JP2722971B2 - Digital signal synchronization method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for synchronizing digital signals for FM multiplex broadcasting, and more particularly to a method for synchronizing digital signals suitable for a mobile receiver.

[0002]

2. Description of the Related Art In FM multiplex broadcasting, a digital signal is put on a sub-carrier path of 76 kHz to transmit another program.
This digital signal forms one packet with a 16-bit header and 272-bit data as shown in FIG.
A format in which two packets constitute one frame has been proposed. This will be described in more detail.
The last 82 bits of the bit data are data for data error correction. The specific packet is the remaining 19
The 0-bit part is also data for data error correction. This data (parity block data) is used for vertical data error correction, and the trailing 82-bit data is used for horizontal data error correction.

[0003] The header has a 16-bit configuration, and the first 13 packets (hereinafter referred to as group 1) of the frame provided for synchronization are BIC1. Next 123 packets
The parity block (hereinafter, referred to as group 2) is BIC4, and the others are BIC3. Parity is provided at the end of a group of three packets, one for every three packets. The header part of the following 13 packets (hereinafter referred to as group 3) is BIC2.
The header part of the last 123 packets (hereinafter referred to as group 4) is composed of BIC3 and BIC4 just like group 2. It should be noted that the above is conceptually shown, and a packet whose header is BIC3 is a packet whose header is BIC4.
(Parity block) and interleaved.

[0004]

However, a method for synchronizing digital signals of such a format has not yet been known. In particular, in the case of the mobile system, signal loss is likely to occur, and even in such a case, there is a need for a proposal of a method capable of achieving accurate and quick synchronization. SUMMARY OF THE INVENTION The present invention has been made to meet such a demand, and has as its object to provide a method capable of accurately and quickly establishing synchronization even if a signal is lost, focusing on the configuration of a header portion.

[0005]

According to the method of synchronizing a digital signal according to the present invention, one frame is composed of a plurality of bit-serial packet data having data for synchronization in a header portion. There are a group consisting of packets, in which data for synchronization of all packets is the same, and a group including packets having different data for synchronization, and synchronization of the last packet of the preceding group. In the method of synchronizing digital signals in which data for synchronization is different from data for synchronizing the first packet of the succeeding group, the headers of two consecutive packets are extracted and the header of the subsequent packet is missing. In this case, the header portion of one or two packets is further extracted, and the boundary of the group is specified based on the content thereof. Wherein the synchronize whole over arm.

[0006]

[Operation] Even if there is data loss in the header part of a packet near the boundary, the boundary part of the group can be specified by the contents of the header part before and after that, and the head of the frame can be specified by counting the number of packets after that. Can establish synchronization.

[0007]

Synchronization is established by detecting the beginning of one frame, that is, the boundary from parity block 82 to data block 1. However, in the present invention, in consideration of the feature of the data structure of one frame as described above, the boundary between group 1 and group 2, the boundary between group 2 and group 3, or the boundary between group 3 and group 4 is detected.
Then, it is assumed that the point at which a predetermined number of packets have been counted is the beginning of one frame, and synchronization is established. When detecting this boundary, the contents of the header part are examined. If a part of the header part is missing, the number of reference header parts is increased, thereby detecting the boundary.

[0008]

[Table 1]

Table 1 shows the logic of boundary determination. If there is no missing of received data, this boundary can be detected because the header portion changes as shown in the left column of Table 1. Next, a change from group 1 to group 2 which indicates a case where there is a loss will be described. The header part of two successive packets is extracted, and if the latter header part is missing, the header part of the next two packets is extracted. When the header is BIC3 / BIC3, the preceding packet of the two packets is recognized as the first packet of group 2. If it is BIC3 / BIC14, the missing packet is recognized as the first packet of group 2.

Next, regarding the boundary between group 2 and group 3, in this case, the header of the next packet after the missing packet is examined, and if the BIC4 before the loss and BIC2 after the loss, the missing packet is group 3 Is recognized as the head of When the packet before the missing packet is BIC3, the packet having the newly extracted BIC2 header is recognized as the head of group 3.

The operations of groups 3 and 4 and the operations of groups 4 and 1 are performed in the same manner. When the head packet of the group is detected in this way, the head of one frame can be detected based on the number of bits or the number of packets thereafter.

[0012]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 is a block diagram showing a circuit for implementing the method of the present invention. Only the header part of the received data is extracted by the header extraction circuit 1, and the extracted header part is input to the FIFO 2 having a capacity of four headers. The pattern determination circuit 3 is FI
The header part of the preceding two packets is extracted from FO2 and its pattern is examined. If the leading side of the two fetched packets is missing, the packet is discarded and the data of the header of the next packet is fetched from the FIFO2. When the headers of the two packets are both sound, the pattern determination circuit 3 checks whether or not the packet corresponds to the pattern in the left column of Table 1, and if so, a signal indicating which of the groups is the boundary between the groups, Specifically, the number of packets from that time to the beginning of frame 1 is sent to packet counter 4.

When the header portion of the second packet is missing, the header portion of the next two packets is fetched from the FIFO 2 and the boundary pattern of group 2 → 3, group 4 → 1, or group 1 → 2, group 4 → Check whether it is 1 or not,
A signal indicating the boundary is sent to the packet counter 4. The packet counter 4 counts a number determined in accordance with the input from the pattern determination circuit 3, outputs a frame pulse at the end of the counting as the beginning of one frame, and uses this as a descrambling circuit for deinterleaving, a reception data storage circuit ( (Not shown).

[0014]

As described above, according to the present invention, even if the head of one frame is missing, the head of the frame can be detected by detecting the boundary between groups. In detecting the boundary, even if some packets are lost, the detection can be performed without any trouble. Therefore, synchronization can be quickly and accurately established even when the reception condition is poor, such as a mobile receiver for FM multiplex broadcasting.
The present invention is not limited to FM multiplex broadcasting, but is widely applicable to those having a similar data format.

[Brief description of the drawings]

FIG. 1 is a data format diagram according to the present invention.

FIG. 2 is a block diagram of an apparatus for implementing the method of the present invention.

[Explanation of symbols]

 1 Header part extraction circuit 2 FIFO 3 Pattern judgment circuit 4 Packet counter

Continuation of the front page (56) References JP-A-5-268211 (JP, A) JP-A-5-268212 (JP, A) JP-A-5-145500 (JP, A) JP-A-2-67834 (JP) , A) IEICE Technical Report, RC S92-24 IEICE Transactions, VOL. J77-B-II, NO. 1, P. 19−25

Claims (1)

(57) [Claims] 1. A frame is composed of a plurality of bit-serial packet data having data for synchronization in a header portion, and one frame of data is composed of a group composed of a plurality of packets. There is a group having the same data and a group including a packet having data for different synchronization, and a data for synchronizing the last packet of the preceding group and a first packet of the succeeding group. In the method of synchronizing digital signals having different data, the header part of two consecutive packets is extracted, and if the header part of the subsequent packet is missing, the header part of one or two packets is further extracted. The boundary of a group is specified based on the content, and synchronization of the entire frame is synchronized based on the boundary. Term method.