signal transmission apparatus according to claim 1, wherein the encoder and decoder include a differential encoder and a differential decoder. 4. The signal transmission apparatus according to claim 2, wherein the encoder and decoder include a differential encoder and a differential decoder.