Discrete shared spectrum OFDM communication system and method

Abstract

The present invention relates to an OFDM communication system and method for discrete shared spectrum, and belongs to the field of mobile communication technology. The system includes a transmitting end, a receiving end, and a shared information module. The present invention independently encodes the data carried by each subcarrier in the OFDM communication system and independently adds verification information; the subcarriers of the OFDM time-frequency resource block are continuously allocated in the time domain and discretely allocated in the frequency domain; each subcarrier uses an independent pilot signal and independently performs channel estimation and channel equalization; the time-frequency resource block of the OFDM system adopts a method of first mapping the time domain and then mapping the frequency domain; so that the receiving end can receive the correct data block when there are multiple subcarrier interferences in the OFDM system and the subcarriers in the discrete shared frequency domain are unevenly distributed, thereby making the OFDM system suitable for discrete shared spectrum resource systems.

Description

Technical Field

[0001] The present invention belongs to the technical field of mobile communications and relates to an OFDM communication system and method for discrete shared spectrum. Background Art

[0002] In OFDM systems, to maximize frequency utilization and avoid interference between different systems, wireless spectrum resources are typically allocated in blocks, such as 5MHz, 10MHz, or 20MHz bandwidths. This is most typical in current 4G LTE and 5G NR communication systems. In actual network deployments, fixed frequency and bandwidth allocation significantly reduces interference and improves communication efficiency. Mobile operators use fixed frequency bands, while public mobile communication systems utilize continuous spectrum allocation, essentially meeting the needs of everyday high-speed communications.

[0003] In addition to public mobile communications, there are also numerous IoT communication systems, such as wireless data transmission and energy Internet communication needs in industries such as electricity, gas, civil air defense, and water. The frequency bands that can be allocated exclusively for these communication systems are very limited and can only be used in a shared manner. In addition, the spectrum cannot be guaranteed to be continuous, which will greatly limit the communication rate requirements of the mobile IoT.

[0004] China's domestic 223MHz frequency band is a shared frequency band for wireless data transmission in industries such as electricity, gas, civil air defense, and water. According to the China Radio and Television Administration (CNRAA), 223MHz to 235MHz, a total of 12MHz of bandwidth, is designated as a shared frequency band. Subcarriers are allocated at 25kHz intervals, with subcarriers numbered from 0 to 479, for a total of 480 subcarriers. Except for subcarriers dedicated to the light industry and construction sector, the light industry and seismic industry, and the military and seismic industry, all other subcarriers are shared frequencies. The frequencies used by communication systems are discretely distributed across the entire frequency band, and some frequencies can be shared by multiple systems. This is called a discrete shared spectrum system.

[0005] There are many ways to use discrete shared spectrum, such as single subcarrier modulation, which only uses a fixed 25KHz subcarrier. However, this method has a narrow bandwidth and limited rate. Currently, OFDM (Orthogonal Frequency Division Multiplexing) is commonly used for multi-carrier use. In the OFDM system, the time-frequency resource usage is as follows: Figure 1 As shown in the figure, the system is divided into different subcarriers in the frequency domain and different OFDM symbols in the time domain. System resource scheduling is performed using time-frequency resource blocks. Each subcarrier and OFDM symbol corresponds to a resource unit that can carry a modulation symbol. This resource unit is called a resource element.

[0006] In the existing OFDM system, the order in which 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, such as Figure 2 As shown in the figure, resource mapping starts from the first OFDM symbol resource element, that is, the first subcarrier is mapped to the last subcarrier of the first OFDM symbol, and then maps the second OFDM symbol resource element, that is, the first subcarrier is mapped to the last subcarrier of the first OFDM symbol, and so on, and finally all resource blocks are mapped.

[0007] This OFDM system resource block usage method is suitable for current public network systems, specifically those with fixed frequency resources. However, it is not suitable for IoT systems, particularly discrete shared spectrum systems. Specifically, it suffers from the following issues.

[0008] First, existing OFDM communication systems cannot support subcarrier interference detection methods. In the time-frequency resource block mapping, if there are multiple subcarrier interferences, the entire data block will be parsed incorrectly, and it will be impossible to detect which subcarriers are interfered with.

[0009] Second, in public networks or typical OFDM systems, pilots are distributed as evenly as possible in the time and frequency domains to allow the system to estimate the channel characteristics of each resource block element. Because the subcarrier distribution in discrete shared spectrum is inherently non-uniform, a uniform pilot distribution approach is not fully applicable to discrete shared spectrum systems.

[0010] In view of the above problems, the discrete shared spectrum OFDM system has differences in wireless resources from conventional OFDM and requires system redesign. Summary of the Invention

[0011] In view of this, the purpose of the present invention is to provide an OFDM communication system and method for discrete shared spectrum, so as to solve the problem that when the existing OFDM communication system uses discrete shared spectrum resources, the receiving end cannot receive the correct data block due to the presence of multiple subcarrier interference in the time-frequency resource block mapping and the uneven distribution of subcarriers in the discrete shared frequency domain. The present invention independently encodes the data carried by each subcarrier in the OFDM communication system, independently adds verification information, and the subcarriers of the OFDM time-frequency resource block are continuously allocated in the time domain and discretely allocated in the frequency domain. Each subcarrier uses an independent pilot signal, and independently performs channel estimation and channel equalization. The time-frequency resource block of the OFDM system is mapped to the time domain first and then to the frequency domain, so that when the OFDM system has multiple subcarrier interference and the subcarriers in the discrete shared frequency domain are unevenly distributed, the receiving end can receive the correct data block, thereby making the OFDM system suitable for discrete shared spectrum resource systems.

[0012] To achieve the above purpose, if Figure 3-5 As shown, the present invention provides the following technical solutions:

[0013] A discrete shared spectrum OFDM communication system, the system comprising a transmitting end, a receiving end and a shared information module;

[0014] The transmitting end includes a transmission data module 1, a group coding block block module, a subcarrier coding block module, a channel coding module, a modulation module, a pilot module 1 and an OFDM mapping module;

[0015] The receiving end includes an OFDM demapping module, a pilot module 2, a channel estimation module, a channel equalization module, a demodulation module, a channel decoding module, a subcarrier coding block decoding, a group coding block assembly module and a data transmission module 2;

[0016] The shared information module includes group coding block retransmission and subcarrier mapping table, which is completed by signaling interaction between the sending end and the receiving end;

[0017] The data transmission module 1 receives the data block transmitted from the high-level protocol stack, and the transmitting end detects whether the transmission block sequence number of the transmission data block is used up;

[0018] The packet coding block segmentation module processes the transmission data block in segments to obtain segmented packet coding blocks;

[0019] The subcarrier coding block module performs segment processing on the obtained segmented group coding block to obtain segmented subcarrier coding blocks, and independently adds verification information to each of the obtained segmented subcarrier coding blocks; the first segmented subcarrier coding block includes group coding block header information, and the group coding block header information includes a transmission sequence number, an intra-block coding sequence number, and a transmission block end identifier;

[0020] The channel coding module independently encodes the obtained segmented subcarrier code blocks, and uses the modulation module to modulate the encoded segmented subcarrier code blocks to form modulation symbols, i.e., data-carrying symbols. The number of modulation symbols generated by each subcarrier resource is the same as the number of OFDM symbols in the transmission resource block;

[0021] Mapping the generated data symbols and pilot symbols to the subcarrier resources of the transmission resource block using the OFDM mapping module, wherein each data symbol generated by segmented subcarrier coding corresponds to a subcarrier resource on the transmission resource;

[0022] In the OFDM mapping module, the time domain is mapped first and then the frequency domain is mapped;

[0023] After all segmented subcarrier code blocks are mapped to transmission resource blocks, OFDM modulation is performed and the blocks are sent to the air via radio frequency.

[0024] The OFDM demapping module receives frame data from a wireless channel and performs OFDM demodulation on the received data. The OFDM demodulation refers to converting the OFDM signal from a time domain signal to a frequency domain signal and extracting the time-frequency transmission data block data;

[0025] The subcarriers of the time-frequency transmission block data are continuously allocated in the time domain and discretely allocated in the frequency domain;

[0026] Extracting pilot symbols and data symbols of subcarriers from the time-frequency transmission resource block, independently performing channel estimation in the channel estimation module using independent pilot symbols, and then independently performing equalization processing on the data symbols in the channel equalization module;

[0027] The demodulation module demodulates the data symbols after subcarrier equalization to obtain log-likelihood values ​​of the data symbols;

[0028] The channel decoding module performs channel decoding on the obtained log-likelihood value of the data-carrying symbol to obtain subcarrier code block data;

[0029] The block coding assembly module combines consecutive subcarrier coding block data to form a complete block coding block;

[0030] The transmission data block 2 receives the correct packet coding block and puts the packet coding into the corresponding transmission block cache according to the transmission block sequence number; after the transmission data block 2 receives all correct packet coding blocks, it forms a complete data block, submits it to the high-level protocol stack, and clears the cache corresponding to the transmission block sequence number.

[0031] A discrete shared spectrum OFDM communication method, the method comprising the following steps:

[0032] S1: The data transmission module 1 receives a data block transmitted from a high-level protocol stack, and the transmitting end detects whether the transmission block sequence number of the transmission data block is used up. If there is an unused transmission block sequence number, the unused transmission block sequence number is used;

[0033] S2: The block segmentation module performs segmentation processing on the transmission data block to obtain segmented block segmentation blocks;

[0034] S3: The subcarrier code block module segments the obtained segmented group code block to obtain segmented subcarrier code blocks, and independently adds verification information to each of the obtained segmented subcarrier code blocks; the first subcarrier code block includes group code block header information, and the group code block header information includes a transmission sequence number, an intra-block code sequence number, and a transmission block end identifier;

[0035] S4: The channel coding module independently encodes the obtained segmented subcarrier code block, and uses the modulation module to modulate the encoded segmented subcarrier code block to form a modulation symbol, i.e., a data symbol. The modulation symbol generated by each subcarrier resource is the same as the number of OFDM symbols in the transmission resource block;

[0036] S5: Mapping the generated data symbols and pilot symbols to subcarrier resources of the transmission resource block using an OFDM mapping module, wherein each data symbol generated by encoding the subcarrier corresponds to a subcarrier resource on the transmission resource;

[0037] In the mapping in S5, the time domain is mapped first and the frequency domain is mapped later;

[0038] S6: After all subcarrier code blocks are mapped to transmission resource blocks, OFDM modulation is performed and the signal is transmitted to the air via radio frequency.

[0039] S7: The OFDM demapping module receives frame data from the wireless channel and performs OFDM demodulation on the received data. OFDM demodulation converts the OFDM signal from a time domain signal into a frequency domain signal and extracts the time-frequency transmission data block data.

[0040] The subcarriers of the time-frequency transmission data block in S7 are continuously allocated in the time domain and discretely allocated in the frequency domain;

[0041] S8: extracting pilot symbols and data symbols of subcarriers from the transmission data block, independently performing channel estimation in a channel estimation module using the independent pilot symbols, and independently performing equalization processing on the data symbols in a channel equalization module;

[0042] S9: Demodulate and channel decode the data symbols carried by the subcarriers after equalization to obtain subcarrier code block data;

[0043] S10: The block coding assembly module combines the continuous subcarrier coding block data to form a complete block coding block;

[0044] S11: Detect whether the subcarrier coding check of the group coding block is correct. If all subcarrier checks are correct, the group coding block participates in the transmission of the second combination of data blocks; if the check of the first subcarrier coding block is incorrect, it is directly discarded; if the check of the first subcarrier coding block is correct, and the check of other subcarrier check blocks fails, the transport block sequence number and the intra-block coding sequence number in the group coding block header are extracted, and the receiving end retransmits the proposed transport block sequence number and the intra-block coding sequence number through the group coding block retransmission module to notify the sending end to retransmit the correct group coding block of the erroneous subcarrier coding block;

[0045] The receiving end feeds back the subcarrier mapping table to the sending end, indicating which subcarriers carry subcarrier codes that cannot be correctly received, and recommends a list of disabled subcarriers to the sending end. The sending end then ultimately determines which specific subcarriers to use.

[0046] S12: Transmission data block 2 receives the correct packet coding block and puts the packet coding into the corresponding transmission block buffer according to the transmission block sequence number;

[0047] S13: After receiving all correct packet coding blocks, the second transmission data block forms a complete data block, submits it to the upper layer protocol stack, and clears the cache corresponding to the transmission block sequence number;

[0048] Furthermore, the first subcarrier coding block of the group coding block in S2 includes a coding block header, a checksum and bearer data, and the other subcarrier coding blocks consist of bearer data and checksum data.

[0049] Furthermore, the transmission block sequence number in S3 is used cyclically, and the intra-block coding sequence number of each segment is unique.

[0050] Furthermore, the transport block end flag in S3 is set to "1", indicating the last packet coding block in the transport data block, and the transport block end flag is set to "0" indicating an intermediate packet coding block.

[0051] Furthermore, the channel decoding in S9 is to perform soft information decoding on the demodulated data.

[0052] Furthermore, the grouped coding block retransmission comprises the following steps:

[0053] S71: The receiving end receives all the packet coding blocks carried by the transmission resource block, extracts the packet coding blocks from the transmission resource block carrying data in sequence, and checks whether the checksum of each subcarrier coding block in each packet coding block is correct;

[0054] S72: If there is a check error in the subcarrier coding in the packet coding block, the subcarrier number corresponding to the check error is recorded as a basis for whether to continue using the subcarrier frequency point in the future. The packet coding block containing the check error subcarrier coding block needs to be retransmitted. The receiving end notifies the sending end through the transport block sequence number and the intra-block coding sequence number in the packet coding block header;

[0055] S73: Verify that all subcarrier codes in the block are correct, record the subcarrier numbers corresponding to the correct subcarrier codes in the block, and evaluate whether to continue using this correct subcarrier frequency in the future;

[0056] S74: extract the block header information from the correct block code, save the block code block to the corresponding transport block buffer according to the transport block sequence number and the intra-block code sequence number, and check whether all segments of the transport data block have been received after correctly receiving the block code block containing the transport block end flag of 1.

[0057] S75: All the group coding blocks in the transmission data block have been received. The transmission data block bit data are taken from all the group coding blocks and assembled into a complete transmission data block in sequence. The transmission data block is submitted to the high-level protocol stack. The sender receives feedback from the receiver, indicating that all the group coding blocks in the retransmitted transmission data block have been received. The sender clears the retransmitted transmission data block and prepares to send the next transmission data block.

[0058] Furthermore, the S73 evaluates whether the correct subcarrier frequency will continue to be used subsequently, specifically including: setting the preferred initial value of each subcarrier, if the subcarrier coding block checksum analysis corresponding to the subcarrier is correct, the correct subcarrier value preference value will increase by one bonus point; if the subcarrier coding block checksum analysis corresponding to the subcarrier is incorrect, the incorrect subcarrier preference value will be subtracted from the penalty point; the transmitting end gives priority to using subcarriers with larger preference values. During the selection process, if the preference values ​​are the same, the subcarrier frequency can be randomly selected until the number of subcarriers required for the transmission resource block is selected.

[0059] The beneficial effects of the present invention are:

[0060] First, the use of shared spectrum has not been resolved so far. Wireless spectrum needs to be shared, and there is no coordination mechanism between different systems, which easily leads to mutual interference. The present invention proposes the use of OFDM, in which each subcarrier is independently encoded and verification information is independently added. The subcarrier interference situation is monitored during each transmission to determine the spectrum resources available to the system.

[0061] Second: Design the OFDM system transmission resource block, that is, the subcarriers of the OFDM time-frequency resource block are allocated continuously in the time domain, but discretely in the frequency domain. Each subcarrier uses an independent pilot signal for independent channel estimation and channel equalization.

[0062] Third, conventional OFDM systems use time-frequency resource blocks by first mapping them to the frequency domain and then to the time domain. However, in order to detect subcarrier interference, the present invention uses a method that maps the time domain first and then the frequency domain, thus enabling each subcarrier to be used independently in OFDM technology.

[0063] Fourth: The present invention proposes a complete OFDM system solution for the discrete shared spectrum feature, including the receiving and sending processing flow of the physical layer link.

[0064] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings, in which:

[0066] Figure 1 A discrete shared spectrum resource distribution diagram of the prior art;

[0067] Figure 2 This is a diagram of a conventional modulation symbol transmission mapping method in the prior art;

[0068] Figure 3 The discrete shared spectrum OFDM system of the present invention;

[0069] Figure 4 A flow chart of sending a transmission data block according to the present invention;

[0070] Figure 5 This is a flow chart of a receiving end receiving a transmission data block according to the present invention;

[0071] Figure 6 This is a block diagram of discrete shared spectrum wireless link processing in the present invention;

[0072] Figure 7 This is a diagram showing the composition of the first subcarrier coding block in the group coding block of the present invention;

[0073] Figure 8 This is a diagram showing the composition of the block header of the group coding of the present invention;

[0074] Figure 9 A diagram showing the composition of a group coding block according to the present invention;

[0075] Figure 10 This is a diagram showing the structure of a group coding block carried by a transmission resource block of the present invention;

[0076] Figure 11 A pilot distribution diagram on a subcarrier resource block of the present invention;

[0077] Figure 12 This is a diagram of the OFDM mapping method in discrete shared spectrum of the present invention;

[0078] Figure 13 A diagram showing the mapping relationship between transmission data blocks and transmission resource blocks of the present invention;

[0079] Figure 14This is a flow chart of data transmission and reorganization according to the present invention;

[0080] Figure 15 This is a flow chart of subcarrier frequency evaluation and use in the present invention.

[0081] Figure 16 This is a normal AWGN channel simulation performance diagram of the present invention;

[0082] Figure 17 This is a performance simulation diagram of the present invention with random interference subcarriers; DETAILED DESCRIPTION

[0083] The following describes the embodiments of the present invention by means of specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0084] Among them, the accompanying drawings are only for illustrative purposes and represent only schematic diagrams rather than actual pictures, and should not be understood as limiting the present invention. In order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the accompanying drawings.

[0085] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc. indicating directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0086] See also Figures 6 to 17 In order to clearly illustrate the application of the present invention in an actual OFDM system, a discrete shared spectrum power communication system will be used for illustration.

[0087] Part 1: Wireless Link Architecture of Power Communication System

[0088] The wireless link architecture of the power communication system consists of the transmitter and receiver links. Figure 6 shown.

[0089] The transmitting end includes: transmission data block (carrying CRC), block coding block segmentation, subcarrier coding block check, channel coding, debugging, reference signal, OFDM mapping, OFDM modulation and wireless transmission.

[0090] The receiving end includes: wireless reception, OFDM demodulation, OFDM demapping, reference signal, signal estimation, channel equalization, demodulation, channel decoding, subcarrier coding block check, group coding block merging, and transmission data block check.

[0091] In this embodiment, the packet coding block retransmission and subcarrier mapping table are shared information modules between the transmitter and receiver, and are implemented through signaling interactions. For packet coding block retransmission, the receiver must notify the transmitter of the specific retransmitted transmission data block (transmission block sequence number) and packet coding block (intra-block coding sequence number). The packet coding block to be retransmitted is determined by the packet coding block header within the packet coding block. The subcarrier mapping table is fed back to the transmitter by the receiver, indicating which subcarriers carrying subcarrier codes cannot be correctly received, and recommending a list of disabled subcarriers to the transmitter. Ultimately, the transmitter determines which specific subcarriers to use to carry the subcarrier coding blocks.

[0092] In this embodiment, frequency domain resources can be used. This embodiment is applied to a power communication system, namely a dedicated power network communication system. The only frequencies that can be used in this embodiment are subcarriers allocated exclusively to the power system and unallocated shared subcarriers. The subcarrier numbers that can be used by the system 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, and 345. The system cannot use subcarriers dedicated to the light industry and construction sector, the light industry and seismic sector, or the military and seismic sector. However, it is uncertain whether other subcarriers between 223 MHz and 235 MHz are used by other systems. The system uses these subcarrier resources based on the actual wireless scenario.

[0093] In this embodiment, it is initially assumed that the system can use all subcarriers except the subcarriers dedicated to the light industry and construction industry, the subcarriers dedicated to the light industry and seismic industry, and the subcarriers dedicated to the military and seismic industry. During use, subcarrier interference is continuously detected, and the subcarrier mapping table is modified to record the subcarriers that can be used in the system.

[0094] Part II: Key components of power communication systems

[0095] According to the requirements of the present invention, the key processes of this embodiment are described in detail below.

[0096] (1) Transmission data block format requirements

[0097] like Figure 6 In this embodiment, the transmitting end transmits data blocks (with CRC) and the receiving end transmits data blocks for parity checks. In this embodiment, the transmitting end's high-level protocol is responsible for providing the transmission data blocks, and the high-level protocol adds and checks the parity of the transmission data blocks. The transmission data block bit size is determined by the number of particles in the transmission resource block, the modulation method, and the code rate of the channel codec. In this embodiment, after the transmission resource block is determined, the transmission data block size is also determined. The transmission data block size sent by the protocol meets the transmission resource block mapping requirements, and the high-level protocol is responsible for completing the transmission data block padding.

[0098] (2) Block segmentation and merging of group coding blocks

[0099] Based on the transmission resource block size, the transmission data block is divided into multiple block coding blocks. The block coding block header contains the transmission block number and the intra-block coding number. Each block coding block is composed of multiple subcarrier coding blocks. Each subcarrier coding block contains both payload data and check data.

[0100] In this embodiment, the packet coding block header of the packet coding block is defined as 9 bits long, of which the transport block sequence number occupies 2 bits. A cyclic coding method is used, i.e., 0, 1, 2, 3, 0, 1, 2, 3, ..., and up to 4 (2-bit) transport data blocks can be transmitted simultaneously. The transport block end identifier occupies 1 bit, where 0 indicates that the current packet coding block is an intermediate packet coding block of the transport data block, and 1 indicates that the packet coding block is the last packet coding block of the transport data block. The intra-block coding sequence number occupies 6 bits, indicating the packet coding block sequence number of the packet coding block when the block is transmitted. A maximum of 64 block codes can be encoded simultaneously. When a packet coding block is received at the receiving end, all subcarrier coding block parity bits within the coding block are checked. If a parity error occurs in any subcarrier coding block, the packet coding block data needs to be retransmitted. During the retransmission process, the packet coding block header of the packet coding block remains unchanged.

[0101] Each subcarrier code block uses a 4-bit cyclic check code. The receiving end checks whether the check is correct every time it receives a subcarrier code block, and records the statistical results of each subcarrier check at the receiving end as a basis for subsequent use to start the corresponding subcarrier. Figure 7 and Figure 8 shown.

[0102] A complete block coding structure consists of multiple subcarrier coding blocks, where the first subcarrier coding block of each block coding block includes a block coding header, bearer data, and check data. Other subcarrier coding blocks consist of bearer data and check data. Figure 9 shown.

[0103] A complete transmission resource block can carry multiple packet coding blocks. According to the packet coding block header, each resource block can transmit data of 4 different transmission data blocks and can carry up to 64 packet coding blocks, such as Figure 10 shown.

[0104] (3) Channel coding

[0105] Channel coding is performed based on the size of the subcarrier code block, and each subcarrier code block is individually channel-coded and decoded. In this embodiment, a typical Viterbi codec is used, with two coding rates: Viterbi and 1 / 2 / Viterbi / 1 / 3. After the transmitting end passes the Viterbi encoder on bits, if Viterbi 1 / 2 encoding is used, the output number of bits is , while if Viterbi 1 / 3 encoding is used, the output number of bits is bits. Channel decoding at the receiving end uses soft information decoding. The decoder inputs soft information. If Viterbi 1 / 2 decoding is used, the output is , while if Viterbi 1 / 3 decoding is used, the output is .

[0106] (4) Modulation and demodulation process

[0107] This embodiment supports the following modulation schemes: BPSK, QPSK, and 16QAM. The modulation process modulates the bit data of the subcarrier code block into debugging symbols, that is, modulating the bit sequence into a complex number sequence. The demodulation process demodulates the received complex data into log-likelihood values ​​(LLRs), which are finally decoded into a bit sequence by a Viterbi decoder.

[0108] (5)OFDM mapping

[0109] Two types of symbols are mapped on the OFDM time-frequency resources, one is the modulation symbol data of the subcarrier coding block, and the other is the pilot reference symbol.

[0110] In this embodiment, the ratio of resource elements occupied by pilot and subcarrier code block is 1:3, that is, one particle in every four resource elements is used for pilot, and three resource elements are used to transmit subcarrier code block symbols. Each subcarrier resource element in a transmission resource block constitutes a subcarrier resource block, which carries a complete pilot block symbol and a complete subcarrier code block symbol. The pilot symbol is used for channel estimation, estimating the channel characteristics of the subcarrier in the time domain, and then performing channel equalization. Figure 11 shown.

[0111] In OFDM resource mapping, according to the definition of the present invention, mapping is performed first according to the time domain order, and then the frequency domain mapping order. The time domain mapping starts from the first OFDM symbol and increases sequentially to the last OFDM symbol of the transmission resource block. The frequency domain mapping starts from the first subcarrier of the resource block and increases sequentially to the last subcarrier of the transmission resource block. Figure 12 As shown in FIG. 1 , transmission resource blocks are continuously allocated in time, but may be discrete in the frequency domain.

[0112] (6) OFDM modulation and demodulation

[0113] After OFDM mapping is complete, OFDM modulation is performed on the transmitter to form the baseband waveform for wireless transmission. This baseband signal is modulated to the 230MHz frequency band during wireless transmission. On the receiver side, the wireless receiving module receives the 230MHz wireless signal and down-converts it to the baseband signal.

[0114] Part III: Mapping process of transmission data blocks to transmission resource blocks

[0115] In the present invention, the mapping relationship between the transmission data block and the transmission resource block is relatively complex. In this embodiment, Figure 13 Provide explanation.

[0116] (1) Data processing flow at the sending end:

[0117] Step 1: The physical layer link receives a data block to be sent from the higher-level protocol stack, known as a transmission data block. This data block can be either service data or signaling data. The bits in the transmission data block correspond to the transmission resource block size. The higher-level protocol stack is responsible for padding or segmenting the transmission data block and adding a cyclic checksum to the end of the transmission data block. In this embodiment, a 16-bit cyclic checksum is used.

[0118] Step 2: The transmitter receives the transmission data block from the higher-level protocol stack, calculates the size of each block based on the transmission resource block, and then performs block processing. The ratio of block size to subcarrier number is 1:4. The number of bits per block is 4*(N-4)-9, where N is the number of bits carried by the subcarrier block: N = (LR)*M*R.

[0119] like Figure 13 Part (1).

[0120] Step 3: Each group coding block is divided into multiple subcarrier coding blocks. In this embodiment, each group coding block is divided into 4 subcarrier coding blocks, where the first subcarrier coding block carries N-9-4 bits (9 bits are group coding block headers and 4 bits are cyclic check bits), so each group coding block carries a total of 4*(N-4)-8 bits.

[0121] like Figure 13 Part (2).

[0122] Step 4: The group coding block is composed of subcarrier coding blocks, and the length of each subcarrier coding block is N, N = (L-Ref) * M * R,

[0123] Wherein: L is the number of OFDM transmission resource blocks, R is the coding rate, Ref is the number of pilots, and in this embodiment, (1 / 4)L is defined, M is the modulation mode, BPSK is 1, QPSK is 2, and 16QAM is 3.

[0124] like Figure 13 Part (3).

[0125] Step 5: After channel numbering and modulation, each subcarrier code block forms a modulation symbol, which can be directly mapped to the time-frequency resource element of the transmission resource block. The subcarrier resource carries not only the modulation symbols of the subcarrier code block, but also pilot symbols. In this embodiment, the pilot symbol occupies 1 / 4 of the resources of the entire subcarrier resource block.

[0126] like Figure 13 Middle (4) part.

[0127] Step 6: Each subcarrier code block is mapped to a subcarrier resource. Once all subcarrier resources are mapped, a complete transmission resource block is formed.

[0128] Transmit resource blocks and perform FFT transformation on each OFDM symbol to form an OFDM baseband signal in the time domain.

[0129] like Figure 13 Part (5).

[0130] (2) Data processing flow at the receiving end:

[0131] Step 1: The receiving end demodulates the received time-domain OFDM data into frequency-domain OFDM data through wireless reception and OFDM demodulation. The transmission resource block data is extracted from the OFDM data.

[0132] like Figure 13 Part (5).

[0133] Step 2: Extract the data for each subcarrier resource block in each transmission resource block, and extract the pilot data and subcarrier code block modulation data from the subcarrier resource block. Use the pilot data to perform channel estimation and estimate the channel characteristic matrix for the entire subcarrier resource block. This channel characteristic matrix is ​​then used to perform channel equalization on the subcarrier code block modulation data.

[0134] like Figure 13 Middle (4) part.

[0135] Step 3: Demodulate the modulation symbols of each subcarrier code block and perform channel decoding to obtain the subcarrier code block data. In this step, it is necessary to check whether the cyclic check of each subcarrier code block is correct, which will serve as the basis for whether to enable the subcarrier in the future.

[0136] like Figure 13 Part (3).

[0137] Step 4: Parse each subcarrier resource block in the transmission resource block to obtain a group coding block. Each subcarrier coding block carries the same number of bits, and the first subcarrier coding block of each group coding block includes an 8-bit group coding block header.

[0138] In this step, the receiving end checks the parity bits in all block coding blocks. If the parity of a subcarrier coding block in the block coding block is incorrect, the receiving end needs to retransmit the block coding block. In this embodiment, the retransmission is performed based on the block coding block size.

[0139] like Figure 13 Part (2).

[0140] Step 5: After parsing all the packet coding blocks, a complete transmission data block is obtained.

[0141] like Figure 13 Part (1).

[0142] Part 4: Block Retransmission and Transmitted Data Block Reassembly

[0143] In this embodiment, the receiving end has four buffers, corresponding to receiving four different transmission data blocks. After receiving a packet coding block, each receiving buffer needs to check whether the transmission data block is received. If all segments of the transmission data block are received, the transmission data block data is taken from the packet coding block in the buffer, and the complete transmission data block is assembled and sent to the high-level protocol stack. The specific process is as follows: Figure 14 shown.

[0144] Step 1: The receiving end receives all the packet coding blocks carried by the transmission resource block, and extracts the packet coding blocks from the transmission resource block carrying data in turn. Check whether the checksum of each subcarrier coding block in each packet coding block is correct. Figure 14 1, 2 steps in.

[0145] Step 2: If there is a check error in the subcarrier coding in the packet coding block, the subcarrier number corresponding to the check error is recorded as the basis for whether to continue to use the subcarrier frequency point in the future. And the packet coding block where the subcarrier coding block is located needs to be retransmitted. The receiving end notifies the sending end through the transmission block number and the intra-block coding number in the packet coding block header. Figure 14 3, 4, 5 steps in the middle.

[0146] Step 3: Check that the subcarrier codes in the group coding block are correct, and record the subcarrier numbers corresponding to the subcarrier codes in the group coding block to evaluate whether to continue using the subcarrier frequency point in the future. Figure 14 Middle 3, 6 steps.

[0147] Step 4: Extract the block header information from the correct block code, and save the block code block to the corresponding transport block buffer according to the transport block sequence number and the intra-block code sequence number. If a block code block containing a transport block end flag of 1 has been correctly received in the block code block, check whether all segments of the transport data block have been received. Figure 14 7, 8 steps in the middle.

[0148] To further describe, the intra-block coding sequence number in the block coding block header starts from 0 and ends at the last block coding block. The transport block end indicator in the block coding block header indicates whether it is the last block coding block. The transport block end indicator is one bit long, "1" indicates the last block coding block, and "0" indicates an intermediate block coding block.

[0149] Step 5: If all the grouped coding blocks in a transport data block have been received, the transport data block bit data is taken from all the grouped coding blocks, assembled into a complete transport data block in sequence, and the transport data block is submitted to the upper layer protocol stack. The cache of the transport data block is cleared to prepare for receiving the next transport data block. When the sending end receives feedback from the receiving end indicating that all the grouped coding blocks in the transport data block have been received, the sending end clears the transport data block and prepares to send the next transport data block. Figure 14 Step 9 or 10.

[0150] Part 5: Subcarrier Frequency Evaluation Method

[0151] In this embodiment, a preferred value is defined for each subcarrier, and the minimum score of each subcarrier preferred value is 0 points, and the maximum score is 12 points. In this system, the initial value of each subcarrier preferred value is set to 12 points. If the subcarrier code block corresponding to the subcarrier is correct, the subcarrier preferred value is increased by 1 point. If the subcarrier code block corresponding to the subcarrier is wrong, the subcarrier preferred value is reduced by 3 points. Figure 15 shown.

[0152] Step 1: In this embodiment, a total of 480 subcarrier frequencies can be used, and each subcarrier has a preferred value. Since the block coding sequence number in the block coding block is 6 bits in the design, the maximum number of block coding blocks is 64, and each block coding block contains 4 subcarrier coding blocks, so each transmission resource block can use a maximum of 256 subcarrier frequencies. Figure 15 1 step in the middle.

[0153] Step 2: Each time the receiver transmits data on a resource block, it parses the subcarrier code blocks carried on the transmitted resource block and checks whether the subcarrier code block checksum is correct. If the checksum is correct, there is no need to notify the transmitter, and the transmitter will assume that the subcarrier code block checksum is correct. If the checksum is incorrect, the receiver needs to notify the transmitter of the subcarrier code block checksum error transmitted on the specific subcarrier.

[0154] At the transmitting end, if it is determined that the verification of the receiving subcarrier code block is correct, then add 1 to the preferred value of the corresponding subcarrier, otherwise subtract 3. If it is less than the minimum preferred value of 0, then take the minimum value; if it is greater than the maximum preferred value of 12, then take the maximum value of 12. Figure 15 Middle 2 steps.

[0155] Step 3: After the transmitter sends the transmission data block, it must select the available subcarriers. According to the definition of the present invention, the transmitter will sort the 480 candidate subcarrier frequencies according to the preferred value, and give priority to the subcarrier with the larger preferred value. During the selection process, if the preferred values ​​are the same, the subcarrier frequency can be randomly selected until the number of subcarriers required for the transmission resource block is selected. Figure 15 Middle 3 steps.

[0156] Step 5: The transmitter notifies the receiver through the subcarrier mapping table, and the receiver uses the subcarrier mapping to receive the transmission resource block data from the transmitter. Figure 15 4 steps in.

[0157] In order to verify the correctness of the solution, in this embodiment, according to the above design solution and process, the following simulation parameters are adopted, as shown in Table 1. Link simulation is performed.

[0158] Table 1 Simulation parameters

[0159] Simulation parameters Parameter content Subcarrier spacing 25KHz Operating frequency band 223MHz to 235MHz (12MHz) Shared frequency band bandwidth range 480 subcarriers, bandwidth 25x480=12MHz Bearer data bandwidth 40 subcarriers, bandwidth 25x40=1MHz Number of OFDM symbols 36 FFT / IFFT points 1024 Channel Compilation Turbo Codec Modulation method QPSK Channel Model AWGN+frequency random interference model Maximum number of data block retransmissions 4 times

[0160] In the simulation, two channel models, namely the AWGN channel model and the AWGN plus subcarrier random interference channel model, are used for verification.

[0161] First: AWGN channel model, verify that the system works properly, such as Figure 16 shown.

[0162] In the AWGN channel model simulation, there is no subcarrier interference. Figure 16 As can be seen in the figure, when the SNR is relatively poor, the transceiver still cannot correctly transmit and receive after 4 retransmissions (the simulation sets the maximum number of retransmissions to 4), the retransmission probability reaches 0.4 (40%), and the bit error rate is 5%. When the SNR reaches -4dB, the transmission performance improves, but retransmission is basically unnecessary, and the transmission is correct every time. All the design processes and methods of the present invention can work normally.

[0163] Second: AWGN+subcarrier random interference, the system's ability to identify and track interfering subcarriers, such as Figure 17 shown.

[0164] In the AWGN+random interference subcarrier channel simulation, there are two randomly interfering subcarriers during each data block transmission process. Under each simulated SNR condition, the interfering subcarrier is first detected and then removed from the available subcarriers.

[0165] When SNR is -4dB to -1dB, due to the influence of Gaussian white noise, the interfering subcarrier cannot be determined after one retransmission. However, after several retransmissions, the position of the interfering subcarrier can be determined by the method of the present invention. Figure 17 It is obvious that as the SNR increases, the speed of detecting the interfering subcarrier in the present invention becomes faster and faster, and the number of retransmissions required becomes fewer and fewer.

[0166] When SNR=1dB, the performance is completely improved. Although there is subcarrier interference, it only takes one or two data blocks to determine the interfering subcarrier. When SNR=1dB, the number of retransmissions tends to 0 and the bit error rate also tends to 0. The simulation results show that the random interference of subcarriers using the method of the present invention has little effect on communication.

[0167] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A discrete shared spectrum OFDM communication system, characterized by: The system includes a sending end, a receiving end and a sharing information module; The transmitting end includes a transmission data module 1, a group coding block block module, a subcarrier coding block module, a channel coding module, a modulation module, a pilot module 1 and an OFDM mapping module; The receiving end includes an OFDM demapping module, a pilot module 2, a channel estimation module, a channel equalization module, a demodulation module, a channel decoding module, a subcarrier coding block decoding, a group coding block assembly module and a data transmission module 2; The shared information module includes group coding block retransmission and subcarrier mapping table, which is completed by signaling interaction between the sending end and the receiving end; The data transmission module 1 receives data blocks transmitted from a high-level protocol stack, and the transmitting end detects whether the transmission block sequence numbers of the transmitted data blocks are used up; The block coding block segmentation module processes the transmitted data block in segments to obtain segmented block coding blocks; The subcarrier code block module performs segment processing on the obtained segmented group code block to obtain segmented subcarrier code blocks, and independently adds verification information to each obtained segmented subcarrier code block; The first segmented subcarrier coding block includes group coding block header information, wherein the group coding block header information includes a transmission sequence number, an intra-block coding sequence number, and a transmission block end identifier; The channel coding module independently encodes the obtained segmented subcarrier code blocks, and uses the modulation module to modulate the encoded segmented subcarrier code blocks to form modulation symbols, i.e., data-carrying symbols. The number of modulation symbols generated by each subcarrier resource is the same as the number of OFDM symbols in the transmission resource block; Mapping the data symbols and pilot symbols to the subcarrier resources of the transmission resource block using the OFDM mapping module, wherein each data symbol generated by segmented subcarrier encoding corresponds to a subcarrier resource on the transmission resource; In the OFDM mapping module, the time domain is mapped first and then the frequency domain is mapped; After all segmented subcarrier code blocks are mapped to transmission resource blocks, OFDM modulation is performed and the blocks are sent to the air via radio frequency. The OFDM demapping module receives frame data from a wireless channel and performs OFDM demodulation on the received data. The OFDM demodulation refers to converting the OFDM signal from a time domain signal to a frequency domain signal and extracting the time-frequency transmission data block data; The subcarriers of the time-frequency transmission data block data are continuously allocated in the time domain and discretely allocated in the frequency domain; Extracting pilot symbols and data symbols of subcarriers from the time-frequency transmission resource block, independently performing channel estimation in the channel estimation module using independent pilot symbols, and then independently performing equalization processing on the data symbols in the channel equalization module; The demodulation module demodulates the data symbols after subcarrier equalization to obtain log-likelihood values ​​of the data symbols; The channel decoding module performs channel decoding on the obtained log-likelihood value of the data-carrying symbol to obtain subcarrier code block data; The grouped coding block assembly module combines consecutive subcarrier coding block data to form a complete grouped coding block; The transmission data module 2 receives the correct packet coding block and puts the packet coding into the corresponding transmission block cache according to the transmission block sequence number; after the transmission data block 2 receives all correct packet coding blocks, it forms a complete data block, submits it to the high-level protocol stack, and clears the cache corresponding to the transmission block sequence number.

2. A discrete shared spectrum OFDM communication method, characterized by: The method comprises the following steps: S1: The data transmission module 1 receives a data block transmitted from a high-level protocol stack, and the transmitting end detects whether the transmission block sequence number of the transmitted data block is used up. If there is an unused transmission block sequence number, the unused transmission block sequence number is used; S2: The block segmentation module performs segmentation processing on the transmitted data block to obtain segmented block segmentation; S3: The subcarrier code block module segments the obtained segmented group code block to obtain segmented subcarrier code blocks, and independently adds verification information to each obtained segmented subcarrier code block; the first subcarrier code block includes group code block header information, and the group code block header information includes a transmission sequence number, an intra-block code sequence number, and a transmission block end identifier; S4: The channel coding module independently encodes the obtained segmented subcarrier code blocks, and uses the modulation module to modulate the encoded segmented subcarrier code blocks to form modulation symbols, i.e., data symbols. The modulation symbols generated by each subcarrier resource are the same as the number of OFDM symbols in the transmission resource block; S5: Mapping the data symbols and pilot symbols to subcarrier resources of a transmission resource block using an OFDM mapping module, wherein each data symbol generated by encoding the subcarrier corresponds to a subcarrier resource on the transmission resource; In the mapping in S5, the time domain is mapped first and the frequency domain is mapped later; S6: After all subcarrier code blocks are mapped to transmission resource blocks, OFDM modulation is performed and the signal is transmitted to the air via radio frequency. S7: The OFDM demapping module receives frame data from the wireless channel and performs OFDM demodulation on the received data. OFDM demodulation converts the OFDM signal from a time domain signal into a frequency domain signal and extracts the time-frequency transmission data block data. The subcarriers of the time-frequency transmission data block in S7 are continuously allocated in the time domain and discretely allocated in the frequency domain; S8: extracting pilot symbols and data symbols of subcarriers from the transmitted data block, independently performing channel estimation in a channel estimation module using the independent pilot symbols, and independently performing equalization processing on the data symbols in a channel equalization module; S9: Demodulate and channel decode the data symbols carried by the subcarriers after equalization to obtain subcarrier code block data; S10: The block coding assembly module combines the continuous subcarrier coding block data to form a complete block coding block; S11: Detect whether the subcarrier coding check of the group coding block is correct. If all subcarrier checks are correct, the group coding block participates in the transmission of the second combination of data blocks; if the check of the first subcarrier coding block is wrong, it is directly discarded; if the check of the first subcarrier coding block is correct, and the check of other subcarrier check blocks fails, the transport block sequence number and the intra-block coding sequence number in the group coding block header are extracted, and the receiving end retransmits the extracted transport block sequence number and the intra-block coding sequence number through the group coding block retransmission module to notify the sending end to retransmit the correct group coding block of the erroneous subcarrier coding block; The receiving end feeds back the subcarrier mapping table to the sending end, indicating which subcarriers carry subcarrier codes that cannot be correctly received, and recommends a list of disabled subcarriers to the sending end. The sending end then ultimately determines which specific subcarriers to use. S12: Transmission data block 2 receives the correct packet coding block and puts the packet coding into the corresponding transmission block buffer according to the transmission block sequence number; S13: After receiving all correct packet coding blocks, the second transmission data block forms a complete data block, submits it to the upper layer protocol stack, and clears the cache of the corresponding transmission block sequence number.

3. The discrete shared spectrum OFDM communication method according to claim 2, wherein: The first subcarrier coding block of the group coding block in S2 includes a coding block header, a checksum and bearer data, and the other subcarrier coding blocks consist of bearer data and checksum data.

4. The discrete shared spectrum OFDM communication method according to claim 2, wherein: The transmission block sequence number in S3 is used cyclically, and the intra-block coding sequence number of each segment is unique.

5. The discrete shared spectrum OFDM communication method according to claim 2, wherein: The transport block end flag in S3 is set to "1", indicating the last packet coding block in the transport data block, and the transport block end flag is set to "0" indicating an intermediate packet coding block.

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

7. The discrete shared spectrum OFDM communication method according to claim 2, wherein: The grouped coding block retransmission comprises the following steps: S71: The receiving end receives all the packet coding blocks carried by the transmission resource block, extracts the packet coding blocks from the transmission resource block carrying data in sequence, and checks whether the checksum of each subcarrier coding block in each packet coding block is correct; S72: If there is a check error in the subcarrier coding in the packet coding block, the subcarrier number corresponding to the check error is recorded as a basis for whether to continue using the subcarrier frequency point in the future. The packet coding block containing the check error subcarrier coding block needs to be retransmitted. The receiving end notifies the sending end through the transport block sequence number and the intra-block coding sequence number in the packet coding block header; S73: Verify that all subcarrier codes in the block are correct, record the subcarrier numbers corresponding to the correct subcarrier codes in the block, and evaluate whether to continue using this correct subcarrier frequency in the future; S74: extract the block header information from the correct block code, save the block code block to the corresponding transport block buffer according to the transport block sequence number and the intra-block code sequence number, and check whether all segments of the transport data block have been received after correctly receiving the block code block containing the transport block end flag of 1. S75: All the group coding blocks in the transmission data block have been received. The transmission data block bit data are taken from all the group coding blocks and assembled into a complete transmission data block in sequence. The transmission data block is submitted to the high-level protocol stack. The sender receives feedback from the receiver, indicating that all the group coding blocks in the retransmitted transmission data block have been received. The sender clears the retransmitted transmission data block and prepares to send the next transmission data block.

8. The discrete shared spectrum OFDM communication method according to claim 7, wherein: The S73 evaluates whether to continue to use this correct subcarrier frequency point in the future, specifically including: setting the preferred initial value of each subcarrier, if the subcarrier code block checksum analysis corresponding to the subcarrier is correct, the correct subcarrier value preferred value will increase one bonus point; if the subcarrier code block checksum analysis corresponding to the subcarrier is incorrect, the incorrect subcarrier preferred value will be deducted from the penalty point; the transmitting end gives priority to using subcarriers with larger preferred values. During the selection process, if the preferred values ​​are the same, the subcarrier frequency point can be randomly selected until the number of subcarriers required for the transmission resource block is selected.

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