Abstract:
A determination method for determining a frame header mode of a DMB-TH system data structure and a determination apparatus thereof. The determination method comprises generating a signal when signal frequencies at a transmitting terminal and a receiving terminal are identical, providing a predetermined process to process the signal, such that the signal forms a peak when a frequency offset occurs, and determining a type of the frame header mode according to the predetermined process.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates in general to an automatic detection device for a frame header and a method thereof, and in particular, to a detection device and method for a DMB-TH communication protocol or PN signal mode in TDS OFDM systems. 
     2. Description of the Related Art 
     In DMB-TH systems, a data frame typically comprises a 4-layer structure, in which a basic frame is known as a signal frame, including a frame header and a frame body. In DMB-TH systems, the frame header comprises three modes: the frame header signal PN 420  with a length of 420 symbols; the frame header signal PN 595  with a length of 595 symbols; and the frame header signal PN 945  with a length of 945 symbols. During signal transmission, the receiver determines the mode of the frame header of the signal frame, to accordingly perform different processing. 
     Conventionally, the method of determining the frame header mode is based on distance between two peaks generated by the cross correlation of the frame header sequence when frequencies of the transmitter and the receiver are synchronous. 
     However when a specific frequency offset occurs between the transmitter and the receiver, for example, frequency offset exceeding 30 KHz in the PN 420  mode, and frequency offset exceeding 15 KHz in the PN 945  mode, combining multipath effect and low signal to noise ratio (SNR), disturbance to the signal peaks for determining frame header mode renders inaccurate determinations. 
     As shown in  FIG. 1(   a ),  FIG. 1   a  illustrates the peak generation when the signals at the transmitter and receiver are synchronized, where the distance between two adjacent peaks  10   a  and  10   b  can be used to determine the header mode. Please refer to  FIG. 1   b ,  FIG. 1   b  illustrates the peak generation when a frequency difference exists between the signal frequencies at the transmitter and receiver and the peaks are unclear ( 12   b ), resulting in difficulty of frame header mode determination. 
     Thus, a need exists for an amplifier amplifying an input signal without introducing noise to the amplified signal. 
     BRIEF SUMMARY OF THE INVENTION 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     A determination method for determining a frame header mode of a DMB-TH system data structure, comprising generating a signal when signal frequencies at a transmitting terminal and a receiving terminal are identical, providing a predetermined process to process the signal, such that the signal forms a peak when a frequency offset occurs, and determining a type of the frame header mode according to the predetermined process. 
     According to another embodiment of the invention, a determination method for determining a frame header mode of a DMB-TH system data structure is disclosed, comprising generating a signal when signal frequencies at a transmitting terminal and a receiving terminal are identical, providing a plurality of processing methods, from which one processes the signal, determining whether the signal comprises a peak upon an occurrence of a frequency offset, if not, processing the signal with another processing method, until the signal comprises a peak upon an occurrence of a frequency offset, and determining frame header mode according the processing method. 
     According to another embodiment of the invention, a determination apparatus capable of determining a frame header mode of a DMB-TH system data structure is provided, comprising a signal generation device, an amplification device, and a determination device. The signal generation device generates a signal when signal frequencies at a transmitting terminal and a receiving terminal are identical. The amplification device provides a predetermined process to process the signal, such that the signal forms a peak when a frequency offset occurs. The determination device determines a type of the frame header mode according to the predetermined process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1   a  illustrates the peak generation when the signals at the transmitter and receiver are synchronized. 
         FIG. 1   b  illustrates the peak generation when a frequency difference exists between the signal frequencies at the transmitter and receiver. 
         FIG. 2  is a block diagram of an exemplary signal determination device according to the invention. 
         FIG. 3  is a block diagram of an exemplary amplification device according to the invention. 
         FIGS. 4   a ,  4   b , and  4   c  show amplified signal diagrams of PN 420 , PN 595 , and PN 945  according to the invention. 
         FIG. 5  is a flowchart of an exemplary determination method for header mode according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
     In a DMB-TH system or a TDS OFDM system, the header of a data frame has three modes, namely: header signal PN 420  with a length of 420 symbols, comprising a preamble, a PN 255  sequence, and a postamble; header signal PN 595  with a length of 595 symbols, comprising the first 595 symbols of a pseudorandom binary sequence with a length of 1023; and header signal PN 945  with a length of 945 symbols, comprising a preamble, a PN 511  sequence, and a postamble. 
       FIG. 2  is a block diagram of an exemplary signal determination device according to the invention. As shown in  FIG. 2 , signal determination device  2  comprises peak generation device  21 , amplification device  22 , and determination device  23 . Peak generation device  21  provides a threshold, and determines a peak if the signal generated when the signals at the transmitter and receiver are identical exceeds the threshold. Amplification device  22  amplifies the peak generated by the header signal to identify the peak under a high frequency shift situation. Determination device  23  calculates the distance between two adjacent peaks following the amplification process by amplification device  22 , to determine the mode of the header signal. 
       FIG. 3  is a block diagram of an exemplary amplification device according to the invention, comprising delay device  31 , logic device  32 , multiplier  33 , first accumulation device  34 , second accumulation device  35 , first computation device  36 , second computation device  37 , and divider  38 . Delay device  31  performs delay processes on frame header signal  311 . The delay processes comprise 3 types, namely: delay 255 symbols; 511 symbols; and 4375 symbols, wherein each generates a predetermined waveform when processing a particular type of header mode. When determining the mode frame header signal  311 , each delay process is performed thereon to generate an accurate amplification result for a predetermined waveform result. After the delay process, frame header signal  311  is processed to provide delayed frame header signal  312 . Logic device  32  performs phase conjugate process on delayed frame header signal  312 . Multiplier  33  multiplies phase conjugated processed delayed frame header signal  312  by frame header signal  311 . First accumulation device  34  accumulates the results of the multiplication to provide first accumulation  313 . Second accumulation device  35  accumulates delayed frame header signal  312  to provide second accumulation  314 . First computation device  36  squares first accumulation  313  to generate first squared value  315 , second computation device  37  squares second accumulation  314  to generate second squared value  316 . Divider  38  divides first squared value  315  by second squared value  316  to obtain amplification signal  317 . Amplification device  22  utilizes a processing method known as a delayed correlation method. 
       FIG. 4   a  shows an amplified signal diagram of signal PN 420  according to the invention,  FIG. 4   b  shows an amplified signal diagram of signal PN 595  according to the invention,  FIG. 4   c  shows an amplified signal diagram of signal PN 945  according to the invention. As shown in  FIG. 4 , amplification device  22  processes frame header signal  311  to provide amplification signal  317 , and amplification signal  317  can be identified even when high frequency shift occurs. Amplification device  22  utilizes three methods to perform processing of frame header signal  311 , wherein each type of frame header signal  311  corresponds to one method. When processing frame header signal  311  to generate amplification signal  317 , the mode of frame header signal  311  is determined by the method amplification device  22  uses for processing frame header signal  311 . The processed frame header signal  311  is appropriate for determination device  23  to determine the distance between two adjacent amplification signals  317 , to further confirm the type of header mode. 
       FIG. 5  is a flowchart of an exemplary determination method for header mode according to the invention. Upon initialization (S 51 ), the determination method performs cross correlation when the frequencies of the signals at the transmitter and receiver are identical to generate a signal (S 52 ), utilizes amplification device  22  to select a process to perform thereon (S 53 ), determines whether a peak is identified during a severe frequency shift (S 54 ), if not, utilizes another method by amplification device  22  to process the peak, until the peak is identified clearly, determines header mode according to the method amplification device  22  used for processing the peak (S 55 ), confirms the header mode by calculating the distance between two adjacent peaks, and terminates the determination method (S 57 ). 
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.