Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/26—Systems using multi-frequency codes
  • H04L27/2601—Multicarrier modulation systems
  • H04L27/2647—Arrangements specific to the receiver only
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/0012—Modulated-carrier systems arrangements for identifying the type of modulation
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/26—Systems using multi-frequency codes
  • H04L27/2601—Multicarrier modulation systems
  • H04L27/2602—Signal structure
  • H04L27/261—Details of reference signals
  • H04L27/2613—Structure of the reference signals

Definitions

• a signal frame includes a frame header and a frame body.
• the frame header and frame body have the same baseband symbol data rate (7.56Msym/sec). Under this frame structure, more than one choice is provided for practical deployment of the terrestrial broadcasting system in diverse environments for various segments of the DTV market.
• two frame body options are provided in the Chinese DTV terrestrial broadcasting system.
• One is a multi-carrier option, in which encoded data is transmitted in the frequency domain and the frame body is filled with an OFDM symbol.
• the multi-carrier option is derived from Chinese DMB-T.
• the other option is based on single carrier technology, in which encoded data is transmitted in the time domain directly. A particular broadcasting operator can select either one of the options.
• the frame header portion three possible configurations of the signal frames with different signal frame headers are specified.
• a PN sequence is sent for the purpose of synchronization and channel estimation.
• the PN header also serves as a guard time interval for the following frame body.
• the possibility of different configurations of the signal frame offer some degree of scalability and flexibility for the broadcasting operator.
• Three different PN sequences are used in the signal frame header portion for the three configurations. For configurations 1 and 3, a length L PN -chip (e.g., 420) PN sequence is used that is a cyclic extension of a shorter basic m-sequence with length of N (e.g., 255).
• a length LpN-chip e.g., 595
• PN sequence is used that is derived from a longer basic m- sequence with length of N (e.g., 1023).
• the operator will choose one of the three signal frame configurations according to its specific system deployment plan.
• the receiver When the receiver begins to scan DTV signals, it does not have any information on what kind of signal frame configuration is used in a specific DTV channel; therefore, it is necessary for a DTV receiver to detect the signal frame configuration before it can start a time and frequency synchronization phase, a channel estimation phase and a data demodulation phase.
• the capability of scanning DTV programs is required. Detection of the signal frame configuration is one of the most important steps in the procedure of scanning a DTV program.
• the receiver may correlate the received signal with a local PN sequence and detect the embedded PN sequence.
• the receiver can determine whether a certain PN sequence is present or not.
• the receiver With three parallel or successive PN correlators, with each corresponding to a different PN used in the DTV system, the receiver can determine the configuration of the signal frame.
• Low-complexity detection methods and apparatus are provided for detecting signal frame configuration in a DTV receiver or the like.
• the detection takes advantage of a difference in average power between the signal frame header and the signal frame body in certain signal frame configurations.
• the specific frame header length of the signal frame configurations may also be exploited to identify the configuration and simplify the detection algorithm.
• a method of detecting a signal frame configuration of a broadcast signal includes measuring signal power; calculating a short term average of signal power within each of a plurality of selected portions of the signal to produce a sequence of average power values; performing spectral analysis of the average power values to produce a sequence of transformed values; and using the transformed values, determining that the signal frame configuration is or is not one of a plurality of known possible signal frame configurations.
• the method includes that it is not sensitive to carrier frequency error or sampling frequency error and is robust and reliable in various wireless channels. Moreover, it entails only a small amount of computation and minimal additional buffer space for intermediate data storage. The power consumption can be made very low, a particular advantage for portable and mobile DTV receivers when they scan DTV programs. In one embodiment, the method only uses amplitude information of the received signals and can in large part share resources with other modules, such as an AGC module.
• FIG. 1 is a diagram of the structure of a DTV signal frame
• FIG. 2 is a block diagram of a DTV receiver to which the present invention may be applied;
• FIG. 3 shows the short term average power for a signal with signal frame configuration 1 in an AWGN channel with SNR of OdB;
• FIG. 4 shows the spectrum analysis result
• FIG. 5 shows in greater detail the low frequency part of FIG. 4
• FIG. 6 shows the spectrum analysis result
• FIG. 7 shows in greater detail the low frequency part of FIG. 6; - A -
• FIG. 8 shows the spectrum analysis result
• FIG. 9 shows a block diagram of a detector for detecting signal frame configuration
• FIG. 10 shows the plot of an additional phase angle of a decision input as a function of a frame header offset at the start of sampling.
• the signal for terrestrial digital television broadcasting in the Chinese DTV terrestrial broadcasting system is physically organized with a signal frame as shown in FIG. 1.
• a signal frame header portion three possible configurations of the signal frames with different signal frame headers are specified.
• a PN sequence is sent for the purpose of synchronization and channel estimation.
• the PN header also serves as a guard time interval for the following frame body.
• the baseband signal sent at the transmitter is a
• the PN sequence is derived from an m- sequence with length of N.
• Table 1 The three configurations of the signal frame
• the LpN-chip PN sequence is a cyclic extension of the shorter basic m-sequence with length of N.
• the L PN - chip PN sequence is derived from the longer basic m-sequence with length of N.
• the operator will choose one of the three signal frame configurations according to its specific system deployment plan.
• the receiver when the receiver begins to scan DTV signals, it does not have any information on what kind of signal frame configuration is used in a specific DTV channel; therefore, it is necessary for a DTV receiver to detect the signal frame configuration before it can start a time and frequency synchronization phase, a channel estimation phase and a data demodulation phase.
• the capability of scanning DTV programs is required. Detection of the signal frame configuration is one of the most important steps in the procedure of scanning a DTV program.
• the general structure of a DTV receiver is shown in FIG. 2.
• a signal 203 is received by an RF module 201 and sampled in an analog-to-digital converter ADC 205.
• the sampled signal 207 is applied to an automatic gain control (AGC) loop 209 and to a signal frame configuration detector 211, which produces configuration information 213.
• AGC automatic gain control
• the sampled signal 207 and the configuration information 213 are applied to subsequent modules, such as time/frequency synchronization 215, channel estimation 217, OFDM demodulation (221) and equalization (219) for the multi-carrier option, and time equalization (219) for the single carrier option.
• the digital processing module 210 obtains samples of the baseband signal from the ADC. At this moment, one of the most important tasks is to detect the signal frame configuration. Only when the signal frame configuration is known can other modules be started.
• the receiver may correlate the received signal with a local PN sequence and detect the embedded PN sequence.
• the receiver can determine whether a certain PN sequence is present or not.
• the receiver With three parallel or successive PN correlators, with each corresponding to a different PN used in the DTV system, the receiver can determine the configuration of the signal frame.
• the received baseband signal is a
• n ⁇ t represents AWGN noise.
• the signal is sampled with a sampling rate of M 1 Ar 8 (M 1 can be 1, 2, 4, 8, etc.; often 4 or 8 is chosen).
• M 1 can be 1, 2, 4, 8, etc.; often 4 or 8 is chosen.
• the short term average power of the input signal is calculated.
• the down sampled signal is
• L w can be chosen around 420. This sliding average plays the same role as a low pass filter with length of Lw, which will average out a large part of the channel noise. Since only signal power is taken into account, the method is insensitive to the carrier frequency error.
• the average power of the signal frame header is 3dB higher than that of the frame body; therefore, a difference in short term average power can be observed around each frame header.
• P( ⁇ ) is given in FIG. 3, which is simulated in an AWGN channel with OdB SNR using signal frame configuration 1. In a multipath channel, a similar waveform can be observed.
• P(i) is calculated as follows for C time instants.
• a signal with frequency of 1/[(420+378O)Ts] corresponds to the signal Z(m) with the index of
• FIG. 4 shows the spectrum analysis result
• FIG. 5 shows in greater detail the low frequency part of FIG. 4. A peak can be observed in the frequency spectrum having an index of 9.
• FIG. 6 shows the spectrum analysis result
• FIG. 7 shows in greater detail the low frequency part of FIG. 6. A peak can be observed in the frequency spectrum having an index of 8.
• detection of the signal frame configuration can be made using the amplitude value in frequency indices 8 and 9.
• a signal frame configuration detector is shown in FIG. 9.
• the received signal is squared (901), then a short-term averaging operation is performed (903).
• a number C of short term average value power values is collected (905).
• each average is taken over D samples (DTs).
• a DFT is performed using the C short term average power values (907). Based on the results of the DFT, a decision is performed (909).
• the signal frame configuration is 3. Else if
• the signal frame configuration is 1. Else
• the signal frame configuration may be 2. End
• THn is a threshold for detection, which may be 6, for example; TH12 is a threshold for detection, which may be 1 , for example.
• the signal frame configuration is 3.
• the signal frame configuration is 1.
• the signal frame configuration may be 2.
• TH 2 I is a threshold for detection, which may be 8, for example;
• TH 22 is a threshold for detection, which may be 1 , for example.
• the square operator and the short term power averaging module are also essential for and may be shared with the AGC module, shown in FIG. 2. It is notable that in the short term power averaging module, no multiplier is needed. For each incoming sampling time instant, the module only needs to update the accumulated result by adding the incoming sample and subtracting the tail sample, previously stored in a loop buffer. Then the tail sample is replaced by the incoming sample and the tail pointer is adjusted at the same time. No extra calculation is needed at this stage.
• the detector analyzes the C short term power averaging values.
• An FFT of size of C can be used for this purpose.
• not all the frequency elements are needed in the decision algorithm. Only the elements Z(8) and Z(9) are needed.
• elements Z(16), Z(18), etc. can be involved.
• the signal frame configuration is 3. Else if
• the signal frame configuration is 1. Else
• the signal frame configuration may be 2. End
• TH 3 is a threshold for detection, which may be 36, for example; TH 32 is a threshold for detection, which may be 6, for example.
• the following Algorithm D may be used: If
• the signal frame configuration is 3.
• the signal frame configuration is 1. Else
• the signal frame configuration may be 2. End
• TH41 is a threshold for detection, which may be 64, for example; TH42 is a threshold for detection, which may be 8, for example.
• the algorithms described may be used to realize an additional beneficial function, namely the determination of approximate frame header positioning for signal frame configurations 1 and 3.
• the short term average power displays periodic characteristics.
• the basic period is 4200Ts, whose value is shown in the 9-th frequency element in the spectrum of formula (7).
• Y(O) is aligned with the peak of the sampled short term average power (that is to say, Y(O) is aligned with the frame header)
• Y(40k) will tend to align with the frame header and have local peak positive values, while other values tend to be small.
• the value Z(9) can be rewritten as, I ,2 ⁇ 9 * 40k - ;2 ⁇ —
• FIG. 10 shows the additional phase due to the delay ⁇ .
• Z(9) is calculated by (7) or (9).
• the approximate header position ⁇ can be estimated as follows: ⁇ « ZZ ⁇ * 42007; ( 12 )

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Synchronisation In Digital Transmission Systems (AREA)
• Television Systems (AREA)
• Circuits Of Receivers In General (AREA)

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• 2007
  • 2007-11-29 CN CN200710196636.8A patent/CN101453582B/zh not_active Expired - Fee Related
• 2008
  • 2008-11-26 WO PCT/IB2008/054959 patent/WO2009069082A2/en not_active Ceased
  • 2008-11-26 EP EP08854842A patent/EP2220835A2/de not_active Withdrawn

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