CN116668251A

CN116668251A - OFDM communication system and method for discrete shared spectrum

Info

Publication number: CN116668251A
Application number: CN202310562709.XA
Authority: CN
Inventors: 段红光; 周云康; 郑建宏; 罗一静
Original assignee: Chongqing University of Post and Telecommunications
Current assignee: Chongqing University of Post and Telecommunications
Priority date: 2023-05-18
Filing date: 2023-05-18
Publication date: 2023-08-29

Abstract

The invention relates to an OFDM communication system and method of discrete shared spectrum, belonging to the technical field of mobile communication. The system comprises a transmitting end, a receiving end and a shared information module. The invention independently encodes the data carried by each subcarrier in the OFDM communication system, and independently adds check information; subcarriers of the OFDM time-frequency resource block are continuously allocated in a time domain and are discretely allocated in a frequency domain for use; each subcarrier adopts independent pilot signals to independently perform channel estimation and channel equalization; the time-frequency resource block of the OFDM system adopts a mode of firstly mapping a time domain and then mapping a frequency domain; the receiving end can receive the correct data block under the condition that a plurality of subcarrier interferences exist in the OFDM system and the subcarrier distribution of the discrete shared frequency domain is uneven, so that the OFDM system is suitable for the discrete shared frequency spectrum resource system.

Description

OFDM communication system and method for discrete shared spectrum

Technical Field

The invention belongs to the technical field of mobile communication, and relates to an OFDM communication system and method of discrete shared spectrum.

Background

In OFDM systems, to provide frequency utilization and avoid interference between different systems, the radio resource spectrum is typically used with a monolithic allocation, e.g., 5MHz, 10MHz, 20MHz bandwidth, etc., most typically the current 4GLTE and 5GNR communication systems. In the actual deployment of the network, the fixed allocation uses the frequency points and the bandwidths, so that the interference is greatly reduced, and the communication efficiency is improved. The mobile carrier fixes the frequency band, and the public network mobile communication system adopts a continuous spectrum allocation using mode, so that the daily high-speed communication requirement of people is basically met.

Besides public network mobile communication, there are many internet of things communication systems, such as wireless data transmission and energy internet communication requirements in industries of electric power, gas, civil air defense, water service and the like, and frequency points which are distributed independently can be determined and limited for the communication systems, and the communication systems can only be used in a sharing mode, and the frequency spectrum cannot be ensured to be continuous, so that the requirement of the communication rate of the mobile internet of things is greatly limited.

The domestic 223MHz frequency band is a frequency band which can be shared by wireless data in industries such as electric power, gas, civil air defense, water service and the like, 223MHz to 235MHz are required according to the Chinese non-commission, the total 12MHz bandwidth is the shared frequency band, 25KHz bandwidth interval allocation is adopted in the allocation process for use, subcarrier numbers are from 0 to 479, and 480 subcarriers are counted. The method is characterized in that subcarriers special for light industry and building industry, light industry and earthquake industry, military industry and earthquake industry are divided, and other subcarriers are shared frequency points. The frequency points used by the communication system are in discrete distribution state in the whole frequency band, and part of the frequency points can be shared and used by a plurality of systems, which is called a discrete shared spectrum system.

There are many methods for discrete shared spectrum use, with single subcarrier modulation, using only allocated fixed 25KHz subcarriers, but this method is narrow in bandwidth and provides limited rates. The multi-carrier use is currently commonly performed in an OFDM (OFDM, orthogonalFrequency division multiplexing) mode. In the OFDM system, the time-frequency resource usage is shown in fig. 1. The sub-carriers are divided into different sub-carriers in the frequency domain and the OFDM symbols are divided into different time domains. In the scheduling process of system resources, a time-frequency resource block is adopted for scheduling. One modulation symbol may be carried by one resource unit corresponding to each subcarrier and each OFDM symbol, and the resource unit is called a resource element.

In existing OFDM systems, the order in which the modulated symbols are mapped to resource blocks is first the frequency domain mapping order, from low to high, and then the time domain mapping order, as shown in fig. 2. The resource mapping starts from the first OFDM symbol resource element, i.e. the first subcarrier starts to map to the last subcarrier of the first OFDM symbol, then maps the second OFDM symbol resource element, i.e. the first subcarrier starts to map to the last subcarrier of the first OFDM symbol, …, and finally maps all resource blocks.

The OFDM system resource block using method is suitable for the current public network system, namely, a system with fixed frequency domain resources. But is not suitable for internet of things systems, particularly discrete shared spectrum systems. There are in particular the following problems.

First: in the existing OFDM communication system, a method for detecting subcarrier interference cannot be supported, and in the time-frequency resource block mapping, if a plurality of subcarrier interference exists, the whole data block is incorrectly analyzed, and which subcarriers are interfered cannot be detected.

Second,: in a public network or a typical OFDM system, the pilots will be distributed as much as possible in both time and frequency domains so that the system can estimate the corresponding channel characteristics of each resource block element. Because the sub-carrier distribution of the scattered shared frequency domain is uneven, the uniform pilot frequency distribution mode cannot be fully applied to the scattered shared frequency spectrum system.

In view of the above, the discrete shared spectrum OFDM system is different from the conventional OFDM in terms of radio resources, and needs to be redesigned.

Disclosure of Invention

Accordingly, an object of the present invention is to provide an OFDM communication system and method for discrete shared spectrum, which solve the problem that when the existing OFDM communication system uses the discrete shared spectrum resources, due to the mapping of time-frequency resource blocks, there are a plurality of subcarrier interferences and uneven subcarrier distribution in the discrete shared frequency domain, so that the receiving end cannot receive the correct data block. The invention carries out independent coding for the data carried by each subcarrier in the OFDM communication system, independently adds check information, continuously distributes the subcarriers of the OFDM time-frequency resource block on the time domain, uses the discrete distribution on the frequency domain, independently carries out channel estimation and channel equalization by adopting independent pilot signals for each subcarrier, and enables the OFDM system to receive correct data blocks when a plurality of subcarrier interferences exist in the OFDM system and the subcarriers of the discrete shared frequency domain are unevenly distributed by adopting a mode of mapping the time domain and then mapping the frequency domain, thereby being applicable to the discrete shared frequency spectrum resource system.

In order to achieve the above purpose, as shown in fig. 3-5, the present invention provides the following technical solutions:

an OFDM communication system of discrete shared spectrum, the system includes a transmitting end, a receiving end and a shared information module;

the transmitting end comprises a first transmission data module, a block dividing module of a block coding block, a subcarrier coding block module, a channel coding module, a modulation module, a first pilot frequency module and an OFDM mapping module;

the receiving end comprises an OFDM demapping module, a pilot frequency module II, a channel estimation module, a channel equalization module, a demodulation module, a channel decoding module, a subcarrier coding block decoding module, a block coding block assembling module and a data transmission module II;

the shared information module comprises a block code retransmission and subcarrier mapping table, which is completed by signaling interaction of a transmitting end and a receiving end;

the transmitting terminal transmits and detects whether the sequence number of the transmission block of the transmission data block is used up or not;

the block dividing module of the block coding block divides the transmission data block into segments to obtain a divided block coding block;

the sub-carrier coding block module performs segmentation processing on the obtained segmented block coding blocks to obtain segmented sub-carrier coding blocks, and independently adds verification information to each obtained segmented sub-carrier coding block; the first segmented sub-carrier coding block comprises block coding block head information, wherein the block coding block head information comprises a transmission sequence number, an intra-block coding sequence number and a transmission block ending identifier;

The channel coding module independently codes the obtained segmented sub-carrier coding blocks, and the coded segmented sub-carrier coding blocks are modulated by the modulation module to form modulation symbols, namely bearing data symbols, wherein the number of the modulation symbols generated by each sub-carrier resource is the same as the number of OFDM symbols of a transmission resource block;

mapping the formed bearing data symbols and pilot symbols to subcarrier resources of a transmission resource block by using the OFDM mapping module, wherein each subsection subcarrier codes the generated bearing data symbols and corresponds to one subcarrier resource on the transmission resource;

the OFDM mapping module maps a time domain firstly and then maps a frequency domain;

after mapping transmission resource blocks of all the segmented subcarrier coding blocks, OFDM modulation is carried out, and the OFDM modulation is transmitted to the air through radio frequency;

the OFDM demapping module receives frame data from a wireless channel, and performs OFDM demodulation on the received data, wherein the OFDM demodulation refers to converting an OFDM signal from a time domain signal into a frequency domain signal, and extracting time-frequency transmission data block data;

the subcarriers of the time-frequency transmission block data are continuously allocated in the time domain and are discretely allocated in the frequency domain for use;

extracting pilot symbols and bearing data symbols of subcarriers from a time-frequency transmission resource block, independently performing channel estimation in the channel estimation module by utilizing independent pilot symbols, and independently performing equalization processing on the bearing data symbols in the channel equalization module;

The demodulation module demodulates the data carrying symbol after subcarrier equalization to obtain a log likelihood value of the data carrying symbol;

the channel decoding module performs channel decoding on the log likelihood values of the obtained bearing data symbols to obtain subcarrier coding block data;

the block coding assembly module combines continuous subcarrier coding block data to form a complete block coding block;

the second transmission data block receives the correct block code block, and the block code is put into the corresponding transmission block buffer memory according to the transmission block sequence number; and the second transmission data block receives all correct block coding blocks to form a complete data block, and submits the complete data block to a high-level protocol stack to clear the buffer memory of the corresponding transmission block sequence number.

A method of OFDM communication of a discrete shared spectrum, the method comprising the steps of:

s1: the method comprises the steps that a transmission data module receives a data block transmitted from a high-level protocol stack, a transmitting end detects whether a transmission block sequence number of the transmission data block is used up or not, and if an unused transmission block sequence number exists, the unused transmission block sequence number is used;

s2: the block dividing module of the block coding block carries out sectional processing on the transmission data block to obtain a sectional block coding block;

S3: the sub-carrier coding block module performs segmentation processing on the obtained segmented block coding blocks to obtain segmented sub-carrier coding blocks, and independently adds verification information to each obtained segmented sub-carrier coding block; the first sub-carrier coding block comprises block coding block head information, wherein the block coding block head information comprises a transmission sequence number, an intra-block coding sequence number and a transmission block ending identifier;

s4: the channel coding module independently codes the obtained segmented sub-carrier coding blocks, the coded segmented sub-carrier coding blocks are modulated by the modulation module to form modulation symbols, namely bearing data symbols), and the number of the modulation symbols generated by each sub-carrier resource is the same as the number of OFDM symbols of the transmission resource block;

s5: mapping the formed bearing data symbols and pilot symbols to subcarrier resources of a transmission resource block by using an OFDM mapping module, wherein each subcarrier codes the generated bearing data symbols and corresponds to one subcarrier resource on the transmission resource;

the mapping in the S5 is firstly to map the time domain and then to map the frequency domain;

s6: after mapping transmission resource blocks of all subcarrier coding blocks, carrying out OFDM modulation and transmitting the OFDM modulation to the air through radio frequency;

S7: the OFDM demapping module receives frame data from a wireless channel, and performs OFDM demodulation on the received data, wherein the OFDM demodulation refers to converting an OFDM signal from a time domain signal into a frequency domain signal, and extracting time-frequency transmission data block data;

the subcarriers of the time-frequency transmission data block in the S7 are continuously allocated in the time domain and are discretely allocated in the frequency domain for use;

s8: extracting pilot frequency symbols and bearing data symbols of subcarriers from the transmission data block, independently performing channel estimation in a channel estimation module by utilizing independent pilot frequency symbols, and independently performing equalization processing on the bearing data symbols in a channel uniformity module;

s9: demodulating and channel decoding the data carrying symbols after subcarrier equalization to obtain subcarrier coding block data;

s10: the block coding assembly module combines the continuous subcarrier coding block data to form a complete block coding block;

s11: detecting whether the sub-carrier coding check of the block coding is correct or not, wherein all sub-carrier checks are correct, and the block coding participates in the second combination of the transmission data block; the check error of the first subcarrier coding block is directly discarded; the first subcarrier code block is checked correctly, other subcarrier check blocks fail to check, the transmission block sequence number and the intra-block code sequence number in the block code block head are taken out, the receiving end retransmits the proposed transmission block sequence number and the intra-block code sequence number to inform the transmitting end of retransmitting the correct block code block of the error subcarrier code block through a block code block retransmitting module;

The receiving terminal feeds back the subcarrier mapping table to the transmitting terminal, which subcarriers carried on the subcarriers can not be correctly received, recommends the subcarrier mapping table to the forbidden subcarrier list of the transmitting terminal, and the transmitting terminal finally determines which specific subcarriers are used;

s12: the second transmission data block receives the correct block code block, and the block code is put into the corresponding transmission block buffer memory according to the transmission block sequence number;

s13: the second transmission data block receives all correct block coding blocks to form a complete data block, and submits the complete data block to a high-level protocol stack to clear the buffer memory of the corresponding transmission block sequence number;

further, the first subcarrier coding block of the block coding block in S2 includes a coding block header, a checksum and bearing data, and the other subcarrier coding blocks are composed of bearing data and checksum data.

Further, the transmission block sequence numbers in S3 are recycled, and the intra-block coding sequence number of each segment is unique.

Further, in S3, the end of transmission block flag is set to "1" to indicate the last block of the transmission data block, and the end of transmission block flag is set to "0" to indicate the middle block of the transmission data block.

Further, in the step S9, the channel decoding is to perform soft information decoding on the demodulated data.

Further, the block retransmission method includes the following steps:

s71: the receiving end receives all the block coding blocks carried by the transmission resource block, sequentially takes out the block coding blocks from the data carried by the transmission resource block, and checks whether the check of each subcarrier coding block in each block coding block is correct;

s72: if the subcarrier code in the block code block has a check error, the subcarrier number corresponding to the check error is recorded and used as the basis of whether the subcarrier frequency point is continuously used or not, the block code block where the check error subcarrier code block is located needs to be retransmitted, and a receiving end informs a transmitting end through the sequence number of a transmission block in the block code block head and the sequence number of an intra-block code;

s73: all the subcarrier codes in the block coding block are checked to be correct, the subcarrier numbers corresponding to the correct subcarrier codes in the block coding block are recorded, and whether the correct subcarrier frequency points are continuously used or not is evaluated;

s74: the block head information of the block code is taken out from the correct block code, the block code block is stored in the corresponding transmission block buffer according to the transmission block sequence number and the intra-block code sequence number, the block code block containing the transmission block end identifier of 1 is correctly received in the block code block, and whether the transmission data block has received all the segments is checked;

S75: the method comprises the steps that all the block coding blocks in the transmission data block are received, bit data of the transmission data block are taken out from all the block coding blocks, the bit data of the transmission data block are sequentially assembled into a complete transmission data block, the transmission data block is submitted to a high-layer protocol stack, a sending end receives feedback from a receiving end, the feedback indicates that all the block coding blocks in the retransmission transmission data block are received, and the sending end clears the retransmission transmission data block and prepares to send the next transmission data block.

Further, the step S73 of evaluating whether the correct subcarrier frequency point is continuously used in the following steps specifically includes: setting a preferred initial value of each subcarrier, wherein the subcarrier coding block corresponding to the subcarrier is correct in verification and analysis, and the preferred value of the correct subcarrier value is increased by one bonus point; checking and analyzing errors by subcarrier coding blocks corresponding to subcarriers, and subtracting punishment points from the optimal value of the wrong subcarriers; the transmitting end selects the subcarrier with larger preferred value to use, and in the selection process, the preferred value is the same, and the subcarrier frequency point is selected randomly until the number of subcarriers needed by the transmission resource block is selected.

The invention has the beneficial effects that:

first: the invention proposes an OFDM mode, each subcarrier is independently encoded, verification information is independently added, and the spectrum resource which can be used by the system is determined by monitoring the subcarrier interference condition of each transmission.

Second,: the method comprises the steps of designing an OFDM system transmission resource block, namely continuously distributing subcarriers of an OFDM time-frequency resource block in a time domain, and discretely distributing and using the subcarriers in a frequency domain, wherein each subcarrier adopts an independent pilot signal, and channel estimation and channel equalization are independently carried out.

Third,: in the method, in order to detect subcarrier interference, a method of mapping a time domain and then a frequency domain is adopted. Each subcarrier is implemented for separate use in OFDM technology.

Fourth,: the invention provides a complete OFDM system scheme for the characteristic of discrete shared spectrum, and the content comprises a receiving and transmitting processing flow of a physical layer link.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and other advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the specification.

Drawings

For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in the following preferred detail with reference to the accompanying drawings, in which:

FIG. 1 is a prior art distribution diagram of discrete shared spectrum resources;

fig. 2 is a diagram of a conventional modulation symbol transmission mapping scheme in the prior art;

FIG. 3 is a diagram of a discrete shared spectrum OFDM system in accordance with the present invention;

fig. 4 is a flow chart of transmitting a transmission data block according to the present invention;

fig. 5 is a flow chart of the receiving end receiving transmission data blocks in the present invention;

FIG. 6 is a block diagram of a discrete shared spectrum wireless link processing of the present invention;

fig. 7 is a block diagram of the first subcarrier code block in the block code block of the present invention;

FIG. 8 is a block header composition diagram of a block code according to the present invention;

FIG. 9 is a block diagram of a block coded block according to the present invention;

fig. 10 is a block structure diagram of a block coding for transmission resource block bearing according to the present invention;

fig. 11 is a diagram of pilot frequency distribution on a subcarrier resource block in the present invention;

FIG. 12 is a diagram of an OFDM mapping method in a discrete shared spectrum in accordance with the present invention;

fig. 13 is a mapping relationship diagram of a transmission data block and a transmission resource block according to the present invention;

FIG. 14 is a flow chart of the reorganization of transmission data according to the present invention;

fig. 15 is a flow chart of subcarrier frequency point estimation and use in accordance with the present invention.

FIG. 16 is a graph of simulated performance of a normal AWGN channel in accordance with the present invention;

FIG. 17 is a graph of a simulation of the performance of the present invention in the presence of randomly interfering subcarriers;

Detailed Description

Other advantages and effects of the present invention will become apparent to those skilled in the art from the following disclosure, which describes the embodiments of the present invention with reference to specific examples. The invention may be practiced or carried out in other embodiments that depart from the specific details, and the details of the present description may be modified or varied from the spirit and scope of the present invention. It should be noted that the illustrations provided in the following embodiments merely illustrate the basic idea of the present invention by way of illustration, and the following embodiments and features in the embodiments may be combined with each other without conflict.

Wherein the drawings are for illustrative purposes only and are shown in schematic, non-physical, and not intended to limit the invention; for the purpose of better illustrating embodiments of the invention, certain elements of the drawings may be omitted, enlarged or reduced and do not represent the size of the actual product; it will be appreciated by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.

The same or similar reference numbers in the drawings of embodiments of the invention correspond to the same or similar components; in the description of the present invention, it should be understood that, if there are terms such as "upper", "lower", "left", "right", "front", "rear", etc., that indicate an azimuth or a positional relationship based on the azimuth or the positional relationship shown in the drawings, it is only for convenience of describing the present invention and simplifying the description, but not for indicating or suggesting that the referred device or element must have a specific azimuth, be constructed and operated in a specific azimuth, so that the terms describing the positional relationship in the drawings are merely for exemplary illustration and should not be construed as limiting the present invention, and that the specific meaning of the above terms may be understood by those of ordinary skill in the art according to the specific circumstances.

Referring to fig. 6 to 17, for clarity of explanation, the present invention is applied to an actual OFDM system, and an electric power communication system using a discrete shared spectrum will be explained.

A first part: wireless link architecture for power communication system

The wireless link architecture of the power communication system is composed of a transmitting end link and a receiving end link. As shown in fig. 6.

The transmitting end comprises: transmission data block (carrying CRC), block partitioning, subcarrier coding block checking, channel coding, debugging, reference signal, OFDM mapping, OFDM modulation, and wireless transmission.

The receiving end comprises: radio reception, OFDM demodulation, OFDM demapping, reference signals, signal arrival estimation, channel equalization, demodulation, channel decoding, subcarrier coding block check, block combining, transport data block check.

In this embodiment, the block retransmission and subcarrier mapping table is a module for sharing information between the transmitting end and the receiving end, and is completed by signaling interaction. The block code retransmission needs the receiving end to inform the transmitting end of specific retransmission transmission data blocks (transmission block sequence numbers) and block code blocks (intra-block code sequence numbers), and the block code blocks needing retransmission are determined by the block code block heads in the block code blocks. The subcarrier mapping table is fed back to the transmitting end by the receiving end, subcarrier codes carried on which subcarriers can not be correctly received, recommended to the forbidden subcarrier list of the transmitting end, and finally the transmitting end determines which specific subcarriers are used for carrying subcarrier coding blocks.

In this embodiment, frequency domain resources may be used. The embodiment is applied to a power communication system, that is, a power private network communication system, and the frequency that can be used in the embodiment can only be the subcarrier that is allocated and shared by the power system and the subcarrier that is not allocated and shared by the power system. The subcarrier numbers that the system can use are: 20. 26, 28, 33, 37, 40, 44, 46, 48, 52, 56, 58, 202, 204, 206, 209, 212, 215, 218, 300, 306, 308, 313, 317, 320, 324, 326, 328, 332, 336, 340, 342, 345. The system cannot use subcarriers dedicated to light industry and building industry, light industry and earthquake industry and military industry, but other subcarriers in 223MHz to 235MHz cannot determine whether to be used by other systems, and the system uses the subcarrier resources according to actual wireless scene conditions.

In this embodiment, it is assumed that the system can use all subcarriers except for subcarriers dedicated to the light industry and the building industry, dedicated to the light industry and the earthquake industry, and dedicated to the military and the earthquake industry, continuously detect subcarrier interference conditions during use, and modify a subcarrier mapping table to record subcarriers that can be used in the system.

A second part: key component of electric power communication system

The following specifically describes the key procedure of the present embodiment according to the present invention.

(1) Transmission data block format requirements

As in fig. 6, the transmitting-side transport block (carrying CRC) and the receiving-side transport block check. In this embodiment, the transmitting-side higher layer protocol part is responsible for providing the transport data block, and the verification of the transport data block is added and checked by the higher layer protocol. The bit number of the transmission data block is determined by the number of particles of the transmission resource block, the modulation mode and the code rate of the channel coding and decoding. In this embodiment, after determining the transmission resource block, the size of the transmission data block is also determined, and the size of the transmission data block sent by the protocol meets the mapping requirement of the transmission resource block, and the higher layer protocol is responsible for completing the filling of the transmission data block.

(2) Block and merging of block coded blocks

According to the size of the transmission resource block, the transmission data block is subjected to block division processing, the transmission data block can be divided into a plurality of block coding blocks, and the block sequence numbers and the intra-block coding sequence numbers are packaged in the block coding block heads of the block coding blocks. Each block is composed of a plurality of sub-carrier code blocks. Each subcarrier code block contains bearing data and check data.

In this embodiment, a block header length of 9 bits of a block is defined, wherein a transmission block sequence number occupies 2 bits, and a cyclic coding manner, that is, 0,1,2,3,0,1,2,3, is adopted, and at most 4 (2 bits) transmission data blocks can be transmitted simultaneously. The transport block end identifier occupies 1 bit, 0 indicates that the present block is the middle block of the transport block, and 1 indicates that the block is the last block of the transport block. The intra-block coding sequence number occupies 6 bits, which means that the block coding block sequence number is coded by the block coding block when the block is transmitted, and at most 64 block codes are coded simultaneously; when a block code block is received by a receiving end, checking check bits of all sub-carrier code blocks in the code block, and if check errors of one sub-carrier code block exist, retransmitting the block code block data. The block header of the block is kept unchanged during retransmission.

Each subcarrier coding block adopts a cyclic check code with the length of 4 bits, a receiving end checks whether the check of each subcarrier coding block is correct or not every time the receiving end receives the subcarrier coding block, and records the check statistical result of each subcarrier at the receiving end as the basis for starting the corresponding subcarrier in the subsequent use. As shown in fig. 7 and 8.

A complete block structure is formed by a plurality of sub-carrier code blocks, wherein the first sub-carrier code block of each block comprises a block header, bearer data and check data. The other subcarrier coding blocks are composed of bearing data and check data. As shown in fig. 9.

A plurality of block code blocks that can be carried by one complete transmission resource block, as can be seen from the block code block header, each resource block can transmit data of 4 different transmission data blocks, and can carry at most 64 block code blocks, as shown in fig. 10.

(3) Channel coding and decoding

The channel coding is processed in the size of the subcarrier coding block, and each subcarrier coding block is also independently channel coded and decoded. With a typical Viterbi codec in this embodiment, the coding rate may be chosen to be both Viterbi and 1/2Viterbi 1/3. After the Viterbi encoder is performed on the transmitting side by using the bits, if Viterbi 1/2 encoding is used, the output bit number is the bit if Viterbi1/3 encoding is used. When the receiving end carries out channel decoding, a soft information decoding mode is adopted, a decoder inputs soft information, if Viterbi 1/2 decoding is adopted, the soft information is output, and if Viterbi1/3 decoding is adopted, the soft information is output.

(4) Modulation and demodulation process

In this embodiment, a modulation scheme may be supported by: the modulation process is completed by BPSK, QPSK and 16QAM modes, and the bit data of the subcarrier coding block is modulated into a debugging symbol, namely the bit sequence is modulated into a complex sequence. In the demodulation process, the received complex data is demodulated into likelihood pair values (LLR values for short), and finally the Viterbi decoder decodes the LLR into a bit sequence.

(5) OFDM mapping

Two kinds of symbols are mapped on OFDM time-frequency resource, one is modulation symbol data of subcarrier coding block, and the other is pilot reference symbol.

In this embodiment, the ratio of the resource elements occupied by the pilot and subcarrier coding blocks is 1:3, i.e. one of every 4 resource elements is used for pilot frequency, and 3 resource elements are used for transmitting subcarrier coding block symbols. Each subcarrier resource element in a transmission resource block constitutes a subcarrier resource block carrying a complete pilot block symbol and a complete subcarrier coding block symbol. The pilot frequency symbol is used for channel estimation, estimates the channel characteristics of the subcarrier in the time domain, and then carries out channel equalization. As shown in fig. 11.

On the OFDM resource mapping, according to the definition of the invention, mapping is performed according to the time domain sequence, and then the frequency domain mapping sequence is performed. The time domain mapping starts from the first OFDM symbol and increases in sequence to the last OFDM symbol of the transmission resource block. The frequency domain mapping starts from the first subcarrier of the resource block and sequentially increases to the last subcarrier of the transmission resource block for mapping. As shown in fig. 12. Further, the transmission resource blocks are allocated consecutively in time, but discrete states may occur in the frequency domain.

(6) OFDM modulation and demodulation

After the OFDM mapping is complete, OFDM modulation processing is carried out at the transmitting end, and a baseband waveform of wireless transmission is formed. The baseband signal is modulated to the 230MHz band by wireless transmission. At the receiving end, the wireless receiving module performs down-conversion processing on the received 230MHz wireless signal to obtain a baseband signal.

Third section: mapping procedure of transmission data block to transmission resource block

In the present invention, the mapping relationship between the transmission data block and the transmission resource block is relatively complex, and in the present embodiment, will be described with reference to fig. 13.

(1) The data processing flow of the transmitting end comprises the following steps:

step 1: the physical layer link receives a data block, i.e. a transport data block, which may be service data or signaling data, from a higher layer protocol stack to be sent. There is a correspondence between the bit data of the transmission data block and the transmission resource block size. The higher layer protocol stack is responsible for completing the filling or segmentation of the transmission data block, and the cyclic check is added at the tail of the transmission data block, and in this embodiment, a 16-bit cyclic check method is adopted.

Step 2: the transmitting end receives the transmission data blocks of the higher protocol stack, calculates the size of each block coding block according to the transmission resource blocks, and then carries out block division processing. The number of block coded blocks and subcarriers is a 1 to 4 relationship. The number of bits per block coded block is: 4 (N-4) -9, where N is the number of subcarrier coding block bearer bits: n= (L-R) M R.

As in part (1) of fig. 13.

Step 3: each block is divided into a plurality of sub-carrier encoded blocks, in this embodiment, each block is divided into 4 sub-carrier encoded blocks, wherein the first sub-carrier encoded block carries the number of bits N-9-4 (9 bits are the block header of the block and 4 bits are the cyclic check bits), so each block carries the total number of bits 4 x (N-4) -8.

As in part (2) of fig. 13.

Step 4: the block coding block is composed of sub-carrier coding blocks, each sub-carrier coding block length is N, n= (L-Ref) M R,

wherein: l is the number of transmission resource blocks OFDM, R is the code rate, ref is the number of pilots, (1/4) L, M is defined as the modulation mode, BPSK is 1, QPSK is 2, and 16QAM is 3 in this embodiment.

As in part (3) of fig. 13.

Step 5: after each subcarrier coding block is subjected to channel numbering and modulation, a modulation symbol is formed, and the modulation symbol can be directly mapped to time-frequency resource elements of a transmission resource block. The subcarrier resource carries not only the modulation symbols of the subcarrier code blocks but also pilot symbols. In this embodiment, the pilot occupies 1/4 of the resources of the entire subcarrier resource block.

As in part (4) of fig. 13.

Step 6: each subcarrier coding block is mapped to subcarrier resources, and all subcarrier resources are mapped to form a complete transmission resource block.

And transmitting the resource block, and performing FFT change on each OFDM symbol to form an OFDM baseband signal of a time domain.

As in part (5) of fig. 13.

(2) The data processing flow of the receiving end comprises the following steps:

step 1: the receiving end demodulates the received OFDM data of the time domain into the OFDM data of the frequency domain through the wireless receiving and OFDM demodulation processes. Transmission resource block data is extracted from the OFDM data.

As in part (5) of fig. 13.

Step 2: and extracting the data of each subcarrier resource block in each transmission resource block, and extracting pilot frequency data and subcarrier coding block modulation data in the subcarrier resource block. And carrying out channel estimation by utilizing pilot frequency data, and estimating a channel characteristic matrix of the whole subcarrier resource block. And then carrying out channel equalization on the subcarrier code block modulation data by using the channel characteristic matrix.

As in part (4) of fig. 13.

Step 3: and demodulating the modulation symbol of each subcarrier coding block and carrying out channel decoding to obtain subcarrier coding block data. In this step, it is necessary to check whether the cyclic check of each subcarrier code block is correct, as a basis for whether the subcarrier is subsequently enabled.

As in part (3) of fig. 13.

Step 4: and analyzing each subcarrier resource block in the transmission resource block to obtain a block coding block. The number of carrying bits per subcarrier code block is the same, and the first subcarrier code block of each block code block comprises an 8 bit block code block header.

In this step, the receiving end will check the check bits in all the block code blocks, and if there is an incorrect check of the subcarrier code blocks in the block code blocks, the receiving end needs to send a retransmission of this block code block. In the present embodiment, retransmission is performed in a block coding block size.

As in part (2) of fig. 13.

Step 5: and analyzing all the block coding blocks to obtain a complete transmission data block.

As in part (1) of fig. 13.

Fourth part: block retransmission and transport data block reassembly

In this embodiment, the receiving end has 4 buffers, which correspondingly receive 4 different transmission data blocks, each receiving buffer performs a check to determine whether the transmission data block is received after receiving a block coding block, and if all segments of the transmission data block are received, the transmission data block data is taken out from the block coding blocks of the buffers, and the complete transmission data block is assembled and sent to the higher protocol stack. The specific flow is shown in fig. 14.

Step 1: the receiving end receives all the block coding blocks carried by the transmission resource block, and sequentially takes out the block coding blocks from the data carried by the transmission resource block. Checking whether the check of each subcarrier code block in each block code block is correct. As shown in steps 1 and 2 of fig. 14.

Step 2: if the subcarrier codes in the block coding block have check errors, the subcarrier numbers corresponding to the check errors are recorded and used as the basis of whether the subcarrier frequency points are continuously used or not. And the block code block of the sub-carrier code block needs to be retransmitted. The receiving end informs the transmitting end through the transmission block sequence number and the intra-block coding sequence number in the block head of the block coding. As shown in steps 3,4,5 of fig. 14.

Step 3: the subcarrier coding check in the block coding block is correct, and the subcarrier number corresponding to the subcarrier coding in the block coding block is recorded so as to evaluate whether the subcarrier frequency point is continuously used or not. As shown in steps 3 and 6 of fig. 14.

Step 4: and extracting the block header information of the block code from the correct block code, and storing the block code into a corresponding transmission block buffer according to the transmission block sequence number and the intra-block code sequence number. If a block coded block containing a transport block end identifier of 1 has been correctly received in the block coded block. It is checked whether the transport block has received all segments. As shown in steps 7 and 8 of fig. 14.

Further described, the intra-block coding sequence number of the block header starts from 0 to the last block. The transport block end identifier in the block header indicates whether it is the last block of the block. The transport block end identifier has a bit length, "1" indicating the last block, and "0" indicating the middle block.

Step 5: if all the block code blocks in a transmission data block are received, the bit data of the transmission data block are taken out from all the block code blocks, and are assembled into a complete transmission data block in sequence, and the transmission data block is submitted to a higher layer protocol stack. The buffer of the transport block is cleared for preparing to receive the next transport block. And when the sending end receives feedback from the receiving end and indicates that all the block coding blocks in the transmission data block are received, the sending end clearly shows the transmission data block and prepares to send the next transmission data block. As shown in fig. 14, step 9, 10.

Fifth part: subcarrier frequency point evaluation using method

In this embodiment, a preference value is defined for each subcarrier, and the preference value of each subcarrier is divided into 0 min and 12 min at the highest. The initial value of the optimal value of each subcarrier is set to be 12 minutes in the system. If the subcarrier coding block check analysis corresponding to the subcarrier is correct, the subcarrier preference value is increased by 1 minute, and if the subcarrier coding block check analysis corresponding to the subcarrier is incorrect, the subcarrier preference value is subtracted by 3 minutes. As shown in particular in fig. 15.

Step 1: in this embodiment, 480 subcarrier frequency points can be used in total, and each subcarrier has a preferred value. Since the number of intra-block coding sequence numbers in the block coding blocks is 6 bits in design, the maximum number of the intra-block coding sequence numbers is 64 block coding blocks, and each block coding block comprises 4 sub-carrier coding blocks, 256 sub-carrier frequency points can be used at maximum for each transmission resource block. As shown at step 1 in fig. 15.

Step 2: the receiving end analyzes the subcarrier coding block carried on the transmission resource block every time the receiving end transmits the data on the resource block, and checks whether the subcarrier coding block check is correct. If the check is correct, the sending end does not need to be notified, the sending end checks the check of the default subcarrier coding block to be correct, and if the check is wrong, the receiving end needs to notify the sending end of the subcarrier coding block transmitted on a specific subcarrier to be wrong.

At the transmitting end, if the check of the carrier coding block of the receiving terminal is determined to be correct, 1 is added to the preferred value of the corresponding subcarrier, otherwise 3 is subtracted. If smaller than the minimum value 0 of the preferred value, the minimum value is taken, and if larger than the maximum value 12 of the preferred value, the maximum value 12 is taken. As shown in step 2 of fig. 15.

Step 3: after the transmitting end transmits the transmission data block, the available sub-carriers are selected. According to the definition of the invention, the sending end sorts the frequency points of the alternative 480 subcarriers according to the preference value, and preferably selects the subcarriers with larger preference value for use from the big to the small principle. In the selection process, if the preferred values are the same, the subcarrier frequency points are randomly selected until the number of subcarriers needed by the transmission resource block is selected. As shown in step 3 of fig. 15.

Step 5: the transmitting end informs the receiving end through the subcarrier mapping table, and the receiving end uses the subcarrier mapping to receive the transmission resource block data from the transmitting end. As shown at step 4 in fig. 15.

In order to verify the correctness of the scheme, in the present embodiment, according to the above design scheme and flow, the following simulation parameters are adopted, as shown in table 1. And (5) performing link simulation.

Table 1 simulation parameter table

Simulation parameters	Content of parameters
		Subcarrier spacing	25KHz
Operating band range	223MHz to 235MHz (12 MHz)
		Shared band bandwidth range	480 subcarriers, bandwidth 25x480 = 12MHz
Carrying data bandwidth	40 subcarriers, bandwidth 25x40 = 1MHz
		OFDM symbol number	36
FFT/IFFT point number	1024
		Channel coding	Turbo coding and decoding
Modulation scheme	QPSK
		Channel model	AWGN+ frequency point random interference model
Maximum number of retransmissions of a data block	4 times

In the simulation, two channel models, namely an AWGN channel model and an AWGN plus subcarrier random interference channel model are adopted for verification.

First: the AWGN channel model verifies that the system is working properly as shown in fig. 16.

In the simulation of the AWGN channel model, the interference condition of the subcarrier does not exist, and as shown in fig. 16, in the condition of poor SNR, the transceiver end still cannot correctly transmit and receive after 4 times of (4 times of maximum retransmission times are set in the simulation), the retransmission probability reaches 0.4 (40%), the bit error rate is 5%, and when the snr= -4db is reached, the transmission performance is provided, but retransmission transmission is basically not needed, and the transmission can be correct every time. All the design flows and modes of the invention can work normally.

Second,: awgn+ subcarriers interfere randomly, and the system recognizes the ability to track interfering subcarriers, as shown in fig. 17.

In the simulation of AWGN+random interference subcarrier channel, 2 random interference subcarriers exist in each data block transmission process, and under each SNR simulation condition, the interference subcarriers are detected first and then removed from usable subcarriers.

When snr= -4dB to-1 dB, the interference sub-carrier cannot be determined once retransmission due to the influence of gaussian white noise, but after several retransmissions, the position of the interference sub-carrier can also be determined by adopting the method of the invention. As is apparent from fig. 17, as the SNR increases, the speed of detecting the interfering sub-carriers in the present invention is also faster and the number of retransmissions is smaller.

The performance is completely improved when snr=1 dB, the interference sub-carrier can be determined only by transmitting the data block once and twice although the sub-carrier interference exists, when snr=1 dB, the retransmission times tend to 0, the error rate also tends to 0, and the simulation result shows that the random interference sub-carrier has no influence on the communication basically by adopting the method of the invention.

Finally, it is noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications and equivalents may be made thereto without departing from the spirit and scope of the present invention, which is intended to be covered by the claims of the present invention.

Claims

1. An OFDM communication system for discrete shared spectrum, characterized by: the system comprises a sending end, a receiving end and a shared information module;

2. An OFDM communication method of discrete shared spectrum, characterized in that: the method comprises the following steps:

s13: and the second transmission data block receives all correct block coding blocks to form a complete data block, and submits the complete data block to a high-level protocol stack to clear the buffer memory of the corresponding transmission block sequence number.

3. A method of discrete spectrum shared OFDM communication as claimed in claim 2, wherein: the first subcarrier coding block of the block coding block in the S2 comprises a coding block head, check sum bearing data, and other subcarrier coding blocks consist of the bearing data and the check data.

4. A method of discrete spectrum shared OFDM communication as claimed in claim 2, wherein: and S3, the sequence numbers of the transmission blocks are circularly used, and the intra-block coding sequence number of each segment is unique.

5. A method of discrete spectrum shared OFDM communication as claimed in claim 2, wherein: the transmission block end identifier in S3 is set to "1" and indicates the last block coded in the transmission data block, and the transmission block end identifier is set to "0" and indicates the middle block coded block.

6. A method of discrete spectrum shared OFDM communication as claimed in claim 2, wherein: the channel decoding in S9 is to perform soft information decoding on the demodulated data.

7. A method of discrete spectrum shared OFDM communication as claimed in claim 2, wherein: the block retransmission method comprises the following steps:

8. The method for OFDM of the discrete shared spectrum of claim 7, wherein said step S73 of evaluating whether the correct subcarrier frequency point is continued to be used subsequently comprises: setting a preferred initial value of each subcarrier, wherein the subcarrier coding block corresponding to the subcarrier is correct in verification and analysis, and the preferred value of the correct subcarrier value is increased by one bonus point; checking and analyzing errors by subcarrier coding blocks corresponding to subcarriers, and subtracting punishment points from the optimal value of the wrong subcarriers; the transmitting end selects the subcarrier with larger preferred value to use, and in the selection process, the preferred value is the same, and the subcarrier frequency point is selected randomly until the number of subcarriers needed by the transmission resource block is selected.