Method and device for evaluating OFDM (Orthogonal Frequency Division Multiplexing) system

Abstract

The invention relates to the technical field of wireless communication, and discloses a method and a device for evaluating an OFDM (Orthogonal Frequency Division Multiplexing) system. The method comprises the following steps: sampling an OFDM system to obtain a plurality of discrete carrier signals, and calculating an orthogonality index between the discrete carrier signals; calculating an inter-symbol interference level of an overall received signal of the OFDM system, calculating a system efficiency evaluation index, a comprehensive performance index and a spectrum efficiency index according to the inter-symbol interference level, and optimizing the length of a cyclic prefix; the method comprises the following steps: calculating a channel response estimation value of an OFDM system, calculating a noise power estimation value according to the channel response estimation value, calculating a signal-to-noise ratio estimation value according to the channel response estimation value and the noise power estimation value, and further determining a modulation mode of each subcarrier and generating a corresponding modulation signal. According to the method, the continuous time orthogonality theory is converted into a realizable discrete scheme, the length selection of the cyclic prefix is quantitatively analyzed and optimized, and adaptive modulation on the premise of ensuring the transmission quality is realized.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to an OFDM system evaluation method and device. Background Art

[0002] In the current OFDM (Orthogonal Frequency Division Multiplexing) wireless communication experimental teaching system, there are many key technical difficulties and teaching limitations. These problems mainly revolve around the evaluation of carrier orthogonality, the relationship between cyclic prefix (CP) and inter-symbol interference (ISI), and the understanding and application of adaptive modulation principles in the OFDM transmission and reception process. Summary of the invention

[0003] In view of this, an object of the present invention is to overcome the deficiencies in the prior art and to provide an OFDM system evaluation method and device.

[0004] The present invention provides the following technical solutions:

[0005] In a first aspect, an embodiment of the present disclosure provides an OFDM system evaluation method, the method comprising:

[0006] Sampling multiple initial carrier signals of the OFDM system to obtain multiple discrete carrier signals, and calculating the orthogonality index between the discrete carrier signals;

[0007] Obtain a reference signal of the OFDM system, and add a cyclic prefix to the reference signal according to a preset length, process the reference signal after adding the cyclic prefix through a multipath channel model to obtain an overall received signal, calculate the inter-symbol interference level of the overall received signal, and calculate the system efficiency evaluation index, comprehensive performance index and spectrum efficiency index of the overall received signal according to the inter-symbol interference level, and optimize the length of the cyclic prefix according to the inter-symbol interference level and the system efficiency evaluation index;

[0008] A transmitting pilot signal and a receiving pilot signal at specific positions of multiple subcarriers in an OFDM system are obtained, a channel response estimation value of the OFDM system is calculated according to the transmitting pilot signal and the receiving pilot signal, a noise power estimation value of the OFDM system is calculated according to the transmitting pilot signal, the receiving pilot signal and the channel response estimation value, a signal-to-noise ratio estimation value of each subcarrier is calculated according to the channel response estimation value and the noise power estimation value, and a modulation mode of each subcarrier is determined and a corresponding modulation signal is generated by comparing the signal-to-noise ratio estimation value of each subcarrier with a preset signal-to-noise ratio threshold.

[0009] Optionally, sampling multiple initial carrier signals of the OFDM system to obtain multiple discrete carrier signals includes:

[0010] The initial carrier signals are sampled by a preset sampling rate, a preset observation window length, and a preset sliding step length, and the sampled initial carrier signals are subjected to signal normalization processing to obtain a plurality of normalized carrier signals;

[0011] Performing windowing processing on each normalized carrier signal to obtain a plurality of windowed carrier signals, and performing DC offset removal processing on each windowed carrier signal to obtain a plurality of discrete carrier signals;

[0012] Among them, each initial carrier signal is:

[0013] s1(t)=A1cos(2πf1t+φ1)

[0014] s2(t)=A2cos(2πf2t+φ2)

[0015] Wherein, s1(t) is the first initial carrier signal, s2(t) is the second initial carrier signal, A1 and A2 are the amplitudes of the first initial carrier signal and the second initial carrier signal, f1 and f2 are the frequencies of the first initial carrier signal and the second initial carrier signal, φ1 and φ2 are the phases of the first initial carrier signal and the second initial carrier signal, respectively.

[0016] Optionally, calculating an orthogonality index between discrete carrier signals includes:

[0017] Calculate the correlation index between the discrete carrier signals using a preset correlation calculation formula, and calculate the product of the energy of the discrete carrier signals using a preset energy calculation formula;

[0018] Calculate the orthogonality index between the discrete carrier signals by using a preset orthogonality calculation formula and according to the product of the correlation index between the discrete carrier signals and the energy of the discrete carrier signals;

[0019] Among them, the preset correlation calculation formula is:

[0020]

[0021] Where s1[k] is the first discrete carrier signal, is the conjugate complex number of the second discrete carrier signal, N is the number of sampling points, R[n] is the correlation index, and k is the discrete time point at which each initial carrier signal is sampled;

[0022] Among them, the preset energy calculation formula is:

[0023]

[0024] Where E[n] is the product of the energy of each discrete carrier signal;

[0025] Among them, the preset orthogonality calculation formula is:

[0026]

[0027] Where O[n] is the orthogonality index between discrete carrier signals.

[0028] Optionally, calculating the inter-symbol interference level of the overall received signal includes:

[0029] Decomposing the overall received signal into a main path signal and a multipath interference signal, and calculating the energy of the main path signal and the energy of the multipath interference signal respectively;

[0030] Using a preset inter-symbol interference level calculation formula and according to the energy of the multipath interference signal and the energy of the main path signal, an initial inter-symbol interference level is calculated, and a preset normalization formula is used to normalize the initial inter-symbol interference level to obtain an inter-symbol interference level of the overall received signal;

[0031] The preset inter-symbol interference level calculation formula is:

[0032]

[0033] In the formula, ISI level (τ)′ is the initial inter-symbol interference level, h l is the channel coefficient of the lth path, x(n-τ l ) is the reference signal after τ l The signal after sampling delay, h0 is the channel coefficient of the main path, x(n) is the reference signal, L is the channel length, τ is the actual delay, and N is the number of sampling points;

[0034] Among them, the preset normalization formula is:

[0035]

[0036] In the formula, ISI level (τ) is the inter-symbol interference level, CP length is the length of the cyclic prefix.

[0037] Optionally, the system efficiency evaluation index, the comprehensive performance index and the spectrum efficiency index of the overall received signal are calculated according to the inter-symbol interference level, including:

[0038] Obtaining the OFDM symbol length of the reference signal, respectively calculating a first inter-code interference level of the overall received signal including the cyclic prefix and a second inter-code interference level of the overall received signal not including the cyclic prefix, calculating a cyclic prefix overhead rate according to the OFDM symbol length and the length of the cyclic prefix, calculating an inter-code interference level suppression rate according to the first inter-code interference level and the second inter-code interference level, and calculating a system efficiency evaluation index according to the inter-code interference level suppression rate and the cyclic prefix overhead rate using a preset system efficiency evaluation index calculation formula;

[0039] Obtaining a bit error rate, and respectively obtaining a first weight of an inter-symbol interference level, a second weight of a cyclic prefix overhead rate, and a third weight of the bit error rate, and calculating a comprehensive performance indicator using a preset comprehensive performance indicator calculation formula and according to the inter-symbol interference level, the first weight, the cyclic prefix overhead rate, the second weight, the bit error rate, and the third weight;

[0040] Calculate the spectrum efficiency index by using a preset spectrum efficiency index calculation formula and according to the OFDM symbol length and the cyclic prefix length;

[0041] Among them, the calculation formula of the preset system efficiency evaluation index is:

[0042]

[0043] Where η system ISI is the system efficiency evaluation index. no_cp is the second inter-symbol interference level, ISI with_cp is the first inter-symbol interference level, OFDM length is the OFDM symbol length, CP length is the length of the cyclic prefix, ISI suppression is the inter-symbol interference level suppression rate, CP overhead is the cyclic prefix overhead rate;

[0044] Among them, the preset comprehensive performance index calculation formula is:

[0045]

[0046] Where P system is a comprehensive performance indicator, α is the first weight, β is the second weight, BER is the bit error rate, and γ is the third weight;

[0047] The preset spectrum efficiency index calculation formula is:

[0048]

[0049] Where η spectral It is the spectrum efficiency indicator.

[0050] Optionally, optimizing the length of the cyclic prefix according to the inter-symbol interference level and the system efficiency evaluation index includes:

[0051] Obtain all lengths of the cyclic prefix, and respectively calculate the performance evaluation index and the inter-symbol interference level under all lengths of the cyclic prefix;

[0052] Determine, according to a preset optimization formula, a target length of the cyclic prefix that minimizes the system performance evaluation index value among the lengths of the cyclic prefix that satisfy the inter-symbol interference level lower than the preset interference level threshold, and use the target length as the optimized length of the cyclic prefix;

[0053] Among them, the preset optimization formula is:

[0054] CP opt =argmin τ {η system (τ)|ISI level (τ) <ISI threshold}

[0055] In the formula, CP opt is the target length, ISI threshold is the preset interference level threshold.

[0056] Optionally, the OFDM system includes a plurality of subcarrier positions and a plurality of subcarrier specific positions, and a channel response estimate of the OFDM system is calculated according to a transmitted pilot signal and a received pilot signal, and a noise power estimate of the OFDM system is calculated according to the transmitted pilot signal, the received pilot signal and the channel response estimate, including:

[0057] The ratio of the received pilot signal to the transmitted pilot signal at the specific position of each subcarrier is used as the channel response estimation value at the specific position of each subcarrier, the channel response estimation value at each subcarrier position is calculated according to the channel response estimation value at the specific position of each subcarrier by using a linear interpolation algorithm, and the channel response estimation value of the OFDM system is obtained according to the channel response estimation value at the specific position of each subcarrier and the channel response estimation value at each subcarrier position;

[0058] An ideal received signal is calculated based on the transmitted pilot signal and the channel response estimation value, and a noise power estimation value of the OFDM system is calculated based on the received pilot signal and the ideal received signal using a preset noise power calculation formula;

[0059] Among them, the linear interpolation algorithm is:

[0060]

[0061] Where H(k) is the estimated channel response value of subcarrier position k, H(k1) and H(k2) are the estimated channel response values ​​of subcarrier specific positions k1 and k2, respectively. <k<k2;

[0062] Among them, the preset noise power calculation formula is:

[0063]

[0064] Where N0 is the estimated value of noise power, Y p (k) is the received pilot signal, H p (k) is the smoothed value of the channel response estimate at position k and the channel response estimates at N adjacent positions, X p (k) is the sent pilot signal.

[0065] Optionally, calculating the signal-to-noise ratio estimate of each subcarrier according to the channel response estimate and the noise power estimate includes:

[0066] Calculate the power gain of the channel response estimate, calculate the power of the sent pilot signal, and calculate the initial signal-to-noise ratio of each subcarrier using a preset signal-to-noise ratio calculation formula based on the power gain of the channel response estimate, the power of the sent pilot signal, and the noise power estimate;

[0067] Performing time domain smoothing processing on the initial signal-to-noise ratio of each subcarrier to obtain an estimated signal-to-noise ratio value of each subcarrier;

[0068] Among them, the preset signal-to-noise ratio calculation formula is:

[0069] SNR k =|H k | 2 ·E[|X k | 2 ] / N0

[0070] In the formula, SNR k is the estimated value of signal-to-noise ratio, |H k | 2 is the power gain of the channel response estimate, E[|X k | 2 ] is the power of sending the pilot signal.

[0071] Optionally, determining a modulation mode of each subcarrier and generating a corresponding modulation signal by comparing the estimated signal-to-noise ratio value of each subcarrier with a preset signal-to-noise ratio threshold value includes:

[0072] Obtaining a preset bit error rate requirement value, and determining a preset signal-to-noise ratio threshold value according to the bit error rate requirement value using a preset signal-to-noise ratio threshold calculation formula, wherein the preset signal-to-noise ratio threshold value includes a first signal-to-noise ratio threshold value and a second signal-to-noise ratio threshold value;

[0073] If the estimated signal-to-noise ratio value of the subcarrier is less than the first signal-to-noise ratio threshold, determine its modulation mode as BPSK modulation and generate a corresponding modulation signal;

[0074] If the estimated signal-to-noise ratio value of the subcarrier is greater than the first signal-to-noise ratio threshold and less than the second signal-to-noise ratio threshold, determine its modulation mode as QPSK modulation and generate a corresponding modulation signal;

[0075] If the estimated signal-to-noise ratio value of the subcarrier is greater than the second signal-to-noise ratio threshold, determine its modulation mode as 16QAM modulation and generate a corresponding modulation signal;

[0076] The preset signal-to-noise ratio threshold calculation formula is:

[0077]

[0078] Where, γ1 and γ2 are the first signal-to-noise ratio threshold and the second signal-to-noise ratio threshold, respectively. target It is the preset bit error rate requirement value.

[0079] In a second aspect, an OFDM system evaluation device is provided in an embodiment of the present disclosure, the device comprising:

[0080] A first calculation module is used to sample multiple initial carrier signals of the OFDM system to obtain multiple discrete carrier signals and calculate the orthogonality index between the discrete carrier signals;

[0081] The second calculation module is used to obtain a reference signal of the OFDM system, add a cyclic prefix to the reference signal according to a preset length, process the reference signal after adding the cyclic prefix through a multipath channel model to obtain an overall received signal, calculate the inter-symbol interference level of the overall received signal, and calculate the system efficiency evaluation index, comprehensive performance index and spectrum efficiency index of the overall received signal according to the inter-symbol interference level, and optimize the length of the cyclic prefix according to the inter-symbol interference level and the system efficiency evaluation index;

[0082] The third calculation module is used to obtain the transmission pilot signal and the reception pilot signal at specific positions of multiple subcarriers in the OFDM system, calculate the channel response estimation value of the OFDM system according to the transmission pilot signal and the reception pilot signal, calculate the noise power estimation value of the OFDM system according to the transmission pilot signal, the reception pilot signal and the channel response estimation value, calculate the signal-to-noise ratio estimation value of each subcarrier according to the channel response estimation value and the noise power estimation value, and determine the modulation mode of each subcarrier and generate a corresponding modulation signal by comparing the signal-to-noise ratio estimation value of each subcarrier with a preset signal-to-noise ratio threshold.

[0083] Beneficial effects of this application:

[0084] The evaluation method of the OFDM system provided in the embodiment of the present application samples multiple initial carrier signals of the OFDM system to obtain multiple discrete carrier signals, and calculates the orthogonality index between each of the discrete carrier signals; obtains the reference signal of the OFDM system, and adds a cyclic prefix to the reference signal according to a preset length, processes the reference signal after the cyclic prefix is ​​added through a multipath channel model to obtain an overall received signal, calculates the inter-symbol interference level of the overall received signal, and calculates the system efficiency evaluation index, the comprehensive performance index and the spectrum efficiency index of the overall received signal according to the inter-symbol interference level, and calculates the system efficiency evaluation index, the comprehensive performance index and the spectrum efficiency index of the overall received signal according to the inter-symbol interference level, and calculates the system efficiency evaluation index, the comprehensive performance index and the spectrum efficiency index of the overall received signal according to the inter-symbol interference level and the system efficiency evaluation index. The estimation index optimizes the length of the cyclic prefix; obtains the transmission pilot signal and the reception pilot signal at specific positions of multiple subcarriers in the OFDM system, calculates the channel response estimation value of the OFDM system according to the transmission pilot signal and the reception pilot signal, and calculates the noise power estimation value of the OFDM system according to the transmission pilot signal, the reception pilot signal and the channel response estimation value, calculates the signal-to-noise ratio estimation value of each subcarrier according to the channel response estimation value and the noise power estimation value, and determines the modulation mode of each subcarrier and generates a corresponding modulation signal by comparing the signal-to-noise ratio estimation value of each subcarrier with a preset signal-to-noise ratio threshold. The present application transforms the continuous-time orthogonality theory into an achievable discrete calculation scheme, intuitively demonstrates the impact of the change in the length of the cyclic prefix on the signal-to-noise ratio, quantitatively analyzes and optimizes the selection of the length of the cyclic prefix, establishes a quantitative relationship between the target bit error rate and the modulation mode selection threshold, and realizes adaptive modulation under the premise of ensuring transmission quality.

[0085] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0086] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and 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 creative work. In each of the drawings, similar components are numbered similarly.

[0087] Figure 1 A flowchart of an OFDM system evaluation method provided by an embodiment of the present application is shown;

[0088] Figure 2 A schematic structural diagram of an OFDM system evaluation device provided in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0089] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0090] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. In contrast, when an element is referred to as being "directly on" another element, there is no intermediate element. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only.

[0091] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0092] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0093] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of the template are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0094] Example 1

[0095] like Figure 1 FIG. 1 is a flowchart of an OFDM system evaluation method according to an embodiment of the present application. The OFDM system evaluation method provided by the embodiment of the present application includes the following steps:

[0096] Step S110: sampling a plurality of initial carrier signals of the OFDM system to obtain a plurality of discrete carrier signals, and calculating an orthogonality index between the discrete carrier signals.

[0097] In this embodiment, each initial carrier signal of the OFDM (Orthogonal Frequency Division Multiplexing) system is first sampled by a preset sampling rate (for example, not less than twice the highest carrier frequency), a preset observation window length (at least including a complete carrier cycle) and a preset sliding step size (such as 25%-50% of the window length).

[0098] In order to unify the signal amplitude range and facilitate subsequent processing, the sampled initial carrier signals are normalized. The specific process can be: first calculate the maximum amplitude value of each initial carrier signal, and then divide each initial carrier signal by the maximum amplitude value to obtain multiple normalized carrier signals.

[0099] In order to reduce spectrum leakage and improve the accuracy of frequency domain analysis, each normalized carrier signal is subjected to windowing processing. The specific process may be: determining a Hanning window function, multiplying each normalized carrier signal by the Hanning window function respectively, and obtaining a plurality of windowed carrier signals.

[0100] In order to eliminate the DC component in the signal and highlight the AC characteristics, the DC offset is removed from each windowed carrier signal. The specific process may be: calculating the average value of each windowed carrier signal, subtracting each windowed carrier signal from the average value, and finally obtaining multiple discrete carrier signals.

[0101] It should be noted that, in this embodiment, each initial carrier signal is:

[0102] s1(t)=A1cos(2πf1t+φ1)

[0103] s2(t)=A2cos(2πf2t+φ2)

[0104] Wherein, s1(t) is the first initial carrier signal, s2(t) is the second initial carrier signal, A1 and A2 are the amplitudes of the first initial carrier signal and the second initial carrier signal, f1 and f2 are the frequencies of the first initial carrier signal and the second initial carrier signal, φ1 and φ2 are the phases of the first initial carrier signal and the second initial carrier signal, respectively.

[0105] Furthermore, the correlation index between the discrete carrier signals is calculated using a preset correlation calculation formula:

[0106]

[0107] Where s1[k] is the first discrete carrier signal, is the conjugate complex number of the second discrete carrier signal, N is the number of sampling points, R[n] is the correlation index, and k is the discrete time point at which each initial carrier signal is sampled.

[0108] Then, the product of the energies of each discrete carrier signal is calculated using the preset energy calculation formula:

[0109]

[0110] Wherein, E[n] is the product of the energies of each of the discrete carrier signals.

[0111] Next, the orthogonality index between each discrete carrier signal is calculated using a preset orthogonality calculation formula:

[0112]

[0113] Wherein, O[n] is an orthogonality index between the discrete carrier signals, and its value range is [0, 1]. When O[n] is 0, it indicates complete orthogonality, and when O[n] is 1, it indicates complete correlation.

[0114] Preferably, the relevant parameters and trend changes of the entire process can be displayed through the visual display screen of the OFDM system, such as: the initial carrier signal, the normalized carrier signal, the windowed carrier signal, the discrete carrier signal, the real-time orthogonality index, the orthogonality curve formed by multiple real-time orthogonality indicators, the change trend of the orthogonality index and the time domain waveform of each carrier signal, etc.

[0115] The evaluation of carrier orthogonality in the existing OFDM system has the following problems: it mainly relies on qualitative analysis of spectrum observation, lacks real-time quantitative evaluation methods, and cannot accurately measure the orthogonality changes under non-ideal conditions. Therefore, this application proposes a carrier orthogonality calculation method based on normalized correlation coefficients. The core innovation lies in converting the continuous-time orthogonality theory into a feasible discrete calculation scheme, which not only realizes real-time quantitative evaluation, but also can accurately measure the orthogonality changes under non-ideal conditions, providing strong support for the optimization and improvement of OFDM systems.

[0116] Step S120, obtain a reference signal of the OFDM system, and add a cyclic prefix to the reference signal according to a preset length, process the reference signal after adding the cyclic prefix through a multipath channel model to obtain an overall received signal, calculate the inter-symbol interference level of the overall received signal, and calculate the system efficiency evaluation index, comprehensive performance index and spectrum efficiency index of the overall received signal based on the inter-symbol interference level, and optimize the length of the cyclic prefix based on the inter-symbol interference level and the system efficiency evaluation index.

[0117] In this embodiment, a reference signal generated by an OFDM system is first obtained, and a cyclic prefix of a variable preset length is added to the reference signal. Considering the influence of the multipath channel, the reference signal after adding the cyclic prefix is ​​processed through the multipath channel model to obtain the overall received signal:

[0118]

[0119] Where h(l) is the channel coefficient of the lth path, x(nl) is the signal after the transmitted signal is delayed by l samples, and y(n) is the overall received signal received by the receiving end.

[0120] Then, the overall received signal is decomposed into the main path signal (y main (n) = h0x(n)) and multipath interference signal The energy of the main path signal and the energy of the multipath interference signal are calculated respectively, and the initial inter-symbol interference level is calculated according to the energy of the multipath interference signal and the energy of the main path signal using the preset inter-symbol interference level calculation formula:

[0121]

[0122] In the formula, ISI level (τ)′ is the initial inter-symbol interference level, h l is the channel coefficient of the lth path, x(n-τ l ) is the reference signal after τ l The signal is delayed by samples, h0 is the channel coefficient of the main path, x(n) is the reference signal, L is the channel length, τ is the actual delay, and N is the number of sampling points.

[0123] Next, the initial inter-symbol interference level is normalized using a preset normalization formula to obtain the inter-symbol interference level of the overall received signal:

[0124]

[0125] In the formula, ISI level (τ) is the inter-symbol interference level, CP length is the length of the cyclic prefix.

[0126] Further, the OFDM symbol length of the reference signal is obtained, and the first inter-code interference level of the overall received signal including the cyclic prefix and the second inter-code interference level of the overall received signal not including the cyclic prefix are calculated respectively, the cyclic prefix overhead rate is calculated according to the OFDM symbol length and the length of the cyclic prefix, the inter-code interference level suppression rate is calculated according to the first inter-code interference level and the second inter-code interference level, and the system efficiency evaluation index is calculated according to the inter-code interference level suppression rate and the cyclic prefix overhead rate using a preset system efficiency evaluation index calculation formula:

[0127]

[0128] Where η system ISI is the system efficiency evaluation index. no_cp is the second inter-symbol interference level, ISI with_cp is the first inter-symbol interference level, OFDM length is the OFDM symbol length, CP length is the length of the cyclic prefix, ISI suppression is the inter-symbol interference level suppression rate, CP overhead It is the cyclic prefix overhead rate, and its value range is generally (0, 1). It indicates the proportion of additional overhead and affects the system spectrum efficiency.

[0129] Obtain the bit error rate, and respectively obtain the first weight of the inter-symbol interference level, the second weight of the cyclic prefix overhead rate, and the third weight of the bit error rate, and calculate the comprehensive performance index according to the inter-symbol interference level, the first weight, the cyclic prefix overhead rate, the second weight, the bit error rate, and the third weight using a preset comprehensive performance index calculation formula:

[0130]

[0131] Where P system is a comprehensive performance indicator, α is the first weight, β is the second weight, BER is the bit error rate, and γ is the third weight.

[0132] The spectrum efficiency index is calculated using a preset spectrum efficiency index calculation formula and according to the OFDM symbol length of the reference signal and the length of the cyclic prefix:

[0133]

[0134] Where η spectral It is the spectrum efficiency indicator.

[0135] Further, all optional lengths of the cyclic prefix are obtained, and the performance evaluation index and the inter-code interference level under all lengths of the cyclic prefix are calculated according to the above method. According to the preset optimization formula, the target length of the cyclic prefix that minimizes the system performance evaluation index value is determined among the lengths of the cyclic prefix that satisfy the inter-code interference level lower than the preset interference level threshold, and the target length is used as the optimized length of the cyclic prefix:

[0136] CP opt =argmin τ {η system (τ)|ISI level (τ) <ISI threshold}

[0137] In the formula, CP opt is the target length, ISI threshold is the preset interference level threshold.

[0138] Preferably, the relevant parameters and trend changes of the entire process can be displayed through the visual display screen of the OFDM system, such as: the time domain waveform of the reference signal, the time domain waveform of the reference signal after adding the cyclic prefix, the time domain waveform of the overall received signal, system efficiency evaluation indicators, comprehensive performance indicators and spectrum efficiency indicators, etc.

[0139] In OFDM systems, multipath effects can cause inter-symbol interference (ISI), and cyclic prefixes (CP) are traditionally used to eliminate the effects of ISI. The prior art has the following problems: lack of an intuitive method for displaying the relationship between CP and ISI, inability to observe the effects of parameter changes on the system in real time, and difficulty in quantitatively analyzing the selection of the optimal CP length. The present application uses the above method to intuitively display the effects of CP length changes on ISI, achieves real-time adjustment and observation of system parameters, and can quantitatively analyze and optimize CP length selection.

[0140] Step S130, obtaining the transmit pilot signal and the receive pilot signal at specific positions of multiple subcarriers in the OFDM system, calculating the channel response estimate of the OFDM system according to the transmit pilot signal and the receive pilot signal, and calculating the noise power estimate of the OFDM system according to the transmit pilot signal, the receive pilot signal and the channel response estimate, calculating the signal-to-noise ratio estimate of each subcarrier according to the channel response estimate and the noise power estimate, and determining the modulation mode of each subcarrier and generating a corresponding modulation signal by comparing the signal-to-noise ratio estimate of each subcarrier with a preset signal-to-noise ratio threshold.

[0141] It should be noted that the OFDM system includes multiple subcarrier positions including multiple subcarrier specific positions, and pilot extraction is performed based on pre-designed subcarrier specific positions. Specifically, at the signal transmitting end, a known pilot sequence is inserted at a subcarrier specific position at a fixed interval L (for example, every 4 subcarrier positions), and these positions are known at the signal receiving end. When the signal receiving end obtains the OFDM symbol and completes the FFT transformation, it only needs to directly extract the signal at the corresponding subcarrier specific position according to these predetermined subcarrier specific positions (for example, for L=4, it is subcarrier index 0, 4, 8, ...), and these extracted signals are received pilot signals. This pilot extraction method based on specific positions avoids the complex pilot detection process and improves system efficiency.

[0142] In the OFDM system, the core of channel estimation is to estimate the channel response by comparing the difference between the received pilot signal and the transmitted pilot signal. The specific process is: first, at the specific position of each subcarrier, the received pilot signal is divided by the transmitted pilot signal to obtain the channel response estimation value at the specific position of each subcarrier. Then, the linear interpolation algorithm (or spline interpolation algorithm) is used to infer the channel response estimation value at each subcarrier position from the channel estimation value at the specific position of these subcarriers, and finally the channel response estimation value of the entire OFDM system in the frequency domain is obtained.

[0143] Wherein, the linear interpolation algorithm is:

[0144]

[0145] Where H(k) is the estimated channel response value of the subcarrier position x, H(k1) and H(k2) are the estimated channel response values ​​of the subcarrier specific positions k1 and k2, respectively. <k<k2。

[0146] Furthermore, in the OFDM system, noise power estimation is achieved by comparing the difference between the received pilot signal and the ideal received signal at a specific position of the subcarrier. Specifically, the transmitted pilot signal is multiplied by the channel response estimate to obtain the ideal received signal. Then, using the preset noise power calculation formula, the square of the difference between the received pilot signal and the ideal received signal is the noise power. Finally, the noise power at the specific position of all subcarriers is averaged to obtain the noise power estimate of the OFDM system:

[0147]

[0148] Where N0 is the estimated value of noise power, Y p (k) is the received pilot signal, H p(k) is the frequency domain smoothing value of the channel response estimation value at the kth position and the channel response estimation values ​​at its adjacent N positions (smoothing in the frequency domain removes the noise), X p (k) is the sent pilot signal.

[0149] Furthermore, in the OFDM system, the signal-to-noise ratio calculation of each subcarrier is performed based on the previously obtained channel estimation value and noise power estimation value. Specifically, for the kth subcarrier, the power gain of the channel response estimation value is first calculated, and the power of the transmitted pilot signal is calculated. Using the preset signal-to-noise ratio calculation formula, the product of the power gain of the channel response estimation value and the power of the transmitted pilot signal is divided by the noise power estimation value to calculate the initial signal-to-noise ratio of each subcarrier:

[0150] SNR k =|H k | 2 ·E[|X k | 2 ] / N0

[0151] In the formula, SNR k is the estimated value of signal-to-noise ratio, |H k | 2 is the power gain of the channel response estimate, E[|X k | 2 ] is the power of sending the pilot signal.

[0152] It should be noted that in order to improve the reliability of the signal-to-noise ratio estimation, the calculated signal-to-noise ratio estimation value is usually smoothed in the time domain, that is, using the exponential sliding average method:

[0153] SNR smooth (n) = α·SNR smooth (n-1)+(1-α)·SNR k (n)

[0154] In the formula, SNR smooth (n) is the estimated value of the signal-to-noise ratio after smoothing, and α is the smoothing factor (usually 0.8 to 0.9, which can reduce the impact of instantaneous fluctuations on the estimated value of the signal-to-noise ratio).

[0155] It can be understood that in the adaptive modulation of the OFDM system, the selection of the modulation mode is completed based on the comparison between the estimated signal-to-noise ratio value of each subcarrier and the preset signal-to-noise ratio threshold. Specifically, the preset bit error rate requirement value is obtained, and the preset signal-to-noise ratio threshold calculation formula is used to determine the preset signal-to-noise ratio threshold according to the bit error rate requirement value, wherein the preset signal-to-noise ratio threshold includes a first signal-to-noise ratio threshold and a second signal-to-noise ratio threshold:

[0156]

[0157] Where, γ1 and γ2 are the first signal-to-noise ratio threshold and the second signal-to-noise ratio threshold, respectively. target It is the preset bit error rate requirement value.

[0158] Then the estimated signal-to-noise ratio value of each subcarrier is compared with these thresholds: if the estimated signal-to-noise ratio value of the subcarrier is less than the first signal-to-noise ratio threshold, its modulation mode is determined to be BPSK modulation and a corresponding modulation signal is generated; if the estimated signal-to-noise ratio value of the subcarrier is greater than the first signal-to-noise ratio threshold and less than the second signal-to-noise ratio threshold, its modulation mode is determined to be QPSK modulation and a corresponding modulation signal is generated; if the estimated signal-to-noise ratio value of the subcarrier is greater than the second signal-to-noise ratio threshold, its modulation mode is determined to be 16QAM modulation and a corresponding modulation signal is generated.

[0159] It should be noted that the setting of the above signal-to-noise ratio threshold is determined based on the minimum signal-to-noise ratio estimation value required by different modulation modes under specific bit error rate requirements, and this embodiment does not limit this.

[0160] Furthermore, after the OFDM system assigns the corresponding modulation mode (BPSK / QPSK / 16QAM) to each subcarrier, it will generate the corresponding modulation control word (usually represented by 2 bits, such as 00 for BPSK, 01 for QPSK, and 10 for 16QAM). These control signals will be sent to the modulator to control the modulation mapping process of each subcarrier. At the same time, it is also necessary to notify the signal receiving end through some method (such as control channel) to ensure that the signal receiving end can demodulate correctly.

[0161] It should be noted that in the performance monitoring of the OFDM system, the data collection process needs to track two key information at the same time: one is the real-time collection of the received data stream, including the signal data received by each subcarrier; the other is to record the dynamic changes of each subcarrier modulation method (that is, the time and frequency of switching from BPSK to QPSK, or from QPSK to 16QAM, etc.). The collected raw data will be used for subsequent performance analysis and system evaluation.

[0162] Preferably, the relevant parameters and trend changes of the whole process can be displayed through the visual display screen of the OFDM system, for example: the modulation mode distribution of each subcarrier and the status information of the OFDM system.

[0163] In the prior art, OFDM wireless communication experimental teaching systems usually use fixed modulation methods when conducting signal transmission and reception experiments. They cannot intuitively understand and master the adaptive modulation principles in actual communication systems. They lack real-time monitoring and visual display functions for subcarrier channel status, which is not conducive to understanding the relationship between channel conditions and modulation mode selection. This application establishes a quantitative relationship between the target bit error rate and the modulation mode selection threshold through the above method, and realizes adaptive modulation under the premise of ensuring transmission quality. The real-time calculation and intuitive display of system performance indicators are realized, which is convenient for teaching demonstrations and experimental observations.

[0164] The evaluation method of the OFDM system provided in the embodiment of the present application samples multiple initial carrier signals of the OFDM system to obtain multiple discrete carrier signals, and calculates the orthogonality index between each of the discrete carrier signals; obtains the reference signal of the OFDM system, and adds a cyclic prefix to the reference signal according to a preset length, processes the reference signal after the cyclic prefix is ​​added through a multipath channel model to obtain an overall received signal, calculates the inter-symbol interference level of the overall received signal, and calculates the system efficiency evaluation index, the comprehensive performance index and the spectrum efficiency index of the overall received signal according to the inter-symbol interference level, and calculates the system efficiency evaluation index, the comprehensive performance index and the spectrum efficiency index of the overall received signal according to the inter-symbol interference level, and calculates the system efficiency evaluation index, the comprehensive performance index and the spectrum efficiency index of the overall received signal according to the inter-symbol interference level and the system efficiency evaluation index. The estimation index optimizes the length of the cyclic prefix; obtains the transmission pilot signal and the reception pilot signal at specific positions of multiple subcarriers in the OFDM system, calculates the channel response estimation value of the OFDM system according to the transmission pilot signal and the reception pilot signal, and calculates the noise power estimation value of the OFDM system according to the transmission pilot signal, the reception pilot signal and the channel response estimation value, calculates the signal-to-noise ratio estimation value of each subcarrier according to the channel response estimation value and the noise power estimation value, and determines the modulation mode of each subcarrier and generates a corresponding modulation signal by comparing the signal-to-noise ratio estimation value of each subcarrier with a preset signal-to-noise ratio threshold. The present application transforms the continuous-time orthogonality theory into an achievable discrete calculation scheme, intuitively demonstrates the impact of the change in the length of the cyclic prefix on the signal-to-noise ratio, quantitatively analyzes and optimizes the selection of the length of the cyclic prefix, establishes a quantitative relationship between the target bit error rate and the modulation mode selection threshold, and realizes adaptive modulation under the premise of ensuring transmission quality.

[0165] Example 2

[0166] like Figure 2 FIG. 2 is a schematic diagram of a structure of an OFDM system evaluation device 200 in an embodiment of the present application, wherein the device comprises:

[0167] The first calculation module 210 is used to sample multiple initial carrier signals of the OFDM system to obtain multiple discrete carrier signals and calculate the orthogonality index between the discrete carrier signals;

[0168] The second calculation module 220 is used to obtain a reference signal of the OFDM system, add a cyclic prefix to the reference signal according to a preset length, process the reference signal after adding the cyclic prefix through a multipath channel model to obtain an overall received signal, calculate the inter-symbol interference level of the overall received signal, and calculate the system efficiency evaluation index, comprehensive performance index and spectrum efficiency index of the overall received signal according to the inter-symbol interference level, and optimize the length of the cyclic prefix according to the inter-symbol interference level and the system efficiency evaluation index;

[0169] The third calculation module 230 is used to obtain the transmission pilot signal and the reception pilot signal at specific positions of multiple subcarriers in the OFDM system, calculate the channel response estimation value of the OFDM system according to the transmission pilot signal and the reception pilot signal, calculate the noise power estimation value of the OFDM system according to the transmission pilot signal, the reception pilot signal and the channel response estimation value, calculate the signal-to-noise ratio estimation value of each subcarrier according to the channel response estimation value and the noise power estimation value, and determine the modulation mode of each subcarrier and generate a corresponding modulation signal by comparing the signal-to-noise ratio estimation value of each subcarrier with a preset signal-to-noise ratio threshold.

[0170] The evaluation device of the OFDM system provided in the embodiment of the present application converts the continuous-time orthogonality theory into a feasible discrete calculation scheme, intuitively demonstrates the impact of the change in the length of the cyclic prefix on the signal-to-noise ratio, quantitatively analyzes and optimizes the selection of the cyclic prefix length, establishes a quantitative relationship between the target bit error rate and the modulation mode selection threshold, and realizes adaptive modulation under the premise of ensuring transmission quality.

[0171] In several embodiments provided in the present application, it should be understood that the disclosed devices and methods can also be implemented in other ways. The device embodiments described above are merely schematic. For example, the flowcharts and structure diagrams in the accompanying drawings show the possible architecture, functions and operations of the devices, methods and computer program products according to multiple embodiments of the present invention. In this regard, each box in the flowchart or block diagram can represent a module, a program segment or a part of a code, and the module, a program segment or a part of a code contains one or more executable instructions for implementing the specified logical function. It should also be noted that in an alternative implementation, the functions marked in the box can also occur in a different order from the order marked in the accompanying drawings. For example, two consecutive boxes can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the structure diagram and / or the flow chart, and the combination of boxes in the structure diagram and / or the flow chart, can be implemented with a dedicated hardware-based system that performs a specified function or action, or can be implemented with a combination of dedicated hardware and computer instructions.

[0172] In addition, the functional modules or units in the various embodiments of the present invention may be integrated together to form an independent part, or each module may exist independently, or two or more modules may be integrated to form an independent part.

[0173] If the function is implemented in the form of a software function module and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention is essentially or partly contributed to the prior art or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including several instructions to enable a computer device (which can be a smart phone, a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium can be a non-volatile storage medium or a volatile storage medium. For example, the storage medium can be: a U disk, a mobile hard disk, a read-only memory (ROM, Read-Only Memory), a random access memory (RAM, Random Access Memory), a disk or an optical disk, and other media that can store program codes.

[0174] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. An OFDM system evaluation method, characterized in that: The method comprises: Sampling a plurality of initial carrier signals of an OFDM system to obtain a plurality of discrete carrier signals, and calculating an orthogonality index between the discrete carrier signals; Acquire a reference signal of the OFDM system, and add a cyclic prefix to the reference signal according to a preset length, process the reference signal after adding the cyclic prefix through a multipath channel model to obtain an overall received signal, calculate the inter-symbol interference level of the overall received signal, and calculate the system efficiency evaluation index, comprehensive performance index and spectrum efficiency index of the overall received signal according to the inter-symbol interference level, and optimize the length of the cyclic prefix according to the inter-symbol interference level and the system efficiency evaluation index; Acquire a transmit pilot signal and a receive pilot signal at specific positions of a plurality of subcarriers in the OFDM system, calculate a channel response estimate of the OFDM system according to the transmit pilot signal and the receive pilot signal, calculate a noise power estimate of the OFDM system according to the transmit pilot signal, the receive pilot signal and the channel response estimate, calculate a signal-to-noise ratio estimate of each of the subcarriers according to the channel response estimate and the noise power estimate, and determine a modulation mode of each of the subcarriers and generate a corresponding modulation signal by comparing the signal-to-noise ratio estimate of each of the subcarriers with a preset signal-to-noise ratio threshold.

2. The OFDM system evaluation method according to claim 1, characterized in that: The sampling of multiple initial carrier signals of the OFDM system to obtain multiple discrete carrier signals includes: Sampling each of the initial carrier signals by a preset sampling rate, a preset observation window length, and a preset sliding step length, performing signal normalization processing on each sampled initial carrier signal, and obtaining a plurality of normalized carrier signals; Performing windowing processing on each of the normalized carrier signals to obtain a plurality of windowed carrier signals, and performing DC offset removal processing on each of the windowed carrier signals to obtain a plurality of discrete carrier signals; Wherein, each of the initial carrier signals is: s1(t)=A1cos(2πf1t+φ1) s2(t)=A2cos(2πf2t+φ2) Wherein, s1(t) is the first initial carrier signal, s2(t) is the second initial carrier signal, A1 and A2 are the amplitudes of the first initial carrier signal and the second initial carrier signal, f1 and f2 are the frequencies of the first initial carrier signal and the second initial carrier signal, φ1 and φ2 are the phases of the first initial carrier signal and the second initial carrier signal, respectively.

3. The OFDM system evaluation method according to claim 2, characterized in that: The calculating the orthogonality index between the discrete carrier signals comprises: Calculating the correlation index between the discrete carrier signals using a preset correlation calculation formula, and calculating the product of the energy of the discrete carrier signals using a preset energy calculation formula; Calculating the orthogonality index between the discrete carrier signals by using a preset orthogonality calculation formula and according to the product of the correlation index between the discrete carrier signals and the energy of the discrete carrier signals; Wherein, the preset correlation calculation formula is: Where s1[k] is the first discrete carrier signal, is the conjugate complex number of the second discrete carrier signal, N is the number of sampling points, R[n] is the correlation index, and k is the discrete time point at which each of the initial carrier signals is sampled; Wherein, the preset energy calculation formula is: Wherein, E[n] is the product of the energies of each discrete carrier signal; Wherein, the preset orthogonality calculation formula is: Wherein, O[n] is the orthogonality index between the discrete carrier signals.

4. The OFDM system evaluation method according to claim 1, characterized in that: The calculating the inter-symbol interference level of the overall received signal comprises: Decomposing the overall received signal into a main path signal and a multipath interference signal, and calculating the energy of the main path signal and the energy of the multipath interference signal respectively; Calculate an initial inter-symbol interference level using a preset inter-symbol interference level calculation formula and according to the energy of the multipath interference signal and the energy of the main path signal, and normalize the initial inter-symbol interference level using a preset normalization formula to obtain an inter-symbol interference level of the overall received signal; The preset inter-symbol interference level calculation formula is: In the formula, ISI level (τ)′ is the initial inter-symbol interference level, h l is the channel coefficient of the lth path, x(n-τ l ) is the reference signal after τ l The signal after sampling delay, h0 is the channel coefficient of the main path, x(n) is the reference signal, L is the channel length, τ is the actual delay, and N is the number of sampling points; Wherein, the preset normalization formula is: In the formula, ISI level (τ) is the inter-symbol interference level, CP length is the length of the cyclic prefix.

5. The OFDM system evaluation method according to claim 4, characterized in that: The calculating the system efficiency evaluation index, the comprehensive performance index and the spectrum efficiency index of the overall received signal according to the inter-symbol interference level includes: Obtaining the OFDM symbol length of the reference signal, respectively calculating a first inter-code interference level of the overall received signal including the cyclic prefix and a second inter-code interference level of the overall received signal not including the cyclic prefix, calculating a cyclic prefix overhead rate according to the OFDM symbol length and the length of the cyclic prefix, calculating an inter-code interference level suppression rate according to the first inter-code interference level and the second inter-code interference level, and calculating the system efficiency evaluation index according to the inter-code interference level suppression rate and the cyclic prefix overhead rate using a preset system efficiency evaluation index calculation formula; Obtaining a bit error rate, and respectively obtaining a first weight of the inter-symbol interference level, a second weight of the cyclic prefix overhead rate, and a third weight of the bit error rate, and calculating the comprehensive performance indicator by using a preset comprehensive performance indicator calculation formula and according to the inter-symbol interference level, the first weight, the cyclic prefix overhead rate, the second weight, the bit error rate, and the third weight; Calculate the spectrum efficiency index by using a preset spectrum efficiency index calculation formula and according to the OFDM symbol length and the length of the cyclic prefix; Among them, the calculation formula of the preset system efficiency evaluation index is: Where η system is the system efficiency evaluation index, ISI no_cp The second intersymbol interference level, ISI with_cp For the first inter-symbol interference level, OFDM length is the OFDM symbol length, CP length is the length of the cyclic prefix, ISI suppression is the inter-symbol interference level suppression rate, CP overhead is the cyclic prefix overhead rate; Among them, the preset comprehensive performance index calculation formula is: Where P system is the comprehensive performance indicator, α is the first weight, β is the second weight, BER is the bit error rate, and γ is the third weight; The preset spectrum efficiency index calculation formula is: Where η spectral is the spectrum efficiency indicator.

6. The OFDM system evaluation method according to claim 5, characterized in that: The optimizing the length of the cyclic prefix according to the inter-symbol interference level and the system efficiency evaluation index comprises: Obtaining all lengths of the cyclic prefix, and respectively calculating the performance evaluation index and the inter-symbol interference level under all lengths of the cyclic prefix; Determine, according to a preset optimization formula, a target length of the cyclic prefix that minimizes the system performance evaluation index value among the lengths of the cyclic prefix that satisfy the inter-symbol interference level lower than the preset interference level threshold, and use the target length as the optimized length of the cyclic prefix; Wherein, the preset optimization formula is: CP opt =argmin τ {or system (t)|ISI level (t) <ISI threshold } In the formula, CP opt is the target length, ISI threshold is the preset interference level threshold.

7. The OFDM system evaluation method according to claim 1, characterized in that: The OFDM system includes a plurality of subcarrier positions and a plurality of subcarrier specific positions, and the calculating a channel response estimate of the OFDM system according to the transmitted pilot signal and the received pilot signal, and the calculating a noise power estimate of the OFDM system according to the transmitted pilot signal, the received pilot signal and the channel response estimate, comprises: Taking the ratio of the received pilot signal to the transmitted pilot signal at the specific position of each subcarrier as the channel response estimation value at the specific position of each subcarrier, calculating the channel response estimation value at each subcarrier position according to the channel response estimation value at the specific position of each subcarrier by using a linear interpolation algorithm, and obtaining the channel response estimation value of the OFDM system according to the channel response estimation value at the specific position of each subcarrier and the channel response estimation value at each subcarrier position; Calculate an ideal received signal according to the transmitted pilot signal and the channel response estimation value, and calculate a noise power estimation value of the OFDM system according to the received pilot signal and the ideal received signal using a preset noise power calculation formula; Wherein, the linear interpolation algorithm is: Where H(k) is the estimated channel response value of subcarrier position k, H(k1) and H(k2) are the estimated channel response values ​​of subcarrier specific positions k1 and k2, respectively. <k<k2; Wherein, the preset noise power calculation formula is: Where N0 is the estimated value of the noise power, Y p (k) is the received pilot signal, H p (k) is the smoothed value of the channel response estimate at position k and the channel response estimates at N adjacent positions, X p (k) is the sending pilot signal.

8. The OFDM system evaluation method according to claim 7, characterized in that: The calculating the signal-to-noise ratio estimation value of each subcarrier according to the channel response estimation value and the noise power estimation value comprises: Calculating the power gain of the channel response estimation value, and calculating the power of the transmitted pilot signal, and calculating the initial signal-to-noise ratio of each of the subcarriers according to the power gain of the channel response estimation value, the power of the transmitted pilot signal and the noise power estimation value using a preset signal-to-noise ratio calculation formula; Performing time domain smoothing processing on the initial signal-to-noise ratio of each of the subcarriers to obtain an estimated signal-to-noise ratio value of each of the subcarriers; Wherein, the preset signal-to-noise ratio calculation formula is: SNR k =|H k | 2 ·E[|X k | 2 ] / N0 In the formula, SNR k is the estimated value of the signal-to-noise ratio, |H k | 2 is the power gain of the channel response estimate, E[|X k | 2 ] is the power of the sent pilot signal.

9. The OFDM system evaluation method according to claim 8, characterized in that: The determining the modulation mode of each subcarrier and generating a corresponding modulation signal by comparing the estimated signal-to-noise ratio value of each subcarrier with a preset signal-to-noise ratio threshold value comprises: Obtaining a preset bit error rate requirement value, and determining the preset signal-to-noise ratio threshold value according to the bit error rate requirement value using a preset signal-to-noise ratio threshold calculation formula, wherein the preset signal-to-noise ratio threshold value includes a first signal-to-noise ratio threshold value and a second signal-to-noise ratio threshold value; If the estimated signal-to-noise ratio value of the subcarrier is less than the first signal-to-noise ratio threshold, determining its modulation mode as BPSK modulation and generating a corresponding modulation signal; If the estimated signal-to-noise ratio value of the subcarrier is greater than the first signal-to-noise ratio threshold and less than the second signal-to-noise ratio threshold, determine its modulation mode as QPSK modulation and generate a corresponding modulation signal; If the estimated signal-to-noise ratio value of the subcarrier is greater than the second signal-to-noise ratio threshold, determine its modulation mode as 16QAM modulation and generate a corresponding modulation signal; The preset signal-to-noise ratio threshold calculation formula is: Where, γ1 and γ2 are the first signal-to-noise ratio threshold and the second signal-to-noise ratio threshold, respectively. target is the preset bit error rate requirement value.

10. An OFDM system evaluation device, characterized in that: The device comprises: A first calculation module is used to sample multiple initial carrier signals of the OFDM system to obtain multiple discrete carrier signals, and calculate the orthogonality index between the discrete carrier signals; A second calculation module is used to obtain a reference signal of the OFDM system, add a cyclic prefix to the reference signal according to a preset length, process the reference signal after the cyclic prefix is ​​added through a multipath channel model to obtain an overall received signal, calculate the inter-symbol interference level of the overall received signal, and calculate the system efficiency evaluation index, comprehensive performance index and spectrum efficiency index of the overall received signal according to the inter-symbol interference level, and optimize the length of the cyclic prefix according to the inter-symbol interference level and the system efficiency evaluation index; a third calculation module, configured to obtain a transmission pilot signal and a reception pilot signal at specific positions of a plurality of subcarriers in the OFDM system, calculate a channel response estimation value of the OFDM system according to the transmission pilot signal and the reception pilot signal, calculate a noise power estimation value of the OFDM system according to the transmission pilot signal, the reception pilot signal and the channel response estimation value, calculate a signal-to-noise ratio estimation value of each of the subcarriers according to the channel response estimation value and the noise power estimation value, and determine a modulation mode of each of the subcarriers and generate a corresponding modulation signal by comparing the signal-to-noise ratio estimation value of each of the subcarriers with a preset signal-to-noise ratio threshold.

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