CN102761501A - Method and device for evaluating signal-noise power in CMMB system - Google Patents
Method and device for evaluating signal-noise power in CMMB system Download PDFInfo
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- CN102761501A CN102761501A CN2011101076485A CN201110107648A CN102761501A CN 102761501 A CN102761501 A CN 102761501A CN 2011101076485 A CN2011101076485 A CN 2011101076485A CN 201110107648 A CN201110107648 A CN 201110107648A CN 102761501 A CN102761501 A CN 102761501A
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Abstract
The invention discloses a method for evaluating signal-noise power in a CMMB (China Mobile Multimedia Broadcasting) system. The method comprises the steps as follows: step 1, carrying out signal synchronous processing for received data, and transforming the received data to the frequency domain from the time domain through fast Fourier transform (FFT); step 2, extracting scattered pilots in each signal frame from data in the frequency domain; step 3, carrying out corresponding position subtraction for the data of the scatted pilots in two adjacent frame signals with the same scatted pilot distribution pattern according to the two scatted pilot distribution patterns in the signals of the CMMB system so as to obtain the difference of the scatted pilots; and step 4, calculating average power according to the difference of the scatted pilots in each signal frame, thereby obtaining the real-time noisy power of the current signal frames. The invention further discloses a device for evaluating signal-noise power in a CMMB receiving system for the method. The invention is simple to implement, and the method has high evaluation precision, so that the method is suitable for the field of multi-carrier digital wireless communication.
Description
Technical field
The present invention relates to the digital information transmission field, particularly relate to the signal noise power estimation method in a kind of CMMB (China MobileMultimedia Broadcasting, China Mobile's DMB TV) system.The invention still further relates to a kind of signal noise power estimation means that is used for the CMMB receiving system of said method.
Background technology
CMMB is the China Mobile multimedia broadcasting industry standard of China national General Bureau of Radio, Film and Television in October, 2006 promulgation, and this standard was in formal enforcement on November 1 in 2006.It is a kind of wireless broadcast system based on multi-carrier OFDM (OFDM) technology, adopts advanced channel error correction coding and multi-carrier OFDM modulation technique, has improved antijamming capability and to ambulant support; Adopt the time slot radiation pattern to reduce the power consumption at terminal.According to the imagination of the CMMB network coverage, the CMMB signal realizes that by S-band satellite overlay network and U wave band ground overlay network signal covers.S-band satellite overlay network broadcast channel is used for direct reception, and the Ku wave band is up, and S-band is descending; Distribution channels is used for ground supplement and transmits reception, and the Ku wave band is up, and the Ku wave band is descending, transfers S-band to by ground supplement forwarded device and sends to the CMMB terminal.For realizing effective covering of crowded city mobile multimedia broadcast television signal, adopt the emission of U wave band terrestrial wireless to make up U wave band ground, city overlay network.
According to the CMMB standard, comprise LDPC (low-density checksum) error correcting code in the CMMB system, receiving terminal need be used the real-time noise power that receives signal when LDPC deciphers.
In addition; The CMMB system has inserted some redundant datas according to the distribution pattern of standard code in the frequency-region signal frame; These redundant datas all are known for the transmitting-receiving two-end of CMMB system, can be used for the transmission error that signal calculated superposes at receiving terminal in transmission course.
Summary of the invention
The technical problem that the present invention will solve provides the signal noise power estimation method in a kind of CMMB system, its realize simple and estimated accuracy higher; For this reason, the present invention also will provide a kind of signal noise power estimation means that is used for the CMMB receiving system of said method.
For solving the problems of the technologies described above, the signal noise power estimation method in the CMMB of the present invention system comprises the steps:
Step 1 is carried out signal Synchronization to the data that receive and is handled, and through FFT with the data that received by spatial transform to frequency domain;
Step 2 is extracted the distribution pilot tone in each signal frame in frequency domain data;
Step 3, two kinds of being had in the signal according to the CMMB system scatter the pilot distribution pattern, the distribution pilot data in two frame signals of adjacent identical distribution pilot distribution pattern is carried out correspondence position subtract each other, and it is poor to obtain scattering pilot tone;
Step 4 is calculated its average power by the distribution pilot tone difference in each signal frame, promptly obtains the real-time noise power of current demand signal frame.
The signal frame body of said reception data is used multi-carrier modulation.
Described signal frame body is the multi-carrier signal frame symbol that meets the CMMB standard.
The signal noise power estimation means that is used for the CMMB receiving system of said method of the present invention comprises:
Pilot extraction unit is used for extracting the distribution pilot tone that receives signal;
The pilot tone memory cell is connected with said pilot extraction unit, is used to store the distribution pilot tone that is extracted;
The pilot tone difference computational unit; Be connected with the pilot tone memory cell with said pilot extraction unit; The distribution pilot frequency sequence of the distribution pilot frequency sequence that said pilot extraction unit is extracted and the previous same distribution pattern of pilot tone cell stores; Carry out data by correspondence position and subtract each other, obtain the noise sequence of pilot frequency locations;
Average power is calculated the unit; Be connected with said pilot tone difference computational unit; Calculate the power that all scatter the noise signal of pilot frequency locations according to said noise sequence; And calculate in each signal frame the mean value that all scatter the noise power of pilot tones, obtain the real-time noise power of current demand signal frame.
The present invention is based on the characteristics of signal frame structure in the CMMB system, through the pilot tone simple operation of frequency domain data, and the statistical average of data, just can obtain the real-time noise power of signal, thereby guarantee the operate as normal of channel decoding in the CMMB system; And method of the present invention and device are realized simple and estimated accuracy is higher, have solved in the CMMB system LDPC decoding for the demand of real-time noise power results; Be applicable to the multi-carrier digital wireless communication field.
Description of drawings
Below in conjunction with accompanying drawing and embodiment the present invention is done further detailed explanation:
Fig. 1 is the CMMB receiving system structural representation that contains the signal noise power estimation means.
Fig. 2 is the structural representation of signal noise power estimation means.
Embodiment
Channel decoding in the CMMB system need be used the signal in real time noise power result who receives data; Based on CMMB signal frame structure and signal statistics; The present invention proposes the simple and estimated accuracy higher signal noise power estimation method of a kind of realization, and the signal noise power estimation means that is used for said method.
Because pilot signal is inserted in the signal frame, so the signal noise power estimation means is in after the fast Fourier transform (FFT) module in the CMMB receiver at frequency domain.Fig. 1 is a CMMB receiving system theory diagram that meets the CMMB standard; The radio frequency analog signal that receives at first gets into a demodulation module 100; Produce a baseband complex signal after the data demodulates, and carry out signal Synchronization and handle, guarantee that the frequency departure of reception signal is very little; The baseband complex signal of accomplishing Synchronous Processing gets into a FFT module 200; To receive data is frequency domain from spatial transform; Frequency domain data after the conversion gets into descrambling module 300 and carries out the data de-scrambling computing, the data entering signal noise power estimation apparatus 400 after the descrambling, the noise average power that adds owing to transmission-channel interference in the estimating received signal in real time; Afterwards the noise power result is sent into channel decoding module 500, the work of auxiliary channel decoding.
In conjunction with shown in Figure 2, said in one embodiment signal noise power estimation means 400 comprises pilot extraction unit 410, pilot tone memory cell 420, and pilot tone difference computational unit 430, average power is calculated unit 440.
After descrambling, at first get into pilot extraction unit 410 from the frequency domain data of FFT conversion module 200 outputs; The interior distribution pilot distribution pattern of CMMB receiver according to standard code; In a ROM address table, prestore in advance and scatter the position of pilot tone, thereby extract the distribution pilot tone that receives in the signal.
Scatter the pilot distribution pattern owing to there are two kinds in the signal of CMMB system, so will be according to the corresponding distribution pilot data that extracts corresponding distribution pilot distribution pattern of the sequence number that receives signal frame.Though the distribution pattern of CP continuous pilot all is identical at each signal frame in the signal frame; Extract more convenient, but because the negligible amounts of CP continuous pilot in each signal frame only accounts for 2% of total carrier wave number; Estimate that if be used for signal noise power its estimated accuracy is difficult to guarantee.The present invention adopts the distribution pilot data to carry out the estimation of signal noise power; Subcarrier data in each signal frame has 12.5% to be to scatter pilot tone; Even part is scattered pilot tone and when transmission, is received channel distortions, Zong but, still can guarantee the precision that signal noise power is estimated because number is more.The distribution pilot tone that extracts is sent into pilot tone memory cell 420 on the one hand; These distribution pilot tones of scattering stored previous same distribution pattern in pilot tone and the pilot tone memory cell 420 are sent into pilot tone difference computational unit 430 together simultaneously; Scattering pilot frequency sequence correspondence position data with two groups subtracts each other; Because the distribution pilot tone of correspondence position is identical in two groups of data sequences, cancel out each other, and the additional noise of data is incoherent in two sequences; Therefore the difference result after subtracting each other only is left noise signal, thereby has obtained the noise sequence of pilot frequency locations.The noise sequence that obtains is sent into average power calculate unit 440; Calculate the power that all scatter the noise signal of pilot frequency locations; And calculate in each signal frame the mean value that all scatter the noise power of pilot tones; Just obtain the real-time noise power of current demand signal frame, send into subsequent communication channel decoding module 500 at last, the auxiliary channel work decoding.
More than through embodiment the present invention has been carried out detailed explanation, but these are not to be construed as limiting the invention.Under the situation that does not break away from the principle of the invention, those skilled in the art also can make many distortion and improvement, and these also should be regarded as protection scope of the present invention.
Claims (4)
1. the signal noise power estimation method in the CMMB system is characterized in that:
Step 1 is carried out signal Synchronization to the data that receive and is handled, and through FFT with the data that received by spatial transform to frequency domain;
Step 2 is extracted the distribution pilot tone in each signal frame in frequency domain data;
Step 3, two kinds of being had in the signal according to the CMMB system scatter the pilot distribution pattern, the distribution pilot data in two frame signals of adjacent identical distribution pilot distribution pattern is carried out correspondence position subtract each other, and it is poor to obtain scattering pilot tone;
Step 4 is calculated its average power by the distribution pilot tone difference in each signal frame, promptly obtains the real-time noise power of current demand signal frame.
2. method according to claim 1 is characterized in that: the signal frame body of said reception data is used multi-carrier modulation.
3. method according to claim 2 is characterized in that: described signal frame body is the multi-carrier signal frame symbol that meets the CMMB standard.
4. a signal noise power estimation means that is used for the CMMB receiving system of each said method of claim 1-3 is characterized in that, comprising:
Pilot extraction unit is used for extracting the distribution pilot tone that receives signal;
The pilot tone memory cell is connected with said pilot extraction unit, is used to store the distribution pilot tone that is extracted;
The pilot tone difference computational unit is connected with the pilot tone memory cell with said pilot extraction unit, distribution pilot frequency sequence that said pilot extraction unit is extracted and pilot tone cell stores previous
The distribution pilot frequency sequence of same distribution pattern carries out data by correspondence position and subtracts each other, and obtains the noise sequence of pilot frequency locations;
Average power is calculated the unit; Be connected with said pilot tone difference computational unit; Calculate the power that all scatter the noise signal of pilot frequency locations according to said noise sequence; And calculate in each signal frame the mean value that all scatter the noise power of pilot tones, obtain the real-time noise power of current demand signal frame.
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Application publication date: 20121031 |