An OFDM adaptive digital modulation and time domain extension transmission method based on channel reciprocity

Abstract

An OFDM adaptive digital modulation and time domain expansion transmission method based on channel reciprocity belongs to the field of wireless communication technology. The purpose of the present invention is to solve the problem that the existing method cannot fully utilize the subcarrier power and spectrum resources, resulting in the transmission speed of the communication system being limited. The present invention uses channel state information and noise power to perform adaptive modulation, and uses high-order modulation for subcarriers with large channel gain, and uses low-order modulation for subcarriers with small channel gain. In order to make fuller use of subcarrier power and make the transmission rate closer to the theoretical upper limit, the method of the present invention adds more modulation gears to obtain higher resolution. The method of the present invention refers to the equal gain combining method, increases the duration of the symbol to 2 times or more to obtain time diversity gain, so that the same modulation method can obtain multiple transmission speeds, and fully utilizes the subcarrier channel power to make it closer to the theoretical upper limit. The method of the present invention can be applied to the field of wireless communication technology.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless communications, and in particular relates to an OFDM adaptive digital modulation and time domain extension transmission method based on channel reciprocity. Background Art

[0002] With the public's growing demand for fast data transmission and multimedia services, the wireless communications sector faces the challenge of improving transmission speed and quality. However, limited spectrum resources pose a constraint on wireless communications. Therefore, improving spectrum efficiency and system capacity has become a research focus. OFDM technology partitions the available channel into multiple subchannels and uses adaptive techniques to allocate bits or power appropriately to these subchannels, thereby enhancing system performance and more efficiently utilizing spectrum resources. The water-filling algorithm is the theoretical foundation for resource allocation. Ideally, the power of a water-filling algorithm is continuous. However, some subcarriers may experience severe fading, resulting in a lower theoretical optimal power. However, in real-world systems, discrete coded modulation schemes are used, and the user transmission rate on each subcarrier is also discrete, failing to meet the theoretical bound of the water-filling theorem. Furthermore, if the power allocated to a subchannel is so low that the target bit error rate (BER) cannot be achieved even with BPSK, the channel must be shut down and no energy allocated. This wastes some of the theoretically available spectrum resources and limits the transmission speed of the communication system.

[0003] In summary, in order to improve the transmission speed of the communication system, it is very necessary to propose a method that can more fully and effectively utilize subcarrier power and spectrum resources. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem that the existing methods cannot fully utilize subcarrier power and spectrum resources, resulting in the transmission speed of the communication system being limited. An OFDM adaptive digital modulation and time domain expansion transmission method based on channel reciprocity is proposed to make the actual discrete modulation system closer to the theoretical value of continuous water injection, thereby achieving an improvement in the transmission speed of the communication system.

[0005] The technical solution adopted by the present invention to solve the above technical problems is:

[0006] An OFDM adaptive digital modulation and time domain extension transmission method based on channel reciprocity, the method specifically comprising the following steps:

[0007] Step 1: Divide the entire communication frequency band into N sub-bands. The receiving end estimates the channel and noise power of the n-th sub-band and obtains the channel response H of the n-th sub-band. n And the noise power N n , n=1,2,…,N;

[0008] The transmitter obtains the channel response H based on the channel reciprocity n And the noise power N n ;

[0009] Step 2: The transmitter receives the channel response H of the nth subband n And the noise power N n Calculate the equivalent noise floor B of the nth subband n ;

[0010] Then according to the equivalent noise floor B n Calculate the power P allocated to the nth subband n , and according to P n and B n Calculate the signal-to-interference-plus-noise ratio (SINR) of the nth subband n ;

[0011] According to the signal-to-interference-and-noise ratio SINR of the nth subband n To select the modulation mode and extension times q of the nth subband n ; And synchronize the modulation mode and extension times of each sub-band to the receiving end;

[0012] Step 3: record the bit information of a frame sent by the nth subband as b n , using the modulation method of the nth sub-band to b n Modulate and get the modulation result S of the nth sub-band n , the modulation result S n The number of symbols in is denoted as K n ;

[0013] According to the number of extensions q of the nth subband n The modulation result S n Expand and obtain the extended symbol sequence X of the nth subband n , and in the extended symbol sequence X n In the k×q n +1 to (k+1)×q n The symbols are the same, k=0,1,…,K n -1;

[0014] Step 4: Process the extended symbol sequence of each sub-band separately, and then send the processed data to the channel through the RF module;

[0015] Step 5: The receiving end receives a signal from the channel using a radio frequency module and processes the received signal to obtain a processed extended symbol sequence;

[0016] For the extended symbol sequence R of the nth subband after processing n , and then the extended symbol sequence R nPerform equal gain superposition to obtain the symbol sequence Y n , and then the symbol sequence Y n Demodulate and restore the bit information transmitted by the nth sub-band.

[0017] Furthermore, the equivalent background noise B n for:

[0018]

[0019] Among them, B n Represents the equivalent noise floor of the nth subband.

[0020] Furthermore, the equivalent background noise B n Calculate the power P allocated to the nth subband n , specifically:

[0021] P n =(λ-B n ) +

[0022] Where n = 1, 2, ..., N, P n is the power allocated to the nth subband, λ is the Lagrange multiplier;

[0023] function(·) + Satisfies: If λ-B n If it is greater than 0, then P n =λ-B n , if λ-B n Less than or equal to 0, then P n =0;

[0024] The Lagrange multiplier λ makes the power allocated to each subband satisfy: Among them, P all is the total transmit power.

[0025] Furthermore, according to P n and B n Calculate the signal-to-interference-plus-noise ratio (SINR) of the nth subband n , specifically:

[0026]

[0027] Furthermore, in step 4, the extended symbol sequence of each subband is processed separately, specifically as follows:

[0028] For the spreading symbol sequence X of the nth subband n , for X n Mapping, IFFT and framing are performed in sequence.

[0029] Furthermore, the signal to interference and noise ratio SINR of the nth subband n To select the modulation mode and extension times q of the nth subband n , specifically:

[0030] Step 21: Select M modulation modes and calculate the lower bound of the signal-to-interference-and-noise ratio of each modulation mode without expansion using the water-filling algorithm;

[0031] Step 2: Set the expansion factor q n The value range is 1, 2, ..., Q, and the expansion factor q n Under the condition of m-th modulation mode, the lower bound of signal to interference noise ratio is adjusted to SINR_lb m -3q n After traversing various modulation modes and expansion factors, M×Q signal-to-interference-and-noise ratio thresholds are obtained;

[0032] Step 2 and 3: For the nth subband, start from the value less than the signal to interference and noise ratio SINR n Select the one closest to SINR from all threshold values n The modulation mode and expansion factor corresponding to the selected threshold value are respectively used as the modulation mode and expansion factor of the nth subband.

[0033] Furthermore, in step 5, the received signal is processed, specifically:

[0034] Perform synchronization, FFT and equalization processing on the signal received by the receiving end.

[0035] Furthermore, the pair of extended symbol sequences R n Perform equal gain superposition to obtain the symbol sequence Y n , specifically:

[0036] The extended symbol sequence R n The k×qth n +1 to (k+1)×q n The symbols are superimposed, and the superposition result is divided by K n , the result of the division operation is used as the symbol sequence Y n The k+1th symbol in, k=0,1,…,K n -1.

[0037] Furthermore, the value of M is 7, and the M modulation modes specifically include 8PSK, 16PSK, 4QAM, 8QAM, 16QAM, 32QAM and 64QAM.

[0038] The beneficial effects of the present invention are:

[0039] The adaptive digital modulation and time domain expansion method of the present invention is based on the reciprocity and water filling theorem of the channel, and uses channel state information and noise power to perform adaptive modulation. Subcarriers with large channel gains use high-order modulation, and subcarriers with small channel gains use low-order modulation. In order to make better use of the subcarrier power and bring the transmission rate closer to the theoretical upper limit, the method of the present invention adds more modulation gears to obtain higher resolution. The method of the present invention refers to the equal gain combining method, and increases the duration of the symbol to 2 times or more to obtain time diversity gain, so that the same modulation method can obtain multiple transmission speeds, making full use of the subcarrier channel power to bring it closer to the theoretical upper limit.

[0040] For subcarriers in traditional systems where BPSK also fails to achieve the target BER, the method of the present invention increases the symbol duration so that the superimposed SINR meets the target BER requirement. This allows data sent by these subcarriers to be transmitted normally even with lower allocated power, ensuring full utilization of spectrum resources. By utilizing subcarriers that would otherwise be discarded in traditional systems, the method of the present invention brings the theoretical upper bound of the water-filling algorithm closer, thereby increasing the transmission rate of the communication system. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a flow chart of an OFDM adaptive digital modulation and time domain extension transmission method based on channel reciprocity of the present invention;

[0042] Where: FFT stands for Fast Fourier Transform, IFFT stands for Inverse Fast Fourier Transform;

[0043] Figure 2 is a flow chart of the adaptive modulation module in the method of the present invention;

[0044] Figure 3 This is a flow chart of the adaptive demodulation module in the method of the present invention;

[0045] Figure 4 is a flow chart of the adaptive bit and power allocation algorithm in the method of the present invention;

[0046] Figure 5 is a schematic diagram of the relationship between the selected modulation mode and the signal-to-interference-and-noise ratio (SINR);

[0047] Figure 6 The figure is a schematic diagram of selecting a modulation mode and an extension number according to a signal-to-interference-and-noise ratio (SINR) in the method of the present invention. DETAILED DESCRIPTION

[0048] Specific implementation method 1: Combination Figure 1 、 Figure 2 and Figure 3This embodiment describes an OFDM adaptive digital modulation and time domain extension transmission method based on channel reciprocity, and the method specifically includes the following steps:

[0049] Step 1: Divide the entire communication frequency band into N sub-bands according to the requirements. The receiving end estimates the channel and noise power of the n-th sub-band and obtains the channel response H of the n-th sub-band. n And the noise power N n , n=1,2,…,N;

[0050] The transmitter obtains the channel response H based on the channel reciprocity n And the noise power N n ;

[0051] Step 2: The transmitter receives the channel response H of the nth subband n And the noise power N n Calculate the equivalent noise floor B of the nth subband n ;

[0052] Then according to the equivalent noise floor B n Calculate the power P allocated to the nth subband n , and according to P n and B n Calculate the signal-to-interference-plus-noise ratio (SINR) of the nth subband n ;

[0053] According to the signal-to-interference-and-noise ratio SINR of the nth subband n To select the modulation mode and extension times q of the nth subband n (It should be noted that the modulation mode and spreading number selected for each sub-band can be different); and the modulation mode and spreading number of each sub-band are synchronized to the receiving end (the receiving end can select the superposition and demodulation mode according to the modulation mode and spreading number);

[0054] Step 3: record the bit information of a frame sent by the nth subband as b n , using the modulation method of the nth sub-band to b n Modulate and get the modulation result S of the nth sub-band n , the modulation result S n The number of symbols in is denoted as K n , that is, K n is the total number of symbols to be sent in one frame for the nth subband;

[0055] According to the number of extensions q of the nth subband n The modulation result S n Expand and obtain the extended symbol sequence X of the nth subband n , and in the extended symbol sequence X nIn the k×q n +1 to (k+1)×q n The symbols are the same, k=0,1,…,K n -1;

[0056] Step 4: Process the extended symbol sequence of each sub-band separately, and then send the processed data to the channel through the RF module;

[0057] Step 5: The receiving end receives a signal from the channel using a radio frequency module and processes the received signal to obtain a processed extended symbol sequence;

[0058] For the extended symbol sequence R of the nth subband after processing n , and then the extended symbol sequence R n Perform equal gain superposition to obtain the symbol sequence Y n , and then the symbol sequence Y n Demodulate and restore the bit information transmitted by the nth sub-band.

[0059] The method of the present invention lengthens the duration of the modulation symbol, for example, the same symbol lasts for q n sampling points to obtain time diversity gain. Compared with the optional parameters of the traditional adaptive modulation method, the method of the present invention adds one dimension, which greatly increases the flexibility. The signal-to-noise ratio gain obtained by equal gain merging is used to achieve fractional channel capacity allocation, improve the resolution, and make the channel capacity of the actual system closer to the continuous upper bound obtained by the water filling algorithm. In addition, for systems with fewer modulation gears, when switching the modulation mode alone is not enough to provide sufficient SINR gain, the method of the present invention can be used to adjust q n Parameters are used to provide greater SINR differentiation. For subchannels where the allocated power is too low, even BPSK is insufficient to guarantee the target BER, this method achieves fractional rate allocation, fully utilizing this energy to better utilize spectrum resources and increase transmission rates.

[0060] Specific embodiment 2: This embodiment differs from the specific embodiment 1 in that: the equivalent background noise B n for:

[0061]

[0062] Among them, B n Represents the equivalent noise floor of the nth subband.

[0063] Other steps and parameters are the same as those in the first embodiment.

[0064] Specific embodiment three: This embodiment differs from specific embodiment one or two in that: the equivalent background noise B nCalculate the power P allocated to the nth subband n , specifically:

[0065] P n =(λ-B n ) +

[0066] Where n = 1, 2, ..., N, P n is the power allocated to the nth subband, λ is the Lagrange multiplier;

[0067] function(·) + Satisfies: If λ-B n If it is greater than 0, then P n =λ-B n , if λ-B n Less than or equal to 0, then P n =0, that is, when λ-B n When it is less than or equal to 0, no power is allocated to the nth sub-band, that is, no data is sent through the nth sub-band;

[0068] The Lagrange multiplier λ makes the power allocated to each subband satisfy: Among them, P all is the total transmit power. Therefore, the Lagrange multiplier λ represents the "level" of power allocation, which is used to ensure that the sum of the power values ​​allocated to all subbands is less than or equal to the total power.

[0069] Other steps and parameters are the same as those in the first or second embodiment.

[0070] Specific embodiment 4: This embodiment differs from the specific embodiments 1 to 3 in that: n and B n Calculate the signal-to-interference-plus-noise ratio (SINR) of the nth subband n , specifically:

[0071]

[0072] The other steps and parameters are the same as those in the first to third embodiments.

[0073] Specific embodiment 5: This embodiment differs from any one of specific embodiments 1 to 4 in that: in step 4, the extended symbol sequence of each sub-band is processed separately, specifically:

[0074] For the spreading symbol sequence X of the nth subband n , for X n Mapping (specifically, mapping data to available subcarriers), IFFT and framing are performed in sequence.

[0075] The other steps and parameters are the same as those in the first to fourth embodiments.

[0076] Specific implementation method six: combination Figure 4 and Figure 6 The present embodiment is different from any one of the specific embodiments 1 to 5 in that: the signal to interference noise ratio SINR of the nth sub-band n To select the modulation mode and extension times q of the nth subband n , specifically:

[0077] Step 21: Select M modulation modes and calculate the lower bound of the signal-to-interference-plus-noise ratio (SINR) of each modulation mode without expansion according to the water-filling algorithm;

[0078] Take M-QAM modulation as an example:

[0079] SINR_lb=(2 r -1) / Γ

[0080] Where SINR_lb represents the lower bound of the signal-to-interference-plus-noise ratio of the M-QAM modulation scheme without spreading (i.e., when the spreading factor is 0); r is the bit rate of the M-QAM modulation scheme (e.g., 2 for 4QAM and 4 for 16QAM); Γ is the difference in signal-to-noise ratio between the M-QAM modulation scheme and the Shannon capacity;

[0081] Under the awgn (additive white Gaussian noise) channel, P BER represents the target bit error rate;

[0082] In the Rayleigh channel,

[0083] Step 2: Set the expansion factor q n The value range is 1, 2, ..., Q, and the expansion factor q n Under the condition of m-th modulation mode, the lower bound of signal to interference noise ratio is adjusted to SINR_lb m -3q n After traversing various modulation modes and expansion factors, M×Q signal-to-interference-and-noise ratio thresholds are obtained;

[0084] Step 2 and 3: For the nth subband, start from the value less than the signal to interference and noise ratio SINR n Select the one closest to SINR from all threshold values n The modulation mode and expansion factor corresponding to the selected threshold value are respectively used as the modulation mode and expansion factor of the nth subband.

[0085] The other steps and parameters are the same as those in the first to fifth embodiments.

[0086] The obtained M×Q threshold values ​​are sorted in ascending order to obtain the mapping relationship between the modulation mode and the number of extensions and the subband SINR, such as Figure 6 As shown, the modulation / demodulation mode control information and the extension / overlay times control information of each sub-band can be obtained by using the sub-band SINR. Figure 5 , Figure 6 With more threshold values.

[0087] The SINR lower bounds of different modulation modes do not need to be calculated in real time, but can be calculated offline and stored as constants, q n The selection method can be changed flexibly. It can be set continuously to [1,2,3,4], or an integer power of 2 can be selected, such as [1,2,4,8]. It can also be selected arbitrarily according to actual conditions.

[0088] Specific embodiment 7: This embodiment differs from any one of specific embodiments 1 to 6 in that: in step 5, the received signal is processed as follows:

[0089] Perform synchronization, FFT and equalization processing on the signal received by the receiving end.

[0090] The other steps and parameters are the same as those in the first to sixth embodiments.

[0091] Specific embodiment eight: This embodiment differs from any one of specific embodiments one to seven in that: the extended symbol sequence R n Perform equal gain superposition to obtain the symbol sequence Y n , specifically:

[0092] The extended symbol sequence R n The k×qth n +1 to (k+1)×q n The symbols are superimposed, and the superposition result is divided by K n , the result of the division operation is used as the symbol sequence Y n The k+1th symbol in, k=0,1,…,K n -1.

[0093] The other steps and parameters are the same as those in the first to seventh embodiments.

[0094] Specific embodiment nine: This embodiment differs from any one of specific embodiments one to eight in that: the value of M is 7, and the M modulation modes specifically include 8PSK, 16PSK, 4QAM, 8QAM, 16QAM, 32QAM and 64QAM.

[0095] The other steps and parameters are the same as those in Specific Embodiments 1 to 8.

[0096] The modulation methods that can be selected in the method of the present invention include but are not limited to the above-mentioned modulation methods.

[0097] The above examples are merely illustrative of the calculation model and process of the present invention and are not intended to limit the embodiments of the present invention. Persons skilled in the art will readily appreciate that other variations or modifications based on the above description are possible. This list of embodiments is not exhaustive; however, any obvious variations or modifications derived from the technical solution of the present invention remain within the scope of protection of the present invention.

Claims

1. An OFDM adaptive digital modulation and time domain extension transmission method based on channel reciprocity, characterized in that: The method specifically comprises the following steps: Step 1: Divide the entire communication frequency band into N sub-bands. The receiving end estimates the channel and noise power of the nth sub-band and obtains the channel response of the nth sub-band. and noise power , ; The transmitter obtains the channel response based on channel reciprocity and noise power ; Step 2: The transmitter responds to the channel of the nth subband and noise power Calculate the equivalent noise floor of the nth subband ; Then according to the equivalent noise floor Calculate the power allocated to the nth subband , and according to and Calculate the signal to interference noise ratio of the nth subband ; According to the signal-to-interference-noise ratio of the nth subband To select the modulation mode and extension times q of the nth subband n ; And synchronize the modulation mode and extension times of each sub-band to the receiving end; Step 3: record the bit information of a frame sent by the nth subband as b n , using the modulation method of the nth sub-band to b n Modulate and get the modulation result S of the nth sub-band n , the modulation result S n The number of symbols in is denoted as K n ; According to the number of extensions q of the nth subband n The modulation result S n Expand and obtain the extended symbol sequence X of the nth subband n , and in the extended symbol sequence X n In the k×q n +1 to (k+1)×q n The same sign, k=0,1,…,K n -1; Step 4: Process the extended symbol sequence of each sub-band separately, and then send the processed data to the channel through the RF module; Step 5: The receiving end receives a signal from the channel using a radio frequency module and processes the received signal to obtain a processed extended symbol sequence; For the extended symbol sequence R of the nth subband after processing n , and then the extended symbol sequence R n Perform equal gain superposition to obtain the symbol sequence Y n , and then the symbol sequence Y n Demodulate and restore the bit information transmitted by the nth sub-band.

2. The OFDM adaptive digital modulation and time domain extension transmission method based on channel reciprocity according to claim 1, characterized in that: The equivalent noise floor for: in, Represents the equivalent noise floor of the nth subband.

3. The OFDM adaptive digital modulation and time domain extension transmission method based on channel reciprocity according to claim 2, characterized in that: According to the equivalent noise floor Calculate the power allocated to the nth subband , specifically: in, , The power allocated to the nth subband, is the Lagrange multiplier; function Satisfied: If Greater than 0, then ,like Less than or equal to 0, then ; Lagrange multiplier Make the power allocated to each sub-band satisfy: ,in, is the total transmit power.

4. The OFDM adaptive digital modulation and time domain extension transmission method based on channel reciprocity according to claim 3, characterized in that: The basis and Calculate the signal to interference noise ratio of the nth subband , specifically: 。 5. The OFDM adaptive digital modulation and time domain extension transmission method based on channel reciprocity according to claim 4, characterized in that: In step 4, the extended symbol sequence of each sub-band is processed separately, specifically: For the spreading symbol sequence X of the nth subband n , for X n Mapping, IFFT and framing are performed in sequence.

6. The OFDM adaptive digital modulation and time domain extension transmission method based on channel reciprocity according to claim 5, characterized in that: The signal to interference noise ratio according to the nth sub-band To select the modulation mode and extension times q of the nth subband n , specifically: Step 21: Select M modulation modes and calculate the lower bound of the signal-to-interference-and-noise ratio of each modulation mode without expansion using the water-filling algorithm; Step 2: Set the expansion factor q n The value range is 1, 2, ..., Q, and the expansion factor q n Next, The lower bound of the signal-to-interference-noise ratio of the modulation method is adjusted to -3q n After traversing various modulation modes and expansion factors, M×Q signal-to-interference-and-noise ratio thresholds are obtained; in, Indicates that without extension, The lower bound of the signal-to-interference-noise ratio of the modulation method; Step 2 and 3: For the nth subband, from less than the signal to interference noise ratio Select the closest threshold value from all threshold values The modulation mode and expansion factor corresponding to the selected threshold value are respectively used as the modulation mode and expansion factor of the nth subband.

7. The OFDM adaptive digital modulation and time domain extension transmission method based on channel reciprocity according to claim 6, characterized in that: In step 5, the received signal is processed, specifically: Perform synchronization, FFT and equalization processing on the signal received by the receiving end.

8. The OFDM adaptive digital modulation and time domain extension transmission method based on channel reciprocity according to claim 7, characterized in that: The extended symbol sequence R n Perform equal gain superposition to obtain the symbol sequence Y n , specifically: The extended symbol sequence R n The k×qth n +1 to (k+1)×q n The symbols are superimposed, and the superposition result is divided by K n , the result of the division operation is used as the symbol sequence Y n The k+1th symbol in, k=0,1,…,K n -1.

9. The OFDM adaptive digital modulation and time domain extension transmission method based on channel reciprocity according to claim 8, characterized in that: The value of M is 7, and the M modulation modes specifically include 8PSK, 16PSK, 4QAM, 8QAM, 16QAM, 32QAM and 64QAM.

Images