CN103581096B - OFDM modulating and demodulating method and digital signal emitting and receiving system - Google Patents
OFDM modulating and demodulating method and digital signal emitting and receiving system Download PDFInfo
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Abstract
The invention discloses an OFDM modulating and demodulating method containing time domain training sequences and a digital signal emitting and receiving system. The principle of the OFDM modulating and demodulating method is that input data symbols are grouped with N input data symbols as one group to be converted in a time domain mode, the N is the number of subcarriers of the OFDM symbols, a cyclic prefix of each group input data symbols is established, the input data symbols are expanded into time domain data with the length of N+P, the P is the length of the cyclic prefix, the time domain training sequence with the length of P and a negation sequence for the time domain training sequence are generated for each group of time domain data, the time domain training sequences and the negation sequences of the time domain training sequences are overlapped on the groups of the time domain data to obtain bas band time domain symbols. By means of the technical scheme of the OFDM modulating and demodulating method, the complexity of reconstitution CP-OFDM symbols is reduced, noise caused by reconstitution is reduced, the channel estimating performance is improved, and a digital signal emitting and receiving system using the OFDM modulating and demodulating method can have better noise resistance.
Description
Technical Field
The present invention relates to a modulation and demodulation method in a communication system and a system using the modulation and demodulation method, and more particularly, to an OFDM modulation and demodulation method including a time domain training sequence based on multiple carriers and a digital signal transmission and reception system using the modulation and demodulation method.
Background
CP-OFDM technology is widely used in modern communication systems. In a TDS-OFDM system different from the TDS-OFDM system, for example, in a DTMB multi-carrier mode, a time domain training sequence is inserted between OFDM symbols, and the time domain training sequence is used to complete synchronization and channel estimation of a receiving end. The TDS-OFDM technology effectively improves the utilization rate of frequency resources. However, the TDS-OFDM system must reconstruct the CP-OFDM symbol when recovering data of the frequency domain since a cyclic prefix is not used. And more noise compared with CP-OFDM is necessarily introduced in the process of reconstruction.
Disclosure of Invention
The invention aims to provide an OFDM modulation and demodulation method containing a time domain training sequence and a digital signal transmitting and receiving system, which effectively combine CP-OFDM and TDS-OFDM and improve the structure of the existing digital signal transmitting and receiving system.
In accordance with the above object, an OFDM modulation method including a time domain training sequence according to the present invention includes the steps of: step one, performing time domain transformation on input data symbols by taking N as a group of groups, wherein N is the number of subcarriers of an OFDM symbol; step two, constructing a cyclic prefix of each group of input data symbols, and expanding the input data symbols to time domain data with the length of N + P, wherein P is the length of the cyclic prefix; generating a time domain training sequence with the length of P and an inverted sequence of the time domain training sequence for each group of time domain data; and step four, superposing the time domain training sequence and the negation sequence of the time domain training sequence to each group of time domain data to obtain a baseband time domain symbol.
According to the above main features, step four superimposes one of the time domain training sequence and the inverted sequence of the time domain training sequence on the first P data of the time domain data, and superimposes the other on the last P data of the time domain data.
According to the main characteristics, the baseband time domain symbol obtained by the superposition in the step four is:(ii) a Where k represents the kth set of time domain data,is an input data symbol in the time domain,is a baseband time-domain symbol that is,is a time domain training sequence.
According to the above object, the OFDM demodulation method including time domain training sequence of the present invention includes synchronization, channel estimation and equalization, the synchronization step transforms the baseband data group to obtain time domain data of the baseband synchronization symbol group after channel response, wherein the last P data of each group of baseband synchronization symbols is a time domain training sequence 2 times undisturbed; in the channel estimation step, a time domain training sequence which is not interfered is used for channel estimation to obtain channel impact response; and in the equalization step, the time domain training sequence subjected to channel impulse response is subtracted from the baseband data to obtain a baseband time domain symbol.
According to the main characteristics, the synchronization step subtracts the baseband data received first from the baseband data received later, and removes the cyclic prefix to obtain a 2-time domain training sequence.
According to the above main feature, the baseband synchronization symbol obtained by subtracting the baseband data received first from the baseband data received later is:
(ii) a Wherein k represents the k-th set of baseband data received,for the baseband time-domain symbol(s),in order to be the baseband synchronization symbol,is an input data symbol in the time domain,is a time domain training sequence. In the present invention, the-nth data of a group of data is defined as the nth last of the previous group of data, and will not be described in detail later.
According to the main characteristics, for each group of baseband data with the same time domain training sequence, the channel estimation step averages multiple groups of continuous baseband data to obtain a 2P length sequence for channel estimation, wherein the 2P length sequence comprises a time domain training sequence and an inverted sequence of the time domain training sequence.
According to the main characteristics, the channel estimation step averages continuous M groups of baseband data to obtain:；
wherein,；(ii) a Wherein,for the baseband data after the averaging to be,is an input data symbol in the time domain,is a set of training sequences in the time domain,is the channel impulse response.
According to the above main features, for each set of baseband data with different time domain training sequences, the channel estimation step uses the time domain training sequence 2 times of the undisturbed time domain training sequence to perform channel estimation.
According to the main feature, for a set of baseband data, the equalization step decomposes the received baseband data into(ii) a Wherein,is the k-th set of baseband data,is a training sequence or an inverted sequence of training sequences passing through the channel impulse response,is the channel impulse response and is the channel impulse response,is an average power ofWhite gaussian noise of (1); and subtracting the time domain training sequence subjected to channel impulse response and the inverted sequence of the time domain training sequence from the baseband data, and converting to obtain a baseband time domain symbol.
According to the above purpose, the digital signal transmitting system implementing the OFDM modulation method of the present invention includes a randomization unit, a forward error correction coding unit, a constellation mapping and interleaving unit, a system information generating unit, a multiplexing unit, a CP-OFDM constructing unit, a time domain training sequence superimposing unit, a frame header forming unit, a framing unit, a baseband post-processing unit, and an orthogonal up-conversion unit; the input data code stream is scrambled by a scrambling code through a randomization unit, then enters a forward error correction coding unit for forward error correction coding, then enters a constellation mapping and interleaving unit to form a symbol stream, is subjected to constellation mapping and then is interleaved, then is multiplexed with system information through a multiplexing unit to form an input data symbol, enters a CP-OFDM construction unit, then passes through a time domain training sequence superposition unit, is superposed by using a frame header as a time domain training sequence to form a frame body, then the frame header generated by the frame body and the frame header formation unit is multiplexed into a signal frame through a framing unit, is converted into an output signal through a baseband post-processing unit, and is converted into a radio frequency signal through an orthogonal up-conversion unit.
According to the above object, a digital signal receiving system for implementing the OFDM demodulation method of the present invention includes a synchronization unit, an equalization unit, a channel estimation unit, a demultiplexing unit, a system information decoding unit, a constellation demapping and deinterleaving unit, and a decoding unit; the synchronization unit synchronizes the baseband data groups to obtain baseband synchronization symbol groups; the channel estimation unit carries out channel estimation on the time domain training sequence which is not interfered to obtain channel impact response; the equalization unit subtracts the time domain training sequence subjected to channel impulse response from baseband data to obtain a baseband time domain symbol; the demultiplexing unit transforms and decomposes the baseband time domain symbol to obtain system information and a data symbol; the system information decoding unit extracts data symbols according to the system information; the constellation demapping and deinterleaving unit demaps and deinterleaves the data symbols; and finally, the decoding unit decodes to obtain the final data information.
According to the above purpose, the input of the digital signal transmitting system implementing the OFDM modulation method of the present invention is a channel of control information and at least a channel of service data, and the transmitting system includes a scrambling unit, a forward error correction coding unit, a constellation mapping and symbol interleaving unit, a frame header generating unit, a CP-OFDM symbol constructing unit, a time domain training sequence superimposing unit, a multi-frame synchronization channel generating unit, a multi-frame framing unit, a baseband post-processing unit, and an orthogonal up-conversion unit; the method comprises the steps that each path of service data is independently coded and modulated, the service data and control information are scrambled through a scrambling unit respectively, then the service data and the control information enter a forward error correction coding unit to be subjected to forward error correction coding, then enter a constellation mapping and interleaving unit to form a symbol stream, are subjected to constellation mapping, are interleaved to form input data symbols, enter a CP-OFDM (content protection-orthogonal frequency division multiplexing) construction unit, are subjected to time domain training sequence superposition through a time domain training sequence superposition module to form a subframe by using a frame header as a time domain training sequence, are subjected to superposition to form a subframe, are subjected to multiframe composition by a multiframe framing unit through a subframe and multiframe synchronous channel, are converted into output signals through a baseband post-processing unit, and.
According to the above object, a digital signal receiving system implementing the OFDM demodulation method of the present invention includes a demultiplexing frame unit, a synchronization unit, an equalization unit, a channel estimation unit, a demultiplexing unit, a control information constellation demapping and deinterleaving unit, a control information demapping and deinterleaving unit, a service data constellation demapping and deinterleaving unit, and a service data demapping and decoding unit; wherein, the multiframe decoding unit decodes the received multiframe into a plurality of subframes; for each subframe, the synchronization unit synchronizes the baseband data group to obtain a baseband synchronization symbol group; the channel estimation unit carries out channel estimation on the time domain training sequence which is not interfered to obtain channel impact response; the equalization unit subtracts the time domain training sequence subjected to channel impulse response from baseband data to obtain a baseband time domain symbol; the demultiplexing unit transforms and decomposes the baseband time domain symbols to obtain control information and service data; the control information constellation demapping and deinterleaving unit performs constellation demapping and deinterleaving on the control information; the control information decoding unit decodes the data to obtain the information of modulation, coding and the like of the service data of each path; the service data constellation demapping and deinterleaving unit demaps and deinterleaves each path of service data; and the service data decoding unit decodes the data to obtain each path of service data.
By adopting the technical scheme of the invention, the complexity of reconstructing the CP-OFDM symbol can be reduced, the noise caused by reconstruction is reduced, and the performance of channel estimation is improved, so that the digital signal transmitting and receiving system using the OFDM modulation and demodulation method can have better anti-noise capability.
Drawings
In the present invention, like reference numerals refer to like features throughout, wherein:
FIG. 1 is a schematic diagram of an OFDM modulation method of the present invention;
FIG. 2 is a diagram of the superposition of training sequences on CP-OFDM symbols;
FIG. 3 is a schematic diagram of the demodulation method of the present invention;
fig. 4 is a structural diagram of a first digital signal transmission system to which the OFDM modulation method of the present invention is applied;
fig. 5 is a structural diagram of a first digital signal receiving system to which the OFDM modulation method of the present invention is applied;
fig. 6 is a structural diagram of a second digital signal transmission system to which the OFDM modulation method of the present invention is applied;
fig. 7 is a structural diagram of a second digital signal receiving system to which the OFDM modulation method of the present invention is applied.
Detailed Description
The technical scheme of the invention is further explained by combining the drawings and the embodiment.
The invention firstly provides a modulation and demodulation mode combining CP-OFDM and TDS-OFDM, which is mainly used for modulating data symbols from a transmitting end to baseband symbols and demodulating the baseband symbols from a receiving end to the data symbols.
As shown in fig. 1, the present invention comprises the following steps at the transmitting end:
1. and adding a cyclic prefix to the input data symbol to construct a CP-OFDM symbol structure meeting the requirement.
2. And superposing the time domain training sequence on the CP-OFDM symbol.
Constructing CP-OFDM symbols
The input data symbols may be obtained by mapping the information bit stream with constellation points through various forward error correction codes. The forward error correction code may be an LDPC code, an RS code, a BCH code, a convolutional code, or the like, and the constellation point mapping may be various QAM, PSK, or APSK, which is not limited in the present invention. Grouping input data symbols into groups of N, e.g. k. N is the number of subcarriers of the OFDM symbol. Each group of signals is transformed as follows
Obtaining the time domain. Extending each group into by constructing a cyclic prefixWhere P is the length of the guard interval.
Superimposed time domain training sequence
Generating a time domain training sequence with the length of P for each group of time domain dataAnd an inverted sequence of the time domain training sequence. The time domain training sequence may be a PN, a time domain representation of a frequency domain PN, a CAZAC sequence, or the like, which is not limited in the present invention. The training sequences may be the same for each group or different for each group, which is not limited by the present invention. Respectively superposing the P time domain training sequences and the negations thereof on each group of time domain data to obtainAs shown in fig. 2. The superposition mode is as follows:
and sequentially outputting the obtained group of data to obtain the baseband time domain symbol. In the present invention, the-nth data of a group of data is defined as the nth last of the previous group of data, and will not be described in detail later.
As shown in fig. 3, the receiving end of the present invention comprises the following steps:
1. synchronization
2. Channel estimation
3. Equalization
Synchronization
The kth group of data received by the receiving end isAnd is defined asThen, then
. Wherein,is the channel impulse response and is the channel impulse response,is an average power ofWhite gaussian noise.
First, received baseband data is converted as follows
. Wherein
Definitions hereinIs the baseband synchronization symbol(s).
Note that each groupIs undisturbedTo do soIs an average power ofWhite gaussian noise. Thus, it is possible to provideIs thatPass throughA defined channel and an average power ofWhite gaussian noise. Accordingly, the receiving end can adopt the letAnd localAn associated method and a corresponding set of algorithms synchronize the received data. The present invention is not limited to these sophisticated synchronization algorithms. For convenience of explanation here, the received data is first grouped in a way corresponding to the transmitted data packet, as is readily seen in practice, fromTo obtainOf (2) aThe packet information is not required and the received data stream can be directly transformed.
Channel estimation
Channel estimation method 1
Can also be obtained by using the transformations mentioned in the synchronizationThen according toWithout interference contained inAnd performing channel estimation. The present invention is also not limited to these sophisticated channel estimation algorithms.
Channel estimation method two
If the time domain training sequences of each group of data transmitted are the same, the method is thatThe baseband data received from consecutive M groups may be averaged to obtain:
wherein
。
Increasing M is effective in causingThe interference experienced by the midamble in the middle time domain is reduced. And isThe method comprises the following steps of containing continuous 2P time domain training sequences, wherein the 2P length sequence comprises a time domain training sequence and an inverted sequence of the time domain training sequence:. The 2P continuous time domain training sequences can increase the multipath length which can be resisted by channel estimation to 2P, and greatly exceed the limit of the length P of the cyclic prefix. And even under the condition that the multipath length is less than or equal to P, the 2P continuous time domain training sequences can greatly increase the precision of channel estimation.
Equalization
The channel estimation is set to obtain accurate channel impact responseAnd is and. The last N data of the kth group of baseband data received by the receiving end
. Wherein
. Due to the fact thatAndall known, the receiving end can obtainAnd receive it fromIs subtracted to obtain
. For N of each groupIs transformed into
Wherein
. In a clear view of the above, it is known that,can pass throughIs obtained byCan also be passedAnd (4) calculating. Thus, various mature OFDM equalization algorithm estimation can be utilized. The present invention is not limited to these sophisticated equalization algorithms.
The modulation and demodulation method containing the time domain training sequence has the following beneficial effects:
1. for TDS-OFDM systems, such as DTMB, the "tail" of a frame signal due to multipath must be superimposed on the head of the signal in order to reconstruct CP-OFDM. This superposition necessarily adds the "tail" part of the noise to the reconstructed CP-OFDM symbol as well. This problem is not present in CP-OFDM systems such as DVB-T and DVB-T2. The invention can avoid overlapping unnecessary noise.
The channel estimation of the TDS-OFDM system can use a training sequence that does not exceed the guard interval of the system at the longest. The system of the present invention can regard the time domain training sequence superimposed on the tail of one frame and the time domain training sequence superimposed on the cyclic prefix of the next frame as a longer training sequence, and the length of the longer training sequence is twice of the guard interval. And by combining methods such as multi-frame averaging and the like, the multipath length which can be resisted by channel estimation can be greatly increased, and the precision is improved.
The present invention also designs various transmitting and receiving systems which can utilize the above modulation method including the time domain training sequence, and the structure thereof can refer to fig. 4-7.
The first digital signal transmitting system structure shown in fig. 4 includes a randomizing unit, a forward error correction coding unit, a constellation mapping and interleaving unit, a system information generating unit, a multiplexing unit, a CP-OFDM constructing unit, a frame header forming unit, a time domain training sequence superimposing unit, a framing unit, a baseband post-processing unit, and an orthogonal up-conversion unit.
The input data code stream is scrambled by scrambling codes through a randomization unit, then enters a forward error correction coding unit for forward error correction coding, then enters a constellation mapping and interleaving unit to form a symbol stream, and is subjected to constellation mapping and interleaving, and then is multiplexed with system information through a multiplexing unit to form an input data symbol, and enters a CP-OFDM construction unit, and the CP-OFDM is utilized to construct a data symbol structure with a CP, namely time domain data. In some systems (e.g. DTMB), the frame header is a group of specific PN sequences, but the time domain training sequence of the present invention is not limited to its type, and may be a PN, a time domain representation of a frequency domain PN, or a CAZAC sequence, etc., so that the frame header is superimposed on the CP-OFDM time domain data as the time domain training sequence, and the purpose of adding the frame header and the time domain training sequence can be achieved at the same time. Then, the obtained baseband symbol is used as a frame body of a frame structure of the first system, then the frame body and a frame header generated by the frame header forming unit are multiplexed into a signal frame through the framing unit, and are converted into an output signal (within 8MHz bandwidth) through the baseband post-processing unit, and are converted into a radio frequency signal (within UHF and VHF frequency ranges) through the orthogonal up-conversion unit.
The structure of a digital signal receiving system corresponding to the above-described digital signal transmitting system is shown in fig. 5. The receiving end comprises a synchronization unit, an equalization unit, a channel estimation unit, a demultiplexing unit, a system information decoding unit, a constellation de-mapping and de-interleaving unit and a de-coding unit.
The synchronization unit transforms the baseband data group to obtain time domain data of the baseband synchronization symbol group after channel response. And the channel estimation unit performs channel estimation on the time domain training sequence which is not interfered to obtain channel impact response. The equalization unit subtracts the time domain training sequence subjected to the channel impulse response from the baseband data to obtain a baseband time domain symbol, and transmits the baseband time domain symbol to the demultiplexing unit. The demultiplexing unit transforms and decomposes the baseband time domain symbols to obtain system information and data symbols, the system information decomposing unit extracts the data symbols according to the system information and sends the data symbols to the constellation demapping and deinterleaving unit, and then demapping, deinterleaving and de-encoding are carried out on the data symbols to obtain final data information.
The second digital signal transmitting system structure shown in fig. 6 includes a scrambling unit, a forward error correction coding unit, a constellation mapping and symbol interleaving unit, a CP-OFDM symbol constructing unit, a time domain training sequence superimposing unit, a multi-frame synchronization channel generating unit, a multi-frame framing unit, a baseband post-processing unit, and an orthogonal up-conversion unit.
The inputs to the second system architecture include one/more traffic data streams and one control information stream. Each path of service data stream uses independent coding and modulation, and the coding and modulation mode can be flexibly configured according to actual needs. The service data is scrambled by a scrambling unit, then enters a forward error correction coding unit for forward error correction coding, then enters a constellation mapping and interleaving unit to form a symbol stream, and is subjected to constellation mapping and then interleaving to form an input data symbol. The control information also performs the above processing. The processed service data and control information form the data symbol of the modulation method of the invention by IDFT transformation and frame head addition, enter CP-OFDM to construct the unit, utilize CP-OFDM of the invention to construct the data symbol structure with CP, namely the time domain data, superpose the training sequence of the time domain on this structure, in some systems, the frame head is a group of specific PN/PN-MC sequences, but the training sequence of the time domain of the invention does not limit its type, can be PN, time domain representation or CAZAC sequence of the PN frequency domain PN, therefore superpose the frame head on CP-OFDM time domain data as the training sequence of the time domain, can achieve the purpose of adding frame head and training sequence of the time domain at the same time. Then, the obtained baseband symbol is used as a subframe of a frame structure of a third system, then the subframe and a multiframe synchronous channel are combined into a multiframe through a multiframe framing unit, the multiframe is converted into an output signal through a baseband post-processing unit, and the output signal is converted into a radio frequency signal through frequency conversion of an orthogonal up-conversion unit.
The structure of a digital signal receiving system corresponding to the above-described digital signal transmitting system is shown in fig. 7. The receiving end comprises a de-multiplexing frame unit, a synchronization unit, an equalization unit, a channel estimation unit, a de-multiplexing unit, a control information constellation de-mapping and de-interleaving unit, a control information de-encoding unit, a service data constellation de-mapping and de-interleaving unit and a service data de-encoding unit.
The multiframe decoding unit decodes the received multiframe into a plurality of subframes, and for each subframe, the synchronization unit synchronizes the baseband data group to obtain a baseband synchronization symbol group. And the channel estimation unit performs channel estimation on the time domain training sequence which is not interfered to obtain channel impact response. The equalization unit subtracts the time domain training sequence subjected to the channel impulse response from the baseband data to obtain a baseband time domain symbol, and transmits the baseband time domain symbol to the demultiplexing unit. The demultiplexing unit transforms and decomposes the baseband time domain symbols to obtain control information and service data. The constellation demapping, deinterleaving and de-encoding are firstly carried out on the control information to obtain the information such as modulation and encoding of the service data of each path, and then the demapping, deinterleaving and de-encoding are carried out on the service data of each path according to the information to obtain the service data of each path.
Those skilled in the art will recognize that the foregoing description is merely one or more embodiments of the present invention, and is not intended to limit the invention thereto. Any equivalent changes, modifications and equivalents of the above-described embodiments are within the scope of the invention as defined by the appended claims, and all such equivalents are intended to fall within the true spirit and scope of the invention.
Claims (7)
1. An OFDM demodulation method containing time domain training sequence includes synchronization, channel estimation and equalization, which is characterized in that:
in the synchronization step, a baseband data group is transformed to obtain time domain data of a baseband synchronization symbol group subjected to channel response, wherein the last P data of each group of baseband synchronization symbols are 2 times of an undisturbed time domain training sequence;
in the channel estimation step, a time domain training sequence which is not interfered is used for channel estimation to obtain channel impact response;
the equalization step subtracts the time domain training sequence after channel impulse response from the baseband data to obtain a baseband time domain symbol,
wherein, the baseband time domain symbol is:
where k denotes the kth set of time domain data, sk，mIs an input data symbol of the time domain, xk，mIs a baseband time domain symbol, pk，mIs a training sequence in the time domain and,
in the synchronization step, the baseband data received later is subtracted by the baseband data received first, and the cyclic prefix is eliminated to obtain a 2-time domain training sequence, wherein the obtained baseband synchronization symbol is as follows:
where k denotes the k-th set of baseband data received, xk，mIs a baseband time domain symbol, x'k，mFor baseband synchronization symbols, sk，mIs an input data symbol of the time domain, pk，mIs a time domain training sequence, where N is the number of subcarriers of an OFDM symbol and P is the length of a cyclic prefix.
2. The OFDM demodulation method according to claim 1, wherein the channel estimation step averages consecutive groups of baseband data to obtain a 2P-length sequence for channel estimation, wherein the 2P-length sequence includes a time domain training sequence and an inverted sequence of the time domain training sequence, for each group of baseband data having the same time domain training sequence.
3. The OFDM demodulation method comprising time domain training sequence as claimed in claim 2, wherein the channel estimation step averages the consecutive M groups of baseband data to obtain:
wherein,；
wherein,is the averaged baseband data, sk，mIs an input data symbol of the time domain, p0，p1，…，pP-1Is a set of time domain training sequences, hlIs the channel impulse response, and L is the number of channel impulse responses.
4. The OFDM demodulation method comprising time domain training sequences according to claim 1, wherein the channel estimation step uses 2 times of the time domain training sequence without interference for the different baseband data of each set of time domain training sequences to perform channel estimation.
5. The OFDM demodulation method comprising time domain training sequence as claimed in claim 1, wherein for a set of baseband data, the equalizing step decomposes the received baseband data into
Wherein, yk，mIs the k-th set of baseband data,is the training sequence of channel impulse response or the inverse sequence of the training sequence or zero, hlIs the channel impulse response, nk,m+PIs the average power N0White gaussian noise of (1); and subtracting the time domain training sequence subjected to channel impulse response and the inverted sequence of the time domain training sequence from the baseband data, and converting to obtain a baseband time domain symbol.
6. A digital signal receiving system applying the OFDM demodulation method including the time domain training sequence of claim 1, wherein the receiving system includes a synchronization unit, an equalization unit, a channel estimation unit, a demultiplexing unit, a system information decoding unit, a constellation demapping and deinterleaving unit, and a decoding unit; the synchronization unit synchronizes the baseband data groups to obtain baseband synchronization symbol groups; the channel estimation unit carries out channel estimation on the time domain training sequence which is not interfered to obtain channel impact response; the equalization unit subtracts the time domain training sequence subjected to channel impulse response from baseband data to obtain a baseband time domain symbol; the demultiplexing unit transforms and decomposes the baseband time domain symbol to obtain system information and a data symbol; the system information decoding unit extracts data symbols according to the system information; the constellation demapping and deinterleaving unit demaps and deinterleaves the data symbols; and finally, the decoding unit decodes to obtain the final data information.
7. A digital signal receiving system applying the OFDM demodulation method including the time domain training sequence of claim 1, wherein the receiving system includes a demultiplexing frame unit, a synchronization unit, an equalization unit, a channel estimation unit, a demultiplexing unit, a control information constellation demapping and deinterleaving unit, a control information demapping and deinterleaving unit, a service data constellation demapping and deinterleaving unit, and a service data deinterleaving unit; wherein, the multiframe decoding unit decodes the received multiframe into a plurality of subframes; for each subframe, the synchronization unit synchronizes the baseband data group to obtain a baseband synchronization symbol group; the channel estimation unit carries out channel estimation on the time domain training sequence which is not interfered to obtain channel impact response; the equalization unit subtracts the time domain training sequence subjected to channel impulse response from baseband data to obtain a baseband time domain symbol; the demultiplexing unit transforms and decomposes the baseband time domain symbols to obtain control information and service data; the control information constellation demapping and deinterleaving unit performs constellation demapping and deinterleaving on the control information; the control information decoding unit decodes the data to obtain the modulation and coding information of the service data of each path; the service data constellation demapping and deinterleaving unit demaps and deinterleaves each path of service data; and the service data decoding unit decodes the data to obtain each path of service data.
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