KR101190053B1 - Cognitive radio transmitter and receiver for improving data transfer rate - Google Patents

Abstract

A cognitive radio transmitter and a cognitive radio receiver are provided. The cognitive radio transmitter compares the number of usable even subcarriers with the number of usable odd subcarriers and selects a greater number of usable subcarrier groups from among the even and odd subcarrier groups as subcarriers for data transmission. Accordingly, the cognitive radio transmitter can transmit data by transmitting only half of signals corresponding to one symbol according to OFDM.

Description

Cognitive radio transmitter and receiver for improving data transfer rate

The present invention relates to a cognitive radio transmitter and a cognitive radio receiver, and more particularly, to a cognitive radio transmitter and a cognitive radio receiver for performing radio communication suitably for a radio wave environment.

Cognitive Radio (CR) communication technology refers to a radio technology that makes an operation suitable for a current radio wave environment by measuring an radio wave environment and setting operating parameters of the radio device according to the measured radio wave environment. For example, wireless devices with cognitive radio technology can maximize transmission capacity to match channel characteristics, minimize device-to-device interference, facilitate interoperability between different systems, or find time away from the primary user by looking for unused frequencies. The technique used for this can be applied.

Orthogonal Frequency Division Multiplexing (OFDM) may be applied to cognitive radio communication technology. In such an OFDM-based cognitive radio system, fast fourier transform (FFT) and inverse FFT (IFFT) are used for multiplexing of signals. In addition, the FFT pruning technique may be used to reduce the amount of computation of the FFT.

When the FFT Pruning technique is applied, the part of the IFFT / FFT structure in which 0 data is partially input is not calculated. Therefore, the wireless device can reduce the processing time due to the reduction of the total computation amount. However, since the number of data combinations varies in the part where zero data exists, the circuit design for the FFT operation is complicated.

As described above, when the FFT pruning technique is used, the wireless device has no hardware size reduction effect because the entire subcarrier should be used when there is no data having a value of zero. On the other hand, if the number of data increases to zero, the wireless device can reduce the amount of computation, and thus can reduce the processing time and power required by the calculation.

However, in terms of data rate, the processing time is shortened due to the decrease in the amount of computation. However, since the receiver has to wait until all output signals of the IFFT corresponding to one cycle of the OFDM symbol arrive, the data rate increase effect of the wireless device cannot be obtained. There is this.

The present invention has been made to solve the above problems, and an object of the present invention is to compare the number of usable even subcarriers and the usable odd subcarriers, and the number of available subcarriers in the even subcarrier group and the odd subcarrier group is large. A cognitive radio transmitter and a cognitive radio receiver for selecting a group as a subcarrier for data transmission are provided.

According to an embodiment of the present invention, a cognitive radio transmitter includes: a spectrum sensing unit detecting availability information of subcarriers of a plurality of channels; A comparison unit comparing the available even subcarriers with the available odd subcarriers using the detected subcarrier availability information, and selecting a greater number of available subcarrier groups among the even subcarrier group and the odd subcarrier group; A subcarrier allocator for allocating a subcarrier group selected by the comparator to a subcarrier for input data transmission and modulating the input data to the assigned subcarrier; An IFFT processor for processing inverse fast fourier transform (IFFT) signals output from the subcarrier allocation unit; And a transmitter for transmitting the IFFT processed signal to the outside.

The comparison unit transmits the usable subcarrier number information and the channel information of the usable subcarrier for the group having many usable subcarriers among the even and odd subcarriers to the subcarrier assignment unit.

In addition, the subcarrier allocator may modulate data to an allocated subcarrier based on OFDM (Orthogonal Frequency Division Multiplexing) and multiplex the modulated signal.

The IFFT processor may perform IFFT processing on the signal output from the subcarrier allocation unit using a split-radix FFT pruning technique.

Also, the IFFT processor may perform a split-radix FFT pruning technique using a pruning matrix.

The IFFT processor may include a pruning matrix generator configured to generate a pruning matrix; And a split-radix FFT unit performing a split-radix FFT process using the generated pruning matrix.

The IFFT processor may output only half of signals corresponding to one symbol according to OFDM.

The IFFT processor transmits half of the symbol interval signal for the first data for 0 to T / 2 intervals for one symbol interval T of one subcarrier, and the second data for the T / 2 to T intervals. One half of the symbol interval signal may be transmitted.

On the other hand, the cognitive radio receiver according to an embodiment of the present invention, the receiver for receiving a signal containing two symbol data half in one symbol period of one subcarrier; And an FFT processor configured to perform FFT processing on the received signal.

The FFT processor may split a signal received during one symbol period into half, and restore the half received signal to a signal corresponding to one symbol.

In addition, when the received signal is received by an even subcarrier, the FFT processor may double the signal corresponding to half of a symbol to restore a signal corresponding to one symbol.

In addition, when the received signal is received by an odd subcarrier, the FFT processor is configured to apply a signal corresponding to half of a symbol.

By multiplying by 2 times, the signal corresponding to one symbol may be restored.

In addition, the FFT processing unit may perform FFT processing on the recovered signal using a split-radix FFT pruning technique.

The FFT processor may perform a split-radix FFT pruning technique using a pruning matrix.

According to various embodiments of the present invention, a cognitive radio for comparing the number of usable even subcarriers and the number of usable odd subcarriers and selecting a greater number of usable subcarrier groups from among even and odd subcarrier groups as subcarriers for data transmission. Since the transmitter and the cognitive radio receiver can be provided, the cognitive radio transmitter can transmit data by transmitting only half of signals corresponding to one symbol according to OFDM. Accordingly, the cognitive radio transmitter can further output and transmit signals for other symbols for the remaining half of the symbol period, thereby improving the data rate.

In addition, the cognitive radio transmitter implements a split-radix FFT pruning technique using a pruning matrix, thereby simplifying and efficiently designing a circuit.

1A is a diagram illustrating a structure of a Cognitive Radio (CR) transmitter according to an embodiment of the present invention;
1B is a diagram illustrating a structure of a Cognitive Radio (CR) receiver according to an embodiment of the present invention;
2 illustrates an example of an eight-point Split-radix FFT pruning structure according to an embodiment of the present invention;
3 is a diagram illustrating a structure of an FFT processor using a pruning matrix to implement pruning in a split-radix IFFT according to an embodiment of the present invention;
4 is a diagram illustrating a circuit structure of an SDF SRFFT BF control unit according to an embodiment of the present invention;
5 is a diagram illustrating a circuit structure of a pruning matrix control unit 312 according to an embodiment of the present invention.
6A-6D are graphs of IFFT output signals, in accordance with one embodiment of the present invention;
7 is a graph comparing the number of complex cumulative numbers of various types of 1024-point FFT algorithms according to an embodiment of the present invention;
8 is a diagram illustrating a probability density distribution of empty subcarriers according to an embodiment of the present invention.

Hereinafter, with reference to the drawings will be described the present invention in more detail.

FIG. 1A is a diagram illustrating a structure of a Cognitive Radio (CR) transmitter 100 according to an embodiment of the present invention. As shown in FIG. 1, the cognitive radio transmitter includes a spectrum sensing unit 110, a comparator 120, a subcarrier allocator 130, an inverse fast fourier transform (IFFT) processor 140, and a transmitter 150. Include.

The spectrum sensing unit 110 detects a spectral state of a radio wave of a place where the currently recognized wireless transmitter 100 is located. Specifically, the spectrum sensing unit 110 detects whether subcarriers of various channels are being used by a specific device. The spectrum sensing unit 110 determines that the subcarrier is not in use by another device as an available subcarrier.

The spectrum sensing unit 110 outputs availability information of subcarriers of various channels to the comparator 120.

In cognitive wireless communication technology, spectrum sensing technology is the most important frequency resource sharing technology for determining whether a subcarrier occupied or used by a primary user is an unused subcarrier. Spectrum sensing techniques include non-cooperative spectrum sensing and cooperative spectrum sensing.

As such, the spectrum sensing unit 110 detects whether subcarriers of various channels are being used by other devices using the spectrum detection technique.

The comparator 120 compares the number of usable even subcarriers with the number of usable odd subcarriers using the subcarrier availability information received from the spectrum sensing unit 110. Here, the even subcarriers represent subcarriers corresponding to even numbers in the order of the channels of the lower frequencies. The odd subcarriers represent subcarriers corresponding to the odd numbered channels in order of the lowest frequency.

For example, the sum of even subcarriers may be expressed as Equation 1 below.

[Equation 1]

Here, 2m represents an input signal carried on an even subcarrier.

In addition, the sum of the odd subcarriers can be expressed as Equation 2 below.

[Equation 2]

Here, 2m + 1 represents an input signal carried on an odd subcarrier.

As described above, the comparison unit 120 compares the number of usable even subcarriers with the number of usable odd subcarriers, and determines whether there are more available subcarriers among the even and odd subcarriers. The comparator 120 selects a subcarrier of a larger number as a subcarrier for data transmission.

The comparator 120 transmits information about the subcarriers having a large number of usable subcarriers to the subcarrier allocator 130. Here, the comparator 120 transmits the usable subcarrier number information and the usable subcarrier channel information for the group having many usable subcarriers among the even subcarriers and the odd subcarriers to the subcarrier allocator 130.

For example, if there are three available even subcarriers and two available odd subcarriers, the comparator 120 selects an even subcarrier as a subcarrier for transmission, and the information that three even subcarriers are three and three even subcarriers. Each channel information on the subcarrier allocation unit 130 is transmitted.

The subcarrier allocator 130 assigns a subcarrier group selected by the comparator 120 among the even subcarriers and the odd subcarriers as subcarriers for input data transmission. The subcarrier allocator 130 modulates the input data to each subcarrier, multiplexes it, and transmits the multiplexed data to the IFFT processor 140.

At this time, the subcarrier allocation unit 130 modulates data to the assigned subcarriers based on Orthogonal Frequency Division Multiplexing (OFDM). The subcarrier assignment unit 130 multiplexes the modulated signal based on OFDM.

The IFFT processor 140 performs IFFT processing on the multiplexed signal. In addition, the IFFT processor 140 outputs an IFFT processed signal for data transmission. At this time, the IFFT processor 140 is applied with a split-radix FFT pruning technique to reduce the amount of calculation of the IFFT. In this case, the IFFT processor 140 according to the present embodiment uses a pruning matrix to efficiently design a hardware for pruning. As such, since the IFFT processor 140 implements the split-radix FFT pruning technique using the pruning matrix, circuit design can be simplified and efficiently. The implementation of the pruning matrix and related circuits will be described later in detail.

Also, the IFFT processor 140 outputs only half of signals corresponding to one symbol according to OFDM. The IFFT-treated transmission signal using only odd subcarriers or only even carriers is symmetrical in half of one OFDM symbol signal interval T time. That is, in the IFFT processed transmission signal, a signal corresponding to 0 to T / 2 time and a signal corresponding to T / 2 to T time are symmetrical with each other. Therefore, even if the IFFT processor 140 transmits only a signal corresponding to 0 to T / 2 time, the receiving end can restore the signal corresponding to the remaining T / 2 to T time using symmetry. Therefore, the IFFT processor 140 outputs only half of the signals corresponding to one symbol according to OFDM (that is, only signals corresponding to 0 to T / 2 time).

Therefore, the IFFT processor 140 may output a signal corresponding to one symbol only for 0 to T / 2 time, and output a signal corresponding to another symbol for the remaining T / 2 to T time. Through this, the IFFT processor 140 may increase the data rate.

The transmitter 150 wirelessly transmits the IFFT processed signal from the IFFT processor 140 to an external device.

The cognitive radio transmitter 100 having such a structure outputs an IFFT processed signal for data transmission. In particular, since the cognitive radio transmitter 100 outputs only half of signals corresponding to one symbol according to OFDM, the cognitive radio transmitter 100 can additionally output and transmit signals for other symbols for the remaining symbol periods. In addition, since the cognitive radio transmitter 100 implements a split-radix FFT pruning technique using a pruning matrix, circuit design can be simplified and efficiently.

FIG. 1B is a diagram illustrating a structure of a Cognitive Radio receiver (CR) 200 according to an embodiment of the present invention. As shown in FIG. 1B, the cognitive radio receiver 200 includes a receiver 210 and an FFT processor 220.

The receiver 210 receives a signal that is IFFT-processed and transmitted from the cognitive radio transmitter 100. In this case, the receiver 210 receives a signal including two data in one symbol period.

The FFT processor 220 performs FFT processing of the received signal. The FFT processor 220 first separates signals by half for one period of an OFDM symbol. In addition, the FFT processor 220 restores a signal corresponding to one symbol using a signal corresponding to half of a symbol.

Specifically, when the received signal is received by an even subcarrier, the FFT processor 220 doubles a signal corresponding to half of a symbol and restores a signal corresponding to one symbol. In addition, when the received signal is received by an odd subcarrier, the FFT processor 220 corresponds to a signal corresponding to half of a symbol.

By multiplying by 2 times, the signal corresponding to one symbol is restored.

Thereafter, the FFT processor 220 performs FFT processing on the restored signal using a split-radix FFT pruning technique. In addition, the FFT processor 220 performs a split-radix FFT pruning technique using a pruning matrix.

As described above, the cognitive radio receiver 200 receives two data in one symbol period for one subcarrier. Thus, the cognitive radio receiver 200 may increase the data reception rate.

2 illustrates an example of an eight-point Split-radix FFT pruning structure, in accordance with an embodiment of the invention.

The split-radix FFT pruning technique corresponds to a technique that computes only the values necessary to obtain the output X (k) of the final stage and does not perform unnecessary operations in a split-radix FFT structure having a small amount of computation.

As shown in FIG. 2, when only X (0) and X (1) are subject to calculation, Split-radix FFT pruning processes only the calculation process of the solid line portion. In addition, the calculation process of the dotted portion required to obtain the values of X (2) to X (7) is not processed.

As such, assuming that L = 2 ^d and L <N = 2 ^r in a state where only L nonzero outputs of N outputs of the Split-radix FFT are intended to be obtained, Split-radix FFT pruning The algorithm leaves the first d steps in the split-radix FFT structure and modifies the remaining (rd) steps so that they do not perform unnecessary calculations caused by (NL) zero inputs.

Therefore, according to the split-radix FFT pruning technique, since the cognitive radio transmitter 100 does not perform unnecessary operations generated by an input of zero, the computation speed of the FFT can be improved.

In the meantime, the IFFT processor 140 may design a circuit using a pruning matrix. That is, the IFFT processor 140 uses a pruning matrix to use pruning for split-radix IFFT and implements split-radix IFFT pruning through efficient hardware design of the pruning matrix. Since the IFFT and the FFT correspond to the inverse relationship with each other, the following description will be based on the FFT. However, referring to the description of Split-radix FFT pruning, it is of course possible to infer the case of Split-radix IFFT pruning. And the cognitive radio device represents a cognitive radio transmitter or a cognitive radio receiver.

In the case of a split-radix FFT of size N (N = 2 ^r ), the cognitive radio device generates a pruning matrix (M _i ) of N × r. Individual elements of the pruning matrix (M _i ) are associated with the intermediate nodes of the split-radix FFT structure. Accordingly, the cognitive radio device checks the element values of the corresponding matrix before multiplying the rotation factors at each node and determines whether or not to multiply the rotation factors at the nodes.

The pruning matrix (M _i ) is created by the position of the output values of the nonzero FFT. The last column of the pruning matrix is associated with the output values. Thus, if the output value is not 0, the element value of the last column of the corresponding row is 1, and if the output value is 0, the element value of the last column of the corresponding row is 0.

As such, the cognitive wireless device determines the values of the last column (ie, the r-th column) and obtains the values of the (r-1) th column from the r-th column. A cognitive radio device first groups the elements of the last column into two groups of N / 2, and if there is an element with a value of 1 among the elements of the intermediate group, the corresponding two elements of the r-1th columns are set to 1, or 0.

In a similar fashion, the cognitive radio device (rk) th column to generate the (rk + 1) th column, a second element enclosed by ^k by one N / 2 ^k groups if there is one in the group of parameters corresponding to the second column elements We make the matrix with one element as one or zero. The matrix generated by this process becomes a pruning matrix.

M _i described in Equation 3 below represents a pruning matrix corresponding to the split-radix FFT pruning structure for the case where only X (0) and X (1) are not zero, as shown in FIG. 2.

[Equation 3]

Hereinafter, referring to FIG. 3, an FFT processor (which is inversely related to the IFFT processor 140 of FIG. 1) in which a pruning matrix is used to implement pruning in a split-radix FFT will be described. 3 is a diagram illustrating a structure of an FFT processor using a pruning matrix to implement pruning in a split-radix IFFT according to an embodiment of the present invention. As shown in FIG. 3, the FFT processing unit includes a pruning matrix generation unit 310 and a split-radix FFT unit 320.

The pruning matrix generator 310 includes a plurality of pruning matrix controllers 312 and a delay unit 314. At this time, the number of pruning matrix controllers 312 and delay units 314 is the same as the number of columns of the pruning matrix. In FIG. 3, the pruning matrix controller 312 is described as a single-path delay feedback (SDF) pruning matrix.

As shown in FIG. 3, the pruning matrix generator 310 inputs data on whether or not the subcarrier is available as a result of spectrum sensing to the pruning matrix controller 312 located at the far right of the last column of the pruning matrix. That is, a value other than 0 is input to the rightmost Pruning matrix controller 312 when a corresponding subcarrier is available, and 0 is input when the corresponding subcarrier is unavailable.

Through this, the pruning matrix generator 310 generates the elements of the last second column of the pruning matrix, generates the elements of the last third column with the elements of the last second column, and generates the elements of all the columns according to this rule. In FIG. 3, the multiplication process of the rotation factor is performed at each node using the generated pruning matrix elements. In the pruning matrix generator 310 of FIG. 3, the AND gate 316 is determined. Implemented through If the element value of the pruning matrix is 1, the output value of the AND gate 316 is the rotation factor value 318. If the element value of the pruning matrix is 0, the output value of the AND gate 316 is 0 and the rotation factor The multiplication process is omitted.

The split-radix FFT unit 320 multiplies the rotation factor values 318 processed as described above with a split-radix FFT butterfly operation result. As shown in FIG. 3, the split-radix FFT unit 320 includes a plurality of SDF SRFFT Single-path Delay Feedback Split-radix FFT Butterfly (BF) control units 322, delay units 324, and multipliers 326. It consists of The leftmost SDF SRFFT BF controller 322 performs a split-radix FFT butterfly operation on an input value x (n). The result of the split-radix FFT butterfly operation, which is sequentially output from the left, is multiplied by the rotation factor value 318 through the multiplier 326, and then the split-radix FFT butterfly operation is performed by the next SDF SRFFT BF controller 322. Will repeat. Through this process, the split-radix FFT unit 320 outputs X (k) on which the FFT is performed from the input x (n).

At this time, synchronization is required in a process in which the rotation factor values 318 processed by the pruning matrix generator 310 are multiplied with the result of the split-radix FFT butterfly operation, and the delay unit 314 of the pruning matrix generator 310 is performed. ) And the delay unit 324 of the Split-radix FFT unit 320 performs synchronization.

For example, the necessary delay for the kth column (that is, the kth stage) is expressed as in Equation 4 below.

[Equation 4]

Hereinafter, a circuit structure of the SDF SRFFT BF control unit 322 will be described with reference to FIG. 4. 4 is a diagram illustrating a circuit structure of an SDF SRFFT BF control unit 322 according to an embodiment of the present invention.

In FIG. 4, the R-2 BF 400 performs a radix-2 FFT Butterfly operation. As shown in FIG. 4, the split-radix FFT structure has irregular positions of addition and subtraction as compared with a general radix-2 FFT structure. Thus, as shown in Fig. 4, two control circuits are required. The first control circuit 410 controls the execution timing of the subtraction. The second control circuit 420 then controls the execution timing of the addition. As such, the SDF SRFFT BF controller 322 controls the execution of addition and subtraction by using the first control circuit 410 and the second control circuit 420.

Hereinafter, a circuit structure of the pruning matrix control unit 312 will be described with reference to FIG. 5. 5 is a diagram illustrating a circuit structure of the pruning matrix controller 312 according to an embodiment of the present invention.

As shown in FIG. 5, the pruning matrix control unit 312 groups the elements of each row in order to generate the elements of the pruning matrix. Specifically, the kth column of the ^r columns bundles 2 ^{r-k + 1} elements. If there is an element with a value of 1 in this group, the values of the elements in the k-1th column will be 1, or 0. Here, the process of processing whether there is 1 in each group is executed by the OR gate 500 shown in FIG.

As described above, the FFT processor using the pruning matrix to implement pruning in the split-radix FFT may be implemented by the circuits of FIGS. 3 to 5. In particular, since the pruning matrix is used to implement the split-radix FFT processing circuit, a simpler circuit can be designed. In addition, the IFFT processor 140 of FIG. 1 may be implemented based on such a circuit structure.

As described above, the cognitive radio transmitter 100 of FIG. 1 compares the number of even subcarriers and odd subcarriers using information on subcarriers sensed by the spectrum sensing unit 110. The subcarrier allocation unit 130 of the cognitive radio transmitter 100 selects an even or odd subcarrier group having a large number and allocates transmission data to an input side corresponding to each subcarrier of the selected subcarrier group.

Hereinafter, the symmetry of the IFFT output signal will be described with reference to FIGS. 6A to 6D. 6A through 6D are graphs illustrating IFFT output signals according to an embodiment of the present invention.

6A illustrates a graph of the sum of sine terms of even subcarriers for one symbol of an 8 point IFFT according to an embodiment of the present invention. In FIG. 6A, the horizontal axis represents a symbol of one period. As shown in FIG. 6A, the sum of the sine terms of the even subcarriers may be symmetric changed about half of the symbol period (the point at which the x-axis value is 0.5).

 6B is a graph illustrating the sum of cosine terms of even subcarriers for one symbol of an 8 point IFFT according to an embodiment of the present invention. In FIG. 6B, the horizontal axis represents a symbol of one period. As shown in FIG. 6B, the sum of cosine terms of even subcarriers may be symmetric about half of a symbol period (a point at which an x-axis value is 0.5).

6C is a graph illustrating the sum of sine terms of odd subcarriers for one symbol of an 8 point IFFT according to an embodiment of the present invention. In FIG. 6C, the horizontal axis represents a symbol of one period. As shown in FIG. 6C, the sum of the sine terms of the odd subcarriers may be symmetric changed from the half of the symbol period (the point at which the x-axis value is 0.5).

 FIG. 6D illustrates a graph of the sum of cosine terms of odd subcarriers for one symbol of an 8 point IFFT according to an embodiment of the present invention. FIG. In FIG. 6D, the horizontal axis represents a symbol of one period. As shown in FIG. 6D, it may be confirmed that the sum of cosine terms of odd subcarriers is symmetric about half of a symbol period (a point at which an x-axis value is 0.5).

As described above, it can be seen that an IFFT output signal using only even subcarriers or an IFFT signal using only odd subcarriers is symmetric about a half point of a symbol period or a sign is symmetrically changed. Therefore, even if the cognitive radio transmitter 100 transmits only half of a signal for one symbol using only odd subcarriers or only even subcarriers, the receiver uses half of the signal for one symbol to symmetry the signal corresponding to one symbol. Can be used to recover.

Hereinafter, this symmetry will be proved using a formula.

Inverse Discrete Fourier Transform (IDFT) is defined as follows.

When the input signal is complex, it develops as follows.

The graphs for the sin and cosin terms for the X _n value correspond to the graphs of FIGS. 6A to 6D.

Hereinafter, the symmetry of the even subcarriers and the odd subcarriers will be proved by the equation.

For even subcarriers,

As described above, since x _{p + N / 2} becomes the same value as x _p , it can be seen that the IFFT output is symmetric with respect to the half point of the symbol for even subcarriers.

The odd subcarriers are as follows.

As described above, since x _{p + N / 2} is equal to −x _p , it can be confirmed that, for odd subcarriers, the sign is symmetric with respect to the point where the IFFT output is half of the symbol.

As described above, since an input consisting of only odd subcarriers or only even subcarriers is repeated with an symmetrical IFFT output signal, the cognitive radio transmitter 100 has a half period of a symbol unlike a typical IFFT signal in which an odd subcarrier and even subcarrier inputs are mixed. The data can be transmitted with only the signal of.

If the number of odd subcarriers of an unused subcarrier (i.e. available subcarriers) is n and the number of even subcarriers is m (assuming m> n), then the number of data that can be sent during an OFDM symbol period processed by a typical IFFT is n + m.

However, according to the present embodiment, since m is a larger number, the cognitive radio transmitter 100 transmits data by assigning only m even subcarriers which are a larger number group. At this time, since the cognitive radio transmitter 100 transmits data of one symbol using half symbol periods, the cognitive radio transmitter 100 can transmit data twice during one symbol period. Therefore, since the cognitive radio transmitter 100 transmits data twice during one symbol period using m even subcarriers, 2m data is transmitted during one symbol period.

As such, the cognitive radio transmitter 100 according to the present embodiment transmits 2m data during one symbol period. On the other hand, when transmitting through a general IFFT process, the transmitter transmits n + m data in one period. Here, since 2m> n + m, it can be seen that the number of data transmitted in one symbol period of the cognitive radio transmitter 100 according to the present embodiment is larger.

Accordingly, the cognitive radio transmitter 100 may improve the data rate by using only even subcarriers or only odd subcarriers.

As described above, the IFFT-processed transmission signal using even or odd subcarriers in the transmitter has a symmetry between a signal corresponding to 0 to T / 2 time and a signal corresponding to T / 2 to T time during T time of one symbol signal interval of OFDM. Is repeated. Therefore, the receiver does not receive the entire OFDM symbol signal of the transmitter and receives only the signal corresponding to 0 to T / 2 time for FFT processing.

In this case, the FFT size is reduced to 1/2 so that the computation time is reduced to 1/2 compared to the conventional method. In addition, according to the present embodiment, the cognitive radio transmitter 100 may continuously transmit other data in T / 2 to T time, thereby increasing the data rate. Proof of this is as follows.

For even subcarriers:

As can be seen from the above equation, the DFT processing result at the receiver is output as 1/2 of the data value transmitted from the transmitter. Accordingly, the receiver may recover the data value received from the transmitter by doubling the FFT result.

Hereinafter, the case of odd subcarriers will be described.

For odd subcarriers:

As can be seen from the above equation, in the case of odd subcarriers, the receiver is applied to the received IFFT signal.

By multiplying by, we can restore the original signal through the same process as in the even case.

As described above, the cognitive radio transmitter 100 transmits only a signal corresponding to half of a symbol period using only even subcarriers or only odd subcarriers. Then, the receiver recovers the signal corresponding to one symbol period by using the signal corresponding to half of the symbol period.

The cognitive radio transmitter 100 according to the present embodiment can reduce the amount of calculation of split-radix FFT pruning using this principle. This will be described with reference to FIG. 7.

7 corresponds to a graph comparing the number of complex cumulative numbers of various types of 1024-point FFT algorithms according to an embodiment of the present invention.

In this figure, the horizontal axis shows the number of nonzero outputs, and the vertical axis shows the number of complex multiplications. As the number of L decreases, all the Pruning algorithms and Transform decomposition algorithms have much less computation than the general FFT algorithm, and the split-radix FFT pruning technique has less computation than other algorithms.

The graph also shows that the radix-2 FFT pruning technique requires less computation than the transform decomposition using radix-2 FFTs on sub-transforms. Therefore, although the graph shows the average number of complex multiplications of the split-radix FFT pruning, the split-radix FFT pruning shows less computation than the transform decomposition using the split-radix FFT for the sub-transform.

That is, it can be confirmed from FIG. 7 that the split-radix FFT pruning technique according to the present embodiment has the least amount of calculation.

Hereinafter, the probability density distribution of empty subcarriers (that is, usable subcarriers) will be described with reference to FIG. 8. 8 is a diagram illustrating a probability density distribution of empty subcarriers according to an embodiment of the present invention.

In general, in the OFDM-based cognitive radio technology, the number of empty subcarriers has a Gaussian distribution (normal distribution) in which the average number of empty subcarriers is m as shown in FIG. And when the maximum number of empty subcarriers after m after the spectrum sensing, m, the number distribution of empty even subcarriers has a uniform distribution between 0 and m having an average number of m / 2 as shown in FIG.

According to the present embodiment, after comparing the number of odd subcarriers and the number of even subcarriers, a plurality of groups of subcarriers are selected and data can be transmitted twice in one symbol period. Therefore, according to the present embodiment, as shown in (c) of FIG. 8, the number of empty subcarriers is greater than m / 2, the average value is 3m / 4, and has a uniform distribution characteristic from m / 2 to m. do.

That is, one period of an OFDM symbol is selected by selecting a large number of even or odd subcarrier groups according to the present embodiment, rather than the general scheme of transmitting data using empty subcarriers after spectrum sensing (FIG. 8B). In the case of using the method of transmitting data twice during the period (Fig. 8 (c)), it can be seen that the average data rate is improved.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the present invention.

100: cognitive radio transmitter 110: spectrum sensing unit
120: comparison unit 130; Subcarrier allocation unit
140: IFFT processor 150: transmitter
200: Cognitive wireless receiver 210: Receiver
220: FFT processing unit

Claims (14)

A spectrum sensing unit detecting availability information of subcarriers of a plurality of channels;
A comparison unit comparing the available even subcarriers with the available odd subcarriers using the detected subcarrier availability information, and selecting a greater number of available subcarrier groups among the even subcarrier group and the odd subcarrier group;
A subcarrier allocator for allocating a subcarrier group selected by the comparator to a subcarrier for input data transmission and modulating the input data to the assigned subcarrier;
An IFFT processor for processing inverse fast fourier transform (IFFT) signals output from the subcarrier allocation unit; And
And a transmitter for transmitting the IFFT processed signal to the outside.
Wherein,
A cognitive radio transmitter for transmitting usable subcarrier number information and usable subcarrier channel information for a group having a large number of usable subcarriers among an even subcarrier and an odd subcarrier to the subcarrier assignment unit. delete The method of claim 1,
The subcarrier assignment unit,
A cognitive radio transmitter characterized by modulating data on an allocated subcarrier based on Orthogonal Frequency Division Multiplexing (OFDM) and multiplexing the modulated signal. The method of claim 1,
The IFFT processing unit,
And a IFFT process of the signal output from the subcarrier allocation unit using a split-radix FFT pruning technique. The method of claim 4, wherein
The IFFT processing unit,
A cognitive radio transmitter which performs split-radix FFT pruning technique using a pruning matrix The method of claim 5,
The IFFT processing unit,
A pruning matrix generator for generating a pruning matrix; And
And a split-radix FFT unit configured to perform split-radix FFT processing by using the generated pruning matrix. The method of claim 1,
The IFFT processing unit,
Cognitive radio transmitter, characterized in that for outputting only half of the signal corresponding to one symbol according to the OFDM. The method of claim 7, wherein
The IFFT processing unit,
For one symbol interval T of one subcarrier, half the symbol interval signal for the first data is transmitted during the 0 to T / 2 period, and half the symbol interval signal for the second data for the T / 2 ~ T period. A cognitive radio transmitter, characterized in that for transmitting. A receiving unit for receiving a signal in which two symbol data are half included in one symbol period of one subcarrier; And
And a FFT processor for FFT processing the received signal. 10. The method of claim 9,
The FFT processing unit,
Cognitive radio receiver, characterized in that for separating the signal received during one symbol period in half, and restores the received signal corresponding to half to the signal corresponding to one symbol. The method of claim 10,
The FFT processing unit,
If the received signal is received by an even subcarrier, the cognitive radio receiver characterized in that to recover the signal corresponding to one symbol by doubling the signal corresponding to half of the symbol. The method of claim 10,
The FFT processing unit,
When the received signal is received by an odd subcarrier, it corresponds to a signal corresponding to half of the symbol.

Cognitive radio receiver, characterized in that to recover the signal corresponding to one symbol by multiplying by two times. The method of claim 10,
The FFT processing unit,
A cognitive radio receiver for performing FFT processing on a recovered signal using a split-radix FFT pruning technique. The method of claim 13,
The FFT processing unit,
A cognitive radio receiver, which performs a split-radix FFT pruning technique using a pruning matrix.

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