CN101115047A - OFDM receiving and dispatching system for high speed mobile environment - Google Patents
OFDM receiving and dispatching system for high speed mobile environment Download PDFInfo
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Abstract
An orthogonal frequency division multiplexing OFDM transceiver system that is applicable to high speed mobile environment belongs to the technical field of digital communication and is characterized in that at the sending end, the data is segmented and goes through fast reverse fourier transform respectively, and OFDM sub-symbols after transformation are directly cascaded and are attached with a zero protective suffix, thus a relatively big sub-carrier interval is acquired and intercarrier interference caused by Doppler-spread is lessened, but the sensitivity of the system to inter sub-symbol interference. At the receiving end, an interference cancellation receiving device and method that uses sub-carrier given information is designed and the inter sub-symbol interference caused by multipath delay spread is eliminated. The invention causes little or no loss in spectral efficiency of OFDM system, and under the same channel condition, the system of the invention can improve the moving speed supported by traditional methods by about 1.6 times.
Description
Technical Field
The invention relates to the technical field of digital communication, in particular to an Orthogonal Frequency Division Multiplexing (OFDM) modulation device for improving the moving speed of a receiver and a receiving method and a device thereof.
Background
Orthogonal frequency division multiplexing (hereinafter abbreviated as OFDM) is widely regarded as an efficient broadband multi-carrier transmission technology, and is adopted in a plurality of broadband transmission technology standards such as the european digital television broadcasting standard DVB-T, the wireless local area network standard IEEE 802.11a, the wireless metropolitan area network standard IEEE 802.16, and the like. However, while broadband services are available, there is an increasing demand for mobility, for example, high-speed mobile applications such as high-speed railways (350 km/h) can enjoy services such as high-definition television broadcasting and wireless broadband internet access. Therefore, improving the capability of the OFDM broadband transmission system against time-varying multipath channels and improving the moving speed of the receiver of the OFDM broadband transmission system have become major problems of the OFDM system.
Due to the broadband characteristics of the signal and the movement of the receiver, the transmission channel exhibits characteristics of large doppler spread and large multipath delay spread, so that the OFDM system is simultaneously affected by intersymbol interference and large inter-subcarrier interference (hereinafter referred to as ICI). In the conventional OFDM system, a transmitting end maps the same symbol to a group of subcarriers, and a receiving end employs a self-cancellation method to mitigate ICI introduced by carrier frequency offset. This approach may lose more than 50% of the throughput and may not effectively mitigate ICI introduced by doppler spreading. Other approaches propose the use of multi-layer equalizers for the receiver to suppress ICI. But the equalizer usually needs ideal channel information, which is difficult to guarantee in practical application.
Disclosure of Invention
The invention designs an orthogonal frequency division multiplexing receiving and transmitting system suitable for a high-speed mobile environment. The purpose is to improve the moving speed of the receiver of the OFDM broadband transmission system under the time-varying multipath channel.
The idea of the invention is that at a sending end, data of the sending end is divided into two parts, fast inverse Fourier transform (IFFT) is respectively carried out, two OFDM sub-symbols generated after the transform are cascaded, and a zero protection suffix is added, so that a larger sub-carrier interval is obtained, and ICI caused by Doppler spread is relieved. But thereby also increases the sensitivity of the system to inter-subsymbol interference (hereinafter ISI). At the receiving end, an interference elimination receiving device and method using the known information of the sub-carrier are designed, and the inter-sub-symbol interference caused by the multipath delay spread is eliminated.
Specifically, the data is divided into two parts, mapsIs expressed as two-part frequency domain subcarrier signal, which is assumed to be respectively expressed as a first sub-symbol frequency domain subcarrier signal X 1 [k]And a second sub-symbol frequency domain sub-carrier signal X 2 [k]K is more than or equal to 0 and less than N, and N is the number of subcarriers of the OFDM system. For the frequency domain subcarrier signal X 1 [k]And X 2 [k]And preprocessing is carried out, the number of the preprocessed subcarrier signals is L, L is a positive integer which is greater than or equal to the maximum delay spread, and the corresponding index is marked as vector m. Thereafter, X 1 [k]And X 2 [k]The signals are respectively input into two IFFT units, the output of the IFFT is cascaded, and the sending signal is
Wherein
Wherein, F (N) (k，x[n]) Represents x [ n ]]Performing N-order DFT operation; f -(N) (n，X[k]) Represents X [ k ]]The N-th order IDFT (hereinafter referred to as inverse discrete fourier transform).
And adding a P-length zero suffix to the tail of the cascaded transmission signal to form a new OFDM symbol, wherein P is the sampling number of the zero suffix and is a positive integer greater than or equal to the maximum delay spread.
At the receiving end, a typical OFDM receiver needs to perform frame synchronization to determine the boundary of each OFDM symbol, and then, the received P-long suffix is added to the head of the OFDM symbol first, so that the linear convolution in the OFDM symbol is equivalent to the cyclic convolution, and then, the N-point fast fourier transform (hereinafter referred to as FFT) is performed on the received signal, and the FFT output can be used in the method and apparatus for interference cancellation reception according to the present invention.
Another aspect of the invention, namely, as describedThe interference elimination receiving device realizes the interference elimination processing of the FFT output. The output of the receiver FFT is divided into even and odd outputs, denoted as
(Vector)
Andto pairAnd
the following treatments were carried out:
wherein, F (N) ∈C N×N Denotes an N-th order normalized DFT (discrete Fourier transform) matrix whose element is F i，j (N) ，0≤i，j＜N；
Is a DFT matrix F (N) Of elements of the submatrix
Is a DFT matrix F (N) Of another half of the submatrix of which the elements are
S is F e Is/are as followsSub-matrix with L rows from F e The corresponding row index mark corresponds to the vector m of the preprocessing index mark of the sending end, and the elements of the vector mS (i，j) ＝F e(m(i)，j) 。R known Is from corresponding
And extracting the vector m corresponding to the index mark from the L multiplied by 1 vector generated by the extracted sub-vector. L is a positive integer equal to or greater than the maximum delay spread.
The above-mentioned combined matrix [ F o |S]Is a reversible Vandermonde (Vandermonde) matrix. Since the matrix S is selected according to the known carrier insertion position at the transmitting end, the coefficient matrix F e [F o |S] -1 The calculation can be carried out in advance in the design of the system, and the operation of matrix inversion in the operation process of the system is not caused.
The interference elimination receiving device also comprises a secondary receiving device which is operated by simple addition and subtraction operationAnd
recovering the first sub-symbol frequency domain sub-carrier signal
And a second sub-symbol frequency domain sub-carrier signal
Will be provided with
And
are respectively expressed as vector quantitiesAnd
the calculation method is expressed as:
the interference cancellation receiving apparatus according to the present invention achieves the purpose of its design, that is, the inter-sub-symbol interference introduced by the symbol concatenation of the transmitting terminal is cancelled. Thereafter, the recovered two-sub-symbol frequency domain sub-carrier signal is subjected to a conventional Least Squares (LS) or Minimum Mean Square Error (MMSE) method
And
and performing channel estimation and equalization processing.
The invention features a transmitter and a receiver, wherein: the transmitter includes: a first serial to parallel converter (102), two pre-processing units (1031) and (1032), N/2 point IFFT units (1011) and (1012), a first parallel to serial converter (104), wherein,
a first serial-to-parallel converter (102) for parallelizing N-L data inputted serially, wherein N is the subcarrier number of the OFDM system, L is an integer which is more than or equal to zero and less than N and is the number of subcarrier signals added in the processing of the two preprocessing units, and the output end of the serial-to-parallel converter is connected with the input ends of the two preprocessing units;
two pre-processing units (1031) and (1032) for pre-processing the parallel data streams mapped to the input terminals of the two IFFT units, the input terminals being connected to the output terminal of the first serial-to-parallel converter for outputting two frequency domain sub-symbols X respectively 1 And X 2 To the input ends of the two IFFT units; the preprocessing unit processes the N-L data input from the first serial-to-parallel converter in three steps:
the preprocessing unit (1031) first generates L 1 A number of arbitrarily designated known data symbols, including null data symbols, L 1 Is an integer greater than or equal to zero and less than or equal to L, and is randomly placed to the frequency domain sub-symbol X 1 As X to be output on the sub-carrier of 1 A portion of which corresponds to L 1 The subcarrier index set is marked as K 1 ，K 1 The value range of the element(s) is an integer which is more than or equal to 1 and less than or equal to N/2; then, the preprocessing unit (1032) generates a non-negative integer L 2 A known or zero data symbol, L 2 ＝L-L 1 And randomly placed to the frequency domain sub-symbol X 2 As X to be output on the sub-carrier of 2 A portion of which corresponds to L 2 Subcarrier index setThe combined mark is K 2 ，K 2 The value range of the element(s) is an integer of 1 or more and N/2 or less, and K 1 ∩K 2 = Ω, i.e. K 1 And K 2 Do not overlap; if K 1 ∩K 2 Not equal to Ω, then repeated random mapping to X 2 Until K 1 ∩ K 2 = omega and is represented by K 1 And K 2 Union of K 1 ∪K 2 Generating a subcarrier index vector m;
the N-L data output by the first serial-parallel converter are sent to two preprocessing units, and the preprocessing units respectively and arbitrarily place the N-L data to X 1 And X 2 On subcarriers with no value set, where X 1 In which a positive integer N/2-L is placed 1 Data, X 2 In which a positive integer N/2-L is placed 2 Data, satisfying that the data subcarrier index and the index vector m are not overlapped;
two preprocessing units respectively output processed X 1 And X 2 ；
Two N/2 point IFFT units (1011) and (1012) for generating two OFDM sub-symbols, wherein the input ends are respectively connected with the output ends of the two preprocessing units, and the output ends are connected with the input end of the first parallel-serial converter;
a first parallel-to-serial converter (104) for serially cascading the outputs of the two IFFT units to form a new OFDM symbol and adding a zero suffix, wherein the input end of the first parallel-to-serial converter is connected with the output ends of the two IFFT units to output a sending signal;
the receiver includes: a second serial-to-parallel converter (204), an N-point FFT unit (202), an interference cancellation receiving apparatus (201), two channel estimation and equalization units (2031) and (2032), a second parallel-to-serial converter (205), wherein,
a second serial-to-parallel converter (204) for parallelizing the serial input data stream, the input being the received transmitter transmit signal, the output being connected to the input of the N-point FFT unit;
an N-point FFT unit (202) for converting an input time domain signal into a frequency domain signal, wherein the input end is connected with the output end of the second serial-parallel converter, and the output end is connected with the input end of the interference elimination receiving device;
an interference elimination receiving device (201) for eliminating inter-sub-symbol interference and inter-sub-carrier interference, wherein the input end is connected with the output end of the N-point FFT unit (202), and the output end is connected with the input ends of the two channel estimation and equalization units; the interference cancellation receiving device includes: even decimator, odd decimator, fixed coefficient linear filter, subcarrier decimator, benefit basic subcarrier generator, adder, subtractor, wherein:
an even extractor for extracting the frequency domain subcarrier signal corresponding to the even index mark output by the N-point FFT unit of the receiving end
The input end is connected with the parallel output end of the N-point FFT unit, and the output end is connected with the input end of the subcarrier extractor and the input end of the adder;
an odd extractor for extracting the frequency domain subcarrier signals corresponding to the odd index marks output by the N-point FFT unit of the receiving end
The input end is connected with the parallel output end of the N-point FFT unit, and the output end is connected with the input end of the fixed coefficient linear filter; a fixed coefficient linear filter for generating a difference signal of the first sub-symbol with respect to the second sub-symbol
The fixed coefficient linear filter is provided with two input ends, one input end is connected with the output end of the complementary base subcarrier generator, the other input end is connected with the output end of the odd extractor, and the output end is simultaneously connected with the input ends of the adder and the subtracter; the fixed coefficient linear filter is configured toThe next three steps produce
Generating coefficient matrix F of the fixed coefficient linear filter e [F o |S -1 Including normalizing the DFT matrix F according to the N order (N) Is/are as follows
Sub-matrix F o And F e The matrix elements of which are respectively
And
regenerated into F e Is/are as follows
S of submatrix, L rows thereof from F e The corresponding row index mark corresponds to the vector m of the preprocessing index mark of the sending end, and the element S of the vector m (i，j) ＝F e(m(i，j) (ii) a Matrix F o Is combined with the matrix S to form
Combined matrix [ F o |S]Calculating an inverse matrix [ F ] of the combined matrix o |S] -1 And the matrix F e Right-hand multiplication to obtain the above-mentioned linear filter with fixed coefficients
Coefficient matrix F e [F o |S] -1 ；
Obtained according to the odd decimator described above
(Vector)
And the L x 1 vector R generated by the base-complementary subcarrier generator known Are combined to form one
Input combination matrix of
Combining the above inputs into a matrix
And the coefficient matrix F e [F o |S] -1 Right multiplication to generate output vector of fixed coefficient linear filter
And output
A subcarrier extractor for extracting K from the output signal of the even extractor according to the subcarrier index set described by the preprocessing unit 1 And K 2 Extracting integer L known sub-carriers, the input end is connected with the output end of the even extractor, and the output end is generated by the complementary base sub-carrierThe input ends of the devices are connected;
a base-complementary subcarrier generator for generating base-complementary subcarriers R from at least an integer number L of known subcarriers obtained by the subcarrier extractor known To satisfy
A solvable base supplementing requirement; the input end is connected with the output end of the subcarrier extractor, and the output end is connected with the input end of the fixed coefficient linear filter; the base-complementing subcarrier generator generates R according to the following two steps known ：
Marking K to index set described in preprocessing unit 1 The corresponding subcarrier signal is taken as R to be output after being negated known The sub-carrier signal element corresponding to the index mark marks K to the index set described in the preprocessing unit 2 The corresponding subcarrier signal is directly used as R to be output known The subcarrier signal element corresponding to the index marker;
output R known ；
An adder for adding the output of said fixed coefficient linear filter and the output of said even decimator, said adder having two inputs, one input connected to the output of said even decimator and one input connected to said fixed coefficient linear filter, and outputting the first recovered sub-symbol frequency domain signalA first output of the interference cancellation receiving means (201);
a subtractor for subtracting the output of said fixed coefficient linear filter from the output of said even decimator, said subtractor having two inputs, one input connected to the output of said even decimator and one input connected to the output of said fixed coefficient linear filter, and outputting a recovered second sub-symbol frequency domain signal
A second output of the interference cancellation receiving means (201);
two channel estimation and equalization units (2031 to 2032) for estimating the channel and equalizing the received signal by Least Squares (LS) or Minimum Mean Square Error (MMSE) algorithm, the input end is connected with the output end of the interference cancellation receiving device, the output end is connected with the input end of the second parallel-serial converter;
and the second parallel-serial converter (205) is used for serially cascading the parallel outputs of the two channel estimation and equalization units, and the input end of the second parallel-serial converter is connected with the output ends of the two channel estimation and equalization units and outputs a received signal.
As described above, the ofdm transceiver system suitable for a high speed mobile environment is characterized in that the transmitter includes M preprocessing units and M N/N point IFFT units, where M is a positive integer greater than or equal to 2 and less than or equal to N. The difference signal in the fixed coefficient linear filter contains M-1 sub-signals, which are the difference between the first frequency domain sub-symbol and the second frequency domain sub-symbol, the difference between the second frequency domain sub-symbol and the third frequency domain sub-symbol, and so on until the difference between the M-1 frequency domain sub-symbol and the M frequency domain sub-symbol.
One advantage of the invention is that the sensitivity of the system to ICI is effectively reduced, and the moving speed of the receiver is increased, which is about 1.6 times higher than that of the conventional method under the same condition, as shown by theoretical analysis and simulation, with a signal-to-noise ratio of 20 dB. In addition, the modulation and receiving method and the device also have the advantages of flexible structure, simple algorithm and easy realization.
It should be noted that most practical OFDM systems insert zero subcarriers for suppressing the out-of-band interference, and these subcarrier information can be used in the above interference cancellation receiving method and apparatus to cancel the inter-subcarrier interference. In addition, when the existing zero subcarriers are insufficient, part of the subcarriers can be preset to be zero at the transmitting end to achieve the same purpose. Therefore, compared with the prior self-elimination method, the overhead of the OFDM broadband transmission system can be greatly reduced.
The above objects and advantages are achieved in a method and apparatus for OFDM modulation and interference cancellation of signals in an OFDM wideband transmission system, wherein digital information symbols are OFDM modulated by applying IFFT to data segments to generate a plurality of OFDM sub-symbols and directly concatenating the OFDM sub-symbols. From the comparison of the performance of fig. 7, it can be seen that the method proposed by the present invention is applied to two doppler spread cases (f) compared to the OFDM system without interference cancellation and the OFDM system applying the self-cancellation method d T s =0.126 and f d T s = 0.081), the method proposed by the invention is used in f d T s Performance and conventional method at f =0.126 d T s The performance is similar when the value is 0.081. Considering that a large number of zero subcarriers exist in the OFDM system generally, the frequency spectrum efficiency of the OFDM system is little or even not lost, and the moving speed supported by the system can be improved by about 1.6 times compared with that supported by the traditional method under the same channel condition.
Drawings
Fig. 1 is a schematic structural diagram of an OFDM modulation apparatus according to the present invention.
Fig. 2 is a schematic diagram of the position of the interference cancellation receiving device in the OFDM receiver according to the present invention.
Fig. 3 is a schematic structural diagram of an interference cancellation receiving apparatus according to the present invention.
Fig. 4 is a flowchart illustrating a preprocessing method in the OFDM modulation apparatus according to the present invention.
FIG. 5 shows a base-complementary subcarrier R of the base-complementary subcarrier generator in the interference cancellation receiving apparatus of the present invention known Is used for generating the method.
Fig. 6 is a flowchart illustrating the operation of the method for calculating the fixed coefficient linear filter in the interference cancellation receiving apparatus according to the present invention.
Fig. 7 is a graph comparing the performance of the method of the present invention with the non-interference cancellation method and the self-cancellation method.
Detailed Description
According to an aspect of the present invention, there is provided an OFDM modulation apparatus (see fig. 1) comprising two N/2-point IFFT units, where N is the number of OFDM system subcarriers, for generating two OFDM subsymbols; a serial-to-parallel converter for parallelizing a serial data stream; two preprocessing units for preprocessing the parallel data streams mapped to the two IFFT unit input terminals; and the parallel-serial converter is used for serially cascading the outputs of the two IFFT units to form a new OFDM symbol and adding a zero suffix.
The present invention also provides a method for preprocessing at a transmitting end (see fig. 4), where the method includes: l subcarriers are randomly selected from frequency domain sub-symbol X 1 And X 2 Select a parallel zero or known value, whose subcarrier index sets are respectively marked as K 1 And K 2 And satisfy K 1 ∩K 2 = phi, the union of the two index-marker sets yields the index vector m. Specifically, the preprocessing unit 1031 first generates L 1 A number of arbitrarily designated known data symbols, including null data symbols, L 1 Is an integer greater than or equal to zero and less than or equal to L, and is randomly placed in the frequency domain sub-symbol X 1 As X to be output on the sub-carrier of 1 A portion of which corresponds to L 1 The index set of each subcarrier is marked as K 1 ，K 1 The value range of the element(s) is an integer which is more than or equal to 1 and less than or equal to N/2; the second preprocessing unit 1032 then generates a non-negative integer L 2 A known or zero data symbol, L 2 ＝L-L 1 And randomly placed to the frequency domain sub-symbol X 2 As X to be output on the sub-carrier of 2 A portion of which corresponds to L 2 The subcarrier index set is labeled K 2 ，K 2 Is obtained by takingThe value range is an integer of 1 or more and N/2 or less, and K 1 ∩K 2 = Ω, i.e. K 1 And K 2 Do not overlap; if K 1 ∩K 2 Not equal to Ω, then repeated random mapping to X 2 Until K 1 ∩K 2 = omega and is represented by K 1 And K 2 Union of K 1 ∪K 2 Generating a subcarrier index vector m; since there are many zero subcarriers in an actual OFDM system, assuming that the OFDM system has S zero subcarriers, if S ≧ L, the vector m can be selected among the zero subcarriers. If S < L, L-S sub-carriers are set to zero at the transmitting end except that the S zero sub-carriers are selected. The first serial-parallel converter outputs N-L data to twoA preprocessing unit for respectively and arbitrarily placing the same to X 1 And X 2 On subcarriers with no value set, where X 1 In which positive integer N/2-L1 data, X 2 In which a positive integer N/2-L is placed 2 Data, satisfying that the data subcarrier index and the index vector m are not overlapped; the two preprocessing units respectively output the processed X 1 And X 2 。
According to another aspect of the present invention, there is provided an interference cancellation receiving apparatus in an OFDM broadband transmission system receiver. The position of the interference cancellation receiver in the OFDM receiver is shown in fig. 2. A typical OFDM system receiver first needs to determine the boundary of the OFDM symbol, then the received P long suffix is added to the OFDM symbol header first, making the linear convolution within the OFDM symbol equivalent to a cyclic convolution, and each OFDM symbol is then subjected to an N-point FFT. The input of the interference elimination receiving device is connected with the parallel output end of the N-point FFT unit, and the output of the interference elimination receiving device is connected with the channel estimation and equalization unit.
The interference cancellation receiving apparatus provided by the present invention (see fig. 3) includes: even extractor for extracting frequency domain subcarrier signal corresponding to the even index mark at the output end of the N-point FFT unit and representing as vector
Odd decimator for extracting frequency domain subcarrier signals corresponding to odd index marks at output end of the N-point FFT unit and representing the frequency domain subcarrier signals as vectors
A subcarrier extractor for extracting the frequency domain subcarrier signal corresponding to the index mark vector m from the even extractor; a base-complementary subcarrier generator for generating base-complementary subcarrier vectors R from the frequency-domain subcarrier signals extracted by the subcarrier extractor known (ii) a A fixed coefficient linear filter for the vector R obtained from the base-complementary subcarrier generator known And vectors obtained by the above-mentioned odd decimator
In the method, the vector is calculated by adopting the formula (4)
An adder for slave vector
Vector obtained by equation (3)
And vectors obtained from fixed coefficient linear filters
Adding to obtain sub-symbol frequency domain sub-carrier signal after eliminating interferenceA subtractor for slave vector
Vector obtained by equation (3)
And vectors obtained from fixed coefficient linear filters
Subtracting to obtain sub-symbol frequency domain sub-carrier signal after interference elimination
The invention also provides a base-complementing subcarrier R in the base-complementing subcarrier generator known The method corresponds to the method for preprocessing the sending end. The method comprises the following steps: for vectors
Middle index mark k 1 The negative of the subcarrier signal element is taken as a vector R known Middle index mark k 1 Sub-carrier signal elements of, i.e.
For vector
Middle index mark k 2 Directly as a vector R known Middle index mark k 2 Sub-carrier signal elements of, i.e.
The invention also provides a method for calculating vector by using the fixed coefficient linear filter
The method of (1). The calculation method comprises the following steps: first, a coefficient matrix of the fixed coefficient linear filter is generated, including the DFT matrix F (N) Is/are as follows
Submatrix F o And F e Is/are as followsSub-matrix S, forming a
Combined matrix [ F ] o |S]Calculating the inverse matrix [ F ] of the combined matrix o |S] -1 And the DFT matrix F (N) Sub-matrix F of e Multiplying by the right side to obtain the above solidsOf constant-coefficient linear filters
Coefficient matrix F e [F o |S] -1 The calculation of the coefficient matrix can be performed in advance during the system design; obtained from the odd decimator
(Vector)
And the L x 1 vector R generated by the base-complementary subcarrier generator known Form a
Input combination matrix of
Finally, the above-mentioned inputs are combined into matrix
And the coefficient matrix F e [F o |S] -1 Right multiplication (see equation 4) to obtain a vector
Other objects, features and advantages of the present invention will be better understood from the following detailed description of the embodiments of the OFDM modulation apparatus and the method and apparatus for interference cancellation reception at a receiving end for the OFDM modulation apparatus according to the present invention with reference to the accompanying drawings.
An OFDM modulation apparatus proposed by the present invention is described with reference to fig. 1. Fig. 1 shows an OFDM modulation apparatus for generating a concatenation of two OFDM subsymbols, comprising: a serial-to-parallel converter 102 for parallelizing the serial data stream; two N/2-point IFFT units 1011 to 1012 for generating two OFDM sub-symbols; two preprocessing units 1031 to 1032 for preprocessing the parallel data streams mapped to the input terminals of the two IFFT units; a parallel-to-serial converter 104, for performing serial concatenation on the outputs of the two IFFT units 1011 to 1012 to form a new OFDM symbol and add a zero suffix.
At this time, the frequency domain subcarrier signal output by the first serial-to-parallel converter 102 is divided into two parts, which are respectively denoted as X 1 [k]And X 2 [k]K is more than or equal to 0 and less than N, and N is the number of subcarriers of the OFDM system. For X in two pretreatment units 1 [k]And X 2 [k]And preprocessing, wherein the number of the preprocessed subcarrier signals is L. Thereafter, X 1 [k]And X 2 [k]The two IFFT units are input and performed, the output of the IFFT unit is input to the parallel-to-serial converter 104, and the parallel-to-serial converter 104 performs serial concatenation on the output of the IFFT unit according to equations (1) and (2) and adds a zero suffix.
An embodiment of the interference cancellation receiving apparatus proposed by the present invention at a receiver installation location is described below with reference to fig. 2. As shown in fig. 2, the input of the interference cancellation receiving apparatus 201 according to the present invention is connected to the parallel output of the N-point FFT unit 202, and its output is connected to two channel estimation and equalization units 2031 to 2032. First, a received signal in which an OFDM symbol boundary is determined and suffix copying is performed is input to the serial-parallel converter 204; then, the serial-to-parallel converter 204 parallelizes the serial received signal and outputs it to an N-point FFT unit 202; then, the parallel output of the N-point FFT unit 202 is connected to the input end of the interference cancellation receiving apparatus 201 according to the present invention; then, the output of the interference cancellation receiving apparatus 201 of the present invention is input to two channel estimation and equalization units 2031 to 2032, and the channel estimation and equalization are respectively performed on the frequency domain subcarrier signals after the interference cancellation; finally, the outputs of the two channel estimation and equalization units are input to the parallel-to-serial converter 205, and the parallel data is serialized and output.
An embodiment of the interference cancellation receiving apparatus proposed by the present invention is described below with reference to fig. 3. As shown in FIG. 3, as a preferred embodiment, the interference cancellation receiving apparatus includes an even decimator 301 and an odd decimator 302, whose outputs areAn input terminal connected to the parallel output terminal of the N-point FFT unit 202 for respectively extracting the frequency domain subcarrier signal vectors corresponding to the even index marks output by the N-point FFT unit 202
Frequency domain subcarrier signal vectors corresponding to odd index marksA subcarrier extractor 303 having an input coupled to the output of the even extractor 301 for extracting at least L known subcarriers; a complementary base subcarrier generator 304 having an input coupled to an output of said subcarrier extractor 303, using a secondary vector
The extracted not less than L known sub-carriers generate vector R known (ii) a A fixed coefficient linear filter 305 having two inputs, one input coupled to the output of the complementary base subcarrier generator 304 and one input coupled to the output of the odd decimator 302, for generating a combining matrix using the outputs of the complementary base subcarrier generator 304 and the odd decimator 302And with a matrix F of fixed coefficients calculated in advance e [F o |S] -1 Right multiplication to generate an output vectorAn adder 306 having two inputs, one input coupled to the output of the even decimator 301 and one input coupled to the fixed coefficient linear filter 305, for adding and outputting the recovered first sub-symbol frequency domain signal
A subtractor 307 having two inputs, one input connected to the output of the even decimator 301 and one input connected to the fixed coefficient linear filter 305, for performing subtraction and outputting the recovered second sub-symbol frequency domain signal
Fig. 4 illustrates an embodiment of a preprocessing method at a transmitting end according to the present invention. As shown in fig. 4, the preprocessing method at the transmitting end includes the following steps: first, in step S401, the pre-processing unit generates a non-negative integer L 1 A known or zero data symbol and randomly placed to the frequency domain sub-symbol X 1 On the sub-carrier of (a), which corresponds to L 1 The subcarrier index set is labeled K 1 (ii) a Then, in step S402, the preprocessing unit generates a non-negative integer L 2 A known or zero data symbol, L 2 ＝L-L 1 And randomly placed to the frequency domain sub-symbol X 2 On the sub-carrier of which it corresponds to L 2 The subcarrier index set is labeled K 2 And K is 1 ∩K 2 = Ω, i.e. the two sets of marks intersect as null and do not overlap each other; if K 1 ∩K 2 Not equal to omega, repeatedly and randomly placing the X 2 Up to K 1 ∩K 2 = Ω and is represented by K 1 And K 2 Union of K 1 ∪K 2 And generates a subcarrier index vector m. In step S403, K is selected 1 And K 2 Union yields L 1 +L 2 The subcarrier index marks the vector m. Finally, in step S404, the first serial-to-parallel converter outputs N-L data to two preprocessing units, which place them at X, respectively 1 And X 2 On subcarriers with no value set, where X 1 In which a positive integer N/2-L is placed 1 Data, X 2 In which a positive integer N/2-L is placed 2 Data, satisfying that the data subcarrier index and the index vector m are not overlapped; the two preprocessing units respectively output the processed X 1 And X 2 。
FIG. 5 is a diagram illustrating a complementary base subcarrier R in the complementary base subcarrier generator according to the present invention known One embodiment of a method of generation. The method corresponds to a preprocessing method of the transmitting end. As shown in FIG. 5, said one R known The generation method comprises the following steps: first, in step S501, the vector output from the subcarrier extractor 303 is subjected to decimation
The middle index is marked as k 1 The negative of the subcarrier signal element is taken as a vector R known Middle index mark k 1 Sub-carrier signal elements of, i.e.
Then, in step S502, the vector output from the subcarrier extractor 303 is subjected to
Middle index mark k 2 Directly as vector R kown Middle index mark k 2 Sub-carrier signal elements of, i.e.
Fixed coefficient linear filtering according to the present invention is described below with reference to fig. 6One embodiment of a method of computing. As shown in fig. 6, the calculation method includes the steps of: first, in step S601, a coefficient matrix F of the fixed coefficient linear filter is calculated e [F o |S] -1 This step can be performed in advance at the time of system design; next, in step S602, the frequency domain subcarrier signal vector corresponding to the odd index mark is output by the odd decimator 302
Next, in step S603, the obtained vector R is output by the base-complementary subcarrier generator 304 kown (ii) a Next, in step S604, the vector is calculated
Sum vector R known Combining to generate a filter output matrixNext, in step S605, the filter input matrix generated in step S604 and the fixed coefficient matrix F calculated in advance in step S601 e [F o |S] -1 Right multiplication to generate output vector of fixed coefficient linear filter
The foregoing description of the preferred embodiments will enable any person skilled in the art to make or use the present invention. It will be apparent that various modifications can be made to the embodiments, and the basic principles of the invention can be applied to other embodiments. Thus, the present invention is not intended to be limited to the embodiments shown above, but is to be accorded the widest scope consistent with the principles of the invention and novel features disclosed herein.
FIG. 7 compares the error rate performance obtained by the apparatus and method of the present invention with that obtained without interference cancellation (reference [1 ]]) And self-erasing method (document [2 ]]) Error rate performance of. Among them, document [1 ]]See y.li release in 1998 for international cooperation between electrical and electronic engineersArticle "robust OFDM channel estimation under fast dispersive fading channel" (robustchannel estimation for OFDM systems with fast dispersive periodic channels) "in conference communication (ieee transactions communication), document [2]See the article "inter-carrier interference self-cancellation method in OFDM mobile communication system (inter-carrier interference self-cancellation system)" published in 2001 by zhao in the institute of electrical and electronics engineers (international institute of electrical and electronics engineers). Simulation referring to the 802.16e-2006 standard, the entire 20MHz system bandwidth is divided into N =2048 subcarriers, which includes 319 zero subcarriers. OFDM symbol length T s =102.4 μ s. The system uses QPSK modulation. The multipath channel satisfies the broad stationary uncorrelated scattering assumption (WSSUS). Multipath satisfies an exponential delay profile with a corresponding channel power of
l∈[0，L]，
Where k = (L + 1)/log (2L + 2), L =127. The time-varying features of each path conform to the Jakes doppler envelope. The simulation includes two normalized Doppler spreads, i.e., f d T s =0.126 and f d T s =0.081, and the maximum receiver speeds for these two normalized doppler spreads are 350km/s and 225km/s, respectively, at a carrier frequency of 3.8 GHz. For comparison, we also simulate document [1 ]]Conventional interference cancellation method without doing so and document [2 ]]The number of subcarriers of the self cancellation method of (3) is the same. FIG. 7 shows a bit signal on the abscissaNoise ratio E b /N o The ordinate is the bit error rate BER, and the six performance curves in the graph are respectively from top to bottom: left triangle dotted line is document [1]Interference cancellation method is not performed in f d T s Curve at = 0.126; cross dotted line is document [2 ]]Self-elimination method at f d T s Curve at = 0.126; right triangle dotted line is document [1]Method at f d T s Curve at = 0.081; the solid line of the hexagram is the method provided by the invention at f d T s Curve at = 0.126; lower triangular dotted line is document [2 ]]Method at f d T s Curve at = 0.081; the solid line of the five-pointed star is the method proposed by the present invention at f d T s Curve at = 0.081. It can be seen from fig. 7 that the proposed method, which yields better performance in both doppler spread cases than the two methods described above, is at f d T s Performance when =0.126 and interference cancellation method is not performed in f d T s Performance is similar when = 0.081. Considering that 319 zero subcarriers exist in the system and the number is far larger than the delay spread of the channel, the method provided by the invention does not need to select additional zero subcarriers. Compared with the self-elimination method, the method has no loss of spectral efficiency and can improve the moving speed of the receiver by nearly 1.6 times.
Claims (2)
1. An orthogonal frequency division multiplexing transceiving system suitable for use in a high-speed mobile environment, comprising a transmitter and a receiver, wherein:
the transmitter includes: a first serial to parallel converter (102), two pre-processing units (1031) and (1032), N/2 point IFFT units (1011) and (1012), a first parallel to serial converter (104), wherein,
a first serial-to-parallel converter (102) for parallelizing N-L data inputted serially, wherein N is the number of subcarriers of the OFDM system, L is an integer which is more than or equal to zero and less than N and is the number of subcarrier signals added in the processing of the two preprocessing units, and the output end of the serial-to-parallel converter is connected with the input ends of the two preprocessing units;
two pre-processing units (1031) and (1032) for pre-processing the parallel data streams mapped to the input terminals of the two IFFT units, the input terminals being connected to the output terminal of the first serial-to-parallel converter for outputting two frequency domain sub-symbols X respectively 1 And X 2 To the two IFFT units; the preprocessing unit processes the N-L data input from the first serial-to-parallel converter according to the following three steps:
the preprocessing unit (1031) first generates L 1 All fingersFixed known data symbols, including null data symbols, L 1 Is an integer greater than or equal to zero and less than or equal to L, and is randomly placed to the frequency domain sub-symbol X 1 As X to be output on the sub-carrier of 1 A portion of which corresponds to L 1 The subcarrier index set is labeled K 1 ，K 1 The value range of the element(s) is an integer which is more than or equal to 1 and less than or equal to N/2; then, the preprocessing unit (1032) generates a non-negative integer L 2 A known or zero data symbol, L 2 ＝L-L 1 And randomly placed to the frequency domain sub-symbol X 2 As X to be output on the sub-carrier of 2 A portion of which corresponds to L 2 The subcarrier index set is marked K 2 ，K 2 The value range of the element(s) is an integer of 1 or more and N/2 or less, and K 1 ∩K 2 = Ω, i.e. K 1 And K 2 Do not overlap; if K 1 ∩K 2 Not equal to Ω, then repeated random mapping to X 2 Up to K 1 ∩K 2 = omega and is represented by K 1 And K 2 Union K of 1 ∪K 2 Generating a subcarrier index vector m;
the N-L data output by the first serial-parallel converter are sent to two preprocessing units, and the preprocessing units respectively and arbitrarily place the N-L data to X 1 And X 2 On subcarriers with no value set, where X 1 In which a positive integer N/2-L is placed 1 Data, X 2 In which a positive integer N/2-L is placed 2 Data, satisfying that the data subcarrier index and the index vector m are not overlapped;
two preprocessing units respectively output processed X 1 And X 2 ；
Two N/2 point IFFT units (1011) and (1012) for generating two OFDM sub-symbols, wherein the input ends are respectively connected with the output ends of the two preprocessing units, and the output ends are connected with the input end of the first parallel-serial converter;
a first parallel-to-serial converter (104) for serially cascading the outputs of the two IFFT units to form a new OFDM symbol and adding a zero suffix, wherein the input end of the first parallel-to-serial converter is connected with the output ends of the two IFFT units to output a sending signal; the receiver includes: a second serial-to-parallel converter (204), an N-point FFT unit (202), an interference cancellation receiving apparatus (201), two channel estimation and equalization units (2031) and (2032), a second parallel-to-serial converter (205), wherein,
a second serial-to-parallel converter (204) for parallelizing the serial input data stream, the input being the received transmitter transmit signal and the output being connected to the input of the N-point FFT unit;
an N-point FFT unit (202) for converting an input time domain signal into a frequency domain signal, wherein the input end is connected with the output end of the second serial-parallel converter, and the output end is connected with the input end of the interference elimination receiving device;
an interference elimination receiving device (201) for eliminating inter-sub-symbol interference and inter-sub-carrier interference, wherein the input end is connected with the output end of the N-point FFT unit (202), and the output end is connected with the input ends of the two channel estimation and equalization units; the interference cancellation receiving apparatus includes: even decimator, odd decimator, fixed coefficient linear filter, subcarrier decimator, complement base subcarrier generator, adder, subtracter, wherein:
an even extractor for extracting the frequency domain subcarrier signal corresponding to the even index mark output by the N-point FFT unit of the receiving end
The input end is connected with the parallel output end of the N-point FFT unit, and the output end is connected with the input end of the subcarrier extractor and the input end of the adder;
an odd extractor for extracting the frequency domain subcarrier signals corresponding to the odd index marks output by the N-point FFT unit of the receiving end
The input end is connected with the parallel output end of the N-point FFT unit, and the output end is connected with the input end of the fixed coefficient linear filter;
fixed coefficient linear filteringMeans for generating a difference signal of the first sub-symbol with respect to the second sub-symbolThe fixed coefficient linear filter is provided with two input ends, one input end is connected with the output end of the complement base subcarrier generator, the other input end is connected with the output end of the odd decimator, and the output end is simultaneously connected with the input ends of the adder and the subtracter; the fixed coefficient linear filter is generated in the following three steps
Generating coefficient matrix F of the fixed coefficient linear filter e [F o |S] -1 Including normalizing the DFT matrix F according to the N order (N) Is/are as follows
Submatrix F o And F e The matrix elements of which are respectively
And
(ii) a Regenerated into F e Is/are as follows
S of submatrix, L rows thereof from F e The corresponding row index mark corresponds to the vector m of the preprocessing index mark of the sending end, and the element S of the vector m (i，j) ＝F e(m(i)，j) (ii) a Matrix F o Is combined with the matrix S to form
Combined matrix [ F ] o |S]Calculating an inverse matrix [ F ] of the combined matrix o |S] -1 And the matrix F e Right multiplication to obtain the fixed coefficient linear filter
Coefficient matrix F e [F o |S] -1 ；
Obtained according to the odd decimator described above(Vector)
And the L x 1 vector R generated by the base-complementary subcarrier generator known Are combined to form aInput combination matrix of
Combining the above inputs into a matrixAnd the coefficient matrix F e [F o |S] -1 Right multiplication to generate output vector of fixed coefficient linear filter
And output
A subcarrier extractor for extracting K from the output signal of the even extractor according to the subcarrier index set described by the preprocessing unit 1 And K 2 Extracting an integer L of known subcarriers, wherein the input end of the L of known subcarriers is connected with the output end of the even extractor, and the output end of the L of known subcarriers is connected with the input end of the complementary base subcarrier generator;
a base-complementary subcarrier generator for generating base-complementary subcarriers R from at least an integer number L of known subcarriers obtained by the subcarrier extractor known To satisfy
A solvable base filling requirement; the input end is connected with the output end of the subcarrier extractor, and the output end is connected with the input end of the fixed coefficient linear filter; the base-complementing subcarrier generator is generated according to the following two stepsR known ：
Marking K to index set described in preprocessing unit 1 The corresponding subcarrier signal is taken as R to be output after being negated known The sub-carrier signal element corresponding to the index mark marks K to the index set described in the preprocessing unit 2 The corresponding subcarrier signal is directly used as R to be output known The subcarrier signal element corresponding to the index marker;
output R known ；
An adder for adding the output of said fixed coefficient linear filter and the output of said even decimator, said adder having two inputs, one input connected to the output of said even decimator and one input connected to said fixed coefficient linear filter, and outputting the first recovered sub-symbol frequency domain signal
A first output of the interference cancellation receiving means (201);
a subtractor for subtracting the output of said fixed coefficient linear filter from the output of said even decimator, said subtractor having two inputs, one input connected to the output of said even decimator and one input connected to the output of said fixed coefficient linear filter, and outputting the second recovered subsymbol frequency domain signal
A second output of the interference cancellation receiving means (201);
two channel estimation and equalization units (2031 to 2032) for estimating the channel and equalizing the received signal by Least Square (LS) or Minimum Mean Square Error (MMSE) algorithm, the input is connected with the output of the interference cancellation receiving device, the output is connected with the input of the second parallel-serial converter;
and the second parallel-serial converter (205) is used for serially cascading the parallel outputs of the two channel estimation and equalization units, and the input end of the second parallel-serial converter is connected with the output ends of the two channel estimation and equalization units to output a received signal.
2. The ofdm transceiver system of claim 1, wherein the transmitter comprises M preprocessing units and M N/M point IFFT units, M being a positive integer greater than or equal to 2 and less than or equal to N. Wherein the difference signal in the fixed coefficient linear filter contains M-1 sub-signals, which are the difference between the first frequency domain sub-symbol and the second frequency domain sub-symbol, the difference between the second frequency domain sub-symbol and the third frequency domain sub-symbol, and so on until the difference between the M-1 frequency domain sub-symbol and the M frequency domain sub-symbol.
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| CN102938669A (en) * | 2012-11-20 | 2013-02-20 | 杭州电子科技大学 | Method for suppressing Doppler spread in high-speed mobile environment |
| CN103475613A (en) * | 2012-06-06 | 2013-12-25 | 中兴通讯股份有限公司 | Signal sending and receiving method and relevant equipment |
| CN107018111A (en) * | 2017-03-22 | 2017-08-04 | 上海微小卫星工程中心 | Two-way diversity ICI is conjugated removing method |
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| CN1635724A (en) * | 2003-12-31 | 2005-07-06 | 上海贝尔阿尔卡特股份有限公司 | OFDM communication method and apparatus |
| WO2006070756A1 (en) * | 2004-12-28 | 2006-07-06 | Matsushita Electric Industrial Co., Ltd. | Wireless receiving apparatus, wireless transmitting apparatus, and interference signal removing method |
| JP4898707B2 (en) * | 2005-12-27 | 2012-03-21 | パナソニック株式会社 | Radio transmission apparatus and multicarrier signal generation method |
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| CN103475613A (en) * | 2012-06-06 | 2013-12-25 | 中兴通讯股份有限公司 | Signal sending and receiving method and relevant equipment |
| CN102938669A (en) * | 2012-11-20 | 2013-02-20 | 杭州电子科技大学 | Method for suppressing Doppler spread in high-speed mobile environment |
| CN107018111A (en) * | 2017-03-22 | 2017-08-04 | 上海微小卫星工程中心 | Two-way diversity ICI is conjugated removing method |
| CN107018111B (en) * | 2017-03-22 | 2020-03-17 | 上海微小卫星工程中心 | Dual-path diversity ICI conjugate eliminating method |
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