EP1841107A2

EP1841107A2 - T-MMB receiver compatible with DAB

Info

Publication number: EP1841107A2
Application number: EP07104786A
Authority: EP
Inventors: Donshan Beijing Nufront Tech. Co. Ltd. Bao; Jiaqing Beijing Nufront Tech. Co. Ltd. Wang; Hao Beijing Nufront Tech. Co. Ltd. Zhu; Fei Beijing Nufront Tech. Co. Ltd Liu; Qi Beijing Nufront Tech. Co. Ltd Cheng
Original assignee: Beijing Nufront Software Tech Co Ltd; Beijing Nufront Mobile Multimedia Technology Co Ltd
Priority date: 2006-03-30
Filing date: 2007-03-23
Publication date: 2007-10-03
Also published as: CN1972391A; CN100546349C; EP1841107A3

Abstract

The invention discloses a Terrestrial Mobile Multimedia Broadcasting T-MMB receiver compatible with Digital Audio Broadcasting DAB, wherein the receiver comprises a RF demodulation unit, a synchronization unit, an Orthogonal Frequency Division Multiplexing OFDM demodulation unit and a channel demodulation and decoding unit. The invention utilizes the ideal base band model and the synchronization position of the T-MMB system and characteristics of the T-MMB channel to identify a transmission mode of the received signal; and RF demodulate, OFDM demodulate and channel decode the received signal. Moreover, in the OFDM demodulation process, the control information in the FIC can be obtained, and the data can be demodulated according to the obtained control information, to thereby implement the T-MMB receiver compatible with the DAB system which improves the reliability of the multimedia broadcast service.

Description

BACKGROUND OF THE INVENTION

FIELD OF INVENTION

The present invention relates to a digital information transmission technology, in particularly to a Terrestrial Mobile Multimedia Broadcasting (T-MMB) receiver compatible with Digital Audio Broadcasting (DAB).

DESCRIPTION OF PRIOR ART

Digital multimedia broadcasting refers to a multimedia broadcasting method used in a handheld terminal. The digital multimedia broadcasting standards more focused in the field are the European standard DVB-H (Digital Video Broadcasting Handheld) and the Korean standard T-DMB (Terrestrial Digital Multimedia Broadcasting,) currently.
T-DMB is developed on a basis of the Digital Audio Broadcasting (DAB). The DAB digital broadcasting was developed by the famous EUREKA-147 which is an association consisted of 12 members. The system was initially named DAB and always used to distinguish the real DAB broadcasting from other digital audio broadcasting standards. In 1994, EUREKA-147 was selected to be an international digital audio broadcasting standard by the International Organization for Standardization (ISO). Today, digital broadcasting according to this standard have been either implemented or under test in most part of the world. In September 1988, European Union first carried out the EUREKA-147 DAB experiment in the World Radio Administrative Conference. The EUREKA-147 DAB mode was standardized in 1995, and is used as a typical DAB system. It has been well developed in other countries and regions than Europe, such as Canada, Singapore, Australia, etc. As compared with the conventional AM/FM broadcasting system, the DAB has advantages of saved spectrum resources, low transmission frequency, large capacity of information, excellent audio quality, etc. It is the third generation broadcasting following the conventional AM (amplitude modulation)/FM (frequency modulation) broadcasting. Digital broadcasting has advantages of anti-noise, anti-interference, anti-transmission attenuation of noise resistance, interference proof, resistance against attenuation in electric wave transmission and adaptability to high-speed mobile reception, etc. It provides a CD-level stereo audio quality and nearly no distortion in signal.
T-DMB is a Terrestrial Digital Multimedia Broadcasting system introduced from Korea. Strictly, it's still an European international standard. This standard is modified based on EUREKA-147 DAB system developed by European manufacturers in order to broadcast an on-air digital TV program to a handheld device such as mobile phone, personal digital assistant (PDA) and portable TV, etc. T-DMB has been commercialized in Korea. In Korea, a new license has been issued to T-DMB broadcast operators. Meanwhile, the mobile digital TV broadcasting system DVB-H developed in Europe has just been put into test.
T-DMB fully utilizes the technical advantage of DAB (capable of receiving a signal reliably in a high-speed mobile environment), and functionally extends the transmission of single audio information to various carriers such as data, text, graphics and video, etc. T-DMB can implement a high-quality transmission by compressing, encoding, modulating, and transmitting the digitalized audio, video signal and various data service signals in a digital state, while having multimedia characteristics for providing data information transmission of large capacity, high efficiency, and strong reliability. Transition from DAB to T-DMB means a great stride from a digital audio broadcasting to a digital multimedia broadcasting, which enables any digital information to be delivered by using a digitalized platform system. This system can provide a user with integrated audiovisual information service including audio and video, as well as entertainment enjoyment.
DVB-H is a transmission standard specified for providing a portable/handheld terminal with multimedia service via a terrestrial digital broadcasting network, after the European DVB organization has issued a series of standards of digital TV transmission.
DVB-H is a standard based on both the data broadcasting (DVB) and DVB-Transmission (T), and is considered to be an extended application of the DVB-T standard. Although it is a transmission standard, it actually focuses on a protocol implementation. Front end of the system is comprised of a DVB-H encapsulator and a DVB-H modulator. The DVB-H encapsulator is responsible for encapsulating Internet Protocol (IP) data into a second generation Motion Picture Experts Group (MPEG-2) system transmission stream. The DVB-H modulator is responsible for channel-coding and modulating. A system terminal is comprised of a DVB-H demodulator and a DVB-H terminal. The DVB-H demodulator is responsible for channel-demodulating and decoding. The DVB-H terminal is responsible for displaying and processing related services.
DVB-H maintains partly compatibility with a DVB-T receiving circuit, while much technology improvement has been made to satisfy requirement of receiving characteristics of the handheld device, such as low power consumption, high-speed mobility, common platform and no-interruption in switching network service, etc., so as to ensure a normal view indoors, outdoors, in walking or in a traveling car. To increase service time of battery, the terminal powers off a part of the receiving circuit periodically to save power consumption. To satisfy requirement for portability, antenna of a DVB terminal becomes less and is more flexible to move. The transmission system can ensure to receive a DVB-H service successfully at various moving speeds. The system has a strong inference proof capability, and provides enough flexibility to satisfy applications with different transmission bandwidths and channel bandwidths.
Depending on the application background of digital multimedia broadcasting, the success or failure of the transmission standard is mainly determined by: energy saving capability and power consumption, cost, mobile reception performance, single frequency network performance, multi-traffic and multi-service selection, support for high frequency spectrum efficiency and high capability, and user experience.
However, both the T-DMB and the DVB-H standards have disadvantages at different levels. The frequency spectrum efficiency of the T-DVB is low. The T-DMB doesn't provide sufficient information throughput to satisfy such a high quality service as mobile TV, and doesn't provide a sufficient energy saving measure for a receiver. Since the DVB-H is derived from the DVB-T (a fixed receiving system), based on which room for mobile environment optimization is very limited, the DVB-H can't provide sufficient energy saving mechanism for the receiver, and sacrifice some other performance indexes, e.g. a switching time increases to 5s, and the number of the available operation frequencies is small.
It can be seen that the reliability of the existing multimedia broadcasting service is not high.

SUMMARY OF THE INVENTION

In consideration of the above, a main object of the present invention is to provide a terrestrial mobile multimedia broadcasting receiver compatible with DAB, which can improve the reliability of multimedia broadcasting service.
According to the above main object, the present invention provides a terrestrial mobile multimedia broadcasting receiver compatible with DAB, comprising a Radio Frequency RF demodulation unit, a synchronization unit, an Orthogonal Frequency Division Multiplexing OFDM demodulation unit and a channel demodulation and decoding unit, wherein,
the RF demodulation unit is configured to RF-demodulating a RF signal received from outside, and output the RF-demodulated signal to the synchronization unit and the OFDM demodulation unit;
the synchronization unit is configured to identify a transmission mode corresponding to the signal from the RF demodulation unit, and output a result of mode identification to the OFDM demodulation unit, and determine a synchronization position of the received signal according to the result of the mode identification and output the synchronization position to the OFDM demodulation unit;
the OFDM demodulation unit is configured to extract a phase reference symbol, a Fast Information Channel FIC symbol and a data symbol from the signal from the RF demodulation unit according to the result of the mode identification and the synchronization position output from the synchronization unit; OFDM-demodulate and decode the FIC symbol according to the phase reference symbol and a channel selection indication received from outside, to obtain a control information in the FIC which is output to the channel demodulation and decoding unit; OFDM-demodulate the data symbol according to the control information in the FIC; and output the OFDM-demodulated FIC symbol and data symbol to the channel demodulation and decoding unit;
the channel demodulation and decoding unit is configured to channel-demodulating and decoding the received data symbol according to the control information and the FIC symbol from the OFDM demodulation unit, and output the channel demodulated and decoded data symbol.
The OFDM demodulation unit is further configured to output the extracted phase reference symbol and/or FIC symbol and/or data symbol to the synchronization unit; and notify the RF demodulation unit of a type of the currently extracted symbol by using a symbol indication signal;
the synchronization unit is further configured to perform carrier-recovery according to the received phase reference symbol and/or FIC symbol and/or data symbol, and output the carrier-recovered phase signal to the RF demodulation unit;
the RF demodulation unit is further configured to RF-demodulate the RF signal received from outside according to the received symbol indication signal and the phase signal.
The RF demodulation unit comprises a tuner, an Analog/Digital (A/D) conversion module, a down-frequency conversion module, a low pass filter, a downsample module, a gain control (AGC) module and a free oscillation clock, wherein,
the tuner is configured to amplify the received RF signal according to the received AGC control signal to perform selection of a frequency band; transform the selected signal from a RF frequency band to a fixed intermediate frequency; and output the transformed RF signal to the A/D conversion unit;
the A/D conversion unit is configured to A/D convert the received signal according to a clock signal supplied from the free oscillation clock, and output the converted signal to the down-frequency conversion module;
the AGC module is configured to detect a power of a signal output from the downsample module according to the symbol indication signal from the OFDM demodulation unit, generate a AGC control signal, and output it to the tuner;
the down-frequency conversion module is configured to frequency down-convert the received signal according to a phase signal supplied from the synchronization unit, and output it to the AGC module, the synchronization unit and the OFDM demodulation unit via the low pass filter and the downsample module.
The synchronization unit comprises a mode identification module, a frame synchronization module, a timing recovery module and a carrier recovery module, wherein,
the mode identification module is configured to judge a frame length and/or a protected gap length and/or a null symbol length of a signal from the downsample module, determine a transmission mode corresponding to the received signal, and output a result of mode identification to the frame synchronization module and the OFDM demodulation unit;
the frame synchronization module is configured to determine a frame start position of the received signal according to the result of the mode identification supplied from the mode identification module; perform symbol-synchronization and carrier-synchronization according to the obtained start position, and determine a synchronization position, i.e. a frame boundary and a symbol boundary; and output the obtained frame boundary and the symbol boundary to the OFDM demodulation unit;
the timing recovery module is configured to obtain a timing position according to a frequency-offset corrected phase reference symbol from the carrier recovery module, and output it to the OFDM demodulation unit;
the carrier recovery module is configured to obtain a fraction frequency offset estimation and an integer frequency offset estimation according to the phase reference symbol from the OFDM demodulation unit, add the fraction frequency offset to the integer frequency offset to obtain a result of the frequency offset estimation, and fraction-frequency-offset correct the phase reference symbol; perform fraction-frequency-offset estimation according to the FIC symbol and/or the data symbol from the OFDM demodulation unit to obtain a fraction frequency offset estimation as the result of the frequency offset estimation; output the result of the frequency offset estimation to the down-frequency conversion module; correct the phase reference symbol according to the result of the frequency offset estimation, and output the corrected phase reference symbol to the timing recovery module.
The mode identification module comprises a frame length detector, and/or a protected gap length detector, and/or a null symbol length detector, and a mode decider;
the frame length detector is configured to detect a frame length of a signal, and output the detected result to the mode decider;
the protected gap length detector is configured to detect a protected gap length of a signal, and output the detected result to the mode decider;
the null symbol length detector is configured to detect a null symbol length of a signal, and output the detected result to the mode decider;
the mode decider is configured to perform mode-decision according to the detected result from the frame length detector, and/or the protected gap length detector, and/or the null symbol length detector, and output the result of the mode identification.
The frame synchronization module comprises: an energy-in-window statistics sub-module, a divider, a delayer and a peak detection sub-module, wherein,
the energy-in-window statistics sub-module is configured to make statistics on a signal energy in a preset window and output a statistics result to the divider;
the divider is configured to calculate a quotient of the statistics results in two adjacent windows under control of the delayer, and output the quotient to the peak detection sub-module;
the peak detection sub-module is configured to compare the received quotient with the preset threshold, and output the frame boundary and the symbol boundary according to the comparison result.
The timing recovery module comprises: an IFFT sub-module, a Modulo sub-module and a local maximum position sub-module, wherein
the IFFT sub-module is configured to IFFT process the corrected phase reference symbol from the carrier recovery module, and output it to the modulo sub-module;
the modulo sub-module is configured to perform a modular operation on the received phase reference symbol in the time-domain, and output a Modulo result to the local maximum position sub-module;
the local maximum position sub-module is configured to locate a timing position for fine synchronization by finding a local maximum position in a preset window, and output the obtained timing position to the OFDM demodulation unit.
The carrier recovery module comprises: a first fraction frequency offset estimator, a second fraction frequency offset estimator, a third fraction frequency offset estimator, a fraction frequency offset corrector, an integer frequency offset corrector, an integer frequency offset estimator, an adder, a selector, a low pass filter sub-module and a digital control oscillator, wherein
the first fraction frequency offset estimator is configured to fraction-frequency-offset estimate the received data symbol, and output a fraction frequency offset to the selector as the frequency offset estimation result;
the second fraction frequency offset estimator is configured to fraction-frequency-offset estimate the received FIC symbol, and output a fraction frequency offset to the selector as the frequency offset estimation result;
the third fraction frequency offset estimator is configured to fraction-frequency-offset estimate the received phase reference symbol, and output a fraction frequency offset to the fraction frequency offset corrector;
the fraction frequency offset corrector is configured to fraction-frequency-offset correct the received phase reference symbol according to the fraction frequency offset output from the third fraction frequency offset estimator; and output the fraction-frequency-offset corrected phase reference symbol to the integer frequency offset estimator and the adder;
the integer frequency offset estimator is configured to integer-frequency-offset estimate the received and fraction-frequency-offset corrected phase reference symbol, and output the integer frequency offset to the adder and the integer frequency offset corrector;
the integer frequency offset corrector is configured to integer-frequency-offset correct the received and fraction-frequency-offset corrected phase reference symbol according to the integer frequency offset output from the integer frequency offset estimator; and output the integer-frequency-offset corrected phase reference symbol to the selector and the timing recovery module;
the adder is configured to calculate a sum of the fraction frequency offset estimation from the third fraction frequency offset estimator and the integer frequency offset estimation from the integer frequency offset estimator, and output the sum to the selector as the frequency offset estimation result;
the selector is configured to select one from the received frequency offset estimation results to output to the low pass filter sub-module;
the low pass filter sub-module is configured to low pass filter the received frequency offset estimation result, and output to the AGC module via the digital control oscillator.
The OFDM demodulation unit comprises: a symbol classification and extraction module, a FIC decoding module, a channel data selection module and a Fourier Transform FFT module, wherein,
the symbol classification and extraction module is configured to extract the phase reference symbol, the FIC symbol and the data symbol from the signal from the downsample module according to the timing position from the timing recovery module, the frame boundary and the symbol boundary from the frame synchronization module, and the mode identification result from the mode identification module; output the extracted phase reference symbol, FIC symbol and data symbol to the carrier recovery module; output the extracted phase reference symbol and FIC symbol to the FIC decoder; output the extracted FIC symbol and data symbol to the channel data selection module; and output the type for the currently extracted symbol to the AGC module by using the symbol indication signal;
the FIC decoding module is configured to demodulate and decode the received FIC symbol according to the received phase reference symbol and channel selection indication to obtain channel data position and length information, channel modulation scheme information and channel-coding scheme information; output the channel data position and length information to the channel data selection module; and output the channel modulation scheme information and a channel-coding scheme information to the channel demodulation and decoding unit;
the channel data selection module is configured to select the data in corresponding channel from the data symbol output from the symbol classification and extraction module, according to the channel data position and length information from the FIC decoder; and output the FIC symbol and the selected channel data from the symbol classification and extraction module to the FFT module;
the FFT module is configured to OFDM-demodulate the received FIC symbol and the selected channel data, and output the demodulated FIC symbol and the selected channel data to the channel demodulation and decoding unit.
The FIC decoding module comprises: a FFT sub-module, a frequency-domain deinterleaving sub-module, a differential quadrature phase shift keying DQPSK demodulation sub-module, a 1/3 convolutional decoding sub-module and a channel information extractor, wherein
the FFT sub-module is configured to FFT process the received FIC symbol, and output the processed FIC signal to the frequency-domain deinterleaving sub-module;
the frequency-domain deinterleaving sub-module is configured to frequency-domain deinterleave the received FIC symbol, and output the processed FIC symbol to the DQPSK demodulation sub-module;
the DQPSK demodulation sub-module is configured to DQPSK demodulate the received FIC symbol, and output the DQPSK demodulated FIC symbol to the 1/3 convolutional decoding sub-module;
the 1/3 convolutional decoding sub-module is configured to 1/3 convolutional decoding the received FIC symbol, and output the decoded FIC symbol to the channel information extractor;
the channel information extractor is configured to extract the channel data position and length information, the channel modulation scheme information and the channel-coding scheme information from the received FIC symbol according to the received channel selection indication; output the channel data position and length information to the channel data selection module; and output the channel modulation scheme information and the channel-coding scheme information to the channel demodulation and decoding unit.
The channel demodulation and decoding unit comprises: the frequency-domain deinterleaving module, a differential demodulator, a time-domain deinterleaving module and a forward error correction scheme FEC decoder, wherein
the frequency-domain deinterleaving module is configured to channel-demodulate the received FIC symbol and the selected channel data; and output the channel-demodulated FIC symbol and selected channel data to the differential demodulator;
the differential demodulator is configured to differential-demodulate the received and selected channel data according to the channel modulation scheme information from the FIC demodulator and the FIC symbol from the frequency-domain deinterleaving module; and output the differential-demodulated selected channel data to the time-domain deinterleaving module;
the time-domain deinterleaving module is configured to channel-decode the received and selected channel data, and output the channel-decoded selected channel data to the FEC decoder;
the FEC decoder is configured to channel-decode the received and selected channel data according to the channel coding scheme information from the FIC decoder; and output the decoded selected channel data.
It can be seen from the above technical solutions that the present invention utilizes the ideal base band model and the synchronization position of the T-MMB system and characteristics of the T-MMB channel to identify the transmission mode of the received signal, and to RF demodulate, OFDM demodulate and channel-demodulate the received signal. Moreover, in the OFDM demodulating process, the control information in the FIC can be obtained, and the data can be demodulated according to the received control information, to thereby implement the terrestrial mobile multimedia broadcasting receiver compatible with DAB, which improves the reliability of the multimedia broadcasting service.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an illustrative diagram of a structure of a T-MMB receiver compatible with a DAB system according to the present invention;
Fig. 2 is a schematic diagram of a T-MMB transmitter compatible with a DAB system;
Fig. 3 is a view of constellation for 8-level phase shift keying (8PSK);
Fig. 4 is a view of constellation for 16-level amplitude and phase shift keying (16APSK);
Fig. 5 is a schematic diagram of a frame structure for a T-MMB compatible with a DAB system;
Fig. 6 is a schematic diagram of a service organization construction for a T-MMB compatible with a DAB system;
Fig. 7 is a schematic diagram of a structure of a new service sub-channel for a T-MMB compatible with a DAB system;
Fig. 8 is a schematic diagram of user application information for a T-MMB compatible with a DAB system;
Fig. 9 is an overall diagram of a structure of a T-MMB receiver compatible with a DAB system according to an embodiment of the present invention;
Fig. 10 is a principal block diagram of mode identification for a T-MMB receiver compatible with a DAB system according to an embodiment of the present invention;
Fig. 11 is a principal block diagram of frame synchronization for a T-MMB receiver compatible with a DAB system according to an embodiment of the present invention;
Fig. 12 is a flowchart of frame synchronization for a T-MMB receiver compatible with a DAB system according to an embodiment of the present invention;
Fig. 13 is a schematic block diagram of timing recovery for a T-MMB receiver compatible with a DAB system according to an embodiment of the present invention;
Fig. 14 is a principal block diagram of carrier recovery for a T-MMB receiver compatible with a DAB system according to an embodiment of the present invention; and

Fig. 15 is a schematic block diagram of FIC demodulation and decoding for a T-MMB compatible with a DAB system according to an embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, the present invention will be further described in detail by referring to the drawings and the embodiments in order to clarify the objects, technical solutions and advantages of the present invention.
The principal idea of the present invention is to implement a T-MMB receiver compatible with a DAB system, by utilizing an ideal base band model, various non-ideal factors such as frame synchronization, carrier synchronization, and timing synchronization, etc. of the T-MMB system, and characteristics of a T-MMB channel.
The T-MMB is a digital multimedia broadcasting method based on a multimedia service extension of the digital audio broadcasting (DAB) system. The T-MMB is incorporated with the latest technologies, in consideration with frequency resources, complexity of receiver, frequency spectrum utilization ratio, and the system performance, etc. It can implement exact compatibility with DAB, low cost design, low power consumption design, perfect frequency availability, support for mobile reception and single frequency network implementation, high frequency spectrum efficiency, multi-service, and high service quality, etc. The T-MMB has the characteristics as follows.

(1) It has an exact compatibility with EUREKA-147 (DAB), DAB-IP and the Korean T-DMB. The T-MMB fully utilizes a technical advantage of the DAB for receiving a signal reliably in a high-speed mobile environment, and functionally extends the transmission of single audio information to various carriers such as data, text, graphics and video, etc.
(2) The disadvantage of low frequency band efficiency for the T-DMB system is overcome.
(3) An advanced channel error correction coding technology, a low density parity check code (LDPC) and a high-efficient and low-complexity DAPSK modulation scheme are adopted.
(4) As compared with other modes such as DVB-H, it has advantages of low complexity, low power consumption, perfect frequency availability, and perfect compatibility, etc.

Fig. 1 is an illustrative diagram of a structure of a T-MMB receiver compatible with a DAB system according to the present invention. As illustrated in Fig. 1, the T-MMB receiver compatible with the DAB system according to the present invention comprises: a RF (Radio Frequency) demodulation unit 101, a synchronization unit 102, an Orthogonal Frequency Division Multiplexing (OFDM) demodulation unit 103 and a channel demodulation and decoding unit 104.
The RF demodulation unit 101 RF-demodulates a RF signal received from outside, and outputs the RF-demodulated signal to the synchronization unit 102 and the OFDM demodulation unit 103.
The synchronization unit 102 receives the signal output from the RF demodulation unit 101; identifies a transmission mode corresponding to the received signal, and outputs the result of the mode identification to the OFDM demodulation unit 103; determines a synchronization position of the received signal according to the result of the mode identification, and outputs the synchronization position to the OFDM demodulation unit 103.
Herein, the synchronization position can include a frame boundary, a symbol boundary and a timing position.
The OFDM demodulation unit 103 extracts a phase reference symbol, a Fast Information Channel (FIC) symbol and a data symbol from the signal obtained from the RF demodulation unit 101, according to the result of the mode identification output from the synchronization unit 102; OFDM-demodulates and decodes the FIC symbol according to the phase reference symbol and a channel selection indication received from outside, to obtain control information in the FIC which is then output to the channel demodulation and decoding unit 104; OFDM-demodulates the data symbol according to the control information in the FIC; and outputs the OFDM-demodulated FIC symbol and data symbol to the channel demodulation and decoding unit 104.
Herein, the channel selection indication received from outside comes from a user for a receiving terminal, and is used for selectively receiving a DAB, DAB-IP, T-DMB or T-MMB signal. The control information includes channel position and length information for selecting channel data, a channel modulation scheme for channel demodulation, and a channel coding scheme for channel decoding.
The channel demodulation and decoding unit 104 channel-demodulates and decodes the received data symbol according to the control information and the FIC symbol from the OFDM demodulation unit 103, and output the channel demodulated and decoded data symbol.
The RF signal received from the above T-MMB receiver compatible with the DAB system includes the DAB/DAB-IP/T-DMB/T-MMB signal from the T-MMB transmitter compatible with the DAB system as illustrated in Fig. 2. The T-MMB transmitter comprises a DAB service path, a DAB-IP service path and a T-DMB service path, which are respectively input interfaces for the DAB, DAB-IP and T-DMB service to be compatible with the DAB service, the DAB-IP service and the T-DMB service.
The T-MMB transmitter in Fig.2 employs a DQPSK (Differential Quadrature Phase Shift Keying)/8DPSK/16DAPSK modulation scheme and a LDPC Coding for channel modulation and channel coding.
Fig. 3 is a view of constellation for 8PSK. As illustrated in Fig. 3, for every OFDM symbol, a 3K-bit vector ${(p_{l, n})}_{n = 0}^{3 K - 1}$
(p_l,n can be referred to Section 14.4.2 of ETSI EN 300 401[1]) needs to be mapped to K 8PSK symbols in the following way: $q_{l, m} = e^{j Φ_{l, m}}, m = 0, 1, 2, \dots, K - 1,$

wherein K is the number of sub-carriers, and Φ_l,m is a phase.
Fig. 4 is a view of constellation for 16APSK. As illustrated in Fig.4, for every OFDM symbol, a 4K-bit vector ${(p_{l, n})}_{n = 0}^{4 K - 1}$
can be mapped to K 16APSK symbols in the following way: $q_{l, m} = A_{l, n} e^{j Φ_{l, m}}, m = 0, 1, 2, \dots, K - 1$

wherein Φ_l,m is illustrated in Table 5, and A_l,m = α^{p l,4 m}
The DAB-compatible system, i.e. the DAB/DAB-IP/T-DMB/T-MMB system, has four transmission modes for selection, as seen from the DAB Standard ETSI EN300 401. With different transmission modes, parameters and schemes for channel modulation and coding vary. In the present invention, the T-MMB receiver compatible with the DAB system needs to employ corresponding parameters and schemes to channel-demodulate and decode the signal, by identifying the transmission mode of the signal.
Fig. 5 is a schematic diagram of a frame structure for a T-MMB compatible with the DAB system. As illustrated in Fig. 5 of the present invention, a signal for each frame among the signals received from the T-MMB receiver compatible with the DAB system is comprised of a null symbol, a phase reference symbol, and several FIC symbols and several data symbols which are determined by different modes.
In the signal received from the receiver, the null symbol is used for frame synchronization of the receiver. The phase reference symbol provides a phase reference for a subsequent differential phase modulation and demodulation on the data. Information on the phase reference symbol can be used for carrier synchronization since it is known to the receiver.
The FIC symbol includes information on a T-MMB service organization construction as shown in Fig. 6, information on a T-MMB new service sub-channel construction as shown in Fig. 7, and information on a T-MMB user application as shown in Fig. 8.
According to the service indication information format in the FIC of the DAB (ETSI EN300 401), service indication information of the T-MMB system is added. A service type description of the T-MMB system is added to the FIG type 0/ extension mode 2 (FIG0/2) of the DAB in order to implement the T-MMB service organization construction as shown in Fig. 6.
Sub-channel information is newly added to the FIG type 0/ extension mode 15 (FIG0/15) of the DAB, and includes a Sub-channel identifier (SubChId), a sub-channel start address (Start Address), a modulation type (ModuType), a protection level (PL) and a sub-channel size (Sub-channel Size), in order to implement the T-MMB new service sub-channel construction as shown in Fig. 7.
User application type information is newly added to the FIG type 0/extension mode 13 (FIG0/13) of the DAB, and a size for capacity units (CUs) of the corresponding T-MMB service in the main service channel (MSC) of the DAB system is adjusted, in order to implement the T-MMB user application information as shown in Fig. 8. The capacity for CUs is calculated as follows: ^nx32 bits, wherein n(=2) represents that the system employs the DQPSK modulation, n(=3) represents that the system employs the 8DPSK modulation, and n(=4) represents that the system employs the 16DAPSK modulation.
The above is the general description of the T-MMB receiver compatible with the DAB system in the present invention. The T-MMB receiver compatible with the DAB system in the present invention will be described in detail in the embodiments of the present invention.
The overall description for the T-MMB receiver compatible with the DAB system according to the invention has been given as above. Hereinafter, a detail description for the T-MMB receiver compatible with the DAB system will be given according to an exemplary embodiment of the invention.
Fig. 9 is an overall diagram of the structure of the T-MMB receiver compatible with the DAB system according to the embodiment of the present invention. As illustrated in Fig. 9, the T-MMB receiver compatible with the DAB system according to the embodiment comprises a RF demodulation unit 901, a synchronization unit 902, an OFDM demodulation unit 903 and a channel demodulation and decoding unit 904.
The RF demodulation unit 901 includes a tuner, an Analog/Digital (A/D) conversion module, a down-frequency conversion module, a low pass filter, a downsample module, a gain control (AGC) module and a free oscillation clock. The above functional modules are used for RF-demodulating the signal from the transmitter.
The synchronization unit 902 includes a mode identification module, a frame synchronization module, a timing recovery module and a carrier recovery module.
The OFDM demodulation unit 903 includes a symbol classification and extraction module, a FIC decoder, a channel data selection module and a Fourier Transform (FFT) module.
The channel demodulation and decoding unit 904 includes a frequency-domain deinterleaving module, a differential demodulator, a time-domain deinterleaving module and a forward error correction scheme (FEC) decoder.
The T-MMB receiver compatible with the DAB system in the present embodiment will be described in conjunction with the detail modules in the respective functional units.
In the RF demodulation unit 901, the tuner which is as an analog front end amplifies the received RF signal to perform frequency band selection under control of the AGC module. Since a voltage for AGC for controlling a high-frequency end is provided by an intermediate frequency (IF) part, it transforms the selected signal from the RF frequency band to a fixed IF, and outputs the transformed signal to the A/D conversion unit.
Herein, the frequency band selection can be implemented by changing a frequency division coefficient of a Phase Locked Logic (PLL). The IF signal is filtered by a filter with a 1.536MHz bandwidth. The IF signal is transformed to a lower IF (2.048MHz) by using a local oscillation in the IF unit. Herein, the transformed signal becomes a band-pass signal close to the base band.
The AGC module detects a power of the signal output from the downsample module according to the symbol indication signal from the OFDM demodulation unit 903, generates an AGC control signal, and output it to the tuner, to thereby ensure the A/D converted signal to have an optimal dynamic range when field strength for the received signal is changed continuously in the mobile channel reception environment.
The A/D conversion unit A/D-converts the received signal according to a clock signal supplied from the free oscillation clock, and outputs the converted signal to the down-frequency conversion module. Since the analog signal is converted to the digital lower IF signal via the tuner by using a quad-sample Ts (8.192MHz), a sampling clock of the A/D conversion module is a free-oscillation without a phase lock.
The down-Frequency conversion module performs down-frequency conversion by using a multiplier to obtain a digital base band I/Q signal; passes the obtained I/Q signal through a low pass filter to remove out-of-band interference, and performs quad-sampling by using the downsampler to obtain data of 2.048MHz from data of 8.192MHz, and output them to the AGC module, the mode identification module and the frame synchronization module in the synchronization unit 902, and the symbol classification and extraction module in the OFDM demodulation unit 903.
In the synchronization unit 902, the mode identification module judges characteristics of the signal from the RF demodulation unit 901, such as a frame length, a protected gap length, a null symbol length, etc., determines a transmission mode corresponding to the received signal, and outputs the result of the mode identification to the frame synchronization module and the symbol classification and extraction module in the OFDM demodulation unit 903. Fig. 10 is a principal block diagram of mode identification for the T-MMB receiver compatible with the DAB system according to the embodiment of the present invention. As illustrated in Fig. 10, the mode identification module comprises a frame length detector, a protected gap length detector, a null symbol length detector and a mode decider. The mode identification module detects the frame length, the protected gap length and the null symbol length of the signal, and performs mode judgment based on the detected result of the frame length, the protected gap length and the null symbol length by using the mode decider. In the implementation, only one or more of the frame length detection, the protected gap length detection and the null symbol length detection can be done.
The frame synchronization module determines a frame start position of the received signal according to the result of the mode identification supplied from the mode identification module; performs symbol synchronization and carrier synchronization according to the obtained start position, and determines a synchronization position, i.e. a frame boundary and a symbol boundary; and outputs the obtained frame boundary and the symbol boundary to the symbol classification and extraction module in the OFDM demodulation unit 903.
The T-MMB transmission frame is comprised of a null symbol, a phase reference symbol and a number of OFDM symbols. The frame synchronization detection refers to judge the position of the null symbol precisely, so as to determine the start position of the frame.
Since energy of the null symbol is zero, it is simple and effective to perform frame synchronization detection by using the energy distribution of the received signal. One of the most intuitionistic methods is to detect a break edge of the received signal, to thereby determine start and end positions of the null symbol. In this method, however, it causes a large error by a great fuzzy due to channel interference. A more reliable energy-ratio algorithm can be used as follows: $τ = \underset{n}{MAX} {\frac{E [r_{n + W} r_{n + 2 W}]}{E [r_{n} r_{n + W}]}},$

wherein r is a received signal, τ is an end position of the null symbol, E[a,b] represents a total energy in an interval [a,b], n represents a sequence number of the received signal, and W represents the length of some interval.
If energy ratio calculation is performed once for each code element in each frame and then a maximum value is determined, it is computationally complicate and is not necessary, since the maximum offset of the synchronization position is determined by the maximum delay of the channel. After the synchronization position is detected in the received data for the first frame, only the energy ratios of the m code-elements previously to and next to the same position for the subsequent respective frames needs to be calculated, in order to obtain the maximum value for determining the synchronization position of the respective frames, wherein the value m is designed according to the maximum delay of the channel.
Fig. 11 is a principal block diagram of frame synchronization for the T-MMB receiver compatible with the DAB system according to the embodiment of the present invention. As illustrated in Fig. 11, the frame synchronization module comprises an energy-in-window statistics sub-module, a divider, a delayer and a peak detection sub-module. The energy-in-window statistics sub-module makes statistics on signal energy in a preset window, and outputs the statistics result to the divider. The divider calculates a quotient of the statistics results in the two adjacent windows under control of the delayer, and outputs it to the peak detection sub-module. The peak detection sub-module compares the received quotient with the preset threshold, and outputs the frame boundary and the symbol boundary according to the comparison result.
Fig. 12 is a flowchart of frame synchronization for the T-MMB receiver compatible with the DAB system according to the embodiment of the present invention. As illustrated in Fig.12, since the first detected synchronization position is possibly incorrect due to the channel interference, the capture of the exact frame synchronization position is determined upon detection of the synchronization position for several successive frames. It then enters a tracking phase. As above, it is only necessary to perform the tracking calculation in 2m+1 windows. If the maximum energy ratio for several successive frames is less than a threshold, it's considered to be out-of-synchronization, and it re-enters the synchronization-capturing phase.
According to the timing recovery principle shown in Fig. 13, the timing recovery module locates a timing position for a fine synchronization by performing an IFFT process on the frequency-offset corrected phase reference symbol from the carrier recovery module by the IFFT sub-module, performing a modular operation in the time domain by the Modulo sub-module, and finding the local maximum position with the preset window by the local maximum position sub-module; and then outputs the obtained timing position to the symbol classification and extraction module in the OFDM demodulation unit 903. With respect to the frame boundary and the symbol boundary output from the frame synchronization module, the timing position output from the timing recovery module is used for the fine synchronization.
Both the frame synchronization module and the timing recovery module are used for locating the frame boundary and the symbol boundary of the received signal, so that the subsequent symbol classification and extraction module can distinguish among the null symbol, the phase reference symbol, the FIC symbol and the data symbol.
The carrier recovery module obtains a fraction frequency offset estimation by using related characteristics of protected gap utilization according to the phase reference symbol from the symbol classification and extraction module in the OFDM demodulation unit 903; fraction-frequency-offset corrects the phase reference symbol, performs an integer frequency offset estimation, and add the fraction frequency offset to the integer frequency offset to obtain the result of the frequency offset estimation. If the FIC symbol and the data symbol from the symbol classification and extraction module in the OFDM demodulation unit 903 is received, it's assumed that there is no integer frequency offset and only the fraction frequency offset estimation is to be performed. The fraction frequency offset estimation is obtained as the result of frequency offset estimation by using the related characteristics of protected gap utilization. The carrier recovery module obtains a phase signal by performing processes on the result of frequency offset estimation by the low pass filter and the digital control oscillator, and outputs it to the down-frequency conversion module in the RF demodulation unit 901 to control it. The carrier recovery module corrects the phase reference symbol according to the result of the frequency offset estimation, and outputs the corrected phase reference symbol to the timing recovery module.
Fig. 14 is a principal block diagram of carrier recovery for the T-MMB receiver compatible with the DAB system according to the embodiment of the present invention. As illustrated in Fig. 14, the carrier recovery module comprises a fraction frequency offset estimator 1, a fraction frequency offset estimator 2, a fraction frequency offset estimator 3, a fraction frequency offset corrector, an integer frequency offset corrector, an integer frequency offset estimator, an adder, a selector, a low pass filter sub-module and a digital control oscillator. The fraction frequency offset estimator 1 and the fraction frequency offset estimator 2 fraction-frequency-offset estimate the received data symbol and the FIC symbol respectively, and output the fraction frequency offset to the selector as the frequency offset estimation result. The fraction frequency offset estimator 3 fraction-frequency-offset estimates the received phase reference symbol, and outputs the fraction frequency offset to the fraction frequency offset corrector. The fraction frequency offset corrector fraction-frequency-offset corrects the received phase reference symbol according to the fraction frequency offset output from the fraction frequency offset estimator 3, and outputs the fraction-frequency-offset corrected phase reference symbol to the integer frequency offset estimator and the adder. The integer frequency offset estimator integer-frequency-offset estimates the received and fraction-frequency-offset corrected phase reference symbol, and outputs the integer frequency offset to the adder and the integer frequency offset corrector. The adder calculates a sum of the fraction frequency offset estimation from the fraction frequency offset estimator 3 and the integer frequency offset estimation from the integer frequency offset estimator, and outputs the sum to the selector as the frequency offset estimation result. The selector selects one from the received frequency offset estimation results and outputs it to the AGC module in the RF demodulation unit 901 via the low pass filter sub-module and the digital control oscillator. Meanwhile, the integer frequency offset corrector integer-frequency-offset corrects the fraction-frequency-offset corrected phase reference symbol according to the integer frequency offset, and outputs the integer-frequency-offset corrected phase reference symbol to the timing recovery module.
In the OFDM demodulation unit 903, the symbol classification and extraction module extracts the phase reference symbol, the FIC symbol and the data symbol from the signal from the downsample module of the RF demodulation unit 901 according to the timing position from the timing recovery module in the synchronization unit 902, the frame boundary and the symbol boundary from the frame synchronization module in the synchronization unit 902, and the mode identification result from the mode identification module in the synchronization unit 902; outputs the extracted phase reference symbol, FIC symbol and data symbol to the carrier recovery module in the synchronization unit 902; outputs the extracted phase reference symbol and FIC symbol to the FIC decoder; outputs the extracted FIC symbol and data symbol to the channel selection module; and notifies a type for the currently extracted symbol to the AGC module in the RF demodulation unit 901 by using the symbol indication signal.
The FIC decoder demodulates and decodes the received FIC symbol according to the received phase reference symbol and channel selection indication from the user at the receiving end, to obtain channel information of the selected channel, i.e. a control information including channel data position and length information, channel modulation scheme information and channel-coding scheme information; outputs the channel data position and length information to the channel data selection module; outputs the channel modulation scheme information to the differential demodulator in the channel demodulation and decoding unit 904; and outputs the channel-coding scheme information to the FEC decoder in the channel demodulation and decoding unit 904. Fig. 15 is a principal block diagram of FIC demodulation and decoding for the T-MMB receiver compatible with the DAB system according to the embodiment of the present invention. As illustrated in Fig. 15, the FIC decoder employs the fixed DQPSK demodulation and 1/3 convolutional decoding when recovering the FIC information, since the fixed DQPSK modulation and 1/3 convolutional coding FIC encoder are employed for the FIC symbol to recover the FIC symbol in the transmitter. The channel information extractor can obtain the service type of the selected channel according to the channel selection indication from the user at the receiving end and the user application information indication in the FIC symbol as illustrated in Fig. 8. The channel information extractor can obtain the channel data position and length information for channel data selection according to the channel selection indication from the user at the receiving end and the new service sub-channel construction indication in the FIC symbol as illustrated in Fig. 7. The channel information extractor can obtain the modulation scheme information for data differential demodulation of the selected channel according to the channel selection indication from the user at the receiving end and the new service sub-channel construction indication in the FIC symbol as illustrated in Fig. 7. The channel information extractor can obtain the coding scheme information for data FEC decoding of the selected channel according to the channel selection indication from the user at the receiving end and the new service sub-channel construction indication in the FIC symbol as illustrated in Fig. 7.
The channel data selection module selects data in a corresponding channel (i.e. any of DAB/DAB-IP/T-DMB/T-MMB signals) from the data symbol output from the symbol classification and extraction module, according to the channel data position and length information from the FIC decoder; and outputs the FIC symbol and the selected channel data from the symbol classification and extraction module to the FFT module.
Herein, the FIC symbol from the symbol classification and extraction module isn't OFDM demodulated and is used for differential-demodulating the selected channel data in the subsequent step. In this embodiment, it is possible that the symbol classification and extraction module does not output the FIC symbol to the channel data selection module, but the FIC decoder outputs the OFDM-demodulated FIC symbol directly to the differential demodulator in the channel demodulation and decoding unit 904.
The FFT module OFDM-demodulates the received FIC symbol and the selected channel data, and outputs the demodulated FIC symbol and the selected channel data to the frequency-domain deinterleaving module in the channel demodulation and decoding unit 904.
In the channel demodulation and decoding unit 904, the frequency-domain deinterleaving module channel-demodulates the received FIC symbol and the selected channel data; and outputs the demodulated FIC symbol and the selected channel data to the differential demodulator.
The differential demodulator determines the modulation scheme corresponding to the selected data according to the channel modulation scheme information from the FIC decoder in the OFDM demodulation unit 903; differential-demodulates the received and selected channel data according to the modulation scheme corresponding to the selected channel data and the FIC symbol from the frequency-domain deinterleaving module; and outputs the differential-demodulated selected channel data to the time-domain deinterleaving module. In this embodiment, the differential demodulator can differential-demodulates the DQPSK, 8DPSK and 16DAPSK modulated signals.
The time-domain deinterleaving module channel-decodes the received and selected channel data, and outputs the channel-decoded selected channel data to the FEC decoder.
The FEC decoder determines the coding scheme corresponding to the selected channel data according to the channel coding scheme information from the FIC decoder in the OFDM demodulation unit 903; FEC error-correction decodes i.e. channel-decodes the received and selected channel data according to the coding scheme corresponding to the selected channel data; and outputs the decoded selected channel data to the user at the receiving end. In this embodiment, the FEC decoder can decode the convolution-coded, LDPC coded data.
The above is only the preferred embodiments of the present invention and the present invention is not limited to the above embodiments. Therefore, any modifications, substitutions and improvements to the present invention are possible without departing from the spirit and scope of the present invention.

Claims

A Terrestrial Mobile Multimedia Broadcasting T-MMB receiver compatible with Digital Audio Broadcasting DAB, comprising a Radio Frequency RF demodulation unit, a synchronization unit, an Orthogonal Frequency Division Multiplexing OFDM demodulation unit and a channel demodulation and decoding unit, wherein the RF demodulation unit is configured to RF-demodulating a RF signal received from outside, and output the RF-demodulated signal to the synchronization unit and the OFDM demodulation unit;
the synchronization unit is configured to identify a transmission mode corresponding to the signal from the RF demodulation unit, and output a result of mode identification to the OFDM demodulation unit, and determine a synchronization position of the received signal according to the result of the mode identification and output the synchronization position to the OFDM demodulation unit;
the OFDM demodulation unit is configured to extract a phase reference symbol, a Fast Information Channel FIC symbol and a data symbol from the signal from the RF demodulation unit according to the result of the mode identification and the synchronization position output from the synchronization unit; OFDM-demodulate and decode the FIC symbol sequentially according to the phase reference symbol and a channel selection indication received from outside, to obtain control information in the FIC which is output to the channel demodulation and decoding unit; OFDM-demodulate the data symbol according to the control information in the FIC; and output the OFDM-demodulated FIC symbol and data symbol to the channel demodulation and decoding unit;
the channel demodulation and decoding unit is configured to channel-demodulating and decoding the received data symbol according to the control information and the FIC symbol from the OFDM demodulation unit, and output the channel demodulated and decoded data symbol.
The receiver according to Claim 1, wherein the OFDM demodulation unit is further configured to output the extracted phase reference symbol and/or FIC symbol and/or data symbol to the synchronization unit; and notify the RF demodulation unit of a type of the currently extracted symbol by using a symbol indication signal;
the synchronization unit is further configured to perform carrier recovery according to the received phase reference symbol and/or FIC symbol and/or data symbol, and output the carrier-recovered phase signal to the RF demodulation unit;
the RF demodulation unit is further configured to RF-demodulate the RF signal received from outside according to the received symbol indication signal and the phase signal.
The receiver according to Claim 2, wherein the RF demodulation unit comprises: a tuner, an Analog/Digital (A/D) conversion module, a down-frequency conversion module, a low pass filter, a downsample module, a gain control AGC module and a free oscillation clock, wherein
the tuner is configured to amplify the received RF signal according to the received AGC control signal to perform selection of a frequency band; transform the selected signal from a RF frequency band to a fixed intermediate frequency; and output the transformed RF signal to the A/D conversion unit;
the A/D conversion unit is configured to A/D convert the received signal according to a clock signal supplied from the free oscillation clock, and output the converted signal to the down-frequency conversion module;
the AGC module is configured to detect a power of a signal output from the downsample module according to symbol indication signal from the OFDM demodulation unit, generate a AGC control signal, and output it to the tuner;
the down-frequency conversion module is configured to down-frequency convert the received signal according to a phase signal supplied from the synchronization unit, and output it to the AGC module, the synchronization unit and the OFDM demodulation unit via the low pass filter and the downsample module.
The receiver according to Claim 3, wherein the synchronization unit comprises a mode identification module, a frame synchronization module, a timing recovery module and a carrier recovery module, wherein
the mode identification module is configured to judge a frame length and/or a protected gap length and/or a null symbol length of a signal from the downsample module, determine a transmission mode corresponding to the received signal, and output a result of mode identification to the frame synchronization module and the OFDM demodulation unit;
the frame synchronization module is configured to determine a frame start position of the received signal according to the result of the mode identification supplied from the mode identification module; perform symbol synchronization and carrier synchronization according to the obtained start position, and determine a synchronization position, i.e. a frame boundary and a symbol boundary; and output the obtained frame boundary and the symbol boundary to the OFDM demodulation unit; the timing recovery module is configured to obtain a timing position according to a frequency-offset corrected phase reference symbol from the carrier recovery module, and output it to the OFDM demodulation unit;
the carrier recovery module is configured to obtain a fraction frequency offset estimation and an integer frequency offset estimation according to the phase reference symbol from the OFDM demodulation unit, add the fraction frequency offset to the integer frequency offset to obtain a result of frequency offset estimation, and fraction-frequency-offset correct the phase reference symbol; perform fraction-frequency-offset estimation according to the FIC symbol and/or the data symbol from the OFDM demodulation unit to obtain a fraction frequency offset estimation as the result of the frequency offset estimation; output the result of the frequency offset estimation to the down-frequency conversion module; correct the phase reference symbol according to the result of the frequency offset estimation, and output the corrected phase reference symbol to the timing recovery module.
The receiver according to Claim 4, wherein the mode identification module comprises a frame length detector, and/or a protected gap length detector, and/or a null symbol length detector, and a mode decider;
the frame length detector is configured to detect a frame length of a signal, and output the detected result to the mode decider;
the protected gap length detector is configured to detect a protected gap length of a signal, and output the detected result to the mode decider;
the null symbol length detector is configured to detect a null symbol length of a signal, and output the detected result to the mode decider;
the mode decider is configured to perform mode decision according to the detected result from the frame length detector, and/or the protected gap length detector, and/or the null symbol length detector, and output the result of the mode identification.
The receiver according to Claim 4, wherein the frame synchronization module comprises: an energy-in-window statistics sub-module, a divider, a delayer and a peak detection sub-module, wherein
the energy-in-window statistics sub-module is configured to make statistics on a signal energy in a preset window and output a statistics result to the divider;
the divider is configured to calculate a quotient of the statistics results in two adjacent windows under control of the delayer, and output the quotient to the peak detection sub-module;
the peak detection sub-module is configured to compare the received quotient with the preset threshold, and output the frame boundary and the symbol boundary according to the comparison result.
The receiver according to Claim 4, wherein the timing recovery module comprises an IFFT sub-module, a Modulo sub-module and a local maximum position sub-module, wherein
the IFFT sub-module is configured to IFFT process the corrected phase reference symbol from the carrier recovery module, and output it to the modulo sub-module;
the modulo sub-module is configured to perform a modular operation on the received phase reference symbol in the time-domain, and output a Modulo result to the local maximum position sub-module;
the local maximum position sub-module is configured to locate a timing position for fine synchronization by finding a local maximum position in a preset window, and output the obtained timing position to the OFDM demodulation unit.
The receiver according to Claim 4, wherein the carrier recovery module comprises a first fraction frequency offset estimator, a second fraction frequency offset estimator, a third fraction frequency offset estimator, a fraction frequency offset corrector, an integer frequency offset corrector, an integer frequency offset estimator, an adder, a selector, a low pass filter sub-module and a digital control oscillator, wherein
the first fraction frequency offset estimator is configured to fraction-frequency-offset estimate the received data symbol, and output a fraction frequency offset to the selector as the frequency offset estimation result;
the second fraction frequency offset estimator is configured to fraction-frequency-offset estimate the received FIC symbol, and output a fraction frequency offset to the selector as the frequency offset estimation result;
the third fraction frequency offset estimator is configured to fraction-frequency-offset estimate the received phase reference symbol, and output a fraction frequency offset to the fraction frequency offset corrector;
the fraction frequency offset corrector is configured to fraction-frequency-offset correct the received phase reference symbol according to the fraction frequency offset output from the third fraction frequency offset estimator; and output the fraction-frequency-offset corrected phase reference symbol to the integer frequency offset estimator and the adder;
the integer frequency offset estimator is configured to integer-frequency-offset estimate the received and fraction-frequency-offset corrected phase reference symbol, and output the integer frequency offset to the adder and the integer frequency offset corrector;
the integer frequency offset corrector is configured to Integer-frequency-offset correct the received and fraction-frequency-offset corrected phase reference symbol according to the integer frequency offset output from the integer frequency offset estimator; and output the integer-frequency-offset corrected phase reference symbol to the selector and the timing recovery module;
the adder is configured to calculate a sum of the fraction frequency offset estimation from the third fraction frequency offset estimator and the integer frequency offset estimation from the integer frequency offset estimator, and output the sum to the selector as the frequency offset estimation result;
the selector is configured to select one from the received frequency offset estimation results to output to the low pass filter sub-module;
the low pass filter sub-module is configured to low pass filter the received frequency offset estimation result, and output it to the AGC module via the digital control oscillator.
The receiver according to Claim 4, wherein the OFDM demodulation unit comprises a symbol classification and extraction module, a FIC decoding module, a channel data selection module and a Fourier Transform FFT module, wherein
the symbol classification and extraction module is configured to extract the phase reference symbol, the FIC symbol and the data symbol from the signal from the downsample module according to the timing position from the timing recovery module, the frame boundary and the symbol boundary from the frame synchronization module, and the mode identification result from the mode identification module; output the extracted phase reference symbol, FIC symbol and data symbol to the carrier recovery module; output the extracted phase reference symbol and FIC symbol to the FIC decoder; output the extracted FIC symbol and data symbol to the channel data selection module; and output the type for the currently extracted symbol to the AGC module by using the symbol indication signal;
the FIC decoding module is configured to demodulate and decode the received FIC symbol according to the received phase reference symbol and channel selection indication to obtain channel data position and length information, channel modulation scheme information and channel-coding scheme information; output the channel data position and length information to the channel data selection module; and output the channel modulation scheme information and the channel-coding scheme information to the channel demodulation and decoding unit;
the channel data selection module is configured to select data in a corresponding channel from the data symbol output from the symbol classification and extraction module, according to the channel data position and length information from the FIC decoder; and output the FIC symbol and the selected channel data from the symbol classification and extraction module to the FFT module;
the FFT module is configured to OFDM demodulate the received FIC symbol and the selected channel data, and output the demodulated FIC symbol and the selected channel data to the channel demodulation and decoding unit.
The receiver according to Claim 9, wherein the FIC decoding module comprises a FFT sub-module, a frequency-domain deinterleaving sub-module, a differential quadrature phase shift keying DQPSK demodulation sub-module, a 1/3 convolutional decoding sub-module and a channel information extractor, wherein
the FFT sub-module is configured to FFT process the received FIC symbol, and output the processed FIC signal to the frequency-domain deinterleaving sub-module; the frequency-domain deinterleaving sub-module is configured to frequency-domain deinterleave the received FIC symbol, and output the processed FIC symbol to the DQPSK demodulation sub-module;
the DQPSK demodulation sub-module is configured to DQPSK demodulate the received FIC symbol, and output the DQPSK demodulated FIC symbol to the 1/3 convolutional decoding sub-module;
the 1/3 convolutional decoding sub-module is configured to 1/3 convolutional decoding the received FIC symbol, and output the decoded FIC symbol to the channel information extractor;
the channel information extractor is configured to extract the channel data position and length information, the channel modulation scheme information and the channel coding scheme information from the received FIC symbol according to the received channel selection indication; output the channel data position and length information to the channel data selection module; and output the channel modulation scheme information and the channel coding scheme information to the channel demodulation and decoding unit.
The receiver according to Claim 9, wherein the channel demodulation and decoding unit comprises a frequency-domain deinterleaving module, a differential demodulator, a time-domain deinterleaving module and a forward error correction scheme FEC decoder, wherein
the frequency-domain deinterleaving module is configured to channel-demodulate the received FIC symbol and the selected channel data; and output the channel-demodulated FIC symbol and the selected channel data to the differential demodulator; the differential demodulator is configured to differential-demodulate the received and selected channel data according to the channel modulation scheme information from the FIC demodulator and the FIC symbol from the frequency-domain deinterleaving module; and output the differential-demodulated selected channel data to the time-domain deinterleaving module;
the time-domain deinterleaving module is configured to channel-decode the received and selected channel data, and output the channel-decoded selected channel data to the FEC decoder;
the FEC decoder is configured to channel-decode the received and selected channel data according to the channel coding scheme information from the FIC decoder; and output the decoded selected channel data.