Link self-adaption method for OFDM (Orthogonal Frequency Division Multiplexing) system under narrowband interference

Abstract

The invention discloses a link self-adaption method for an OFDM (Orthogonal Frequency Division Multiplexing) system under narrowband interference, and relates to the field of mobile communication. Comprising the following steps: establishing a bit mutual information three-dimensional lookup table in the presence of narrowband interference, compensating an equalized signal-to-noise ratio under the narrowband interference, predicting a block error rate under the narrowband interference, and dynamically adjusting a modulation coding mode under the narrowband interference. According to the method, the block error rate of the link is ensured to be within the target block error rate under the narrow-band interference, and the throughput of the system is improved; meanwhile, the modification of a receiver structure is avoided, and the cost of suppressing narrowband interference is reduced; and the transmission reliability and the transmission efficiency of the communication equipment are improved in an industrial environment or an environment with limited spectrum resources.

Description

Technical Field

[0001] The present invention relates to the field of mobile communications, and in particular, to a link adaptation method for an Orthogonal Frequency Division Multiplexing (OFDM) system under narrowband interference. Background Art

[0002] As an important foundation of the new generation of information technology revolution, mobile communication technology is closely related to multiple industries such as transportation, commerce, and industry. Against the background of the commercial deployment of 5G mobile communication systems, mobile communication technology is constantly updated and upgraded at a rapid pace to meet various business requirements that may arise in the future. However, with the continuous increase in the number of devices accessing the network and the channel bandwidth, the reliability of 5G faces more severe challenges.

[0003] Wireless communication systems usually assume that the noise is Additive White Gaussian Noise (AWGN) with the same bandwidth as the signal, and the receiver is designed based on this assumption. However, in real scenarios, as the useful signal bandwidth continues to increase, interference will exhibit sparse characteristics in the frequency spectrum, and this interference is called Narrowband Interference (NBI). Narrowband interference is a common non-Gaussian noise, characterized by occupying an effective bandwidth in the frequency domain that is relatively narrow enough compared to the signal operating bandwidth, showing frequency-domain sparsity. Narrowband interference widely exists in real environments, especially in industrial environments, where the problem of narrowband interference is more severe due to the complex electromagnetic environment. Narrowband interference mainly comes from spectrum sharing, device non-ideality or faults, and malicious attacks. Narrowband interference caused by spectrum sharing usually occurs when different communication devices coexist in the same frequency band, such as the coexistence of primary users and secondary users in cognitive radio, and the coexistence of narrowband Internet and LTE systems. With the increase in wireless communication standards and the number of access devices, this type of interference problem will become more serious. Narrowband interference caused by environmental or device non-ideality mainly comes from the harmonic and intermodulation signals of radar devices, shortwave radios, or other communication devices, and these signals also often exhibit narrowband characteristics. Thus, it can be seen that narrowband interference is particularly prominent in practical applications, especially in complex industrial environments.

[0004] For narrowband interference, common countermeasures are to suppress narrowband interference through various digital signal processing techniques, such as narrowband interference suppression methods based on notch filters, compression sensing, sparse Bayesian learning, and deep learning. These techniques do not require knowledge of the impact of narrowband interference on the communication system. Instead, they only need to design corresponding suppression algorithms to complete interference suppression. However, these methods often require changing the receiver structure, which is costly in practical applications and difficult to implement. Therefore, how to improve the transmission reliability of OFDM systems under narrowband interference without changing the receiver structure is an urgent problem to be solved.

[0005] Link adaptation technology is a common communication technology. It dynamically adjusts the modulation coding scheme (MCS) or transmission power of the signal according to the channel conditions to maximize the throughput under a certain block error rate requirement, greatly improving the transmission efficiency without changing the receiver structure. Link adaptation technology first needs to predict the transmission performance of the system in the current channel environment, and then design an adaptation strategy to select the corresponding MCS based on the predicted performance. Due to the existence of coding, the theoretical transmission performance of communication systems often cannot be expressed by a closed-form expression and needs to be predicted using physical layer abstraction methods. Under the condition of only Gaussian noise, common physical layer mapping methods include Exponential Effective SINR Mapping (EESM) and Mutual Information Effective SINR Mapping (MIESM). Through the mapping function, the equalized signal-to-noise ratio is mapped to the e-exponent domain or mutual information, then the mapped values on all subcarriers are averaged and mapped back to the effective signal-to-noise ratio, and finally, the block error rate is predicted by querying the Additive White Gaussian Noise Single Input Single Output (AWGN-SISO) table using the effective signal-to-noise ratio. However, for non-Gaussian noise such as narrowband interference, the physical layer mapping methods based on Gaussian noise cannot be directly used, and a new mapping table needs to be established. Moreover, due to the unknown position of narrowband interference, the true noise power in each subcarrier does not match the noise power used in the design of the equalizer, resulting in the deterioration of the equalization effect of the equalizer. Since the mapping table under AWGN is designed based on the matched equalizer, for OFDM systems under narrowband interference, the equalized signal-to-noise ratio cannot be directly mapped, and compensation calculation needs to be performed on the equalized signal-to-noise ratio.

[0006] Therefore, those skilled in the art are committed to developing a link adaptation method for OFDM systems under narrowband interference. It includes establishing a three-dimensional look-up table of Received Bit Mutual Information Rate (RBIR) in the presence of narrowband interference, an equalized signal-to-noise ratio compensation method under narrowband interference, a predicted block error rate method under narrowband interference, and an MCS dynamic adjustment strategy under narrowband interference. Summary of the Invention

[0007] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to improve the transmission reliability of OFDM systems under narrowband interference.

[0008] To achieve the above object, the present invention provides a link adaptation method for OFDM systems under narrowband interference, which selects MCS based on the performance prediction results and target block error rate of OFDM systems under narrowband interference, and adjusts MCS through ACK information.

[0009] Further, based on the MIESM method, the performance prediction of OFDM systems under narrowband interference is carried out.

[0010] Further, the narrowband interference is modeled using the Bernoulli-Gaussian model to obtain the RBIR of QAM modulation under narrowband interference, and a three-dimensional look-up table of RBIR under narrowband interference is constructed.

[0011] Further, in the case of mismatch between the true statistical information of noise and the noise statistical information used when designing the equalizer, the equalized equivalent signal-to-noise ratio is obtained.

[0012] Further, according to the ACK situation of the actual link, MCS is adjusted in real time.

[0013] Further, the MIESM method is used to predict the block error rate, the largest MCS that meets the target block error rate condition is selected according to the predicted block error rate, and MCS is adjusted according to the ACK information fed back from the previous transmission.

[0014] Further, it includes the following steps:

[0015] Step 1: Calculate the equivalent noise power when only Gaussian noise exists on the subcarrier and the equivalent noise power when both Gaussian noise and narrowband interference exist.

[0016] Step 2: Calculate the equalized signal-to-noise ratio when only Gaussian noise exists on the subcarrier and the equalized signal-to-noise ratio when both Gaussian noise and narrowband interference exist.

[0017] Step 3: Use the post - equalization signal - to - noise ratio, post - equalization signal - to - interference - plus - noise ratio, and narrow - band interference occurrence probability to select the three - dimensional look - up table of RBIR under narrow - band interference for the corresponding modulation mode, and obtain the RBIR on the sub - carrier;

[0018] Step 4: Take the average of the RBIRs on all sub - carriers to obtain the average RBIR of the OFDM block;

[0019] Step 5: Use the average RBIR of the OFDM block to select the Gaussian - noise RBIR look - up table under the corresponding modulation mode, and perform reverse look - up to obtain the effective signal - to - noise ratio under Gaussian noise;

[0020] Step 6: According to the effective signal - to - noise ratio, query the AWGN - SISO block error rate look - up table to obtain the block error rate;

[0021] Step 7: According to the target block error rate and the ACK information of the previous transmission block, select an appropriate MCS for transmission.

[0022] Further, in Step 1, according to the statistical information of narrow - band interference, the result of channel estimation, and the result of noise estimation, calculate the equivalent noise power.

[0023] Further, in Step 2, use the equivalent noise power to calculate the post - equalization signal - to - noise ratio.

[0024] Further, in Step 3, select the three - dimensional look - up table of RBIR under narrow - band interference, and obtain the RBIR on the sub - carrier through three - dimensional interpolation method.

[0025] Narrow - band interference has a serious impact on communication systems. For narrow - band interference, the existing countermeasures are to suppress narrow - band interference through various digital signal processing techniques. Such methods often require changing the receiver structure, which is costly in practical applications and difficult to implement. The present invention designs a link adaptation method for OFDM systems under narrow - band interference, which can complete reliable transmission of the link under narrow - band interference without changing the receiver structure. The present invention is based on the MIESM method and can complete the performance prediction of the OFDM system under narrow - band interference only knowing the statistical information of narrow - band interference. Based on the performance prediction result and the target block error rate, select an appropriate MCS, and adjust the MCS through ACK information.

[0026] Before performing link adaptation, it is necessary to first predict the link performance. Existing MIESM link performance prediction methods are all derived under the background of Gaussian noise, and their results are not applicable to non-Gaussian noise such as narrowband interference. The present invention models narrowband interference using a Bernoulli-Gaussian model, and derives the RBIR of quadrature amplitude modulation (QAM) under narrowband interference when only the statistical information of narrowband interference is known, and constructs a three-dimensional look-up table of RBIR under narrowband interference based on the derived expression. The present invention modifies the symbol mutual information formula of QAM modulation under Gaussian noise, replaces the likelihood function from Gaussian with the form of Bernoulli-Gaussian, and through mathematical derivation, obtains the numerical expressions of the symbol mutual information and RBIR of QAM modulation under narrowband interference, and constructs a three-dimensional look-up table.

[0027] The MIESM method usually performs subsequent mapping based on the signal-to-noise ratio after equalization. In the traditional MIESM method considering Gaussian noise, the statistical information of the noise on each subcarrier is the same and known, and the designed MMSE equalizer can effectively extract the transmitted signal from the received signal. However, for the OFDM system under narrowband interference, the noise statistical information within each subcarrier is uncertain, there are two cases, and the noise variance used when designing the equalizer is also different from the above two cases. Therefore, the equalizer cannot effectively extract the transmitted signal from the received signal. To ensure the accuracy of performance mapping, it is necessary to ensure that the OFDM system under narrowband interference and the OFDM system under AWGN have the same equalization performance, and the signal-to-noise ratio after equalization obtained will have a certain degree of attenuation. The present invention calculates the true equivalent signal-to-noise ratio after equalization in the case where the true statistical information of the noise and the noise statistical information used when designing the equalizer are mismatched. The present invention assumes that the true noise power within a certain subcarrier is N1, but the estimated value of the noise power used when designing the equalizer is N2. It is further assumed that the true noise power within a certain subcarrier is N3, and the estimated value of the noise power used when designing the equalizer is also N3. Based on the MSE criterion, making the mean square error of the signal after equalization and the true transmitted signal equal in the above two cases, the equivalent noise power N3 within this subcarrier is derived, and then the equivalent signal-to-noise ratio after equalization is derived.

[0028] The bit error rate prediction technology based on MIESM may produce prediction errors of the bit error rate, resulting in a deteriorated link adaptation effect. While selecting the MCS according to the bit error rate prediction result, the present invention adjusts the MCS in real time according to the ACK situation of the actual link. The present invention first uses an improved MIESM method to predict the bit error rate, and selects the largest MCS that meets the target bit error rate condition according to the currently predicted bit error rate. Secondly, the MCS is adjusted according to the ACK information fed back in the previous transmission. If ACK is fed back, the MCS remains unchanged. If NACK is fed back, the MCS is lowered by one level from the original selection.

[0029] Compared with the prior art, the present invention has the following obvious substantial features and remarkable advantages:

[0030] 1. The present invention ensures that the bit error rate of the link is within the target bit error rate under narrowband interference, improving the throughput of the system. At the same time, it avoids the modification of the receiver structure and reduces the cost of suppressing narrowband interference. It improves the transmission reliability and transmission efficiency of communication devices in industrial environments or environments with limited spectrum resources.

[0031] 2. The present invention can accurately predict the performance of the OFDM system under narrowband interference only knowing the statistical information of narrowband interference.

[0032] 3. After the equivalent of the signal-to-noise ratio after equalization in the present invention, the accuracy of bit error rate prediction can be greatly improved.

[0033] 4. By introducing a dynamic adjustment strategy for MCS, the present invention can effectively increase the robustness of the link adaptation method and reduce link interruptions caused by link performance prediction errors.

[0034] The following will further illustrate the concept, specific structure and technical effects of the present invention with reference to the accompanying drawings to fully understand the purpose, features and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a flowchart of a link adaptation method under narrowband interference according to a preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0036] The following introduces multiple preferred embodiments of the present invention with reference to the accompanying drawings of the specification to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the protection scope of the present invention is not limited to the embodiments mentioned in the text.

[0037] In the drawings, components with the same structure are denoted by the same numerals, and components with similar structures or functions throughout are denoted by similar numerals. The dimensions and thicknesses of each component shown in the drawings are arbitrarily illustrated, and the present invention does not limit the dimensions and thicknesses of each component. For clarity of illustration, the thicknesses of some components in the drawings are appropriately exaggerated in some places.

[0038] I. System Model

[0039] Based on the 5G uplink, the present invention considers a SISO-OFDM system, and the signal model on the i-th subcarrier is

[0040] y i =H i s i +w i +e i , i = 0, 1, …, N-1, #(1.1)

[0041] where N is the total number of subcarriers, y i is the received symbol on the i-th subcarrier, H i is the channel coefficient on the i-th subcarrier, s i is the transmitted symbol on the i-th subcarrier, w i is the additive white Gaussian noise on the i-th subcarrier, which follows a complex Gaussian distribution, e i is the narrowband interference on the i-th subcarrier. Using a band-limited Gaussian model, it can be expressed as

[0042]

[0043] where ψ i is a selection row vector, and only the (i + 1)-th element of this row vector is 1, and the remaining elements are all 0. F N is an N×N Fourier transform matrix, a′ k is the narrowband interference on the k-th subcarrier, a′ k =b k a k , b k is a Bernoulli random variable, indicating whether there is narrowband interference on the k-th subcarrier. Let the support set of the narrowband interference be Π, For k within the support set, a k is a band-limited Gaussian noise, and the power spectral density is which follows a complex Gaussian distribution,

[0044] Simplifying Equation (1.2), we can obtain

[0045]

[0046] For the second summation The sum is 1 if and only if k = i, and 0 when k ≠ i. Therefore, Equation (1.3) is further simplified to

[0047]

[0048] Therefore, for the Gaussian noise plus narrowband interference w i +e i on the i-th subcarrier, it follows the following distribution

[0049]

[0050] where ρ is the occurrence probability of the narrowband interference.

[0051] II. Implementation Process

[0052] The implementation process of a link adaptation method for an OFDM system under narrowband interference disclosed by the present invention is as Figure 1 shown.

[0053] Before application, the RBIR look-up tables corresponding to QPSK, 16QAM, and 64QAM modulations under narrowband interference should be established respectively. The input parameters of the look-up table are the occurrence probability ρ of the narrowband interference, the post-equalization signal-to-noise ratio SNR assuming only Gaussian noise exists, and the post-equalization signal-to-interference-plus-noise ratio SINR assuming both Gaussian noise and narrowband interference exist simultaneously.

[0054] The steps to apply this link adaptation method are as follows: 1. Calculate the equivalent noise power on all subcarriers assuming only Gaussian noise exists and assuming both Gaussian noise and narrowband interference exist simultaneously according to the statistical information of the narrowband interference, the result of channel estimation, and the result of noise estimation; 2. Calculate the post-equalization signal-to-noise ratio on a certain subcarrier assuming only Gaussian noise exists and the post-equalization signal-to-interference-plus-noise ratio assuming both Gaussian noise and narrowband interference exist simultaneously using the two calculated equivalent noise powers; 3. Select the three-dimensional narrowband interference look-up table corresponding to the modulation mode using the calculated post-equalization signal-to-noise ratio, post-equalization signal-to-interference-plus-noise ratio, and narrowband interference occurrence probability, and calculate the RBIR on this subcarrier through three-dimensional interpolation; 4. Take the average of the RBIRs on all subcarriers to obtain the average RBIR of this OFDM block; 5. Select the Gaussian noise look-up table corresponding to the modulation mode using the average RBIR of this OFDM block to obtain the effective signal-to-noise ratio under Gaussian noise; 6. Look up the AWGN-SISO table according to the effective signal-to-noise ratio to obtain the block error rate, which is the predicted result of the block error rate of the OFDM system under the original narrowband interference; 7. Select an appropriate MCS for transmission according to the block error rate requirement and the ACK information of the previous transmission block.

[0055] III. Method for Establishing Bit Mutual Information Look-up Table

[0056] In the method for predicting the block error rate based on MIESM, the calculation of symbol mutual information and RBIR is usually under the condition of Gaussian noise. For an OFDM system under narrowband interference, the noise exhibits non-Gaussian characteristics, and it is necessary to establish an RBIR look-up table for narrowband interference. Under the condition of narrowband interference, the symbol mutual information of QAM modulation can be expressed as

[0057]

[0058] where \(u = w / H\), \(M\) is the number of bits corresponding to the modulation symbol on the current subcarrier, \(SNR\) and \(SINR\) are the signal-to-noise ratio after equalization assuming only Gaussian noise on the current subcarrier and the signal-to-noise ratio after equalization assuming both Gaussian noise and narrowband interference on the current subcarrier respectively, \(\rho\) is the occurrence probability of narrowband interference on the current subcarrier, \(u\) follows a Bernoulli complex Gaussian distribution with variance \(1 / SNR\) or \(1 / SINR\), and the symbol mutual information can be obtained using the Monte Carlo method. RBIR is the quotient of symbol mutual information and the number of bits corresponding to the modulation symbol, and is expressed as

[0059]

[0060] Taking \(\rho\), \(SNR\) and \(SINR\) as three look-up dimensions, a three-dimensional RBIR look-up table corresponding to the modulation method can be constructed.

[0061] IV. Calculation of equivalent noise power and signal-to-noise ratio after equalization

[0062] For an OFDM system under narrowband interference, the actual noise power in a single subcarrier is or However, in noise estimation, the mean square value of the noise in the entire resource grid is usually taken as the estimated value of the noise power. Since narrowband interference randomly appears in each subcarrier with probability \(\rho\), the estimated value of the noise is not the same as the actual value of the noise. When equalizing, the actual noise power is not equal to the noise power used when designing the equalizer, and the equalizer cannot effectively recover the transmitted signal from the received signal. In the AWGN-SISO look-up table, the equalizer used is designed under the condition of ideal known noise power. Therefore, the equalization situations of the two links before and after mapping are not equivalent, and it is necessary to calculate the equivalent noise power.

[0063] Assume Case 1: The noise in a certain subcarrier is \(w\), and the noise power is while the noise power used when designing the equalizer is Assume Case 2: The noise in a certain subcarrier is \(w\) eff , and the noise power is while the noise power used when designing the equalizer is also For Case 1, the equalizer coefficients are

[0064]

[0065] After equalization, we get

[0066]

[0067] Then the estimated error after equalization is

[0068]

[0069] Therefore, the mean square value of the estimated error is

[0070]

[0071] For an equalizer designed using the true noise power, the mean square value of the estimated error after equalization is

[0072]

[0073] To ensure a system that designs the equalizer using an inaccurate estimate of the noise but the actual noise is has performance equivalent to a system that designs the equalizer using an accurate estimate of the noise We can set the mean square errors of the two equal to each other, i.e.,

[0074]

[0075] Therefore, for a SISO - OFDM system with an actual noise power of but using a noise estimate value of to design the equalizer, the equivalent signal - to - noise ratio Γ k after equalization on the k - th sub - carrier is

[0076]

[0077] where H k is the channel coefficient on the k - th sub - carrier.

[0078] V. Block Error Rate Prediction

[0079] First, under two scenarios: assuming only Gaussian noise exists and assuming both Gaussian noise and narrow - band interference exist simultaneously, according to the estimated value of the noise power, use Equation (1.14) to calculate the equivalent signal - to - noise ratios Γ AWGN and Γ NBI , and second, according to the narrow - band interference RBIR mapping function and the AWGN's RBIR inverse mapping function obtained from Equations (1.6) and (1.7), map the signal - to - noise ratios after equalization on all sub - carriers to a single effective signal - to - noise ratio, denoted as

[0080]

[0081] where Φ NBI is the narrowband interference RBIR mapping function obtained according to Equations (1.6) and (1.7), which is in the form of a three-dimensional look-up table. By inputting the occurrence probability of narrowband interference on the k-th subcarrier and assuming the post-equalization signal-to-noise ratio Γ AWGN,k under the condition of only Gaussian noise, and the post-equalization signal-to-noise ratio Γ NBI,k under the condition of coexistence of Gaussian noise and narrowband interference, the RBIR on the k-th subcarrier is obtained through three-dimensional interpolation in the look-up table. is the inverse function of the RBIR mapping function in the AWGN case, which maps the RBIR back to the effective signal-to-noise ratio. Finally, by querying the AWGN-SISO error block rate look-up table, the predicted error block rate is obtained.

[0082] VI. Link Adaptation Strategy

[0083] According to the predicted result of the error block rate, the highest MCS that meets the error block rate requirement is selected for transmission. At the same time, since there may be a deviation between the predicted result of the error block rate and the actual error block rate, a dynamic adjustment strategy for the MCS needs to be formulated. The present invention performs dynamic adjustment of the error block rate according to the ACK information of the base station at the previous moment. When the base station returns NACK at the previous moment, the MCS selected at this moment is lowered by one level.

[0084] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative labor. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field of the present invention based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art should be within the protection scope determined by the claims.

Claims

1. A link adaptation method for OFDM systems under narrowband interference, characterized in that Select the MCS based on the performance prediction results of the OFDM system under narrowband interference and the target block error rate, and adjust the MCS through ACK information.

2. The link adaptation method for an OFDM system under narrowband interference according to claim 1, wherein Based on the MIESM method, perform performance prediction of the OFDM system under narrowband interference.

3. The link adaptation method for an OFDM system under narrowband interference according to claim 1, wherein Model the narrowband interference using the Bernoulli-Gaussian model, obtain the RBIR of QAM modulation under narrowband interference, and construct a three-dimensional lookup table of RBIR under narrowband interference.

4. The link adaptation method for an OFDM system under narrowband interference according to claim 1, wherein Under the condition of mismatch between the true statistical information of the noise and the noise statistical information used when designing the equalizer, obtain the equivalent signal-to-noise ratio after equalization.

5. The link adaptation method for an OFDM system under narrowband interference according to claim 1, wherein Adjust the MCS in real time according to the ACK situation of the actual link.

6. The link adaptation method for an OFDM system under narrowband interference according to claim 1, characterized in that Use the MIESM method to predict the block error rate, select the largest MCS that meets the target block error rate condition according to the predicted block error rate, and adjust the MCS according to the ACK information fed back in the previous transmission.

7. The link adaptation method for an OFDM system under narrowband interference according to claim 1, wherein It includes the following steps: Step 1: Calculate the equivalent noise power when only Gaussian noise exists on the subcarrier and the equivalent noise power when both Gaussian noise and narrowband interference exist. Step 2: Calculate the signal-to-noise ratio after equalization when only Gaussian noise exists on the subcarrier and the signal-to-noise ratio after equalization when both Gaussian noise and narrowband interference exist. Step 3: Use the signal-to-noise ratio after equalization, the signal-to-interference-plus-noise ratio after equalization, and the occurrence probability of narrowband interference to select the three-dimensional lookup table of RBIR under narrowband interference corresponding to the modulation mode, and obtain the RBIR on the subcarrier. Step 4: Take the average of the RBIRs on all subcarriers to obtain the average RBIR of the OFDM block. Step 5: Use the average RBIR of the OFDM block to select the Gaussian noise RBIR lookup table corresponding to the modulation mode, and obtain the effective signal-to-noise ratio under Gaussian noise. Step 6: According to the effective signal-to-noise ratio, query the AWGN-SISO block error rate lookup table to obtain the block error rate. Step 7: According to the target block error rate and the ACK information of the previous transmission block, select an appropriate MCS for transmission.

8. The link adaptation method for an OFDM system under narrowband interference as claimed in claim 7, wherein In step 1, calculate the equivalent noise power according to the statistical information of narrowband interference, the result of channel estimation, and the result of noise estimation.

9. The link adaptation method for an OFDM system under narrowband interference as claimed in claim 7, wherein In step 2, calculate the signal-to-noise ratio after equalization using the equivalent noise power.

10. The link adaptation method for an OFDM system under narrowband interference as claimed in claim 7, wherein In step 3, select the three-dimensional lookup table of RBIR under narrowband interference, and obtain the RBIR on the subcarrier through three-dimensional interpolation method.

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