OFDM (Orthogonal Frequency Division Multiplexing) communication method, device and system

Abstract

The invention discloses an OFDM (Orthogonal Frequency Division Multiplexing) communication method, device and system, and the method comprises the steps: generating a transmission frame which comprises a plurality of OFDM symbols; a first OFDM symbol of the transmission frame is a synchronous pilot symbol, and a second OFDM symbol is a reference pilot symbol; based on the transmission frame, configuring at least two demodulation modes according to channel conditions or communication requirements; when the first demodulation mode is configured, the receiving end performs differential phase shift keying differential demodulation on subsequent data symbols based on the reference pilot symbols; and when a second demodulation mode is configured, the receiving end performs channel estimation by using the reference pilot symbol, and performs quadrature amplitude modulation equalization and demodulation on subsequent data symbols according to a channel estimation result. According to the invention, ultralow pilot frequency overhead can be realized, the pilot frequency overhead is compressed to only two symbols, a synchronization sequence and a reference pilot frequency sequence in each frame, and the frequency spectrum utilization rate is greatly improved.

Description

Technical Field

[0001] This application relates to the field of wireless communication, and more specifically, to an OFDM communication method and system thereof. Background Technology

[0002] In applications such as the Internet of Things (IoT) and private power wireless networks, the Sub-GHz band (e.g., 223-235MHz, 470-510MHz) is widely used due to its excellent propagation characteristics. However, this band faces challenges such as spectrum fragmentation and narrow available bandwidth. Existing technologies mainly suffer from the following drawbacks: 1. Limited performance of traditional narrowband technologies: Although LPWAN technologies based on narrowband modulation (e.g., LoRa, NB-IoT) have long coverage, their transmission rates are low (usually below 100kbps) and latency is high, making it difficult to meet the growing demands for high-speed data acquisition and real-time control. 2. High overhead and complexity of classic OFDM systems: To combat multipath fading and achieve coherent demodulation, traditional OFDM systems require the insertion of a large number of continuous pilot symbols in the time-frequency domain for channel estimation. This leads to a decrease in spectral efficiency, and the receiver needs to include complex channel estimation and equalization modules, increasing power consumption and cost. 3. Poor spectrum adaptability: Existing solutions struggle to efficiently utilize the discontinuous and discretely allocated frequency points of the Sub-GHz band, resulting in low spectrum utilization. 4. MIMO application overhead is huge: In multiple-input multiple-output (MIMO) systems, in order to estimate the channel matrix between multiple inputs and multiple outputs, it is usually necessary to allocate independent pilot resources for each transmit antenna stream (layer). The pilot overhead increases linearly with the number of antennas, which severely restricts the application of MIMO technology in low-overhead scenarios.

[0003] Therefore, how to provide a communication method that can balance high spectral efficiency, low implementation complexity, strong spectral adaptability, and flexible extension to MIMO has become an urgent problem to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a novel OFDM communication scheme. This invention designs a dual-pilot transmission frame containing only synchronization pilot symbols and reference pilot symbols, simplifying the pilot overhead of each frame to two symbols, with one for the synchronization pilot sequence and one for the reference pilot sequence. This completely solves the problems of large pilot overhead and low spectral efficiency in traditional schemes, laying a low-overhead frame structure foundation for subsequent demodulation and extension. Simultaneously, based on the dual-pilot transmission frame, two demodulation modes are designed that can be flexibly switched according to channel conditions: DPSK differential demodulation mode and QAM equalized demodulation mode, adaptable to different channels and communication requirements. Furthermore, relying on the extremely simplified dual-pilot frame structure, MIMO multi-stream transmission is achieved without increasing additional pilot overhead.

[0005] To address the aforementioned issues, this application proposes an OFDM communication method comprising the following steps: A transmitting end generates a transmission frame based on the raw information bitstream to be processed. The transmission frame includes multiple OFDM symbols; the first OFDM symbol of the transmission frame is a synchronization pilot symbol, and the second OFDM symbol is a reference pilot symbol; based on the transmission frame, at least two demodulation modes are configured according to channel conditions or communication requirements. The reference pilot symbol provides a phase reference starting point for the first demodulation mode and a channel estimation basis for the second demodulation mode; when configured in the first demodulation mode, the receiving end performs differential phase shift keying (DSK) differential demodulation on subsequent data symbols based on the reference pilot symbol; when configured in the second demodulation mode, the receiving end performs channel estimation using the reference pilot symbol and performs quadrature amplitude modulation equalization and demodulation on subsequent data symbols based on the channel estimation result.

[0006] The OFDM communication method described above includes the following steps in which the transmitting end generates a transmission frame based on the raw information bit stream to be processed: determining configuration parameters according to the application scenario; performing channel coding and bit interleaving on the raw information bit stream; inputting the channel-coded and bit-interleaved information bit stream into the modulation module to generate frequency domain modulation symbols; and inputting the frequency domain modulation symbols into the OFDM framing module to generate frequency domain frame data and mapping the frequency domain frame data.

[0007] In the OFDM communication method described above, the transmission frame achieves non-contiguous available spectrum mapping by skipping disabled subcarriers in the frequency domain.

[0008] In the OFDM communication method described above, when configured in the first demodulation mode, the data symbols are modulated using differential phase shift keying. The receiver uses the reference pilot symbol as the starting point of the phase reference to directly perform differential demodulation on subsequent data symbols.

[0009] In the OFDM communication method described above, when configured in the second demodulation mode, the data symbols employ high-order orthogonal amplitude modulation. The receiver uses the reference pilot symbols to perform channel estimation, obtains the channel frequency response, and performs frequency domain equalization and coherent demodulation on subsequent data symbols based on the channel frequency response.

[0010] The OFDM communication method described above further includes supporting multiple-input multiple-output (MIMO) transmission modes; in MIMO transmission mode, reference pilot symbols carry pilot sequences of multiple spatial streams after orthogonalization; the receiver estimates the complete channel matrix between the multiple streams based on the reference pilot symbols, which is used for subsequent MIMO detection and demodulation of data.

[0011] The OFDM communication method described above, in the multiple-input multiple-output transmission mode, further includes multiple-input multiple-output pilot design for frequency domain modulation symbols.

[0012] The OFDM communication method described above includes the following steps: generating a basic pilot sequence; and performing different cyclic shifts on the basic pilot sequence for each transmit antenna's corresponding spatial stream to generate orthogonal pilot sequences.

[0013] A communication device includes a processor, a memory, and a transceiver, characterized in that the memory stores program instructions that, when executed by the processor, cause the device to perform the method described in any of the preceding claims.

[0014] A communication system includes a transmitting end device and a receiving end device. The transmitting end device is used to generate and transmit transmission frames as defined by the method described above. The receiving end device can be configured to support a first demodulation mode or a second demodulation mode, and can further support the multiple-input multiple-output transmission mode described above.

[0015] This application has the following beneficial effects: (1) This application sets the transmission frame to include two types of OFDM symbols: step pilot symbols and reference pilot symbols. By simplifying the pilot symbols, compared with the traditional OFDM system's design of inserting a large number of pilot symbols, this application minimizes the pilot overhead from the bottom layer of the frame structure, solving the problem of low spectrum efficiency in the traditional scheme. This application can transmit more effective data under the same spectrum resources, and the spectrum utilization rate is significantly improved.

[0016] (2) This application is based on the transmission frame design and is configured with two modes: differential phase shift keying differential demodulation and quadrature amplitude modulation equalization and demodulation. The demodulation mode can be flexibly switched according to channel conditions or communication requirements, which enables the communication system to adapt to different channel environments (such as fast channel changes and stable channel), and solves the problem that traditional solutions are difficult to adapt to multiple scenarios at the same time.

[0017] (3) Based on the basic pilot sequence, this application generates pilot sequences for each spatial stream through different cyclic shifts, so that each sequence has natural orthogonal characteristics. The receiver can accurately separate the channel components corresponding to each transmitting antenna from the superimposed pilot signals based on this orthogonality. The complete channel matrix between multiple streams can be estimated without complex separation algorithms, which effectively improves the accuracy and stability of MIMO channel estimation and lays a reliable foundation for subsequent multiple input multiple output detection and demodulation.

[0018] (4) By setting a mapping rule to skip disabled subcarriers, this application allows the system to directly adapt to discrete and discontinuous available frequency points without making additional modifications to the transmission frame structure and modulation and demodulation logic. This solves the problem that traditional OFDM schemes have difficulty utilizing discrete frequency points in the Sub-GHz band and cause waste of spectrum resources, maximizes the exploitation of spectrum value in scarce frequency bands, and improves the overall spectrum resource utilization efficiency.

[0019] (5) This application enables a single hardware / algorithm platform to cover a wide range of scenarios, from wide coverage low rate to local high rate, by using configurable carrier spacing and symbol duration, thereby reducing R&D and deployment costs. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings.

[0021] Figure 1 This is a flowchart of an OFDM communication method provided according to an embodiment of this application; Figure 2 This is a flowchart illustrating a low-complexity OFDM demodulation method suitable for high-mobility scenarios, provided according to an embodiment of this application. Figure 3 The transmission frame structure is generated according to the OFDM framing module provided in the embodiments of this application; Figure 4 This is a high spectral efficiency OFDM demodulation method applicable to fixed or slowly varying channel scenarios, provided according to embodiments of this application. Figure 5 The transmission frame structure is generated by the OFDM framing module provided in another embodiment of this application; Figure 6 This is a schematic diagram of the internal structure of a communication device according to an embodiment of this application. Figure 7 This is a schematic diagram of the internal structure of a communication system provided according to an embodiment of this application. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0023] This application provides an OFDM communication method, including the following steps: Step S1: The transmitting end generates a transmission frame based on the original information bit stream to be processed. The transmission frame includes multiple OFDM symbols. The first OFDM symbol of the transmission frame is a synchronization pilot symbol, and the second OFDM symbol is a reference pilot symbol.

[0024] Step S2: Based on the transmission frame, configure at least two demodulation modes according to channel conditions or communication requirements.

[0025] Step S3: When configured as the first demodulation mode, the receiver performs differential phase shift keying differential demodulation on subsequent data symbols based on the reference pilot symbols.

[0026] Step S4: When configured in the second demodulation mode, the receiver uses the reference pilot symbols to perform channel estimation, and performs quadrature amplitude modulation equalization and demodulation on subsequent data symbols based on the channel estimation results.

[0027] The transmission frame includes at least one OFDM symbol, wherein: the first OFDM symbol (symbol 0) is defined as a synchronization pilot symbol, mainly used for time and frequency synchronization at the receiver. The second OFDM symbol (symbol 1) is defined as a reference pilot symbol, which carries core reference information.

[0028] Two demodulation modes can be configured using the OFDM symbols described above: The first demodulation mode is differential mode, corresponding to Example 1: suitable for mobile scenarios with rapidly changing channels. Data symbols employ differential phase-shift keying (DPSK) modulation, and their modulation information is determined based on the modulation information of the previous symbol using Gray mapping differential rules. The receiver uses the reference pilot symbol as the starting point for phase reference and directly performs differential demodulation on subsequent data symbols, without requiring independent channel estimation and equalization processes.

[0029] The second demodulation mode is the equalization mode, corresponding to Example 2: suitable for fixed scenarios where the channel changes slowly. The data symbols can employ high-order quadrature amplitude modulation (QAM). The receiver uses the reference pilot symbols to perform channel estimation, obtain the channel frequency response, and accordingly perform frequency domain equalization and coherent demodulation on subsequent data symbols.

[0030] Furthermore, this application supports Multiple-Input Multiple-Output (MIMO) transmission extension, corresponding to Embodiment 3. In MIMO mode: the reference pilot symbol carries the pilot sequence of multiple spatial streams (layers) after orthogonalization. Based on the pilot symbol, the receiver estimates the complete channel matrix between the multiple streams for subsequent MIMO detection (such as MMSE detection). This MIMO framework can be combined with any of the demodulation modes described above.

[0031] Furthermore, the transmission frame structure supports non-contiguous available spectrum mapping, achieved by skipping disabled subcarriers. The carrier spacing and symbol duration of the OFDM symbols can be dynamically configured to adapt to different coverage and rate requirements.

[0032] Example 1 like Figure 2 As shown, this embodiment provides a low-complexity OFDM demodulation method suitable for high-mobility scenarios. The transmitting end uses Differential Phase Shift Keying (DPSK) modulation to generate data symbols and constructs a simplified transmission frame containing synchronization pilot symbols and reference pilot symbols. After synchronization, the receiving end does not need to perform channel estimation and equalization. It directly uses the phase of the reference pilot symbol as the starting reference point, calculates the received phase difference between adjacent symbols, and recovers the original information bits symbol by symbol according to the differential mapping rule. This method, through a channel-estimate-free differential demodulation mechanism, significantly reduces the computational complexity and power consumption of the receiver while ensuring transmission reliability. Specifically, it includes the following steps:

[0033] Step S110: Configure parameters.

[0034] The parameter configuration includes setting the carrier spacing to 25kHz, OFDM symbol effective duration to 40μs, cyclic prefix (CP) to 5μs, modulation mode to QPSK, tail-biting convolutional coding, and code rate to 0.5.

[0035] Step S120: The sending end obtains the original information bit stream to be transmitted.

[0036] Step S130: The transmitting end performs channel coding on the information bit stream and then performs bit interleaving.

[0037] Step S140: The transmitting end inputs the information bit stream after channel coding and bit interleaving into the DPSK modulation module to perform differential mapping to generate frequency domain modulation symbols.

[0038] The DPSK modulation module uses the provided BPSK / QPSK / 8PSK Gray mapping differential table to perform differential operations between the current input bit and the modulation bit of the previous symbol to generate the current modulation symbol.

[0039] Step S150: The transmitting end inputs the frequency domain modulation symbols into the OFDM framing module, generates frequency domain frame data, and maps the frequency domain frame data.

[0040] like Figure 3The diagram shows the transmission frame structure generated by the OFDM framing module, using a carrier spacing of 25kHz as an example. Symbol 0 in the transmission frame structure is a known synchronization sequence (similar to the ZC sequence), symbol 1 is a known reference pilot sequence, and symbols 2 to N are DPSK modulated data symbols. The effective duration is 40μs, and the cyclic prefix is ​​5μs.

[0041] During mapping, disabled subcarriers are skipped based on spectrum licensing information.

[0042] Step S160: The transmitting end performs an inverse fast Fourier transform on the frequency domain data of each frame to convert it into a time domain signal.

[0043] Step S170: The transmitter adds a cyclic prefix to the time-domain waveform of each OFDM symbol and then performs radio frequency transmission.

[0044] Understandably, in this embodiment, the transmission frame serves as a frequency domain resource grid, containing sequentially arranged pilot symbols and data symbols. After processing such as IFFT, the frequency domain frame is converted into a time domain signal for transmission.

[0045] The transmission frame includes at least one OFDM symbol. According to the above, the first OFDM symbol (symbol 0) is defined as a synchronization pilot symbol, primarily used for time and frequency synchronization at the receiver. The second OFDM symbol (symbol 1) is defined as a reference pilot symbol, carrying core reference information.

[0046] Step S180: The receiving end receives the radio frequency signal and down-converts the radio frequency signal from analog to digital to baseband digital signal.

[0047] Step S190: The receiver uses the synchronization pilot symbol in the received signal to complete time synchronization and carrier frequency offset estimation and correction.

[0048] Step S1100: Based on the synchronization result, the receiver determines the start position of the frame and correctly segments the subsequent OFDM symbols.

[0049] Step S1110: The receiver removes the cyclic prefix portion of each OFDM symbol.

[0050] Step S1120: The receiver performs a fast Fourier transform on the reference pilot symbol to convert it to the frequency domain, extracts the received phase information of the symbol on each effective subcarrier, and uses the received phase information as the initial phase reference for the entire differential demodulation chain.

[0051] Step S1130: The receiver performs differential demodulation based on the initial phase reference and outputs bit information.

[0052] Perform an FFT on the first data symbol (symbol 2). Calculate the received phase difference between symbol 2 and symbol 1 (reference pilot) on each subcarrier. Based on the received phase difference and the known DPSK Gray mapping rule, directly demodulate the bit information (soft bits) carried by symbol 2.

[0053] For each subsequent data symbol, the phase difference between it and the received signal of the previous symbol is directly calculated using the above operation. The phase difference is then mapped back to the bit information to achieve differential demodulation without channel estimation.

[0054] The above completely skips the traditional channel estimation, interpolation, and frequency domain equalization modules.

[0055] Step S1140: The receiving end deinterleaves the bit information output by differential demodulation, and then sends it to the channel decoder for decoding, finally recovering the original transmitted information bits.

[0056] Example 2 like Figure 4 As shown in the illustration, this application provides a high-spectrum-efficiency OFDM demodulation method suitable for fixed or slowly varying channel scenarios. The transmitting end uses high-order quadrature amplitude modulation (QAM) to generate data symbols and constructs a transmission frame identical to the first mode, containing synchronization and reference pilot symbols. After synchronization, the receiving end uses the known reference pilot symbols to estimate the channel frequency response, obtains full-bandwidth channel information through interpolation, and then performs frequency domain equalization and coherent demodulation on all subsequent data symbols to recover the original information bits. This method achieves high-data-rate transmission of high-order modulation while maintaining low pilot overhead through accurate channel estimation and equalization based on a single pilot. Specifically, it includes the following sub-steps: Step S310: Configure parameters.

[0057] The parameter configuration includes setting the carrier spacing to 25kHz, the modulation method to 16QAM, LDPC encoding, and a code rate of 2 / 3.

[0058] Step S320: The sending end obtains the original information bit stream to be transmitted.

[0059] Step S330: The transmitting end performs channel coding on the information bit stream.

[0060] Channel coding can employ LDPC coding with a code rate of 2 / 3 to enhance error resilience.

[0061] Step S340: The transmitting end inputs the channel-coded information bit stream into the QAM modulation module to generate frequency domain modulation symbols.

[0062] The modulation module is replaced with a standard 16QAM mapper. The encoded bitstream is mapped according to the constellation diagram of the selected modulation order (e.g., 16QAM) to generate frequency-domain QAM modulation symbols. It is worth noting that, unlike Example 1, differential operations are not performed in this step.

[0063] Step S350: The transmitting end inputs the frequency domain modulation symbols into the OFDM framing module, generates frequency domain frame data, and maps the frequency domain frame data.

[0064] Among them, such as Figure 5 As shown, the frame structure provided in this embodiment is the same as that in Embodiment 1, but the carrier spacing is reduced to 12.5 kHz. The symbol duration is increased, with an effective duration of 80 μs and a cyclic prefix of 10 μs.

[0065] This embodiment creates a transmission frame containing N+1 OFDM symbols (N being the number of data symbols) and fills it with pilot symbols. Symbol 0 is filled with a known synchronization sequence (such as the ZC sequence) as the synchronization pilot symbol. Symbol 1 is filled with a known reference pilot sequence as the reference pilot symbol.

[0066] The QAM modulation symbols generated in step 340 are then mapped sequentially to positions 2 through N in the frame. When mapping all the symbols (pilots and data) to OFDM subcarriers, disabled subcarriers are skipped based on spectrum licensing information.

[0067] Step S360: The transmitting end performs an inverse fast Fourier transform on the frequency domain data of each frame to convert it into a time domain signal.

[0068] Step S370: The transmitter adds a cyclic prefix to the time-domain waveform of each OFDM symbol and then performs radio frequency transmission.

[0069] The baseband signal is processed by radio frequency and then transmitted through an antenna.

[0070] Step S380: The receiver receives the radio frequency signal and down-converts it into a baseband digital signal.

[0071] Step S390: The receiver uses the synchronization pilot symbol in the received signal to complete time synchronization and carrier frequency synchronization.

[0072] Step S3100: Based on the synchronization result, the receiver determines the frame start position and segments each OFDM symbol.

[0073] Step S3110: The receiver removes the cyclic prefix from each OFDM symbol.

[0074] Step S3120: The receiver uses the reference pilot symbols to perform channel estimation and determine the preliminary channel frequency response estimate.

[0075] First, a Fast Fourier Transform (FFT) is performed on symbol 1 (reference pilot symbol) to transform it to the frequency domain. At the pilot subcarrier position, the received signal Y_pilot is compared with the locally known original pilot sequence P_known to calculate a preliminary estimate of the channel frequency response. .

[0076] Step S3130: The receiver performs channel information difference on the preliminary channel frequency response estimates to determine all channel frequency response estimates.

[0077] This utilizes an interpolation algorithm (such as linear interpolation) based on the channel estimate at the pilot subcarrier. The channel frequency response estimates at all data subcarrier locations are derived. .

[0078] Step S3140: The receiver uses all channel frequency response estimates to perform frequency domain equalization and coherent demodulation of the data symbols and outputs bit information.

[0079] The receiver performs an FFT on each subsequent data symbol (symbol 2 to symbol N) to obtain the frequency domain received signal Y_data. This is then used in conjunction with the estimated channel. Compensate Y_data.

[0080] For example, zero-forcing equalization can be used: , where k is the subcarrier index and X_est is the estimated value of the equalized symbol.

[0081] The equalized complex symbol X_est is compared with the standard QAM constellation diagram, and the corresponding bit information (soft decision or hard decision) is determined based on its position.

[0082] Step S3150: The receiving end sends the demodulated bit stream to the corresponding channel decoder for decoding to recover the original transmitted information bits.

[0083] In Example 2, since the channel remains essentially unchanged within the frame, channel estimation based on a single reference symbol is sufficiently accurate. Compared to QPSK in Example 1, 16QAM doubles the throughput under the same bandwidth, achieving high spectral efficiency transmission.

[0084] Example 3 This embodiment provides an efficient OFDM transmission method for multiple-input multiple-output (MIMO) systems. While maintaining a simplified dual-pilot frame structure, it supports multiple spatial stream transmission by performing a cyclic shift orthogonal design on the reference pilot symbols. Specifically, the transmitter uses the same basic pilot sequence to generate orthogonal sequences with different cyclic shift versions, and superimposes them on the same time-frequency resources of the same reference pilot symbol for transmission, thus carrying pilot information for multiple spatial streams. The receiver, based on these pilot symbols, separates and estimates the complete channel matrix between the multiple streams through correlation operations, and then performs MIMO detection and demodulation on subsequent data symbols.

[0085] This method achieves a doubling of spectral efficiency without adding any additional pilot overhead and can be flexibly combined with the first or second demodulation mode to form a complete low-overhead, high-performance MIMO solution. Specifically, it includes the following steps: Step S410: Configure parameters.

[0086] The parameter configuration includes setting it to 2x2 MIMO, carrier spacing of 50kHz (for higher data rates), modulation mode of 64QAM, and combining it with a second demodulation mode.

[0087] Step S420: The sending end obtains the original information bit stream to be transmitted.

[0088] Step S430: The transmitting end divides the information bit stream into multiple independent spatial streams, and each stream is channel coded separately.

[0089] Step S440: The transmitting end divides each stream after channel coding into bits and modulates it independently according to the configured modulation method (such as 64QAM) to generate frequency domain modulation symbols corresponding to each stream.

[0090] As can be seen in Embodiment 2, each stream is independently modulated using 64QAM to generate the corresponding frequency domain modulation symbol.

[0091] Step S450: After the transmitter generates frequency domain modulation symbols, it performs MIMO pilot design and then performs radio frequency transmission.

[0092] MIMO pilot design includes generating a basic pilot sequence and an orthogonal pilot sequence.

[0093] First, generate a basic pilot sequence, producing a known basic pilot sequence P_base (such as a pseudo-random PN sequence or ZC sequence).

[0094] Regenerate orthogonal pilot sequences: For each transmit antenna corresponding to the spatial flow Layer i, perform different cyclic shifts on the basic pilot sequence to generate orthogonal pilot sequences.

[0095] For Layer 0, the pilot sequence is: .

[0096] For Layer 1, the pilot sequence is: , where N is the cyclic shift value, which can be half the effective length of the symbol.

[0097] After generating the basic pilot sequence and the orthogonal pilot sequence, a MIMO transmission frame containing N+1 OFDM symbols is created. Symbol 0 is filled with a known synchronization sequence (each stream can send the same or a synchronization sequence with a known relationship). All subcarriers of symbol 1 are used as reference pilot symbols. On this symbol, the pilot sequences P_0 and P_1 generated by all spatial streams and subjected to cyclic shifting and orthogonal processing are superimposed and transmitted simultaneously on the same time-frequency resources. That is, the signal transmitted on each subcarrier is the sum of the pilot values ​​of all streams on that subcarrier.

[0098] The data modulation symbols generated in step S440 are mapped to the corresponding positions of symbols 2 to N of the corresponding stream. The data symbols of each stream occupy the same time-frequency resource grid. When mapping all symbols (pilots and data), disabled subcarriers are skipped according to the spectrum license.

[0099] After mapping, IFFT is performed on the frequency domain data of each frame and each transmit antenna link to convert it into the time domain signal of each antenna. A CP is then added for each antenna and each OFDM symbol.

[0100] The baseband signal of each antenna is transmitted by the corresponding antenna via an independent radio frequency link.

[0101] Step S460: Each receiving antenna at the receiving end independently receives the signal and down-converts it into a baseband digital signal.

[0102] Step S470: The receiver uses the synchronization pilot symbol with superimposed power in the received signal to complete time and frequency synchronization under multiple input multiple output.

[0103] Step S480: Based on the synchronization result, the receiver determines the frame start position and segments each OFDM symbol for each receiving antenna.

[0104] Step S490: The receiver removes the CP for each symbol received by each antenna.

[0105] Step S4100: The receiver performs MIMO channel estimation and constructs the channel matrix.

[0106] The FFT is performed on symbol 1 (reference pilot symbol) received by each receiving antenna to obtain the frequency domain received signal vector Y_pilot.

[0107] Using the known basic pilot sequence P_base and the cyclic shift value N_i of each stream, the channel components H_00, H_01, H_10, and H_11 from the superimposed received signal Y_pilot are separated and estimated through correlation operations or algorithms based on cyclic shift orthogonality, thereby constructing a 2x2 channel matrix H.

[0108] Step S4110: Perform MIMO detection of data symbols based on the constructed channel matrix to obtain the symbol estimate for each independent spatial stream.

[0109] First, for each subsequent data symbol (symbol 2 to symbol N), each receiving antenna performs an FFT on the received symbol to obtain the frequency domain received signal vector Y_data at that moment.

[0110] MIMO detection is performed using the channel matrix H on the corresponding subcarrier estimated in step S4100. For example, minimum mean square error (MMSE) detection is used: the detection matrix is ​​calculated. Then estimate the transmitted symbol vector: Each element of X_est corresponds to a symbol estimate of the emitted spatial stream.

[0111] Step S4120: Perform coherent demodulation and channel decoding on the symbol estimates of each independent spatial stream obtained after MIMO detection, and output the original transmitted information bits.

[0112] The symbol estimate X_est_i for each independent spatial stream is coherently demodulated. This embodiment uses a second demodulation mode, such as 64QAM demodulation. The demodulated bit streams from each stream are then channel-decoded and finally combined to recover the original transmitted information bits.

[0113] Example 4 This embodiment enables a single hardware / algorithm platform to cover a wide range of scenarios, from broad coverage and low data rates to localized high data rates, through configurable carrier spacing and symbol duration, thus reducing R&D and deployment costs. This embodiment is specifically designed for low-latency, high-bandwidth industrial control scenarios. It includes the following sub-steps: Step S510: Configure parameters.

[0114] In this embodiment, physical layer parameters can be dynamically configured according to the low latency and high bandwidth requirements of industrial control scenarios.

[0115] The carrier spacing is set to 125 kHz, which is significantly larger than the 25 kHz in Examples 1 and 2, to shorten the symbol duration. The effective OFDM symbol duration is set to 8.5 μs, and the wavelet spacing is set to 125 kHz. The cyclic prefix (CP) duration is set to 0.53 μs, and the CP ratio is set to 0.0625. The modulation scheme is set to 16QAM or 16PSK. The modulation order is 16QAM / PSK. Turbo coding is used with a code rate of 2 / 3. The total bandwidth is set to 10 MHz. The number of available carriers is set to 80. The subframe length is set to 190 μs. The total number of symbols is set to 20. The transmission bytes are set to 400~800 bytes. The maximum spectral efficiency is set to 3.4 bps / Hz. The maximum one-way rate is set to 33.6 Mbps. The latency is set to within 2 ms to meet the requirements of industrial control scenarios.

[0116] Step S520: The sending end obtains the original information bit stream to be transmitted (data packet size is 400-800 bytes).

[0117] Step S530: The sending end performs Turbo encoding on the information bit stream.

[0118] The bitrate is 2 / 3.

[0119] Step S540: The transmitting end modulates the encoded bit stream according to the configured modulation method (such as 16QAM or 16PSK) to generate frequency domain modulation symbols.

[0120] Step S550: The transmitting end inputs the generated frequency domain modulation symbols into the OFDM framing module for OFDM framing.

[0121] First, create a transport frame containing N+1 OFDM symbols (e.g., N=18 data symbols, plus 1 synchronization symbol and 1 reference pilot symbol). Then, fill in the pilot symbols, filling the first symbol with a known synchronization sequence. Fill the second symbol with a known reference pilot sequence.

[0122] Modulation symbols are mapped to the positions of subsequent data symbols in the frame. Within a 10MHz bandwidth, the signal is mapped onto 80 available subcarriers, skipping out-of-band and disabled subcarriers.

[0123] Step S560: The transmitting end performs IFFT on the framed frequency domain data block and converts it into a time domain signal.

[0124] Step S570: After adding a 0.53μs CP to each OFDM symbol, the transmitter transmits the baseband signal after radio frequency processing.

[0125] Step S580: The receiver receives the radio frequency signal and down-converts it into a baseband digital signal.

[0126] Step S590: The receiver uses the synchronization pilot symbol in the received signal to complete time synchronization and frequency synchronization under the configured 125kHz carrier spacing parameter.

[0127] Step S5100: Based on the synchronization results, the receiver determines the starting position of the short symbol boundary and segments each OFDM symbol.

[0128] Step S5110: The receiver removes the CP of each symbol.

[0129] Step S5120: The receiving end determines whether the current frame is working in the first demodulation mode or the second demodulation mode according to the system preset or signaling indication, and determines the demodulation method.

[0130] If it is the first demodulation mode (differential mode): then starting from the reference pilot symbol, differential demodulation is performed on the 16PSK modulated data (the process is the same as in Example 1, but the modulation order is 16PSK).

[0131] If it is the second demodulation mode (equalization mode): channel estimation and interpolation are performed using reference pilot symbols, and equalization and coherent demodulation are performed on the 16QAM modulated data (the process is the same as in Example 2, but the modulation order is 16QAM).

[0132] Step S5130: The receiving end performs Turbo decoding on the demodulated bit stream to recover the original information bits.

[0133] Example 5 like Figure 6 As shown, this embodiment provides a communication device, including a processor, a memory, and a transceiver. The memory stores program instructions, which, when executed by the processor, cause the communication device to perform the method flow described in embodiments one to four. The transceiver is capable of converting digital baseband signals to and from radio frequency analog signals in the air, and performing the transmission operations at the transmitting end and receiving end in the method flow described in embodiments one to four.

[0134] The transceiver, acting as the RF front-end, connects to the antenna and converts the baseband digital signal generated by the processor into an analog RF signal in the transmit path. After power amplification, the signal is transmitted through the antenna. In the receive path, the RF signal received by the antenna is amplified with low noise, down-converted, and converted back into a baseband digital signal before being sent to the processor. It also supports MIMO transmission mode, including multiple parallel RF transceiver channels, and supports operation at different center frequencies and discontinuous frequency bands.

[0135] Example 6 like Figure 7As shown, this embodiment provides a communication system, including a transmitting end device and a receiving end device. The transmitting end device is used to generate and transmit transmission frames as defined by the methods described in Embodiments 1 to 4. The receiving end device can be configured to support the first demodulation mode or the second demodulation mode, and can further support the MIMO transmission mode as in Embodiment 3.

[0136] This application also provides a computer storage medium storing computer instructions, which, when invoked, are used to execute the method flow described in embodiments one to four.

[0137] The embodiments disclosed in this invention provide a computer-readable storage medium storing computer program instructions that, when executed on a computer, cause the computer to perform the method flow described in embodiments one to four above.

[0138] This invention provides a processor for processing the method flow described in embodiments one to four above.

[0139] In this embodiment of the invention, the processor can be an integrated circuit chip with signal processing capabilities. The processor can be a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0140] The various methods, steps, and logic diagrams disclosed in the embodiments of this invention can be implemented or executed. The general-purpose processor can be a microprocessor or any conventional processor. The steps of the methods disclosed in the embodiments of this invention can be directly implemented by a hardware decoding processor, or implemented by a combination of hardware and software modules in the decoding processor. The software modules can reside in random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, registers, or other mature storage media in the art. The processor reads information from the storage medium and, in conjunction with its hardware, completes the steps of the above methods.

[0141] The storage medium can be memory, such as volatile memory or non-volatile memory, or may include both volatile and non-volatile memory.

[0142] Non-volatile memory can be read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), or flash memory. Volatile memory can be random access memory (RAM), which is used as an external cache. By way of example, but not limitation, many forms of RAM are available, such as Static Random Access Memory (SRAM), Dynamic Random Access Memory (DRAM), Synchronous DRAM (SDRAM), Double Data Rate Synchronous DRAM (DDRSDRAM), Enhanced Synchronous DRAM (ESDRAM), Synchlink DRAM (SLDRAM), and Direct Rambus RAM (DRRAM).

[0143] This application has the following beneficial effects: (1) This application sets the transmission frame to include two types of OFDM symbols: step pilot symbols and reference pilot symbols. By simplifying the pilot symbols, compared with the traditional OFDM system's design of inserting a large number of pilot symbols, this application minimizes the pilot overhead from the bottom layer of the frame structure, solving the problem of low spectrum efficiency in the traditional scheme. This application can transmit more effective data under the same spectrum resources, and the spectrum utilization rate is significantly improved.

[0144] (2) This application is based on the transmission frame design and is configured with two modes: differential phase shift keying differential demodulation and quadrature amplitude modulation equalization and demodulation. The demodulation mode can be flexibly switched according to channel conditions or communication requirements, which enables the communication system to adapt to different channel environments (such as fast channel changes and stable channel), and solves the problem that traditional solutions are difficult to adapt to multiple scenarios at the same time.

[0145] (3) Based on the basic pilot sequence, this application generates pilot sequences for each spatial stream through different cyclic shifts, so that each sequence has natural orthogonal characteristics. The receiver can accurately separate the channel components corresponding to each transmit antenna from the superimposed pilot signals based on this orthogonality. The complete channel matrix between multiple streams can be estimated without complex separation algorithms, which effectively improves the accuracy and stability of MIMO channel estimation and lays a reliable foundation for subsequent MIMO detection and demodulation.

[0146] (4) By setting a mapping rule to skip disabled subcarriers, this application allows the system to directly adapt to discrete and discontinuous available frequency points without making additional modifications to the transmission frame structure and modulation and demodulation logic. This solves the problem that traditional OFDM schemes have difficulty utilizing discrete frequency points in the Sub-GHz band and cause waste of spectrum resources, maximizes the exploitation of spectrum value in scarce frequency bands, and improves the overall spectrum resource utilization efficiency.

[0147] (5) This application enables a single hardware / algorithm platform to cover a wide range of scenarios, from wide coverage low rate to local high rate, by using configurable carrier spacing and symbol duration, thereby reducing R&D and deployment costs.

[0148] Although the examples referenced in this application are described for illustrative purposes only and not for limiting the scope of this application, changes, additions and / or deletions to the implementation may be made without departing from the scope of this application.

[0149] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An OFDM communication method, characterized in that, Includes the following steps: The transmitting end generates a transmission frame based on the raw information bit stream to be processed. The transmission frame includes multiple OFDM symbols; the first OFDM symbol of the transmission frame is a synchronization pilot symbol, and the second OFDM symbol is a reference pilot symbol. Based on the transmission frame, at least two demodulation modes are configured according to channel conditions or communication requirements. The reference pilot symbol provides a phase reference starting point for the first demodulation mode and a channel estimation basis for the second demodulation mode. When configured in the first demodulation mode, the receiver performs differential phase shift keying differential demodulation on subsequent data symbols based on the reference pilot symbols; When configured in the second demodulation mode, the receiver uses the reference pilot symbols to perform channel estimation and performs quadrature amplitude modulation equalization and demodulation on subsequent data symbols based on the channel estimation results.

2. The OFDM communication method as described in claim 1, characterized in that, The sending end generates a transmission frame based on the raw information bitstream to be processed, including the following steps: Determine the configuration parameters based on the application scenario; The transmitting end performs channel coding on the original information bit stream and then performs bit interleaving; The transmitting end inputs the information bit stream after channel coding and bit interleaving into the modulation module to generate frequency domain modulation symbols; The transmitting end inputs the frequency domain modulation symbols into the OFDM framing module to generate frequency domain frame data and then maps the frequency domain frame data.

3. The OFDM communication method as described in claim 2, characterized in that, The transmission frame achieves non-contiguous available spectrum mapping by skipping disabled subcarriers in the frequency domain.

4. The OFDM communication method as described in claim 1, characterized in that, When configured in the first demodulation mode, the data symbols are modulated using differential phase shift keying. The receiver uses the reference pilot symbol as the starting point of the phase reference to directly perform differential demodulation on subsequent data symbols.

5. The OFDM communication method as described in claim 1, characterized in that, When configured in the second demodulation mode, the data symbols adopt high-order quadrature amplitude modulation. The receiver uses the reference pilot symbols to perform channel estimation, obtain the channel frequency response, and perform frequency domain equalization and coherent demodulation on subsequent data symbols based on the channel frequency response.

6. The OFDM communication method as described in claim 1, characterized in that, It also includes support for multiple input multiple output transmission modes; In multiple-input multiple-output transmission mode, the reference pilot symbol carries pilot sequences of multiple spatial streams that have undergone orthogonalization. The receiver estimates the complete channel matrix between multiple streams based on the reference pilot symbols, which is used for subsequent multiple-input multiple-output detection and demodulation of data.

7. The OFDM communication method as described in claim 6, characterized in that, In the multiple-input multiple-output transmission mode, it also includes multiple-input multiple-output pilot design for frequency domain modulation symbols.

8. The OFDM communication method as described in claim 7, characterized in that, Multiple-input multiple-output pilot design includes: Generate the basic pilot sequence; For each transmit antenna, the fundamental pilot sequence is cyclically shifted in different ways to generate orthogonal pilot sequences.

9. A communication device, comprising a processor, a memory, and a transceiver, characterized in that, The memory stores program instructions that, when executed by the processor, cause the device to perform the method as described in any one of claims 1 to 8.

10. A communication system, characterized in that, It includes a transmitting end device and a receiving end device, the transmitting end device being used to generate and transmit a transmission frame as defined by the method as described in claim 1, and the receiving end device being configurable to support the first demodulation mode or the second demodulation mode, and may further support the multiple-input multiple-output transmission mode as described in any one of claims 6-8.

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