HK1106903A

HK1106903A - Terrestrial mobile multimedia broadcasting receiver for general digital audio broadcasting system

Info

Publication number: HK1106903A
Application number: HK07112426.2A
Authority: HK
Inventors: 鲍东山; 王加庆; 朱浩; 刘飞; 程琦
Original assignee: 北京新岸线移动多媒体技术有限公司
Priority date: 2006-03-30
Filing date: 2007-11-14
Publication date: 2008-03-20

Description

Terrestrial mobile multimedia broadcasting receiver compatible with digital audio broadcasting

Technical Field

The present invention relates to Digital information transmission technology, and more particularly, to a Digital Audio Broadcasting (DAB) compatible Terrestrial Mobile multimedia broadcasting (T-MMB) receiver.

Background

Digital Multimedia Broadcasting refers to a Multimedia Broadcasting mode for Handheld terminals, and currently, Digital Multimedia Broadcasting standards which are much concerned in the industry are the european standard Digital video Broadcasting Handheld (DVB-H) specification and the korean standard Digital Multimedia Broadcasting (T-DMB) specification.

T-DMB was developed based on digital Audio broadcasting DAB (digital Audio broadcasting). DAB digital broadcasting was developed by a consortium of 12 members, known as EUREKA-147, and the system was originally named DAB and has been used as a standard for distinguishing real DAB broadcasting from other digital audio broadcasting. In 1994, ulika (Eureka) -147 was selected by the international organization for standardization (ISO) as the international standard for digital audio broadcasting. Today, most of the world is testing either digital broadcasting that already implements this standard. Europe Eury-147 DAB standard: in 9 months 1988, the euro has first conducted experiments on eureka-147 DAB at the world radio administration, the eureka-147 DAB system was standardized in 1995, which is a typical DAB system, and has been developed to a considerable extent in countries and regions in the world, such as canada, singapore, australia, and the like, in addition to europe. Compared with the traditional AM/FM broadcasting system, DAB has the advantages of spectrum resource saving, low transmitting power, large information amount, excellent tone quality and the like, and is the third generation broadcasting following the traditional AM and FM broadcasting. The digital broadcast has the advantages of noise resistance, interference resistance, wave propagation fading resistance, suitability for high-speed mobile reception and the like, provides CD-level stereo sound quality, and has almost zero signal distortion.

T-DMB is a terrestrial digital multimedia broadcasting system introduced in korea, and is still an international standard in europe in a strict sense. The standard is based on the Eureka-147 DAB system developed by European manufacturers, and some modifications are made to broadcast digital television programs over the air to handheld devices such as mobile phones, Personal Digital Assistants (PDAs) and portable televisions. T-DMB has already come into the commercial stage in korea. Korea has issued a new license to T-DMB broadcasting operators. Meanwhile, the DVB-H mobile digital tv broadcasting system developed in europe has just started to perform experimental work.

The T-DMB fully utilizes the technical advantage that DAB can reliably receive signals in a high-speed mobile environment, and functionally expands single audio information to various carriers such as data, characters, graphics, videos and the like. The T-DMB performs compression, encoding, modulation, transmission, and other processing on digitized audio and video signals and various data service signals in a digital state, can realize high-quality transmission, has multimedia characteristics, and provides data information transmission with large capacity, high efficiency, and strong reliability. From DAB to T-DMB, which means the transition from digital audio broadcasting to digital multimedia broadcasting, any digital information can be delivered by a digital platform system, which can provide users with comprehensive audiovisual information services including audio and video and entertainment enjoyment.

DVB-H is a transmission standard established by the european DVB organization for providing multimedia services to portable/handheld terminals via terrestrial digital broadcast networks after the introduction of the series of standards for digital television transmission.

DVB-H is a standard that builds on both the data broadcast (DVB) and DVB-transmission (T) standards and is considered an extended application of the DVB-T standard, although it is a transmission standard, in fact focuses on protocol implementation. The front end of the system consists of a DVB-H packaging machine and a DVB-H modulator, wherein the DVB-H packaging machine is responsible for packaging Internet Protocol (IP) data into a second generation of moving picture experts group (MPEG-2) system transmission stream, and the DVB-H modulator is responsible for channel coding and modulation; the system terminal is composed of a DVB-H demodulator and a DVB-H terminal, wherein the DVB-H demodulator is responsible for channel demodulation, decoding and decoding, and the DVB-H terminal is responsible for displaying and processing related services.

The DVB-H keeps part of compatibility with a DVB-T receiving circuit, and meanwhile, in order to meet the receiving characteristics of a handheld device, such as low power consumption, high mobility, uninterrupted service of a common platform and network switching and the like, normal watching on an indoor vehicle, an outdoor vehicle, a walking vehicle or a running vehicle is ensured, and a plurality of technical improvements are made. In order to prolong the service time of the battery, the terminal periodically turns off a part of receiving circuits so as to save power consumption; in order to meet the requirement of portability, the antenna of the DVB terminal is smaller and more flexible to move; the transmission system can ensure that the DVB-H service can be successfully received under various moving speeds; the system has strong anti-interference capability and can provide enough flexibility to meet different transmission bandwidths and channel bandwidth applications and the like.

The background of the application of digital multimedia broadcasting determines that the success or failure of a transmission standard mainly depends on: power saving capability and consumption, cost, mobile reception performance, single frequency network performance, multi-service and multi-service selection, high spectral efficiency and high capacity support, user perception.

And the two standards of T-DMB and DVB-H have different levels of defects: T-DMB having a low spectrum utilization rate does not provide sufficient information throughput to satisfy high quality service T-DMB such as mobile tv and does not provide sufficient power saving measures for the receiver; since DVB-H inherits DVB-T (fixed reception system), the space for optimization for mobile environment on this basis is very limited, DVB-H fails to provide a receiver with sufficient power saving mechanism and sacrifices some other performance indicators, such as increasing the switching time to 5 seconds, and in addition, the available operating frequency points are less.

Therefore, the reliability of the existing multimedia broadcasting service is not high.

Disclosure of Invention

In view of the above, it is a primary object of the present invention to provide a DAB-compatible terrestrial mobile multimedia broadcasting receiver, which can improve the reliability of a multimedia broadcasting service.

In accordance with one of the above-mentioned primary objects, the present invention provides a DAB-compatible terrestrial mobile multimedia broadcasting receiver, comprising: a radio frequency demodulation unit, a synchronization unit, an Orthogonal Frequency Division Multiplexing (OFDM) demodulation unit and a channel demodulation decoding unit, wherein,

the radio frequency demodulation unit is used for carrying out radio frequency demodulation on a radio frequency signal received from the outside and outputting the signal after the radio frequency demodulation to the synchronization unit and the OFDM demodulation unit;

the synchronization unit is used for identifying a transmission mode corresponding to the signal from the radio frequency demodulation unit, outputting a mode identification result to the OFDM demodulation unit, determining a synchronization position of the received signal according to the mode identification result and outputting the synchronization position to the OFDM demodulation unit;

the OFDM demodulation unit is used for extracting a phase reference symbol, a Fast Information Channel (FIC) symbol and a data symbol from a signal from the radio frequency demodulation unit according to the mode identification result and the synchronization position output by the synchronization unit; according to the phase reference symbol and a channel selection indication received from the outside, sequentially carrying out OFDM demodulation and decoding on the FIC symbol to obtain control information in the FIC, and outputting the control information in the FIC to a channel demodulation decoding unit; performing OFDM demodulation on the data symbols according to the control information in the FIC; outputting the FIC symbol and the data symbol after OFDM demodulation to a channel demodulation decoding unit;

the channel demodulation decoding unit is configured to perform channel demodulation decoding on the received data symbol by using 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; informing the radio frequency demodulation unit of the currently extracted symbol type through 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 a phase signal obtained by carrier recovery to the radio frequency demodulation unit;

the radio frequency demodulation unit is further configured to perform radio frequency demodulation on a radio frequency signal received from the outside by using the received symbol indication signal and the phase signal.

The radio frequency demodulation unit includes: a tuner, an analog/digital a/D conversion module, a down conversion module, a low pass filter, a down sampling module, a gain control AGC module, and a free running clock, wherein,

the tuner is used for amplifying the received radio frequency signal according to the received AGC control signal to complete frequency band selection; converting the selected signal from the radio frequency band to a fixed intermediate frequency; outputting the converted radio frequency signal to the A/D conversion unit;

the A/D conversion unit is used for carrying out A/D conversion on the received signal according to a clock signal provided by a free oscillation clock and outputting the signal to the down-conversion module;

the AGC module detects the signal power output by the down-sampling module according to the symbol indication signal from the OFDM demodulation unit, generates an AGC control signal and outputs the AGC control signal to the tuner;

the down-conversion module is configured to perform down-conversion processing on the received signal according to the phase signal provided by the synchronization unit, and output the down-converted signal to the AGC module, the synchronization unit, and the OFDM demodulation unit through the low-pass filter and the down-sampling module.

The synchronization unit includes: a pattern recognition module, a frame synchronization module, a timing recovery module and a carrier recovery module, wherein,

the mode identification module is used for judging the frame length, and/or the length of a guard interval, and/or the length of a null symbol of the signal from the down-sampling module, determining a transmission mode corresponding to the received signal, and outputting a mode identification result to the frame synchronization module and the OFDM demodulation unit;

the frame synchronization module is used for determining the frame starting position of the received signal according to the pattern recognition result provided by the pattern recognition module; carrying out symbol synchronization and carrier synchronization according to the obtained initial position, and determining a synchronization position, namely a frame boundary and a symbol boundary; outputting the obtained frame limit and symbol limit to the OFDM demodulation unit;

the timing recovery module is configured to obtain a timing position by using the phase reference symbol from the carrier recovery module after the frequency offset correction, and output the timing position to the OFDM demodulation unit;

the carrier recovery module is used for obtaining estimation of fractional frequency offset and integer frequency offset estimation according to the phase reference symbol from the OFDM demodulation unit, adding the fractional frequency offset and the integer frequency offset to obtain a frequency offset estimation result, and correcting the fractional frequency offset of the phase reference symbol; estimating fractional frequency offset according to the FIC symbol and/or the data symbol from the OFDM demodulation unit to obtain estimation of the fractional frequency offset as a frequency offset estimation result; outputting the frequency offset estimation result to the down-conversion module; and correcting the phase reference symbol according to the frequency offset estimation result, and outputting the corrected phase reference symbol to the timing recovery module.

The pattern recognition module includes: a frame length detector, and/or a guard interval length detector, and/or a null symbol length detector, and a mode decision device;

the frame length detector is used for detecting the frame length of the signal and outputting the detection result to the mode decision device;

the guard interval length detector is used for detecting the guard interval length of the signal and outputting the detection result to the mode decision device;

the null symbol length detector is used for detecting the null symbol length of the signal and outputting the detection result to the mode decision device;

and the mode decision device is used for carrying out mode decision according to the detection results from the frame length detector, the guard interval length detector and the null symbol length detector and outputting the obtained mode identification result.

The frame synchronization module includes: an intra-window energy statistics submodule, a divider, a delayer and a peak detection submodule, wherein,

the window internal energy counting submodule is used for counting the signal energy in a preset window and outputting a counting result to the divider;

the divider is used for calculating the quotient of the statistical results in the two adjacent windows under the control of the delayer and outputting the quotient to the peak detection submodule;

and the peak detection submodule is used for comparing the received quotient with a preset threshold value and outputting a frame limit and a symbol limit according to a comparison result.

The timing recovery module includes: an IFFT sub-module, a modulo sub-module, and a local maximum position sub-module, wherein,

the IFFT sub-module is configured to perform IFFT processing on the corrected phase reference symbol from the carrier recovery module, and output the processed phase reference symbol to the modulo sub-module;

the module-solving submodule is used for solving the module of the received phase reference symbol in the time domain and outputting a module-solving result to the local maximum position submodule;

and the local maximum position submodule is used for finding out the position of the local maximum to position the timing position of fine synchronization by using a preset window and outputting the acquired timing position to the OFDM demodulation unit.

The carrier recovery module comprises: a first fractional frequency offset estimator, a second fractional frequency offset estimator, a third fractional frequency offset estimator, a fractional frequency offset corrector, an integer frequency offset estimator, a summer, a selector, a low pass filter sub-module, and a digitally controlled oscillator, wherein,

the first fractional frequency offset estimator is used for performing fractional frequency offset estimation on the received data symbols and outputting the fractional frequency offset to the selector as a frequency offset estimation result;

the second fractional frequency offset estimator is configured to perform fractional frequency offset estimation on the received FIC symbol, and output the fractional frequency offset to the selector as a frequency offset estimation result;

the third fractional frequency offset estimator is used for performing fractional frequency offset estimation on the received phase reference symbol and outputting the fractional frequency offset to the fractional frequency offset corrector;

the fractional frequency offset corrector is used for performing fractional frequency offset correction on the received phase reference symbol according to the fractional frequency offset output by the third fractional frequency offset estimator; outputting the phase reference symbol after fractional frequency offset correction to the integer frequency offset estimator and the adder;

the integer frequency offset estimator is used for performing integer frequency offset estimation on the received phase reference symbol after fractional frequency offset correction and outputting the integer frequency offset to the adder and the integer frequency offset corrector;

the integer frequency offset corrector is used for performing integer frequency offset correction on the received phase reference symbol after fractional frequency offset correction according to the integer frequency offset output by the integer frequency offset estimator; outputting the integer frequency offset corrected phase reference symbol to the selector and the timing recovery module;

the adder is used for calculating the sum of the fractional frequency offset estimation from the third fractional frequency offset estimator and the integer frequency offset estimation from the integer frequency offset estimator and outputting the sum as a frequency offset estimation result to the selector;

the selector is used for selecting one of the received frequency offset estimation results and outputting the selected frequency offset estimation result to the low-pass filtering submodule;

and the low-pass filtering submodule is used for performing low-pass filtering on the received frequency offset estimation result and outputting the frequency offset estimation result to the AGC module through the numerical control oscillator.

The OFDM demodulation unit includes: a symbol classification extraction module, an FIC decoding module, a channel data selection module and a Fourier transform FFT module, wherein,

the symbol classification extraction module is used for extracting a phase reference symbol, a FIC symbol and a data symbol from the signal from the down-sampling 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 pattern recognition result from the pattern recognition module; outputting the extracted phase reference symbol, FIC symbol and data symbol to the carrier recovery module; outputting the extracted phase reference symbol and FIC symbol to the FIC decoder; outputting the extracted FIC symbol and data symbol to a channel data selection module; outputting the currently extracted symbol type to the AGC module through a 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 the channel selection indication, and obtain channel data position and length information, channel modulation mode information, and channel coding mode information; outputting the channel data position and length information to the channel data selection module; outputting the channel modulation mode information and the channel coding mode information to the channel demodulation decoding unit;

the channel data selection module is used for selecting data in a corresponding channel from the data symbols output by the symbol classification extraction module according to the channel data position and length information from the FIC decoder; outputting the FIC symbols from the symbol classification extraction module and the selected channel data to the FFT module;

the FFT module is configured to perform OFDM demodulation on 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 includes: FFT submodule, frequency domain de-interleaving submodule, differential phase shift keying DQPSK demodulation submodule, 1/3 convolution decoding submodule and channel information extractor, wherein,

the FFT submodule is used for carrying out FFT processing on the received FIC symbols and outputting the processed FIC symbols to the frequency domain de-interleaving submodule;

the frequency domain de-interleaving submodule is used for performing frequency domain de-interleaving processing on the received FIC symbol and outputting the processed FIC symbol to the DQPSK demodulation submodule;

the DQPSK demodulation sub-module is configured to perform DQPSK demodulation on the received FIC symbol, and output the FIC symbol after DQPSK demodulation to the 1/3 convolutional decoding sub-module;

the 1/3 convolutional decoding submodule is configured to perform 1/3 convolutional decoding on the received FIC symbol, and output the decoded FIC symbol to the channel information extractor;

the channel information extractor is used for extracting channel data position and length information, channel modulation mode information and channel coding mode information from the received FIC symbols according to the received channel selection indication; outputting the channel data position and length information to the channel data selection module; and outputting the channel modulation mode information and the channel coding mode information to the channel demodulation decoding unit.

The channel demodulation decoding unit includes: a frequency domain de-interleaving module, a differential demodulator, a time domain de-interleaving module and a forward error correction mode FEC decoder, wherein,

the frequency domain de-interleaving module is used for performing channel demodulation on the received FIC symbols and the selected channel data; outputting the FIC symbol after channel demodulation and the selected channel data to a differential demodulator;

the differential demodulator is configured to perform differential demodulation on the received selected channel data according to the channel modulation mode information from the FIC decoder and the FIC symbol from the frequency domain deinterleaving module; outputting the selected channel data after differential demodulation to a time domain de-interleaving module;

the time domain de-interleaving module is used for performing channel decoding on the received selected channel data and outputting the channel-decoded selected channel data to the FEC decoder;

the FEC decoder is used for carrying out channel decoding on the received selected channel data according to the channel coding mode information from the FIC decoder; outputting the decoded selected channel data.

According to the technical scheme, the transmission mode of the received signal is identified, and the received signal is subjected to radio frequency demodulation, OFDM demodulation and channel demodulation by utilizing the ideal baseband model and the synchronous position of the T-MMB system and the characteristics of the T-MMB channel; in addition, in the OFDM demodulation process, the control information in the FIC can be acquired, and then data demodulation is carried out according to the acquired control information, so that the T-MMB receiver compatible with the DAB system is realized, and the reliability of the multimedia broadcast service is improved.

Drawings

Fig. 1 is an exemplary structural diagram of a T-MMB receiver compatible with the DAB system in the present invention.

Fig. 2 is a schematic diagram of a T-MMB transmitter compatible with the DAB system.

Fig. 3 is an 8-point phase shift keying (8PSK) constellation.

Fig. 4 is a 16-point amplitude and phase coherent keying (16APSK) constellation.

Fig. 5 is a frame structure diagram of a T-MMB compatible with the DAB system.

Fig. 6 is a schematic diagram of the T-MMB service organization structure compatible with the DAB system.

Fig. 7 is a schematic diagram of a structure of a T-MMB new service sub-channel compatible with the DAB system.

Fig. 8 is a schematic diagram of T-MMB subscriber application information compatible with the DAB system.

Fig. 9 is a general structural diagram of a T-MMB receiver compatible with the DAB system in the embodiment of the present invention.

FIG. 10 is a schematic block diagram of the pattern recognition of the T-MMB receiver compatible with the DAB system in the embodiment of the present invention.

Fig. 11 is a schematic block diagram of frame synchronization of a T-MMB receiver compatible with the DAB system in an embodiment of the present invention.

Fig. 12 is a flow chart of frame synchronization of a T-MMB receiver compatible with the DAB system in an embodiment of the present invention.

Fig. 13 is a schematic block diagram of timing recovery of a T-MMB receiver compatible with the DAB system in an embodiment of the present invention.

Fig. 14 is a schematic block diagram of carrier recovery of a T-MMB receiver compatible with the DAB system in an embodiment of the present invention.

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

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and examples.

The basic idea of the invention is: the T-MMB receiver compatible with the DAB system is realized by utilizing an ideal baseband model of the T-MMB system, various non-ideal factors such as frame synchronization, carrier synchronization, timing synchronization and the like and the characteristics of a T-MMB channel.

The T-MMB is a digital multimedia broadcasting mode based on the multimedia service expansion of a digital audio broadcasting DAB system, integrates the latest technology, comprehensively considers the factors such as frequency point resources, receiver complexity, frequency spectrum utilization rate and system performance, and can realize the following steps: the method is completely compatible with DAB, low in cost design, low in power consumption design, good in frequency point availability, capable of supporting mobile reception, single frequency network implementation, high spectrum efficiency, multi-service, high-quality service and the like. T-MMB has several properties:

(1) fully compatible with Eureka-147 (DAB), DAB-IP and Korea T-DMB. The T-MMB fully utilizes the technical advantage that DAB can reliably receive signals in a high-speed mobile environment, and functionally expands single audio information to various carriers such as data, characters, graphics, videos and the like.

(2) The disadvantage of low frequency band efficiency of the T-DMB system is overcome.

(3) Advanced channel error correction coding techniques, low density parity check codes (LDPC) and efficient low complexity DAPSK modulation schemes are employed.

(4) Compared with other systems such as DVB-H and the like, the system has the advantages of low complexity, low power consumption, good frequency point availability, good compatibility and the like.

Fig. 1 is an exemplary structural diagram of a T-MMB receiver compatible with the DAB system in the present invention. As shown in fig. 1, the T-MMB receiver compatible with the DAB system in the present invention includes: radio Frequency demodulation section 101, synchronization section 102, Orthogonal Frequency Division Multiplexing (OFDM) demodulation section 103, and channel demodulation decoding section 104.

A radio frequency demodulation unit 101 that performs radio frequency demodulation on a radio frequency signal received from the outside and outputs the radio frequency-demodulated signal to the synchronization unit 102 and the OFDM demodulation unit 103;

a synchronization unit 102 for receiving the signal output by the rf demodulation unit 101; identifying a transmission mode corresponding to the received signal, outputting a mode identification result to the OFDM demodulation unit 103, determining a synchronization position of the received signal according to the mode identification result, and outputting the synchronization position to the OFDM demodulation unit 103;

wherein the synchronization position may include: frame boundary, symbol boundary and timing position;

OFDM demodulation section 103 for extracting a phase reference symbol, a Fast Information Channel (FIC) symbol, and a data symbol from the signal from rf demodulation section 101 based on the pattern recognition result output from synchronization section 102; according to the phase reference symbol and the channel selection indication received from the outside, the FIC symbol is OFDM demodulated and decoded to obtain control information in the FIC, and control information in the FIC is obtained, and the obtained control information is output to the channel demodulation decoding unit 104; performing OFDM demodulation on the data symbols according to the control information in the FIC; outputs the FIC symbol and the data symbol after OFDM demodulation to the channel demodulation decoding unit 104;

the channel selection indication received from the outside comes from a receiving end user and is used for selecting and receiving DAB, DAB-IP, T-DMB or T-MMB signals; the control information includes: channel position and length information for selecting channel data, a channel modulation mode for channel demodulation, and a channel coding mode for channel decoding;

channel demodulation decoding section 104 performs channel demodulation decoding on the received data symbols using the control information and FIC symbols from OFDM demodulation section 103, and outputs the channel-demodulated decoded data symbols.

The radio frequency signals received by the above-mentioned DAB system-compatible T-MMB receiver include DAB/DAB-IP/T-DMB/T-MMB signals from the DAB system-compatible T-MMB transmitter shown in fig. 2. The T-MMB transmitter comprises: the DAB service path, the DAB-IP service path and the T-DMB service path are input interfaces of the DAB service, the DAB-IP service and the T-DMB service respectively and are used for being compatible with the DAB service, the DAB-IP service and the T-DMB service.

The T-MMB transmitter shown in fig. 2 performs channel modulation and channel coding using a differential phase shift keying (DQPSK)/8DPSK/16DAPSK modulation scheme and LDPC coding.

Fig. 3 is an 8PSK constellation diagram. As shown in FIG. 3, for each OFDM symbol, a vector of 3K-bits (p)_l，n)_n＝0 ^3K-1(wherein p is_l，nSee ETSI EN 300401 [1 ]]Section 14.4.2) needs to be mapped into K8 PSK symbols by:

img id="idf0001" file="A20061014576600201.GIF" wi="216" he="24" img-content="drawing" img-format="GIF"/

where K is the number of subcarriers,. phi_l，mIs the phase.

Fig. 4 is a 16APSK constellation. As shown in FIG. 4, for each OFDM symbol, a vector of 4K-bits (p)_l，n)_n＝0 ^4K-1Mapping into K16 APSK symbols by:

img id="idf0002" file="A20061014576600202.GIF" wi="239" he="24" img-content="drawing" img-format="GIF"/

wherein phi_l，mAs shown in the table 5 below, the following examples,img id="idf0003" file="A20061014576600203.GIF" wi="110" he="24" img-content="drawing" img-format="GIF"/。

compatible DAB system, namely DAB/DAB-IP/T-DMB/T-MMB system has four transmission modes in total which can be selected, see DAB standard ETSI EN 300401 in detail. When different transmission modes are adopted, parameters and modes adopted by channel modulation and coding are different, and the T-MMB receiver compatible with the DAB system needs to perform channel demodulation and decoding on signals by identifying the transmission modes of the signals and adopting the corresponding parameters and modes.

Fig. 5 is a frame structure diagram of a T-MMB compatible with the DAB system. As shown in fig. 5, the signal of each frame received by the T-MMB receiver compatible with the DAB system according to the present invention is composed of a null symbol, a phase reference symbol, and FIC symbols and data symbols determined by different patterns.

In the signal received by the receiver, the null symbol is used for the frame synchronization of the receiver; the phase reference symbol provides a phase reference for differential phase modulation and demodulation of subsequent data; since the information of the phase reference symbols is known to the receiver, it can also be used as carrier synchronization.

The FIC symbol includes T-MMB service organization structure information as shown in fig. 6, T-MMB new service subchannel structure information as shown in fig. 7, and T-MMB user application information as shown in fig. 8.

The T-MMB service organization structure shown in fig. 6 can be implemented by adding the service indication information of the T-MMB system according to the format of the service indication information in the FIC of DAB (ETSI EN 300401), and adding the service type description of the T-MMB system in fig. 0/FIG 0/2.

Adding new sub-channel information in FIG type 0/extended mode 15(FIG0/15) of DAB, specifically comprising: the Sub-channel identifier (subchidd), the Start Address (Start Address), the modulation type (ModuType), the Protection Level (PL), and the Sub-channel Size (Sub-channel Size) of the Sub-channel, so that the new traffic Sub-channel structure of T-MMB as shown in fig. 7 can be implemented.

Adding user application Type (user application Type) information in FIG Type 0/extended mode 13(FIG0/13) of DAB; the T-MMB subscriber application information as shown in fig. 8 can be implemented by adjusting the size of the Capacity Unit (CU) of the corresponding T-MMB service in the Main Service Channel (MSC) of the DAB system. The capacity of a CU is calculated as follows: n × 32bits, where n ═ 2 represents that the system adopts the DQPSK modulation mode, n ═ 3 represents that the system adopts the 8DPSK modulation mode, and n ═ 4 represents that the system adopts the 16DAPSK modulation mode.

The above is a general description of the T-MMB receiver of the present invention compatible with the DAB system. The following is a detailed description of a DAB system compatible T-MMB receiver in an embodiment of the present invention.

Fig. 9 is a general structural diagram of a T-MMB receiver compatible with the DAB system in the embodiment of the present invention. As shown in fig. 9, the T-MMB receiver compatible with the DAB system in this embodiment includes: a radio frequency demodulation unit 901, a synchronization unit 902, an OFDM demodulation unit 903 and a channel demodulation decoding unit 904.

The radio frequency demodulation unit 901 includes: a tuner, an analog/digital (A/D) conversion module, a down conversion module, a low pass filter, a down sampling module, A Gain Control (AGC) module, and a free running clock. The functional module is used for performing radio frequency demodulation on the signal from the transmitter.

The synchronization unit 902 includes: the device comprises 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 extraction module, a FIC decoder, a channel data selection module and a Fourier transform (FFT) module.

The channel demodulation decoding unit 904 includes: a frequency domain de-interleaving module, a differential demodulator, a time domain de-interleaving module, and a Forward Error Correction (FEC) decoder.

Next, a description is given of the T-MMB receiver compatible with the DAB system in this embodiment, with reference to specific modules in each functional unit.

In the rf demodulation unit 901, the tuner serving as the analog front end amplifies the received rf signal under the control of the AGC module to complete the frequency band selection; since the voltage for controlling the tuner AGC is supplied by the if section, the selected signal is converted from the rf band to a fixed if; the converted signal is output to an A/D conversion unit.

The frequency band selection can be realized by changing the frequency division coefficient of a Phase Lock Loop (PLL). The intermediate frequency signal is filtered through a 1.536MHz bandwidth filter. A local oscillator in the intermediate frequency unit converts the intermediate frequency signal to a small intermediate frequency (2.048MHz), which is now a bandpass signal near baseband.

And an AGC module, which detects the signal power output by the down-sampling module according to the symbol indication signal from the OFDM demodulation unit 903, generates an AGC control signal, and outputs the AGC control signal to the tuner, so as to ensure that the signal obtained by a/D conversion can have the best dynamic range when the field strength of the received signal is continuously changed under the environment of a mobile receiving channel.

And the A/D conversion module is used for carrying out A/D conversion on the received signal according to a clock signal provided by the free oscillation clock and outputting the signal to the down-conversion module. Since the analog signal becomes a digital small intermediate frequency signal after being subjected to quadruple sampling Ts (8.192MHz) by the tuner, the sampling clock of the a/D conversion module is free-running without being phase-locked.

The down-conversion module realizes down-conversion through a multiplier to obtain a digital baseband I/Q signal; the out-of-band interference of the obtained I/Q signals is removed by a low-pass filter, quadruple extraction is completed by a down sampler, and after 2.048MHz data is obtained from 8.192MHz data, the data is output to an AGC module, a mode identification module in a synchronization unit 902, a frame synchronization module and a symbol classification extraction module in an OFDM demodulation unit 903.

In the synchronization unit 902, the pattern recognition module determines characteristics of the frame length, the guard interval length, the null symbol length, and the like of the signal from the radio frequency demodulation unit 901, determines a transmission mode corresponding to the received signal, and outputs a pattern recognition result to the frame synchronization module and the symbol classification extraction module in the OFDM demodulation unit 903. FIG. 10 is a schematic block diagram of the pattern recognition of the T-MMB receiver compatible with the DAB system in the embodiment of the present invention. As shown in fig. 10, the pattern recognition module includes: a frame length detector, a guard interval length detector and a null symbol length detector mode decision device. The mode identification module firstly detects the frame length, the guard interval length and the empty symbol length of the signal, and then carries out mode judgment on the detection results of the frame length, the guard interval length and the empty symbol length through the mode decision device. In specific implementation, only one or more of frame length detection, guard interval length detection and null symbol length detection may be performed.

The frame synchronization module is used for determining the frame starting position of the received signal according to the pattern recognition result provided by the pattern recognition module; carrying out symbol synchronization and carrier synchronization according to the obtained initial position, and determining a synchronization position, namely a frame boundary and a symbol boundary; the obtained frame boundary and symbol boundary are output to a symbol classification extraction module in the OFDM demodulation unit 903.

The T-MMB transmission frame consists of null symbols, phase reference symbols and a certain number of OFDM symbols, so that the frame synchronization detection is to accurately judge the positions of the null symbols so as to determine the initial position of the frame.

Since the energy of the null symbol is zero, the frame synchronization detection using the energy distribution of the received signal is simple and effective. The most intuitive method is to detect the abrupt edge of the received signal to determine the starting and ending positions of the null symbol, but this method is interfered by the channel to cause larger ambiguity and larger error. Therefore, a more reliable energy ratio algorithm is adopted, which is described in detail as follows:

img id="idf0004" file="A20061014576600231.GIF" wi="183" he="39" img-content="drawing" img-format="GIF"/

where r is the received signal, τ represents the end position of the null symbol, E [ a, b ] represents the total energy of the [ a, b ] interval, n represents the sequence number of the received signal, and W represents the length of a certain interval.

If the energy ratio is calculated once per symbol of each frame and then the maximum value is determined, it is obvious that the amount of calculation is too large and is not necessary because the maximum delay of the channel determines the maximum offset of the synchronization position. Therefore, after the synchronization position is detected in the first frame of received data, only m symbols around the same position of each frame are needed to be subjected to energy ratio calculation to obtain the maximum value so as to determine the synchronization position of each frame, and the size of m is designed according to the maximum time delay of a channel.

Fig. 11 is a schematic block diagram of frame synchronization of a T-MMB receiver compatible with the DAB system in an embodiment of the present invention. As shown in fig. 11, the frame synchronization module includes: the system comprises an in-window energy statistics submodule, a divider, a delayer and a peak detection submodule. The in-window energy counting submodule counts signal energy in a preset window and outputs a counting result to the divider; the divider calculates the quotient of the statistical results in two adjacent windows under the control of the delayer and outputs the quotient to the peak detection submodule; and the peak detection submodule compares the received quotient with a preset threshold value and outputs a frame limit and a symbol limit according to a comparison result.

Fig. 12 is a flow chart of frame synchronization of a T-MMB receiver compatible with the DAB system in an embodiment of the present invention. As shown in fig. 12, due to channel interference, the synchronization position detected for the first time is likely to be wrong, and therefore, it is necessary to detect the synchronization position for several consecutive frames before determining that the frame synchronization position is captured accurately, and then enter the tracking phase, according to the above description, the tracking calculation is performed only in the window of 2m +1, and if the maximum energy ratio of several consecutive frames is less than a threshold, it is considered that synchronization is lost, and the synchronization capturing phase is re-entered.

The timing recovery module, according to the timing recovery principle shown in fig. 13, uses the phase reference symbol from the carrier recovery module after the frequency offset correction, and after the IFFT processing of the IFFT sub-module, performs modulo in the time domain by the modulo sub-module, and finds the position of the local maximum in the local maximum position sub-module by using a preset window to locate the fine synchronization timing position, and outputs the obtained timing position to the symbol classification extraction module in the OFDM demodulation unit 903. The timing position output by the timing recovery module is used for fine positioning relative to the frame boundary and symbol boundary output by the frame synchronization module.

The frame synchronization module and the timing recovery module are used for positioning the frame boundary and the symbol boundary of the received signal, so that the subsequent symbol classification extraction module can distinguish the null symbol, the phase reference symbol, the FIC symbol and the data symbol.

A carrier recovery module, which classifies and extracts the phase reference symbol from the OFDM demodulation unit 903 according to the symbol, and obtains an estimate of fractional frequency offset by using the guard interval and using the correlation characteristics; correcting fractional frequency offset of the phase reference symbol, then estimating integer frequency offset, and adding the fractional frequency offset and the integer frequency offset to obtain a frequency offset estimation result; if receiving FIC symbols and data symbols from the symbol classification extraction module in the OFDM demodulation unit 903, considering that there is no integer frequency offset, only performing fractional frequency offset estimation, and obtaining fractional frequency offset estimation as a frequency offset estimation result by using a guard interval and using correlation characteristics; a phase signal obtained by low-pass filtering the frequency offset estimation result and processing the frequency offset estimation result by a digital controlled oscillator is output to a down-conversion module in the radio frequency demodulation unit 901 to control the down-conversion module; and correcting the phase reference symbol according to the frequency offset estimation result, and outputting the corrected phase reference symbol to the timing recovery module.

Fig. 14 is a schematic block diagram of carrier recovery of a T-MMB receiver compatible with the DAB system in an embodiment of the present invention. As shown in fig. 14, the carrier recovery module includes: the device comprises a fractional frequency offset estimator 1, a fractional frequency offset estimator 2, a fractional frequency offset estimator 3, a fractional frequency offset corrector, an integer frequency offset estimator, an adder, a selector, a low-pass filter sub-module and a digital controlled oscillator. The fractional frequency offset estimator 1 and the fractional frequency offset estimator 2 are used for respectively carrying out fractional frequency offset estimation on the received data symbols and FIC symbols and outputting the fractional frequency offset to the selector as a frequency offset estimation result; the fractional frequency offset estimator 3 is used for performing fractional frequency offset estimation on the received phase reference symbol and outputting the fractional frequency offset to the fractional frequency offset corrector; the fractional frequency offset corrector corrects the fractional frequency offset of the received phase reference symbol according to the fractional frequency offset output by the fractional frequency offset estimator 3; outputting the phase reference symbol after the fractional frequency offset correction to an integer frequency offset estimator and an adder; the integer frequency offset estimator carries out integer frequency offset estimation on the received phase reference symbol after fractional frequency offset correction and outputs the integer frequency offset to the adder and the integer frequency offset corrector; the adder calculates the sum of the fractional frequency offset estimation from the fractional frequency offset estimator 3 and the integer frequency offset estimation from the integer frequency offset estimator, and outputs the calculated sum as a frequency offset estimation result to the selector; the selector selects one of the received frequency offset estimation results, and outputs the selected frequency offset estimation result to an AGC module in the radio frequency demodulation unit 901 through a low-pass filtering sub-module and a digital controlled oscillator. Meanwhile, the integer frequency offset corrector carries out integer frequency offset correction on the received phase reference symbol after fractional frequency offset correction according to the integer frequency offset; outputting the phase reference symbol after the integer frequency offset correction to a timing recovery module;

in the OFDM demodulation unit 903, the symbol classification extraction module extracts a phase reference symbol, an FIC symbol, and a data symbol from a signal from the down-sampling module of the rf demodulation unit 901, based on the timing position of the timing recovery module from the synchronization unit 902, the frame boundary and the symbol boundary from the frame synchronization module of the synchronization unit 902, and the pattern recognition result from the pattern recognition module of the synchronization unit 902; the extracted phase reference symbol, FIC symbol, and data symbol are output to the carrier recovery module of synchronization unit 902; outputting the extracted phase reference symbol and FIC symbol to a FIC decoder; outputting the extracted FIC symbol and data symbol to a channel data selection module; the currently extracted symbol type is signaled to an AGC module in the rf demodulation unit 901 through a symbol indication.

The FIC decoder demodulates and decodes the received FIC symbol according to the received phase reference symbol and a channel selection indication from a receiving end user to obtain channel information of the selected channel, namely control information, comprising channel data position and length information, channel modulation mode information and channel coding mode information; outputting the channel data position and length information to a channel data selection module; outputs the channel modulation mode information to the differential demodulator in the channel demodulation decoding unit 904; the channel coding scheme information is output to the FEC decoder in the channel demodulation decoding unit 904. FIG. 15 is a schematic block diagram of FIC demodulation and decoding of a T-MMB receiver compatible with the DAB system according to an embodiment of the present invention. As shown in fig. 15, since the FIC symbol is recovered at the transmitter using fixed DQPSK modulation and 1/3 convolutional encoding FIC decoder, the FIC decoder uses fixed DQPSK demodulation and 1/3 convolutional decoding in recovering FIC information; the channel information extractor can obtain the service type of the selected channel according to the channel selection indication from the receiving end user and the user application information indication shown in fig. 8 in the FIC symbol; the channel information extractor can obtain the position and length information for channel data selection according to the channel selection indication from the receiving end user and the new service subchannel structure indication shown in fig. 7 in the FIC symbol; the channel information extractor can obtain modulation mode information for differential demodulation of the selected channel data according to a channel selection indication from a receiving end user and a new service subchannel structure indication shown in fig. 7 in the FIC symbol; the channel information extractor may obtain the coding mode information for FEC decoding of the selected channel data according to the channel selection indication from the receiving end user and the new service subchannel structure indication shown in fig. 7 in the FIC symbol.

The channel data selection module selects data in a corresponding channel, namely any signal in DAB/DAB-IP/T-DMB/T-MMB, from the data symbols output by the symbol classification extraction module according to the position and length information of the channel data from the FIC decoder; the FIC symbols from the symbol classification extraction module and the selected channel data are output to the FFT module.

Wherein, the FIC symbol from the symbol classification extraction module is not OFDM demodulated, and is used for the subsequent differential demodulation processing of the selected channel data; in this embodiment, the symbol classification and extraction module may not output the FIC symbol to the channel data selection module, but the FIC decoder directly outputs the FIC symbol after OFDM demodulation to the differential demodulator in the channel demodulation and decoding unit 904.

The FFT module performs OFDM demodulation on 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 decoding unit 904.

In the channel demodulation decoding unit 904, the frequency domain de-interleaving module performs channel demodulation on the received FIC symbols and the selected channel data; the demodulated FIC symbols and selected channel data are output to a differential demodulator.

A differential demodulator for determining a modulation scheme corresponding to the selected channel data according to the channel modulation scheme information from the FIC decoder in the OFDM demodulation unit 903; carrying out differential demodulation on the received selected channel data according to a modulation mode corresponding to the selected channel data and the FIC symbol from the frequency domain de-interleaving module; and outputting the selected channel data after differential demodulation to a time domain de-interleaving module. The differential demodulator in the embodiment can perform differential demodulation on signals modulated by adopting DQPSK, 8DPSK and 16DAPSK modes.

And the time domain de-interleaving module is used for carrying out channel decoding on the received selected channel data and outputting the channel-decoded selected channel data to the FEC decoder.

An FEC decoder, which determines the coding mode corresponding to the selected channel data according to the channel coding mode information from the FIC decoder in the OFDM demodulation unit 903; performing FEC decoding on the received selected channel data according to the coding mode corresponding to the selected channel data, namely channel decoding; and outputting the decoded selected channel data to a receiving end user. The FEC decoder in this embodiment can decode data encoded by convolutional coding or LDPC coding.

The above description is only for the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A T-MMB (terrestrial multimedia broadcasting) receiver for Digital Audio Broadcasting (DAB) compliant terrestrial mobile multimedia broadcasting, comprising: a radio frequency demodulation unit, a synchronization unit, an Orthogonal Frequency Division Multiplexing (OFDM) demodulation unit and a channel demodulation decoding unit, wherein,

2. The receiver of claim 1, wherein the OFDM demodulation unit is further to output the extracted phase reference symbols, and/or FIC symbols, and/or data symbols to the synchronization unit; informing the radio frequency demodulation unit of the currently extracted symbol type through a symbol indication signal;

3. The receiver of claim 2, wherein the radio frequency demodulation unit comprises: a tuner, an analog/digital a/D conversion module, a down conversion module, a low pass filter, a down sampling module, a gain control AGC module, and a free running clock, wherein,

4. The receiver of claim 3, wherein the synchronization unit comprises: a pattern recognition module, a frame synchronization module, a timing recovery module and a carrier recovery module, wherein,

5. The receiver of claim 4, wherein the pattern recognition module comprises: a frame length detector, and/or a guard interval length detector, and/or a null symbol length detector, and a mode decision device;

6. The receiver of claim 4, wherein the frame synchronization module comprises: an intra-window energy statistics submodule, a divider, a delayer and a peak detection submodule, wherein,

7. The receiver of claim 4, wherein the timing recovery module comprises: an IFFT sub-module, a modulo sub-module, and a local maximum position sub-module, wherein,

8. The receiver of claim 4, wherein the carrier recovery module comprises: a first fractional frequency offset estimator, a second fractional frequency offset estimator, a third fractional frequency offset estimator, a fractional frequency offset corrector, an integer frequency offset estimator, a summer, a selector, a low pass filter sub-module, and a digitally controlled oscillator, wherein,

9. The receiver of claim 4, wherein the OFDM demodulation unit comprises: a symbol classification extraction module, an FIC decoding module, a channel data selection module and a Fourier transform FFT module, wherein,

10. The receiver of claim 9, wherein the FIC decoding module comprises: FFT submodule, frequency domain de-interleaving submodule, differential phase shift keying DQPSK demodulation submodule, 1/3 convolution decoding submodule and channel information extractor, wherein,

11. The receiver of claim 9, wherein the channel demodulation decoding unit comprises: a frequency domain de-interleaving module, a differential demodulator, a time domain de-interleaving module and a forward error correction mode FEC decoder, wherein,