This application is based on and claims the benefit of priority from prior Japanese Application No. 2009-049649, filed on Mar. 3, 2009, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a frame number detecting device which obtains a frame number in transmission data in the broadcasting and communication field.
2. Description of the Related Art
In the broadcasting and communication field, data is transmitted in units of blocks of a predetermined length such as frames. A receiver detects an identifier, such as a frame synchronization signal, stored in the transmitted data for every frame. Thereby, the receiver establishes frame synchronization, and performs decoding on a frame-by-frame basis.
For example, in Digital Terrestrial Multimedia Broadcast (DTMB), which is the terrestrial digital broadcasting standard in China (People's Republic of China), a frame consists of a frame body (hereinafter also referred to as FB) and a frame header (hereinafter also referred to as FH). The frame body stores therein 3780 symbols indicating a combination of modulated source stream data and system information. The frame header stores therein a known pseudo-random noise sequence for identifying the frame (hereinafter referred to as PN sequence).
A PN sequence in a frame header is generated by a linear feedback shift register (LFSR). The LFSR is capable of generating a known cyclic PN sequence, and produces known frame headers by cyclically extending the generated PN sequence defined by the generating polynomial. Since including a known PN sequence, a frame header can be used not only for detecting frame synchronization but also as a pilot signal, and thus can be used for decoding processing including transmission path response estimation and the like.
DTMB has three modes, i.e., FH Mode 1 to FH Mode 3. In FH Mode 1 and FH Mode 3, a PN sequence in a frame header has a pattern which is not the same throughout all frames, but changes on a frame-by-frame basis. PN sequences in respective frame headers have patterns that change on a frame-by-frame basis without following a single pattern throughout frames. For this reason, in order to use a PN sequence in a frame header as a pilot signal in FH Mode 1 and FH Mode 3, it is necessary to estimate a PN sequence in a frame header for every frame.
Now, the LFSR in FH Model, for example, generating 255 kinds of PN sequences by varying an initial value set in the LFSR in FH model. Some of the 255 kinds of PN sequences which the LFSR in FH Mode 1 is capable of generating are employed as PN sequence patterns for frame headers. In FH Mode 1, PN sequences in respective frame headers correspond respectively to initial values of the LFSR. The relationship between frame numbers allocated to respective frames and the initial values of the LFSR is specified in the specification.
In DTMB, a superframe is defined by a predetermined number of frames depending on each mode. The time length of a superframe is fixed to 125 ms. A superframe is assumed to be used in systems requiring time checking such as a GPS. Superframe synchronization can be established by estimating a frame number.
Moreover, estimating a frame number of a frame is equivalent to estimating perfectly a PN sequence included in the frame, and thus to estimating perfectly a pilot signal. In sum, the decoding performance is expected to be improved if a frame number can be detected.
Conceivable methods for obtaining a frame number include a method by pattern matching. In the method by pattern matching, a table is first prepared in which initial values of the LFSR are associated with PN sequences used for frame headers. Then, the frame number of a current frame is determined by pattern matching of the PN sequence of the frame header with the initial values of the LFSR by use of the table.
However, this method has a drawback of an increase in circuit size since requiring a relatively large table for holding the initial values of the LFSR.
Meanwhile, Japanese Patent Application Publication No. 2003-273824 discloses a matched filter which allows a reduction in size and in power consumption of a correlation operational circuit for synchronization detection, and a correlation detection method using the matched filter. However, the detection of a frame number using the technique in Japanese Patent Application Publication No. 2003-273824 has a problem that the number of correlation operations increases with the number of frame numbers, consequently requiring an extremely long period of time for the detection of a frame number.
According to an aspect of the present invention, a frame number detecting device includes: a symbol counter that receives a received signal including frames each of which is formed of a predetermined number of symbols, and outputs a count value as a symbol number for each of the symbols by incrementing the count value by one every time one symbol is inputted, each of the frames including a frame synchronization signal including a part obtained by shifting a frame synchronization signal of a different frame on a symbol-by-symbol basis according to a predetermined rule; a sequence storage that stores a synchronization sequence based on at least one of the plurality of frame synchronization signals included in the received signal; a pattern matching unit that performs pattern matching between the synchronization sequence stored in the sequence storage and the received signal; a timing detector that detects the frame synchronization signals of the respective frames on the basis of a result of the pattern matching performed by the pattern matching unit, and outputs the symbol numbers received at the respective detected timings; and a frame number obtaining unit that obtains each frame number of the received signal on the basis of the predetermined rule and the symbol numbers received from the timing detector.
According to another aspect of the present invention, a frame number detecting device includes a symbol counter that receives a received signal including frames each of which is formed of a predetermined number of symbols, and outputs a count value as a symbol number for each of the symbols by incrementing the count value by one every time one symbol is inputted, each of the frames including a frame synchronization signal including a part obtained by shifting a frame synchronization signal of a different frame on a symbol-by-symbol basis according to a predetermined rule; a sequence generator that generates a synchronization sequence based on at least one of the plurality of frame synchronization signals included in the received signal; a pattern matching unit that performs pattern matching between the synchronization sequence generated by the sequence generator and the received signal; a timing detector that detects the frame synchronization signals of the respective frames on the basis of a result of the pattern matching performed by the pattern matching unit, and outputs the symbol numbers received at the respective detected timings; and a frame number obtaining unit that obtains each frame number of the received signal on the basis of the predetermined rule and the symbol numbers received from the timing detector.
A description will be given of embodiments of the present invention in detail below with reference to the drawings.
First, a DTMB broadcast signal will be described with reference to
As shown in
A received signal shown in
A synchronization sequence storage 13 stores therein a pattern which is partially or entirely the same as that of a PN sequence included in each frame header of the received signal (hereinafter referred to as a synchronization sequence). The pattern matching unit 11 is also given a synchronization sequence from the synchronization sequence storage 13.
The pattern matching unit 11, to which symbols of the received signal are sequentially inputted, performs pattern matching processing between the received signal of a predetermined symbol length and the synchronization sequence received from the synchronization sequence storage 13, and outputs, to the timing detector 14, a result of correlation between the received signal and the synchronization sequence received from the synchronization sequence storage 13.
Here, various methods can be employed for the pattern matching processing performed by the pattern matching unit 11, including sliding correlation processing and matching filtering, for example. The pattern matching unit 11 outputs, for example, an impulse-shaped correlation waveform representing correlation between the received signal and the synchronization sequence.
The timing detector 14 detects the timing that gives the highest correlation value in each frame, and outputs, as a synchronization detected symbol number, a symbol number received from the symbol counter 12 at the detected timing, to an averaging unit 15 and a frame number detector 16.
Likewise,
After that, in the same way, the PN sequence in frame headers for DTMB broadcast signal inverts its shift direction for every frame number, and increases or decreases its shift amount by one symbol for every two frame numbers. In other words, a part of the sequence A is included in each of the frame headers of the frames.
The synchronization sequence storage 13 stores therein a synchronization sequence which corresponds to the sequence A. The pattern matching unit 11 sequentially compares the received signal with the sequence A. Then, the timing detector 14 obtains, from the outputs of the pattern matching unit 11, sequence A detection timings in the received signal sequentially inputted to the pattern matching unit 11. Since every frame includes a part or whole of the sequence A, a peak of correlation values appears for every frame. The peak position for each frame shifts by a number of symbols corresponding to the frame number in accordance with the feature shown in
For example, assume a case where the timing detector 14 firstly detects the sequence A at a certain timing, then secondly detects the sequence A at a timing earlier by one symbol than the certain timing, and then thirdly detects the sequence A at a timing later by one symbol than the certain timing. In this case, it can be estimated that the firstly-detected sequence A is included in the frame of the frame number 0.
The symbol counter 12 is set to its initial value at a certain symbol timing, and increments a count value every time a symbol of the received signal is inputted thereto. After that, the symbol counter 12 is reset when reaching the number of symbols constituting a frame. In other words, the counted values from the symbol counter 12 (symbol numbers) are in one-to-one correspondence with the positions of respective symbols in one frame. Thus, it is possible to determine where in a frame the sequence A is inserted, by obtaining a sequence A detection timing on the basis of symbol numbers from the symbol counter 12.
The averaging unit 15 constituting a frame number obtaining unit averages the synchronization detected symbol numbers received from the timing detector 14. For example, the averaging unit 15 averages two or more of the synchronization detected symbol numbers consecutively received. A symbol number corresponding to the frame number 0 can be obtained by the averaging of the two or more consecutive synchronization detected symbol numbers, as will be described later. The averaging unit 15 outputs, to the frame number detector 16 as a reference symbol number, the symbol number corresponding to the frame number 0 obtained by the averaging.
The frame number detector 16 constituting a frame number obtaining unit is sequentially given the synchronization detected symbol numbers from the timing detector 14. On the basis of comparison of the reference symbol number with a currently-received synchronization detected symbol number and a transition status of the sequentially-received synchronization detected symbol numbers, the frame number detector 16 detects a frame number currently being received, and outputs the detected frame number.
With reference to
The symbol counter 12 is set to its initial value at a certain timing, and therefore symbol numbers which the symbol counter 12 respectively output for symbols of a head frame are uncertain. The pattern matching unit 11 is given, from the synchronization sequence storage 13, a synchronization sequence which corresponds to a part or whole of PN sequence included in every frame header of the received signal. Thereby, the pattern matching unit 11 performs pattern matching between the received signal and the synchronization sequence while the symbol counter 12 increments a count value every time a symbol of the received signal is inputted thereto. In the case of FH Mode 1, a symbol number to be outputted from the timing detector 14 is any of 0 to 4199.
The timing detector 14 is given the correlation result from the pattern matching unit 11, determines that a synchronization sequence is detected at each timing at which the correlation value reaches its peak, and outputs, as a synchronization detected symbol number, the counted value (symbol number) of the symbol counter 12 at the timing. Here, a synchronization detected symbol number is detected for every frame.
In the first embodiment, the detection of only three or more synchronization detected symbol numbers allows obtaining the synchronization detected symbol number corresponding to the frame number 0 (reference symbol number) and obtaining the frame number of a currently received frame in which a synchronization detected symbol number is detected, by use of the fact that the synchronization detected symbol number has the feature shown in
Specifically, the averaging unit 15 obtains the reference symbol number by the averaging of two or more consecutive synchronization detected symbol numbers. For example, consider a case where four consecutive synchronization detected symbol numbers are 195, 205, 194 and 206, as shown in
In this case, the averaging unit 15 detects that the reference symbol number is 200 by (195+205+194+206)/4=200. As shown in
Note that, the averaging unit 15 is capable of detecting the reference symbol number by the averaging of and an even number, two or more, of synchronization detected symbol numbers. If the calculation result in its averaging processing includes decimal number, the averaging unit 15 rounds off the calculation result in its averaging processing.
Alternatively, the averaging unit 15 may sequentially average symbol numbers received from the timing detector 14, and sequentially output reference symbol numbers. Still alternatively, the averaging unit 15 may perform average processing after power on, after switching of channels, for every predetermined frame cycles or at other timings, hold reference symbol numbers obtained by the processing, and then output the reference symbol numbers.
The frame number detector 16 calculates a frame number currently received (current frame number) on the basis of a synchronization detected symbol number currently received from the timing detector 14 (current synchronization detected symbol number) and the reference symbol number received from the averaging unit 15.
As shown in
current frame number A=(¦current synchronization detected symbol number−reference symbol number¦*2)−X (here, X=1 when current synchronization detected symbol number <reference symbol number; otherwise X=0);
current frame number B=225−(¦current synchronization detected symbol number−reference symbol number¦*2)−Y (here, Y=1 when current synchronization detected symbol number=reference symbol number; otherwise Y=0) (1),
where * represents multiplication.
When the reference symbol number is 200 and the current synchronization detected symbol number is 207, the two current frame number candidates A and B can be calculated by the following formulae (2):
current frame number A=(¦207−200¦*2)−0=14;
current frame number B=225−(¦207−200¦*2)−1=210 (2).
Subsequently, the frame number detector 16 determines whether the current frame number is smaller than or larger than the frame number 112 (i.e., current frame number A or current frame number B), by using a transition status of synchronization detected symbol numbers having been received.
It is assumed here that the two synchronization detected symbol numbers having been received are m and 1, and the current synchronization detected symbol number is n. As is apparent from
Accordingly, the frame number detector 16 determines that: the current frame number is smaller than 112 when ¦1−m¦<¦m−n¦ is satisfied; the current frame number is larger than 112 when ¦1−m¦>¦m−n¦ is satisfied.
For example, when the timing detector 14 has detected that the synchronization detected symbol numbers are the symbol number 206 shown in
It is apparent here that the frame number detector 16 may employ various methods other than the method shown in the aforementioned example to detect the current frame number. For example, the frame number detector 16 may obtain the current frame number by using different formulae other than the formulae (1), or by referring to a table which is prepared in advance and in which the relationship between the symbol number and the frame number is described.
As described above, with the frame number detecting device according to the first embodiment, a frame number can be detected with a small circuit size since the synchronization sequence storage 13 has only to store a synchronization sequence which corresponds to a part or whole of the PN sequence included in one frame header. Further, a frame number can be detected in a short period of time and with a small amount of calculation since the detection of only three synchronization detected symbol numbers is needed to obtain the current frame number. Furthermore, a frame number can be detected without establishing frame synchronization.
Note that, as described above, the synchronization sequence storage 13 does not necessarily have to store symbols which are identical to all the symbols constituting a PN sequence included in the frame header. The synchronization sequence storage 13 has only to store a part of the symbols of the PN sequence which are enough to specify, in the pattern matching processing, the symbol number that gives the highest correlation value in each frame.
The second embodiment is different from the first embodiment in that a synchronization sequence generator 23 is provided instead of the synchronization sequence storage 13.
The synchronization sequence generator 23 is formed of the same circuit as the LFSR shown in
Other configurations and advantageous effects of the second embodiment are the same as those of the first embodiment. In addition, the frame number detecting device according to the second embodiment has an advantage of realizing a smaller circuit size than that of the first embodiment since the amount of data of a synchronization sequence to be stored is smaller than that of the first embodiment.
In the embodiments described above, a description has been given of an example in which the received signal is time domain data. However, the present invention is applicable in the same manner to a case where the received signal is frequency domain data.
Number | Date | Country | Kind |
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2009-049649 | Mar 2009 | JP | national |