Simplified OFDM modulation method

Abstract

The invention discloses a simplified OFDM (Orthogonal Frequency Division Multiplexing) modulation method, which belongs to the technical field of mobile communication, and adopts a new OFDM modulation scheme that firstly, an infinitely long discrete sequence is assumed, and then inverse Fourier transform is directly carried out on the sequence to complete OFDM modulation, so that the cyclic shift operation is avoided, and the OFDM modulation efficiency is improved. The technical problems that in the prior art, in the OFDM modulation process, the storage space requirement is large, and OFDM modulation time delay is high are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of mobile communications, and in particular relates to a simplified OFDM modulation method. Background Art

[0002] As the basic modulation scheme of modern communication, OFDM modulation has the advantages of high rate, high bandwidth, high channel utilization, etc., and is widely used in wireless communication standards. In actual hardware implementation, the commonly used implementation structure is as follows: IFFT, i.e. inverse Fourier transform, is obtained by FFT-SHIFT, and CP, i.e. cyclic sequence, is added to IFFT, and finally windowing is performed.

[0003] Among them, FFT-SHIFT is used to perform a cyclic shift of N / 2 on the frequency domain subcarriers, where N is the number of IFFT points, because the subcarriers of the protocol are usually numbered from the negative frequency domain to the positive frequency domain to facilitate subcarrier management in the frequency domain.

[0004] For example, for OFDM modulation with N subcarriers, let the sequence of input IFFT be: The actual sequence entering the OFDM modulation module is: FFT-SHIFT is used to reorder the actual sequence to obtain .

[0005] FFT-SHIFT is usually implemented using RAM, that is, the first N / 2 data of the sequence are first cached in RAM, then the next N / 2 data are output, and finally the first N / 2 data are output. This solution requires a RAM with a depth of N / 2 and will generate a delay of N / 2 sampling times.

[0006] For example, for 32-bit 4096 baseband data, a 2048-deep and 32-bit wide RAM is required. Under the premise of the popularization of MIMO technology, the demand for RAM has increased exponentially, which will lead to considerable resource consumption in the design. The inventors found in actual use that these existing technologies have at least technical problems such as sacrificing calculation accuracy, high OFDM modulation delay, and large storage space requirements; OFDM stands for Orthogonal Frequency Division Multiplexing technology. Summary of the invention

[0007] In view of the problems of high OFDM modulation delay and large storage space requirement in the prior art, the present invention proposes a simplified OFDM modulation method, the purpose of which is to reduce the OFDM modulation delay and its storage space.

[0008] The following steps are involved: Step 1: Assume an infinitely long discrete sequence and then directly perform inverse Fourier transform on the sequence; Step 2: Determine the positive and negative signals of the discrete sequence after the inverse Fourier transform; Step 3: Add a cyclic prefix to the discrete sequence that has completed the determination; Step 4: Perform a windowing operation on the discrete sequence to which the cyclic prefix is ​​added to complete OFDM modulation.

[0009] Preferably, step 1 is performed by assuming As an infinitely long discrete sequence with a period of N, we get: , N=2^m, m=1,2,3,4…; right Circularly shift m sampling points to obtain a new periodic signal , periodic signal The expression is: ; N = 2^m, m = 1, 2, 3, 4…; Then, according to the inverse Fourier transform formula, the periodic signal Perform an inverse Fourier transform.

[0010] Preferably, the inverse Fourier formula used in step 1 is: , , k is the index in the x(k) sequence; , j is an imaginary number.

[0011] Better, for signal To perform inverse Fourier transform, the process is as follows: , , , make , then we get the following equation: , .

[0012] Better, because For a sequence with a period of N, as long as the summation period is N, the summation has nothing to do with the starting point, so the following equation can be obtained: , , when hour, , = .

[0013] Preferably, the process of determining whether the signal is positive or negative in step 2 after the inverse Fourier transform is as follows: , determined as a positive signal; , judged as a negative signal.

[0014] Compared with the prior art, the technical solution of the present invention has the following advantages / benefits: 1. Since the present invention replaces the steps of first performing FFT-SHIFT and then performing inverse Fourier transform in the prior art with first performing inverse Fourier transform and then inverting the formula, the demand for RAM cache sequence is reduced, and the storage space demand in the OFDM modulation process can be significantly reduced. For example, for 4x4MIMO OFDM signal modulation, 4x2kx32 RAM can be cancelled, which significantly reduces resource requirements.

[0015] 2. The solution of first performing inverse Fourier transform and then inverting the formula used in the present invention can significantly reduce OFDM modulation delay because it does not require the use of RAM to implement the FFT-SHIFT operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 It is a structural schematic diagram of a simplified OFDM modulation method of the present invention. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention. Therefore, the detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the claimed invention, but merely represents the selected embodiments of the present invention.

[0019] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and thus, once an item is defined in one drawing, it may not be further defined or explained in the subsequent drawings.

[0020] Example: like Figure 1 As shown, the present invention provides a simplified OFDM modulation method, comprising the following steps: Step 1: Assume an infinitely long discrete sequence and then directly perform inverse Fourier transform on the sequence; Step 2: Determine the positive and negative signals of the discrete sequence after the inverse Fourier transform; Step 3: Add a cyclic prefix to the discrete sequence that has completed the determination; Step 4: Perform a windowing operation on the discrete sequence to which the cyclic prefix is ​​added to complete OFDM modulation.

[0021] Step 1: Assume As an infinitely long discrete sequence with a period of N, we get: , N=2^m, m=1,2,3,4…; right Circularly shift m sampling points to obtain a new periodic signal , periodic signal The expression is: ; N = 2^m, m = 1, 2, 3, 4…; Then, according to the inverse Fourier transform formula, the periodic signal Perform an inverse Fourier transform.

[0022] The inverse Fourier formula used in step 1 is: , , k is the index in the x(k) sequence; , j is an imaginary number.

[0023] Signal To perform inverse Fourier transform, the process is as follows: , , , make , then we get the following equation: , .

[0024] because For a sequence with a period of N, as long as the summation period is N, the summation has nothing to do with the starting point, so the following equation can be obtained: , , when hour, , = .

[0025] Step 2: The process of judging whether the signal is positive or negative after the inverse Fourier transform is as follows: , determined as a positive signal; , judged as a negative signal.

[0026] Step 3: Add a cyclic prefix: In order to reduce the inter-symbol interference caused by the multipath effect, a cyclic prefix needs to be added before each discrete sequence, that is, the signal after the inverse Fourier transform A Cyclic Prefix is ​​added before the cyclic prefix, and technicians in this field can customize the cyclic prefix according to different requirements.

[0027] Step 4: Add the cyclic prefix to the signal Windowing is performed to make the signal The amplitude of the cycle edge gradually transitions to zero.

[0028] Applies a raised cosine window function to a signal Each subcarrier time domain signal is a windowing operation, and the raised cosine window function used is as follows: , , Where β is the roll-off factor, T is the signal length before windowing, is the length of the windowed signal, and t is a natural number.

[0029] At this point, the OFDM modulation process is completed.

[0030] The above are only preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be regarded as limiting the present invention, and the protection scope of the present invention should be based on the scope defined by the claims. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A simplified OFDM modulation method, characterized in that: The following steps are involved: Step 1: Assume an infinitely long discrete sequence and then perform an inverse Fourier transform on the sequence; Step 2: Determine the positive and negative signals of the discrete sequence after the inverse Fourier transform; Step 3: Add a cyclic prefix to the discrete sequence that has completed the determination; Step 4: Perform a windowing operation on the discrete sequence to which the cyclic prefix is ​​added to complete OFDM modulation.

2. A simplified OFDM modulation method according to claim 1, characterized in that: In step 1, by assuming that x(k) is an infinitely long discrete sequence with a period of N, we obtain: ， ； Cyclic shift of the sequence x(k) by m sampling points yields a new periodic signal y(k). The expression of the periodic signal y(k) is: ; ; Then, the periodic signal y(k) is subjected to inverse Fourier transform according to the inverse Fourier transform formula.

3. A simplified OFDM modulation method according to claim 2, characterized in that: The inverse Fourier formula used in step 1 is: , , k is the index in the x(k) sequence; , j is an imaginary number.

4. A simplified OFDM modulation method according to claim 3, characterized in that: The inverse Fourier transform of the periodic signal y(k) is performed as follows: , ， ， Let k=k+m, then we get the following equation: ， 。 5. A simplified OFDM modulation method according to claim 4, characterized in that: Since the sequence x(k) is a sequence with a period of N, when the summation period is N, the summation process is independent of the starting point, so the following equation can be obtained: ， ， When m=N / 2, ， 。 6. A simplified OFDM modulation method according to claim 5, characterized in that: The process of determining the positive or negative signal of the sequence after the inverse Fourier transform in step 2 is as follows: , determined as a positive signal; , judged as a negative signal.

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