JP2705445B2 - Frame synchronization method for mobile communication - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frame synchronization system for mobile communication in a system employing a voice activation system in a mobile digital satellite communication system.

[0002]

2. Description of the Related Art In general, a mobile satellite communication system is composed of a small number of central stations and a large number of slave stations communicating with the central station. However, since the time rate at which many slave stations actually transmit as voice data is extremely low, so-called voice activation that does not output a transmission signal when there is no voice in order to effectively utilize the power of a limited communication satellite, This system saves the power of communication satellites. Conventionally, the format of a burst signal of this type of voice activation system is such that a preamble word (PW) and a unique word (UW) are arranged before voice-encoded voice data, as shown in FIG. A unique word is inserted at each frame period while speech is continuously input. The preamble word is inserted in order to improve the synchronization pull-in characteristic in the receiving side demodulator. The unique word is arranged with a fixed period frame length in order to determine the start timing of the audio data and to remove the phase uncertainty generated at the time of demodulation based on the detection pattern. The conventional frame synchronization circuit starts by detecting a unique word in a received signal, and once a unique word is detected, a time position at which the next unique word is expected to be received is one frame length later. Therefore, a unique word window (also referred to as a unique word aperture), which is a window for detecting a unique word having a width of one to several bits, is opened at a detection predicted time position one frame length later until the unique word detection is performed. The unique word is detected only at that timing. In this way, when N unique words are detected consecutively N times in one frame period, it is recognized that frame synchronization has been established for the first time, and this N times is called backward protection. In addition, when a unique word is missed during frame synchronization, if frame synchronization is lost by detecting only one mistake, there is a great possibility that frame synchronization will be lost. It will be off. This M times is called forward protection. As described above, according to the conventional frame synchronization method, upon receiving a voice burst, frame synchronization is established through a backward protection process, and when frame synchronization is lost, synchronization is lost after a forward protection process. The unique word aperture was opened only for one frame synchronization in a state other than the out-of-frame state, and did not perform any unique word detection operation on any signal received at any other timing.

[0003]

The frame synchronization method using the conventional voice activation method and employing the forward protection and the backward protection is such that when a new burst is transmitted, the receiving side still has the previous frame timing. , The unique word aperture can only be opened at the previous frame timing,
Unable to detect unique word at new frame timing of new voice burst. Also, once the frame synchronization is lost after the forward protection process period, the frame synchronization cannot be established until the frame synchronization pull-in operation is performed again. There is a disadvantage that the time during which reception is not possible increases. As a method of remedying this drawback, a method of detecting the end of burst of a voice burst and de-synchronizing a received frame may be considered. However, if the mobile station is shadowed due to, for example, entering the shadow of a building, the end of the burst at the receiving end is delayed, and the head of the new voice burst is eventually discarded. Signals were not a valid solution either.

A frame synchronization system for mobile communication according to the present invention comprises:
A first frame for receiving a burst signal having a unique word at the beginning of a voice data signal in a mobile digital satellite communication system, extracting the unique word, and establishing frame synchronization through forward protection and backward protection processes.
A frame synchronization circuit and a frame from the first frame synchronization circuit.
Input a timing signal and make a predetermined determination.
Means for providing an operation permission signal to one frame synchronization circuit.
In the frame synchronization system for mobile communication having the control circuit described above, the first signal capable of receiving the burst signal in parallel.
Frame that performs the same operation as the frame synchronization circuit of FIG.
And a control circuit, wherein the control circuit has the first and second
Frame synchronization operation in one of the frame synchronization circuits
And the first frame that started the frame synchronization operation
After the frame synchronization is established by the system synchronization circuit, the first frame
When the frame synchronization circuit shifts to the forward protection state, the second
To start the frame synchronization operation in the frame synchronization circuit
Operating means and the second frame synchronization circuit are in a frame synchronization state
Before the first frame synchronization circuit
When the synchronization state is restored, the second frame synchronization circuit
Operation procedure for stopping operation and first frame synchronization circuit
Before returning to frame synchronization.
When the synchronization circuit shifts to the frame synchronization state, the first
An operation procedure for stopping the operation of the frame synchronization circuit;
Frame synchronization circuit goes out of synchronization from forward protection state
Stops the operation of the first frame synchronization circuit when shifting
Operating procedure for controlling the first and second
If one of the frame synchronization circuits is
The first or second frame synchronization circuit during the other operation.
Select the frame timing signal from the
The frame synchronization circuit is in the forward protection state and is
When the synchronization circuit is out of frame, the first
Selects frame timing signal from frame synchronization circuit
And the first frame synchronization circuit is in the forward protection state,
When the second frame synchronization circuit is in the back protection, the second
Select the frame timing signal from the frame synchronization circuit
Operating procedure.

Next, the operation of this embodiment will be described with reference to FIG. As a process of establishing frame synchronization, the control circuit 3
First, the frame synchronization circuit 1 outputs an operation permission signal 11 for permitting the frame synchronization operation (step 1), and the frame synchronization circuit 2 does not output the operation permission signal 21 for permitting the frame synchronization operation. The frame synchronization circuit 1 starts by detecting a unique word from the received signal. Once the unique word is detected, the frame synchronization circuit 1 sends a backward protection state signal 12 and a frame timing signal 14 for notifying the control circuit 3 that the backward protection process is in progress. Output (step 2), then at the time position where the unique word is expected to be received,
A unique word aperture is opened, a unique word is detected only at that timing, and frame synchronization establishment is declared when N unique words are detected N consecutive times.
At this point, the frame synchronization state signal 13 is output to the control circuit 3, and the output of the rear protection state signal 12 is stopped (step 3). During this time, the control circuit 3 outputs the frame timing signal 14 from the frame synchronization circuit 1 to the outside as a correct frame timing signal. That is, when the operation of the frame synchronization circuit 2 is stopped, the frame timing signal 14 from the frame synchronization circuit 1 is selected. Up to this point, the frame synchronization circuit 2 does not operate at all.

Next, when a unique word detection error occurs while the frame synchronization circuit 1 is in the frame synchronization state (step 4), the frame synchronization circuit 1 sends a forward protection state signal 15 for notifying that the forward protection process is in progress. Output to Thus, the control circuit 3 outputs the operation permission signal 21 to the frame synchronization circuit 2 (Step 5). Frame synchronization circuit 2
Starts the detection of the unique word in the received signal. Here, before the frame synchronization circuit 2 detects the unique word before the frame synchronization circuit 2 re-detects the unique word and returns from the forward protection process, the frame synchronization circuit 1 outputs the forward protection state signal 15. The output is stopped (step 6), the control circuit 3 cancels the operation permission signal 21 to the frame synchronization circuit 2, and the frame synchronization circuit 2 stops the operation (step 7). The control circuit 3 continues to select the frame timing signal 14 from the frame synchronization circuit 1. Here, even when the frame synchronization circuit 1 does not shift to the rear protection state while the frame synchronization circuit 1 outputs the front protection state signal 15 and does not output the rear protection state signal 22 with the frame synchronization lost, the control is also performed. The circuit 3 selects the frame timing signal 14 from the frame synchronization circuit 1. If the frame synchronization circuit 2 enters the backward protection state first, the frame synchronization circuit 2 transmits the backward protection state signal 22.
And a frame timing signal 24 to the control circuit 3 (step 8). When the control circuit 3 receives the rear protection state signal 22 from the frame synchronization circuit 2 while the front protection state signal 15 from the frame synchronization circuit 1 is being input,
The frame timing signal 24 of the frame synchronization circuit 2 is selected and output to the outside (step 9).

Although not shown in FIG. 2, before the frame synchronization circuit 2 releases the rear protection state signal 22 and outputs the frame synchronization signal 23, the frame synchronization circuit 1 releases the front protection state signal 15 and Upon returning to the synchronized state, the control circuit 3 releases the operation permission signal 21 to the frame synchronization circuit 2 to stop the operation, and selects and outputs the frame timing signal 14 of the frame synchronization circuit 1 to the outside.

If the frame synchronization circuit 1 releases the front protection process signal 15 and returns to the frame synchronization state, the frame synchronization circuit 2 enters the frame synchronization state, releases the rear protection process signal 22, and resets the frame synchronization state. When the signal 23 is output, the control circuit 3 stops the operation permission signal 11 to the frame synchronization circuit 1 and outputs the frame timing signal 24 from the frame synchronization circuit 2 to the outside (step 9). Further, when the frame synchronization circuit 1 shifts from the forward protection state to the out-of-frame state, that is, when the forward protection state signal 15 and the frame synchronization state signal 13 are stopped, the control circuit 3 releases the operation permission signal 11 and releases the frame synchronization. The operation of the circuit 1 is stopped.

[0009]

As described above, according to the present invention, by providing two frame synchronizing circuits and these control circuits, the second function of interpolating between bursts in which frame timing does not continue conventionally is provided. Since the frame synchronization circuit can start the frame synchronization operation from the beginning of a new burst signal, the frame synchronization signal can be quickly established and the frame timing signal can be generated. Therefore, there is an effect that a high quality voice transmission line can be formed without discarding the voice signal at the head of the new burst.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a time chart of each signal of the present embodiment.

FIG. 3 shows a signal format common to the present embodiment and a conventional example.

[Description of Signs] 1, 2 frame synchronization circuit 3 control circuit 11, 21 operation permission signal 12, 22 backward protection state signal 13, 23 frame state synchronization signal 14, 24 frame timing signal 15, 25 forward protection state signal

Claims (1)

(57) [Claims] In a mobile digital satellite communication system, a burst signal having a unique word at the beginning of a voice data signal is received, the unique word is extracted, and frame synchronization is established through forward protection and backward protection processes . 1 frame synchronization circuit and the first frame synchronization
Predetermined judgment by inputting frame timing signal from circuit
To give an operation permission signal to the first frame synchronization circuit.
And a control circuit having a means for obtaining the burst signal.
A second frame synchronizing circuit having the same function as that of the first
A second frame synchronization circuit, wherein the control circuit is
Frame to either one of the first and second frame synchronization circuits.
Start the frame synchronization operation and start the frame synchronization operation
After frame synchronization is established in the first frame synchronization circuit
Then, the first frame synchronization circuit has shifted to the forward protection state.
In this case, the frame synchronization operation is performed by the second frame synchronization circuit.
The starting means and the second frame synchronization circuit
Before the transition to the frame synchronization state, the first frame synchronization
When the path returns to the frame synchronization state, the second frame
An operation procedure for stopping the operation of the system synchronization circuit, and a first frame.
Before the frame synchronization circuit returns to the frame synchronization state.
2. When the frame synchronization circuit 2 has shifted to the frame synchronization state
Operation to stop the operation of the first frame synchronization circuit
Procedure and the first frame synchronization circuit are synchronized from the forward protection state.
A first frame synchronization circuit when a transition to an out-of-period state occurs;
An operation procedure for controlling so as to stop the operation of
Or one of the second frame synchronization circuits stops operating
State, the other active first or second flip-flop.
Selects frame timing signal from frame synchronization circuit
And the first frame synchronization circuit is in the forward protection state,
2 frame synchronization circuit is out of frame
The frame timing from the first frame synchronization circuit
Signal is selected, and the first frame synchronization circuit
State and the second frame synchronization circuit is in backward protection.
The frame timing from the second frame synchronization circuit
A frame synchronization circuit for mobile communication, comprising: