CN101605120B - Method and device for decoding iterated internal code and evaluating channel for orthogonal frequency division multiplexing system - Google Patents
Method and device for decoding iterated internal code and evaluating channel for orthogonal frequency division multiplexing system Download PDFInfo
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Abstract
The invention discloses a method and a device for decoding an iterated internal code and evaluating a channel for an orthogonal frequency division multiplexing system. The iterating method comprises the following steps: at a transmitting end, carrying out internal code encoding and intraframe interleaving by a code with a long short code; at a receiving end, calculating circular convolution of an OFDM time domain data block and an evaluation value of channel time domain impulse response based on an initial evaluation value of the channel time domain impulse response; completing constellation de-mapping according to the channel evaluation and the result of circular convolution to acquire bit soft information; carrying out intraframe de-interleaving and internal code decoding on the bit soft information to acquire decoded bit soft information, carrying out intraframe interleaving on the decoded bit soft information, and remapping the constellation; and updating the evaluation value of the channel time domain impulse response according to the remapped result, and carrying out channel evaluation post-treatment. The method and the device can improve channel evaluation precision, and reduce system error rate, thereby improving system performance, in particular mobile performance, and ensuring complexity and controllable time delay of the system.
Description
Technical field
The present invention relates to digital information transmission technical field, relate in particular to a kind of iteration inner code decoder and channel estimation methods and device that is used for ofdm system.
Background technology
The broadband wireless transmission faces the frequency selective fading problem that multipath effect causes.OFDM (Orthogonal Frequency Division Multiplexing, OFDM) technology can effectively be resisted multipath effect, has been widely used in as in the wireless communication systems such as WLAN (wireless local area network), wireless MAN, digital audio and video broadcasting.
In the ofdm system of radio communication, channel frequency domain response or time domain impulse response directly affect the service behaviour of system accurately.The received signal of receiving terminal is the result after transmission signal and the channel impulse response convolution, in order correctly to recover transmit frame signals, need obtain channel frequency domain response or time domain impulse response accurately.
The decoding of receiver and channel estimating are the right challenges of wireless communication system demand side in the ofdm system.At receiving terminal, need to make up the circular convolution of i frame time domain OFDM data piece and channel impulse response, through obtaining i frame frequency numeric field data symbol after the OFDM demodulation.The frequency domain data symbol is through after separating mapping, deinterleaving, decoding, for the frequency domain data with demodulation is used to upgrade channel estimating, need through interweave again, all or part of frequency domain data symbol that has recovered of processing such as mapping again.Do not use iterative algorithm in some prior aries but directly utilize training sequence to carry out channel estimating.Training sequence owing to multipath effect, not only is subjected to noise jamming at receiving terminal, but also is subjected to the interference of data in transmission course.When directly utilizing training sequence to estimate, it is low to obtain the channel estimation results accuracy, and performance can sharply descend when especially having big Doppler frequency-shift.Use long code decoding and long interweaving to decipher and channel estimating in some prior aries in the ofdm system in addition, the complexity and the time-delay degree of the rapid increase of this method meeting system, and precision of channel estimation is low, error rate of system is high.
Summary of the invention
The objective of the invention is at the deficiencies in the prior art, provide a kind of short ISN and intra-frame interleaving of using to realize iteration inner code decoder and the method and the device of channel estimating accurately.
For achieving the above object, technical scheme of the present invention provides a kind of iteration inner code decoder and channel estimation methods that is used for ofdm system, may further comprise the steps:
S1 utilizes the long interior code coder of short code to carry out the ISN coding i signal frame Bit data to be sent;
S2, the significant bit number according to an orthogonal frequency division multiplex OFDM data block can be carried carries out intra-frame interleaving to the data of carrying out after ISN is encoded;
S3 carries out constellation mapping with the data behind the intra-frame interleaving and obtains frequency domain data symbol to be sent, and M frequency domain data symbol formed a block of frequency domain data, and wherein M is the length of data block;
S4 carries out the OFDM modulation to described block of frequency domain data, obtains time-domain data blocks, then described time-domain data blocks is formed i ofdm signal frame at interval with protection and sends.
Wherein, in step S1, carry out a kind of in convolution code, NR sign indicating number, Gray code and the RM sign indicating number of ISN employed sign indicating number of when coding.
Wherein, in step S3, what the method for " will carry out data behind the intra-frame interleaving carry out constellation mapping obtain frequency domain data symbol to be sent " can be in pulse amplitude modulation, quadrature amplitude modulation and the phase shift keying is a kind of.
The present invention also provides a kind of iteration inner code decoder of ofdm system and signal acceptance method of channel estimating of being used for, and it may further comprise the steps:
B1 utilizes the training sequence information of carrying in i the ofdm signal frame that is received, and obtains channel time domain impulse response estimated value; According to described ofdm signal frame, calculate the circular convolution of OFDM time-domain data blocks and channel time domain impulse response estimated value, and described circular convolution is carried out discrete Fourier transform, realize the OFDM demodulation;
B2 carries out constellation according to the frequency domain data symbol of channel frequency domain impulse response estimated value after to demodulation and separates mapping, obtains the soft information that constellation is separated the Bit data after the mapping;
B3 carries out deinterleaving in the frame to the soft information of described Bit data, and to the inner code decoder that the result of deinterleaving in the described frame carries out soft inputting and soft output, the soft information of the Bit data after obtaining respectively deciphering, i.e. its log-likelihood ratio or its constant times;
B4 carries out intra-frame interleaving to log-likelihood ratio or its constant times of each Bit data after the described decoding, carries out constellation then and shines upon;
B5, the frequency domain data symbol that obtains after utilizing described constellation to shine upon again upgrades the estimated value of channel time domain impulse response, carries out the channel estimating reprocessing then, so far finishes iteration one time; Judge whether to reach maximum iteration time, if then return the signal reception that step B 1 carries out next frame, otherwise repeating step B2～B5 carries out next iteration.
Employed sign indicating number can be convolution code, NR sign indicating number, Gray code or RM sign indicating number when wherein, carrying out inner code decoder in step B3.
Wherein, training sequence information can be the training sequence in training signal frame, the ofdm signal frame, pilot tone that block of frequency domain data comprises, or with the training sequence of ofdm signal frame stack.
Wherein, training sequence can be pseudo random sequence.
The present invention also provides a kind of signal acceptance method that utilizes above-mentioned iteration inner code decoder that is used for ofdm system and channel estimating to carry out the device of channel estimating, and it comprises:
The initial channel estimation module, the training sequence information that is used for utilizing i ofdm signal frame being received to carry obtains channel time domain impulse response estimated value;
The circular convolution constructing module is used for according to described ofdm signal frame, calculates the circular convolution of OFDM time-domain data blocks and channel time domain impulse response estimated value, and it carries out discrete Fourier transform with described circular convolution, realizes the OFDM demodulation;
Separate mapping block, carry out constellation according to the frequency domain data symbol of channel frequency domain impulse response estimated value after and separate mapping, obtain the soft information that constellation is separated the Bit data after the mapping demodulation;
De-interleaving block in the frame is used for the soft information of described Bit data is carried out deinterleaving in the frame;
The inner code decoder module to the inner code decoder that the result of deinterleaving in the described frame carries out soft inputting and soft output, obtains deciphering the soft information of each Bit data of back, i.e. its log-likelihood ratio or its constant times;
Interleaving block again in the frame is used for log-likelihood ratio or its constant times of each Bit data after the described decoding are carried out interweaving in the frame again;
Mapping block again, be used for in the described frame again the data of interleaving block output carry out constellation and shine upon again;
The channel estimating update module, the frequency domain data symbol that obtains after utilizing described constellation to shine upon again upgrades the estimated value of channel time domain impulse response; And
Control module is used to produce the timing control signal of described system, and sends to each module in the described system.
Wherein, this device can also comprise the channel estimating post-processing module, and the channel estimating post-processing module is used for that the estimated value after the renewal of channel estimating update module is carried out time-domain filtering, amplitude limit denoising, smoothing denoising and energy normalized and handles.
According to embodiments of the present invention, at the transmitting terminal of ofdm system, the ISN coding and the intra-frame interleaving that adopt the long sign indicating number of short code to carry out; At receiving terminal, the time domain or the frequency domain sequence symbol that utilize frame structure to carry obtain the initial channel estimation result, make up the circular convolution of time domain OFDM data piece and channel impulse response, finish constellation based on channel estimating and circular convolution result and separate mapping, deinterleaving and inner code decoder and obtain deciphering each bit soft information; To the bit soft information after the decoding carry out interweaving again in the frame, constellation shines upon the estimated value that obtains frequency domain data again, utilize the soft information updating channel estimating of the frequency domain data that recovers, obtain more precise channels estimated value, thereby further make up the circular convolution of time domain OFDM data piece and channel impulse response more accurately, so will obtain better system performance.
Technique scheme has following advantage: realized iteration inner code decoder and channel estimating accurately by using short ISN and intra-frame interleaving, can improve precision of channel estimation, reduce error rate of system, thereby performance, the especially travelling performance of system are provided; The complexity of system and the controllability of time-delay have also been guaranteed simultaneously.
Description of drawings
Fig. 1 is the flow chart of the signaling method of the iteration inner code decoder that is used for ofdm system of the embodiment of the invention and channel estimating;
Fig. 2 is the frame structure schematic diagram of TDS-OFDM system;
Fig. 3 is a kind of frame structure schematic diagram that pilot tone ZP-OFDM system is arranged;
Fig. 4 is a kind of frame structure schematic diagram that does not have pilot tone CP-OFDM system;
Fig. 5 is that the iteration inner code decoder that is used for ofdm system and the channel estimating of the embodiment of the invention carried out the flow chart that signal receives;
Fig. 6 is the iteration inner code decoder that is used for ofdm system of the embodiment of the invention and the decision region schematic diagram that channel estimation methods carries out the QPSK symbol-modulated;
Fig. 7 is under channel 1 environment, and the iteration inner code decoder of the embodiment of the invention and channel estimation methods are applied to a kind of performance of BER curve that does not have the TDS-OFDM system of outer sign indicating number coding, QPSK symbol-modulated;
Fig. 8 is under channel 2 environment, and the iteration inner code decoder of the embodiment of the invention and channel estimation methods are applied to a kind of performance of BER curve that does not have the TDS-OFDM system of outer sign indicating number coding, QPSK symbol-modulated;
Fig. 9 is under channel 1 environment, and the iteration inner code decoder of the embodiment of the invention and channel estimation methods are applied to the performance of BER curve of the TDS-OFDM system of the outer sign indicating number coding of a kind of LDPC of employing, QPSK symbol-modulated;
Figure 10 is under channel 2 environment, and the iteration inner code decoder of the embodiment of the invention and channel estimation methods are applied to the performance of BER curve of the TDS-OFDM system of the outer sign indicating number coding of a kind of LDPC of employing, QPSK symbol-modulated.
Wherein, BER is the error rate, and SNR is a signal to noise ratio.
Embodiment
Below in conjunction with drawings and Examples, the specific embodiment of the present invention is described in further detail.Following examples are used to illustrate the present invention, but are not used for limiting the scope of the invention.
Fig. 1 for the iteration inner code decoder that is used for ofdm system of the embodiment of the invention and the flow chart of signaling method.As shown in Figure 1, this method may further comprise the steps:
S1 utilizes the long interior code coder of short code to carry out the ISN coding i signal frame Bit data to be sent.
S2 according to the significant bit number that an orthogonal frequency division multiplex OFDM data block can be carried, delays time than short intra-frame interleaving to the data of carrying out after ISN is encoded.
S3 will carry out data behind the intra-frame interleaving and carry out constellation mapping and obtain frequency domain data symbol to be sent, and M frequency domain data symbol formed a block of frequency domain data, and wherein M is the length of data block.That wherein, will carry out that data behind the intra-frame interleaving carry out that constellation mapping obtains that the method for frequency domain data symbol to be sent can be in pulse amplitude modulation, quadrature amplitude modulation and the phase shift keying is a kind of.For example, carry out the QPSK constellation mapping, adjacent per two Bit datas are one group and are mapped to a QPSK constellation symbol.
S4 carries out the OFDM modulation to block of frequency domain data, obtains time-domain data blocks, then described time-domain data blocks is formed i ofdm signal frame at interval with protection and sends.
The selection of carrying out ISN employed sign indicating number of when coding has multiple, (16,8,6) NR (Nordstrom-Robinson) sign indicating number for example, and its code length is 16 bits, 8 bit information positions, minimum free distance is 6.In addition, be applicable to that the sign indicating number that soft inputting and soft is exported also has Gray code, RM sign indicating number, convolution code etc.For example use the NR coding, the Bit data input NR encoder after interweaving between per 8 bit frame obtains 16 Bit datas, comprises 8 information bits and 8 redundant bits.
For different ofdm systems, the frame structure difference of its signal frame.
For example, Fig. 2 is the frame structure schematic diagram of TDS-OFDM system.As shown in Figure 2, when sending signal, i frame frequency domain data symbol waiting for transmission is X
i(k), wherein do not contain pilot tone and virtual subnet carrier wave.Block of frequency domain data { X
i(k) }
K=0 M-1Behind inverse discrete fourier transform, obtain time-domain data blocks { x
i[n] }
N=0 M-1, training sequence is filled in the protection between time-domain data blocks at interval, and for example length is the known pseudo-random training sequence { c of L
i[n] }
N=0 L-1A complete TDS-OFDM system signal frame is formed in time-domain data blocks (frame) and protection (frame head) at interval.One group of signal frame and a time slot head constitute a complete time slot, and wherein, the time slot head is filled identical pseudorandom training sequence { c at interval with the protection of first signal frame
i[n] }
N=0 L-1Wherein M is the length of data block.
Last example is concrete an enforcement of the iteration inner code decoder and the channel estimation methods of the present invention's proposition, and it adopts QPSK gray mappings and NR sign indicating number ISN coding.Utilize training sequence to obtain initial channel estimation at receiving terminal, utilize the initial channel estimation result to carry out OFDM demodulation, constellation then and separate in deinterleaving in mapping, the frame, inner code decoder, the frame estimated value that step such as interweave again, constellation shines upon again obtains block of frequency domain data, utilize the correct frequency domain data feedback renewal channel estimating of recovering in the frame frequency numeric field data piece, obtain the estimated value of precise channels frequency domain response more or time domain impulse response, estimated value is carried out necessary reprocessing, as time-domain filtering, amplitude limit denoising, smoothing denoising and energy normalized etc.Channel frequency domain response after the renewal or time domain impulse response estimated value can be used to further auxiliary OFDM and separate the mediation inner code decoder, so realize iteration inner code decoder and channel estimating.
And for example, Fig. 3 is a kind of frame structure schematic diagram that pilot tone ZP-OFDM system is arranged.As shown in Figure 3.When sending signal, i frame frequency domain data symbol waiting for transmission is X
i(k), become length with the virtual subnet carrier wave set be the block of frequency domain data { X of M to frequency domain data symbol to be transmitted
i(k) }
K=0 M-1, wherein some frequency domain data symbol waiting for transmission is known, promptly block of frequency domain data comprises pilot tone.Block of frequency domain data { X
i(k) }
K=0 M-1Behind inverse discrete fourier transform, obtain time-domain data blocks { x
i[n] }
N=0 M-1The nil symbol that length is L is filled in protection before time-domain data blocks at interval.Time-domain data blocks (frame) and nil symbol protection (frame head) is at interval formed one and complete pilot tone ZP-OFDM system signal frame is arranged.One group of signal frame constitutes a complete time slot, the virtual subnet carrier wave that comprises in the block of frequency domain data of unlike signal frame is identical, but pilot tone can be different, and for example pilot tone can be the certain rules variation, and perhaps first signal frame of each time slot can comprise more pilot than other signal frame.
For another example, Fig. 4 is a kind of frame structure schematic diagram that does not have pilot tone CP-OFDM system.As shown in Figure 4.When carrying out the signal transmission, i frame frequency domain data symbol waiting for transmission is X
i(k), become length with the virtual subnet carrier wave set be the block of frequency domain data { X of M to frequency domain data symbol waiting for transmission
i(k) }
K=0 M-1, wherein do not comprise pilot tone.Block of frequency domain data { X
i(k) }
K=0 M-1Behind inverse discrete fourier transform, get time-domain data blocks { x
i[n] }
N=0 M-1The Cyclic Prefix that length is L is filled in protection before time-domain data blocks at interval.Time-domain data blocks (frame) and Cyclic Prefix (frame head) are formed a complete no pilot tone CP-OFDM system signal frame.A training signal frame and one group of data frame signal constitute a complete time slot.The structure of training signal frame and data frame signal is identical, but the data block of training signal frame d[n] }
N=0 M-1For known, promptly the effective subcarrier in the block of frequency domain data carries known frequency domain data symbol.
The TDS-OFDM system of Fig. 2 correspondence, frame head is a time domain PN sequence in the signal frame, is used for synchronous and initial channel estimation etc.The frequency domain symbol piece obtains time-domain data blocks to be sent through inverse fourier transform after the constellation mapping.PN sequence and time-domain data blocks are formed frame structure as shown in Figure 2, obtain one group of TDS-OFDM system signal frame.
The ZP-OFDM system that pilot tone is arranged of Fig. 3 correspondence, the training information that system frame structure carries is the pilot tone of frequency domain, signal heads is a time domain nil symbol padding sequence in the frame.Frequency domain data symbol, pilot sub-carrier and virtual subnet carrier wave are formed the block of frequency domain data that length is M together after the constellation mapping.Described block of frequency domain data obtains time-domain data blocks behind inverse discrete fourier transform.Nil symbol and time-domain data blocks are formed frame structure as shown in Figure 3, and obtaining one has pilot tone ZP-OFDM system signal frame.
The no pilot tone CP-OFDM system of Fig. 4 correspondence, first signal frame of time slot is the training signal frame, and its data block is known, and data block provides protection by Cyclic Prefix, and the signal heads in the frame is the data block padding sequence, and the Cyclic Prefix protection is provided.Frequency domain data symbol and virtual subnet carrier wave are formed the block of frequency domain data that length is M together, do not comprise pilot tone.Described block of frequency domain data obtains time-domain data blocks behind inverse discrete fourier transform.Cyclic Prefix and time-domain data blocks are formed frame structure as shown in Figure 4, and obtaining one group does not have pilot tone CP-OFDM system signal frame.
Fig. 5 is the iteration inner code decoder that is used for ofdm system of the embodiment of the invention and the signal acceptance method flow chart of channel estimating.As shown in Figure 5, may further comprise the steps:
B1 utilizes the training sequence information of carrying in i the ofdm signal frame that is received, and obtains channel time domain impulse response estimated value; According to described ofdm signal frame, calculate the circular convolution of OFDM time-domain data blocks and channel time domain impulse response estimated value, and described circular convolution is carried out discrete Fourier transform, realize the OFDM demodulation.
Wherein, for different ofdm systems, obtain the method difference of channel time domain impulse response estimated value.
For example, for TDS-OFDM signal frame shown in Figure 2, its first signal frame carries out the first time during iteration, and utilizing the time slot head is the Cyclic Prefix of the first frame signal training sequence, directly calculates initial channel time domain impulse response estimated value { h
i[n] }
N=0 L-1, conversion obtains initial channel frequency domain response estimation value { H through the M point discrete Fourier
i[n] }
N=0 M-1Non-first frame signal is carried out the first time during iteration, utilize the channel estimation results of front signal frame to carry out interpolation arithmetic and obtain the channel impulse response estimation value.
And for example, for the ZP-OFDM signal frame that pilot tone is arranged shown in Figure 3, the training sequence information that its frame structure carries is pilot tone.The pilot tone that the one or more signal frames that utilize to receive carry is not comprised the initial channel frequency response estimated value { H of the block of frequency domain data of virtual subnet carrier wave by the method for frequency domain interpolation
i[n] }
N=0 M-1, for the block of frequency domain data that comprises the virtual subnet carrier wave, initial channel frequency domain impulse response estimated value is set to zero.
For another example, for no pilot tone CP-OFDM signal frame shown in Figure 4, its first signal frame is the training signal frame, and its time-domain data blocks is known, and time-domain data blocks provides protection by Cyclic Prefix, therefore can directly calculate initial channel impulse response estimated value.To comprising the block of frequency domain data of virtual subnet carrier wave, initial channel frequency domain response estimation value is set to zero; Non-first frame signal is carried out the first time during iteration, utilize the channel estimation results of front signal frame to carry out interpolation calculation and obtain the channel impulse response estimation value.
And for different ofdm systems, it is also different with the method for the circular convolution of channel time domain impulse response estimated value to calculate the OFDM time-domain data blocks.
For example, for TDS-OFDM system shown in Figure 2, received signal be pseudo random sequence and data block respectively with the linear convolution of channel time domain impulse response, so pseudo random sequence part and data block portions mutual interference mutually in the received signal.The channel estimation value of utilizing step B1 to obtain deducts the linear convolution of pseudo random sequence and channel time domain impulse response from received signal, eliminate the interference of training sequence to data block, obtains the linear convolution of data block and channel time domain impulse response.In computational process, can utilize the character of circular convolution, can obtain the circular convolution result { y of time-domain data blocks and channel time domain impulse response by linear convolution through simple operation
i[n] }
N=0 M-1
And for example, for the ZP-OFDM system that pilot tone is arranged shown in Figure 3, each signal frame is filled protection at interval by nil symbol, therefore can directly obtain the linear convolution of time-domain data blocks and channel time domain impulse response.Utilize the character of circular convolution, can be by linear convolution through simple operation computation cycles convolution results { y
i[n] }
N=0 M-1
For another example, for shown in Figure 4 no pilot tone CP-OFDM system, each signal frame is filled protection at interval by Cyclic Prefix, therefore can directly obtain circular convolution result { y from received signal
i[n] }
N=0 M-1
In above-mentioned three kinds of situations, time-domain data blocks { x
i[n] }
N=0 M-1With channel time domain impulse response { h
i[n] }
N=0 L-1Circular convolution { y
i[n] }
N=0 M-1Obtain frequency domain data symbol { Y through discrete Fourier transform (DFT)
i[n]
N=0 M-1, realize the OFDM demodulation.
B2 carries out constellation according to the frequency domain data symbol of channel frequency domain impulse response estimated value after to demodulation and separates mapping, obtains the bit soft information after constellation is separated mapping.To carry out the method that constellation mapping obtains frequency domain data symbol to be sent be quadrature amplitude modulation if will carry out data behind the intra-frame interleaving in the step S3 of signaling method, and it is as follows that constellation is separated mapping steps:
Suppose that noise variance is σ
w 2, block of frequency domain data is carried out phasing handles:
H wherein
i *[n] represents H
iThe conjugation of [n].Z
iThe bit soft information that the constellation of [n] real part correspondence is separated after the mapping is shown below:
In like manner, the constellation of the imaginary part correspondence bit soft information of separating after the mapping is shown below:
B3 carries out to the soft information of described Bit data that deinterleaving obtains { S in the frame
i[n] }
N=0 2M-1, be one group with tactic bit soft information after the deinterleaving in 16 frames, input NR decoder carries out soft input soft output decode, the log-likelihood ratio of each bit after obtaining deciphering or its integral multiple.
B4 carries out interweaving in the frame to log-likelihood ratio or its integral multiple of each bit after the decoding again, carries out constellation then and shines upon.Concrete steps are as follows: the bit soft information after the log-likelihood ratio of each bit behind the inner code decoder or its integral multiple obtain interweaving through intra-frame interleaving, it is shone upon processing again through constellation, and obtain the soft information of QPSK symbol.The concrete operations that constellation shines upon again can utilize the tanh function to carry out filtering to the back bit information that interweaves, promptly
Under the actual transmissions environment, the channel transfer characteristic that each signal frame experienced is different, it is channel possibility life period selectivity, therefore the credibility of each bit signal is different, the definitional part judgement is: symbol space is divided into decision region and non-decision region, only the symbol in the decision region is adjudicated.Therefore for filtered bit sequence
Set a confidential interval Ω, as shown in Figure 6, when
When falling into confidential interval,
Be judged to from its that nearest symbol.QPSK modulation is that the signal map with two bits is a QPSK symbol, therefore has only and works as
With
When two adjacent bit all fall into confidential interval Ω, could recover a QPSK symbol
B5, the frequency domain data symbol that obtains after utilizing described constellation to shine upon again upgrades the estimated value of channel time domain impulse response.Concrete steps are: for partly adjudicated the data symbol that recovers by step B4
The time domain OFDM data piece that obtains according to step B1 and the circular convolution { Y of channel impulse response
i[n] }
N=0 M-1, utilize
Obtain the channel information of a subcarrier; For the subcarrier of unsentenced symbol correspondence, keep the channel frequency domain impulse response of this point constant, promptly
Thus, upgrade a channel estimating.
Carry out the channel estimating reprocessing then, so far finish iteration one time, judge whether to reach maximum iteration time then, if then return the signal reception that step B1 carries out next frame, otherwise repeating step B2～B5 carries out next iteration.Wherein, the channel frequency domain response estimation after step B5 obtains upgrading
Its length is data block length, considerably beyond the maximum delay expansion, need carry out the processing of time-domain filtering, amplitude limit denoising, smoothing denoising and energy normalized usually, and the specific implementation step is:
(1). according to the limited feature of channel impulse response length, the channel impulse response result is carried out time-domain filtering, for example the channel impulse response result is blocked to known length;
(2). according to current snr of received signal information, set the channel magnitude thresholding, channel impulse response is set to zero in the amplitude position that is lower than the channel magnitude thresholding as a result;
(3). utilize the weighted average of existing channel estimation results and current channel estimation results, channel estimation results is carried out time domain or frequency domain smoothing;
(4). according to the reference value of channel impulse response energy, channel impulse response be multiply by the energy normalized compensating factor.
In the present embodiment, training sequence information can be the training sequence in training signal frame, the OFDM Frame, or with the training sequence of ofdm signal frame stack.
The present invention is directed to TDS-OFDM system shown in Figure 2 and carried out Computer Simulation, main simulation parameter is as shown in table 1.Two kinds of used channel models are typical wireless multipath Rayleigh fading channel as shown in table 2 in the emulation, wherein, channel 1 is that Chinese pbs film TV is managed the single frequency network model that general bureau proposes in the Digital Television test report, and it comprises the 0dB echo that time-delay reaches 30us; Channel 2 is the Brazilian A models that are used for the place test.
Table 1
| Symbol rate | 7.56M symbol/second |
| OFDM subcarrier planisphere | QPSK |
| OFDM sub-carrier number N d | 3780 |
| Doppler frequency- |
0/25/50Hz |
| Training sequence length | 420 |
Table 2
For comparative analysis, simulation result has provided BER (Bit Error Rate, the bit error rate) performance curve that the TDS-OFDM system obtains under known channel time domain impulse response, employing iteration inner code decoder and channel estimation methods, the non-iteration inner code decoder of employing and three kinds of situations of channel estimation methods.Fig. 7 is under channel 1 environment, a kind of performance of BER curve of TDS-OFDM system under above-mentioned three kinds of situations that does not have outer sign indicating number coding, QPSK symbol-modulated; Fig. 8 is under channel 2 environment, the performance of BER curve of TDS-OFDM system under above-mentioned three kinds of situations.From Fig. 7 and Fig. 8 as can be seen, Doppler frequency-shift f
dWhen equaling 0Hz, the TDS-OFDM system performance of BER under above-mentioned three kinds of situations is suitable; When existing bigger spectrum to rein in frequency displacement, the error performance that adopts iteration inner code decoder provided by the invention and channel estimation methods to obtain obviously is better than the method for traditional non-iteration inner code decoder and channel estimating.
Fig. 9 is under channel 1 environment, and outer sign indicating number adopts the performance of BER curve of TDS-OFDM system under above-mentioned three kinds of situations of LDPC sign indicating number, QPSK symbol-modulated; Figure 10 is under channel 2 environment, the performance of BER curve of TDS-OFDM system under above-mentioned three kinds of situations.As can be seen from Figure 9, fast-changing channel 1 time, the TDS-OFDM system that adopts non-iteration inner code decoder and channel estimation methods almost can't operate as normal, and the TDS-OFDM system bit error rate characteristic that adopts iteration inner code decoder provided by the invention and channel estimation methods to obtain obviously is better than traditional non-iteration inner code decoder and channel estimation methods.
As can be seen from the above embodiments, embodiments of the invention have been realized channel estimating and iteration inner code decoder accurately by using short ISN and intra-frame interleaving, and can improve precision of channel estimation, reduce error rate of system, thereby the serviceability and the travelling performance of system are provided; Simultaneously, Duan ISN and intra-frame interleaving have also guaranteed the complexity of system and the controllability of time-delay.
The above only is a preferred implementation of the present invention; should be pointed out that for those skilled in the art, under the prerequisite that does not break away from the technology of the present invention principle; can also make some improvement and modification, these improve and modification also should be considered as protection scope of the present invention.
Claims (9)
1. one kind is used for the iteration inner code decoder of ofdm system and the signaling method of channel estimating, it is characterized in that, may further comprise the steps:
S1 utilizes the long interior code coder of short code to carry out the ISN coding i signal frame Bit data to be sent;
S2, the significant bit number according to an orthogonal frequency division multiplex OFDM data block can be carried carries out intra-frame interleaving to the data of carrying out after ISN is encoded;
S3 carries out constellation mapping with the data behind the intra-frame interleaving and obtains frequency domain data symbol to be sent, and M frequency domain data symbol formed a block of frequency domain data, and wherein M is the length of data block;
S4 carries out the OFDM modulation to described block of frequency domain data, obtains time-domain data blocks, then described time-domain data blocks is formed i ofdm signal frame at interval with protection and sends.
2. the iteration inner code decoder of ofdm system and the signaling method of channel estimating of being used for as claimed in claim 1, it is characterized in that, in described step S1, carry out a kind of in convolution code, NR sign indicating number, Gray code and the RM sign indicating number of ISN employed sign indicating number of when coding.
3. the iteration inner code decoder of ofdm system and the signaling method of channel estimating of being used for as claimed in claim 1, it is characterized in that, in described step S3, the method for " will carry out data behind the intra-frame interleaving carry out constellation mapping obtain frequency domain data symbol to be sent " is a kind of in pulse amplitude modulation, quadrature amplitude modulation and the phase shift keying.
4. one kind is used for the iteration inner code decoder of ofdm system and the signal acceptance method of channel estimating, it is characterized in that, may further comprise the steps:
B1 utilizes the training sequence information of carrying in i the ofdm signal frame that is received, and obtains channel time domain impulse response estimated value; According to described ofdm signal frame, calculate the circular convolution of OFDM time-domain data blocks and channel time domain impulse response estimated value, and described circular convolution is carried out discrete Fourier transform, realize the OFDM demodulation;
B2 carries out constellation according to the frequency domain data symbol of channel frequency domain impulse response estimated value after to demodulation and separates mapping, obtains the soft information that constellation is separated the Bit data after the mapping;
B3 carries out deinterleaving in the frame to the soft information of described Bit data, and the result of deinterleaving in the described frame is carried out the inner code decoder that soft inputting and soft is exported, the soft information of each Bit data after obtaining deciphering;
B4 carries out intra-frame interleaving to the soft information of each Bit data after the described decoding, carries out constellation then and shines upon;
The concrete steps of B4 are as follows: the bit soft information after the log-likelihood ratio of each bit behind the inner code decoder or its integral multiple are obtained interweaving through intra-frame interleaving, shine upon processing again through constellation, obtain the soft information of QPSK symbol, the concrete operations that constellation shines upon again are that the back bit information that interweaves is carried out filtering;
Symbol space is divided into decision region and non-decision region, only the symbol in the decision region is adjudicated, for filtered bit sequence
Set a confidential interval Ω, when
When falling into confidential interval,
Be judged to from its that nearest symbol;
B5, the frequency domain data symbol that obtains after utilizing described constellation to shine upon again upgrades the estimated value of channel time domain impulse response, carries out the channel estimating reprocessing then, so far finishes iteration one time; Judge whether to reach maximum iteration time, if then return the signal reception that step B1 carries out next frame, otherwise repeating step B2～B5 carries out next iteration.
5. the iteration inner code decoder of ofdm system and the signal acceptance method of channel estimating of being used for as claimed in claim 4, it is characterized in that a kind of in convolution code, NR sign indicating number, Gray code and the RM sign indicating number of employed sign indicating number when in described step B3, carrying out inner code decoder.
6. the iteration inner code decoder of ofdm system and the signal acceptance method of channel estimating of being used for as claimed in claim 4, it is characterized in that, described training sequence information is the training sequence in training signal frame, the described ofdm signal frame, the pilot tone that block of frequency domain data comprises, or with the training sequence of described ofdm signal frame stack.
7. the iteration inner code decoder of ofdm system and the signal acceptance method of channel estimating of being used for as claimed in claim 4 is characterized in that described soft information is log-likelihood ratio or constant times.
8. a signal acceptance method that utilizes described iteration inner code decoder that is used for ofdm system of claim 4 to 7 and channel estimating carries out the device of channel estimating, and it comprises:
The initial channel estimation module, the training sequence information that is used for utilizing i ofdm signal frame being received to carry obtains channel time domain impulse response estimated value;
The circular convolution constructing module is used for according to described ofdm signal frame, calculates the circular convolution of OFDM time-domain data blocks and channel time domain impulse response estimated value, and it carries out discrete Fourier transform with described circular convolution, realizes the OFDM demodulation;
Separate mapping block, carry out constellation according to the frequency domain data symbol of channel frequency domain impulse response estimated value after and separate mapping, obtain the soft information that constellation is separated the Bit data after the mapping demodulation;
De-interleaving block in the frame is used for the soft information of described Bit data is carried out deinterleaving in the frame;
The inner code decoder module to the inner code decoder that the result of deinterleaving in the described frame carries out soft inputting and soft output, obtains deciphering the soft information of each Bit data of back;
Interleaving block again in the frame is used for log-likelihood ratio or its constant times of each Bit data after the described decoding are carried out interweaving in the frame again;
Mapping block again, be used for in the described frame again the data of interleaving block output carry out constellation and shine upon again;
The channel estimating update module, the frequency domain data symbol that obtains after utilizing described constellation to shine upon again upgrades the estimated value of channel time domain impulse response; And
Control module is used to produce the timing control signal of described system, and sends to each module in the described system.
9. iteration inner code decoder and the channel estimating apparatus that is used for ofdm system as claimed in claim 8, it is characterized in that, described device also comprises the channel estimating post-processing module, and described channel estimating post-processing module is used for that the estimated value after the described channel estimating update module renewal is carried out time-domain filtering, amplitude limit denoising, smoothing denoising and energy normalized and handles.
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| CN108712353B (en) * | 2018-03-29 | 2021-05-11 | 江苏中科羿链通信技术有限公司 | Soft iteration channel estimation method |
| CN108540268B (en) * | 2018-04-17 | 2020-12-18 | 电子科技大学 | IDMA-based joint iteration channel estimation method |
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