CN101267414A - A Smart Orthogonal Frequency Division Multiple Access Downlink Communication System and Communication Method - Google Patents

Abstract

An Orthogonal Frequency Division Multiple Access downlink communication system and communication method, in which the communication information to be sent to each user at the transmitting end is subjected to various processing such as IFFT transformation and digital-to-analog conversion with a large number of points to obtain broadband analog orthogonal frequency division Multiplex signals, and process the received radio frequency signals at multiple receiving ends so that each receiving end can obtain their corresponding user narrowband discrete signals, and perform analog-to-digital conversion, spectrum shifting and After various processes including filtering, each discrete narrowband baseband signal is obtained, and then the FFT transformation with a smaller number of points is performed on it to obtain the corresponding communication information, so that the wireless resources of the broadband communication system can be flexibly adapted to the needs of multiple users. Different service requirements and terminal processing capabilities, thereby reducing the implementation complexity and power consumption of mobile terminals.

Description

A Smart Orthogonal Frequency Division Multiple Access Downlink Communication System and Communication Method

technical field

The invention relates to a smart OFDM downlink communication system and communication method.

Background technique

In wireless communication systems, especially in broadband mobile communication systems, air signal transmission technology is becoming the focus of research. In order for the broadband mobile communication system to obtain higher spectral efficiency, such as up to 10bps/Hz, to support the communication needs of various scenarios and support various adaptive control technologies, its signal transmission technology must be better than any previous Better performance of similar techniques while maintaining manageable implementation complexity.

The current broadband mobile communication signal transmission technology is mainly single carrier multiple access technology represented by Code Division Multiple Access (CDMA) and multi-carrier multiple access technology represented by Orthogonal Frequency Division Multiplexing (OFDM). In the broadband wireless communication environment, in order to compensate the influence of channel fading, the equalizer at the receiving end of the CDMA-based single-carrier transmission system is becoming more and more complex, which limits the application of this technology. The multi-carrier multiple access system represented by OFDM has many advantages such as supporting flexible frequency domain resource scheduling, simple equalization algorithm at the receiving end, and easy combination with multi-antenna technology, making it increasingly become the future broadband wireless communication system. One of the main multiple access technology solutions.

In existing transmission systems such as WiMAX, WiBro, etc., the downlink mobile terminal transmitter and base station receiver adopt a symmetrical structure, that is, the points of the inverse Fourier transform (IFFT) used by the transmitter and the Fourier transform ( FFT) with the same number of points. In the future broadband mobile communication system, with the widening of the operating bandwidth of the system and the development of multi-rate and multimedia services, the bandwidth occupied by a single user in the downlink will become more and more asymmetrical to the system bandwidth. At this time, if the existing system transmission scheme is adopted, for a terminal that only supports low-rate services, in order to demodulate OFDM symbols carrying low-rate services, it must also support and perform FFT transformation with a large number of points, so its implementation is complicated. The degree and cost are difficult to control.

Therefore, how to solve the problems existing in the existing OFDM technology has become an urgent technical task for those skilled in the art.

Contents of the invention

The purpose of the present invention is to provide a smart OFDMA downlink communication system and communication method, so that the wireless resources of the broadband communication system can smartly adapt to different service requirements and terminal processing capabilities of multiple users, thereby reducing mobile Implementation complexity and power consumption of the terminal.

In order to achieve the above and other objectives, the present invention provides a smart OFDMA downlink communication system and communication method, wherein the smart OFDMA downlink communication system includes: a transmitting end, which uses Perform various processes on the communication information to be sent to each user to obtain a broadband analog OFDM baseband signal, and perform frequency conversion on the broadband analog OFDM baseband signal according to a preset carrier frequency to obtain radio frequency signal, and transmit the subcarrier allocation information of the radio frequency signal and the information to be sent to each user in the broadband analog OFDM baseband signal, wherein, the information to be sent to each user Various processing of information includes subcarrier mapping processing, inverse Fourier transform of the preset first point, and digital-to-analog conversion according to the preset first sampling interval; and multiple receiving ends, which are used to receive the transmitted The received radio frequency signal and the subcarrier allocation information of each user's information in the broadband analog OFDM baseband signal, and perform various processing on the received radio frequency signal so that each receiving end can obtain the corresponding user narrowband Discrete baseband signals, and perform Fourier transform of the respective preset second points on the user narrowband discrete baseband signals, and then extract corresponding communication information of each user according to the subcarrier allocation information, wherein the received radio frequency signals are The processing includes each receiving end performing frequency conversion, filtering and analog-to-digital conversion according to the subcarrier allocation information in the wideband analog OFDM signal, the preset processing bandwidth and the preset carrier frequency according to the received information of each user .

The transmitting end includes: a subcarrier mapping module for mapping the modulated communication information to be sent to each user to each corresponding subcarrier, and for performing the first calculation on each subcarrier The Fourier inverse transform module of the inverse Fourier transform, the cyclic prefix adding module for adding a prefix to the signal after the Fourier inverse transform according to preset rules, and the signal output by the cyclic prefix adding module with the first sampling A digital-to-analog conversion module for performing digital-to-analog conversion at intervals to obtain a broadband analog OFDM baseband signal, used to perform frequency conversion on the broadband analog OFDM baseband signal with a preset carrier frequency to obtain a radio frequency signal An up-conversion module, wherein any one of the multiple receiving ends includes: sub-bands in the broadband analog OFDM baseband signal according to the preset carrier frequency and the received information of the corresponding user The carrier allocation information performs corresponding frequency conversion on the received radio frequency signal to obtain a first down-conversion module of the first broadband analog baseband signal with a corresponding frequency offset, and is used to convert the RF signal according to the preset processing bandwidth of the corresponding user. Perform analog low-pass filtering on the frequency offset first broadband analog baseband signal to obtain a first low-pass filtering module for the corresponding user narrowband analog baseband signal, for processing the user narrowband analog baseband signal according to the preset processing bandwidth of the corresponding user Perform analog-to-digital conversion at a second sampling interval to obtain a first analog-to-digital conversion module for the user narrowband discrete baseband signal, a first prefix removal module for removing a prefix of the user narrowband discrete baseband signal according to preset rules, A first Fourier transform module for performing a second-point Fourier transform on the prefix-removed user narrowband discrete baseband signal, and for obtaining the occupancy of each user from the signal output by the first Fourier transform module according to the received subcarrier allocation information. A first subcarrier demapping module for signals on subcarriers, a first channel equalization module for performing frequency domain equalization processing on signals output by the first subcarrier demapping module, and in addition, among the multiple receiving ends Any one of the receivers may further include: a second down-conversion module for performing corresponding frequency conversion on the received radio frequency signal according to a preset carrier frequency to obtain a second wideband analog baseband signal, and a second down-conversion module for corresponding to the preset carrier frequency The user's processing bandwidth performs analog-to-digital conversion on the second broadband analog baseband signal at a first sampling interval to obtain a second analog-to-digital conversion module of the first broadband discrete baseband signal, which is used to perform the analog-to-digital conversion according to the received information of the corresponding user. The subcarrier allocation information in the broadband analog OFDM signal performs corresponding spectrum shifting on the first broadband discrete baseband signal to obtain a spectrum shifting module of a second wideband discrete baseband signal with frequency offset, which is used according to The preset processing bandwidth of the corresponding user performs corresponding filtering on the second broadband discrete baseband signal with frequency offset to obtain the second low-pass filtering module of the oversampled narrowband discrete baseband signal of the corresponding user, which is used according to the preset The bandwidth of the broadband analog OFDM baseband signal and the preset processing bandwidth of the corresponding user perform corresponding downsampling on the narrowband discrete baseband signal oversampled by the user to obtain the downsampling of the critically sampled narrowband discrete baseband signal of the user A module, a second prefix removal module for removing the prefix of the user narrowband discrete baseband signal according to preset rules, and a second prefix removal module for removing the prefix of the user narrowband discrete baseband signal according to the preset processing bandwidth of the corresponding user The second Fourier transform module of the Fourier transform, used to obtain the second subcarrier demapping module of the signal on the subcarrier occupied by each user from the signal output by the second Fourier transform module according to the received subcarrier mapping rule information . A second channel equalization module for performing frequency domain equalization processing on the signal output by the second subcarrier demapping module, wherein the second points of the Fourier transforms used by the multiple receiving ends are respectively less than or equal to the The first points of the inverse Fourier transform adopted by the transmitting end, when the second points of the Fourier transform adopted by the plurality of receiving ends are respectively N ₁ , N ₂ ... N _n , the second sampling intervals adopted respectively are T ₁ , T ₂ ... T _n , the first number of points of the inverse Fourier transform adopted by the transmitter is N, and the first sampling interval adopted by it is T, then the condition is satisfied: N _k T _k =NT, k =1, 2...n, n is the number of downlink receiving ends, and the subcarrier allocation information includes frequency offset position information and subcarrier mapping rules of each user.

The smart OFDMA downlink communication method includes steps: 1) performing corresponding subcarrier mapping processing on the communication information to be sent to each user after preprocessing; 2) performing preprocessing on the communication information processed through subcarrier mapping Set the inverse Fourier transform of the first point; 3) add a prefix to the communication information to be sent to each user after the inverse Fourier transform according to preset rules; 4) use the preset first Perform digital-to-analog conversion at the sampling interval to form a broadband analog OFDM baseband signal; 5) perform frequency conversion processing on the broadband analog OFDM baseband signal according to a preset carrier frequency to obtain a radio frequency signal; 6) transmit The radio frequency signal and the subcarrier allocation information of the information to be sent to each user in the broadband analog OFDM baseband signal; 7) receiving the radio frequency signal sent to and the information to be sent to each user Subcarrier allocation information of user information in the broadband analog OFDM baseband signal, and according to the subcarrier allocation information, the preset processing bandwidth of each user and the preset carrier frequency, the radio frequency The signal is converted into a narrowband discrete baseband signal of each user; 8) removing the prefix of the narrowband discrete baseband signal of each user according to a preset rule; Fourier transform of each preset second number of points; 10) Extracting the communication signals of each user from the Fourier transformed signal according to the subcarrier allocation information, and performing equalization processing on the communication signals to obtain corresponding communication signals of each user information.

Wherein, the preprocessing includes channel coding and digital modulation, and the second point number is less than or equal to the first point number, and the step 7) further includes the step of: (1) according to the subcarrier allocation information and preset loading convert the radio frequency signal into a first broadband analog baseband signal with frequency offset; (2) process the broadband analog baseband signal with frequency offset according to the preset processing bandwidth of each user through analog low-pass filtering to obtain The user narrowband analog baseband signal; (3) perform analog-to-digital conversion on the user narrowband analog baseband signal according to the preset processing bandwidth of each user at a respective preset second sampling interval to obtain corresponding user narrowband discrete baseband signals , and the product of the second number of points and the corresponding second sampling interval is equal to the product of the first number of points and the first sampling interval, in addition, the step 7) may also include the step of: (1) according to the preset Assuming that the carrier frequency converts the radio frequency signal into a second broadband analog baseband signal, the center frequency of the second broadband analog baseband signal is zero; (2) according to the preset broadband analog OFDM baseband signal bandwidth by The first sampling interval carries out analog-to-digital conversion to the second broadband analog baseband signal to obtain the first broadband discrete baseband signal; (3) according to the received information of each user in the broadband analog OFDM baseband signal The subcarrier allocation information in the corresponding spectrum shift of the first broadband discrete baseband signal to obtain the second wideband discrete baseband signal with frequency offset; (4) according to the preset processing bandwidth of each user for the Perform corresponding digital low-pass filtering on the second broadband discrete baseband signal of frequency offset to obtain an oversampled narrowband discrete baseband signal; 5) According to the bandwidth of the preset broadband analog OFDM baseband signal and the processing bandwidth of each user Corresponding downsampling is performed on each of the oversampled narrowband discrete baseband signals to obtain each critically sampled user narrowband discrete baseband signal, and the product of the first number of points and the first sampling interval is equal to the second number of points and the The product of the second sampling interval, the subcarrier allocation information includes frequency offset position information and subcarrier mapping rules of each user.

In summary, the smart OFDMA downlink communication system and communication method of the present invention can be less than or equal to the IFFT transformation points (subcarrier number) of the transmitting end because the FFT transformation point number (subcarrier number) of the receiving end, so the present invention The wireless resources of the broadband communication system can be flexibly adapted to different service requirements and terminal processing capabilities of multiple users, thereby reducing the implementation complexity and power consumption of the mobile terminal.

Description of drawings

FIG. 1 is a schematic diagram of the basic architecture of the smart OFDMA downlink communication system of the present invention.

Detailed ways

Please refer to Fig. 1, the smart OFDMA downlink communication system of the present invention at least includes: a transmitting end and a plurality of receiving ends, for simplification of illustration, only two receiving ends are illustrated in Fig. 1, namely the first The receiving end and the second receiving end are not limited to this illustration.

The transmitting end is used to perform various processes on the communication information to be sent to each user to obtain a broadband analog OFDM baseband signal, and to perform various processing on the broadband analog OFDM baseband signal according to a preset carrier frequency performing frequency conversion to obtain a radio frequency signal, and transmitting the radio frequency signal and the subcarrier allocation information of the information to be sent to each user in the broadband analog OFDM baseband signal, wherein the The processing of the information transmitted to each user includes subcarrier mapping processing, inverse Fourier transform of the preset first point, and digital-to-analog conversion according to the preset first sampling interval. The subcarrier allocation information includes the frequency of each user. Offset location information and subcarrier mapping rules.

The transmitting end mainly includes: a channel coding module, a modulation module, a subcarrier mapping module, an inverse Fourier transform module, a cyclic prefix adding module, a digital-to-analog conversion module, an up-conversion module and a transmitting module.

The channel encoding module is used to encode the original bit information to be sent to each user. The encoding method is known to those skilled in the art and will not be repeated here.

The modulation module is used to digitally modulate the coded bit information to be sent to each user. The modulation method is known to those skilled in the art and will not be repeated here.

The sub-carrier mapping module is used to map the modulated information symbols to be sent to each user to corresponding sub-carriers for transmission according to a specific mapping rule. Since no occupied sub-carriers transmit zero, each modulated The information symbol is $\{{\tilde{a}}_k\left(m\right),m=\mathrm{0,1},...,N_k-1\},$ After subcarrier mapping, the output is a parallel symbol data block {a _k (m), m=0, 1, ..., N-1}, assuming that after subcarrier mapping, the modulated N _k information symbols occupy The subcarrier sequence number set of the OFDM symbol is Ω, and the frequency offset of the group of N _k subcarriers in all subcarriers of the OFDM symbol is ε _k subcarriers. It should be noted that the specific mapping rules are defined by those skilled in the art It is well known and will not be repeated here.

The inverse Fourier transform module is used to perform an inverse Fourier transform of the first number of points on each subcarrier, for example, for a parallel symbol data block {a _k (m), m=0, 1, ..., N -1} After N-point IFFT transformation, the corresponding data block sequence {b _k (m), m=0, 1, ..., N-1} is formed, and the relationship between them obeys $b_k\left(\mathrm{no}\right)=\frac{1}{\sqrt{N}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{a}_k\left(m\right)\exp (j2\mathrm{\πmn}/N),$ Here, {b _k } also represents a number of elements, which is a column vector of the same size as N for IFFT transformation.

The cyclic prefix adding module is used to add a prefix to the inverse Fourier-transformed signal according to preset rules, and usually adds a guard interval of a specific length to the head of the parallel data block output by the IFFT transform to reduce inter-channel interference ( Preferably, the length of the guard interval should be greater than the maximum channel delay extension length). For example, a part of the tail of the data block output by the IFFT transformation is copied to its front end to form the final data block symbol with a cyclic prefix, that is, the data sequence {b _k (n), n=0, 1,... , N-1} is transformed into a complete OFDM symbol data sequence {c _k (n), n=-C,...,-1, 0, 1,..., N-1}, where C is a cycle prefix length, obviously, $c_k\left(\mathrm{no}\right)=\frac{1}{\sqrt{N}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{a}_k\left(m\right)\exp (j2\mathrm{\πmn}/N),$ n=-C, . . . , -1, 0, 1, . . . , N-1.

The digital-to-analog (D/A) conversion module is used to perform digital-to-analog conversion on the signal output by the cyclic prefix addition module at the first sampling interval to obtain an analog signal, that is, a discrete data sequence {c _k (n) , n=-C, ..., -1, 0, 1, ..., N _k -1} carry out digital-to-analog conversion with the first sampling interval T to obtain continuous OFDM symbol waveform s _k (t), and ${\mathrm{the\; s}}_k\left(t\right)=\frac{1}{\sqrt{\mathrm{NT}}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{a}_k\left(m\right)\exp \left(j2\mathrm{\πm\ΔFt}\right),$ t=[-CT, NT), ΔF is the OFDM symbol subcarrier spacing transmitted by the base station.

The up-conversion module is used to perform frequency conversion on the analog signal with a preset carrier frequency to obtain a radio frequency signal, that is, to convert the analog signal s _k (t) into a radio frequency signal ${\widetilde{\mathrm{the\; s}}}_k\left(t\right)=R_e\left[{\mathrm{the\; s}}_k\left(t\right)\exp \left(j2\mathrm{\π}{f}_{c}t\right)\right],$ Where R _e [·] represents the real part, and f _c is the carrier frequency of the signal transmitted by the transmitting end.

The transmitting module is used to send the radio frequency signal and the subcarrier allocation information of the information to be sent to each user in the broadband analog OFDM baseband signal (here, it is assumed that the frequency offset position is ε _k subcarriers). It is assumed here that the processing bandwidth of the kth user is the occupied bandwidth of N _k subcarriers, and the processing bandwidth may be greater than the occupied bandwidth according to different subcarrier mapping rules.

The multiple receiving ends are respectively used to receive the radio frequency signal sent by the transmitting end and the subcarrier allocation information of the information of each user in the broadband analog OFDM baseband signal (which includes the information of each user frequency offset position information and subcarrier mapping rules), and perform various processing on the received radio frequency signals so that each receiving end can obtain their respective corresponding user narrowband discrete baseband signals, and then carry out respective preset second After the two-point Fourier transform, the corresponding user communication signals are extracted according to the subcarrier allocation information, and finally the corresponding user communication information is obtained after channel equalization, and the various processes performed on the received radio frequency signals include: Each receiving end performs frequency conversion, filtering and analog-to-digital conversion according to the subcarrier allocation information in the broadband analog OFDM signal, the preset processing bandwidth and the preset carrier frequency according to the received information of each user. It should be noted that the second points of the Fourier transforms adopted by the plurality of receiving ends are respectively less than or equal to the first points of the inverse Fourier transforms adopted by the transmitting end, if the Fourier transforms respectively adopted by the plurality of receiving ends The second number of points are respectively N ₁ , N ₂ ... N _n , the second sampling intervals adopted respectively are T ₁ , T ₂ ... T _n , the first number of points of the inverse Fourier transform adopted by the transmitting end is N, and the first sampling interval it adopts is T, then the condition is satisfied: N _k T _k = NT K = 1, 2...n

If the plurality of receiving ends adopt the structure of the first receiving end, each receiving end at least includes: a first receiving module, a first down-conversion module, a first low-pass filtering module, a first mode A digital conversion module, a first prefix removal module, a first Fourier transform module, a first subcarrier demapping module and a first channel equalization module.

The first receiving module is used to receive the radio frequency signal sent to and usually receive information through the antenna, the frequency offset position information and subcarrier mapping rule of the information of each user in the broadband analog OFDM baseband signal Information can be transmitted and received by designing specific signaling channels in the system according to the receiving capabilities of the minimum configured users. This technology is already known to those skilled in the art and will not be repeated here.

移频-(f_c+Δf_k)，使其变换为有频偏的第一宽带模拟基带信号r_k(t)，若假定第k个接收端所接收的信号为经过准静态多径信道传送至的信号，因此信号在该信道传输的时间范围内，该信道的等效基带冲击响应可以表示为 $h_k\left(t\right)=\underset{l=0}{\overset{L-1}{\mathrm{\Σ}}}\mathrm{\δ}(t-{\mathrm{\τ}}_l){\mathrm{\α}}_l,n=0,...,{\mathrm{\τ}}_{\max }-1,$ 其中L为信道路径总数，α_l为第l条路径的复衰减因子，τ_l为第l条路径的时延扩展，τ_max为所有路径的最大时延扩展，为分析简便，若进一步假设接收端理想同步，并且省略噪声项，则第k个用户有频偏的第一宽带模拟基带信号r_k(t)可以表示为The first down-conversion module is used to perform a corresponding frequency conversion on the received radio frequency signal according to the preset carrier frequency and the frequency offset position information of the received information of the corresponding user in the wideband analog OFDM baseband signal. Transform to obtain the corresponding first broadband analog baseband signal with frequency offset, wherein the center frequency of the first broadband analog baseband signal with frequency offset is the information of the corresponding user in the broadband analog OFDM baseband signal The negative value of the frequency offset in , set the carrier frequency as f _c , which is the same as the carrier frequency of the transmitting end, and the frequency offset position of the user's information in the broadband analog OFDM baseband signal The information is usually represented by carrier offset. For example, the specific carrier offset of the kth receiver is set to Δf _k , which is an integer multiple of the OFDM modulation subcarrier spacing at the receiver, that is, Δf _k =ε _k ΔF. The RF signal that the down conversion module will receive

Frequency shift-(f _c +Δf _k ) to transform it into the first broadband analog baseband signal r _k (t) with frequency offset, if it is assumed that the signal received by the kth receiver is transmitted through a quasi-static multipath channel to the signal, so the signal is transmitted in the time range of the channel, the equivalent baseband impulse response of the channel can be expressed as $h_k\left(t\right)=\underset{l=0}{\overset{L-1}{\mathrm{\Σ}}}\mathrm{\δ}(t-{\mathrm{\τ}}_l){\mathrm{\α}}_l,\mathrm{no}=0,...,{\mathrm{\τ}}_{\max }-1,$ where L is the total number of channel paths, α _l is the complex attenuation factor of the l-th path, τ _l is the delay spread of the l-th path, and τ _max is the maximum delay spread of all paths. terminal ideally synchronized, and the noise term is omitted, then the first broadband analog baseband signal r _k (t) of the kth user with frequency offset can be expressed as

${\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;\&Delta;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; NT</span>}}}\underset{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;m\&Delta;F</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;\&Delta;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; .</span>$

The first low-pass filtering module is configured to perform analog low-pass filtering on the frequency-offset first broadband analog baseband signal according to the preset processing bandwidth of the corresponding user to obtain a corresponding user narrowband analog baseband signal. The first broadband analog baseband signal r _k (t) with a frequency offset of a user can be filtered out of the out-of-band interference signal of the received signal by low-pass filtering. Assuming that the low-pass filter can completely filter out the out-of-band signal, the kth user’s narrowband The analog baseband signal can be expressed as:

${\stackrel{\&OverBar;}{r}}_k\left(t\right)=\frac{1}{\sqrt{\mathrm{NT}}}\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}\underset{m\&Element;\mathrm{\&Omega;}}{\mathrm{\&Sigma;}}{a}_k\left(m\right){\mathrm{\&alpha;}}_l\exp \left(j2\mathrm{\&pi;m\&Delta;F}(t-{\mathrm{\&tau;}}_l)\right)\exp (-j2\mathrm{\&pi;\&Delta;}{f}_{k}t),$ Ω is the set of subcarriers containing useful signals.

The first analog-to-digital (A/D) conversion module is configured to perform analog-to-digital conversion on the user narrowband analog baseband signal at a second sampling interval according to the preset processing bandwidth of the corresponding user to obtain the user narrowband discrete baseband signal , the kth user narrowband analog baseband signal r _k (t) is sampled at the second sampling interval T _k , if the user narrowband analog baseband signal r _k (t) is converted into a discrete baseband signal after A/D conversion { d _k (n)}, then the sampling value at time nT _k can be expressed as:

$d_k\left(n_k\right)=\frac{1}{\sqrt{N_k{T}_k}}\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}\underset{m\&Element;\mathrm{\&Omega;}}{\mathrm{\&Sigma;}}{a}_k\left(m\right){\mathrm{\&alpha;}}_l\exp \left(j2\mathrm{\&pi;m\&Delta;F}(n_k-{\mathrm{\&tau;}}_l)\right)\exp (-j2\mathrm{\&pi;\&Delta;}{f}_k{n}_k),$ Correspondingly, the kth user narrowband discrete baseband signal output by A/D conversion can be expressed as:

为采样间隔T_k归一化的第l条路径的时延扩展，ε_k为接收端OFDM解调子载波间隔归一化的第k个移动终端特定的载波偏移量，即ε_k＝Δf_k/ΔF，并且ε_k为整数。 $d_k\left(\mathrm{no}\right)=\frac{1}{\sqrt{N_k}}\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}\underset{m\&Element;\mathrm{\&Omega;}}{\mathrm{\&Sigma;}}{a}_k\left(m\right){\mathrm{\&alpha;}}_l\exp (j2\mathrm{\&pi;m}(\mathrm{no}-{\widetilde{\mathrm{\&tau;}}}_l)/N_k)\exp (-j2\mathrm{\&pi;}{\mathrm{\&epsiv;}}_k\mathrm{no}/N_k),$ in

is the delay spread of the l-th path normalized by the sampling interval T _k , and ε _k is the specific carrier offset of the k-th mobile terminal normalized by the OFDM demodulation subcarrier spacing at the receiving end, that is, ε _k = Δf _k /ΔF, and ε _k is an integer.

The first prefix removal module is used to remove the prefix of the user narrowband discrete baseband signal according to preset rules, for example, in the kth user narrowband discrete signal sequence {d _k (n)} output by A/D conversion The first C sampling values of the data are discarded, and the subsequent N sampling values are taken to form a parallel data sequence {e _k (n), n=0, 1, 2, ..., N _k -1} with a length of N _k , and e _k (n)=d _k (n+C+1), n=0, 1, 2, . . . , N _k −1.

The first Fourier transform module is used to perform a second-point Fourier transform on the prefix-removed user narrowband discrete baseband signal, that is, for the parallel data sequence {e _k (n), n=0, 1, 2, ..., N _k -1} performs N _k point FFT transformation, after FFT transformation, the parallel data sequence is transformed into the corresponding parallel data sequence {g _k (m), m=0, 1, 2,..., N _k -1 }, the mutual relationship obeys

${\mathrm{<span\; class="notranslate">\; g</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; N</span>}}}\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; e</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;mn</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; .</span>$

In fact,

${\mathrm{<span\; class="notranslate">\; g</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\underset{{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; \&Element;</span>\mathrm{<span\; class="notranslate">\; \&Omega;</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>$

0≤m≤N _k -1, m+ε _k ∈Ω

in, $h_k\left(m^{\&prime;}\right)=\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_l\exp (-j2\mathrm{\&pi;}{m}^{\&prime;}{\widetilde{\mathrm{\&tau;}}}_l/N_k),$ is the channel frequency response on the m'th subcarrier of the kth receiver. It should be noted that in order to ensure that the subcarrier bandwidth of each receiving end demodulates the OFDM symbol is the same as the subcarrier bandwidth of the transmitted OFDM symbol, the duration of the effective part of the OFDM symbol (excluding the cyclic prefix) received by each receiving end must be the same as that of the base station The duration of the effective part of the transmitted OFDM symbol is the same, that is, N _k T _k =NT, wherein, T _k is the second sampling interval adopted by the A/D conversion module of the kth receiving end, and N _k is the second sampling interval adopted by the kth receiving end The second point number of FFT transformation in the FFT transformation module of the end, N is the first point number of IFFT transformation in the IFFT transformation module of the transmitting end, T is the first sampling interval of the D/A conversion in the D/A conversion module of the transmitting end.

The first subcarrier demapping module is used to extract the communication signal of each user on the corresponding subcarrier from the Fourier transformed signal according to the received subcarrier allocation information, and the output signal g _k (m)=H _k of the Fourier transform (m+ε _k )a _k (m+ε _k ), 0≤m≤N _k -1, m+ε _k ∈Ω can be seen, the mth communication signal output by subcarrier demapping is the transmitted signal +ε data symbols transmitted on _k subcarriers.

The first channel equalization module is used to perform frequency domain equalization processing on the communication signal transmitted on the corresponding subcarrier output by the demapping of the subcarrier, for zero-forcing (ZF) equalization, and using ideal channel estimation, set the output The signal vector is {y _k (m)}, then

y _k (m)=g _k (m)/H _k (m+ε _k ), m=0, ..., N _k -1, m+ε _k ∈ Ω, where H _k (m+ε _k ) is the channel frequency response of the kth user on the m+ _εkth subcarrier.

If the plurality of receiving ends adopt the structure of the second receiving end, each receiving end at least includes: a second receiving module, a second down-conversion module, a second analog-to-digital conversion module, a spectrum shifting module, a second lower A pass filtering module, a downsampling module, a second prefix removal module, a second Fourier transform module, a second subcarrier demapping module and a second channel equalization module.

The second receiving module is used to receive the communication information sent to, and the second down-converting module is used to perform corresponding frequency conversion on the received radio frequency signal according to a preset carrier frequency to obtain a second broadband analog baseband signal, Wherein, the center frequency of the second broadband analog baseband signal is 0, and the second analog-to-digital conversion module is configured to perform processing on the second broadband analog baseband signal at a first sampling interval according to the preset processing bandwidth of each user. analog-to-digital conversion to obtain a first wideband discrete baseband signal, and the spectrum shifting module is used to perform frequency offset position information on the wideband analog OFDM baseband signal according to the received information of the corresponding user to the first The wideband discrete baseband signal is shifted correspondingly to obtain a corresponding second wideband discrete baseband signal with frequency offset, wherein the center frequency of the second wideband discrete baseband signal with frequency offset is the information of the corresponding user in the broadband analog The negative value of the frequency offset in the OFDM baseband signal, the second low-pass filter module is used to respond to the second broadband discrete baseband signal with frequency offset according to the preset processing bandwidth of the corresponding user low-pass filtering to obtain an oversampled narrowband discrete baseband signal, and the lower adopting module is used to process the oversampled narrowband signal according to the bandwidth of the preset wideband analog OFDM baseband signal and the processing bandwidth of the corresponding user The discrete baseband signal is correspondingly down-sampled to obtain a critically sampled user narrowband discrete baseband signal, the second prefix removal module is used to remove the prefix of the user narrowband discrete baseband signal according to a preset rule, and the second Fourier transform The module is used to perform Fourier transform of the second number of points on the user's narrowband discrete baseband signal with the prefix removed according to the preset processing bandwidth of the corresponding user, and the second carrier demapping module is used to extract each user from the Fourier transformed signal. For the communication signal on the corresponding subcarrier, the second channel equalization module is used to perform frequency domain equalization processing on the communication signal output by demapping the subcarrier, wherein the product of the first number of points and the first sampling interval Equal to the product of the second number of points and the second sampling interval, as can be seen from the above, the structure of the second receiving end is different from that of the first receiving end only in that it completes the spectrum shift and low-pass filtering of the radio frequency signal in the discrete domain, so The internal structure of each module will not be described in detail here.

In addition, the plurality of receiving ends may also adopt different structures, for example, some receiving ends adopt the structure of the first receiving end, and another part of receiving ends adopt the structure of the second receiving end, which will not be repeated here.

The smart OFDMA downlink communication method of the present invention mainly comprises the following steps:

1) The communication information to be sent to each user is subjected to corresponding subcarrier mapping after preprocessing.

2) performing inverse Fourier transform of the preset first point number on the communication information mapped by the subcarrier, wherein the preprocessing includes channel coding and digital modulation of the communication signal, etc., and those skilled in the art may also perform The communication signal is subjected to different preprocessing, and the modulated information is assumed to be a parallel symbol data block {a _k (m), m=0, 1, ..., N-1}, which is transformed by N-point IFFT to form a corresponding The data block sequence {b _k (m), m=0, 1, ..., N-1}, the relationship between each other obeys:

${\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; N</span>}}}\underset{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;mn</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \{</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0,1</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; .</span>$

3) Adding a prefix to the communication information to be sent to each user after the inverse Fourier transform according to preset rules, usually by copying a symbol of a certain length at the end of the signal obtained after the inverse Fourier transform to its front end to form A cyclic prefix, for example, copying a part of the tail of the data block output by the IFFT transformation to its front end to form a final data block symbol with a cyclic prefix, that is, the data sequence {b _k (n), n=0, 1, ..., N-1} is transformed into a complete OFDM symbol data sequence {c _k (n), n=-C, ..., -1, 0, 1, ..., N-1}, where, C is the cyclic prefix length, obviously,

$c_k\left(\mathrm{no}\right)=\frac{1}{\sqrt{N}}\underset{m=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{a}_k\left(m\right)\exp (j2\mathrm{\&pi;mn}/N),$ n=-C, . . . , -1, 0, 1, . . . , N-1.

4) Perform digital-to-analog conversion on the prefixed information at a preset first sampling interval to form a broadband analog OFDM baseband signal, for example, the discrete data sequence {c _k (n), n=-C , ..., -1, 0, 1, ..., N _k -1} perform digital-to-analog conversion with the first sampling interval T to obtain continuous OFDM symbol waveform s _k (t), then:

${\mathrm{the\; s}}_k\left(t\right)=\frac{1}{\sqrt{\mathrm{NT}}}\underset{m=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{a}_k\left(m\right)\exp \left(j2\mathrm{\&pi;m\&Delta;Ft}\right),t=[-\mathrm{CT},\mathrm{NT}),$ ΔF is the OFDM symbol subcarrier spacing transmitted by the base station.

5) Perform frequency conversion processing on the broadband analog OFDM baseband signal according to the preset carrier frequency to obtain a radio frequency signal. In this embodiment, the preset carrier frequency is f _c , that is, the analog signal s _k (t) Convert to RF signal

${\widetilde{\mathrm{the\; s}}}_k\left(t\right)=R_e\left[{\mathrm{the\; s}}_k\left(t\right)\exp \left(j2\mathrm{\&pi;}{f}_{c}t\right)\right],$ Where R _e [·] represents the real part, and f _c is the carrier frequency of the signal transmitted by the transmitting end.

6) Send the radio frequency signal and the subcarrier allocation information of the information to be sent to each user in the broadband analog OFDM baseband signal, wherein the subcarrier allocation information includes the frequency of each user Offset position information and subcarrier mapping rule information.

7) receiving the radio frequency signal sent to and the subcarrier allocation information of the information to be sent to each user in the broadband analog OFDM baseband signal (that is, the frequency offset position information and subcarrier mapping of each user rule information), and convert the radio frequency signal into a narrowband discrete baseband signal of each user according to the frequency offset position information of each user, the processing bandwidth and the preset carrier frequency, if the frequency conversion is performed on the radio frequency signal in the analog domain Processing, then described step 7) further includes steps:

(1) Convert the radio frequency signal into a first broadband analog baseband signal with a frequency offset according to the frequency offset position information of each user and a preset carrier frequency, wherein the first broadband analog baseband signal with a frequency offset The center frequency of the signal is the negative value of the frequency offset corresponding to the user's information in the broadband analog OFDM baseband signal, for example, for the Kth receiving end, its effect on the received radio frequency signal Frequency shift-(f _c +Δf _k ) to convert it into a broadband analog baseband signal r _k (t) with frequency offset. In the case of ideal synchronization and omitting the noise term, the kth broadband analog The baseband signal r _k (t) can be expressed as

${\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;\&Delta;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; NT</span>}}}\underset{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;m\&Delta;F</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;\&Delta;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; .</span>$

(2) According to the preset processing bandwidth of each user, the first broadband analog baseband signals with frequency offsets are respectively subjected to analog low-pass filtering to obtain corresponding narrowband analog baseband signals of each user, for example, for the kth The first wideband analog baseband signal r _k (t) with frequency offset can be low-pass filtered to filter out the out-of-band interference signal of the received signal. Assuming that the low-pass filter can completely filter out the out-of-band signal, the Kth user’s narrowband analog baseband signal Can be expressed as:

${\stackrel{\&OverBar;}{r}}_k\left(t\right)=\frac{1}{\sqrt{\mathrm{NT}}}\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}\underset{m\&Element;\mathrm{\&Omega;}}{\mathrm{\&Sigma;}}{a}_k\left(m\right){\mathrm{\&alpha;}}_l\exp \left(j2\mathrm{\&pi;m\&Delta;F}(t-{\mathrm{\&tau;}}_l)\right)\exp (-j2\mathrm{\&pi;\&Delta;}{f}_{k}t),$ Ω is the set of subcarriers containing useful signals.

(3) Perform analog-to-digital conversion on the narrowband analog baseband signals of each user at a preset second sampling interval according to the preset processing bandwidth of each user to obtain a narrowband discrete baseband signal of the user, such as an analog baseband signal r _k (t) The kth user narrow-band discrete signal output after A/D conversion can be expressed as:

为采样 $d_k\left(\mathrm{no}\right)=\frac{1}{\sqrt{N_k}}\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}\underset{m\&Element;\mathrm{\&Omega;}}{\mathrm{\&Sigma;}}{a}_k\left(m\right){\mathrm{\&alpha;}}_l\exp (j2\mathrm{\&pi;m}(\mathrm{no}-{\widetilde{\mathrm{\&tau;}}}_l)/N_k)\exp (-j2\mathrm{\&pi;}{\mathrm{\&epsiv;}}_k\mathrm{no}/N_k),$ in

for sampling

The delay spread of the l-th path normalized by the interval T _k , ε _k is the specific carrier offset of the k-th mobile terminal normalized by the OFDM demodulation subcarrier interval at the receiving end, that is, ε _k = Δf _k / ΔF, and ε _k is an integer. And if the frequency spectrum is shifted to the radio frequency signal in the discrete domain, then the step 7) includes the steps of:

(1) converting the radio frequency signal into a second broadband analog baseband signal according to a preset carrier frequency, the center frequency of the second broadband analog baseband signal being zero;

(2) performing analog-to-digital conversion on the second broadband analog baseband signal at a first sampling interval according to the preset broadband analog OFDM baseband signal bandwidth to obtain a first broadband discrete baseband signal;

(3) According to the frequency offset position information of the received information of each user in the broadband analog OFDM baseband signal, the first wideband discrete baseband signal is correspondingly shifted to obtain a frequency offset The second broadband discrete baseband signal, the center frequency of the second broadband discrete baseband signal with frequency offset is the negative value of the frequency offset of the information of each user in the broadband analog OFDM baseband signal;

(4) performing corresponding digital low-pass filtering on the second broadband discrete baseband signal with frequency offset according to the preset processing bandwidth of each user to obtain an oversampled narrowband discrete baseband signal;

(5) According to the bandwidth of the preset broadband analog OFDM baseband signal and the processing bandwidth of each user, the narrowband discrete baseband signal oversampled by the user is correspondingly down-sampled to obtain the critically sampled user narrowband discrete baseband Signal.

8) removing the prefix of each user's narrowband discrete baseband signal according to a preset rule, usually removing the cyclic prefix of each user's narrowband discrete baseband signal, for example, the kth user's narrowband discrete signal sequence {d _k (n)} The first C sampling values in are discarded, and the subsequent N sampling values are taken to form a parallel data sequence {e _k (n), n=0, 1, 2, ..., N _k -1 of length N _k }, then e _k (n)=d _k (n+C+1), n=0, 1, 2, . . . , N _k -1.

9) Perform the Fourier transform of the corresponding preset second points of the narrowband discrete baseband signals of each user whose prefix is removed according to the preset processing bandwidth of each user to obtain corresponding communication information. Of course, in order to obtain corresponding communication information, it is also necessary Performing frequency-domain equalization on the Fourier-transformed signal is a technology known to those skilled in the art, and will not be described in detail here. For example, for the parallel data sequence {e _k (n), n=0, 1 , 2,..., N _k -1} perform N _k point FFT transformation to obtain the corresponding parallel data sequence {g _k (m), m=0, 1, 2,..., N _k -1}, then :

${\mathrm{<span\; class="notranslate">\; g</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\underset{{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; \&Element;</span>\mathrm{<span\; class="notranslate">\; \&Omega;</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>$

0≤m≤N _k -1, n+ε _k ∈ Ω

in, $h_k\left(m^{\&prime;}\right)=\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_l\exp (-j2\mathrm{\&pi;}{m}^{\&prime;}{\widetilde{\mathrm{\&tau;}}}_l/N_k),$ is the channel frequency response on the m'th subcarrier of the kth receiver.

10) Extracting the communication signals of each user on the corresponding subcarriers from the Fourier transformed signals according to the received subcarrier allocation information.

11) Perform frequency-domain equalization processing on the communication signal transmitted on the corresponding sub-carrier output by demapping the sub-carrier. The only thing to note is that in order to ensure that the subcarrier bandwidth of the demodulated OFDM symbol at each receiving end is the same as the subcarrier bandwidth of the transmitted OFDM symbol, the duration of the effective part (excluding the cyclic prefix) of the OFDM symbol received at each receiving end must be equal to The duration of the effective part of the OFDM symbol transmitted by the base station is the same, that is, N _k T _k =NT, wherein, T _k is the second sampling interval adopted by the A/D conversion module of the kth receiving end, and N _k is the kth The second number of points of FFT transformation in the FFT transformation module of the receiving end, N is the first number of points of IFFT transformation in the IFFT transformation module of the transmitting end, and T is the first sampling interval of D/A conversion in the D/A conversion module of the transmitting end, thus It can be seen that the second number of points of the Fourier transform in the smart OFDMA downlink communication method is less than or equal to the first number of points of the inverse Fourier transform.

In summary, the smart OFDMA downlink communication system and communication method of the present invention form a broadband OFDMA signal by adopting a higher sampling frequency and a larger number of IFFT transformations at the transmitting end, and at each receiving end The narrowband baseband signal of each user is obtained through frequency conversion and filtering, and the information symbols of each user are demodulated by FFT transformation with a smaller number of points, so that the wireless resources of the broadband communication system can be flexibly adapted to the different business needs and needs of multiple users. terminal processing capability, thereby reducing the implementation complexity and power consumption of the mobile terminal.

Claims (14)

1. A smart OFDMA downlink communication system, characterized in that it comprises: The transmitting end is used to perform various processes on the communication information to be sent to each user to obtain a wideband analog OFDM baseband signal, and perform processing on the wideband analog OFDM baseband signal according to a preset carrier frequency frequency conversion to obtain a radio frequency signal, and then transmit the radio frequency signal and the subcarrier allocation information of the information to be sent to each user in the broadband analog OFDM baseband signal, wherein the Various processing for each user's information includes subcarrier mapping processing, inverse Fourier transform of the preset first point, and digital-to-analog conversion according to the preset first sampling interval; A plurality of receiving ends are respectively used to receive the radio frequency signal and the subcarrier allocation information of the information of each user in the broadband analog OFDM baseband signal, and perform various processing on the received radio frequency signal so that Each receiving end obtains the respective corresponding user narrowband discrete baseband signals, performs Fourier transform on the user narrowband discrete baseband signals with respective preset second points, and then extracts corresponding communication information of each user according to the subcarrier allocation information, Wherein, the various processes performed on the received radio frequency signal include the subcarrier allocation information in the broadband analog OFDM signal, the preset processing bandwidth and the preset The carrier frequency performs frequency conversion, filtering and analog-to-digital conversion. 2. The smart OFDMA downlink communication system as claimed in claim 1, characterized in that: the second points of the Fourier transforms adopted by the plurality of receiving ends are less than or equal to the Fourier transform adopted by the transmitting end The first point of the inverse transformation. 3. The smart OFDMA downlink communication system as claimed in claim 1, characterized in that: the second points of the Fourier transforms adopted by each of the plurality of receiving ends are respectively N ₁ , N ₂ … N _n , the preset second sampling intervals used for analog-to-digital conversion are respectively T ₁ , T ₂ ... T _n , the first number of points of the inverse Fourier transform used by the transmitter is N, and the adopted The first sampling interval is T, and the condition is satisfied: N _k T _k =NT, k=1, 2...n, n is the number of downlink receiving ends. 4. smart OFDMA downlink communication system as claimed in claim 1, is characterized in that described transmitter comprises: A subcarrier mapping module, configured to map the modulated communication information to be sent to each user to each corresponding subcarrier; An inverse Fourier transform module, configured to perform an inverse Fourier transform of the first point number on each of the subcarriers; A cyclic prefix adding module is used to add a prefix to the inverse Fourier-transformed signal according to preset rules; A digital-to-analog conversion module, configured to perform digital-to-analog conversion on the signal output by the cyclic prefix addition module at the first sampling interval to obtain a broadband analog OFDM baseband signal; The frequency up-conversion module is used to perform frequency conversion on the broadband analog OFDM baseband signal with a preset carrier frequency to obtain a radio frequency signal. 5. smart OFDMA downlink communication system as claimed in claim 1, is characterized in that any receiving end of described multiple receiving end comprises: The first down-conversion module is configured to perform corresponding conversion on the received radio frequency signal according to the subcarrier allocation information in the broadband analog OFDM baseband signal according to the preset carrier frequency and the received information of the corresponding user. frequency conversion to obtain a first broadband analog baseband signal with a frequency offset; The first low-pass filtering module is configured to perform analog low-pass filtering on the first broadband analog baseband signal with a frequency offset according to the preset processing bandwidth of the corresponding user to obtain a corresponding user narrowband analog baseband signal; The first analog-to-digital conversion module is configured to perform analog-to-digital conversion on the user narrowband analog baseband signal at a second sampling interval according to the preset processing bandwidth of the corresponding user to obtain a corresponding user narrowband discrete baseband signal; A first prefix removal module, configured to remove the prefix of the user narrowband discrete baseband signal according to preset rules; The first Fourier transform module is used to perform a second-point Fourier transform on the user narrowband discrete baseband signal from which the prefix has been removed; The first subcarrier demapping module is configured to obtain the signal on the subcarrier occupied by each user from the signal output by the first Fourier transform module according to the received subcarrier allocation information; The first channel equalization module is configured to perform frequency domain equalization processing on the signal output by the first subcarrier demapping module. 6. smart OFDMA downlink communication system as claimed in claim 1, is characterized in that any receiving end of described multiple receiving ends comprises: The second down-conversion module is configured to perform corresponding frequency conversion on the received radio frequency signal according to a preset carrier frequency to obtain a second broadband analog baseband signal, wherein the center frequency of the second broadband analog baseband signal is zero; The second analog-to-digital conversion module is configured to perform analog-to-digital conversion on the second broadband analog baseband signal at a first sampling interval according to a preset processing bandwidth of a corresponding user to obtain a first broadband discrete baseband signal; The spectrum shifting module is configured to perform corresponding spectrum shifting on the first wideband discrete baseband signal according to the subcarrier allocation information in the wideband analog OFDM baseband signal according to the received information of the corresponding user to obtain an effective a frequency-offset second broadband discrete baseband signal; The second low-pass filtering module is configured to perform corresponding digital low-pass filtering on the second broadband discrete baseband signal with frequency offset according to the preset processing bandwidth of the corresponding user to obtain a corresponding oversampled narrowband discrete baseband signal; The downsampling module is used to downsample the oversampled narrowband discrete baseband signal according to the preset bandwidth of the broadband analog OFDM baseband signal and the preset processing bandwidth of the corresponding user to obtain critical sampling The user's narrowband discrete baseband signal; The second prefix removal module is used to remove the prefix of the user's narrowband discrete baseband signal according to preset rules; the second Fourier transform module is used to remove the user's narrowband discrete prefix according to the preset processing bandwidth of the corresponding user The baseband signal is subjected to a Fourier transform of the second number of points; The second subcarrier demapping module is configured to obtain the signal on the subcarrier occupied by each user from the signal output by the second Fourier transform module according to the received subcarrier allocation information; The second channel equalization module is configured to perform frequency domain equalization processing on the signal output by the second subcarrier demapping module. 7. The smart OFDMA downlink communication system according to claim 1, wherein the subcarrier allocation information includes frequency offset position information and subcarrier mapping rules of each user. 8. A smart OFDMA downlink communication method, characterized in that it comprises steps: 1) Subcarrier mapping processing is performed on the communication information to be sent to each user after preprocessing; 2) performing inverse Fourier transform of the preset first point on the communication information processed by the subcarrier mapping; 3) adding a prefix to the communication information to be sent to each user after the inverse Fourier transform according to preset rules; 4) performing digital-to-analog conversion on the prefixed information at a preset first sampling interval to form a broadband analog OFDM baseband signal; 5) performing frequency conversion processing on the broadband analog OFDM baseband signal according to a preset carrier frequency to obtain a radio frequency signal; 6) sending the radio frequency signal and the subcarrier allocation information of the information to be sent to each user in the broadband analog OFDM baseband signal; 7) receiving the radio frequency signal sent to and the subcarrier allocation information of the information to be sent to each user in the broadband analog OFDM baseband signal, and according to the subcarrier allocation information, preset The processing bandwidth and the preset carrier frequency convert the radio frequency signal into a narrowband discrete baseband signal for each user; 8) removing the prefix of each user's narrowband discrete baseband signal according to a preset rule; 9) Perform Fourier transform of each preset second point corresponding to each user's narrow-band discrete signal from which the prefix is removed according to the preset processing bandwidth of each user; 10) Extracting the communication signals of each user from the Fourier-transformed signal according to the subcarrier allocation information, and performing equalization processing on the communication signals to obtain corresponding communication information of each user. 9. The smart OFDMA downlink communication method according to claim 8, characterized in that: said preprocessing includes channel coding and digital modulation. 10. The smart OFDMA downlink communication method according to claim 8, characterized in that: the second number of points is less than or equal to the first number of points. 11. smart OFDMA downlink communication method as claimed in claim 8, is characterized in that described step 7) also comprises the step: (1) converting the radio frequency signal into first wideband analog baseband signals with frequency offsets according to the subcarrier allocation information and the preset carrier frequency; (2) respectively subjecting the first broadband analog baseband signals with frequency offsets to analog low-pass filtering according to the preset processing bandwidths of each user to obtain corresponding narrowband analog baseband signals of each user; (3) Perform analog-to-digital conversion on the narrowband analog baseband signals of each user at respective preset second sampling intervals according to the preset processing bandwidth of each user to obtain corresponding narrowband discrete baseband signals of each user. 12. smart OFDMA downlink communication method as claimed in claim 8, is characterized in that described step 7) also comprises the step: (1) converting the radio frequency signal into a second broadband analog baseband signal according to a preset carrier frequency, the center frequency of the second broadband analog baseband signal being zero; (2) performing analog-to-digital conversion on the second broadband analog baseband signal at a first sampling interval according to the preset broadband analog OFDM baseband signal bandwidth to obtain a first broadband discrete baseband signal; (3) According to the subcarrier allocation information of the received information of each user in the broadband analog OFDM baseband signal, the corresponding spectrum shift is performed on the first broadband discrete baseband signal respectively to obtain each frequency A second broadband discrete baseband signal biased; (4) performing corresponding digital low-pass filtering on each of the second broadband discrete baseband signals with frequency offset according to the preset processing bandwidth of each user to obtain each oversampled narrowband discrete baseband signal; (5) According to the bandwidth of the preset wideband analog OFDM baseband signal and the processing bandwidth of each user, the oversampled narrowband discrete baseband signals are respectively down-sampled to obtain each critically sampled narrowband user Discrete baseband signal. 13. The smart OFDMA downlink communication method as claimed in claim 10 or 11 or 12, characterized in that: the product of the first number of points and the first sampling interval is equal to the second number of points and The product of the second sampling interval. 14. The smart OFDMA downlink communication method according to claim 8, characterized in that: the subcarrier allocation information includes frequency offset position information and subcarrier mapping rules of each user.

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